Sol-gel-based porous Ti-doped tungsten oxide films for high-performance dual-band electrochromic smart windows

Dual-band electrochromic smart windows(DESWs)with independent control of the transmittance of near-infrared and visible light show great potential in the application of smart and energy-saving buildings.The current strategy for building DESWs is to screen materials for composite or prepare plasmonic nanocrystal films.These rigorous preparation processes seriously limit the further development of DESWs.Herein,we report a facile and effective sol-gel strategy using a foaming agent to achieve porous Ti-doped tungsten oxide film for the high performance of DESWs.The introduction of foaming agent polyvinylpyrrolidone during the film preparation can increase the specific surface area and free carrier concentration of the films and enhance their independent regulation ability of near-infrared electrochromism.As a result,the optimal film shows excellent dual-band electrochromic properties,including high optical modulation(84.9%at 633 nm and 90.3%at 1200 nm),high coloration efficiency(114.9 cm^(2) C^(-1) at 633 nm and 420.3 cm^(2) C^(-1) at 1200 nm),quick switching time,excellent bistability,and good cycle stability(the transmittance modulation losses at 633 and 1200 nm were 11%and 3.5%respectively after 1000 cycles).A demonstrated DESW fabricated by the sol-gel film showed effective management of heat and light of sunlight.This study represents a significant advance in the preparation of dual-band electrochromic films,which will shed new light on advancing electrochromic technology for future energy-saving smart buildings.

Niobium Tungsten Oxide in a Green Water‑in‑Salt Electrolyte Enables Ultra‑Stable Aqueous Lithium‑Ion Capacitors

Aqueous hybrid supercapacitors are attracting increasing attention due to their potential low cost,high safety and eco-friendliness.However,the narrow operating potential window of aqueous electrolyte and the lack of suitable negative electrode materials seriously hinder its future applications.Here,we explore high concentrated lithium acetate with high ionic conductivity of 65.5 mS cm−1 as a green“water-in-salt”electrolyte,providing wide voltage window up to 2.8 V.It facilitates the reversible function of niobium tungsten oxide,Nb18W16O93,that otherwise only operations in organic electrolytes previously.The Nb18W16O93 with lithium-ion intercalation pseudocapacitive behavior exhibits excellent rate performance,high areal capacity,and ultra-long cycling stability.An aqueous lithium-ion hybrid capacitor is developed by using Nb18W16O93 as negative electrode combined with graphene as positive electrode in lithium acetate-based“water-in-salt”electrolyte,delivering a high energy density of 41.9 W kg−1,high power density of 20,000 W kg−1 and unexceptionable stability of 50,000 cycles.

Synthesis and electrical characterization of tungsten oxide nanowires

Tungsten oxide nanowires of diameters ranging from 7 to 200 nm are prepared on a tungsten rod substrate by using the chemical vapour deposition （CVD） method with vapour-solid （VS） mechanism.Tin powders are used to control oxygen concentration in the furnace,thereby assisting the growth of the tungsten oxide nanowires.The grown tungsten oxide nanowires are determined to be of crystalline W18O49. I-V curves are measured by an in situ transmission electron microscope （TEM） to investigate the electrical properties of the nanowires.All of the I-V curves observed are symmetric,which reveals that the tungsten oxide nanowires are semiconducting. Quantitative analyses of the experimental I-V curves by using a metal semiconductor-metal （MSM） model give some intrinsic parameters of the tungsten oxide nanowires,such as the carrier concentration,the carrier mobility and the conductivity.

