2016年9月29日星期四

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.

If you have any other question or inquiry of tungsten oxide, please feel free to contact us through the following methods:
Tel.: +86 592 5129696/86 592 5129595
Fax: +86 592 5129797

Tungsten Oxide Photodegradation Organic Pollutant

Tungsten oxide is an ideal photocatalyst in transition metal oxide which has properties of high catalytic property, low cost, nontoxic and stable. It is now used to degrade organic pollutant such as ethanal, chloroform and fuel into inorganic material. The principle is degrade it into CO2 and H2O, it has high degradation efficient and wide application prospect.
According to thermodynamic argument, the electron hole on the surface of tungsten oxide oxidizes the OH- and hydrone into OH- (free radical). OH- has strong oxidation capability, it can oxidize most of organic and inorganic pollutant and degrade them into innoxious substance like CO2 and H2O. On the other side, active electron on the surface of tungsten oxide has strong reducing capability, it can reduce and remove heave metal ion in the water.

Tungsten Oxide Crystalline Structure

Early research is mainly about applying nano powder semiconductor catalyst in eliminating pollutant in water, but the recovery of catalyst is difficult, it needs dynamic mixing to maintain the suspension of catalyst, the active ingredients loss is significant. Besides that, granule catalyst may cause secondary pollution, it is hard to realize industrialization. In order to overcome the above shortcomings, people use the method of immobilization of photocatalyst which means immobilizing the WOcatalyst on the glass substrate. However, it lowers the specific surface area of catalyst, causes the reacting area with light reducing, affect catalytic activity. The combination strength of catalyst and substrate reduces, the acid and alkali resistance of substrate material is worse. Thus it isn’t suitable for industrial application.

In recent years, many newly developed nano structure catalyst, such as nanohole, nanotube, nanowire and nanorod. Its large specific surface area can promote the photocatalytic activity and photovoltaic conversion which greatly draw people’s attention. For example, use electrochemical anodic oxidation to prepare WO3 nano porous array can largely enlarge the specific surface area of thin film catalyst. It has better photocatalytic property than powder catalyst.

If you have any other question or inquiry of tungsten oxide, please feel free to contact us through the following methods:
Tel.: +86 592 5129696/86 592 5129595
Fax: +86 592 5129797

Tungsten Oxide Preparing Tungsten Disulfide Lubricant

Tungsten disulfide is a kind of solid inorganic lubricant material. The appearance and physical property is similar to calcium disulfide. The physical and chemical property of tungsten disulfide shows that it can not only be used in the regular lubricant, but also can be applied under certain high temperature, low temperature, high load, high vacuum and corrosion circumstances. It can be used with powder appearance, or can be mixed with lubricant, graphite, metal powder or plastic as compound materials.

With the development of scientific technology, the requirement for lubricant material has also been promoted. To solve the lubricant problems, tungsten disulfide has draw people’s attention like other innovative materials. Although there are many methods to prepare tungsten disulfide, the thorough material about its preparing method is rare. The method using tungsten oxide to prepare high purity tungsten disulfide is easy to operate and can assure the quality of the product.

Tungsten Oxide and WS2

Preparing method:
Raw material: Tungsten oxide (WO3); Sulfuric acid: 20% aqueous solution; Sodium sulfate: 20% aqueous solution.
(1) Adding a certain amount of tungsten oxide into tray, then press it properly. Put the tray into the middle of tubular reactor, connect the conduit, seal the gaps between all interfaces with wax or stop-leak compound. Open the outlet valve of container of sulfuric acid and sodium sulfide, the hydrogen sulfide gas is obtained.
(2) Lead hydrogen sulfide from the bottom of container. After the outlet gas of the container is non-explosive gas (use tube to gather gas to test), clean the bottle by connecting sodium hydroxide container.
(3) Adjust flow rate of sulfuric acid and sodium sulfide solution to keep the pressure of system under 3.92~4.90kPa. Charge with electricity, upper the temperature to a certain value, and keep it stable, lower the temperature to 400℃ when input hydrogen sulfide. Then stop inputting and keep it to room temperature.
Under high temperature, tungsten oxide reacts with hydrogen sulfide, tungsten disulfide with chemical formula WS1.98一WS2.12 is obtained. This method is easy to operate and stable.

If you have any other question or inquiry of tungsten oxide, please feel free to contact us through the following methods:
Tel.: +86 592 5129696/86 592 5129595
Fax: +86 592 5129797

Tungsten Oxide Nanorod

Since indium storage property of nanocrystalline transition metal oxide (MO,M=Co, Ni, Cu, Fe) is found, other transition metal oxide such as CuO, Fe2O3, Fe2O4, Co3O4, WOcan be transited by chemical reaction MOx+2xLi+=M+xLi2O. Its capacity is far better than graphite anode material in lithium ion battery. Among which WO3 is the most stable oxide of tungsten under room temperature. It is not only environmental friendly, but also is cheap. It has potential to be widely applied as lithium ion battery anode material. However, tungsten oxide in lumpish has low electric conductivity, its volume changes greatly during charge-discharge process. Thus results in the instability of WO3. One of the improving methods is to synthesis WO3 nano material of different appearance. Then lithium storage property of the material is improved.

