Figure shows the potential and concentration profiles in the EDL region calculated using the GMPNP model for a fixed total current density of 1 mA/cm 2 with a Faradaic efficiency of CO of 0.8. The boundary condition for the potential at the OHP is varied to demonstrate the build-up of potassium ions in the EDL with increasing potential. As discussed previously, all voltage values are referenced against φ σ =0 and are thus given in V vs PZC. The concentration of K + cations increases till the steric limit a -3 K+ , where a K+ is the effective size of the solvated K + ion (Figure ). Once this steric limit is reached, the EDL profile grows in thickness away from the OHP with a constant density of counter-ions (cations in this case). Therefore, at higher voltages relative to φ T , the nature of the EDL can no longer be described as a diffuselayer, but rather, it assumes the form of a condensed layer of counter-ions which builds in thickness with applied potential . We will discuss our results in the context of the impact of the condensed double layer on CO 2 transport in section 3.1 and the pH in section 3.2. Section 3.3 discusses the impact of changing the alkali metal type in the electrolyte on the nature of the EDL.