Method for producing hydrogen and carbon nanotubes through methane decomposition and use thereof as electrode materials

Abstract

The present invention relates to a method for producing hydrogen and carbon nanotubes through methane decomposition, and a use thereof as electrode materials. More specifically, the present invention provides a method for producing electrode materials for batteries, wherein methane decomposition is promoted using a nickel-based catalyst to simultaneously produce a high yield of carbon nanotubes and high-purity hydrogen, and the produced carbon nanotubes are used to produce the electrode materials for batteries.

Description

Method for producing hydrogen and carbon nanotubes through methane decomposition and their application as electrode materials

[0001] The present invention relates to a method for producing hydrogen and carbon nanotubes through methane decomposition and their utilization as electrode materials. More specifically, it relates to a method for producing high-yield carbon nanotubes and high-purity hydrogen simultaneously by promoting methane decomposition using a nickel-based catalyst, and the carbon nanotubes produced in this manner can be utilized as electrode materials.

[0002]

[0003] Extreme climate change is occurring as global warming accelerates due to the emission of greenhouse gases, particularly carbon dioxide, from the use of fossil fuels. Consequently, hydrogen is gaining attention as a clean energy source and a substitute for fossil fuels. When hydrogen burns with oxygen, it releases only heat and water, without emitting other greenhouse gases such as carbon dioxide. Due to these advantages, research on hydrogen production is actively underway to prevent the acceleration of global warming and climate change.

[0004] Meanwhile, as an energy source, methane is gaining attention as a potential replacement for traditional fossil fuels, not only because it is the main component of natural gas and has abundant reserves, but also because it can be obtained from biological resources. In particular, research and development efforts are being made to convert methane into hydrogen, which is attracting attention as a clean fuel.

[0005] Conventional research on converting methane into hydrogen gas has largely been conducted using two methods. Steam reforming of methane (SMR), the process currently used primarily for hydrogen production, involves feeding high-temperature steam into the methane reforming reaction, which requires endothermic processing; this process necessitates high energy and steam. Since the SMR process simultaneously generates CO2 and CO₂ gases—greenhouse gases derived from steam—it presents problems such as requiring complex purification processes and incurring a significant environmental burden. Additionally, it has the disadvantage of requiring a Pressure Swing Adsorption (PSA) process to produce high-purity hydrogen, which can result in the emission of carbon dioxide as a byproduct. The Water Gas Shift reaction requires not only methane but also carbon monoxide for hydrogen production.

[0006] As an alternative to the aforementioned SMR, the Thermo-Catalytic Decomposition (TCD) process, which requires relatively less energy, is being proposed. Unlike the SMR process, the TCD process does not involve conversion into CO2 or CO2 gases; instead, the products are separated into carbon deposits and hydrogen gas, a clean fuel, which simplifies the purification process and offers the advantage of being environmentally friendly. Methane decomposition is known as an eco-friendly hydrogen production method capable of producing high-purity hydrogen without carbon dioxide emissions. Since it leaves only pure hydrogen and solid carbon after decomposition, separation is easy. Furthermore, because the methane decomposition reaction requires only methane as a reactant, it simplifies the production process and reduces costs.

[0007] The catalysts used in the above TCD process are classified into metal-based catalysts and carbon-based catalysts. As a prior art regarding metal-based catalysts, Manoj Pudukudy et al. disclose a catalyst prepared by adding 0.05% to 0.2% of Pt, a promoter, to Ni / CeO2 using CeO2 as the support and Ni as the active material. Although the dispersion and specific surface area of ​​Ni can be increased by adding Pt, there is a problem in that an additional step is required to activate the catalyst and reduce NiO present on the catalyst surface to Ni using H2, and Pt, which is relatively expensive, is used.

[0008] Ismael Gonzalez et al. disclose a NiCu alloy catalyst prepared without a separate support. Although it is possible to produce carbon nanotubes (CNTs) of smaller diameter by preventing the aggregation of Ni through the addition of Cu to Ni, there is a problem in that the methane conversion rate is very low at around 6% and consequently the H2 purity is also low, making it very difficult to produce CNTs and high-purity hydrogen simultaneously.

[0009] Jeong Bin Choi et al. disclose a method for synthesizing a catalyst using a urea impregnation method, in which Ni-phyllosilicates are formed evenly dispersed on a SiO2 support due to the slow hydrolysis of urea, which strengthens metal-support interactions and contributes to the formation of small, uniform nickel nanoparticles. However, there are problems such as the need for an additional step to activate the catalyst by reduction using H2, a relatively low methane conversion rate (30%), and the fact that it is difficult to simultaneously produce CNTs and high-purity hydrogen, with the methane conversion rate decreasing to less than 10% within 10 minutes.

[0010] The carbon-based catalyst mentioned above has the advantages of a lower price, excellent high-temperature stability, and resistance to impurities such as sulfur compared to metal-based catalysts. However, while carbon-based catalysts are cheaper than metal-based catalysts, the fact that the process requires creating high-temperature conditions of 800 to 1,000°C means that the price competitiveness of the methane decomposition process is inevitably reduced when relying solely on hydrogen gas production. Therefore, it is necessary to add value to the materials generated from the methane decomposition reaction.

[0011] International published patent WO2021 / 102521 A1 discloses a technology for producing high-quality crystalline carbon materials by pyrolyzing biomass to produce activated carbon, and then depositing carbon produced by decomposing methane onto the activated carbon. However, the crystalline carbon material has a very low specific surface area, and there is a problem that it has low potential for use as an electrode material requiring a high specific surface area and conductivity.

