Interaction of Mass Transport and Reaction Kinetics during Electrocatalytic CO Oxidation in a Thin-Layer Flow Cell

The interplay between electrocatalytic CO oxidation kinetics and mass transport in a thin-layer flow cell with a polycrystalline platinum electrode was experimentally studied and numerically simulated. The experiments were performed in a flow cell under controlled electrolyte flow. The computations are based on four different models for mass transport, coupled with a three-step reaction mechanism for CO oxidation that includes surface coverage effects. A zero-dimensional model neglecting mass transport effects on the overall reaction rate is applied to verify the effect of the kinetic parameters on the Faradaic current qualitatively. Transport models of increasing complexity, one-, two-, and three-dimensional, are used to analyze the impact of diffusion and convection on the total reaction rate in the flow cell. The numerical simulation, based on a time-resolved three-dimensional transport model coupled with the electrocatalytic kinetics, resolves profiles of temporal and spatial concentrations, velocities, and surface coverages. Mass transfer limitations of the electrocatalytic reaction rate are primarily caused by CO diffusion normal to the electrode. Both the two- and the three-dimensional models can quantitatively predict the Faradaic current as a function of potential measured in the experimental setup.