Production of graphene
A method of producing graphene by the electrochemical insertion of alkylammonium cations in a solvent into graphite is disclosed.
1. A method for producing graphene and graphite nanoplatelet structures having a thickness of less than 100 nm, in an electrochemical cell, comprising:
passing a current through the electrochemical cell, wherein the electrochemical cell comprises:
(a) a negative electrode which is graphitic;
(b) a positive electrode; and
(c) an electrolyte which comprises ions in a solvent, said ions comprising cations and anions, wherein the cations comprise alkylammonium ions, and thereby producing graphene and graphite nanoplatelet structures having a thickness of less than 100 nm in the electrochemical cell.
2. The method of claim 1 , wherein the negative electrode comprises a layered graphite compound in which the cations can be intercalated.
3. The method of claim 1 , wherein the negative electrode comprises a graphite compound that is selected from highly ordered pyrolytic graphite, natural graphite and synthetic graphite.
4. The method of claim 1 , wherein the alkylammonium cations comprise tetraalkyl ammonium cations.
5. The method of claim 4 , wherein the tetraalkyl ammonium cations are selected from tetrabutyl ammonium, tetraethylammonium and tetramethyl ammonium.
6. The method of claim 1 , wherein the alkylammonium cations comprise trialkyl ammonium cations.
7. The method of claim 6 , wherein the trialkyl ammonium cations are selected from tributyl ammonium, triethylammonium and trimethyl ammonium.
8. The method of claim 1 , wherein the alkylammonium cations comprise dialkyl ammonium cations.
9. The method of claim 8 , wherein the dialkyl ammonium cations are selected from dibutyl ammonium, diethylammonium and dimethyl ammonium.
10. The method of claim 1 , wherein the anions are selected from tetrafluoroborate, perchlorate and hexafluorophosphate.
11. The method of claim 1 , which is carried out at a temperature from 20° C. to 100° C.
12. The method of claim 1 which further comprises separating the graphene or graphite nanoplatelet structures having a thickness of less than 100 nm from the electrolyte by at least one technique selected from:
(a) filtering;
(b) using centrifugal forces to precipitate the graphene or graphite nanoplatelet structures; and
(c) collecting the graphene or graphite nanoplatelet structures at the interface of two immiscible solvents.
13. The method of claim 1 , wherein the graphene or graphite nanoplatelet structures having a thickness of less than 100 nm are electrochemically exfoliated from at least one electrode and wherein the method further comprises ultrasonicating the graphene or graphite nanoplatelet structures.
14. The method of claim 1 which comprises electrochemically functionalizing graphite at the negative electrode by oxidation in nitric acid or by fluorination with hydrofluoric acid, prior to the step of passing current through the electrochemical cell.
15. The method of claim 1 , wherein the positive electrode is graphitic.
16. The method according of claim 1 , wherein the negative electrode is selected from highly ordered pyrolytic graphite, natural graphite and synthetic graphite, and wherein the alkylammonium cations comprise tetraalkyl ammonium.
17. The method of claim 1 in which at least one of (i) the negative electrode is selected from highly ordered pyrolytic graphite, natural graphite and synthetic graphite, and the alkylammonium cations comprise trialkyl ammonium, and (ii) the negative electrode is selected from highly ordered pyrolytic graphite, natural graphite and synthetic graphite, and the alkylammonium cations comprise dialkyl ammonium.
18. The method of claim 1 , wherein the negative electrode is selected from highly ordered pyrolytic graphite, natural graphite and synthetic graphite, the cations comprise tetraalkyl ammonium and the anions are selected from tetrafluoroborate, perchlorate and hexafluorophosphate.
19. The method of claim 1 , wherein the negative electrode is selected from highly ordered pyrolytic graphite, natural graphite and synthetic graphite, the cations comprise trialkyl ammonium and the anions are selected from tetrafluoroborate, perchlorate and hexafluorophosphate.
20. The method of claim 1 , wherein the negative electrode is selected from highly ordered pyrolytic graphite, natural graphite and synthetic graphite, the cations comprise dialkyl ammonium and the anions are selected from tetrafluoroborate, perchlorate and hexafluorophosphate.
21. The method of claim 1 wherein the solvent is selected from N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), N,N′-dimethyl formamide (DMF), and mixtures thereof.