The strategies employed by cyanobacteria to optimize carbon fixation can be used to develop effective systems for CO2 utilization from low to atmospheric CO2 concentrations. The coimmobilization of CA with FDh at concentrations comparable to the natural carboxysome allows the fast interconversion of HCO3 -and CO2, following the pH equilibrium. Without additional buffers, CA does not improve the CO2R activity as its presence leads to a lower local pH that increases the FDh activity but is directly counteracted by the decrease in local CO2 concentration that reduces the activity as the concentration drops below the Km. Additional buffers such as MOPS are required to mitigate changes in local pH and prevent the increase in local pH that drives the HCO3 -/CO2 equilibrium towards HCO3 -. CA improved the current density when MOPS was added to the solution, with a greater current density increase as the bulk CO2 concentration decreased. This was due to an increased local CO2 concentration, as HCO3 -can act to replenish depleted CO2 without large local pH changes. By raising the bulk pH, the amount of dissolved inorganic carbon is increased, leading to increases in CO2R and demonstrating an ap-proach that can be used to mimic the carboxysome for atmospheric concentration CO2R. At atmospheric CO2 concentrations, CA co-immobilization at an optimal pH of 7.75 allowed quantifiable formate production of 0.69 ± 0.04 µmol cm -2 for direct CO2R without preconcentration at atmospheric concentrations. In this designed bioelectrochemical system, the co-immobilization of CA and FDh within mesoporous electrodes mimics the nanoconfinement of CA and RuBisCO within the carboxysome's protein shell, and the alkaline pH mimics the cyanobacterial cytosol.