ELECTROLYSIS METHODS THAT UTILIZE CARBON DIOXIDE FOR MAKING COATED NANOCARBON ALLOTROPES
20230160078 · 2023-05-25
Inventors
Cpc classification
C25B11/091
CHEMISTRY; METALLURGY
B82Y40/00
PERFORMING OPERATIONS; TRANSPORTING
C01B32/05
CHEMISTRY; METALLURGY
C01P2002/78
CHEMISTRY; METALLURGY
C01P2002/88
CHEMISTRY; METALLURGY
C01B2202/20
CHEMISTRY; METALLURGY
D06M7/00
TEXTILES; PAPER
D01F9/12
TEXTILES; PAPER
C01B32/18
CHEMISTRY; METALLURGY
C01P2002/90
CHEMISTRY; METALLURGY
C01B2204/04
CHEMISTRY; METALLURGY
B82Y30/00
PERFORMING OPERATIONS; TRANSPORTING
C01P2002/72
CHEMISTRY; METALLURGY
C01B32/174
CHEMISTRY; METALLURGY
H01B1/04
ELECTRICITY
International classification
Abstract
The embodiments of the present disclosure relate to a method and apparatus for producing a carbon nanomaterial product (CNM) product that may comprise carbon nanotubes and various other allotropes of nanocarbon. The method and apparatus employ a consumable carbon dioxide (CO.sub.2) and a renewable carbonate electrolyte as reactants in an electrolysis reaction in order to make CNTs. In some embodiments of the present disclosure, operational conditions of the electrolysis reaction may be varied in order to produce the CNM product with a greater incidence of a desired allotrope of nanocarbon or a desired combination of two or more allotropes.
Claims
1. A method for producing a carbon nanomaterial (CNM) product, the method comprising steps of: (a) heating an electrolyte media to obtain a molten electrolyte media; (b) positioning the molten electrolyte media between an anode and a steel cathode of an electrolytic cell; (c) introducing a source of carbon into the electrolytic cell; (d) applying a electrical current to the cathode and the anode in the electrolytic cell; and (e) collecting the CNM product from the cathode, wherein the CNM product comprises a minimum relative-amount of a metal-coated CNM product.
2. The method of claim 1, further comprising a step of introducing an excessive amount of a metal into the molten electrolyte media.
3. The method of claim 2, wherein the excessive amount of metal is introduced by introducing a metal-containing additive, introducing the excessive amount of metal by degrading an inner wall of the electrolytic cell, introducing the excessive amount of metal by degrading the anode or any combination thereof.
4. The method of claim 2, wherein the metal is nickel, iron, titanium, tin, copper, vanadium, cobalt, zinc, magnesium, aluminum, ruthenium, silver, iridium, palladium, rhodium, or platinum.
5. The method of claim 2, wherein the metal is introduced as a metal, metal mix, a metal oxide or metal oxide mix, a metal salt or metal salt mix, or any combination thereof.
6. The method of claim 1, wherein the electrical current has a current density of between about 0.1 A/cm.sup.2 and about 0.3 A/cm.sup.2.
7. The method of claim 1, wherein the steel cathode comprises galvanized steel, stainless steel or any combination thereof.
8. The method of claim 1, further comprising a step of introducing a metal additive into the electrolyte media or the molten electrolyte media.
9. The method of claim 5, wherein the metal additive is added in an amount of between about 0.25 wt % and 1.5 wt %, relative to the amount of the electrolyte media or the molten electrolyte media.
10. The method of claim 5, wherein the metal additive is a nickel-containing additive.
11. The method of claim 1, wherein the anode comprises nickel.
12. The method of claim 1, wherein the anode has a high-nickel content.
13. The method of claim 1, further comprising a step of adding a nickel-containing additive, wherein the anode comprises a Nichrome alloy and the minimum relative-amount of the metal coated CNT is between about 5 wt % and 99.5 wt % of the total weight of the CNM product.
14. The method of claim 1, wherein the anode is made of substantially pure nickel.
15. The method of claim 1, wherein the metal-coated CNM is magnetic and moves when in a magnetic field.
16. The method of claim 1, further comprising a step of introducing a doping additive component into the electrolytic cell, wherein the metal-coated CNM is doped and atoms of the doping additive component are directly incorporated throughout the doped, coated CNM to impart desired physical and/or chemical properties to the doped, metal-coated CNM that are different than an undoped, coated CNT.
17. A carbon nanomaterial (CNM) comprising a metal-coated carbon nanotube (CNT).
18. A carbon nanomaterial (CNM) comprising a metal-coated graphitic carbon, a metal-coated nano-bamboo, a metal-coated conical carbon nanofiber, a metal-coated nano-pearl, a metal-coated nano-onion, a metal-coated hollow nano-onion, a metal-coated nano-flower, a metal-coated nano-dragon, a metal-coated branch and trunk CNT (a metal-coated nano-tree), a metal-coated nano-belt, a metal-coated nano-rod, a metal-coated long and/or straight CNT, a metal-coated high aspect ratio CNT, a metal-coated thin CNT and a macroscopic assembly of CNTs, including densely packed, straight metal-coated CNTs, a metal-coated nano-sponge or a metal-coated nano-web.
19. The carbon nanomaterial of claim 15, wherein the metal coated CNM comprises an external coating of nickel.
20. Use of a desired metal-coated allotrope in one or more of a medical device, a structural enhancement additive, a strength enhancement additive, an electrical conductivity enhancement additive, a thermal conductivity enhancement additive, or a flexibility enhancement additive, a hardness enhancement additive, a durability enhancement additive, a lubrication enhancement additive, or as a catalyst, electric vehicles, cables or wires, athletic equipment, a pharmaceutical drug delivery system, an electronic, a battery, a super capacitor, a sensor, a plastic, a polymer, a textile, a hydrogen storage system, a light absorbing enhancement for a surface, an electromagnetic shielding enhancement for a surface, a surface treatment, a surface coating, a paint or a water treatment system, wherein the desired allotrope is a metal-coated carbon nanotube (CNT), a metal-coated graphitic carbon, a metal-coated nano-bamboo, a metal-coated conical carbon nanofiber, a metal-coated nano-pearl, a metal-coated nano-onion, a metal-coated hollow nano-onion, a metal-coated nano-flower, a metal-coated nano-dragon, a metal-coated branch and trunk CNT (a metal-coated nano-tree), a metal-coated nano-belt, a metal-coated nano-rod, a metal-coated long and/or straight CNT, a metal-coated high aspect ratio CNT, a metal-coated thin CNT and a macroscopic assembly of CNTs, including densely packed, straight metal-coated CNTs, a metal-coated nano-sponge or a metal-coated nano-web.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0144] These and other features of the present disclosure will become more apparent in the following detailed description in which reference is made to the appended drawings.
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DETAILED DESCRIPTION
[0178] The embodiments of the present disclosure relate to methods and apparatus for producing a carbon nanomaterial (CNM) product that comprises various desired carbon allotropes, such as: carbon nanotubes (CNTs), graphitic carbon, nano-bamboo, conical carbon nanofibers, nano-pearl carbon, coated CNTs, nano-onions, hollow nano-onions, nano-flowers, nano-dragons, branch and trunk CNTs (nano-trees), nano-belts, nano-rods, long and/or straight CNTs, high aspect ratio CNTs, thin CNTs and macroscopic assemblies of CNTs. The methods and apparatus employ carbon dioxide (CO.sub.2) as a reactant in an electrolysis reaction in order to make these varied constituents of the CNM product. The embodiments of the present disclosure provide a range of controlled variations of the electrolysis methods and apparatus of the present disclosure to selectively provide a CNM product that has a high degree of purity of one or more of these allotropes.
[0179] Some embodiments of the present disclosure relate to methods and apparatus for producing a CNM product that comprises various desired carbon allotropes, with a higher relative amount of a specific desired carbon allotrope. For example, the higher relative amount of a first desired carbon allotrope may be at least 20 wt % (based upon the weight of the first desired carbon allotrope as compared to the total weight of the CNM product). In some embodiments of the present disclosure, the higher relative amount of the first desired carbon allotrope may be at least 25 wt %, at least 30 wt %, at least 35 wt %, at least 40 wt %, at least 50 wt %, at least 60 wt %, at least 70 wt %, at least 80 wt %, at least 90 wt %, at least 91 wt %, at least 92 wt %, at least 93 wt %, at least 94 wt %, at least 95 wt %, at least 96 wt %, at least 97 wt %, at least 98 wt %, at least 99 wt % or at least 99.5 wt % of the total weight of the CNM product, made according to the embodiments described herein. Some embodiments of the present disclosure produce a CNM product with a high purity of the desired allotrope.
Definitions
[0180] 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 disclosure belongs.
[0181] As used herein, the term “about” refers to an approximately +/−10% variation from a given value. It is to be understood that such a variation is always included in any given value provided herein, whether or not it is specifically referred to.
