VDI 4635 Blatt 3.1:2025-04 - Draft

Water electrolysis refers to the process of splitting water using electrical energy, resulting in the products hydrogen and oxygen. In the context of water electrolysis, a distinction can be made between the low-temperature processes, which are generally carried out at temperatures below 100 °C. These include alkaline electrolysis (AEL), polymer electrolyte membrane electrolysis (PEMEL) and alkaline membrane electrolysis (AEMEL). High-temperature electrolysis (HTEL) is also to mention, which is operated with water vapour above 600 °C. The standard describes the basic principles for planning water electrolysis systems. This is based on the definitions of terms and system parameters as well as the specific features of the four electrolysis technologies covered. Furthermore, the preparation of the water, the necessary conditioning of the electrical energy and the preparation of the hydrogen product are discussed.