Remarkably active catalysts for the electroreduction of O2 to H2O for use in an acidic electrolyte containing concentrated methanol

Focusing on methanol tolerance, a series of heat-treated metalloporphyrins were investigated by steady-state voltammetry with a rotating disk electrode. The heat-treated CoTPP/FeTPP (tetraphenylporphyrin) shows the optimum catalytic activity for oxygen reduction with an onset catalytic potential [0.9 V vs, reversible hydrogen electrode (RHE)] close to that of platinum black catalyst (1.0 V vs. RHE). However. the catalytic activity for oxygen reduction on platinum black catalyst is severely affected by the presence of 1.0 M methanol, resulting in a negative shift uf the catalytic potential and a significant decrease in catalytic current. The catalytic activity for oxygen reduction on the heat-treated metalloporphyrin is not appreciably affected by the presence of the same amount of methanol in an acidic electrolytic solution. The catalytic activity of the heat-treated binary metalloporphyrin catalyst is better than that of only a heat-treated single metalloporphyrin. The best heat-treatment (HT) temperature for HT-CoTPP/FeTPP is 600 degreesC. The catalytic kinetic process is analyzed using various polarization curves for oxygen reduction at different rotation rates. The slopes obtained from the Koutecky-Levich plots have verified that the heat-treated metalloporphyrins can catalyze a four-electron reduction of oxygen to water over a wide potential range. (C) 2000 The Electrochemical Society.