increasing attention, especially in light of the urgent drive to upscale electrochemical process designs in recent years. We will focus here, however, on a considerably less studied effect of mass transport: the kinetic competition that arises from exchanging volatile reaction intermediates between the electrocatalyst surface and bulk electrolyte. This reaction model was first proposed by Behm et al. and coined the "desorption-re-adsorption-reaction" mechanism. Basis for the underlying mechanism is the desorption of a specific surface-bound and usually closed-shell reaction intermediate, whose subsequent fate creates a bifurcation in the reaction pathway: either to re-adsorb onto the surface toward full conversion, or to entirely diffuse away and thus be detected as an early partially-converted product. Electrocatalytic selectivity is thus driven by the competition between surface kinetics and diffusion.