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Mineo, G.; Bruno, E.; Mirabella, S. WO3 Nanostructures for Energy Storage. Encyclopedia. Available online: https://encyclopedia.pub/entry/43960 (accessed on 17 May 2024).
Mineo G, Bruno E, Mirabella S. WO3 Nanostructures for Energy Storage. Encyclopedia. Available at: https://encyclopedia.pub/entry/43960. Accessed May 17, 2024.
Mineo, Giacometta, Elena Bruno, Salvo Mirabella. "WO3 Nanostructures for Energy Storage" Encyclopedia, https://encyclopedia.pub/entry/43960 (accessed May 17, 2024).
Mineo, G., Bruno, E., & Mirabella, S. (2023, May 08). WO3 Nanostructures for Energy Storage. In Encyclopedia. https://encyclopedia.pub/entry/43960
Mineo, Giacometta, et al. "WO3 Nanostructures for Energy Storage." Encyclopedia. Web. 08 May, 2023.
WO3 Nanostructures for Energy Storage
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This entry is adapted from the peer-reviewed paper 10.3390/nano13081418

Electrochemical energy storage devices are one of the main protagonists in the ongoing technological advances in the energy field, whereby the development of efficient, sustainable, and durable storage systems aroused a great interest in the scientific community. Batteries, electrical double layer capacitors (EDLC), and pseudocapacitors are characterized in depth in the literature as the most powerful energy storage devices for practical applications. Pseudocapacitors bridge the gap between batteries and EDLCs, thus supplying both high energy and power densities, and transition metal oxide (TMO)-based nanostructures are used for their realization. Among them, WO3 nanostructures inspired the scientific community, thanks to WO3’s excellent electrochemical stability, low cost, and abundance in nature. 

energy storage electrochemical characterization WO3 pseudocapacitor

1. Crystal Structure Properties

WO3 is an n-type semiconductor with high electrochemical stability in acidic environments, and high intrinsic density (>7 g∙cm−3) [1]. Its energy storage performances strongly depend on the crystal structure, which can make the ions’ intercalation easier in an electrochemical environment.
In its crystalline form, WO3 is made of octahedra sharing corners and edges, where each W atom is linked to six O atoms, as Figure 1 shows [2]. Thanks to the high coordination number, WO3 possesses many crystalline phases, which depend on the rotation direction and tilting angles of the WO6 octahedra (Figure 1a) with respect to the ideal cubic perovskite-like structure, whose stability depends on temperature [3]. The hexagonal phase is metastable, and it is turned into a monoclinic I phase when the temperature is higher than 400 °C [4],[5]. A unique feature of h-WO3 is that WO6 octahedra share corner oxygen atoms in three- and six-membered ring arrangements along the (001) plane. This sharing forms three different types of tunnels in the W-O bulk structure, which are triangular and hexagonal cavities along the ab plane and square windows along the c axis, as shown in Figure 1b,c. According to the literature, these cavities can act as preferential ions intercalation channel for applications in electrochemical environment [3].
Nanomaterials 13 01418 g003 550
Figure 1. (a) Tilt patterns and stability temperature domains of the different polymorphs of WO3; (b) the structure of h-WO3 shown with the c-axis perpendicular and (c) parallel to the plane. Reproduced by [4].

2. WO3 Nanostructure Synthesis Approaches

The nanotechnology advantages in a multitude of applications made the large-scale synthesis of nanostructures a crucial point for the development of new promising technologies. The electrochemical activity of WO3 nanostructures towards energy storage strongly depends on the morphology and crystal structure, and consequently, on the synthesis techniques. WO3 can be easily synthesized in a nanostructured form by different approaches, such as Vapor-Phase and Liquid-Phase Synthesis.
The Vapor-Phase Synthesis involves the condensation of a vaporized source material onto the substrate, using an expensive experimental setup [4]. Two types of deposition can be distinguished: Physical Vapor Deposition (or PVD) and Chemical Vapor Deposition (or CVD). Baek et al. [6], synthesized a dense WO3 nanowire film on a W substrate by thermal evaporation (Figure 2a). Shankar et al. [7] synthesized WO3 nanorods by using a hot filament chemical vapor deposition (HFCVD) with carbon nanotubes as a template (Figure 2b). For practical application, the low-cost, large-scale synthesis of nanostructures is necessary. In this scenario, Liquid Phase Syntheses, such as sol-gel, electrochemical anodization, and hydrothermal, are very attractive being characterized by simple equipment, low costs, and high reproducibility. Room temperatures are compatible with these processes, and good control and reproducibility can be achieved. Peroxotungstic acid (H2W2O11) is generally used as a precursor for the WO3 synthesis, thanks to its high stability at room temperature and in an acidic environment [4]. Yang et al. [8] synthesized mesoporous WO3 film by using a simple sol-gel route (Figure 2c). Electrochemical anodization is widely used for the industrial synthesis of metal oxide films, thanks to its simplicity. Zheng et al. [9] synthesized a nanostructured WO3 film by using a typical anodization route with a W foil as the anode (Figure 2d). Unfortunately, the high voltages required for the synthesis and the difficulty to achieve the desired nanostructured morphology make the anodization technique difficult to perform for the WO3 nanostructure synthesis. The hydrothermal procedure represents one of the greenest, simplest, and most versatile procedures among all the Liquid Phase Synthesis methods viable for the synthesis of WO3 nanostructures. It does not require any external potential and the preparation of the precursor solution occurs in just a few steps. Nanostructure formation can occur both in high and low temperature and pressure conditions. Moreover, the morphology and crystallinity of nanostructures strongly depend on precursor solution components, and on reaction time and temperature [10]. For example, Mineo et al. [11] synthesized WO3 nanorods by using a simple hydrothermal route with NaCl as the capping agent (Figure 2e), which confines the growth along the c-axis.
Nanomaterials 13 01418 g004 550
Figure 2. SEM images of WO3 nanostructures (nanowires, nanorods, mesoporous and nanostructured film, nanospheres, and nanorods, respectively) synthesized (a) by thermal evaporation [6]; (b) by hot wire CVD [7]; (c) by sol-gel method [8]; (d) by electrochemical anodization [9]; and (e) by hydrothermal synthesis [11]. Reproduced with permission.

