The efficiency of phenomenological surface kinetics is most usually paired with a more elaborate transport model, either in the underlying transport equations themselves, considered electrode geometry, or both. While early such models focused mainly on planar electrodes , the approach has since been extended to include also, e.g., macroscale so-called "volume averaged" simulations as well as the simulations of pores . We specifically highlight in Figure two recent studies on GDEs . These examples nicely demonstrate how elaborate transport models, coupled to BV surface kinetics, can predict complex concentration profiles in the diffusion layer; both as a function of electrolyte composition and electrode geometry. Such fundamental insight into transport processes within a GDE is key to its future design and optimization . Upon developing an elaborate 2D model for ion migration, Butt et al. investigated the influence of electrolyte composition on the local reaction environment within a GDE catalyst nanopore. Figure ) shows simulated concentration profiles for the reactant CO 2 as a function of its distance from the catalyst surface at different KHCO 3 buffer concentrations. Increasing K + concentration predicts lower CO 2 solubility (modeled here through a 'Sechenov-corrected' Henry's constant ), but also induces steric hindrance at the electric double layer due to ion crowding. Together these two effects limit the CO 2 that can reach the surface and react, thus affecting catalytic performance.