Continuous Coordination Modulation with Differing Heteroatoms Unveils Favorable Single-atom Ni Sites for Near-unity CO Selectivity in CO2 Electroreduction

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, 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 VRHE in the H-cell and a CO partial current density of 396.8 mA cm–2 at –1.15 VRHE 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.