Method for producing a functionalized semiconductor or conductor material and use thereof

Abstract

The invention relates to a method for producing a functionalised semiconductor or conductor material from a layered structured base material by electrolytic exfoliation in an electrolysis cell, comprising at least one electrode pair consisting of first and second electrodes, and an aqueous and/or alcoholic electrolyte solution, containing sulphuric acid and/or at least one salt selected from sulphate and/or hydrogen sulphate and/or perchlorate and/or persulphate salt, comprising the steps of: a) bringing the electrodes into contact with the electrolyte solution; b) electronically exfoliating the base material by applying a voltage between the first and the second electrode; c) separating the functionalised conductor or semiconductor material from the electrolyte solution, wherein at least the first of the electrodes of the electrode pair contains the layered, carbon-based base material, the first electrode being connected as an anode, wherein at least one organic compound is added to the electrolyte solution before and/or during and/or immediately after the electrolytic exfoliation, wherein the organic compound is selected from i) anodically oxidisable organic molecules containing at least one alcohol group and/or at least one amino group and/or at least one carboxyl group, and/or ii) organic molecules containing at least one isocyanate group and/or at least one halide group and/or at least one epoxide group and/or at least one diazonium group and/or at least one peroxide group and/or at least one azide group and/or cyclic esters and/or cyclic amides, and/or iii) precursors or monomers of electrically conductive polymers, and/or iv) free-radical polymerisable, water-soluble vinyl monomers which have in their structure at least one amino group and/or at least one anionic functional group.

Claims

1. A method for producing a surfactant-free dispersion of functionalised semiconductor or conductor material from a two-dimensional layered structured carbon-based base material by electrolytic exfoliation in an electrolysis cell, comprising at least one electrode pair consisting of first and second electrodes, and an aqueous and/or alcoholic electrolyte solution containing sulphuric acid and/or at least one salt selected from sulphate and/or hydrogen sulphate and/or perchlorate and/or persulphate salt, comprising the steps of: a) bringing the electrode pair(s) into contact with the electrolyte solution, b) electrolytically exfoliating the base material by applying a voltage between the first and the second electrode, wherein at least the first of the electrodes of the electrode pair(s) contains the two-dimensional layered structured carbon-based base material, the first electrode being connected as an anode, c) separating the functionalised semiconductor or conductor material from the electrolyte solution, and d) dispersing the functionalised semiconductor or conductor material after separation, without the use of surfactants, wherein at least one organic compound is added to the electrolyte solution before and/or during the electrolytic exfoliation, wherein the organic compound is selected from i. monomers of electrically conductive polymers, and/or ii. free radical polymerisable, water-soluble vinyl monomers which have in their structure at least one amide group and/or at least one anionic functional group.

2. The method according to claim 1, wherein the semiconductor or conductor material is selected from graphene, graphene derivatives, and carbon-based semiconductor or conductor polymers.

3. The method according to claim 1, wherein the two-dimensional layered structured carbon-based base material is selected from semiconductive or conductive carbon modifications, and carbon-based semiconductor or conductor polymers in the form of two-dimensionally structured carbon-based base material.

4. The method according to claim 1, wherein the second electrode comprises a metal.

5. The method according to claim 1, wherein the voltage is 1 to 20 V.

6. The method according to claim 1, wherein the monomers of electrically conductive polymers are selected from aromatic amines, anilines, pyrroles, thiophenes and/or their derivatives.

7. The method according to claim 2, wherein the second electrode comprises a metal.

8. The method according to claim 3, wherein the second electrode comprises a metal.

9. The method according to claim 8, wherein the voltage is 1 to 20 V.

10. The method according to claim 2, wherein the monomers of electrically conductive polymers are selected from aromatic amines, anilines, pyrroles, thiophenes and/or their derivatives.

11. The method according to claim 3, wherein the monomers of electrically conductive polymers are selected from aromatic amines, anilines, pyrroles, thiophenes and/or their derivatives.

Description

EMBODIMENTS

(1) The present invention is described in more detail by the following drawings and embodiments, without this being intended to limit the breadth of the previously defined claims:

(2) FIG. 1: Schematic illustration of in situ exfoliation and functionalisation of graphite,

(3) FIG. 2: Proposed mechanism of in situ functionalisation,

(4) FIG. 3: RAMAN spectra of a) EG and b) PPy-functionalised EG,

(5) FIG. 4: a) XPS overview spectra of EG and EG-PPy, b) high-resolution XPS spectrum of the C1s region of EG, c) high-resolution XPS spectrum of the C1s region of EG-PPY and d) high-resolution XPS spectrum of the N1s region of EG-PPY,

(6) FIG. 5: RAMAN spectrum of PANI-functionalised EG,

(7) FIG. 6: a) high-resolution XPS spectrum of the C1s region of EG-PANI and b) high-resolution XPS spectrum of the N1s region of EG-PANI,

(8) FIGS. 7: a) TGA, b) AFM and c) RAMAN analyses of SPANI-functionalised EG (EG-SPANI),

