CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority to the Singapore application no. 10202251273F filed October 5, 2022, the contents of which are hereby incorporated by reference in their entirety for all purposes.

TECHNICAL FIELD

[0002] This application relates to a method of and an apparatus for producing graphene from carbon dioxide.

BACKGROUND

[0003] Graphene, a 2D material, possesses remarkable electronic, optical, and thermal properties, making it applicable to various domains, including flexible electronics, transistors, and photodetectors. Numerous methods have been explored to synthesize graphene including high-temperature annealing of SiC and chemical vapor deposition (CVD) growth on a metal foil exposed to hydrocarbon. Among these techniques, CVD shows promise for large-scale, high-quality graphene production. However, it is essential to note that the CVD-based growth of graphene typically employs flammable hydrocarbon precursors (e.g., CH4) that decompose into carbon and H2 gas, which raises safety concerns regarding the handling and exhaust of flammable gases. Furthermore, the production of graphene through CVD is characterized by high energy consumption, primarily due to the feedstock heat value of carbon precursors such as CH4, C2H2, and the reducing gas of H2. This energy-intensive nature results in a significant carbon footprint, with the production of 1 g of CVD-based graphene emitting over 115 tons of CO ₂ Consequently, achieving the synthesis of graphene with enhanced technical safety and reduced carbon emissions holds significant importance.

SUMMARY

[0004] In one aspect, the present application discloses a method of producing graphene. The method includes maintaining a molten salt bath in a carbonaceous environment; immersing a cathode made of copper, an anode and a reference electrode of an electrode system in the molten salt bath; and applying a negative potential at the cathode to form graphene at the cathode.

[0005] In another aspect, the present application discloses an apparatus for producing graphene. The apparatus includes a cell structure including a molten salt bath maintained in a carbonaceous environment; and an electrode system having a cathode made of copper, an anode and a reference electrode immersed in the molten salt bath, wherein the electrode system is configured to provide a negative potential at the cathode for forming graphene at the cathode.

[0006] According to another aspect, the present application discloses an apparatus for producing graphene. The apparatus includes a cell structure including a molten salt bath maintained in a carbonaceous environment; and an electrode system having a cathode made of copper and an anode immersed in the molten salt bath, wherein at least one of the cathode and the anode is configured as a respective reference electrode, wherein applying a cell potential across the cathode and the anode forms graphene at the cathode

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Various embodiments of the present disclosure are described below with reference to the following drawings:

[0008] FIG. 1 is a parametric view of an apparatus for producing graphene according to embodiments of the present disclosure; [0009] FIG. 2 is a detailed view of FIG. 1 illustrating the electrochemical reactions in the apparatus;

[0010] FIG. 3 is a method for producing graphene according to embodiments of the present disclosure;

[0011] FIG. 4 is a parametric view of an apparatus for producing graphene according to other embodiments of the present disclosure;

[0012] FIG. 5 A is parametric view of an apparatus for producing graphene according to embodiments of the disclosure;

[0013] FIG. 5B is a sectional view of a reactor according to embodiments of the disclosure;

[0014] FIG. 5C is a sectional view of a reference electrode according to embodiments of the disclosure;

[0015] FIG. 6 is a plot showing a relationship between potential and temperature for various reactions based on thermodynamic calculations;

[0016] FIG. 7 is a chart showing a XRD pattern of the copper foil cathode according to an example,

[0017] FIG. 8 shows cyclic voltammetry (CV) curves of the example of FIG 7;

[0018] FIG. 9 shows the optical images of the copper cathode with black carbon layer (graphene-like nanosheet) attached thereto after electrolysis;

[0019] FIGs. 10A to 10D are scanning electron microscope characterization images of the graphene-like nanosheet of FIG. 9;

[0020] FIGs 1 1 A to HE shows transmission electron microscopes (TEM) images and diffraction patterns of the graphene-like nanosheet of FIG. 9;

[0021] FIGs 12A and 12B shows the XPS survey scan and O Is scans of copper-catalyzed carbon dioxide-derived graphene-like nanosheet, respectively; [0022] FIG. 13A are optical images of raw copper foil as-received (left), copper foil after electrochemical polishing (middle), and copper foil after ten cycles of CV scan (right);

[0023] FIG. 13B shows decomposition cell voltage of molten into solid carbon as a function of temperature;

[0024] FIGs. 14A and 14B illustrates cell voltages and corresponding current densities of chronoamperometry electrolysis as a function of the applied potential.

[0025] FIG. 14C are optical images of the Cu foil with varying applied potential for the MSCO2RR electrolysis;

[0026] FIG. 15 A shows cyclic voltammetry (CV) curves measured with a single crystalline Cu(100) cathode, which was coupled to an inert Pt foil anode, between -1.3 and 0 V (relative to Ag/Ag2SC>4 reference electrode) at a scan rate of 50 mV/s under an Ar atmosphere at 760 °C; [0027] FIGs. 15B to 15F shows FESEM characterizations of the single crystalline Cu(100) foil surface of after MSCO2RR (electrolysis potential and temperature were fixed at -0.75 V and 760 °C, respectively) of different electrolysis durations from 6 seconds to 54 seconds;

[0028] FIGs. 16A to 16H shows FESEM images of the copper cathode surface after the chronoamperometry electrolysis at -0.75 V (vs. Ag/Ag2SO4) under 760 °C and carbon dioxide atmosphere for 72 seconds and 90 seconds;

[0029] FIGs 17A to 17G shows FESEM images of the copper cathode surface after the chronoamperometry electrolysis @ -0.75 V (vs. Ag/Ag2SC>4) for 5 minutes under 760 °C and CO2 atmosphere;

[0030] FIGs 17 H to 17J shows corresponding EDS mapping results of FIG. 17G;

[0031] FIG. 17K is a sum spectrum shown in FIG. 17G, wherein the Cu signal originated from the Cu foil growth substrate;

[0032] FIG. 17L is an optical image of the copper foil after the MSCO2RR electrolysis for 5 min; [0033] FIGs. 18A to 18G shows FESEM images of the copper cathode surface after the chronoamperometry electrolysis -0.75 V (vs. Ag/AgzSCU) for 20 min under 760 °C and CO2 atmosphere;

[0034] FIGs. 18H to 18J shows corresponding EDS mapping results of FIG. 18G;

[0035] FIG. 18K is a sum spectrum shown in FIG. 18G, wherein the Cu and Cl signal originated from the Cu foil growth substrate and residual hydrochloric acid, respectively;

[0036] FIG. 18L is an optical image of the Cu foil after the MSCO2RR electrolysis for 20 minutes.

