Coupling Microkinetics with Continuum Transport Models to Understand Electrochemical CO_{2} 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 CO_{2} reduction to CO on Au electrodes in a flow reactor configuration. We find the key parameters, including CO_{2} 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 CO_{2} concentration and current density towards CO as a function of electrode position. We further discuss two strategies to improve CO_{2} availability: increasing the shear or flow rate of CO_{2} and the introduction of a defect in between the electrode. In both cases, increased CO_{2} 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.