Aerobic oxidative desulfurization via magnetic mesoporous silica-supported tungsten oxide catalysts

It is usually difficult to remove dibenzothiophenes from diesel fuels by oxidation with molecular oxygen as an oxidant.In the study,tungsten oxide was supported on magnetic mesoporous silica by calcination to form a magnetically separable catalyst for oxidative desulfurization of diesel fuel.By tuning different calcining temperatures,the catalyst calcined at 500℃showed a high catalytic activity with molecular oxygen as the oxidant.Under optimal reaction conditions,the sulfur removal of DBT reached 99.9%at 120℃after 8 h.Furthermore,the removals of 4-methyldibenzothiophene and 4,6-dimethyldibenzothiophene could also get up to 98.2%and 92.3%under the same conditions.The reaction mechanism was explored by selective quenching experiments and FT-IR spectra.

Structures and optical properties of tungsten oxide thin films deposited by magnetron sputtering of WO_3 bulk:Effects of annealing temperatures

Tungsten oxide thin films were deposited on glass substrates by the magnetron sputtering of WO3 bulk at room temperature. The deposited films were annealed at different temperatures in air. The structural measurements indicate that the films annealed below 300℃ were amorphous, while the films annealed at 400 ℃ were mixed crystalline with hexagonal and triclinic phases of WO3. It was observed that the crystallization of the annealed films becomes more and more distinct with an increase in the annealing temperature. At 400 ℃, nanorod-like structures were observed on the film surface when the annealing time was increased from 60 min to 180 min. The presence of W=O stretching, W-O-W stretching, W-O-W bending and various lattice vibration modes were observed in Raman measurements. The optical absorption behaviors of the films in the range of 450-800 nm are very different with changing annealing temperatures from the room temperature to 400 ℃. After annealing at 400 ℃, the film becomes almost transparent. Increasing annealing time at 400 ℃ can lead to a small blue shift of the optical gap of the film.

Hydrogen Reduction of Tungsten Oxides Part Ⅰ:Reduction of WO_(2.90),W_(20)O_(58) and WO_3

The hydrogen reduction of tungsten oxides WO_(2.90),W_(20)O_(58) and WO_3 were directly studied using high temperature X-ray diffraction analysis.The differences between tetragonal WO_(2.90) and monoclinic W_(20)O_(58) were discussed.Pure β-W was obtained from oxide WO_(2.90),while there appears small amount of WO_2 during the reduction of W_(20)O_(58) to β-W.

Hydrogen Reduction of Tungsten Oxides Part Ⅱ:Reduction of WO_(2.72) and WO_2,Transformation of β-W

The hydrogen reduction of tungsten oxides WO_(272)and WO_2 were studied directly using high-temperature X-ray diffraction analysis,The pure β-W was obtained from the reduction of WO_(272)The transformation of β-W to x-W was also studied in both hydrogen and nitrogen.The forming condition of β-W from WO_2 was discussed.Finally.a complete schematic diagram of reduction of tungsten oxides was given in this paper.

Towards an optical coupler using fine-wire:a study of the photovoltaic effect of a heterojunction formed in a single fine-wire of tungsten oxides

Nanodevices using the photovoltaic effect of a single nanowire have attracted growing interest. In this paper, we consider potential applications of the photovoltaic effect to optical signal coupling and optical power transmission, and report on the realization of a heterojunction formed between WO2 and WO3 in a fine-wire having a diameter on the micrometer scale. Using a laser beam of 514.5 nm as a signal source, the WO2-WO3 heterojunction yields a maximum output power of up to 37.4 pico watt per heterojunction. Fast responses （less than a second） of both photovoltaic voltage and current are also observed. In addition, we demonstrate that it is a simple and effective way to adapt a commercial Raman spectrometer for the combined functions of fabrication, material characterization and photovottaic measurement of an optical signal coupler and optical power transmitter based on a fine-wire. Our results show an attractive perspective of developing nanowire or fine-wire elements for coupling optical signals into and for powering a nanoelectronic or nano-optoelectronic integrated circuit that works under the condition of preventing it from directly electrically connecting with the optical coupler.