[0037] FIGs. 19A to 19E shows FETEM images of carbon spheres obtained after the chronoamperometry electrolysis at -0.75 V (vs. Ag/Ag2SC>4) under 760 °C and CO2 atmosphere for 20 min;

[0038] FIGs. 19F to 19H shows corresponding EDS mapping results of FIG. 19E;

[0039] FIG. 191 is a sum spectrum of the carbon sphere cluster shown in FIG. 19E, wherein the Cu signal originated from the TEM copper mesh;

[0040] FIG. 20 is a schematic diagram illustrating the growth mechanism and mode of the MSCCERR-derived graphene on Cu foil, including three stages of (i) homogeneous Cu- catalyzed graphene island growth and agglomeration, (ii) heterogeneous Cu-catalyzed graphite sheet and carbon-catalyzed CS growth, and (iii) homogeneous carbon-catalyzed CS growth;

[0041] FIGs. 21A to 21D shows Raman spectra of the MSCChRR-derived graphene obtained at 10 mA/cm ² for 18 s under 760°C, 800°C, 900°C, and 1000°C,

[0042] FIG. 21E shows an ID/IG ratio of the graphene obtained in FIG. 21 A to 21D;

[0043] FIG. 21F shows an ED/IG ratio of the graphene obtained in FIG. 21A to 21D;

[0044] FIG. 22A is a schematic diagram illustrating the PMMA-assisted graphene transfer procedure; [0045] FIG. 22B is an optical microscopy image of the PMMA-transferred MSCO2RR- derived graphene on the SiOi/Si substrate;

[0046] FIG. 22C shows Raman spectra of the MSCChRR-derived graphene before (on the Cu foil) and after (on the SiCh/Si substrate) the transfer;

[0047] FIG. 22D is an AFM image; and

[0048] FIG. 22E shows the corresponding step test of the MSCChRR-derived graphene on the SiOi/Si substrate.

DETAILED DESCRIPTION

[0049] The following detailed description is made with reference to the accompanying drawings, showing details and embodiments of the present disclosure for the purposes of illustration. Features that are described in the context of an embodiment may correspondingly be applicable to the same or similar features in the other embodiments, even if not explicitly described in these other embodiments. Additions and/or combinations and/or alternatives as described for a feature in the context of an embodiment may correspondingly be applicable to the same or similar feature in the other embodiments.

[0050] In the context of various embodiments, the articles “a”, “an” and “the” as used with regard to a feature or element include a reference to one or more of the features or elements.

[0051] In the context of various embodiments, the term “about” or “approximately” as applied to a numeric value encompasses the exact value and a reasonable variance as generally understood in the relevant technical field, e g., within 10% of the specified value.

[0052] As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

[0053] The term “potential” may generally be used to refer to an electric potential applied to a conductive structure, such as an electrode, in relative to or with reference to another conductive structure, such as another electrode. For the sake of brevity, the term "potential" may be used to refer to any one or more of the terms "electric potential", "electrical potential ", “electrical potential energy”, "potential difference", etc., as will be understood from the context. [0054] The present disclosure relates to apparatus and methods for producing graphene from molten salt in a carbonaceous environment. As examples, the apparatus and methods may produce graphene from carbon dioxide while realizing a fast, high purity, high yield and selectivity of homogeneous catalytic conversion of carbon dioxide to graphene. The apparatus and method for producing graphene may be utilized in various applications, such as semiconductors, thermal paints, concrete, biomedical devices, etc. The chemical synthesis of the graphene the molten salt electrochemistry and sustainability are also described hereinbelow. [0055] In some embodiments, a process of molten salt CO2 reduction reaction (MSCO2RR) is described. MSCO2RR is an enabling technology to capture and transfer CO2 into value-added carbon nanostructures, including carbon spheres and carbon nanotubes, thus is green and environmentally friendly. MSCO2RR utilizes CO2, a greenhouse gas, as the carbon source for synthesizing carbon nanostructures in a solution phase, and its water-free molten electrolyte eliminates the hydrogen evolution reaction, thus ensuring a safer, Fh-free, CCh-negative carbon synthesis process. Further, the CO2 source may be pure CO2, air, or flue gas, which may reduce the need for extensive system shielding and sealing, making it highly scalable compared to CVD. Moreover, since the whole process does not consume electrolytes, there is no need for any complex or expensive catalysts, therefore enabling a low-cost and economical solution. In addition, renewable energy/energy sources may be utilized to drive the electrolysis as described above.

[0056] Various embodiments of the present disclosure enable a direct and fast conversion of a carbonaceous source, such as carbon dioxide gas, to graphene using a liquid phase molten salt in an electrolysis setting. In some embodiments, by employing a three-electrode system, which includes a cathode, an anode, and a reference electrode, the thermodynamic-calculation- guided cathode potential for graphene growth or graphene production may be precisely controlled As a result, the controllable growth of carbon dioxide-derived graphene is realized. The obtained graphene may possess decent crystallinity and graphitization degree, uniform morphology, near 100% yield and purity. The crystallinity may also be either amorphous or crystalline depending on the controllable conditions

[0057] To aid understanding and not to be limiting, a detailed description of various embodiments of an apparatus for producing graphene and a method for producing graphene will be described below with reference to the appended figures. For the sake of brevity, the following will describe various examples with respect to the apparatus and method for producing graphene, but it will be understood that the apparatus and method may be used in multiple scenarios such as in the field of semiconductors, coating materials, construction, biomedical applications, etc.

[0058] FIG. 1 is a schematic diagram of an apparatus 100 for producing graphene. The apparatus 100 includes a cell structure 140 including a molten salt bath 80 and an electrode system 1 10. The molten salt bath 80 may be maintained in a carbonaceous environment 81, or in other words, the molten salt is maintained in contact with a carbon source or carbon compound/material. In some embodiments, the molten salt bath 80 may be maintained in the carbonaceous environment 81 at an elevated temperature. For example, the elevated temperature may be in the range of 300°C to 1000°C, preferably between 760°C to 1000°C. The electrode system 1 10 may be a 3-electrode system which includes a cathode 1 12 such as a copper cathode, an anode 114 such as a platinum anode, and a reference electrode 116 such as a Ag/AgzSCh reference electrode In some embodiments, the cathode 112 is made of copper with at least 99.99% purity. In some embodiments, the cathode 112 cathode is a single crystalline copper foil cathode. The electrodes 112/114/116 may be disposed space apart from each other. The placement of the three electrodes 112/114/116 in the molten salt 80 may include positioning each of the electrodes 112/114/116 at equidistant. In some examples, the electrodes 112/114/116 may be vertically parallel or horizontally parallel. The cathode 112, the anode 114 and the reference electrode 116 may each be in the form or shape of a foil (such as the cathode 112 in FIG. 1), a wire (such as the reference electrode 116 in FIG. 1) or a coiled type (such as the anode 1 14 in FIG 1). It may be appreciated that the form or shape of each of the electrodes 112/114/116 may be interchangeable and determined based on the specific applications.

