Understanding dynamic mass transport effects in pulsed CO2 electrolysis

Electrochemical carbon dioxide reduction (CO₂R) holds considerable potential for using renewably sourced electricity to convert CO₂ to valuable chemicals and fuels. Of the catalysts explored for this process, copper (Cu)-containing materials are uniquely capable of generating more valuable C₂₊ products with high faradaic efficiency (FE), and recent studies have demonstrated that the microenvironment surrounding the Cu catalyst plays a significant role in dictating selectivity. For instance, enhancements in local pH and CO₂ availability at the cathode surface have been demonstrated to suppress hydrogen (H₂) evolution and improve C₂₊ selectivity. It has also been demonstrated that films of an organic material enhance selectivity to C₂₊ products through control of mass transfer and/or stabilization of intermediates to these products.

Pulsed electrolysis has also been demonstrated to improve the selectivity of CO₂ electrolysis on a Cu catalyst towards C₂₊ products, but the mechanisms behind this enhancement are poorly understood. In this talk, we discuss modeling methodologies for simulating the dynamic microenvironment in pulsed CO₂ electrolysis. Specifically, we develop a time-dependent continuum model of CO₂R on a Cu catalyst that replicates experimentally observed enhancements in selectivity. This work shows that pulsing results in dynamic changes in the pH and CO₂ concentration near the Cu surface due to mass transport within the boundary layer. Furthermore, the capacity to access a metastable state of increased pH, CO₂ concentration, and thermodynamic driving potential in pulsed electrolysis drives enhancements in the selectivity of C₂₊ products, as well as the total current density. Using these insights, a variety of pulse shapes are explored to establish operating conditions that maximize the rate of C₂₊ product formation and minimize the rates of H₂ and C₁ product formation.