Method and system for producing doped carbon nanomaterials

Abstract

An effective method for producing doped carbon nanomaterials from molten carbonate materials is provided. A system and process for producing doped carbon nanomaterials is disclosed. A carbonate electrolyte containing a doping component is supplied between an anode and a cathode immersed in the carbonate electrolyte contained within a cell during electrolysis. The carbonate electrolyte is heated to a molten state. An electric current is applied to the anode, the cathode, and the molten carbonate electrolyte disposed between the anode and the cathode. Morphology factors maximize carbon nanotube versus graphene, carbon nanoonions, and hollow carbon nanosphere nanomaterial products. The resulting carbon nanomaterial growth is collected from the cathode of the cell.

Description

[Technical Field]

[0001] Copyright A portion of the disclosure of this application contains material that is subject to copyright protection. The copyright owner has no objection to the ability of anyone to copy the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.

[0002] Priority This application claims priority to U.S. Provisional Patent Application No. 62 / 461,641, filed February 27, 2017, the entire contents of which are incorporated herein by reference.

[0003] The present invention relates to the production of doped carbon nanomaterials (carbon nanomaterials with small amounts of impurities added), and in particular to the production of doped carbon nanomaterials from molten carbonate electrolytes (electrolytic solutions). [Background technology]

[0004] Prior to the recognition of various unique carbon nanoscale structures, such as fullerenes, nanotubes, and nanofibers, beginning in 1985, the reduction of carbonates from hydroxides and barium chloride / carbonate melts to (macroscopic, visible, macroscopic) carbon in inorganic molten electrolytes was recognized as early as the late 1800s. Today, the primary methods for producing carbon-doped nanomaterials are arc discharge, laser ablation of carbon substrates, and catalytic thermal chemical vapor deposition (CVD). Doping these carbon nanomaterials provides favorable properties, first observed in carbon nanotube products. These techniques are expensive and difficult to implement on a large scale, resulting in the current high cost of doped carbon nanotubes. Related graphene and carbon nano-onion structures are even more expensive to synthesize using these techniques.

[0005] Some CVD-doped carbon nanotubes have extraordinary and useful properties, including high electrical conductivity, catalysis, heavy metal removal, enhanced oxygen reaction rates, and improved charge storage. Sulfur-doped carbon has several potential applications, including heterogeneous catalysis, adsorption, and energy conversion and storage. However, to date, few approaches have been developed to intrinsically incorporate sulfur into the carbon matrix. N-type doped carbon has several potential applications, including oxygen oxidation and reduction, fuel cell catalysts, supercapacitors, and sensors. Boron doping is well known for creating metallic carbon nanotubes and enhancing their conductivity. Similarly, p-type doping of carbon can significantly affect their properties and applications, including lowering elongation-break, acting as an aerobic oxidation catalyst, and in batteries and ultrasensitive sensors. Boron and nitrogen are the most studied carbon dopants (impurities added to carbon) due to their similar size (and atomic number) to carbon.

[0006] Carbon nanomaterials have great potential as a material resource. Their excellent properties, including strength, electrical and thermal conductivity, flexibility, and durability, have led to applications ranging from reinforced composites, capacitors, lithium-ion batteries, nanoelectronics, and catalysts to key components in lightweight, high-strength building materials. Chemical vapor deposition or metal-organic reactions using arc discharge are among the most valuable, yet expensive, methods for producing carbon nanomaterials. When doping carbon nanomaterials using these methods is attempted, it is typically achieved as a post-synthesis treatment following these expensive synthesis steps. A recent innovation is the use of melt electrolysis for carbon nanomaterial production. In this process, a molten carbonate electrolyte is placed between a cathode and an anode, a transition metal nucleating agent is added, and an electric current is applied to the cathode. This process, in a single step and with low energy, produces a carbon residue on the cathode, which may contain carbon nanomaterials. The cathode in the melt electrolytic production of carbon nanotubes is the electrode on which the carbon product is deposited.

[0007] Previously, it was recognized in the prior art that carbon nanomaterials produced by molten carbonate electrolysis are undoped. It was not anticipated or even considered that doped carbon nanomaterials could be produced in a simple one-step synthesis by adding a doping component during electrolysis. The reasoning behind the hypothesis was that both the control of doping and the control of electrolyte deposition are highly orchestrated and complex activities. Therefore, it has never been fully considered that both doping and electrolyte growth of carbon nanomaterials can occur synergistically simultaneously in a molten medium at 700-800°C.

[0008] Therefore, there are generally limitations on the types of carbon nanotubes that can be produced on substrates by melt electrolysis. An inherent challenge with using undoped carbon nanomaterials is that while they retain excellent qualities of strength, thermal conductivity, and flexibility, they are not differentiated when it comes to target qualities such as electronic wire replacements, specialty catalysts, heavy metal adsorbents, or improved oxygen or charge storage materials. These undoped carbon nanomaterials alone would not be candidates to expand the current carbon nanomaterial market. Low-cost, high-strength doped carbon nanomaterials constitute a significant potential market for these materials as lighter-weight replacements for wires, catalysts, and electrodes.

[0009] Thus, there is a demand for the production of doped carbon nanomaterials, including carbon nanotubes, graphene, carbon nano-onions, and hollow carbon nanospheres, which could further enhance the utility of carbon nanomaterials. Lack of uniformity poses a challenge to the deployment of doped carbon nanomaterials produced by molten carbonate electrolysis. Previous barriers to doped carbon nanomaterials produced from molten carbonate carbon nanotube synthesis from carbon dioxide are being overcome, enabling one-pot molten electrolyte production of doped carbon nanomaterials. These materials are suitable for differentiated qualities such as electronic wire replacements, specialized catalysts, heavy metal adsorbents, or improved oxygen or charge storage materials. However, no doping element has been identified that enables the production of doped carbonate electrosynthesized carbon nanomaterials.

[0010] The electrolytic process for producing carbon nanotube products is based on the assumption that there is no effect of doping additives on the electrolyte, or on the cathode where carbon nanomaterials are formed, or on the anode where oxygen is produced in the electrolyte separation of molten carbonate into carbon and oxygen. In the electrolytic process, the cathode serves to provide nucleation sites but is not considered a source of dopants, and the anode forms a stable oxygen layer that is effective as an electrocatalyst for oxygen production during electrolysis, but is not considered a source of dopants during synthesis.

[0011] For example, it was previously thought that only the most dominant electrolyte additives affect the growth rate of carbon nanomaterials and are related to their morphology; therefore, the only additives of importance to the electrolyte are transition metal salts, which are reduced on the cathode and act as nucleating agents, producing oxides that form tangled rather than straight carbon nanotubes. Salt or gas additives in the electrolyte were not considered as potential sources of dopants during carbon nanomaterial growth. Summary of the Invention [Problem to be solved by the invention]

[0012] Thus, there is a need for an effective method for producing doped carbon nanomaterials from molten carbonate materials. There is also a need to selectively produce different morphologies of doped carbon nanomaterials, such as carbon nanotubes, carbon nano-onions, graphene, or hollow carbon nanospheres, each of which has unique utilities such as high strength, electrical conductivity, lubricity, high surface catalytic properties, and ion storage in batteries. There is also a need to control both the morphology and doping of carbon nanomaterials during molten carbonate electrolysis. [Means for solving the problem]

[0013] In one aspect, a method for producing doped carbon nanomaterials is disclosed. A carbonate electrolyte is heated to obtain a molten carbonate electrolyte. The molten carbonate electrolyte is placed between an anode and a cathode in a cell. A nanomaterial doping element, such as lithium sulfate or a sulfur dioxide (SO2) gas anode, is included in the cell's electrolyte. An electric current is passed through the anode and cathode in the cell. Doped or undoped carbon nanomaterial growth is recovered from the cell's cathode.

[0014] Another example is a method for producing undoped carbon nano-onions. Graphene or hollow carbon nanospheres are disclosed. A carbonate electrolyte is heated to obtain a molten carbonate electrolyte. The molten carbonate electrolyte is placed between an anode and a cathode in a cell. The transition metal that promotes carbon nanotube growth is removed, and a nanomaterial morphology selection factor, such as adding zinc oxide or applying an alternating current, is included. An electric current is passed through the cathode and anode in the cell. Undoped carbon nanomaterial growth, primarily consisting of carbon nano-onions, graphene platelets, or hollow carbon nanospheres, is recovered.

[0015] Another example is a system for producing carbon nanomaterials. The system includes a current source. The system includes a cell that holds a molten carbonate electrolyte between a cathode and an anode. A carbon nanomaterial doping component is located within the cell. The current source is capable of passing a current through the cathode and the anode within the cell, producing a doped carbon nanomaterial growing from the cathode within the cell.

[0016] Further aspects of the present invention will become apparent to those skilled in the art upon review of the detailed description of the various embodiments, with reference to the figures and brief description provided below. [Brief explanation of the drawings]

[0017] [Figure 1A] FIG. 1A is a block diagram of an electrolysis system for producing doped carbon nanomaterials from carbonates.

[0018] [Figure 1B] FIG. 1B is an illustration of several different techniques for producing carbon nanotubes and multiple forms of graphene carbon.