[0059] The electrode system 110 may further include a controller 118 in signal communication with the cathode 112, the anode 114 and the reference electrode 116. The controller 118 may include a power source or a voltage source. The controller 118 may be configured to apply a potential on the cathode 1 12, the anode 1 14 and/or the reference electrode 116. In some embodiments, the controller 118 may be configured to apply a precise potential on the cathode 112, the anode 114 and/or the reference electrode 116 based on a targeted or preset potential value. When the cathode 112, the anode 114 and the reference electrode 116 are immersed in the molten salt bath 80, the electrode system 110 may provide a negative potential at the cathode 1 12 for forming graphene 82 at the cathode 1 12. In some embodiments, the graphene 82 is a multilayer graphene.

[0060] In some embodiments, the carbonaceous environment 81 may correspond to the molten salt bath 80 being held in an atmosphere 81 with a carbonaceous gas, such as one of or a mixture/combination of pure carbon dioxide gas, flue gas, exhaust, air, and carbon dioxide/argon mixed gas. The cell structure or container 140 may be enclosed such that the molten salt bath 80 is confined with the carbonaceous gas collectively by the container 140, wherein a supply of carbonaceous gas is provided through at least one inlet of the cell structure to create the carbonaceous environment. In other embodiments, the container 140 may be open thus allowing a constant supply of carbonaceous gas from the surrounding atmosphere. [0061] In alternative embodiments, the carbonaceous environment may include the carbonaceous gas being directly injected into the molten salt bath 80. In some embodiments, the carbonaceous gas may be injected via bubbling into the molten salt bath. For example, the carbonaceous gas may be bubbled into the molten salt bath via a conduit, such as a stainless- steel tube or a corundum tube.

[0062] In some embodiments, the molten salt bath 80 may include a salt such as: an alkali metal carbonate, an alkaline-earth metal carbonate, a chloride, a fluoride, a metal oxide, and a combination thereof. Specifically, the alkali metal carbonate may include L12CO3, NajCOs, K2CO3, Rb2CO3, and CS2CO3. The alkaline-earth metal carbonate may include BeCCh, MgCCh, CaCCh, SrCCh, BaCCh. The chloride may include LiCl, NaCl, KC1, CaCh. The fluoride may include LiF, NaF, and KF. The metal oxide may include IJ2O, CaO, GeCh, SnC>2, CuO, Fe20s, Fe3CU, BaGeOi, Na2SnO3.

[0063] In some examples, the molten salt bath 80 may be held in a container 140 or a crucible. As non-limiting examples, the container 140 may be an alumina crucible, a graphite crucible or a stainless-steel container. In some embodiments, the container 140 may include a heater or may be heated such that the molten salt bath 80 is maintained at the elevated temperature.

[0064] FIG. 2 illustrates the mechanism of carbon dioxide (CO2) capturing and the conversion of carbon dioxide into graphene according to an embodiment. As an example, the MSCO2RR uses Li2CO3-based molten carbonate electrolyte. Under the electrolysis reaction, the reduction of COs ² ' into graphene takes place at the cathode surface (reaction 1 below). The oxygen evolution reaction or the oxygen evolution through the discharge of released O ² ' takes place at the anode (reaction 2 below). The decomposed CO, ² ' is replenished by the combination between O ² ' and gaseous CO2 (reaction 3 below) which is the CO ² capture reaction, resulting in the net electro reduction of CO2 into carbon and O ₂ . Therefore, the net reaction is the electrosplitting of CO2 into solid graphene flakes 82 and gaseous O ² (reaction 4 below).

Reaction 1 : Cathode reaction: CO ₃ ² ' + 4e" — > C + 3O ² '

Reaction 2: Anode reaction: 2O ² - ^ O ₂ + 4e-

Reaction 3: CO ₂ Capture: O ² ’ + CO2 — CO ₃ ² ’

Reaction 4: Net reaction: co, > c - O ₂

[0065] The graphene as produced according to the present disclosure does not require additional chemical reactions to functionalize the graphene. The reason being during the CO2RR via molten salt electrolysis, due to cathodic deoxygenation of CO ₃ ² ' and the surface modification effect of molten salt, cathodic carbon products (i.e., graphene) can be in operando functionalized. In some embodiments, the graphene 82 is functionalized in operando with one or a combination of a surface oxygen-containing functional group. As examples, the surface oxygen-containing functional group may include an epoxide(C-O) functional group, a hydroxyl (C-O) functional group and a carboxylate (C=O) functional group The fabricated graphene thus may be directly applied to fields such as semiconductors, thermal paints, concrete and biomedical chip, which reduces costs and is energy-saving and environmentally friendly.

[0066] Referring to FIG. 3, a method 300 for producing graphene is disclosed according to various embodiments of the present disclosure. The method 300 includes in stage 310, maintaining a molten salt bath in a carbonaceous environment. The carbonaceous environment may include holding the molten salt bath in an atmosphere with a carbonaceous gas; confining the molten salt bath with a carbonaceous gas; and injecting a carbonaceous gas into the molten salt bath. The method 300 may also include in stage 320, immersing a cathode made of copper and an anode of an electrode system in the molten salt bath; and in stage 330, applying a negative potential at the cathode to form graphene at the cathode. In some embodiments, the method 300 may further include functionalizing in operando the graphene with one or a combination of a surface oxy gen-containing functional group. The surface oxy gen-containing functional group may include an epoxide(C-O) functional group, a hydroxyl (C-O) functional group and a carboxylate (C=O) functional group. In some embodiments, the molten salt bath may be maintained at an elevated temperature. In some embodiments, the method includes determining a magnitude of the negative potential and a duration of the negative potential to be applied to the cathode based on a targeted thickness of the graphene prior to applying the negative potential at the cathode. Therefore, this allows a thickness of the graphene produced to be controlled, based on the magnitude and duration of the negative potential applied.

