As CA consumes HCO3 -to increase local CO2 levels, the concentration of HCO3 -becomes important to the performance of the system due to its contribution to the total inorganic carbon pool. Since the bulk concentration of HCO3 -is intrinsically linked to the concentration of CO2 and pH, HCO3 -levels are low in solutions purged with dilute CO2 and are further depleted within the porous electrode when coupled to fast CO2 hydration kinetics serving to offset local substrate consumption. In pH 7 MOPS, FEM shows that CA significantly reduces the HCO3 -levels within the electrode at 1% CO2 (0.59 vs 1.91 mM at -0.6 V vs SHE; bulk [HCO3 -] = 1.96 mM) (Figure ). Since the predicted local HCO3 -concentrations in 1% CO2 experiments are much lower than the KM of CA for HCO3 -dehydration (8.3 mM), the consumption of HCO3 -within the electrode pores begins to limit CA's ability to replenish local CO2 concentrations during electrocatalysis. 43 As the concentration of dissolved CO2 is fixed by Henry's law and the [HCO3 -] is dependent on the pH equilibrium between CO2 and HCO3 -in solution (pKa: 6.28, Figure ), increasing the solution pH shifts the CO2/HCO3 -equilibrium by elevating dissolved HCO3 -levels while keeping dissolved CO2 concentrations relatively constant (Figure ). As a result, raising the solution pH increases the total dissolved carbon pool available for CO2R ~10× per pH unit when paired with fast CO2 hydration kinetics. This bulk increase gives higher local HCO3 -concentrations as a result of increasing the solution pH (Figure ). The increased local carbon concentrations at higher bulk pH values act to increase activity, but the associated local pH increase is detrimental to enzymatic CO2R (Fig. ).