Epitaxial Anatase TiO2Nanorods Array with Reduced Interfacial Charge Recombination for Solar Water Splitting

We report an epitaxial growth of anatase TiO2 nanorods array (ANRs) on a niobium-doped TiO2 (NTO)/SrTiO3 (STO) single crystal substrate and its impact on charge transport and collection properties for photoelectrochemical (PEC) water splitting. The NTO film (∼6 at.% of Nb) with a thickness of ∼250 nm, was initially deposited as a transparent conducting electrode on a STO single crystal substrate by pulsed laser deposition. Subsequently, the anatase TiO2 nanorods array, with an average length of ∼200 nm, was grown on the NTO/STO substrate by a two-step hydrothermal method. Epitaxial relationship between the TiO2 nanorods and the substrate was investigated by X-ray diffraction and transmission electron microscopic analysis. From impedance spectroscopy measurements, we found that the resistance of the ANRs is much lower than that of anatase TiO2 nanoparticle-based films, which originates from the single crystalline nature of the ANRs and lower interfacial resistance due to epitaxial growth. For PEC water splitting, the lower bulk and interfacial resistance of the ANRs facilitates better charge transport and collection, thereby improving the photocurrent density and rate of hydrogen evolution.