MULTI-LAYERED GRAPHENE MATERIAL HAVING A PLURALITY OF YOLK/SHELL STRUCTURES

Abstract

Multi-layered graphene materials and methods of making and use are described herein. A multi-layered graphene material can include a plurality of graphene layers having a plurality of intercalated nano- or microstructures that form a plurality of yolk/shell type structures. Each yolk/shell type structure can include at least two graphene layers that form a shell-like structure that encompasses a void space having at least one of the plurality of nano- or microstructures. The void space has a volume sufficient to allow for volume expansion of the at least one of the plurality of nano- or microstructures without deforming the shell-like structure.

Claims

1. A multi-layered graphene material comprising a plurality of graphene layers having a plurality of intercalated nano- or microstructures that form a plurality of yolk/shell type structures, each yolk/shell type structure comprising at least two graphene layers that form a shell-like structure that encompasses a void space having at least one of the plurality of nano- or microstructures, wherein the void space has a volume sufficient to allow for volume expansion of the at least one of the plurality of nano- or microstructures without deforming the shell-like structure.

2. The multi-layered graphene material of claim 1, wherein the void space has a volume sufficient to allow for at least 50% volume expansion, preferably 200% to 600% volume expansion of the at least one of the plurality of nano- or microstructures without deforming the shell-like structure.

3. The multi-layered graphene material of claim 1, wherein each of the plurality of yolk-shell type structures encompasses a single nano- or microstructure or at least two nano- or microstructures.

4. The multi-layered graphene material of claim 1, wherein the nano- or microstructure(s) fills 1% to 80%, or 30% to 60%, of the volume of each void space.

5. The multi-layered graphene material of claim 1, wherein the average volume of each void space is 5 nm.sup.3 to 10.sup.6 μm.sup.3.

6. The multi-layered graphene material of claim 1, wherein the plurality of yolk-shell type structures are configured to allow fluid, gas, or ions to enter and exit the structures.

7. The multi-layered graphene material of claim 1, wherein the material has a flow flux of 1×10.sup.−9 to 1×10.sup.−4 mol m.sup.−2s.sup.−1Pa.

8. The multi-layered graphene material of claim 1, wherein the plurality of yolk-shell type structures are configured to retain the plurality of nano- or microstructures in the void spaces.

9. The multi-layered graphene material of claim 1, wherein the graphene layers are reduced graphene oxide layers.

10. The multi-layered graphene material of claim 1, wherein the nano- or microstructures comprise silicon or an oxide or alloy thereof.

11. The multi-layered graphene material of claim 1, wherein the nano- or microstructures comprises a metal, a metal oxide, a carbon-based nano- or microstructure, a metal organic framework, a zeolitic imidazolated framework, a covalent organic framework, or any combination thereof.

12. The multi-layered graphene material of claim 11, wherein the metal is a noble metal selected from the group consisting of palladium (Pd), platinum (Pt), gold (Au), rhodium (Rh), ruthenium (Ru), rhenium (Re), or iridium (Ir), osmium (Os), any combinations or alloys thereof or a transition metal selected from the group consisting of silver (Ag), copper (Cu), iron (Fe), nickel (Ni), zinc (Zn), manganese (Mn), chromium (Cr), molybdenum (Mo), tungsten (W), or tin (Sn), or any combinations or oxides or alloys thereof.

13. The multi-layered graphene material of claim 1, wherein each nano- or microstructures has a diameter of 1 nm to 1000 nm, preferably 1 nm to 50 nm, or more preferably 1 nm to 5 nm.

14. The multi-layered graphene material of claim 1, wherein the material is in the form of a sheet or film, wherein the sheet or film has a thickness of 10 nm to 500 μm.

15. The multi-layered graphene material of claim 1, wherein the material comprises 10 wt. % to 90 wt. % of the plurality of nano- or microstructures.

16. An energy storage device comprising the multi-layered graphene material of claim 1.

17. The energy storage device of claim 16, wherein the energy storage device is a rechargeable battery.

18. A catalytic membrane for catalyzing a chemical reaction, the membrane comprising the multi-layered graphene material of claim 1.

19. A method of making the multi-layered graphene material of claim 1, the method comprising: (a) obtaining a composition comprising a plurality of graphene oxide layers having a plurality of intercalated composite nano- or microstructures that form a plurality of core/shell type structures, each core/shell type structure comprising at least two graphene layers that form a shell-like structure that encompasses at least one of the plurality of composite nano- or microstructures, wherein the composite nano- or microstructures comprise a removable polymeric matrix; and (b) calcining the composition to reduce the graphene oxide layers to graphene layers and to remove the polymeric matrix to produce the multi-layered graphene material of claim 1.