(9) FIG. 8: XPS analysis by EG-SPANI: a) overview spectrum and high-resolution XPS spectra of b) the C1s region, c) the S2p region and d) the N1s region,

(10) FIG. 9: Schematic illustration of the mass production of EG-SPANI (=exfoliated graphene functionalised with sulphonated polyaniline) by a continuous system,

(11) FIG. 10: a) TGA and b) AFM analyses of PNIPAM-functionalised EG (EG-PNIPAM),

(12) FIG. 11: XPS analysis of EG-PNIPAM a) overview spectrum and b) high-resolution spectrum of the N1s region,

(13) FIG. 12: TGA analyses of a) EG functionalised with poly(methylene-bis-acrylamide) (PAM) b) EG functionalised with sulphonated polystyrene,

(14) FIGS. 13: a) TGA, b) XPS overview spectrum and c) XPS N1s region analyses of a butylamine-functionalised EG d) increased degree of butylamine functionalisation detected by TGA,

(15) FIGS. 14: a) TGA and b) XPS spectra of, using valeric acid, pentyl-functionalised EG,

(16) FIG. 15: Proposed mechanism for direct post-functionalisation of EG immediately after the exfoliation,

(17) FIGS. 16: a, b) RAMAN and c) TGA spectra of polypyrrole-functionalised EG using direct post-functionalisation,

(18) FIG. 17: XPS analysis of polypyrrole-functionalised EG using direct post-functionalisation, a) overview spectrum, b) C1s region and c) N1s region,

(19) FIG. 18: TGA analysis of EG after direct post-functionalisation with a) valeric acid, b) butylamine and tert-Octylamine,

(20) FIG. 19: Zeta potential measurements of aqueous dispersions of functionalised graphenes,

(21) FIG. 20: Charge and discharge curve of a half-cell lithium-ion battery with LiCoO.sub.2/EG-SPANI (90/10) as the cathode material,

(22) FIG. 21: Cyclic voltammetry measurements of 3-electrode supercapacitors with a free-standing film of functionalised graphene (EG-SPANI) as an electrode.

CHARACTERISATION OF THE MATERIALS PRODUCED

(23) SEM images were obtained using a field emission scanning electron microscope (Gemini 1530 LEO) with an accelerating voltage of 10 keV. AFM characterisation was carried out on a Veeco Nanoskop-IIIa—MultiMode PicoForce (Digital Instruments). Raman spectroscopy and mapping were carried out with a Bruker RFS 100/S spectrometer (laser wavelength 532 nm). The XPS analyses were carried out on a Thermo Scientific K-Alpha X-ray photoelectron spectrometer with a basic chamber pressure of between ˜10.sup.−8-10.sup.−9 mbar and an Al anode as X-ray source (X-ray radiation of 1496 eV). Spot sizes of 400 μm were used. Overview spectra were recorded with an average of 10 scans, a transmission energy of 200.00 eV and a step size of 1 eV. High-resolution spectra were recorded with an average of 10 scans with a transmission energy of 50.00 eV and a step size of 0.1 eV. The sheet resistances of the EG films were measured with a four-point resistance measuring system using a Keithley 2700 Multimeter (probe spacing: 0.635 mm, Rs=4.532 V/I).

Embodiment 1

(24) Electrochemical Exfoliation and In Situ Functionalisation of Graphite with Polypyrrole and Production of a Dispersion of Polypyrrole-Functionalised Graphene (EG-PPy)

(25) The graphite exfoliation was carried out in a two-electrode system, wherein graphite foils (2 cm×3 cm, 100 mg per foil) (Alfa Aesar, 99.99% purity) were used as working anodes and gold foils of the same dimensions were used as cathodes. The gold electrodes were arranged parallel to the graphite electrodes with a fixed distance of 2 cm. The electrolyte for the exfoliation was prepared by dissolving ammonium sulphate (0.1 M, 0.8 g) in 60 ml deionised water. Pyrrole (7 μl, “Reagent Grade”, 98% purity) was dissolved in 10 ml water to obtain a 0.01 M monomer solution. After the electrodes were immersed in the electrolyte (6 cm.sup.2 active electrode area in the solution), a constant potential of 10 V was applied to start the exfoliation process, at the same time the monomer solution was added at a rate of 20 ml/h using a syringe pump.

(26) After the exfoliation was complete and the graphite foil had been consumed, the suspended graphene flakes were separated using a 0.2 μm PC (polycarbonate) filter and washed with deionised water. The washing process was repeated three times (3×400 ml) to wash out any residues such as ammonium sulphate and pyrrole monomers. The light grey product (polypyrrole-functionalised graphene, EG-PPY, 60 mg) was then dispersed in deionised water (30 ml) using mild ultrasound treatment (30 min ultrasound bath). This dispersion was left to stand for 24 hours in order to allow non-exfoliated, non-functionalised platelets and larger particles to sediment. The supernatant dispersion was then removed. The aqueous dispersion obtained in this way contained graphene in a concentration of 0.1-0.2 mg/ml and was stable for one week, i.e. there was no sedimentation of the particles.