[0019] [Figure 2A] Figure 2A shows an SEM image of the product and a potential graph of the electrolysis measured using an inert iridium anode and a Monel cathode.

[0020] [Figure 2B] Figure 2B shows an SEM image of the carbon nanotube product using a copper or Monel anode with more nickel powder added to a lithium carbonate (Li2CO3) electrolyte at 770 °C.

[0021] [Figure 3A] FIG. 3A is an SEM image of product growth at the cathode-electrolyte interface under low nickel powder / iridium anode conditions, shown with the product peeled off from a Monel cathode.

[0022] [Figure 3B] Figure 3B is an SEM image of the absence of a nucleating agent, showing that nanostructures such as platelets, rather than carbon nanotubes, account for most of the product formation.

[0023] [Figure 3C] FIG. 3C is an SEM image without a nucleating agent, showing the growth of very thin graphene platelets and small carbon particles.

[0024] [Figure 4A]Figure 4A shows different SEM images of carbon nanotubes and carbon nano-onions produced using a nickel-chromium anode and a Monel cathode.

[0025] [Figure 4B] FIG. 4B is an SEM image of the nano-onion carbon product obtained without current cycling, and the carbon nanotube containing hollow nanosphere product.

[0026] [Figure 4C] Figure 4C is an SEM image of nano-onion carbon obtained by adding zinc oxide to Li2CO3 electrolyte at 770 °C without cycling.

[0027] [Figure 5] FIG. 5 is an SEM image of the boron-doped carbon nanotube product.

[0028] [Figure 6] Figure 6 shows SEM images of sulfur- or nitrogen-doped carbon nanotube products formed by electrolysis of Li2CO3 with either dissolved lithium sulfate (Li2SO4) or lithium phosphate (LiPO3), the respective sources of sulfur or phosphorus within the carbon nanotubes.

[0029] [Figure 7A] FIG. 7A is a table of experimental data showing that the carbonate electrolyte absorbs carbon dioxide at a rate sufficient to sustain maximum rates of molten electrolyte electrolysis and provides sufficient insulation so that molten carbonate electrosynthesis is self-heating and / or generates useful residual heat.

[0030] [Figure 7B] FIG. 7B plots the data obtained from the experimental data of FIG. 7A.

[0031] [Figure 7C]FIG. 7C is a graph showing that proper insulation retains most of the heat in the molten electrolysis chamber.

[0032] [Figure 7D] FIG. 7D is a graph showing that molten carbonate electrosynthesis is self-heating.

[0033] [Figure 8] FIG. 8 illustrates a synergistic pathway for doped or undoped carbon nanotube materials, including carbon nanotubes, graphene, carbon nano-onions, or hollow carbon nanosphere carbon nanomaterials.

[0034] While the invention is susceptible to various modifications and alternative forms, specific forms have been shown by way of example in the drawings and are described in detail herein. It should be understood, however, that the disclosure is not intended to be limited to the particular forms disclosed. Rather, the invention is intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. DETAILED DESCRIPTION OF THE INVENTION

[0035] The present invention can be embodied in many different forms. Representative examples are shown in the drawings and described in detail herein. The present disclosure is an example or illustration of the principles of the present disclosure and is not intended to limit the broad interpretation of the disclosure to the described examples. To that extent, elements or limitations disclosed, for example, in the Excerpt, Summary of the Invention, and Detailed Description sections, but not expressly set forth in the claims, should not be incorporated into those claims, either individually or collectively, by implication, inference, or otherwise. Furthermore, for purposes of the detailed description, unless expressly stated otherwise, the singular includes the plural, and vice versa, and the word "including" means "including without limitation." Furthermore, words meaning approximations such as "about," "almost," "approximately," and "approximately" are used herein to mean, for example, "at, near, or in the vicinity of," or "within 3 to 5%," or "within acceptable manufacturing tolerances," or logical combinations thereof.

[0036] FIG. 1A is a block diagram of an example system 100 for producing doped carbon nanomaterials from carbonate materials. The system 100 includes a carbonate furnace 102, an electrolysis chamber 104, and a collector 106. While the furnace 102, electrolysis chamber 104, and collector 106 are shown as separate components in FIG. 1A, they may be located within the same physical structure. The electrolysis chamber 104 includes a chamber 110 (cell) that holds a molten carbonate electrolyte produced by heating the carbonate in the furnace 102 and further includes a morphology element 120 to maximize the production of carbon nanotubes (compared to graphene, nano-onions, and hollow nanospheres). The chamber 110 contains a doping element 122 to maximize product formation of doped carbon nanomaterials relative to undoped carbon nanomaterials. The anode 112 and cathode 114 are coupled to a power source 116. The anode 112 and cathode 114 are inserted into the chamber 110. Carbon dioxide (CO) from a CO source 118 is injected into the molten carbonate electrolyte. CO is optionally injected into the molten carbonate electrolyte to react with oxygen and renew the electrolyte rather than being consumed. Without CO injection, the electrolyte would be consumed and its level would drop during the electrolysis reaction because the overall reaction of the electrolyte involves CO being converted to O at the anode 112 and converted to carbon nanomaterials at the cathode 114. The injection of CO can be active (e.g., bubbling), or passive (direct dissolution from a gas at the air / electrolyte interface), or a combination of the two (gas inflow or electrolyte mixing). A variety of CO sources may be CO source 118.

[0037] The carbonate furnace chamber 102 heats a carbonate electrolyte, such as pure lithium carbonate (Li2CO3), to its melting point to produce a molten carbonate electrolyte. There may be various ways to power the carbonate furnace chamber 102, such as solar energy or a conventional power generator. A transition metal is added via a distributor to act as a catalyst. The molten carbonate electrolyte is electrolyzed by placing it between the anode 112 and cathode 114 in the electrolysis chamber 104.

[0038] FIG. 1B is an illustration of different techniques for producing carbon nanotube and graphene carbon morphologies using the example system 100 shown in FIG. 1A. FIG. 1B shows a first process 120 and a second process 130 for producing carbon nanotube carbon morphologies on the cathode 114. FIG. 1B shows a first process 140, a second process 150, and a third process 160 for producing graphene carbon morphologies on the cathode 114. Processes 120, 130, 140, 150, and 160 are not limited to the theory or mechanism of using the system of FIG. 1A. As can be seen with reference to processes 120 and 130 in FIG. 1B, a reaction in the presence of nucleation seeds, such as those using certain transition metals, results in the separation of carbon from carbonate, leaving carbon products, such as carbon nanotubes, on the cathode 114 from the nucleation sites. Such growth may occur as a tip growth mechanism, as shown in process 120 of FIG. 1B, or as a root growth mechanism, as shown in process 130. Of course, other growth mechanisms are also possible. As can be seen with reference to processes 140, 150, and 160 of FIG. 1B, a pulsed electrolysis current is applied to separate carbon from carbonates in the absence of nucleation seeds of a selected transition metal, forming carbon products that combine into carbon nanotube forms, such as the graphene products shown. The first process 140 uses an unbiased cathode 114. As in the second process 150, the cathode 114 may be forward biased. In process 160 of FIG. 1B, carbon nanotube forms are extruded from the cathode 114 during alternating current reversal periods. The resulting carbon products are collected at the collector 106, while oxygen is produced at the anode 112. The separated carbon nanomaterial may be washed with a solvent or separated from the molten electrolyte by high-temperature phase separation or filtration.

[0039] In this example, elements for carbon nanotube growth are added to the cell 110, which contains an anode 112, a cathode 114, and a carbonate electrolyte. The elements for carbon nanotube growth may include nickel, copper, chromium, iron, brass, manganese, titanium, zirconium, molybdenum, tantalum, cobalt, silicon, carbon, and alloys or mixtures thereof. In the presence of transition metals such as nickel, which serve as nucleation sites, carbon nanotube formation and growth occurs readily in a molten lithium carbonate electrolyte under a wide variety of conditions. The transition metal is provided by anode dissolution during initial stabilization of the anode surface, or, in the case of an inert oxygen anode such as iridium, is added to the electrolyte as a metal or salt. As described below, the elements for carbon nanotube growth may be transition metals or transition metal salts added to the cathode material, anode material, or electrolyte. In this example, the carbonate electrolyte at 770°C is lithium carbonate (Li2CO3), with a current of 0.1 A / cm 2 The electrolysis was carried out in a solution containing 1 wt% nickel metal powder for carbon nanotube growth, which was initially added to a carbonate electrolyte. The cathode 114 was made from Monel or copper alloy.

[0040] FIG. 2A shows an SEM image of nanotube-type product morphology with the addition of more nickel powder to the Li2CO3 electrolyte at 770°C. FIG. 2A also shows a graph 210 of the product and a graph of the electrolysis potential measured for the process using an inert iridium anode and a Monel cathode. FIG. 2A also shows an SEM image 200 of the carbon product when electrolysis was performed with an iridium anode. Iridium is very stable and does not release transition metal nucleation ions into the electrolyte. Even in this case, when nickel powder is instead added to the electrolyte to induce nucleation at the cathode, a uniform carbon nanotube product is observed in the SEM image 200.

