Green hydrogen

Green hydrogen is hydrogen produced by splitting water with renewable electricity. Its climate impact depends on the electricity source, production equipment, and handling of the hydrogen.

Water electrolysis: A process that uses electricity to split water into hydrogen and oxygen. Electrolysis is the production step that defines green hydrogen.
Ammonia: A nitrogen-and-hydrogen compound used widely in fertilizers and chemical production. Green hydrogen can supply the hydrogen feedstock for lower-emission ammonia.
Gray hydrogen: Hydrogen produced from fossil fuels without capturing most of the resulting carbon dioxide. It is the common fossil-based route that green hydrogen is intended to displace.
Life-cycle assessment: A method for estimating environmental impacts across a product's or process's life cycle. It captures emissions from electricity, equipment, water supply, and hydrogen delivery.
Levelized cost of hydrogen: An estimate of average hydrogen production cost per unit over a facility's lifetime. It tracks how electricity prices, electrolyzer costs, and operating hours affect competitiveness.
Proton-exchange membrane electrolysis: An electrolysis method that uses a proton-conducting polymer membrane as its electrolyte. This electrolyzer type can respond quickly to variable renewable electricity.
Haber process: An industrial process that synthesizes ammonia from nitrogen and hydrogen. Replacing fossil-derived hydrogen can reduce emissions from this major industrial process.
Blue hydrogen: Hydrogen produced from fossil fuels with carbon capture applied to some process emissions. Its climate performance depends on capture rates and upstream methane emissions, unlike electrolysis-based production.
Greenhouse gas emissions: Releases of gases that contribute to warming by trapping heat in the atmosphere. The emissions benefit depends on how clean the electricity and supply chain are.
Electrolyzer: A device that uses electricity to drive a chemical reaction, such as splitting water into hydrogen and oxygen. Efficiency, durability, and manufacturing capacity constrain the scale-up of green hydrogen.

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