Figure 4. The electrochemical performance and simulated local environment of FDh with and without CA co-immobilisation.

(a) Experimental and simulated partial current densities for HCOO⁻ quantified by ion chromatography from controlled potential electrolysis of 50 pmol FDh immobilised on a mesoporous ITO electrode. Points represent averages of at least three independent stepped-chronoamperometry experiments, where filled circles used co-immobilised CA (40 pmol) on the electrode surface and unfilled no CA. Error bars represent the standard deviation (b) Average pH and (c) CO₂ concentration within the mesoporous electrode from the FEM at steady state. For a-c lines represent simulated results from the FEM, with solid lines are with CA and dashed lines without. (d) Effect of CO₂ concentration on CO₂R activity. The line represents the enzyme Michaelis-Menten kinetics determined from solution assay (K_M = 0.420 mM) ¹⁷ and the points are the concentrations used in this work. e) Effect of pH on activity. The line represents the enzyme pH activity determined from solution assay ¹⁷ and the points are the average values from FEM within the mesoporous electrode for the system used. Dashed vertical lines are the bulk solution pH. Solution conditions; Purple: CO₂ purged 0.1 M KHCO₃ and 0.05 M KCl (pH 6.67); Orange: CO₂ purged 0.05 M KHCO₃, 0.05 M MES and 0.05 M KCl (pH 6.45); Blue: N₂ purged 0.132 M MES + 0.05 M KHCO₃ (pH 6.45). All experiments conducted at 20°C.