Strategies for Enhancing the Electrocatalytic Activity of M-N/C Catalysts for the Oxygen Reduction Reaction

The development of highly active and durable nonprecious metal catalysts that can replace expensive Pt-based catalysts for the oxygen reduction reaction (ORR) is of pivotal importance in polymer electrolyte membrane fuel cells. In this line of research, metal and nitrogen codoped carbon (M-N/C) catalysts have emerged as the most promising alternatives to Pt-based catalysts. This review provides an overview of recently developed synthetic strategies for the preparation of M-N/C catalysts to enhance the catalytic activity of the ORR. We present five major strategies, namely the use of metal-organic frameworks as hosts or precursors, the use of sacrificial templates, the addition of heteroelements, the preferential generation of active sites, and a biomimetic approach. For each strategy, the advantages capable of boosting catalytic activity in the ORR are summarized, and notable examples and their catalytic performances are presented. The ORR activities and measurement conditions of high-performing M-N/C catalysts are also tabulated. Finally, we summarize this review with some suggestions for future studie