Sodium ion storage performance of magnetron sputtered WO3 thin films

Deciphering Sodium-Ion Storage: 2D-Sulfide versus Oxide Through Experimental and Computational Analyses

Transition metal derivatives exhibit high theoretical capacity, making them promising anode materials for sodium-ion batteries. Sulfides, known for their superior electrical conductivity compared to oxides, enhance charge transfer, leading to improved electrochemical performance. Here, a hierarchical WS2 micro-flower is synthesized by thermal sulfurization of WO3. Comprising interconnected thin nanosheets, this structure offers increased surface area, facilitating extensive internal surfaces for electrochemical redox reactions. The WS2 micro-flower demonstrates a specific capacity of ≈334 mAh g-1 at 15 mA g-1, nearly three times higher than its oxide counterpart. Further, it shows very stable performance as a high-temperature (65 °C) anode with ≈180 mAh g-1 reversible capacity at 100 mA g-1 current rate. Post-cycling analysis confirms unchanged morphology, highlighting the structural stability and robustness of WS2. DFT calculations show that the electronic bandgap in both WS2 and WO3 increases when going from the bulk to monolayers. Na adsorption calculations show that Na atoms bind strongly in WO3 with a higher energy diffusion barrier when compared to WS2, corroborating the experimental findings. This study presents a significant insight into electrode material selection for sodium-ion storage applications.

Unraveling the Structure and Properties of Layered and Mixed ReO3-WO3 Thin Films Deposited by Reactive DC Magnetron Sputtering

Tungsten trioxide (WO₃) is a well-known electrochromic material with a wide band gap, while rhenium trioxide (ReO₃) is a "covalent metal" with an electrical conductivity comparable to that of pure metals. Since both WO₃ and ReO₃ oxides have perovskite-type structures, the formation of their solid solutions (ReO₃-WO₃ or Re _x W_1-x O₃) can be expected, which may be of significant academic and industrial interest. In this study, layered WO₃/ReO₃, ReO₃/WO₃, and mixed ReO₃-WO₃ thin films were produced by reactive DC magnetron sputtering and subsequent annealing in air at 450 °C. The structure and properties of the films were characterized by X-ray diffraction, optical spectroscopy, Hall conductivity measurements, conductive atomic force microscopy, scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoemission spectroscopy. First-principles density functional theory calculations were performed for selected compositions of Re _x W_1-x O₃ solid solutions to model their crystallographic structure and electronic properties. The calculations predict metallic conductivity and tetragonal distortion of solid solutions in agreement with the experimental results. In contrast to previously reported methods, our approach allows us to produce the WO₃-ReO₃ alloy with a high Re content (>50%) at moderate temperatures and without the use of high pressures.

Designing a Graphene Coating-Based Supercapacitor with Lithium Ion Electrolyte: An Experimental and Computational Study via Multiscale Modeling

Graphene electrodes are investigated for electrochemical double layer capacitors (EDLCs) with lithium ion electrolyte, the focus being the effect of the pore size distribution (PSD) of electrode with respect to the solvated and desolvated electrolyte ions. Two graphene electrode coatings are examined: a low specific surface area (SSA) xGNP-750 coating and a high SSA coating based on a-MWGO (activated microwave expanded graphene oxide). The study comprises an experimental and a computer modeling part. The experimental part includes fabrication, material characterization and electrochemical testing of an EDLC with xGNP-750 coating electrodes and electrolyte 1M LiPF6 in EC:DMC. The computational part includes simulations of the galvanostatic charge-discharge of each EDLC type, based on a continuum ion transport model taking into account the PSD of electrodes, as well as molecular modeling to determine the parameters of the solvated and desolvated electrolyte ions and their adsorption energies with each type of electrode pore surface material. Predictions, in agreement with the experimental data, yield a specific electrode capacitance of 110 F g-1 for xGNP-750 coating electrodes in electrolyte 1M LiPF6 in EC:DMC, which is three times higher than that of the high SSA a-MWGO coating electrodes in the same lithium ion electrolyte.

A Review on the Properties and Applications of WO3 Nanostructure-Based Optical and Electronic Devices

Tungsten oxide (WO3) is a wide band gap semiconductor with unintentionally n-doping performance, excellent conductivity, and high electron hall mobility, which is considered as a candidate material for application in optoelectronics. Several reviews on WO3 and its derivatives for various applications dealing with electrochemical, photoelectrochemical, hybrid photocatalysts, electrochemical energy storage, and gas sensors have appeared recently. Moreover, the nanostructured transition metal oxides have attracted considerable attention in the past decade because of their unique chemical, photochromic, and physical properties leading to numerous other potential applications. Owing to their distinctive photoluminescence (PL), electrochromic and electrical properties, WO3 nanostructure-based optical and electronic devices application have attracted a wide range of research interests. This review mainly focuses on the up-to-date progress in different advanced strategies from fundamental analysis to improve WO3 optoelectric, electrochromic, and photochromic properties in the development of tungsten oxide-based advanced devices for optical and electronic applications including photodetectors, light-emitting diodes (LED), PL properties, electrical properties, and optical information storage. This review on the prior findings of WO3-related optical and electrical devices, as well as concluding remarks and forecasts will help researchers to advance the field of optoelectric applications of nanostructured transition metal oxides.

