Chapter 01 · Climate & transitionEnergy & Transition
Alkaline electrolyzer
Definition
An electrolyser that produces hydrogen by passing an electric current through water in an alkaline electrolyte (typically potassium hydroxide solution). Hydrogen forms at the cathode and oxygen at the anode, with the gases separated by a diaphragm. It is the longest-established electrolysis technology, used industrially for over a century.
References
Working principle; maturity (GW-scale proven); comparison with PEM, AEM and SOEC.
Installed capacity by technology 2020–2023; ~700 MW added in 2023, >80% in China; chlor-alkali baseline.
Overview
What it means
Alkaline systems are the industrial reference point among the four main electrolyser types (alkaline, PEM, AEM, solid oxide). They are favoured for large-scale, steady operation because of lower capital cost and longevity, but operate at lower pressures and respond less flexibly to fluctuating renewable power than PEM systems.
IEA data show alkaline technology made up the largest share of installed electrolysis capacity through 2023.
How it is used
Alkaline electrolysers are deployed in centralised "green hydrogen" plants, especially where long operating hours are expected, and dominate in China, which accounted for over 80% of global capacity additions in 2023. They are also long established in the chlor-alkali industry (over 20 GW installed).
Why it matters
Low-emission hydrogen is needed for sectors that are hard to electrify (fertilisers, steel, shipping fuels). Alkaline electrolysis is currently the cheapest proven route at scale, so its costs and deployment pace strongly influence how fast a hydrogen economy can grow.