[0182] As used herein, the term “allotrope” may be used interchangeably with “physical form”, “structure”, “morphology”, “nanocarbon allotrope”, nanocarbon physical form”, “nanocarbon structure” or “nanocarbon morphology”, these terms—and similar terms—all refer to the three-dimensional shape—and associated physical chemical properties—of the nano-scaled structures that are found as a constituent within a CNM product, made according to the embodiments described herein.
[0183] As used herein, the terms “desired relative-amount”, “relative amount” or “minimal relative-amount” both refer to a relative amount that a desired allotrope contributes to the total amount of a CNM product, where that relative amount is greater than at least 70 wt %, in some embodiments, of the total amount of the CNM product made, the term “high purity” may be employed herein. In some embodiments of the present disclosure, the relative amount of a desired allotrope is greater than 75 wt % of total amount of the CNM product made, is greater than 80 wt % of total amount of the CNM product made, is greater than 85 wt % of total amount of the CNM product made, is greater than 90 wt % of total amount of the CNM product made, is greater than 95 wt % of total amount of the CNM product made, is greater than 97.5 wt % of total amount of the CNM product made or is greater than 99 wt % of total amount of the CNM product made.
[0184] Embodiments of the present disclosure will now be described and include references to the Examples and the figures.
[0185] Some embodiments of the present disclosure relate to a method for producing a CNM product that comprises a greater amount of a desired allotrope, relative to other allotropes present in the CNM product. The method comprises the steps of heating a carbonate electrolyte to obtain a molten-carbonate electrolyte; positioning the molten carbonate electrolyte between an anode and a cathode in an electrolytic cell; applying an electrical current to the cathode and the anode in the electrolytic cell; and, collecting a CNM product from the cathode.
[0186] In some embodiments of the present disclosure, the method further comprises a step of selecting the material of the anode or cathode in order to synthesize a greater amount of a desired allotrope, relative to other allotropes present in the CNM product. In some embodiments of the present disclosure, the method further comprises a step of selecting an additive and adding a selected amount of the selected additive to the electrolyte in order to synthesize the desired nanocarbon allotrope. In some embodiments of the present disclosure, the method comprises a step of applying a selected current density of the electrical current in order to synthesize the desired nanocarbon allotrope. In some embodiments of the present disclosure, the method comprises a step of applying the electrical current for a selected period of time in order to synthesize the desired nanocarbon allotrope.
[0187] The step of heating the carbonate electrolyte can be achieved by various means, as would be appreciated by the skilled reader. For example, a heating apparatus such as an oven or furnace can be used to heat the electrolyte to a sufficient temperature so that it transitions into a molten, liquid state. As such, any heating apparatus that can achieve the temperatures required to heat the electrolyte to its melting point are contemplated herein. In some embodiments of the present disclosure, the method further comprises a step of aging the molten electrolyte whereby the molten electrolyte is held in the molten state at a substantially constant temperature to allow a steady state to be achieved. For example, the molten electrolyte may be aged for between 1 hour and 48 hours.
[0188] The molten electrolyte is then positioned between an anode and cathode of an electrolytic cell, which may also be referred to as a case. The electrolytic cell may be any type of vessel that can maintain its structural integrity in the face of the electrochemical environment that occurs during the electrolysis reactions of the present disclosure. The electrolytic cell may have one or more walls that may be made of a desired material or that are coated with a desired material that will not degrade in the environment of the electrolysis reaction. Table 1 below provides a detailed list of various electrode materials suitable for use in the embodiments of the present disclosure. In some embodiments of the present disclosure, the electrolytic cell is made of substantially pure alumina. In other embodiments of the present disclosure, the electrolytic cell is made of stainless steel with or without a lining that is comprised of another metal, such as Inconel, Nichrome or Monel, or a combination thereof. In some embodiments of the present disclosure, the electrolytic cell is a tubular vessel with a closed end. In other embodiments of the present disclosure, the electrolytic cell is a rectangular vessel with one or more compartments.
[0189] In some embodiments of the present disclosure, the electrolyte may be melted inside the electrolytic cell or it may be melted outside the cell and transferred thereto. Because the electrolysis reaction will typically occur over a time period whereby the molten electrolyte could cool, the electrolytic cell can be configured with its own integral heating apparatus, or it may be self heated by the CO.sub.2 dissolution reaction and the electrolysis reaction, or it may be configured to be heated by an external heating apparatus that is external to the electrolytic cell so that the electrolyte is maintained in the molten state for the desire period of time.
[0190] In some embodiments of the present disclosure, the electrolytic cell maybe configured to maintain the electrolyte temperature at least at about 400° C., at least at about 500° C., at least at about 550° C., at least at about 600° C., at least at about 650° C., at least at about 675° C., at least at about 700° C., at least at about 725° C., at least at about 750° C., at least at about 775° C., at least at about 800° C., at least at about 825° C., at least at about 850° C., at least at about 875° C., at least at about 900° C., at least at about 1000° C. or great than 1000° C.
[0191] The anode can be made of various metals or alloys. Some anodes can be made of materials that comprise a metal that is resistant to corrosion by oxidation (or otherwise, such the noble metals: such as iridium, platinum, gold, ruthenium, rhodium, osmium, palladium or any combination thereof. Anodes may also be made of a non-noble metal that is a substantially pure metal, such as nickel, or a mixture of metals. Some non-limiting examples of suitable materials for the anodes of the present disclosure include: substantially pure nickel, an alloy that is comprised of substantially mostly nickel, an alloy that has a high-nickel content or an alloy that is comprised of some nickel. As used herein, an alloy with greater than 50 wt % nickel is referred to a high-nickel content alloy. Suitable examples of alloys for use as an anode include, but are not limited to: Inconel 718 (at least about 72 wt % nickel content), Inconel 600 (about 52.5 wt % nickel content) or other Inconels, such as, but not limited to Inconel 625 (about 58 wt % nickel content), Nichrome A (composed of about 80 wt % nickel and about 20 wt % chromium), Nichrome C (composed of about 60 wt % nickel, about 24 wt % iron and about 16 wt % chromium). Anodes made from lower nickel content alloys may also be suitable for use in some embodiments of the present disclosure, including Incoloy alloys—such as Incoloy 800 composed of about 40 wt % iron, about 30-35 wt % nickel and about 19-23 wt % chromium). In some embodiments of the present disclosure, the anode may be monolithic or it may be a composite that is composed of different materials.
[0192] In one embodiment the anode may be planar in shape and it can be made of various dimensions. In some embodiments of the present disclosure, the anode may be made of wire that is rolled into a substantially flat coil with an upper face and a lower face. In some embodiments of the present disclosure, the anode may be perforated. In other embodiments, the anode may be configured of various shapes and surface modifications to maximize the active area of electrolysis. The upper and lower faces of the anode may have substantially equal areas that are suitable for fitting within the electrolytic cell. In some embodiments, the anode face has a surface area that is between about 1 cm.sup.2 and about 100,000 cm.sup.2; between about 10 cm.sup.2 and 50,000 cm.sup.2; or between about 100 cm.sup.2 and about 10,000 cm.sup.2. In some embodiments of the present disclosure, the anode may have two or more anode faces, each with a surface area within these ranges. In some embodiments, the anode may be larger with a larger surface area. The skilled person will appreciate that the size of the electrolytic cell may dictate the size of the anode and vice versa. The anode may be arranged to be generally aligned with a horizontal plane, or a vertical plane, or a plane that is not parallel to either the horizontal or vertical plane.
[0193] The cathode can be made of various metals or alloys. Some cathodes can be made of materials that comprise steel, galvanized steel, stainless steel, copper, or any combinations thereof. Some further non-limiting examples of suitable materials for the anodes of the present disclosure include: nickel, Nichrome C, Monel (about 67 wt % nickel and about 31-33 wt % copper) and Muntz brass (about 60 wt % copper and about 40 wt % zinc).
[0194] In one embodiment the cathode may be planar in shape and can be made of various dimensions. In some embodiments of the present disclosure, the cathode may be made of wire that is rolled into a flat coil with an upper face and a lower face. In other embodiments the cathode may be configured of various shapes and surface modifications to maximize the active area of electrolysis. The upper and lower faces of the coiled cathode may have substantially equal areas that are suitable for fitting within the electrolytic cell. In some embodiments, the coiled cathode faces have a surface area that is between about 1 cm.sup.2 and about 5000 cm.sup.2; between about 2 cm.sup.2 and 3000 cm.sup.2; or between about 3 cm.sup.2 and about 1000 cm.sup.2. In some embodiments, the cathode may be larger with a larger surface area. The skilled person will appreciate that the size of the electrolytic cell and/or the size of the anode may dictate the size of the cathode for example, the electrodes may be substantially similar sizes. The cathode may be arranged to be generally aligned with a horizontal plane or a vertical plane, or a plane that is not parallel to either the horizontal or vertical plane.
