Methods for preparing carbon materials, carbon materials themselves, and their applications in fuel cells.

Abstract

A method for preparing a nitrogen-modified mesoporous dendritic carbon material includes the following steps: First, a metal acetylene oxide is prepared as a carbon precursor. The carbon precursor is then mixed with a nitrogen precursor to form a starting material mixture. Next, a first heat treatment is performed on the starting material mixture under vacuum at a temperature in the range of 40 to 80°C to form a metal inclusion compound. In a next step, a second heat treatment is performed under vacuum at a temperature in the range of 120 to 220°C to prepare an intermediate while decomposing the metal inclusion compound. The intermediate is treated to remove the metal, and finally, the treated intermediate is consolidated by a third heat treatment at a temperature in the range of 200 to 1000°C under vacuum or in an inert gas atmosphere to obtain the nitrogen-modified mesoporous dendritic carbon material. A nitrogen-modified mesoporous dendritic carbon material and its use in fuel cells are also provided.

Description

Technical Field

[0001] This invention relates to a method for preparing nitrogen-modified mesoporous dendritic carbon materials, a carbon material obtainable by said method, and the use of such carbon materials as catalyst supports in fuel cells. Background Technology

[0002] A fuel cell is a system for generating energy, particularly electricity through the electrochemical reaction of hydrogen and oxygen. In most cases, a fuel cell comprises multiple individual cells, each including an anode, a cathode, and a membrane disposed between these electrodes. The anode and cathode contain catalytically active materials, particularly platinum or platinum alloys, which are applied to a porous support material, particularly porous carbon materials with a high specific surface area, and are especially present in the pores of the carbon material. Additionally, ionomers are typically used in the anode and cathode as binders and proton conductors.

[0003] It has been shown that the pore size, especially the pore diameter, in the support material is one of the main parameters affecting the mass transfer resistance of the electrode, and thus a decisive factor in the achievable performance of the fuel cell. In a 500m... 2 In known carbon materials with high specific surface areas of / g or greater, most pores typically have a diameter of less than 2.0 nm, while only a small fraction of pores have a larger diameter.

[0004] US2020 / 0044261 A1 discloses a porous carbon material used as a catalyst support in fuel cells. This carbon material belongs to the so-called mesoporous carbon nanodendrite class (also known as "MCND," an abbreviation for "mesoporous carbon nanodendrites"). These nanodendrites possess high specific surface areas, for example, in the range of 400 to 1520 m². 2 Within the range of / g, and a large proportion of pores with a diameter greater than 2.0nm.

[0005] Regarding the working efficiency of fuel cells ( Another decisive influence is the wettability of the ionomer to the catalytically active material, where high wettability is required to prevent insufficient interaction between the ionomer and the catalytically active material from limiting proton conductivity and mass transfer. It has been shown that ionomers are not uniformly distributed in known carbon-based support materials.

[0006] DE 10 2017 207 730 A1 describes a carbon material used as a catalyst layer in a fuel cell, the carbon material having a carbon lattice for improving the distribution of ionomers, with nitrogen atoms inserted into the carbon lattice. In this way, the distribution of ionomers is improved based on the Coulomb interaction between the nitrogen functional groups embedded in the carbon lattice and the ionic groups of the ionomers, especially anionic groups such as sulfonic acid groups. To prepare the carbon material, graphitized carbon material is oxidized with nitric acid and subsequently heat-treated in an ammonia stream.

[0007] However, it is still impossible to achieve nitrogen-modified support materials with a sufficiently large specific surface area, or it can only be achieved through complex synthetic routes (e.g., through subsequent surface functionalization).

[0008] Therefore, there is also a need for carrier materials used in fuel cells, which can achieve improved mass transfer, increased proton conductivity, and better operating efficiency. Summary of the Invention

[0009] Therefore, the object of the present invention is to provide such a carrier material and a simple and inexpensive method for providing such a carrier material. In particular, the object of the present invention is to provide a carrier material capable of enabling fuel cells with improved operating efficiency.

