Representative Nyquist plots measured at 0.2 V vs. RHE (pre-onset) show that enzyme-coated electrodes exhibit larger semi-circles, indicative of the resistive nature of TiO2 at positive applied potentials and the absence of catalysis (Fig. ). Conversely, moving into the conductive TiO2 regime at -0.2 V vs RHE, two semi-circles were identified. The low frequency arc of bare IO-TiO2 electrodes displayed a linear response indicative of Warburg impedance (Fig. ), while its size diminishes upon the establishment of a faradaic current by adding H2ase or FDH, which further decreases in the presence of CA. In contrast, the high frequency arcs remain unchanged, indicating non-faradaic behaviours.