[0067] In some embodiments, the method 300 further includes pre-processing the molten salt bath in a galvanostatic electrolysis system to remove moisture and impurities. The galvanostatic electrolysis system includes a graphite cathode and a inert anode, such as a platinum anode. For example, the galvanostatic electrolysis setup may include a graphite rod cathode and an inert platinum foil as the anode. The platinum foil may be polished with sandpapers after each electrolysis for re-use.

[0068] In some embodiments, the method 300 further includes electrochemically polishing the cathode prior to immersing the cathode in the molten salt bath. The cathode may be electrochemically polished in phosphoric acid with the applicaiton of a voltage across the galvanostatic electrolysis setup. After polishing, the copper foil may be thoroughly rinsed with deionized water, and sonicated in a solvent and blow-dried with a gas.

[0069] In some embodiments, the electrode system may include a reference electrode 116. In some embodiments, the potential applied at the cathode 112 may be a negative potential relative to the anode and/or a negative potential relative to the reference electrode 116. The reference electrode 116 may aid in providing a reference potential for controlling the potential applied at the cathode 112. Therefore, with the provision of the reference electrode 116, accurate/timely control of the potential applied at the cathode 116 may be achieved.

[0070] In some embodiments, the controller 118 may control the negative potential at the cathode 112 within a range. In some embodiments, the negative potential applied on the cathode 112 is a negative potential in relative to the reference electrode over a predetermined duration. For example, the negative potential may be in a range of -6V to -0.001 V relative to the reference electrode 116, and the predetermined duration may be in a range of 1 second to 200 hours. In some embodiments, the negative potential may be in the range of -0.5V to -0.9V, relative to the reference electrode 116, and the predetermined duration may be in the range of 6 seconds to 20 minutes. As some examples, the predetermined duration may be 15 seconds, 30 seconds, 1 minute, 5 minutes, or 20 minutes, to form graphene 82 on the cathode 1 12.

[0071] In some embodiments, the negative potential applied on the cathode 112 may be controlled at a constant potential relative to the reference electrode 116, e g. a fixed -0.05 V potential relative to the reference electrode 116. In other examples, the constant potential may be -0.58 V, -0.60 V, -0.62 V or -0.64 V relative to the reference electrode 116. In some embodiments, the negative potential may be controlled in a stepwise manner in relative to the reference electrode, e.g., first step at -0.03 V, next step at -0.04 V and final step at -0.05 V in relative to the reference electrode 116.

[0072] In some embodiments, the anode 114 may be made a material selected from the group consisting of a metalmaterial, a metal alloymaterial, a cermetmaterial, a ceramicmaterial, a nonmetalmaterial, and a metal/metal oxide plated material. Specifically, the metal material may include nickel, platinum, palladium, copper, iron, iridium, titanium, and gold. The metal alloy material may include NiioCunFe, NinFeioCu, 304 stainless steel, and Inconel 718. The cermet material may be Ni-TiCh, (l-x)CaTiC>3-xNi). The ceramic material may include SnCh and RuCfi-TiCfi. The non-metallic material may include graphite, carbon and glassy carbon. The metal/metal oxide plated material may include Pt coated Ti, AI2O3 coated Ni, and NiO/NiAh loaded Pt.

[0073] In some embodiments, the reference electrode 116 may be made from an inert conductive material such as platinum, silver, gold and graphite. In other embodiments, the reference electrode 116 may be made from Ag/Ag2SC>4 or Ag/AgCl.

[0074] Referring to FIG. 4, embodiments of an apparatus 200 for producing graphene is disclosed. Similar to the above embodiments, the apparatus 200 includes a molten salt bath 80 and an electrode system 210. The molten salt bath 80 may be maintained in a carbonaceous environment. In some embodiments, the molten salt bath 80 may be maintained in the carbonaceous environment at an elevated temperature. The electrode system 210 may be a 2- electrode system which includes a cathode 212 and an anode 214 disposed space apart from each other. The electrode system 210 may further include a controller 218 in signal communication with the cathode 212 and the anode 214. The cathode 212 and the anode 214 may be immersed in the molten salt bath 80. When the cathode 212 and the anode 214 are immersed in the molten salt bath 80, and by way of applying a potential at the cathode 212, graphene 82 is formed at the cathode 212.

[0075] In some embodiments, one or both of the cathode 212 and the anode 214 may act as a respective reference electrode. For example, the anode 214 may be taken as a reference electrode such that the cell potential applied on the cathode 212 is relative to the reference electrode or the anode 214 to form graphene 82. In other examples, as the cathode 212 is coupled to the anode 214, both the cathode 212 and the anode 214 act as respective reference electrodes. Therefore, the three-electrode system as described in previous embodiments is now a pseudo-three-electrode system which is in a two-electrode configuration. The two-electrode configuration is used to control the cell potential to produce graphene this in alternative to controlling the cathode potential or the potential applied on the cathode. As an example of the cell potential range, the cell potential may be in a range of 0.001V to 100V. In some embodiments, the cell potential may be a constant potential, e.g. a fixed 1.0 V. In some embodiments, the cell potential may be a stepwise potential, e.g., first step at 0.3 V, next step at 0.4 V and final step at 1.0 V.

Examples

[0076] FIG. 5A and 5B illustrates an apparatus 400 of the present disclosure according to various examples. The apparatus may include a molten salt reactor 410 with a vertical split tube furnace 420 (working temperature < 1100 °C ± 1 °C). Electrodes, thermocouples 418, gas inlet, and outlet tubes 419 may be inserted into a chamber of the reactor 410 via designated tube holes on the reactor lid 413, securely sealed by tightening the nut around the Viton O-ring 412. The lid may then be further sealed to the reactor body using a Viton O-ring 415 and KF 100 clamp. To maintain a controlled environment, the reactor may be flange-sealed 416 to an Ar-purged glovebox 430 (99.9995% purity, Air Liquid) with H2O and O2 concentrations lower than 0.01 ppm to prevent gaseous phase impurities from oxidizing the Cu foil and affecting electrolysis. The operating temperature on the reactor lid within the glovebox may be regulated by circulating cooling water in a ring-shape water tank 417 attached to the upper part of the reactor body. Inside the molten salt electrochemical reactor 410, an alumina (99%) crucible 440 (OD*lDxH=75*67xl05 mm) may be fixed to the reactor 410 by a support 442. A rectangular copper foil cathode 432 with a dimension of 1.5x4x0.025 cm (99.999%, Alfa Aesar, item NO. #00097) and a L-shaped platinum foil anode 434 (99 99%, 0.2 mm thick) are both assembled to a Mo lead wire (ODxL=3x500 mm). This assembly is sealed within a two-end open alumina (99%) tube (ODxIDxL=8x5x450 mm) using alumina adhesive cement (Aluseal adhesive cement No. 2, Sauereisen). The nominal electrochemically active surface area which is immersed in molten salt has an area of 3 cm ² for the copper cathode and 5 cm ² for the platinum anode, with current density measured in terms of the cathodic active surface area. An Ag/Ag2SCU reference electrode 436 may be used. The reactor chamber's temperature may be calibrated using a Type K thermocouple 419. The working gas atmosphere inside the sealed reactor 410 may be switched between high-purity Ar (99.9995%, Air Liquid) and CO2 (99.995%, Air Liquid). The gas flow rates may be controlled at 50 seem for Ar and 100 seem for CO2, respectively, using a mass flow controller (GE50A, MKS Instruments). The gas pressure may be maintained at 1 atm throughout the process. The reactor outlet gas may be directed into a bubbler and then released into a fume hood.

