Kinetics of CH 3OH oxidation on PtRu/C studied by impedance and CO stripping voltammetry

Abstract

The kinetics of the CH 3OH oxidation reaction at 60 °C on well-alloyed platinum–ruthenium supported on carbon (Pt 50Ru 50/C) was studied by electrochemical impedance spectroscopy and compared with carbon-supported platinum (Pt/C). The reaction rate of the overall CH 3OH 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 (CO ad) stripping voltammetry allowed the understanding of the methanol oxidation reaction. The change in the reaction rate of the oxidation of CH 3OH to CO ad 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 CO ad to CO 2 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.