The basic technologies and terminology of the H2 technologies are listed here for better understanding. Further information on the individual points can be accessed via the links to external websites:
Electrolysis uses electricity to split water into hydrogen and oxygen. A large proportion of the energy is then chemically stored in the hydrogen, while losses are released into the environment in the form of heat. The two predominant electrolysis technologies are alkaline electrolysis and PEM electrolysis.
In alkaline electrolysis, electrodes are immersed in a circulating solution of water and potassium hydroxide (20--40 % by weight). The two half-cells are separated by an ion-conducting membrane (diaphragm). By applying voltage to the electrons, hydrogen is produced at the cathode.
Instead of the ion-conducting membrane (see alk. Electrolysis), the proton exchange membrane electrolysis has a proton-conducting membrane that is connected to the electrodes on both sides. A solid, highly porous polymer electrolyte lies between the electrodes (corrosion-resistant precious metals) and the associated bipolar plates. This enables the flow of current from the bipolar plates to the electrode as well as the transport of water and the product gases. Metals such as iridium are required due to the acid. Applying a voltage produces hydrogen.
Methanation is used to produce methane (CH4) from hydrogen. This requires carbon as a material, which is provided by carbon dioxide (CO2) during methanation. A distinction is made between chemical and biological methanation. Methane is the main component of natural gas and can therefore be used in the same way and utilize the same infrastructure.
The Haber-Bosch process is used for the production of ammonia (NH3). Ammonia is one of the most important chemicals for the production of fertilizers. In the Haber-Bosch process, hydrogen and nitrogen react under high pressure and high temperatures to form ammonia. This process is already used in this form today, but with hydrogen from natural gas.
In Fischer-Tropsch synthesis, synthesis gas (CO + H2) is used to produce hydrocarbons that are similar to fossil crude oil. The same products as from crude oil can then be produced from this with the existing infrastructure. Fischer-Tropsch synthesis is a well-known process, but it has not yet reached large-scale or mass production.
In methanol synthesis, methanol is obtained from a synthesis gas (H2 + CO). Methanol is an important raw material for industry and is already widely used today. In addition, methanol can replace many fossil raw materials through climate-friendly production (methanol-to-olefins, methanol-to-jet, ...). The hydrogen required should come from renewable sources using water electrolysis.