1. TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to a composite electrode with in situ polymerized polyaniline comprising a composition of polyaniline, organic sulfonate, polysaccharide, imidazolium buffer and organic chemicals whereby said composite electrode can be used in various applications such as gas sensor, chemical sensor, electrochemical transducer, solar cell, super capacitor, corrosion protection layer etc. 2. BACKGROUND OF THE INVENTION

Conductive polymers such as polypyrrole, polyaniline and polythiophene have been used in a wide variety of electrochemical applications. The widespread use of these conducting polymers is due to some reasons such as ease of preparation, reproducible electrochemical characteristics, manufacturability for in volume production and low cost.

Polyaniline (PANI) is one of the most important intrinsically conducting polymers due to the advantages of simple preparation, good chemical stability and high conductivity. For example, PANI and its composites are widely used as gas sensing materials for the detection of a number of chemicals. Polymerization of aniline is often catalyzed by oxidizing agent such as ammonium persulfate. The resulting polyaniline materials can appear in a number of forms depending on the charge at the nitrogen atoms. Typically different forms of polyaniline materials exhibit different degree of conductivity but invariably the polyaniline powder has no natural adhesion on electrode surface and only slightly soluble in most solvents. The low solubility of polyaniline in common organic solvents causes difficulty in preparing polyaniline for casting or printing applications.

In miniaturized sensing devices, the electrodes are close to each other and electrical contacts are often inaccessible for electro-polymerization. Electrical contacts in miniaturized cells may liable to electrical shorting when the device is immersed in monomer solution. Therefore, other methods such as drop coating, solvent casting, screen printing or inkjet printing is more appropriate for applying polyaniline materials on electrode surface when electro-polymerization of the aniline monomer is not possible due to miniature size of the electrode.

If polyaniline composite paste is to be prepared, the paste can be dispensed or printed onto the working electrode surface for a variety of applications such as in chemical sensors, amperometric cell and conductometric electrodes. Moreover, it is important that the ink or paste composition comprises binding component which is able to hold the polyaniline materials together while maintaining the conductive characteristic and electrochemical properties of polyaniline composite. In addition to this, curing at near ambient temperature within short period of time is preferred because it will be convenient in manufacturing process as well as afford high throughput.

Therefore, adhesion of the polyaniline materials on the electrode surface is the most important requirement in the preparation of polyaniline composite electrode. Furthermore, the dispensed or printed polyaniline layer must exhibit strong adhesion to a wide range of electrode surface such as platinum, carbon, silver, silicon nitride, silicon, polysilicon, silicon oxide, polyester, FR4 or glass. Likewise if the polyaniline composite electrode is to be used as transducers in chemical sensors, the polyaniline composite layer must also able to provide good adhesion with a variety of polymeric sensing membranes such as PVC, acrylate, urethane or silicone rubber acting a sensing top layer.

It would hence be extremely advantageous to develop a method for preparing of polyaniline composite electrode through depositing homogenous phase of polyaniline conductive polymer on electrode surface by a coating technique such as solution casting method. In situ polymerized doped polyaniline which comprises of polyaniline, polysaccharide, organic sulfonate dopant and imidazolium buffer are drop coated to generate homogenous phase of low impedance polymeric networks. The obtained polyaniline composite not only exhibits good adhesion to electrode surface and but also affords reproducible electrochemical characteristics. 3. SUMMARY OF THE INVENTION

Accordingly, it is the primary aim of the present invention to provide a composite electrode with in situ polymerized polyaniline whereby the polyaniline composite exhibits good adhesion to a wide range of electrode surface. It is another object of the present invention to provide a composite electrode with in situ polymerized polyaniline whereby the polyaniline ink can be prepared for casting or printing application.

It is another object of the present invention to provide a composite electrode with in situ polymerized polyaniline which can be prepared within the binding matrix to produce homogenous solution of doped polyaniline.

Yet another object of the present invention is to provide a composite electrode with in situ polymerized polyaniline whereby the polyaniline is soluble in common organic solvent.

Yet another object of the present invention is to provide a composite electrode with in situ polymerized polyaniline which can be drop coated to afford homogenous phase of low impedance polymeric networks.

Other and further objects of the invention will become apparent with an understanding of the following detailed description of the invention or upon employment of the invention in practice. According to a preferred embodiment of the present invention there is provided,

A polyaniline composite electrode comprising: an electrically-conductive substrate; a composition supported on said substrate; characterized in that said composition comprising: polyaniline; organic sulfonate; polysaccharide; imidazolium buffer; organic chemicals functioning as diluents in adjusting the viscosity of polyaniline ink; wherein in situ polymerized polyaniline is carried out to prepare said polyaniline composite electrode.