[0041] Figure 2B shows SEM images 220, 222, 224, and 226 of carbon nanotube growth from copper or Monel anodes when increasing amounts of nickel powder were added to the Li2CO3 electrolyte at 770 °C. Images 220 and 222 show the growth from a copper cathode when an iridium anode was used with 0.5 wt% cobalt oxide (CoO) added to the electrolyte instead. Image 224 shows the growth from a copper cathode when a nickel-chromium anode was used with 1 wt% nickel addition. Image 226 shows the growth from a Monel cathode when a nickel-chromium anode was used with 1 wt% nickel addition.

[0042] The products in images 220, 222, 224, and 226 in Figure 2B are from electrolysis using a nickel-chromium anode rather than an iridium anode. SEM images 220, 222, and 224 show the production of uniform carbon nanotubes, demonstrating the formation of short carbon nanotubes at the copper cathode. SEM image 226 shows the formation of long carbon nanotubes at the Monel cathode. As shown in images 220 and 222 in Figure 2A, uniform carbon nanotube products are formed using an iridium anode without the addition of nickel powder by adding 0.5 wt% cobalt oxide (CoO) to the electrolyte. Monel alloys are alloys composed of nickel, copper, and small amounts of iron, manganese, carbon, and silicon. Different carbonate electrolytes, such as lithium carbonate, sodium carbonate, potassium carbonate, strontium carbonate, rubidium carbonate, cesium carbonate, barium carbonate, and calcium carbonate, may also be used.

[0043] Images 300 and 302 in Figure 3A show product growth at the cathode-electrolyte interface under low-amount nickel powder / iridium anode conditions, using a product exfoliated from a Monel cathode. As shown in image 300, the sample includes layer 310, transition layer 312, and graphene layer 314. Images 300 and 302 illustrate the limited availability of nucleation metals in an iridium anode with only 0.1 wt% nickel powder added to a Li2CO3 electrolyte at 770°C. The product in SEM image 300 is 5 cm 2 0.1A / cm2 on a Monel cathode 2 This figure shows the product after extended (48 hours) molten carbonate CO2 electrolysis under conditions of 302, 303, 304, 305, 306, 307, 308, 309, 310, 311, 312, 313, 314, 315, 316, 317, 318, 319, 320, 321, 322, 323, 324, 325, 326, 327, 328, 329, 330, 331, 332, 333, 334, 335, 336, 337, 338, 339, 340, 341, 342, 343, 344, 345, 346, 347, 348, 349, 350, 351, 352, 353, 354, 355, 356, 357, 358, 359, 360, 361, 362, 363, 364, 365, 366, 367, 368, 369, 370, 371, 372, 373, 374, 375, 376, 377, 378, 379, 380, 381, 382, ​​383, 384, 385, 386, 387, 388, 389, 390, 400, 401, 402, 403, 404, 405, 406, 407, 40

[0044] Figure 3B shows SEM images 320, 322, 324, and 326, which demonstrate that in the absence of a nucleating agent, nanostructures such as platelets, rather than carbon nanotubes, dominate the product growth. Figure 3C shows SEM images 330, 332, 334, and 336, which demonstrate that in the absence of a nucleating agent, very thin graphene platelets and small carbon particles grow. SEM images 330 and 332 show the product formed with a Monel cathode, and SEM images 334 and 336 show the product formed with an iron cathode.

[0045] The products of images 320, 322, 324, and 326 in FIG. 3B and images 330, 332, 334, and 336 in FIG. 3C are 0.1 A / cm 2 This image shows that carbon nanotube product morphology does not form when a transition metal nucleating agent is not included in the electrolysis cell. The product in SEM image 320 was produced using a copper cathode coupled with a nickel anode. This process is an extended pure Li2CO3 electrolysis at 770°C, using a large 100 cm 2A planar copper cathode and nickel anode were used. Using the same electrolyte, SEM image 322 shows the cathode product using an iron cathode and iridium anode, without the addition of a transition metal (nickel) to the electrolyte. The eutectic mixed carbonate of lithium, sodium, and potassium, LiNaK, lowers the melting point of the carbonate below 400°C. Potassium carbonate significantly inhibits carbon nanotube formation. The electrolysis product in the potassium carbonate electrolyte mixture begins to exhibit disordered nanostructure characteristics above 600°C, and this tendency increases with increasing temperature. However, LiNaK carbonate has not been observed to produce carbon nanotubes in high yields. The electrolysis of LiNaK, but not pure lithium, produces only low yields of carbon nanotubes (less than 15%) under all electrolysis conditions. SEM image 324 shows the product formed in the potassium carbonate mixed (with lithium and sodium) electrolyte at 770°C. The product shown in SEM image 324 is complex, but the majority of the product consists of very thin, multi-layered graphite platelets, with the largest observed width being ~10 mm wide (not shown). SEM image 326 shows that at low temperatures, platelets form in lithium carbonate, even with the addition of iron oxide and lithium oxide. SEM image 326 shows that Li2CO3 at 730 °C with 8 wt% lithium oxide (Li2O) and 0.4 wt% iron oxide (Fe2O3) exhibits a 0.1 A / cm 2 Figure 1 shows the products formed by electrolysis of HCl using a nickel anode and iron cathode.

[0046] As shown in SEM images 330, 332, 334, and 336 in Figure 3C, when platinum or iridium anodes are used, limited or no nucleation metal is included, and little or no nickel is added to the Li2CO3 electrolyte at 770 °C, no carbon nanotubes are observed and the product consists of very thin multilayer graphene sheets. The electrolysis time was 0.5 h, and the iridium electrode and Monel cathode were used, with a current of 0.1 A / cm 2When the electrolysis time is limited to 30 minutes with an iridium electrode, the product is uniform, multilayered graphene sheets, with no other carbon nanostructures. With a platinum electrode, a low electrolysis potential (1.2 V) and an iron cathode, the current density is 0.1 A / cm. 2 After 1.5 hours of electrolysis, small carbon particles intermingle with the primary carbon platelet product, as shown in SEM image 330. Image 330 shows the product produced using an iridium anode and only 0.1 wt% nickel powder added to a Li2CO3 electrolyte at 770°C. SEM image 332 shows the product produced using a 5 cm 2 Monel cathode, 0.1A / cm 2 Figure 3 shows the product of extended (48 hours) molten carbonate CO electrolysis. The resulting product has thin, multi-layered graphene. SEM images 334 and 336 show the product from an experiment without nickel. When a platinum anode is used, no nucleation metal is used, and no nickel is added to the electrolyte, no carbon nanotubes are observed, and the product consists of very thin multi-layered graphene sheets and small carbon particles, as shown in SEM images 334 and 336. The product is 5 cm 2 iron cathode, Li2CO3 electrolyte at 770 °C, and 0.1 A / cm 2 It was produced by electrolysis at 400 K for 3 hours.

[0047] Figure 4A shows a current of 0.1 A / cm using a nickel-chromium anode and a Monel cathode. 24A shows an SEM image 400 of long carbon nanotube growth using a constant electrolysis current of 0.1 A / cm at a measured electrolysis potential of 1.6 V. FIG. 4A also shows an SEM image 402 of carbon nano-onions produced under the same conditions with the addition of a current cycling step. FIG. 4A also includes a graph 404 showing the current cycling (cycles) to produce the carbon nano-onions in image 402, rather than the carbon nanotube product. That is, SEM image 400 shows the results of electrolysis of CO in Li2CO3 at 770°C, aging for 24 hours (to obtain an equilibrated electrolyte), immersing a Monel cathode and a nickel-chromium anode, and then electrolyzing at 0.1 A / cm at a measured electrolysis potential of 1.6 V. 2 Figure 1 shows the carbon nanotube wool product produced by applying a constant electrolysis current of 1000 kJ / cm. The electrode composition can also be used to control the morphology of the carbon nanomaterial product. The nickel anode generates oxygen during electrolysis, even at low overpotentials. A stable nickel oxide surface layer forms within the first few minutes of electrolysis, and low levels of nickel ions (Ni 2+ ), but enough of it is released into the electrolyte and redeposited on the cathode as carbon nanotube nucleation points. 2It also functions as an effective and stable anode when a voltage (a 0.2 V increase in voltage) is required, while releasing both nickel and chromium into the electrolyte. It is observed that, upon extended electrolysis, longer carbon nanotube products are formed. These longer carbon nanotubes, or "carbon nanotube wool," reach long, macroscopic lengths (0.2 to 2 mm, barely noticeable) while retaining their nanoscale diameters when Monel (a nickel-copper alloy) is used as the cathode instead of iron, titanium, or nickel, while very small carbon nanotubes are synthesized using a copper cathode. Comparing SEM images 220, 222, and 224 in FIG. 2B with images 226 and 200 in FIG. 2A and SEM image 400 in FIG. 4A reveals that carbon nanotubes of various lengths may be uniformly produced. That is, lengths may be greater than 100 μm, between 1 and 100 μm, or less than 1 μm.

