The Merit and the Context of Hydrogen Production from Water and Its Effect on Global CO2 Emission

For a green economy to be possible in the near future, hydrogen production from water is a sought-after alternative to fossil fuels. It is, however, important to put things into context with respect to global CO2 emission and the role of hydrogen in curbing it. The present world annual production of hydrogen is about 70 million metric tons, of which almost 50% is used to make ammonia, NH3 (that is mostly used for fertilizers), and about 15% is used for other chemicals [1]. The hydrogen produced worldwide is largely made by steam CH4 reforming (SMR), which is one of the most energy-intensive processes in the chemical industry [2]. It releases, based on reaction stoichiometry, 5.5 kg of CO2 per 1 kg of H2 (CH4+ 2 H2O → CO2 + 4 H2). When the process itself is taken into account, in addition, the production [3] becomes about 9 kg of CO2 per kg of H2 and, this ratio can be as high as 12 [4]. This results in the production of about one billion tons/year of CO2. The world annual CO2 emission from fossil fuels is, however, much larger: it is about 36 billion tons, of which roughly 25% is emitted while generating electricity and heat, 20% due to transport activity and 20% from other industrial processes. Because of the link between global warming and CO2 emissions, there is an increasing move towards finding alternative approaches for energy vectors and their applications.