2016年6月27日星期一

Tungsten Oxide Thin Film Electrode Preparation Method

Nano semiconductor material used as photocatalyst to photolysis water has gained well efficiency. TiO2 has high catalytic activity and stability is widely used as a kind of photocatalytic material. But its band gap is big (~3.2 eV), it can only be motivated by ultraviolet with short wave length, its light transaction efficiency is low (~4%). Tungsten oxide is an indirect band series transition semiconductor material. Compared to TiO2, it has narrow band gap (2.5~3.0 eV), the relevant absorbing wave length is 410~500nm and well photoelectric responsive property in visible light area.
WO3 Thin Film Electrode
Tungsten oxide thin film electrode preparation method:
Raw material: FTO glass; tungstic acid; hydrogen peroxide; acetone.
(1) Be ready with clean FTO glass as the substrate of depositing WO3. Cut FTO glass into 1.2cm*2.5cm pieces and clean it by ultrasound and ultraviolet. The clean and flatness of FTO substrate has big effect on adhesive force and uniformity of thin film electrode. So before depositing thin film electrode, the FTO glass should be well cleaned. Firstly, clean the dirties on the surface by ethyl alcohol. Then put the substrate in acetone and ultrasound for 30min to eliminate the ethyl alcohol and oil contamination on the surface. After that, ultrasound it in water for 20 min to eliminate the residual acetone. Finally dry it by nitrogen gas. Then put it into ultraviolet disinfectant tank to sterilize.
(2) Weigh 0.02g tungstic acid and dissolve it by 20ml 30% hydrogen peroxide. Stay it for 12 hours to obtain transparent tungstic acid solution, it will be used as electrolyte solution to deposit WO3.
(3) Use substrate obtained from step (1) as working electrode, measure 30 micro liter tungstic acid solution, dispensing it evenly on the surface of FTO conductive glass. Dry it under room temperature, colorless thin film is obtained.
(4) Put the deposited thin film from step (3) into tube furnace, calcinating it for 2 hours under 500℃, colorless WO3 electrode is obtained.
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Tungsten Oxide Maintains Strength of Steel Against Fouling

While we love ceramics and glass, there’s just no denying it—steel is one of the most important materials to modern living. So this is big—researchers at Harvard University’s John A. Paulson School of Engineering and Applied Sciences have devised a way to improve the ubiquitous steel by protecting its surface from fouling and corrosion.
While there are varying grades of steel today, the surface has remained largely unchanged—meaning that steel is still rather susceptible to corrosion and abrasion. Both disrupt the mechanical stability of steel, among other materials, and have a huge economic impact. According to the Wikipedia page on fouling, “one estimate puts the losses due to fouling of heat exchangers in industrialized nations to be about 0.25% of their GDP. Another analysis estimated (for 2006) the economical loss due to boiler and turbine fouling in China utilities at 4.68 billion dollars, which is about 0.169% of the country’s GDP.”
Harvard researchers have developed a scalable technique to give steel a metal oxide coating to prevent liquids from sticking to its susceptible surface. The new coating, a rough nanoporous tungsten oxide layer, “is the most durable anti-fouling and anti-corrosive material to date, capable of repelling any kind of liquid even after sustaining intense structural abuse.
To prevent performance degradation, aka mechanical instability, the team applied the tungsten oxide coating with electrochemical deposition. Instead of creating an even coating, the method grew tiny islands of the metal oxide floating on steel’s surface.
Tungsten Oxide Coated Steel
(Accelerated corrosion test, in which unmodified stainless steel (300 grade) (right sample) and the lower part of the TO-SLIPS sample with a 600-nm-thick porous TO film on steel (left sample) were exposed to very corrosive Glyceregia stainless steel etchant. (a–h) Images show corrosion evolution as a function of contact time.)
While that may sound like a weakness for the coating, one of the researchers points out just how valuable those islands are: “If one part of an island is destroyed, the damage doesn’t propagate to other parts of the surface because of the lack of interconnectivity between neighboring islands. This island-like morphology combined with the inherent durability and roughness of the tungsten oxide allows the surface to keep its repellent properties in highly abrasive applications, which was impossible until now.”
The material is tested by scratching it with stainless steel tweezers, screwdrivers, diamond-tipped scribers, and pummeling it with hundreds of thousands of hard, heavy beads,” according to the release. “Then, the team tested its anti-wetting properties with a wide variety of liquids, including water, oil, highly corrosive media, biological fluids containing bacteria and blood. Not only did the material repel all the liquid and show anti-biofouling behavior but the tungsten oxide actually made the steel stronger than steel without the coating.
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Tungsten Oxide Thin Film Electrode Oxidation Glucose