Fabrication of oxygen-defective tungsten oxide nanorods for deep oxidative desulfurization of fuel

Owing to the increasingly serious environmental issues caused by the sulfur burnt in fuel, desulfurization has become an important topic. In this work, an amphiphilic oxygen-defective tungsten oxide was synthesized by a colloidal chemistry method. The amphiphilic property and oxygen defects were well characterized, and the structure of the oxygen-defective tungsten oxide catalyst was investigated. In addition, the catalyst was employed in oxidative desulfurization system of fuel,and deep desulfurization was achieved. It was found that the very high oxidative desulfurization performance of oxygendefective tungsten oxide catalyst resulted from both the amphiphilic property and oxygen defects. This work can provide a strategy for preparation of highly active metal oxide catalysts with oxygen defects in oxidative desulfurization reaction of fuel.

Morphology-controlled preparation of tungsten oxide nanostructures for gas-sensing application

A novel three-dimensional（3D） hierarchical structure and a roughly oriented one-dimensional（1D） nanowire of WO3 are selectively prepared on an alumina substrate by an induced hydrothermal growth method.Each hierarchical structure is constructed hydrothermally through bilateral inductive growth of WO3 nanowire arrays from a nanosheet preformed on the substrate.Only roughly oriented 1D WO3 nanowire can be obtained from a spherical induction layer.The analyses show that as-prepared 1D nanowire and 3D hierarchical structures exhibit monoclinic and hexagonal phases of WO3,respectively.The gas-sensing properties of the nanowires and the hierarchical structure of WO_3,which include the variations of their resistances and response times when exposed to NO2,are investigated at temperatures ranging from room temperature（20 ℃） to 250 ℃ over 0.015 ppm-5 ppm NO2.The hierarchical WO3 behaves as a p-type semiconductor at room temperature,and shows p-to-n response characteristic reversal with the increase of temperature.Meanwhile,unlike the1 D nanowire,the hierarchical WO3 exhibits an excellent response characteristic and very good reversibility and selectivity to NO2 gas at room temperature due to its unique microstructure.Especially,it is found that the hierarchical VO3-based sensor is capable of detecting NO2 at a ppb level with ultrashort response time shorter than 5 s,indicating the potential of this material in developing a highly sensitive gas sensor with a low power consumption.

Amorphous hybrid tungsten oxide–nickel hydroxide nanosheets used as a highly efficient electrocatalyst for hydrogen evolution reaction

There are more challenges for alkaline hydrogen evolution reaction(HER)via simultaneously expediting the electron-coupled water dissociation process(Volmer step)and the following electrochemical H_(2) desorption(Heyrovsky step).Hybrid amorphous electrocatalysts are highly desirable for efficient hydrogen evolution from water-alkali electrolyzers due to the bifunctionality for the different elementary steps of HER and optimal interactions with water molecules and the reactive hydrogen intermediates(Had).Herein,the synthesis of amorphous hybrid ultrathin(tungsten oxide/nickel hydroxide)hydrate(a-[WO_(3)/Ni(OH)_(2)]·0.2H_(2)O)nanosheets on nickel foam(NF)for efficient alkaline HER is described.The structural and composition features of a-[WO_(3)/Ni(OH)_(2)]·0.2H_(2)O are characterized in detailed.The resulting a-[WO_(3)/Ni(OH)_(2)]·0.2H_(2)O/NF electrocatalyst with the synergistic effect of both hybrid components for the HER elementary steps shows greatly improved the activity and durability for the HER with a low overpotential of-41 and-163 mV at-10 and-500 mA·cm^(-2),respectively,a Tafel slope as low as-72.9 mV·dec^(-1),and long-term stability of continuous electrolysis for at least 150 h accompanying by inappreciable overpotential change in 1 M KOH.In the hybrid a-[WO_(3)/Ni(OH)_(2)]·0.2H_(2)O,Ni(OH)_(2) and WO_(3) moieties are separately responsible for accelerating dissociative adsorption of water and weakening Had adsorption strength,which is beneficial to the improvement of the alkaline HER activity.