In another aspect there is provided, A method of preparing polyaniline composite electrode comprising steps of: i. mixing polysaccharide and organic sulfonic acid to produce positively charged polysaccharide and organic sulfonate salt solution; ii. mixing said polysaccharide-sulfonate salt solution with aniline to form doped monomer solution; iii. adding imidazolium buffer to said doped aniline monomer solution; iv. performing electropolymerization towards said doped aniline monomer solution to form doped polyaniline ink; v. applying said polyaniline ink on electrode surface; vi. curing said applied polyaniline ink under inert environment 4. BRIEF DESCRIPTION OF THE DRAWINGS

Other aspect of the present invention and their advantages will be discerned after studying the Detailed Description in conjunction with the accompanying drawings in which: FIG. 1 is a polyaniline composite electrode of the present invention which is prepared via in situ polymerization of polyaniline.

FIG. 2 is a flow chart of preparation method for polyaniline composite electrode. FIG. 3 is the aniline monomer solution in cellulose acetate-camphor sulfonate-methyl imidazolium dopant.

FIG. 4 is the polyaniline composite ink doped with camphor sulfonate which appears as dark colour solution.

FIG. 5 is the doped polyaniline composite electrode with camphor sulfonate dopant.

FIG. 6 is an exemplary of cyclic voltammetry graph of in situ polymerized polyaniline in cellulose acetate-camphor sulfonate.

5. DETAILED DESCRIPTION OF THE DRAWINGS

In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those or ordinary skill in the art that the invention may be practised without these specific details. In other instances, well known methods, procedures and/or components have not been described in detail so as not to obscure the invention. The invention will be more clearly understood from the following description of the embodiments thereof, given by way of example only with reference to the accompanying drawings which are not drawn to scale.

Referring to FIG. 1 , there is shown the polyaniline (PANI) composite electrode of the present invention which is prepared via in situ polymerization of polyaniline. Said polyaniline composite electrode comprises of an electrically- conductive substrate and a composition supported on said substrate, wherein said composition comprising conductive polyaniline, organic sulfonate dopant, polysaccharide, imidazolium buffer and organic chemicals functioning as diluents in adjusting the viscosity of the doped polyaniline or polyaniline ink.

Referring to FIG. 2, there is shown a flow chart of preparation method for polyaniline composite electrode. Said preparation method for polyaniline composite electrode typically comprises of six steps, whereby said preparation method can be carried at room temperature without heat requirement. In the first step, polysaccharide-sulfonate salt solution is prepared by mixing polysaccharide and organic sulfonic acid to produce positively charged polysaccharide and organic sulfonate salt solution. Preferably, at least 1 % by weight to 10 % by weight of polysaccharide and at least 1 % by weight to 30 % by weight of organic sulfonic acid is used in the preparation of polysaccharide-sulfonate salt solution. For example, a solution of polysaccharide such as cellulose acetate and organic sulfonic acid such as camphor sulfonic acid is prepared by mixing the reagents in polar solvent such as tetrahydrofuran. Alternatively other polysaccharides low impedance polymeric materials such as ethyl cellulose, cellulose, chitosan, starch, dextrin, maltodextrin, beta-glucan, chitin, mannan, galactan, fructan or combination thereof can be used in place of cellulose acetate. Other organic sulfonic acid such as dodecyl benzene sulfonic acid, polystyrene sulfonic acid, toluene sulfonic acid, Nafion, apolate or combination thereof can be used in place of camphor sulfonic acid. Other solvent such as ethanol, 2-methoxyethanol, 2- propanol, acetone, 2-butanone, cyclohexanone, diethyl ether, methanol, trifluoroethanol, N-methyl pyrrolidone or combination thereof can be used in place of tetrahydrofuran. Depending on the ratio of polysaccharide to organic sulfonic acid, polysaccharide-sulfonate white solid salt is precipitated out from the solution. In this case ethanol is added to re-dissolve the salt precipitate. Said organic sulfonate functions as dopant for positively charged conductive polyaniline. Said positively charged polysaccharide is used as polymeric cation counterion for organic sulfonate dopant and to provide electrical path during electropolymerization. Uncharged polysaccharide is used to form low impedance polymeric networks as binder for polyaniline and other components.

