4.1 SAMPLES PREPARATION Ti-substituted Fe2O3 nanorod photoanodes were grown on F:SnO2 (FTO) substrates following a process in two steps. First, Ti-doped akaganeite (Ti:-FeOOH) films were elaborated by aqueous chemical growth (ACG) as detailed elsewhere. Second, the akaganeite phase was converted in hematite by 600°C annealing in air or in a furnace quartz tube in presence of N2 flow (3 l/h). The annealing ramp is presented in Figure . We used an aqueous solution with pH value of 1.4. The hydrothermal activation temperature during the growth was 95 °C and the deposition time of 24 h. These growth parameters allowed us to obtain brushlike nanorods, with nanorods perpendicularly oriented on the FTO substrate. Nanorods have typical 50 nm width and 200 nm length. Following this procedure, we obtained 9% average Ti substitution level, with increasing gradient from the FTO substrate toward the tip of the nanorods . For XPEEM and STXM measurements the samples were prepared collecting Ti-doped iron oxyhydroxide (FeOOH) powder from the flasks used for the ACG process and left several days at room temperature for dehydration. The FeOOH powder was then annealed at 600°C either in air or under N2 controlled flow conditions to obtain the hematite phase. Hematite powder was drop-casted using a solvent carrier of 1:1 isopropanol in ultra-pure water, either on gold-plated Si wafers for S-XPEEM or on location-tagged holey TEM SiN membranes, for STXM, spectro-ptychography, and STEM measurements. No signs of surface sample alteration were observed due to the use of isopropanol -water mixture carrier. Such alterations would have hindered especially the data recorded in XPEEM, strongly sensitive to surface topmost atomic layers. In addition, the PEC results are fully coherent with the XPEEM ones.