(27) For dispersions in other solvents, the product (polypyrrole-functionalised graphene, EG-PPY, 60 mg) was dispersed after washing with water in, for example, ethanol or ethylene glycol (30 ml in each case) using mild ultrasound treatment and left to stand for 24 hours. The supernatants obtained in this way yielded stable dispersions with a graphene content of 0.2-0.3 mg/ml (ethanol) and 0.5-0.6 g/ml (ethylene glycol).

(28) The reaction was scaled up by using thicker graphite foils while maintaining the electrode area in the electrolyte and with an increased pyrrole concentration (in constant proportion to the weight of the graphite electrode).

(29) Successful functionalisation could be demonstrated using X-ray photoelectron spectroscopy (XPS). The oxygen content was 11.46 atom % for EG and 9.52 atom % for EG-PPy.

(30) In the case of EG-PPy, in contrast to EG, nitrogen was also detected in a concentration of 2.79 atom %, which can be attributed to the polypyrrole groups (FIG. 4a).

(31) The high-resolution spectrum of the N1s region (FIG. 4d) shows a main band at 400 eV which can be attributed to the —NH groups as well as a band at 401 eV which can be attributed to the polaron structure (C—N.sup.+) of polypyrrole.

(32) The high-resolution spectrum of the C1s region (FIG. 4c) shows three main bands at 284.35 eV, 285.4 eV and 287.2 eV, which can be attributed to the C═C, C—OH and C═O bonds.

(33) In contrast, unfunctionalised EG shows five different bands (FIG. 4b). In addition to the bands at 284.4 eV, 285.2 eV and 287.2 eV (C═C, C—OH and C═O bonds), two further bands occur at 286.5 eV and 290.2 eV, which are attributed to epoxy (C—O—C) and carboxylate groups (O—C═O) (FIG. 4b). The absence of epoxy groups in the case of functionalised EG shows that graphene undergoes less oxidation during the exfoliation, which is attributed to a protective effect of PPy functionalisation of the basal plane.

(34) The high quality of functionalised graphene can be illustrated using RAMAN spectroscopy. While a relatively high intensity ratio of the D and G peaks of 0.52 (FIG. 3a) in the spectrum of EG indicates a considerable degree of defect sites (due to the attack of hydroxyl radicals on the exposed graphene surfaces), by adding the 0.01 M aqueous pyrrole solution during the exfoliation, the graphene surface can be protected by the polypyrrole functionalities formed, which is illustrated by a low I.sub.D-I.sub.G ratio of 0.13 (FIG. 3b).

(35) A thin film of EG-PPy was made by filtering a dispersion on a PC filter paper. The sheet resistance of the film was determined using a four-point resistance measuring system and the layer thickness using SEM, from which a conductivity of approximately 500 S/cm was determined.

(36) Zeta potential measurements of aqueous dispersions showed the stability of EG-PPy dispersions over a wide pH range (FIG. 19).

Embodiment 2

(37) Electrochemical Exfoliation and In Situ Functionalisation of Graphite with Polyaniline and Production of a Dispersion of Polyaniline-Functionalised Graphene (EG-PANI)

(38) The graphite exfoliation was carried out in a two-electrode system, wherein graphite foils (2 cm×3 cm, 100 mg per foil) (Alfa Aesar, 99.99% purity) were used as working anodes and gold foils of the same dimensions were used as cathodes. The gold electrodes were arranged parallel to the graphite electrodes with a fixed distance of 2 cm. The electrolyte for the exfoliation was prepared by dissolving ammonium sulphate (0.1 M, 0.8 g) in 60 ml deionised water. Aniline (10 μl, Acros Organics, 99.8% purity) was dissolved in 26 μl H.sub.2SO.sub.4 and 10 ml water to obtain a 0.01 M monomer solution. After the electrodes were immersed in the electrolyte (6 cm.sup.2 active electrode area in the solution), a constant potential of 10 V was applied to start the exfoliation process, at the same time the monomer solution was added at a rate of 15 ml/h using a syringe pump.

(39) After the exfoliation was complete and the graphite foil had been consumed, the suspended graphene flakes were separated using a 0.2 μm PC (polycarbonate) filter and washed with deionised water. The washing process was repeated three times (3×400 ml) to wash out any residues such as ammonium sulphate and aniline monomers. The light grey product (polyaniline-functionalised graphene, EG-PANI, 60 mg) was then dispersed in deionised water (30 ml) using mild ultrasound treatment (30 min ultrasound bath). This dispersion was left to stand for 24 hours in order to allow non-exfoliated, non-functionalised platelets and larger particles to sediment. The supernatant was then removed. The aqueous dispersion obtained in this way contained graphene in a concentration of 0.1-0.2 mg/ml and was stable for one week.

