Solar water splitting in a photoelectrochemical cell (PEC) is an attractive approach to generate hydrogen fuel from the abundant solar energy source in a benign and environmentally friendly manner. In this field, TiO₂ and Fe₂O₃ are some of the most extensively studied candidates for use as photoanodes. This is because they consist of naturally abundant elements and are photostable in a wide pH range. However, the major drawback of TiO₂ for water splitting is its wide bandgap (3.2 eV). Though Fe₂O₃ has a narrow bandgap (2.0–2.1 eV), its conduction band minimum (CBM) is still ~200 mV below the water reduction potential. Recently, Fe₂TiO₅, one of the Fe-Ti-O ternary oxide compounds, has received a considerable interest as a new candidate material to overcome the intrinsic limitations of TiO₂ and Fe₂O₃ while maintaining their strengths. That is, Fe₂TiO₅ has a favorable bandgap (2.1 eV), chemical robustness, and band edges that straddle the water oxidation and reduction potentials. These properties make Fe₂TiO₅ a promising photoanode candidate for solar water splitting.

In this presentation, we report a new electrochemical method to prepare a high quality Fe₂TiO₅ film to systematically investigate its photoelectrochemical properties. The synthesis is based on the interaction between metals and catechol where catechol acts as a chelating agent to solubilize metal ions in a plating solution. When the catechol ligands are removed by applying electrochemical bias, the resulting insoluble metal ions or metal-catechol complexes are deposited onto the FTO surface. Using this method, we deposit a film that contains atomically well mixed Fe and Ti, which are then converted to crystalline Fe₂TiO₅ after annealing at a moderate temperature. This method also allows facile doping of the Fe₂TiO₅ film, enabling us to investigate the effect of both bulk and surface composition tuning on its photoelectrochemical properties.