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 BiVO 4 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 VO 4 3− (formed by hydrolysis from the initially added VO 3 − species) or with hydroxide ions, produced BiVO 4 or Bi 2 O 3 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 VO 3 − -containing electrolyte, the content of Bi 2 O 3 in the film increased instead of BiVO 4 . Stripping efficiency of the predeposited bismuth layer was increased at acidic electrolytes and resulted in higher BiVO 4 content in electrodeposited films, whereas hydrolytic conversion of VO 3 − to VO 4 3− was promoted in basic electrolytes. Formation of Bi 2 O 3 was also favored by the use of alkaline electrolytes (e.g., pH 10) for the electrodeposition. Photoelectrochemical experiments showed the electrosynthesized BiVO 4 to be an n-type semiconductor, and reproducible photocurrents were obtained using a Na 2 SO 4 supporting electrolyte.