Experimental 𝑍(𝑓) spectra were fitted using the equivalent circuit (𝑅1||𝑄1) -(𝑅2||𝑄2) -𝑅3 shown in Figure . 𝑅1 (𝑅2) and 𝑄1 (𝑄2) are the resistances (𝑅𝑖 ) and the constant-phase-elements (CPE, 𝑄𝑖 ) associated to the semiconductor photoanode (Helmholtz layer). As detailed in Supporting Information, the values of the capacitance, 𝐶, associated with the space charge layer in the semiconducting photoanode in contact with the electrolyte, can be calculated with Equation S4, using 𝑄𝑖 and 𝑁 𝑖 parameters extracted from the fit (Figure ). Mott-Schottky plots, expressing 1 𝐶 2 ⁄ as a function of the voltage obtained at 900 kHz for both photoanodes, are presented in Figure . It is important to mention here that Mott-Schottky plots obtained for all frequencies in the interval 10 Hz -900 kHz are similar. 𝐶(𝑓) slopes for multiple potential values are quasi-parallel, particularly for applied potentials between 1.1 and 1.4 V (Figure ). The simplest model used to fit Mott-Schottky plots supposes a linear variation with the voltage of 1 𝐶 2 ⁄ . In reality, this linearity depends on several parameters: the semiconductor state (accumulation, depletion or inversion), the presence of surface states, the size of the surface features on the photoanode, pH value of the electrolyte, donor levels in the semiconductor, crystallographic structure of the material, etc. For a comparative analysis between the S1 and S2 samples we consider that for potentials between 1.1 and 1.4