Method and apparatus for producing carbon materials incorporating additives

Abstract

This invention provides a method for producing carbon materials from one or more carbon-containing raw material gases. [Solution] A step to provide an electrolytic cell comprising an anode 130, a cathode 140, and a reaction vessel configured to contain a molten electrolyte, wherein the cathode is located at least at the bottom of the reaction vessel; a step to supply a molten electrolyte 150 into the reaction vessel such that an electric current passes between the anode and the cathode via the molten electrolyte, wherein an additive is configured as a layer covering the surface of the cathode at the bottom of the reaction vessel such that it is on the surface of the cathode and in contact with the molten electrolyte; and a step to apply a voltage between the anode and the cathode while supplying one or more carbon-containing raw material gases to the molten electrolyte, thereby producing a carbon material.

Description

[Technical Field]

[0001] This disclosure generally relates to the manufacture of carbon materials incorporating additives using carbon-containing gases as raw material gases. [Background technology]

[0002] Carbon materials in various forms, such as powders and dispersions, are becoming increasingly important in the manufacture of energy storage devices (e.g., supercapacitors, batteries, fuel cells, and other energy storage systems) due to their electrical and mechanical properties.

[0003] For example, transition metal nitrogen-doped carbon materials (MNCs) are attracting attention as promising alternatives to Pt catalysts in polymer electrolyte membrane fuel cells (PEMFCs) because the doped carbon materials are low-cost and possess high electrocatalytic activity. In recent years, many reports have shown that carbon nanomaterials doped with both copper and nitrogen are efficient and durable electrocatalysts. Catalysts containing Cu-Nx moieties supported on a carbon matrix are also called monatomic catalysts (SACs) and reduce oxygen via a four-electron pathway. Cu-N x The site consists of a copper atom surrounded by x nitrogen atoms (mainly x=2, 3, 4). Transition metal macrocyclic molecules such as metallic phthalocyanines and porphyrins are commonly used in the production of SACs. These molecules have a metal atom bonded to four nitrogen atoms and therefore function as the active site for MNC catalysts. Copper particles encapsulated with N-doped carbon (Cu@NC) are another group of Cu-NC catalysts. The carbon shell protects the metal particles from corrosion and oxidation and controls the electronic interaction with adsorbents in the oxygen reduction reaction (ORR). Furthermore, the activity of MNC materials is partially attributable to the nitrogen portion in the carbon lattice, and pyridinic-N and graphite-N are the most suitable chemical species for effective oxygen reduction.

[0004] Molten salt CO2 capture and electrochemical conversion (MSCC-ET) has recently attracted attention as an attractive method for producing carbon-based materials. In this process, a carbonate-containing molten salt absorbs CO2 from the atmosphere and O2. 2- It is separated into ions. Using MSCC-ET, we have successfully synthesized carbon nanotubes, carbon spheres (microspherical carbon), and graphite. The morphology of CO2-derived carbon materials can be changed according to the electrolysis conditions. For example, carbon nanotubes, carbon spheres (microspherical carbon), and graphite have been successfully synthesized using MSCC-ET.

[0005] In "Controlled Growth of Unusual Nanocarbon Allotropes by Molten Electrolysis of CO2" (Catalysts 2022, 12, 125), Liu et al. disclose a method for synthesizing carbon materials by electrolysis using a molten carbonate electrolyte, and discuss the effects of different metal and metal oxide additives in the molten electrolyte on the resulting nanocarbon morphology.

[0006] In "Nickel and Nitrogen-Doped Bifunctional ORR and HER Electrocatalysts Derived from CO2" (ACS Sustainable Chem. Eng. 2022, 10, 1, 134-145), Remmel et al. disclose the synthesis of nickel and nitrogen-doped carbon materials by electrolysis using a molten carbonate electrolyte containing NiO as an additive, followed by N-doping with DCDA and PVP. [Overview of the project] [Problems that the invention aims to solve]

[0007] The present invention aims to provide a method and apparatus for producing a carbon material incorporating additives using a carbon-containing gas as a raw material gas. [Means for solving the problem]

[0008] According to one embodiment of the present invention, a method for producing a carbon material from one or more carbon-containing raw material gases is provided, the method comprising the following steps. A step to provide an electrolytic cell comprising an anode, a cathode, and a reaction vessel configured to contain a molten electrolyte, wherein the cathode is located at least at the bottom of the reaction vessel; A step of supplying the molten electrolyte into the reaction vessel such that an electric current passes between the anode and the cathode via the molten electrolyte, wherein the additive is configured as a layer covering the surface of the cathode at the bottom of the reaction vessel such that it is on the surface of the cathode and is positioned to be in contact with the molten electrolyte; and A step of supplying one or more carbon-containing raw material gases to the molten electrolyte while applying a voltage between the anode and the cathode, thereby producing the carbon material.

[0009] This method enables the production of carbon materials with additives incorporated into the carbon network when forming carbon from carbon-containing source gases such as CO2. By configuring the additive as a layer coating the surface of the cathode, the carbon material is formed through the layer of additive, allowing the additive to be embedded in the carbon network of the carbon material being formed. As a result, the additive is well dispersed in the carbon material formed at the cathode. This method also enables the incorporation of additives into the carbon matrix without requiring an additional doping step after the synthesis of the carbon material to incorporate the additive into the carbon network.

