Due to the severe consequences of the climate change by the excessive use of fossil fuels, the energy system of mankind has to be transformed into a renewable one. The best and easiest way is the generation of renewable energy from sunlight, wind, water, waves, and biomass. However, due to the intermittent nature of renewable energy sources like sun light, wind, and waves, the storage of electrical or chemical energy is needed. An obvious way is, to generate hydrogen by electrolysis or photoelectrolysis of water and to store it. For a prospective industrial implementation of the photoelectrolysis of water large area photoelectrode materials have to be developed.