[0010] According to the present invention, this objective is achieved by a method for preparing a nitrogen-modified mesoporous dendritic carbon material, the method comprising the following steps: firstly, preparing a metal acetylene oxide as a carbon precursor; subsequently, mixing the carbon precursor with a nitrogen precursor to form a starting material mixture; then, performing a first heat treatment of the starting material mixture under vacuum at a temperature in the range of 40 to 80°C to form a metal inclusion compound; in a next step, performing a second heat treatment under vacuum at a temperature in the range of 120 to 220°C to prepare an intermediate while decomposing the metal inclusion compound; treating the intermediate to remove the metal; and finally, consolidating the treated intermediate by performing a third heat treatment at a temperature in the range of 200 to 1000°C under vacuum or in an inert gas atmosphere to obtain the nitrogen-modified mesoporous dendritic carbon material.

[0011] According to the method of the present invention, a nitrogen-modified mesoporous dendritic carbon material is provided for the first time, which simultaneously has a large specific surface area, a large proportion of pores with a diameter of more than 2.0 nm, and a carbon lattice in which carbon atoms are partially replaced by nitrogen.

[0012] The method according to the invention can be carried out in particular as a one-pot synthesis, thereby keeping the consumption and cost of preparing carbon materials low. This is a simplification compared to subsequent modification of carbon supports with nitrogen-containing functional groups, thus enabling the preparation of carbon materials in a less time-consuming manner. Unlike nitrogen groups generated solely through surface modification, incorporating nitrogen into the carbon lattice also improves the stability of nitrogen functionalization.

[0013] The metal acetylenide is preferably selected from the group consisting of silver acetylenide, copper acetylenide, and combinations thereof. Silver acetylenide is particularly preferred.

[0014] The nitrogen precursor can be selected from the group consisting of urea, aminocyanide, melamine, and combinations thereof. In other words, solid nitrogen precursors are particularly useful, thereby simplifying the process.

[0015] The carbon and / or nitrogen precursors can be dissolved in a solvent, prepared into a slurry, or wetted with a solvent before being mixed into a starting material mixture. The same or different solvents can be used for both precursors. The solvent is preferably an alcohol having one to four carbon atoms, and methanol is particularly preferred.

[0016] In the starting material mixture, the molar ratio of nitrogen to carbon is particularly set in the range of 0.05 to 1.5, preferably in the range of 0.1 to 1.0, and particularly preferably in the range of 0.3 to 0.92.

[0017] The proportion of nitrogen to be inserted into the carbon lattice of the carbon material prepared by the method according to the invention can be predetermined by the molar ratio of nitrogen to carbon in the starting material mixture. At a nitrogen-to-carbon molar ratio less than 0.05, carbon materials with excessively low nitrogen proportions are produced, resulting in no expected improvement in wetting with ionomers. At a nitrogen-to-carbon molar ratio greater than 0.92, the carbon material can exhibit a reduced specific surface area and / or lower stability. Furthermore, at a nitrogen-to-carbon molar ratio greater than 0.92, no further improvement in the advantages caused by nitrogen is expected.

[0018] The first heat treatment, particularly the drying step, of the starting material mixture used to form the metal inclusion compound is to remove the solvent present in the starting material mixture.

[0019] Simultaneously, a metal inclusion compound is formed in the first heat treatment, which is used as a reactive metal inclusion compound in the subsequent second heat treatment.

[0020] The formation of metal inclusion compounds as a starting point for generating mesoporous dendritic structures is essentially known from US 2020 / 0044261A1.

[0021] The first heat treatment is performed at a temperature in the range of 40 to 80°C. At lower temperatures, the yield in forming metal inclusion compounds may be reduced, while at higher temperatures, the starting material mixture may undergo excessively rapid transformation, thus failing to obtain the desired carbon material structure.

[0022] The first heat treatment is carried out for a period of 12 to 24 hours, preferably 14 to 22 hours, and particularly preferably 18 to 20 hours.

[0023] The second heat treatment is especially direct after the first heat treatment.

[0024] In the second heat treatment, a basic carbon lattice for the subsequent carbon material is formed in the intermediate, wherein carbon atoms are partially replaced by nitrogen atoms. Metals from the carbon precursor, in particular, form metal nanoparticles, at which the carbon lattice is formed.

[0025] The decomposition of the metal inclusions proceeds as a self-decomposing and explosive reaction, and the resulting metal nanoparticles can be at least partially transformed into metal aggregates.

