Facile growth of aligned WO3nanorods on FTO substrate for enhanced photoanodic water oxidation activity

Abstract

We demonstrate a facile hydrothermal method to grow oriented WO₃ nanorods on a transparent conductive substrate without the assistance of any seed layer or structure directing agent for photocatalytic applications. The effects of hydrothermal growth conditions such as reaction time, precursor solution, and post annealing temperature on the crystalline phase and morphology of the WO₃ on the FTO substrate are discussed. XRD studies reveal that the as-prepared orthorhombic WO₃·0.33H₂O nanorods are transformed to the hexagonal phase by post annealing at 400 °C. Moreover, post annealing above 500 °C converts them to monoclinic WO₃ nanorods on the FTO substrate, which is the photoactive crystal phase of WO₃ for water oxidation. The synthesized WO₃ nanorods were revealed to have a single crystalline structure by HRTEM analysis. The photoelectrochemical water splitting properties of the annealed WO₃ nanorod arrays were investigated in 0.5 M Na₂SO₄ under AM 1.5G illumination. The optimized WO₃ nanorod arrays exhibit a photocurrent of 2.26 mA cm⁻² at 1.23 V (versus RHE), and an incident photon-to-current conversion efficiency (IPCE) of as high as 35% at 400 nm for the photoelectrochemical oxidation of water. This simple hydrothermal method can allow the use of WO₃ for photoanodic applications with high efficiency.