[0012]

[0013] Meanwhile, the demand for secondary batteries is steadily increasing in line with the trends of future industrial changes, such as electrification and wireless technology. While the application fields of secondary batteries—including wireless home appliances, robots, drones, and electric vehicles—are expected to expand significantly, lithium-ion batteries are commercially available and widely known; however, they possess low energy density despite their stable cycle characteristics. To achieve specific capacity levels, the development of next-generation batteries with higher energy density than lithium-ion batteries is necessary.

[0014] During the methane decomposition reaction, carbon nanotubes (CNTs), a type of solid carbon, can be generated as a byproduct in addition to hydrogen. These are one of the candidates for next-generation secondary batteries and can be used as sulfur carriers in the cathodes of lithium-sulfur batteries. When carbon materials are used as sulfur carriers in lithium-sulfur batteries, it is easy to impart porous properties to existing cathode materials and maximize the amount of active material within the cathode material. Among carbon materials, carbon nanotubes (CNTs) exhibit excellent pore characteristics and high electrical conductivity, making them highly effective as sulfur carriers for lithium-sulfur battery cathode materials. Furthermore, the capacity and output converted per mass of the cathode material can be maximized. Additionally, the properties imparted to these carbon nanotubes through the modification process are expected to provide simultaneous catalytic capabilities for the conversion reaction and interactions with the reaction intermediate, lithium polysulfide.

[0015] Therefore, the methane decomposition reaction produces high-purity hydrogen without emitting carbon dioxide and is environmentally friendly and economical because it is easy to simplify the reaction. In addition, carbon nanotubes produced as a byproduct can be used as electrode materials for lithium-sulfur batteries, which are emerging as next-generation secondary batteries.

[0016]

[0017] As a result of efforts to solve the above problem, the inventors confirmed through excellent electrochemical performance that it is possible to promote the methane decomposition reaction using a nickel-based catalyst to produce hydrogen and carbon nanotubes, and to fabricate electrodes by using the produced carbon nanotubes as electrode materials for lithium-sulfur batteries and lithium-ion batteries, thereby completing the present invention.

[0018]

[0019] [Prior Art Literature]

[0020] [Patent Literature]

[0021] 1. International Patent Publication WO2021 / 102521 A1

[0022] 2. Republic of Korea Registered Patent No. 10-2634715

[0023]

[0024] [Non-patent literature]

[0025] 1. Manoj Pudukudy et al., J. Chem., 2018, 42, 14843--14856

[0026] 2. Ismael Gonzalez et al., Catalysis Today 149 (2010) 352-357

[0027] 3. Jeong Bin Choi et al., Carbon Letters (2023) 33:477-488

[0028] 4. Shahla Karimi et al., International Journal of Hydrogen Energy, Volume 46, Issue 39, 17 June 2021, Pages 20435-20480

[0029]

[0030] The objective of the present invention is to provide a production method for producing hydrogen and carbon nanotubes by performing a methane decomposition reaction using a nickel-based catalyst, and to provide electrode materials for lithium sulfur and lithium-ion batteries using the produced carbon nanotubes.

[0031]

[0032] To achieve the above objective, the present invention provides a method for producing hydrogen and carbon nanotubes from methane, comprising: (a) a methane decomposition step of reacting methane with a nickel-based catalyst to decompose methane; and (b) a step of obtaining gaseous hydrogen produced in the methane decomposition step and separating solid-state synthesized carbon nanotubes from the catalyst.

[0033] The present invention provides a positive electrode for a lithium-sulfur battery characterized by comprising carbon nanotubes produced by the above method and having a discharge capacity of 500 to 1000 mAh / g for 100 cycles under operating conditions of 1.7 to 2.8 V and 0.1 to 3.0 C.

[0034] The present invention provides a negative electrode for a lithium-ion battery characterized by comprising carbon nanotubes produced by the above method and having a discharge capacity of 100 to 400 mAh / g for 100 cycles under operating conditions of 0.01 to 3.0 V and 100 to 2000 mA / g.

[0035]

[0036] According to the present invention, carbon nanotubes and high-purity hydrogen can be obtained by promoting methane decomposition using a nickel-based catalyst. It is environmentally friendly as it obtains hydrogen, a high-value-added product, by utilizing methane, a type of greenhouse gas. Furthermore, by synthesizing carbon nanotubes through methane decomposition under moderate conditions of atmospheric pressure, the present invention can save energy compared to existing manufacturing processes and achieve effective application in the high-value-added next-generation secondary battery industry.

[0037]

[0038] Figure 1 is a schematic diagram illustrating the manufacturing process of the present invention, in which carbon nanotubes synthesized after methane decomposition are obtained using the nickel-based catalyst of the present invention to manufacture a battery.

[0039] Figure 2 is a diagram showing the methane conversion rate, hydrogen purity, and carbon production rate relative to catalyst mass as a result of the methane decomposition reaction in Example 1 of the present invention.

[0040] Figure 3 is a diagram showing an SEM image of carbon nanotubes produced as a result of the methane decomposition reaction in Example 1 of the present invention.

[0041] Figure 4 is a diagram showing the methane conversion rate, hydrogen purity, and carbon production rate relative to catalyst mass as a result of the methane decomposition reaction in Example 2 of the present invention.

[0042] Figure 5 is a diagram showing an SEM image of carbon nanotubes produced as a result of the methane decomposition reaction in Example 2 of the present invention.

