Asymmetric Atomic Tin Catalysts with Tailored p-Orbital Electron Structure for Ultra-Efficient Oxygen Reduction

Abstract

Atomically dispersed transition metal–nitrogen–carbon (M–N–C) catalysts guide by the d-band center theory have been extensively studied for oxygen reduction reaction (ORR) in various energy conversion and storage processes. However, asymmetric p-block metal single-atom catalysts (SACs) toward ORR have rarely been reported, and the origin of their catalytic activity is still unclear. Here, an asymmetric N, O coordinated Sn SAC is developed as an efficient ORR electrocatalyst. Remarkably, the optimized Sn SAC (e.g., Sn–N/O–C) exhibit outstanding ORR performance with a half-wave potential of 0.910 V in alkaline media, outperforming most state-of-the-art ORR catalysts. More importantly, the Sn–N/O–C possesses a long-term durability in both alkaline and acidic electrolytes. Besides, Zn–air batteries based on the Sn–N/O–C cathode also show a higher energy density (254 mW cm^-2) than that of their reported M–N–C counterparts. Theoretical calculations suggest that the asymmetric N, O coordinated atomic Sn sites have a stronger binding interaction with O₂ and better charge transfer ability compared with the symmetric SnN₄ sites, thereby facilitating the ORR process. This work provides a nitrogen-, oxygen-coordinated engineering strategy for the rational design of highly active and durable carbon-based catalysts with atomic p-block metal sites for ORR and beyond.