Promoting Electrochemical CO 2 Reduction to Formate via Sulfur‐Assisted Electrolysis

Abstract Electrochemical CO 2 reduction reaction (CO 2 RR) provides a renewable approach to transform CO 2 to produce chemicals and fuels. Unfortunately, it faces the challenges of sluggish CO 2 activation and slow water dissociation. This study reports the modification of Bi‐based electrocatalyst by S, which leads to a remarkable enhancement in activity and selectivity during electrochemical CO 2 reduction to formate. Based on comprehensive in situ examinations and kinetic evaluations, it is observed that the presence of S species over Bi catalyst can significantly enhance its interaction with K + (H 2 O) n , facilitating fast dissociation of water molecules to generate protons. Further in situ attenuated total reflectance surface‐enhanced infrared absorption spectroscopy (ATR‐SEIRAS) and in situ Raman spectroscopy measurements reveal that S modification is able to decrease the oxidation state of Bi active site, which can effectively enhance CO 2 activation and facilitate HCOO * intermediate formation while suppressing competing hydrogen evolution reaction. Consequently, the S‐modified Bi catalyst achieves impressive electrochemical CO 2 RR performance, reaching a formate Faradaic efficiency (FE formate ) of 91.2% at a formate partial current density of ≈135 mA cm −2 and a potential of −0.8 V versus RHE in an alkaline electrolyte.