ELECTROCATALYTIC OXIDATION OF OXALIC-ACID AT ELECTRODES COATED WITH POLYMERIC METALLOPHTHALOCYANINES

The overpotential normally associated with the electrochemical oxidation of oxalic acid in aqueous solution is greatly reduced at glassy carbon surfaces modified with polymeric metallophthalocyanine films. The cobalt derivative is particularly active, displaying a peak potential approximately 750 mV less positive than that obtained at a bare electrode. The electrocatalytic process appears to involve initial Co(II) --> Co(III) oxidation, and the mechanistic details have been examined using cyclic voltammetry and rotating disk electrochemical methods. The overall reaction is quite rapid, and Levich plots obtained at coated electrodes show only slight deviations from linearity, even at high rotation rates. The observed catalytic current depends linearly on oxalic acid concentration and varies only slightly with film thickness, suggesting that internal charge transport is not rate-limiting under these conditions. The data indicate that the electrocatalytic oxidation of oxalic acid at polymeric cobalt phthalocyanine-coated electrodes belongs to the SR kinetic regime.