WO2012064292A1

WO2012064292A1 - A method for preparing polymer/oxygen-free graphene composites using electrochemical process

Info

Publication number: WO2012064292A1
Application number: PCT/TH2011/000036
Authority: WO
Inventors: Adisorn Tuantranont; Chakrit Sriprachabwong; Anurat Wisitsoraat; Ditsayut Phokharatkul
Original assignee: National Science and Technology Development Agency
Current assignee: National Science and Technology Development Agency
Priority date: 2010-11-11
Filing date: 2011-08-25
Publication date: 2012-05-18
Anticipated expiration: 2013-05-11

Abstract

This invention demonstrates the preparation and use of polymer/oxygen-free graphene composites through an electrolytic exfoliation process. Two graphite rods are placed in an electrolysis cell filled with an electrolyte and a constant potential in the range of 3-10 V is applied between them using a regulated dc power supply for 4- 10 hours and black precipitates of graphene will be formed in the solution. The electrolyte is the solution of conductive polymer, e.g. Polythiophene (PTh), Poly 3,4- ethyldioxythiophene /Polystyrenesulfonic acid (PEDOT/PSS), Polyaniline (PANI), Polypyrol (PPy), Polyphenelyne vinylene (PPV), Polyacetylene (PA), Polythienylene and their derivatives. The precipitated product is then centrifuged at a speed of 10,000-20,000 rpm to remove large agglomerates by decanting the supernatant portion of the dispersion. The dispersed solution is then used as an ink for ink-jet printing.

Description

A METHOD FOR PREPARING POLYMER/OXYGEN-FREE GRAPHENE COMPOSITES USING ELECTROCHEMICAL PROCESS

TECHNICAL FIELD

The present invention relates to the field of nanocomposite materials and particularly concerns with the preparation of polymer-graphene composites by electrochemical processes.

[0001] The composite obtained through said method can readily be used to deposit electrically conductive layers on a given substrate by inkjet printing mean for a variety of applications including transparent conductors, transparent antenna, electrochemical electrodes and so on.

BACKGROUND OF THE INVENTION

Nanotechnology is the science concerned with an invention that is very small in the nanometer or molecular scale. Nanotechnology can be classified into three major fields including nanomaterials, nanoelectronics and nanobiotechnology. Among these, nanomaterials, which concern the creation of nanostructured materials, is considered as the most important basis that support other aspects of nanotechnology. There are a wide range of nanostructured materials including nanopowders, nanotubes, nanofibre nanorod, nanowires, nanoplates, etc. These materials are very useful in the field of gas/chemical/biosensor technology because their high specific surface area can enable ultra sensitive detection at molecular or atomic level.

Graphene is the latest nanocarbon material with a two dimensional (2D) honeycomb hexagonal structure of sp² covalently bonded carbon atoms. Its unique atomic configuration leads to various astonishing properties including a very large surface area of 2630 m /g (double of single-walled carbon nanotubes (SWCNTs)), very high electrical/thermal conductivity, a tunable band gap, room-temperature Hall effect, high mechanical strength (200 times greater than steel) and high elasticity. As a result, graphene has been widely studied for various electronic applications such as transistors, memory device, photovoltaic (solar cell), gas/chemical/biosensors, etc. In particular, graphene has several advantages over CNTs due to two major issues. Unlike CNTs, graphene can be produced with no metallic impurities that are undesirable in many applications such as electrochemical sensing. Secondly, graphene can be manufactured from low-cost graphite.

Graphene can generally be synthesized by several methods including micromechanical cleavage, epitaxial growth via ultra-high vacuum graphitation, chemical synthesis through oxidation of graphite, chemical vapor deposition (CVD), solvothermal synthesis, and other innovative methods, for example "wet ball graphite milling in polymer and organic solvent" [Ref. 1], which has advantages of high graphene production yield and throughput but suffers from complexity and impurities from ball milling. In another method [Refs. 2-3], graphene is produced by means of "ultrasonic dispersion, liquid-solid graphite separation". This method is more preferred compared to the previously mentioned method due to lower cost and better graphene purity but it provides low production yield/ throughput and can not yield a single-layer graphene. Other interesting methods are "graphitation of amorphous carbon thin layer under photonic and/or electronic irradiation" [Ref. 4] and "graphite oxidation and two-step temperature exfoliation" [Ref. 5], both of which offer high production yield of a single-layer graphene but suffer from high cost and complexity. In addition, graphene have been synthesized by electrolytic exfoliation, which is an electrochemical process [Ref. 6-8]. In the report, graphene is produced by applying a dc voltage to graphite rods immersed in polystyrene solution, causing oxidation reaction to exfoliate graphene from graphite. When compared to many other methods, the electrolytic exfoliation method offers many advantages including ability to produce stable graphene in solution, capability to form single-layer graphene, ease of large scale production and low cost.

