Nitrogen, phosphorus and iron doped carbon nanospheres with high surface area and hierarchical porous structure for oxygen reduction

Nitrogen, phosphorus and Fe doped carbon nanospheres have been synthesized by a facile method in which polyacrylonitrile nanospheres are pyrolyzed in the presence of diammonium phosphate and iron trichloride hexahydrate. The specific surface area of the catalyst is high up to 771.3 m2 g−1, and it has a hierarchical micro-meso-macroporous structure. In an alkaline medium, the catalyst exhibits high electrocatalytic activity towards the oxygen reduction reaction (ORR) as well as excellent stability and methanol tolerance—superior in each case to commercial Pt/C catalyst. The effects that adding Fe salt and phosphorus on the structure and performance of the catalyst are also investigated. We suggest that the catalyst's excellent electrocatalytic performance may be attributed to: (1) the synergistic effect, which provides more catalytic sites for the ORR, due to the nitrogen and phosphorus co-doping; (2) the strong promotion by trace Fe residues; and (3) the high surface area and excellent mass transport rate arising from the hierarchical porous structure.