Axial Sulfur Ligand-Induced Coordination Symmetry Breaking in Co–N4 Motifs for Enhanced Oxygen Reduction Reaction and Durable Rechargeable Zinc-Air Batteries

Abstract

The precise control of a single-atom catalysts local atomic structure represents a critical foundation for designing advanced electrocatalysts with specific activity and selectivity for energy conversion and storage. This work presents a facile and novel synthesis of a high-performance cobalt (Co) single atom catalysts (S–Co–N–C) featuring a dynamic, symmetry-broken S−Co−N4 moiety, achieved through controlled pyrolysis of Co-impregnated γ-cyclodextrin metal-organic framework (Co-CDMOF). Experimental and density functional theory (DFT) analyses demonstrate that the axial sulfur (S) coordination induces asymmetric electron distribution and optimizes the electronic nature of the Co site, thereby facilitating a rapid oxygen reduction reaction (ORR) pathway. Subsequently, the optimized S–Co–N–C demonstrates a high positive half-wave potential (E1/2 of ~0.79 V vs. RHE) and robust stability relative to the Pt/C. Furthermore, the S–Co–N–C electrocatalyst performs effectively as an air-cathode in rechargeable zinc-air batteries (ZABs), delivering a high power density of ~135 mW cm-2 and excellent cycling stability over 200 h of operation. This investigation establishes a promising method for designing axial coordination configuration of single-atom catalysts (SACs) and highlights the promising potential of cyclodextrin-based MOF as a highly versatile platform for fabricating advanced materials for energy conversion and storage.