Efficient conversion of CO2 to formic acid at nanostructured CuBi catalyst: Electrochemical, spectroscopic and DFT studies

Bismuth-based catalysts have been recognized for their high efficiency as electrocatalysts for CO 2 reduction to formate. In this work, Bi-rich CuBi bimetallic catalysts are co-electrodeposited and evaluated for their performance towards CO 2 conversion to formate and formic acid. The optimized CuBi catalysts with a Cu/Bi ratio of 20.5/79.5 showed a high Faradaic efficiency of 92% for formate formation at –0.8 V vs. RHE in an H-type cell. In addition, pure formic acid was produced with a Faradaic efficiency of ∼98% at –90 mA cm –2 using a three-compartment membrane electrode assembly (MEA) cell system with an acidic-ion exchange bead electrolyte. The in-situ electrochemical Raman spectroscopic measurements revealed the reduction of the initial bismuth oxides on the surface to metallic bismuth during the CO 2 reduction process. The in-situ electrochemical attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy was employed to study the kinetics of the CO 2 reduction, revealing that the formate generation predominantly occurred through the adsorbed *OCHO intermediate in a bidentate configuration. This has been further confirmed by the density functional theory (DFT) calculation. The high catalytic performance of the optimized CuBi catalyst was mainly due to Bi as the dominant component, which served as active sites, while additional Cu modified the electronic structure and facilitated the formation of *OCHO intermediate. This work demonstrates the effectiveness of the integration of electrochemical, in situ spectroscopic and DFT approaches to gain fundamental understanding of the reaction kinetics, which would greatly facilitate the design of advanced electrochemical processes for clean energy and environmental applications.