Progress in Nonmetal-Doped Graphene Electrocatalysts for the Oxygen Reduction Reaction

Owing to energy shortages and environmental pollution, green energy sources such as polymer electrolyte fuel cells and metal-air batteries play a more and more important role, whereby the oxygen reduction reaction (ORR) is the rate-determining step. Development of high-efficiency and stable catalysts to facilitate the ORR is of importance. Graphene is a new type of material with two-dimensional structure and high surface area, which has wide-ranging applications in many fields. However, graphene with zero band gap shows low electrocatalytic activity toward the ORR. Introduction of nonmetal atoms can change the electronic arrangement, generate active sites, and further improve the catalytic activity of graphene. Some nonmetal-doping strategies (e.g., N, S, and P doping) can promote ORR activity. Herein, the recent development of nonmetal-doped graphene catalysts for ORR is reviewed. Some common synthetic methods for nonmetal-doped graphene materials are summarized, and the active sites and possible reaction mechanisms for ORR on various nonmetal-doped graphene catalysts are discussed.