Engineering Geometric Asymmetry in Co─N ₄ Sites by Chlorination Coordination for Enhanced Peroxymonosulfate Activation

Abstract Breaking the geometric symmetry of metal–N 4 moieties represents an effective strategy to modulate the electronic environment of single‐atom catalysts (SACs) for enhanced peroxymonosulfate (PMS) activation. Herein, a chlorine‐engineered cobalt SAC (Co/Cl/AC) is constructed by covalently bonding Cl atoms to the carbon matrix adjacent to Co─N 4 sites. The introduced asymmetry redistributes local charge density and downshifts the Co d‐band center, thereby facilitating PMS adsorption and promoting a non‐radical 1 O 2 generation pathway. As a result, Co/Cl/AC achieves superior catalytic performance for volatile organic compounds (VOCs) degradation, with 97.9% toluene removal and ≈80% CO 2 mineralization. Experimental results and DFT calculations reveal that Cl coordination enhances electron transfer, strengthens Co─N interactions, and lowers the energy barrier for PMS decomposition. This work provides mechanistic insights into halogen‐induced symmetry breaking and demonstrates a rational design strategy for constructing high‐performance SACs in advanced oxidation processes.