WO2024076310A1 - Procédé et appareil de production de graphène - Google Patents

Procédé et appareil de production de graphène Download PDF

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Publication number
WO2024076310A1
WO2024076310A1 PCT/SG2023/095001 SG2023095001W WO2024076310A1 WO 2024076310 A1 WO2024076310 A1 WO 2024076310A1 SG 2023095001 W SG2023095001 W SG 2023095001W WO 2024076310 A1 WO2024076310 A1 WO 2024076310A1
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Prior art keywords
cathode
recited
graphene
group
molten salt
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PCT/SG2023/095001
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English (en)
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Andrew Wong
Fei Yu
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National University Of Singapore
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Publication of WO2024076310A1 publication Critical patent/WO2024076310A1/fr

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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/15—Nano-sized carbon materials
    • C01B32/182—Graphene
    • C01B32/184—Preparation
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B1/00—Electrolytic production of inorganic compounds or non-metals
    • C25B1/01—Products
    • C25B1/135—Carbon
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
    • C25B1/00—Electrolytic production of inorganic compounds or non-metals
    • C25B1/50—Processes

Definitions

  • This application relates to a method of and an apparatus for producing graphene from carbon dioxide.
  • 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.
  • 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.
  • flammable hydrocarbon precursors e.g., CH4
  • 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.
  • 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.
  • 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
  • FIG. 1 is a parametric view of an apparatus for producing graphene according to embodiments of the present disclosure
  • FIG. 2 is a detailed view of FIG. 1 illustrating the electrochemical reactions in the apparatus
  • FIG. 3 is a method for producing graphene according to embodiments of the present disclosure
  • FIG. 4 is a parametric view of an apparatus for producing graphene according to other embodiments of the present disclosure.
  • FIG. 5 A is parametric view of an apparatus for producing graphene according to embodiments of the disclosure.
  • FIG. 5B is a sectional view of a reactor according to embodiments of the disclosure.
  • FIG. 5C is a sectional view of a reference electrode according to embodiments of the disclosure.
  • FIG. 6 is a plot showing a relationship between potential and temperature for various reactions based on thermodynamic calculations
  • FIG. 7 is a chart showing a XRD pattern of the copper foil cathode according to an example
  • FIG. 8 shows cyclic voltammetry (CV) curves of the example of FIG 7;
  • FIG. 9 shows the optical images of the copper cathode with black carbon layer (graphene-like nanosheet) attached thereto after electrolysis
  • FIGs. 10A to 10D are scanning electron microscope characterization images of the graphene-like nanosheet of FIG. 9;
  • FIGs 1 1 A to HE shows transmission electron microscopes (TEM) images and diffraction patterns of the graphene-like nanosheet of FIG. 9;
  • FIGs 12A and 12B shows the XPS survey scan and O Is scans of copper-catalyzed carbon dioxide-derived graphene-like nanosheet, respectively;
  • 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);
  • FIG. 13B shows decomposition cell voltage of molten into solid carbon as a function of temperature
  • FIGs. 14A and 14B illustrates cell voltages and corresponding current densities of chronoamperometry electrolysis as a function of the applied potential.
  • FIG. 14C are optical images of the Cu foil with varying applied potential for the MSCO2RR electrolysis
  • 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;
  • 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;
  • 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;
  • 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;
  • FIGs 17 H to 17J shows corresponding EDS mapping results of FIG. 17G;
  • FIG. 17K is a sum spectrum shown in FIG. 17G, wherein the Cu signal originated from the Cu foil growth substrate;
  • FIG. 17L is an optical image of the copper foil after the MSCO2RR electrolysis for 5 min;
  • 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;
  • FIGs. 18H to 18J shows corresponding EDS mapping results of FIG. 18G;
  • 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;
  • FIG. 18L is an optical image of the Cu foil after the MSCO2RR electrolysis for 20 minutes.
  • 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;
  • FIGs. 19F to 19H shows corresponding EDS mapping results of FIG. 19E;
  • 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;
  • 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;
  • 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,
  • FIG. 21E shows an ID/IG ratio of the graphene obtained in FIG. 21 A to 21D;
  • FIG. 21F shows an ED/IG ratio of the graphene obtained in FIG. 21A to 21D;
  • FIG. 22A is a schematic diagram illustrating the PMMA-assisted graphene transfer procedure
  • FIG. 22B is an optical microscopy image of the PMMA-transferred MSCO2RR- derived graphene on the SiOi/Si substrate
  • FIG. 22C shows Raman spectra of the MSCChRR-derived graphene before (on the Cu foil) and after (on the SiCh/Si substrate) the transfer;
  • FIG. 22D is an AFM image
  • FIG. 22E shows the corresponding step test of the MSCChRR-derived graphene on the SiOi/Si substrate.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • renewable energy/energy sources may be utilized to drive the electrolysis as described above.
  • 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.
  • a carbonaceous source such as carbon dioxide gas
  • 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
  • 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.
  • the molten salt bath 80 may be maintained in the carbonaceous environment 81 at an elevated temperature.
  • 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
  • the cathode 112 is made of copper with at least 99.99% purity.
  • 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.
  • 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.
  • 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.
  • 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.
  • the electrode system 110 may provide a negative potential at the cathode 1 12 for forming graphene 82 at the cathode 1 12.
  • the graphene 82 is a multilayer graphene.
  • 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.
  • 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.
  • the container 140 may be open thus allowing a constant supply of carbonaceous gas from the surrounding atmosphere.
  • the carbonaceous environment may include the carbonaceous gas being directly injected into the molten salt bath 80.
  • the carbonaceous gas may be injected via bubbling into the molten salt bath.
  • the carbonaceous gas may be bubbled into the molten salt bath via a conduit, such as a stainless- steel tube or a corundum tube.
  • 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.
  • 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.
  • the molten salt bath 80 may be held in a container 140 or a crucible.
  • the container 140 may be an alumina crucible, a graphite crucible or a stainless-steel container.
  • the container 140 may include a heater or may be heated such that the molten salt bath 80 is maintained at the elevated temperature.
  • FIG. 2 illustrates the mechanism of carbon dioxide (CO2) capturing and the conversion of carbon dioxide into graphene according to an embodiment.
  • 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).
  • the graphene as produced according to the present disclosure does not require additional chemical reactions to functionalize the graphene.
  • cathodic carbon products i.e., graphene
  • the graphene 82 is functionalized in operando with one or a combination of a surface oxygen-containing functional group.
  • C-O epoxide
  • C-O hydroxyl
  • a method 300 for producing graphene 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.
  • 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 molten salt bath may be maintained at an elevated temperature.
  • 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.
  • 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.
  • 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.
  • 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.
  • the electrode system may include a reference electrode 116.
  • 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.
  • the controller 118 may control the negative potential at the cathode 112 within a range.
  • the negative potential applied on the cathode 112 is a negative potential in relative to the reference electrode over a predetermined duration.
  • 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.
  • 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.
  • 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.
  • 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.
  • the constant potential may be -0.58 V, -0.60 V, -0.62 V or -0.64 V relative to the reference electrode 116.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • one or both of the cathode 212 and the anode 214 may act as a respective reference electrode.
  • 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.
  • 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.
  • the cell potential may be in a range of 0.001V to 100V.
  • the cell potential may be a constant potential, e.g. a fixed 1.0 V.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • CV Cyclic voltammetry
  • 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.
  • 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.
  • the film may be attached to a SiOz/Si substrate at the water surface.
  • 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.
  • 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).
  • CV cyclic voltammetry
  • SP300 potentiostat
  • 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.
  • EDS energy dispersive spectroscopy
  • 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.
  • 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 Ag wire may be filled with Li2CO3-Ag2SO4-filled.
  • An epoxy adhesive glue (Araldite) may be used to seal the open end of the alumina tube.
  • 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.
  • the activated corundum Ag/Ag2SO4 reference electrode may be cooled to room temperature ready for use.
  • 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.
  • 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.
  • 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.
  • carbon dioxide-derived graphene with high yield, purity, selectivity and Faradaic efficiency is achieved.
  • FIGs 6 to 12B illustrates some example methods of producing graphene according to the present disclosure.
  • the crucible was maintained in a carbon dioxide atmosphere (purity 99.995%), and heated to the fixed electrolysis temperature of 800 °C.
  • FIG. 9 shows the optical images of the copper cathode which includes black carbon layer attached onto it after electrolysis.
  • 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.
  • FIGs. 12A-B shows the XPS survey scan and O Is scans of copper- catalyzed carbon dioxide-derived graphene, respectively.
  • C-0 i.e., epoxide and hydroxyls functional group
  • 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.
  • 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
  • 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.
  • FIG. 13 A 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.
  • 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.
  • 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).
  • 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.
  • 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.
  • 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.
  • FIG. 20 schematically illustrated the time-dependent growth mechanism and mode of solution-phase MSCChRR-derived graphene, which is of the multilayer type.
  • 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.
  • the graphene is more continuous and thicker, transforming into graphite sheets.
  • the carbon spheres are gradually deposited either on top of the graphite sheet surface or on the other carbon spheres.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • the average thickness of the transferred graphene on the SiOi/Si substrate was estimated to be around 8.97 nm.
  • 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).
  • 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.
  • 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, s featuring reasonable graphene quality.

