2.1. Resource management capabilities

To begin with, resource-rich countries should adopt efficient resource utilization methods. According to a survey by the World Resources Institute, 59% of the land, 41% of the water, and 89% of the energy are used globally, indicating that there are problems of overexploitation and waste in natural resource utilization (Li et al., 2022b). Therefore, resource-rich countries should adopt effective methods, including ecological agriculture, low-energy production technology, recycling technology, and advanced information technology, to utilize natural resources. These methods reduce the use of natural resources and bring ecological conservation benefits.

Further, resource-rich countries should ensure their resource supply through diversification. According to Deloitte’s figures, more than 80% of China’s raw materials are imported, and they often face various supply risks (including price risk and supply interruption risk). This shows that a single source of supply to ensure sufficient supply is difficult. Therefore, resource-rich countries should ensure their resource supply through diversification to avoid the risks brought by a single source of supply and make full use of their unique advantages. Ensuring supply through diversification can simultaneously effectively reduce the impact of the crisis and increase national competitiveness.

Lastly, resource-rich countries must undertake the principle of permanent measurement and distribution considering ensuring the benefits of the people and committing to permanent guarantees. The “2030 Sustainable Development Goals” clearly defined the principle of “fundamentally equitable, reasonable, inclusive, balanced benefits and sharing opportunities for all countries” (Biglari et al., 2022). According to the 2030 Sustainable Development Goals Report in 2017, although the world’s poor population has generally declined in recent years (from 1.86 billion to 1.07 billion), the gap between the poor population is widening. This shows that although resource-rich countries have many resources, owning to one-sided resource allocation, they have not effectively brought about fair, reasonable, and inclusive development. Therefore, resource-rich countries must undertake the principle of permanent measurement and distribution, focusing on fairness and inclusiveness in the process of resource utilization and distribution, and ensure that resource utilization and distribution do not further widen the gap between the rich and poor. Simultaneously, resource-rich countries should pay attention to social responsibility, promote the fair use and sharing of resources and enhance the country’s image and credibility by cooperation with all sectors of society.

In conclusion, as a country rich in natural raw material resources, developing effective resource management capabilities is the key to determining whether it can achieve sustainable development. To reduce waste through effective resource utilization; in contrast, to ensure a large supply of raw materials through a diversified strategy to avoid the impact of the crisis, considering how to find the best method between optimizing the use and avoiding waste is essential.

2.2. Sustainable resources using

The sustainable use of resources is the key to ensuring the sustainable development of resource-rich countries. That needs to start from many aspects, including scientific and technological innovation (Su and Fan, 2022), policies and regulations (Ahmed et al., 2022), market mechanisms (Tian and Feng, 2022), and public education (Zou and Zhang, 2022).

To begin with, scientific and technological innovation is an important guarantee for the sustainable use of resources. Resource-rich countries should increase investment and efforts in scientific and technological innovation, promote technologies such as new energy, new materials, and new processes, improve resource utilization efficiency, and reduce resource consumption intensity (Ke et al., 2022). Simultaneously, the transformation and application of scientific and technological strides should be strengthened, and the coordinated development of resource utilization and environmental protection should be promoted (Ding et al., 2022).

Additionally, policies and regulations are important to safeguard the sustainable use of resources. Resource-rich countries should establish a sound policy and regulatory system, improve resource taxation and resource compensation mechanisms, and encourage resource-saving and environmentally friendly production and consumption methods (Lee et al., 2022). Simultaneously, strengthen the implementation of policies and regulations, strengthen resource management and supervision, and prevent excessive exploitation and waste of resources (Xu et al., 2022).

Furthermore, the market mechanism is an important means for the sustainable use of resources. Resource-rich countries should strengthen market supervision, establish a fair, transparent, and effective market mechanism, and promote the formation of resource prices and the optimization of resource allocation (Beumer et al., 2022). Simultaneously, enterprises should be encouraged and supported to carry out resource-saving and environmentally friendly production and operation (Li et al., 2023), as well as promote the coordinated development of resource utilization and environmental protection (Arslan et al., 2022).

Finally, public education is important to safeguard the sustainable use of resources. Resource-rich countries should strengthen public education, popularize resource-saving and environmentally friendly production and consumption knowledge, and enhance public awareness and understanding of sustainable resource utilization (Owojori et al., 2022). Simultaneously, the participation of social organizations and civil forces should be strengthened to promote the coordinated development of resource utilization and environmental protection (Bonnedahl et al., 2022).

2.3. Investment opportunities and advantages

Resource-rich countries can use their natural resources to make large-scale investments to boost their local economies. Numerous industrial plants and related infrastructure are built using local resources (Hu et al., 2023a). There are abundant energy development projects, agricultural production, tourism development projects, financial services, educational services, and medical services that are implemented through large-scale investment using local natural resources (Fahad et al., 2022). In addition, because local people focus more on local culture, historical heritage, and locally endemic species, they invest considerable manpower and material resources in protecting local cultural heritage, endemic species, and the ecological environment to protect local cultural heritage, endemic species, and the ecological environment (Barrile et al., 2022).

Because resource-rich countries have energy cost advantages, open markets, and abundant overseas markets (remarkably the ability to use low-cost energy to mine other energy to promote industrial structure upgrading) (Hu and Zhang, 2023). Resource-rich countries can effectively use this competitive advantage for development. For example, “Competitive Situation of China’s Integrated Circuit Industry in 2018” shows that China’s IC industry has formed a certain competitive advantage. “Competitive Situation of Indian IT Industry in 2018” shows that the Indian IT industry has formed a certain competitive advantage (Liu et al., 2022).

With the increasing level of globalization (according to 2018 IMF data, global GDP was almost balanced between 2016 and 2017), the competition among countries is becoming increasingly fierce (Buckley, 2022). Considering how to use the advantages and disadvantages among countries to promote competitive advantages among countries has great practical significance. Subsequently, attracting external parties to expand the domestic market is a necessary consideration.

In short, as a resource-rich country, it can use its massive renewable energy as internal support to promote the expansion of the international market and ensure that the local cultural heritage, endemic species, and ecological environment are fully protected. It is one of the advantages that cannot be ignored to attract external parties to market expansion in the domestic market by supporting corresponding laws and regulations with a large amount of manpower and material resources.

2.4. Social and economic impacts

The resource management capabilities and resource development methods of resource-rich countries affect environmental sustainability and directly affect the sustainable development of the country’s society and economy.

To begin with, the resource management capabilities of resource-rich countries directly affect their economic development. Resource development has always been the economic pillar of many countries, but in the process of resource development, if good resource management ability does not exist, it wastes many resources and may lead to environmental damage and social unrest (Mlachila and Ouedraogo, 2020). In addition, relying solely on the development of certain resources may lead to a single economic structure, lack of economic diversity, and increase economic risks (Frances et al., 2023). Consequently, resource-rich countries should develop diversified industries and promote the coordination of resource development and economic development.

Further, the resource management capabilities of resource-rich countries affect the sustainable development of society. In the process of resource development, social equity, and people’s livelihood issues need to be taken into consideration. If resource development is not conducive to people’s livelihood and social equity, it can lead to social instability and social unrest (Badeeb et al., 2017). Consequently, resource-rich countries should fully consider social equity and people's livelihood issues in resource development and take measures to protect people’s livelihood and rights.

Lastly, the resource management capabilities of resource-rich countries can affect the attitude and cooperation of the international community. Global resources are limited, and resource development and management methods in resource-rich countries affect the fairness of global resource distribution. If resources are not developed and managed appropriately, it may lead to trade restrictions and sanctions against the country by the international community and may lead to tensions in international relations (Germond-Duret, 2014). Therefore, resource-rich countries should cooperate with the international community to adopt sustainable resource management methods to promote the fairness and sustainability of global resource distribution.

3.1. Environmental issues and public health crises

The inconsistency between resource-rich and resource-scarce countries, and its impact on sustainable development, especially regarding environmental issues and public health crises, have attracted the attention of scholars (Abid et al., 2022; Nazar et al., 2022). Due to resource scarcity, resource-scarce countries face severe challenges, notably in addressing climate change, protecting biodiversity, and reducing pollution (Hu, 2023).

According to a survey conducted by the International Energy Agency, in resource-scarce countries most affected by climate change, nearly 90% of the population cannot receive healthy water supplies (Salehi, 2022). In addition, the agency found that nearly half of the world’s population currently lives in highly uneven climate conditions, which would make it difficult for resource-scarce countries to implement effective climate change adaptation strategies (Birkmann et al., 2022).

The biodiversity estimate shows that the majority of countries experiencing significant biodiversity loss are resource-scarce countries (Habibullah et al., 2022). The assessment shows that biodiversity is declining dramatically due to increasing population pressure, agricultural expansion, mining, logging, fishing, tourism development, and other forms of expansion.

Due to limited resources, it is difficult for resource-scarce countries to effectively treat gaseous waste gas, industrial wastewater, agricultural chemicals, raw material waste, and biological waste. According to a survey conducted by the Global Health Department, most resource-scarce countries cannot have the capacity to effectively dispose of the aforementioned waste, which can pose a huge risk to public health (Narayanamoorthy et al., 2022).

In short, resource-scarce countries face enormous challenges in addressing climate change, protecting biodiversity, and reducing the public health risks posed by waste products because of their limited resources. For a country with limited resources to have a sustainable development system that can truly guarantee the health and happiness of the people, pay more attention to related issues and take strong and practical actions to promote sustainable development.

3.2. Insufficient infrastructure

With the development of the population, economy, and ecological system in countries worldwide, the problem of resource imbalance has become increasingly prominent. Some countries have many natural resources, while others barely have any. Such imbalances can have major implications for sustainable global development.

Regarding transport, resource-scarce countries often lack efficient road and rail networks. This causes people to face the problem of inconvenient transportation in their daily life and business activities. Additionally, this affects the development of agriculture and manufacturing because the lack of good transportation infrastructure makes it difficult to transport materials (Zhao et al., 2022). Simultaneously, it may also harm the tourism industry, as tourists need good transport infrastructure to reach their desired destinations (Hafid et al., 2022).

Regarding communications, resource-scarce countries often face difficulties. Many people lack basic communication tools such as mobile phones and the Internet. This makes people limited in information transfer and communication (Zhang et al., 2022). This can harm economic development, as modern economies require efficient communication networks to support commerce and trade.

In the energy sector, some resource-scarce countries lack reliable energy supplies. This makes people face the problem of power outages and lack of fuel in daily life. Simultaneously, it also hurts the development of the industry and manufacturing industry because these industries require a lot of energy to support the production process (Jamil, 2022). The lack of a reliable energy supply can lead to instability in energy prices, which can adversely affect the economy.

Regarding water resources, some resource-scarce countries are facing the problems of water resource shortages and water pollution. This makes people face drinking water difficulties and sanitation problems in their daily life. Simultaneously, it negatively affects agriculture and fisheries, as these industries require sufficient water resources to support the production process (Morin-Crini et al., 2022).

Some resource-scarce countries cannot function properly due to inadequate infrastructure. According to the “2018 Gross National Product” (GDP) and “2018 Capacity Distribution” (CDI), more than 90% of people in low- and middle-income countries live without access to electricity, water, and healthcare services (Torres et al., 2019; Yakubu et al., 2022). In addition, more than 85% of people live without access to necessary education services and necessary road construction jobs (Singh et al., 2023). This means that most low-income countries do not have access to advanced, information technology (IT)-based services in communication, capacity, education, healthcare, capacity development, and agriculture and therefore cannot develop sustainably (Cai et al., 2023; Bai et al., 2023). Equally important: since low-income countries cannot have the capacity to develop new sources of energy or use new sources of energy to replace traditional sources of energy (such as crude oil, natural gas, or hydropower), they are unable to harness new sources of energy to reduce their impact on climate change, which also hinders the implementation of the Sustainable Development Goals in low-income countries.

Some low-income countries possess large quantities of natural gas, atomic energy, or mining resources (including copper, iron, or gold) but cannot develop these natural gas, atomic energy, or mining resources. This prevents them from implementing sustainable development goals. Example: As recently as July 1, 2008, Nigeria was in the midst of a complex situation, in which it had vast reserves of atomic energy, natural gas, copper, iron, and gold but was unable to develop them (Afolabi, 2019).

In summary, the irrational distribution of natural resources leaves some countries with large amounts of natural resources at the expense of others, who do not benefit for specific reasons, including inadequate infrastructure, that can impede the implementation of the Sustainable Development Goals.

3.3. Poverty and social inequality

Many resource-scarce countries often face poverty and social inequality, another important factor that makes sustainable development difficult. Due to economic and resource scarcity, populations in many resource-scarce countries live in extreme poverty, lacking food, water, and basic medical facilities (Seferidi et al., 2022). In some countries, the problems of resource scarcity and social inequality reinforce each other, forming a vicious circle that leads to unstable, unjust, and unsustainable social development (Schüle et al., 2019).

A report issued by the United Nations noted that although Africa is rich in natural resources, its per capita GDP is the lowest in the world. According to data from the World Bank, the poverty rate in sub-Saharan Africa is as high as 40%, and approximately 400 million people live in extreme poverty (Salecker et al., 2020). These data show a strong link between poverty and resource scarcity and suggest that achieving Sustainable Development Goals can be enormously challenging in the absence of resources.

Therefore, a range of policies and measures are required to address poverty and social inequality in resource-scarce countries (Wang et al., 2023). These include improving infrastructure, strengthening education and training, promoting technological innovation, reducing agricultural and food waste, improving public health and medical facilities, promoting social justice and equality, and improving political stability and governance. Only through the implementation of these measures can a stable, prosperous, and sustainable social system be established in resource-scarce countries.

3.4. Environmental damage and climate change

Other important issues facing resource-scarce countries are environmental destruction and climate change. The development of the economy and society requires many resources and much energy consumption, which leads to the destruction of the environment and the collapse of the ecosystem (Waheed et al., 2019). Environmental damage and climate change are particularly problematic in some countries, including oil-exporting countries. These countries depend on the export of resources, including oil; however, the greenhouse gas emissions and environmental damage caused by these exports have attracted global attention (Yusuf et al., 2020).

Simultaneously, climate change has brought many challenges to resource-scarce countries. These countries cannot generally adapt to climate change, so the impact of climate change has a great impact on their economic and social development. Extreme weather events such as droughts, floods, and sea-level rise can lead to reduced agricultural harvests, water shortages, and infrastructure damage (Beillouin et al., 2020). These factors may further exacerbate poverty and social inequality, leading to social instability and unsustainable development.

To address these challenges, a series of measures are needed. These measures include reducing greenhouse gas emissions, improving energy efficiency, promoting renewable energy, protecting ecosystems and natural resources, strengthening environmental monitoring and management, promoting a low-carbon economy, and strengthening the ability to adapt to climate change (Bi et al., 2023). These measures help to mitigate the effects of climate change and environmental damage and promote sustainable economic and social development, thereby achieving sustainable development goals for resource-scarce countries (Fernando et al., 2022).

In conclusion, the challenges faced by resource-scarce countries are multifaceted, including economic development, social stability, poverty and social inequality, environmental damage, and climate change. To achieve the Sustainable Development Goals, a series of comprehensive measures are needed, including improving infrastructure, strengthening education and training, promoting technological innovation, reducing waste, improving public health and medical facilities, promoting social justice and equality, and strengthening environmental protection and resilience to climate change. Sustainable development in resource-scarce countries and global sustainable development goals can solely be achieved through international cooperation and joint efforts.

4.1. People’s living standards

Improving people’s living standards has always been a vital objective of national development and a crucial aspect of sustainable development. The effective adoption of sustainable development strategies plays a pivotal role in achieving this goal. Resource-rich countries can employ sustainable development principles, utilizing their abundant natural resources to develop diverse industries, create employment opportunities, and stimulate economic growth, thus enhancing the living standards of their citizens. For instance, China’s implementation of sustainable development practices has resulted in a nominal increase of 6.9% in the country’s total GDP and a real increase of 7.3% in the per capita disposable income of rural residents (Shi et al., 2019). However, it is important to note that resource-scarce countries can also enhance their citizens’ living standards through the adoption of sustainable development strategies.

Resource-scarce countries implement sustainable development, save energy, reduce waste, protect natural ecology, and make efficient use of natural resources. In South Africa, where resources such as land, water, oil, and electricity are scarce, the South African Department of Energy uses a “Strategic Energy Plan” to implement sustainable energy development. According to the department’s 2018 annual energy audit, South Africa reduced its electricity consumption by 43.77 million megajoules; from 2006 to 2016, the actual change in South Africa’s electricity energy efficiency was significant (+14.3%) (Baker and Phillips, 2019). Additionally, South Africa has greatly reduced the waste of natural resources and improved the living standards of local people by reducing waste, promoting recycling, and strengthening the integration of industrial chains.

