WO2023161695A1

WO2023161695A1 - Electrochemical process for producing a nanocrystalline carbon with 1d, 2d, or 3d structure and/or a nanocrystalline diamond and/or an amorphous carbon and/or a metal-carbon nanomaterial composite and/or a mixture thereof

Info

Publication number: WO2023161695A1
Application number: PCT/IB2022/057992
Authority: WO
Inventors: Rungkiat NGANGLUMPOON
Original assignee: Crystallyte Co Ltd
Current assignee: Crystallyte Co Ltd
Priority date: 2022-02-25
Filing date: 2022-08-26
Publication date: 2023-08-31
Anticipated expiration: 2024-08-25

Abstract

A new process for producing a nanocrystalline carbon with a 1D, 2D, or 3D structure and/or a nanocrystalline diamond and/or an amorphous carbon and/or a metal-carbon nanomaterial composite, said composite containing a post-transition metal or a transition metal, and/or a mixture thereof, by electrochemically reducing a carbon source which is a carbonate salt or a bicarbonate salt under ambient temperature and pressure at an onset potential not greater than 10 Volt in presence of an electrolyte and at least one electrode, said electrode comprising a metallic material comprising one or more of the following: a post-transition element, a transition element, an oxide, and an alloy thereof. The ambient temperature and pressure and the onset potential enabled by embodiments simplify the production, and the nanocrystalline carbon yield can be scaled up to reach a mass production scale. A product obtained from the new process comprises a nanocrystalline carbon with a 1D, 2D, or 3D structure and/or a nanocrystalline diamond and/or an amorphous carbon and/or a metal-carbon nanomaterial composite, said composite containing a post-transition metal or a transition metal. Such product can be a mixture that contains various carbon structures, comprising: a nanocrystalline diamond, an amorphous carbon, a graphitic carbon, and a metal-carbon nanomaterial composite, said composite containing a post-transition metal or a transition metal. Said product may further comprise a graphite or a graphene.

Description

ELECTROCHEMICAL PROCESS FOR PRODUCING A NANOCRYSTALLINE CARBON WITH 1 D, 2D, OR 3D STRUCTURE AND/OR A NANOCRYSTALLINE DIAMOND AND/OR AN AMORPHOUS CARBON AND/OR A METAL-CARBON NANOMATERIAL COMPOSITE AND/OR A MIXTURE THEREOF

The present disclosure claims priority to the earlier International Application No. PCT/IB2022/051665, filed February 25, 2022, the entire disclosure of which is incorporated into

5 the present disclosure by way of reference.

FIELD OF INVENTION

The present disclosure relates to the production of a carbon nanomaterial, including a nanocrystalline carbon with a ID, 2D, or 3D structure and/or a nanocrystalline diamond and/or

10 an amorphous carbon and/or a metal-carbon nanomaterial composite, said composite containing a post-transition metal or transition metal, and/or a mixture thereof, particularly when said production of carbon nanomaterials involves electrochemical reduction.

BACKGROUND OF THE INVENTION

Carbon nanomaterials, including a nanocrystalline carbon with a ID, 2D, or 3D structure

15 and/or a nanocrystalline diamond and/or an amorphous carbon and/or a metal-carbon nanomaterial composite, said composite containing a post-transition metal or transition metal, and/or a mixture thereof, have demonstrated many useful properties, such as their excellent thermal and electrical conductivities. Thus, they find their applications in various technological/industrial fields such as medical, electronics and energy storage. Because carbon

20 nanomaterials do not naturally occur in sufficient quantity, effective means of artificial synthesis is necessary to satisfy the rising demand.

The naturally abundant carbonate and bicarbonate salts are the main carbon sources for the natural formation of crystalline solid carbon allotropes, such as graphite and diamond. For this reason, carbonate and bicarbonate salts have been gaining attention in the relevant arts as

25 promising carbon sources for the artificial production of several carbon allotropes and carbon nanomaterials. For example, the US patent publication No.US4254091A discloses a process for the synthesis of diamonds by heating the carbonate and oxalate salts of iron, manganese, calcium, and magnesium at temperatures between 550 and 1600 °C, while maintaining a pressure in the range of 29 to 45 kilobars. Nevertheless, the process requires extremely high energy and is not applicable for the production of carbon nanomaterials.

Next, the US patent publication No. US 2014/0202874 Al discloses a method for producing graphite and various carbon nanomaterials such as graphene, fullerenes, and carbon nanotubes by the electrolysis of carbon dioxide and/or carbonate ion. This process takes place mainly in an electroplating chamber containing molten inorganic carbonate as electrolyte, thereby requiring very high energy in order to melt the electrolyte.

Further, the European patent publication No. EP 2737937 Al discloses a process carried out under ambient temperature and pressure to electrochemically reduce CO2 captured in the form of bicarbonate or carbonate salts in carbon-capturing solvents, such as chilled ammonia and strong basic solution, in order to produce a hydrocarbon or organic acid.

None of the abovementioned prior art involving the use of carbonate/bicarbonate salts has effectively solved a technical problem of producing a carbon nanomaterial by a significantly less energy-intensive process.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a new process for industrially producing a carbon nanomaterial. The inventor has found that embodiments according to the concept of the present invention enable the production of such products at a significantly less energy-intensive condition, as well as satisfactory yield and reaction time.

In the first, second and third aspects, the present invention provides a new process for producing a nanocrystalline carbon with a ID, 2D, or 3D structure and/or a nanocrystalline diamond and/or an amorphous carbon and/or a metal-carbon nanomaterial composite, said composite containing a post-transition metal or a transition metal, and/or a mixture thereof. The embodiments’ characterizing features, involving electrochemical reduction of a carbonate salt or a bicarbonate salt in presence of an electrolyte, allow said process to be carried out under ambient temperature and pressure and at an onset potential not greater than 10 Volt. Said conditions, which simplify the production, are effects that distinguishes a process in accordance with the present invention from the currently available ones. The metal-carbon nanomaterial composite product yield per a single run of an embodiment, which depends on the type of metal electrode and reaction time of a batch, is approximately 10 - 100 mg cm^ h"¹. Such yield is conducive to the scale-up to a mass production scale.

