Comparison of Catalytic Activities of Carbon Supported Pt and Pt-Ru Catalysts for Methanol Oxidation in Neutral and Basic Media by Cyclic Voltammetry


Abstract: The catalytic activities of an equal amount of 3 different carbon supported catalysts containing 10% Pt, 20% Pt + 10% Ru, and 30% Pt were evaluated in neutral and basic media for methanol oxidation by cyclic voltammetry. The prominent oxidation peak for methanol appeared in the forward anodic sweep at around 1.0 V in neutral medium, while in basic medium it appeared at significantly lower potential close to 0.2 V. The peak current for methanol oxidation was higher on a catalyst containing higher Pt loading. The comparison of polarization behavior of 20% Pt + 10% Ru and 30% Pt catalysts showed that the presence of Ru increases the catalytic activity at the lower polarization region. The enhancement of catalytic activity by Ru was more obvious in basic medium as compared with neutral medium. The heterogeneous rate constants were evaluated from peak current data. At room temperature, the heterogeneous rate constant for methanol oxidation on a given catalyst was higher in basic medium as compared with neutral medium. The effect of temperature on peak current was investigated. At lower temperature, the catalytic activities were lower in neutral medium but approached near that in basic medium at higher temperature owing to the higher apparent enthalpy of activation ``\Delta H*'' for methanol oxidation in neutral medium. The \Delta H* values were calculated from the analysis of peak current data and found to be in the range 24 to 27 kJ mol^{-1} in neutral medium and 15 to 17 kJ mol^{-1} in basic medium.

Keywords: Cyclic voltammetry, methanol, neutral and basic media, fuel cell catalysts, kinetics, enthalpy of activation.

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