Hydrogen can be used in a variety of applications. Basically, a distinction can be made between its energetic application and its use as a material. In material use, the chemical properties of the hydrogen molecule are exploited in the form of reactions with other chemical elements. Thus, hydrogen can be used to form new chemical compounds together with other elements or to change the composition and properties of existing compounds. On the other hand, hydrogen can be used to generate energy. Here, the chemical energy bound in the hydrogen is converted into electricity and/or heat. 

The production of so-called e-fuels is a special case. In this process, a synthetic liquid fuel is produced on the basis of green hydrogen and green carbon dioxide. The synthetic fuel is comparable to conventional fossil fuels in terms of its properties. Thus, although the hydrogen is initially used as a raw material to synthesize the e-fuel, the combustion of the fuel (for example, in an aircraft turbine or in the internal combustion engine of a truck) is ultimately aimed at converting the chemically bonded energy into heat.

The production of such e-fuels is not discussed further in this course. You can find detailed information on e-fuels here: