Strong and uniform Sn-S bond strength in tin sulfides-based electrocatalysts enables efficient CO2-to-formate conversion

Electrochemical CO₂ reduction reaction (CO₂RR) represents a sustainable approach to alleviate the global concern associated with excessive CO₂ emission. Recently, metal-based sulfides are emerged as a special class of electrocatalysts for efficient formate production, which however suffer from massive S loss during CO₂RR due to the compositional reduction. Herein, we synthesize a series of tin sulfides with high crystallinity (i.e., SnS, Sn₂S₃, and SnS₂) as model catalysts, and reveal that the strength distribution of Sn-S bonds in atomic configurations is essential for efficient formate production. Typically, the strong and uniformly distributed Sn-S bonds in SnS₂ are beneficial for inhibiting S leaching and forming favorable Sn/SnS₂ heterointerfaces for CO₂RR, while the weaker Sn-S bonds in SnS promote the reduction into metallic Sn. Specially, the Sn₂S₃ with mixed bonding strengths undergoes consecutive dissociation, starting from cleaving the weakest Sn-S bonds and then inducing accelerative reduction. Resultantly, the SnS₂ achieves the highest Faraday efficiency of 93.8%±0.59% at −1.0 V_RHE and a high partial current density of 195.3 mA cm⁻² at −1.2 V_RHE. This study could provide insight into the role of metal-sulfur bonds in catalysts for efficient CO₂-to-formate conversion.