Resource-scarce countries can save energy, reduce waste and protect natural ecology by adopting sustainable development strategies. In South Africa, the South African Department of Energy adopts a “Strategic Energy Plan” to implement sustainable energy development (Mutezo and Mulopo, 2021). South Africa has greatly reduced the waste of natural resources and improved the living standards of local people by reducing waste, promoting recycling, and strengthening the integration of industrial chains. Sustainable development can effectively improve people’s living standards in the country and protect the natural environment. In recent years, countries worldwide have faced serious challenges of environmental pollution and its impact on sustainable development (Seddon et al., 2020). Resource-rich countries must realize that their natural resources are limited, and overuse of these resources may lead to environmental damage, thereby affecting sustainable development. Many oil-exporting countries have neglected environmental protection in the process of economic development, resulting in problems such as oil field pollution, deforestation, and wildlife extinction. Consequently, these countries need to adopt sustainable development strategies to ensure that their natural resources are used rationally and protected.

Conversely, resource-scarce countries may face greater challenges due to environmental pollution and climate change, as they often rely more heavily on the environment for their economic and social development. Sustainable development is particularly crucial for these countries, as it enables them to address environmental challenges, promote resource efficiency, and ensure the long-term sustainability of their economic and social progress.

In summary, the adoption of sustainable development principles is instrumental in improving people’s living standards and protecting the natural environment in both resource-rich and resource-scarce countries.

4.2. Ecological environment

In recent years, the detrimental impact of environmental pollution on sustainable development has become increasingly evident, posing a significant global challenge. According to the 2015 Global Environmental Responsibility Report, more than 600,000 people die each day due to air, water, and other forms of pollution. It is projected that at least 158 million individuals will succumb to air, water, and soil pollution within the next three decades (Vohra et al., 2021). Moreover, the emission of chemical substances, including carbon dioxide and methane from fossil fuel consumption, such as coal, oil, and natural gas, has adverse effects on global climate change and ecosystems. Thus, protecting the environment has become an imperative requirement for sustainable development.

Environmental protection plays a pivotal role in implementing sustainable development for several reasons. Firstly, it helps mitigate environmental impacts by reducing resource and energy waste, maximizing the efficient utilization of limited resources, and preventing wasteful practices. Further, environmental protection contributes to minimizing the adverse effects of chemicals on ecosystems. The substantial decline in global biodiversity over the past fifty years, as documented in the 2017 Review of Ecology, can be attributed, in part, to the harmful effects of excessive chemical use (Sugai et al., 2019). The harm to ecosystems caused by large quantities of chemicals is one of the reasons for this. Therefore, protecting the environment helps to reduce harm to the ecosystem while simultaneously helping to ensure the safety of people’s lives. Lastly, protecting the environment helps promote sustainable development. Currently, all countries in the world have issued various laws and regulations to strictly monitor and protect the public interest, strengthen the monitoring of relevant departments, develop new energy sources, reduce waste gas and waste, start “low-carbon” and “no-waste gas” production methods and carry out “low energy consumption” and “zero waste” behaviors (Hu et al., 2023b). These measures are actions taken to ensure people’s survival. Ensuring ecological security, reducing the use of chemical substances, optimizing energy distribution, and innovatively applying new energy can help bring people into a truly “low energy consumption” era.

In conclusion, protecting the environment is a vital component of sustainable development. It aids in reducing negative impacts on ecosystems, promotes low energy consumption and zero waste practices, and ensures sustainable development. Therefore, all countries must adopt effective policy measures, fully recognize the importance of environmental protection, and promote the restoration of ecosystems, thereby enabling humanity to transition into a genuine era of low energy consumption and achieve sustainable development.

4.3. Energy production and utilization methods

Sustainable development aims to protect the environment, meet current needs, and ensure future social, economic, and cultural development. One of the key influencing factors is the improvement of energy production and utilization, which plays an important role in mitigating the differences between resource-rich and resource-scarce countries.

Taking China as an example, China is a country with scarce energy, but the government’s emphasis on energy utilization has led China to vigorously promote new energy power generation in 2016, and its total installed capacity of new energy power generation has increased by more than 200% between 2016 and 2019. According to the “2019 China New Energy Power Generation Market Development Report”, the total installed capacity of new energy power generation in the country reached 73,000 MW in 2019, accounting for 26.4% of the country’s total installed capacity. Among them, wind power capacity accounts for 61.0%of all new energy installed capacity, solar energy capacity accounts for 20.1%, and biomass energy, hydropower energy, and geothermal energy account for 7.3%, 5.3%, and 2.6%, respectively (Li et al., 2022a).

China has made substantial improvements in conventional energy generation. Relying on a variety of traditional power generation methods, including nuclear power, gas, thermal power, hydropower, and coal power, China achieved 35% of low-carbon power generation in 2018, and the proportion of low-carbon power generation in 2019 exceeded 40% (Fan et al., 2020). Conventional power generation is an essential source for safeguarding public life in China.

Countries should address resource disparities through concerted efforts and robust policies. Pertinent departments should strengthen the formulation and implementation of laws and regulations about new energy and its utilization, fostering the production and consumption of new energy sources. Moreover, countries should enhance cooperation, establish labor divisions, and avoid unnecessary competition in traditional energy utilization. Additionally, promoting the development and utilization of advanced storage, recycling, and renewable energy technologies is essential in reducing waste in traditional energy consumption.

In conclusion, endeavors to bridge resource disparities between countries significantly contribute to promoting sustainable development. Strengthening the production and utilization of new energy, optimizing traditional energy utilization to minimize waste, and international collaboration are effective means of advancing sustainable development.

2.1. SDE and environmental regulation policy

The debate on how environmental regulation policies affect sustainable development is a recent development in the literature. Specifically, after the Paris accord, the worldwide economists tended to analyze the association at firm and national level while focusing on the direct and indirect channels.

The environmental regulation policies play a crucial role in supporting the sustainable development (Appiah et al., 2023). For instance, Sun et al. (2023) observed the same outcome while analyzing the impacts of environmental regulations on green growth via triggering the green energy markets for China's coastal areas. Another study on China by Zheng et al. (2023) assessed the effects of environmental regulations on green total factor productivity (a proxy for sustainable development) and concluded that favorable impacts of environmental regulation. This phenomenon is observed for 108 cities in the Yangtze River Economic Belt, China. Also, the same results were deduced by Jin et al., 2023a, Jin et al., 2023b for China, while using the green total factor productivity as measure for sustainable development. Additionally, there are some researchers which use some other economic variables to measure sustainable development and analyze how such variables respond to the environmental regulations. For example, Wang et al., 2023a, Wang et al., 2023b, Wang et al., 2023c deploy green transformation performance as measure of sustainable development, while taking data for 49 large- and medium-sized iron and steel firms in China. It was affirmed that environmental regulations foster the green transformation performance. Binh An et al. (2023) identified that environmental regulations exhibited a supportive behavior towards sustainable development through enhancing the environmental quality in top eight advanced nations. Sadiq et al. (2023) developed the sustainable development index in order to measure the sustainable development. The results demonstrated that environmental regulations significantly promoted the development in ASEAN nations. The same phenomenon was witnessed by Zhao et al. (2022), Zheng et al. (2023), & Zou and Zhang (2022) for China, Abban et al. (2022) and Ahmad et al. (2021) for G7 nations, Hao et al. (2022) for selected global economies, and Zhou et al., 2022a, Zhou et al., 2022b for China.

Based on the above anecdotal evidence, it can be inferred that environmental regulations play a vital direct and indirect role in determining the sustainable development. Therefore, it is rational to further hypothesize that environmental regulation can significantly contribute in triggering the sustainable development efficiency.

2.2. SDE and human capital

Huma capital, among the several important drivers of economic development, plays a key role in achieving the sustainable development through triggering the productivity, economic diversification, and innovation (Schultz, 1993). The exploration of the nexus between human capital and sustainable is not a new phenomenon. However, the available literature indicate that majority of the previous studies intended to analyze the indirect effects of human capital on sustainable development. However, the pertinent literature lacks the direct effects of human capital on sustainable development, calling for more exploration in this area.

Assessing the effects of human capital on sustainable development, Friderichs et al. (2023) observed that human capital's role is significant via disrupting the income inequality in South Africa. Wang et al., 2023a, Wang et al., 2023b, Wang et al., 2023c also reported that human capital was among the crucial economic variables which significantly enhanced the sustainable development through improving the environmental quality for the sample of 208 nations. The same results were documented by Saqib et al. (2023) for selected 16 European economies. Also, Nkemgha et al., 2023a, Nkemgha et al., 2023b witnessed that human capital triggered the erection of new infrastructure, industrialization process, and consequently economic growth. The study concluded that human capital was a crucial variable for boosting the sustainable development in Africa. A study on China by Jin et al., 2023a, Jin et al., 2023b assessed the effects of innovative human capital on sustainable development through the channel of green total factor productivity. The findings suggested the important role of human capital innovation in upsurging the green total factor productivity. Similarly, Hondroyiannis et al. (2022) for selected global nations, Opoku et al. (2022) for OECD nations, Shahbaz et al. (2022) for China, and Rafi et al. (2021) for India reported that human capital played an essential role in fostering the sustainable development through boosting various macroeconomic variables.

The above review supports the argument that human capital is an essential factor to put the economy on the path of sustainable development. However, the dashboards leave a difficult task for readers to understand the measurement of sustainable development as the pertinent studies use several proxies to measure the sustainable development (Hirai and Comim, 2022). Simply put, majority of the previous studies analyze the indirect effects of human capital on sustainable development. Hence, the prior literature calls for developing a more comprehensive measure for sustainable development to assess the direct effects while hypothesizing the favorable effects of human capital on sustainable development.

2.3. SDE and urbanization

Urbanization is one the crucial economic drivers which significantly influence the sustainable development (Hoselitz, 1957). The mainstream literature dashboard argues that, on the one side, urbanization process significantly thrives the economic growth, and on the other side, it deteriorates the environmental quality through emitting the carbon emissions. Hence, the effects of urbanization on sustainable development remains contradictory. Further, most of the studies assess the effects of urbanization on sustainable development indirectly.

Many studies (Dilanchiev et al., 2023; Khan and Majeed, 2023; Fan et al., 2023; Chen et al., 2023; Liang et al., 2022; & Zhou et al., 2022a, Zhou et al., 2022b) have identified that urbanization considerably escalates the economic growth through creating the jobs, erecting the infrastructure, and expanding the market size. Contrarily, some of the studies argued that urbanization disrupt the economic growth process by increasing the enormous resources depletion (Pata and Ertugrul, 2023; and Chien et al., 2023) and income inequality (Zhao et al., 2023; Wang et al., 2023a, Wang et al., 2023b, Wang et al., 2023c; Sun (2023). In a similar vein, numerous studies (Naqvi et al., 2023; Chen et al., 2023; Huo et al., 2023; Lee et al., 2023; Li et al., 2023; Numan et al., 2023; Xie et al., 2023a, Xie et al., 2023b; & Liu et al., 2023a, Liu et al., 2023b) that deduced that urbanization process had adverse effects on sustainable development through degrading the environmental quality while the studies relied on the various proxies to measure the environmental quality.

Based on above review, it can be inferred that urbanization, one the one hand, supports the economic growth and on the other hand, it deteriorates the environmental quality. Thus, the effects likely effects of urbanization process on sustainable development remain contradictory or may be overall harmful since sustainable development requires an upsurge in economic growth along with green environment. Therefore, it is logical to hypothesize that urbanization may have positive or adverse effects on the sustainable development.

2.4. SDE and industrialization

Industrialization, as a basic pillar, significantly influences sustainable development by accelerating the economic growth process. The popular literature generally contends that, on the one hand, industrialization process considerably boosts economic growth but, on the other hand, it degrades environmental quality by producing carbon emissions. As a result, the consequences of industrialization on sustainable development continue to be inconsistent.

For instance, Nkemgha et al., 2023a, Nkemgha et al., 2023b, Shah et al. (2023), Liao et al. (2023), and Naeem et al. (2023) infer that industrialization plays a key role in determining the economic growth through enhancing the infrastructure, increasing the productivity, creating jobs, promoting the transfer of technology and innovation, and enhancing the trade. However, some scholars argue that industrialization is accountable for social inequality through causing the income inequality (Ali, 2023a; Ali, 2023b; Khan et al., 2023). Similarly, several studies (Naeem et al., 2023; Liao et al., 2023; Voumik and Ridwan, 2023; Caglar and Askin, 2023; Xie et al., 2023a, Xie et al., 2023b; & Rehman et al., 2023) assess the effects of industrialization and deduce that environmental degradation rises due to industrialization.

Based on the above literature, it can be inferred that industrialization encourages the economic growth along with discouraging the environmental sustainability and causing the income inequality. Such literature-based contradictory findings pose the query whether industrialization can contribute towards sustainable development or not. Therefore, it is logical to hypothesize the positive or negative effects of industrialization on sustainable development efficiency.

2.5. Refreshing the literature gap

The above critical review indicates that environmental regulation policies, human capital, industrialization, urbanization, and GDP play an essential role in shaping sustainable development efficiency. However, the prior literature did focus on the following aspects: First, the prior literature could not deploy a comprehensive indicator to measure the efficiency of sustainable development and analyze its response to environmental regulation policies.

4.1. Non-parametric panel data model (with time-varying trend and coefficients functions)

This segment briefly introduces the non-parametric method deployed to compute the time-varying trend and coefficients. Following Li et al. (2011), and Zhang et al. (2021), the local linear dummy variable estimate (LLDVE) is utilized and developed in Churchill et al. (2019) and Hailemariam et al. (2019) as per instructions of Moghaddam and Lloyd-Ellis (2022). 

Next, the study tends to deploy the novel Wavelet Quantile Correlation (WQC) by Kumar and Padakandla (2022). The WQC method offers several advantages, one of which is its ability to estimate the presence of asymmetric links between selected series by calculating results at different quantiles. Estimating quantile-wise results offers a significant advantage in generating robust findings by addressing the influence of outliers resulting from economic shocks (Rehman et al., 2023; Naeem et al., 2023; Farid et al., 2021; Naeem et al., 2020; Umar et al., 2022; Balli et al., 2019; Chishti et al., 2023).

${\mathrm{WQC}}_{\mathrm{\tau }}({\mathrm{d}}_{\mathrm{j}}\left[\mathrm{X}\right],{\mathrm{d}}_{\mathrm{j}}\left[\mathrm{Y}\right]=\frac{{\text{qcov}}_{\mathrm{t}}({\mathrm{d}}_{\mathrm{j}}\left[\mathrm{X}\right],{\mathrm{d}}_{\mathrm{j}}\left[\mathrm{Y}\right]}{\sqrt{var\left({\mathrm{\theta }}_{\mathrm{\tau }}\left({\mathrm{d}}_{\mathrm{j}}\left[\mathrm{Y}\right]-{\mathrm{Q}}_{\mathrm{\tau },{\mathrm{d}}_{\mathrm{j}}\left[\mathrm{Y}\right]}\right)\right)var\left({\mathrm{d}}_{\mathrm{j}}\left[\mathrm{X}\right]\right)}}$

Where X, and Y = the independent and dependent series, respectively. Further, the time-period given in the WQC's outcome-based heatmaps can be split into three-time scales (viz, short run, medium run, and long-run) to understand the association between series across the different time horizons.

4.3. Non-parametric panel granger causality test

As a second robustness check, the study opts to deploy the novel non-parametric panel granger causality (NPPGC) test by Dong et al. (2021). There are numerous panel granger causality tests to detect the bidirectional causality; however, these tests lack to tackle the advanced econometric issues such as cross-sectional dependence, outliers' effect, and heterogeneity in the panel data. Therefore, Dong et al. (2021) propounded a novel NPPGC test to compute the robust and nonlinear causality between the panel series via a hybrid 

4.4. Parametric panel data model

Primarily, the study aims at deploying the nonparametric panel method elaborated in the previous section to explore the time-varying effects of shocks in ERP and HC with the consort some other economic series on SDE for Chinese provinces. However, to justify the application of LLDVE technique, the study briefly discusses the two parametric, viz., Difference GMM by Arellano and Bond (1991) and CS-ARDL by Chudik and Pesaran (2015) as benchmark exercise.

The above both (Difference GMM, and CS-ARDL) methods belong to the advanced econometric techniques. Diff. GMM is extended form of the GMM method and CS-ARDL is the extension of ARDL technique. Among the several benefits, both techniques tackle not only the basic econometric issues such as autocorrelation and heteroscedasticity but also handle the advanced econometric issues such as cross-section dependence, heterogeneity, and endogeneity (Paleologou, 2022; Noureen et al., 2022). Further, both methods are famous in computing dynamic association among the modeled series. Hence, both methods are good representative of parametric methods' family which can estimate the consistent and reliable results.