An embodiment in accordance with the first aspect is a process for producing a nanocrystalline carbon with a ID, 2D, or 3D structure and/or a nanocrystalline diamond and/or an amorphous carbon and/or a metal-carbon nanomaterial composite, said composite containing a post-transition metal or a transition metal, and/or a mixture thereof. Said process is carried out by electrochemically reducing a carbon source which is a carbonate salt or a bicarbonate salt. The electrochemical reduction takes place under ambient temperature and pressure at an onset potential not greater than 10 Volt in presence of an electrolyte and at least one electrode. Said electrode comprises a metallic material comprising one or more of the following: a posttransition element, a transition element, an oxide, and an alloy thereof.

An embodiment in accordance with the second aspect is a process for producing a nanocrystalline carbon with a ID, 2D, or 3D structure and/or a nanocrystalline diamond and/or an amorphous carbon and/or a metal-carbon nanomaterial composite, said composite containing a post-transition metal or a transition metal, and/or a mixture thereof. Said process comprises steps of: (a) depositing a metallic material in the particulate form on a substrate to form a cathode; and (b) electrochemically reducing a carbonate salt or a bicarbonate salt in presence of: an electrolyte that is separated into an anolyte and a catholyte, an anode submerged in said anolyte, and said cathode submerged in said catholyte. Said catholyte comprises a mixture of (a) l-butyl-3-methylimidazolium tetrafluoroborate ([bmim] [BF4]), ammonium sulfate ((NFL^SCh), or choline chloride, (b) water, and (c) the carbonate salt or the bicarbonate salt. Said electrochemically reducing the carbonate salt or the bicarbonate salt occurs under ambient temperature and pressure at an onset potential not greater than 10 Volt.

An embodiment in accordance with the third aspect is a process for producing a nanocrystalline carbon with a ID, 2D, or 3D structure and/or a nanocrystalline diamond and/or an amorphous carbon and/or a metal-carbon nanomaterial composite, said composite containing a post-transition metal or a transition metal, and/or a mixture thereof. Said process comprises steps of: (a) depositing a metallic material in the particulate form on a substrate to form a cathode; and (b) electrochemically reducing a carbonate salt or a bicarbonate salt in presence of: an electrolyte, an anode and said cathode which are submerged in said electrolyte. Said electrolyte comprises a mixture of (a) l-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]), ammonium sulfate ((NFL^SCh), or choline chloride, (b) water, and (c) the carbonate salt or the bicarbonate salt. Said electrochemically reducing the carbonate salt or the bicarbonate salt occurs under ambient temperature and pressure at an onset potential not greater than 10 Volt.

In an embodiment, the carbonate salt or the bicarbonate salt is dissolved in the electrolyte . In such case, it is preferable that the carbonate salt or the bicarbonate salt is dissolved at a concentration within the range of 0. 1 to 10 M.

Thus, it is preferable that the carbonate salt or the bicarbonate salt is water-soluble.

Preferred carbonate salts include: sodium carbonate (Na2CO3),

Preferred bicarbonate salts include: potassium bicarbonate (KHCO3), and ammonium bicarbonate (NH4HCO3).

In an embodiment, the carbonate salt is prepared by saturating a strong basic aqueous solution with CO2. In such embodiment, it is preferred that the strong basic aqueous solution contains sodium hydroxide (NaOH) or potassium hydroxide (KOH). Also in such embodiment, it is preferred that the concentration of the strong basic aqueous solution is within the range of 1 - 10 M.

In an embodiment, the bicarbonate salt is prepared by saturating an ammonia aqueous solution with CO2. In such embodiment, it is preferred that the concentration of the ammonia aqueous solution is within the range of 1 - 10 M.

In another embodiment, the bicarbonate salt is prepared by saturating a tertiary amine aqueous solution with CO2. In such embodiment, it is preferred that the tertiary amine aqueous solution contains dimethylethanolamine (DMAE). Also in such embodiment, it is preferred that the concentration of the tertiary amine aqueous solution is within the range of 1 - 10 M.

Preferably, the metallic material comprises one or more of the post-transition element and the transition element. Preferably, the post-transition element is bismuth (Bi) and the transition element is silver (Ag). In an embodiment where the metallic material is deposited on a substrate, said substrate is preferably a tin (Sn) or copper (Cu) foil.

Among possible combinations of metallic materials and substrates, the present inventors found that markedly greater yields are enabled by either the combination of bismuth (Bi) deposited upon a tin (Sn) foil, or silver (Ag) deposited upon a copper (Cu) foil.

Preferably, the electrodeposition method is used to deposit particulate metal upon a substrate.

Preferably, the substrate deposited with the metallic material is exposed to the ambient air with the time in a range of 30 minutes to 24 hours for the post-treatment of the electrode.

Preferably, the anolyte and catholyte are the same electrolyte. Preferably, the catholyte is a mixture containing (a) an ionic salt, (b) the carbonate salt or the bicarbonate salt, and (c) water.

Preferably, said ionic salt comprises a cation selected from ammonium cation, imidazolium cation, and a mixture thereof. Preferably, the concentration of said ionic salt in the electrolyte is within a range of 0.1 - 10 M. Preferably, said ammonium cation is ammonium cation (NH4⁺) or choline cation. Preferably, said imidazolium cation is l-butyl-3- methylimidazolium ([bmim]).

Preferably, the anion of said ionic salt is selected from the group comprising tetrafluoroborate (BF-f), hexafluorophosphate (PFr, )- halides (CP, Br", F", I"), hexafluoroantimonate (SbFr,-)- sulfate (SO4² )- and nitrate (NOyf

Optionally, the electrolyte is separated into an anolyte and a catholyte. Even more preferably, the electrolyte is separated by a membrane. Preferably, the anolyte is an aqueous solution. Said aqueous solution comprises potassium bicarbonate (KHCO3) and water.

Accordingly, the present disclosure provides examples to illustrate the conditions of such processes and the characteristic properties of such products. The preferred embodiments will be described in detail later on.

