Orbital Interactions in Bi-Sn Bimetallic Electrocatalysts for Highly Selective Electrochemical CO₂ Reduction toward Formate Production

A highly selective and durable electrocatalyst for carbon dioxide (CO₂) conversion to formate is developed, consisting of tin (Sn) nanosheets decorated with bismuth (Bi) nanoparticles. Owing to the formation of active sites through favorable orbital interactions at the Sn-Bi interface, the Bi-Sn bimetallic catalyst converts CO₂ to formate with a remarkably high Faradaic efficiency (96%) and production rate (0.74 mmol h⁻¹ cm⁻²) at −1.1 V versus reversible hydrogen electrode. Additionally, the catalyst maintains its initial efficiency over an unprecedented 100 h of operation. Density functional theory reveals that the addition of Bi nanoparticles upshifts the electron states of Sn away from the Fermi level, allowing the HCOO* intermediate to favorably adsorb onto the Bi-Sn interface compared to a pure Sn surface. This effectively facilitates the flow of electrons to promote selective and durable conversion of CO₂ to formate. This study provides sub-atomic level insights and a general methodology for bimetallic catalyst developments and surface engineering for highly selective CO₂ electroreduction.