[0077] To synthesize graphene via MSCO2RR, 140 g of Li2CCL (> 99%, Sigma Aldrich) is loaded into the alumina crucible 440 and undergoes dehydration at 300 °C under an Ar atmosphere for an extended duration, such as 24 hours. Subsequently, the ILCO ; may be heated and maintained at 780 °C for 2 hrs under a CO2 atmosphere to achieve complete melting. To remove moisture and metallic impurities, the molten LijCCh may undergo pre-electrolysis for 4 hrs through a two-electrode galvanostatic electrolysis with a current density of 20 mA/cm ² . The electrolysis setup may include a graphite rod cathode (99.995%, <I> 5 mm, 3.34 cm ² active surface area) and an L-shaped inert platinum foil (5 cm ² active surface area) serving as the anode. The platinum foil may be polished with grit #2000, #3000, and #5000 silicon carbide sandpapers after each electrolysis for re-use, ensuring the removal of the oxide layer and maintaining good oxygen evolution reaction activity.

[0078] To decrease surface roughness, a process of electrochemical polishing may be performed on the copper cathode The as-received raw copper foil may be employed as the working electrode (+), paired with another similar-sized copper foil as the counter electrode (-). The pair of copper electrodes may be electrochemically polished in phosphoric acid (> 85 wt.%) for 30 minutes, with an applied voltage of -1.9 V. After polishing, the copper foil may be thoroughly rinsed with deionized water, sonicated in ethanol for 5 minutes, blow-dried with nitrogen gas, and promptly transferred into the glovebox 430 for storage and subsequent use. The carbon dioxide-to-graphene electrolysis is then carried out in purified LizCCh, employing a three-electrode configuration with the electrochemically polished copper foil as the cathode, inert platinum as the anode, and corundum Ag/AgzSCh as the reference electrode.

[0079] In some examples, in order to prevent oxidation, all the electrodes 432/434/436 may be stored in the glovebox 430. Cyclic voltammetry (CV) measurements may be performed under an Ar atmosphere to avoid carbon dioxide interference, while the other electrolysis experiments may be conducted under the carbon dioxide atmosphere. After the electrolysis process, the copper foil cathode 432 may be lifted from the molten salt and allowed to cool naturally in the reactor's upper part, this prior to the copper foil cathode 432 being taken out of the glovebox 430 for further treatment. The graphene-attached copper foil may then be subjected to leaching with ~2 M diluted hydrochloric acid to dissolve frozen salts on the copper foil. The copper foil may then be rinsed with ethanol and acetone for several times, dried with a nitrogen gas flow, and transferred back to the glovebox 430 for storage and subsequent usage. [0080] A PMMA layer (950 K A4, Microchem Inc.) may be spin-coated onto the graphene/copper foil at 1000 rpm for 1 minute, followed by baking at 170 °C for 3 minutes. Subsequently, the growth copper foil substrate may undergo etching in 1 M (NFhjzSzOs solution for an extended duration, for example leaving the etched copper foil overnight This process results in a PMMA/graphene self-standing film, which may then be thoroughly washed with deionized water to remove residual etchant. Finally, the film may be attached to a SiOz/Si substrate at the water surface. To enhance the interaction between graphene and the SiOz/Si substrate, the PMMA/graphene/SiOz/Si structure may be baked at 180 °C for 3 hours. Subsequently, the structure may be soaked in acetone for 1 hour for three cycles at room temperature to dissolve the PMMA polymer. The resulting graphene/SiCh/Si substrate is then ready for further characterization. [0081] Example substrates as prepared above may be subjected to cyclic voltammetry (CV) tests, chronoamperometry, and chronopotentiometry electrolysis using a potentiostat (SP300, Biologic) equipped with a booster (2 A, 30 V). The structures and morphologies of the obtained MSCChRR-derived carbon materials may be characterized using a field-emission scanning electron microscope (FESEM, JSM-7610 FPlus) and a transmission electron microscope (TEM, JEM-21 OOF). Elemental compositions of the carbon materials may be measured with energy dispersive spectroscopy (EDS) mapping, which is equipped with both SEM and TEM. XRD pattern of the copper foil may be collected with a Bruker system with Cu K-a radiation (X = 1.5418 A). Raman analysis may be conducted using a Renishaw inVia micro-Raman spectrometer with a laser at 532 nm. Optical images of the transferred graphene on SiCh/Si substrate may be obtained using a Keyence 4K digital microscope (VHX-7000 series). AFM tests may be performed with a BRUKER Dimension Icon.