BRIEF DESCRIPTION OF DRAWINGS

Fig 1 shows a schematic diagram of an electrochemical cell for electrochemically reducing a carbonate salt or a bicarbonate salt in accordance with a preferred embodiment (not to scale).

Fig 2 shows a schematic diagram of an electrochemical cell for electrochemically reducing a carbonate salt or a bicarbonate salt in accordance with an alternative embodiment (not to scale).

Fig 3 A shows a Raman spectrum exhibiting merged peaks of a product of Example 1.

Fig. 3B shows a matching of lattice spacing, as obtained from Selected Area Electron Diffraction (SAED), of the product of Example 1.

Fig 3C shows a first Transmission Electron Microscopy (TEM) image of the product of Example 1.

Fig 3D shows a second Transmission Electron Microscopy (TEM) image of the product of Example 1.

Fig 3E shows Energy Dispersive X-ray (EDX) peaks of the product of Example 1.

Fig 4 shows a Raman spectrum exhibiting merged peaks of a product of Example 2. Fig 5 shows a Raman spectrum exhibiting merged peaks of a product of Example 3.

Fig 6 shows a Raman spectrum exhibiting merged peaks of a product of Example 4.

Fig 7A shows a Raman spectrum exhibiting merged peaks of a product of Example 5.

Fig 7B shows a matching of lattice spacing, as obtained from Selected Area Electron Diffraction (SAED), of the product of Example 5.

Fig 7C shows a first Transmission Electron Microscopy (TEM) image of the product of Example 5.

Fig 7D shows a second Transmission Electron Microscopy (TEM) image of the product of Example 5.

Fig 7E shows Energy Dispersive X-ray (EDX) peaks of the product of Example 5.

Fig 8 shows a Raman spectrum exhibiting merged peaks of a product of Example 6.

Fig 9 shows a Raman spectrum exhibiting merged peaks of a product of Example 7.

Fig 10 shows a Raman spectrum exhibiting merged peaks of a product of Example 8.

Fig 11 shows a Raman spectrum exhibiting merged peaks of a product of Example 9.

Fig 12 shows a Raman spectrum exhibiting merged peaks of a product of Example 10.

Fig 13 A shows a Raman spectrum exhibiting merged peaks of a product of Example 11.

Fig 13B shows a matching of lattice spacing, as obtained from Selected Area Electron Diffraction (SAED), of the product of Example 11.

Fig 13C shows a first Transmission Electron Microscopy (TEM) image of the product of Example 11.

Fig 13D shows a second Transmission Electron Microscopy (TEM) image of the product of Example 11.

Fig 13E shows Energy Dispersive X-ray (EDX) peaks of the product of Example 11.

Fig 14 shows a Raman spectrum exhibiting merged peaks of a product of Example 12.

Fig 15 shows a Raman spectrum exhibiting merged peaks of a product of Example 13.

Fig 16A shows a Raman spectrum exhibiting merged peaks of a product of Example 14.

Fig 16B shows a matching of lattice spacing, as obtained from Selected Area Electron Diffraction (SAED), of the product of Example 14.

Fig 16C shows a first Transmission Electron Microscopy (TEM) image of the product of Example 14.

Fig 16D shows a second Transmission Electron Microscopy (TEM) image of the product of Example 14.

Fig 16E shows Energy Dispersive X-ray (EDX) peaks of the product of Example 14. DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

It is to be understood that the following detailed description will be directed to embodiments, provided as examples for illustrating the concept of the present invention only. The present invention is in fact not limited to particular embodiments described, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of this invention will be limited only by the appended claims.

The detailed description of the invention is divided into various sections only for the reader’s convenience and disclosure found in any section may be combined with that in another section.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

It must be noted that as used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise.

The term “about” when used before a numerical designation, e.g., dimensions, time, amount, and such other, including a range, indicates approximations which may vary by ( + ) or ( - ) 10 %, 5 % or 1 %, or any sub-range or sub-value there between.

“Comprising” or “comprises” is intended to mean that the compositions and processes include the recited elements, but not excluding others. “Consisting essentially of’ when used to define compositions and methods, shall mean excluding other elements of any essential significance to the combination for the stated purpose. Thus, a process or product consisting essentially of the elements as defined herein would not exclude other materials or steps that do not materially affect the basic and novel characteristic(s) of the claimed invention. “Consisting of’ shall mean excluding more than trace elements of other ingredients and substantial steps. Embodiments defined by each of these transition terms are within the scope of this invention.

Electrochemical cell

Fig 1 shows a schematic diagram of an electrochemical cell in which a process for producing a carbon nanomaterial is conducted in accordance with a preferred embodiment, which does not feature a membrane (200). In this preferred embodiment, the receptacle (100) contains an electrolyte (110) that is a mixture containing a carbonate salt or a bicarbonate salt. Further, this preferred electrochemical cell (10) is a 3-electrode system wherein an anode (320), a cathode (420), and a reference electrode (430) are immersed in, and thus in a direct contact with, the same electrolyte (110). The receptacle (100) further comprises two vents (350, 450) to provide outlets of gas byproducts. Preferably, the vents (350, 450) are located at the upper part or top of the receptacles (100) and nearby the anode (320) and cathode (420). The electrodes (320, 420, 430) are electrically connected to a power supply (500), which according to the preferred embodiment is a source of direct current electricity.

Fig 2 shows a schematic diagram of an electrochemical cell in which a process for producing a carbon nanomaterial is conducted in accordance with an alternative embodiment. This alternative electrochemical cell (10) comprises a receptacle (100) and a membrane (200) which separates the receptacle (100) into an anode region (300) and a cathode region (400). The receptacle (100) receives and contains an electrolyte which is in turn separated by the membrane (200) into an anolyte (310) and a catholyte (410), contained in the anode region (300) and the cathode region (400), respectively. This arrangement allows options whereby the anolyte (310) and the catholyte (410) may be the same or different substances. Further, this alternative electrochemical cell (10) is a 3-electrode system wherein electrodes (320, 420, 430) are immersed in, and thus in a direct contact with, the electrolyte (310, 410). In the anode region (300), the electrode is an anode (320). The anode region (300) further comprises a vent (350) to provide a passage of oxygen out from the anode region (300). Preferably, the vent (350) is located at the upper part or top of the anode region (300). In the cathode region (400), the electrodes comprise a cathode (420) and a reference electrode (430). The cathode region (400) further comprises a vent (450) to provide a passage of gas byproducts out from the cathode region (400). Preferably, the vent (450) is located at the upper part or top of the cathode region (400). The electrodes (320, 420, 430) are electrically connected to a power supply (500), which according to an alternative embodiment is a source of direct current electricity.