[0195] In some embodiments of the present disclosure, the size and orientation of the cathode can be selected to substantially mirror the size and orientation of the anode. In some embodiments of the present disclosure, the anode and the cathode may be generally aligned with a horizontal plane and vertically spaced apart from each other. In other embodiments of the present disclosure, the anode and cathode may be generally aligned with a vertical plane and horizontally spaced apart from each other. As the skilled person will appreciate, the distance between the electrodes must permit the passage of sufficient electric current therebetween but the amperage of the electric current and the size of the electrolytic cell may also influence how far apart the electrodes are spaced apart. In some embodiments of the present disclosure, the electrodes maybe spaced apart from each other by about 0.25 cm, about 0.5 cm, about. 0.75 cm, about 1 cm, about 1.25 cm, about 1.5 cm, about 1.75 cm, about 2 cm, about 3 cm, about 4 cm, about 5 cm, about 7.5 cm, about 10 cm, about 15 cm, about 20 cm, about 30 cm or further.
[0196] Some embodiments of the present disclosure relate to a larger, scaled up electrolysis cell and set of electrodes. For example, in some embodiments of the present disclosure, the electrodes may each have a face with a surface area of between about 1 m.sup.2 and about 10 m.sup.2, between about 2 m.sup.2 and about 9 m.sup.2, between about 3 m.sup.2 and about 8 m.sup.2, between about 4 m.sup.2 and about 7 m.sup.2, between about 5 m.sup.2 and about 6 m.sup.2. As will be appreciated by those skilled in the art, the dimensions of the electrodes can match each other, or not, or be configured in a sandwiched configuration, with one electrode positioned between two of the other electrodes or other arrangements, and the dimensions of the electrodes can determine the dimensions of the electrolytic cell in which the electrodes are used.
[0197] In order to initiate and maintain the electrolysis reaction within the electrolytic cell, an electric current is applied and passes between the anode and cathode through the molten electrolyte therebetween. In some embodiments of the present disclosure, the electric current may be an alternating current or a direct current. In some embodiments of the present disclosure, the current may be between about 0.01 amps (A) and about 5 A. In some embodiments of the present disclosure, the current may be between about 0.025 A and about 4 A; between about 0.05 A and about 3 A; between about 0.075 A and about 2 A; between about 0.1 A and about 1 A. In some embodiments of the present disclosure the current is about 0.5 A. In some embodiments of the present disclosure, the current may be between about 5 A and about 500,000 A; or between about 500 A and 50,000 A. In other embodiments of the present disclosure, the current may be between about 5,000 A and about 50,000 A
[0198] In some embodiments of the present disclosure, the current is applied at a substantially constant current density. For example, the current density of the applied current may be between about 0.001 A/cm.sup.2 and about 1 A/cm.sup.2. In some embodiments the current density of the applied current may be between about 0.0025 A/cm.sup.2 and about 0.75 A/cm.sup.2; between about 0.005 A/cm.sup.2 and about 0.5 A/cm.sup.2; between about 0.0075 A/cm.sup.2 and about 0.25 A/cm.sup.2; or between about 0.01 A/cm.sup.2 and about 0.1 A/cm.sup.2. In other embodiments of the present disclosure, the current density of the applied current may be between about 1 A/cm.sup.2 and about 10 A/cm.sup.2. In some embodiments, low current density is used to control conductivity during formation of the CNM product.
[0199] In some embodiments of the present disclosure, the method further comprises a step of ramping up the electrical current in staged increases of current over a prescribed time course. For example, a first period of a first constant current density, followed by a second period of a second constant current density, followed by a third period of a third constant current density, followed by a fourth period of a fourth constant current density and so on until a final current density is applied for the duration of the electrolysis process. In these examples, the time periods may be the same or different and they may range from one minute to one hour and any time therebetween. In these examples, the constant current densities may be the same or different and they may range from as little as 0.005 A/cm.sup.2 to 0.75 A/cm.sup.2. In other embodiments the ramped electrical current, may increase and/or decrease in a non-stepwise manner, such as by oscillations or by linear, ramped changes or by other variations.
[0200] In some embodiments of the present disclosure, the method further comprises the step of introducing, which may also be referred to herein as adding, an additive, or more than one additive, into the carbonate electrolyte media. This introducing step can be achieved by various approaches, depending on what the nature of the additive is. This step of introducing the additive into the carbonate electrolyte can occur before, during or after the carbonate electrolyte is heated to a molten state. Non-limiting examples of such additives include: a lithium-containing additive (such as lithium phosphate; lithium oxide and other lithium-containing salts); an iron-containing additive (such as iron-containing salts, including iron oxide); a magnesium-containing additive (such as a magnesium salt, including magnesium oxide); a transition metal nucleating agents (such as Fe.sub.2O.sub.3, nickel powder, a chromium powder); a transition metal salt of one or more of iron, nickel, chromium, nickel, copper, manganese, titanium, zirconium, molybdenum, tantalum, or cobalt. For clarity, additives that do not include any iron (including iron-containing salts) are collectively referred to herein as “iron-free” additives. In non-limiting embodiments of the present disclosure, the iron-free additives include: additives that are substantially devoid of any iron, additives that comprise a trace amount of iron and/or additives that include an amount of iron that does not participate in the electrolysis reaction in any substantial or meaningful way. Examples of the iron-free additive include, but are not limited to: a lithium-containing additive, a cobalt-containing additive, a nickel containing additive and a chromium-containing additive. According to the embodiments of the present disclosure, the additive may introduced in an amount of between about 0.01 wt % to 10 wt %, relative to the amount of the electrolyte media or the molten electrolyte media. In some embodiments of the present disclosure, the additive may be introduced in an amount between about 0.05 wt % and about 7.5 wt %, relative to the amount of the electrolyte media or the molten electrolyte media. In some embodiments of the present disclosure, the additive may be introduced in an amount between about 0.075 wt % and about 5 wt %, relative to the amount of the electrolyte media or the molten electrolyte media.
[0201] As a further example, in some embodiments of the present disclosure, the lithium-containing additive may be added in an amount of between 0.01 wt % and about 10 wt %, or between about 0.05 wt % and about 9 wt %, or between about 0.075 wt % and about 8 wt %.
[0202] As a further example, in some embodiments of the present disclosure, an iron-containing additive may be added in an amount of between 0.01 wt % and about 5 wt %, or between about 0.05 wt % and about 2.5 wt %, or between about 0.075 wt % and about 1.25 wt % and in further embodiments the iron-containing additive is added in an amount of between about 0.05 wt % and 0.15 wt %.
[0203] As a further example, in some embodiments of the present disclosure, a nickel-containing additive (either as a nickel powder or a nickel salt) may be added in an amount of between 0.01 wt % and about 5 wt %, or between about 0.05 wt % and about 2.5 wt %, or between about 0.075 wt % and about 1.25 wt % and in further embodiments the nickel-containing additive is added in an amount of between about 0.05 wt % and 0.15 wt %.
[0204] As a further example, in some embodiments of the present disclosure, a cobalt-containing additive (either a cobalt powder or a cobalt salt) may be added in an amount of between 0.01 wt % and about 5 wt %, or between about 0.05 wt % and about 2.5 wt %, or between about 0.075 wt % and about 1.25 wt % and in further embodiments the cobalt-containing additive is added in an amount of between about 0.05 wt % and about 0.15 wt %.
[0205] As a further example, in some embodiments of the present disclosure, a chromium-containing additive (either as a chromium powder or chromium salt) may be added in an amount of between 0.01 wt % and about 5 wt %, or between about 0.05 wt % and about 2.5 wt %, or between about 0.075 wt % and about 1.25 wt % and in further embodiments the chromium-containing additive is added in an amount of between about 0.05 wt % and about 0.15 wt %.
[0206] In some embodiments, the transition metal nucleating agent may be a transition metal oxide. In some embodiments of the present disclosure, the nucleating agent may be incorporated into the CNM product, so that atoms of the nucleating agent form part of one or more allotropes of the CNM product. In some embodiments of the present disclosure, the incorporated nucleating agent may be magnetic. In some embodiments of the present disclosure, a portion of the nanomaterial product may be responsive to a magnetic field (by moving when near to or inside the magnetic field) and a portion may be non-responsive to a magnetic field (by not moving), and these two classes of nanomaterial products may be separated by applying an external magnetic field.
[0207] The total duration of the electrolysis synthesis process may be between about 10 minutes and about 156 hours.
[0208] In some embodiments of the present disclosure, the step of selecting may be configured so that the CNM product comprises a desired combination of two or more desired allotropes. For example, the step of selecting can be varied, in a controlled fashion, so that the CNM product comprises a first allotrope and a second allotrope or further allotropes. Further, the step of selecting can be configured so that a desired relative quantities of the first allotrope and the second allotrope, relative to each other within the CNM product, can be achieved. For example, it may be desired that the amount of the first allotrope is greater than, less than or substantially equal to the amount of the second allotrope present in the CNM product.
[0209] As will be appreciated by those skilled in the art, the specific variations of the electrolysis process conditions, also referred to herein as operational parameters, described herein may be further varied when the physical scale of the electrolysis process is increased.
