Dual-Pathway Mechanism and Nonlinear Dynamics in the Electrooxidation of Methanol on Platinum

Elucidating the mechanism of the electro-oxidation of alcohols on Pt is critical for applications ranging from energy conversion and storage to the chemicals industry and catalyst development. In the work reported here, time-resolved ATR-SEIRA spectra were recorded during the oscillatory electro-oxidation of methanol on Pt electrodes, under galvanostatic conditions. Correlations between the coverages of adsorbed CO and bidentate adsorbed formate observed during the potential oscillations confirm that adsorbed CO is the main intermediate in the complete oxidation of methanol to CO2, while adsorbed formate mediates partial oxidation of methanol to formic acid and methyl formate. UV-vis reflectance measurements revealed a shift in the oxidation of the Pt surface to more positive potentials in the presence of methanol, as a consequence of methanol and Pt oxidation reactions competing for adsorbed OH. Combined with the ATR-SEIRAS results, this work provides spectroscopic evidence for the involvement of surface oxides in the oscillatory behavior. In particular, we show how chaotic oscillations emerge due to, and are mediated by, the competition between methanol and surface oxidation reactions for adsorbed OH.