Enhanced Photocatalytic Performance Depending on Morphology of Bismuth Vanadate Thin Film Synthesized by Pulsed Laser Deposition

We have fabricated high quality bismuth vanadate (BiVO₄) polycrystalline thin films as photoanodes by pulsed laser deposition (PLD) without a postannealing process. The structure of the grown films is the photocatalytically active phase of scheelite-monoclinic BiVO₄ which was obtained by X-ray diffraction (XRD) analysis. The change of surface morphology for the BIVO₄ thin films depending on growth temperature during synthesis has been observed by scanning electron microscopy (SEM), and its influence on water splitting performance was investigated. The current density of the BiVO₄ film grown on a glass substrate covered with fluorine-doped tin oxide (FTO) at 230 °C was as high as 3.0 mA/cm² at 1.23 V versus the potential of the reversible hydrogen electrode (<i>V</i>_RHE) under AM 1.5G illumination, which is the highest value so far in previously reported BiVO₄ films grown by physical vapor deposition (PVD) methods. We expect that doping of transition metal or decoration of oxygen evolution catalyst (OEC) in our BiVO₄ film might further enhance the performance

Plasmonic Silver Nanoparticle-Impregnated Nanocomposite BiVO₄ Photoanode for Plasmon-Enhanced Photocatalytic Water Splitting

Herein, we developed a fully solution-deposited nanocomposite photoanode based on silver nanoparticle (NP)-impregnated bismuth vanadate (BiVO₄) films. The synthesized Ag NPs exhibit diameters of few nanometers and uniform matrix dispersion, which were confirmed by high-resolution transmission electron microscopy. The photoanode composed of the Ag NP-incorporated nanocomposite BiVO₄ showed a remarkable enhancement in both low potential and the saturated photocatalytic current densities in comparison with the pristine BiVO₄ film. The observed experimental results are attributed to the improved carrier generation and enhanced charge separation by the localized surface plasmon resonance-mediated effect as suggested by electrochemical impedance spectroscopy and a numerical simulation

Tailoring Crystallographic Orientations to Substantially Enhance Charge Separation Efficiency in Anisotropic BiVO₄ Photoanodes

In photoelectrochemical (PEC) water splitting, BiVO₄ is considered the most promising photoanode material among metal oxide semiconductors because of its relatively narrow optical bandgap and suitable band structure for water oxidation. Nevertheless, until now, the solar-to-hydrogen conversion efficiency of BiVO₄ has shown significant limitations for commercialization because of its poor charge transport. Various strategies, including the formation of a heterojunction and doping of electron donors, have been implemented to enhance the charge transport efficiency; however, fundamental approaches are required for further enhancement. In this regard, we report the fundamental approach for BiVO₄ thin film photoanodes by fabricating epitaxial oxide thin films with different crystallographic orientations for PEC water splitting. The crystalline anisotropy generally reveals distinct physical phenomena along different crystallographic orientations. In the same vein, in terms of the anisotropic properties of BiVO₄, the electrical conductivity of BiVO₄ is greater along the <i>ab</i>-plane than along the <i>c</i>-axis. Consequently, as the crystallographic orientation of the BiVO₄ thin film changes from (001) to (010), the charge transport properties in the epitaxial BiVO₄ thin film are significantly enhanced. Thus, at 1.23 V_RHE, the photocurrent density of the epitaxial BiVO₄ (010) thin film (2.29 mA cm^–2) is much higher than that of the epitaxial BiVO₄ (001) thin film (0.74 mA cm^–2) because of significant enhancement in charge transport properties even for undoped BiVO₄. These results strongly suggest that the growth of epitaxial BiVO₄ thin films with specific crystallographic orientations has great potential to considerably improve the charge transport efficiency of photoanodes for solar water splitting