A comparative study of organic cobalt complex catalysts for oxygen reduction in polymer electrolyte fuel cells

Reduction of platinum catalysts loading is a central issue in polymer elect rolyte fuel cells. As alternatives for platinum, some organic metal chelate compounds are tested as cathode catalysts, such as cobalt aza-complexes or cobalt complexes possessing aminophenyl moieties featured as Co-N-4 or Co- N2O2 chelate structures. The way of immobilization of catalysts on the grap hite surface influences their stability its well as the performance of oxyg en reduction. Heat-treated catalysts supported on graphite at 600 degreesC show much better oxygen reduction abilities than as-received metal complexe s. The original chemical structure of metal complexes affects crucially the catalytic ability, though initial structures of molecules are no more inta ct after the heat treatment. The catalytic activity of these complexes may originate from the central chelate unit CoN4 on the carbon substrate, and t his unit is assumed to constitute the basic coordination site for an oxygen molecule. Electropolymerized catalysts impart a high level of oxygen reduc tion ability, probably due to the improved molecular orientation for oxygen coordination and formation of good chelate sites on the graphite surface.