Coupling microkinetics with continuum transport models to understand electrochemical CO2 reduction in flow reactors

Abstract

We present a multiscale approach that couples ab-initio microkinetic simulations and two- dimensional (2D) continuum transport models to study electrochemical CO2 reduction to CO on Au electrodes in a flow reactor configuration. We find the key parameters including CO2 concentration, pH, the current density towards CO and the Tafel slopes to strongly depend on the applied poten- tial and position on the electrode. We find a rapid decrease in the CO2 concentration and current density towards CO as a function of electrode position. We further discuss two strategies to improve CO2 availability: increasing the shear/flow rate of CO2, and the introduction of a defect in between the electrode. In both cases, increased CO2 availability results in increased CO current density at the higher potentials. We find good agreement between a 1D continuum transport model with an effective boundary layer thickness corresponding to the shear rate used for the 2D simulations. Finally, we provide a phenomenological model that can be used instead of the microkinetic model to accelerate the multiscale simulations when extended to higher dimensions and more complicated reactor geometries.