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

Introducing S vacancies into tin disulfide (SnS 2 ) is crucial for regulating its electrocatalytic CO 2 reduction activity. However, conventional methods for generating vacancies often result in uncontrolled defect concentrations. In this study, SnS 2 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 SnS 2 derived from SnCl 2 exhibits a high S-vacancy concentration, its Faradaic efficiency (FE) for formic acid reaches only 48.2%. In contrast, SnS 2 derived from SnSO 4 contains fewer vacancies and exhibits an FE of 85.6%. Adjusting the KSCN/Sn salt ratio and applying H 2 posttreatment can further optimize the S-vacancy concentration and enhance the CO 2 reactivity. DFT calculations confirm that introducing an appropriate S-vacancy concentration can enhance the CO 2 adsorption capacity, improve the affinity for the *OCHO intermediate, and accelerate the CO 2 RR kinetics. This precise vacancy engineering highlights the significance of balancing the defect concentration and catalytic efficiency.