Sulfur-Dopant-Promoted Electroreduction of CO2 over Coordinatively Unsaturated Ni-N-2 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.

Automated summary

Introducing alien sulfur atoms to tune the local electronic density of unsaturated NiN2 species enhances the efficiency of electrochemical CO2-to-CO conversion. The sulfur dopants improve CO selectivity and activity, reducing energy barriers for the electroreduction of CO2 to CO. This leads to a high CO Faradaic efficiency and large CO current density in H-cell measurements.