Currently, graphene has been widely applied in conjunction with polymers in order to improve their mechanical and electrical properties. Graphene has been blended with various types of polymers such as epoxy, polystyrene (PS), polyaniline (PANI), polyurethane (PU), polyvinyldene fluoride (PVDF), Nafion, polycarbonate, polyethylene terephthalate (PET), polyvinyl alcohol (PVA), poly 3,4-ethyldioxythiophene (PEDOT), etc in order to improve their mechanical strength. Different blending methods and suitable graphene compositions for various polymers have been reported [Ref. 9-12]. In addition, graphene has been mixed with conductive polymer such as PANI and PEDOT to enhance their electrical conductivity. It has been reported that graphene-PEDOT composite in thin-film form offers superior transparency, conductivity, flexibility as well as temperature stability suitable for a variety of applications [Ref. 13]. For example, highly conductive graphene film has been coated on various polymer films for electronic packaging [Ref. 14-15]. However, polymer-graphene mixing process usually requires multi-step chemical-reaction processes, which are complicated and not cost effective. Therefore, simpler polymer-graphene preparation processes are highly needed for practical applications.

[0002] Polymer-graphene composite, which are normally prepared in solution form, can be used by several means such as spin-coating, spray coating and inkjet printing. Inkjet printing technology is well-known for two-dimensional image creation in Art work or printed documents. Recently, it has become a promising method for plastic microelectronic circuit fabrication with much lower cost and simpler manufacturing process than standard photolithographic technology. It only requires a specially designed desktop inkjet printer with graphic design software to draw the layout and print several layers to obtain the desired circuit with a. high resolution of 5-10 microns. In addition, it uses non-contact patterning and low temperature process so that a wide variety of substrates can be used. It is thus a promising platform for various industrial applications such as low cost and disposable sensors, etc. Recently, biosensors, gas sensors and several types of transducers fabricated by inkjet printing have been demonstrated. For example, a high performance transistor-type biosensor has been developed by inkjet printing of a polymer- graphene active layer [Ref. 16].

REFERENCE CITED 1. "Method for preparing multi-layer graphene" CN patent pending Ser. no. 101,704,520 (Institute of Fujian Kaili Special Graphic C and Huaqiao University).

2. "Method for preparing multi-layer graphene" CN patent pending Ser. no. 101,746,755 (Institute of Chongqing University).

3. "Preparation method of functional nano-graphene" CN patent pending Ser. no. 101,654,243 (Institute of Qingdao University).

4. "Method of Production of Graphene" U.S. Patent pending Ser. no. 2010,247801 (the institute Commissariat Energie Atomique).

5. Jang Bor Z., "Dispersible and conductive Nano Graphene Platelets" U.S. Patent pending Ser. no. 2,010,247801. 6. G. Wang, B. Wang, J. Park, Y. Wang, B. Sun, J. Yao, "Highly efficient and large-scale synthesis of graphene by electrolytic exfoliation" Carbon, 2010, 47, 3242.

7. N. Liu, F. Luo, H. Wu, Y. Liu, C. Zhang, J. Chen, "One-Step Ionic Liquid-Assisted Electrochemical Synthesis of Ionic Liquid-Functionalized Graphene Sheet Directly from Graphite" Adv. Funct. Mater. 2008, 18, 1518. 8. J. Lu, J. X. Yang, J. Wang, A. Lim, S. Wang, K. P. Loh, "One-Pot Synthesis of Fluorescent Carbon Nanoribbons, Nanoparticles, and Graphene by the Exfoliation of Graphite in Ionic Liquids" ACS Nano. 2009, 3, 2367.

9. "Polymer Compositions Containing Graphene Sheets And Graphite" International patent pending, Ser. No. WO 2,010,1 15,173 Institutional Vorbeck Materials Corp 10. S. Stankovichl, D. A. Dikin, G. H. B. Dommett, K. M. Kohlhaas, E. J. Zimney, E. A. Stach, R. D. Piner, S. B. T. Nguyen, R. S. Ruoff, "Graphene-Based Composite Materials" Polymer, 2006, 442, 282.

