Promoting Electrochemical CO₂ Reduction to Formate via Sulfur-Assisted Electrolysis

Electrochemical CO₂ reduction reaction (CO₂RR) provides a renewable approach to transform CO₂ to produce chemicals and fuels. Unfortunately, it faces the challenges of sluggish CO₂ 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 CO₂ 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⁺(H₂O)_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 CO₂ activation and facilitate HCOO^* intermediate formation while suppressing competing hydrogen evolution reaction. Consequently, the S-modified Bi catalyst achieves impressive electrochemical CO₂RR 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. © 2024 Wiley-VCH GmbH.