Photoelectrochemical behavior of titania nanotube array grown on nanocrystalline titanium

Surface nanocrystallization of titanium metal is processed by a high-energy shot peening treatment for drastic subdivision of bulk crystalline grains. Titania nanotube array directly grown on the nanocrystalline titanium substrate is achieved by a controlled anodization process. Field emission scanning electron microscopy, X-ray diffraction, and impedance spectroscopy analysis are conducted to investigate surface morphology, crystal phase, and electrical conductivity, respectively. The photoelectrochemical performance of the tailored titania nanotubes/titanium nanocrystallites has been investigated under UV light illumination. When the microstructure of the titanium substrate is modified from bulk crystals to nanocrystallites, the obtained titania nanotube array exhibits an independent structure with enlarged pore size and thinned tube wall, which is ascribed to the intensified anodic oxidation of ultrafine titanium crystallites along intergranular boundaries. Owing to the promoted interfacial electron transfer of the titania/nanocrystalline titanium, the complex impedance predominated by the charge transfer resistance has been significantly decreased in the electrochemical process. Both photocurrent and photovoltage responses have accordingly enhanced as well in the photoelectrochemical process.