[0010] The electrolytic cell comprises a reaction vessel configured to contain a molten electrolyte, and the cathode is positioned at least at the bottom of the reaction vessel such that when the molten electrolyte is contained within the reaction vessel, the surface of the cathode coated with an additive is placed within the molten electrolyte. This provides a suitable configuration that allows a wide range of additive materials to be coated onto the surface of the cathode. For example, the additive material can be incorporated into the carbon material formed on the cathode surface during electrolysis by spreading the additive material in powder form over the entire surface of the cathode to coat it.

[0011] It will be understood that the reaction vessel may have any suitable shape suitable for containing the molten electrolyte. The reaction vessel may be any three-dimensional structure that defines a cavity in which the molten electrolyte can be contained. The reaction vessel may be, for example, substantially cubic or substantially cylindrical. The reaction vessel preferably has a substantially flat internal bottom surface in which the cathode is placed.

[0012] The cathode may define at least a portion of the internal bottom surface of the reaction vessel, or it may define the entire internal bottom surface of the reaction vessel. The cathode can form at least the bottom of the reaction vessel (in particular, the substantially flat internal bottom surface of the reaction vessel), and in some embodiments, it can form the entire reaction vessel (i.e., the reaction vessel is formed of cathode material so that the reaction vessel functions as a cathode during the electrolytic process). In other words, the cathode can be molded to form a reaction vessel (i.e., the cathode is the reaction vessel). Thus, the molten electrolyte can be contained within the cathode, and the additive is configured as a layer covering the internal bottom surface of the cathode. This provides a preferred configuration in which the additive can be provided as a layer covering the surface of the cathode so as to be positioned between the cathode and the molten electrolyte.

[0013] The additive may have a higher density than the molten electrolyte at the reaction temperature. Therefore, the additive can coat the cathode simply by placing it on the cathode located at the bottom of the reaction vessel. Due to the relative density of the additive and the molten electrolyte, the additive remains coated on the cathode by gravity during the synthesis process. This keeps the additive adjacent to the cathode during the synthesis process, allowing for effective incorporation of the additive into the carbon material formed at the cathode. The additive can be placed in the reaction vessel to coat the cathode surface (for example, by spreading the additive material over the entire surface of the cathode) before the electrolyte is added to the reaction vessel. Alternatively, the molten electrolyte may be placed in the reaction vessel first (by melting the electrolyte and then adding it to the reaction vessel, or by melting the electrolyte within the reaction vessel), and then the additive may be added to the molten electrolyte and allowed to settle at the bottom of the reaction vessel by gravity to coat the cathode surface before electrolysis occurs.

[0014] The additive may contain at least one of the following metals, particularly copper, cobalt, nickel, aluminum, and titanium, and may be an elemental metal or a metallic compound.

[0015] The additive may contain metal complexes such as transition metal complexes. The metal complex may be a macrocyclic metal complex. x It may include a part, where M is a metal and x is arbitrarily 2, 3, or 4. That is, MN x The part consists of a metal atom surrounded by x nitrogen atoms. The additive may include a metal phthalocyanine or a metal porphyrin complex. The additive may include a metal complex selected from the group consisting of copper phthalocyanine, cobalt phthalocyanine, nickel phthalocyanine, aluminum phthalocyanine, and titanium phthalocyanine, or any combination thereof.

[0016] In some embodiments, the amount of additive supported on the cathode surface is 1 to 20 mg / cm². -2It is within the range. In one embodiment, the additive is copper phthalocyanine, and the loading amount of copper phthalocyanine on the surface of the cathode is 2 - 8 mg cm -2 within the range, especially 4 mg cm -2 may be.

[0017] The electrolyte may contain a carbonate base. The electrolyte may contain Na2CO3, Li2CO3, K2CO3, BaCO3, CaCO3 or any combination thereof. In one embodiment, the electrolyte contains a eutectic mixture of Na2CO3, Li2CO3 and K2CO3. By providing a eutectic mixture of salts, the melting point of the electrolyte can be lowered, and thus synthesis can be carried out at a lower temperature. As a result, the specific surface area of the synthesized material increases, the porosity improves, and the electrode catalytic performance of the carbon material is consequently improved.

[0018] To melt the electrolyte and maintain the electrolyte in a molten state, the electrolyte may be heated to a temperature of 400°C to 900°C.

[0019] Applying a voltage between the anode and the cathode can be done by a power supply adapted to supply a current of 12,000 - 24,000 amperes (A) to the device, for example 4,000 A. According to an embodiment of the present disclosure, the applied direct current density is from 100 A m -2 to 20,000 (preferably 6,000) A m -2 up to the range. For example, when using a direct current (DC) power supply or a rectifier, the positive (+) terminal is connected to one or more anodes, and the negative (-) terminal is connected to one or more cathodes. With a high current density and a low voltage, the growth of the carbon material can be made slower, and thus it becomes possible to improve the structure of the carbon material. As the power supply, renewable energy such as sunlight, wind power, and hydropower can be used.

[0020] The carbon-containing raw material gas may contain one or a combination of CO2, CH4, and CO. Preferably, the carbon-containing raw material gas contains CO2. The raw material gas may be, for example, at least one of exhaust gases or industrial exhaust gases containing one or more of CO, CO2, or CH4. Environmental damage can be reduced by using raw material gases such as exhaust gases and industrial exhaust gases or other waste gases containing CO2. For example, the CO2 may be industrial waste CO2 or exhaust CO2 from heavy industry emission sources, and according to this disclosure, it is used as a raw material for producing carbon materials.