11. T. Kuila, S. Bhadra, D. Yao, N. H. Kim, S. Bose, J. H. Lee, " Recent Advances in Graphene Based Polymer Composites" Prog. Polym. Sci. 2010, 35, 1350.

12. J. R. Potts, D. R. Dreyer, C. W. Bielawski, R. S. Ruoff, "Graphene-Based Polymer Nanacomposite" Polymer, 2011, 52, 5.

13. Y. Xu, Y. Wang, J. Liang, Y. Huang, Y. Ma, X. Wan, Y. Chen, "A hybrid material of graphene and poly (3,4-ethyldioxythiophene) with high conductivity, flexibility, and transparency" Nano Research, 2009, 2, 343.

14. U.S. Patent Application No. US2, 010,247,892 title "Electroconductive Particle And Anisotropic Conductive Film Comprising Same" institutional Korea Inst Sci & Tech.

15. International Patent Application No. WO 2,010,086,176 title "Conductive polymer composition" of the institution, Korea Inst Sci & Tech 16. U.S. Patent Application No. US2, 010,135,854 title "Biosensor Having Transistor Structure and Method of Fabricating The Same" institutional Korea Electronics Telecomm.

SUMMARY OF THE INVENTION

The invention provides preparation method of polymer-graphene composite by an electrochemical process and presents characteristics of prepared polymer-graphene composite as a function of process parameters such as applied voltage. In addition, physical and electrical characteristics examined by transmission electron microscopy (TEM), atomic force microscopy (AFM), Raman Spectroscopy, Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), 4-point probe measurement and cyclic voltametry are reported. The unique property of produced graphene is oxygen-free while the polymer-graphene composites are demonstrated to be highly transparent and conductive.

The invention also includes the use of polymer-graphene composite produced by the said method as an ink for inkjet printing to deposit electrically conductive layers on a given substrate for a variety of applications including transparent conductors, transparent antenna, electrochemical electrodes, and so on.

Various purposes and characteristics of the invention will appear more clearly when considered in conjunction with the accompanying drawings and description. The best invention is in the form, which will be described next.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows a drawing of apparatus for preparation of polymer-graphene composite by electrochemical method.

Fig. 2 is an Atomic force microscopic (AFM) images of graphene-PEDOT:PSS layers coated on a silicon substrate.

Fig. 3 is a typical transmission electron microscopic images of graphene synthesized in the PEDOT:PSS polymer matrix.

Fig. 4 is a typical select area electron diffraction (SAED) pattern of synthesized graphene sheets.

Fig. 5 shows a typical Raman spectrum of graphene synthesized in the PEDOT:PSS polymer matrix.

Fig. 6 shows a typical FTIR spectra of PEDOT/PSS, graphene-PEDOT/PSS and washed graphene-PEDOT/PSS. Synthesized voltage and time are 8 Vand 40 hours, respectively.

Fig. 7 is a Graph showing the effect of voltage on the particle size of graphene dispersed in the PEDOT:PSS solution measured by dynamic light scattering. Fig. 8 is a graph Conductivity vs. Voltage of graphene-PEDOT/PSS thin films synthesized at different electrolytic times.

Fig. 9: Optical transmittance spectra in UV/VIS region (300-800 nm) of spin-coated PEDOT/PSS and graphene-PEDOT/PSS thin films synthesized at various electrolytic voltages for 40 hours. Inset is transmittance at 550 nm vs. voltage.

Fig. 10: Photograph of (a) inkjet printed graphene-PEDOT/PSS film and (b) RFID antenna on transparencies.

Fig. 11 : Photograph of fabricated electrode and SEM micrographs of SPCE, inkjet-printed PEDOT:PSS on SPCE and printed graphene-PEDOT:PSS on SPCE. Fig. 12: Cyclic voltammogram of 1 mM salbutamol on (a) graphene-PEDOT:PSS and (b) PEDOT electrode and (c) SPCE electrode. Scan rate was lOOmVs^-1. Buffer solution was 50 mM phosphate buffer (pH 7.0).

DETAILED DESCRIPTION OF THE INVENTION

Description of the invention will be done by providing instance with reference to drawings, and photographs to illustrate and describe examples more clearly. The scope of the invention will adhere to the attached claims.

