Tungsten Trioxide Nanostructures for Photoelectrochemical Water Splitting: Material Engineering and Charge Carrier Dynamic Manipulation

Abstract

To address the energy crisis and environmental problems, the applications of solar energy have received intensive attention. Converting solar energy to hydrogen using a photoelectrochemical (PEC) cell is one of the most promising approaches to meet future energy demands. As an earth abundant metal oxide, tungsten trioxide (WO3), which has a moderate band gap (2.5–2.7 eV), ideal valence band position, and high resistance to photocorrosion, has been widely utilized in PEC photoanodes. To obtain a WO3 photoanode with high PEC efficiency, tremendous efforts have been made to improve the light absorption capacity, charge carrier dynamics, and oxygen evolution activity. In this report, the recent advances in WO3 photoanode optimization, including morphology design, dopants doping, heterojunction fabrication, and surface modification are summarized. In this review, these developments and representative applications of WO3 photoanodes in unassisted water splitting devices are also discussed. Finally, perspectives on the significant challenges and future prospects for the development of WO3 photoanodes for PEC water splitting are provided.

Tuning the Photoresponse of Nano‐Heterojunction: Pressure‐Induced Inverse Photoconductance in Functionalized WO3 Nanocuboids

“…[38] Above 6.5 GPa, the compression resulted in a new peak at about 1.91 Å and led to the narrowing of the other two maxima at about 1.8 and 2.1 Å. The ratio of the peak areas corresponding to the coordination numbers is 3:2:1 (WO 3 O 2 O 1 ) in the pressure range of 8.4-24 GPa, and 2:3:1 (WO 2 O 3 O 1 ) in the pressure range of 29-34 GPa, encompassing the structural transition in WO 3 . Taking into account that the WO 3 /CuO system is heterogeneous and tungsten atoms can be located in different local environments, the interpretation of the RDF changes for pressures above 6.5 GPa is more complicated.…”

“…We propose that there are at least two main contributions coming from tungsten atoms. First, those located in compressed WO 3 give the XRD patterns and are responsible for the peaks in the RDFs at 1.8 and 2.1-2.2 Å. Second, those located in a highly symmetric environment (weakly distorted W 5+ O 6 octahedron) with an average WO bond length of about 1.91 Å; such a bond length is typical for reduced tungsten ions and can be found, for example, in cubic Na x WO 3 .…”

“…A unique reversible transition from positive to inverse photoconductivity is observed during compression and decompression. The origin of the IPC is intimately connected to the depletion of the conduction channels by electron trapping and the chromic property of WO 3 . This synergistic rationale may afford a simple and powerful method to improve the optomechanical performance of any hybrid material.…”

Facile assembly of a graphitic carbon nitride film at an air/water interface for photoelectrochemical NADH regeneration

“…[7][8][9][10] Converting solar energy to chemical energy using a photoelectrochemical cell is one of the most promising approaches to meet future energy demands. [11][12][13] However, the exploitation of g-C 3 N 4 in photoelectrochemical cells has been limited by the difficulty in coating a layer of high-quality, homogenous g-C 3 N 4 film onto a conductive substrate. 14,15 Inspired by conventional semiconductor photocatalysts, previous studies have used tedious two-step methods (e.g., spin-coating, electrophoretic deposition) to prepare g-C 3 N 4 film photoelectrodes.…”

Sol-gel synthesis of highly reproducible WO3 photoanodes for solar water oxidation

“…Extensive research efforts have led to numerous synthetic strategies to produce efficient and translucent WO 3 photoanodes, for example, by electrodeposition [20], solgel [23], sputtering [24], hydrothermal [25,26], and solvothermal methods [27]. In terms of efficiency losses occurring through optical absorption, charge transport and surface catalysis processes of the WO 3 photoanodes, various strategies have been developed to minimize the losses, including morphology control of the nanostructured electrodes (such as nanorods [25], nanoflakes [28][29][30][31], and nanoporous films [23,32]), heterojunction construction [33,34], and electrocatalyst decoration [35][36][37]. Despite the progress hitherto, establishing efficient and highly reproducible WO 3 photoanodes remains a challenge.…”