4.5. Data and preliminary analysis

The recent paper aims at divulging the time-varying effects of positive and negative shocks in environmental regulation policies (PERP & NERP), positive and negative shocks in human capital (PHC & NHC), industrialization (INDS), urbanization (URB), and GDP on sustainable development efficiency (SDE). The study deploys “Command-and-control environmental regulation” as a measure of ERP, “human capital index” as a measure of HC, “industrial structure” as a measure of INDS, “urbanization” as a measure of URB, and GPD (per-capita) as measure of GDP for each province of China. Further, sustainable development, comprehensively, is the balanced economic growth in each sector of an economy along with maintaining the environmental quality (Bhattacharya and Bose, 2023). Simply put, the balanced growth along with environmental sustainability can represent the sustainable development. Hence, it is rational to measure the sustainable development efficiency (SDE) with carbon-adjusted GDP (Zhang et al., 2021).  

 The annual data for above series at are retrieved from China Statistical Yearbook (https://www.chinayearbooks.com/), China Industrial Enterprise Database (https://www.epschinastats.com/db_industrialenterprises.html), and China Emission Accounts and Datasets (https://www.ceads.net/) for 30 provinces of China from 1998 to 2017 due to the data availability restrictions. All the modeled series are in logarithmic form.

5.1. Parametric methods' results

The results above highlight several inconsistencies. For instance, there are contradictory findings concerning the impact of industrialization, and unexpected positive effects have been identified despite negative shocks to human capital. Additionally, the coefficients of PERP, INDS, and GDP are significant, yet their magnitudes are relatively low. These observations suggest that point estimates obtained through parametric methods may be imprecise. There may be two reasons for these inconsistencies in the results. Firstly, misspecification in the model tends to cause the inconsistent results. Secondly, the parametric methods compute only the on average effects of regressors on the dependent series while reporting a single point estimate. Thus, these methods cannot depict how PERP, NERP, PHC, and NHC influence the SDE over-time. Such loopholes in the outcome of parametric methods inspire to deploy nonparametric panel technique. Therefore, the next section reports the findings of non-parametric panel method.

5.2. Nonparametric panel technique results

This segment elaborates the outcome of the time-varying coefficients, and the common trend of SDE along with the province specific-trend functions.

5.2.1. Time-varying coefficients functions

Fig. 4 visualizes the LLDVE estimate-based time varying coefficient function of PERP, NERP, PHC, NHC, URB, INDS, and GDP to analyze their time-varying effects on SDE in China. The LLDVE results plainly suggest that the nexus between PERP-SDE is significantly time-varying. Specifically, the PERP coefficient exhibits a negative but insignificant influence on SDE till 2003. After that, it demonstrates a sharp rising trend that peaks in 2008 and before plummeting, with insignificant effects observed during 2013–2016. Subsequently, an upward and significant trend is observed. The reason being, the rapid industrialization process in 1990 in China tended to cause the severe environmental issues along with boosting economic growth. To handle the devastative environmental degradation, the Chinese government established “State Environmental Protection Administration” in 1998 through enforcing the environmental laws. Also, in 2006, Chinese authorities launched “Circular Economy Promotion Law” in order to promote sustainable development. Therefore, in Fig. 4, it can be seen an upward trend in ERP which demonstrates the favorable effects, specifically, after 2004. Economically, the such positive shocks in ERP trigger the sustainable development through promoting the new and clean technologies. This process tends to expand the labor market by creating the new jobs. It leads to trigger the SDE along with improving the environmental quality by reducing the greenhouse gases, specifically, carbon emissions (Jin et al., 2023a, Jin et al., 2023b; and Wang et al., 2023a, Wang et al., 2023b, Wang et al., 2023c). Also, the positive trends in ENP encourage the sustainable development efficiency through decreasing the waste and natural resources depletion. Similarly, such positive changes in ERP boost the sustainable development through promoting the international collaboration in order to address the global environmental issues in China. Furthermore, another notable aspect in the graph is a sudden fall in NERP coefficient function after 2008. The likely reason is global financial crises which was started in 2007 and ended in 2008. In response, the global economy has to endure a significant fall in each sector of economy including the Chinese economy (Zou and Zhang, 2022). Therefore, ERP exhibits a downward trend while affecting the sustainable development efficiency.

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Fig. 4. Nonparametric local linear estimates of common trend and coefficient functions. Note: The confidence interval for each estimate is 95% for significance level.

Conversely, NERP has significant and time-varying effects on SDE such that during the all-time period, the NERP show an adverse effect on SDE except for time (i.e., 1998–2000) which exhibits the insignificant negative effects. Logically, the negative shocks in ERP hurt the sustainable development through disrupting the new and clean technologies process. This process tends to contract the labor market by hindering the jobs. It results in dwindling the economic growth along with deteriorating the environmental quality by increasing the greenhouse gases, specifically, carbon emissions. Summing up, the results plainly indicate that upward trend in ERP significantly supports and the downward trend in ERP deteriorates the sustainable development efficiency in China. The aforementioned findings are distinct, as prior studies (Zhao et al., 2022; Zhang et al., 2021; Zhou et al., 2022a, Zhou et al., 2022b; Ahmed et al., 2022) have overlooked the asymmetric effects of ERP on sustainable development.

As for the effects of PHC, the results determine that PHC coefficient's function visualizes the time-varying nexus with SDE such that the upward trend in human capital significantly encourages the SDE specifically after 2009. It implies that PHC plays a supportive role in triggering the SDE after 2009. While before 2009, the effects remain positive but insignificant. There may be several reasons for these results. For instance, Chinese government has taken several education reforms since 2005. In 2010, the “New Curriculum” was introduced to promote the technical and innovative education across the China (Opoku et al., 2022). Also, Chinese authorities invest a large chunk of budget on rural education in order to enhance the overall education level at nation-level as 32 billion dollars were invested on rural education in 2018 (Chen et al., 2023). Since the rise in education level and technological progress tend to increase the number of efficient workers (Solow, 1956), this process leads to enhance the number of efficient human capital. Thus, economically, it can be argued that the upward trends in the human capital market tends to enhance the productivity level in an economy on account of higher level of education, skills and experience. It leads to trigger the economic growth (Hondroyiannis et al., 2022; Opoku et al., 2022; and Shahbaz et al., 2022). Contemporality, the higher level of education, skills and experience foster the process of innovation which consequently, improve the environment along with thriving the economic growth through boosting the green technologies. Also, the ability for better decision making on account of education and experience increases the efficiency; it, in response, boosts the growth along with improving the environmental quality. Fan et al. (2023), Chen et al. (2023), and Liang et al. (2022) support the above findings and argue that human capital is an essential source to boost the sustainable development process.

Focusing on the negative shocks in the human capital (NHC), it can be witnessed that the downward trend in HC significantly discourages the SDE process over the most of the time. It clearly suggests that any external shock that disrupt the human capital progress results in decreasing the SDE. Logically, it can be inferred that the downfall in the human capital causes the depletion of natural resources inefficiently due to heavily dependence on fossil fuels and low ratio of green technologies. This process tends to hurts the environmental quality along-with increasing the economic growth, implying the downfall in SDE. Again, this is another unique aspect of the study which confirms the adverse effects of NHC on SDE.

Whereas the effects of GDP on SDE are concerned, the findings suggest that GDP has a significant and positive impact on SDE, particularly after 2003. Moreover, these favorable effects vary over time, with the strongest impact observed until 2007, followed by a decline that likely reflects the adverse effects of the global financial crisis in 2007–08. However, a gradual recovery is evident thereafter, which accelerates significantly after 2014. The results imply that overall GDP significantly contributes in fostering the SDE over-time, specifically, after 2014. Plausibly, the rising budget allocation by Chinese authorities to trigger the sustainable development plays a key role in this regard. For example, $366 billion dollars were allocation by China's National Development and Reform Commission for renewable energy sector development in 2008. In 2012, a package of $1.9 billion were allocated to encourage the use of environmentally friendly products. Further, China released $382 billion under the program of “13th Five-Year Plan for Energy Development” in 2015, $290 billion under program of “Guiding Opinions on Accelerating the Development of Green Finance” in 2016, and $5 billion in 2019 in order to promote green energy development through green finance (Naeem et al., 2022a, Naeem et al., 2022b, Siddique et al., 2023). All such measures significantly contribute in thriving the economic growth by fulfilling the energy demand. This process leads to enhance the economic growth along with improving the environmental quality through increasing the SDE.

Regarding the effects of industrialization (INDS), the results indicate that SDE process has to face significant loss on account of INDS as the negative association is observed. Further, these linkages are dynamic over time, with the magnitude of adverse effects appearing to increase and become more intense during 2016–17 (Karim et al., 2022d, Naeem et al., 2023c). Economically, the Chinese economy heavily relies on the industrial sector as its contribution to GDP was recorded by 39.4% in 2021 (Investopedia, 2022) with the growth rate of 8.1% (World Bank, 2022). The rapid growth in industrial sector requires a large amount of energy which is mainly stemmed from fossil fuels. For instance, coal accounted for 63.6% of total electricity generation in 2021 (Statista, 2023). This process, ultimately, leads to degrade the environment which results in a downward trend in SDE. These results are in the line with Naeem et al. (2023), Liao et al. (2023), Naeem et al., 2022, Naeem et al., 2023a, Naeem and Karim, 2021 and Voumik and Ridwan (2023).

In the case of urbanization, the same findings are witnessed as of INDS. However, the magnitude of adverse effects tends to fall over time such that it becomes insignificantly positive after 2014. Also, Naqvi et al. (2023), Chen et al. (2023), Huo et al. (2023), and Lee et al. (2023) support the above results while arguing that urbanization impedes sustainable development growth process through producing the greenhouse gases.

5.2.2. Common and province-specific trend function

This segment of the paper visualizes the LLDVE-based estimates of common trend for SDE, as given in Fig. 4, along with the province specific trend functions for each province, as depicted in Fig. 5A, and B. The notable aspect of the LLDVE method is that it allows the trend function to evolve with unknown functional forms over the time to capture the likely trending phenomenon, unlike the parametric methods which assume the linear trend in the panel models. Also, province-specific trends are documented in order to confirm whether the heterogeneous trends across the provinces exist or not.

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Fig 5. A Nonparametric local linear estimates of province-specific trend functions. Note: The confidence interval for each estimate is 95% for significance level.

B. Nonparametric local linear estimates of province-specific trend functions. Note: The confidence interval for each estimate is 95% for significance level.

Regarding the common trend function for SDE, it can be observed that the common trend has, overall, an upward and significant trend, implying that SDE is consistently escalating over time. Particularly, a sharp upward has been witnessed since 1998, followed by a slight downfall after 2001 till 2004. Possibly, the downfall from 2001 to 2004 reflects the deteriorating impact of the 9/11 event (Karim et al., 2023b, Mbarki et al., 2023, Naeem et al., 2023b). The same downward trend is also observed after 2007, implying the adverse effects of the financial crisis in 2007–08. Another decline can be seen after 2014, indicating the possible negative effects of the financial crisis in 2014 (Karim et al., 2022b, Karim et al., 2023a, Karim and Naeem, 2022, Pham et al., 2022, Siddique et al., 2022). Summing up, SDE's common trend has the predominant upward trend while also depicting the adverse effects of various economic shocks over time (Benlagha et al., 2022, Billah et al., 2022, Farid et al., 2023, Karim et al., 2022a, Karim et al., 2022c, Karim et al., 2023a).

This segment also visualizes the province-specific trend patterns in order to affirm that whether these trends follow the pattern of common trend function or not as depicted in Fig. 5A and B. It can be observed that, out of 30 provinces, 18 provinces' individual trends closely follow the pattern of common trend, implying that these provinces have gaining the same benefits regarding enhancing the SDE. The remaining 12 provinces' individual trends demonstrate the significant differences from the common trend function, implying heterogeneity across these provinces from the main trend function. Further, most of these 12 provinces' individual trend pattern remain above the common trend pattern, indicating that SDE rate is high in these provinces as compared to the national level SDE rate.

5.3. Robustness check

To assess the robustness of the main results based on LLDVE estimates, the study relies on two novel methods: Wavelet Quantile Correlation (WQC) method and non-parametric panel granger causality (NPPGC) test.

5.3.1. Wavelet quantile correlation

To do so, the study converts the provincial level annual data into quarterly data, following Chishti et al. (2023), Qingquan et al. (2020), and Shahbaz et al. (2018), in order to capture the detailed information. Next, all series are summed to make them representative of all provinces. Before diving into discussion of the WQC outcome, it is worth noting that the results of WQC are visualized in heatmaps and the color-bar given in right-side of each heatmap exhibits the significance and intensity of the effects. Further, it is assumed that quantiles 1–3 indicate the short-run, quantiles 4–6 indicate medium-run, and quantiles 7–9 indicate the long-run. The vertical axis of each heatmap shows the sample time. All the results are reported in Fig. 6. (See Fig. 7.)

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Fig. 6. Wavelet correlation method's results.

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Fig. 7. Non-parametric panel granger causality test outcome.

Regarding the effects of PERP, the results plainly support the outcome of LLDVE. The findings reveal that PERP has approximately insignificant impact on SDE during short to long run over 1998Q1 to 2007Q4 with the exception of 3rd to 6th quantiles in 2002Q4 that show significantly positive effects. After 2008Q1, SDE gains the considerable benefits on account of PERP. On the other hand, the NERP demonstrates the significant adverse effects on SDE level during the all (short-long) runs over the all-time, implying that the negative shocks in ERP disrupt the process of SDE in China, supporting the LLDVE estimate (Alawi et al., 2023, Appiah et al., 2022, Arfaoui et al., 2023).

In the case of PHC and NHC, the results exhibit that PHC predominantly supports and NHC discourages the SDE level over the time across the various time horizons. Similarly, INDS significantly deteriorates the SDE process over most of the time across different time horizons except for a few quantiles in the short and medium run which demonstrate the favorable effects. The same results are observed in the case of URB. In the case of GDP, it is visualized that GDP plays an essential role in fostering the SDE as GDP possesses clearly positively effects on SDE across all runs over most of the time period. Summing up, WQC estimates validate the main results by supporting the estimates of LLDVE.

6.1. Policy recommendations

The results of this study are of utmost importance for deriving policy recommendations. The findings provide confirmation of the time-varying association between positive and negative shocks in environmental regulation policies, as well as positive and negative shocks in human capital, industrialization, urbanization, and GDP, and their impact on sustainable development efficiency (SDE). These results highlight the critical role of considering the dynamic interplay between these factors when formulating effective policies.

Firstly, the findings reveal that positive and negative shocks in environmental regulation policies (ERP) have the favorable and adverse effects on development efficiency, respectively, over the time. In particularly, the negative shocks in ERP are more sensitive to SDE. Before implementing the relevant policies, it is worthy to enhance the risk profile of SDE projects to delink the plausible effects of other economic shocks. It will help in understanding the exact effects of relevant variable's policies implication on the SDE. Possibly, the phase-wise policies can assist in triggering the ERP process.

Phase 1: Short-term measures.

In the initial phase, the authorities should focus on setting more stringent standards for pollution control by strengthening the regulatory bodies accountable for enforcement. Contemporarily, the policy-makers should suggest to increase the penalties for non-compliance in order to generate the finance as ERP heavily rely on the environmental regulatory funds. Also, this step may assist in avoiding the budget deficit while sparing the funds for ERP.

Phase 2: Mid-term measures.

In the second phase, the rise in ERP subsidies along with enhancing the transparency of regulatory enforcement can help in increasing the influence of ERP. Such steps may help in increasing the effectiveness of ERP, resulting fostering efficiency of sustainable development.

Phase 3: Long-term measures.

In the third phase, the authorities should increase the public awareness in order to obtain the feedback on the regulatory authorities for improvement. Also, the provision of research & development-based budget can help the triggering the environmental regulation through promoting the new technologies. These phase-wise policy implications can encourage the upward trend in ERP and disrupt the negative trend in ERP; ultimately, this process can foster the SDE.

Second, the shocks in human capital are highly sensitive to the SDE, calling for applying the optimal policies which can improve the positive trend in human capital while minimizing the effects of adverse shocks.

Phase 1: Short-term measures.

Initially, the authorities should target the enhancement of human capital through promoting the literacy and numeracy, along with encouraging the vocational and technical skills development.

Phase 2: Mid-term measures.

In the next stage, the authorities should prefer to minimize the negative shocks in human capital by preventing workplace accidents, improving workplace safety, and reducing exposure to hazardous substances. Additionally, the provision of affordable access to medical care for all citizens can also assist in minimizing the adverse shocks in human capital.

Phase 3: Long-term measures.