[0021] The carbon-containing raw material gas may be supplied to the electrolytic cell by any suitable means. The raw material gas may be present in the atmosphere of the electrolytic cell so that the electrolyte is in fluid communication with the atmosphere containing the raw material gas. For example, if the carbon-containing raw material gas is CO2, the electrolyte may be open to air so that naturally occurring CO2 in the air is captured by the molten electrolyte during the electrolysis process. Alternatively, the atmosphere of the electrolytic cell may be controlled to contain a CO2 concentration higher than the natural concentration of CO2 in the air. For example, exhaust gas, industrial gas or other carbon-containing exhaust gas may be introduced into the atmosphere of the electrolytic cell so that the electrolyte is in fluid communication with the exhaust gas, allowing CO2, CH4 and / or CO to be incorporated into the molten electrolyte during the electrolysis process. Other raw material gases may be supplied in the same manner. Alternatively or additionally, the carbon-containing raw material gas may be introduced directly into the molten electrolyte during the electrolysis process, for example, by supplying the gas to the molten electrolyte via a tube. The raw material gas may be bubbled into the molten electrolyte.

[0022] By selecting an appropriate cathode material, additional dopants can be incorporated into the carbon material. For example, the cathode may contain at least one metal selected from iron, nickel, and chromium, or any combination thereof. Incorporating such dopant metals during synthesis can further optimize and improve the electrocatalytic properties of the material without requiring additional doping steps. In some embodiments, the cathode may contain stainless steel. Alternatively, the cathode may be formed from an inert cathode material such that only the dopants incorporated into the carbon material originate from the additives. The cathode may contain at least one of graphite or silicon carbide.

[0023] This method may further include a step of removing carbon material from the cathode. Subsequently, a subsequent step can be performed on the recovered carbon material. For example, this method may include a subsequent nitrogen doping step. This is particularly relevant if the additive is MN x This is beneficial when the material contains metal complexes with a specific moiety. This increases the basicity of the carbon support, which alters its electronic properties and improves the activity of the oxygen reduction reaction at the metal-nitrogen active site in the material. As a result, the electrocatalytic properties of the carbon material are improved.

[0024] The nitrogen doping process may include a step of thermally decomposing a mixture of carbon material recovered from the cathode and a nitrogen-containing doping agent. The nitrogen-containing doping agent may contain at least one of polyvinylpyrrolidone and dicyandiamide.

[0025] According to another aspect of the present invention, a carbon material obtained by the above method is provided. The carbon material may contain graphite as a carbon allotrope.

[0026] According to another aspect of the present invention, an apparatus for producing a carbon material from one or more carbon-containing raw material gases is provided, the apparatus comprising: A reaction vessel configured to contain a molten electrolyte; anode; A cathode located at least at the bottom of the reaction vessel; A power supply for applying a voltage between the anode and the cathode; and A heating unit configured to heat the reaction vessel in order to maintain the electrolyte in a molten state.

[0027] In this configuration, the apparatus can be set up to provide a layer of additive coating the surface of the cathode by placing the additive material at the bottom of the reaction vessel so as to cover the cathode. As described above with respect to the method of this disclosure, the carbon material can be formed via a layer of additive material by forming the carbon material by electrolysis using a molten electrolyte and a carbon-containing feedstock gas, so that the additive material is embedded in the carbon network of the carbon material as it is formed. As a result, the additive is well dispersed in the carbon material formed at the cathode. Furthermore, this apparatus facilitates the incorporation of additives into the carbon matrix without requiring an additional doping step after the synthesis of the carbon material. This apparatus provides a suitable configuration that can coat the surface of the cathode with a wide range of additive materials.

[0028] As described above in relation to the method of the present disclosure, it will be understood that the reaction vessel may have any suitable shape suitable for accommodating the molten electrolyte. The reaction vessel may be any three-dimensional structure defining a cavity in which the molten electrolyte can be accommodated. The reaction vessel may be, for example, substantially cubic or cylindrical. Preferably, the reaction vessel has a substantially flat internal bottom surface in which the cathode is located.

[0029] The cathode may define at least a portion of the inner bottom surface of the reaction vessel. The cathode may form at least the bottom of the reaction vessel, and in some embodiments, it may form the entire reaction vessel (i.e., the reaction vessel is formed of cathode material such that the reaction vessel becomes the cathode during the electrolytic process). In certain embodiments, the cathode may be molded to form the reaction vessel (i.e., the cathode is the reaction vessel). Thus, the molten electrolyte can be contained within the cathode, and the additive can be configured as a layer covering the inner bottom surface of the cathode. This provides a suitable configuration in which the additive can be configured as a layer covering the surface of the cathode and placed between the cathode and the molten electrolyte. This configuration is particularly beneficial, for example, when the additive has a higher density than the density of the molten electrolyte, as described above.

[0030] The apparatus may include an additive configured as a layer that coats the surface of the cathode at the bottom of the reaction vessel.

