How is hydrogen produced?
Source: U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Hydrogen Production (public domain)
To use hydrogen for energy, it must be separated from the other elements in the molecules where it occurs. Hydrogen atoms can be separated from water, hydrocarbons, and biomass.
The two most common methods for producing hydrogen are steam reforming and electrolysis (water splitting).
Steam reforming is a widely used method of hydrogen production
Steam reforming is currently the least expensive way to produce hydrogen, and it accounts for most of the commercially produced hydrogen in the United States. This method is used in industries to separate hydrogen atoms from carbon atoms in methane (CH4). The steam reforming process results in carbon dioxide emissions.
Electrolysis uses electricity
Electrolysis is a process that splits hydrogen from water using an electric current. The process can be used on a large or small scale. Electrolysis does not produce any emissions other than hydrogen and oxygen, and the electricity used in electrolysis can come from renewable sources such as wind or solar energy. If the electricity used in electrolysis is produced from fossil fuels, then pollution and carbon dioxide emissions are indirectly associated with electrolysis.
Other methods of producing hydrogen
Research is underway to develop other ways to produce hydrogen. These methods include using microbes that use light to make hydrogen, converting biomass into liquids and separating the hydrogen, and using solar energy technologies to split hydrogen from water molecules.