WO3 Nanorod SEM

Preparing method: By hydrothermal method, tungsten oxide nanorod can be prepared on the indium tin oxide substrate.
Raw material: Sodium tungstate (AR: analytically pure); NaCl (AR); oxalic acid (AR); methylene blue (AR); hydrochroric acid. All solution is prepared by deionized water. ITO electric glass is under ultrasound for 10min in acetone, ethyl alcohol and deionized water, then dry it.

Preparing process:
(1) Dissolve 8.25g sodium tungstate in 25ml deionized water, then adding hydrochloric acid to adjust PH value into 2.0.
(2) Then dilute the solution to 250ml, put in PH meter, adding oxalic acid into solution, adjust PH value to 2.3, the precursor solution is obtained.
(3) Adding 0.3g sodium chloride into hydrothermal reactor, put in the ITO glass and make sure it is slanted. Then adding 20ml precursor solution, sealed it and thermal reacting for 4 hours under 170℃.
(4) After the reaction is done, cool it down to room temperature. Clean the ITO with deionized water and dry it. Tungsten nanorod of even size and bigger density is obtained.

If you have any other question or inquiry of tungsten oxide, please feel free to contact us through the following methods:
Tel.: +86 592 5129696/86 592 5129595
Fax: +86 592 5129797

Tungsten Oxide Nanotube

When particle size of some material reaches to nano grade (1~100nm), it can show many special reactions. It can be widely applied in functional information display, catalyst, magnetic material. Among which, tungsten oxide has various crystalline structure, it has a large amount of non-stoichiometry oxide form and has multi-functional broad-band gap semiconductor material. WO3 is widely applied in gas sensor, photocatalyst, gasochromism, electrochromism, photochromism and solar cell due to its unique electricity, optical configuation, and magnetic property. Apart from that, temperature induces structure phase transition which results in the changes of volume, resistance and color greatly draw people’s attention. The research on its special structure has become the focus of recent study.

WO3 Nanotube SEM

The traditional preparing method of tungsten oxide nanotube need extra coating and sculpture process, the quality of nanotube greatly depends on the control of processing steps. By coaxial electrospinning, hollow nano fiber can be obtained, manufacturing process is simplified.

Raw material: PVA; ammonium metatungstate; absolute ethyl alcohol; aluminum foil; deionized water.
Preparing process:
(1) Weigh a certain amount of PVA to dissolve in deionized water, stirring it for 4hous in constant temperature of 80℃ and prepare it to 15% PVA solution. Then add 24ml alcohol and 6g ammonium metatungstate solution into 60ml PVA solution.
(2) Dilute another 15% PVA solution to 10% as inner pipe solution by deionized water. Inject both inner and outer pipe solution into injector, then inject them into electrostatic spinning coaxial needle.
(3) Under electric voltage 9~15kV, keep spinning with receiving distance of aluminum foil for 10~12cm. Dry the obtained composite fiber in thermotank for 12 hours, keep the temperature to 600℃ by putting it in muffle furnace, and then cool it down to get WO3 nanotube.

If you have any other question or inquiry of tungsten oxide, please feel free to contact us through the following methods:
Tel.: +86 592 5129696/86 592 5129595
Fax: +86 592 5129797

Tungsten Oxide Nanowire

In recent years, one-dimensional nano material such as nanowire, nanorod, nanotube are becoming popular due to its special properties. Tungsten oxide is a special N type semiconductor material, and also one of the oxide semiconductors which can realize quantum size effect. It shows great property in electrochromism, photochromism, gasochromism and is applied in various fields like chemical sensor, fuel cell and electronic device.

Tungsten oxide has crystalline form of orthogonality, monoclinic, cube and hexagonal. Among which hexagonal tungsten oxide is paid much attention due to its special hexagonal panel, many metal ion can inlaying in it. So as to form hexagonal tungsten bronze MxWO3( M = Li +、Na +、K +). It shows great application prospect in negative electrode materials and Iithium ion rechargeable battery.
WO3 Nanowire SEM

Use sodium tungstate and hydrochloric acid as raw material, potassium oxalate and potassium sulphate as additive, hexagonal tungsten oxide nanowire can be synthesized by hydrothermal method.

Raw material: Na2WO4·2H2O; hydrochloric acid, potassium oxalate; potassium sulphate; absolute ethyl alcohol, all analytic grade; deionized water.

Preparing method:

(1) Weigh 3.68g Na2WO4·2H2O to dissolve in 20ml deionized water, stir it and adding 3mol HCL until PH=1.
(2) Keep stirring until there is no light yellow anticipation any more, adding in certain amount of K2C2O4 and K2SO4, keep stirring for 30min.
(3) Move the solution to 100ml stainless ste with polytetrafluoroethylene liner, adding deionized water to 3/4 of the reactor, seal and react under 150℃ for 12h.
(4) Cool it down to room temperature, wash it by deionized water and absolute ethyl alcohol, dry under 60℃, tungsten oxide nanowire is obtained.

If you have any other question or inquiry of tungsten oxide, please feel free to contact us through the following methods:
Tel.: +86 592 5129696/86 592 5129595
Fax: +86 592 5129797