[0043] Figure 6 is a diagram showing the methane conversion rate, hydrogen purity, and carbon production rate relative to catalyst mass as a result of the methane decomposition reaction in Example 3 of the present invention.

[0044] Figure 7 is a diagram showing an SEM image of carbon nanotubes produced as a result of the methane decomposition reaction in Example 3 of the present invention.

[0045] Figure 8 is a diagram showing a TEM image obtained after a washing step to separate carbon nanotubes produced as a result of the methane decomposition reaction in Example 3 of the present invention from the catalyst.

[0046] Figure 9 is a diagram showing the XRD pattern obtained after a washing step to separate carbon nanotubes produced as a result of the methane decomposition reaction in Example 3 of the present invention from the catalyst.

[0047] FIG. 10 is a diagram showing the methane conversion rate, hydrogen purity, and carbon production rate relative to catalyst mass as a result of the methane decomposition reaction in Example 4 of the present invention.

[0048] Figure 11 is a diagram showing an SEM image of carbon nanotubes produced as a result of the methane decomposition reaction in Example 4 of the present invention.

[0049] FIG. 12 is a diagram showing the methane conversion rate, hydrogen purity, and carbon production rate relative to catalyst mass as a result of the methane decomposition reaction in Example 5 of the present invention.

[0050] Figure 13 is a diagram showing an SEM image of carbon nanotubes produced as a result of the methane decomposition reaction in Example 5 of the present invention.

[0051] Figure 14 is a diagram showing a TEM image obtained after a washing step to separate carbon nanotubes produced as a result of the methane decomposition reaction in Example 5 of the present invention from the catalyst.

[0052] FIG. 15 is a diagram showing an XRD pattern obtained after a washing step to separate carbon nanotubes produced as a result of the methane decomposition reaction in Example 5 of the present invention from the catalyst.

[0053] FIG. 16 is a graph showing the rate capability when carbon nanotubes (CNT) obtained in Example 3 of the present invention are used as the positive electrode of a lithium-sulfur battery and operated at different current densities (0.2 to 1.0 C).

[0054] Figure 17 is a graph showing the charge and discharge cycle capacity obtained at a current density of 0.5 C by utilizing the carbon nanotube (CNT) obtained in Example 3 of the present invention as the positive electrode of a lithium-sulfur battery.

[0055] Figure 18 is a graph showing the rate capability when carbon nanotubes (CNT) obtained in Example 3 of the present invention are used as the negative electrode of a lithium-ion battery and operated at different current densities (100 to 1000 mA / g).

[0056] Figure 19 is a graph showing the charge and discharge cycle capacity obtained at a current density of 500 mA / g by utilizing the carbon nanotube (CNT) obtained in Example 3 of the present invention as the negative electrode of a lithium-ion battery.

[0057] FIG. 20 is a graph showing the rate capability when carbon nanotubes (CNT) obtained in Example 5 of the present invention are used as the positive electrode of a lithium-sulfur battery and operated at different current densities (0.2 to 1.0 C).

[0058] Figure 21 is a graph showing the charge and discharge cycle capacity obtained at a current density of 0.5C by utilizing the carbon nanotube (CNT) obtained in Example 5 of the present invention as the positive electrode of a lithium-sulfur battery.

[0059] Figure 22 is a graph showing the rate capability when carbon nanotubes (CNT) obtained in Example 5 of the present invention are used as the negative electrode of a lithium-ion battery and operated at different current densities (100 to 1000 mA / g).

[0060] Figure 23 is a graph showing the charge and discharge cycle capacity obtained at a current density of 500 mA / g by utilizing the carbon nanotube (CNT) obtained in Example 5 of the present invention as the negative electrode of a lithium-ion battery.

[0061] FIG. 24 is a diagram showing the methane conversion rate, hydrogen purity, and carbon production rate relative to catalyst mass as a result of the methane decomposition reaction in Comparative Example 1 of the present invention.

[0062] FIG. 25 is a drawing showing an SEM image of carbon nanotubes produced as a result of the methane decomposition reaction in Comparative Example 1 of the present invention.

[0063]

[0064] Specific details for implementing the invention

[0065] All technical and scientific terms used herein are as generally understood by a skilled expert in the art to which this invention pertains, unless specifically defined otherwise. Furthermore, the nomenclature of terms used herein is widely known and commonly used in the art.

[0066]

[0067] The present invention has confirmed that it is possible to produce carbon nanotubes with a high yield and hydrogen of high purity by promoting methane decomposition using a nickel-based catalyst, and to achieve effective application in the next-generation secondary battery industry with high added value by synthesizing carbon nanotubes through methane decomposition under moderate conditions at atmospheric pressure, thereby saving energy compared to existing manufacturing processes.

[0068] Accordingly, in one aspect, the present invention relates to a method for producing hydrogen and carbon nanotubes from methane, comprising: (a) a methane decomposition step of reacting methane with a nickel-based catalyst to decompose methane; and (b) a step of obtaining gaseous hydrogen produced in the methane decomposition step and separating solid-state synthesized carbon nanotubes from the catalyst.

[0069]

[0070] The process of the present invention will be described in detail below.

[0071] The method for producing hydrogen and carbon nanotubes from methane according to the present invention comprises the following steps:

[0072] (a) a methane decomposition step for decomposing methane by reacting methane with a nickel-based catalyst; and

[0073] (b) a step of obtaining gaseous hydrogen produced in the methane decomposition step and separating solid-phase synthesized carbon nanotubes from the catalyst.