[0082] FIG. 5C illustrates an Ag/Ag2SO4 reference electrode 450 according to examples of the disclosure. The Ag/Ag2SO4 reference electrode 450 may be a custom-made reference electrode which includes a one-ended-closed alumina tube 452 and a silver (Ag) wire 454 passing through from an open end of the alumina tube 452 to a closed end of the alumina tube 452. The open end of the alumina tube may be sealed by epoxy adhesive glue 456. The reference electrode may further include a form material 458 such as Li2CO3-Ag2SO4 disposed interior of the alumina tube 452. The process of making the Ag/Ag2SC>4 reference electrode is as follows. The one-end-closed alumina tube (99%, OD=8 mm, ID=5 mm, L=50 cm) may be cleaned with acetone (>99%), ethanol (99%), and deionized (DI) water respectively, and dried in an oven at 60 °C overnight before putting into the glovebox. The Ag wire (99.99%, <p= 1 mm, L=55 cm) may be wiped with acetone (>99%) and ethanol (99%) respectively, and transferred back to the glovebox after cleaning. The Ag wire may be filled with Li2CO3-Ag2SO4-filled. 1g dehydrated Li2CC>3 (> 99%, Sigma Aldrich) and 0.1 mmol Ag2SC>4 (99.999%, Alfa Aesar) were weighed respectively, mixed, and filled into the prepared alumina tube. The alumina tube may be shaken sufficiently such that the salt reaches the tube bottom. Thereafter, the Ag wire was inserted into and went deep into the bottom of the tube. The [.hCO i-AgiSO-i-filled Ag-wire- inserted alumina tube was heated to 780 °C at a heating rate of 5 °C/minutes, maintained for 30 minutes to melt the Li ₂ CO3-Ag2SO4 electrolyte, prior to being cooled down to the room temperature. An epoxy adhesive glue (Araldite) may be used to seal the open end of the alumina tube. After the glue has set, the sealed corundum Ag/Ag ₂ SCU tube may be soaked in molten Li ₂ CO ₃ at 780 °C for 8 hours, to activate the alumina membrane and thus achieving the ionic conduction via the alumina tube wall/membrane. Finally, the activated corundum Ag/Ag2SO4 reference electrode may be cooled to room temperature ready for use.

[0083] In some examples of the present disclosure, Pure U2CO3 or a salt mixture comprising Li ₂ COi (e.g., Li ₂ CO3-Na ₂ CO ₃ -K ₂ CO3, LizCOi-CaCOi-KiCOi, Li ₂ CO3-Ba ₂ CO ₃ ) is disposed into a container such as an alumina crucible, a graphite crucible or a stainless-steel container. The container filled with salt is maintained in an atmosphere such as high purity carbon dioxide, flue gas or air, and heated to a corresponding electrolysis temperature such as 760 °C, 780 °C or 800 °C. Three electrodes, a pure copper cathode in a foil form, inert anode in a coil form such as a platinum electrode, a platinum-coated Titanium electrode or a homemade Ag/Ag ₂ SC>4 electrode, and a reference electrode in a wire form such as a platinum electrode or a silver electrode, are immersed into the molten salt spaced apart from each other. The electrolysis is performed by applying a negative potential on the pure copper cathode, for example, at a potential of -0.58 V, -0.60 V, -0.62 V or -0.64 V, relative to the platinum reference electrode for a short duration of time, such as 15 seconds, 30 seconds or 1 minute. Thereafter, the carbon dioxide-derived solid graphene may be collected at the copper cathode. The collected carbon dioxide-derived solid graphene are washed by 1-7 M diluted hydrochloric acid and deionized water respectively, collected by methods such as suction filtration or centrifugation, before being dried in the oven for usage. In this example, by using high purity U2CO3 salt without any other additives and high purity copper foil without any other elements doped within, excludes the adverse interferences from other influencing factors during the graphene growth. As a result, carbon dioxide-derived graphene with high yield, purity, selectivity and Faradaic efficiency is achieved.

[0084] FIGs 6 to 12B illustrates some example methods of producing graphene according to the present disclosure. 180 grams of Li?CO, (purity >99.0%) was filled into an alumina crucible (purity 99%, OD=75 mm, H=90 mm). The crucible was maintained in a carbon dioxide atmosphere (purity 99.995%), and heated to the fixed electrolysis temperature of 800 °C. Thereafter, three electrodes, a copper foil cathode (purity 99.99%, 2 cm by 1.5 cm by 0.3 mm, 3 cm ² ), a coiled platanium wire anode (purity 99.99%, <I> 1 mm, 6 cm ² ), and a Ag/Ag2SC>4 reference electrode, were immersed into the molten Li->CO with a 3 cm spacing apart from each other. The electrolysis was conducted by applying a fixed negative potential (e.g., -1.13 V vs Ag/Ag2SO4 electrode) on the cathode for 30 seconds. Thereafter, the carbon dioxide-derived solid graphene was collected at the copper cathode. The collected carbon dioxide-derived solid graphene are washed by 2 M diluted hydrochloric acid and deionized water respectively, collected by suction filtration (0.4 pm filter membrane) and finally dried at 60 °C overnight in the oven for usage.

[0085] Based on thermodynamic calculations, as shown in FIG. 6, the decomposition of U2CO3 into IJ2O, solid carbon and gaseous oxigen requires lowest potential and energy which is thermodynamically preferred compared to other possible competing reactions. This indicates that to achieve a high selectivity and current efficiency of carbon dioxide conversion into high yield and purity graphene, the cell potential should be higher than the onset potential for graphene growth while be lower than potentials for other competing reactions which will decrease the current efficiency. Namely, the overall cell potential should be controlled to fall in the hatched area in FIG. 6.

[0086] Further, to understand the onset cathode potential (relative to Ag/Ag2SO4) of the carbon deposition and fine-tune the growth of graphene by tuning the cathodic potential within the effective range, cyclic voltammetry (CV) curves were obtained by using copper as cathode, coiled pltanium wire as anode and homemade Ag/AgzSCh as quasi reference electrode The XRD pattern (FIG. 7) of the utilized Cu foil cathode was confirmed to be amorphous copper. The obtained Cu-based CV curves are shown in FIG. 8.

[0087] FIG. 9 shows the optical images of the copper cathode which includes black carbon layer attached onto it after electrolysis. Both optical images (FIG. 9) and SEM characterization images (FIG. 10) demonstrated cathode carbon products were flake like. TEM images (FIG. 11A-B) also confirmed their flake feature. The carbon dioxide-derived graphene exhibited very high yield, purity and selectivity. The graphene sizes were on a relatively large scale, i.e., at least millimeter level. Diffraction patterns of the products (FIG. 11D-E) at the red and yellow dots in FIG. 11C were consistent with the diffraction patterns of typical graphene and demonstrated decent crystallinity, indicating the obtained copper-catalyzed carbon products are graphene.