[0048] SEM image 402 shows that by varying the electrolysis current, rather than using a direct current, as shown in current graph 404, a completely different morphology of the electrolysis product can be obtained. In this example, the same electrolysis conditions that produced the product shown in image 400 were applied, except that the potential was kept below 1.2 V and cycled. Instead of long carbon nanotubes, the product at the cathode was observed to be carbon "nano-onions," as shown in image 402. The observed nano-onion carbon morphology represents a novel product obtained from simple CO electrolysis by limiting the electrolysis to constant current density and cycling low potentials. Nano-onion carbon products could be worth over a million US dollars per ton if synthesized via the more expensive CVD method.

[0049] Figure 4B shows initial images 440 of carbon nanotube containing nano-onion carbon products obtained without current cycling when zinc-coated iron was used as the cathode or zinc oxide (ZnO) was added to the electrolyte and iridium was used as the anode. SEM image 442 shows hollow nanosphere products (along with carbon nanotubes) formed with a lithium / magnesium mixed carbonate electrolyte. SEM image 444 shows the predominantly thin-walled carbon nanotube product using a lithium / calcium mixed carbonate electrolyte.

[0050] SEM image 440 shows larger carbon nano-onion products produced by applying direct current (DC) rather than alternating current (AC) as the electrolysis current. Instead, a zinc-coated (galvanized) iron cathode and an iridium anode are used in the electrolysis. Zinc has a melting point of 420°C, which facilitates the production of these larger-looking carbon nano-onion products. However, when a low-current pre-electrolysis step is added, transition metal nucleation points begin to form on the cathode, and uniform carbon nanotube products predominate (not shown). Replacing the pure Li2CO3 electrolyte with a mixture containing 5% lithium borate (LiBO2), 11.4% magnesium carbonate (MgCO3), 0.6% zinc oxide (ZnO), and 83 wt% lithium carbonate (Li2CO3), along with this low-current pre-electrolysis step, results in the formation of a product consisting mostly of hollow nanospheres (along with carbon nanotubes), as shown in the washed product in SEM image 442. The product in SEM image 442 contains magnesium oxide (MgO) deposits (suggesting that, unlike lithium oxide (LiO), MgO is highly soluble in LiCO). A similar mixture of electrolyte with calcium carbonate (CaCO) rather than magnesium carbonate (MgCO) results in a primarily thin-walled carbon nanotube product, as shown in image 444.

[0051] Figure 4C shows SEM images 460, 462, and 464 of nano-onion carbon products, rather than carbon nanotubes, obtained by adding zinc oxide to a Li2CO3 electrolyte at 770°C without cycling. SEM images 460, 462, and 464 show carbon nano-onion products formed from CO2 on a copper cathode during extended electrolysis. The electrolysis products in SEM images 460, 462, and 464 were obtained by adding zinc oxide to a Li2CO3 electrolyte at 770°C with a copper cathode and nickel anode at 0.2 A / cm 2 By applying an average electrolysis potential of 1.2 V, prolonged electrolysis (19.5 hours at 20 A, total charge 3.9 Ah / cm) was achieved. 2 ) results in uniform and larger (0.5 to 1 μm) carbon nano-onion products. These electrosyntheses are performed at 100 cm 2 This was performed with a flat electrode. Smaller carbon nano-onions (not shown) were formed with shorter electrolytic charging times.

[0052] Figure 5 shows two SEM images 500 and 502 of boron-doped carbon nanotubes (BNCs) formed during electrosynthesis in a Li2CO3 electrolyte with 9 wt% additive at 770°C. At 770°C, 5 cm3 of BNCs were synthesized in 5 g (grams) of lithium metaborate (LiBO2) and 50 g of lithium carbonate (Li2CO3). 2The characteristics of boron-doped carbon nanotubes formed at a cathode of 1000 W (Ah) are shown in SEM images 500 and 502. The effect of increasing LiBO2 concentration on the products in images 500 and 502 is shown by a shift in the Raman spectrum, shown in spectrograph 510, and an increase in the electrical conductivity of the carbon product, shown in graph 512. Graph 512 illustrates the relationship between increasing the concentration of LiBO2 dissolved in the Li2CO3 electrolyte and the electrical conductivity of the carbon nanotube product. Spectrograph 510 shows the Raman spectrum of boron-doped carbon nanotubes. Graph 512 shows the spectrum from bottom (black) to top (gray) for electrosynthesis using 50 g of Li2CO3 with 1.5 g, 3 g, 5 g, and 8 g of LiBO2.

[0053] Pure boron oxide (BO) has a melting point of 450°C and is white, but is transparent when melted, forming a glassy insulator. However, when molten BO contains dissolved lithium oxide (LiO) (melting point 1438°C, white, transparent melt), it becomes an electrochemically conductive liquid. The binary system of BO and LiO has a complex phase diagram, with a wide range of homogeneous liquid phases above 767°C. Lithium metaborate, LiBO (melting point 849°C, white), a chemically bonded salt of boron and lithium oxides, is highly soluble in LiCO, melts transparent, retains very high electrochemical conductivity, and is a good additive for the one-pot synthesis of boron-doped, highly electrically conductive carbon nanotubes (BOC).

[0054] The carbonate electrolysis method for converting CO2 into doped carbon nanotubes is simple and, without being bound by any theory, involves a single step in which the desired dopant is added during synthesis, e.g., in carbonate electrolysis, with the simultaneous production of oxygen and dissolved lithium oxide. Li2CO3(liquid)+dopant→C(CNT doped) + Li2O(dissolved) + O2(gas) (1) Li2CO3 is consumed by electrolysis, but is continually replenished by the reaction of this excess Li2O, formed as a product in the electrolysis reaction (1), with CO2 from the air (or high concentrations of CO2 obtained from the exhaust). Li2O(dissolved)+CO2(gas)→Li2CO3(liquid) (2) The final reaction (combination of reactions (1) and (2)) is: CO2(gas)+dopant→C(CNT doped ) + O2(gas) (3)

[0055] The washed, boron-doped product (boron-doped product) is shown in images 500 and 502. As the level of LiBO2 added (greater than 10% by mass) increases, the level of heterogeneous impurities in the carbon nanotube product increases (not shown). In particular, very high-quality, straight carbon nanotubes were formed in systems containing 50 g of Li2CO3 plus electrolytes containing less than 10% LiBO2 by mass, e.g., 1.5 g, 3 g, or 5 g of LiBO2, respectively. However, as can be inferred from SEM images 500 and 502, amorphous carbon nanoparticles were present in the product, within the range of 10%. When 5 g of LiBO2 was added, a distribution of carbon nanotube diameters (200 to 500 nm (nanometers)) was observed, which was somewhat larger than that observed when no LiBO2 was added. When 8 g of LiBO2 (>10%) was added, the carbon nanotube diameters were very broadly distributed, ranging from 150 nm to 1.5 μm, indicating that the addition of more LiBO2 led to heterogeneity. High levels of LiBO2 may alter the reduction macroenvironment at the cathode, and / or boron deposition on the nickel nuclei may lead to the formation of nickel boride (NiB) rather than pure nickel, resulting in less nanostructure and a more heterogeneous growth pattern. When 17 wt% LiBO2 was added to the Li2CO3 electrolyte, microparticles, rather than nanotubes, became the dominant product.

[0056] To determine whether the resulting carbon nanotubes were boron-doped or a mixture of boron and pure carbon nanotubes, Raman spectra were recorded using a 532 nm incident laser and are shown in graph 510 of Figure 5. For conventional (boron-free) electrosynthesized carbon nanotubes produced from pure lithium carbonate electrolyte, E 2g The G band associated with graphite in planar modes of symmetry is at 1575 cm -1However, in the LiBO2-added samples, the G band shifts to a higher wavenumber. This upshift indicates that holes (hole carriers) are transferred from the boron to the carbon nanotubes. The charge transfer shortens the C-C bonds, increasing the force constant and enhancing the lattice frequency of the carbon nanotubes. Thus, the shift of the G band to a higher frequency is attributed to the deformation of the graphite structure due to the increased boron concentration. As shown in images 500 and 502, when either 1.5 g, 3 g, 5 g, or 8 g of LiBO2 was added to the electrolyte before electrosynthesis, after synthesis, the G band of the product shifted to 1583, 1587, 1589, and 1600 cm, respectively. -1 According to the linear relationship between the G band shift and the boron doping level in Ishii et al.'s study, the boron content was estimated to be about 0.7 to about 2 at% (atomic percent). Furthermore, the D-G ratio, which is the intensity ratio between the D band associated with amorphous graphite and the G band of graphite (graphite), increases with increasing added LiBO2. This indicates that the number of defects increases with increasing boron doping level. Boron doping is a key factor in the formation of B X C Y Generate domains, e.g., low doping levels 34 BC3, high doping level B4C, B 13The presence of C2 domains and increased defects in the carbon nanotubes. Each of these features in the spectrum indicates that the resulting sample is boron-doped carbon nanotubes, rather than a mixture of elemental boron and pure carbon nanotubes. It should be noted that the boron content in the boron-doped carbon nanotubes differs significantly from the boron / carbon ratio (B / Cratio) in the electrolyte. For example, when 50 g of Li2CO3 and 8 g of LiBO2 are added, the boron / carbon ratio in the electrolyte is 31 at%; however, the resulting boron content in the resulting carbon nanotube sample is only about 2%. There is no indication that excess LiBO2 in the electrolyte is detrimental (other than increased conductivity, as will be shown further), and this large difference between the percentage of boron added to the electrolyte and the percentage of boron in the product is related to the reduction voltage of lithium metaborate to elemental boron, which, according to thermodynamic calculations of the reaction (4) from the entropies and enthalpies of the individual species, is less than 2.15 V at 770 °C (1043 K). This is higher than the reduction of carbonate to carbon, which is less than 1.6 V, and if they are simultaneously deposited at the cathode (depending on the reaction rate), carbon formation at the cathode would be favored over boron. 2LiBO2 → 2B + Li2O + 3 / 2O2 (4)

