The influence of chloride ion on the oxidation and dissolution of platinum has been studied by using Electrochemical Quartz Crystal Microbalance (EQCM) in combination with Inductively Coupled Plasma (ICP) analysis to clarify the deterioration mechanism of platinum catalyst in the Polymer Electrolyte Fuel Cell (PEFC). Platinum was electroplated on an Au-QCM electrode in 2% H 2PtCl6 solution and used as the working electrode. A mass gain of the platinum electrode was observed during anodic polarization in 0.5 M H2SO4 solution ([Cl-] free solution) due probably to the formation of Pt oxide. The oxide film was not stable in the whole range of potential used in this study. On the other hand, a mass loss due to the dissolution of Pt as chloride complex ions was observed in more positive potentials than 0.85 V vs. SHE in chloride-containing solutions. As the chloride concentration increased, platinum showed a higher dissolution rate with the formation of chloride complexes, PtCl42- and PtCl 62-. The amount of dissolved PtCl62- tended to increase with the increase of anodic potential limit. The EQCM results revealed that the dissolution of Pt was accelerated when potential was cycled between cathodic and anodic limits. The ICP analysis of the solution after anodic polarization supported the results obtained by EQCM.
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