Photoelectrochemical and water photoelectrolysis properties of ordered TiO2nanotubes fabricated by Tianodization in fluoride-free HCl electrolytes

Abstract

Described is the synthesis of TiO₂ nanotube array films by anodization of Ti foil in HCl electrolytes containing different H₂O₂ concentrations. Highly ordered nanotube arrays up to 860 nm in length, 15 nm inner pore diameter, and 10 nm wall thickness were obtained for one hour anodizations using a 0.5 M HCl aqueous electrolyte containing 0.1–0.5 M H₂O₂ concentrations for anodization potentials between 10–23 V. The use of ethylene glycol as the electrolyte medium significantly alters the anodization kinetics and resulting film morphologies; nanotube bundles several microns in length achieved for anodization potentials between 8 V and 18 V in only a few minutes. The nanotube arrays obtained from the ethylene glycol electrolytes show relatively higher photocurrents, ≈0.8 mA cm⁻² under AM 1.5. Under 100 mW cm⁻² AM 1.5 illumination a 500 °C annealed 1 cm² nanotube array sample, obtained by anodization of a Ti foil sample in ethylene glycol + 0.5 M HCl + 0.4 M H₂O₂ electrolyte, demonstrates a hydrogen evolution rate of approximately 391 μL h⁻¹ by water photoelectrolysis, time-power normalized evolution rate of 3.9 mL W⁻¹ h⁻¹, with water splitting confirmed by the 2 : 1 ratio of evolved hydrogen to oxygen.