EXAMPLES
[0210] The constituents of the molten electrolyte mixtures described herein are commercially available: lithium carbonate (Li.sub.2CO.sub.3; Alfa Aesar, about 99% pure), lithium oxide (Li.sub.2O, 99.5%, Alfa Aesar), lithium phosphate (Li.sub.3PO.sub.4, 99.5%), iron oxide (Fe.sub.2O.sub.3, 99.9%, Alfa Aesar), and boric acid (H.sub.3BO.sub.3, Alfa Aesar 99+%).
[0211] For the electrodes described herein: Nichrome A (0.04-inch-thick), Nichrome C (0.04-inch-thick), Inconel 718, Inconel 600 (0.25-in thick), Inconel 625 (0.25-in thick), Monel 400, Stainless Steel 304 (0.25-in thick), Muntz Brass (0.25-in thick), nickel, iridium, were all purchased from regular commercial metal sources. Composite electrodes were fabricated with these purchased materials or purchased as used.
[0212] For the additives described herein: Ni powder was 3-7 μm (99.9%, Alfa Aesar), Cr powder was <10 μm (99.2%, Alfa Aesar), Co powder was 1.6 μm (99.8%, Alfa Aesar) and iron oxide was 99.9% Fe.sub.2O.sub.3 (Alfa Aesar). The Inconel 600 (100 mesh) was purchased from Cleveland Cloth. The electrolysis was a conducted in a high form crucible >99.6% alumina (Advalue).
[0213] Specific electrolyte compositions of each electrolyte are described herein. The electrolyte was pre-mixed by weight in the noted ratios then metal or metal oxide additives are added if used. The cathode was mounted vertically across from the anode and immersed in the electrolyte. Generally, the electrodes were immersed subsequent to electrolyte melt. For several, noted, electrolyses, once melted, the electrolyte was maintained at 770° C. (“aging” the electrolyte) prior to immersion of the electrolytes followed by immediate electrolysis. Generally, the electrolysis was driven with a described constant current density. As noted, for some electrolyses, the current density was ramped in several steps building to the applied electrolysis current, which was then maintained at a constant current density. Otherwise, the electrolyses were initiated, and held, at a single constant current. The electrolysis temperature was about 770° C., unless otherwise indicated herein.
[0214] Sources of carbon included CO.sub.2 captured directly from the air, and CO.sub.2 from the exhaust of a natural gas electric power plant. In the embodiments of the present disclosure, the electrolytic splitting can occur as direct air carbon capture with or without CO.sub.2 pre-concentration, with concentrated CO.sub.2, or gases that comprise CO.sub.2, for example exhaust gases.
[0215] The CNM product made by the examples below were washed (with either deionized water, 6 M HCl, concentrated HCl) to remove excess electrolyte, separated from the washing solution, and analyzed by PHENOM Pro Pro-X scanning electron microscope (SEM, with EDX), FEI Teneo LV SEM, and by FEI Teneo Talos F200X TEM (with EDX). XRD powder diffraction analyses were conducted with a Rigaku D=Max 2200 XRD diffractometer and analyzed with the Jade software package. Raman spectroscopy was measured with a LabRAM HR800 Raman microscope (HORIBA) with 532.14 wavelength incident laser light, with a high resolution of 0.6 cm.sup.−1.
[0216] In some embodiments of the present disclosure, the CNM product made according to the methods, apparatus and systems described herein above, may result in a high purity of a desired allotrope where such desired allotrope are doped. Without being bound by any particular theory, if a doping component, also referred to as a dopant, is introduced into the method, apparatus or system, then atoms of the dopant may be directly incorporated into various of the graphitic structures of the CNM product and the desired allotrope therein. When atoms of the doping component are directly introduced into the CNM product, as it is being built in situ upon the cathode, the resulting doped CNM product has desired chemical physical properties that are different than a CNM product (a non-doped CNM product) that does not include atoms of the doping component. Without being bound by any particular theory, the doping component may include at least one material with a group IIIA element, a non-carbon group IVA element, a group VA element, a group VIA chalcogenide element, or at least one material with gold, platinum, iridium, iron or other row 4, 5, or 6 metals. In some embodiments of the present disclosure, the doping component comprises: a chemical species with oxygen atoms, halide atoms, one or more of nitrate, a phosphate, a thiophosphate, a silicate, a thionyl chloride, a sulfur chloride, a silicon chloride, a thiophosphate, a thionyl nitrate, a silicon nitrate, a silicon nitrite, a sulfur oxide and a nitrous oxide gas. Without being bound by any particular theory, the desired chemical properties of the doped CNM product may include: a greater electrical conductivity (as compared to a non-doped CNM product), enhanced electrical charge storage (as compared to a non-doped CNM product), a heterogeneous catalytic property, a homogeneous catalytic property, a fuel cell catalytic property, an aerobic oxidation catalytic property, an enhanced reaction activity property and any combination thereof. The desired physical chemical properties of the doped CNM product made according to the embodiments of the present disclosure may have a wide variety of applications, such as: a catalysts, heavy metal removal, energy storage, sorption applications, batteries, ultra-sensitive sensors and combinations thereof.
[0217] In some embodiments of the present disclosure, the CNM product made according to the methods, apparatus and systems described herein above, may result in a desired allotrope that is magnetic. For clarity, a magnetic CNM product and the magnetic allotropes therein are physically movable with a magnetic field. Without being bound by any particular theory, if a magnetic additive component, is introduced into the method, apparatus or system, then a carbide-driven growth of the various of the graphitic structures within the magnetic CNM product may occur. In some embodiments of the present disclosure, the magnetic additive component comprises at least one of a magnetic material addition component, a carbide-growth component and any combination thereof. In some embodiments of the present disclosure, the magnetic material addition component is wherein the magnetic material additive component is one or more of iron, nickel, cobalt, gadolinium, samarium, neodymium, steel and alloys comprising one or more magnetic materials with ferromagnetic properties, paramagnetic properties, diamagnetic properties and any combination thereof. In some embodiments of the present disclosure, the iron-based additive is one or more of cast iron powder, iron metal, steel, stainless steel, an iron containing metal alloy, an iron oxide, FeO, Fe.sub.2O.sub.3, Fe.sub.3O.sub.4, or an iron containing salt. Within the magnetic CNM product, the magnetic additive component is incorporated or formed as one or more nodules, that may be covered in one or more layers of graphitic carbon, on the magnetic CNM product. In some embodiments of the present disclosure, the carbide-growth component may be a metal carbide, such as: iron carbide, a nickel carbide, a cobalt carbide; a zirconium carbide, a chromium carbide, a tantalum carbide, a hafnium carbide and any combination thereof. In some embodiments of the present disclosure, the carbide-growth component may be a non-metal carbide, such as silicon carbide, a germanium carbide and any combination thereof. The magnetic additive component may be added to the methods, apparatus and systems of the present disclosure, as a chemical additive or it may originate from one or more walls of the electrolysis cell, from the anode, from the cathode, the electrolyte media and any combination thereof.
Example 1—Electrolysis Process Conditions for Making a Nanocarbon Product with a High Purity of Desired Allotropes
[0218] In order to make CNM product an electrolysis reaction was conducted in an electrolysis cell that comprised a vessel, an anode and a cathode. The vessel was made of pure alumina (commercially available from AdValue, approximately 99.6% pure alumina) and it had a closed end. The vessel contained a 770° C. molten Li.sub.2CO.sub.3 electrolyte.
[0219] The anode was made of various materials and it was configured to generate oxygen during the electrolysis reaction.
[0220] The cathode was made of brass and it was also configured into a substantially flat coil.
[0221] Carbon dioxide from the air was directly captured by the molten electrolyte during the electrolysis reaction.
[0222] The electrochemical operating parameters that were varied were the composition and/or configuration of the cathode and anode, the additives used and their concentrations to the Li.sub.2CO.sub.3 electrolyte, the current density and the time of the electrolysis. Electrolyte additives that are varied included Fe.sub.2O.sub.3, nickel, chromium powder or combinations thereof. Electrolysis reactions were varied over a range of electrolysis current densities. Variations of the electrodes include the use of cathode metal electrodes such as Muntz brass Monel, or Nichrome alloys. Anode variations include noble anodes such as iridium, various nickel containing anodes including nickel, Nichrome A or C, Inconel 600, 625, or 718, or specific layered combinations of these metals. Alloy composition of the metals used as electrodes is presented in Table 1. Metal variation was further refined by combining the metals in Table 1 as anodes, for example using a solid sheet of one Inconel alloy, layered with a screen or screens of another Inconel alloy, such as an anode of Inconel 625 with 3 layers of (spot welded) 100 mesh Inconel 600 screen.
