A final extremely important takeaway from Fig. is that the pH near the electrode will be inevitably high at commercially-viable current densities (>200 mA/cm 2 ) in all of the most commonly-used electrolytes, regardless of the choice of catalyst or electrolyte (Fig. ). Due to the extremely large quantity of hydroxide generated as a by-product of water reduction and limitations in transporting hydroxide away from the electrode, we predict the pH within the catalyst layer will greater than 12, even for a 1 M KHCO3 buffered electrolyte. While the use of a 0.1 M KHCO3 electrolyte can, and has, been used in an H-cell to approach the local pH values reached at high current densities (Fig. ), these conditions are reached only when CO2 is largely depleted and over a small current density/potential range. It is worth noting that the locally alkaline conditions could potentially be avoided by using an acidic electrolyte, but the reaction kinetics for CO2 would have to outweigh the heavily-favoured hydrogen evolution rate in acidic media. In any of these cases all changes in local pH will also ultimately have to be paid for in the overall cell potential, regardless of the locally corrected cathode potential. In brief, the results presented in Fig. show a convergence towards local conditions that have far-reaching implications for not only catalytic activity, but the stability and maximum efficiency of an entire CO2 reduction system, as discussed in later sections.