From the linear fits in Figure , we estimate the flat band values, 𝑉 𝑓𝑏 , of 0.1 V and 0.8 V and carrier concentrations, 𝑁 𝑑 , of 4.210 and 5.410 for S1 and S2, respectively. We recall that these values are obtained using a simple linear fit analysis without any consideration about nanorods dimensions (width, length) or density (as number of nanorods / cm 2 ). However, their relative variation is relevant here to compare the electric properties of S1 and S2 samples. It is known that the presence of surfaces states at the semiconductor/electrolyte interface results in the Fermi level pinning, and, in this case, the Mott-Schottky plot presents a plateau (or double kink) where the 𝐶(𝑉) is (quasi-)constant. In this region, the applied voltage drops within the Helmholtz layer instead the depletion region in the semiconductor. This flat region can be observed indeed in the case of the S1 sample for voltages between 1.4 and 1.5 V (marked region in Figure ). To the contrary, nothing is visible for the S2 photoanode. As shown in previous studies two kind of surface states may co-exist at the interface between the hematite-based photoanode and the electrolyte, one at higher oxidative energies, lying at the bottom of the conduction band and a second at lower energies. While the first kind is beneficial for the PEC process, the second plays a detrimental role as being inactive from the PEC point of view, driving recombination of charges at the interface. In the present case, we identify the first kind (i.e. beneficial, at higher oxidative energy) of surface states leading to lower flat band value for the S1 sample. This determines higher band bending at the interface with the electrolyte (Figure ), and, consequently, better charge a)