Evaluation of methanol oxidation catalysts by rotating disc voltammetry

Rotating disc voltammetry of 0.1 M methanol at thick catalyst layers shows significant increases in current with increasing rotation rate. Although a mass transport limited current was not reached, due to inhibition of methanol oxidation by Pt oxide at high potentials, linear Koutecky-Levich plots were obtain in the mixed kinetic-mass transport region. For a carbon supported Pt catalyst, the slopes of the Koutecky-Levich plots corresponded to a methanol oxidation efficiency of ca. 50% (average n-value of 3.1 electrons per molecule), while the efficiency was ca. 100% for a PtRu black catalyst. The methanol diffusion coefficient obtained with the PtRu black catalyst was in good agreement with literature values. Koutecky-Levich plots provide mass transport corrected kinetic currents, in the mixed kinetic-mass transport region, that complement values obtained at lower potentials by cyclic voltammetry or at constant potential.