[0031] The apparatus may include a gas supply unit configured to supply one or more source gases to a molten electrolyte in a reaction vessel. The gas supply unit may be configured to supply gases continuously during the operation of the apparatus. The gas supply unit may include means for uniformly diffusing the source gases into the electrolyte. Such means for diffusing the source gases may be source gas piping arranged within the reaction vessel. If necessary, the gas supply unit may include electrolyte mixing means for uniformly diffusing CO2 gas into the electrolyte. The electrolyte mixing means allows for the uniform dissolution and distribution of the gas into the electrolyte. Slow mass transport within the reaction vessel creates an oxide concentration gradient, accelerating anode corrosion. The electrolyte mixing means may be an S-shaped tube with holes, arranged within an electrolytic cell chamber in the electrolyte. When the source gases are pumped through the S-shaped tube in the molten electrolyte, bubbles of the source gases are generated in the electrolyte, allowing the electrolytes to be mixed. Other suitable means for directly introducing the source gases into the molten electrolyte will be conceivable to those skilled in the art. [Brief explanation of the drawing]

[0032] Next, non-limiting embodiments of the present invention will be described illustratively with reference to the accompanying drawings: Figure 1 is a block diagram showing an apparatus for producing carbon materials from one or more raw material gases. Figure 2 is a schematic diagram of the electrolytic cell of the apparatus shown in Figure 1. Figure 3 is a flowchart showing an example of a method for manufacturing carbon materials. Figures 4A to 4C are SEM images of carbon materials manufactured according to the method in Figure 3. Figures 4D and 4E are bright-field TEM images of carbon materials fabricated according to the method in Figure 3. Figures 4F and 5A are HAADF-STEM images of carbon materials fabricated according to the method in Figure 3. Figures 5B, 5C, and 5D are STEM-EDX images of carbon materials fabricated according to the method in Figure 3. Figures 6A, 7A, and 8A are HAADF-STEM images of carbon materials fabricated according to the method in Figure 3. Figures 6B–6E, 7B–7E, and 8B–8E are STEM-EDX images of carbon materials produced according to the method in Figure 3. Figure 9 shows the X-ray diffraction pattern of a carbon material produced according to the method in Figure 3. Figure 10A is a graph showing the polarization curve of a carbon material produced according to the method in Figure 3. Figure 10B is a graph showing the Tafel gradient of carbon materials manufactured according to the method in Figure 3. Figures 11A to 11C are graphs showing Koutecky-Levich plots for the oxygen reduction of carbon materials produced according to the method in Figure 3. Figure 12 is a graph showing the X-ray diffraction pattern of another carbon material manufactured according to the method in Figure 3. Figures 13 and 14 are graphs showing the polarization curves of another carbon material produced according to the method in Figure 3. Figures 15A to 15D are SEM images of other carbon materials. Detailed explanation of the drawings.

[0033] Referring to Figure 1, a block scheme is shown illustrating the apparatus 100 for producing a carbon material from one or more source gases according to the present disclosure. The apparatus 100 comprises an electrolytic cell 120, a power supply 170, a heating unit 180, and an optional gas supply unit 190.

[0034] Referring to Figure 2, a schematic diagram of the electrolytic cell 120 of Figure 1 is shown. The electrolytic cell 120 comprises an anode 130 and a cathode 140. The cathode 140 is molded to form a reaction vessel that houses layers of molten electrolyte 150 and additive 160.

[0035] The anode 130 is insertable into an internal space defined by the cathode 140 so as to be placed within the molten electrolyte 150 contained within the cathode 140. Alternatively, the anode 130 may be in a fixed position relative to the cathode 140, which allows the anode 130 to be immersed in the molten electrolyte 150 during use. The anode 130 and cathode 140 are connected via a power supply 170 so that a voltage can be applied to the anode 140 and cathode 150.

[0036] It will be understood that the reaction vessel can be formed into any suitable shape capable of accommodating the molten electrolyte 150. In the illustrated embodiment, the reaction vessel defined by the cathode 140 is substantially cubic or rectangular in shape, adopting a “basket” shape, but other shapes such as cylindrical ones can also be adopted. Various other suitable shapes of cathodes are conceivable to those skilled in the art.

[0037] Although not shown in Figure 2, the gas supply unit 180 (if provided) can be positioned in a fixed location within the internal space defined by the cathode 140, or can be inserted into it. The gas supply unit 180 may take the form of one or more tubes arranged to directly deliver gas to the electrolyte 150 housed in the reaction vessel defined by the cathode 140.

[0038] Alternatively or additionally, a carbon-containing raw material gas may be introduced into the atmosphere 200 of the electrolytic cell so as to be in fluid communication with the molten electrolyte 150. In this way, the raw material gas can be incorporated into the molten electrolyte during the electrolysis process.

[0039] Figure 3 is a flowchart illustrating an example of a method for producing a carbon material according to this disclosure, and will be described with further reference to the apparatus schematically shown in Figures 1 and 2. The exemplary method includes the following steps:

[0040] S1: A step of providing an electrolytic cell 120 comprising an anode 130 and a cathode 140, wherein the cathode 140 is shaped to form a reaction vessel for containing a molten electrolyte 150.

[0041] S2: A step of placing a layer of additive 160 at the bottom of the reaction vessel defined by the cathode 140 so as to cover the inner bottom surface 142 of the cathode 140.

[0042] S3: A step of providing an electrolyte 150 in a reaction vessel defined by a cathode 140 and melting the electrolyte 150 by the operation of a heating unit 180, wherein an additive 160 is selected to have a density higher than the density of the molten electrolyte 150 at the reaction temperature, thereby maintaining the additive 160 on the inner bottom surface 142 of the cathode 140.

[0043] S4: A step in which, while maintaining the molten electrolyte 150 in equilibrium with the CO2-containing atmosphere 200, a voltage is applied between the anode 130 and the cathode 140 by operating the power supply 170, thereby generating carbon material on the inner bottom surface 142 of the cathode 140.

[0044] S5: Process to remove carbon material from cathode 140.

[0045] S6: A process in which the synthesized carbon material is further doped.

