Abstract
Coordination modulation is a key strategy for enhancing the catalytic activity of single-atom catalysts (SACs) in CO(2) electroreduction. However, achieving such modulation within the same framework by incorporating an array of heteroatoms with differing electronic properties remains unexplored, despite its potential for optimizing active sites. Here, we investigate unprecedentedly three Ni-based SACs (N(3)Ni-C, N(3)Ni-N, and N(3)Ni-O), where varying coordinating atoms (C, N, and O) modulate continuously the electronic structure to explore their effects on CO(2) electroreduction. Compared to the N(3)Ni-N catalyst with classic Ni-N(4) coordination, N(3)Ni-C demonstrates significantly enhanced CO(2) conversion, achieving remarkably a near-unity Faradaic efficiency for CO (99.3%) at -0.7 V(RHE) in the H-cell and a CO partial current density of 396.8 mA cm(-2) at -1.15 V(RHE) in the flow cell, whereas N(3)Ni-O exhibits inferior performance. Operando and computational investigations reveal that both C- and O-coordination enhance CO(2) hydrogenation by elevating the Ni d-band center, thereby strengthening *COOH intermediate adsorption. However, the concurrent promotion of the hydrogen evolution reaction competes with CO(2) reduction, ultimately leading to opposite effects on performance. This work provides atomic-level insights into CO(2) electroreduction mechanisms and offers compelling strategies for improving SAC performance via coordination modulation with heteroatoms.