[0026] The second heat treatment is carried out for a period of 10 to 20 minutes, preferably 12 to 18 minutes, and particularly preferably 14 to 16 minutes.

[0027] The intermediate is preferably treated by washing with concentrated acid, preferably concentrated nitric acid or concentrated sulfuric acid, to remove the metal. Basically any oxidizing acid that will not decompose the carbon skeleton of the intermediate can be used.

[0028] The term “metal” in connection with the first and second heat treatments and the treatment of intermediates means any form of metal derived from carbon precursors and also includes nanoparticles, aggregates, oxides and other metal compounds that may be formed, particularly in the first and second heat treatments.

[0029] Apart from unavoidable impurities, the processed intermediates are especially free of metals.

[0030] After the intermediate is treated, an optional drying step may follow to remove the solvent and washing liquid used during the washing process.

[0031] The process of consolidating the treated intermediate by performing a third heat treatment is used to form nitrogen-modified mesoporous dendritic carbon materials from the treated intermediate, wherein the third heat treatment is used to achieve the desired stability of the carbon materials.

[0032] The temperature of the third heat treatment is in the range of 200 to 1000°C. Preferably, the third heat treatment is carried out at a temperature in the range of 600 to 900°C.

[0033] This temperature range represents a particularly good trade-off between achievable carbon material stability (which generally increases with increasing temperature) and achievable pore size (which generally decreases with increasing temperature).

[0034] Temperatures below the temperature of the final heat treatment step can be used, particularly in the method according to the invention, as described in the prior art, for example, US2020 / 0044261 A1. At temperatures above 1000°C, it is anticipated that nitrogen intercalated into the carbon lattice of the carbon material is at least partially removed from the carbon lattice by thermal decomposition, making it impossible or at most only to a reduced extent to achieve the desired improved wettability with ionomers.

[0035] The third heat treatment is carried out for a period of 12 to 24 hours, preferably 14 to 22 hours, and particularly preferably 18 to 20 hours.

[0036] The object of the present invention is also achieved by a nitrogen-modified mesoporous dendritic carbon material that can be obtained according to the previously described method, wherein the carbon material has a carbon lattice in which carbon atoms are partially replaced by nitrogen atoms.

[0037] The carbon material according to the invention exhibits greater polarity due to the nitrogen atoms present in the carbon lattice, thereby achieving improved wetting ability against ionomers known in the prior art. Furthermore, the nitrogen atoms improve the proton conductivity of the catalyst layer comprising the carbon material.

[0038] Furthermore, nitrogen is stably embedded within the carbon lattice, thereby eliminating or at least reducing the decomposition of nitrogen-containing groups under conditions present during fuel cell operation, particularly compared to nitrogen-containing functional groups that can be generated through subsequent surface modification of the carbon support.

[0039] Preferably, 0.5 to 1.5% by weight of carbon atoms in the carbon lattice, and preferably 0.5 to 1.2% by weight of carbon atoms in the carbon lattice, are replaced by nitrogen atoms. At lower proportions, sufficient improvement in charge distribution cannot be achieved, while higher proportions may result in less stable carbon materials and / or carbon materials with reduced specific surface area.

[0040] The proportion of nitrogen atoms in a carbon lattice can be determined by elemental analysis of carbon materials.

[0041] To improve the electrical conductivity and stability of carbon materials, carbon materials can be graphitized, meaning that the carbon lattice mainly exhibits sp0 properties. 2 Hybridized carbon atoms.

[0042] The carbon lattice can include pyridine and / or pyrrole units via nitrogen atoms. Due to their aromatic characteristics, pyridine and pyrrole units can be advantageously incorporated into graphite-based carbon lattices, thereby allowing for minimal structural distortion of the carbon lattice.

[0043] The carbon material preferably has a content of 900 to 3000 μm. 2 / g, preferably 1000 to 2150m 2 / g, with a preferred concentration of 1300 to 2150 mg 2 Specific surface area S within the range of / g BET The specific surface area was determined using the BET method with a nitrogen adsorption isotherm.