The apparatus for preparation of polymer-graphene composite by electrochemical method is shown in Fig. 1. Graphite rod is used as starting material for graphene synthesis. Two graphite rods are placed in an electrolysis cell filled with an electrolyte and a constant potential in the range of 3-12 V is applied between them using a regulated dc power supply for 4-10 hours. The electrolyte is the solution of conductive polymer, e.g. Polythiophene (PTh), Poly 3,4- ethyldioxythiophene/Polystyrenesulfonic acid (PEDOT/PSS), Polyaniline (PANI), Polypyrol (PPy), Polyphenelyne vinylene (PPV), Polyacetylene (PA), Polythienylene and their derivatives. As the electrolytic process proceeds, the graphite anode is corroding and black precipitates of graphene will be gradually formed in the solution. The precipitated product is then centrifuged at a speed of 10,000-20,000 rpm to remove large agglomerates by decanting the supernatant portion of the dispersion. The dispersed solution can then be used as an ink for ink-jet printing.

The typical topography of graphene dispersed in PEDOT:PSS polymer characterized by atomic force microscopy (AFM) is illustrated in Fig. 2. AFM sample is prepared by dropping the graphene - PEDOT/PSS solution onto a silicon substrate and drying overnight at room temperature before AFM measurement. From the 2x2 micron AFM image, several graphene sheets with nanometer-scale thickness are overlapping and the average height (thickness) of graphene sheets is estimated to be in the range of 0.7-1 nm.

The morphology of graphene-PEDOT/PSS composite is further examined by transmission electron microscopy (TEM) as demonstrated in Fig. 3. TEM samples are prepared by dropping the solution onto the carbon/copper grid TEM and drying in a desiccator over night. It can be seen that it contains polygon sheets with unequal sides mixed and surrounded by very smooth material. In addition, polygon sheets are seen to have some thickness variation, suggesting more than one overlapping material layers. Their average diameter is estimated to be around 500 nm. The polygon sheet is confirmed to be graphene by selected area electron diffraction (SAED) from a region near an edge of a sheet as demonstrated in Figure 4. The electron diffraction pattern is very well matched to that of standard single crystal graphite with a hexagonal structure. Thus, the thin polygon sheet is affirmed to be graphene.

Raman Spectroscopy is used to study the quality of graphene structure synthesized in PEDOT/PSS's matrix. For Raman analysis, graphene powder is extracted from graphene- PEDOT/PSS solution by centrifugation at 10,000 rpm, washing in DI water and ethanol and drying in an oven temperature at 80 °C. Raman spectrum from extracted graphene powder synthesized at electrolytic voltage of 8 V is shown in Fig. 5. It is evident that all spectra contain three peaks at -1330, -1580 and -2600 cm^"1, corresponding to D, G and 2D bands, respectively. In addition, G band is considerably sharper and stronger than D and 2D bands. G band is well- known to be associated to sp² honey comb graphitic carbon structure. It can be used to distinguished graphene from SWCNTs. G band of SWCNTs is relatively broad because it contains two degenerate peaks (G+ and G-) while G band of graphene has only one sharp peak, which is evident in Fig. 5. High quality graphene will have low D peak due to low edge defect density attainable from wide and thin graphene structures. 2D band is contributed by zone- boundary defects and its shape can be used to differentiate graphene from graphite and suggest type of graphene. Single-layer graphene has only a single sharp 2D peak and 2D band will be broaden and contain more than one components for multi-layer graphene and graphite. From Fig.5, 2D band is relatively broad compared to G band suggesting that all synthesized graphenes have multiple layers.

The functional groups of PEDOT/PSS, graphene-PEDOT/PSS and washed graphene powders are characterized by FTIR as illustrated in Fig. 6. The peaks at 1157, 1121 and 1012 cm^"1 correspond to two S-0 and one S-phenyl band of sulfonic acid while peaks at 1532, 1356, 952, 845 and 704 cm⁴ are attributed to C=C, C-C and C-S bonds in the thiophene backbone. It can be seen that the functional groups of graphene-PEDOT/PSS are almost exactly the same those of PEDOT/PSS film and IR reflectance of graphene-PEDOT/PSS film is approximately 5% lower than that of PEDOT/PSS film. Thus, graphene does not contribute additional functional group to the mixture. The FTIR spectrum of washed graphene in Fig. 6 confirms that the synthesized structures are graphene not graphene oxide, which typically exhibits C-0 and C=0 peaks between 1600-1800 cm^"1. Thus, the produced graphene is oxygen-free. This property is uniquely derived from this preparation method and desirable for a variety of applications. It should be noted that the graphene-PEDOT/PSS was sysnthesized at 8V for 40 hours and FTIR results from graphene- PEDOT/PSS produced at other voltages are not shown because they are approximately the same.

