Facile Fabrication of WO₃ Nanoplates Thin Films with Dominant Crystal Facet of (002) for Water Splitting

Abstract

Single crystalline orthorhombic phase tungsten trioxide monohydrate (O-WO 3 •H 2 O, space group: Pmnb) nanoplates with a clear morphology and uniform size distribution have been synthesized by the hydrothermal method and fabricated on the surface of fluorine doped tin oxide (FTO) coated glass substrates with selective exposure of the crystal facet by the finger rubbing method. The rubbing method can easily arrange the O-WO 3 •H 2 O nanoplates along the (020) facet on the FTO substrate. The O-WO 3 •H 2 O nanoplate can be converted to monoclinic phase WO 3 (γ-WO 3 , space group: P21/n) with dominant crystal facet of (002) without destroying the plate structure. Crystal morphologies, structures, and components of the powders and films have been determined by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman, X-ray photoelectron spectroscopy, etc. The band gap energies of the O-WO 3 •H 2 O and γ-WO 3 nanoplates were determined as ca. 2.26 and 2.49 eV, respectively. Photoelectrochemical properties of the films with (002) dominant crystal facet have also been checked for discussion of further application in water oxidation. The advantage of (002) facet dominant film was investigated by comparing to one spin-coated γ-WO 3 thin film with the same thickness via photoelectrochemical characterizations such as photocurrent, incident photon to current efficiency, and electrochemical impedance spectroscopy.

Tuning of the crystal engineering and photoelectrochemical properties of crystalline tungsten oxide for optoelectronic device applications

“…The photocatalytic reactivity of a photocatalyst is significantly affected by its surface environment, such as its surface electronic and atomic structures, which critically depend on the different crystal facets. 21,51 The tuning of the surface atomic structure by crystal facet engineering can easily adjust the properties of the semiconductor, such as the electronic band structure, surface energy and surface active sites, the adsorption of a reactant, and the desorption of reaction products. 52 The crystal facet engineering of semiconductors such as TiO 2 53 and BiVO 4 11,54 has become a very important means of fine-tuning their physicochemical properties.…”

“…In addition, the rubbing method can be used to fabricate films with a one-axis orientation without needing to consider the crystal lattice matching between the rubbing materials and substrates. 21,51,84 For the rubbing process, a dilute polyethylenimine (PEI) ethanol solution was first spin-coated on the substrates. The particles were then placed on the PEI-coated substrates and rubbed smooth by a finger protected by a powder-free latex exam finger cot.…”

Porous WO3 with Hierarchical Structure on FTO Substrates: Fabrication and Photoelectrochemical Water Oxidation Performance

“…It suggests that the heat treatment can readily promote the WO 3 ·0.33H 2 O to dehydrate to form WO 3 . In addition, in comparison with the diffraction lines of the referenced monoclinic WO 3 bar-chart, the prepared WO 3 samples all reveal much higher relative diffraction intensity for the (200) peak, indicating the existence of preferred orientation along [200] direction [10]. Figure 1b-c show the scanning electron microscope (SEM) images of the WO 3 films before and after etching.…”

Efficient Degradation of Refractory Organics Using Sulfate Radicals Generated Directly from WO3 Photoelectrode and the Catalytic Reaction of Sulfate

“…Some photoanode materials, such as TiO 2 [16][17][18][19], WO 3 [20][21][22][23][24][25][26][27][28][29], Fe 2 O 3 [30,31], ZnO [32,33], and BiVO 4 [34][35][36] have been widely investigated because of their considerably high incident light-to-current conversion efficiencies. Among them, WO 3 is a promising material impacting many research fields [37] for its specific properties.…”