AN ELECTRICAL GENERATOR AND METHOD OF GENERATING AN ELECTRICAL CURRENT

Abstract

The present invention provides an electrical generator comprising one or more graphene sheets, each graphene sheet comprising first and second electrical contacts and having a surface extending between the first and second electrical contacts arranged to contact a flow of an ion-containing fluid, wherein each surface is provided with a polymer coating having a thickness of less than 100 nm.

Claims

1. An electrical generator comprising one or more graphene sheets, each graphene sheet comprising first and second electrical contacts and having a surface extending between the first and second electrical contacts arranged to contact a flow of an ion-containing fluid, wherein each surface is provided with a polymer coating having a thickness of less than 100 nm.

2. The electrical generator according to claim 1 comprising a plurality of said graphene sheets arranged in an array wherein each graphene sheet is in electrical contact with at least a further graphene sheet.

3. The electrical generator according to claim 2, wherein the plurality of graphene sheets have a tessellating shape, preferably hexagonal, square or rectangular.

4. The electrical generator according to any claim 1, wherein the first and second electrical contacts are located at distal portions of each graphene sheet.

5. The electrical generator according to claim 1, wherein the one or more graphene sheets are obtainable by the deposition of graphene on a surface of a substrate by MOCVD or CVD.

6. The electrical generator according to claim 5, wherein the surface of the substrate comprises a III-V semiconductor material.

7. The electrical generator according to claim 5, wherein the substrate comprises a support selected from the group consisting of silicon, silicon carbide, silicon dioxide, silicon nitride or sapphire.

8. The electrical generator according to claim 1, wherein each graphene sheet has a graphene layer structure comprising from 1 to 50 graphene layers.

9. The electrical generator according to claim 1, wherein the graphene sheets are doped, preferably wherein the graphene sheets are n-type doped and/or p-type doped, preferably with one or more of Br, N, Mg and P.

10. The electrical generator according to claim 1, wherein the polymer coating comprises PMMA.

11. The electrical generator according to claim 1, wherein the polymer coating has a thickness of from 1 nm to 7 nm.

12. The electrical generator according to claim 1, wherein the polymer coating is doped, preferably wherein the polymer coating is p-type doped, preferably wherein the polymer coating is doped with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane.

13. A method of generating an electrical current, the method comprising passing a flow of an ion-containing fluid across the surface of at least one of the one or more graphene sheets of the electrical generator according to claim 1.

14. The method according to claim 13, the method further comprising intermittently regenerating the electrical generator by washing and/or drying the polymer coating of at least one of the one or more graphene sheets.

15. The electrical generator according to claim 6, wherein the substrate comprises a support selected from the group consisting of silicon, silicon carbide, silicon dioxide, silicon nitride or sapphire.

Description

FIGURES

[0052] The present invention will now be described further with reference to the following non-limiting Figures, in which:

[0053] FIG. 1 shows a cross section of a prior art electrical generator.

[0054] FIG. 2 shows an exemplary electrical generator according to the present disclosure.

[0055] FIG. 3 shows a plot illustrating the voltage generated over time with regular droplets of ionic fluid striking a graphene sheet coated with PMMA:F.sub.4TCNQ, after 15 minutes.

[0056] FIG. 1 illustrates an example of a prior art electrical generator (101). The generator (101) comprises a silicon dioxide (SiO.sub.2) substrate (102) having a polymer coating (103), such as PMMA or PET, disposed thereon. A single graphene layer (104) is disposed on the surface of the polymer coating. The single graphene layer comprises electrical contacts (105) so as to have a surface of the graphene layer (104) extending between the electrical contacts (105). The surface of the graphene layer is arranged to contact a flow of a sodium chloride

[0057] (NaCl) aqueous solution (106). The electrical generator may be connected by the electrical contacts to an electrical circuit. The flow of the sodium chloride solution (106) across the surface of the graphene layer (104) extending between the electrical contacts (105) may generate an electrical current/potential difference.