The CdIn2 S4 /WO3 Nanosheet Composite Has a Significantly Enhanced Photo-electrochemical Cathodic Protection Performance and Excellent Electron Storage Capability

Photo-electrochemical cathodic protection (CP) technology is considered to be a green metallic corrosion protection technology that uses solar energy to protect from corrosion and does not consume any anode materials. In this work, a CdIn₂ S₄ /WO₃ nanocomposite photoelectrode was prepared, and its photo-electrochemical CP performance and mechanism were studied and analyzed. WO₃ has a well band matching with CdIn₂ S₄ , leading to a significantly enhanced photo-electrochemical CP performance of the nanocomposite. Meanwhile, as confirmed in this work, the CdIn₂ S₄ /WO₃ nanocomposite can store photoinduced electrons under light illumination through intercalation reactions and changing the valence state of tungsten. Moreover, it can discharge in the dark state to provide continuous CP for the coupled metals. This research will promote the practical application process of the photo-electrochemical CP technology.

New Insights on the Conversion Reaction Mechanism in Metal Oxide Electrodes for Sodium-Ion Batteries

Due to the abundance and low cost of exchanged metal, sodium-ion batteries have attracted increasing research attention for the massive energy storage associated with renewable energy sources. Nickel oxide (NiO) thin films have been prepared by magnetron sputtering (MS) deposition under an oblique angle configuration (OAD) and used as electrodes for Na-ion batteries. A systematic chemical, structural and electrochemical analysis of this electrode has been carried out. The electrochemical characterization by galvanostatic charge–discharge cycling and cyclic voltammetry has revealed a certain loss of performance after the initial cycling of the battery. The conversion reaction of NiO with sodium ions during the discharge process to generate sodium oxide and Ni metal has been confirmed by X-ray photoelectron spectra (XPS) and micro-Raman analysis. Likewise, it has been determined that the charging process is not totally reversible, causing a reduction in battery capacity.

Effect of the Ammonium Tungsten Precursor Solution with the Modification of Glycerol on Wide Band Gap WO3 Thin Film and Its Electrochromic Properties

Tungsten trioxide (WO₃) is a wide band gap semiconductor material, which is commonly not only used, but also investigated as a significant electrochromic layer in electrochromic devices. WO₃ films have been prepared by inorganic and sol-gel free ammonium tungstate ((NH₄)₂WO₄), with the modification of glycerol using the spin coating technique. The surface tension, the contact angle and the dynamic viscosity of the precursor solutions demonstrated that the sample solution with a 25% volume fraction of glycerol was optimal, which was equipped to facilitate the growth of WO₃ films. The thermal gravimetric and differential scanning calorimetry (TG-DSC) analysis represented that the optimal sample solution transformed into the WO₃ range from 220 °C to 300 °C, and the transformation of the phase structure of WO₃ was taken above 300 °C. Fourier transform infrared spectroscopy (FT-IR) spectra analysis indicated that the composition within the film was WO₃ above the 300 °C annealing temperature, and the component content of WO₃ was increased with the increase in the annealing temperature. The X-ray diffraction (XRD) pattern revealed that WO₃ films were available for the formation of the cubic and monoclinic crystal structure at 400 °C, and were preferential for growing monoclinic WO₃ when annealed at 500 °C. Atomic force microscope (AFM) images showed that WO₃ films prepared using ammonium tungstate with modification of the glycerol possessed less rough surface roughness in comparison with the sol-gel-prepared films. An ultraviolet spectrophotometer (UV) demonstrated that the sample solution which had been annealed at 400 °C obtained a high electrochromic modulation ability roughly 40% at 700 nm wavelength, as well as the optical band gap (E_g) of the WO₃ films ranged from 3.48 eV to 3.37 eV with the annealing temperature increasing.

Plasmochromic Nanocavity Dynamic Light Color Switching

Static plasmonic metal-insulator-nanohole (MIN) cavities have been shown to create high chromaticity spectral colors for display applications. While on-off switching of said devices has been demonstrated, introducing active control over the spectral color of a single cavity is an ongoing challenge. Electrochromic oxides such as tungsten oxide (WO₃) offer the possibility to tune their refractive index (2.1-1.8) and extinction (0-0.5) upon ion insertion, allowing active control over resonance conditions for MIN based devices. In combination with the dynamic change in the WO₃ layer, the utilization of a plasmonic superstructure allows creation of well-defined spectral reflection of the nanocavity. Here, we employ inorganic, electrochromic WO₃ as the tunable dielectric in a MIN nanocavity, resulting in a theoretically achievable resonance wavelength modulation from 601 to 505 nm, while maintaining 35% of reflectance intensity. Experimental values for the spectral modulation result in a 64 nm shift of peak wavelength with high reproducibility and fast switching speed. Remarkably, the introduced device shows electrochemical stability over 100 switching cycles while most of the intercalated charge can be regained (91.1%), leading to low power consumption (5.6 mW/cm^-2).