[0074] In the present invention, the catalyst may be (i) a catalyst in which nickel is impregnated on a cerium oxide carrier; or (ii) a catalyst in which nickel alone is supported on boron-doped carbon, or in which nickel and a metal other than nickel are supported together on boron-doped carbon.

[0075] In the present invention, it is preferable that the catalyst is impregnated with 1 to 50 wt% of nickel on a cerium oxide carrier.

[0076] In the present invention, the catalyst (ii) in which nickel alone is supported on boron-doped carbon or nickel and a metal other than nickel are supported together on boron-doped carbon can be prepared by reacting a reducing agent and a nickel precursor or a nickel and a metal other than nickel precursor with a gas containing carbon dioxide.

[0077] The boron-containing reducing agent used in the present invention may be boron oxide (B2O3), boric acid (H2BO3), or boron hydride. The boron hydride may be an alkali metal or alkaline earth metal boron hydride used alone or as a mixture of two or more types; specifically, it may be lithium boron hydride (LiBH4), sodium boron hydride (NaBH4), potassium boron hydride (KBH4), magnesium boron hydride (Mg(BH4)2), calcium boron hydride (Ca(BH4)2), or strontium boron hydride (Sr(BH4)2). Additionally, sodium detraborate (Na2B4O5(OH) 4· It may be 8H2O) or barium tetraborate (BaB2O4), but is not limited thereto.

[0078] In the present invention, the nickel precursor may be selected from one or more of the group consisting of nickel, nickel salt, nickel oxide, and nickel hydrate, but is not limited thereto.

[0079] In the present invention, the metal precursor other than nickel may be selected from one or more of the group consisting of transition metals, alkali metals, alkaline earth metals, precious metals, rare earth metals, salts of these metals, oxides of these metals, and hydrates of these metals, but is not limited thereto.

[0080] The transition metal other than nickel is zinc (Zn), cobalt (Co), copper (Cu), titanium (Ti), iron (Fe), or manganese (Mn); the alkali metal is lithium (Li), sodium (Na), or cesium (Cs); the alkaline earth metal is magnesium (Mg), calcium (Ca), or strontium (Sr); the precious metal is gold (Au), platinum (Pt), or silver (Ag); and the rare earth metal may be cerium (Ce).

[0081] In the present invention, the methane decomposition step may be performed at a temperature of 500 to 1000 ℃, but is not limited thereto. At a temperature lower than 500 ℃, the carbon nanotubes may not be uniform and the yield may be low. The rate of increase of the temperature may be 1 to 10 ℃ / min.

[0082] In the present invention, the methane decomposition step can be performed under absolute pressure conditions of 0.5 to 10 atm.

[0083] In the present invention, after step (b), a step of washing the carbon nanotubes separated from the catalyst using one or more selected from the group consisting of acid, hot water, cold water, and alcohol may be further included. The main purpose of the washing step is to separate the carbon nanotubes generated after the methane decomposition step from the catalyst.

[0084] In the present invention, after the washing step, a drying step may be additionally included at a temperature of 70°C or higher and under atmospheric pressure conditions.

[0085]

[0086] One embodiment of the present invention provides a method for manufacturing a battery using carbon nanotubes generated from methane decomposition, comprising: a methane decomposition step of reacting a catalyst and methane gas to cause a methane decomposition reaction; a washing step of separating carbon nanotubes produced in the methane decomposition step from the catalyst; and a battery manufacturing step of manufacturing a battery using carbon nanotubes obtained after the washing step.

[0087] Accordingly, the present invention relates to a cathode for a lithium-sulfur battery, characterized in that it comprises carbon nanotubes prepared by the above method and has a discharge capacity of 500 to 1000 mAh / g for 100 cycles under operating conditions of 1.7 to 2.8 V and 0.1 to 3.0 C, preferably 0.2 to 1.0 C.

[0088] In another aspect, the present invention relates to a negative electrode for a lithium-ion battery comprising carbon nanotubes prepared by the above method, characterized by having a discharge capacity of 100 to 400 mAh / g for 100 cycles under operating conditions of 0.01 to 3.0 V and 100 to 2000 mA / g, preferably 100 to 1000 mA / g.

[0089]

[0090] The embodiments of the present invention will be described in detail below for reference, but are not intended to limit the scope thereof. Various changes and modifications are possible within the scope and spirit of the present invention, and it is obvious that such changes and modifications fall within the scope of the appended claims.

[0091]

[0092] [Example]

[0093] Preparation Example 1: Preparation of Ni2O / CeO2 Methane Decomposition Catalyst

[0094] 0.8 g of cerium oxide (CeO2, >99.95%, Sigma-Aldrich), 0.991 g of nickel(II) hexahydrate (Ni(NO3)2·6H2O, 94.5-105.5%, Sigma-Aldrich), and 10 ml of distilled water were added to a 20 ml vial, stirred at 500 rpm for 30 minutes at 50 ℃, and then dried at 100 ℃ for more than 12 hours to obtain a sample in which nickel ions were impregnated into cerium oxide. The dried sample was placed in an alumina crucible, placed in a furnace, and calcined by introducing air (Air, >99.9%, Samo Co., Ltd) at a rate of 80 ml / min. At this time, the reactor temperature was raised to 700 ℃ at a rate of 5 ℃ / min and maintained for 5 hours to complete the calcination, and the calcined sample was cooled to room temperature. This was ground to produce a powder form, thereby obtaining a catalyst in which 20 wt% nickel is impregnated into cerium oxide. The catalyst is denoted as Ni2O / CeO2.