3. Affinity of WO3 for Energy Storage Applications

WO3 nanostructures possess structural flexibility, stability in an acidic environment, and resistance to electrochemical corrosion, which makes it a suitable candidate for electrochemical energy storage. The electrochemical reactions occur at the electrode surface and involve electron and ion transfer, so high exposed surface and good conductivity are preferable and the optimization of several factors, such as specific surface area and mass loading, affect the energy storage activity of WO3. Unfortunately, stoichiometric WO3 is characterized by poor electron conductivity, which can be improved by properly tailoring the morphology and crystallinity of WO3-based nanostructures, or by using carbon-based nanocomposites during the electrode preparation [12],[13],[14],[15],[16]. It was demonstrated that in comparison to other polymorphisms, 1D hexagonal WO3 nanostructures possess the highest energy storage performances, thanks to the presence of triangular and hexagonal cavities and square windows in the crystal structure (Figure 1b). These tunnels can provide accommodation sites for many cations during the electrochemical process, by facilitating electrolyte ion insertion and storage in the WO3 matrix thanks to its multiple oxidation states [3].
State-of-the-art research on WO3 demonstrates that it exhibits a pseudocapacitor behavior with quasi-rectangular cyclic voltammetry (CV) curves [11],[13],[15],[17],[18]. According to Dunn et al. [19] the charge storage mechanism in WO3 can be described in terms of surface and diffusion-limited contributions and occurs at the electrode–electrolyte interface. Surface-limited contributions are related to the adsorption/desorption of charge on the surface, while diffusion-limited contributions result from redox reactions that occur at the surface during which the W oxidation state changes as follows [20]:
WO 3 + xM + + xe − ⇌ M x WO 3 − x
in which M+ represents the cation of the used electrolyte (H+, Na+, Li+).
WO3 is characterized by many oxidation states, which promote redox reactions at the active material surface. The high theoretical capacitance and the possibility to easily tailor the morphological and crystal properties of WO3 make it a suitable candidate for the development of an efficient anode in energy storage devices, such as symmetric and asymmetric supercapacitors. These WO3 features have aroused a great interest in the scientific community, and many efforts have been made to pave the way to the development of very efficient WO3-based energy storage devices.

