Transient Numerical Simulation of CO2 Conversion to Useful Products in a Flow Electrolyzer

Abstract The transient two-dimensional continuum numerical model was developed for the cathodic section of a flow electrolyzer with a catholyte flow channel to investigate the unsteady characteristics of the electrochemical CO2 reduction reaction. The Tafel model kinetic parameters for CO2 reduction over a copper catalyst were estimated from the experimental data of Kuhl et al. in a H-cell. Governing equations, including continuity, momentum, and charge balance with closure models, were solved using COMSOL Multiphysics v6.1. We validated our transient flow electrolyzer simulation results with the experimental data of Ren et al. at different operating conditions. The transient flow electrolyzer numerical model was used to observe the evolution of average concentrations and current densities in the catalyst layer. Specifically, the dynamic responses of the local microenvironment under different cathodic potential pulsing profiles were evaluated, revealing how transient operation modulates intermediate accumulation, reactant depletion, and the migration of OH– ions away from the catalyst layer. Evaluation of diverse cathodic potential profiles revealed that while standard pulse and on/off modes limit transport due to reduced electromigration forces, the amplitude mode (cathodic potential pulsing at higher voltage) significantly enhances multi-carbon (C2+) product pathways and delivers superior current density compared to static operation by optimizing reactive species reorientation. In addition, our transient numerical model was used to study the effect of catholyte flow rate over total current density, average local CO2 concentration in the catalyst layer, and average local pH in the catalyst layer. This transient continuum modeling framework provides essential insights into managing mass transport and local reaction environments in dynamic flow electrolyzers.