[0088] Moreover, FIGs. 12A-B shows the XPS survey scan and O Is scans of copper- catalyzed carbon dioxide-derived graphene, respectively. As only carbon and oxygen elements are observed in the survey scan (FIG. 12A) of the carbon dioxide-derived graphene, this demonstrates low contamination and high purity feature of our disclosed method of graphene production. The O Is spectra (FIG. 12B) was fitted for C-0 (i.e., epoxide and hydroxyls functional group) peaks and C=O (i.e., carboxylate functional groups) peaks. The fitted results denoted that molten salt derived graphene contained epoxide, hydroxyl and carboxylate functional groups. This indicates that during the CO2RR via molten salt electrolysis, cathodic carbon products can be in operando functionalized and added with surface functional groups such as epoxide(C-O), hydroxyl (C-O) and carboxylate (C=O) functional groups which were due to cathodic deoxygenation of COs ² ’ and the surface modification effect of molten salt [0089] The above example demonstrates the uniqueness of copper in catalyzing graphene converted from carbon dioxide via molten salt. The carbon dioxide-derived graphene are produced in a relatively large scale (i.e., at least millimeter level) and ultrafast (i.e., tens of seconds level) way by using a three-electrode system. The as synthesized graphene has near -100% yield, purity and selectivity, decent crystallinity. Furthermore, due to the nature of synthesis in molten melt, the graphene are functionalized in operando with surface oxygencontaining functional groups attached such as epoxide(C-O), hydroxyl (C-O) and carboxylate (C=O) functional groups, which can be applied into many fields including but not limited to metals, concrete, foldable screens and solar panels. Such a well-controlled, facile, green and environmentally friendly invented method of graphene production converted from carbon dioxide has good commercial value.

[0090] Various other examples of the MSCO2RR were also carried out using the three- electrode configuration comprising a pure copper foil cathode, an inert pure platinum anode, an Ag/Ag2SCU reference electrode, and the pure molten LFCCh electrolyte in a sealed reactor heated by a vertical split tube furnace In the following examples, copper foil, specifically a single crystalline Cu(100) foil or 99.99% purity copper foil, was used as the substrate. This enables uniform crystal orientation and minimizes grain boundaries, facilitating the production of reliable and conclusive data on graphene growth tunability. As shown in FIG. 13 A, the as- received single crystalline Cu(100) foil underwent electrochemical polishing in phosphoric acid to reduce its surface roughness, resulting in a smoother surface for graphene synthesis. FIG. 13B illustrates the decomposition cell voltage of molten Li2CO3 (melting point: 723°C) into solid carbon as a function of temperature, such as -1.25 V at 760 °C and -1.18 V at 1000 °C

T1 with each temperature step being 20°C. The inset in FIG. 13B shows the optical and FESEM images of the graphene-deposited Copper foil surface after MSCO2RR process.

[0091] The various examples performed indicated the various potential window for graphene deposition on the single crystalline Cu(100) cathode. Cyclic voltammetry (CV) curves (e.g. FIG. 15 A) were scanned with no distinct reduction peaks observed after ten cycles of CV scans, but significant carbon depositions were evident on the copper cathode (FIG 13 A), indicating COr' reduction into carbon during the forward CV scan. The oxidation peak, centered around -0.3 V, corresponded to carbon oxidation during the backward CV scan. Moreover, with an increase in the CV scan cycle, both cathodic limit current density and oxidation peak current density rose as well (insets of FIG. 13B), illustrating the irreversible redox reaction. Due to the fast reaction kinetics facilitated by the high thermal and ionic conductivity of the molten salt, critical growth parameters, especially potential and time, required precise fine-tuning to synthesize maximum ~10 nm thick multilayer graphene or even 0.335 nm thick single layers.

[0092] In various examples, the onset potential for graphene growth was demonstrated by applying five different cathodic potentials ranging from -0.5 to -0.9 V (relative to Ag/AgzSCh reference electrode) with a -0.1 V step, or step-wise potentials, while maintaining the electrolysis temperature and time fixed at 760 °C and 90 s, respectively. As the cathodic potential increased from -0.5 to -0.9 V, the overall cell voltage and current density (in terms of the cathode) were enhanced accordingly (FIG. 14A to 14C). At cathodic potentials lower than -0.7 V, the practical cell voltage did not exceed the theoretically calculated cell voltage threshold value of -1.25 V at 760 °C for COi ² ' reduction into carbon, leading to almost no Faradic current (FIG 14A to 14C). As shown in FIG. 14C, when the cathodic potential exceeded -0.7 V, evident black carbon deposition covered the surface of the molten-salt- immersed Cu foil after only 90 s, alongside the frozen salts, signifying the occurrence of COs ² ' reduction reaction. In contrast, without magnification, obvious black carbon deposits were not visible. By integrating thermodynamic calculations with the potential-dependent electrolysis outcomes, an approximate onset cathodic potential of -0.7 V for graphene growth in our system was determined. Accordingly, a cathodic potential of -0.75 V was chosen for subsequent studies of graphene growth mechanism.

[0093] Referring to FIG. 15A to 15F, several examples of MSCChRR-derived graphene on the single crystalline Cu(100) foil in the solution-phase of molten LizCCh are shown. The examples include varying electrolysis time from 6 seconds to 20 minutes, while keeping the cathodic potential and electrolysis temperature fixed at -0.75 V and 760 °C, respectively. Referring to FIG. 15B, within the first 6 seconds of electrolysis, homogeneous catalysis by Cu resulted in the growth of many small, discrete graphene islands on the relatively rough Cu surface. As the electrolysis time increased to 12 s (FIG. 15C), the discrete graphene islands kept growing and agglomerated with each other, displaying less exposed white contrast areas in SEM images (i.e., a less exposed rough Cu surface due to the graphene coverage). The graphene surface exhibited a distinct texture due to the influence of the relatively rough substrate, and it appeared clean without any impurities. At 18 seconds of electrolysis (FIG. 15D), agglomerated graphene islands become a larger continuous graphene domain, covering an area of hundreds of square microns on the Cu foil surface. Subsequently, after 36 seconds, the Cu-catalyzed graphene continued to grow, while on the graphene surface, carbon sphere (CS) particles, with white contrast in SEM images and catalyzed by graphene, started to emerge (FIG. 15E). As the electrolysis time increased to 54 seconds (FIG. 15F), 72 seconds (FIG 16A to 16D), 90 seconds (FIG. 16E to 16H), and 5 minutes (FIG. 17A to 17G), continuous growth of Cu-catalyzed graphene/graphite sheets was observed, along with an increasing number of CSs. Some CSs exhibited chain growth, with one on top of the other (FIG. 16D, 16H and 17F), indicating the formation of a carbon sphere-catalyzed carbon sphere cluster. The simultaneous growth of copper-catalyzed graphene/graphite and carbon- (graphene or carbon sphere) catalyzed carbon sphere demonstrated heterogeneous catalysis. Finally, after 20 minutes (FIG. 18A to 18G), the graphene grew thicker, eventually forming a graphite microsheet with a thickness around ~1 pm (FIG. 18E). Meanwhile, on top of the graphite microsheet, the carbon sphere cluster forest formed, and the number of carbon spheres continued to expand, indicating homogeneous catalysis by carbon.