In the final stage, a regular and consistent evaluation and monitoring process can help in assessing whether the deployed policies to enhance human capital and avoid the negative shocks in human capital fall in the area of success and further measures can be taken to triggers these policies to accomplish the targeted goals.

Third, the results suggest that industrialization and urbanization have harmful effects on SDE. The following step-wise policies can be drawn.

Phase 1: Short-term measures.

At initial stage, to accommodate expanding industrial and urban areas, the government should center on planning and infrastructure development. Policies should be put in place to ensure that industrial development is sustainable and does not harm the environment. Emissions limits, garbage collection schedules, and limits on material use are all examples of possible measures. Similarly, Urbanization strategies should focus on providing appropriate housing, transportation, and public services such as healthcare and education. Infrastructure development should prioritize green areas and public parks to create a healthy living environment.

Phase 2: Mid-term measures.

The second stage should push for environmentally friendly industrialization practices and technologies to be widely adopted. Clean technology and energy efficiency practices could be more widely adopted with the help of government policies like tax credits, grants, and subsidies.

Phase 3: Long-term measures.

The final phase should focus on monitoring and evaluating the effectiveness of the policies implemented in the previous phases, along with promoting sustainable urbanization. This could include policies to promote public transportation, walking, and cycling, and discourage the use of private vehicles. Green buildings and energy-efficient technologies should also be promoted to reduce energy consumption.

6.2. Limitations and future directions of research

The study focuses on the time-varying effects of the positive and negative shocks in environmental regulation policies, the positive and negative shocks in human capital, industrialization, urbanization, and GDP on sustainable development efficiency for Chinese provinces. Although China is the large economy and the analysis regarding the Chinese nation can be generalized to the global economies for policy-making purpose, it is more suitable to perform the same analysis for other large economies such as USA, Japan, Germany, and India in order to derive more comprehensive policy-based results for global economies to foster the development efficiency across the world. Another limitation is that the study's model includes environmental regulation policies and human capital in order to examine their asymmetric effects on development efficiency. The results have the global appeal which can generalized to the other economy as a benchmark finding. The future scholar can further assess the issue of development efficiency by extending the recent study's model through integrating some other important variables such as artificial intelligence technologies, green technologies, circular economy, and trade war. Besides, more disaggregated-level (cities-level) analysis, event analysis, and recent economic shocks-based analysis can assist in divulging the new sights in this area to put an economy on the track of sustainable development.

2.1. Literature search

This review begins with a bibliometric survey of the literature [[15], [16], [17], [18], [19], [20]] on the nexus between energy and SDGs. Due to our accessibility to academic databases, we selected the Web of Science database for bibliometrics in the review. As an international authoritative database, Web of Science contains a wealth of research in a wide range of domains [21] and has been used as the only database in many bibliometric studies [[22], [23], [24], [25], [26]]. The literature search process for this review is shown in Fig. 2. Given energy, sustainable development, and nexus as the main topics, we entered the queries “(TS¹ = energy or TS = SDG7) and (TS = Sustainable Development) and (TS = nexus or TS = interaction or TS = link or TS = influence)” in Web of Science. With reference to Kar et al. [27] and Hafez et al. [28], the inclusion criteria for the literature were: 1) in English; 2) type of article or review; 3) published between 2010/1/1 and 2022/6/30 (from five years before the release of the 2030 Agenda for Sustainable Development to the present), while the exclusion criteria were: 1) in other languages; 2) type of bibliography, book (chapter), proceeding, report, or other; 3) published before 2010. Following these queries, inclusion and exclusion criteria, we obtained a total of 10,432 articles. By quickly browsing their titles to remove those irrelevant (e.g., out of scope) and duplicate, we obtained 9438 articles. We made statistics on these 9438 articles according to their published years and journals, applied CiteSpace² [29] to identify high-impact articles, and applied VOSviewer [30] to identify frequencies of keywords and their co-occurrences. To facilitate the delivery of published core and unique evidence in the next section, we further browsed the abstracts of the 9438 articles to remove those with little, ambiguous or essentially repetitive information, and also removed articles without full text. We ended up with 728 articles. In short, in this review, the bibliometrics in this section were conducted with 9438 articles, whereas the evidence in Section 3 was primarily distilled from 728 relatively most relevant articles. Note that although this review is intended to be comprehensive and systematic, it has limitations. For example, it only searched Web of Science for articles in English and therefore missed potential studies in other databases (e.g., Scopus, Google Scholar) or in other languages; it relied on publicly available literature and therefore may have missed the nexus that has not yet been published or studied.

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Fig. 2. Flow chart of literature search for this review.

2.2. Basic research status

As observed from Fig. 3(a), before SDGs were proposed in 2015, only a few articles initially discussed the relationship between energy and other factors (mainly water) based on the concept of sustainable development [[31], [32], [33], [34], [35]]. With the formal proposal of SDGs, the number of articles on the nexus between energy and SDGs has been increasing year by year. Fig. 3(b) shows that Journal of Cleaner Production (746 articles), Sustainability (718 articles), and Renewable and Sustainable Energy Review (380 articles) were the journals that published the largest number of nexus articles, together accounting for one-fifth of the total retrieved articles. Meanwhile, Journal of Cleaner Production (23,343 citations), Renewable and Sustainable Energy Reviews (19,354 citations), Energy Policy (7475 citations), and Applied Energy (7178 citations) were the most cited.

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Fig. 3. Knowledge graph of the energy and sustainable development nexus research in the literature during 2010–2022. (a) The cumulative number of articles published. (b) Top ten journals in total published articles and their citations (c) Article co-citation (i.e., two or more articles are cited by one or more subsequent articles at the same time) network. The size of the node indicates the frequency of the article cited within the scope of the literature survey here, and the line segment indicates that there is a co-citation between articles. (d) Keyword co-occurrence network. These keywords are derived from article titles, abstracts, and keywords. The size of the node indicates the frequency of the keyword.

The CiteSpace analysis of the 9438 articles identified six important categories, as shown in Fig. 3(c). Climate change is one of the most important issues of concern to the international community. It is found that the nexus between energy and sustainable development is broadly related to climate change (Category#1). One interesting concept in this category is “environmental livelihood security” established by Biggs et al. [36], which features a balance between natural resource supply and human demand for environmental livelihoods in delivering sustainable development under climate change. Articles in both Category#2 (energy-water-food nexus, a typical concrete case of the nexus between energy and SDGs) and Category#4 (nexus informatics) focus on the nexus of energy with water and/or food (for a detailed review of energy-water-food nexus, see Albrecht et al. [37]). Specifically, Category#2 focuses more on case studies of the energy-water-food nexus in specific countries and regions, while Category#4 gradually suggests that energy-water-food should be combined with other concepts in subsequent nexus research. For example, Rasul [38] studied energy-water-food development in South Asia (Category#2); Liu et al. [39] argued that energy-water (-food) studies should be coupled with other SDGs to enhance synergies among more goals (Category#4). In Category#3 (planetary boundaries), the 2030 Agenda for Sustainable Development is the most cited. In addition, Pradhan et al. [40] conducted a preliminary analysis of the correlation between indicators representing energy and SDGs in 227 countries. Articles in Category#5 (economic growth) conceptually put forward some directions of SDG research from an economic perspective. For example, Le Blanc [41] proposed to create an SDG interaction network at the economic development level. Articles in Category#6 mainly focus on energy consumption. For example, Ringler et al. [32] explored how to optimize the energy-water-land-food nexus framework to improve energy use efficiency.

The VOSviewer analysis of article titles, abstracts and keywords highlighted the vocabulary with an occurrence frequency of more than 50 times, as shown in Fig. 3(d). It can be found or verified that: 1) relationships do exist between SDGs, and studies on energy have already involved SDGs such as “food” (SDG2), “education” (SDG4), “water” (SDG6), “urbanization” (SDG11), and “global warming” (SDG13); 2) studies on energy have covered many energy-related aspects, such as “renewable energy”, “energy efficiency”, “fossil fuel”, “energy consumption”, “CO₂ emission”, “energy production”, “biomass”, and “economic development”; 3) the main research subjects are mostly developing countries, such as “China” and “India”; 4) the main research purpose is likely to serve “policymaker”; and 5) many studies are likely to be conducted using a “model”.

2.3. Nexus research method

3.1. Point-to-point evidence

Energy and No poverty (SDG1). Many studies believe that there is a synergy between energy and poverty eradication. Nerini et al. [12] proposed that promoting energy development could bring new jobs, inspire new industries, and increase the income of the poor; without energy, it is impossible to end poverty. Xu et al. [58] found that developing photovoltaics (PV) in China's rural areas could help eradicate poverty (known as “PV poverty alleviation” in China). Improving energy efficiency will save energy. The saved energy resources could be used to build more infrastructure or produce more basic materials to help alleviate poverty [59]. At the same time, clean energy development helps improve climate conditions and reduce environmental pollution, thereby reducing the number of people living in poverty due to severe or extreme weather [60]. However, some studies also indicate that energy development may sometimes exacerbate poverty (trade-off). For example, “PV poverty alleviation” projects in some rural areas in China had a funding gap in the initial stage and required loans by local residents, which increased the burden on the poor [61]. Therefore, appropriate financial support policies should also be prepared to make such energy projects affordable for the poor.

Energy and Zero hunger (SDG2). Affordable, reliable and modern energy can help reduce hunger and increase food security. For agriculture, establishing a widely-covered power grid improves agricultural mechanization and modernization, which can enhance the efficiency and yield of food production [62]. As mentioned above, decarbonizing the energy structure helps improve the climate environment [63]; this is conducive to increasing food production and avoiding loss. For example, climate change might lead to a more than 10% reduction in maize and sorghum yields in South Asia, which could be avoided by decarbonizing the energy mix [64]. Note that bioenergy and hydropower are quite relevant to agriculture. First-generation food-based bioenergy might lead to a 35% increase in global food prices in a 2 °C future [65], but the development of second- (non-food) and third-generation (algae) bioenergy could avoid competition with food [66]. Hydropower may interfere with agricultural irrigation; in the dry season, there is a trade-off between irrigation and power generation for water needs [67]. In addition, while the establishment of good energy supply facilities can improve irrigation systems, it may also lead to a shift in agricultural production from food staples to cash crops, affecting local food supply [68,69].

Energy and Good health and well-being (SDG3). Developing affordable, clean energy to replace high-emission, high-pollution fossil energy provides co-benefits for the environment, climate, and human health. The combustion of conventional fossil fuels produces large amounts of air pollutants, such as SO₂, NO₂ and PM, leading to more than five million deaths worldwide each year from cardiovascular, respiratory, lung cancer, and hypertension [70]. The greenhouse effect caused by excessive use of fossil energy may exacerbate psychological problems such as post-traumatic stress disorder, depression, excessive anxiety, mental illness, and suicidal tendencies [71]. In contrast, a reduction in CO₂ emissions per million tones might reduce the number of deaths caused by the greenhouse effect by 34–161 per year in China [72]; through universal access to clean fuels such as electricity and biogas, the probability of cooking-induced diseases might be reduced by one-third in low- and middle-income countries [73]. In addition, energy is essential to the operation of hospitals, medical centers and healthcare facilities.

Energy and Quality education (SDG4). There is a clear synergy between the development of energy and the improvement of education quality. A modern energy system provides the infrastructural foundation for education to flourish. A reliable electricity supply network is essential for universities and schools to carry out educational and teaching activities [74]. Universal access to affordable modern energy is particularly important for improving educational conditions and promoting learning opportunities in remote and backward areas [75]. In turn, good education not only helps the public understand the value of sustainable development and makes it easier to implement energy policies, but also enhances the capability of energy sector staff [76]. According to a study of the APEC (Asia-Pacific Economic Cooperation) countries, education could improve modern energy use and environmental awareness; for every 1% increase in education level, CO₂ emissions could be reduced by 0.169% [77].

Energy and Gender equality (SDG5). Energy modernization and renewable energy development can accelerate the upgrading of energy and industrial structures and optimize the allocation of industrial resources. As a result, the number of jobs suitable for women is expected to increase substantially [78]. Affordable energy prices lower the cost of living for households and perhaps create some additional educational opportunities for women and girls. Women could therefore compete more fairly with men in middle and senior level jobs, and their employment, income, work environment, and social status are expected to improve [79]. In addition, in many families, women are often the cooks. Clean cooking fuels can reduce the harm to their bodies [80]. However, there are case studies that warn about trade-off risks. For example, with affordable electrification in some traditional rural areas of developing countries, men may spend more time on leisure and relaxation, such as watching television and surfing the Internet, while women have to take on additional work previously performed by men, increasing local gender inequality [81].

Energy and Clean water and sanitation (SDG6). Conventional energy is usually utilized through combustion and requires water to cool the equipment. Developing clean energy and improving energy efficiency can reduce the need for cooling and thus save water. For example, conventional tower thermal power plants consume 550–10,000 L/MWh of water, but solar power consumes only 125 L/MWh [82]. Using waste heat from nuclear power reactors to desalinate seawater can help obtain more freshwater resources [83]. However, there may be trade-offs between energy and water. For example, natural gas drilling fluids that seep into aquifers contaminate groundwater resources; improper discharge of wastewater from energy use pollutes freshwater; hydropower development may lead to evaporation losses of water, damaging water-related ecosystems and affecting downstream water use [84]; and hydrogen production from electrolysis of water by renewable electricity (green hydrogen) requires more water than from fossil feedstock (grey and blue hydrogen) [85]. In addition, the construction of modern energy systems can better sustain the operation of water transmission, pumping, and purification facilities, which helps ensure universal access to clean drinking water [[86], [87], [88], [89]]. Due to the close linkage between energy and water, the energy-water nexus has formed a relatively mature research architecture in the literature [90,91], as reflected in bibliometrics.

Energy and Decent work and economic growth (SDG8). Energy access and development promotes jobs and employment and underpins economic and social development. During the low-carbon energy transition, energy, industrial and economic structures and employment patterns are expected to undergo rapid changes, which will provide new opportunities for a country to reshape social productivity and improve international competitiveness. An irrational energy transition that does not take into account the development circumstance and inertia is detrimental to the economy and can lead to massive job losses in traditional industries [92,93] (trade-off); in contrast, the orderly development of clean energy can help steadily decouple economic growth from fossil energy and environmental degradation [94], thus improving the quality and sustainability of the economy and providing more decent works. For IEA (International Energy Agency) members, every 1% increase in renewable energy consumption might have the potential to grow the economy by 0.29% [95]. For China, if carefully planned, the development of wind and PV industries could drive 2.8 million job growth by 2050 under a 1.5 °C scenario, fully offsetting the loss of 2.2 million jobs from the reduction of the coal power industry [96]. Moreover, the world is now widely connected through energy networks, and even local energy developments may influence global energy markets and employment [97].

Energy and Industry innovation and infrastructure (SDG9). Energy development spurs industry innovation [98] and infrastructure renewal. For example, a significant increase in the share of renewable energy requires an accelerated shift away from coal industries and investment in new infrastructure. A strong and resilient infrastructure, in turn, is a major prerequisite for energy development. Digital, informationized and intelligent modern infrastructure, as well as advanced industrial technologies such as big data and block-chain, can improve energy efficiency and innovation and facilitate universal access to reliable modern energy services [99]. For example, China's high-speed rail reduced energy intensity of cities along railways by 9.3% [100]. However, there are trade-off risks, too rapid energy decarbonization potentially leading to temporary industrial unrest [101], and the transfer of energy-intensive industries from developed countries to the detriment of industrial innovation and new infrastructure development in developing countries [102]. It is important to emphasize that delivering SDG7 or energy transition does not mean blindly phasing out existing conventional infrastructure without assessing its impact on the entire chain and stranded assets and the capability of new infrastructure to fill the gaps [103]. Under carbon neutrality, developing countries should make prudent decisions regarding their existing fossil fuel-based infrastructure (e.g., coal power capacity) to ensure the security of energy supply [104].

Energy and Reduced inequalities (SDG10). Ensuring energy affordability and universality often helps reduce energy poverty and improve local, national and global inequalities in multiple ways. As mentioned earlier, improving energy efficiency can reduce material inequality by directing more energy resources to improving material conditions. In building modern energy systems, energy supply is expected to be progressively decentralized, allowing the public to have more equal and easier access to energy services, such as electricity and heat. Electricity is vital for the dissemination of knowledge and information, which improves educational inequality [75]. Some studies show that energy development plays an important role in increasing the income of the poor and reducing income inequality [105]. A 1% increase in the number of people access to electricity might reduce global income inequality by 0.05% [106]. However, there are also studies that argue for a trade-off between energy and reduced inequalities. For example, because it is often more difficult to attract capital inflows than developed countries, developing countries tend to face greater pressure on government public expenditure for an affordable clean energy transition [107]; accelerating the phasing-out of fuel cars and the spread of electric vehicles would severely affect traveling cost and efficiency for people in cold regions, leading to geographic inequality [108]; subsidizing roof PV may be biased against people who do not own a house [109]. In short, affordability matters. If energy prices are expensive for the poor or vulnerable, inequalities would get worse even if the energy mix is cleaner.

