Abstract
<jats:p> Mass transport can significantly affect electrocatalytic selectivity as surface-bound reaction intermediates are exchanged between the electrode and bulk electrolyte. The underlying desorption–re-adsorption–reaction mechanism allows an intermediate to escape the surface as a partially converted product or re-adsorb for continued conversion, but it is still not clear how the catalyst morphology affects this competition. Here, we focus on the role of the electrocatalyst surface morphology and its effective representation in transport-coupled kinetic models. Using CO selectivity during CO <jats:sub>2</jats:sub> reduction on copper as a model system, we compare predictions from a 1D diffusion model, where surface roughness serves as a single morphological descriptor, against a more advanced 3D diffusion model that explicitly resolves the full catalyst geometry. We analyze the results in terms of overlapping diffusion spheres between neighboring catalyst particles and find that the two models largely agree across the experimentally relevant parameter space due to a simple disparity in length scales. As diffusion occurs on a ∼µm scale, spatially resolved features of typical nm-sized catalyst particles are inconsequential. Surface roughness thus emerges as a surprisingly robust descriptor of electrocatalytic selectivity within the desorption–re-adsorption–reaction mechanism. </jats:p>