20. A method of making the multi-layered graphene material of claim 1, the method comprising: (a) obtaining a composition comprising a plurality of graphene oxide layers having a plurality of intercalated nano- or microstructures that form a plurality of core/shell type structures, each core/shell type structure comprising at least two graphene layers that form a shell-like structure that encompasses at least one of the nano- or microstructures of the plurality of intercalated nano- or microstructures; (b) calcining the composition to reduce the graphene oxide layers to graphene layers; and (c) partially etching away the plurality of intercalated nano- or microstructures to produce the multi-layered graphene material of any one of claims 1 to 19, wherein partial etching of the plurality of nano- or microstructures converts the core/shell type structure into a yolk/shell type structure that encompasses a void space having at least one nano- or microstructure, wherein the void space has a volume sufficient to allow for volume expansion of the at least one nano- or microstructure without deforming the shell-like structure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Advantages of the present invention may become apparent to those skilled in the art with the benefit of the following detailed description and upon reference to the accompanying drawings.

[0031] FIG. 1 is a schematic of an embodiment of a method of making the graphene materials of the present invention.

[0032] FIG. 2 is a schematic of another embodiment of a method of making the graphene materials of the present invention.

[0033] FIG. 3 is a transmission electron microscope (TEM) image of synthesized graphene oxide (GO).

[0034] FIG. 4 is a Fourier transform infrared (FT-IR) spectrum of synthesized graphene oxide (GO).

[0035] FIG. 5 are X-ray diffraction (XRD) patterns of (a) graphite powder and (b) GO.

[0036] FIG. 6 is a scanning electron microscope (SEM) image of silicon powder.

[0037] FIG. 7 is a SEM image of Si@SiO.sub.2 particles.

[0038] FIG. 8 is a SEM image of Si@SiO.sub.2 particles for energy dispersive X-ray (EDX).

[0039] FIG. 9 are EDX results for Si@SiO.sub.2 particles.

[0040] FIG. 10 is a SEM image of cross-section of Si@SiO.sub.2/rGO film of the present invention for EDX.

[0041] FIG. 11 is a magnified SEM image of a cross-section of a Si@SiO.sub.2/rGO film of FIG. 10.

[0042] FIG. 12 is a SEM image of the Si@SiO.sub.2/rGO film of FIG. 10 for EDX.

[0043] FIG. 13 are EDX results of the Si@SiO.sub.2/rGO film of FIG. 12.

[0044] FIG. 14 is a SEM image of a cross-section of Si/rGO yolk/shell film of the present invention.

[0045] FIG. 15 is a magnified cross-section SEM image of Si/rGO yolk/shell film of FIG. 14.

[0046] FIG. 16 is a SEM image of the Si/rGO yolk/shell film of FIG. 14 for EDX.

[0047] FIG. 17 are EDX results of the Si/rGO yolk/shell film of FIG. 16.

[0048] FIG. 18 are element maps for Si/rGO yolk-shell film of FIG. 17: (a) SEM image; (b) carbon; (c) oxygen; (d) silicon.

[0049] While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and may herein be described in detail. The drawings may not be to scale.

DETAILED DESCRIPTION OF THE INVENTION

[0050] A solution that overcomes the problems associated with storage capacity and poor charge-discharge cycles for lithium type devices has been discovered. The solution is premised on a multi-layered graphene material that is structured to have a plurality of yolk/shell like structures created from a plurality of graphene layers and a plurality of nano- or microstructures intercalated therein. In certain non-limiting aspects, the nano- or microstructure can be electrically active materials (e.g., they attract and hold lithium ions). Without wishing to be bound by theory, it is believed that when the multi-layered graphene material is lithiated or charged, the nano- or microstructure expands (due to the addition of the lithium ion to the nano- or microstructure) inside the graphene layers and causes minimal to no deformation or expansion of the graphene layers. Notably, this architecture enables three dimensional expansion of the nano- or microstructure in the void space created between graphene layers and intercalated structures.

[0051] These and other non-limiting aspects of the present invention are discussed in further detail in the following sections with reference to the Figures.

A. Preparation of a Multi-Layered Graphene Materials

[0052] FIGS. 1 and 2 are schematics of methods of preparing multi-layered graphene materials having yolk-shell type structure. The methods can include one or more steps that can be used in combination to make a multi-structured graphene material.

[0053] 1. Preparation of a Multi Nano-or Microstructure Yolks/Multi-Graphene Layer Shell Type-Structure

[0054] Referring to FIG. 1, step 1 of method 100 can include obtaining a plurality of graphene oxide layers 102 and a plurality of nano- or microstructure(s) composites 104. The nano- or microstructure(s) composite can include nano- or microstructure(s) 106 described below encapsulated in or coated with a removable polymeric matrix 108. The graphene layers used as starting materials can be obtained from a commercial source or made according to conventional processes. In a preferred embodiment, the graphene layers are graphene oxide layers.

[0055] a. Nano- and Microstructure Shapes and Materials

[0056] The nano- or micro structures can be made according to conventional processes (e.g., metal oxide nano- or microstructures made using alcohol or other reducing processes) or purchased through a commercial vendor. Non-limiting examples of nano- or microstructures that can be used include structures having a variety of shapes and/or made from a variety of materials. By way of example, the nanostructures can have the shape of a wire, a particle (e.g., having a substantially spherical shape), a rod, a tetrapod, a hyper-branched structure, a tube, a cube, or mixtures thereof. In a particular instance, the nanostructures are nanoparticles that are substantially spherical in shape. Selection of a desired shape has the ability to tune or modify the function of the graphene material. Non-limiting examples of nano- or microstructure materials that can be used include a metal, a metal oxide, a silicon compound, a carbon-based compound (e.g., a single or multi walled carbon nanotube), a metal organic framework compound, a zeolitic imidazolated framework compound, a covalent organic framework compound, a zeolite, or any combination thereof.

