Recent Advances and Prospects of Metal-Based Catalysts for Oxygen Reduction Reaction

Fuel cells, as one of the most promising technologies in sustainable energy conversion systems, hold great expectations for commercial applications. Cathode oxygen reduction reaction (ORR) kinetics of fuel cells are very slow and require a large overpotential to make the reaction occur, which greatly limits the energy output of fuel cells. Therefore, designing and preparing a highly active and stable ORR catalyst has become a great challenge. Herein, recent advances in platinum-based and platinum-free materials in metal-based catalysts are focused on, including structural properties, synthesis methods, performance characterization, and catalytic mechanisms. Although platinum-based precious metal catalysts have excellent performance, high prices limit the scale of commercial fuel cells. Nonprecious metal catalysts (e.g., transition metal nitrogen-doped carbon-based catalysts (M-N/C), transition metal compounds (transition metal oxides-TMOs, transition metal carbides-TMCs, transition metal nitrides/transition metal oxynitrides-TMNs/TMNOs), layered double hydroxides-LDHs) completely eliminate dependence on precious metals and exhibit excellent ORR catalytic activity and stability. Finally, the ideas for future design and preparation of new ORR catalysts and challenges in the future of research work are discussed.