Nanoporous WO₃ Gasochromic Films for Gas Sensing

Abstract

Nanoporous tungsten oxide (WO3) films have been widely applied in gasochromic and electrochromic windows due to their high hydrogen diffusion ability. However, a high annealing temperature is required to remove the organic template, which may also collapse the structure of the functional materials. As a photocatalyst, the electron holes in the valence band of WO3 generated after UV irradiation exhibit a high oxidation activity and can degrade organic materials. Here, nanoporous WO3 films with pore sizes ranging from 10 to 16 nm were prepared through sol–gel methods with poly­(ethylene glycol)-block-poly­(propylene glycol)-block-poly­(ethylene glycol) (P123) as an organic template and WO3 as a photocatalytic assistant after UV radiation treatment in a low-temperature environment. After UV degradation treatment, P123 was suitably removed, and the orthorhombic structure of the WO3 film was notably preserved. WO3 could promote the ultraviolet (UV) degradation process of templates. The prepared WO3 nanoporous film exhibited a good thermal stability, fast coloring/bleaching and an excellent cycling performance after annealing at 200 °C. Thermal insulation experiments verified that gasochromic windows with nanoporous films achieve a high energy-saving potential.

Determination of W(V) in WO3 Photochromism Using Localized Surface Plasmon Resonance of Ag Nanoparticles

“…Electrochromic smart windows that use Prussian Blue have also been investigated. , However, WO 3 is more beneficial because it possesses a similar absorption coefficient, but a toxic KCN is not required for the synthesis. The blue coloration of WO 3 has also been utilized for other applications such as rewritable electrochromic displays, a shielding device to protect a camera from light, and gasochromic films for gas sensing. − Considering that 99.9% of the incident light (775 nm) is absorbed by WO 3 -based devices (surface area exposed to light: 1 cm 2 ), i.e., transmittance and absorbance are 0.1% and 3.0, respectively, the necessary amount of W­(V) is calculated to be 4.38 × 10 –7 mol cm –2 using the absorption coefficient obtained in this study. To evaluate the WO 3 amount to get the desired function, we have to know the quantum yield of the formed W­(V) per photon absorbed by WO 3 or per electron injected under the applied potential.…”

Gasochromic Hydrogen Sensors: Fundamentals, Recent Advances, and Perspectives

“…Organic templates have often been used in the preparation of nanoporous WO 3 materials, although high-temperature annealing to remove them can lead to structure collapses, destroying the nanoporous structure. Xue et al have recently adopted a novel strategy to synthesize nanoporous WO 3 films with the assistance of UV irradiation, (43) the scheme of which is shown in Fig. 3.…”

“…(40,41) Second, the morphology of WO 3 can be adjusted by either chemical or physical methods. (42,43) Typical morphologies of WO 3 nanoparticles are nanoplates, (44,45) nanofibers, (46,47) nanospheres, (48) nanorods, (49,50) and hierarchical structures. (51,52) Third, WO 3 has been investigated as efficient functional nanomaterials for sensing various gases, such as H 2 , (53,54) acetone, (55,56) H 2 S, (57,58) NO 2 , (59,60) and NH 3 .…”

Effect of Precursor Concentration on the Structural, Optical, and Electrical Properties of WO3 Thin Films Prepared by Spray Pyrolysis

“…At ideal molarity concentration, the average crystallite size (Davg) for the WO3 Film improved as the FWHM decreased t. Measurement of the microstrain is a significant parameter in determining the mechanical stability of the films. Equations ( 10), (11), and ( 12) were used to determine microstrain(ε), the density of dislocation (δ), and stacking fault (SF) [38]. Microstrain, dislocation density, and stacking fault all decreased with diffraction angle, indicating a reduction in lattice defects at the interplanar spacing of the crystal [39,40].…”

“…The recent finding of potential uses in organic light-emitting diodes has revived interest in tungsten oxide WO3 thin films [6]. It has organic photovoltaic devices [7], super hydrophilic [8], photocatalysis [9], electrochromic devices [10], gaschromic [11], photocatalytic [12], and photoluminescence (PL) properties [13]. It can be used in fuel cell applications [14], gas sensors [15], and other applications.…”