When the only buffer system in the electrolyte was CO2 and its conjugate base HCO3 -, which is inherently present when CO2 is purged into solution at neutral pH (eq. 1), CA co-immobilization at concentrations comparable to the natural carboxysome (~mM, 40 pmol loaded, Table ) had no significant effect on the enzymatic CO2R rate with negligible difference in reduction cur-rent densities from cyclic voltammetry (Figure ). Constant potential electrolysis was performed in triplicate for product quantification at each applied potential and formate quantified using ion chromatography to calculate FEs and average partial current densities (Figure ).