Fundamentals on kinetics of electrochemical reduction of CO2 at a bismuth electrode

• Published in: Journal of electroanalytical chemistry (Lausanne, Switzerland) Switzerland), 2022-01, Vol.904, p.115924, Article 115924
• Main Authors: Qin, Su-Fang, Xie, Yuan-Jiang, Wang, Yi, You, Le-Xing, Fang, Jian-Hui, Sun, Jian-Jun
• Format: Article
• Language: English
• Subjects: Bismuth; Bismuth electrode; Carbon dioxide; Chemical reduction; CO2 electrochemical reduction; Diffusion coefficient; Electron transfer; Electron transfer coefficient; Kinetics; Molecular dynamics; Potassium sulfate; Reaction kinetics; Standard heterogeneous rate constant
• ISSN: 1572-6657; 1873-2569
• DOI: 10.1016/j.jelechem.2021.115924

We report that CO2 reduction reaction in K2SO4 solution is a totally irreversible process at bismuth electrodes. Two obvious reduction peaks are observed, which are ascribed to one electron transfer for hydrogen evolution of H3O+ at lower potentials and two electrons transfer for CO2 reduction at higher potentials, respectively. It is firstly reported that CO2 reduction at bismuth electrodes is of a diffusion-controlled process. These new findings may identify electrochemical reaction kinetic questions and be helpful to understanding the electrochemical conversion between CO2 and carbon–neutral renewable energy. [Display omitted] •CO2RR displays an irreversible process at a bismuth electrode in K2SO4 solution.•It is first reported that CO2RR is a diffusion-controlled electrochemical process.•Electron transfer coefficient of CO2RR is obtained as 0.18.•Diffusion coefficient of CO2 is found to be 1.98 × 10−5 cm2·s−1.•Standard heterogeneous rate constant of CO2RR is estimated to be 3.4 × 10−3 cm·s−1. Electrochemical reduction of CO2 into renewable carbon–neutral fuels has been extensively studied. Current attentions mainly focus on the development of high-performance materials and molecular dynamics, fundamentals on kinetics of electrochemical reduction of CO2 are still unclear. Herein, we design a simplified electrochemical process, CO2-saturated K2SO4 solution at bismuth electrodes, to elucidate the electrochemical reaction kinetics of CO2 reduction reaction. A totally irreversible process for CO2 reduction reaction occurs and this reaction can be described as CO2 + H2O + 2e− → HCOO− + OH−. It is firstly reported that the reduction of CO2 at bismuth electrodes is of a diffusion-controlled process, and the diffusion coefficient of CO2 is (1.98 ± 0.22) × 10−5 cm2·s−1. From the well-defined linear sweep voltammograms, electron transfer coefficient is obtained as 0.18 ± 0.01. Combining with the half-wave potential (−1.503 ± 0.002 V vs. Ag/AgCl (sat. KCl)) from differential pulse voltametric results, the standard heterogeneous rate constant is estimated to be (3.4 ± 0.2) × 10−3 cm·s−1. These new findings may identify electrochemical reaction kinetic questions and be helpful to understanding the electrochemical conversion between CO2 and carbon–neutral renewable energy.