Sulfur-Dopant-Promoted Electroreduction of CO₂ over Coordinatively Unsaturated Ni-N₂ Moieties

Atomically dispersed nickel–nitrogen–carbon (Ni-N-C) moieties are promising for efficient electrochemical CO₂-to-CO conversion. To improve the intrinsic electrocatalytic activity, it is essential but challenging to steer the coordination environment of Ni centers for promoting the CO formation kinetics. Here, we introduce alien sulfur atoms to tune the local electronic density of unsaturated NiN₂ species. A coordinated structure evolution is detected and S vacancies are generated at high overpotentials, as confirmed by X-ray absorption spectroscopy. The sulfur dopants enhance CO selectivity and activity over normal unsaturated NiN₂ structure, reaching a high CO Faradaic efficiency of 97 % and a large CO current density of 40.3 mA cm⁻² in a H-cell at −0.8 V and −0.9 V (vs. RHE), respectively. DFT calculations reveal both doped S atoms and evolved S vacancies in the NiN₂ coordination environment contribute to the reduced energy barriers for CO₂ electroreduction to CO.