[0094] TEM measurements confirmed that the carbon spheres were amorphous, without any identified metallic cores but with attached oxygen elements (FIG. 19A to FIG. 191). The oxygen content mainly comprises surface oxygen-containing functional groups resulting from molten Li2CC>3 surface modification and CCh ² ' deoxygenation at the cathode during electrolysis.

[0095] FIG. 20 schematically illustrated the time-dependent growth mechanism and mode of solution-phase MSCChRR-derived graphene, which is of the multilayer type. During the initial short period (FIG. 20G(i)), due to the low carbon solubility of copper, the carbon decomposes from the CCh ² ' precipitated and are deposited onto the copper foil surface. This leads to the growth of graphene islands that may agglomerate to form larger domains, demonstrating homogeneous copper-catalyzed graphene island growth and agglomeration. As the deposition time increases (FIG. 20G(ii)), the graphene is more continuous and thicker, transforming into graphite sheets. Simultaneously, the carbon spheres are gradually deposited either on top of the graphite sheet surface or on the other carbon spheres. This shows the heterogeneous catalysis of simultaneous copper-catalyzed graphite growth and carbon- catalyzed carbon sphere growth As the deposition time is further extended (FIG. 20G(iii)), the graphite sheet surface is fully covered by carbon spheres, carbon sphere-catalyzed carbon sphere growth became dominant, displaying homogeneous carbon-catalyzed carbon sphere growth. It is evident that the solution-phase graphene growth on the Cu foil was surface unself- limited, in contrast to C VD-based surface self-limited gas-phase graphene growth on the copper foils.

[0096] Additionally, when the electrolysis time and temperature were fixed at 18 seconds and 760 °C, respectively, the carbon sphere amount was significantly increased with higher cathodic potentials, going from -0.75 V to -0.85 V and -0.95 V. Therefore, by increasing the electrolysis time and enhancing the cathodic potential both contributed to an increase in graphene thickness and the amount of generated carbon spheres. Consequently, to confine surface unself-limited graphene growth towards graphite nanosheets and avoid carbon sphere impurity deposition, fine-tuning the combination of electrolysis parameters, such as cathodic potential or growth time, may be needed. For example, with a chosen cathodic potential of - 0.75 V, approximately 18 s was identified as the time window for multilayer graphene growth without any CS impurities under 760 °C in molten LiiCOs.

[0097] Temperature also plays a role on the quality of graphene synthesized under the solution phase, as temperature plays a role in altering mass transport and reaction kinetics within the molten salt. FIG. 13B illustrates that an increase in temperature may lower the decomposition cell voltage (i.e., energy barrier) for the CO3 ² '-to-C reduction reaction. Therefore, the reaction kinetics under the same cathodic potential may vary under different elevated temperatures. A temperature-dependent two-electrode galvanostatic electrolysis was performed by applying a current density of 10 mA/cnf for 18 seconds. The Raman spectra of graphene synthesized under 760 °C (FIG. 21 A) displayed D and G peaks with an ID/IG ratio of -0.88 and a broad 2D peak with an BD/IG ratio of -0 27. The relatively higher ID/IG indicated a lower graphitization degree, and an FD/IG ratio lower than 1 suggested multilayer graphene. Therefore, the graphene synthesized under 760 °C was identified as multilayer graphene but with a relatively low graphitization degree. The graphene synthesized under 800 °C showed similar Raman characteristics to that synthesized under 760 °C (FIG. 21B), likely due to the small temperature difference. However, at higher temperatures, such as 900 °C and 1000 °C (FIG. 21C and 21D), the Raman peaks of typical carbon materials became more prominent and sharper, with a relatively decreased ID/IG ratio (FIG. 2 IE) and an increased ED/IG ratio (FIG. 21F). At 1000 °C, a typical temperature for CVD-based graphene synthesis, solution-phase MSCCERR-derived graphene achieved an average ID/IG ratio of -0.65 and an ED/IG ratio of -0.53, indicating multilayer graphene with a relatively good graphitization degree. Therefore, temperature served as an essential growth parameter affecting the quality of solution-phase synthesized graphene, as elevated temperatures can optimize the overall graphene quality.

[0098] To further characterize the properties of MSCCERR-derived graphene, the graphene synthesized under 1000°C with 10 mA/cm ² for 18 seconds was first transferred from the Cu(l 00) metal growth substrate to the desired target substrate, 300 nm SiCE/Si in this case. The widely used polymer-assisted and chemical etching wet transfer method was employed, using polymethyl methacrylate (PMMA) as the transfer media and (NH 4)8268 as the Copper etchant. FIG. 22A schematically illustrated the PMMA-assisted graphene transfer procedure, with additional details available in the experimental section. In FIG. 22B, the optical microscopy image of the PMMA-transferred MSCCERR-derived graphene on the SiCE/Si substrate displayed noticeable polymer residues and defects such as folded wrinkle, crack, and ripple. Polymer residues and defects was common issues faced by the PMMA-transferred graphene. However, the Raman spectra (FIG. 22C) of the graphene, before (on the Cu foil) and after (on the SiCE/Si substrate) the transfer, exhibited good coincidence, indicating a successful transfer. Based on the AFM step test results (FIGs. 22D and 22E), the average thickness of the transferred graphene on the SiOi/Si substrate was estimated to be around 8.97 nm. Thus, the as-synthesized and transferred MSCCERR-derived graphene was of the multilayer type, consisting of approximately 27 layers, which aligned with the obtained ED/IG ratio in the Raman spectra (FIG. 22C). Moreover, the root mean square roughness of the MSCCERR-derived multilayer graphene film in FIG. 22D was approximately -1.98 nm, and may be further improved by using a copper substrate with higher smoothness.

[0099] The surface unself-limited growth mechanism revealed three evolutionary stages of MSCChRR-derived graphene growth: homogeneous copper -catalyzed graphene island growth and agglomeration, heterogeneous copper-catalyzed graphite sheet and carbon-catalyzed CS growth, and homogeneous carbon-catalyzed CS growth. Moreover, higher temperatures were used to enhance the overall graphene quality. The resulting multilayer graphene exhibited an FD/IG ratio of -0.53 and a surface roughness of -1.98 nm, showcasing reasonable graphene quality.

[00100] All examples described herein, whether of apparatus, methods, materials, or products, are presented for the purpose of illustration and to aid understanding, and are not intended to be limiting or exhaustive. Modifications may be made by one of ordinary skill in the art without departing from the scope of the invention as claimed.