Development of novel photocatalysts for solar hydrogen production

• Main Author: Morton, Craig D.
• Other Authors: Alexander, Bruce ; Coutroubis, Alexander
• Published: University of Greenwich 2012
• Subjects: 500; QC Physics
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.571435

Photocatalysts, typically nanoparticulate semiconductors, can be used to split water into hydrogen and oxygen. If solar light is used for this, it opens the possibility of a renewable source of hydrogen. However, extension of photocatalytic response into the visible region of the solar spectrum is required. A new visible light activated photocatalyst is reported herein. Iron vanadate, FeVO4, was first synthesised using a low-temperature, aqueous precipitation reaction. The material prepared was found to be predominantly amorphous and required thermal treatment. The resultant material was characterised using XRD, SEM, IR spectroscopy, Raman spectroscopy and magnetic susceptibility measurements. Materials annealed above 600 °C were found to consist mainly of FeVO4, although traces of hematite were found. Diffuse-reflectance UV spectroscopy and subsequent Tauc plots revealed a band gap of ca. 2.00 eV corresponding to an indirect transition. Photocurrent-voltage characteristics recorded under simulated solar illumination indicate that photocurrents are sensitive to annealing temperature and the thickness of the deposit. However, although photocurrent-voltage plots show that electrodes prepared from a suspension of nanoparticulate FeVO4 powders were photo-responsive, these electrodes were found to be mechanically unstable. Films were prepared directly onto the electrode by using a sol-gel approach. Raman spectroscopy, XRD and diffuse-reflectance UV-visible spectroscopy has revealed the electrode films to be crystalline in nature, significantly more stable, with an indirect band gap in the visible region of 2.00 eV. Higher photocurrent densities were observed for the sol-gel prepared electrodes compared to those deposited from aqueous suspensions of pre-formed powders. It was determined that these photocurrents were dependant on film thickness, annealing time and temperature, and sol pH.