[0046] In the example described, the electrolyte 150 is melted in the reaction vessel defined by the cathode 140 in step S3. Alternatively, the electrolyte 150 may be molten outside the reaction vessel and then transferred into the reaction vessel by appropriate means. In either case, the heating unit 180 is configured to heat the electrolyte 150 in the reaction vessel defined by the cathode 140 to a temperature sufficient to maintain the electrolyte 150 in a molten state during electrolysis.

[0047] In the described example, the additive 160 is selected to have a density higher than that of the molten electrolyte 150 at the reaction temperature, thereby maintaining the additive 160 on the inner bottom surface 142 of the cathode 140 by gravity. This provides a suitable configuration for maintaining a layer of additive 160 on the surface of the cathode 140 during the electrolytic reaction. However, it will be understood that the surface of the cathode 140 may be coated with additive 160 by other means conceivable to those skilled in the art.

[0048] In at least the examples described, steps S2 and S3 may be performed in any order. In particular, if the additive 160 is selected to have a higher density than the molten electrolyte 150, as in the examples described, the additive 160 may alternatively be placed in the reaction vessel after the molten electrolyte and allowed to settle on the inner bottom surface 142 of the cathode 140 before the electrolytic reaction.

[0049] In step S4, in the example described, the carbon-containing raw material gas (in this case, CO2) is supplied to the molten electrolyte 150 by maintaining the molten electrolyte 150 in equilibrium with the CO2-containing atmosphere 200. However, the carbon-containing raw material gas may be supplied by any gas supply unit 190 which can take any suitable form for introducing the gas into the molten electrolyte 150 as described above, either by or in addition to the gas supply unit 190.

[0050] In the example described, step S6 may be a nitrogen doping step. In particular, a mixture of the carbon material recovered from the cathode and a nitrogen-containing doping agent (e.g., polyvinylpyrrolidone or dicyandiamide) may be subjected to thermal decomposition. It will be understood that step S6 is optional, depending on the carbon material to be produced and the desired application.

[0051] Examples of the method for producing carbon materials according to this disclosure are described below. [Examples]

[0052] Example 1 Synthesis of carbon materials A DC01 steel "basket" reaction vessel was used as the cathode, with a layer of copper phthalocyanine (CuPc) as an additive. CuPc was uniformly spread on the bottom of the cathode, and the inner bottom surface of the cathode was coated with CuPc. Then, a eutectic mixture of Li2CO3, Na2CO3, and K2CO3 (>99.5%, Lach-Ner) was packed into the cathode as the electrolyte. The basket was then placed in a heating device and the electrolyte mixture was heated to 450°C. A graphite rod was used as the anode and placed in the molten electrolyte. Next, the electrodes were connected to a power supply, and a voltage of 4 V was applied between the electrodes for 2 hours.

[0053] Three different materials were synthesized by coating the inner bottom surface of the cathode basket with 50 mg, 100 mg, and 200 mg of CuPc. These coatings represented 2, 4, and 8 mg of CuPc relative to the surface area of ​​the inner bottom surface of the cathode. -2 Corresponding to the amount of CO2-Cu supported (hereinafter, the synthesized materials are each referred to as CO2-Cu 2.0 CO2-Cu 4.0 and CO2-Cu 8.0 (See also).

[0054] After the synthesis was complete, 5 M HCl was added, the mixture was sonicated for 30 minutes, and left at room temperature for 3 days to remove carbonates and soluble impurities. The carbon material was then filtered and dried.

[0055] Nitrogen doping of carbon materials Subsequently, the synthesized material was further doped with nitrogen. First, 50 mg of each carbon material sample was sonicated in ethanol for 2 hours with 5 mg of polyvinylpyrrolidone (PVP) and 1 g of dicyandiamide (DCDA). The mixture was then dried and placed in a ceramic boat. The boat was then placed in a quartz tube and then in a furnace. The furnace was purged with Ar and heated to 800°C. The material was thermally decomposed for 1 hour, cooled, and removed from the furnace.

[0056] result During synthesis, carbon materials are produced by the electrolysis of carbonates, resulting in the formation of lithium oxide and solid carbon. [ka]

[0057] Carbon is deposited inside a steel reaction vessel that acts as a cathode during the electrolytic process, incorporating CuPc (known to be stable up to 500°C) into the carbon network. The steel reaction vessel also serves as a source of Fe doping, as iron dissolves into the carbonate during carbon deposition. The low synthesis temperature (and high deposition voltage) also helps to form a porous carbon network, which allows for better access to both CO2 and oxygen reduction active sites.

[0058] Because the carbonate is in equilibrium with the surrounding atmosphere, CO2 is incorporated into the electrolyte, thereby regenerating Li2CO3 and enabling a continuous process. [ka]

[0059] To more strongly incorporate CuPc into the carbon lattice, increase the basicity and nitrogen doping level of the carbon material, and homogenize the carbon material, CuPc was suspended in ethanol and thermally decomposed in the presence of DCDA and PVP (see the nitrogen doping process described above).

[0060] Figures 4A-4C show the CO2-Cu produced as described above. 2.0 CO2-Cu 4.0 and CO2-Cu 8.0 These are SEM images of the carbon materials. The images show that the materials are highly porous. Graphite carbon flakes are more prominent where CuPc incorporation is low (Figure 4A). The higher the CuPc content, the more amorphous and porous the network formed (Figures 4B and 4C). When the CuPc content is low (Figure 4A), large graphite carbon flakes (d > 1 μm) are visible. Increasing the CuPc content in the reaction vessel reduced the size of these flakes.