[0044] In order to achieve a large mass transfer effect through the carbon material, the carbon material particularly has a Vt value in the range of 0.25 to 0.75, preferably 0.30 to 0.65, and particularly preferably 0.35 to 0.6. 介孔 / V 总计 The ratio of V to V 介孔 V represents the volume of all pores in the carbon material having a pore size in the range of 2.5 to 6.0 nm. 总计 This represents the total volume of all the pores in the carbon material.

[0045] In other words, the carbon material according to the invention has a significant proportion of so-called mesopores with a size of 2.5 nm to 6.0 nm, which are particularly advantageous for rapid mass transfer in fuel cell applications.

[0046] The pore size and volume discussed in this paper can be determined by means of nitrogen adsorption isotherms, especially by numerical analysis of nitrogen adsorption isotherms using the DFT model (DFT: density functional theory).

[0047] Regarding gas diffusion velocity, the carbon material particularly exhibits a velocity between 80 and 220 cm⁻¹. 3 (STP) / g, preferably 100 to 200 cm 3 (STP) / g, preferably 110 to 190 cm⁻¹ 3 Nitrogen absorption volume V in the range of (STP) / g N:0.4-0.8 V N:0.4-0.8 This represents the nitrogen volume within the relative pressure range p / p0 of 0.4 to 0.8 of the nitrogen adsorption isotherm. For carbon materials with a very low proportion of mesoporous structures, an even lower nitrogen absorption volume V is required. N:0.4-0.8 This may be characteristic, thus suggesting insufficient mass transfer in such carbon materials. Above 220 cm⁻¹ 3 Nitrogen absorption volume V (STP) / g N:0.4-0.8 The possible result is carbon materials that may have excessively low mechanical stability.

[0048] The abbreviation "STP" here stands for "Standard Temperature and Pressure," meaning a temperature of 0°C and a pressure of 1 bar.

[0049] The carbon material can have a thickness of 0.5 to 0.9 cm. 3 / g, preferably 0.53 to 0.86cm 3 / g, with a particularly preferred content of 0.55 to 0.74cm 3 dV in the range of / g 2.5-6nm Value, wherein dV 2.5-6nm The value describes the cumulative volume of a pore with a diameter in the range of 2.5 to 6.0 nm relative to a unit of weight. The value can be obtained by differentiating the cumulative pore volume with respect to the pore diameter and then integrating over the corresponding range of pore diameters.

[0050] Furthermore, the object of the present invention is achieved through the use of the nitrogen-modified mesoporous dendritic carbon material previously described as a catalyst support in fuel cells.

[0051] In fuel cells, carbon materials are used in particular in the catalyst layers of the electrodes (i.e., the anode and / or cathode).

[0052] As the catalytically active material in the catalyst layer, at least one noble metal deposited in the porous structure of a carbon material can be used. The catalytically active material preferably comprises platinum or a platinum alloy, such as an alloy of platinum with palladium, cobalt, and / or nickel.

[0053] The catalyst layer also includes an ionomer as a binder. The ionomer is preferably a sulfonic acid-based thermoplastic, such as perfluorosulfonic acid (PFSA). (PFSA). This perfluorosulfonic acid is available from DuPont under the name "Nafion", from Solvay under the name "Aquivion", from 3M under the name "Dyneon" or from Asahi Glass under the name "Dyneon". This ionomer can interact particularly advantageously with nitrogen in the carbon lattice, thereby obtaining improved wettability of carbon materials.

[0054] Other features and advantages of the invention are revealed by the following description of exemplary embodiments, as well as by the accompanying drawings, which should not be construed as limiting. Attached Figure Description

[0055] In the attached diagram:

[0056] - Figure 1 A schematic block diagram illustrating a method for preparing nitrogen-modified mesoporous dendritic carbon materials according to the present invention is shown.

[0057] - Figure 2 Shown according to Figure 1 The SEM image of the intermediate obtained by the method of the present invention,

[0058] - Figure 3 Show at a higher magnification Figure 2 Details of the SEM image,

[0059] - Figure 4 Shown according to Figure 1 TEM image of the intermediate obtained by the method of the present invention.

[0060] - Figure 5 The cumulative specific surface area of ​​the carbon materials in Examples 1 to 5 is shown as a function of pore diameter.

[0061] - Figure 6 The cumulative specific surface area of ​​the carbon materials in Examples 6 to 9 is shown as a function of pore diameter.