(40) For dispersions in other solvents, the product (polyaniline-functionalised graphene, EG-PANI, 60 mg) was dispersed after washing with water, for example, in ethanol or ethylene glycol (30 ml in each case) using mild ultrasound treatment and left to stand for 24 hours. The supernatants obtained in this way yielded stable dispersions with a graphene content of 0.2-0.3 mg/ml (ethanol) and 0.5-0.6 g/ml (ethylene glycol).

(41) The reaction was scaled up by using thicker graphite foils while maintaining the electrode area in the electrolyte and with increased aniline concentration (in constant proportion to the weight of the graphite electrode).

(42) Successful functionalisation could be demonstrated using X-ray photoelectron spectroscopy (XPS).

(43) The oxygen content was 11.46 atom % for EG and 6.68 atom % for EG-PANI. In the case of EG-PANI, in contrast to EG, nitrogen was also detected in a concentration of 2.02 atom %, which can be attributed to the polyaniline groups (FIG. 6a, 6b).

(44) The high-resolution spectrum of the N1s region (FIG. 6b) shows three bands at 399 eV, 400 eV and 401 eV which can be attributed to the C═N, —NH and —NH.sup.+ groups of polyaniline.

(45) The high-resolution spectrum of the C1s region (FIG. 6a) shows three main bands at 284.4 eV, 285.2 eV and 286.5 eV, which can be attributed to the C═C, C—OH and C═O bonds, while the proportion of epoxy groups is low.

(46) The high quality and low defect density of functionalised graphene can be illustrated using RAMAN spectroscopy. By adding the 0.01 M aqueous aniline solution during the exfoliation, the graphene surface can be protected by the polyaniline functionalities formed, which is illustrated by a low I.sub.D-I.sub.G ratio of 0.12 (FIG. 5).

(47) A thin film of EG-PANI was made by filtering a dispersion on a PC filter paper. The sheet resistance of the film was determined using a four-point resistance measuring system and the layer thickness using SEM, from which a conductivity of approximately 400 S/cm was determined.

(48) Zeta potential measurements of aqueous dispersions showed the stability of EG-PANI dispersions in the neutral pH range and low stability under acidic conditions (FIG. 19).

Embodiment 3

(49) Electrochemical Exfoliation and In Situ Functionalisation of Graphite with Sulphonated Polyaniline and Production of a Dispersion of EG-SPANI (=Exfoliated Graphene Functionalised with Sulphonated Polyaniline)

(50) The graphite exfoliation was carried out in a two-electrode system, wherein graphite foils (2 cm×3 cm, 100 mg per foil) (Alfa Aesar, 99.99% purity) were used as working anodes and gold foils of the same dimensions were used as cathodes. The gold electrodes were arranged parallel to the graphite electrodes with a fixed distance of 2 cm. The electrolyte for the exfoliation was prepared by dissolving ammonium sulphate (0.1 M, 0.8 g) in 60 ml deionised water. Aniline sulphonic acid (18 mg, Sigma-Aldrich, 95% purity) was dissolved in 26 μl H.sub.2SO.sub.4 and 10 ml water to obtain a 0.01 M monomer solution. After the electrodes were immersed in the electrolyte (6 cm.sup.2 active electrode area in the solution), a constant potential of 10 V was applied to start the exfoliation process, at the same time the monomer solution was added at a rate of 15 ml/h using a syringe pump.

(51) After the exfoliation was complete and the graphite foil had been consumed, the suspended graphene flakes were separated using a 0.2 μm PC (polycarbonate) filter and washed with deionised water. The washing process was repeated three times (3×400 ml) to wash out any residues such as ammonium sulphate and aniline monomers. The dark grey product (polyaniline sulphonate-functionalised graphene, EG-SPANI, 60 mg) was then dispersed in deionised water (30 ml) using mild ultrasound treatment (30 min ultrasound bath). This dispersion was left to stand for 24 hours in order to allow non-exfoliated, non-functionalised platelets and larger particles to sediment. The supernatant dispersion was then removed. The aqueous dispersion obtained in this way contained graphene in a concentration of 0.3-0.4 mg/ml and was stable for one week.

(52) For dispersions in other solvents, the product (polyaniline sulphonate-functionalised graphene, EG-SPANI, 60 mg) was dispersed after washing with water, for example, in ethanol or ethylene glycol (30 ml in each case) using mild ultrasound treatment and left to stand for 24 hours. The supernatants obtained in this way yielded stable dispersions with a graphene content of 0.4-0.5 mg/ml (ethanol) and 0.8-1.0 g/ml (ethylene glycol).

(53) The reaction was scaled up by using thicker graphite foils while maintaining the electrode area in the electrolyte and with increased aniline concentration (in constant proportion to the weight of the graphite electrode).

(54) Successful functionalisation could be demonstrated by thermogravimetry (TGA), where the functionalised EG-SPANI showed an almost 5 wt. % higher loss of mass compared to unfunctionalised EG (FIG. 7a).

(55) The AFM investigations showed a layer thickness of 4 nm and 1.2 nm for the edges and basal planes of the platelets (FIG. 7b). RAMAN measurements showed a low I.sub.D/I.sub.G ratio of 0.12 and thus a low defect density (FIG. 7c).

