Defect-Mediated Selectivity: Sulfur Vacancy Engineering in Tin Sulfide Boosts CO₂ Electroreduction to Formate

Introducing S vacancies into tin disulfide (SnS2) is crucial for regulating its electrocatalytic CO2 reduction activity. However, conventional methods for generating vacancies often result in uncontrolled defect concentrations. In this study, SnS2 with identical nanolayer structures but varying S-vacancy concentrations was synthesized by reacting different tin salts with high-temperature molten potassium thiocyanate. The results show that although SnS2 derived from SnCl2 exhibits a high S-vacancy concentration, its Faradaic efficiency (FE) for formic acid reaches only 48.2%. In contrast, SnS2 derived from SnSO4 contains fewer vacancies and exhibits an FE of 85.6%. Adjusting the KSCN/Sn salt ratio and applying H2 posttreatment can further optimize the S-vacancy concentration and enhance the CO2 reactivity. DFT calculations confirm that introducing an appropriate S-vacancy concentration can enhance the CO2 adsorption capacity, improve the affinity for the *OCHO intermediate, and accelerate the CO2RR kinetics. This precise vacancy engineering highlights the significance of balancing the defect concentration and catalytic efficiency.