[0062] - Figure 7 The cumulative specific surface area of ​​the carbon materials in Examples 10 to 13 is shown as a function of pore diameter.

[0063] - Figure 8 The derivatives of the pore volume with respect to the pore diameter as a function of the pore diameter are shown in Examples 1 to 5.

[0064] - Figure 9 The derivatives of the pore volume with respect to the pore diameter as a function of the pore diameter are shown in Examples 6 to 9.

[0065] - Figure 10 The derivative of the pore volume with respect to the pore diameter as a function of the pore diameter is shown in Examples 10 to 13.

[0066] - Figure 11 The relative weights of the intermediates in Examples 1 to 5 are shown as a function of temperature.

[0067] - Figure 12 The relative weights of the intermediates in Examples 6 and 7 are shown as a function of temperature, and

[0068] - Figure 13 The relative weights of the intermediates in Examples 10 and 13 are shown as a function of temperature.

[0069] A commercially available porous three-dimensional carbon material from Akzo Nobel was used as a comparative example. This material is sold under the trade name "KETJENBLACK EC300j" and is used in fuel cells.

[0070] The method of the present invention will be explained in detail below with reference to Examples 2 to 13.

[0071] Step S1: Preparation of metal acetylene compounds as carbon precursors

[0072] First, metal acetylene oxides were prepared as carbon precursors. Figure 1 Step S1 in the process.

[0073] Therefore, an ammonia-containing silver nitrate aqueous solution was prepared by adding 20.34 mL of ammonia solution (20% by weight of ammonia) to 414 mL of silver nitrate aqueous solution (1.275 mg of silver nitrate), so that the molar ratio of ammonia to silver was adjusted to about 29:1.

[0074] The solution is then flushed with nitrogen or argon for 10 to 20 minutes to remove any oxygen present in the solution.

[0075] Then, gaseous acetylene is flushed through the solution for about 5 minutes while being treated with ultrasound, until the solution turns yellow.

[0076] Subsequently, acetylene was flushed through the solution for another 5 minutes without ultrasonic treatment. The solution then changed color to gray and eventually became colorless, with a grayish-white precipitate forming.

[0077] Once a precipitate forms, the acetylene flow is interrupted and the precipitate is obtained by filtering the solution via a membrane filter. The precipitate is washed with methanol and then filtered again. Here, the precipitate is kept moist to prevent it from exploding.

[0078] Step S2: Mix the carbon precursor and nitrogen precursor to form a starting material mixture.

[0079] Weigh the required amount of nitrogen precursor and dissolve it completely in methanol. Place the nitrogen precursor solution in a Teflon reactor beforehand.

[0080] The carbon precursor filtrate was then added, and mixed with the nitrogen precursor in this manner (see [link to original text]). Figure 2 Step S2 in the process.

[0081] Table 1 records the nitrogen precursors used in Examples 2 to 13 and the molar ratio of nitrogen to carbon used in the starting material mixture.

[0082] In all embodiments, silver acetylene was used as the carbon precursor.

[0083] Table 1: Overview of the Implementation Examples.

[0084]

[0085] * Comparative Examples

[0086] Step S3: First heat treatment

[0087] The Teflon reactor containing acetylene silver as a carbon precursor and nitrogen precursors used separately is placed in a stainless steel cylinder with a diameter of 50 mm and a height of 70 mm and sealed with a stainless steel lid.

[0088] The cover has two valves, one of which is connected to a vacuum pump, while the other valve is configured to release the vacuum inside the stainless steel cylinder and fill it with air. An additional positive pressure valve is arranged between the stainless steel cylinder and the valve connected to the vacuum pump as a safety measure.

[0089] The stainless steel cylinder is sealed and the vacuum pump is turned on to dry the starting material mixture and create an airless atmosphere inside the stainless steel cylinder.

[0090] The stainless steel cylinder is heated to 80°C under vacuum using a hot jacket or hot bath overnight, for a total duration of approximately 20 hours. Alternatively, a furnace can be used for heating.

[0091] In this way, metal inclusion compounds are generated in a Teflon reactor through a first heat treatment. Figure 1 Step S3 in the process.