(56) X-ray photoelectron spectroscopy (XPS) showed a nitrogen content of 2.15 atom % and a sulphur content of 0.62 atom %, which can be attributed to the polyaniline sulphonate groups (FIG. 8a).

(57) The high-resolution spectrum of the N1s region shows a main band at 400 eV which can be attributed to the —NH groups as well as the band at 401 eV which can be attributed to the polaron structure (C—N.sup.+) of polyaniline sulphonate. The high-resolution spectrum of the C1s region (FIG. 8b) shows three main bands at 284.35 eV, 285.4 eV and 287.2 eV, which can be attributed to the C═C, C—OH and C═O bonds. The high-resolution spectrum of the sulphur region (FIG. 8c) shows two bands at 167.4 eV and 168.6 eV, which can be attributed to the sulphonic acid or sulphonate groups of the polyaniline sulphonate.

(58) A thin film of EG-SPANI was made by filtering a dispersion on a PC filter paper. The sheet resistance of the film was determined using a four-point resistance measuring system and the layer thickness using SEM, from which a conductivity of approximately 800 S/cm was determined.

(59) Zeta potential measurements of aqueous dispersions showed the stability of EG-SPANI dispersions over a wide pH range (3-10) with a zeta potential of below −40 mV (FIG. 19).

Embodiment 4

(60) Mass Production of EG-SPANI (=Exfoliated Graphene Functionalised with Sulphonated Polyaniline) by a Continuous System

(61) The graphite exfoliation was carried out in a continuous system, wherein graphite foils (5 cm×30 cm, 2.3 mg per foil) (Alfa Aesar, 99.99% purity) were used as working anodes and copper foils of the same dimensions were used as cathodes. The copper electrodes were attached to the reactor wall, where the graphite electrodes were immersed in the electrolyte from above (FIG. 9). The electrolyte for the exfoliation was prepared by dissolving ammonium sulphate (0.1 M, 46.2 g), aniline sulphonic acid (1 g, Sigma-Aldrich, 95% purity) and 1.4 ml H.sub.2SO.sub.4 in 3.5 l deionised water and flows continuously through a pump into the system at constant speed. After the electrodes were immersed in the electrolyte (150 cm.sup.2 active electrode area in the solution), a constant potential of 10 V was applied to start the exfoliation process and the polymerisation process.

(62) After the exfoliation was complete and the graphite foil had been consumed, the suspended graphene flakes were separated using a 0.2 μm PC (polycarbonate) filter and washed with deionised water. The washing process was repeated three times (2 l) to wash out any residues such as ammonium sulphate and aniline monomers. The dark grey product (polyaniline sulphonate-functionalised graphene, EG-SPANI, 2.2 mg) was then dispersed in deionised water (150 ml) using mild ultrasound treatment (30 min, 30% amplitude, 2 watts). This dispersion was left to stand for 24 hours in order to allow non-exfoliated, non-functionalised platelets and larger particles to sediment. The supernatant dispersion was then removed. The aqueous dispersion obtained in this way contained graphene in a concentration of 0.5 mg/ml and was stable for several weeks.

Embodiment 5

(63) Electrochemical Exfoliation and In Situ Functionalisation of Graphite with Poly-N-Isopropylacrylamide and Production of a Dispersion of EG-PNIPAM (=Poly-N-Isopropylacrylamide-Functionalised Graphene)

(64) The graphite exfoliation was carried out in a two-electrode system, wherein graphite foils (2 cm×3 cm, 100 mg per foil) (Alfa Aesar, 99.99% purity) were used as working anodes and gold foils of the same dimensions were used as cathodes. The gold electrodes were arranged parallel to the graphite electrodes with a fixed distance of 2 cm. The electrolyte for the exfoliation was prepared by dissolving ammonium sulphate (0.1 M, 0.8 g) in 60 ml deionised water. N-isopropylacrylamide (30 mg, 0.25 mmol, Sigma, purity 97%) was dissolved in 10 ml water to obtain a 0.02 M monomer solution. After the electrodes were immersed in the electrolyte (6 cm.sup.2 active electrode area in the electrolyte solution), a constant potential of 10 V was applied to start the exfoliation process, at the same time the monomer solution was added at a rate of 20 ml/h using a syringe pump.

(65) After the exfoliation was complete and the graphite foil had been consumed, the suspended graphene flakes were separated using a 0.2 μm PC (polycarbonate) filter and washed with deionised water. The washing process was repeated three times (3×400 ml) to wash out any residues such as ammonium sulphate and aniline monomers. The dark grey product (poly-N-isopropylacrylamide-functionalised graphene, EG-PNIPAM, 60 mg) was then dispersed in deionised water (30 ml) using mild ultrasound treatment (30 min ultrasound bath). This dispersion was left to stand for 24 hours in order to allow non-exfoliated, non-functionalised platelets and larger particles to sediment. The supernatant dispersion was then removed. The aqueous dispersion obtained in this way contained functionalised graphene in a concentration of 0.3-0.4 mg/ml and was stable for one week.

