Separated Growth of Bi-Cu Bimetallic Electrocatalysts on Defective Copper Foam for Highly Converting CO2 to Formate with Alkaline Anion-exchange Membrane beyond KHCO3 Electrolyte

Abstract Tuning the geometric and electronic structure of bimetallic electrocatalyst to facilitate a specific reaction pathway and offer more active sites is a promising avenue for enhancing activity and selectivity of electrocatalytic CO2 reduction reaction (eCO2RR). Owing to formation of Bi-Cu interface through the separated growth of Bi and Cu atoms on defective copper foam, the Bi-Cu bimetallic electrode converts CO2 to formate with an allured Faradaic efficiency (94.37 %) and partial current density (27.85 mA cm-2) at -0.91 V versus reversible hydrogen electrode (RHE). Notably, such electrode with tight moss-like structure delivers the excellent durability under 58 h electrolysis, outperforming most of the current Bi-based catalysts. Moreover, we have experimentally shown that KOH is a better electrolyte than KHCO3 due to the lower solution resistance and more confinement of free CO2 gas, and the alkaline anion-exchange membrane is more ideal than the cation-exchange membrane counterpart, owing to the enhancement of formate selectivity by suppressing the evolution of H2. This study inspires a complete set of concepts for highly converting CO2 to formate that contains the design of effective electrocatalysts, the role of growth substrate, the effect of different electrolytes and membranes.