Electrocatalytic oxidation of formaldehyde on platinum under galvanostatic and potential sweep conditions studied by time-resolved surface-enhanced infrared spectroscopy

When formaldehyde is oxidized on a Pt electrode under galvanostatic (constant current) conditions, the electrode Potential oscillates spontaneously. The oscillatory behavior has been examined by time-resolved surface-enhanced infrared absorption spectroscopy (SEIRAS) for understanding the mechanism and kinetics of the reaction at the molecular scale. SEIRAS reveals that CO and formate are adsorbed on the electrode surface and that their band intensities (coverages) oscillate synchronously with the oscillation of potential. SEIRAS coupled to cyclic voltammetry or linear sweep voltammetry suggests that formaldehyde is oxidized to CO2 via two parallel processes: the direct path via adsorbed formate and the indirect path via adsorbed CO. The two processes are kinetically coupled and autocatalytically activate and deactivate formaldehyde oxidation to yield the potential oscillations. The oxidation of the electrode surface also contributes to the oscillations for large applied currents.