[0092] Step S4: Second heat treatment

[0093] Directly following the first heat treatment, that is, without removing the metal inclusion compound from the stainless steel cylinder or removing the stainless steel cylinder from the furnace, a second heat treatment is performed under vacuum to prepare an intermediate by decomposing the metal inclusion compound. Figure 1 Step S4 in the process.

[0094] Therefore, the stainless steel cylinder was heated to 220°C in a furnace under vacuum for 15 minutes.

[0095] This heating initiates a self-decomposing and explosive reaction of silver acetylene, thereby obtaining a carbon material with a carbon lattice in the intermediate, in which carbon atoms are partially replaced by nitrogen from the nitrogen precursor.

[0096] Step S5: Processing of intermediates

[0097] Remove the intermediate obtained in step S4 from the Teflon reactor and immerse it in a 65% concentrated nitric acid solution at 25°C for 30 minutes.

[0098] In this way, the silver contained in the intermediate and the carbon compounds on the surface of the carbon material are washed out. Figure 1 Step S5 in the process.

[0099] The intermediate was then washed with water to remove all trace amounts of nitric acid and other silver.

[0100] Finally, the intermediate treated in this way is dried under vacuum at 80°C for at least 12 hours.

[0101] For all Examples 2 to 13, the same residence time in nitric acid and the same drying time were used.

[0102] Figure 2 and Figure 3 The image shows a SEM photograph of the intermediate from Example 2 after step S5 (i.e., after washing with nitric acid), in which... Figure 3 Show at a higher magnification Figure 2 Detailed photos.

[0103] These photos clearly show the three-dimensional mesoporous dendritic structure of the resulting intermediates. It is important to note that, due to... Figure 2 and Figure 3 At the available resolution, one can basically see the so-called primary aggregates formed by primary particles, as well as secondary aggregates that include multiple primary aggregates.

[0104] The primary particles themselves have desired mesopores with pore diameters in the range of 2.5 to 6.0 nm, which are crucial for their subsequent application as catalyst supports in fuel cells.

[0105] pass Figure 4 The TEM photograph of the intermediate from Example 2 shown illustrates the porous structure of the primary aggregate.

[0106] Step S6: Consolidation of the intermediate / Third heat treatment

[0107] The washed intermediate was transferred to a tube furnace and purged with argon for at least 10 minutes.

[0108] The intermediate was then heated for 20 hours in an inert gas atmosphere using argon as the inert gas, wherein for each of Examples 2 to 13, the temperatures recorded in Table 1 were used. Figure 1 Step S6 in the process.

[0109] Heating was performed at a rate of 400 K / h, and an inert gas atmosphere was maintained at a flow rate of 50 mL / min for argon.

[0110] Nitrogen-modified mesoporous dendritic carbon materials were obtained. The performance of the carbon materials obtained in Examples 2 to 13 and the comparative example 1 are shown in Tables 2 and 3.

[0111] Table 2: Properties of carbon materials.

[0112]

[0113] * Comparative Examples

[0114] Elemental analysis

[0115] Elemental analysis was used to determine the nitrogen content in the carbon lattice of carbon materials. For this purpose, a Thermo Flash 1112 elemental analyzer from THERMO FINNIGAN was used to determine the proportions of carbon, hydrogen, nitrogen, and sulfur.

[0116] Samples were calcined at a firing temperature of 1020 °C using dynamic flash combustion (a modified Dumas method) in the presence of V₂O₅ as an oxidant. Decomposition was carried out in a manually layered reactor with WO₃ / Cu / Al₂O₃ layers. The produced gases were identified and quantified by gas chromatography (GC).

[0117] Microstructure analysis

[0118] To investigate the microporous and mesoporous structures of the samples and to determine the specific surface area, nitrogen isotherms (physical adsorption isotherms) were determined at 77 K using a QUANTACHROME Autosorb-1 analyzer.

[0119] The samples were transferred into glass tubes with a diameter of 4 mm, and the glass tubes were filled with a layer of glass wool and a glass rod to minimize the dead volume.

[0120] Select sample mass to achieve greater than 10m 2 The absolute surface area is thus used to reduce measurement errors.

[0121] The sample is degassed under vacuum at 90°C for at least 24 hours to remove any adsorbates, such as water or gas, present before measurement. Higher degassed temperatures are not chosen to avoid decomposition of nitrogen-containing groups in the carbonaceous material.

