Efficient Oxygen Reduction Catalysts of Porous Carbon Nanostructures Decorated with Transition Metal Species

Developing substitutes of noble metal catalysts toward oxygen reduction reaction (ORR) at the cathode is of vital importance for promoting low-temperature polymer electrolyte membrane fuel cells. Transition metal species have been one of the hot areas of interest due to their low cost, high activity, and long-term stability. The design of porous carbon nanostructures decorated with transition metal species plays a vital role in enhancing ORR catalytic performance. Here, the recent breakthroughs in porous carbon nanostructures decorated with transition metal species (including nanoparticles and atomically dispersed supported metal) are discussed. The porous nanostructures can provide large surface area as well as abundant pore channels, leading to sufficient exposure of active sites and efficient mass transfer. These nanostructures can be synthesized by several approaches, including the templated method, the self-templated method, the impregnation process, and so on. Furthermore, the ORR performance and the exploration of active sites are also discussed for further enhancement of the ORR catalysts. Finally, the challenges and prospects are discussed, which would push forward the development of ORR catalysts in the near future.