Current oscillations during the oxidation of formic acid on Pt(100) as studied by in situ time-resolved infrared reflection absorption spectroscopy

Current oscillations in the electrochemical oxidation of formic acid on a Pt(100) single crystal electrode were studied by time-resolved infrared reflection absorption spectroscopy (IRAS) in a dilute perchloric acid aqueous solution. In situ IRAS measurements were made possible by improving functional designs in an spectroelectrochemical cell. Two different kinds of on-top CO absorptions were observed in the spectra while the oscillations were taking place. A higher frequency band at 2060 cm−1 was observed at the bottom of the oscillation spikes (so-called inactive states) and the lower one at 2050 cm−1, at the top of the spikes (active states). On the other hand, the amount of CO2 production (which was derived from organic intermediates), remained constant irrespective of the spikes in the oscillations. These results do not support the traditional view that the oxidative removal and accumulation of adsorbed CO species are the origin of the oscillations, rather they support a modified view that they are caused by the adsorption and desorption of OH species in the presence of adsorbed CO on the electrode.