Electrocatalytic reduction of O2 and H2O2 by adsorbed cobalt tetramethoxyphenyl porphyrin and its application for fuel cell cathodes

In this paper, the mechanism and kinetics of oxygen and hydrogen peroxide electrochemical reduction that is catalyzed by an adsorbed cobalt tetramethoxyphenyl porphyrin (CoTMPP) on a graphite electrode were investigated using cyclic voltammetry (CV) and the rotating disk electrode (RDE) technique. The temperature and anion effects on O-2 and H2O2 electroreduction processes were also studied. The pH dependencies of cobalt redox centers, and oxygen and hydrogen peroxide reductions were measured for the purpose of exploring the reaction mechanism. In neutral solutions, the oxygen reduction reaction was observed to be a two-electron process, producing H2O2 in the low potential polarization range. In the high potential polarization range, an overall four-electron reduction Of O-2 to H2O was found to be the dominating process. The kinetic parameters obtained from the RDE experiments indicate that in a neutral solution, the reduction rate at the step from H2O2 to H2O is faster than that seen from O-2 to H2O2. Carbon particle-based air cathodes catalyzed by CoTMPP were fabricated for metal-air fuel cell application. The obtained non-noble catalyst content cathodes show considerably improved performance and stability. Crown Copyright (c) 2006 Published by Elsevier B.V. All rights reserved.