Carbonate and Bicarbonate salts

In the present invention, the carbon source comprises a carbonate salt or a bicarbonate salt. Preferably, a water-soluble carbonate/bicarbonate salt is used. Examples of preferred carbonate salts include: Na2CO Examples of preferred bicarbonate salts include: KHCO3 and NH4HCO3. The carbonate salt is prepared preferably by saturating a strong basic aqueous solution with CO2. The bicarbonate salt is prepared preferably by saturating an ammonia aqueous solution or a tertiary amine aqueous solution with CO2. In addition, the carbonate salt or the bicarbonate salt may be supplied to the electrolyte in any desired form, for example, in solid, liquid, gaseous, or solvated form, depending on the phase stability at the operating temperature and pressure. Preferably, the carbonate salt or the bicarbonate salt is dissolved in the electrolyte (i.e. supplied in the solvated form).

Pressure

A process according to the concept of the present invention may be carried out in various conditions which may be adjusted according to the circumstantial requirements. The applicable pressure is within a range of about 1 to about 20 atm.

The pressure in accordance with the preferred embodiment is an ambient pressure. The ambient pressure refers to a common or usual condition surrounding any person in a room. An ambient pressure for operating the process is preferably 1 atm. Because a process in accordance with the preferred embodiment allows the electrochemical reduction to occur effectively at such ambient pressure, it obviates the need to pressurize, depressurize, vacuumize or control the pressure at any part of the electrochemical cell (10) and thus substantially simplifies the production.

Temperature

A process according to the concept of the present invention may be carried out in various conditions which may be adjusted according to the circumstantial requirements. The applicable temperature is within a range of about 10 °C to about 60 °C.

The temperature in accordance with the preferred embodiment is an ambient temperature . The ambient temperature refers to a common or usual condition surrounding any person in a room. Preferably, the ambient temperature is within a range of about 15 °C to about 50 °C. More preferably, the ambient temperature is about 30 °C. Because a process in accordance with the preferred embodiment allows the electrochemical reduction to occur effectively at such ambient temperature, it obviates the need to heat, cool or control the temperature at any part of the electrochemical cell (10) and thus substantially simplifies the production.

Onset potential

Generally, the onset potential of the electrochemical cell (10) is at least of the electric potential sufficient to initiate the electrochemical reduction of the carbonate salt or the bicarbonate salt. Preferably, the onset potential across the electrodes (320, 420, 430) is substantially constant during the electrochemical reduction.

The onset potential of the electrochemical cell (10) depends on the electrode being selected. In an embodiment, the electrochemical cell (10) comprises a power supply (500) to provide the onset potential, which is preferably within a range of about 0. 1 to about 10 V, more preferably within a range of about 0.7 to about 3 V, and even more preferably at about 1.6 V. Preferably, the power supply (500) is adapted to monitor the onset potential. Even more preferably, the power supply (500) is adapted to regulate the onset potential to accord with a preset value. In the following Examples, the power supply (500) is a potentiostat which is capable of both monitoring and regulating the onset potential. A potentiostat’s equivalent devices for an industrial scale production include a rectifier which is as well applicable to the concept of the present invention.

Electrolyte

According to the concept of the present invention, an electrolyte, which may be separated into an anolyte (310) and a catholyte (410), is an ion-containing fluid. Preferably, the anolyte (310) is an aqueous electrolyte and the catholyte (410) is a mixture containing a carbonate salt or a bicarbonate salt, an ionic salt, and water. Preferably, the anolyte (310) and the catholyte (410) are the same electrolyte, which is the mixture of (a) an ionic salt, (b) a carbonate salt or a bicarbonate salt, and (c) water.

According to the concept of the present invention, all known ionic salts may be part of the mixture that forms the electrolyte. Preferably, the ionic salts in an embodiment are compounds represented by Formula (I):

[A]n⁺ [Y]n- - (I) wherein: n is 1 or 2;

[Y]_n‘ is selected from the group comprising tetrafluoroborate ([BF?"), hexafluorophosphate ([ PFr, ]’), halides (C1‘, Br, F", I"), hexafluoroantimonate ([ SbFr, ]’), sulfate ([SO ’]), and nitrate ([NOa]");

[A]⁺ is selected from —

(a) the group comprising ammonium cations represented by Formula (II):

R¹, R², R³, and R⁴ being selected from hydrogen atom, Cl-C6-alkyl, Cl-C6-alkoxy, Cl- C6-aminoalkyl, Cl-C6-hydroxylalkyl, C5-C12-aryl, and C5-C12-aryl-Cl-C6-alkyl groups; and

(b) the group comprising imidazolium cations represented by Formula (III):

R, R¹, and R² being selected from Cl-C6-alkyl, Cl-C6-alkoxy, Cl-C6-aminoalkyl, C5- C12-aryl, and C5-C12-aryl-Cl-C6-alkyl groups.

The preferred combination of (a) the ionic salt, (b) the carbonate salt or the bicarbonate salt, and (c) water, is as follows: the (a) ionic salt being a mixture of l-butyl-3- methylimidazolium tetrafluoroborate ([bmim][BF4]), ammonium sulfate ((NFL^SCh) or chlorine chloride, (b) the carbonate salt or the bicarbonate salt, and (c) water.

In some embodiments, the ionic salt also functions as a stabilizer of nanoparticle s/carbon nanomaterial formed at the at least one electrode during the electrochemical reduction of the carbonate salt or the bicarbonate salt in the electrochemical cell (10). Preferably, the ionic salt is selected from ([bmim][BF4]), (NEL^SCh, and choline chloride.