[0057] Boron doping is known to produce metallic carbon nanotubes and enhance the conductivity of carbon nanotubes (synthesized by CVD). To investigate the effect of boron dopant on the conductivity of molten carbonate-synthesized carbon nanotubes, samples with increasing boron dopant levels were prepared and compared to the products shown in images 500 and 502 in Figure 5. For comparison, the conductivity of amorphous carbon nanoparticles, straight carbon nanotubes, and entangled carbon nanotubes electrosynthesized from a Li2CO3 melt was also measured. Carbon nanotubes synthesized in a 9 wt% LiBO2 electrolyte exhibited an order of magnitude higher conductivity than straight carbon nanotubes (formed in pure Li2CO3) and 30 times higher conductivity than amorphous carbon nanoparticles or electrosynthesized entangled carbon nanotubes (adding oxides, e.g., 4 m Li2O (10.7 wt%) in the Li2CO3 electrolyte, adds defects and results in entangled carbon nanotubes). Among the boron-doped samples, the conductivity first increased with the addition of 1.5 g of LiBO2 to the composite electrolyte, increased up to 5 g of LiBO2, and then decreased with increasing LiBO2 concentration. While boron doping improves conductivity, too much boron (more than 10 wt% in the electrolyte) leads to a degradation of the quality (decreased amount of carbon nanotubes and increased nanoparticles), and thus a maximum in conductivity was observed with the addition of LiBO2.

[0058] A successful and straightforward route for the one-pot electrosynthesis of boron-doped carbon nanotubes from carbon dioxide via the addition of a soluble lithiated dopant to a molten carbonate electrolyte has been demonstrated, suggesting that similar routes are possible for the synthesis of other doped carbon nanotubes, such as those doped with nitrogen, phosphorus, or sulfur. Inserting different dopants into carbon nanomaterials at different concentrations alters both their physical and chemical properties.

[0059] Boron and nitrogen have been the most studied carbon dopants due to their similar size (and atomic number) to carbon. The common polyatomic anions, metaphosphates, nitrates, and sulfates (lithium metaphosphate (LiPO3), lithium nitrate (LiNO3), or lithium sulfate (Li2SO4)), in which lithium is the cation, are soluble in molten lithium electrolytes. The 3e required to form elemental boron as a dopant from lithium metaborate - Compared to the reduction of LiBO2, LiPO3, and LiNO3, 5e is required to form phosphorus or nitrogen elements, respectively. - Reduction is required, Li2SO4 is 6e to form sulfur - reduction of carbon nanotubes is required. Boron, phosphorus, and nitrogen are less electronegative (negatively charged) than carbon, while sulfur is more electronegative (negatively charged). Thus, roughly (based on electronegativity, without predicting competing chemical reactions), carbon may be easier to form electrolytically from oxides than boron, phosphorus, or nitrogen, making the latter oxides promising candidates as co-reduced elemental dopants in the electrosynthesis of carbon nanotubes, while sulfur may be a thermodynamically favorable reduction product for carbon nanotubes and may suppress carbon nanotube formation in sulfate-containing electrolytes.

[0060] Figure 6 shows SEM images 600 and 602 of sulfur- and nitrogen-doped carbon nanotube products formed by electrolysis of Li2CO3 containing either dissolved Li2SO4 or LiPO3 as a source of either sulfur or phosphorus in the carbon nanotubes. SEM image 600 shows a long (300 to 600 μm) product of P-type heteroatoms, with a current density of 0.03 A / cm 2 Low current density of 0.8Ah / cm 2The nanotubes were produced electrolytically using a conventional (nickel 200) anode with no nickel powder added to the electrolyte, with a charge of 1000 vol%. LiPO3 was used to facilitate salt solubility in the lithium carbonate electrolyte. Variations that improved the length and yield of phosphorus-containing carbon nanotubes include increasing the LiPO3 content from 1% to 5 mol% and using a Monel cathode instead of galvanized steel. Electron dispersive spectroscopy (EDS) of the carbon nanotube product measured 0.3% mol of phosphorus in the product nanotubes. This is well below the electrolyte concentration of phosphorus, and the P-type heteroatom may provide a weak lattice structure compatible with carbon nanotubes.

[0061] SEM image 602 shows sulfur-containing carbon nanotubes from molten carbonate electrolysis using 0.1 mol% sulfate, followed by 2 hours of electrolysis at 1 A (using a conventional galvanized steel cathode and a nickel 200 wire anode, without the addition of nickel metal powder). Electron dispersive analysis of the carbon nanotube product measured 0.1 mol% sulfur in the carbon nanotube product. As in previous experiments, nucleation at the cathode was promoted by applying successive low, constant currents (10 min each) increasing from 0.05, 0.10, 0.25, to 0.5 A, followed by extended electrolysis at higher currents. During the first 10 min, the lowest current electrolysis occurred at potentials between 0.4 and 0.5 V, consistent with expected nucleation from nickel on the cathode; subsequent constant current increments occurred at increasing potentials between 1 and 2 V, respectively. In electrolysis of high sulfate concentrations, such as 1 mol% (or 3 or 5 mol%) Li2SO4 in Li2CO3 at 770 °C, no formation of carbon products (carbon nanotubes or otherwise) was observed at the cathode. The potential at which a 1 A current was measured was lower with increasing Li2SO4 (lower than the 1-2 V electrolysis potential measured without Li2SO4). The lack of carbon nanotube formation at higher sulfate concentrations is due to the electronegativity of sulfur relative to carbon, which thermodynamically favors the formation of the former over the latter. Reducing the sulfate concentration (relative to carbonate) to improve the energetics of carbon formation creates a pathway for sulfur-containing carbon nanotube formation.

[0062] Carbon nanotube production has also been observed from the electrolysis of LiNO3 in a Li2CO3 electrolyte at 770 °C. In this case, carbon nanotube yield is improved with 5 mol% lithium nitrate dissolved in the electrolyte compared to 1 mol%. The added dissolved lithium nitrate is thought to be in equilibrium with the lithium nitrate in the molten electrolyte. This is similar to the known solid-state thermal decomposition of solid LiNO3, which occurs above 500 °C. LiNO3 → LiNO2 + 1 / 2O2 (5) Electron dispersive analysis indicates the presence of nitrogen in the carbon nanotube product after electrolysis.

[0063] Dopants have been shown to be introduced by dissolving an oxide containing the dopant in the electrolyte during electrolysis. It is clear that pure elements or other salts can also be used to introduce the dopant additive. Examples of such additives include, by way of illustration and not limitation, sulfur, boron, thionyl chloride, sulfur chloride, silicon chloride, boron chloride, boron chlorate, thionyl nitrate, silicon nitrate, and the like. nitrous acid Contains silicon, boron nitride, and boron nitrate.

[0064] This example demonstrates that dopants can be injected into the electrolyte in the gas phase rather than by dissolution of a solid or liquid in the electrolyte. Molten carbonate-carbon dioxide electrolyte separation occurs easily (high current density) and with low energy (low electrolysis potential) using low-temperature or high-temperature inlet gases, which can be 0.04% (atmospheric), 5 to 13% (natural gas or coal-fired power plant flue gas), 33% (cement flue gas), or 100% CO2. Here, the gases are mixed to simulate coal plant flue gases, which contain average concentrations of sulfur dioxide (SO2) and nitrogen oxides (NOx). NOx, SO2, and CO2 are added continuously in the correct ratio to air through the air duct inlet before entering the carbonate electrolyzer. The CO2 inlet rate is measured and controlled at 76 L / min (equivalent to 200 kg of CO2 converted to carbon nanomaterials daily) by a calibrated Omega mass flow controller (MA5400 / 500) with a limit of 131 L / min. NOx is produced in the laboratory by the reaction of copper metal with nitric acid, the ratio being controlled by the strength of the acid and the relative thickness of the copper. Low concentrations of nitric acid (4 mol of nitric oxide (NO)) produce more NO, while high concentrations form pure brown nitrogen dioxide (NO2). Copper ions (Cu 2+ ) enters the electrolytic cell, the 4 molar nitric acid gradually changes from colorless to blue. Similarly, sulfur dioxide (SO2) is produced by the direct reaction of sulfur powder with sulfuric acid. The inlet gas flow rate is monitored by an in-line Digi-Sense Hot Wire, a thermoanemometer with NIST traceable calibration. NOx and SO2 injected into the electrolytic cell at low ppm levels did not affect the physical and chemical characteristics or formation of the observed carbon nanotubes.

