Metal-Free N, P-Codoped Porous Carbon Fibers for Oxygen Reduction Reactions

Developing efficient oxygen reduction reaction (ORR) catalysts is deemed important and valuable for fuel cells and rechargeable metal-air batteries. Various metal-free electrocatalysts are highly considered as desirable ORR electrocatalysts due to their enhanced ORR activity and durability. Here, we report a facile, low cost and effective strategy to synthesize metal-free N, P-codoped porous carbon fibers (NPCF) via the simple pyrolysis of inexpensive polypyrrole as nitrogen source and phosphoric acid as phosphorus source. Results indicate that the NPCF-2 catalyst with large surface area (1569.3 m2 g−1) and high density of graphitic N, pyridinic N and P-C bonding exhibits outstanding alkaline ORR catalytic activity, long-term durability and high methanol tolerance, which is ascribed to the homogenous distribution of nitrogen and phosphorus atoms in the carbon fibers, rich micro/mesoporous structure and the synergistic effects of nitrogen and phosphorus atoms around the adjacent carbon atoms. Especially, the active graphitic N, pyridinic N and P atoms in the carbon fibers can regulate the electronic structure of carbon atoms, making the nitrogen, phosphorus and adjacent carbon atoms as active sites to promote ORR performance. This work provides a simple scalable and low-cost approach to produce metal-free N, P-codoped porous carbon as effective alternative to Pt-based electrocatalysts.