A mean-field microkinetic model of the catalytic surface reaction predicts J surf by breaking the process down to a series of consecutive elementary reaction steps, deriving a rate expression for each, and solving the resulting set of ordinary differential equations. Near-surface concentrations and turnover frequencies predicted in this way subsequently serve as boundary conditions when coupling to mass transport. While there are many excellent reviews on recent mkm developments , it is clear that the overall approach hinges upon the reliability of the assumed reaction mechanism and input kinetic parameters. The huge benefit, but also cost, of a 1p-mkm is its predictive quality through explicitly calculated reaction energies and barriers at an ab initio level. Such calculations are nowadays becoming increasingly tractable within density functional theory (DFT), at least within small simulation cells and simple solvation models. Including a more advanced description of the electrolyte as well as the effect of applied potential at the solid/liquid interface, however, represent the forefront in the field. The vast majority of studies currently still include U only at the level of thermodynamic reservoirs via the so-called computational hydrogen electrode while relying on BEP scaling relations, vanishingly small or fitted barriers for the reaction kinetics . Possibly more critical, however, is the almost standard approximation of a 1D transport-coupled model that assumes uniform concentration profiles regardless of the catalyst's 2D or 3D morphology. The selectivity is measured against further reduced carbon-coupled products and plotted as a function of applied potential U. Key here is the kinetic competition between the surface-and solution-reaction of a ketene (Kt) intermediate to form acetate (Ac -), as illustrated in the figure's inset. This competition is resolved via a diffusion-coupled 1p-mkm, predicting a complex "U-shaped" selectivity profile with U that shifts with pH and catalyst roughness (ρ). Adapted from the study by Heenen et al. .