[0065] This example demonstrates that carbonate electrolytes can absorb carbon dioxide at a rate sufficient to sustain the highest rates of molten carbonate electrolysis, and that with sufficient insulation, molten carbonate electrolysis can self-heat and / or generate useful excess heat. Figure 7 is a data table 700, experimentally measured and recorded, showing the extremely rapid rate at which carbon dioxide is absorbed from the gas phase into molten lithium carbonate and molten lithium carbonate mixtures. Even at the lowest carbon dioxide concentration studied (0.04% carbon dioxide using common air), the current is 0.1 A / cm. 2 During electrolysis, conducted at a constant current density of 1000 kJ / cm, the current density was sufficient to maintain and renew all of the molten lithium carbonate in an open-air system. During electrolysis, lithium oxide is co-produced at the cathode and continuously reacts with carbon dioxide, renewing the electrolyte. Figure 7B shows a graph 710 representing the rate of carbon dioxide absorption from the data in data table 700. As shown in data table 700 in Figure 7A, the absorption rate of carbon dioxide gas bubbled into even a small amount (50 g) of molten lithium carbonate is not limited until the carbon dioxide inflow rate well exceeds 0.3 L per minute, and as expected (not shown), it further increases with additional lithium oxide concentration (as produced by the faster electrolysis rate). The cumulative carbon dioxide absorbed on the vertical axis is limited to just below 100% due to the natural lithium carbonate concentration occurring at equilibrium in the lithium carbonate electrolyte. The fastest electrolysis experimented here was at 1 amp / cm. 2 and the CO2-containing gas must be bubbled through the electrolyte, otherwise the electrolyte will be consumed and the electrolyte level will drop appreciably relative to the electrolyte when the mass of the electrolyte is held constant by bubbling.

[0066] 7C is a graph 720 showing that the majority of heat is retained within the molten electrolysis chamber with sufficient insulation. In a kiln constructed using 9 x 4.4 x 2.4 inch refractory bricks with 24 x 9 x 4 inch refractory bricks (purchased from BNZ Materials) and heating elements and control circuitry from a commercial Paragon Caldera kiln, improved heat retention was observed with increasing levels of insulation when a custom radiant heat shield cut from 0.034 inch thick mirror-finished 304 stainless steel (purchased from onlinemetals.com) was added as an intermediate vessel to the kiln. One-inch thick, highly insulating, rigid ceramic insulation with high temperature resistance and very low heat flow (0.28 K at 800°C, part number 6841K5 ultra-high temperature ceramic insulation purchased from Mcmaster.com) was installed as a thermal protection barrier on all sides, and is visible as a white outer border on the kiln cover during construction in addition to the gray furnace chamber mortar. Before adding the carbonate electrolysis chamber, a fourth layer of insulation (in addition to the brick, radiant barrier, and ceramic insulation) was added to the kiln in the form of mineral insulation (yellow-green, Mcmaster.com product No. 9328K43, 2-inch thick, extra-high temperature 65-C mineral wool insulation sheet), and finally, an outer coat of pink R-30 Home Depot insulation was added as a final layer of insulation against heat loss, as seen in the photo below (before reinserting the electrolysis chamber). R-30 exterior insulation (purchased from Home Depot as general house insulation) was finally added before adding the outermost layer of the kiln.

[0067] FIG. 7D is a graph 730 showing that molten electrolyte electrosynthesis is self-heating. The major breakthrough was reaching the limit of thermal equilibrium, where the molten carbonate process does not require any external heating, despite the high temperature of the molten salt process. A custom-built kiln using a carbonate electrolysis chamber was heated to 725°C (above the melting point of lithium carbonate electrolyte), then all heating power switches in the kiln were turned off and the kiln was unplugged. 0.1 / cm 2 In constant electrolysis, the carbon dioxide to carbon nanotube process was independently maintained at a constant temperature of 727°C. Due to the exothermic nature expected for the reaction of CO2 with Li2O, which constantly renews the electrolyte (and absorbs CO2), this temperature is observed to rise to 737°C when CO2 (unheated, pure) is bubbled in at a very precise rate comparable to the rate at which CO2 is consumed by electrolysis. This temperature is reached when the current density (proportional to the CO2 flow rate) is 0.5 A / cm 2 If the current density is increased to 0.3 A / cm, the temperature rises to 787°C. 2 The graph 720 in FIG. 7C shows the temperature drop at 0.3 A / cm 2 The graph shows the results of electrolysis at a constant current density of 750°C, which was maintained constant throughout the electrolysis. An outlier measurement during the experiment was not included in graph 720 due to a poor thermocouple connection, which has since been corrected.

[0068] One-step molten carbonate electrosynthesis of doped carbon nanotubes is demonstrated for boron, nitrogen, sulfur, and phosphorus doped carbon nanotubes. In a similar manner, numerous dopant source materials and types allow for the electrosynthesis of carbon nanotubes with numerous dopants. By applying this straightforward synthesis method to a wide variety of simple additives, electrosynthesis enables a broader portfolio of doped carbon nanomaterials, including boron, silicon, germanium, nitrogen, phosphorus, arsenic, antimony, sulfur, selenium, tellurium, gold, alkali or alkaline earth metals, nickel, copper, iron, manganese, titanium, zinc, zirconium, molybdenum, tantalum, platinum, iridium, cobalt, silicon, and (C 12 The term "doped carbon nanomaterial" refers to a material containing one or more carbon isotopes (other than ).

[0069] If the material to be deposited with carbon nanomaterials requires a higher electrolysis potential than that required for depositing carbon from carbonates, it is possible to deposit the material using a two-step molten carbonate synthesis. For example, a one-step electrolysis at 770 °C for the electrolysis of Li2CO3 containing nickel powder and lithium silicate (Li4SiO4) results in no silicon in the deposited product. A two-step electrosynthesis process can deposit the desired material. The first step involves electrolysis in an electrolyte of 0.42 g of nickel powder and 52 g of Li2CO3 (without Li4SiO4). Then, in the second step, the electrodes are moved to a second electrolyte consisting of 18.4 g of Li4SiO4 and 40.2 g of Li2CO3 (without nickel powder), and electrolysis continues. The observed electrolysis potentials are 1.4 V for the first step and 2.3 V for the second step. The washed final product exhibits carbon nanotubes, as observed in SEM images. In the resulting nanotubes, silicon-based carbon was observed, as determined by electron dispersive spectroscopy and Raman spectroscopy at 480 cm -1This was evidenced by both the formation of a new silicon peak at 1000 .mu.m.

[0070] Figure 8 is a schematic illustration, without being bound by any theory or route, of known and new synergistic routes for one-step electrolysis of molten carbonate 800 to form nucleated carbon nanotubes or carbon nano-onions, graphene, or hollow carbon nanospheres, which may be doped or undoped. Figure 8 shows known synthetic sequence pathways 810 and 820.

[0071] In Figure 8, Route 820 does not use a nucleating agent and provides a facile route to forming nano-onions, graphene, or hollow carbon nanospheres. In Route 821, zinc oxide (ZnO) or magnesium oxide (MgO) is added to a carbonate electrolyte, which induces the formation of carbon nano-onions, graphene, or hollow carbon nanospheres, respectively. In Route 823, an alternating current (AC) rather than a direct current (DC) electrolysis current is applied between the anode and cathode to form graphene or carbon nano-onions (by including ZnO in the electrolyte or providing zinc cobalt on the cathode). In Route 825, potassium carbonate (K2CO3) induces the formation of graphene platelets on the cathode.

[0072] In FIG. 8, Route 810 provides a facile route to the formation of carbon nanotubes and carbon nanofibers using nucleating agents. Nucleating agents are specific transition metals, or combinations thereof, which may be dissolved in the electrolyte, released from the anode, or contained in the cathode, and form nucleation sites for carbon nanotube or carbon nanofiber growth from the cathode. In Route 811, specific nucleating agents, such as copper, induce short carbon nanotubes. In Route 815, specific nucleating agents, such as nickel and chromium, induce long carbon nanotube growth. In Route 813, increased dissolved oxygen levels are added to the carbonate electrolyte, resulting in high levels of SP. 3 The defects cause the carbon nanotubes to be measured and are observed to be tangled rather than straight. In route 812, a thin-walled agent such as calcium carbonate (CaCO3) is added to reduce the solubility of oxygen in the carbonate electrolyte, resulting in the formation of thin-walled carbon nanotubes. In route 814, natural abundance carbon nanotubes are added. 12 C is 13 C, leading to the production of carbon nanotubes with buried or closed cores, thick-walled, thin-core carbon nanotubes, or solid carbon nanofibers.

[0073] 8 also shows synthesis sequences 830 and 840, characterized by the addition of a dopant source to the molten carbonate electrolyte in sequence 830 and sequence 840. This allows for the selection of either the intrinsic (undoped) or doped pathways for pathways 811-815 and pathways 821-825. Carbon nanomaterial products, including a portfolio of either doped or undoped carbon nanotube forms, may be derived from pathways 811-815, or may be doped carbon nano-onions, graphene, or hollow nanospheres derived from pathways 821-835.

[0074] In FIG. 8, pathway 830 shows that omitting the dopant source from the molten carbonate electrolyte leads to the production of native (intrinsic, undoped) carbon nanomaterial formed at the cathode.

