Bi-Zr-Modulated CO2 Microenvironment Enables High-Rate CO2 Electroreduction.

Abstract

Engineering the local chemical environment is an emerging strategy to enhance the performance of electrochemical CO₂ reduction reactions (CO₂RR). Bismuth-zirconium composite catalysts (Bi-Zr-KB, where KB = Ketjen Black) are developed to leverage Zr incorporation to modulate the local CO₂ microenvironment in an alkaline flow-cell system. Among the catalysts synthesized with various Bi/Zr ratios, the Bi-Zr-KB sample with a Bi/Zr ratio of 2 demonstrated the highest performance, achieving a current density of -176 mA cm^-2 and a formate Faradaic efficiency of 88% at -0.6 V vs reversible hydrogen electrode; representing a 1.4-fold enhancement over the Bi-only catalyst. Material characterizations (X-ray photoelectron spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray absorption near edge structure) confirmed the reduction of Bi species to metallic Bi during electrolysis, while Zr remained chemically stable. Electrochemical impedance spectroscopy and in situ Raman spectroscopy revealed that Zr incorporation suppresses local pH rise (≈0.3 units lower), facilitating improved CO₂ availability near active sites. Density functional theory calculations using Bi, Bi₂O₃, and ZrBi models showed interfacial Bi-Zr phases enable uniform CO₂ adsorption and enhanced charge transfer across surface orientation. These findings highlight Zr role in modulating catalyst microenvironment to overcome CO₂ mass transport limitations and achieve high-rate CO₂ conversion to formate.