Tungsten oxide nanostructures and their electrochromic performance

The electrochromic behaviour of tungsten oxide (WOx) bulk forms has attracted huge research interest for decades owing to advantages of fast response time, good reversibility and high colouration efficiency compared with other electrochromic materials. Nanomaterials have certainly brought in new opportunities and opened the door for better, higher and smarter devices fabrication. This thesis will first investigate, explore, and understand the electrochromic performance of WOx in the nanoscale, and identify ways to enhance its performance via effective doping electrolyte selection and heat treatment. Moreover, the thesis will evaluate the prototype device performance based on our new understandings obtained in this project. The main findings are as follows: • Successfully synthesised crystalline WOx-based nanomaterials using a simple solvothermal technique, and achieved a series of La-, Ce- and Na-doped nanomaterials. The results show that the dopants caused distortion of the parental WOx¬ frameworks and increased the oxygen vacancy inside the structure, which is beneficial for the chromic properties. • The best electrochromic performance was obtained from Ce/W = 1 : 15 samples which presented 44.3% for optical contrast colouration efficiency of 67.3 cm2 C−1. • Conducted in-situ phase transition investigations using both WO3 nanoparticles and W18O49 nanowires, and found out that temperature was affecting the relaxation of W-O framework and phase transition. Based on the investigation, the 187.6 cm-1 band has identified as a fingerprint band for the phase transition from γ- to β- of the WO3 nanoparticle at 275 °C. W18O49 nanowires exhibit better thermal stability than the WO3 nanoparticles. • Intensive electrochemical investigations of La- and Ce-doped WOx structures were exhibit better diffusion kinetics, stability and colouration efficiency compare with plain WOx. These improvements are contributed to the improved oxygen vacancy (Vo). DLi+ of the Ce-doped samples were much higher than that of the plain W18¬O49 nanowires, by 177%, 102% and 84% for the 1:15, 1:10 and 1:5 samples respectively. DLi+ values of all La-doped samples were over 100% higher than those of the plain W18O49. The La-doped thin films increased the stability by 9%, 4% for intercalation, and 25% and 23% for de-intercalation, for La/W = 1:15 and 1:10 samples respectively, against the plain W18O49. • Provided experimental evidence to explain the degradation of chromic thin films, which is related to the Li+ trapping and loss of Vo in the WOx the structures. • The 350 °C annealed W18O49 thin film sample showed better diffusion kinetics by 25% for intercalation and 30% for de-intercalation compared with the un-annealed W18O49 samples. Stabilities also showed 31% improvement for the de-intercalation, against the un-annealed W18O49 sample. • Fabricated electrochromic device prototypes, and investigated the influence of various electrolytes, an optimal combination of LiClO4/PPC/PC polymer electrolyte has been developed, to improve the performance in ion kinetics and switching time of W18O49. These results have shown that WOx nanomaterials via further effective modification including doping with rare-earth elements or proper heat treatment are promising and practical candidate for the creation of fast, reliable and highly efficient electrochromic devices/smart windows for various applications

In situ fabrication of dendritic tin-based carbon nanostructures for hydrogen evolution reaction

In this work, dendritic tin-based carbon (Sn/C) nanostructures with four different morphologies were synthesized by a facile two-step carbonization and chemical vapor deposition method and were then evaluated for their performance in hydrogen evolution reaction. The Sn/C dendrites are approximately 0.5 – 4.5 µm in length, each having secondary branches in different directions. The four morphologies of the Sn/C dendrites namely nanoflowers (Sn_NCF1), nanospheres (Sn_NCF2), nanocubes (Sn_NCF3) and nanocuboids (Sn_NCF4), behave differently in their electrochemical performance, with Sn_NCF2 and Sn_NCF1 performing better. Sn_NCF2 demonstrates optimal HER performance compared to other Sn based samples with onset potential and overpotential of 100 and 260 mV, respectively. The higher electrochemical surface area observed in Sn_NCF2 was originated from the presence of more catalytic sites which contributed to the enhanced HER activity and better current density, against other Sn-based samples. In addition to the improved HER performance, Sn_NCF2 demonstrates excellent stability with less than 6% degradation of its initial current after operating for over 8 h in acidic media

In situ investigations of the phase change behaviour of tungsten oxide nanostructures