Atomic tailoring-induced deficiency in tungsten oxides for high-performance energy-related devices

Nowadays,tungsten oxides,as a typical transition metal oxide,are widely and intensively investigated owing to their excellent material properties and device properties.Controlling oxygen defi ciency in tungsten oxides is typically the key to enhance their performances for a variety of critical technological applications.With a gradual increase of oxygen defi ciency,various non-stoichiometric tungsten oxides can be formed by re-adjustment of the atomic arrangement,which exhibits superior performances than their traditional stoichiometric counterparts.This review mainly focuses on the recent advances in oxygen-defi cient tungsten oxides from the point of atomic structures,including the forming mechanism of non-stoichiometric tungsten oxides and the superiority of these oxygen-defi cient tungsten oxides in energy-related devices.Finally,the challenge and perspective of oxygen-defi cient tungsten oxides are also discussed.

Tungsten oxide-anchored Ru clusters with electron-rich and anti-corrosive microenvironments for efficient and robust seawater splitting

Ruthenium(Ru)has been recognized as a prospective candidate to substitute platinum catalysts in water-splitting-based hydrogen production.However,minimizing the Ru contents,optimizing the water dissociation energy of Ru sites,and enhancing the long-term stability are extremely required,but still face a great challenge.Here,we report on creating tungsten oxide-anchored Ru clusters(Ru-WO_(x))with electron-rich and anti-corrosive microenvironments for efficient and robust seawater splitting.Benefiting from the abundant oxygen vacancy structure in tungsten oxide support,the Ru-WO_(x)exhibits strong Ru-O and Ru-W bonds at the interface.Our study elucidates that the strong Ru-O bonds in Ru-WO_(x)may accelerate the water dissociation kinetics,and the Ru-W bonds will lead to the strong metal-support interaction and electrons transfer fromWto Ru.The optimal Ru-WO_(x)catalysts exhibit a low overpotential of 29 and 218mVat the current density of 10 mA cm^(−2) in alkaline and seawater media,respectively.The outstanding long-term stability discloses that the Ru-WO_(x)catalysts own efficient corrosion resistance in seawater electrolysis.We believe that thiswork offers new insights into the essential roles of electron-rich and anti-corrosivemicroenvironments in Ru-based catalysts and provide a new pathway to design efficient and robust cathodes for seawater splitting.

Oxygen-deficient tungsten oxide nanoflowers for dynamically tunable near-infrared light transmittance of smart windows

Electrochromic smart windows have attracted much attention in energy-saving buildings because of their ability to selectively modulate visible(VIS)and near-infrared(NIR)light transmittance.As is known,the NIR region accounts for about 50%of the total solar radiation.Therefore,reducing the NIR transmittance of windows will play a crucial role in reducing the energy consumption of buildings.However,for most of the reported electrochromic materials(ECMs)-based windows,it remains a longlasting challenge about how to achieve a low NIR transmittance during the past decades.In this work,we synthesize oxygendeficient tungsten oxide(WO_(3−x))nanoflowers(NFs)by a simple and efficient method that is facile for their mass production.The WO_(3−x)NFs exhibit low NIR transmittance of only 4.11%,0.60%,and 0.19%at 1200,1600,and 1800 nm,respectively,due to the localized surface plasmon resonance(LSPR)effect.Besides,the WO_(3−x)NFs exhibit an excellent dual-band modulating ability for both VIS and NIR light.They are able to operate in three distinct modes,including a bright mode,a cool mode,and a dark mode.Moreover,the WO_(3−x)NFs exhibit a fast bleaching/coloring time(1.54/6.67 s),and excellent cycling stability(97.75%of capacity retention after 4000 s).