[0057] Non-limiting examples of metals include noble metals, transition metals, or any combinations or any alloys thereof. Noble metals include palladium (Pd), platinum (Pt), gold (Au), rhodium (Rh), ruthenium (Ru), rhenium (Re), osmium (Os), iridium (Ir) or any combinations or alloys thereof. Transition metals include iron (silver (Ag), Fe), copper (Cu), nickel (Ni), zinc (Zn), manganese (Mn), chromium (Cr), molybdenum (Mo), tungsten (W), or tin (Sn), or any combinations or alloys thereof. In some embodiments, the nano- or micro structure includes 1, 2, 3, 4, 5, 6, or more transition metals and/or 1, 2, 3, 4 or more noble metals. The metals can be obtained from metal precursor compounds. For example, the metals can be obtained as a metal nitrate, a metal amine, a metal chloride, a metal coordination complex, a metal sulfate, a metal phosphate hydrate, metal complex, or any combination thereof. Examples of metal precursor compounds include, nickel nitrate hexahydrate, nickel chloride, cobalt nitrate hexahydrate, cobalt chloride hexahydrate, cobalt sulfate heptahydrate, cobalt phosphate hydrate, platinum (IV) chloride, ammonium hexachloroplatinate (IV), sodium hexachloroplatinate (IV) hexahydrate, potassium hexachloroplatinate (IV), or chloroplatinic acid hexahydrate. These metals or metal compounds can be purchased from any chemical supplier such as Sigma-Aldrich (St. Louis, Mo., USA), Alfa-Aeaser (Ward Hill, Mass., USA), and Strem Chemicals (Newburyport, Mass., USA). Metal oxides include silica (SiO.sub.2), alumina (Al.sub.2O.sub.3), titania (TiO.sub.2), zirconia (ZrO.sub.2), germania (GeO.sub.2), stannic oxide (SnO.sub.2), gallium oxide (Ga.sub.2O.sub.3), zinc oxide (ZnO), hafnia (HfO.sub.2), yttria (Y.sub.2O.sub.3), lanthana (La.sub.2O.sub.3), ceria (CeO.sub.2), or any combinations or alloys thereof. The metal or metal oxide nano- or microstructures can be stabilized with the addition of surfactants (e.g., CTAB, PVP, etc.) and/or through controlled surface charge.

[0058] MOFs are compounds having metal ions or clusters coordinated to organic molecules to form one-, two-, or three-dimensional structures that can be porous. In general, it is possible to tune the properties of MOFs for specific applications using methods such as chemical or structural modifications. One approach for chemically modifying a MOF is to use a linker that has a pendant functional group for post-synthesis modification. Any MOF either containing an appropriate functional group or that can be functionalized in the manner described herein can be used in the disclosed carbon nanotubes. Examples include, but are not limited to, IRMOF-3, MOF-69A, MOF-69B, MOF-69C, MOF-70, MOF-71, MOF-73, MOF-74, MOF-75, MOF-76, MOF-77, MOF-78, MOF-79, MOF-80, DMOF-1-NH.sub.2, UMCM-1-NH.sub.2, and MOF-69-80. Non-limiting examples of zeolite organic frameworks include zeolite imidazole framework (ZIFs) compounds such as ZIF-1, ZIF-2, ZIF-3, ZIF-4, ZIF-5, ZIF-6, ZIF-7, ZIF-8, ZIF-9, ZIF-10, ZIF-11, ZIF-12, ZIF-14, ZIF-60, ZIF-62, ZIF-64, ZIF-65, ZIF-67, ZIF-68, ZIF-69, ZIF-70, ZIF-71, ZIF-72, ZIF-73, ZIF-74, ZIF-75, ZIF-76, ZIF-77, ZIF-78, ZIF-79, ZIF-80, ZIF-81, ZIF-82, ZIF-86, ZIF-90, ZIF-91, ZIF-92, ZIF-93,

[0059] ZIF-95, ZIF-96, ZIF-97, ZIF-100 and hybrid ZIFs, such as ZIF-7-8, ZIF-8-90. Covalent organic frameworks (COFs) are periodic two- and three-dimensional (2D and 3D) polymer networks with high surface areas, low densities, and designed structures. COFs are porous, and crystalline, and made entirely from light elements (H, B, C, N, and O). Non-limiting examples of COFs include COF-1, COF-102, COF-103, PPy-COF 3 COF-102-C.sub.12, COF-102-allyl, COF-5, COF-105, COF-108, COF-6, COF-8, COF-10, COF-11Å, COF-14 Å, COF-16 Å, OF-18 Å, TP-COF 3, Pc-PBBA, NiPc-PBBA, 2D-NiPc-BTDA COF, NiPc COF, BTP-COF, HHTP-DPB, COF-66, ZnPc-Py, ZnPc-DPB COF, ZnPc-NDI COF, ZnPc-PPE COF, CTC-COF, H2P-COF, ZnP-COF, CuP-COF, COF-202, CTF-1, CTF-2, COF-300, COF-LZU, COF-366, COF-42 and COF-43. Non-limiting examples of zeolites include Y-zeolites, beta zeolites, mordenite zeolites, ZSM-5 zeolites, and ferrierite zeolites. Zeolites may be obtained from a commercial manufacturer such as Zeolyst (Valley Forge, Pa., U.S.A.).

