Recoverable Cathode Performance Loss in Direct Methanol Fuel Cells

Abstract

This paper addresses the performance loss due to oxidation of a platinum cathode catalyst in continuous operation of the direct methanol fuel cell. Saturation oxide coverage is reached within 2 h at oxidizing potentials of the cathode in the absence of gas-phase oxygen. This rate of platinum oxide formation is too fast to fully explain the slow rate of cathode performance degradation. There is an indication that oxide reconstruction may be responsible for long-term cathode performance degradation beyond the initial 2 h. Cathode performance loss in the oxygen reduction reaction is fully recoverable via reduction of platinum oxide formed on the surface. Because the methanol anode is a relatively easily polarizable electrode, it cannot serve as a counter electrode for lowering the cathode potential with an external voltage source. However, the oxidized Pt can be reduced to its catalytic form by air-starving the cathode and consuming the remaining oxygen in the oxidation of crossover methanol. The subsequent depletion of oxygen in the cathode plenum leads to a potential drop below the level required for complete reduction of surface Pt oxides (hydroxides).