Electrode material for fuel cell and preparation method thereof

Abstract

The invention belongs to the field of fuel cells, and particularly relates to an electrode material for a fuel cell and a preparation method thereof, and the preparation method comprises the following steps: preparing polyimide containing amino POSS (Polyhedral Oligomeric Silsesquioxane); carrying out primary pyrolysis, and sequentially carrying out acid etching, cleaning and drying on a product to obtain primary carbonized polyimide; and grinding the primary carbonized polyimide, performing pyrolysis again, and sequentially performing acid etching, cleaning and drying on the product to obtain the electrode material for the fuel cell. The electrode material has a good graphite structure and a rich pore structure, so that ions and electrons can be quickly transferred in pores while the good conductivity of the material can be ensured; meanwhile, introduction of non-metal nitrogen heteroatoms can increase active sites, the electrochemical activity of the material is remarkably improved, and the material is suitable for being used as an electrode material of a fuel cell.

Description

Technical Field

[0001] The present invention belongs to the field of fuel cells, and particularly relates to an electrode material for a fuel cell and a preparation method thereof. Background Art

[0002] The increase in global energy consumption, mainly from limited fossil fuel resources, may lead to the depletion of reserves and an increase in environmental problems, which may ultimately lead to serious health problems. Therefore, there is an urgent need to explore and develop pollution-free, renewable, and sustainable energy sources. Nature produces a large amount of biomass waste every day (including agricultural waste, by-products and residues, lignocellulosic biomass, woody biomass). Biomass currently accounts for 15% of global energy consumption because it is easily convertible into gaseous, liquid, and solid-phase materials. However, a large amount of biomass dumped or burned in the open air will cause the release of harmful pollutants. The emergence of fuel cells and other electrochemical devices has paved the way for a series of applications of biomass in clean energy.

[0003] A fuel cell has the same composition as a common battery. A single cell consists of a positive electrode, a negative electrode, and an electrolyte diaphragm and electrolyte solution. The difference is that the active substances of a common battery are stored inside the battery, and the limited internal space restricts the storage amount of the active substances, thereby restricting the capacity of the common battery. However, neither of the two electrodes of a fuel cell contains active materials, and the electrodes are only catalytic elements. Therefore, a fuel cell can be regarded as an efficient energy conversion machine that can effectively utilize electrochemical energy. When the battery operates, fuel and oxygen are continuously supplied from the outside for reaction. When the fuel input is not interrupted and the reaction is continuous, the fuel cell can continue to generate electricity.

[0004] The polarization loss caused by the oxygen reduction reaction (ORR) in fuel cells and metal-air batteries has become one of the key factors seriously affecting the overall performance of these energy storage and conversion devices. So far, platinum and its alloys are considered to be the best electrocatalysts for accelerating the ORR process. In addition to the high cost, they also have the disadvantages of poor stability and susceptibility to cross effects, which are becoming the main obstacles to the commercialization of these electrochemical power devices. Generally speaking, in order to reduce costs and encourage wide use, researchers are mainly committed to replacing expensive platinum-based catalysts with ORR catalysts with lower costs. In search of platinum-free catalysts, promising alternatives have been found, including non-precious metal catalysts, nanostructured transition metal oxides, and nitrogen-doped carbon materials, etc.

[0005] Among the various types of catalysts mentioned above, whether they are non-noble metal catalysts or nanostructured transition metal catalysts, they are prone to react with acids in an acidic environment to produce metal salts, thereby reducing the catalytic activity of the catalysts. In an alkaline environment, metals react with alkalis to produce metal hydroxides, resulting in the loss of metals and affecting the reaction rate. If these two types of metal catalysts are used in large quantities, it will cause a large loss of metal resources, pollute the environment on the one hand, and increase costs on the other hand. Therefore, people have been vigorously promoting various advanced metal-free ORR catalysts to replace platinum-based materials.

[0006] In summary, if the electrocatalyst for oxygen reduction reaction cannot achieve high activity, high stability, and low cost, the platinum-based catalyst cannot be replaced, and then the large-scale practical application of fuel cells will be difficult to achieve. Here, the nitrogen-doped carbon structure can be used as a metal-free catalyst, which has advantages such as catalytic activity, long-term operation stability, and tolerance to cross effects, and is much better than platinum for oxygen reduction in alkaline fuel cells. Nitrogen-doped porous carbon materials have been proven to be one of the most promising high-efficiency ORR catalysts because they can regulate the charge redistribution of carbon atoms, enhance the electron transport ability, and introduce edge defects, which is beneficial to electron transfer. Nitrogen-doped carbon structure materials also become the most promising materials for cathode and anode electrode materials in future fuel cells. However, the nitrogen-doped carbon structure materials prepared by existing technologies have a low specific surface area and low catalytic efficiency, which limits their application. Summary of the Invention

[0007] The purpose of the present invention is to provide an electrode material for fuel cells and a preparation method thereof. The carbon material prepared by modifying polyimide with amino-POSS endows the carbon material with a high specific surface area and a porous structure to solve the problems raised in the above background technology.

[0008] To achieve the above purpose, the present invention provides the following technical solution: A preparation method of an electrode material for fuel cells, comprising the following steps: (1) Add dianhydride monomers and diamine monomers to an organic solvent, stir and react for a period of time, then add amino-POSS, and continue to react to generate a polyamic acid solution; the mass of amino-POSS is 0.1-5 wt% of the sum of the masses of dianhydride monomers and diamine monomers; Specifically, the stirring reaction time is 2 - 4 h, and the continuous reaction time is 5 - 8 h. Further, the process steps are as follows: Add the diamine monomer into an organic solvent. Under continuous stirring conditions, add the dianhydride monomer into the organic solvent in 3 - 5 portions at intervals of 3 - 8 minutes each. After the addition of the dianhydride monomer is completed, stir and react for 2 - 4 h, then add amino-POSS and continue to react for 5 - 8 h to form a polyamic acid solution. Reacting the dianhydride monomer and the diamine monomer for a period of time in advance before adding amino-POSS can not only promote the polymerization reaction but also make amino-POSS evenly dispersed in the resin matrix.