[0095]

[0096] Preparation Example 2: Preparation of Ni / CB Methane Decomposition Catalyst

[0097] 5 g of sodium boron hydride (NaBH4, >98.0%, Samchun) and 0.259 g of nickel powder (Ni powder, >99.99%, Sigma-Aldrich) were evenly mixed and placed in an alumina crucible. The mixture was then placed in a furnace and purged for 30 minutes while flowing carbon dioxide (CO2, >99.99%, Samo Co., Ltd) at a rate of 80 ml / min. Afterward, the temperature of the furnace was raised to 500 ℃ at a rate of 5 ℃ / min and maintained for 2 hours to complete the calcination, and the calcined sample was cooled to room temperature. Subsequently, the sample was washed with hot water, cold water, and ethanol.

[0098] For the hot water washing, 200 ml of distilled water was placed in a 250 ml beaker and stirred at 500 rpm for 30 minutes at 80 ℃, after which the washed material was filtered through a 1.2 µm polycarbonate filter. Subsequently, the washing process was repeated four more times. Next, for the cold water washing, 200 ml of distilled water was placed in a 250 ml beaker and stirred at 500 rpm for 30 minutes at 25 ℃, after which the washed material was filtered through a 1.2 µm polycarbonate filter. Subsequently, the washing process was repeated three more times. Finally, for the ethanol washing, 200 ml of ethanol was placed in a 250 ml beaker and stirred at 500 rpm for 30 minutes at 25 ℃, after which the washed material was filtered through a 1.2 µm polycarbonate filter. The precipitate from which salts had been removed through the above washing process was dried at 100 ℃ for one day.

[0099] The dried sample was placed in an alumina crucible, placed in a furnace, and purged for 30 minutes while flowing argon (Ar, >99.999%, Samo Co., Ltd) at a rate of 80 ml / min. Subsequently, the furnace temperature was raised to 950 ℃ at a rate of 5 ℃ / min and maintained for 2 hours to complete calcination, after which the calcined sample was cooled to room temperature. This was ground into a powder to obtain a catalyst in which nickel is supported on boron-doped carbon. The catalyst is denoted as Ni / CB.

[0100]

[0101] Preparation Example 3: Preparation of Ni-Zn / CB Methane Decomposition Catalyst

[0102] A catalyst in which nickel and zinc are supported on boron-doped carbon was obtained by the same method as in Preparation Example 2, except that 0.496 g of zinc bromide (ZnBr2, >98.0%, Sigma-Aldrich) was added to 5 g of sodium boron hydride (NaBH4, >98.0%, Samchun) and 0.259 g of nickel powder (Ni powder, >99.99%, Sigma-Aldrich). The catalyst is denoted as Ni-Zn / CB.

[0103]

[0104] Preparation Example 4: Preparation of Ni-Ce / CB Methane Decomposition Catalyst

[0105] A catalyst in which nickel and cerium were supported on boron-doped carbon was obtained by the same method as in Preparation Example 2, except that 0.379 g of cerium oxide (CeO2, >99.95%, Sigma-Aldrich) was added to 5 g of sodium boron hydride (NaBH4, >98.0%, Samchun) and 0.259 g of nickel powder (Ni powder, >99.99%, Sigma-Aldrich). The catalyst is denoted as Ni-Ce / CB.

[0106]

[0107] Preparation Example 5: Preparation of Ni-Co / CB Methane Decomposition Catalyst

[0108] A catalyst in which nickel and cobalt were supported on boron-doped carbon was obtained by the same method as in Preparation Example 2, except that 0.130 g of cobalt powder (Co powder, >99.8%, Alfa Aesar) was added to 5 g of sodium boron hydride (NaBH4, >98.0%, Samchun) and 0.259 g of nickel powder (Ni powder, >99.99%, Sigma-Aldrich). The catalyst is denoted as Ni-Co / CB.

[0109]

[0110] Example 1: Production of hydrogen and carbon nanotubes through methane decomposition experiments using Ni2O / CeO2

[0111] 0.2 g of the Ni2O / CeO2 catalyst prepared in Preparation Example 1 was packed inside the reactor, and the reactor was heated from 20 ℃ to 750 ℃ ​​at a rate of 5 ℃ / min using an electric furnace and maintained at 750 ℃. Nitrogen (N2, >99.999%, Samo Co., Ltd) and methane (CH4, >99.999%, Samo Co., Ltd) were supplied at a constant flow rate of 45 ml / min and 5 ml / min, respectively, for 25 minutes. Inside the reactor, methane reacted with the catalyst to undergo a methane decomposition reaction, and as a result, hydrogen and carbon nanotubes were obtained and qualitative and quantitative analysis was performed using mass spectroscopy.

[0112] At this time, the methane conversion rate was approximately 75%, the purity of the obtained hydrogen was approximately 75%, and the amount of carbon nanotubes estimated from the hydrogen production was about 15% relative to the mass of the catalyst. The quantification and SEM images for this are shown in Fig. 2 and Fig. 3, respectively. The SEM image in Fig. 3 indicates that the carbon nanotubes are mixed with the catalyst and are evenly distributed.