[0075] In Figure 8, pathway 840 shows that a dopant source can be used for the molten carbonate electrolyte to produce doped (e.g., boron, sulfur, nitrogen, or phosphorus) carbon nanomaterials at the cathode. In Figure 8, pathway 840 shows that the desired dopant source can be used as a variety of individual or combined sources in molten carbonate electrolysis. The dopant source (source) can be added directly to the electrolyte as a dopant-containing salt, covalent compound, or elemental compound in solid, liquid, or gas form, or can be added as a dopant using materials contained in the anode or cathode electrodes.

[0076] Nucleation factors may be combined synergistically, specific types and concentrations of one or more transition metals may be added, oxides may be added or removed, carbon isotopes may be added or removed, and these may be used in conjunction with carbonate configuration, electrolysis, charge, time and temperature to produce carbon nanotubes with different morphologies.

[0077] On the other hand, a new route 840 allows for the formation of non-native doped carbon nanomaterials (doped carbon nanomaterials) by adding a source containing a dopant directly during molten carbonate electrolysis, providing doped carbon materials with specific, desirable, and distinct chemical and physical properties, and further, the electrolysis can be performed directly, without the need for post-treatment doping.

[0078] Furthermore, one or more new routes from route 820 enable the direct formation of new, unique carbon nanomaterial morphologies (other than carbon nanotubes) in molten carbonate electrolysis by eliminating the use of nucleating agents. New routes 821, 823, and 825, and synergistic combinations of these routes, form cathode products such as carbon nano-onions, graphene, or hollow nanospheres.

[0079] Dopant atoms introduced during molten carbonate electrolysis are directly incorporated into the construction of carbon nanomaterials at the cathode during electrolysis, forming non-native (but not inherently) doped carbon nanomaterials with specific, desirable, and distinct chemical and physical properties. The electrolysis is performed directly, without the need for post-doping. These processes may produce high-yield, easy-to-synthesize, low-energy, and doped carbon nanomaterials with diverse morphologies (although uniform depending on the specific route used). These nanomaterials possess high conductivity, high strength, high capacitance, high explosion resistance, unique catalytic functionality, and pollutant adsorption capabilities. Molten carbonate electrolysis removes atmospheric and / or anthropogenic carbon dioxide from the environment. Significant effects of electrolysis configuration and conditions on carbon morphology, doping (addition of trace impurities), Raman spectroscopy, SEM, and carbon nanotube conductivity have been demonstrated. The same activation behavior as plated (galvanized) cathodes can be achieved without the zinc coating, paving the way for the investigation of various alternatives to uncoated cathode electrodes. This doping is achieved directly through the addition of dopant content, and morphology control is achieved through several techniques, including the removal of nucleating agents from the electrolyte.

[0080] Carbon nanomaterials are highly conductive and can be made to be round, solid, or hollow, or flat, thin, or thick-walled, or long or short, and with a variety of chemical and physical properties. The expanded portfolio of inexpensively synthesized molten carbonate electrolysis products is useful in similar applications with other materials, such as metals, composites, woven or embedded in wire, cable, wire or cloth, textiles, batteries, catalysts, optical devices, packaging materials, lightweight, shatter-resistant, and blast-resistant building and ceramic materials, and electronic devices.

[0081] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular references "a," "an," and "the" are intended to include the plural references as well, unless the context clearly dictates otherwise. Furthermore, to the extent that words such as "include," "includes," "a," "has," "with," and similar terms are used in either the detailed description and / or claims, these terms are equivalent to the term "comprising."

[0082] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly used by those skilled in the art. Furthermore, terms defined in commonly used dictionaries should be interpreted in a way that is consistent with their meaning in the context of the relevant art, and unless expressly defined as such herein, such terms should not be interpreted in an idealized or overly formal way.

[0083] Described herein is a method for producing carbon nanomaterials, the method comprising: (1) heating a carbonate electrolyte to obtain a molten carbonate electrolyte; (2) disposing the molten carbonate electrolyte between an anode and a cathode in a cell; (3) including a carbon nanomaterial doping component in the cell; (4) including a nanomaterial-selective component in the cell; (5) passing a current between the cathode and the anode in the cell; and (6) collecting doped carbon nanomaterial growth from the cathode in the cell. The nanomaterial component may be free of transition metals, and the method may further comprise passing an alternating current electrolysis current through the electrolyte. The electrolysis current may be selected for carbon nano-onion product growth. The method may further comprise adding zinc oxide to the electrolyte, and the electrolysis current may be selected for graphene platelet product growth. The method may further comprise adding magnesium oxide to the electrolyte, and the electrolysis current may be selected for hollow carbon nanosphere product growth. The nanomaterial-selective component may disperse a transition metal, and the nanomaterial-selective component may be selected for carbon nanotube product growth. The doping component may be free of doping additives, and the doping component may be selected for intrinsic nanomaterial growth from the cathode. The doping component may include at least one of a solid electrolyte additive, a liquid electrolyte additive, a gas electrolyte additive, a cathode material, or an anode material. The doping component may be a solid salt, element, or covalent mixture, and the doping component may be dissolved, reacted, or suspended in the electrolyte. The doping component may include at least one material containing a Group 3 element.The doping component may include at least one material containing a Group 1 element, or at least one material containing a Group 2 element, or at least one material containing a Group 4 element other than carbon, or at least one material containing a Group 5 element, or at least one material containing a Group 6 chalcogenide element, or at least one material containing gold, platinum, iridium, iron, or other Period 4, 5, or 6 metals. The doping component may include species using oxygen atoms, or halogen atoms. Thionyl chloride, sulfur chloride, silicon chloride, thionyl nitrate, silicon nitrate, and silicon nitrite The doping component may include one or more of the following: a) a metal; b) a metal; c) a metal; d) a metal; e) a metal; f) a metal; g) a metal; g) a metal; h ...

[0084] Also disclosed is a method for producing doped carbon nanomaterials. The method includes: (1) providing a carbonate electrolyte containing a doping component between an anode and a cathode in a cell; (2) heating the carbonate electrolyte to a molten state; (3) passing a current between the anode and the cathode through the carbonate electrolyte disposed between the anode and the cathode; and (4) collecting carbon nanomaterial growth from the cathode of the cell. The doping component may be dissolved, reacted, or suspended in the electrolyte. The doping component may include at least one material containing one of boron, silicon, germanium, nitrogen, phosphorus, arsenic, antimony, sulfur, selenium, tellurium, gold, platinum, iridium, or iron. The cathode or the anode may comprise at least one metal or alloy selected from the group consisting of nickel, copper, chromium, iron, manganese, titanium, zinc, zirconium, molybdenum, tantalum, platinum, iridium, cobalt, silicon, and carbon. The carbon nanomaterial growth may comprise at least one of carbon nanotubes, graphene, carbon nano-onions, and hollow carbon nanospheres. The carbonate may comprise at least one of alkali or alkaline earth carbonates, or may comprise at least one metal oxide additive, or may comprise at least one of lithium, barium, calcium, magnesium, or zinc oxide. The nanomaterial may have a length of at least 100 μm, or may have a length of 1 to 100 μm, or may have a length of less than 1 μm.

[0085] Also disclosed is a system for producing carbon nanomaterials, the system comprising a current source, a cell holding a molten carbonate electrolyte between an anode and a cathode, and a doping component of carbon nanomaterial within the cell, the current source capable of passing a current through the cathode and the anode within the cell, and producing doped carbon nanomaterial from the cathode of the cell.

[0086] While various embodiments of the present invention have been described above, it should be understood that these embodiments are presented by way of example only, and not limitation. Many modifications to the disclosed embodiments may be made in accordance with the disclosure herein without departing from the spirit and scope of the present invention. Thus, the breadth and scope of the present invention should not be limited to the above-described embodiments. Rather, the scope of the present invention should be defined according to the following claims and their equivalents.

[0087] While the present invention has been shown and described in one or more embodiments, equivalent alterations and modifications (alternatives) are possible and will become apparent to those skilled in the art upon reading and understanding this specification and the accompanying drawings. Furthermore, while one particular feature of the invention may be disclosed in connection with one of several implementations, such feature may be combined with one or more features of other implementations, as may be known or suitable or desirable for a particular application. [Explanation of symbols]

[0088] 100 systems, 110 chambers (cells)

Claims

1. 1. A method for producing doped carbon nanomaterials, comprising: heating a carbonate electrolyte selected from the group consisting of lithium carbonate, sodium carbonate, potassium carbonate, strontium carbonate, rubidium carbonate, cesium carbonate, barium carbonate, and calcium carbonate to obtain a molten carbonate electrolyte; disposing the molten carbonate electrolyte between an anode and a cathode in a cell; including within the cell at least one of a solid electrolyte additive, a liquid electrolyte additive, a gaseous electrolyte additive, a cathode material, and an anode material, a carbon nanomaterial doping component that dissolves or reacts to introduce dopant atoms into the molten carbonate electrolyte, the carbon nanomaterial doping component further comprising at least one material selected from the group consisting of silicon, germanium, nitrogen, phosphorus, arsenic, antimony, sulfur, selenium, tellurium, gold, alkali metals, alkaline earth metals, nickel, copper, chromium, iron, manganese, titanium, zinc, zirconium, molybdenum, tantalum, platinum, iridium, and cobalt; applying a current to the cathode and the anode in the cell; collecting the doped carbon nanomaterial growth from the cathode in the cell; the doped carbon nanomaterial comprises the dopant atoms of the carbon nanomaterial doping component directly incorporated in the construction of the doped carbon nanomaterial in the cathode, and when the molten carbonate electrolyte contains a transition metal nucleating agent, the doped carbon nanomaterial comprises doped carbon nanotubes and / or doped carbon nanofibers; When the transition metal nucleating agent is not included in the molten carbonate electrolyte, the doped carbon nanomaterial includes at least one of doped carbon nano-onions, doped hollow carbon nanospheres, and doped graphene platelets, and further includes: The method, wherein passing an electric current comprises passing an alternating current through the molten carbonate electrolyte.