Glucose exists in the nature by photosynthesis. Due to its abundant volume, low cost and reproducible, it is regarded as the main energy substrates to produce hydrogen. Glucose is the main waste of agriculture, food and paper-making industry, improper disposition will cause damage to environment. Recently many PEC systems produce hydrogen by glucose.
Tungsten oxide connect with electrocatalyst to produce hydrogen from glucose shows good photocatalytic activity, deposit electrocatalyst on the surface of photocatalyst can promote photocatalytic activity of semiconductor. Electrocatalyst deposited on the surface of semiconductor will form a layer of cover. By changing electron distribution in the system, the surface property of WO3 will be affected, so the photocatalytic activity is improved. Usually if Fermi level of WO3 is higher than the two combined material, electron will keep migrating from WO3 to depositing electrocatalyst. The shallow well potential Schottk energy barrier which can trap electron will form on the surface of metal and electrocatalyst. It provides effective trap potential for separating of photo electron and electron hole, it can resist the composite of photo electron and electron hole further, also the separating efficiency of charge carrier, thus to improve the quantum efficiency of photocatalyst.
Use FTO/WO3/Ni(OH)2 thin film electrode in reduction of glucose experiment. Through this experiment, we can find that exposure of WO3 thin film electrode without Ni(OH)2 barely have photoelectrocatalytic glucose effect. Depositing Ni(OH)2 on the surface of tungsten oxide thin film can enhance photoelectric effect. Below is the raman spectrum and ultraviolet visible light absorption curve comparison of FTO/WOthin film electrode and FTO/WO3/Ni(OH)2.
WO3 NiOH2 raman spectrumWO3 NiOH UV light
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Tungsten Oxide Solar Cell

Research and application of solar cell is the focus of nowadays research on power field, how to improve the efficiency and lowering the cost are the two key problems of solar cell. The manufacturing cost of silica solar cell is too expensive which can not be widely applied. Nano TiO2 solar cell has gradually replaced the traditional one. Its manufacturing cost is only the 1/5~1/10, the photoelectric efficiency is maintained at 10%, its service life can reach 20 years. But how to promote the conversion rate is always the focus of research.
Solar Cell
Nano tungsten oxide material has the advantages like non toxic,harmless, easy to prepare, stable property, low price and fine visible light responsive, it is an ideal semiconductor photo anode material which is widely applied in photoelectrochemical field like photo degradation water, photo degradation organic pollutant and solar cell.
Photo anode material of dye-sensitized solar cell mostly uses TiO2, the main reason is compared to ruthenium photochromics, TiO2 is the best energy level of semiconductor. Tungsten oxide is the common used photo anode catalytic material of PEC photoelectrochemical cell. Compared to TiO2 and ZnO (energy gap 3.4eV), it has smaller energy gap (2.5~2.8eV). Among which the perovskite structure will be easier to control by adjusting A and B site. So tungsten based oxide photo anode is a kind of material which has potential in photoelectrochemical solar cell anode.
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Tungsten Oxide in Polymer Electrolyte Fuel Cell Electrode