TABLE-US-00001 TABLE 1 Compositions of various alloys used (weight percentage). Ni Fe Cu Zn Cr Mo Nb & Alloy % % % % % % Ta % Nichrome C 60 24 16 Nichrome A 80 20 Inconel 600 52.5 18.5 19.0 3.0 3.6 Inconel 718 72% min 6-10 14-17 Inconel 625 58 5 max 20-23 8-10 4.15-3.15 Monel 67 31.5 Muntz Brass 60 40
[0223] Several thousand runs of different combinations of electrolyses operating conditions were performed in order to achieve the embodiments of the present disclosure. A fascinating, but rarely observed, product occurred in less than 30 of those many electrolyses had nano-morphology analogous to the macro-structure of bamboo, but had been only observed as a low fraction of the total product. Table 2 summarizes the systematic optimization of electrolysis conditions in 770° C. Li.sub.2CO.sub.3 to optimize and maximize the electrolytic formation of this nano-bamboo. A few prior electrolyses producing nano-bamboo were associated with nickel electrodes, or started with ramping up of the current to encourage nucleation. Experiment Electrolysis #I in the top row of Table 2 includes both these features including nickel as both the cathode and anode. A ramping increase in the electrolysis current was also applied as follows: an initial 10-minutes electrolysis at a constant 0.01 and then 0.02 A/cm.sup.2 for a further 10 minutes, followed by 5 minutes at 0.04 and then 0.08 A/cm.sup.2 for a further 5 minutes, after which the constant current electrolysis was conducted at 0.2 A/cm.sup.2, as shown in Table 2. Nano-bamboo was evident in the product SEM, but constituted a minority (30 wt %) of the total product. As seen in Electrolysis #II in Table 2, an increase in the nano-bamboo product was achieved with the direct addition of Ni and Cr additive powders to the electrolyte, and the anode was replaced by a noble metal (iridium) accompanied by a 5-fold decrease in current density. As noted in Table 2, this Electrolysis #II has the first majority, 60 wt %, of the nano-bamboo product. Coulombic efficiency quantifies the measured available charge (current multiplied by the electrolysis time) to the measured number of 4 electrons per equivalent of C in the product. Coulombic efficiency tends to drop off with a lower current density, and in this case the coulombic efficiency of the synthesis was 79%. The coulombic efficiency may approach higher values at low current density by lowering system impurities.
TABLE-US-00002 TABLE 2 Systematic variation of CO.sub.2 splitting conditions in 770° C. Li.sub.2CO.sub.3 to optimize formation of nano-bamboo and nano-pearl carbon allotropes. Current Additives Electrolysis density Product Electrolysis # Cathode Anode (wt % powder) time A/cm.sup.2 Description I Nickel Nickel — 4 h 0.2 30% nano-bamboo carbon 40% regular CNT rest: graphitic Carbon II Muntz Iridium 0.4% Ni 18 H 0.08 60% nano-bamboo brass 0.4% Cr carbon 10% regular CNT rest: graphitic Carbon III Muntz Inconel 718 0.81% Ni 18 h 0.08 89% 30-120 μm Brass 2 layers powder nano-bamboo Inconel 600 carbon IV Muntz Inconel 718 0.81% Ni 18 h 0.08 94% 30-80 μm Brass 2 layers powder carbon nano- Inconel 600 bamboo, 6% conical carbon nanofiber V Muntz Inconel 718 0.81% Ni 18 h 0.08 94% 30-80 μm Brass 2 layers powder carbon nano-bamboo, Inconel 600 6% conical carbon nanofiber VI Nichrome C Nichrome C 0.4% Ni 3 h 0.4 95% nano-bamboo 0.4% Cr carbon VII Monel Nichrome C 0.81% Ni 18 h 0.08 95% hollow nano- onions VIII Monel Nichrome C 0.4% Ni 18 h 0.08 97% nano-pearl 0.4% Cr carbon IX Monel Nichrome C 0.4% Ni 18 h 0.08 97% nano-pearl 0.4% Cr carbon
[0224] Without being bound by any particular theory, the low current ramping, pre-electrolysis conditions can have benefits and disadvantages. For example, as a benefit the current ramping conditions may support the reduction and deposition of initial graphene layers to facilitate ongoing reduction and growth. In addition, lower current can favor transition metal deposition at the cathode and formation of nucleation sites. While at low concentrations compared to carbonate (from CO.sub.2) in the electrolyte. The analysis of bound versus free metal cations in the molten electrolyte for a reduction potential calculation has been a challenge. However, without Nernst activity and temperature correction, the reduction rest potentials of Ni, Fe, Cr and Cu and CO.sub.2 at room temperature are CO.sub.2(IV/0)=−1.02, Cr(III/0)=−0.74, Fe(II/0)=−0.44, Co(II/0)=−0.28, Ni(II/0)=−0.25, Fe(III/0)=−0.04, Cu(II/0)=0.34, and Co(III/0)=1.82. Note however, that the free activity of tetravalent carbon as carbonate C(IV)O.sub.3.sup.2− formed by the reaction of C(IV)O.sub.2 with electrolytic oxide in pure molten carbonate solutions was many orders of magnitude higher than the dissolved transition metal ion activity in the electrolysis electrolyte. This helps favor the thermodynamic and kinetic reduction of the tetravalent carbon, over metal deposition at the cathode. However, the practical observation was that, for the majority of molten carbonate CO.sub.2 electrolyses studied, the initial low current ramping does not appear to promote the highest purity carbon deposition.
[0225]
[0226] The first row (Panels #III) of
[0227] The continued use of high concentrations of added transition metal powder to the electrolyte, and low current density, but a change of electrodes yields another distinct nano carbon allotrope termed here as “hollow nano-onions”. Specifically, in Electrolysis #VII in Table 2 and
[0228]
[0229]
[0230] The top row of
[0231] The conical CNF, nano-bamboo and nano-pearl are new and unusual high yield carbon allotropes as synthesized by molten electrolysis. Similar CVD synthesized morphologies have been synthesized by CVD. In particular the CVD conical CNF structure has been widely characterized as shown in the upper row of
[0232]
[0233]
Example 2—Electrochemical Conditions to Synthesize a CNM Product with Nickel Coated CNTs, a Nano-Onion Allotrope or a Nano-Flower Allotrope
[0234]
[0235] A nickel anode or an excess of added nickel leads to nickel coated CNTs. Rather than forming alternative allotropes, such as nano-bamboo or nano-pearl, the use of excess nickel, particularly when employed with: (i) a stainless steel cathode; (ii) when utilized at higher electrolysis current densities; and, (iii) with the activation by an initial current ramp tends to coat the carbon nanotube with nickel. This was summarized in the top row of Table 3 as Electrolysis #X, in which 0.81 wt % Ni powder was added to the Li.sub.2CO.sub.3 electrolyte, and Nichrome C was used as the anode. The electrolysis was conducted at 0.20 A/cm.sup.2 and exhibits a coulombic efficiency of 98.9%. The Ni coating was further improved (appearing more uniform in the SEM) in Electrolysis XI in Table 3 and as the top row in
[0236] Without being bound by any particular theory, the presence of an excess amount of nickel, along with the other articulated operational parameters of the electrolysis reaction, contributed towards the external coating of nickel forming on the outer surface of the CNTs. The excess nickel can be established in the electrolysis reaction as a result of additive (including as the metal, a metal mix, a metal oxide, a mix of metal oxides, a metal salt or a metal salt mix) melting point of Li.sub.2CO.sub.3 is 723° C. Another the inner walls of the electrolytic cell degrading during the electrolysis reaction, the cathode degrading during the electrolysis reaction, the anode degrading during the electrolysis reaction or any combination thereof. As such, when methods employ other articulated operational parameters—including a steel cathode—that resulted in nickel coated CNTs, an excess amount of other metals or metal-containing compounds may also result in CNTs that are coated in the other metals. For example, an excessive amount of a metal—other than nickel—such as, but not limited to: iron, titanium, tin, copper, vanadium, cobalt, zinc, magnesium, aluminium, ruthenium, silver, iridium, palladium, rhodium, and platinum are contemplated as resulting in a metal-coated CNM product and metal-coated CNT allotropes within the CNM product. In addition, excess amounts of metal mixes, metal oxides or any combination thereof are also contemplated herein. In summary, a coating on a allotrope that comprises one metal, a metal mix or a metal oxide are collectively referred to as a metal-coated allotrope.
[0237] In some embodiments of the present disclosure, the entire CNM product may be coated. In some embodiments of the present disclosure, the desired allotrope within the CNM product may be coated in metal. For example, employing the embodiments described herein, methods may be employed so that one or more desired allotropes are coated in metal, where such desired allotropes include, but are not limited to: metal-coated carbon nanotubes (CNTs), metal-coated graphitic carbon, metal-coated nano-bamboo, metal-coated conical carbon nanofibers, metal-coated nano-pearls, metal-coated nano-onions, metal-coated hollow nano-onions, metal-coated nano-flowers, metal-coated nano-dragons, metal-coated branch and trunk CNTs (metal-coated nano-trees), metal-coated nano-belts, metal-coated nano-rods, metal-coated long and/or straight CNTs, metal-coated high aspect ratio CNTs, metal-coated thin CNTs and macroscopic assemblies of CNTs, including densely packed, straight metal-coated CNTs, metal-coated nano-sponges and metal-coated nano-webs. In some embodiments of the present disclosure, the relative amount of the metal-coated allotrope—within the total amount of the allotrope present in the CNM product—is between about 5 wt % and about 99.5 wt %. In other embodiments of the present disclosure, the relative amount of the metal-coated allotrope is between about 7.5 wt % and about 97.5 wt %, between about 10 wt % and about 95 wt %, between about 20 wt % and about 92.5 wt % or between about 30 wt % and about 90 wt %.
