Effect of cobalt bis(dicarbollides) on electrochemical oxygen reduction on Pt electrode in methanol-acid solution

Electrochemical oxygen reduction on a platinum electrode has been investigated in methanol-0.05 M H₂SO₄ aqueous solutions in the presence of acids of cobalt bis(dicarbollide) (H⁺B⁻, H⁺(1,2-C₂B₉H₁₁)₂-3-Co]⁽⁻⁾) or its hexachlorinated derivative (H⁺BCl⁻, H⁺ (8,8′,9,9′,12,12′-Cl₆-(1,2-C₂B₉H₈)₂-3-Co)]⁽⁻⁾). Methanol oxidation was suppressed with H⁺BCl⁻ significantly, and selective oxygen reduction was achieved on a platinum electrode. The efficiency of oxygen reduction to H₂O, which depended on the electrode potential, was lower by 2% to 20% than that without H⁺BCl⁻. The mechanism was investigated by surface-enhanced infrared absorption spectroscopy (SEIRAS). H⁺BCl⁻ suppresses formation of both the catalytic poison, linear CO (ads.), from methanol and the formate, the intermediate of the non-CO path of methanol oxidation.