While solar cells are becoming more and more widespread, storing the produced energy is difficult. Of the many possible solutions, the splitting of water into H2
by a photoelectrochemical cell offers an elegant approach. The hydrogen can then easily be stored, transported and burned in a fuel cell. As most features in photoelectrodes are on the nano- or microscale, electron microscopy is very powerful. We study material systems such as Fe2
and attempt to identify performance bottlenecks.