Development of an alkaline fuel cell stack with bipolare configuration

Kurzfassung

Alkaline fuel cell stacks are mostly build in monopolare configuration of the cells. At the German Aerospace Center a bipolare plate for alkaline fuel cells was developed and characterized in a short stack. Caused by the sealing concept two different bipolare plate types are needed. Therefore, the number of cells can only varieties by 2 if the end plates are not changed. The single cell as well as the short stack was characterized by various methods. Caused by the used electrodes the differential pressure between electrolyte and gas phase must be limited to few of ten mbar. At higher differential pressures the gas crosses the electrode and penetrates the electrolyte or the electrolyte crosses the electrode and electrolyte comes into the flow fields. In contrast to PEFC, electrode supported by a metal net as conductor and mechanical support can be used in the AFC. Therefore, the structure of the flow field can be crude, this means width and deep canals are possible. Consequently, the pressure loss over the flow field is very low. The single cell as well as the short stack was operated at pressures few ten mbar about the normal pressures. This fact allows to operate the AFC without a compression but with a simple fan. The developed cell design is also used for the characterization of the fuel cell components like electrodes and diaphragms. The test facility for the single cell and for the stack is full computer controlled and allows the variation of the operation conditions, e.g. flow of the electrolyte, hydrogen flow, oxygen or air flow and cell temperature.