: Ahn, J.; Zylka, D.; Heinzel, A.; Ledjeff, K.

Abstract
For solar energy systems long term energy storage with a high efficiency is required. Hydrogen is a suitable energy carrier, its generation by water electrolysis, the conversion into heat by (catalytic) combustion and into electrical energy by fuel cells is the present state of the art. Electrolyzer and fuel cell with a solid polymer electrolyte show several advantages compared to cells with liquid electrolyte. In compact modules high energy densities and high efficiencies are realized without a costly and complicated peripheral gas and electrolyte management system. The current work is concerned with the construction of a pressure electrolyzer, a hydrogen/oxygen fuel cell and the development of a "reversible" system which works as electrolyzer and fuel cell as well. The modification of the fuel cell for the use of methanol as a fuel is a promising goal. Methanol is an attractive fuel for a back up system in the case of exhausted hydrogen reverse. The electrochemical reactions of hydro gen, oxygen and methanol at membrane/electrode composites are investigated.