Two-Phase Flow Model to Define the Mass Transport in a Bicarbonate Electrolyzer for a CO2 Reduction Reaction

Extensive consumption of fossil fuels has brought environmental issues and an energy crisis. Electrochemical CO2 reduction by carbon neutral energy sources (such as solar and wind power) is a promising avenue to address the above challenges. However, CO2 reduction generally involves multiphysical/chemical processes, including chemical/electrochemical reactions, ion transport, bubble behaviors, and two-phase flow. The complex interactions among these processes make it rather difficult to analyze the effect of an individual process on the electrode performance based on the experimental method. In this work, a two-phase flow and mass transport model is developed for a bicarbonate electrolyzer cathode to analyze the interplays among various processes. The results reveal that the formation of a two-phase flow can effectively prompt the transport of chemical species and lower the overpotential, thereby improving the performance of CO2 reduction. The simulation suggests that an electrode porosity of similar to 0.75 is preferred to obtain the maximum performance of CO2 reduction. In addition, the performance of CO2 reduction can be remarkably improved at a higher concentration due to the increased reaction kinetics and alleviated concentration overpotential. Attributing to the buffer effect of bicarbonate, the flow rate of the electrolyte exhibits less influence on the electrode performance of CO2 reduction. In all, the developed model can contribute to the understanding of physical/chemical processes in CO2 reduction and provide a guideline for the design of electrodes in a bicarbonate electrolyzer.