Kinetics of CH3OH oxidation on PtRu/C studied by impedance and CO stripping voltammetry

The kinetics of the CH3OH oxidation reaction at 60 °C on well-alloyed platinum-ruthenium supported on carbon (Pt50Ru50/C) was studied by electrochemical impedance spectroscopy and compared with carbon-supported platinum (Pt/C). The reaction rate of the overall CH3OH oxidation increased with increasing electrode potential for both Pt/C and PtRu/C. In the case of Pt/C, when the electrode potential was E ⩽ 450 mV vs. RHE only a capacitive behavior was observed. Resistive and pseudo-inductive types of behavior were evident above 500 and 600 mV vs. RHE. In the case of PtRu/C, a similar change in behavior was observed, except that the two types of behavior were observed at 200 mV lower electrode potentials than for Pt/C. Correlation of the impedance data with pre-adsorbed carbon monoxide (COad) stripping voltammetry allowed the understanding of the methanol oxidation reaction. The change in the reaction rate of the oxidation of CH3OH to COad as a function of the electrode potential as well as the promotional effect of Ru was evident from a change in the frequency where the frequency deviated from the ∼90° phase angle. The change in the reaction rate of the oxidation of COad to CO2 as a function of the electrode potential as well as the alloying with Ru was evident from a change in the frequency where the phase angle approached zero.