Today, hydrogen is produced by steam methane reforming (SMR), which is responsible for 830 million tons of carbon dioxide emission annually. Zero-emission processes are water electrolysis and methane cracking. Water electrolysis is more energy-intensive for hydrogen production than SMR and methane cracking processes.

As seen from the enthalpy diagrams (https://pubs.acs.org/doi/10.1021/acs.iecr.1c01679) presented below, considering only thermodynamics, water electrolysis requires 285.8 kJ/mol, SMR requires 63.4 kJ/mol, and methane cracking requires 37.7 kJ/mol. Methane cracking is the least energy-intensive process. If converted to the units of energy needed to produce 1 kg of hydrogen, it works out to be for water electrolysis: 39.7 kWh/kg, SMR: 8.7 kWh/kg, and methane cracking: 5.2 kWh/kg. Considering the in-efficiencies involved at various stages of production today, the energy required for water electrolysis is 50-60 kWh/kg; SMR 12-15 kWh/kg; and methane cracking 25 kWh/kg. (see: https://doi.org/10.1016/j.ijhydene.2022.10.144).

Water electrolysis may not become economically viable even with 100% efficiency; it requires 39.7 kWh to produce 1 kg of hydrogen, whose energy content is 33 kWh. Thus, the input energy is more than the output energy. As the technology matures, the methane cracking process will become more efficient and compete with SMR. Then, why is there a global push for developing water electrolysis instead of methane cracking to produce zero-emission hydrogen?

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