According to the concept of the present invention, the anolyte may also be an aqueous solution. Preferably, the anolyte that is an aqueous solution comprises a salt as a solute and water as a solvent. According to an embodiment, the preferred aqueous solution contains a cation comprising Na⁺, K⁺, or Cs⁺ and an anion comprising HCCF". SC>4²", or Cl".

In some embodiments, the anolyte is an aqueous solution of potassium bicarbonate (KHCO3).

Membrane

In some embodiments, a membrane (200) is present to separate the receptacle (100) into an anode region (300) and a cathode region (400), and thus the electrolyte into the anolyte (310) and the catholyte (410), in order to prevent oxidation of the carbon nanomaterial in the electrolyte (310, 410). The membrane (200) further prevents the gaseous anodic products, such as oxygen, from mixing with the gaseous cathodic products, such as hydrogen, thereby enhancing the transportation of protons (H⁺) from the anode region (300) to the cathode region (400). Preferably, the membrane (200) arranged thus causes the contents of the two regions (300, 400) to have different pH conditions.

In one embodiment, the membrane (200) comprises a polymer fdm. Preferably, the membrane (200) is a proton-conductive membrane made of a polymer film which allows the transportation of protons only. Preferred examples of such proton-conductive membrane include those commercially available under the tradename ofNAFION™, specifically NAFION™ 961, NAFION™ 430, or NAFION™ 117.

Electrode

According to an embodiment, an electrode in the electrochemical cell (10) is categorized into a cathode (420), and/or an anode (320). The cathode (420) is an electrode having more negative potential than the other electrode, while the anode (320) is an electrode having less negative potential than the other electrode.

Preferably, at least one electrode is formed of the metallic material in the particulate form deposited upon a substrate, or formed of the metallic material in the form of metallic foil without further deposition of particulate metal. Preferably, said electrode, being formed of the metallic material in either of the foregoing forms, is the cathode (420).

The metallic material in the particulate form can be deposited upon the substrate by means of any deposition method such as electrodeposition, chemical vapor deposition, and thin- fdm deposition, carried out in an ambient condition. Preferably, the metallic material in the particulate form is deposited upon the substrate by means of electrodeposition carried out under ambient conditions. Preferably, the solution used in the electrodeposition contains the metallic material intended to be deposited upon the substrate, which may be in any form or derivatives including ions and radicals.

The metallic material being deposited upon the substrate according to an embodiment is selected from one or more of the following: a post-transition element, a transition element, an oxide, and an alloy thereof. Preferably, the metallic material being deposited upon the substrate is selected from one or more of the following: a post-transition element, and a transition element. More preferably, the post-transition element is bismuth (Bi); and the transition element is silver (Ag).

The substrate upon which the metallic material in the particulate form is deposited can also be a metal sheet such as a metal foil, including a copper (Cu) foil, tin (Sn) foil, titanium (Ti) foil, or a non-metal sheet such as glass sheet, or a rigid body of aluminum (Al), silicon (Si), carbon (C), etc. Preferably, the substrate is a metal foil. More preferably, the substrate is a copper (Cu) foil, tin (Sn) foil, bismuth (Bi) foil, aluminum (Al) foil, or titanium (Ti) foil.

As a post-treatment step, the electrode is then exposed to the ambient air or oxygencontaining atmosphere at the room temperature in order to create a thin oxide layer before the start of electrochemical reduction. This post-treatment step is carried out for 30 minutes - 24 hours.

In some embodiments, at least one electrode is essentially free of a carbon-based material before the carbonate salt or the bicarbonate salt is reduced electrochemically. Preferably, said electrode is the cathode (420).

In some embodiments, the substrate is configured to have a certain size, and/or shape in order to provide a greater specific surface area, upon which more metallic material in the particulate form may be deposited.

Preferably, the anode (320) is a platinum foil, platinum mesh, platinum rod, or graphite rod. More preferably, the anode (320) is a platinum foil or platinum mesh.

In some embodiments, the electrochemical cell further comprises a reference electrode (430) to provide a 3-electrode cell system. Preferably, the reference electrode (430) is an Ag/AgCl electrode.

Reaction time

According to an embodiment, the electrochemical reduction occurs in the electrochemical cell (10) as a batch operation. The crystal structure and crystal size of the resulting product depends on the nature of electrode used, the energy supplied, and the reaction time, among others. Prolonging the reaction time results in a larger crystallite size being formed. According to the embodiments, the crystallite size is measured by Raman peaks.

According to the embodiments, the reaction time for each batch of production can be ranged from about 5 minutes to 140 minutes. Preferably, the reaction time for each batch of production is about 30 minutes to 120 minutes.

Nanocrystalline carbon with a ID, 2D, or 3D structure and/or a nanocrystalline diamond and/or an amorphous carbon and/or a metal-carbon nanomaterial composite, said composite containing a post-transition metal or a transition metal, and/or a mixture thereof

In an embodiment, the process for producing a nanocrystalline carbon with a ID, 2D, or 3D structure and/or a nanocrystalline diamond and/or an amorphous carbon and/or a metal- carbon nanomaterial composite, said composite containing a post-transition metal or a transition metal, and/or mixture thereof in the electrochemical cell (10) is preferably carried out as a batch operation.

The nanocrystalline carbon with the ID, 2D, or 3D structure and/or the nanocrystalline diamond and/or the amorphous carbon and/or the metal-carbon nanomaterial composite, said composite containing a post-transition metal or transition metal, and/or the mixture thereof is formed at at least one electrode. Preferably, said product is formed at the cathode (420).

The carbon product obtained from a process in accordance with a preferred embodiment comprises a graphite and/or a graphene and/or a graphitic carbon having an average crystallite domain size of about 1-100 nm and/or the nanocrystalline diamond and/or the amorphous carbon, and/or the metal-carbon nanomaterial composite, said composite containing the posttransition metal or the transition metal, and/or the mixture thereof.

In some embodiments, the carbon product being produced is further separated from the electrode (320, 420) by a known separation process. Preferably, said separation process is a mechanical removal process, such as mechanical abrasion, or ultrasonication.

