Hydrogen manufacturing – a review and its Sustainability

Hydrogen is a highly versatile energy vector and most importantly its oxidation which releases energy is a green process with no associated emissions. Hence it is considered as a green alternative which can supply and simultaneously reduce global warming. This gas however does not occur naturally in sufficient quantities and needs to be synthesized using different resources. The two most feasible methods of producing H2 are steam methane reforming process and water splitting by electrolysis. Therefore, these two processes are reviewed first and subsequently a complete sustainability analysis has been performed using currently available data. It is found that input raw materials such as methane and water will be required in ‘giga tonnage’ quantity every year. Although availability of water does not pose supply risk, methane production falls far short of the requirement and becomes a supply risk. The conversion of these into H2 requires energy and results in the production of ‘giga tons’ of CO2. For e.g., the production of 1 giga ton of H2 using the steam methane reforming process requires ~ 3.6 EJ of energy and releases ~ 10 giga tons of CO2. The water splitting electrolysis on the other hand requires ~ 198 EJ of energy and releases anywhere from 102 giga tons to 220 giga tons of CO2 depending on the electricity generation mix. Additionally, they also create ecological impact in the form of acidification, marine toxicity, particulate emissions and so on which affects all life forms on earth. This analysis clearly shows that complete transitioning to H2 based energy supply is not sustainable and only a fraction of the energy needs can be supplemented.