For industry, the most relevant types of electrolysis are alkaline electrolysis (AEC), proton exchange membrane electrolysis (PEMEC) and solid oxide electrolysis (SOEC). In all processes, water is split into its components hydrogen and oxygen. The technologies differ in the choice of membrane and electrolyte. Alkaline electrolysis (AEC) In actual practice, alkaline electrolysis is the technology used most frequently. A potassium hydroxide solution (KOH) is used as the electrolyte. The technology is already available on a large scale. Besides the low investment costs and long service life, it has the advantage of using practically no critical raw materials at all. The main disadvantage is the low dynamic response to load changes. Proton exchange membrane electrolysis (PEMEC) Compared to alkaline electrolysis, proton exchange membrane electrolysis is a much newer method, but it is also available on an industrial scale. Its main component is the proton exchange membrane. It prevents the two products, oxygen and hydrogen, from mixing, resulting in higher hydrogen purity. PEMEC electrolysis makes fast load changes and a compact design possible. On the downside, expensive catalyser materials are needed. Solid oxide or high-temperature electrolysis (SOEC) With this method, the water is fed into the system as water vapour. As a result, it is possible for very high efficiencies of up to 85% to be achieved. The cells operate at temperatures of up to 900 °C. A solid ceramic material serves as the electrolyte. Another advantage of the SOEC is that it is also suitable for the use of CO electrolysis to produce synthesis gas. However, the high temperatures result in low load change capability and high material requirements.