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.

Understanding dynamic mass transport effects in pulsed CO2 electrolysis

ACS Spring Meeting 2021

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