[0113]

[0114] Example 2: Production of hydrogen and carbon nanotubes through methane decomposition experiments using Ni / CB

[0115] 0.1 g of the Ni / CB catalyst prepared in Preparation Example 2 was packed inside the reactor, and the reactor was heated from 20 ℃ to 850 ℃ at a rate of 5 ℃ / min using an electric furnace and maintained at 850 ℃. Nitrogen (N2, >99.999%, Samo Co., Ltd) was supplied at a constant flow rate of 45 ml / min, and methane (CH4, >99.999%, Samo Co., Ltd) was supplied at a constant flow rate of 5 ml / min. Inside the reactor, methane reacted with the catalyst to undergo a methane decomposition reaction, and as a result, hydrogen and carbon nanotubes were obtained and qualitative and quantitative analysis was performed using mass spectroscopy.

[0116] At this time, the methane conversion rate was approximately 80%, the purity of the obtained hydrogen was approximately 90%, and the amount of carbon nanotubes estimated from the hydrogen production was approximately 90% relative to the mass of the catalyst. The quantification and SEM images for this are shown in Figures 4 and 5, respectively. The SEM image in Figure 5 shows that the carbon nanotubes are mixed with the catalyst and are evenly distributed.

[0117] A washing step was performed to separate the obtained carbon nanotubes from the catalyst. 5M hydrochloric acid, hot water, and ethanol were used for the washing. For the hydrochloric acid washing, 250ml of 5M hydrochloric acid was placed in a 250ml beaker and stirred at 500rpm for 30 minutes at 70℃, after which the washed product was filtered through a 1.2㎛ polycarbonate filter. This washing process was then repeated two more times. Next, for the hot water washing, 250ml of distilled water was placed in a 250ml beaker and stirred at 500rpm for 30 minutes at 70℃, after which the washed product was filtered through a 1.2㎛ polycarbonate filter. This washing process was then repeated two more times. Finally, for the ethanol washing, 250ml of ethanol was placed in a 250ml beaker and stirred at 500rpm for 30 minutes at 70℃, after which the washed product was filtered through a 1.2㎛ polycarbonate filter. Afterwards, the above washing process was repeated two more times. The precipitate from which the catalyst was removed through the above washing process was dried at 80°C for one day.

[0118]

[0119] Example 3: Production of hydrogen and carbon nanotubes through methane decomposition experiments using Ni-Zn / CB

[0120] Hydrogen and carbon nanotubes were obtained and washed in the same manner as in Example 2, except that the catalyst Ni-Zn / CB prepared in Preparation Example 3 was used.

[0121] At this time, the methane conversion rate was approximately 90%, and the purity of the obtained hydrogen was approximately 95%; the amount of carbon nanotubes estimated from the hydrogen production was about 105% relative to the catalyst mass. Quantification and SEM images regarding this are shown in Figures 6 and 7, respectively. The SEM image in Figure 7 indicates that the carbon nanotubes are evenly distributed mixed with the catalyst. Figures 8 and 9 show the TEM image and XRD pattern obtained after a washing step to separate the obtained carbon nanotubes from the catalyst. Figures 8 and 9 confirm that graphite carbon is obtained from the catalyst and that it is carbon nanotube. This indicates that methane decomposes into solid carbon and hydrogen on the Ni-Zn / CB catalyst, and that the carbon is in the form of carbon nanotubes. Therefore, the Ni-Zn / CB catalyst is most suitable for the simultaneous production of carbon nanotubes and high-purity hydrogen.

[0122]

[0123] Example 4: Production of hydrogen and carbon nanotubes through methane decomposition experiments using Ni-Ce / CB

[0124] Hydrogen and carbon nanotubes were obtained and washed in the same manner as in Example 2, except that the catalyst Ni-Ce / CB prepared in Preparation Example 4 was used.

[0125] At this time, the methane conversion rate was approximately 60%, the purity of the obtained hydrogen was approximately 75%, and the amount of carbon nanotubes estimated from the hydrogen production was approximately 95% relative to the mass of the catalyst. The quantification and SEM images for this are shown in Fig. 10 and Fig. 11, respectively. The SEM image in Fig. 11 shows that the carbon nanotubes are mixed with the catalyst and are evenly distributed.

[0126]

[0127] Example 5: Production of hydrogen and carbon nanotubes through methane decomposition experiments using Ni-Co / CB

[0128] Hydrogen and carbon nanotubes were obtained and washed in the same manner as in Example 2, except that the catalyst Ni-Co / CB prepared in Preparation Example 5 was used.

[0129] At this time, the methane conversion rate was approximately 90%, the purity of the obtained hydrogen was approximately 65%, and the amount of carbon nanotubes estimated from the hydrogen production was about 75% relative to the catalyst mass. Quantification and SEM images regarding this are shown in Figs. 12 and 13, respectively. Through the SEM image in Fig. 13, it can be confirmed that almost no carbon nanotubes are generated on the catalyst. Figs. 14 and 15 are TEM images and XRD patterns obtained after a washing step to separate the obtained carbon nanotubes from the catalyst. Through Figs. 14 and 15, it can be confirmed that graphite carbon is obtained from the catalyst, but it is in the form of graphene rather than carbon nanotubes, or that while a very small amount of carbon nanotubes is present, it exists mostly in the form of amorphous carbon. This means that methane is decomposed into solid carbon and hydrogen by the Ni-Co / CB catalyst, and the carbon at this stage is mostly amorphous carbon rather than in the form of carbon nanotubes. It can be confirmed that Ni-Co / CB catalysts are more suitable for hydrogen production than carbon nanotubes.

[0130]

[0131] Example 6: Electrochemical measurement of lithium-sulfur batteries and lithium-ion batteries using CNTs obtained from Ni-Zn / CB

[0132] The carbon nanotubes synthesized in Example 3 were applied as a positive electrode to a lithium-sulfur battery to verify their electrochemical properties.