[0060] In some embodiments, the nano- or microstructures 106 are particles. The diameter of the core nano- or microstructures 106 can be 1 nm to 5,000, 1 nm to 1000 nm, 10 nm to 100 nm, 1 nm to 50 nm, or 1 nm to 5 nm, or 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, nm, or any range or value there between.

[0061] The amount of nano- or microstructures (e.g., nanoparticles) in the multi-layer graphene material depends, inter alia, on the use of the multi-layer graphene material. In a particular instance, the multi-layer graphene material can include 10 wt. % to 90 wt. %, 20 wt. % to 80 wt. %, 30 wt. % to 70 wt. %, 40 wt. % to 60 wt. %, or any range or value there between of the nano- or microstructures. In embodiments when the multi-layer graphene material is used, as in catalytic applications, the amount of catalytic metal present in the particle(s) in the nanostructure ranges from 0.01 to 100 parts by weight of “active” catalyst structure per 100 parts by weight of multi-layer graphene material, from 0.01 to 5 parts by weight of “active” catalyst structure per 100 parts by weight of multi-layer graphene material. If more than one catalytic metal is used, the molar percentage of one metal can be 1 to 99 molar % of the total moles of catalytic metals in the multi-layer graphene material.

[0062] b. Polymeric Matrix

[0063] The polymeric matrix can be made from any polymer. The polymers are available from commercial vendors or made according to conventional chemical reactions. In some embodiments, the polymer is a thermoset polymer or blend thereof. The polymer matrix can be made from a composition having a thermoplastic polymer and can also include other non-thermoplastic polymers, additives, and the like, that can be added to the composition.

[0064] Thermoset polymeric matrices are cured or become cross-linked and tend to lose the ability to become pliable or moldable at raised temperatures. Non-limiting examples of thermoset polymers used to make the polymer film include epoxy resins, epoxy vinylesters, alkyds, amino-based polymers (e.g., polyurethanes, urea-formaldehyde), diallyl phthalate, phenolic polymers, polyesters, unsaturated polyester resins, dicyclopentadiene, polyimides, silicon polymers, cyanate esters of polycyanurates, thermosetting polyacrylic resins, phenol formaldehyde resin (bakelite), fiber reinforced phenolic resins (Duroplast), benzoxazines, or co-polymers thereof, or blends thereof. In addition to these, other thermoset polymers known to those of skill in the art, and those hereinafter developed, can also be used in the context of the present invention. The thermoset polymer can be included in a composition that includes said polymer and additives. Non-limiting examples of additives include coupling agents, antioxidants, heat stabilizers, flow modifiers, etc., or any combinations thereof. In some embodiments, one or more monomers capable of being polymerized when exposed to heat, light or electromagnetic force are used. Such monomers can be precursor materials suitable for forming thermoset polymers. The polymers and/or monomers are available from commercial vendors or made according to conventional chemical reactions.

[0065] Thermoplastic polymeric matrices have the ability to become pliable or moldable above a specific temperature and solidify below the temperature. The polymeric matrix of the material can include thermoplastic or thermoset polymers, co-polymers thereof, and blends thereof that are discussed throughout the present application. Non-limiting examples of thermoplastic polymers include polyethylene terephthalate (PET), a polycarbonate (PC) family of polymers, polybutylene terephthalate (PBT), poly(l,4-cyclohexylidene cyclohexane-1,4-dicarboxylate) (PCCD), glycol modified polycyclohexyl terephthalate (PCTG), poly(phenylene oxide) (PPO), polypropylene (PP), polyethylene (PE), polyvinyl chloride (PVC), polystyrene (PS), polymethyl methacrylate (PMMA), polyethyleneimine or polyetherimide (PEI) and their derivatives, thermoplastic elastomer (TPE), terephthalic acid (TPA) elastomers, poly(cyclohexanedimethylene terephthalate) (PCT), polyethylene naphthalate (PEN), polyamide (PA), polysulfone sulfonate (PSS), sulfonates of polysulfones, polyether ether ketone (PEEK), polyether ketone ketone (PEKK), acrylonitrile butyldiene styrene (ABS), polyphenylene sulfide (PPS), co-polymers thereof, or blends thereof. In addition to these, other thermoplastic polymers known to those of skill in the art, and those hereinafter developed, can also be used in the context of the present invention. In some aspects of the invention, the preferred thermoplastic polymers include polypropylene, polyamide, polyethylene terephthalate, a polycarbonate (PC) family of polymers, polybutylene terephthalate, poly(phenylene oxide) (PPO), polyetherimide, polyethylene, co-polymers thereof, or blends thereof. In more preferred aspects, the thermoplastic polymers include polypropylene, polyethylene, polyamide, a polycarbonate (PC) family of polymers, co-polymers thereof, or blends thereof. The thermoplastic polymer can be included in a composition that includes said polymer and additives. Non-limiting examples of additives include coupling agents, antioxidants, heat stabilizers, flow modifiers, colorants, etc., or any combinations thereof.