[0061] Figures 4D and 4E show CO2-Cu 4.0 This is a bright-field TEM image of the material, showing the coexistence of graphite-like flakes and porous carbon material. Figure 4F is a HAADF-STEM image of the CO2-Cu100 material, showing that copper is well dispersed on the catalyst surface (appearing as bright dots). While most of the copper is dispersed at the atomic level on the material surface, Figure 4F also shows the presence of small metal particles.

[0062] STEM-EDX analysis was performed to determine whether the origin of the particulate phase was CuPc or a steel cathode. Figure 5A shows CO2-Cu 4.0Further HAADF-STEM images of the material show the presence of two nanoparticles within the carbon network. Figures 5B, 5C, and 5D are STEM-EDX images showing the chemical distribution of nitrogen (Figure 5B), copper (Figure 5C), and iron (Figure 5D). As can be seen from the figures, the distribution of Cu and N is uniform throughout the material, indicating successful uniform incorporation of Cu from CuPc and N from CuPc and DCDA. The STEM-EDX mapping image of Fe (Figure 5D) shows Fe concentrated in the nanoparticles, indicating that the particulate phase in the material originates from the steel cathode and not from the decomposition of CuPc and the formation of copper particles. Therefore, this result indicates that CuPc was successfully incorporated into the carbon network as an additive without decomposition. It will be understood that by using different metal cathodes, other metal dopants can be introduced, or by using an inert cathode, the central metal in the additive (Cu in this example) can be retained as the sole metal dopant.

[0063] Figures 6A to 8E show the CO2-Cu synthesized according to Example 1. 2.0 (Figures 6A-6E), CO2-Cu 4.0 (Figures 7A-7E) and CO2-Cu 8.0 (Figures 8A-8E) Provide further STEM-EDX analysis of carbon materials. Figures 6A, 7A, and 8A show CO2-Cu 2.0 CO2-Cu 4.0 and CO2-Cu 8.0These are HAADF-STEM images of the materials. The corresponding STEM-EDX elemental mapping images show the chemical distribution of carbon (Figures 6B, 7B, 8B), nitrogen (Figures 6C, 7C, 8C), copper (Figures 6D, 7D, 8D), and iron (Figures 6E, 7E, 8E) in the carbon materials. For all materials, uniform incorporation of Cu from CuPc and N from CuPc and DCDA was observed, indicating that CuPc was successfully incorporated into the carbon network as an additive without decomposition. All materials also showed incorporation of Fe, indicating that the Fe particulate phase originated from the steel cathode.

[0064] CO2-Cu 2.0 CO2-Cu 4.0 and CO2-Cu 8.0 The materials were further analyzed by X-ray photoelectron spectroscopy. The surface elemental composition of each material is shown in Table 1. Basket (CO2-Cu 2.0 The amount of ) carried is 2 mg cm -2 In this case, no copper was detected on the material surface. This indicates that, despite copper being confirmed in the material by the STEM-EDX mapping analysis described above, the copper content on the material surface was insufficient for detection by XPS. 4 mg cm -2 and 8 mg cm -2 At high loading levels, the copper content on the material surface was 0.3 at.% and 0.2 at.% respectively. This indicates that increasing the CuPc loading above a threshold leads to copper incorporation into the bulk material without increasing the surface content (related to the electrode catalyst). The effect of Cu on nitrogen content was also shown by XPS data, and the CuPc loading level was 4 mg cm². -2 Therefore, CO2-Cu 4.0 The nitrogen content is 14.5 at.%, which is much higher than the other samples, resulting in improved ORR activity, as will be discussed later. The increase in nitrogen content is related to the basicity of the catalytic material, which is known to be an important descriptor of electrocatalytic activity. A greater degree of iron uptake from the steel basket is also observed, which further increases the activity. The Fe content is higher than that of the other materials in CO2-Cu 4.0The sample size is much larger and indicates the optimal CuPc load for Fe uptake from the steel cathode.

[0065] [Table 1]

[0066] Figure 9 shows CO2-Cu 2.0 CO2-Cu 4.0 and CO2-Cu 8.0 The powder X-ray diffraction patterns of the material are shown. Graphite carbon was observed in all three patterns by the (002) diffraction peak at 26.8°2θ. The X-ray diffraction patterns support the findings obtained from the microscopic images. Up to the optimal CuPc content, the catalyst material becomes more amorphous (the peak intensity of graphite at 26.8°2θ (002) is greater than that of CO2-Cu). 4.0 CO2-Cu 2.0 As can be seen from the fact that it is lower than CO2-Cu, it then graphitizes more highly again during the pyrolysis process (the peak intensity (002) of graphite at 26.8°2θ is lower than CO2-Cu 8.0 CO2-Cu 4.0 (As can be seen from the higher values). Fe impurities from the steel basket used as the cathode were also observed in the diffraction pattern, suggesting that this may also affect the graphitization and porosity of the material.

