A recent study, conducted by Xiaoyu Huang, Minghui Xie, Xiaowei Li, and Chenning Deng from the Chinese Research Academy of Environmental Sciences, revealed significant differences in the environmental impacts and carbon footprints of various hydrogen production methods in China [1]. The analysis, based on a life cycle assessment (LCA), indicated that gray hydrogen produced from coal has the highest environmental impact and carbon emissions, while green hydrogen from proton exchange membrane (PEM) electrolysis has the lowest [1]. This finding aligns with global reviews suggesting that green hydrogen generally has substantially lower production emissions compared to blue hydrogen [2].
Hydrogen is gaining increasing attention as a clean energy carrier due to its high energy density and diverse production and usage methods, with countries like China, the United States, Germany, and Japan prioritizing its development [1]. Global demand for hydrogen is projected to rise significantly, with China's demand estimated to reach approximately 130 million tons by 2060, more than triple its current demand of over 30 million tons [1]. Hydrogen energy products are categorized by source into gray, blue, and green hydrogen [1]. Gray hydrogen is derived from fossil fuels or industrial by-products, often producing substantial carbon dioxide [1]. Blue hydrogen incorporates carbon capture and storage (CCS) technology into gray hydrogen production to reduce CO2 emissions [1]. Green hydrogen is produced through water electrolysis using renewable energy sources like photovoltaics and wind power [1].
The study utilized a localized endpoint-destructive life cycle impact assessment method, gathering data from existing literature and supplementing it with international lists and localized power conversion for data not readily available in China [1]. The functional unit for the assessment was 1 kg of gaseous hydrogen product [1]. Six types of hydrogen products were evaluated: gray H2 (coal), gray H2 (gas), blue H2 (coal), blue H2 (gas), green H2 (alkaline electrolysis water, AEW), and green H2 (PEM) [1]. The LCA covered stages from feedstock acquisition to hydrogen production, excluding transportation or downstream applications of the hydrogen [1].
The results showed that gray H2 (coal) had the highest environmental impact, measured at 1203 mPt, and the highest carbon emission, at 23.79 kgCO2eq [1]. Gray H2 (gas) followed with an environmental impact of 780 mPt and carbon emissions of 16.51 kgCO2eq [1]. Blue H2 (coal) had an environmental impact of 724 mPt and carbon emissions of 11.23 kgCO2eq, while blue H2 (gas) showed an impact of 442 mPt and emissions of 5.56 kgCO2eq [1]. In contrast, green H2 (AEW) recorded an environmental impact of 202 mPt and carbon emissions of 1.63 kgCO2eq [1]. Green H2 (PEM) demonstrated the lowest environmental impact at 199 mPt and the lowest carbon emission at 1.55 kgCO2eq [1]. Another global review also indicated that green hydrogen’s production emissions range from 0.67 kgCO2-eq/kgH2 to 1.74 kgCO2-eq/kgH2, which are substantially lower than blue hydrogen’s range of 1.21 kgCO2-eq/kgH2 to 4.56 kgCO2-eq/kgH2 [2]. Brown hydrogen, produced via coal gasification, has been found to have the highest global warming, acidification, and resource depletion impacts among various options [5]. Conversely, green hydrogen from electrolysis using wind energy has the lowest environmental impacts in terms of global warming, acidification, eutrophication, and resource depletion [5]. While some sources conventionally define green hydrogen from renewable electricity as having zero carbon intensity [4], the specific LCA in China calculated a value of 1.55 kgCO2eq for green H2 (PEM) [1].
To mitigate environmental impacts and carbon footprints, the study suggested that efforts for green hydrogen should primarily focus on substituting and reducing feedstocks, particularly electricity [1]. For gray hydrogen, the focus should be on reducing pollutants, and for blue hydrogen, both aspects should be addressed [1]. Adjusting the hydrogen production structure to promote the substitution of green for gray hydrogen is crucial for reducing overall carbon emissions in the industry [1]. Hydrogen is considered a promising alternative due to its potential to reduce reliance on fossil fuels and contribute to climate action and affordable clean energy [5].
The development of green hydrogen production plants is underway globally, including a 20 MW hydrogen electrolyzer plant in China planned for expansion to 60 MW by 2024, and a 10 MW PEM electrolyzer plant in Germany [3]. However, challenges persist, such as the need for efficient and safe hydrogen storage and distribution infrastructure [3]. This study, published as a preprint, provides foundational insights for environmental management policies related to hydrogen energy development, though further peer review is pending [1].