[0066] In step 2, the graphene oxide layers 102 and the composites 104 can be suspended in an aqueous and/or nonaqueous medium and then vacuum filtered to intercalate the plurality of nano- or microstructure(s) composites between single graphene oxide layers 110 to form intercalated graphene material 112. Intercalated graphene material 112 includes a plurality of graphene oxide layers 110 with the composite 104 (e.g., a core) dispersed between the graphene layers. Two graphene oxide layers 110 form a shell-like material around the composite 104, thereby forming a core-shell type structure. The composites 104 can be in full or substantially full contact with graphene layers 110. In some embodiments, 50% to 100%, 50% to 99%, 60% to 95%, or 50%, 60%, 70%, 80%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 99.1%, 99.2%, 99.3%, 99.4%, 99.5%, 99.6%, 99.7%, 99.8%, 99.9%, or any range or value there between, of the surface of the composite 104 contacts the graphene layers 110.

[0067] In step 3, the intercalated graphene material 112, can be heated in the presence of air and/or inert gases (e.g., calcined) to remove the polymeric matrix 108 encapsulating the nano- or microstructure(s) 106, convert the nano- or microstructure(s) 106 to their oxide form, and/or convert the graphene oxide layers 110 to reduced graphene oxide layers 116 and form graphene material 118. Temperatures for heat treatment (e.g., calcining) can range from 500° C. to 1000° C., 700° C. to 900° C., or 500° C., 525° C., 550° C., 575° C., 600° C., 625° C., 650° C., 675° C., 700° C., 725° C., 750° C., 775° C., 800 ° C., 825° C., 850° C., 875° C., or 900° C., or any range or value there between. Removal of the polymeric matrix 108 forms void spaces 114 between the reduced graphene layers 116 and the nano- or microstructures 106. The plurality of nano- or microstructures 106 that have been uncoated during the calcination process are located in the void spaces 114 and between two reduced graphene layers 116, thereby forming a multi-yolk/shell like structure 118. After calcination, the formed graphene material 118 can be cooled to ambient temperatures, and then packaged for sale or distribution, stored, used in further processes or applications, formed into a sheet or film or any combination thereof.

[0068] c. Multi Nano-or Microstructure Yolks/Multi-Graphene Layer Shell Type-Structure

[0069] The multi-layered graphene material 118 includes void spaces 114 and each void space 114 includes a plurality of nano- or microstructures 106 or “multi-yolks”. As shown in FIG. 1, each void space 114 of the graphene material 118 includes 3 nano- or microstructure yolks, however, it should be understood that each void space can include 2, 3, 4, 5, or more nano- or microstructure yolks. The average volume of each void space can be 5 nm.sup.3 to 1,000,000 nm.sup.3 (10.sup.6 μm.sup.3) or 10 nm.sup.3 to 10.sup.5 μm.sup.3, 100 nm.sup.3 to 10.sup.4 μm.sup.3, or any range there between. The nano- or microstructure(s) 106 can fill less than 50%, 40%, 30%, or 20% of the volume of each void space (e.g., 49%, 48%, 47%, 46%, 45%, 44%, 43%, 42%, 41%, 40%, 39%, 38%, 37%, 36%, 35%, 34%, 33%, 32%, 31%, 30%, 29%, 28%, 27%, 26%, 25%, 24%, 23%, 22%, 21%, 20%, 19%, 18%, 17%, 16%, 15%, 14%, 13%, 12%, 11%, 10% or less). The void spaces can have a volume sufficient to allow for volume expansion of the nano- or microstructure without deforming the graphene shell. In some instances, the void space can have volume sufficient to allow for at least 50% volume expansion, preferably 200% to 600%, or 50%, to 550%, 100% to 500%, 250% to 450% or any value there between (e.g., 50%, 75%, 100%, 125%, 150%, 175%, 200%, 225%, 250%, 275%, 300%, 325%, 350%, 375%, 400%, 425%, 450%, 475%, 500%, 525%, 550%, 575%, 600%) volume expansion of at least one of the nano- or microstructures 106 without deforming the graphene layers 116 (shell). In some instances, the graphene material has a flow flux of 1×10.sup.−9 to 1×10.sup.−4 mol m.sup.−2s.sup.−1Pa.

