Strong and Uniform Sn–S Bond Strength in Tin Sulfides-Based Electrocatalysts Enables Efficient CO2-to-Formate Conversion
Electrochemical CO2 reduction (CO2RR) to formate offers a sustainable route to value-added chemicals, but metal sulfide catalysts suffer from sulfur loss via spontaneous metal reduction, degrading performance. This study synthesizes three highly crystalline tin sulfides—SnS, Sn2S3, and SnS2—via solid-state reaction to probe the role of Sn–S bond strength distribution in CO2RR. SnS, with weaker Sn–S bonds, undergoes nearly complete reduction to metallic Sn, yielding a maximum formate Faradaic efficiency (FE) of 89.1% and partial current density of 138.2 mA cm−2. Sn2S3, possessing mixed bond strengths, experiences accelerative reduction initiated by cleavage of the weakest Sn–S bonds, resulting in inferior FE (73.5%) and current density (73.5 mA cm−2). In contrast, SnS2 with strong and uniformly distributed Sn–S bonds exhibits enhanced compositional stability, generating abundant Sn/SnS2 heterointerfaces that serve as favorable active sites. Consequently, SnS2 achieves a peak formate FE of 93.8% ± 0.59% at −1.0 VRHE and a partial current density of 195.3 mA cm−2 at −1.2 VRHE, surpassing both SnS and Sn2S3. This work establishes a direct correlation between Sn–S bond strength uniformity and catalytic durability, providing a design principle for stabilizing metal sulfide electrocatalysts against sulfur leaching in CO2-to-formate conversion.