Supported Pt and Pt-Ru catalysts prepared by potentiostatic electrodeposition for methanol electrooxidation

Abstract

Methanol electrooxidation was investigated on Pt-Ru electrocatalysts supported on glassy carbon. The catalysts were prepared by electrodeposition from solutions containing chloroplatinic acid and ruthenium chloride. Bulk composition analysis of the Pt-Ru catalyst was performed using an X-ray detector for energy dispersive spectroscopy analysis (EDX). Three different compositions were analyzed in the range 0-20 at.% Ru content. Tafel plots for the oxidation of methanol in solutions containing 0.1-2 M CH3OH, and in the temperature range 23-50 °C showed a reasonably well-defined linear region. The slope of the Tafel plots was found to depend on the ruthenium composition. The lower slope was determined for the Pt catalyst, varying between 100 and 120 mV dec-1. The values calculated for the alloys were higher, ranging from 120 to 140 mV dec-1. The reaction order for methanol varies from 0.5 to 0.8, increasing with the ruthenium content. The activation energy calculated from Arrhenius plots was found to change with the catalyst composition, showing a lower value around 30 kJ mol-1 for the alloys, and a higher value, of 58.8 kJ mol-1, for platinum. The effect of ruthenium content is explained by the bifunctional reaction mechanism.