After being separated from the electrode (320, 420), the carbon product may contain residue of the metallic material originally deposited upon the electrode (320, 420). The metallic material can be further removed from the carbon product by means of a conventional chemical removal process, preferably acid leaching. Preferably, said acid leaching involves the use of nitric acid (HNO3), hydrochloric acid (HC1), or a mixture thereof.

In some embodiments, the separation process of the carbon product from the electrode (320, 420) comprises the following steps:

(1) mechanically removing the solid product from the electrode (320, 420)

(2) placing the solid product that was removed by step (1) in a microcentrifuge tube

(3) slowly dropping a mixture of nitric acid and hydrochloric acid into the microcentrifuge tube to perform acid leaching. Preferably, the mixture of nitric acid and hydrochloric acid is in a molar ratio of 1:3 in 0.3 ml of the solution

(4) shaking the solution before ultrasonicating the solution for approximately 5 minutes

(5) centrifuging the solution to separate the solid product from the solution

(6) collecting the solid product and neutralizing the solid product with deionized water (DI water). Preferably, the neutralization is conducted three times.

The abovementioned process results in a nanocrystalline carbon with a ID, 2D, or 3D structure and/or a nanocrystalline diamond and/or an amorphous carbon product and/or a metal- carbon nanomaterial composite, said composite containing a post-transition metal or a transition metal, and/or a mixture thereof, which is a mixture having various carbon structures. Said structures are inclusive of, and selectable from: an amorphous carbon, a graphite, a graphene, a nanocrystalline diamond, and a metal-carbon nanomaterial composite, said composite containing a post-transition metal or a transition metal.

Examples of embodiments

Fourteen Examples were carried out for the preferred and alternative embodiments. In all of the Examples, the following paragraphs apply:

Electrochemical reductions took place in a three -electrode cell system at a pressure of about 1 atm. and at a temperature of about 30 ± 5 °C. If a membrane (200) was used for separating the electrolyte (110) into the anolyte (310) and the catholyte (410), said membrane was NAFION™ 117; and if a reference electrode (430) was used, said reference electrode was Ag/AgCl with a 3.5 mol/L potassium chloride (KC1) solution. The carbon sources were dissolved in the electrolyte (110) or the catholyte (410), as the case may be. The electrochemical reduction’s onset potentials were measured by a potentiostat. After the reaction time, the carbon nanomaterial product was formed at the cathode (420), which was then removed from the electrolyte (110) or the catholyte (410), as the cases may be, and dried.

Moreover, where a metal element in the particulate form was deposited upon a metal foil substrate, the deposition was carried out by way of electrodeposition at ambient conditions, wherein a solution of nitrate salt at a concentration of 0.001-1 M was used as a precursor. The voltage applied for said electrodeposition was about -0. 1 to -10 V. More particularly, where the metal element in the particulate form was silver (Ag), the deposition time was about 2-2,000 seconds; where the metal element in the particulate form was bismuth (Bi), the deposition time was about 60-3,600 seconds. After the said deposition time, the electrode, i.e. the substrate upon which the intended particulate metal element had been deposited, was left in the ambient air for 30-720 minutes as a post-treatment step before being used in the electrochemical reduction.

Further, where a strong basic aqueous solution, an ammonia aqueous solution, or a tertiary amine aqueous solution, was saturated with carbon dioxide gas (CO2), such saturation was carried out in order to prepare a carbonate salt or a bicarbonate salt. In such case, CO2 was purged through those solutions at ambient conditions. The flow rate of CO2 per volume of the solution was within a range of 0.04 - 40 cm³ CCh/cm³ solution per minute, and the purging time was within a duration of 1-1,000 minutes.

Table 1 in the next sheet shows the particulars of Examples 1-14. Description of the product obtained from each Example shall follow Table 1.

Example 1 produced a metal-carbon composite product in the form of metallic Ag/Ag oxides and nanocrystalline carbon with a ID, 2D, and 3D structure. Fig. 3A shows the Raman spectrum of the product of Example 1. Moreover, the Selected Area Electron Diffraction (SAED) analysis revealed the lattice spacing of said product as 0.239, 0.206, 0.182, 0.147 and 0.124 nanometer (nm), which, as shown in Fig. 3B, matched the lattice spacing references of i-Carbon, n-diamond, and cubic silver. Next, images from the Transmission Electron Microscopy (TEM) are shown in Figs. 3C and 3D. Finally, the peaks from Energy Dispersive X-ray (EDX) analysis, shown in Fig. 3E, revealed the following atomic percentages of said product: 58.9 % carbon; 8.78 % nitrogen; 7.22 % oxygen; 9.15 % fluorine; 10.49 % copper; and 5.47 % silver. All the foregoing results confirmed that the product of Example 1 comprised nanocrystalline diamond comprising n-diamond, i-Carbon, graphitic carbon, and amorphous carbon structures.

Example 2 produced a metal-carbon composite product in the form of metallic Ag/Ag oxides and nanocrystalline carbon with a ID, 2D, and 3D structure. According to Fig. 4, as observed from the shown Raman spectrum, the carbon product obtained from Example 2 comprised graphitic carbon and amorphous carbon structures.

Example 3 produced a metal-carbon composite product in the form of metallic Ag/Ag oxides and nanocrystalline carbon with a ID, 2D, and 3D structure. According to Fig. 5, as observed from the shown Raman spectrum, the carbon product obtained from Example 3 comprised graphitic carbon and amorphous carbon structures.

Example 4 produced a metal-carbon composite product in the form of metallic Ag/Ag oxides and nanocrystalline carbon with a ID, 2D, and 3D structure. According to Fig. 6, as observed from the shown Raman spectrum, the carbon product obtained from Example 4 comprised nanocrystalline diamond, graphitic carbon, and amorphous carbon structures.

