Electrodes immobilised with H2ase demonstrate distinct behaviours between Rct and Re as a function of applied potential (Fig. ). The potential-and enzyme-independent Rct suggests that the resistivity of the electrical double layer is determined by the bare IO-TiO2 electrode and is decoupled from the faradaic process. Upon the introduction of CA, a significant decrease in Re is observed, consistent with PFV traces in Fig. . Regarding capacitance, Ce exhibits enzyme-independent behaviour and increases with cathodic potential, consistent with reported observations for TiO2-based electrodes (Fig. ) . The value of Cdl depends on the electrode area and local ion concentrations.