Bipolar Concept for Alkaline Fuel Cells

Abstract

Alkaline fuel cells (AFC) are an attractive alternative to PEFCs, because AFCs have significant cost advantages. AFCs require neither noble metal catalysts nor an ex¬pensive electrolyte; in addition, the corrosion problems are not so severe in alkaline sy¬stems than in acid systems. Due to these advantages AFC may be used for various applications in future. Alkaline fuel cell (AFC) stacks are frequently realized with mo¬nopolare plates, where the single cells are externally connected to the complete stack. At the DLR a AFC short stack as test system and for laboratory application was de¬veloped using a bipolar configuration. Therefore this stack does not require an external connection for the cells. The bipolar stack concept has to take care for distribution and separation of three media like some PEFC stacks, in the case of AFC the reaction gases and the liquid electro¬lyte – in the case of PEFC the reaction gases and the water for the cooling circuit. The DLR AFC stack was developed for a non-pressurized system, so the pressure drop over the short stack is only few mbars for all media, reactions gases and electroly¬te. The short stack is used as test facility of various electrodes and combinations of electrodes. The AFC were characterized by V-i characteristics and electrochemical impedance spectroscopy.