[0122] In 10 -5 The absorption and desorption isotherms of nitrogen are recorded within the range of ≤p / p0≤0.995, where p0 represents the saturation pressure and p represents the actual gas pressure.

[0123] Specific surface area S is determined using the BET method. BET .

[0124] Value V N:0.4-0.8 This represents the difference in volume of nitrogen adsorbed at a p / p0 value of 0.8 versus a p / p0 value of 0.4, expressed in cm⁻¹. 3 (STP) / g or cc(STP) / g.

[0125] The micropores and mesopores present were characterized by numerical analysis using a DFT model based on the adsorption branch of the nitrogen isotherm, with a QSDFT kernel (QSDFT: quenched solid density functional theory) having models for slit pores (diameter <2nm) and columnar pores (diameter >2nm).

[0126] Numerical analysis was used to obtain the volume V of all pores with diameters ranging from 2.5 to 6.0 nm. 介孔 and the total volume V of all holes 总计 .

[0127] The derivative of the pore volume with respect to the diameter, dV(d), is calculated using values ​​obtained from QSDFT analysis.

[0128] As is clear from Table 2, the carbon materials that can be obtained by the method according to the present invention have a large specific surface area S. BET In particular, its specific surface area is many times higher than that of Comparative Example 1.

[0129] The ratio V obtained from these embodiments 介孔 / V 总计 It can also be seen that the carbon material obtained according to the method of the present invention has a high proportion of mesopores with pore diameters in the range of 2.5 to 6.0 nm.

[0130] This can also be seen from Figures 5 to 7 The plot shown represents the cumulative specific surface area as a function of the pore diameter. It can be seen that a significant proportion of the specific surface area S is generated by pores with diameters ranging from 2.5 to 6.0 nm. BET .

[0131] exist Figures 8 to 10 The figure shows the derivative of volume with respect to pore diameter as a function of pore diameter. In this figure, the pore size distribution becomes particularly apparent. In particular, it can be seen that in all embodiments, there is a narrow distribution of pores with very small pore diameters. However, carbon materials obtained according to the method according to the invention additionally have a significant proportion of pores with pore diameters in the range of 2.5 to 6.0 nm, especially a larger proportion than in the case of Comparative Example 1 (see Figure 1). Figure 8 ).

[0132] Figures 11 to 13The relative weights of the intermediates from Examples 1 to 5, 6 and 7 or 10 and 13 as a function of temperature are shown, determined by thermogravimetric analysis using a PerkinElmer STA-8000. For thermogravimetric analysis, the samples to be measured were pre-placed in a ceramic crucible and mass loss was recorded under an argon atmosphere at a heating rate of 5 K / min. Heating was performed after calibration at 1.1 bar in a temperature range of 23 to 1100 °C.

[0133] A third heat treatment is required to obtain sufficient stability of the carbon material. This third heat treatment is particularly important for removing organic residues from the intermediates that negatively impact the performance of the carbon material of this invention. However, at the same time, further decomposition of the carbon material occurs at high temperatures, meaning the temperature in the third heat treatment step should not exceed 1000°C.

[0134] Therefore, carbon materials can be prepared in a simple manner by the method of the present invention. These carbon materials are nitrogen-modified and thus exhibit improved interaction with ionomers, and on the other hand, they contain mesoporous dendritic structures with a large surface area, which facilitates mass transfer in fuel cell applications. This is associated with a large specific surface area for achieving high efficiency in such applications.

Claims

1. A method for preparing nitrogen-modified mesoporous dendritic carbon materials, the method comprising the following steps: - Preparation of metal acetylene compounds as carbon precursors. - Mix the carbon precursor with the nitrogen precursor to form a starting material mixture. - The starting material mixture is subjected to a first heat treatment under vacuum at a temperature ranging from 40 to 80°C to form a metallic inclusion compound. - A second heat treatment is performed under vacuum at a temperature in the range of 120 to 220°C to prepare an intermediate in the process of decomposing the metal inclusion compound, wherein a carbon lattice is formed in the intermediate in which carbon atoms are partially replaced by nitrogen atoms. - Process the intermediate to remove the metal, and - The nitrogen-modified mesoporous dendritic carbon material is obtained by solidifying the treated intermediate through a third heat treatment at a temperature in the range of 200 to 1000°C, under vacuum or in an inert gas atmosphere.

