S-doped Ag-Sn Alloy Hollow Microbox for High-Performance CO₂ Electroreduction to Formate

The dynamic catalyst's restructuring creates a new catalytic surface that is essential for boosting the efficiency of electrochemical carbon dioxide reduction reaction (CO₂RR). In this work, we synthesize Ag-decorated SnS₂ hollow microboxes using a coprecipitation method followed by a hydrothermal treatment. Based on a collection of in-situ/ex-situ characterizations including in-situ Raman spectroscopy, rapid freeze-quench (RFQ) ¹¹⁹Sn Mössbauer spectroscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), we discover that the Ag-decorated SnS₂ (Ag@SnS₂) hollow microboxes undergo dynamic reduction and reconstruction during the electrochemical CO₂RR, leading to the in-situ formation of S-doped Ag-Sn alloy (S-Ag₃Sn/Sn) hollow microboxes. This transformation results in a remarkable formate selectivity of 92.4% with a formate partial current density of 97.3 mA·cm^-2 at -0.8 V versus RHE in an H-cell. In-situ attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) measurements and density functional theory (DFT) calculations indicate that both S-doping and Ag-Sn alloying enhance the CO₂ adsorption and improve the stability of *OCHO intermediate. This work offers a facile strategy for designing highly active and selective electrocatalyst for CO₂RR.