Construction of an SnS-based heterostructure catalyst for electrochemical CO2 reduction to formate over a wide potential window.

SnS has emerged as an attractive catalyst for the electrochemical CO2 reduction reaction (CO2RR) to formate, while its long-term operational stability is hindered by the self-reduction of Sn2+ and sulfur dissolution. Thus, maintaining high current efficiency across a wide negative potential range to achieve high production rates of formate remains a significant challenge. In this study, we present a heterostructure constructed with SnS and CuS for efficient CO2RR to formate. The SnS-CuS (30) exhibits a remarkable formate Faradaic efficiency (FEf) of 93.94 % at -1 V vs. reversible hydrogen electrode (RHE) and demonstrates long-term stability for 7.5 h, maintaining high activity (with an average FEf of 85.6 %) across a wide negative potential range (from -0.8 to -1.2 V (vs. RHE)). The results reveal that the heterogeneous interface between SnS and CuS mitigates the self-reduction issue of SnS by sacrificing Cu²⁺, highlighting that the true active species is SnS, which effectively resists structural changes during the electrolysis process under the protection of CuS. The synergistic interaction within the CuS and SnS heterostructure, combined with the tendency for electron self-conduction, enables the catalyst to maintain high formate activity and selectivity across a wide potential range. Furthermore, theoretical results further indicate that the incorporation of CuS enhances CO2 adsorption and lowers the energy barrier for the formation of formate intermediates. This study inspires the concept of applying protective layers to active species, promoting high selectivity in Sn-based electrocatalysts.