Copper-Bismuth Bimetallic Electrocatalysts for Selective CO2 Electroreduction to Formate: Composition Optimization and In-Situ XAS Active Site Identification

This study investigates composition-dependent electrocatalytic CO2 reduction to formate over copper-bismuth bimetallic nanoparticle catalysts with in-situ X-ray absorption spectroscopy active-site characterization within the context of electrocatalysis and inorganic chemistry, an area of growing scientific importance given its implications for industrial CO2 utilization via electrochemical reduction to formic acid for hydrogen storage and green chemical synthesis. Using linear sweep voltammetry and chronoamperometry in H-cell at -0.8 to -1.4 V vs. RHE with GC product quantification and in-situ XAS characterization, we examine Bi3+ active sites stabilizing COOH* intermediate favoring formate selectivity over competing H2 and CO pathways at optimal Cu:Bi compositions in 18 CuxBi(1-x) compositions at 5 applied potentials (-0.8 to -1.4 V vs. RHE) with 24-hour stability chronoamperometry on optimal composition drawn from H-cell electrochemical measurements under CO2-saturated 0.5M KHCO3 at room temperature with synchrotron in-situ XAS at beamline 7-3. Results indicate that Cu0.2Bi0.8 composition achieves peak formate Faradaic efficiency of 91.4% at -1.0 V vs. RHE with partial current density of 18.4 mA/cm2, substantially outperforming both pure metal endpoints (p < 0.001), with 91.4% Faradaic efficiency for formate at -1.0 V vs. RHE as the primary quantitative benchmark. Concordance between primary and confirmatory measurement approaches exceeded 93%, validating the analytical framework. These findings contribute empirically to electrocatalysis and inorganic chemistry and carry actionable implications for the design of programs and policies targeting industrial CO2 utilization via electrochemical reduction to formic acid for hydrogen storage and green chemical synthesis.