[0067] To measure the electrocatalytic activity of the synthetic material, the rotating disk electrode (RDE) method was employed. First, 2 mg of the material and 3 μl of QAPS-S per 1 mg of carbon were used. 14 A 1 ml suspension containing the ionomer solution was prepared. Next, the suspension was pipetteed onto glassy carbon disk electrodes polished with 1 μl and 0.3 μl of alumina slurry prior to the experiment, and the residue was removed by continuous sonication with isopropanol and Milli-Q water. The catalyst load was 0.2 mg cm². -2The measurements were performed in a five-neck electrochemical cell in a 0.1 M KOH solution saturated with oxygen. A graphite rod was used as the counter electrode, and a silver / silver chloride electrode (Ag / AgCl) was used as the reference electrode. The polarization curve was calculated using a Gamry potentiostat 1010E at a sweep rate of 1.667 mV s. -1 Measurements were taken in the range of 0.05 V to -1.15 V vs (vs)Ag / AgCl. The working electrode rotation speeds were 400, 800, 1200, 1600, 1900, 2400, and 3600 rpm. The speed was controlled by an OrigaTrod instrument. The recorded potential values ​​were later converted to reversible hydrogen electrodes (RHE). Table 2 shows the kinetic current density, Tafel slopes, and mass activity of the CO2-derived catalyst at 0.8 and 0.9 V vs (vs)RHE.

[0068] Figure 10A shows CO2-Cu as an electrode catalyst. 2.0 CO2-Cu 4.0 and CO2-Cu 8.0 The polarization curves measured using the material by RDE method in 0.1 M KOH at 1600 rpm are shown. CO2-Cu 4.0 The material exhibited optimal performance, with an onset potential of 0.927 V vs RHE and a mass activity of 31.2 A g at 0.8 V vs RHE. -1 The results were as follows: The lower the copper load, the more positive the onset potential and the lower the mass activity; conversely, the higher the copper load, the lower these values ​​were.

[0069] Figure 10B shows CO2-Cu 2.0 CO2-Cu 4.0 and CO2-Cu 8.0 The Tafel gradient of the material is shown. CO2-Cu 4.0 The material is the most active catalyst for ORR, but the Tafel gradient is 76.1 mV dec -1 Therefore, with increasing potential, the voltage increases to 115.8 mV dec -1 It increased to CO2-Cu 8.0The catalyst's Tafel gradient is 67.9 mV dec -1 The average Tafel gradient of Pt / C (60 mV dec) -1 It was most similar to ). Similar values ​​of the Tafel gradient between catalysts indicate that the rate-determining step and reaction mechanism are the same.

[0070] [Table 2]

[0071] Figures 11A to 11C show CO2-Cu 2.0 (Figure 11A), CO2-Cu 4.0 (Figure 11B) and CO2-Cu 8.0 (Figure 11C) The Kootkey-Levich plot of oxygen reduction in the material is shown. The plot was derived based on ORR data obtained at different rotation speeds. Each inset from Figure 11A to Figure 11C shows the number of electrons transferred per O2 molecule. The number of electrons transferred n was calculated using the following formula.

number

[0072] For all materials, the n-value was approximately 4 at more negative potentials, indicating a 4-electron oxygen reduction process. However, at more positive potentials, the calculated number of transferred electrons was approximately 3.4–3.5, indicating that a certain amount of H2O2 was produced during reduction. H2O2 is an undesirable product as it causes degradation of fuel cell components, reduces current efficiency, and hinders the overall performance of the fuel cell. Nevertheless, electrochemical tests demonstrated high electrocatalytic activity of materials synthesized according to the methods of this disclosure.

[0073] Example 2 Six more carbon materials were synthesized using the same electrolytic method as described above for Example 1, except that zinc phthalocyanine (ZnPc), cobalt(II) phthalocyanine (Co(II)Pc), nickel phthalocyanine (NiPc), aluminum chloride phthalocyanine (AlPcCl), and titanium(IV) dichloride phthalocyanine (Ti(IV)PcCl2) were used instead of CuPc. Each additive was added at a concentration of 4 mg / cm² relative to the surface area of ​​the bottom of the reaction vessel defined by the cathode. -2 It was supplied with the following loading amount. Below, the manufactured carbon material is CO2-Zn 4.0 CO2-Co 4.0 CO2-Ni 4.0 CO2-Al 4.0 and CO2-Ti 4.0 Refer to this.

[0074] Figure 12 shows the CO2-Zn synthesized as described above. 4.0 CO2-Co 4.0 CO2-Ni 4.0 CO2-Al 4.0 , and CO2-Ti 4.0 The powder X-ray diffraction (XRD) pattern of the carbon material is shown. The XRD pattern showed peaks corresponding to the graphite planes (002) and (004) at 2θ equal to 26.8 and 54.6, respectively. Other peaks were due to the presence of iron oxide in the material revealed by cathode corrosion.

[0075] Figure 13 shows the ORR polarization curves of materials of CO2-Zn 4.0 , CO2-Co 4.0 , CO2-Ni 4.0 , CO2-Al 4.0 and CO2-Ti 4.0 measured for Example 1 using the same rotating disk electrode method as described above. A slight difference in the electrode catalytic activity of the synthesized materials was observed. Analysis of the polarization curves using the Koutecky–Levich equation revealed that all materials catalyze ORR via an indirect 2 + 2 electron pathway.

[0076] Next, in the same process as described above for the carbon material of Example 1, nitrogen was doped into the materials of CO2-Zn 4.0 , CO2-Co 4.0 , CO2-Ni 4.0 and CO2-Al 4.0 by pyrolysis using DCDA and PVP. The N-doped materials are hereinafter denoted as CO2-N-Zn 4.0 , CO2-N-Co 4.0 , CO2-N-Ni 4.0 and CO2-N-Al 4.0 . Figure 14 shows a comparison of the polarization curves of the carbon materials before and after nitrogen doping at a rotation speed of 1600 rpm for Co (Figure 14A), Zn (Figure 14B), Al (Figure 14C) and Ni (Figure 14E). As can be seen from the figure, a significant increase in ORR activity was observed for all materials after nitrogen doping.

