Photoelectrochemical Water Splitting Using Dense and Aligned TiO2 Nanorod Arrays

Abstract

Dense and aligned TiO 2 nanorod arrays are fabricated using oblique‐angle deposition on indium tin oxide (ITO) conducting substrates. The TiO 2 nanorods are measured to be 800–1100 nm in length and 45–400 nm in width with an anatase crystal phase. Coverage of the ITO is extremely high with 25 × 10 6 mm−2 of the TiO 2 nanorods. The first use of these dense TiO 2 nanorod arrays as working electrodes in photoelectrochemical (PEC) cells used for the generation of hydrogen by water splitting is demonstrated. A number of experimental techniques including UV/Vis absorption spectroscopy, X‐ray diffraction, high‐resolution scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, and photoelectrochemistry are used to characterize their structural, optical, and electronic properties. Both UV/Vis and incident‐photon‐to‐current‐efficiency measurements show their photoresponse in the visible is limited but with a marked increase around ≈400 nm. Mott–Schottky measurements give a flat‐band potential (VFB) of +0.20 V, a carrier density of 4.5 × 10 17 cm−3, and a space‐charge layer of 99 nm. Overall water splitting is observed with an applied overpotential at 1.0 V (versus Ag/AgCl) with a photo‐to‐hydrogen efficiency of 0.1%. The results suggest that these dense and aligned one‐dimensional TiO 2 nanostructures are promising for hydrogen generation from water splitting based on PEC cells.