The demand for green hydrogen will grow exponentially in the future, without it being clear how the demand will be met. Of course, this also applies to the supply of hydrogen for mobile applications. There are essentially four candidates for industrial hydrogen production: alkaline electrolysis, SOEC electrolysis, AEM and PEM electrolysis. These technologies have specific advantages and disadvantages that further limit the universal industrial use for the production of green hydrogen. The situation is examined against the background of decentralized supply units, which are of particular importance for mobile applications. The focus is on the stack—the stacked electrolysis cells—as the heart of the electrolyzers, which ultimately determines the performance of the electrolyzer. Dimensioning, manufacturability and availability of the required materials are discussed, as well as their consequences are shown.