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 potential 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 or 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.