U.S. Department of Energy - Energy Efficiency and Renewable Energy
Fuel Cell Technologies Office – Hydrogen Production
The development of clean, sustainable, and cost-competitive hydrogen production processes is key to a viable future clean energy economy. Hydrogen production technologies fall into three general categories: thermal processes, electrolytic processes, and photolytic processes.
Some thermal processes use the energy in various resources, such as natural gas, coal, or biomass, to release hydrogen, which is part of their molecular structure. In other processes, heat, in combination with closed-chemical cycles, produces hydrogen from feedstocks such as water—these are known as "thermochemical" processes.
Electrolytic processes use electricity to split water into hydrogen and oxygen, a process that takes place in an electrolyzer. Hydrogen produced via electrolysis can result in zero greenhouse gas emissions, depending on the source of the electricity used. The source of the required electricity—including its cost and efficiency, as well as emissions resulting from electricity generation—must be considered when evaluating the benefits of hydrogen production via electrolysis. The two electrolysis pathways of greatest interest for wide-scale hydrogen production, which result in near-zero greenhouse gas emissions, are electrolysis using renewable sources of electricity and nuclear high-temperature electrolysis.
Photolytic processes use light energy to split water into hydrogen and oxygen. Currently in the very early stages of research, these processes offer long-term potential for sustainable hydrogen production with low environmental impact.