The effect of voltage on the graphene particle size in the dispersion measured by dynamic light scattering (DLS) is shown in Fig. 7. It can be seen that the particle size tends to increase as the applied voltage increases and there are particles with two different average sizes at high applied voltage of more than 3 V. At low voltage of 3 V, all graphene particles have the average size of 2016 nm. For the voltage of 5 V, 82.2. % and 17.2% of particles have the average sizes of 4159 and 326.2 nm, respectively. At higher voltage of 8 V, the two average particle sizes increase to 4738 and 226.3 nm and their concentrations are 90.2% and 9.8%, respectively.

Graphene-PEDOT/PSS thin film is deposited on transparencies by inkjet printing with varying electrolytic voltages and times. The electrical conductivity and optical transmittance of deposited film are characterized for transparent electrode applications by four-point probe measurement and UV/VIS spectroscopy.

The conductivity of spin-coated graphene-PEDOT/PSS thin films prepared at different electrolytic voltages and times are shown in Fig. 8. The conductivity is calculated from the sheet resistance measured by four point probe and the film thickness determined from stylus profiler. The thickness of all inkjet printed films is found to be approximately 90 nm. It can be seen that the conductivity of graphene-PEDOT/PSS thin films monotonically increases with time and applied voltage. The time dependence of conductivity is approximately linear with some statistical variation while its voltage dependence is nonlinear. At low voltage of 3 and 5 V, the conductivity is slowly increasing with voltage, then rapidly rising when the voltage increases to 8 V and going up slowly again as the voltage increases further. The improved electrical conductivity can be attributed to graphene' s high 2D electrical conductivity, which is also depending on the quality of produced graphene structure. The observed voltage dependence of conductivity implies that the quality of graphene is critically improved at the electrolytic voltage between 6 V and 8 V and further voltage increment only slightly enhances electrical conductivity. Moreover, the conductivity of optimized graphene-PEDOT/PSS film is more than 3 times higher than that of unloaded PEDOT/PSS film (-6.2 S/cm). The optical transmittance spectra in UV/VIS region (300-800 nm) of inkjet printed PEDOT/PSS and graphene-PEDOT/PSS thin films synthesized at different voltages for 40 hours are shown in Fig. 9. It is seen that PEDOT/PSS thin film has high transmittance in visible region. With the presence of graphene, the transmittance spectra of PEDOT/PSS thin films are modified differently depending on electrolytic voltage. At the low voltage of 3 V, the transmittance only slightly decreases by a fraction of percent in a short wavelength region between 350 and 550 nm while the transmittance remains approximately the same at higher wavelengths. In contrast, the transmittance monotonically decreases throughout the visible region when the electrolytic voltage increases to 5 V and 8 V and the reduction considerably increases as the electrolytic voltage increases. When the voltage increases to 12 V, the transmittance, however, only slightly decreases further and most reduction occurs in the short wavelength region. To quantitatively evaluate the influence of voltage, the transmittance at the center of visible region (550 nm) is calculated and plotted as a function of electrolytic voltage as shown in the inset of Fig. 8. It is evident that the transmittance decreases by around 3% as the voltage increases from 3 to 8 V but then becomes much less voltage dependent when the voltage further increases to 12 V. Thus, the observed voltage dependence of transmittance indicates that the absorption due to graphene is critically increased at the electrolytic voltage of around 8 V and beyond.

