Precise Construction of Asymmetric Ni–N ₃ Sites Coupled with Carbon Vacancies for Highly Efficient CO ₂ Electroreduction

ABSTRACT Regulating the coordination environment and defect structure of single‐atom catalysts (SACs) is pivotal for advancing electrocatalytic CO 2 reduction. Here, through controlled chemical etching and optimizing Ni 2+ ion‐exchange steps, we construct Ni‐based SACs featuring asymmetric Ni–N 3 coordination coupled with adjacent carbon vacancies (Ni–N 3 –C V ). The introduction of carbon vacancies elevates the spin state of the Ni center and enhances electron transfer, thereby promoting CO 2 activation ( * CO 2 ). Transitioning from symmetric Ni–N 4 to low‐coordination Ni–N 3 sites further tunes the d‐band center, markedly reduces the free‐energy barrier for * COOH formation, and facilitates * CO desorption. As a result, Ni–N 3 –C V exhibits outstanding CO 2 ‐to‐CO performance, achieving a CO Faradaic efficiency of 97.9% at −0.8 V vs. RHE and maintaining >80% selectivity over a broad potential range. Density functional theory (DFT) calculations and operando spectroscopy elucidate the cooperative roles of carbon vacancies and asymmetric coordination in optimizing intermediate adsorption and reaction energetics. This work underscores the synergistic interplay between unsaturated coordination and defect engineering in tailoring local electronic structures, offering a robust strategy for enhancing the intrinsic activity of M–N–C SACs for efficient CO 2 reduction.