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

Results are presented from experiments conducted on the electrochemical oxi dation of formic acid at polycrystalline Pt under constant current conditio ns. Sulfuric acid and perchloric acid with and without small amounts of HCl were used as supporting electrolytes. The onset of distinctive instabiliti es, not observed in the HCl-free perchloric acid solution, occurred when th e concentration of HCl reached 5 X 10(-6) M. For [HCl] = 1 X 10(-6) M, the observed instabilities were essentially the same as those seen in the HCl-f ree solution. The result indicates that instabilities might be used for the detection of fairly small anion concentrations. Instabilities observed usi ng the sulfuric acid solution and those observed using the perchloric acid solution were drastically different. A greater extent of adsorption of a gi ven anion cannot be the only reason for the different behaviors. It is argu ed that anions are directly involved in the oxidation process. (C) 2000 Els evier Science S.A. All rights reserved.