Energy and Sustainable cities and communities (SDG11). Cities are densely populated, asset-intensive, and vulnerable to disasters [110]. The use of fossil energy causes urban pollution to a greater or lesser extent, for example, traffic fuels cause urban air pollution. Energy modernization and decarbonization can promote urban modernization and inclusiveness, reduce urban climate risks, improve urban air quality, and protect urban ecology [111]. For example, a reliable and efficient power supply is a prerequisite for providing high-quality living services to city residents, popularizing low-carbon transportation modes such as subways and electric vehicles, and building safe and carbon-neutral residential, commercial, and business districts [112]. It is also noted that urban layout may have an impact on the diffusion of clean energy [113]. Urban spatial-based planning and management is beneficial for achieving synergic sustainable development of energy and cities.

Energy and Responsible consumption and production (SDG12). The massive use of fossil energy for consumption and production leads to environmental irresponsibility, and the relatively low energy efficiency of the past leads to energy waste [114]. In order to deliver sustainable and responsible development, fundamental changes in past production and consumption patterns are required. Some studies argue that improving energy efficiency increases social productivity, which may expand the demand for the quantity and type of resources; therefore, the total amount of resources consumed by society may not be saved (known as the “rebound effect”) [115,116]. In addition, there is the controversy that the development of nuclear electricity production is irresponsible for the safety of society [117] (trade-off). However, most studies justify that the development of clean and efficient modern energy helps reduce waste [118,119] and pollution and is an important way to establish low-carbon, environmental-friendly and responsible consumption and production throughout the entire socioeconomic system [120,121].

Energy and Climate action (SDG13). SDG13 is actually consistent with the requirements of the United Nations Framework Convention on Climate Change [122] and the Paris Agreement [123]. As bibliometrics show, energy is highly correlated with climate change. CO₂ and other greenhouse gases produced from the use of fossil energy are the main anthropogenic cause of global warming. Replacing fossil energy with non-fossil energy and substantially increasing the share of renewable energy in the energy mix are acknowledged as core measures to achieve carbon neutrality and combat climate change and its impacts [49]. The IPCC AR6 suggests that in order to limit warming to below 1.5 °C, the share of low-carbon energy in the global primary energy supply might need to exceed 70% by 2050 [49]. For China to achieve its 2060 carbon neutrality, the share of non-fossil energy might need to reach approximately 80% by 2050 [124]. Responsibility for and exposure to global climate change varies by region and country [[125], [126], [127]]. Although accounting for only a small fraction of global emissions, low-income countries and small island states are the most vulnerable to the impacts of climate change [125]. The process of decarbonization of energy systems in developed countries and large emitters will largely determine future temperature increases [[128], [129], [130]]. They should align their energy transition with global climate governance, and lead more ambitious actions to strengthen the NDCs and achieve carbon-neutral energy systems.

Energy and Life below water (SDG14). The ocean is rich in energy. Marine energy that has been gradually put into use mainly includes offshore wind energy, offshore solar energy, tidal energy, wave energy, and marine bioenergy. Stable marine ecology provides a sustainable output environment for marine energy [131]. However, the construction of offshore energy facilities, such as offshore drilling platforms and wind turbines, compresses the space for marine life and may damage the marine ecological environment [132]; and nuclear leaks may cause significant damage to life below water and on land and even entire ecosystems [133] (trade-off). In addition, the burning of conventional fuels releases large amounts of CO₂, which forms carbonic acid in the seawater and exacerbates ocean acidification. It is expected that clean energy can be popularized in marine operations as early as possible to conserve the marine ecosystem [134]. For example, climate change might reduce marine fishing potential in Indonesian zones by more than 20%, which might be avoided by popularizing clean energy [135].

Energy and Life on land (SDG15). Appropriate development of modern energy in poor and backward areas can reduce the demand for fuelwood and reduce the destruction of forests, grasslands and land, thereby preserving terrestrial and vegetative creatures and maintaining the local ecosystem and biodiversity [136]. Conserving biodiversity can provide both nature-based solutions (carbon sinks) and technological solutions (bioenergy with carbon capture and storage (BECCS)) for achieving carbon neutrality. However, there may also be trade-offs between the development of energy and the conservation of land and biodiversity. For example, the construction of wind turbines and PV may take up useful land and ecological space; improper collection of biological materials would disrupt the inherent biological chain and cause irreversible damage to the ecological environment [137]; geothermal exploitation may accelerate the loss of stratigraphic water and cause land subsidence [138]; and a heavy reliance on BECCS to offset CO₂ in the future would have side effects on land, biodiversity, food and water [[139], [140], [141]]. It is emphasized that the protection of life (both on land and below water), biodiversity and other critical ecological resources must be prioritized when developing energy.

Energy and Peace justice and strong institutions (SDG16). Energy development has inspired the establishment of many government institutions and international organizations (e.g., the IEA) that help provide a peaceful, just and rules-based environment for energy and related activities. Peaceful societies, equitable access to justice, and accountable institutions are important safeguards for energy development at all levels. For example, differences in access to energy endowments may lead to political and violent conflict; some hydropower and nuclear developments may lead to local social conflict and discord if affected residents are not adequately consulted [142] (trade-off). The involvement of fair, value-neutral, and credible institutions can serve as a bridge of communication to help resolve these disputes and make more locally appropriate energy decisions. Due to the significant national and international energy connections, an unpeaceful and unjust environment, even locally, may affect international energy supplies and prices, potentially leading to energy shortages in countries with high import dependence [143]. In some regions where market conditions are poor and market rules cannot work, impartial intervention by government institutions is a key driver of energy development [144].

Energy and Partnerships for the goals (SDG17). Energy has initiated many partnerships among countries in a wide range of areas such as resource, technology, finance, and knowledge. For example, renewable energy technologies and investments are an important element of the “Belt and Road” Initiative [145]. Partnerships can play an important role in global energy interconnection, sharing and cooperation to drive modernization and sustainability of energy systems on a global scale. Especially during the COVID recovery period, active partnerships among countries can promote political consensus on energy issues, increase enthusiasm for the development of renewable energy, and reduce barriers and costs to energy development. However, nuclear energy development may hinder interregional cooperation due to different perceptions of and reliance on nuclear energy [146]; and differences in the competitiveness of renewable energy technologies may also lead to trade conflicts and damage to partnerships [147] (trade-off). More inclusive bilateral and multilateral negotiations, rather than unilateral adjustments, can better resolve those conflicts and promote win-win partnerships.

3.2. Summary and implication

The point-to-point review clearly shows that there are nexuses between energy and all 16 other SDGs. While the exact nexus may depend on the context, a strong indication is that the transition to low-carbon and efficient energy systems that provide universally affordable, reliable and modern energy services has the potential to create synergies with all aspects of SDGs, reflecting the need to transform energy systems in order to deliver SDGs. This also reinforces the importance of achieving carbon neutrality. By promoting greener, healthier, and more climate-resilient energy systems, carbon neutrality can serve as a supporting lever for all-round sustainable development. However, literature evidence also warns that if energy transition and clean energy development are not properly rolled out, trade-offs may occur with three-quarters of goals, including human well-being (SDG1, SDG5, SDG10 and SDG16), material condition (SDG2, SDG6, SDG8, SDG9 and SDG12), natural environment (SDG14 and SDG15), and even partnerships (SDG17). Therefore, in the pursuit of SDG7 and carbon neutrality, policymakers should no longer consider energy development in isolation, but need to simultaneously consider compatibility with sustainable development and make decisions from a systematic perspective. Energy development targets, policies and measures, when contextualized and with attention to balancing rapid action and prudent planning, can help reduce trade-offs and increase synergies between energy and SDGs.

Note that if the growing demand for energy services is accessed predominantly through fossil energy rather than clean energy, which may occur where economies and decarbonization capacities lag far behind, additional trade-offs with SDG3 (good health and well-being), SDG11 (sustainable cities and communities) and SDG13 (climate action) may arise (the literature surveyed in this review did not clearly show a negative impact of energy development on quality education; however, this does not necessarily indicate that there are absolutely no trade-offs between SDG7 and SDG4). In particular, climate change caused by fossil energy consumption has huge worldwide impacts and will adversely affect almost all SDGs [148]. To fully achieve sustainable development, climate change mitigation and just transition worldwide, the international community should further work together and support each other. In addition to reducing fossil energy consumption and increasing the share of non-fossil energy with the greatest ambition, developed countries should provide financial and technological support to help developing countries improve their capabilities to decarbonize their energy systems without compromising SDGs [49,123,149]. With international support and investment, developing countries could do well to accelerate the development of renewable energy and to meet the growing demand for energy services with low-carbon energy wherever possible. All countries should enhance the sharing of knowledge, experience, actions and policies for energy development, and strengthen cooperation and partnerships to improve renewable, efficient, energy-saving and emissions-reducing technologies.

4.1. Research evolution trend

From duality to pluralism. Fig. 4 shows the development of the nexus studies of energy with SDGs in the literature: from duality nexus such as energy-water [91], energy-food [150], energy-poverty [151], and energy-climate [152] to ternary nexus such as energy-water-food [153], energy-health-climate [154], energy-poverty-climate [155], and energy-water-climate [156]. As extremely important material resources, energy, water, and food influence not only the development of material condition, but also the development of human well-being and natural environment. Therefore, some studies have further coupled energy-water-food with another goal to carry out quaternary nexus, such as energy-water-food in the context of poverty alleviation [157], the impact of university education on energy-water-food [158], and the impact of energy-water-food on human health [159]. Several studies have also attempted to construct a quinary nexus of energy, water, food, climate change, and social justice [160]. In the future, energy-related nexus research could continue to better connect, extend and enrich the evidence to paint a more nuanced picture of energy and sustainable development.

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Fig. 4. Trends in the study of the energy and sustainable development nexus: from duality to pluralism.

From static to dynamic. Early studies mainly focused on the static nexus between energy and SDGs at a snapshot in time [12,38,161], while subsequent studies gradually began to examine the dynamics of the nexus across time. Using a correlational network, a recent study by Wu et al. [162] showed that some SDGs decoupled and then recoupled as sustainable development progressed; they therefore emphasized the need to analyze the evolution of SDG interactions. Some studies have also attempted to use scenario analysis to explore the dynamic nexus between energy and SDGs in the future. For example, the scenarios in Howard et al. [154] found that the clean energy development, initially characterized by high costs, had limited effects on improving public health and reducing medical expenditures; however, as energy efficiency continued to improve, the large-scale penetration of renewable energy would gradually promote physical health and improve the overall economic benefits to society. In achieving energy transition and sustainable development, dynamic nexus analysis can help policymakers adjust targets, policies and measures to the latest context and development requirements in a timely manner.

From theory to practice. Early SDG nexus studies put forward theoretical concepts [36,161]. Based on interdisciplinary knowledge of the potential nexus between energy and SDGs, Nerini et al. [12] called for future research to better support the implementation of SDG7 in practice. In recent years, studies have gradually started to veer toward guiding practice. For example, Weitz et al. [163] analyzed how SDG7's Target7.2 and Target 7.3 interacted with targets of other SDGs in Sweden to support priority setting in the country's policies and plans; Ramos and Laurenti [164] used regression analysis to analyze the relationships between Spain's SDGs to help the country develop a roadmap to achieve sustainable development; based on global data from 2000 to 2016, Hegre et al. [165] evaluated SDG compatibility through principal components analysis to help the international community formulate SDG development strategies. With carbon neutrality, recent studies have started to focus on the carbon-neutral transformation of energy systems [[166], [167], [168], [169], [170]], but there are still gaps in research on the pathways, mechanisms and supporting policies for synergizing energy and SDGs under carbon neutrality.

4.2. Prototype research framework

Establishing a sound nexus framework can help better articulate synergies or trade-offs among multiple goals, and systematically reveal potential impacts of different development targets, policies, and scenarios on nexuses [171]. This can assist policymakers in designing better strategies to coordinate sustainable development. As shown in Fig. 5, this review further proposes the following four-step prototype research framework for scientific analysis of the energy and sustainable development nexus.

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Fig. 5. A four-step prototype research framework for scientific analysis of the energy and sustainable development nexus.

Defining research boundary. The first step is to define the research boundary according to key factors such as the context and socioeconomic development stage of the research subject (e.g., country, region, city). Research subjects in different circumstances and stages of development may have different priorities in energy development. For example, for some poor islands, the first priority is often to ensure universal access to affordable energy as early as possible [172]; while for regions that already have universal energy access and propose carbon neutrality, the first priority is often to increase the role of renewable energy, improve energy efficiency, and establish highly decarbonized energy systems [173].

Building nexus system. The second step is to identify the SDGs that need to be particularly focused on for the research subject in parallel with energy development, according to contextualized factors such as actual needs and priorities for sustainable development, public aspirations, existing policies and scientific perceptions, to build the nexus research system. The constructed nexus system with different coverage of SDGs serves different research and decision-making needs. For example, an energy-water nexus system informs a synergic development pathway for the two goals; while an energy-water-food-climate system not only informs the energy-water-food interaction, but also reflects the feedback of the climate system to material resources [174].

Assessing nexus relationship. The final step is to assess the nexus between energy and SDGs. Different energy development targets, policies and pathways may lead to different evolution of SDG indicators [13]. Existing studies have created energy development scenarios under, for example, carbon neutrality, representative concentration pathways, and shared socioeconomic pathways [39,40,148]. After setting energy development targets and scenarios, quantitative methods such as integrated assessment models, system dynamics models, input-output models or econometric models can be applied in combination with qualitative methods such as literature surveys and expert consultants to assess the dynamics of SDG indicators and their interactions, thus providing policy implications for energy and sustainable development synergies in practice.

4.3. Going forward

In conclusion, serving the practical needs of human society and habitat system development is a critical starting and ending point of nexus research. The development of energy systems toward carbon neutrality will radiate and have lasting effects on all aspects of society, economy and environment. Therefore, nexus research could move beyond discussions of material resources, such as energy-water-food, to larger cross-systems. More research could be done on the impact of the transition to low-carbon efficient energy systems on important human and non-material elements, such as social equality, income distribution, welfare and well-being, talent education, and natural environment, as well as on synergic strategies and mechanisms between energy and multidimensional SDGs. A “new-era” nexus for energy development – spanning the domains of human well-being, material condition, and natural environment – is urgently expected to provide more granular and context-specific evidence, data, suggestions and solutions to align energy development with the full range of sustainable development.

2.1. Membrane gas separation (MGS)

Membrane gas separation (MGS) is a pre-combustion technology, such as shown in Fig. 3 that is utilized in various sectors including and not limited to the extraction of nitrogen from ambient air, hydrogen recovery from ammonia plants (Ramírez-Santos et al., 2018) as well as hydrogen recovery from hydrocarbons used in petrochemical applications, organic vapor removal from air streams and CO₂ capture from natural gas streams (Membranes for Gas Separation, 2022). In this technology of CO₂ capture, a feed stream containing CO₂ is flown adjacent to the membrane, where gas molecules are absorbed on one side of the dense membrane, diffuse across the membrane and finally desorb on the other side to a gas end phase, such as shown in Fig. 4.

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Fig. 3. Pre-combustion carbon capture.

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Fig. 4. Membrane gas separation.

2.1.1. Physical limitation and operation

Two main key parameters are considered for gas separation which are the permeability of a single species in the gas mixture and the separation factor (selectivity). These two parameters share a tradeoff relationship as the separation factor has been observed to decrease with the increase of the permeability (Robeson, 2008). Which is why an upper boundary limit relationship is followed to classify and compare the performance of different membranes according to the permeability and the selectivity, which follows this equation (Robeson, 2008):(1)${�}_{�}=�{�}_{��}^{�}$Where P_i is the permeability of the targeted species, k is the front factor, " role="presentation" style="box-sizing: border-box; margin: 0px; padding: 0px; display: inline-block; font-style: normal; font-weight: normal; line-height: normal; font-size: 14.4px; text-indent: 0px; text-align: left; text-transform: none; letter-spacing: normal; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;" tabindex="0">$�$ is the selectivity, and n is the slope of the resultant log-log graph (Robeson, 2008), just as shown in Fig. 5.

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Fig. 5. CO₂ upper bound limit plot (Robeson, 2008), (Park et al., 2007), data adapted from (Park et al., 2007) – Alpha: represents the CO₂ selectivity.

