Nitrogen and Sulfur Co-Doped Porous Carbon Derived from Sophora Flower as an Efficient Oxygen Reduction Electrocatalyst for Zinc-Air Battery

Exploiting efficient and low-price electrocatalysts for oxygen reduction reaction (ORR) is very important to the practical application of high-performance zinc-air battery. In this paper, nitrogen (N) and sulfur (S) co-doped porous carbon ORR catalysts derived from abundantly available and environmental waste sophora flowers (N, S-ASFC, abbreviation of "activated sophora flowers carbon") have been successfully prepared by a two-step heat treatment process (a synchronous carbonization and activation process followed by a doping process). Compared to pristine ASFC and single N-doped ASFC, the series of N, S-ASFC catalysts present superior electrocatalytic activity for oxygen reduction reaction (ORR). Meanwhile, the ORR catalytic activities of N, S-ASFC catalysts can be rationally modulated by simply adjusting the reaction temperature of doping process. The optimized N, S-ASFC-800 catalyst exhibits excellent activity and stability to ORR in alkaline system, which is approaching to the commercial Pt/C catalyst (20%). More importantly, the good performance and high stability of the real zinc-air battery using N, S-ASFC-800 as cathode further demonstrate this catalyst is a favorable and promising candidate to replace noble metal-based ORR catalysts for the practical application in zinc-air batteries.