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Abstract

L'invention divulgue un procédé et un appareil de production de graphène. Le procédé comprend le maintien d'un bain de sel fondu dans un environnement carboné ; l'immersion d'une cathode constituée de cuivre, d'une anode et d'une électrode de référence d'un système d'électrode dans le bain de sel fondu ; et l'application d'un potentiel négatif au niveau de la cathode pour former du graphène au niveau de la cathode. L'appareil de production de graphène comprend une structure cellulaire comprenant un bain de sel fondu maintenu dans un environnement carboné ; et un système d'électrode ayant une cathode constituée de cuivre, une anode et une électrode de référence immergées dans le bain de sel fondu, le système d'électrode étant configuré pour fournir un potentiel négatif au niveau de la cathode pour former du graphène au niveau de la cathode.
PCT/SG2023/095001 2022-10-05 2023-09-29 Procédé et appareil de production de graphène WO2024076310A1 (fr)

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Citations (3)

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US20160115601A1 (en) * 2013-05-30 2016-04-28 The University Of Manchester Electrochemical process for production of graphene
CN105624722A (zh) * 2016-01-05 2016-06-01 北京金吕能源科技有限公司 一种电解二氧化碳制备石墨烯或碳纳米管的方法
US20200378014A1 (en) * 2019-05-28 2020-12-03 C2Cnt Llc Process for the facile electrosynthesis of graphene from co2

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US20160115601A1 (en) * 2013-05-30 2016-04-28 The University Of Manchester Electrochemical process for production of graphene
CN105624722A (zh) * 2016-01-05 2016-06-01 北京金吕能源科技有限公司 一种电解二氧化碳制备石墨烯或碳纳米管的方法
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