(66) Successful functionalisation could be demonstrated by TGA, where the functionalised EG-PNIPAM showed a loss of mass of more than 40 wt. % compared to unfunctionalised EG (FIG. 10a).

(67) The AFM investigations showed a layer thickness of 3 nm, which shows the presence of functional groups on the surface (FIG. 10b).

(68) X-ray photoelectron spectroscopy (XPS) showed a nitrogen content of 0.86 atom % and an increase in the C/O ratio, which can be attributed to PNIPAM functionalisation (FIG. 11a). The high-resolution spectrum of the N1s region shows a main band at 400 eV which can be attributed to the —NH groups as well as the band at 401 eV which can be attributed to the amide structure of PNIPAM (FIG. 11b).

(69) A thin film of EG-PNIPAM was made by filtering a dispersion on a PC filter paper. The relatively high sheet resistance of the film of ˜140Ω/□ (determined with a four-point resistance measuring system) is due to the presence of the PNIPAM insulator on the graphene surface.

(70) The method was carried out successfully in an analogous manner with other vinyl monomers, such as methylene-bis-acrylamide and sodium 4-vinylbenzenesulphonate, which could be polymerised on the surface of the graphene. Successful functionalisation with poly(methylene-bis-acrylamide) (PAM) and poly(sodium 4-vinylbenzenesulphonate) (PSS) was demonstrated analogously to example 4 by TGA (FIGS. 12a and 12b).

(71) In addition, stable aqueous dispersions with EG-PAM (0.25 mg/ml) and EG-PSS (0.4 mg/ml) could be produced.

Embodiment 6

(72) Electrochemical Exfoliation and In Situ Functionalisation of Graphite with Butylamine

(73) The graphite exfoliation was carried out in a two-electrode system, wherein graphite foils (2 cm×3 cm, 100 mg per foil) (Alfa Aesar, 99.99% purity) were used as working anodes and gold foils of the same dimensions were used as cathodes. The gold electrodes were arranged parallel to the graphite electrodes with a fixed distance of 2 cm. The electrolyte for the exfoliation was prepared by dissolving ammonium sulphate (0.1 M, 0.93 g) and butylamine (30 mg, 0.41 mmol, Aldrich, 99.5% purity) in 70 ml deionised water. After the electrodes were immersed in the electrolyte (6 cm.sup.2 active electrode area in the electrolyte solution), a constant potential of 10 V was applied to start the exfoliation process. After the exfoliation was complete and the graphite foil had been consumed, the suspended graphene flakes were separated using a 0.2 μm PC (polycarbonate) filter and washed with deionised water. The washing process was repeated three times (3×400 ml) to wash out any residues such as ammonium sulphate and butylamine. The dark grey product (60 mg) was then dispersed in deionised water (30 ml) using mild ultrasound treatment (30 min ultrasound bath). This dispersion was left to stand for 24 hours in order to allow non-exfoliated, non-functionalised platelets and larger particles to sediment. The supernatant dispersion was then removed. The aqueous dispersion obtained in this way contained functionalised graphene in a concentration of 0.1 mg/ml and was stable for one week.

(74) A residual mass of 66 wt. % was determined in TGA measurements, wherein the loss was essentially due to the separation of the butyl groups at 374° C. (FIG. 13a).

(75) X-ray photoelectron spectroscopy (XPS) showed a nitrogen content of 1.11 atom %, which can be attributed to the butylamine groups (FIG. 13b). The high-resolution spectrum of the N1s region shows three main bands which can be attributed to the amide, amine and NH3+ groups (FIG. 13c).

(76) The degree of functionalisation could be increased by increasing the butylamine concentration (150 mg, 2 mmol) under otherwise the same conditions as above. This could also be demonstrated by an increased loss of mass in the TGA down to a residual mass of 51 wt. % (FIG. 13d).

(77) The method was successfully carried out in an analogous manner with other amines, such as tert-Octylamine, melamine and 2-amino-2-(hydroxymethyl)-1,3-propanediol (TRIS).

Embodiment 7

(78) Electrochemical Exfoliation and In Situ Functionalisation of Graphite with Valeric Acid

(79) The graphite exfoliation was carried out in a two-electrode system, wherein graphite foils (2 cm×3 cm, 100 mg per foil) (Alfa Aesar, 99.99% purity) were used as working anodes and gold foils of the same dimensions were used as cathodes. The gold electrodes were arranged parallel to the graphite electrodes with a fixed distance of 2 cm. The electrolyte for the exfoliation was prepared by dissolving ammonium sulphate (0.1 M, 0.93 g) and valeric acid (30 mg, 0.3 mmol, Alfa Aesar, 99% purity) in 70 ml deionised water. After the electrodes were immersed in the electrolyte (6 cm.sup.2 active electrode area in the electrolyte solution), a constant potential of 10 V was applied to start the exfoliation process.

