Electrochemical oxidation of oxalic acid by Rh octaethylporphyrin adsorbed on carbon black at low overpotential

We have demonstrated the electrocatalytic oxidation of oxalic acid by carbon-supported Rh octaethylporphyrin at low overpotential in acidic solutions. As a result of C–C bond cleavage, CO2 generation from oxalic acid was clearly verified. The onset potential of oxalic acid oxidation was much lower than those for noble-metals and Co macrocycles. Repeated scans in cyclic voltammetry indicated that oxalic acid oxidation by Rh porphyrins is a stable reaction. Oxalic acid oxidation was suppressed by the presence of halides. The suppression effect of halides increases with increasing the atomic number in order: Br− > Cl− > F−. The reaction rates drastically decreased with an increase in pH of the test solutions. The suppression effect of halides and pH dependence are best explained on the basis of the competitive adsorption of oxalic acid and other anions on Rh(III) octaethylporphyrin.