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

Abstract

HIGHLIGHT This journal isThe photocatalysis, chromism, and sensing capabilities of nanostructured tungsten oxides, such as tungsten trioxide (WO 3 ), its suboxides (WO x , 0<x<3) and hydrates (WO 3 ⋅nH 2 O, n = 1/3 (0.33), 0.5, 0.75, 1, 2, etc.); the tungsten bronzes M x WO 3 (M = Li, Na, K, Rb, Cs and NH 4 ); and metal tungstates (such as Bi 2 WO 6 and CuWO 4 ) have attracted much attention. To improve these properties, many strategies have been pursued, such as morphology control, doping, and heterostructuring. Crystal facet engineering has recently become a very important method of fine-tuning the physicochemical properties of semiconductors. The photocatalytic reactivity of a photocatalyst is significantly affected by its surface environment, including its surface electronic and atomic structures, which strongly depend on the crystal facets. It is believed that crystals with different exposed facets will have different properties, with the exposure of highly activated facets enhancing the photocatalytic and sensing properties. This article describes the synthesis of 2D WO 3 crystals with the {002} facet primarily exposed, octahedral WO 3 or WO 3 · nH 2 O with exposed {111} facets, and WO 3 films with dominant orientations, such as orientation along the {002} facet. WO 3 doping, WO 3 -based heterostructuring and their applications are also presented in this paper.

Large-mesopore hierarchical tungsten trioxide hydrate with exposed high energy facets: Facile synthesis and enhanced photocatalysis

“…As is well known, surface atomic arrangement and coordination intrinsically determine the adsorption, surface transfer, and desorption; therefore, exposed facets, surface morphology, structure, and particle size have been manipulated extensively for various semiconductor photocatalysts in the literature [20][21][22][23][24][25][26]. Although different dimensional nanostructures of WO 3 have been prepared [27][28][29][30][31][32], three-dimensional layered structure is desirable when applied to photocatalysis, for it might provide much more reactive sites.…”

Enhanced photochemical performance of hexagonal WO3 by metal-assisted S–O coupling for solar-driven water splitting

“…7. The pure h-WO 3 , our reference system, has the CBM 0.3 eV lower than the H + /H 2 potential, and its VBM is more positive (about 1.9 eV) than O 2 /H 2 O potential [8]. The VBM of S, (Sn, S) and (Pb, S) has been lifted up a lot where the CBM also shifts upwards in some degree, which endows the h-WO 3 with the enhanced reducing ability.…”

“…However, the monodoping always generates localized donor or acceptor states, which plays a detrimental role in photocatalytic activity of the materials [16,24]. Last but not the least, the majority of the research of WO 3 -based water splitting materials were focused on dealing with the most stable monoclinic WO 3 [25], whereas very few investigations were focused on relatively stable hexagonal phase of WO 3 which was generally applied to smart window or photothermal agent [8,[26][27][28][29].…”

“…However, some drawbacks and limitations also exist in WO 3 . Since the ideal band gap for water splitting should be 1.6-2 eV, the band gap of WO 3 is still too large to achieve high quantum yield in solar spectrum and WO 3 exhibits poor performance for hydrogen production as its bottom of the conduction band is nearly 0.3 eV below the hydrogen redox potential [8].…”

Effect of Surface Passivation on Photoelectrochemical Water Splitting Performance of WO3 Vertical Plate-Like Films

“…In the past decades, numerous researchers have focused on discovering novel solid-state catalysts that can effectively split water using either unbiased or externally biased electrodes. Since wide-band gap semiconductors like TiO2 [2] and ZnO [3] were studied as photocatalysts for water-splitting, more recent efforts have turned to WO3 due to its bandgap of 2.6 eV [4], its photostability in acidic conditions [5] and its good hole mobility [6].…”