V vs SHE (Figure ), with a FE of 91 ± 5 and 96±6 % from 2 h experiments to produce sufficient product for quantification in the presence and absence of CA co-immobilization respectively. Exemplar CVs are also shown in Figure . In 1% CO2 purged pH 7 MOPS solutions, a larger increase in jformate of 3.1× from -16.3 ± 0.35 to -51 ± 7 µA cm -2 was observed upon CA co-immobilization, with FEs of 63 ± 2 and 74 ±5 % in the absence and presence of CA coimmobilization, respectively. In the absence of CA, the addition of MOPS reduces the pH increase within the electrode compared to NaHCO3 (pH 8.61 vs 7.15 and pH 8.65 vs 7.03 at -0.6 V vs SHE, bulk pH= 7.0). A slightly increased local pH was witnessed in the FEM when CA was immobilized (7.34 vs 7.15 and 7.10 vs 7.03 for 10 and 1% CO2 purged MOPS, respectively (Figure )). The depletion of CO2 within the porous electrode dominates the observed electrochemical response (Figure ) and the minimal increase in local pH has little effect on the enzyme activity (Figure ). The addition of CA promotes the conversion of HCO3 -and H + into CO2 to offset local substrate consumption in MOPS containing solutions, increasing the local [CO2], reducing the [HCO3 -] with only a small increase in the local pH (Figure ). This contrasts the activity of CA observed in solutions without MOPS in which the large local pH increase promoted the reverse reaction to liberate H + and consume CO2 to resist the pH change. The co-immobilization of CA results in significantly elevated local CO2 concentrations (1.03 vs 0.29 mM and 66 µM vs 18 µM at -0.6 V vs SHE for 10% and 1% bulk CO2, respectively (Figure )), causing a large improvement in the rate of enzymatic CO2R.