Figure 3. The electrochemical performance and simulated local environment of H₂ase with and without CA co-immobilisation.

(a) Experimental and simulated partial current densities for H₂ production from controlled potential electrolysis with 20 pmol H₂ase immobilised on a mesoporous ITO electrode (H₂ quantified by online GC). 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 within the porous electrode from FEM at steady state at different applied potentials. For a-b lines represent simulated results from FEM, solid lines are with CA and dashed lines without. For N₂ purged MES the absence of HCO₃ ⁻ and CO₂ means the model results are identical with and without CA and as such are perfectly overlaid. (c) Effect of pH on activity. The solid black line represents the enzyme pH activity determined from solution assay ³² and the points are the average pH value from FEM within the porous electrode at −0.65 V vs SHE. Dashed vertical lines are the bulk solution pH. Solution conditions for a-c; Purple: CO₂ purged 0.1 M KHCO₃ + 0.05 M KCl (pH 6.67); Orange: CO₂ purged 0.05 M KHCO₃+ 0.05 M MES + 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. note: the simulated results for N₂ purged 0.132 M MES with and without CA (blue solid and dashed lines, respectively) are identical and directly overlaid.