Coupling Microkinetics with Continuum Transport Models to Understand CO2R on Planar and Optimized Patterned Electrodes

Electrochemical CO 2 reduction has emerged as an attractive technique to sustainably produce valuable fuels and chemicals, while reducing CO 2 emissions. In addition to the specific electrode material, the microenvironment local to the electrode interface – e.g., the electrolyte pH, CO 2 concentration, buffer concentration – plays a significant role in determining the selectivity and activity of the electrolyzer. In this work, we demonstrate a multi-scale approach, where microkinetic simulations of Au are coupled to a two-dimensional continuum transport model in a flow reactor configuration. Specifically, concentrations and potentials solved for in the continuum model are fed into microkinetic models along the planar electrode surface, which return concentration fluxes that are used to update the continuum model. We find that local quantities at the electrode interface, such as the CO 2 concentration and pH, vary not only with the applied potential and flow rate, but also with position on the electrode. We investigate two ways to increase CO 2 availability at the interface: (1) increasing the applied flow rate, thus reducing the boundary layer thickness, and (2) introducing an inert defect in the middle of the electrode, allowing CO 2 to partially replenish within the depletion boundary layer. Inspired by the effect of a single inert defect, we explore electrodes patterned with inert defects and multiple catalyst materials, i.e. a generalized tandem system. We show how the specific pattern of the electrode can be optimized in order to target a specific desired product. The different parts of the electrode have different goals that work together: converting CO 2 to CO, converting CO to C 2+ products, and allowing concentrations to replenish through the boundary layer. Overall, our aim is to demonstrate the need for multi-dimensional, multi-scale approaches to simulating CO 2 reduction to elucidate the reaction environment near the electrode. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL release number: LLNL-ABS-857537.