Photo-induced carbon dioxide reduction on hexagonal tungsten oxide via an oxygen vacancies-involved process

Although converting the greenhouse gasses carbon dioxide(CO_(2))into solar fuels is regarded as a convenient means of solar energy storage,the intrinsic mechanism on how the high chemical inertness linear CO_(2)molecules is activated and converted on a semiconductor oxide is still elusive.Herein,by creating the oxygen vacancies on the typical hexagonal tungsten oxide(WO3),we realize the continuous photoinduced CO_(2)reduction to selectively produce CO under light irradiation,which was verified by isotope labeling experiment.Detailed oxygen vacancies evolution investigation indicates that light irradiation can simultaneously induce the in-situ formation of oxygen vacancies on hexagonal WO3,and the oxygen vacancies promote the adsorption and activation of CO_(2)molecules,leading to the CO_(2)reduction to CO on the hexagonal WO3via an oxygen vacancies-involved process.Besides,the existence of water further promotes the formation of CO_(2)reduction intermediate,further promote the CO_(2)photoreduction.Our work provides insight on the mechanism for converting CO_(2)into CO under light irradiation.

A review article based on composite graphene@tungsten oxide thin films for various applications

Graphene and its derivatives are the hot topics of research during this decade due to their excellent thermal conductivities,mechanical strength,current densities,electron motilities,and large surface area.This review article explores the outstanding applicability and features of graphene derivatives.The transition metal oxides(TMOs)have also gained considerable research attention due to their unique physicochemical properties in photocatalytic,self-cleaning,and gas sensing applications.Among TMOs,tungsten metal oxides have received a tremendous response as they are naturally abundant,low in cost,less toxic,environmental friendly,and can be manufactured using various physical and chemical methods.It exhibits a cubic perovskite-like structure based on the corner-sharing of regular octahedra with the oxygen atoms at the corner and the tungsten atoms at the centre of each octahedron.It also shows structural polymorphism and sub stoichiometric phase transitions,which attracted the attention of researchers over the past few years to explore their potential in various applications.Pairing graphene and its derivatives with tungsten oxide(WO_(3))to create heterojunction could be an auspicious tool to improve photocatalysis,energy storage,medical,electrochromism,and energy efficiency conversion.In addition,composite exhibits significantly higher efficiency than either individual material due to their well-matched band edge positions,efficient charge separation,and light-harvesting abilities.The morphology and heterojunction were found to be quite beneficial in improving the overall performance of the composite.In this review article,the noteworthy endeavors and turning points are accomplished utilizing heterojunction between WO_(3)and graphene derivatives for different applications.This review article will also provide the research gap and excite new ideas for further improvement of graphene-based tungsten oxide nanocomposites.Conclusively,the scope of future research work to design the ternary composite with high efficiency utilizing WO_(3)and graphene is also explored.

Electron beam evaporated gold doped tungsten oxide nanostructured films for sensor applications

Gas sensors play a vital role in monitoring environmental pollution for human health,safety,and the detection of various gasses in the environment.Nanostructured metal oxide thin films have been widely used in sensor applications owing to their unique properties.In this study,pure and gold(Au)doped nanostructured tungsten trioxide(WO_(3))films were deposited on glass substrates by electron beam evaporation at room temperature.The microstructure of the WO_(3) films changed from nanoflakes to nanorods upon variation of the wt%of Au.The sensing properties of WO_(3) based nanostructure films were measured using a computer-controlled system.The gas sensing results showed that the Au-doped WO_(3) films exhibited a higher sensitivity than the undoped films.The 15 wt%Au-doped WO_(3) nanostructure films showed high sensitivity towards ethanol and the response(sensitivity)value was 89.The response and recovery times for 15 wt%Au-doped WO_(3) were 8 and 10 s,respectively.