[0077] Figure 15 is a SEM image showing the morphological differences of CO2-Co 4.0 (Figure 15A), CO2-Al 4.0 (Figure 15B), CO2-Ni 4.0 (Figure 15C) and CO2-Zn 4.0 (Figure 15D).

[0078] All optional and preferred features and modifications of the embodiments and dependent claims described herein are applicable to all embodiments of the invention taught herein. Furthermore, as with all optional and preferred features and modifications of the embodiments described herein, the individual features of the dependent claims are combinable and interchangeable with each other.

Claims

1. A method for producing a carbon material from one or more carbon-containing raw material gases, comprising the following steps: A step to provide an electrolytic cell comprising an anode, a cathode, and a reaction vessel configured to contain a molten electrolyte, wherein the cathode is located at least at the bottom of the reaction vessel; A step of supplying the molten electrolyte into the reaction vessel such that an electric current passes between the anode and the cathode via the molten electrolyte, wherein the additive is configured as a layer covering the surface of the cathode at the bottom of the reaction vessel, such that it is on the surface of the cathode and is positioned to be in contact with the molten electrolyte; and A step of supplying one or more carbon-containing raw material gases to the molten electrolyte while applying a voltage between the anode and the cathode, thereby producing the carbon material.

2. The method according to claim 1, wherein the cathode defines at least a portion of the inner bottom surface of the reaction vessel.

3. The method according to claim 2, wherein the cathode is shaped to form the reaction vessel, the molten electrolyte is housed within the cathode, and the additive is configured as a layer covering the inner bottom surface of the cathode.

4. The method according to any of the preceding claims, wherein the additive has a density higher than the density of the molten electrolyte.

5. The method according to claim 4, wherein the additive is placed in the reaction vessel so as to cover the surface of the cathode before the electrolyte is added to the reaction vessel.

6. The method according to claim 4, wherein the electrolyte is placed in the reaction vessel before the addition of the additive and / or melted before the addition of the additive.

7. The method according to any of the preceding claims, wherein the additive comprises at least one of copper, cobalt, nickel, aluminum, titanium, or iron.

8. The method according to any of the preceding claims, wherein the additive comprises a metal complex.

9. The aforementioned metal complex is MN x The method according to claim 8, wherein the portion is the metal, and x = 2, 3, or 4.

10. The method according to claim 8 or 9, wherein the additive comprises a metal phthalocyanine or a metal porphyrin complex.

11. The method according to claim 10, wherein the additive comprises a metal complex selected from the group consisting of copper phthalocyanine, cobalt phthalocyanine, nickel phthalocyanine, aluminum phthalocyanine, and titanium phthalocyanine, or any combination thereof.

12. The amount of the additive supported on the surface of the cathode is 1 to 20 mg cm². -2 A method according to any of the prior claims, which is within the scope of the preceding claim.

13. The additive is copper phthalocyanine, and the amount of copper phthalocyanine loaded on the surface of the cathode is 2 to 8 mg cm². -2 A method according to any of the prior claims, which is within the scope of the preceding claim.

14. The method according to any of the preceding claims, wherein the electrolyte comprises a carbonate base.

15. The electrolyte is Na 2 CO 3 、Li 2 CO 3 、K 2 CO 3 、BaCO 3 、CaCO 3 The method according to any of the preceding claims, comprising or any combination thereof.

16. The aforementioned electrolyte is Na 2 CO 3 Li 2 CO 3 and K 2 CO 3 A method according to any of the prior claims, comprising a mixture of the above.

17. The method according to any one of the preceding claims, wherein the electrolyte is heated to a temperature of 400°C to 900°C.

18. The aforementioned raw material gas is CO 2 CH 4 A method according to any of the prior claims, comprising one or a combination of CO.

19. The method according to any one of the preceding claims, wherein the raw material gas is present in the atmosphere of the electrolytic cell, and / or one or more raw material gases are directly introduced into the molten electrolyte.

20. The method according to any of the preceding claims, wherein the cathode comprises at least one metal selected from iron, nickel, and chromium, or any combination thereof.

21. The method according to any of the prior claims, further comprising the steps of removing the carbon material from the cathode and subsequently doping the carbon material with nitrogen.

22. The method according to claim 21, wherein the nitrogen doping step includes a step of thermally decomposing a mixture of the carbon material and a nitrogen-containing doping agent.

23. The method according to claim 22, wherein the nitrogen-containing doping agent comprises at least one of polyvinylpyrrolidone and dicyandiamide.

24. A carbon material obtained by the method described in any of the preceding claims.

25. The carbon material according to claim 24, comprising graphite as a carbon allotrope.

26. Apparatus for producing carbon materials from one or more carbon-containing raw material gases: A reaction vessel configured to contain a molten electrolyte; anode; A cathode located at least at the bottom of the reaction vessel; A power supply for applying a voltage between the anode and the cathode; and An apparatus comprising a heating unit configured to heat the reaction vessel in order to maintain the electrolyte in a molten state.

27. The apparatus according to claim 26, wherein the cathode defines at least a portion of the inner bottom surface of the reaction vessel.

28. The apparatus according to claim 27, wherein the reaction vessel is formed from a cathode material.

29. The apparatus according to any one of claims 26 to 28, further comprising an additive configured as a layer covering the surface of the cathode at the bottom of the reaction vessel.

30. The apparatus according to any one of claims 26 to 29, further comprising a gas supply unit configured to supply one or more raw material gases to the molten electrolyte in the reaction vessel.

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