The first important aspect of the build-up of counter-ions in the EDL at higher potentials is the accessibility of the catalyst surface for the CO 2 molecule. The rate at which CO 2 can diffuse to the catalyst surface, puts an upper limit to the activity that is achievable through catalysis and is therefore a critical parameter for CO 2 ER performance. The diminishing of CO 2 concentration in the EDL at high applied voltages (Figure ) is a direct consequence of the steric effect incorporated in the GMPNP model. Fig- ure 3 shows a comparison between the concentration profiles in the EDL obtained using a reaction-diffusion model, a PNP model which solves the migration, diffusion and reaction processes selfconsistently but assumes point species and a GMPNP model which corrects the PNP for steric effects. It is evident that inclusion of migration in the PNP and GMPNP models drastically influences the activity of charged species in the EDL region. The volume exclusion in the GMPNP model has important consequences for the extent of cation concentration at the OHP which, for the PNP model, reach unphysically high concentrations (significantly higher than the steric limit, Figure ). Despite a very high cation accumulation at the OHP for the PNP model, the assumption of point species results in no exclusion of CO 2 from the EDL region as is predicted by the GMPNP model (Figure ). This highlights the importance of considering volume-exclusion in mass transport models attempting to resolve the EDL in electrocatalytic systems such as CO 2 ER. According to Figure , the CO 2 concentration is completely depleted at potentials more cathodic than ∼-0.2 V vs PZC at the OHP. Since there is no experimental evidence suggesting that CO 2 reduction completely terminates at high applied potentials, the result in Figure leads us to the hypothesis that the CO molecule diffuses to the catalyst surface at high applied potentials due to many-body correlations in the presence of the solvated cations in the EDL region, albeit with a diminished dif- fusivity due the condensed nature of the EDL. Complex manybody correlations arising from the mutual interaction of chemical species (including water molecules) are expected to play a role especially in the EDL with a high concentration of counter-ions and the presence of competing electrostatic and van der Waals forces. In addition, the identity of the solvated cation should also have an influence on the rate of diffusion of CO 2 . Cations have been shown to influence the CO 2 reduction rate through numerous experimental as well as computational studies however, this influence has not been studied from the perspective of changing diffusion coefficient of the CO 2 molecule. The modeling results presented in this study use Fick's law of diffusion with constant values of diffusion coefficients for all species (Fick diffusivity values are tabulated in the SI). The EDL is however a multi-component non-dilute solution where considerable deviations from the Fick's diffusivities can be expected due to non-ideal behaviour. We are currently conducting force-field molecular dynamics (MD) simulations to study the diffusion of CO 2 in such an EDL environment. The effect of cation type will be discussed further in the context of Figure later in the text.