In the second step aniline monomer solution is prepared by adding approximately 5 % by weight to 30 % weight of aniline to the polysaccharide- sulfonate salt solution, for example cellulose acetate-camphor sulfonate doped electrolyte. Positively charged polysaccharide is formed along with camphor sulfonate dopant. In the third step approximately 1 % by weight to 5 % by weight of imidazolium buffer such as methyl imidazole-methyl imidazolium solution, dodecyl imidazole, decyl imidazole or other polymeric imidazolium ion such as poly(4-vinyl imidazole) or combination thereof is added to said aniline monomer solution to increase the conductivity of the mixture as well as to provide stable electrical current path during electropolymerization in a potentiostat setup and assists oxidation of aniline.

In the fourth step reference electrode such as silver-silver chloride reference electrode, counter electrode such as platinum counter electrode and inert working electrode such as glassy carbon working electrodes are immersed into the buffered aniline monomer solution. In situ electropolymerization occurs towards said aniline monomer solution to form doped polyaniline. In a potentiostat setup the aniline monomer is polymerized by controlling the current density across the solution. The solution turns into dark in colour as doped polyaniline is formed.

In the fifth step, the doped polyaniline or the polyaniline ink can be applied on said electrically-conductive substrate or electrode surface using the preferred coating technique such as screen printing, stencil printing, inkjet printing, solution casting and spin coating. The conductive polyaniline function as active sensing agent or as electrochemical transducer. Approximately 25 % by weight to 85 % by weight of organic chemical or solvent is added as diluents in each mixing to adjust the viscosity of the polyaniline ink. Said organic chemicals comprises of the chemicals such as 2-methoxyethanol, n-methyl pyrrolidone, carbitol, butyl glycol, acrylic acid, pyruvic acid, ethyl acetate, tetrahydrofuran, toluene, xylene, propanol or combination thereof. Therefore, the concentration of said doped polyaniline can be controlled by the volume of organic chemicals to be added. In the sixth step, the applied polyaniline ink is cured under inert environment to evaporate off the solvents under continuous flow of nitrogen gas. The deposited doped conductive polyaniline is characterized by performing cyclic voltammetry between -1V to 1V in potassium chloride solution. The example of the CV plot is described in FIG. 6. Exemplary embodiment of the method of the invention is described hereinafter and should not be construed to limit the scope of the present invention.

Example 1

Preparation of polyaniline-cellulose acetate-camphor sulfonate composite solution:

Polysaccharide-sulfonate salt solution was prepared by mixing 500 mg cellulose acetate and 74.8 mg camphor sulfonic acid (0.322 mmol). 10 ml of tetrahydrofuran (THF) was added into the mixture to achieve homogenous colourless solutions. After that, said homogenous solutions were mixed with 0.3 g (3.22 mmol) aniline and 500 μΙ_ methyl imidazole-methyl immidazolium buffer solution. The mixture was stirred continuously until colourless viscous aniline monomer solution is obtained as illustrated in FIG. 3. The material was then electrochemically polymerized by using potentiostat such as Autolab PGSTAT Model 128N for 600 seconds. The polymerization cycles were repeated for 10 times at 2 mA cm ^"2 current density in a three-electrode cell, whereby platinum stick as counter electrode, silver-silver chloride (Ag/AgCI) wire as reference electrode and glassy carbon stick as working electrode. The polyaniline composite ink doped with camphor sulfonate is obtained which appears as dark solution as shown in FIG. 4. FIG. 5 shows the polyaniline composite electrode prepared by in situ polymerization of aniline monomer in cellulose-camphor sulfonate solution.

Example 2

Preparation of PANI-CSA Nano Composite Electrode

Screen printed carbon electrodes (SPE) with 4 mm diameter were cleaned ultrasonically with deionized water for 1 minute. 30 μΙ_ of PANI-CSA ink composition was dropped onto the cleaned carbon surface and dried over an hour under continuous flow of nitrogen gas. The Electrode was characterized with cyclic voltammetric using potentiostat such as Autolab PGSTAT Model 128N with scan at -1V to +1V and scan rate at 0.1V/s in 0.1 M KCI solution. The cyclic voltammetry graph is shown in FIG. 6. While the polyaniline conducting polymers is applied for chemical sensor in the aforementioned embodiment, the present invention is not restricted to this but may alternatively be applied to other applications such as a gas sensor, electrochemical transducer, solar cell, super capacitor, electrode in lithium battery, corrosion protection layer etc.

While the preferred embodiment of the present invention and its advantages has been disclosed in the above Detailed Description, the invention is not limited thereto but only by the scope of the appended claim.