[0238] Without being bound by any particular theory, the exclusion of transition metals from the molten electrolysis environment may prevent their activity as nucleation points for carbon growth and suppress the growth of carbon nanotubes. Suppression of the metal nucleated growth of CNTs, such as through use of a noble metal anode, was an effective means to promote the growth of another nanocarbon: carbon nano-onions. Here, another molten electrolysis pathway was found to ensure a high nano-onion product yield, through addition of lithium phosphate to the electrolyte. As summarized in Electrolyses XII and XIII in Table 3, with the addition of 8 wt % Li.sub.3PO.sub.4 to the Li.sub.2CO.sub.3 electrolyte, the product was nearly pure (97-98%) carbon nano-onions, as summarized in Table 3. This nano-onion product was the observed to be the case for a wide range of electrolysis synthesis current densities (0.08 to 0.20 A/cm.sup.2), with either Muntz Brass or Monel as the cathode, and with (Electrolysis #XII) or without (Electrolysis #XIII) inclusion of an initial current ramp step during the electrolysis.
[0239] A variation of the low current density, Muntz Brass cathode, Nichrome C anode, aged electrolyte leads to a fascinating new high purity molten electrolysis nanocarbon allotrope: nano-flowers. Specifically, after the 24 aging of the electrolyte, an excess (0.081 wt %) of chromium metal powder was added to the electrolyte. The electrolysis was conducted at 0.08 A/cm.sup.2 and exhibits a coulombic efficiency of 78%. The electrolyses are repeated (as Electrolyses #XIV and XV) and yield the same results as summarized in Table 3, and shown by SEM in
TABLE-US-00003 TABLE 3 Systematic variation of CO.sub.2 electrolysis splitting conditions in 770° C. Li.sub.2CO.sub.3 to optimize formation of nickel coated CNTs and onion, flower, dragon, belt and rod nanocarbon allotropes. Current Additives Electrolysis density Product Electrolysis # Cathode Anode (wt % powder) time A/cm.sup.2 Description X SST Nichrome C 0.81% Ni 3 h 0.2 60% Ni particle coated CNT 40% 5-10 μm CNT XI SST Nickel — 4 h 0.15 89% 50-150 μm straight CNT & Ni particle coated CNT XII Muntz Nichrome C 8% Li.sub.3 PO.sub.4 4 h 0.2 98% nano-onions Brass XIII Monel Nichrome C 8% Li.sub.3 PO.sub.4 18 h 0.08 97% nano-onions XIV Muntz Nichrome C 0.81% Co 18 h 0.08 97% nano-flowers Brass XV Muntz Nichrome C 0.81% Co 18 h 0.08 97% nano-flowers Brass XVI Monel Inconel718 0.1% Fe.sub.2O.sub.3 2 h 0.4 94% 50-100 μm nano-dragon XVII Muntz Inconel 718 0.1% Li.sub.2O 4 h 0.13 nano-trees: Brass 2 layers 98% 80-200 μm Inconel 600 CNT with branches and trunk XVIII Muntz Inconel 718 0.1% Fe.sub.2O.sub.3 18 h 0.08 80% nano-belt Brass XIX Monel Iridium 0.81% Ni 18 h 0.08 91% nano-rod CNT
Example 3—Electrochemical Operating Parameters to Synthesize a CNM Product with Desired Allotropes of: Nano-Dragons, Nano-Trees, Nano-Belts and Nano-Rods
[0240]
[0241]
[0242]
[0243]
[0244]
[0245]
[0246] Variation of the electrochemical conditions of CNT product formation to those of Electrolysis #XVI lead to a change in allotrope from carbon nanotubes to another fascinating morphology referred to here as nano-dragons and presented in Table 3 and
[0247] It is known that the addition of low levels of lithium oxide has led to high quality of CNTs. With use of a specific anode (Inconel 718 with two layers of Inconel 600) the quality of the product was retained, but the morphology of the CNT changes substantially. The inventors have previously observed larger transition metal nodule growth from the CNTs. With the addition of Li.sub.2O, branched carbon nano-trees are included as Electrolysis #XVII in Table 3 and
[0248] TEM and HAADF elemental analysis of the nano-flower, nano-dragon, nano-belt and nano-tree structures are presented in
[0249]
[0250] In
[0251] Without aging the electrolyte (freshly melted electrolyte), the low current density (0.08 A/cm.sup.2, exhibiting a coulombic efficiency of 80%), long term growth (18 hour) growth of carbon nanotubes with a Monel cathode, iridium anode, 0.81% Ni, and no ramped current activation step, leads to squat, ring-like nano-rod allotropes, as seen in
Example 4—Raman Spectroscopy and XRD Analysis of Various Nano-Carbon Allotropes
[0252]
[0253]
TABLE-US-00004 TABLE A Reference numbers used in FIG. 15, 16A and 16B. # text 1502 Multi-wall Carbon Nanotube 1503 Hollow Nano-onion 1504 Helical Carbon Nanotube 1505 Nano-dragon 1506 Nano-flower 1507 Nano-tree 1508 Bamboo-shaped CNT 1509 Nano-pearl 1510 Nano-rod 1511 Carbon Nanofiber 1512 Nano-belt 1513 Nano-bamboo 1602 2θ = 20-25 degree 1604 2θ = 30-60 degree 1605 Graphite C 1606 Lithium Nickel Oxide Li.sub.2Ni.sub.8O.sub.10 1607 Lithium Chromium Oxide LiCrO.sub.2 1608 Cohenite Fe.sub.3C 1609 Lithium Copper Oxide Li.sub.2CUO.sub.2
[0254]
[0255] The top row and middle row of
[0256]
[0257] The intensity ratio between D band and G band (I.sub.D/I.sub.G), which may also be referred to herein as the I.sub.D/I.sub.G ratio, is a useful parameter to evaluate the relative number of defects and degree of graphitization and, therefore, the I.sub.D/I.sub.G ratio can be presented as a range of values (or as a specific number) in order to distinguish one type of nanocarbon structure from another, such as the allotropes described herein. Table 4 summarizes Raman band peak locations and includes calculated (I.sub.D/I.sub.G) and (I.sub.2D/I.sub.G) peak ratios for the various carbon allotropes. A higher ratio I.sub.D/I.sub.G or a shift in I.sub.G frequency is thought to be a measure of increased defects in the carbon graphitic structure. It is also thought that defects that can occur in the graphitic structure include replacement of carbon sp.sup.2 bonds, typical of the hexagonal carbon configuration in the graphene layers comprising the structures, with sp.sup.3, and increase in pores or missing carbon in the graphene, and enhance defects that cause formation of heptagonal and pentagonal, rather than the conventional hexagonal graphene building blocks of graphene.
TABLE-US-00005 TABLE 4 Raman spectra of a diverse range of carbon allotropes formed by molten electrolysis. CO.sub.2 molten electrolysis product description v.sub.D(cm.sup.−1) v.sub.G(cm.sup.−1) v.sub.2D(cm.sup.−1) I.sub.D/I.sub.G I.sub.2D/I.sub.G Multi-wall Carbon Nanotube 1342.4 1576.5 2688.7 0.30 0.60 Hollow Nano-onion 1346.3 1577 2694.6 0.33 0.61 Helical Carbon Nanotube 1346.1 1578.2 2692.8 0.45 0.40 Nano-dragon 1346.7 1580.3 2695.0 0.67 0.62 Nano-flower 1347.9 1582.7 2692.2 0.78 0.50 Nano-tree 1343.7 1583.7 2696.4 0.82 0.47 Nano-bamboo 1352.0 1586.2 2696.9 1.04 0.72 Nano-pearl 1352.9 1588.5 2689.3 1.05 0.52 Nano-rod 1351.6 1586.0 2695.9 0.78 0.81 Carbon Nanofiber 1348.3 1594.9 2696.0 1.27 0.37 Nano-belt 1348.5 1590.5 2705.1 1.30 0.41
[0258] Typically I.sub.D/I.sub.G for multi-walled carbon nanotubes is in the range of 0.2 to 0.6. Compared to these values, with the exception of the hollow nano-onions, the new carbon allotropes, made according to embodiments of the present disclosure, generally exhibit a higher than 0.6 I.sub.D/I.sub.G, evidence of a higher number of defects and perhaps consistent with the greater morphological complexity of these new allotropes. The nano-bamboo, nano-pearl, nano-rod and nano-belts each exhibit a relatively high level of defects, often associated with greater pores and twists and turns in the structure due to the higher presence of sp.sup.a carbons. As observed from Table 4, the order of the increasing I.sub.D/I.sub.G ratio is:
CNT<hollow nano-onion<dragon<flower<nano-trees<bamboo<pearl<rod<CNF<belt
[0259] The shift to higher frequencies of the frequency, v, of the G band generally correlates with the observed I.sub.D/I.sub.G variation, with variations due to near lying ratios, and with the exception of an unusually large shift observed for nano-bamboo.
