Mechanistic understanding of the antimony–bismuth alloy promoted electrocatalytic CO2 reduction to formate†

Introducing bismuth (Bi) into antimony (Sb) to form Sb–Bi alloys offers a promising way to enhance the electrocatalytic activity of Sb for CO₂ reduction to formate. However, there is currently a lack of mechanistic understanding of such a promotion effect. In this study, we address the knowledge gap by revealing the reaction mechanisms of Sb–Bi alloy catalyzed CO₂ reduction using various in situ spectroscopic techniques. We fabricated a series of Sb–Bi alloy films via a co-sputtering method, which exhibited enhanced formate production with the increase in Bi content in the alloys. Our operando differential electrochemical mass spectroscopy (DEMS) analysis revealed the promoted suppression of the competing hydrogen evolution reaction (HER) with the increase in Bi content. The in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) and Raman spectroscopy results demonstrated that the introduction of Bi into Sb not only changed the reaction intermediates from COOH* to OCHO* during the reaction but also enhanced the stabilization of OCHO* intermediates with decreasing Bi content. In addition, incorporating Bi into Sb improved the local pH near the catalyst surface to promote formate formation. Our work provides deep insights to guide the design of Sb/Bi-based catalysts for efficient electrochemical reduction of carbon dioxide (CO₂R).