Development of new alternative electrode materials is essential in order for the polymer electrolyte fuel cell (PEFC) to be able to reach a broad market. Today, high platinum loadings are required, especially on the cathode, to obtain sufficient activity for oxygen reduction. In addition, electrode degradation causes loss of catalyst surface area and requires high initial loadings to maintain the cell performance over time. There are problems related to Pt also on the anode side where poisoning of the catalyst, by e.g. CO, reduces the activity.
Approaches to improve the electrodes and reduce their costs are continuously evaluated and include alternative catalysts or supports as well as new structures and morphologies of the catalyst layer. Alternative catalysts, based on non-precious metals, Pt alloys/mixtures, and/or novel supports should preferably reduce the total amount of Pt, increase the activity, and be stable in the fuel cell environment. The support material can influence the activity by spill-over effects as well as changing the electronic structure of the catalyst. New support materials can improve the activity, utilization, and stability of the catalyst or of the support itself.
Tungsten oxide is a material which has been extensively investigated for a wide range of applications, mainly, due to its unique electrochromic properties but also for its electrocatalytic activities. The electrochromism allows tungsten oxide to intercalate/deintercalate ions (of e.g. H, Li, Na, K, Pb, Cd) into its structure in the formation of tungsten bronzes. The most widely studied form is the hydrogen tungsten bronze where protons are inserted in the oxide structure as HxWO3 and 0 < x < 1. The bronze formation mechanism has been the subject for numerous studies and it is suggested that the hydrogen atoms form hydroxyl bonds in the tungsten oxide.
WO3 Electrode SEM
The bronze formation is greatly affected by the water content, porosity, and also crystallinity, which in turn affect the catalytic properties of tungsten oxide. At the same time as protons can be incorporated in the WOx structure, they also have a significant mobility which means that WOx functions as a proton conductor under these conditions. Since the hydrogen tungsten bronze formation is dependent on the water content, large variation in conductivity has been reported when varying the relative humidity. Moreover, Pt supported on tungsten oxide has been shown to affect the bronze formation and both an increased intensity of the hydrogen intercalation/deintercalation peaks as well as a shift of the peak potential to higher potentials has been reported.
Tungsten oxide has been evaluated both as support and active catalyst in fuel cell anode as well as cathode electrodes. Sole tungsten oxide has displayed activity for hydrogen oxidation, which was attributed to high porosity and high surface area. Combined Pt and tungsten oxide based catalysts have been investigated for methanol/ethanol oxidation, CO oxidation, hydrogen oxidation as well as oxygen reduction. For methanol oxidation, the Pt on WOx system has shown improved efficiency over Pt catalyst due to both the spill-over of hydrogen from Pt to WOx but also the ability of WOx to provide oxygen atoms at low potentials and thereby avoiding CO-poisoning. Others have attributed the improved performance to an increased electrochemical active surface area (ECSA) of Pt on WOx.
Tungsten oxide is also relatively stable in acidic environment, which is a prerequisite for use in polymer electrolyte fuel cell applications. However, some dissolution of tungsten oxides has been reported. In a previous study, we examined the impact of different metal oxides on the stability and activity of platinum in thin model cathodes in a PEFC. Pt on WOx did exhibit an improved activity for oxygen reduction and possibly also an improved stability compared to Pt alone. Interesting features such as reduced platinum oxide formation and platinum catalyzed hydrogen tungsten bronze formation were also seen when Pt was deposited on WOx.
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Zn Modified Tungsten Oxide Thin Film Electrode

To promote the photoelectrochemical property, we usually take the following methods:
(1) Loading precious simple metal substance such as Pt, Ag, Au. Lay WO3 over FTO with Ag grid, the testing photocurrent density is two times than the one without Ag.
(2) Doping certain amount of metal ion or non-metal ion in tungsten oxide. Doping Ta5+ in WO3 photo electrode, the experiment shows that photoelectric conversion rate of doping electrode is much higher.
(3) Recombine WOwith other inorganic semiconductor material, use impregnation method to prepare CuO/WOcomposite material. It turns out that CuO/WOshows better photo catalytic ethylal.
(4) Recombine WO3 with organic material. Prepare PBrT/WOand PMOT/WOcomposite material. After testing it shows that the composite one has better electrochemical property.

Zn WO3 Film Photoelectrode
This paper mainly focuses on the research of Zn affects WO3 thin film photoelectrode photoelectrochemical property. Use simple cathode electro deposition-impregnation method heating for 3hours in 450℃ to prepare Zn modified tungsten oxide thin film electrode. By testing the photoelectrochemical and photoelectric catalytic activity, a certain amount of Zn doping WOphotoelectrode, its property is greatly improved.
Preparation method:
(1) Use Pt electrode as counter electrode, the saturated calomel electrode as reference electrode, cleaned indium tin oxide electric glass as working electrode. The electro deposition is carried out under room temperature, the applied voltage is -0.6V, deposition time is 1 hour, then blue amorphous form of WO3-x·nH2O thin film is obtained.
(2) After dry in the air, put the thin film in muffle furnace, annealing for 3 hours under 450℃, the heating rate is 2℃·min-1, then we can get tungsten oxide thin film electrode.
(3) Use electro deposition-impregnation method to modify WOelectrode with Zn. Impregnate thin film in Zn(NO3)solution. After dry it in the air, annealing the WO3 thin film contained with Zn in muffle furnace under the same condition with step(2). Finally we can get Zn modified tungsten oxide thin film electrode.
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