Abstract
Despite decades of research on Fe (or Co)-based electrocatalysts for the oxygen reduction reaction (ORR) in acidic medium, such as that in PEM fuel cells, the role of the metal is still one that raises a great deal of controversy. Consequently, the nature of the catalytic site in these non-noble metal ORR catalysts is still a topic of debate. One camp within the scientific community believes that the metal is an integral and electrochemically active part of the catalytic site, while the other believes that the metal is merely a chemical catalyst for the formation of special oxygen-reducing N-doped carbon structures. After presenting the case for the importance of non-noble catalysts at the cathode of PEM fuel cells, we introduce the three models of active sites that were advocated during the 1980s by van Veen, Yeager, and Wiesener and discuss how they have evolved, especially that of Yeager. Wiesener’s model is analyzed in detail through the work of several research groups that have been staunch supporters. The oxygen reduction mechanism on Fe-based and N-doped carbon catalytic sites is also reviewed. It is concluded that all the active sites proposed by van Veen, Yeager, and Wiesener in the 1980s, while different, are in fact simultaneously present in Fe (or Co)-based catalysts active for ORR in acidic medium, except that their activity and relative population in these catalysts are different, depending on the choice of the metal precursor, nitrogen precursor, structural properties of the carbon support, and the synthesis procedure.
Published Version
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