Evidence and Effect of Photogenerated Charge Transfer for Enhanced Photocatalysis in WO₃/TiO₂ Heterojunction Films: A Computational and Experimental Study

Abstract

Keywords: (titanium dioxide, tungsten trioxide, heterojunction, band alignment, density functional theory, hard X-ray photoelectron spectroscopy, transient absorption spectroscopy, photocatalysis) (Abstract: Semiconductor heterojunctions are used in a wide range of applications including catalysis, sensors and solar-to-chemical energy conversion devices. These materials can spatially separate photogenerated charge across the heterojunction boundary, inhibiting recombination processes and synergistically enhance their performance beyond the individual components. In this work, we investigate the WO3/TiO2 heterojunction grown by chemical vapour deposition. This consisted of a highly nanostructured WO3 layer, of vertically aligned nanorods, that was coated then with a conformal layer of TiO2. This heterojunction showed an 2 unusual electron transfer process, where photogenerated electrons moved from the WO3 layer into TiO2. State-of-the-art hybrid density functional theory and hard X-ray photoelectron spectroscopy were used to elucidate the electronic interaction at the WO3/TiO2 interface.Transient absorption spectroscopy showed that recombination was substantially reduced, extending both the lifetime and population of photogenerated charges into timescales relevant to most photocatalytic processes. This increased the photocatalytic efficiency of the material, which is among the highest ever reported for a thin film. In allying computational and experimental methods, we believe this is an ideal strategy for determining the band alignment in metal oxide heterojunction systems.) IntroductionHeterojunction materials may benefit from charge transfer processes by coupling two semiconductors with appropriate band structures in order to drive a particular functionality. 3-5A remarkable example is the ubiquitous commercial TiO2 P25 (Evonik, formerly Degussa), which consists of a ~ 3:1 ratio of anatase (Ebg= 3.20 eV) and rutile (Ebg= 3.00 eV) and is considered the benchmark photocatalyst.

Improving the Selectivity of Photocatalytic NOx Abatement through Improved O2 Reduction Pathways Using Ti0.909W0.091O2Nx Semiconductor Nanoparticles: From Characterization to Photocatalytic Performance

“…For environmental remediation applications, the persistance of toxic pollutants due to the temporary unavailability of the remediation technology can cause severe problems for the environment or people's health. Photocatalysts consisting of TiO 2 -WO 3 mixed oxides and TiO 2 -WO 3 heterojunction films where electron storage and slow electron discharge in the absence of irradiation allow sustained photocatalytic activity in the darkness, have been reported by a few research groups [24][25][26][27][28][29][30] and also tested for anticorrosion 25 or VOC removal applications. 27 The common understanding is that photo-generated electrons can be stored in WO 3 due to a typical tungsten bronze chemistry mediated by proton intercalation, 25 and is supported by clear electrochemical evidence.…”

Water Oxidation Kinetics of Accumulated Holes on the Surface of a TiO2 Photoanode: A Rate Law Analysis

“…9,10 However, coupling TiO2 with narrow bandgap semiconductors and forming heterojunctions can result in synergistic improvements in activity, and may be the more promising strategy. 11,12 Since the first definitive proof that photocatalytic water oxidation in plants occurs on a manganese cluster (photo-system II), 13 numerous mimics have emerged. 14,15 Interest in solar driven fuel synthesis has stimulated the investigation of photocatalysts capable of oxidizing water under solar irradiation, including, in particular, metal oxides due to their stability under oxidizing conditions.…”

Photoelectrochemical Behavior of the Ternary Heterostructured Systems CdS/WO3/TiO2

“…The TiO 2 /WO 3 heterostructured system, used as photocatalyst, has been also highlighted in numerous publications [13]. The reported results of photocatalytic behavior of such a heterostructure are very promising.…”