TRANSIENT CHARACTERISTICS OF METHANOL ELECTROOXIDATION ON PT AND PT-SOLID POLYMER ELECTROLYTE (SPE) ELECTRODES

Very rapid transient measurement of a methanol electrooxidation reaction on Pt and Pt-spe was carried out for the purpose of elucidating the reaction mechanism in acidic solution. After anodic activation treatment we observed a positive reaction current density of 1.2 mA cm-2 as a maximum value at a polarization potential (E-tau) of 0.6 V (vs rhe) at a polarization time (tau) of 38 ms in 1 M CH3OH + 0.5 M H2SO4 for a true Pt surface area at room temperature. In the case of the Pt-spe electrode, which showed higher catalytic activity than Pt under steady-state conditions, the maximum current density of 0.8 mA cm-2 at 0.6 V was observed to appear at tau = 0.1 s, which was smaller than that on Pt itself. These results are discussed in relation to the appearance of a poisoning effect by methanol, and to an enhancement mechanism by the spe. The former maximum current density was corrected for by the negative reduction current of the adsorbed oxygen species and the double layer charging current, and the methanol oxidation current density was estimated as approximately 4 mA cm-2 or more at tau < 20 ms and E-tau = 0.6 V. The above value of the methanol electrooxidation current density was close to the observed one of 5 mA cm-2 at E of 0.6 V by using a potential sweep method of 20 V s-1.