Example 5 produced a metal-carbon composite product in the form of metallic Ag/Ag oxides and nanocrystalline carbon with a ID, 2D, and 3D structure. Fig. 7A shows the Raman spectrum of the product of Example 5. Moreover, the Selected Area Electron Diffraction (SAED) analysis revealed the lattice spacing of said product as 0.304, 0.246, 0.211, 0.151, 0.128, and 0. 123 nanometer (nm), which, as shown in Fig. 7B, matched the lattice spacing references of i- Carbon, hexagonal diamond, and cubic silver. Next, images from the Transmission Electron Microscopy (TEM) are shown in Figs. 7C and 7D. Finally, the peaks from Energy Dispersive X-ray (EDX) analysis, shown in Fig. 7E, revealed the following atomic percentages of said product: 39.62 % carbon; 3.12 % nitrogen; 24.72 % oxygen; 30.85 % copper; and 1.69 % silver. All the foregoing results confirmed that the product of Example 5 comprised nanocrystalline diamond comprising hexagonal diamond, i-Carbon, graphitic carbon, and amorphous carbon structures.

Example 6 produced a metal-carbon composite product in the form of metallic Ag/Ag oxides and nanocrystalline carbon with a ID, 2D, and 3D structure. According to Fig. 8, as observed from the shown Raman spectrum, the carbon product obtained from Example 6 comprised graphitic carbon and amorphous carbon structures.

Example 7 produced a metal-carbon composite product in the form of metallic Ag/Ag oxides and nanocrystalline carbon with a ID, 2D, and 3D structure. According to Fig. 9, as observed from the shown Raman spectrum, the carbon product obtained from Example 7 comprised nanocrystalline diamond, graphitic carbon, and amorphous carbon structures.

Example 8 produced a metal-carbon composite product in the form of metallic Ag/Ag oxides and nanocrystalline carbon with a ID, 2D, and 3D structure. According to Fig. 10, as observed from the shown Raman spectrum, the carbon product obtained from Example 8 comprised nanocrystalline diamond, graphitic carbon, and amorphous carbon structures.

Example 9 produced a metal-carbon composite product in the form of metallic Ag/Ag oxides and nanocrystalline carbon with a ID, 2D, and 3D structure. According to Fig. 11, as observed from the shown Raman spectrum, the carbon product obtained from Example 9 comprised nanocrystalline diamond, graphitic carbon, and amorphous carbon structures.

Example 10 produced a metal -carbon composite product in the form of metallic Ag/Ag oxides and nanocrystalline carbon with a ID, 2D, and 3D structure. According to Fig. 12, as observed from the shown Raman spectrum, the carbon product obtained from Example 10 comprised graphitic carbon and amorphous carbon structures.

Example 11 produced a metal-carbon composite product in the form of metallic Ag/Ag oxides and nanocrystalline carbon with a ID, 2D, and 3D structure. Fig. 13A shows the Raman spectrum of the product of Example 11. Moreover, the Selected Area Electron Diffraction (SAED) analysis revealed the lattice spacing of said product as 0.302, 0.244, 0.212, 0.173, 0.149, and 0.128 nanometer (nm) which, as shown in Fig. 13B, matched the lattice spacing references of i-Carbon and hexagonal diamond. Next, images from the Transmission Electron Microscopy (TEM) are shown in Figs. 13C and 13D. Finally, the peaks from Energy Dispersive X-ray (EDX) analysis, shown in Fig. 13E, revealed the following atomic percentages of said product: 68 % carbon; 2.52 % nitrogen; 13.24 % oxygen; 15.98 % copper; and 0.26 % silver. All the foregoing results confirmed that the product of Example 11 comprised nanocrystalline diamond comprising hexagonal diamond, i-Carbon, graphitic carbon, and amorphous carbon structures. Example 12 produced a metal -carbon composite product in the form of metallic Ag/Ag oxides and nanocrystalline carbon with a ID, 2D, and 3D structure. According to Fig. 14, as observed from the shown Raman spectrum, the carbon product obtained from Example 12 comprised graphitic carbon and amorphous carbon structures.

Example 13 produced a metal-carbon composite product in the form of metallic Bi/Bi oxides and nanocrystalline carbon with a ID, 2D, and 3D structure. According to Fig. 15, as observed from the shown Raman spectrum, the carbon product obtained from Example 13 comprised graphitic carbon and amorphous carbon structures.

Example 14 produced a metal-carbon composite product in the form of metallic Ag/Ag oxides and nanocrystalline carbon with a ID, 2D, and 3D structure. Fig. 16A shows the Raman spectrum of the product of Example 14. Moreover, the Selected Area Electron Diffraction (SAED) analysis revealed the lattice spacing of said product as 0.248, 0.206, 0. 145, 0. 135.0. 124 and 0.118 nanometer (nm), which, as shown in Fig. 16B, matched the lattice spacing references of i-Carbon, hexagonal diamond, and cubic silver. Next, images from the Transmission Electron Microscopy (TEM) are shown in Figs. 16C and 16D. Finally, the peaks from Energy Dispersive X-ray (EDX) analysis, shown in Fig. 16E, revealed the following atomic percentages of said product: 63.51 % carbon; 3.58 % oxygen; 0.66 % fluorine; 7.2 % copper; and 25.05 % silver. All the foregoing results confirmed that the product of Example 14 comprised nanocrystalline diamond comprising hexagonal diamond, i-Carbon, graphitic carbon, and amorphous carbon structures.

List of Drawing References

100 receptacle

110 electrolyte

200 membrane

300 anode region

310 anolyte

320 anode

350 vent

400 cathode region

410 catholyte

420 cathode

430 reference electrode

440 feed 450 vent

500 power supply

Claims

1. A process for producing a nanocrystalline carbon with a ID, 2D, or 3D structure and/or a nanocrystalline diamond and/or an amorphous carbon and/or a metal-carbon nanomaterial composite, said composite containing a post-transition metal or a transition metal, and/or a mixture thereof, by electrochemically reducing a carbon source which is a carbonate salt or a bicarbonate salt under ambient pressure and temperature at an onset potential not greater than 10 Volt in presence of an electrolyte and at least one electrode, said electrode comprising a metallic material comprising one or more of the following: a post-transition element, a transition element, an oxide, and an alloy thereof.

