Non-noble Electrocatalysts for the PEM Fuel Cell Oxygen Reduction Reaction

Non-noble Electrocatalysts for the PEM Fuel Cell Oxygen Reduction Reaction 

Transition Metal Macrocycles for the Oxygen Reduction Reaction 

In 1964, Jasinski reported his pioneering work on using cobalt phthalocyanine, adsorbed on carbon and nickel eleetrodes, as a promising catalyst for the reduction of oxygen [8]. Following Jasinski s work, many other transition metal macrocyclic N4-complexes, including porphyrins, phthalocyanines, and tetraazannulenes, were also explored. The transition metals evaluated inelude Mn, Ru, Pd, Pt, Ir, Cr, Ni, Cu, Zn, Mo, Al, Sn, Sb, Ga, Na, Ag, vanadyl ion, as well as uranyl ion. All of these compounds show a certain level of eleetroeatalytie aetivity towards the ORR [6, 9]. 

Among these catalysts, Fe- and Co-macrocyclic complexes have exhibited the highest electrocatalytic activity. These catalysts also have shown remarkable selectivity they have no catalytic activity towards methanol oxidation. Since then, Fe- and Co-macrocyclic complexes have been extensively studied as the most promising ORR selective materials in the elFort to replace expensive noble metal Pt catalysts for PEM fuel cell apphcations, including DMFC applications. 

It has been recognized that the electrocatalytic activity and stability of Fe- and Co- macrocyclic complexes can be strongly affected by other factors such as the type of central transition metal ion, the ligand structure, the type of support, the method of synthesis, etc. In what follows, these factors will be discussed in more detail. 

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