Examining a potential fuel cell poison - A voltammetry study of the influence of carbon dioxide on the hydrogen oxidation capability of carbon-supported Pt and PtRu anodes

Polymer electrolyte fuel cells being operated on reformed fossil fuels are exposed to large quantities of carbon dioxide. In order to elucidate the extent of the reverse water gas shift of CO2 on hydrogen-covered fuel-cell anodes to CO, an extensive cyclic voltammetry study has been done on Pt and PtRu electrodes in sulfuric acid with varying hydrogen coverage. The electrodes used are representative of those being used in proton exchange membrane fuel cells. The reverse shift reaction is facile on Pt/C, but with the surface not poisoned to the same extent as it does by exposure to CO-saturated solutions. The reaction product is oxidized in a similar fashion to formic acid and methanol on platinum. The results indicate the formation of a stable adlayer, consisting of linear, bridge, and multibonded CO in accordance to what has been proposed for unsupported platinum electrodes. PtRu/C fuel-cell anodes are expected to be considerably more tolerant toward carbon dioxide than Pt/C anodes, with both the reaction suppressed and the adsorbate oxidation occurring at a lower potential. (C) 2001 The Electrochemical Society.