Effect of tungsten oxide on ceria nanorods to support copper species as CO oxidation catalysts

In this work,tungsten oxide with different concentrations(0,0.4 at%,2.0 at%and 3.2 at%)was introduced to the ceria nanorods via a deposition-precipitation(DP)approach,and copper species of ca.10 at%were sequentially anchored onto the modified ceria support by a similar DP route.The aim of the study was to investigate the effect of the amount of tungsten oxide(0,0.4 at%,2.0 at%,and 3.2 at%)modifier on the copper-ceria catalysts for CO oxidation reaction and shed light on the structure-activity relationship.By the aids of multiple characterization techniques including N2 adsorption,high-resolution transmission electron microscopy(HRTEM),powder X-ray diffraction(XRD),X-ray absorption fine structure(XAFS),and temperature-programmed reduction by hydrogen(H2-TPR)in combination with the catalytic performance for CO oxidation reaction,it is found that the copper-ceria samples maintain the crystal structure of the fluorite fcc CeO2 phase with the same nanorod-like morphology with the introduction of tungsten oxide,while the textural properties(the surface area,pore volume and pore size)of ceria support and copper-ceria catalysts are changed,and the oxidation states of copper and tungsten are kept the same as Cu2+and W6+before and after the reaction,but the introduction of tungsten oxide(WO3)significantly changes the metal-support interaction(transfer the CuOx clusters to Cu-[Ox]-Ce species),which delivers to impair the catalytic activity of copper-ceria catalysts for CO oxidation reaction.

Electroreduction of Tungsten Oxide（VI） in Molten Salts with Added Metaphosphate

Tungstate ions WO4^2- are not electrochemically active in chloride melts. Upon introduction of PO3 ions into the melt, two waves appear in the voltammograms at potentials -0.1-- -0.2 V and -0.3-- -0.5 V vs. Pb/Pb2＋ reference electrode. With a PO3- concentration ratio of 0.01〈[PO3-]/[WO42-]〈0.18, the potentiostatic electrolysis product of WO42 at the above mentioned potentials is metallic tungsten; a NaPO3 concentration increase for ratios [PO3-]/[WO42-]〉〉0.18 results in tungsten phosphide in electrolysis product. Cyclic voltammograms and dependence of half-peak potentials on electrode polarization rate indicate the irreversible character of the electrode process. Elec- trode process modeling allows us to state that the first wave in the voltammogram of KC1-NaC1-Na2WOa-NaPO3 sys- tem corresponds to tungsten oxychlorides discharge while the second wave appears due to the discharge of di- tungstate ions. In the voltammograms of Na2WOa-NaPO3 melts, reduction wave was observed at -1.1-- -1.2 V po- tentials. Proportionality of limiting current to NaPO3 concentration, constancy of ld/V1/2 ratio, and IJnFc constant ki- netic value equal to （8.3--9.5）×10-5 cm/s for steady-state wave indicate that electrode process rate is limited by elec- trochemically active particle diffusion to the electrode. Nascent ditungstate ions become electrochemically active in the overall electrode process. Charge transfer stage is reversible.

Tungsten oxide thin films for highly sensitive triethylamine detection

Metal oxide semiconductor(MOS)thin films are promising sensing layer for integration in gas sensor devices for detecting toxic and harmful molecules.Herein,tungsten oxide(WO_(3))thin films are deposited on interdigital electrodes by vacuum thermal evaporation to realize batch fabrication of high-performance gas sensors.Subsequent annealing at different temperatures allows for regulation of the concentration of oxygen vacancies in the WO_(3) films,which has been found to exert a great influence on the sensor properties.In addition,the surface structure of WO_(3) films is also highly dependent on the annealing temperature.Gas sensing investigations show that the WO_(3) sensor annealed at 500℃ pos-sesses the best sensing properties for detecting triethylamine(TEA)including very high response,good selectivity,fast response,and low limit of detection(63 ppb).The excellent sensor performances are attributed to the enhanced adsorption of oxidative oxygen species due to the presence of abundant oxygen vacancies.The scalable fabrication of WO_(3) thin film gas sensors and the oxygen vacancy engi-neering strategy proposed herein may shed some light to developing high performance environmental sensors.