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 VO4
3− (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 resulted in higher BiVO4 content in electrodeposited films, whereas hydrolytic conversion of VO3
− to VO4
3− was promoted in basic electrolytes. Formation of Bi2O3 was also favored by the use of alkaline electrolytes (e.g., pH 10) for the electrodeposition. Photoelectrochemical experiments showed the electrosynthesized BiVO4 to be an n-type semiconductor, and reproducible photocurrents were obtained using a Na2SO4 supporting electrolyte.
The development of cost effective and high-performance electrocatalyst is challenging but essential for realizing industrial hydrogen production by electolyzer. Electrocatalysts for water splitting must have active catalytic performance as well as high stability in strong alkaline or acidic media to be used in commercial elecrolyzer. Transition metal based electrocatalysts are considered as highly promising candidates due to their excellent oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) performance and stability with low materials cost. Recently, binder free self-supported electrocatalysts based on transition metals have emerged as state-ofthe-art catalytic electrodes due to their high activity and robustness. These properties are attributed to lack of catalyst powder aggregation and a strong synergetic effect between the electrode surface and catalyst. In this mini review, recent development in self-supported electrocatalysts for OER, HER and also bifunctional OER & HER are reviewed in terms of superior activity and robust stability. Material design strategies, structural and compositional properties, and catalytic performance of recently reported self-supported electrocatalysts are summarized. Finally, overview of recent studies, challenges and prospects related to self-supported electrocatalysts are discussed.
This study focuses on the preparation of CdSe/ ZnO composite by combining three techniques, namely, electrodeposition, galvanic displacement, and photocathodic deposition. Thus ZnO nanowire array was first electrodeposited on Sn-doped indium oxide (ITO) or polycrystalline Au electrode; then, the metallic zinc codeposited with ZnO was galvanically replaced with Se from a Se 4+ containing aqueous solution, which resulted in a Se/ZnO composite nanowire array. Finally, the Se component in Se/ZnO was photoelectrochemically reduced to Se 2− by irradiation. The Se species reacted with Cd 2+ in the electrolyte phase to produce CdSe/ZnO composite in situ. The deposition details were elucidated in situ by a combination of stripping voltammetry and electrochemical quartz crystal microgravimetry. The composite sample was subsequently characterized by scanning electron microscopy, X-ray powder diffraction, energy-dispersive X-ray analyses, and photoelectrochemical (PEC) measurements. The PEC experiments revealed that the electrodeposited ZnO nanowire array behaved as an n-type semiconductor, which changed to p-type after deposition of Se. The ZnO/CdSe composite showed anodic photocurrents upon light illumination, again consistent with the n-type nature of both the composite components.
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