(80) After the exfoliation was complete and the graphite foil had been consumed, the suspended graphene flakes were separated using a 0.2 μm PC (polycarbonate) filter and washed with deionised water. The washing process was repeated three times (3×400 ml) to wash out any residues such as ammonium sulphate and valeric acid. The dark grey product (60 mg) was then dispersed in deionised water (30 ml) using mild ultrasound treatment (30 min ultrasound bath). This dispersion was left to stand for 24 hours in order to allow non-exfoliated, non-functionalised platelets and larger particles to sediment. The supernatant dispersion was then removed. The aqueous dispersion thus obtained contained graphene in a concentration of 0.1 mg/ml and was stable for one week.

(81) Successful functionalisation could be demonstrated by TGA, where the functionalised EG showed a 4 wt. % greater loss of mass compared to unfunctionalised EG (FIG. 14a).

(82) At the same time, X-ray photoelectron spectroscopy (XPS) showed an increase in the C/O ratio to ˜9 (compared to unfunctionalised EG: ˜7.3) (FIG. 14b), which can be explained in terms of the attack and functionalisation with pentyl radicals on the graphene surface (FIG. 2).

Embodiment 8

(83) Electrochemical Exfoliation of Graphene and Subsequent Functionalisation with Polypyrrole

(84) The graphite exfoliation was carried out in a two-electrode system, wherein graphite foils (2 cm×3 cm, 100 mg per foil) (Alfa Aesar, 99.99% purity) were used as working anodes and gold foils of the same dimensions were used as cathodes. The gold electrodes were arranged parallel to the graphite electrodes with a fixed distance of 2 cm. The electrolyte for the exfoliation was prepared by dissolving ammonium sulphate (0.1 M, 0.93 g) in 70 ml deionised water. After the electrodes were immersed in the electrolyte (6 cm.sup.2 active electrode area in the electrolyte solution), a constant potential of 10 V was applied to start the exfoliation process.

(85) After the exfoliation was complete and the graphite foil had been consumed, pyrrole (100 μl, 1.5 mmol, Sigma-Aldrich, 98% purity) was added and the mixture was homogenised for 5 min in an ultrasound bath and then stirred for 30 min. The suspended graphene flakes were then separated using a 0.2 μm PC (polycarbonate) filter and washed with deionised water. The washing process was repeated three times (3×400 ml) to wash out any residues such as ammonium sulphate and pyrrole. The dark grey product (60 mg) was then dispersed in deionised water (30 ml) using mild ultrasound treatment (30 min ultrasound bath). This dispersion was left to stand for 24 hours in order to allow non-exfoliated, non-functionalised platelets and larger particles to sediment. The supernatant dispersion was then removed. The aqueous dispersion obtained in this way contained functionalised graphene in a concentration of 0.2 mg/ml and was stable for one week.

(86) The proposed mechanism for direct functionalisation is shown in FIG. 15. Through the process of electrochemical exfoliation, there are free radicals on the surface of the EG, which are stabilised by the extensive network of conjugated electrons (FIG. 15b). These radicals and anions can be used as a starting point for free radical and oxidative polymerisation reactions in order to covalently functionalise the graphene surface. Another possible mechanism is the activation of oxygen-containing groups (in particular epoxy) on the graphene surface by electrochemical exfoliation (FIG. 15b).

(87) The RAMAN spectrum showed an I.sub.D/I.sub.G ratio of 0.3. In addition, the RAMAN spectrum indicated three bands at 848.5 cm.sup.−1, 994.9 cm.sup.−1 and 1050.1 cm.sup.−1 (FIG. 16a), which can be attributed to the functionalisation of EG with polypyrrole (EG-PPy) and are not observed in unfunctionalised EG (FIG. 16b).

(88) In addition, successful functionalisation could be demonstrated by TGA, where the functionalised EG showed a 19 wt. % higher loss of mass compared to unfunctionalised EG (FIG. 16c).

(89) XPS measurements showed an oxygen content of 10.92 atom % (EG) and 8.43 atom % (EG-PPy) as well as a proportion of 3.37 atom % nitrogen for EG-PPy which can be attributed to polypyrrole functionalisation (FIG. 17a).

(90) The high-resolution spectrum of the N1s region shows a main band at 400 eV which can be attributed to the —NH groups as well as the band at 401 eV which can be attributed to the polaron structure (C—N.sup.+) of polypyrrole (FIG. 17c). The high-resolution spectrum of the C1s region (FIG. 17b) shows a band at 285.5 eV which is attributed to the C—N bond and which is not detectable in unfunctionalised EG.

Embodiment 9

(91) Electrochemical Exfoliation of Graphene and Direct Functionalisation with Valeric Acid

(92) Due to the effects of electrochemical exfoliation on the surface of graphene and the generation of active/reactive centres (see FIG. 15), the surface can also be functionalised with various other agents which contain, for example, amine groups or carboxylate groups, as will be illustrated in the following example.

