Impurity Effects on Electrode Reactions in Fuel Cells

Abstract

The oxygen reduction reaction (ORR) on platinum-based catalysts in the cathode catalyst layer is affected by several kinds of impurities, such as impurity cations or organic impurities in membrane electrode assemblies and in polymer electrolyte membranes. These impurities may come from outside the cathode chamber, or may be generated inside as decomposition products on the catalyst surface or as crossed-over fuels from the anode. In this chapter the effect of inorganic and organic impurities of 0.1–10 mmol dm^-3 on the kinetics of the ORR investigated by electrochemical measurements is discussed. Cationic species, aldehydes, and alcohols are found to degrade strongly the ORR current. A method to cope with such impurity problems is proposed where small amounts of additives in the membrane electrode assembly or in the membrane suppress the degradation and affect positively the ORR performances at the catalyst surface.