Humic acid-based supercapacitors

1. A supercapacitor electrode comprising a mixture of graphene sheets and humic acid, wherein said humic acid occupies 0.1% to 99% by weight of the mixture and said graphene sheets are selected from a pristine graphene material having essentially zero % of non-carbon elements, or a non-pristine graphene material having 0.001% to 5% by weight of non-carbon elements wherein said non-pristine graphene is selected from the group consisting of graphene oxide, reduced graphene oxide, graphene fluoride, graphene chloride, graphene bromide, graphene iodide, hydrogenated graphene, nitrogenated graphene, chemically functionalized graphene, and a combination thereof; and wherein said mixture has a specific surface area greater than 500 m 2 /g.

2. The supercapacitor electrode of claim 1 , wherein said electrode comprises multiple particulates that are porous and each particulate is composed of multiple humic acid molecules and graphene sheets that are packed into a spherical or ellipsoidal shape.

3. The supercapacitor electrode of claim 1 , wherein said graphene sheets comprise single-layer graphene.

4. The supercapacitor electrode of claim 1 , wherein said graphene sheets contain few-layer graphene having an average thickness no greater than 2 nm or no more than 5 graphene planes per sheet.

5. The supercapacitor electrode of claim 1 , wherein said humic acid contains isolated single molecules.

6. The supercapacitor electrode of claim 1 , wherein said mixture has a specific surface area greater than 1,500 m 2 /g.

7. The supercapacitor electrode of claim 1 , wherein said mixture has a specific surface area greater than 2,000 m 2 /g.

8. The supercapacitor electrode of claim 1 , wherein said graphene sheets or humic acid molecules are functionalized with one or more of conducting polymers, transition metal oxides, or transition metal sulfides.

9. The supercapacitor electrode of claim 1 , wherein said graphene sheets are chemically or physically activated.

10. A supercapacitor comprising an anode, a cathode, a porous separator disposed between said anode and said cathode, a liquid electrolyte in ionic contact with said anode and said cathode, wherein at least one of said anode and said cathode contains said supercapacitor electrode of claim 1 .

11. The supercapacitor as defined in claim 10 , wherein said graphene sheets and/or said humid acid molecules are bonded by or bonded to a conductive binder material selected from the group consisting of a conducting polymer, a polymeric carbon, an amorphous carbon, a petroleum pitch, a coal tar pitch, a meso-phase pitch, and combinations thereof.

12. The supercapacitor as defined in claim 10 , wherein said graphene sheets are activated, surface-functionalized, or surface-coated with functional materials or chemical groups for enhanced capacitance.

13. The supercapacitor as defined in claim 10 wherein said graphene sheets are functionalized with one or more conducting polymers, transition metal oxides, or transition metal sulfides.

14. A supercapacitor comprising an anode, a cathode, a porous separator disposed between said anode and said cathode, a liquid electrolyte in ionic contact with said anode and said cathode, wherein at least one of said anode and said cathode contains a supercapacitor electrode comprising a mixture of graphene sheets and humic acid, wherein said humic acid occupies 0.1% to 99% by weight of the mixture and said graphene sheets are selected from a pristine graphene material having essentially zero % of non-carbon elements, or a non-pristine graphene material having 0.001% to 5% by weight of non-carbon elements wherein said non-pristine graphene is selected from the group consisting of graphene oxide, reduced graphene oxide, graphene fluoride, graphene chloride, graphene bromide, graphene iodide, hydrogenated graphene, nitrogenated graphene, chemically functionalized graphene, and a combination thereof and wherein said mixture has a specific surface area greater than 500 m 2 /g, wherein said anode or cathode further contains a redox pair partner material selected from a metal oxide, a conducting polymer, an organic material, a non-graphene carbon material, an inorganic material, or a combination thereof, wherein said partner material, in combination with graphene sheets or humic acid, forms a redox pair for pseudo-capacitance.

15. The supercapacitor of claim 14 , wherein said metal oxide is selected from RuO 2 , IrO 2 , NiO, MnO 2 , VO 2 , V 2 O 5 , V 3 O 8 , TiO 2 , Cr 2 O 3 , Co 2 O 3 , Co 3 O 4 , PbO 2 , Ag 2 O, or a combination thereof.

16. The supercapacitor of claim 14 , wherein said inorganic material is selected from a metal carbide, metal nitride, metal boride, metal dichalcogenide, or a combination thereof.

17. The supercapacitor of claim 14 , wherein said metal oxide or inorganic material is selected from an oxide, dichalcogenide, trichalcogenide, sulfide, selenide, or telluride of niobium, zirconium, molybdenum, hafnium, tantalum, tungsten, titanium, vanadium, chromium, cobalt, manganese, iron, or nickel in a nanowire, nano-disc, nano-ribbon, or nano platelet form.

18. The supercapacitor of claim 14 , wherein said inorganic material is selected from nano discs, nano platelets, nano-coating, or nano sheets of an inorganic material selected from: (a) bismuth selenide or bismuth telluride, (b) transition metal dichalcogenide or trichalcogenide, (c) sulfide, selenide, or telluride of niobium, zirconium, molybdenum, hafnium, tantalum, tungsten, titanium, cobalt, manganese, iron, nickel, or a transition metal; (d) boron nitride, or (e) a combination thereof; wherein said discs, platelets, or sheets have a thickness less than 100 nm.

19. The supercapacitor of claim 10 , which is selected from a symmetric supercapacitor, an asymmetric supercapacitor, a redox supercapacitor, a lithium-ion capacitor, or a sodium-ion capacitor.