Tailoring Asymmetric Coordination in Single-Atom Catalysts for Highly Efficient and Selective Photocatalytic CO₂ Reduction

Single-atom catalysts (SACs) have emerged as a focal point in energy and environmental research due to their outstanding catalytic performance, optimal atom utilization, and well defined structures, making them excellent platforms for in-depth mechanistic investigations. However, enhancing the electronic properties of the characteristic porphyrin-like M–N4 single-atom configurations to improve photocatalytic CO₂ reduction reaction (CO₂RR) efficiency remains a significant challenge. This study introduces a simple yet effective method to adjust the electronic structure of single-atom sites integrated into hollow g-C₃N₄ by manipulating the microenvironment surrounding the atomically dispersed metal centers. Advanced techniques such as X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) were used to analyze the coordination geometry and charge distribution of the SACs. Additionally, in situ characterization provided insights into the structural evolution and reaction mechanisms occurring during the catalytic process. The results demonstrate that an asymmetric microenvironment around the active sites dramatically enhances the CO₂RR efficiency of the SAC, achieving 100% selectivity. This work offers a practical approach to designing asymmetric single-atom active centers with superior catalytic properties while advancing the understanding of active site behavior and reaction pathways.