Impedance spectroscopy of the electro-oxidation of methanol on polished polycrystalline platinum

The electro-oxidation of methanol on smooth polycrystalline platinum in the presence of a sulfuric acid solution was investigated using impedance spectroscopy. The impedance response of both the electro-oxidation of methanol and the adsorption of hydrogen were measured directly at potentials where these processes are active. The time dependence of the impedance of the adsorption of hydrogen in the presence of methanol was used as an in situ probe of the formation of methanol adsorption products. Monitoring the formation of methanol adsorption products by this method yielded kinetic information for the electro-oxidation of methanol at low potentials that previously has been difficult to obtain. The fitting of the impedance of the electrooxidation of methanol to an appropriate model provided the values of impedance parameters whose potential dependence reveal information about the kinetics of the reaction, changes in the coverage of the adsorbed intermediate, and the effect of coadsorbed oxygen containing species. The results indicate the presence of five different potential regions between 40 and 800 mV vs RHE where a change in the reaction mechanism occurs. The mechanistic changes are interpreted as bring due to the presence of oxygen containing species with different reactivities at different potentials.