The photograph of typical inkjet printed transparent conducting film on transparencies is shown in Fig. 10. It can be seen that the inkjet printed graphene-PEDOT/PSS film is highly uniform and transparent such that the small logos are clearly visible (Fig. 10 (a)). The transparent inkjet printed film is potential for a variety of applications including radio-frequency identification (RFID), flexible organic display and solar cell. Fig. 10 (b) illustrates a transparent RFID antenna prepared by inkjet printing. The transparent antenna is highly desirable for RFID tags on packages of consumer products because it is almost invisible so that it can be placed anywhere on a package without affecting label's visibility. RFID antenna based on inkjet printed graphene- PEDOT/PSS film offers advantages including simple low-temperature fabrication process and low cost. In addition, the polymer-graphene antenna contains no metallic impurities. Thus, it will not be falsely detected by security-checked x-ray scanner. Inkjet printed polymer-graphene film can also be used as an electrochemical sensing layer on a suitable supporting electrodes or substrates including screen printed carbon electrodes (SPCEs), glassy carbon electrode, gold and platinum electrodes. For instance, electrochemical sensor based on inkjet-printed graphene-PEDOT/PSS SPCE has been fabricated over ah area of 3 mm x 5 mm. The electrochemical characteristics of the modified SPCEs are measured by cyclic voltammetry (CV) toward a model analyte, salbutamol, which is a prohibited drug in sport and a banned food additive.

The surface morphologies of fabricated electrochemical electrodes are examined by SEM. Fig. 11 includes a photograph of fabricated electrodes and SEM micrographs of unmodified SPCE, inkjet-printed PEDOT/PSS SPCE and inkjet-printed graphene-PEDOT/PSS SPCE. It can be seen that uncoated SPCE has rough surface with large grains of several microns in size and the surface is smoothen after inkjet printing with PEDOT/PSS or graphene-PEDOT:PSS layers. However, graphene structures are not clearly observed on the SPCE surface because graphene sheet (-0.5 μιη in diameter) is very small compared to the surface roughness and grain of SPCE. The electrochemical efficacy of graphene-PEDOT/PSS electrode is evaluated from CV response in 1 mM salbutamol solution and compared to those of PEDOT:PSS modified and unmodified SPCEs as shown in Fig. 12. It is evident that graphene-PEDOT/PSS modified SPCE exhibits much larger irreversible oxidation peak at -0.78 V than those of PEDOT/PSS modified and unmodified SPCEs, respectively. The oxidation peak of salbutamol at -0.78 V has been explained by oxidative reaction of phenolic hydroxyl group. From the CV responses, the oxidation peak amplitudes of PEDOT/PSS modified and graphene-PEDOT/PSS modified SPCEs are approximately 30 and 150 times higher than that of unmodified SPCE, respectively. Thus, PEDOT/PSS considerably enhances the electrochemical activity of SPCE to salbutamol and the addition of graphene greatly increases the response further. The dramatic enhancement can be attributed to huge reactive surface area, high electronic mobility and excellent electron transfer rate of graphene-PEDOT/PSS composite.

Although this invention has been fully described in conjunction with the attached drawings. It is understood that modification and alteration by those with ordinary skill in related fields is also considered to be within the scope and purpose of the invention. The scope of this invention will be in accordance with the details described in the attached claims. It also covers aspects of the invention that are not specifically mentioned in the claims but are the benefits and results of the invention set forth in the claims. The present method is the best as mentioned in the disclosure of the invention.

Claims

1. A method for preparing polymer-graphene composite using electrolytic exfoliation with two graphite electrodes, functioning as an anode electrode and a cathode electrode, immerged in electrolytic solution of conductive polymer and said two graphite electrodes being applied with DC voltage, the method being characterized in that: said electrolytic solution is conductive polymer solution.

2. The method according to claim 1, wherein the direct potential is in the range of 3-12 volts.

3. The method according to claim 1, wherein the direct potential is applied for 3-40 hours.

4. The method according to claim 1, wherein the electrolyte solution is selected from at least one of conductive polymer solution in a group comprising polythiophene (PTh), poly 3,4- ethyldioxythiophene/polystyrenesulfonic acid (PEDOT/PSS), Polyaniline (PANI), Polypyrol (PPy), Polyphenelyne vinylene (PPV), Polyacetylene (PA), Polythienylene and their derivatives .

5. The method according to claim 1, further comprising subjecting the produced polymer- graphene solution at a speed of 10,000-20,000 rpm to remove large agglomerates by decanting the supernatant portion of the dispersion..

6. The dispersed solution obtained from the method according to any one of claim 1- 5 which is usable as an ink for inkjet printing.

7. The graphene in the dispersed solution obtained from the method according to any one of claim 1 - 5.

8. A multilayer transparent electrode formed by Inkjet printing process using the dispersed solution according to claim 6.

9. A multilayer transparent antenna formed by Inkjet printing process using the dispersed solution according to claim 6.

10. An electrochemical sensing layer formed by Inkjet printing process using the dispersed solution according to claim 6.