For the electrolyte, two zwitterionic Good's buffers were selected for this study: 2-(Nmorpholino)ethanesulfonic acid (MES) (pKa = 6.27) and 3-(N-morpholino)-propanesulfonic acid (MOPS) (pKa = 7.18) (Figure ). These buffers were chosen due to their similar chemical composition to ensure that any changes in enzyme productivity could be attributed to the different pKa as opposed to physical or chemical interactions with the electrode or enzyme. These buffers are also known to not coordinate with the main metals present in enzymes and reference electrodes. The effect of the specific buffer concentration on the enzyme activity was measured for this study and the results presented in the Supporting Information, Enzyme Current Density, and the buffer concentration has been kept below inhibitory levels throughout this study. The electrolyte solution for the CO2RR also contains CO2 and its pH-dependent equilibrium with carbonic acid (H2CO3), bicarbonate (HCO 3 & ) and carbonate (CO 3 2& ), which has been further discussed in the Supporting Information, Equilibria.