Nitrogen-Doped Carbon Electrocatalysts Decorated with Transition Metals for the Oxygen Reduction Reaction

The high cost of catalysts is the main disadvantage of aqueous fuel cells. In a conventional fuel cell, both the anode and cathode reactions need Pt-based catalysts to catalyze the respective electrochemical reactions, for example, the oxygen reduction reaction (ORR) on the cathode. As the ORR is very sluggish, more Pt catalyst is needed to balance the anode and cathode currents. In recent years, many alternative catalysts have been explored for the ORR that are mostly based on carbon, which include nonmetal-decorated carbons and metal-decorated carbons. Carbons codoped with a transition metal and nitrogen have shown the best ORR performance among all nonprecious metal catalysts, which is comparable to Pt under analogous conditions. We review nitrogen-doped carbon nanomaterials decorated with transition metals as ORR catalysts, their synthesis, characterization, and performance, with special emphasis on the mechanism and theoretical aspects of the ORR.