This study appraises the use of in-situ diffraction and spectroscopy techniques, complemented with ex-situ electron microscopy analyses, to investigate the geometry and phase change behaviour of bundled ultrathin W18O49 nanowires and WO3 nanoparticles. Our in-situ X-ray diffraction (XRD) results have shown that the phase transition of WO3 nanoparticles occurs in sequence as the temperature increases, from monoclinic (room temperature) → orthorhombic (350 ºC) → tetragonal (800 °C), akin to bulk WO3; however, W18O49 nanowires remain stable as the monoclinic phase up to 500 °C, after which complete oxidation to WO3 and transformation to the orthorhombic β-phase at 550 °C is observed. The in-situ Raman spectroscopy investigations have shown that as the temperature increases, the Raman peaks downshift toward lower wavenumbers in both structures, which can be attributed to the increased bond lengths in the lattice. We have also demonstrated that the Raman shift at 187.6 cm-1 can be used as a fingerprint band for the phase transition from the γ- to the β-phase of the WO3 nanoparticle. Furthermore, WO3 nanoparticles exhibit the γ- to β-phase conversion at 275 °C, which is about 75 °C lower than the relaxation temperature of 350 °C for the monoclinic γ-W18O49 nanowires. We propose that this fundamental phase transition understanding can offer important guidance for the design and development of WOx-based nanodevices by defining their allowed operating conditions

The Frontier of Tungsten Oxide Nanostructures in Electronic Applications

Electrochromic (EC) glazing has garnered significant attention recently as a crucial solution for enhancing energy efficiency in future construction and automotive sectors. EC glazing could significantly reduce the energy usage of buildings compared to traditional blinds and glazing. Despite their commercial availability, several challenges remain, including issues with switching time, leakage of electrolytes, production costs, etc. Consequently, these areas demand more attention and further studies. Among inorganic-based EC materials, tungsten oxide nanostructures are essential due to its outstanding advantages such as low voltage demand, high coloration coefficient, large optical modulation range, and stability. This review will summarize the principal design and mechanism of EC device fabrication. It will highlight the current gaps in understanding the mechanism of EC theory, discuss the progress in material development for EC glazing, including various solutions for improving EC materials, and finally, introduce the latest advancements in photo-EC devices that integrate photovoltaic and EC technologies

A generic method to synthesise graphitic carbon coated nanoparticles in large scale and their derivative polymer nanocomposites

A versatile Rotary Chemical Vapour Deposition (RCVD) technique for the in-situ synthesis of large scale carbon-coated non-magnetic metal oxide nanoparticles (NPs) is presented, and a controllable coating thickness varying between 1–5 nm has been achieved. The technique has significantly up-scaled the traditional chemical vapour deposition (CVD) production for NPs from mg level to 10 s of grams per batch, with the potential for continuous manufacturing. The resulting smooth and uniform C-coatings sheathing the inner core metal oxide NPs are made of well-crystallised graphitic layers, as confirmed by electron microscopy imaging, electron dispersive spectrum elemental line scan, X-ray powder diffractions and Raman spectroscopy. Using nylon 12 as an example matrix, we further demonstrate that the inclusion of C-coated composite NPs into the matrix improves the thermal conductivity, from 0.205 W∙m−1∙K−1 for neat nylon 12 to 0.305 W∙m−1∙K−1 for a 4 wt% C-coated ZnO composite, in addition to a 27% improvement in tensile strength at 2 wt% addition

Co-Zeolitic Imidazolate Framework@Cellulose Aerogels from Sugarcane Bagasse for Activating Peroxymonosulfate to Degrade P-Nitrophenol

An efficient, green and reusable catalyst for organic pollutant wastewater treatment has been a subject of intense research in recent decades due to the limitation of current technologies. Cellulose based aerogel composites are considered to be an especially promising candidate for next-generation catalytic material. This project was conducted in order to evaluate the behavior and ability of green and reusable sugarcane bagasse aerogels to remove P-Nitrophesnol from waste-water aqueous. Co-Zeolitic imidazolate framework@ sugarcane bagasse aerogels composite catalysts were successfully prepared via simple in situ synthesis. The structure of hybrid aerogels and their efficient catalyst in peroxymonosulfate (PMS) activation for the degradation of p-nitrophenol (PNP) was investigated. As a result, the hybrid aerogels/PMS system removed 98.5% of PNP (10 mg/L) within 60~70 min, while the traditional water treatment technology could not achieve this. In addition, through a free radical capture experiment and electron paramagnetic resonance (EPR), the degradation mechanism of PNP was investigated. Further research found that the hybrid aerogels can effectively activate PMS to produce sulfate (SO∙ −4) and hydroxyl (OH∙ ). Both of them contributed to the degradation of PNP, and SO∙ −4 plays a crucial role in the degradative process. The most important feature of hybrid aerogels can be easily separated from the solution. The obtained results showed that the outer coating structure of cellulose can stabilize Co-ZIF and reduce the dissolution of cobalt ions under complex reaction conditions. Moreover, the prepared hybrid aerogels exhibit excellent reusability and are environmentally friendly with efficient catalytic efficiency. This work provides a new strategy for bagasse applications and material reusability

Piezoelectric Property of Electrospun PVDF Nanofibers as Linking Tips of Artificial-Hair-Cell Structures in Cochlea