2. The process according to claim 1, wherein the carbonate salt or the bicarbonate salt is dissolved in the electrolyte.

3. The process according to claim 2, wherein the carbonate salt or the bicarbonate salt is dissolved in the electrolyte at a concentration within the range of 0. 1 to 10 M.

4. The process according to claim 1, wherein the carbonate salt or the bicarbonate salt is water-soluble.

5. The process according to claim 4, wherein the carbonate salt is Na2CC>3.

6. The process according to claim 4, wherein the bicarbonate salt is KHCO3 or NH4HCO3.

7. The process according to claim 4, wherein the carbonate salt is prepared by saturating a strong basic aqueous solution with CO2.

8. The process according to claim 7, wherein the strong basic aqueous solution contains NaOH or KOH.

9. The process according to claim 7, wherein the concentration of the strong basic aqueous solution is within the range of 1 - 10 M.

10. The process according to claim 4, wherein the bicarbonate salt is prepared by saturating a tertiary amine aqueous solution with CO2.

11. The process according to claim 10, wherein the concentration of the tertiary amine aqueous solution is within the range of 1 - 10 M

12. The process according to claim 10, wherein the tertiary amine aqueous solution contains dimethylethanolamine (DMAE).

13. The process according to claim 4, wherein the bicarbonate salt is prepared by saturating an ammonia aqueous solution with CO2.

14. The process according to claim 13, wherein the concentration of the ammonia aqueous solution is within the range of 1 - 10 M.

15. The process according to claim 1, wherein the metallic material comprises one or more of the following: the post-transition element and the transition element.

16. The process according to claim 1, wherein said at least one electrode is formed of said metallic material in the particulate form deposited upon a substrate.

17. The process according to claim 1, wherein the post-transition element is Bi, and the transition element is Ag.

18. The process according to claim 16, wherein the electrode that is formed of the metallic material in the particulate form deposited upon the substrate is a cathode (420).

19. The process according to claim 18, wherein said metallic material in the particulate form deposited upon the substrate is prepared by an electrodeposition process.

20. The process according to claim 19, wherein the electrodeposition process comprises a post-treatment step which involves exposing said metallic material in the particulate form deposited upon the substrate to the ambient air.

21. The process according to claim 20, wherein said post-treatment step is carried out for 30 minutes - 24 hours.

22. The process according to claim 1, wherein the electrolyte is separated into an anolyte (310) and a catholyte (410).

23. The process according to claim 22, wherein said catholyte is a mixture containing (a) an ionic salt, (b) the carbonate salt or the bicarbonate salt, and (c) water, said ionic salt being a compound represented by Formula (I)

[A]n⁺ [Y]n- - (I) wherein, n is 1 or 2;

[Y] ‘ is selected from the group comprising tetrafluoroborate ([BF4]"), hexafluorophosphate (| PFc, |“). halides (CF, Br", F", I"), hexafluoroantimonate ([ SbFr, ]’), sulfate ([SO₄]²-) and nitrate ([NO3 ]");

[A]⁺ is selected from — (a) the group comprising ammonium cations represented by Formula (II):

, , , m hydrogen atom, C1-C6- alkyl, Cl-C6-alkoxy, Cl-C6-aminoalkyl, Cl-C6-hydroxylalkyl, C5-C12-aryl, and C5-C12-aryl-Cl-C6-alkyl groups; and

(b) the group comprising imidazolium cations represented by Formula

R, R¹, and R² being selected from Cl-C6-alkyl, C1-C6- alkoxy, Cl-C6-aminoalkyl, C5-C12-aryl, and C5-C12-aryl-Cl- C6-alkyl groups.

24. The process according to claim 23, wherein the catholyte contains the ionic salt at the concentration within the range of 0.1 to 10 M.

25. The process according to claim 23, wherein said ionic salt is l-butyl-3- methylimidazolium tetrafluoroborate ([bmim][BF4]), ammonium sulfate ((NH4)2SC>4), or choline chloride.

26. The process according to claim 22, wherein the electrolyte (310, 410) is separated by a membrane (200).

27. A process for producing a nanocrystalline carbon with a ID, 2D, or 3D structure and/or a nanocrystalline diamond and/or an amorphous carbon and/or a metal-carbon nanomaterial composite, said composite containing a post-transition metal or a transition metal, and/or a mixture thereof, said process comprising steps of: depositing a metallic material in the particulate form on a substrate to form a cathode (420); and electrochemically reducing a carbonate salt or a bicarbonate salt in presence of: an electrolyte that is separated into an anolyte (310) and a catholyte (410), an anode (320) submerged in said anolyte (310), and said cathode (420) submerged in said catholyte (410), wherein said catholyte (410) comprises a mixture of (a) l-butyl-3- methylimidazolium tetrafluoroborate ([bmim][BF4]), ammonium sulfate ((NH4)2SO4), or choline chloride, (b) water, and (c) the carbonate salt or the bicarbonate salt, and wherein said electrochemically reducing the carbonate salt or the bicarbonate salt occurs under ambient pressure and temperature at an onset potential not greater than 10 Volt.

28. A process for producing a nanocrystalline carbon with a ID, 2D, or 3D structure and/or a nanocrystalline diamond and/or an amorphous carbon and/or a metal-carbon nanomaterial composite, said composite containing a post-transition metal or a transition metal, and/or a mixture thereof, said process comprising steps of: depositing a metallic material in the particulate form on a substrate to form a cathode (420); and electrochemically reducing a carbonate salt or a bicarbonate salt in presence of: an electrolyte (110), an anode (320) and said cathode (420) which are submerged in said electrolyte (110), wherein said electrolyte (110) comprises a mixture of (a) l-butyl-3- methylimidazolium tetrafluoroborate ([bmim][BF4]), ammonium sulfate ((N L^SCh), or choline chloride, (b) water, and (c) the carbonate salt or the bicarbonate salt, and wherein said electrochemically reducing the carbonate salt or the bicarbonate salt occurs under ambient pressure and temperature at an onset potential not greater than 10 Volt.

29. A process according to claim 27 or 28, wherein said metallic material is Bi, and said substrate is a Sn foil.

30. A process according to claim 27 or 28, wherein said metallic material is Ag, and said substrate is a Cu foil.