2. In claim 1, The method, wherein the alternating current is selected for the growth of the doped carbon nano-onions.

3. In claim 1, further comprising adding zinc oxide to the molten carbonate electrolyte; The method, wherein the alternating current is selected for growth of the doped graphene platelets.

4. 1. A method for producing doped carbon nanomaterials, comprising: heating a carbonate electrolyte selected from the group consisting of lithium carbonate, sodium carbonate, potassium carbonate, strontium carbonate, rubidium carbonate, cesium carbonate, barium carbonate, and calcium carbonate to obtain a molten carbonate electrolyte; disposing the molten carbonate electrolyte between an anode and a cathode in a cell; adding magnesium oxide to the molten carbonate electrolyte; including within the cell at least one of a solid electrolyte additive, a liquid electrolyte additive, a gaseous electrolyte additive, a cathode material, and an anode material, a carbon nanomaterial doping component that dissolves or reacts to introduce dopant atoms into the molten carbonate electrolyte, the carbon nanomaterial doping component further comprising at least one material selected from the group consisting of silicon, germanium, nitrogen, phosphorus, arsenic, antimony, sulfur, selenium, tellurium, gold, alkali metals, alkaline earth metals, nickel, copper, chromium, iron, manganese, titanium, zinc, zirconium, molybdenum, tantalum, platinum, iridium, and cobalt; applying a current to the cathode and the anode in the cell; collecting the doped carbon nanomaterial growth from the cathode in the cell; the doped carbon nanomaterial comprises the dopant atoms of the carbon nanomaterial doping component directly incorporated in the construction of the doped carbon nanomaterial in the cathode, and when the molten carbonate electrolyte contains a transition metal nucleating agent, the doped carbon nanomaterial comprises doped carbon nanotubes and / or doped carbon nanofibers; When the transition metal nucleating agent is not included in the molten carbonate electrolyte, the doped carbon nanomaterial comprises at least one of doped carbon nano-onions, doped hollow carbon nanospheres, and doped graphene platelets; The method wherein the current is selected for growth of the doped hollow carbon nanospheres.

5. In claim 1 or 4, The method further comprising dispersing a transition metal for growth of doped carbon nanotube products.

6. In claim 1 or 4, The method, wherein the heating comprises heating the molten carbonate electrolyte to 700 to 800°C.

7. In claim 1 or 4, The method includes introducing the carbon nanomaterial doping component by adding a salt, covalent bond, or elemental compound containing atoms of the carbon nanomaterial doping component directly to the electrolyte in solid, liquid, or gas form.

8. In claim 1 or 4, The method, wherein the carbon nanomaterial doping component comprises at least one of thionyl chloride, sulfur chloride, silicon chloride, thionyl nitrate, silicon nitrate, and silicon nitrite.

9. In claim 1 or 4, The method, wherein the carbon nanomaterial doping component comprises at least one carbon nanomaterial doping element.

10. In claim 1 or 4, 10. The method of claim 1, wherein the cathode and anode comprise at least one material or alloy selected from the group consisting of nickel, copper, chromium, iron, manganese, titanium, zinc, zirconium, molybdenum, tantalum, platinum, iridium, cobalt, silicon, and carbon.

11. In claim 1 or 4, The method, wherein the carbon nanomaterial doping component comprises a coating on the cathode or the anode.

12. In claim 1, The method, wherein the doped carbon nanomaterial is a doped carbon nanotube.

13. In claim 1, The method, wherein the doped carbon nanomaterial is a doped graphene platelet.

14. 1. A method for producing doped carbon nanomaterials, comprising: heating a carbonate electrolyte selected from the group consisting of lithium carbonate, sodium carbonate, potassium carbonate, strontium carbonate, rubidium carbonate, cesium carbonate, barium carbonate, and calcium carbonate to obtain a molten carbonate electrolyte; disposing the molten carbonate electrolyte between an anode and a cathode in a cell; including within the cell at least one of a solid electrolyte additive, a liquid electrolyte additive, a gaseous electrolyte additive, a cathode material, and an anode material, a carbon nanomaterial doping component that dissolves or reacts to introduce dopant atoms into the molten carbonate electrolyte, the carbon nanomaterial doping component further comprising at least one material selected from the group consisting of silicon, germanium, nitrogen, phosphorus, arsenic, antimony, sulfur, selenium, tellurium, gold, alkali metals, alkaline earth metals, nickel, copper, chromium, iron, manganese, titanium, zinc, zirconium, molybdenum, tantalum, platinum, iridium, and cobalt; applying a current to the cathode and the anode in the cell; collecting the doped carbon nanomaterial growth from the cathode in the cell; the doped carbon nanomaterial comprises the dopant atoms of the carbon nanomaterial doping component directly incorporated in the construction of the doped carbon nanomaterial in the cathode, and when the molten carbonate electrolyte contains a transition metal nucleating agent, the doped carbon nanomaterial comprises doped carbon nanotubes and / or doped carbon nanofibers; When the transition metal nucleating agent is not included in the molten carbonate electrolyte, the doped carbon nanomaterial is at least one of a doped carbon nano-onion and a doped hollow carbon nanosphere.

15. In claim 1, The carbonate electrolyte further comprises at least one of the following metal oxides as an additive: lithium oxide, barium oxide, calcium oxide, magnesium oxide, or zinc oxide.

16. 1. A method for producing doped carbon nanomaterials, comprising: heating a carbonate electrolyte selected from the group consisting of lithium carbonate, sodium carbonate, potassium carbonate, strontium carbonate, rubidium carbonate, cesium carbonate, barium carbonate, and calcium carbonate to obtain a molten carbonate electrolyte; disposing the molten carbonate electrolyte between an anode and a cathode in a cell; including within the cell at least one of a solid electrolyte additive, a liquid electrolyte additive, a gaseous electrolyte additive, a cathode material, and an anode material, a carbon nanomaterial doping component that dissolves or reacts to introduce dopant atoms into the molten carbonate electrolyte, the carbon nanomaterial doping component further comprising at least one material selected from the group consisting of nitrogen, phosphorus, and sulfur; applying a current to the cathode and the anode in the cell; collecting the doped carbon nanomaterial growth from the cathode in the cell; the doped carbon nanomaterial comprises the dopant atoms of the carbon nanomaterial doping component directly incorporated in the construction of the doped carbon nanomaterial in the cathode, and when the molten carbonate electrolyte contains a transition metal nucleating agent, the doped carbon nanomaterial comprises doped carbon nanotubes and / or doped carbon nanofibers; When the transition metal nucleating agent is not included in the molten carbonate electrolyte, the doped carbon nanomaterial comprises at least one of doped carbon nano-onions, doped hollow carbon nanospheres, and doped graphene platelets.

17. 1. A method for producing doped carbon nanomaterials, comprising: heating a carbonate electrolyte selected from the group consisting of lithium carbonate, sodium carbonate, potassium carbonate, strontium carbonate, rubidium carbonate, cesium carbonate, barium carbonate, and calcium carbonate to obtain a molten carbonate electrolyte; disposing the molten carbonate electrolyte between an anode and a cathode in a cell; including within the cell at least one of a solid electrolyte additive, a liquid electrolyte additive, a gaseous electrolyte additive, a cathode material, and an anode material, a carbon nanomaterial doping component that dissolves or reacts to introduce dopant atoms into the molten carbonate electrolyte, the carbon nanomaterial doping component further comprising at least one material selected from the group consisting of germanium, nitrogen, phosphorus, arsenic, antimony, sulfur, selenium, tellurium, gold, an alkali metal, an alkaline earth metal, copper, chromium, iron, manganese, titanium, zinc, zirconium, molybdenum, tantalum, platinum, iridium, and cobalt; applying a current to the cathode and the anode in the cell; collecting the doped carbon nanomaterial growth from the cathode in the cell; the doped carbon nanomaterial comprises the dopant atoms of the carbon nanomaterial doping component directly incorporated in the construction of the doped carbon nanomaterial in the cathode, and when the molten carbonate electrolyte contains a transition metal nucleating agent, the doped carbon nanomaterial comprises doped carbon nanotubes and / or doped carbon nanofibers; When the transition metal nucleating agent is not included in the molten carbonate electrolyte, the doped carbon nanomaterial may be at least one of doped carbon nano-onions, doped hollow carbon nanospheres, and doped graphene platelets. Including, a method.

Images