Effects of anions on chemical instabilities in the oxidation of formic acid

Results are presented from experiments conducted on the electrochemical oxidation of formic acid at polycrystalline Pt under constant current conditions. Sulfuric acid and perchloric acid with and without small amounts of HCl were used as supporting electrolytes. The onset of distinctive instabilities, not observed in the HCl-free perchloric acid solution, occurred when the concentration of HCl reached 5 × 10-6 M. For [HCl] = 1 × 10-6 M, the observed instabilities were essentially the same as those seen in the HCl-free solution. The result indicates that instabilities might be used for the detection of fairly small anion concentrations. Instabilities observed using the sulfuric acid solution and those observed using the perchloric acid solution were drastically different. A greater extent of adsorption of a given anion cannot be the only reason for the different behaviors. It is argued that anions are directly involved in the oxidation process.