Regeneration Oscillation Observed during Oxidation of Methanol, Formic Acid, and Formaldehyde with Chloride Ions

Abstract

A new type of oscillation, which we name regeneration oscillation, is investigated in detail. The regeneration oscillation is the ordinary potential oscillation with the higher turning potential lower than 0.85 V appearing repeatedly after the potential stays at a value higher than 1.0 V for a long time, of the order of 10 min or an hour. The oscillation has been observed during the oxidation of methanol, formaldehyde, and formic acid at 315 K when their concentrations are high, 1 or 10 mol/L (M), in the presence of high chloride ion concentrations, such as 10⁻² M, at a current far lower than the maximum current for the appearance of ordinary oscillation. The reason for the appearance of regeneration oscillation has been found by voltammetry and surface-enhanced infrared absorption spectroscopy to be due to the presence of two potentials for oxidizing adsorbed CO, one shifting to a value higher than 1.0 V and the other remaining unchanged, with increasing chloride ion concentration.