New Electrochemical Synthesis of Fe2TiO5 Photoanode from Metal-Catechol Complexes

Abstract

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.