[0070] 2. Preparation of a Nano-or Microstructure Yolk/Multi-Graphene Layer Shell Type-Structure

[0071] Referring to FIG. 2, step 1 of method 100 can include obtaining a plurality of graphene oxide layers 102 and a plurality of nano- or microstructure(s) 106 described below. As shown nano- or microstructure 106 is a particle loaded with another metal 202, however, nano- or microstructure(s) 106 can be single structures, core-shell, yolk-shell type structures or the like. In step 2, the graphene oxide layers 102 and the nano- or microstructure(s) 106 can be suspended in an aqueous and/or nonaqueous medium and then vacuum filtered to intercalate the plurality of nano- or microstructure(s) 106 between single graphene oxide layers 110 to form intercalated graphene material 204. Intercalated graphene material 204 includes a plurality of graphene oxide layers 110 with the nano- or microstructure(s) 106 dispersed between the graphene layers. Two graphene oxide layers 110 form a shell-like material around one nano- or microstructure 106. The nano- or microstructure(s) 106 can be in full or substantially full contact with graphene layers 110. In some embodiments, 50% to 100%, 50% to 99%, 60% to 95%, or 50%, 60%, 70%, 80%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 99.1%, 99.2%, 99.3%, 99.4%, 99.5%, 99.6%, 99.7%, 99.8%, 99.9%, or any range or value there between, of the surface of the nano- or microstructures 106 contacts the graphene layers 110.

[0072] In step 3, the intercalated graphene material 204, can be heated in the presence of air and/or inert gases (e.g., calcined in air) to remove the polymer, convert the nano- or microstructures 106 to their oxide form and/or reduce the graphene oxide to reduced graphene oxide. Calcining temperatures can range from 500° C. to 1000° C., 700° C. to 900° C., or 500° C., 525° C., 550° C., 575° C., 600° C., 625° C., 650° C., 675° C., 700° C., 725° C., 750° C., 775° C., 800° C., 825° C., 850° C., 875° C., 900° C. or any range or value there between.

[0073] In step 4, the calcined graphene material can be subjected to a process that removes a portion of the outer surface or a shell of the nano- or microstructure(s) 106 to form void spaces 114. The void spaces can have a volume sufficient to allow for volume expansion of the nano- or microstructure without deforming the graphene shell. In some instances, the void space can have volume sufficient to allow for at least 50% volume expansion, preferably 200% to 600%, or 50%, to 550%, 100% to 500%, 250% to 450% or any value there between (e.g., 50%, 75%, 100%, 125%, 150%, 175%, 200%, 225%, 250%, 275%, 300%, 325%, 350%, 375%, 400%, 425%, 450%, 475%, 500%, 525%, 550%, 575%, 600%) of at least one of the nano- or microstructures 106 without deforming the graphene layers 116 (shell). In some instances when the nano- or microstructure(s) 106 are core/shell type structures, yolk/shell nano-or microstructures are formed during the removal of a portion of the outer surface of the nano- or microstructure(s) 106. By way of example, the calcined graphene material can be contacted with an etching solution (e.g., immersed in 10 wt. % HF aqueous solution) for a desired amount of time (e.g., for 5 to 30 minutes) to partially remove a portion or all of the outer surface of shell of nano- or microstructure(s) 106 to form the void space 114. The etching time, etching concentration, or type of etching agent or combinations thereof can be determined to obtain the desired volume of void space or a specific yolk/shell nano- or microstructure. Non-limiting examples of etching agents that can be used include hydrofluoric acid (HF), ammonium fluoride (NH.sub.4F), the acid salt of ammonium fluoride (NH.sub.4HF.sub.2), sodium hydroxide (NaOH), nitric acid (HNO.sub.3), hydrochloric acid (HCl), hydroiodic acid (HI), hydrobromic acid (HBr), boron trifluoride (BF.sub.3), sulfuric acid (H.sub.2SO.sub.4), acetic acid (CH.sub.3COOH), formic acid (HCOOH), or any combination thereof. In a certain embodiment, HF, NH.sub.4F, NH.sub.4HF.sub.2, NaOH or any combination thereof can be used (e.g., in instances where a silica coating is removed from the surface of the nanostructure). In some embodiments, HNO.sub.3, HCl, HI, HBr, BF.sub.3, H.sub.2SO.sub.4, CH.sub.3COOH, HCOOH, or any combination thereof can be used (e.g., to remove an alumina coating from the surface of the nanostructure). In another embodiment, a chelating agent (e.g., EDTA) for Al.sup.3− can be added as an aid for faster etching of alumina in addition of above stated acids. Each etched nano- or microstructure 106 with metal loadings 202 is located in the created void space 114 between two reduced graphene layers 114, thereby forming a yolk-shell like structure.

[0074] a. Nano-or Microstructure Yolk/Multi-Graphene Layer Shell Type-Structure

[0075] The multi-layered graphene material 206 includes void spaces 114 and each void space 114 includes a single nano- or microstructures 106 or “yolk”. The average volume of each void space can be 5 nm.sup.3 to 1,000,000 nm.sup.3 (10.sup.6 μm.sup.3) or 10 nm.sup.3 to 10.sup.5 μm.sup.3, 100 nm.sup.3 to 10.sup.4 μm.sup.3, or any range there between. The nano- or microstructure(s) 106 can fill less than 50%, 40%, 30%, or 20% of the volume of each void space 114. The void spaces can have a volume sufficient to allow for volume expansion of the nano- or microstructure without deforming the graphene shell. In some instances, the void space can have volume sufficient to allow for at least 50% volume expansion, preferably 200% to 600% volume expansion of the at least one of the nano- or microstructures without deforming the graphene layers 116 (shell). In some instances, the graphene material has a flow flux of 1×10.sup.−9 to 1×10.sup.−4 mol m.sup.−2s.sup.−1Pa.

