New-Concept CO-Tolerant Anode Catalysts Using a Rh Porphyrin-Deposited PtRu/C

CO poisoning of the Pt-based anodes (PtRu) of stationary proton exchange membrane fuel cells remains a severe problem for their realization. We tried to counteract this problem using a CO oxidation electrocatalyst. Rh porphyrins, which can catalyze electrochemical CO oxidation in low potential regions, were adsorbed on a carbon-supported PtRu catalyst (PtRu/C) to increase its CO tolerance. The combined electrocatalysts (Rh(porphyrin)−PtRu/C) exhibited significantly higher activity toward CO(2%)-contaminated H2 than the PtRu/C alone; the onset potential for H2 oxidation reaches 0.2 V (vs a reversible hydrogen electrode) on the combined catalyst. In contrast, the composite of PtRu black and Rh(porphyrin) scarcely exhibited CO tolerance. This suggests that the enhancement of CO tolerance in Rh(porphyrin)−PtRu/C is mainly caused by Rh porphyrins on carbon. The significance of Rh porphyrins on carbon was shown by the findings that a mixed catalyst composed of carbon-supported Rh(porphyrin) (Rh(porphyrin)/C) and PtRu/C gave high oxidation activity toward CO(2%)/H2. Rh porphyrin on carbon would decrease the CO concentration around PtRu particles and thus reduce the CO poisoning of PtRu catalysts.