Improving the electron transfer in the oxygen reduction reaction by N/S co-doping for high-performance of Zn–air batteries

Abstract

Designing high-performance carbon-based oxygen reduction catalysts using a facile strategy is an attractive research direction in the field of energy conversion and storage. Herein, N/S co-doped carbon was prepared using κ-carrageenan and melamine as precursors, in which melamine can be decomposed into nitrogen-containing gas for realizing nitrogen doping, and the sulfate groups in κ-carrageenan can be converted for sulfur doping. Such an N/S doping strategy enables a carbon catalyst with a large specific surface area, hierarchical porous structure, and rich defective sites to be achieved, displaying a high positive onset potential (E_onset = 0.98 V) and half wave potential (E_1/2 = 0.89 V), excellent stability, and methanol tolerance. More importantly, S doping could increase the positive charge density of the carbon adjacent to the nitrogen, which is favorable for enhancing the chemisorption of O₂ and weakening the O–O bond, thereby promoting the reaction from O₂ to OH⁻ and improving electron transfer. Furthermore, with this catalyst as the air cathode, the assembled aqueous Zn–air battery exhibits a high open-circuit potential of 1.53 V and a remarkable peak power density of 166.05 mW cm⁻², outperforming the Pt/C catalyst. This work gives a facile and effective strategy to construct high-performance ORR catalysts with four electron transfer for Zn–air batteries.