Five current peaks in voltammograms for oxidations of formic acid, formaldehyde, and methanol on platinum

We have found that five current peaks are present in the voltammograms in the positive and negative sweep directions for the oxidations of formic acid, formaldehyde, and methanol on Pt in the potential range of 0.05-1.8 V, although the experimental conditions for the peaks to appear are different. In particular, a current peak at ca. 0.6 V, the negative slope of which on the positive side is closely related to autocatalysis, inducing oscillation, has been observed even for methanol. We have clarified that the three substances produce very similar voltammograms at a very slow sweep rate, such as 0.1 mV/s, and show some of the same behaviors of the peaks in their voltammograms. All these facts support the idea that the electrochemical oxidation mechanisms for the three substances have the same dominating elementary reaction steps, which induce oscillation phenomena, although with different reaction and adsorption rate constants.