A WO₃Nanoporous-Nanorod Film Formed by Hydrothermal Growth of Nanorods on Anodized Nanoporous Substrate

Abstract

A tungsten oxide (WO 3 ) nanoporous-nanorod film was produced for the first time by hydrothermally growing WO 3 nanorods on nanoporous WO 3 substrate. The nanoporous substrates were prepared using the anodization method; hydrothermal reaction was performed on as-anodized and annealed (200-500 • C) nanoporous substrates for nanorod growth. The as-anodized substrate and the substrates annealed at ≤300 • C dissolved after hydrothermal reaction because of the amorphous and low crystallinity behaviors of the WO 3 substrates. However, the substrates annealed at ≥400 • C did not dissolve during the hydrothermal reaction; instead, nanorods were grown on the substrates, forming a nanoporous-nanorod structure. The WO 3 nanoporous-nanorod film (nanorods grown on substrate annealed at 400 • C) showed good electrochromic properties with high current density (−13.22 and +7.30 mA cm −2 ), good cycling stability, and short coloring (∼6 s) and bleaching (∼3.4 s) times. These good properties are attributed to the combination of two nanostructures (nanoporous and nanorods) that contributed to a large WO 3 surface area. Tungsten oxide (WO 3 ) is a well-known electrochromic material that has the ability to reversibly change color between colorless and blue with the application of electric potential. One of the important criteria to obtain good electrochromic property is the large surface area of the electrochromic material. A large surface area increases the interaction between the electrochromic material and electrolyte (H + or Li + ), which results in faster ion and electron intercalation and de-intercalation processes. A nanostructured electrochromic material is advantageous because of its large surface area. In producing nanostructured WO 3 films, all reported research works have yielded single nanostructured WO 3 film; no combination of WO 3 nanostructures in a film has been reported. The combination of two WO 3 nanostructures is postulated to exhibit the unique properties of both nanostructures, thereby enhancing the electrochromic properties. A WO 3 film comprising two nanostructures is introduced in this work. WO 3 nanorods were grown on a nanoporous WO 3 substrate to form a WO 3 nanoporous-nanorod film. The combination of these structures is hypothesized to produce good electrochromic properties, as the resulting structure possesses a large total surface area of WO 3 (open nanoporous structure and one-dimensional nanorods), which allows more ion and electron intercalation to occur.Porous WO 3 can be synthesized by template-assisted 1 and anodization 2-4 methods. The template-assisted method could produce ordered porous WO 3 , but with large pore diameter size of ∼330 nm. This method also requires several steps to obtain the final porous WO 3 product. Synthesis is initiated by preparing polystyrene sphere monolayer colloidal crystal on a glass slide, followed by transfer of the colloidal crystal template from the glass slide onto a substrate. Tungstic acid solution is then dropped onto the template-substrate, and calcination...

Photoelectrocatalytic activity of immobilized Yb doped WO3 photocatalyst for degradation of methyl orange dye

“…3 . Raman bands are observed at 271, 717, 807 and 946 cm −1 for pure WO 3 [41] . The band located at 946 cm −1 is assigned to the stretching ν (W = O) mode of the bridging oxygen [40,42] .…”

Controlled synthesis of tungsten trioxide with globular clusters constructed of nanoplates by rapid breakdown anodization

“…It should be noted that the formation mechanism of WO 3 •nH 2 O (n=1 or 2) globular clusters under dielectric breakdown conditions is different from that in conventional anodization process [23]. In typical formation of nanopores or nanotubes, the thin film with unique pore structure will be formed on the surface of the W foil due to a balance between chemical/electrochemical dissolve and deposition [24]. However, this is insufficient to explain the formation mechanism of the WO 3 •nH 2 O in powder form under breakdown voltage, specifically regarding the formation of the globular clusters constructed of nanoplates.…”

Development of Tungsten Trioxide Using Pulse and Continuous Electrodeposition and Its Properties in Electrochromic Devices

“…[5][6][7][8][9][10][11][12][13] WO 3 has been identified as a promising inorganic electrochromic material because of its excellent coloration effect, fast redox reaction, and good chemical stability. [14][15][16] However, the understanding of the properties of WO 3 and its potential application in electrochromic devices is still incomplete; thus, our study focuses on properties of WO 3 films. Here, the proton intercalation and deintercalation chemical reactions can be expressed as follows: 17 WO 3 bleached transparent + χH + + χe − HχWO 3 (colored (blue)) [1] It is clear that in its bleached state, the valency of W is 6 + .…”