References

  1. Tian, J.; Lin, B.; Sun, Y.; Zhang, X.; Yang, H Porous WO3 @ CuO Composites Derived from Polyoxometalates @ Metal Organic Frameworks for Supercapacitor. Mater. Lett. 2017, 206, 91–94.
  2. Panwar, N.L.; Kaushik, S.C.; Kothari, S Role of Renewable Energy Sources in Environmental Protection: A Review. Renew. Sustain. Energy Rev. 2011, 15 , 1513–1524.
  3. Castro-Gutiérrez, J.; Celzard, A.; Fierro, V. Energy Storage in Supercapacitors: Focus on Tannin-Derived Carbon Electrodes. . Front. Mater. 2020, 7, 217.
  4. Zheng, H.; Ou, J.Z.; Strano, M.S.; Kaner, R.B.; Mitchell, A.; Kalantar-Zadeh, K Nanostructured Tungsten Oxide—Properties, Synthesis, and Applications. Adv. Funct. Mater 2011, 21, 2175–2196.
  5. Mineo, G.; Scuderi, M.; Bruno, E.; Mirabella, S. ngineering Hexagonal/Monoclinic WO3 Phase Junctions for Improved Electrochemical Hydrogen Evolution Reaction.. ACS Appl. Energy Mater. 2022, 5, 9702–9710..
  6. 36. Baek, Y.; Yong, K. Controlled Growth and Characterization of Tungsten Oxide Nanowires Using Thermal Evaporation of WO3 Powder.. J. Phys. Chem. C 2007,, 111, 1213–1218.
  7. Shankar, N.; Yu, M.F.; Vanka, S.P.; Glumac, N.G. Synthesis of Tungsten Oxide (WO3) Nanorods Using Carbon Nanotubes as Templates by Hot Filament Chemical Vapor Deposition.. Mater. Lett. 2006, 60, 771–774.
  8. Yang, B.; Zhang, Y.; Drabarek, E.; Barnes, P.R.F.; Luca, V. Enhanced Photoelectrochemical Activity of Sol-Gel Tungsten Trioxide Films through Textural Control. Chem. Mater. 2007, 19, 5664–5672.
  9. Zheng, H.; Sadek, A.Z.; Latham, K.; Kalantar-Zadeh, K. Nanoporous WO3 from Anodized RF Sputtered Tungsten Thin Films. . Electrochem. Commun. 2009, 11, 768–771.
  10. Gan, Y.X.; Jayatissa, A.H.; Yu, Z.; Chen, X.; Li, M. Hydrothermal Synthesis of Nanomaterials. J. Nanomater. 2020, 2020, 1699-1713.
  11. 29. Mineo, G.; Moulaee, K.; Neri, G.; Mirabella, S.; Bruno, E H2 Detection Mechanism in Chemoresistive Sensor Based on Low-Cost Synthesized WO3 Nanorods.. Sens. Actuators B Chem 2021, 348, 130704..
  12. Shinde, P.A.; Seo, Y.; Ray, C.; Jun, S.C. Direct Growth of WO3 Nanostructures on Multi-Walled Carbon Nanotubes for High-Performance Fl Exible All-Solid-State Asymmetric Supercapacitor.. Electrochim. Acta 2019, 308, 231–242.
  13. Lokhande, V.; Lokhande, A.; Namkoong, G.; Kim, J.H.; Ji, T. Charge Storage in WO3 Polymorphs and Their Application as Supercapacitor Electrode Material. Results Phys 2019, 12, 2012–2020.
  14. Shi, F.; Li, J.; Xiao, J.; Zhao, X.; Li, H.; An, Q.; Zhai, S.; Wang, K.; Wei, L.; Tong, Y.; et al. Three-Dimensional Hierarchical Porous Lig-nin-Derived Carbon/ WO3 for High-Performance Solid-State Planar Micro-Supercapacitor. Int. J. Biol. Macromol 2021, 190, 11-18.
  15. Jia, J.; Liu, X.; Mi, R.; Liu, N.; Xiong, Z.; Yuan, L.; Wang, C.; Sheng, G.; Cao, L.; Zhou, X.; et al.et al. Self-Assembled Pancake-like Hexagonal Tungsten Oxide with Ordered Mesopores for Supercapacitors. J. Mater. Chem. A 2018, 6, 15330–15339..
  16. Dong, X.; Yang, Q.; Yuan, L.; Qi, D.; Wei, X.; Zhou, X.; Chen, S.; Cao, L.; Zeng, Y.; Jia, J.; et al.et al. Oxygen Vacancy-Rich WO3 Heter-ophase Structure : A Trade-off between Surface-Limited Pseudocapacitance and Intercalation-Limited Behaviour.. Chem. Eng. J. 2021, 425, 131431.
  17. Ji, S.; Chodankar, N.R.; Kim, D. . Aqueous Asymmetric Supercapacitor Based on RuO2—WO3 Electrodes. Electrochim. Acta 2019, 325, 134879.
  18. Zhang, S.; Pan, N. Supercapacitors Performance Evaluation. Adv. Energy Mater 2015, 5, 1401401.
  19. Wang, J.; Polleux, J.; Lim, J.; Dunn, B. 2007 111 Pseudocapacitive Contributions to Electrochemical Energy Storage in TiO 2 (Anatase) Nanoparticles. J. Phys. Chem. C 2007, 111, 14925–14931.
  20. Lokhande, V.C.; Hussain, T.; Shelke, A.R.; Lokhande, A.C.; Ji, T. Substitutional Doping of WO3 for Ca-Ion Based Supercapacitor.. Chem. Eng. J. 2021, 424, 130557.
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Subjects: Electrochemistry
Contributors MDPI registered users' name will be linked to their SciProfiles pages. To register with us, please refer to https://encyclopedia.pub/register :
Giacometta Mineo
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Elena Bruno
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Salvo Mirabella
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Update Date: 09 May 2023
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