B. Articles of Manufacture and Applications of the Multi-layered Graphene Material

[0076] The multi-layered graphene materials 118 and 206 can be included in articles of manufacture, made into sheets, films, or incorporated into membranes. The sheet or film can have a thickness of 10 nm to 500 μm. The article of manufacture can include an electronic device, a gas or liquid separation membrane, a catalytic membrane for catalyzing a chemical reaction, a catalyst material, a controlled release medium, a sensor, a structural component, an energy storage device, a gas capture or storage material, or a fuel cell. In a particular instance, the multi-layer graphene materials of the present invention are used in an energy storage device. Non-limiting examples of energy storage devices include rechargeable batteries (e.g., lithium-ion or lithium-sulfur batteries). In some instances, the multi-layered graphene material with electroactive nano- or microstructures can be included in the electrode of the lithium battery. For example, the multi-layered graphene material with electroactive nano- or microstructures can be included in an anode in lithium-ion batteries when silicon is included in the anode. When the battery is charged, the lithium ions are attracted to the electroactive nano- or microstructures (e.g., silicon) intercalated in the reduced graphene layers 116. The lithium ions can be electrostatically attached to the electroactive nano- or microstructures and form lithiated electroactive nano- or microstructures. Due to the lithiation, the volume of the lithiated electroactive nano- or microstructures is increased as compared to the unlithiated nano- or microstructures. Since the nano- or microstructures are positioned in a 3-dimensional void space, they have sufficient space to expand, while the total volume of the multi-layered graphene material remains substantially unchanged. For example, volume of the multi-layered graphene material, when lithiated or charged, can be within 10%, 5%, 4%, 3%, 2%, 1%, or less of the volume of the multi-layered graphene material, when unlithiated or uncharged.

[0077] In some instances, the multi-layered graphene materials 118 and 206, or membrane that includes the multi-layered graphene materials, can be used in a variety of chemical reactions. Non-limiting examples of chemical reactions include oxidative coupling of methane reaction, a hydrogenation reaction, a hydrocarbon cracking reaction, an alkylation reaction, a denitrogenation reaction, a desulfurization reaction, a Fischer-Tropsch reaction, a syngas production reaction, a 3-way automobile catalysis reaction, reformation reactions, hydrogen generation reaction.

[0078] The methods used to prepare the multi-layered graphene materials 118 and 206 of the present invention can be modified or varied as desired to design or tune the size of the void space, the selection of catalytic metal-containing particles, the dispersion of the nano- or microstructures in the graphene layers, the porosity and pore size of the graphene material, etc., to design an article of manufacture, an energy storage device or other devices, or a catalyst for a specific chemical reaction.

EXAMPLES

[0079] The present invention will be described in greater detail by way of specific examples. The following examples are offered for illustrative purposes only, and are not intended to limit the invention in any manner.

[0080] Instrumentation. Powder X-ray diffraction (XRD) patterns were measured from a Bruker D8 Advance X-ray Diffractometer (Bruker Instruments, U.S.A.) with CuKα radiation λ=0.154056 nm at 40 kV and 40 mA. Scanning electron microscopy (SEM) images and Energy Dispersive X-Ray Spectroscopy (EDX) were taken by a FEI Quanta 600 FEG (FEI Company, U.S.A). Fourier transform infrared spectra (FT-IR) were acquired using a NICOLET-6700 FT-IR spectrometer (Nicolet Instrument Corporation, U.S.A.). Transmission electron microscope (TEM) images were obtained by evaporating a drop of ethanol dispersion of nanoparticles on carbon-coated copper grids followed by the measurement on Tecnai Twin TEM operating at 120 kV (FEI Company, U.S.A).

Example 1

Synthesis and Characterization of Graphene Oxide (GO)

[0081] The oxidation of graphite was carried out following the Hummers' method (Hummers et al., J. Am. Chem. Soc., 1958, 80, 1339-1339). In a typical procedure, KNO.sub.3 (12 g) and graphite (10 g) were added into concentrated H.sub.2SO.sub.4 (98%, 500 mL) under stirring. After 10 min, KMnO.sub.4 (60 g) was added slowly. The mixture was then heated to 35° C. and stirred for 6 hours. Water (800 mL) was then added dropwise under vigorous stirring, resulting in a quick rise of the temperature to about 80° C. The slurry was stirred at 80° C. for another 30 mins. Afterwards, water (2 L) and H.sub.2O.sub.2 (30%, 60 mL) were added in sequence to dissolve insoluble manganese species. The resulting graphite oxide suspension was washed repeatedly by a large amount of water until the solution pH reached a constant value of about 4.0, and finally the suspension was further diluted with water (600 mL). The diluted graphite oxide suspension (200 mL) was transferred into a conical container and the suspension was gently shaken in a mechanical shaker at a speed of 160 rpm for about 6 hours. To remove the small amount of unexfoliated particles, the resulting viscous suspension was centrifuged at 2,000 rpm for 10 min, producing a brown, homogeneous colloidal suspension of GO sheets. The colloidal suspension, when necessary, was further concentrated by centrifugation at 8,000 rpm.