[0260] High levels of Ni, Cr or Co added to the electrolyte (nano-bamboo, nano-pearl, and nano-flower allotropes) also appear to correlate with an increase in defects, and the very high added Ni powder used in the nano-rod synthesis correlates with a very high level defects as indicated by the shift in I.sub.G frequency and an increase in I.sub.D/I.sub.G. Previously, increased concentrations of iron oxide added to the Li.sub.2CO.sub.3 electrolyte had correlated with an increasing degree of disorder in the graphitic structure. Interestingly, it is the synthesis with a low level of added iron oxide powder (but only added prior to the 24 hour aging of the electrolyte) that resulted in the allotrope with the highest level of defects, the nano-belt allotrope.
[0261] Lower defects are associated with applications that require high electrical conductivity and strength, while high defects are associated with applications which permit high diffusivity through the structure such as those associated with increased intercalation and higher anodic capacity in Li-ion batteries and higher charge super capacitor.
[0262] Along with the XRD library of relevant compound spectra, XRD is presented in
[0263] Without being bound by any particular theory, the nanocarbon allotropes made according to embodiments of the present disclosure may lead to unusual physical chemical properties with implications useful to applications, such as those utilizing the high strength, high thermal, magnetic, electronic, piezoelectric, tribological characteristics of graphene-based materials, but which distribute these properties differently throughout the unusual geometries of these novel allotropes. For example, alternative applications such as high capacity lithium anodes, unusual electronics, EMF shielding, improved lubricants, and new structural or polymer composites are contemplated.
[0264] Examples 1 through 4 describe nanocarbon allotropes made according to embodiments of the present disclosure and were analysed by SEM, TEM, TEM with HAADF, Raman and XRD. With the exception of the nano-rod structure, each of the structures was graphitic in nature containing graphene layers arranged in a variety of geometries. The graphene layers exhibit the characteristic, inter-layer spacing of 0.33 to 0.34 nm. Except for the presence of Ni, Fe, Cr and occasionally Cu, which may serve as nucleating growth sites, each of the structures was pure carbon. Generally, intersecting graphene layers did not merge, but in in the nano-tree allotrope the graphene layers bend at intersections leading to the observed branched structure.
[0265] Many of the structures including nano-bamboo, nano-pearl, Ni-coated CNTs and conical CNFs exhibit walls containing concentric graphene layers. The nano-dragon and nano-belt structures include layered planer or planar-twisted graphene layers. Several of the observed structures, including nano-trees, and hollow and filled nano-onions exhibit concentric, highly spherical graphene layers generally composed of carbon and containing a low level of internal transition metal. Without being bound by any particular theory, the embodiments of the present disclosure may provide a new synthetic pathway to the formation of nano-onions via phosphate addition to the electrolyte, which may be facilitated by phosphate selectively binding transition metal ions.
[0266] All electrochemical methods from Electrolysis #IV onward produced a high purity product of the stated allotrope, with the exception of the conical CNFs that were a minority (6%) within a majority of nano-bamboo carbon, and the moderate purity (85%) nano-belt carbon product. Coulombic efficiency of the electrolyses ranged from 79 to 80% at lower current densities of 0.08 A/cm.sup.2, to over 99% at current densities of 0.2 A cm.sup.2 or higher. The high purity products each exhibited sharp XRD graphic peaks, and a moderate (0.3 to 1.3) Raman I.sub.D/I.sub.G ratio indicative of a moderate level of defects in the carbon structure. In addition to a majority of pure, graphitic carbon, the XRD also exhibited different singular or mixed transition metal salts of either iron carbide, or nickel, chromium or copper lithiated oxides.
[0267] TEM HAADF of the new nanocarbon allotropes showed that their inner core was generally free of metals (void, with the walls 100% carbon), but in other areas the void was filled with transition metals of Ni, Fe and/or Cr. With the exception of the nano-rod allotrope, each of the allotropes included distinct graphene layers with a graphene characteristic, inter-layer spacing of 0.33 to 0.34 nm. Depending on the allotrope, adjacent graphene layers were organized either in a planer, cylindrical or spherical geometry. When the internal transition metal was within the allotrope tip, the layered graphene walls are observed to bend in a highly spherical fashion around the metal supporting the transition metal nucleated CNT growth mechanism. The use of a nickel anode, or an excess of added nickel to the electrolyte, lead to coated nickel coated CNTs when stainless steel was used as the electrolysis cathode. Generally, intersecting graphene layers did not merge, but in the nano-tree allotrope, with a trunk CNT and branch CNTs that extend away from the trunk CNT, the graphene layers bend (or are bent) to become part of a CNT intersection consistent with branching.
[0268] Without being bound by any particular theory, molten carbonate electrolysis of CO.sub.2 provides an effective path for the synthesis of a portfolio of the unusual, valuable nanocarbon allotropes of Examples 1 through 4. Mass production of these allotropes from CO.sub.2 may provide a valuable incentive to consume this greenhouse gas. Such allotropes are rare, or were previously non-existent, and are not generally commercially available. However, those that are in use, such as nano-onions—which is known to be made by pyrolysis of nano-diamonds or by CVD—have a high carbon footprint and have associated costs at over $1 million/tonne. CNT production by the molten carbonate electrolysis of CO.sub.2 is a low cost synthesis, comparable to the cost of aluminum oxide splitting in the industrial production of aluminum. The new allotrope synthesis conditions consist of small variations of the scaled molten carbonate electrolysis process with a comparable, straightforward path to scale-up to contribute to consumption of CO.sub.2 and climate change mitigation.
Example 5—Electrolysis Operational Parameters for Making a CNM Product with a High Purity/High Yield of CNTs
[0269] Further embodiments of the present disclosure relate to electrochemical process conditions that yield a high purity, high yield CNT product by electrolysis of CO.sub.2 in 770° C. lithium carbonate. An in depth look at the material composition and morphologies of the products was conducted, particularly around the transition metal nucleation zone of CNT growth. The latter part of this discovery reveals molten electrochemical conditions that produce macroscopic assemblies of CNTs.
[0270]
TABLE-US-00006 TABLE 5 A variety of Electrolytic CO.sub.2 splitting conditions in 770° C. Li.sub.2CO.sub.3 producing a high yield of carbon nanotubes. Current Additives Electrolysis density Product Electrolysis # Cathode Anode (wt % powder) time A/cm.sup.2 Description A Muntz Nichrome C 0.1% Fe.sub.2O.sub.3 0.5 h 0.6 97% Straight Brass 50-100 μm CNT B Muntz Nichrome A 0.1% Fe.sub.2O.sub.3 4 h 0.15 94% Straight Brass 20-80 μm CNT C Muntz Inconel 718 0.1% Fe.sub.2O.sub.3 4 h 0.15 96% curled CNT Brass 0.1% Ni D Muntz Nichrome C 0.1% Fe.sub.2O.sub.3 15 h 0.08 70% Brass 10-30 μm CNT E Muntz Inconel 625 0.1% Fe.sub.2O.sub.3 15 h 0.08 97% Brass 3 layers 20-50 μm CNT Inconel 600 F Muntz Inconel 718 0.1% Fe.sub.2O.sub.3 4 h 0.15 98% straight Brass 2 layers 100-500 μm CNT Inconel 600 G Muntz Inconel 718 0.1% Fe.sub.2O.sub.3 15 h 0.08 90% Curled Brass 3 layers 0.1% Ni CNT or fibers Inconel 600 H Muntz Nichrome C 0.1% Fe.sub.2O.sub.3 1 h 0.4 96% Straight Brass 100-200 μm CNT I Monel Nichrome C 0.1% Fe.sub.2O.sub.3 1 h 0.4 97% Straight 20-50 μm CNT J Monel Nickel / 2 h 0.2 70% thin 10-20 μm CNT Rest: Onions K Monel Nichrome C 0.1% Fe.sub.2O.sub.3 2 h 0.1 97% 30-60 μm straight CNT L Monel Nichrome C 0.5% Fe.sub.2O.sub.3 15 h 0.08 ~25% curled CNT ~70% straight CNT M Monel Iridium 0.81% Cr 18 h 0.08 97% thin 50-100 μm CNT
[0271] The electrochemical process conditions that relate to the high purity CNT synthesis were systematically varied to determine other electrochemical conditions support the high purity, low defect synthesis of straight (non-helical) CNTs. Examples of the conditions which are varied are: composition of the cathode, composition of the anode, additives to the lithium carbonate electrolyte, current density and time of the electrolysis. Variations of the electrodes include the use of cathode metal electrodes such as Muntz brass Monel, or Nichrome alloys. Anode variations include noble anodes such as iridium, various nickel containing anodes including nickel, Nichrome A or C, Inconel 600, 625, or 718, or, specific layered combinations of these metals. Electrolyte additives that are varied include Fe.sub.2O.sub.3, and nickel or chromium powder, and electrolyses are varied over a wide range of electrolysis current densities. Several electrolyses studied here which yield high purity, high yield carbon nanotubes are described in Table 5. Scanning electron microscopy (SEM) of the products of a variety of those CNT syntheses as conducted by CO.sub.2 electrolysis in molten Li.sub.2CO.sub.3 at 770° C. are presented in
