The Nyquist representation plots the imaginary part, |𝑍 𝑖𝑚𝑔 |, as a function of the real part, 𝑍 𝑟𝑒 . Figure presents the Nyquist plots for the S1 and S2 photoanodes, for several voltages (𝑉) between 0.7 V and 1.6 V vs. RHE, and for different frequencies (𝑓) between 10 Hz and 900 kHz. On each plot we distinguish two regions: a) high frequency region (from 3 to 900 kHz) corresponding to a semicircle characterizing the internal resistance and RC-like semiconductor impedance, and b) low frequency region (from 10 Hz to 3 kHz) -characterizing both the Helmholtz layer formation in the electrolyte near the interface with the photoanode and ion diffusion through the Helmholtz layer. First, we observe reduced impedance values for S1 compared to S2. This result reflects a better overall bulk conduction in the first case, due most probably to oxygen vacancies. Indeed, considering that the Ti doping is similar between the S1 and S2 samples, the conduction difference could be explained by oxygen vacancies produced by the annealing under Nitrogen.