Kinetics of Methanol Oxidation on Supported and Unsupported Pt/Ru Catalysts Bonded to PEM

Abstract

AbstractThe kinetics and mechanism of methanol adsorption and oxidation on real Pt/Ru (1:1) electrodes were investigated. In model electrode systems, the addition of supporting proton‐conducting electrolyte is necessary. Therefore, the influence of sulphuric acid on the kinetics of methanol adsorption and oxidation was also investigated. It turns out that the steady state adsorption is not significantly affected by the addition of sulphuric acid. However, if sulphuric acid is used as an additional electrolyte, the rate of methanol adsorption and steady state oxidation decreases, whereas the active surface of the catalyst increases. The mechanism of methanol oxidation is not affected by the addition of sulphuric acid. At low potentials, the adsorption of methanol is found to be much faster than its oxidation. Hence, the oxidation of the methanol intermediate species is believed to be the rate‐determining step under these conditions. This result is confirmed by apparent orders of reaction of about 0.5. At potentials in the range of 0.3–0.5 V, a mixed activation‐adsorption control is supposed, whereas at potentials more positive than 0.5 V, the adsorption of methanol is probably the rds. This is supported by the apparent reaction orders and apparent activation energies of methanol oxidation.