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

We report that CO 2 reduction reaction in K 2 SO 4 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 H 3 O + at lower potentials and two electrons transfer for CO 2 reduction at higher potentials, respectively. It is firstly reported that CO 2 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 CO 2 and carbon–neutral renewable energy. • CO 2 RR displays an irreversible process at a bismuth electrode in K 2 SO 4 solution. • It is first reported that CO 2 RR is a diffusion-controlled electrochemical process. • Electron transfer coefficient of CO 2 RR is obtained as 0.18. • Diffusion coefficient of CO 2 is found to be 1.98 × 10 −5 cm 2 ·s −1 . • Standard heterogeneous rate constant of CO 2 RR is estimated to be 3.4 × 10 −3 cm·s −1 . Electrochemical reduction of CO 2 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 CO 2 are still unclear. Herein, we design a simplified electrochemical process, CO 2 -saturated K 2 SO 4 solution at bismuth electrodes, to elucidate the electrochemical reaction kinetics of CO 2 reduction reaction. A totally irreversible process for CO 2 reduction reaction occurs and this reaction can be described as CO 2 + H 2 O + 2e − → HCOO − + OH − . It is firstly reported that the reduction of CO 2 at bismuth electrodes is of a diffusion-controlled process, and the diffusion coefficient of CO 2 is (1.98 ± 0.22) × 10 −5 cm 2 ·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 CO 2 and carbon–neutral renewable energy.