Structural Dynamics and Evolution of Bismuth Electrodes during Electrochemical Reduction of CO₂ in Imidazolium-Based Ionic Liquid Solutions

Abstract

Real-time changes in the composition and structure of bismuth electrodes used for catalytic conversion of CO2 into CO were examined via X-ray absorption spectroscopy (including XANES and EXAFS), electrochemical quartz crystal microbalance (EQCM), and in situ X-ray reflectivity (XR). Measurements were performed with bismuth electrodes immersed in acetonitrile (MeCN) solutions containing a 1-butyl-3-methylimidazolium ([BMIM]+) ionic liquid promoter or electrochemically inactive tetrabutylammonium supporting electrolytes (TBAPF6 and TBAOTf). Altogether, these measurements show that bismuth electrodes are originally a mixture of bismuth oxides (including Bi2O3) and metallic bismuth (Bi0) and that the reduction of oxidized bismuth species to Bi0 is fully achieved under potentials at which CO2 activation takes place. Furthermore, EQCM measurements conducted during cyclic voltammetry revealed that a bismuth-coated quartz crystal exhibits significant shifts in resistance (ΔR) prior to the onset of CO2 reduction near −1.75 V vs Ag/AgCl and pronounced hysteresis in frequency (Δf) and ΔR, which suggests significant changes in roughness or viscosity at the Bi/[BMIM]+ solution interface. In situ XR performed on rhombohedral Bi (001) oriented films indicates that extensive restructuring of the bismuth film cathodes takes place upon polarization to potentials more negative than −1.6 V vs Ag/AgCl, which is characterized by a decrease of the Bi (001) Bragg peak intensity of ≥50% in [BMIM]­OTf solutions in the presence and absence of CO2. Over 90% of the reflectivity is recovered during the anodic half-scan, suggesting that the structural changes are mostly reversible. In contrast, such a phenomenon is not observed for thin Bi (001) oriented films in solutions of tetrabutylammonium salts that do not promote CO2 reduction. Overall, these results highlight that Bi electrodes undergo significant potential-dependent chemical and structural transformations in the presence of [BMIM]+-based electrolytes, including the reduction of bismuth oxide to bismuth metal and changes in roughness and near-surface viscosity.

High‐Performance Bismuth‐Doped Nickel Aerogel Electrocatalyst for the Methanol Oxidation Reaction

“…When compared with the Ni 55 Bi 45 aerogel, the Bi in the Ni 97 Bi 3 aerogel appears slightly less oxidized. The shapes of the Bi L 3 ‐edges for the Ni 97 Bi 3 and Ni 55 Bi 45 aerogels are similar to the Bi foil, and the whiteline intensity at approximately 13 440 eV is weaker than the reported Bi 2 O 3 . These results, in combination with the XPS results of the Ni 97 Bi 3 and Ni 55 Bi 45 aerogels, and the partial existence of nonuniform Bi particles in the Ni 55 Bi 45 aerogel (see SEM‐EDXS mapping in Figure S4c), indicate that the Bi in the Ni 97 Bi 3 and Ni 55 Bi 45 aerogels is majorly and statistically metallic Bi; however, at the surface Bi is mainly in oxidized state.…”

“…Thes hapes of the Bi L 3 -edges for the Ni 97 Bi 3 and Ni 55 Bi 45 aerogels are similar to the Bi foil, and the whiteline intensity at approximately 13 440 eV is weaker than the reported Bi 2 O 3 . [15] These results, . Furthermore,t he surface area and porosity of the as-prepared aerogels were examined using the N 2 physisorption isotherm method ( Figure S12).…”

High‐Performance Bismuth‐Doped Nickel Aerogel Electrocatalyst for the Methanol Oxidation Reaction

“…Thes hapes of the Bi L 3 -edges for the Ni 97 Bi 3 and Ni 55 Bi 45 aerogels are similar to the Bi foil, and the whiteline intensity at approximately 13 440 eV is weaker than the reported Bi 2 O 3 . [15] These results,…”

Electrochemical Reduction of CO2 to Formate on Easily Prepared Carbon-Supported Bi Nanoparticles

“…Also, as previously stated, the product selectivity and efficiency of the ECO 2 R are strongly affected by a number of parameters including the chemical nature of the electrocatalysts [11,12,13,14], the particle shape/ surface structure [7,8,15,16,17,18,19,20,21,22,23,24,25], atomic composition [24,26,27,28,29,30,31], and particle size [32,33,34,35], among others. Consequently, several electrocatalysts [5,7,8,36,37] as well as experimental conditions such as temperature and pressure [5], pH [38,39], and electrolyte composition [5,40,41,42] have been explored.…”