Fig. 5 shows the relationship between the permeability of CO₂ (log-scale X-axis) and the selectivity of the membrane (log-scale Y-axis) and it shows the tradeoff between increasing one side and the effect it bears on the other. Having a largely permeable membrane arrangement decreases the selectivity and the purity of the output stream of the membrane. It is also observed that through development of membrane materials for gas separation applications, the upper bound limit has been shifted slightly upwards, leaving room for membranes to attain both better permeability and selectivity. What the upper bound limit also indicates, is that for a specific material and a given selectivity, the permeability can be increased to right of the X-axis until it reaches the upper bound limit, where it is no longer physically possible for that given selectivity, and vice versa. An ideal position on the graph would be on the right-middle region of the canvas on the boundaries of the upper bound limit. Additionally, there are membrane materials that have facilitated the surpassing of the Robenson upper bound limit, such as thermally rearranged polymers. It is noted that these polymers are fabricated by in-situ thermal conversion of polyimides with ortho-functional groups. Thermally rearranged polymers suffer from the incapability of being processed, however their precursors are easily dissolved in organic solvents, which allows for their fabrication into hollow fibers/membranes. These membranes are thermally, mechanically, and chemically stable, along with lucrative gas separation abilities (Kim and Lee, 2012).

2.2. Membrane contactor (MC)

A membrane contactor (MC) is mostly a post-combustion-based technology, such as shown in Fig. 6, which separates gaseous and liquid phase materials and provides a higher surface area to promote a better mass transfer between the two. It is a highly flexible technology due to the freedom in controlling the flowrates of both the gas and liquid (absorbent) that are separated. MC also provides a controllable interfacial area that can be modified according to each application. As the case in MGS, MC can also be modulated for more demanding processes and to accommodate scaling-up requirements. Chemical, thermal and mechanical stabilities are essential to maintain high performance and ensure the longevity of the membrane that is used. Given that this membrane is utilized in a wet environment (an absorber in the liquid phase), the membrane material must have a high level of hydrophobicity. According to (Siagian et al., 2019), (Nieminen et al., 2020), polytetrafluorethylene (PTFE), polyvinylidene fluoride (PVDF), Polyethersulfone (PES) and polypropylene (PP), are desirable materials for membranes in MC applications. The process for MC CO₂ capture is shown in Fig. 7

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Fig. 6. Post-combustion carbon capture.

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Fig. 7. Membrane contactor CO₂ capture.

3.1. Economic and financial

There is a physical tradeoff between the selectivity and permeability in MGS-based carbon capture, which affects the overall economics of the system. Additionally, the permeability and selectivity of the membrane determines the area required for the membrane which directly affects the cost at large-scale implementation of this technology. Moreover, a phenomenon known as plasticization, which is a membrane pore swelling, halts the operation of MGS are requires costly substitutions of the membrane stack (Luis et al., 2012). A stable MC operation is dictated by the solvent membrane interaction and their compatibility, otherwise an imminent wetting of the membrane occurs that demands a substitution of both components. Similarly, fouling which is the accumulation of dust and contaminants (i.e., flue gasses), also requires the substitution of the membrane (Scholes, 2020).

3.2. Technical

The permeability and selectivity tradeoff arises as a barrier in the context of dictating the operating levels of the overall inlet and outlet of the system (pressure difference applied). Additionally, plasticization limits the choices of membrane materials as this selection must be optimized to accommodate certain applications based on the corrosivity of the environment and the mixture of the gas (Luis et al., 2012). However, it is worthy to note that the fabrication of S-PEEKM-based membranes which are made from the direct polymerization of sulfonated monomers (Khan et al., 2011a), have shown excellent anti-plasticization properties with superior gas separation performances (Khan et al., 2011b). Moreover, in an MC operation, the solvent/membrane interactions have to be chemically stable and must go through an optimization process for a smooth operation. fouling treatment techniques must be developed and regular maintenance of the membrane material is required (Scholes, 2020), (Favre, 2011).

3.3. Social

In an MGS pre-combustion operation, the selectivity of the membrane determines the loss of important gas species such as CH₄ in a gas mixture with CO₂, as the tradeoff between the permeability and selectivity will hinder the quality of the fuel (CH₄) which will adversely affect the environment (Luis et al., 2012), (Robeson, 2008). Similarly, plasticization hinders the quality of the CO₂ gas purification process over time (Siagian et al., 2019). On the other hand, in MC applications commonly used solvents pose health and safety hazards for both the environment and the people involved in the operating plants such as mono-chlorobenzene (CB) and dimethylformamide (DMF) (Luis et al., 2012)., (Favre, 2011)

4.1. SDG 1 “no poverty”

It was estimated that about 10% of the population was living in poverty in 2015. However, after the recent COVID-19 pandemic it was evident that the number of people living in severe poverty will increase. Hence, nowadays more than 10% of the global population is suffering from severe poverty. That is more than 700,000 people are incapable of meeting their basic needs in life such as education, health, and food. Around 17.2% of these people are living in rural areas where people earn a living of less than 1.90$ per day. As a result, 8% of the people with low income are struggling with extreme poverty. It was reported that one child out of five children suffers from severe poverty. Consequently, in order to protect these children, global poverty must be reduced. In the past, the number of people living in extreme poverty decreased from 36% to 10% of the global population. This reduction indicates that it is possible to significantly reduce global poverty (Nationsa). For this reason, SDG 1 has been directed to end worldwide poverty in all its forms everywhere by the year 2030 (Oliveira et al., 2022). SDG 1 is associated with several targets, where each target is allocated with multiple indicators. These indicators provide guidance on how to accomplish each target related to SDG 1.

Membrane-based carbon capture can bestow numerous advantages by capturing the CO₂ in the atmosphere and combatting climate change. Nevertheless, it is not feasible to deploy carbon capture technologies in underdeveloped and developing countries with low incomes. According to target 1.3 which focuses on nationally appropriate social protection systems and measures for all, it is only possible to deploy nationally suitable social protection systems. Hence, it is not appropriate to employ carbon capture technologies in such countries where they cannot afford the high costs associated with the development and implementation of these technologies. However, there are other positive aspects to the deployment of carbon capture technologies on the poverty levels in developing countries. The development and implementation of carbon capture technologies require large sums of money which can be externally financed. This, in return, allows for the development of innovative energy solutions without any incurred costs (Olfe-Kräutlein, 2020a). On the other hand, the deployment of such technologies in developed countries might indirectly deter the goal of ending worldwide poverty. This occurs as these technologies evolve and advance in developed countries which in return might strengthen the current level of global poverty (Dollar, 1993).

Job creation is one of the significant advantages carbon capture projects provide. As huge investments and finances are offered for deploying carbon capture projects, more job opportunities will be available. Hence, carbon capture technologies reduce unemployment levels and improve human well-being. Based on the International Energy Agency (IEA), by the year 2050, around 2000 carbon capture storage plants need to be built to combat the increasing carbon emissions (Birol, 2010)– (Jarraud and Steiner, 2012). The construction, operation, and development of these plants will require around 100,000 employees by the year 2050. Jobs related to logistics and transportation, material and machine supplies, and various other jobs will be created. These jobs will eventually substantially reduce the unemployment rate and decrease poverty (Olabi et al., 2022d). Moreover, according to Turner et al. (2021), the development of carbon capture technologies and facilities will add 1.8 billion dollars in GDP per year and create around 17,000 jobs in the UK (Turner et al., 2021).

4.2. SDG 2 “zero hunger”

Frequently, carbon capture products in the industrial processes are not engaged directly in the production of food and the difficulties associated with it, as demonstrated by SDG 2. However, the following applications lead to increasing impact on food production in the future, such as taking advantage of the captured CO₂ to increase organic process yield, either in greenhouses or processed into fertilizers. This could be important for some agricultural industries, as using CO₂ could enhance yields by up to 30%, which would have an immediate impact on commercial volumes and supplies. Some examples of utilizing CO₂ for food production include Omega 3 which is produced by the Norwegian business CO₂Bio for fish food and using CO₂ by the Finnish company Solar Foods to develop proteins for human diets (Olfe-Kräutlein, 2020b). Through higher soil organic carbon (SOC) content in the soil, organic farming immediately improves biological resources. In comparison to traditional farming, organic farming provides 50% more crops on average, has better soil fertility, less soil erosion, healthier crops, and superior farm management abilities (Onwonga, 2019).

4.3. SDG 3 “good health and wellbeing”

Ensuring and promoting the health and well-being of all people of all ages is significantly important for sustainable development. Prior to the COVID-19 pandemic, significant progress was sustained in enhancing the health of numerous people. Several targets were allocated to increase life expectancy and hinder the spread of diseases. However, further efforts are required to completely inhibit the spread of diseases and address all health problems. This is feasible by investing more in health facilities and systems, enhancing sanitation, and offering smooth access to health employees (Nationsb). Hence, SDG 3, which promotes the health and well-being of all people, has been put forth to establish clear targets and indicators for achieving all the former objectives.

Membrane-based carbon capture technologies do not directly influence some of the SDG 3 targets, such as targets 3.1 and 3.2 which discuss the reduction in worldwide maternity mortality rates and the end of numerous diseases, respectively. Nevertheless, several technologies employed for CO₂ capture adversely influence the health and well-being of people. For instance, CO₂ separation utilizes amine scrubbing which might potentially lead to several health complications (Dautzenberg and Bruhn, 2013). Moreover, mineralization processes require waste materials that might contain hazardous elements such as heavy metals (Sanna et al., 2014), (Masson-Delmotte et al., 2018b). Additionally, based on the location of the carbon capture facility, the transportation of CO₂ stored in pipelines poses a risk to the surrounding residents. Even though the risk of CO₂ leakage is low, where it is estimated that lower than 0.0008% of CO₂ will be leaked in 10,000 years (Alcalde et al., 2018), the public still perceives this as a potential danger to society (Lyons et al., 2021). However, even small amounts of CO₂ leakage from geographical locations near aquatic mediums might contaminate rivers, soil, lakes, air, and clean water which in turn leads to adverse impacts on the ecosystem and the people's health (Li and Liu, 2016), (Wei et al., 2016). Where it has been reported that the emissions of carbon capture technologies cause a 10-fold increase in the toxins found in freshwater (Chen et al., 2022b). On the other hand, there are positive impacts of membrane-based carbon capture technologies on SDG 3. These positive effects include the usage of stored CO₂ for producing sustainable pharmaceutical products (Olfe-Kräutlein, 2020b). Moreover, carbon capture technologies reduce particulate matter, CO₂, SO₂, and NO₂ pollutants from the atmosphere. The availability of these pollutants in the atmosphere has led to various health issues for people, most specifically related to respiratory diseases (Shaw et al., 2018). Particulate matter emissions only have led to the mortality of around 2804 to 8249 people in 2010 and approximately 9870 and 23,100 people in 2020. However, according to Yang et al. (2021), the deployment of carbon capture technologies helps in mitigating air pollution; this, in return reduces the global mortalities associated with pollution and particulate matter emissions by 23%, which means around 289,000 people will be saved between the year 2015 and 2030.

4.4. SDG 4 “quality education”

In order to meet the requirements of SDG 4's targets, which include guaranteeing free, equitable, and high-quality education for boys and girls (target 4.1) and equal opportunities for men and women to higher education (target 4.3), authorities, mainly nations and regions, and their organizations, are also needed to enhance the educational situation in their areas of accountability (Olfe-Kräutlein, 2020b). Developing and implementing carbon capture technologies call for specialized knowledge in a variety of academic fields and industries. There is an indirect relationship with SDG 4 by employing students and trainees in carbon capture-related learning processes to help provide high-quality education. In addition, through transferring technology, knowledge can be made available to countries that lack the resources or infrastructure to do so (capacity building). This could be viewed as an unintentional good result (Olfe-Kräutlein, 2020b). One of the indirect positive effects of the development of the various carbon capture systems including membrane-based ones on SDG 4 is the increase in the income (SDG1) that will eventually positively affect SDG 4.

4.5. SDG 5 “gender equality”

SDG 5 aims at achieving equality between both genders and empower women and girls by removing discrimination, violence, and gender inequality against women mainly in the workplace. In addition to the ability to make her own decisions and authority over her own life (Eden and Wagstaff, 2021). Carbon capture technologies including membrane-based ones are not anticipated to have any effect on achieving this goal. It is not specifically related to carbon capture and can be affected slightly by encouraging growth and development, which could then result in increasing opportunities for girls and women (Olfe-Kräutlein, 2020b).

4.6. SDG 6 “clean water and sanitation”

Considerable progress has been carried out to increase access to clean water and sanitation. Nevertheless, billions of people still do not have access to clean water. Globally, one out of three people still cannot access clean and safe water, while two in five people do not have access to sanitation facilities (Nationsc). About one-third of the global population is influenced by water scarcity induced by climate change and global warming. Nevertheless, since 1990, about 2.1 billion people have gained the access to clean water and sanitation facilities. However, water scarcity is still a primary issue numerous people are facing (Sanitation Statistics - UNICEF DATA). As a result, SDG 6 was developed to focus on providing clean and safe water and sanitation for all people (Olabi et al., 2022e).

Carbon capture technologies adversely impact the achievement of target 6.3 which emphasizes the improvement of water quality through pollution reduction. The energy needed for carbon capture in power plants negatively influences the efficiency of power plants and produces pollutants and chemicals in the environment. The produced pollutants, wastes, and chemicals increase the toxicity and pollution of freshwater. On the other hand, carbon capture positively impacts target 6.4 which focuses on the sustainable increase of water utilization efficiency. This is reflected by the new designs of carbon capture technologies which lower the utilization of water (Zhu et al., 2021), (Giannaris et al., 2020). Moreover, the utilization of captured CO₂ can be utilized for the removal of dissolved solids from brine water into potable water (Al‒Mamoori et al., 2017). Captured CO₂ can be efficiently utilized in desalination plants for generating fresh water. However, few desalination plants employ captured CO₂ due to their economic disadvantages (Cuéllar-Franca and Azapagic, 2015).

4.7. SDG 7 “affordable and clean energy”

SDG 7 focuses on providing clean and affordable energy to all people. SDG 7 focuses on increasing energy efficiency, allowing for smooth accessibility to energy, and enhancing the integration of renewable energy (Rabaia et al., 2021),(Sayed et al., 2021a) (Olabi et al., 2021c). It is essential to achieve this goal as 13% of the global population does not have access to electricity. The current sources of energy lead to climate change, responsible for 60% of the total greenhouse gas emissions. Consequently, alternative energy sources which do not adversely impact the environment were explored, such as renewable energy sources, including solar energy (Alami et al., 2022b), (Maghrabie et al., 2021), wind energy (Olabi et al., 2021d), (Olabi et al., 2021e), biomass energy (Wilberforce et al., 2021), (Sayed et al., 2021b), geothermal energy (Mahmoud et al., 2021a), (Mahmoud et al., 2021b), and hydro energy (Alnaqbi et al., 2022). Since 2016, the share of renewable energy has rapidly increased, resulting in tremendous growth in solar and wind energy sources (Nationsd). Renewable energy sources on their own are not as reliable as fossil fuel power generation. Renewable energy sources require energy storage systems to account for the frequent fluctuations and intermittencies. Nevertheless, a connection between renewable energy sources and fossil fuel power generation must be made to enhance grid stability. This can be facilitated by the adoption of carbon capture and storage technologies integrated with other energy storage systems. Consequently, carbon capture technologies enhance the performance and generation of renewable energy sources. Thus, integrating carbon capture technologies have strong relations to SDG 7 (Hanak and Manovic, 2020) Furthermore, the main goal of carbon capture technologies is to enhance the production of zero-emission hydrogen and fuel. This enhancement in the zero-emission production positively contributes to SDG 7 (Lee et al., 2020). For instance, in a study conducted by khan et al. (Ali Khan et al., 2021) the usage of carbon capture technologies with steam methane reforming for hydrogen production has significantly reduced the release of emissions. Similarly, Hu et al. (2015) proposed integrating carbon capture technologies to an in-situ steam gasification hydrogen production method to enhance the production of clean and renewable energy. The proposed system helped to produce around 277.67 ml/g of hydrogen.

The main goal of carbon capture by membrane technologies is to ultimately generate clean and reliable energy sources, which in turn increases the accessibility to clean energy. The ultimate goal of carbon capture technologies is to capture CO₂ from the atmosphere to limit its contribution to global warming and climate change (Olabi et al., 2022e). However, the addition of carbon technologies in conventional coal-based power plants increases the Levelized cost of electricity by 35–40%. Due to the high costs of membrane-based carbon capture, the goal of producing clean and affordable energy for all people is hindered (Rubin et al., 2015). On the other hand, the addition of carbon capture technologies to coal-based power plants ensures a reliable supply of energy. This in return satisfies the goal of sustaining an uninterrupted and consistent supply of energy to meet the required energy demand (Mikunda et al., 2021b). Nevertheless, membrane-based carbon capture technologies are energy-intensive, and this leads to a substantial reduction in combustion efficiency and inflation in the electricity price (Al-Mamoori et al., 2017). According to Song et al. (2017) the energy utilization of the mostly utilized carbon capture technology, chemical absorption, is from 2.5 to 3.5 MJ/kg CO₂ (Shakerian et al., 2015), (Oh et al., 2016), while the energy utilization of membrane technology for carbon capture is 3 MJ/kg CO₂ for a membrane area of 70 m² and 3.6 MJ/kg CO₂ for a membrane area of 30 m². However, according to the European Union, the target energy utilization is only at 2 MJ/kg CO₂ (Belaissaoui et al., 2012), (Dechamps and Pilavachi, 2004).

