Preparation of Tungsten Oxide Film and Its Applications

The researchers found that the thickness and content of the tungsten oxide film were found to vary depending on the concentration of the PAA coating solution (1.0-3.0 wt%), and thus the electrode performance of the PAA/WO₃ layer could be easily controlled. The special applications for WO₃ films include photoelectrochemical and electrochromic devices. Clara Santato et al. used a novel sol-gel method to prepare mesoporous tungsten trioxide nanocrystals consisting of preferentially oriented monoclinic phase semiconductor films.

(Credit: Dilek Evecan and Esra Zayim/Current Applied Physics)

The shape and size of WO₃ nanoparticles, porosity and properties of the films depend mainly on the preparation parameters such as tungstate/PEG ratio, PEG chain length and annealing conditions. Well-crystallized WO₃ films have a good photoresponse to the blue region of the solar spectrum (up to 500 nm) and good transparency at wavelengths greater than 550 nm.

Special applications of these nanocrystalline WO₃ films include photoelectrochemical and electrochromic devices. Jinmin Wang et al. reported the synthesis of uniformly crystalline WO₃ nanorods and their assembly without any surfactant. The WO₃ nanorods were synthesized by a simple hydrothermal method without the use of lithium ions and sulfates.

The obtained WO₃ nanorod films were reported to exhibit high electrochromic stability with comparable color display, contrast and coloring/bleaching response. The photoluminescent behavior of BaWO₄ powders treated in microwave-hydrothermal was observed by L.S. Cavalcantea et al. The obtained WO₃ nanorod films were reported to exhibit high electrochromic stability with comparable color display, contrast and coloring/bleaching response.

(Credit: Dilek Evecan and Esra Zayim/Current Applied Physics)

This work opens a new way to prepare mesoporous tungsten oxide film using tungstate precursors with many advantages such as low cost, easy handling, and insensitivity to moisture. Jang-Hoon Ha et al. synthesized one-dimensional (1D) self-assembled single-crystal hexagonal tungsten oxide (h-WO₃) nanostructures using sodium tungstate, ethylenediaminetetraacetic acid (EDTA) sodium salt or ammonium salt, and sodium sulfate by hydrothermal method at 1800 °C. nanostructures. The synthesis of 1D self-assembled h-WO₃ nanowire bundles and sea urchin-like structures was distinguished by Na⁺- and NH⁴⁺- based EDTA salt solutions.

Deepa et al. showed that the structure of surface aggregates was controlled electrochemically; the grain microstructure was optimized and mesoporous films of tungsten oxide were produced at the electrode-electrolyte interface in the presence of a structure-directing agent (Triton) in tungsten peroxide sol at room temperature.

Porous films are expected to be used to build a new ECD with better electrochromato-graphic performance than the common ECD consisting of the corresponding nonporous films. Deepa et al. investigated the effect of polyethylene glycol templates on the microstructure and electrochromato-graphic performance of tungsten oxide. The electrochemical synthesis of WO₃ thin film nanostructures in the presence of a polymeric template (polyethylene glycol 400) in an electroplated sol of peroxotungstic acid (PTA) by potentiostatically controlled surface aggregates formed at the electrode-electrolyte interface is presented.

Reference: V Hariharan, B Gnanavel, R Sathiyapriya, V Aroulmoji. A Review on Tungsten Oxide (WO₃) and their Derivatives for Sensor Applications. International journal of advanced Science and Engineering, Mahendra Publications, 2019, 5, pp.1163 - 1168. ff10.29294/ijase.5.4.2019.1163-1168ff. ffhal-03093589

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