Nonprecious metal catalysts for the molecular oxygen-reduction reaction

This review covers the electrocatalytic activities, the corresponding influence factors and the synthesis methods of non-precious-metal electrocatalysts towards oxygen-reduction re-action (ORR) for fuel-cell systems. In particular, the chalcogenides and the macrocycles containing Co or Fe metals have been focused upon. Due to the scarcity of Pt metal, the Co- and Fe-based chalcogenides are potentially interesting substitutes of Pt although they still show lower catalytic activities for ORR and lower electrochemical and chemical stability in the present fuel-cell electrolytes. Compared to Pt electrocatalysts, the Co- and Fe-based macrocycles, such as TMPP, TPP, Pc and TAA, are among the most promising substitutes for Pt because of their comparable catalytic activities towards ORR and the higher insensitivity to methanol (in direct methanol fuel cells - DMFC) although they still have some drawbacks, namely lower stability and shorter durability. Novel catalyst synthesis methods, modification techniques of catalysts as well as supporting substrates are expected to be developed in the future to satisfy the requirements of commercial fuel cells. (c) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.