Progress in Power-to-Gas Energy Systems

1. Introduction Hydrogen is expected to become a key component in the decarbonized energy systems of the future. Its unique chemical characteristics make hydrogen a carbon-free fuel that is suitable to be used as broadly as fossil fuels are used today. Since hydrogen can be produced by splitting water molecules using electricity as the only energy input needed, hydrogen offers the opportunity to produce a fully renewable fuel if the electricity input also only stems from renewable sources. Once renewable electricity is converted into hydrogen, it can be stored over long periods of time and transported over long, even intercontinental, distances. Underground hydrogen storage, pipelines, compressors, liquefaction-units, and transportation ships are infrastructures and suitable technologies to establish a global hydrogen energy system. Several chemical synthesis routes exist to produce more complex products from green hydrogen to fulfil the demands of various end-users and industries. One exemplary power-to-gas product is methane, which can be used as a natural gas substitute. Furthermore, ammonia, alcohols, kerosene, and all other important products from hydrocarbon chemistry can be synthesized using green hydrogen.