(93) The graphite exfoliation was carried out in a two-electrode system, wherein graphite foils (2 cm×3 cm, 100 mg per foil) (Alfa Aesar, 99.99% purity) were used as working anodes and gold foils of the same dimensions were used as cathodes. The gold electrodes were arranged parallel to the graphite electrodes with a fixed distance of 2 cm. The electrolyte for the exfoliation was prepared by dissolving ammonium sulphate (0.1 M, 0.93 g) in 70 ml deionised water. After the electrodes were immersed in the electrolyte (6 cm.sup.2 active electrode area in the electrolyte solution), a constant potential of 10 V was applied to start the exfoliation process.

(94) After the exfoliation was complete and the graphite foil had been consumed, valeric acid (100 mg, 0.98 mmol, Alfa-Aesar, 99% purity) was added and the mixture was homogenised for 5 min in an ultrasound bath and then stirred for 30 min. The suspended graphene flakes were then separated using a 0.2 μm PC (polycarbonate) filter and washed with deionised water. The washing process was repeated three times (3×400 ml) to wash out any residues such as ammonium sulphate and pyrrole. The dark grey product (60 mg) was then dispersed in deionised water (30 ml) using mild ultrasound treatment (30 min ultrasound bath). This dispersion was left to stand for 24 hours in order to allow non-exfoliated, non-functionalised platelets and larger particles to sediment. The supernatant was then removed. The aqueous dispersion thus obtained contained graphene in a concentration of 0.1 mg/ml and was stable for one week.

(95) Successful functionalisation could be demonstrated by TGA, where the functionalised EG showed a residual mass of almost 63 wt. % compared to unfunctionalised EG.

(96) In addition, the step at approx. 200° C., which is usually attributed to the conversion of epoxy groups, is markedly less pronounced than in unfunctionalised EG, which indicates a reaction between the epoxy groups in EG and valeric acid (FIG. 18a).

Embodiment 10

(97) Electrochemical Exfoliation of Graphene and Direct Functionalisation with Amines

(98) The graphite exfoliation was carried out in a two-electrode system, wherein graphite foils (2 cm×3 cm, 100 mg per foil) (Alfa Aesar, 99.99% purity) were used as working anodes and gold foils of the same dimensions were used as cathodes. The gold electrodes were arranged parallel to the graphite electrodes with a fixed distance of 2 cm. The electrolyte for the exfoliation was prepared by dissolving ammonium sulphate (0.1 M, 0.93 g) in 70 ml deionised water. After the electrodes were immersed in the electrolyte (6 cm.sup.2 active electrode area in the electrolyte), a constant potential of 10 V was applied to start the exfoliation process.

(99) After the exfoliation was complete and the graphite foil had been consumed, butylamine (100 mg, 1.37 mmol, Sigma-Aldrich, 99.5% purity) was added to the electrolyte and the mixture was homogenised for 5 min in an ultrasound bath and then stirred for 30 min. The suspended graphene flakes were then separated using a 0.2 μm PC (polycarbonate) filter and washed with deionised water. The washing process was repeated three times (3×400 ml) to wash out any residues such as ammonium sulphate and pyrrole. The dark grey product (60 mg) was then dispersed in deionised water (30 ml) using mild ultrasound treatment (30 min ultrasound bath). This dispersion was left to stand for 24 hours in order to allow non-exfoliated, non-functionalised platelets and larger particles to sediment. The supernatant was then removed. The aqueous dispersion thus obtained contained graphene in a concentration of 0.1 mg/ml and was stable for one week.

(100) Successful functionalisation could be demonstrated using TGA. In FIG. 18 a it can be seen that the step at approx. 200° C., which is usually attributed to the conversion of epoxy groups, is markedly less pronounced than in unfunctionalised EG. This indicates a reaction between the epoxy groups in EG and butylamine. Functionalisation with tert-Octylamine was demonstrated in an analogous manner by TGA (FIG. 18 b).

Embodiment 11

(101) Functionalised Graphene Powder as a Cathode Additive in Lithium-Ion Batteries

(102) Functionalised graphene (EG-SPANI) was added in a solution-mixing method as a leading additive to typical cathode materials such as LiFePO.sub.4 and LiCoO.sub.2, thus producing electrodes for lithium-ion batteries.

(103) For this purpose, the dispersion produced according to embodiment 3 was mixed with a commercially available cathode material (LiFePO.sub.4/LiCoO.sub.2) in a mass ratio of 1:1 using ultrasound. After filtration and drying of the mixture, it was filled as a cathode material in a half cell in which lithium foil was arranged as the anode.

(104) At a constant current rate of 0.1 C (1 C=170 mAh/g), the material showed a charging and discharging capacity of 120 mAh/g (FIG. 20).

Embodiment 12

(105) Functionalised Graphene as Free-Standing Electrode Films in Super Capacitor Cells

(106) Free-standing films made of functionalised graphene (EG-SPANI) were used as electrodes in a 3-electrode supercapacitor cell, with platinum wire as the counter electrode, AgCl as the reference electrode and 0.1 M of sulphuric acid as the electrolyte. Functionalised graphene showed a good capacity of up to 312 F/g, while unfunctionalised EG had a capacity of less than 20 F/g (FIG. 21).