How Should Iron and Titanium be Combined in Oxides to Improve Photoelectrochemical Properties?

We discuss here for the first time how to combine iron and titanium metal ions to achieve a high photoelectrochemical activity for TiO2-based photoanodes in water splitting devices. To do so, a wide range of photoelectrode materials with tailored Ti/Fe ratio and element vicinity were synthesized by using the versatility of aqueous sol–gel chemistry in combination with a microwave-assisted crystallization process. At low ferric concentrations, single phase TiO2 anatase doped with various Fe amounts were prepared. Strikingly, at higher ferric concentrations, we observed the concomitant crystallization of two polymorphs of Fe2TiO5. The as-synthesized compounds were tested as photoelectrodes and compared with pure nanoparticles of TiO2, Fe2TiO5, and α- or γ-Fe2O3 and with corresponding nanocomposites. When TiO2 is slightly doped by Fe, the performance of this photoelectrode improves particularly in the low-bias region (