Hydrogen as an energy carrier: Production pathways, thermochemical constraints, and electrolysis-based green hydrogen prospects

Hydrogen is widely recognized as a key energy carrier for enabling deep decarbonization across power generation, transportation, and energy-intensive industrial sectors. However, large-scale deployment from renewable energy remains constrained by the efficiency and cost of current production routes. This review provides a comprehensive assessment of hydrogen production technologies, encompassing both thermochemical processes and electrolysis-based green hydrogen systems. Conventional pathways, including steam methane reforming (SMR) and coal and biomass gasification, are evaluated from thermodynamic and kinetic perspectives, with emphasis on reaction energetics, process efficiency, and carbon emissions. The…