Remarkably Active Catalysts for the Electroreduction of O 2 to H 2 O for Use in an Acidic Electrolyte Containing Concentrated Methanol

Abstract

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 of 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°C. The catalytic kinetic process is analyzed using various polarization curves for oxygen reduction at different rotation rates. The slopes obtained from the Koutecký‐Levich plots have verified that the heat‐treated metalloporphyrins can catalyze a four‐electron reduction of oxygen to water over a wide potential range. © 2000 The Electrochemical Society. All rights reserved.