Quasi-core-shell TiO2/WO3 and WO3/TiO2 nanorod arrays fabricated by glancing angle deposition for solar water splitting

Unique quasi-core-shell nanorod arrays of TiO2/WO3 and WO3/TiO2 are fabricated on indium tin oxide coated glass substrates by dynamic shadowing growth using glancing angle deposition. The resulting heterostructures are characterized by X-Ray diffraction, UV-vis absorption spectroscopy, scanning electron microscopy, and photoelectrochemical measurements. The incident-photon-to-current-efficiency and absorbance measurements show that the TiO2-core/WO3-shell structures have a distinct photoresponse in the UV range, with wavelength lambda <= 400 nm, while the WO3-core/TiO2-shell structures show stronger visible light absorption and photocurrent out to lambda similar to 600 nm. Mott-Schottky measurements give a flat-band potential of -0.28 V, a carrier density of 1.47 x 10(20) cm(-3), and a space charge layer of 100 nm for the WO3-core/TiO2-shell samples. These results suggest that the quasi-core-shell nanorods preserves the optical properties and water splitting performance of the core while the surface properties such as the flat band potential of the nanorods are modified by the shell. This approach affords a simple and powerful method for designing nanostructures with improved photoelectrochemical properties.