BiVO4 Thin Films Research Articles

Deposition and characterization of BiVO4 thin films and evaluation as photoanodes for methylene blue degradation

Thin films of bismuth vanadate (BiVO4) are deposited through the solution combustion synthesis technique coupled with the dip-coating process. Thermal gravimetric analyis shows a total mass loss of 71 % besides the formation of the monoclinic phase, about 300 °C, which is also revealed by X-ray diffraction. UV–Vis optical absorption spectra show direct bandgap transition about 2.5 eV for films, in good agreement with semiconducting monoclinic phase. Scanning electron microscopic images reveal that thermal annealing time at 500 °C is a very important parameter to control the thickness and shape of the particles and yields an average thickness of about 800 nm for 10 dip-coated deposited layers, with round-shaped nanometric-sized particles, homogeneously distributed on the film surface. Photoelectrochemical degradation of methylene blue by a bismuth vanadate film deposited on fluor-doped tin oxide substrate shows up as a very efficient process. The first-order rate constant for the photoinduced process is about five times the rate constant for degradation in the dark, showing the capacity of the BiVO4/fluorine-doped tin oxide film for electrochemical degradation, mainly in the presence of light.

Tailoring Interfaces for Electrochemical Synthesis of Semiconductor Films: BiVO4, Bi2O3, or Composites

The mechanistic aspects of a two-step method for the electrodeposition of a BiVO4 semiconductor (previously developed in the Rajeshwar/Tacconi laboratory) were elaborated by the combined application of voltammetry and EQCM. The electrosynthesized films were also characterized ex situ using SEM, EDX, XRD, and XPS. Stripping of pre-electrodeposited bismuth films, followed by reaction either with VO43− (formed by hydrolysis from the initially added VO3− species) or with hydroxide ions, produced BiVO4 or Bi2O3 thin films in situ on the Pt electrode. The deposition potential, pH of the electrolyte, and choice of vanadium precursor were shown to be crucial variables in the composition of the electrodeposited film. When a more positive potential than 0.5 V (vs Ag/AgCl reference) was applied to the Bi-modified electrode in VO3−-containing electrolyte, the content of Bi2O3 in the film increased instead of BiVO4. Stripping efficiency of the predeposited bismuth layer was increased at acidic electrolytes and resulte...

Aqueous Growth of Pyramidal-Shaped BiVO4 Nanowire Arrays and Structural Characterization: Application to Photoelectrochemical Water Splitting

BiVO4 thin films comprised of ordered arrays of pyramidal-shaped nanowires vertically oriented to a fluorine doped tin oxide coated glass substrate have been successfully fabricated by seed-mediated growth in an aqueous BiVO4 suspension. The effect of the growth temperature, 40 to 95 °C, pH, stirring and reaction time on the resulting BiVO4 film morphology was investigated using X-ray diffraction, scanning electron microscopy, and transmission electron microscopy with a growth mechanism proposed. We consider the effects of film morphology in application to photoelectrochemical water splitting.

Structural and Photoelectrochemical Properties of BiVO4 Thin Films

Monoclinic scheelite BiVO4 thin films have been successfully prepared by a chemical solution approach of polymer-assisted deposition. The films are transparent yellow with granular morphology and show a strong absorption in the visible light region. The band gap of BiVO4 films is estimated to be 2.54 eV. The photoresponse of the films on conducting oxide electrode substrates is observed, and the photocurrent increases with the higher energy absorption bands.