The death of hair cells and damage of natural tip links is one of the main causes of hearing-loss disability, and the development of an advanced artificial hearing aid holds the key to assisting those suffering from hearing loss. This study demonstrates the potential of using electrospun polyvinylidene fluoride (PVDF) fibers to serve as the artificial tip links, for long-term hearing-aid-device development based on their piezoelectric properties. We have shown that the electrospun PVDF-fiber web, consisting of fibers ranging from 30–220 nm in diameter with high β-phase content, possesses the high piezoresponse of 170 mV. Analyses based on combined characterization methods including SEM, TEM, XRD, FTIR, Raman, DSC, XPS, PFM and piezoelectricity have confirmed that an optimized value of 15 wt.% PVDF could act as an effective candidate for a tip-link connector in a vibration-frequency prototype. Based on this easily reproducible electrospinning technique and the multifunctionalities of the resulting PVDF fibers, this fundamental study may shed light on the bio-inspired design of artificial, self-powered, high performance, hair-cell-like sensors in cochlea to tackle the hearing loss issue

In situ fabrication of porous biochar reinforced W18O49 nanocomposite for methylene blue photodegradation

In this paper, a novel cow dung based activated carbon (CDAC) was successfully modified by W18O49 nanowires as a photocatalyst using KOH activation and a hydrothermal method. The activity of photocatalytic degradation of methylene blue (MB) under full-spectrum light illumination shows great improvement, and the degradation rate of MB could reach 98% after 240 min (67% for W18O49), with a final degradation rate of 98%. The porous structure with specific surface area of CDAC (∼479 m2 g−1) increases the adsorption of W18O49 reactants and also raises the concentration of reactants in the photocatalytic region. The high electrical conductivity and good electron storage capacity of CDAC allow the electrons excited in the conduction band (CB) of W18O49 to migrate smoothly into CDAC, which are the keys to enhancing the photocatalytic activity. Moreover, the photocatalytic mechanism was proposed. The results show that the CDAC/W18O49 nanowire composite can be used as an efficient photocatalyst for removal of MB dye from wastewater and indicate remarkable future potential in dye wastewater treatment technologies

Novel Au–SiO2–WO3 Core–Shell Composite Nanoparticles for Surface-Enhanced Raman Spectroscopy with Potential Application in Cancer Cell Imaging

This is the final version. Available on open access from Wiley via the DOI in this recordWith the rapid development of nanotechnology during the last decades, the ability to detect and control individual objects at the nanoscale has enabled to deal with complex biomedical challenges. In cancer imaging, novel nanoparticles (NPs) offer promising potential to identify single cancer cells and precisely label larger areas of cancer tissues. Herein, a new class of size tunable core-shell composite (Au-SiO2-WO3) nanoparticles is reported. These nanoparticles display an easily improvable ∼ 103 surface-enhanced Raman scattering (SERS) enhancement factor (EF) with a double Au shell for dried samples over Si wafers and several orders of magnitude for liquid samples. WO3 core nanoparticles of 20-50 nm in diameter are sheathed by an intermediate 10-60 nm silica layer, produced by following the Stöber basedprocess and Turkevich method, followed by a 5-20 nm thick Au outer shell. By attaching 4- mercaptobenzoic acid (4-MBA) molecules as Raman reporters to the Au, high-resolution Raman maps which pinpoint the nanoparticles’ location are obtained. Our preliminary results confirm their advantageous SERS properties for single-molecule detection, significant cell viability after 24 h and in vitro cell imaging using coherent anti-stokes Raman scattering (CARS). Our long-term objective is to measure SERS nanoparticles in vivo using NearInfrared light.Engineering and Physical Sciences Research Council (EPSRC

N-Doped Graphenelike Nanostructures from p-Nitro Aniline-Based Foam: Formation, Structure, and Applications as a Nanofiller

Production of snake foam based on p-nitro aniline (PNA) was considered fun in old-school chemistry laboratories. Herein, we report the fabrication of a new carbon nanomaterial from PNA-based foam. The resulting material, resembling graphene and consisting of nitrogen heteroatoms, is N-doped graphene like nanostructures, and their morphology, structure, and stability are comprehensively examined using combined techniques including C-13 NMR spectroscopy, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). An optimized route was also established for their large-scale production. Further experimental validation of them as a nanofiller in polymer [SEBS (20 wt %) and paraffin wax (80 wt %)]-based nanocomposites was carried out, and we foundthat the thermomechanical properties of the nanocomposites were synchronously improved, which was attributed to the enshrouding effect of the nanofiller to the polymer chains. Owing to their good thermomechanical property and low-cost feature, these new nanomaterials can be further explored as a promising candidate for applications in energy storage, catalysis, and CO2 capture