Quasi-core-shell TiO2/WO3 and WO3/TiO2nanorod arrays fabricated by glancing angle deposition for solar water splitting

Abstract

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 λ ≤ 400 nm, while the WO₃-core/TiO₂-shell structures show stronger visible light absorption and photocurrent out to λ ∼ 600 nm. Mott-Schottky measurements give a flat-band potential of −0.28 V, a carrier density of 1.47 × 10²⁰ 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.