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

Abstract 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.