One such issue pertains to the twist of fate that the most efficient CO2 reduction conditions appear to occur when a highly-alkaline electrolyte is used as a catholyte. While an alkaline catholyte may provide optimal cathode performance, it comes at the cost of system stability due to the interaction between unreacted CO2 and hydroxide in the electrolyte, particularly at current densities less than the CO2 limiting case where higher concentrations of CO2 exist in solution. Our reaction-diffusion model shows that this interaction can decrease the pH within the porous catalyst layer by 1-2 units at lower current densities depending on the replenishment rate from a bulk liquid phase (Fig. ). While this pH change can be accounted for when trying to ascertain the intrinsic activity of the catalyst, a portion of the CO2 crossing the gas-liquid interface will be converted to bicarbonate upon interacting with hydroxide and then carbonate. Not only does this decrease CO2 utilization, but over a long enough operating time it will destroy the expensive KOH catholyte, itself energy-intensively produced through electrochemical reactions. At the moment there is no engineering solution to completely mitigate this effect even at small scales, let alone a more complex >100 cm 2 reactor design. We may then be resigned to the use of neutral-pH catholytes which to date would represent an increase in expected cathode overpotentials. Further, overall cell potentials will be higher due to the need for the oxygen evolution reaction to occur in a similar pH electrolyte, or by using a bipolar membrane to maintain an alkaline anolyte. While CO2hydroxide interactions are typically only considered as a critical issue for alkaline catholytes such as KOH, systems using neutral electrolytes should also aim to balance the generated hydroxide ions with protons generated by the anode reaction. Even in a neutral-pH medium the system's electrolyte balance would similarly be steadily shifted away from the initial condition due our CO2 reagent that can influence pH; in this case, however, the electrolyte could be externally regenerated without additional energy input.