Photocatalytic water oxidation at bismuth vanadate thin film electrodes grown by direct liquid injection chemical vapor deposition method

Abstract

Photoelectrochemical cells (PECs) are devices that can harvest and convert solar energy to produce consumable fuel, e.g. by splitting water into oxygen and hydrogen. Photocatalytic semiconductor materials play a major role in PECs, and their overall efficiency is usually limited by short carrier diffusion length because of structural defects, poor light absorptivity, and sluggish kinetics of photoelectrochemical reactions at the semiconductor electrode. Synthesis of high quality defect-free semiconductor materials using high temperature deposition techniques generally yield films with good adhesion to substrates while improving charge carrier transport and hence the overall efficiency of a PEC. A direct liquid injection chemical vapor deposition (DLI-CVD) technique has been utilized to synthesize monoclinic clinobisvanite phase bismuth vanadate (BiVO4) films for photocatalytic water oxidation. The technique yields dense high quality epitaxial and polycrystalline BiVO4 films on Yttria stabilized zirconia (YSZ) and Fluorine doped tin oxide (FTO) substrates, respectively, at growth temperature in the range of 500–550 °C. The photoelectrochemical characteristics of the films grown on FTO have been studied and a photocurrent value of 2.1 mA/cm2 at 1.23 V vs Normal hydrogen electrode (NHE) (0.5 V vs. Ag/AgCl), with onset potential values as low as 0.23 V vs. NHE (−0.5 V vs. Ag/AgCl), are obtained despite the low porosity of the films. The PEC performance is further improved by synthesizing BiVO4 directly on top of a tungsten oxide interlayer and modifying its surface with FeOOH co-catalyst.