4.8. SDG 8 “decent work and economic growth”

The unemployment rate in 2000 was at 6.4%, and due to global economic growth, the unemployment rate decreased to 5.6% in 2017. However, the high unemployment rate is still a global issue that must be tackled. Hence, SDG 8 was developed to promote sustainable economic growth and employment for all people. Sustainable economic growth generates job opportunities for all people (Nationse). SDG 8 revolves around the concepts of economic growth, employment rates, decent work, resource efficiency, high productivity, and environmental protection (Olabi et al., 2022e).

The significant investments and a large number of carbon capture projects have resulted in lower environmental impacts of conventional power plants, and thus in higher growth of the implemented number of power plants. Where it was witnessed that up to 65 large-scale carbon capture projects were developed by 2020. Around 38 of these projects are in the United States, 13 projects are in Europe, 10 are in Asia, and 3 are in the Middle East. The total rated capacity of these projects is 40 mt-CO₂/year (Page et al., 2020). It is expected that by 2050 the rated capacity will increase to 5635 mt-CO₂/year and the number of carbon capture projects is anticipated to increase to 2000 projects (de Mello Delgado et al., 2021). Furthermore, the impacts of carbon capture technologies on the economy have been thoroughly evaluated in a UK carbon capture storage investment report. The report discussed the influence of carbon capture storage technologies on the economy, job creation, and gross profits. The report indicated that carbon capture storage technologies bring numerous advantages from the imports and exports related to carbon capture storage technologies and job opportunities (Summit, 2017). Due to these advantages, the UK government decided to invest at least 780 million dollars in the promotion and advancement of carbon capture storage technologies. This investment has led to more economic growth as it opened up 3850 full-time equivalent jobs in just the first year (Turner et al., 2020). According to Franz et al. (2014), the average salary for jobs related to carbon capture technologies in the UK is around 6800 dollars per month.

4.9. SDG 9 “industry, innovation and infrastructure”

The scope of SDG 9 is to encourage innovation, advance equitable and sustainable industrialization, and construct resilient infrastructure (MONTES, 2017). Developed nations have offered to help developing and undeveloped nations with their economies. Achieving sustainable economic growth, social and environmental development, and battling climate change within the context of this SDG, requires developing and underdeveloped nations for long-lasting infrastructure investments, sustainable industrial advances, and new technologies. Encouragement of sustainable industries, technical research, and innovation funding could all contribute to sustainable development (Franco et al., 2020).

Target 9.4 aims to improve efficiency in resource utilization and expand the implementation of clean, environmentally friendly technologies and industries. Achieving target 9.4 requires concentrating on forest-based ecological systems like carbon storage, watershed restoration, and outdoor leisure can boost local economies while preventing material development. Limiting carbon and other greenhouse gas emissions might not only slow down climate change but will also lessen its negative effects on the health of ecosystems, such as the increased levels of forest fires in both temperate and boreal forests and the elevated chance of the Amazon rainforest becoming unstable if certain temperature limits are exceeded (Tomaselli et al., 2019).

Carbon capture using membranes has a direct impact on infrastructure and industry. The economic effects of carbon capture may vary by area, industry, and a nation's reliance on fossil fuels (Mikunda et al., 2021c). Developed membrane materials reduce costs associated with carbon capture, which is for the membrane technology highly depends on the CO₂ capture ratio. Post-combustion CO₂ capture utilizing the membrane technology can have an advantage from a reduced CO₂ capture ratio with a 55% drop in cost. The improvement of the membrane performance is recommended to lower the CO₂ capture costs down to $20/tonne CO₂. Membrane systems could one day be an eco-friendly solution for CO₂ capture from power plants and other energy-intensive process sectors because they don't require chemicals, are simple to scale up, and have a comparatively low energy requirement (He, 2018a). Compared to the issues encountered with the use of liquid absorption such as corrosion and foaming, utilization of membrane technology in post-combustion carbon capture, benefits the whole process by cost savings reported as 38–42% and equipment weight reduction of 34–40% (Luliano et al., 2020).

4.10. SDG 10 “reduced inequality”

The target of SDG 10 is to reduce inequality within and among countries. Similar to how poverty has been acknowledged as having multiple dimensions, inequality also has a social, economic, and ecological component. The negative impacts on people when inequality is (excessively) high within a nation have been the subject of extensive research in recent decades. Inequality is considered to be one of our most critical social issues (Breting-Garcia, 2021).

Carbon capture can lessen cities' carbon footprints, improve their sustainability (He, 2018b) and help in reducing inequality. For the general public, carbon capture facilities might also offer sources of revenue and employment. This contrasts with the lopsided advantage enjoyed by nations with plentiful fossil resources, which has recently affected international geopolitics. As a result, carbon capture and storage technologies may make up for the disadvantages experienced by nations and regions without independent access to fossil fuels. Together, these elements could indirectly help to lessen inequality between countries and regions (Olfe-Kräutlein, 2020b). Berdowska and Skorek-Osikowska examined the deployment of membrane carbon capture technology with a cryogenic distillation module for a 600 MW coal power plant employing oxy-combustion technology. The reference system without applying separation and compression of CO₂ and with an air-fired pulverized bed boiler had an electricity break-even price of €94.5/MWh. For a membrane costing €0.7/m², the breakeven price of power for the two technologies under consideration is €81.2/MWh. It should be noted that the effectiveness of the hybrid system is significantly impacted by the membrane selection. The membranes' permeability and oxygen selectivity determine how well the system functions and how much it costs to operate. The hybrid systems’ profitability will increase owing to the projected developments in membrane technology in the coming years. Thus, all of these factors will contribute to higher income and revenue and indirectly to reducing inequality (Berdowska and Skorek-Osikowska, 2013).

4.11. SDG 11 “sustainable cities and communities”

Making cities and communities, safe, resilient, and sustainable is the main goal of SDG 11. Cities contain 55% of the world's population, generate 85% of its GDP, and are yet also responsible for 75% of its greenhouse gas emissions (Vaidya and Chatterji, 2020).

Encouraging CO₂-based fuel and chemical production could be seen as a step in the right direction towards creating more environmentally friendly communities and enhancing sustainability (Olfe-Kräutlein, 2020b) and leading to improved air quality (Target 11.6). Carbon capture has both favorable and unfavorable effects on the environment. The most noticeable result of carbon capture is a 60–80% reduction in greenhouse gas emissions. Lowering the climate change caused by the energy and products utilized by various cities and communities can lead to significant contributions (Olabi et al., 2022d). The sustainability of fossil fuel power plants can be improved by deploying optimal membrane carbon capture technologies that lower their energy consumption and operational expenses. According to Asadi and Kazempoor, at ideal design and operating parameters, the CO₂ capture cost and energy penalties were respectively 13.1$/tCO₂ and 10% by studying a multi-stage membrane system. As the CO₂ content in the gas rises, the cost of CO₂ capture greatly falls and CO₂ removal is improved (Asadi and Kazempoor, 2022).

4.12. SDG 12 “responsible consumption and production”

Around one-third, estimated as 1.3 billion tonnes of the globally produced food is wasted every year. This could potentially mean that not only are there insufficient natural sources to meet the future generation's needs but also most of the currently available resources are being wasted due to inefficient transportation and harvesting strategies. According to the UN, if the global population increases to 9.6 billion by the year 2050, the number of natural resources needed will be threefold the number of natural resources acquired from this planet. All these issues call for responsible and sustainable consumption and production practices. As a result, SDG 12 was developed to drive the need for consuming and producing natural resources without constituting any adverse effects on the planet. SDG 12 thrives on doing more with fewer resources to sustain the current resources for future generations. Furthermore, SDG 12 promotes sustainable consumption and production patterns and practices. Sustainable consumption and production significantly reduce poverty and allow for the transition towards a green and low-carbon society (Nationsf). SDG 12 thrives to enhance the adopted consumption and production practices in companies to enhance the sustainability of natural resources and deflate the waste streams that are allocated on land, water, or air.

The role of carbon capture technologies is to reduce CO₂ emissions and thus contribute to target 12.4 which focuses on reducing chemical and waste released to the atmosphere. Companies can integrate carbon capture technologies to reduce CO₂ emissions. Even though carbon capture technologies might generate waste into the atmosphere, the technologies reduce greenhouse gas emissions for fossil fuel plants by 75–90%. Moreover, employing carbon capture technologies in companies significantly contributes to target 12.6 which stresses the adoption of sustainable practices. On the other hand, the accomplishment of target 12.2 is hindered by carbon capture technologies. Target 12.2 strives for sustainable management and efficient utilization of natural resources. As carbon capture technologies need energy for their operation and materials for their development. These requirements reduce the efficiencies of power plants integrating carbon capture technologies. It is found that carbon capture-based power plants have efficiencies 20–25% lower than conventional coal-based power plants. Moreover, the number of materials required for fossil-fuel plants with carbon capture technologies is far superior to that of conventional fossil-fuel plants. Additionally, carbon capture operations produce chemical waste which adversely influences the environment. Hence, deploying carbon capture projects can potentially increase the produced wastes from the carbon capture process. The carbon capture process might result in the emission of ash, NO_x, sulfur, and NH₃. These consequences hinder the achievement of target 12.5 which focuses on reducing waste generation (Mikunda et al., 2021c). Another negative consequence of the utilization of membrane-based carbon capture technologies is the release of toxins into the environment as a result of integrating amines for membrane absorption (Li and Chen, 2005).

4.13. SDG 13 “climate change”

In 2019, the highest temperatures and the highest levels of greenhouse gas emissions were recorded. The levels of greenhouse gas emissions dropped by 6% in 2020 due to travel restrictions induced by the COVID-19 pandemic (Nationsg). However, this improvement is temporary, and levels of greenhouse gas emissions are yet to increase again when the economy starts recovering from the COVID-19 pandemic. The high levels of greenhouse gas emissions are significantly contributing to global warming and climate change. Climate change is negatively influencing the global population. Climate change is inducing changes in weather patterns, resulting in higher sea levels, and causing more frequent extreme weather conditions. Due to these negative impacts of climate change, it became imperative to take extreme measures for addressing these climate issues. In 2015, the Paris Agreement was created to focus on strengthening the global reaction to the risks of climate change by reducing global temperatures below 2 °C (Nationsg). SDG 13 has been developed to take urgent action to battle climate change and its effects.

Carbon capture technologies combat climate change by significantly contributing to the achievement of SDG 13 (Olabi et al., 2022e). After the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report in 2007, carbon capture technologies have been acknowledged as the primary prevention technologies for reducing CO₂ emissions (IPCC, 2007). The Fifth Assessment Report of IPCC further highlighted the importance of carbon capture technologies as it was estimated that by 2100 the greenhouse gas emissions cannot be reduced below 450 ppm CO₂eq without the utilization of carbon capture technologies. Additionally, the Paris Agreement of reducing temperatures by 2 °C includes carbon capture technologies as key enablers for combatting climate change by significantly reducing CO₂ emissions (Rogelj et al. Masson-Delmotte et al., 2018). Through these integrations of carbon capture technologies into global and national strategies, plans, and policies for combatting climate change the accomplishment of target 13.2 becomes more feasible. Moreover, carbon capture technologies facilitate the accomplishment of target 13.1 which focuses on strengthening resilience to natural disasters related to climate change by reducing 90% of the CO₂ emissions in coal-based power plants (Rubin et al., 2015). Especially, membrane-based carbon capture technologies have high CO₂ capture yields (80–90%) (Mondal et al., 2012). It is essential to focus on CO₂ reduction due to the high CO₂ emissions from anthropogenic activities. It is estimated that the CO₂ emissions from anthropogenic activities will increase to 43.22 billion tonnes by the year 2040 (Sieminski, 2013). However, carbon capture technologies are capable of capturing 33.4 million tonnes per year of CO₂ by 2020 which amounts to only 0.09% of the CO₂ emissions (Theo et al., 2016).

4.14. SDG 14 “life below water”

SDG 14 emphasizes the significance of ocean monitoring in a situation where major pressures are threatening the ocean's capacity to provide economic, social, and benefits to the community. Oceans are a vital part of the mechanisms that keep the Earth's ecosystems alive. With the ability to cycle 93% of the world's carbon dioxide and capture 30% of exhaust emissions, the oceans serve as the principal climate controller. Additionally, over the past few decades, the seas have absorbed 90% of the Earth's heat. The provision of services by healthy aquatic ecosystems includes water filtering, nutrient uptake, and biodiversity preservation. Concerning climate change, the oceans are becoming 10 times more acidic today than they were 65 million years ago due to the absorption of CO₂ from the atmosphere, which harms marine species' welfare, calcification, growth, and diversity. The adverse effects of climate change also include changes in ocean circulation and salinity, as well as an increase in the frequency and severity of weather and climate variations (Recuero Virto, 2018). The aquatic ecosystem and life underwater can benefit significantly from carbon capture. This is mainly a result of the carbonate/bicarbonate/hydrogen system in oceans and seas, being in equilibrium with CO₂ in the atmosphere (Olabi et al., 2022c).

4.15. SDG 15 “life on land”

Nature is essential to the survival of all living things as it provides oxygen and crops, and controls climatic conditions. Even though nature is key to the survival of the population, people have modified about 75% of the earth's surface, reducing the available land for nature and wildlife. As a result, about 1 million species of animals and plants are about to go extinct. Based on the Global Assessment Report about biodiversity and ecosystems, it is now imperative to take transformative actions to shield and restore nature. Nevertheless, the state of nature is rapidly deteriorating, negatively influencing the economy, food security, quality of life, health, and livelihood. The need for sustaining and protecting the nature and ecosystem has paved the way for the development of SDG 15 which highlights the criticality of life on land. SDG 15 sustainably manages ecosystems and wildlife and mitigates biodiversity loss, deforestation, land degradation, and desertification (Nationsh). SDG 15 protects life on land by reducing waste on land and promoting efficient resource utilization of forests, soil, and aquatic ecosystems.

The implementation of carbon capture technologies has positive and negative interactions with the objectives of SDG 15. Target 15.5 is positively correlated with the reduction of CO₂ emissions due to carbon capture technologies. It has been estimated that by 2050, carbon capture technologies will facilitate the capture of 10 to 2.8 GtCO₂ eq per year. The tremendous reductions in CO₂ emissions will eventually hinder the temperature rise by 1.5–2 °C (Ramón and Guillena, 2020). Hence, carbon capture technologies capture CO₂ emissions that would have been otherwise released into the atmosphere and potentially led to air and water pollution (Olabi et al., 2022e). Moreover, the reduction of CO₂ emissions in the atmosphere mitigates extreme climatic changes and hence reduces biodiversity loss (Mikunda et al., 2021c). On the other hand, carbon capture technologies are negatively influencing the objectives of target 15.1 which promotes sustainable usage of terrestrial and inland freshwater ecosystems. Carbon capture technologies have high utilization of energy (as mentioned in SDG 7); this, in return results in the production of wastes, pollutants, and chemicals that could spread to nearby water bodies. Other than polluting water bodies, carbon capture technologies have high water consumption, these technologies generate wastewater due to the toxins and heavy metals intoxicating the water (Oreggioni et al., 2017), (Chisalita et al., 2019).

4.16. SDG 16 “peace, justice and strong institutions”

SDG 16 is more than just a moral agenda, and it is also more than just developing technical capability. It outlines the key responsibility for covering both the purpose of institutions and their philosophy and reasoning place politics at the center of institutions. SDG 16 reflects these issues of attitude by putting importance on both whether institutions function and how they function (OECDWhaites, 2016). SDG 16 goals are unlikely to be directly impacted by the adoption of carbon capture technologies. However, under specific circumstances, indirect beneficial impacts may happen in terms of preserving and furthering the development of a peaceful world. While wealthier countries are primarily responsible for global warming's emissions, developing countries are already taking on the majority of its effects since they are more at risk from both desertification and sea level rise. Therefore, all actions that industrialized nations do to avoid, reduce, or even harvest CO₂ from the atmosphere (known as “negative emission technology,” or NET) may be viewed as actions that promote peace (Olfe-Kräutlein, 2020b).

