Dendritic Cu-Bi bimetallic electrodes for highly selective and durable CO₂ electroreduction to formate: Interfacial...

Electrochemical CO₂ reduction to formate is a promising carbon-neutral strategy but suffers from low selectivity, current density, and stability. Herein, bismuth nanoparticle-decorated dendritic copper (Cu-Bi) electrodes were fabricated on copper foam via a two-step electrodeposition process, significantly increasing the electrochemical active surface area (ECSA). The optimized electrode achieved a high formate partial current density of 13.7 mA cm^-2 with a Faradaic efficiency of 98.5%, and an outstanding yield of 260.1 μmol cm^-2 h^-1 (5.5 times higher than bare Cu foam) at -1.0 V relative to the reversible hydrogen electrode (RHE), while maintaining exceptional stability over 80 h. The superior performance of the Cu-Bi electrode stems from the synergy between Cu and Bi, in which dendritic Cu provides abundant active sites and rapid charge transport, while Bi species account for the high selectivity toward formate formation. The results of density functional theory (DFT) calculations coupled with real-time Raman spectroscopy measurements show that the Cu-Bi interface dramatically reduces the energy barrier for CO₂ activation while stabilizing the crucial *OCHO intermediate, effectively driving the reaction toward formate production and suppressing hydrogen evolution as well as CO formation. This work provides insight into interfacial design for advanced CO₂ reduction electrocatalysts.