Methodological approaches to carbon footprint assessment and certification of low carbon hydrogen

Abstract

The article reviews existing approaches to low-carbon hydrogen certification and offers recommendations for their improvement based on an assessment of the carbon footprint across the entire life cycle. A comprehensive assessment of the carbon footprint of hydrogen produced from water and methane during steam reforming is presented. The assessment concluded that approximately 50% of hydrogen is produced from water, meets the requirements of low-carbon hydrogen (emission levels in the range of 4.2–4.5 kg CO2eq/kg H2) and can be considered for certification as renewable hydrogen. The results of estimating the carbon footprint of hydrogen from hydrogen sulfide demonstrate that for hydrogen sulfide methane reforming and thermal decomposition of hydrogen sulfide, carbon dioxide emissions will be on the order of 1.842 and 2.244 kg CO2/kg H2, respectively. Taking into account associated emissions from natural gas production, the total greenhouse gas emissions for the processes under consideration are 4.649 and 6.129 kg CO2eq/kg H2, respectively, when using grid electricity. When using electricity from hydropower, the total greenhouse gas emissions from hydrogen production through hydrogen sulfide methane reforming and thermal decomposition of hydrogen sulfide will be 2.33 and 2.78 kg CO2/kg H2, respectively, and for an alkaline electrolyzer they are about 2.60 kg CO2/kg H2. Thus, when using low-carbon sources of electricity to power processes, hydrogen sulfide technologies perform comparable to water electrolysis processes, and in some cases even show lower emissions.Additionally, the impact of hydrogen leaks on the greenhouse effect is considered and analyzed, which allows us to conclude that hydrogen is an indirect greenhouse gas.