[0133] When the carbon nanotubes synthesized in Example 3 were used as the cathode of a lithium-sulfur battery, a rate capability test was performed. As shown in Fig. 16, the device operated from a current density of 0.2 C to a current density of 1.0 C, and high capacity was secured even at low current densities, and the capacity was well realized even at a relatively high current density of 1.0 C. In addition, when the current density returned to 0.2 C, the initial capacity was almost maintained.

[0134] When the carbon nanotubes synthesized in Example 3 were used as the cathode of a lithium-sulfur battery, the charge and discharge cycle capacity was measured. As shown in Fig. 17, it was confirmed that when driven at a current density of 0.5C, a discharge capacity of 720 mAh / g was delivered in the first cycle and a discharge capacity of 597 mAh / g was delivered in the 100th cycle.

[0135] When the carbon nanotubes synthesized in Example 3 were used as the negative electrode of a lithium-ion battery, a rate capability test was performed. As shown in Fig. 18, the device operated from a current density of 100 mA / g to 1000 mA / g, securing high capacity even at low current densities and achieving good capacity even at a relatively high current density of 1000 mA / g. In addition, when the current density returned to 100 mA / g, the initial capacity was almost maintained.

[0136] When the carbon nanotubes synthesized in Example 3 were used as the negative electrode of a lithium-ion battery, the charge and discharge cycle capacity was measured. As shown in Fig. 19, it was confirmed that when driven at a current density of 500 mA / g, a discharge capacity of 275 mAh / g was delivered in the first cycle and a discharge capacity of 264 mAh / g was delivered in the 100th cycle.

[0137]

[0138] Example 7: Electrochemical measurement of lithium-sulfur batteries and lithium-ion batteries using CNTs obtained from Ni-Co / CB

[0139] The carbon nanotubes synthesized in Example 5 were applied as a positive electrode to a lithium-sulfur battery to verify their electrochemical properties.

[0140] When the carbon nanotubes synthesized in Example 5 were used as the cathode of a lithium-sulfur battery, a rate capability test was performed. As shown in Fig. 20, the device operated from a current density of 0.2 C to a current density of 1.0 C, and high capacity was secured even at low current densities, and the capacity was well realized even at a relatively high current density of 1.0 C. In addition, when the current density returned to 0.2 C, the initial capacity was almost maintained.

[0141] When the carbon nanotubes synthesized in Example 5 were used as the cathode of a lithium-sulfur battery, the charge and discharge cycle capacity was measured. As shown in Fig. 21, when driven at a current density of 0.5 C, it was confirmed that a discharge capacity of 711 mAh / g was delivered in the first cycle and a discharge capacity of 536 mAh / g was delivered in the 100th cycle.

[0142] When the carbon nanotubes synthesized in Example 5 were used as the negative electrode of a lithium-ion battery, a rate capability test was performed. As shown in Figure 22, the device operated from a current density of 100 mA / g to 1000 mA / g, and high capacity was secured even at low current densities, and the capacity was well realized even at a relatively high current density of 1000 mA / g. In addition, when the current density returned to 100 mA / g, the initial capacity was almost maintained.

[0143] When the carbon nanotubes synthesized in Example 5 were used as the negative electrode of a lithium-ion battery, the charge and discharge cycle capacity was measured. As shown in Fig. 23, when driven at a current density of 500 mA / g, it was confirmed that a discharge capacity of 191 mAh / g was delivered in the first cycle and a discharge capacity of 157 mAh / g was delivered in the 100th cycle.

[0144]

[0145] Comparative Example 1: Production of hydrogen and carbon nanotubes through methane decomposition experiment using Ni10 / Al2O3

[0146] 0.9 g of aluminum oxide (gamma-phase, Al2O3, >99.97%, Alfa Aesar), 0.495 g of nickel(II) hexahydrate (Ni(NO3)2·6H2O, 94.5-105.5%, Sigma-Aldrich), and 10 ml of distilled water were added to a 20 ml vial, stirred at 500 rpm for 30 minutes at 50 ℃, and then dried at 100 ℃ for more than 12 hours to obtain a sample in which nickel ions were impregnated into the aluminum oxide. The dried sample was placed in an alumina crucible, placed in a furnace, and calcined by introducing air (Air, >99.9%, Samo Co., Ltd) at a rate of 80 ml / min. At this time, the reactor temperature was raised to 900 ℃ at a rate of 5 ℃ / min and maintained for 6 hours to complete the calcination, and the calcined sample was cooled to room temperature. This was ground to produce a powder form, thereby obtaining a catalyst in which 10 wt% nickel is impregnated in aluminum oxide. The catalyst is denoted as Ni10 / Al2O3.

[0147] 0.2 g of the above catalyst (Ni10 / Al2O3) was packed inside the reactor, and the reactor was heated from 20 ℃ to 800 ℃ at a rate of 5 ℃ / min using an electric furnace and maintained at 800 ℃. Nitrogen (N2, >99.999%, Samo Co., Ltd) and methane (CH4, >99.999%, Samo Co., Ltd) were supplied at a constant flow rate of 45 ml / min and 5 ml / min, respectively, for 25 minutes. Inside the reactor, methane reacted with the catalyst to undergo a methane decomposition reaction, and as a result, hydrogen and carbon nanotubes were obtained and qualitative and quantitative analysis was performed using mass spectroscopy.