4.17. SDG 17 “partnership for the goals”

SDG 17 demands funding the international alliance for achieving sustainable development on a global scale. In order to carry out the goals of Agenda (2030), collaborations between the public, private, and civil society must be strengthened. It will also be necessary to improve the coordination of policies and actions both locally and globally and to increase international collaboration. SDG 17 calls for efforts to strengthen the abilities for achieving the SDGs and fulfil these requirements (Maltais et al., 2018).

Working with another commercial, governmental, and municipal entities or authorities is a requirement of carbon capture projects. Along with this cooperation, the project management team should budget the necessary funds and take into account how to connect firm policies with the SDGs. Defining and carefully monitoring related metrics is also necessary. All businesses may contribute to the SDGs as part of their sustainable development goals, regardless of the size of their respective industries. On the one hand, although the scope and size of the global targets are unmatched, there are several fundamental aspects that any firm may still contribute (Olabi et al., 2022e). SDG 17 calls for extra assistance from the developed countries to the less developed ones which can include improved international collaboration in the field of carbon capture that is created to equally fulfill the requirements of less developed countries (targets 17.3 and 17.5). It is unclear whether carbon capture will positively contribute to SDG 17 due to numerous essential, possibly partially altruistic prerequisites (Olfe-Kräutlein, 2020b).

The summary of the assessment done on the contribution of membrane-based carbon capture technologies for achieving the 17 SDGs is shown in Fig. 26, which depicts the most influenced SDGs by membrane-based carbon capture technologies (see Fig. 9, Fig. 10, Fig. 11, Fig. 12, Fig. 13, Fig. 14, Fig. 15, Fig. 16, Fig. 17, Fig. 18, Fig. 19, Fig. 20, Fig. 21, Fig. 22, Fig. 23, Fig. 24, Fig. 25). The figure shows that SDGs 13, 9, 7, and 8 are the most influenced SDGs by carbon capture technologies. The CO₂ reductions and the sustainable energy production by these technologies have led to great contributions to SDG 13 and SDG 7. Moreover, as carbon capture technologies are becoming more advanced, they are being adopted by more countries and institutions. These consequences lead to the creation of more jobs and significant economic growth and developments. Due to these positive impacts, SDG 8, SDG 1, and SDG 3 are perceived to be positively correlated with carbon capture technologies.

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Fig. 9. Membrane carbon capture SDG 1 impact summary.

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Fig. 10. Membrane carbon capture SDG 2 impact summary.

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Fig. 11. Membrane carbon capture SDG 3 impact summary.

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Fig. 12. Membrane carbon capture SDG 4 impact summary.

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Fig. 13. Membrane carbon capture SDG 5 impact summary.

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Fig. 14. Membrane carbon capture SDG 6 impact summary.

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Fig. 15. Membrane carbon capture SDG 7 impact summary.

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Fig. 16. Membrane carbon capture SDG 8 impact summary.

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Fig. 17. Membrane carbon capture SDG 9 impact summary.

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Fig. 18. Membrane carbon capture SDG 10 impact summary.

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Fig. 19. Membrane carbon capture SDG 11 impact summary.

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Fig. 20. Membrane carbon capture SDG 12 impact summary.

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Fig. 21. Membrane carbon capture SDG 13 impact summary.

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Fig. 22. Membrane carbon capture SDG 14 impact summary.

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Fig. 23. Membrane carbon capture SDG 15 impact summary.

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Fig. 24. Membrane carbon capture SDG 16 impact summary.

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Fig. 25. Membrane carbon capture SDG 17 impact summary.

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Fig. 26. The influence of membrane-based carbon capture technologies on the SDGs.

3.1. Power to ammonia synthesis (Water Electrolysis)

Hydrogen gas (H₂) and oxygen (O₂) are produced by the electrolysis of water (H₂O). The water-splitting process is done in electrochemical cells which can be categorized according to their configuration, i.e., polymer electrolyte membrane electrolyzers, alkaline electrolyzers, and solid oxide electrolyzers [48]. All cells are composed of an anode, cathode, electrolyte, power source (renewable), and sometimes a membrane. Upon passing an electric current through the electrodes (1.23 V in an ideal case), the covalent bonds will start to break down, allowing hydrogen and oxygen gases to be produced. In the case of an alkaline electrolyzer, potassium hydroxide is commonly used as an electrolyte to avoid acid corrosion; In terms of anodic and cathodic stability, nickel is the most commonly employed electrode [49]. The process of ammonia production using electrolysis includes four units: renewable source (solar or wind), electrolyzer, air separation unit, and Haber Bosch process (Fig. 1). The first electrolysis-based ammonia synthesis was introduced in 1920 based in Haber- bosh process with an energy consumption of 46 ± 2 GJ/tNH₃ [50]. However, this stopped by the 1990 s owing to the high cost of fossil fuels. Several projects for solar to ammonia electrolysis have been initiated in Europe and America. Today, the current trend toward green ammonia is seeking a direct method for ammonia production under mild operating conditions.

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Fig. 1. Process description for green ammonia production [58], https://www.man-es.com/discover/two-stroke-ammonia-engine/green-ammonia-production. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

3.2. Emerging ways for ammonia synthesis

Even though the existing technologies for green ammonia synthesis offer many facilities due to the existing equipment’s from the last century, research and development are seeking a route for direct production of green ammonia without involving the intermediate step of hydrogen production. Many research themes imply a new synthesis concept to obtain a pilot-scale green ammonia production. Examples of these emerging methods are photosynthesis, electrochemical methods, heterogenous and homogenous catalysis, molten salt synthesis, solid-state synthesis, and non-thermal plasmatic synthesis. Such methods rely on mild operation conditions and open the way for direct ammonia production [59], [60].

3.2.1. Electrochemical ammonia production

The electrochemical production route of ammonia is distinguished from conventional NH₃ production by its reaction route, operating conditions, and energy source. The main aspect that distinguishes electrochemical synthesis from electrolysis is the direct synthesis of green ammonia from air and water utilizing renewable energy sources, such as tidal or solar energy. A common process involves oxidizing hydrogen or water at the anode, which releases protons that move over a solid or liquid electrolyte to the cathode side. Nitrogen reacts with the protons in the cathode under mild conditions to produce NH₃ [61], [62]. Typically, NRR “the nitrogen reduction reaction” and HER “the hydrogen evolution reaction” compete at the cathode as follows [63], [64], [65]:

4 In electrolytes with a pH < 6(2)" role="presentation" style="box-sizing: border-box; margin: 0px; padding: 0px; display: inline-block; font-style: normal; font-weight: normal; line-height: normal; font-size: 14.4px; text-indent: 0px; text-align: left; text-transform: none; letter-spacing: normal; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;" tabindex="0">${\mathit{�}}_2\left(\mathit{�}\right)+6{\mathit{�}}^{+}+6{\mathit{�}}^{-}\to 2{\mathit{�}\mathit{�}}_3\left(\mathit{�}\right)$(3)" role="presentation" style="box-sizing: border-box; margin: 0px; padding: 0px; display: inline-block; font-style: normal; font-weight: normal; line-height: normal; font-size: 14.4px; text-indent: 0px; text-align: left; text-transform: none; letter-spacing: normal; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;" tabindex="0">$2{\mathit{�}}^{+}+2{\mathit{�}}^{-}\to {\mathit{�}}_2\left(\mathit{�}\right)$

5 In electrolytes with a pH > 8(4)" role="presentation" style="box-sizing: border-box; margin: 0px; padding: 0px; display: inline-block; font-style: normal; font-weight: normal; line-height: normal; font-size: 14.4px; text-indent: 0px; text-align: left; text-transform: none; letter-spacing: normal; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;" tabindex="0">${\mathit{�}}_2\left(\mathit{�}\right)+6{\mathit{�}}_2\mathit{�}+6{\mathit{�}}^{-}\to 2{\mathit{�}\mathit{�}}_3\left(\mathit{�}\right)$(5)" role="presentation" style="box-sizing: border-box; margin: 0px; padding: 0px; display: inline-block; font-style: normal; font-weight: normal; line-height: normal; font-size: 14.4px; text-indent: 0px; text-align: left; text-transform: none; letter-spacing: normal; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;" tabindex="0">$2{\mathit{�}}_2\mathit{�}+2{\mathit{�}}^{-}\to {\mathit{�}}_2\left(\mathit{�}\right)+2{\mathit{�}\mathit{�}}^{-}$

The main issue facing this process is the thermodynamic stability of the N₂, which requires high energy to defeat the bonding energy (941 kJ/mol) of " role="presentation" style="box-sizing: border-box; margin: 0px; padding: 0px; display: inline-block; font-style: normal; font-weight: normal; line-height: normal; font-size: 14.4px; text-indent: 0px; text-align: left; text-transform: none; letter-spacing: normal; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;" tabindex="0">$�\equiv �$. Therefore, depending on the operating temperature, various electrochemical green ammonia production can be categorized, including low operating temperature up to 100 °C, mid-operating temperature between 100 and 350 °C, molten salt ammonia synthesis between 100 and 500 °C, solid-state ammonia synthesis > 500 °C, and high operating temperature 350 to 700 °C [66].

3.2.1.1. Low-temperature electrochemical ammonia synthesis

Low-temperature ammonia synthesis receives considerable attention among researchers with more than a hundred publications per annum [67]. A typical cell with low operating conditions consists of a platinum anode [66], Ru-based cathode [68], and a high conductive proton membrane, usually Nafion [69]. Most studies are performed at room temperature using liquid aqueous electrolytes such as water that can directly donate the H⁺ proton. Acidic electrolytes are preferable due to their high proton environment. In contrast, in basic electrolytes, there is a high competition between hydrogen evolution reactions and nitrogen reduction reactions, as shown in (equations 3 & 4) [70], [71]. Temperature plays a key role in enhancing NH₃ production rate (10⁻⁸- 10⁻⁵ mol s⁻¹ cm⁻²) at an operating temperature up to 90 °C [65], [72]. Another key factor affecting the overall performance of ammonia production is the type of catalyst. Today, numerous types of catalysts have been studied including noble metals [73], metal (oxides [74], sulfides [75], and nitrides [76]), organometallic complexes [77] etc. A study performed by Zhang et al. [78] involved using a bi-metallic oxide (CoMoO₄) for NH₃ synthesis at atmospheric pressure and room temperature. High faradic efficiency and ammonia yield of 22.86 % and 7.98 mol h⁻¹ g_cat⁻¹ are higher than those obtained using mono metallic oxides. Table 2 summarizes the progress done in preparing ammonia at low-temperature.

Table 2. Different experimental works on low-temperature ammonia synthesis.

T (°C)	Electrolyte	Cathode	Ammonia Yield (mol/s cm−2)	Ref.
50	AEM	Fe	380 × 10−12	[79]
80	Nafion	SmBaCuMO5+	870 × 10−10	[80]
80	Nafion	Sm1.5Sr0.5NiO4	105 × 10−10	[81]
80	SPSF	Sm1.5Sr0.5NiO4	103 × 10−10
Room T	Nafion	Fe/Fe3O4	111 × 10−10	[82]
Room T	AEM	Fe–CuS/C	686 × 10−12	[75]
50	AEM	RuPt	635 × 10−12	[83]
Room T	Nafion	Au nanorods	27 × 10−12	[84]
Room T	Nafion	Fe2O3-CNT	36 × 10−12	[71]

3.2.1.2. Molten-salt ammonia synthesis (Moderate Temperature)

The main challenge facing many aqueous systems for ambient ammonia synthesis is the high hydrogen evolution and slow kinetics. Molten salt electrolytes revealed a promising result with enhanced faradic efficiency. For moderate NH₃ synthesis, in the range of 100 to 400 °C, it utilizes ammonia using a molten state electrolyte. In a typical process, a strong competition of HER during NH₃ synthesis owing to the " role="presentation" style="box-sizing: border-box; margin: 0px; padding: 0px; display: inline-block; font-style: normal; font-weight: normal; line-height: normal; font-size: 14.4px; text-indent: 0px; text-align: left; text-transform: none; letter-spacing: normal; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;" tabindex="0">$�\equiv �$ bonding which can be migrated if H₂ at a gaseous state reacts with nitride ions. A typical cell consists of an electrolyte (molten salt), a porous cathode, and a permeable anode (Fig. 2).

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Fig. 2. Illustration of molten-salt ammonia synthesis, adapted from [85] with permission No. 5441990967119.

Murakami et.al [86] were the first investigators for the electrochemical molten-salt ammonia synthesis at atmospheric pressure. The hydrogen source for this type of synthesis could be gaseous hydrogen or water molecules. Depending on the electrolyte, there are three different configure of this type: molten chloride salts [87], [88], molten hydroxide salts [89], and composite electrodes [90]. Molten chloride salt started to receive great attention owing to the fast dissolution of Li₃N in molten electrolytes as a source of nitride ions. For this type of electrolyte, protons (H⁺) is favourable from water instead of hydrogen gas. However, the low faradic efficiency is observed owing to the possibility of hydroxide ions and carbon dioxide formation [87]. On the other hand, hydroxide molten operates at a lower temperature (200 °C) and is less corrosive with a faradic efficiency up to 35 % at low current density [91]. However, at a higher current density the faradic efficiency reveals a sharp decline owing to H₂ evolution. To tackle the lower efficiency problem, some researchers investigated the integration of a sub fuel cell to recycle the produced hydrogen; others suggested supporting activated carbons to inhibit H₂ evolution for metal-based catalysts [89], [92]. Table 3 shows the progress done in Molten-salt ammonia synthesis (@ Moderate Temperature), while Table 4 shows the progress done at high temperature.

Table 3. Molten-salt ammonia synthesis (Moderate Temperature).

T (°C)	Electrolyte	Cathode	Ammonia Yield (mol/s cm−2)	Ref
450	SDC-ternary carbonate composite electrolyte	La0.6Sr0.4Fe0.8Cu0.2O3−δ	539 × 10−11	[93]
450	LiAlO2 – (Li/Na/K)2CO3	Co3Mo3N-Ag	327 × 10−12	[94]
400	LiAlO2 – (Li/Na/K)2CO3	CoFe2O4-Ag	232 × 10−12	[95]
400	LiCl-KCl-CsCl + Li3N	Porous Ni/Ni	333 × 10−11	[86]
300	LiCl-KCl-CsCl + Li3N	Porous Ni/C	200 × 10−10	[87]
200	NaOH/KOH (Nano-Fe2O3)	Ni	100 × 10−10	[50]
400	LiCl, KCl, CsCl + Li3N	Al	333 × 10−10	[96]

Table 4. High-temperature ammonia synthesis.

T (°C)	Electrolyte	Cathode	Ammonia Yield (mol/s cm-2)	Ref.
550	BaZr0.7Ce0.2Y0.1O3 − δ	Ni-BZCY72	286 × 10−11	[102]
550	BZCY72 “BaZr0.8Y0.2O3 − δ “	La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF)	850 × 10−13	[103]
500	BCY10 “BaCe0.9Y0.1O3 − δ“	Ag-Pd	300 × 10−13	[104]
620	BZCY72 “BaZr0.7Ce0.2Y0.1O3 – δ”	Ni-BZCY72	170 × 10−11	[105]
600	GDC “Ce0.9Gd0.1O2 − δ “	Pt	367 × 10−13	[106]

3.2.1.3. Solid-State ammonia production (High Temperature)

To increase the solid electrolyte's conductivity, ammonia synthesis utilizing solid-state electrolytes is typically carried out at high temperatures. As it is clear from (Fig. 3), a dense electrolyte is inserted between a porous anode and cathode electrodes with H⁺ or O^2–, depending on the ceramic type, migrating through the dense electrolyte [97], [98]. The merit of high operating temperature gives the advantage of higher reaction kinetics and better N₂ activation. However, the thermodynamic equilibrium at high temperatures might negatively impact the yield of ammonia yield and material degradation [99].

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Fig. 3. Direct ammonia synthesis (a) proton conductive ceramic membrane and (b) oxygen ion conductive ceramic membrane.

Different electrode materials were investigated for ammonia synthesis based on noble metals (Pt, Pd, Pd-Ag, Ru). For example, the first investigation involving solid-state ammonia synthesis used Pd as a porous cathode with a production rate of 450 × 10⁻¹¹ mol/s cm⁻². At 500 °C and ambient pressure, Yuan et al. [100] successfully produced NH₃ @ 307 × 10⁻¹¹ mol/s cm⁻² using yttrium-doped barium zirconate (BZY) as an electrolyte and α-Fe₂O₃/BZY as a cathode. A reasonable ammonia production rate was reported using SrCe_0.95Yb_0.05O_3−δ electrolyte and Pd electrodes at 570 °C [101]. A summary of different experimental works concerned with solid state NH₃ synthesis is shown in table 4, and the various electrolytes used for ammonia synthesis are shown in Fig. 4.

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Fig. 4. Different electrolytes used for electrochemical ammonia synthesis.