[0058] The prior art electrical generator (101) is obtained by deposition of graphene on a copper foil followed by coating the graphene layer (104) with a polymer coating (103) such as PMMA or PET and attaching a fused silicon dioxide substrate (102) to the polymer coating (103). The copper foil is then etched away to leave the exposed graphene layer (104) upon which electrical contacts may be provided.

[0059] FIG. 2 illustrates an exemplary electrical generator (201) according to the present invention. The generator (201) comprises a support (202) such as a silicon support, and a substrate (203) disposed thereon, such as a gallium nitride (GaN) substrate.

[0060] The generator (201) comprises a graphene sheet (204) which has a graphene layer structure comprising five individual graphene layers (205) on the surface of the substrate, obtained by deposition of graphene by MOCVD.

[0061] The graphene sheet (204) comprises first and second electrical contacts (206), the graphene sheet (204) has a surface extending between the first and second electrical contacts (206). The surface of the graphene sheet is provided with a polymer coating (207). The polymer coating is preferably provided by spin coating. The surface extending between the electrical contacts is arranged to contact the flow of an ion-containing fluid (208) such as an aqueous sodium chloride solution. The generator (201) is capable of generating an electrical current upon contact of the surface with a flow of an ion-containing fluid when connected to an electrical circuit. The generator (201) may maintain a reasonable electrical output in excess of 30 minutes as a result of the polymer coating (207) physically isolating the graphene sheet (204) from the flow of the ion-containing fluid (208).

EXAMPLES

[0062] A graphene sheet was taken directly from a desiccator where it had been stored since growth. This was cut into three 15 mm×30mm chips which were then painted along the short edge with Ag paint. Onto one of these chips (labelled B) was spin coated PMMA in anisole (0.5% sol) at 10000 rpm for 60 seconds followed by annealing on the hotplate at 125° C. (display 160° C.) for 60 minutes. Onto another chip, the same spin conditions were used but with a 10 mg/mL F.sub.4TCNQ:PMMA 0.52 wt % hybrid solution (labelled C).

[0063] The contact resistance between two electrodes when mounted on a PCB for the bare sample (labelled A) was 21.62 kOhm. This sample was then tested under droplet flow (0.6 M NaCl sol, ˜1 drop per second, 3.3 kΩ resistor) over 30 minutes which led to complete degradation of the sample. The same treatment was repeated for samples B and C over 60 minutes which had contact resistances of 5.04 kOhm and 3.80 kOhm for B and C respectively:

TABLE-US-00001 Contact Resistance T = 0 min T = 5 min T = 15 min T = 30 min T = 60 min Sample (kΩ) peak V peak V peak V peak V peak V A 21.62 0.051 V 0.009 V 0.008 V 0 V 0 V B 5.04 0.127 V 0.062 V 0.032 V 0.024 V 0.020 V C 3.80 0.129 V 0.089 V 0.090 V 0.042 V 0.031 V Contact Resistance T = 0 min T = 5 min T = 15 min T = 30 min T = 60 min Sample (kΩ) peak P peak P peak P peak P peak P A 21.62 7.9e−7 W 2.5e−8 W 1.9e−8 W — — B 5.04 4.9e−7 W 1.2e−6 W 3.1e−7 W 1.7e−7W 1.2e−7 W C 3.80 5.0e−7 W 2.4e−6 W 2.5e−6 W 5.3e−7W 2.9e−7 W

[0064] As can be seen, for inventive examples B and C, the voltage and power produced remain at acceptable levels, whereas for the uncoated sample A, these drop over time such that after 30 minutes, no power is being generated. As well as being long-lasting, inventive examples B and C were regenerated with washing and drying and returned to their high initial performance.

[0065] All percentages herein are by weight unless otherwise stated.

[0066] As used herein, the singular form of “a”, “an” and “the” include plural references unless the context clearly dictates otherwise.

[0067] The foregoing detailed description has been provided by way of explanation and illustration, and is not intended to limit the scope of the appended claims. Many variations in the presently preferred embodiments illustrated herein will be apparent to one of ordinary skill in the art, and remain within the scope of the appended claims and their equivalents.