2. The method according to claim 1, characterized in that, The nitrogen precursor is selected from the group consisting of urea, aminocyanide, melamine, and combinations thereof.

3. The method according to claim 1 or 2, characterized in that, In the starting material mixture, the molar ratio of nitrogen to carbon is set in the range of 0.05 to 1.

5.

4. The method according to claim 3, characterized in that, In the starting material mixture, the molar ratio of nitrogen to carbon is set in the range of 0.1 to 1.

0.

5. The method according to claim 3, characterized in that, In the starting material mixture, the molar ratio of nitrogen to carbon is set in the range of 0.3 to 0.

92.

6. The method according to claim 1 or 2, characterized in that, The third heat treatment is carried out at a temperature in the range of 600 to 900°C.

7. A nitrogen-modified mesoporous dendritic carbon material obtained according to any one of claims 1-6, wherein the carbon material has a carbon lattice in which carbon atoms are partially replaced by nitrogen atoms, and wherein the carbon material has a density of 900 to 3000 μm. 2 The specific surface area within the range of / g, which is determined according to the BET method using a nitrogen adsorption isotherm.

8. The carbon material according to claim 7, characterized in that, In the carbon lattice, 0.5 to 1.5% by weight of carbon atoms are replaced by nitrogen atoms.

9. The carbon material according to claim 7, characterized in that, The carbon material has a range of 1000 to 2150 m. 2 The specific surface area within the range of / g, which is determined according to the BET method using a nitrogen adsorption isotherm.

10. The carbon material according to claim 9, characterized in that, The carbon material has a range of 1300 to 2150 m. 2 Specific surface area within the range of / g.

11. The carbon material according to claim 7, characterized in that, The carbon material has a V value in the range of 0.25 to 0.

75. 介孔 / V 总计 The ratio of V to V 介孔 V represents the volume of all pores in the carbon material having a pore size in the range of 2.5 to 6.0 nm, and V 总计 This represents the total volume of all the pores in the carbon material.

12. The carbon material according to claim 11, characterized in that, The carbon material has a V0 in the range of 0.30 to 0.

65. 介孔 / V 总计 The ratio.

13. The carbon material according to claim 11, characterized in that, The carbon material has a V value in the range of 0.35 to 0.

6. 介孔 / V 总计 The ratio.

14. The carbon material according to claim 7, characterized in that, The carbon material has a thickness of 80 to 220 cm. 3 Nitrogen absorption volume V in the range of (STP) / g N:0.4-0.8 V N:0.4-0.8 This represents the nitrogen volume within the relative pressure range p / p0 of 0.4 to 0.8 of the nitrogen adsorption isotherm.

15. The carbon material according to claim 14, characterized in that, The carbon material has a density of 100 to 200 cm. 3 Nitrogen absorption volume V in the range of (STP) / g N:0.4-0.8 .

16. The carbon material according to claim 14, characterized in that, The carbon material has a thickness of 110 to 190 cm. 3 Nitrogen absorption volume V in the range of (STP) / g N:0.4-0.8 .

17. The carbon material according to claim 7, characterized in that, The carbon material has a thickness of 0.5 to 0.9 cm. 3 dV in the range of / g 2.5-6nm Value, wherein dV 2.5-6nm The value describes the cumulative volume of a pore with a diameter in the range of 2.5 to 6.0 nm relative to a unit of weight. The value can be obtained by differentiating the cumulative pore volume with respect to the pore diameter and then integrating over the corresponding range of pore diameters.

18. The carbon material according to claim 17, characterized in that, The carbon material has a thickness ranging from 0.53 to 0.86 cm. 3 dV in the range of / g 2.5-6nm value.

19. The carbon material according to claim 17, characterized in that, The carbon material has a thickness ranging from 0.55 to 0.574 cm. 3 dV in the range of / g 2.5-6nm value.

20. Use of the nitrogen-modified mesoporous dendritic carbon material according to any one of claims 7 to 19 as a catalyst support in a fuel cell.

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