[0148] At this time, the methane conversion rate was approximately 30%, the purity of the obtained hydrogen was approximately 10%, and the amount of carbon nanotubes estimated from the hydrogen production was about 2.5% relative to the mass of the catalyst. The quantification and SEM images for this are shown in Fig. 24 and Fig. 25, respectively. Through the SEM image in Fig. 25, it can be confirmed that the carbon nanotubes are evenly mixed with the catalyst, but the amount is very small.

[0149]

[0150] Carbon nanotubes are widely studied as carbon-based materials for secondary batteries due to their excellent electrical, mechanical, and chemical properties. As a result of methane decomposition and carbon nanotube fabrication using various types of catalysts, the proportion of carbon nanotubes in the fabricated carbon materials was significantly higher in the case of Ni-Zn / CB and Ni-Co / CB compared to the case synthesized with the Ni10 / Al2O3 catalyst of Comparative Example 1. In particular, as shown in Figures 8, 9, 13, and 14, the carbon nanotubes fabricated using Ni-Zn / CB and Ni-Co / CB have tangled and bent structures, unlike the straight and aligned carbon nanotubes of previous studies. These structural features allow for the formation of a denser three-dimensional conductive network, thereby connecting the electron transport paths within the electrode more tightly. This helps improve electrical conductivity and distribute current evenly throughout the active material. In addition, the bent and tangled structure has greater mechanical flexibility, which can more effectively mitigate deformation caused by repeated volume changes during the charging and discharging process. This can contribute to preventing structural collapse of the electrode and improving its lifespan. Furthermore, if porous spaces are formed between the carbon nanotubes due to the tangled structure, electrolyte penetration is facilitated and a pathway for lithium ion movement is secured. This can increase the ion transfer rate and improve the output performance of the battery. As a result, as shown in Figures 16 to 23, it was confirmed that excellent discharge capacity could be achieved even when the electrode was fabricated using only pure carbon nanotubes without additional processing.

[0151]

[0152] Foregoing, specific parts of the present invention have been described in detail. It will be apparent to those skilled in the art that such specific descriptions are merely preferred embodiments and do not limit the scope of the invention. Accordingly, the actual scope of the invention is defined by the claims and their equivalents.

Claims

1. A method for producing hydrogen and carbon nanotubes from methane comprising the following steps: (a) a methane decomposition step for decomposing methane by reacting methane with a nickel-based catalyst; and (b) a step of obtaining gaseous hydrogen produced in the methane decomposition step and separating solid-phase synthesized carbon nanotubes from the catalyst.

2. A method for producing hydrogen and carbon nanotubes from methane, wherein, in claim 1, the catalyst is characterized as being (i) a catalyst in which nickel is impregnated on a cerium oxide support; or (ii) a catalyst in which nickel is supported alone on boron-doped carbon or in which nickel and a metal other than nickel are supported together on boron-doped carbon.

3. A method for producing hydrogen and carbon nanotubes from methane, wherein, in paragraph 2, the catalyst is characterized by having 1 to 50 wt% of nickel impregnated on a cerium oxide carrier.

4. A method for producing hydrogen and carbon nanotubes from methane, wherein, in paragraph 2, the catalyst (ii) in which nickel is supported alone on boron-doped carbon or nickel and a metal other than nickel are supported together on boron-doped carbon is prepared by reacting a reducing agent and a nickel precursor or a nickel and a metal other than nickel precursor with a gas containing carbon dioxide.

5. A method for producing hydrogen and carbon nanotubes from methane, characterized in that, in claim 4, the reducing agent is selected from one or more of the group consisting of boron oxide (B2O3), boric acid (H2BO3), alkali metal boron hydride, and alkaline earth metal boron hydride.

6. A method for producing hydrogen and carbon nanotubes from methane, characterized in that, in claim 4, the nickel precursor is selected from one or more of the group consisting of nickel, nickel salt, nickel oxide, and nickel hydrate.

7. A method for producing hydrogen and carbon nanotubes from methane, characterized in that, in claim 4, the metal precursor other than nickel is selected from the group consisting of transition metals, alkali metals, alkaline earth metals, precious metals, rare earth metals, salts of these metals, oxides of these metals, and hydrates of these metals.

8. A method for producing hydrogen and carbon nanotubes from methane according to claim 1, characterized in that the methane decomposition step is performed at a temperature of 500 to 1000 ℃.

9. A method for producing hydrogen and carbon nanotubes from methane, characterized in that, in claim 1, the methane decomposition step is performed under absolute pressure conditions of 0.5 to 10 atm.

10. A method for producing hydrogen and carbon nanotubes from methane, wherein, in claim 1, the carbon nanotubes separated from the catalyst after step (b) are further included in the step of washing the carbon nanotubes using one or more selected from the group consisting of acid, hot water, cold water, and alcohol.

11. A method for producing hydrogen and carbon nanotubes from methane, wherein, in claim 10, after the washing step, the step of drying is additionally included under atmospheric pressure conditions at a temperature of 70°C or higher.

12. A positive electrode for a lithium-sulfur battery comprising carbon nanotubes prepared by the method of claims 1 to 11, characterized by having a discharge capacity of 500 to 1000 mAh / g for 100 cycles under operating conditions of 1.7 to 2.8 V and 0.1 to 3.0 C.

13. A negative electrode for a lithium-ion battery characterized by comprising carbon nanotubes prepared by the method of claims 1 to 11, and having a discharge capacity of 100 to 400 mAh / g for 100 cycles under operating conditions of 0.01 to 3.0 V and 100 to 2000 mA / g.

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