Continuous coordination modulation with different heteroatoms unveils favorable single-atom Ni sites for near-unity...

Coordination modulation is a key strategy for enhancing the catalytic activity of single-atom catalysts (SACs) in CO₂ 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 (N₃Ni-C, N₃Ni-N, and N₃Ni-O), where varying coordinating atoms (C, N, and O) modulate continuously the electronic structure to explore their effects on CO₂ electroreduction. Compared to the N₃Ni-N catalyst with classic Ni-N₄ coordination, N₃Ni-C demonstrates significantly enhanced CO₂ 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 N₃Ni-O exhibits inferior performance. Operando and computational investigations reveal that both C- and O-coordination enhance CO₂ hydrogenation by elevating the Ni d-band center, thereby strengthening *COOH intermediate adsorption. However, the concurrent promotion of the hydrogen evolution reaction competes with CO₂ reduction, ultimately leading to opposite effects on performance. This work provides atomic-level insights into CO₂ electroreduction mechanisms and offers compelling strategies for improving SAC performance via coordination modulation with heteroatoms.