[0082] FIG. 3 shows a TEM image of the synthesized graphene oxide. FIG. 4 shows a FT-IR spectrum of the GO powder. The stretching vibration at 3453 cm.sup.−1 refers to the —OH stretch of the oxidized graphene. The vibrational bands at 2920 cm.sup.−1 and 2847 cm.sup.−1 are attributed to alkane (—CH.sub.2) stretches. The absorption band at 1724 cm.sup.−1 corresponds to carbonyl (C═O) stretches from carbonyl or conjugated carbonyl groups. The bands at 1623 cm.sup.−1 has been assigned to carbon-carbon double bond (C═C) stretches. The absorption peaks at 1220 cm.sup.−1 and 1074 cm.sup.−1 are assigned to carbon-oxygen-carbon stretches (C—O—C) from epoxy or ether functionality, and carbon-oxygen stretched (C—O) from alkoxy functionality, respectively. These results are in agreement with literature reports. FIG. 5 shows XRD patterns of phase structure of graphite powder (a) and GO (b). The graphite powder (a) exhibited a sharp peak at 26.5 degrees (a). In contrast, GO powder (b) showed a characteristic broad peak at 11.3 degrees.

Example 2

Synthesis and Characterization of Si@SiO.SUB.2 .Core-Shell Particles

[0083] Silicon powder (0.5 g, 100 nm, Sigma-Aldrich®, U.S.A.) was dispersed in ethanol (200 mL), and then mixed with aqueous ammonium (25%, 6 mL and 20 mL water). Tetraethyl orthosilicate (TEOS) (30 mL) in ethanol (20 mL) was added dropwise to the mixture, and then stirred for 3 days. The resultant particles were purified by centrifugation and washed with ethanol (3 times). After drying at 80° C. under vacuum, a yellow powder of Si@SiO.sub.2 core-shell particles were obtained.

[0084] FIG. 6 shows a SEM image of silicon power used to prepare the core-shell structure. FIG. 7 is the SEM image of Si@SiO.sub.2 core-shell particles as-synthesized in this Example. EDX was used to analyze the component of Si@SiO.sub.2 particles. The white square area was selected for analysis (FIG. 8). From EDX results (FIG. 9), the ratio of Si/SiO.sub.2 was 0.42.

Example 3

Synthesis and Characterization of Si@SiO.SUB.2./Reduced Graphene Oxide Composite Core-Shell Film (Si@SiO.SUB.2./rGO)

[0085] Si@SiO.sub.2 particles (0.1 g, Example 2) and graphene oxide (0.2 g, Example 1) were dispersed in H.sub.2O (20 mL) using a Sonic Dismembrator (Fisher Scientific, Model 550), and then filtered by vacuum to form a film. The film was then sandwiched between graphite plates and loaded in a tubular furnace. After purging the tube with argon, the film was heated from room temperature to 100° C. at 2° C. /min and held for 30 min, heated to 200° C. at 2° C./min and held for 30 min, heated to 800° C. at 5° C. /min and held for 1 hour, then cooled to room temperature under argon.

[0086] FIGS. 10 and 11 are the SEM image of a cross-sectional portion of the Si@SiO.sub.2/rGO film. Layered graphene film (arrow rGO) and encapsulated Si@SiO.sub.2 (dotted circles) were observed. Dotted circles on the image are used to highlight some of the encapsulated Si@SiO.sub.2 in the layered graphene film. FIG. 12 is the SEM image of Si@SiO.sub.2/rGO film prepared for EDX analysis. The portion inside the square was selected for EDX analysis. From the EDX results (FIG. 13) it was determined that the film was composed of the elements carbon, oxygen and silicon.

Example 4

Synthesis and Characterization of Si/Reduced Graphene Oxide Composite Yolk-Shell Membrane (Si/rGO)

[0087] The Si@SiO.sub.2/rGO film of Example 3 was immersed in 10% hydrogen fluoride (HF) for 1 hour and then washed with water until neutral pH is obtained

[0088] FIGS. 14 and 15 are the SEM images of cross-sectional Si/rGO yolk/shell film. From the SEM image, bubbled graphene shell was observed. The film had a thickness of 81.45 μm. FIG. 16 is the SEM image of Si/rGO yolk/shell film for EDX analysis. From the EDX results (FIG. 17) it was determined that the content of silicon and oxygen atoms are reduced when compared with FIG. 13. Without wishing to be bound by theory, it is believed this reduction is due to SiO.sub.2 etched by HF. In addition, the O atom loss was approximately six times of Si, which meant that most O atom loss was from graphene oxide. FIG. 18 shows elemental distribution maps were collected for the Si/rGO yolk-shell film. From these maps, it was determined that C, O, and Si atoms were uniformly distributed in the Si/rGO yolk-shell film.