Abstract
The kinetic parameters of carbon monoxide and methanol oxidation reactions on a high performance carbon-supported Pt–Ru electrocatalyst (HP 20% 1:1 Pt–Ru alloy on Vulcan XC-72 carbon black) have been studied using cyclic voltammetry and rotating disk electrode (RDE) techniques in 0.50 M H 2SO 4 and H 2SO 4 (0.06–0.92 M) + CH 3OH (0.10–1.00 M) solutions at 25.0–45.0 °C. CO oxidation showed an irreversible behaviour with an adsorption control giving an exchange current density of 2.3 × 10 −6 A cm −2 and a Tafel slope of 113 mV dec −1 ( α = 0.52) at 25.0 °C. Methanol oxidation behaved as an irreversible mixed-controlled reaction, probably with generation of a soluble intermediate (such as HCHO or HCOOH), showing an exchange current density of 7.4 × 10 −6 A cm −2 and a Tafel slope of 199 mV dec −1 ( α = 0.30) at 25.0 °C. Reaction orders of 0.5 for methanol and −0.5 for proton were found, which are compatible with the consideration of the reaction between Pt–CO and Ru–OH species as the rate-determining step, being the initial methanol adsorption adjustable to a Temkin isotherm. The activation energy calculated through Arrhenius plots was 58 kJ mol −1, practically independent of the applied potential. Methanol oxidation on carbon-supported Pt–Ru electrocatalyst was improved by multiple potential cycles, indicating the generation of hydrous ruthenium oxide, RuO x H y , which enhances the process.
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