[0272] For Electrolysis #A, the top row of Table 5 presents electrochemical conditions, and the top row of
[0273] In the second row of
[0274] At a low current density of 0.08 A/cm.sup.2, with an electrolyte additive of 0.1 wt % Fe.sub.2O.sub.3, the conventional Muntz Brass and Nichrome electrodes exhibit a significant drop in CNT product purity to 70%. Coulombic efficiency tends to drop off with current density, and in this case the coulombic efficiency of the synthesis was 82%. Product purity can be increased by refining the mix of transition metals available during the electrolytes or increasing surface area. Alloy composition of the metals used as electrodes is presented in Table 1. Metal variation was further refined by combining the metals in Table 1 as anodes, for example using a solid sheet of one Inconel alloy, layered with a screen or screens of another Inconel alloy. This approach is utilized in the lowest row of
[0275]
[0276] The syntheses listed in Table 5 delineate the electrochemical growth conditions for the high purity growth of carbon nanotubes each exhibiting the characteristic concentric multiple graphene cylindrical walls. This is observed in
[0277] On the right side of row 2 of
Example 6—Electrolysis Operating Parameters for Making a CNM Product with High Aspect Ratio CNTs
[0278]
[0279]
[0280]
[0281]
Example 7—Electrolysis Operating Parameters for Making a CNM Product as a Thin CNT Allotrope
[0282]
[0283]
[0284]
[0285] SEM of several of the CNM products, specifically Electrolyses #H, #B and #C, exhibit evidence of nodules that appear as “buds” attached to the CNTs. This nano-bud allotrope is most consistent in Electrolysis #H and are further explored by TEM and HAADF in
Example 8—Electrolysis Operating Parameters for Making a CNM Product with Macroscopic Assembly of Nanocarbon Allotropes
[0286] In addition to synthesizing individual CNTs, this Example 8 provides series of electrolyses that generate useful macroscopic assemblies of CNTs. There has been interest in densely packed CNTs for nano-filtration, and also due to their high density of conductive wires as an artificial neural net. The macroscopic assemblies made according to embodiments of the present disclosure are referred to as nano-sponge, densely packed parallel CNTs, and nano-web CNTs in Table 6 and
TABLE-US-00007 TABLE 6 Systematic variation of CO.sub.2 splitting conditions in 770° C. Li.sub.2CO.sub.3 to optimize formation of macroscopic assemblies of nanocarbons with densely packed carbon nanotubes. Current Additives Electrolysis density Product Electrolysis # Cathode Anode (wt % powder) time (A/cm.sup.2) description N Nichrome Nichrome C 0.81% Ni 4 h 0.2 97% nano-sponge C CNT F Muntz Inconel 718 0.1% Fe.sub.2O.sub.3 4 h 0.15 98% densely Brass 2 layers packed straight Inconel 600 100-500 μm CNT P Muntz Nichrome C 0.1% Fe.sub.2O.sub.3 15 h 0.08 97% 50-100 μm Brass 3 layers nano-web CNT Inconel 600 Q Monel Nichrome C 0.81% Ni 3 h 0.2 92% 5-30 μm nano-web CNT Rest: onions
[0287]
[0288] The Nano-sponge allotrope was formed by Electrolyses #N with Nichrome C serving as both the cathode and the anode, with 0.81% Ni powder added to the 770° C. Li.sub.2CO.sub.3 electrolyte, the initial current ramped upwards (5 min each at 0.008, 0.016, 0.033 and 0.067 A/cm.sup.2), then a 4 h current density of 0.2 A/cm.sup.2 generating a 97% purity nano-sponge at 99% coulombic efficiency. As previously described, long densely packed, parallel carbon nanotubes are produced in Electrolysis #F with a 0.1 wt % Fe.sub.2O.sub.3 additive to the Li.sub.2CO.sub.3 electrolyte, a Muntz Brass cathode and an Inconel 718 anode and 2 layers of Inconel 600 screen at 0.15 A/cm.sup.2. As opposed to the parallel assembly produced in Electrolysis #F, nano-web aptly describes the interwoven carbon nanotubes from Electrolyses #P and #Q, presented in the lower rows of Table 6 and
[0289] The densely packed, straight CNTs define an inter-CNT spacing that ranges from 50 nm to 1 μm, moreover the CNTs are highly aligned, which may also be referred to as a substantially parallel—with each other, providing unusual nano-filtration opportunities for both this size domain and for an opportunity to filter 1D from 3D morphologies. The nano-sponge does not have this alignment feature, and from
Example 9—Raman Spectroscopy and XRD Characterization of the CNM Products of Examples 5-8
[0290]
TABLE-US-00008 TABLE 7 Raman spectra of a diverse range of carbon allotropes and macro-assemblies formed by molten electrolysis. CO.sub.2 Molten Electrolysis Product Description ν.sub.D(cm.sup.−1) ν.sub.G(cm.sup.−1) ν.sub.2D(cm.sup.−1) I.sub.D/I.sub.G I.sub.2D/I.sub.G Nano-web 1342.5 1577 2689.6 0.28 0.50 Densely packed, 1342.5 1577.4 2694.8 0.46 0.49 straight CNTs Nano-sponge 1352.5 1580.6 2687.3 0.67 0.62
[0291]
[0292]
[0293] Interpretation of the Raman spectra provides insight into potential applications of the various carbon allotropes. From
[0294] For the assemblies with increasing I.sub.D/I.sub.G ratio:
[0295] CNT nano-web<Densely packed CNT<CNT nano-sponge
[0296] It has been previously demonstrated that an increased concentration of iron oxide added to the Li.sub.2CO.sub.3 electrolyte had correlated with an increasing degree of disorder in the graphitic structure. It should be noted that these defect levels each remain relatively low as the literature is replete with reports of multi-walled carbon nanotubes made by other synthetic processes with I.sub.D/I.sub.G>1. Lower defects are associated with applications that require high electrical and strength, while high defects are associated with for applications which permit high diffusivity through the structure such as those associated with increased intercalation and higher anodic capacity in Li-ion batteries and higher charge super capacitors.
[0297] Along with the XRD library of relevant compound spectra, XRD is presented in
Example 10—Scaled-Up Electrolysis Operating Parameters for Making a CNM Product with a High Purity of Desired Nanocarbon Allotropes
[0298] This example demonstrates that various nanocarbon allotropes can be electrosynthesized with a high yield with high purity using larger electrodes and simpler, modified conditions. Each of the three cases used in this Example 10 generated three different and high purity allotrope products: (i) CNTs; (ii) carbon nano-onions; or, (iii) carbon nano-pearls, using similar electrolysis operational parameters, but using different anode shapes, as well as different electrolysis current densities, each of which can influence which metals enter the electrolyte. Each of the three electrosyntheses were conducted in a 750° C. molten Li.sub.2CO.sub.3 electrolyte with a Muntz brass cathode with a two sided, active surface area that was about 39 cm tall x 34.5 cm wide (with a surface area of about 1,345.5 cm.sup.2), per side. The cathode was sandwiched by between a stainless steel 304 anode. In the first two cases (i) and (ii) the electrolysis was conducted at a constant current density of about 0.2 A/cm.sup.2 with a 98% CO.sub.2 inlet at 1.9 L/min, and the third (iii) case was conducted at a lower constant current density of about 0.07 A/cm.sup.2 with a CO.sub.2 inlet at 0.8 L/min. In addition to current density, a further difference in the three cases was the shape of the stainless steel anode that sandwiched both sides of the cathode. In the first case (i), the anode was a solid steel plate, a product with a high purity of a CNT allotrope was generated. After washing to remove excess electrolyte, the TGA of the product and the derivative of the TGA is shown in
[0299] In the second case (ii), the anode was a fresh steel (Dutch weave) screen, and as seen in
[0300] The melting point of Li.sub.2CO.sub.3 is 723° C. Another means observed to generate carbon nano-onions—instead of using the screen, a simpler flat plate stainless steel anodes is used, and found to be additionally effective on both the first and on subsequent electrolyses, is initiating the electrolysis at a lower temperature in which the electrolyte is only partially melted. This also forms a highly pure carbon nano-onion product. For example, in repeated runs of the electrolysis reaction a CNM product with carbon nano-onions with demonstrated TGA residues of 5.3% and 7.4%. Without being bound to any theory, this carbon nano-onion formation is in accord with another example of a suppressed formation of nucleation sites on the cathode, which inhibits carbon nanotube formation, and favors highly pure carbon nano-onion formation.
[0301] In the third case (iii), the anode was a sheet of perforated steel. After washing to remove excess electrolyte, the TGA of the product and the derivative of the TGA is shown in