[0009] Further, the stirring rate is 150 - 250 r / min; Further, the dianhydride monomer is selected from one or more of pyromellitic dianhydride, 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, diphenyl sulfone-3,4,3',4'-tetracarboxylic dianhydride, bis(3,4-dicarboxyphenyl) sulfide dianhydride, 2,2'-bis(3,4-dicarboxylic) hexafluoropropane dianhydride, 2,3,3',4'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, bis(3,4-dicarboxyphenyl) methane dianhydride, 2,2-bis(3,4-dicarboxyphenyl) propane dianhydride, m-terphenyl-3,4,3',4'-tetracarboxylic dianhydride, p-terphenyl-3,4,3',4'-tetracarboxylic dianhydride, 1,3-bis(3,4-dicarboxyphenoxy) benzene dianhydride, 1,4-bis(3,4-dicarboxyphenoxy) benzene dianhydride, 1,4-bis(3,4-dicarboxyphenoxy) biphenyl dianhydride, 2,2-bis[(3,4-dicarboxyphenoxy)phenyl] propane dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride.

[0010] Further, the diamine monomer is selected from one or more of p-phenylenediamine, m-phenylenediamine, 3,3'-dimethylbenzidine, 2,2'-dimethylbenzidine, 2,4-diaminotoluene, 2,6-diaminotoluene, 3,5-diaminobenzoic acid, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane (methylenediamine), 3,3'-dimethyl-4,4'-diaminobiphenyl, 2,2'-dimethyl-4,4'-diaminobiphenyl, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 3,3'-dicarboxy-4,4'-diaminodiphenylmethane, 3,3',5,5'-tetramethyl-4,4'-diaminodiphenylmethane, 4,4'-diaminobenzanilide, 3,3'-dimethoxybenzidine, 2,2'-dimethoxybenzidine, 3,3'-diaminodiphenyl ether, 3,3'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminobenzophenone, 4,4'-diaminobenzophenone, 3,3'-diamino-4,4'-dichlorobenzophenone, 3,3'-diamino-4,4'-dimethoxybenzophenone.

[0011] Benefiting from the excellent thermal stability of polyimide, its morphology is well retained after pyrolysis. The structure control of the target nitrogen-doped carbon material can be achieved by selecting polyimide monomers.

[0012] (2) Drop the polyamic acid solution into deionized water to precipitate polyamic acid powder, and obtain polyimide after gradient heating thermal imidization. Polyimide is a low-cost engineering plastic with a rigid aromatic skeleton, which is easy to carbonize and has a high carbon yield. Moreover, the nitrogen-containing five-membered imide heterocyclic groups are evenly distributed in the polyimide skeleton, laying a foundation for the synchronous in-situ doping of nitrogen atoms during the carbonization process. The doping process is easier and the doping effect is more uniform.

[0013] Further, the gradient heating thermal imidization process is as follows: the heating rate is 2-6 °C / min, heat from room temperature to 70-80 °C and keep warm for 0.2-1 h, then heat to 100-110 °C and keep warm for 1-1.5 h, then heat to 130-150 °C and keep warm for 1-1.5 h, then heat to 180-200 °C and keep warm for 1-1.5 h, then heat to 230-250 °C and keep warm for 1-1.5 h, then heat to 260-270 °C and keep warm for 1-1.5 h; (3) The polyimide is pyrolyzed primarily in an inert gas atmosphere, and the product is sequentially etched with acid, washed, and dried to obtain primary carbonized polyimide; the primary pyrolysis temperature is 900 - 1200 °C, and the time is 0.5 - 2 h; (4) After grinding the primary carbonized polyimide, it is pyrolyzed again in an inert gas atmosphere. The product is sequentially etched with acid, washed, and dried, and then the electrode material for fuel cells is obtained; the temperature of the second pyrolysis is 500 - 800 °C, and the time is 2 - 5 h. The acid etching is carried out in two steps. Compared with the common single-step acid etching process in the art, the first acid etching can promote the exposure of internal silicon oxides, which is not only beneficial to the second acid etching, but also promotes the low-temperature carbonization process. After grinding the primary carbonized polyimide, it can also promote the exposure of internal silicon oxides and improve the efficiency of the carbonization process.

[0014] Platinum, as the most common electrode material, has the disadvantages of high price, low abundance, and poor tolerance to impurities. To solve these bottleneck problems of precious metals, the present invention prepares a metal-free heteroatom-doped carbon-based material. The metal-free heteroatom-doped carbon material has become the most promising electrode material due to its low price, controllable pore structure, and high tolerance to impurities. Compared with the conventional hydrothermal carbonization method and template method, the process for preparing the nitrogen-doped carbon material by pyrolysis is simpler and suitable for industrial promotion. By adjusting the carbonization temperature, the nitrogen doping content and type in the nitrogen-doped carbon material can be regulated, thereby optimizing its properties as an electrode material.

[0015] Further, in step (1), the organic solvent is one or more of N,N-dimethylacetamide, dimethyl sulfoxide, N,N-dimethylformamide, and N-methylpyrrolidone.

[0016] Further, in step (1), the amino-containing POSS is one or more of octaaminophenylcage silsesquioxane, octaaminopropylcage silsesquioxane, aminopropylisobutylcage silsesquioxane, and aminopropylisooctylcage silsesquioxane.

[0017] The amino-containing POSS has two functions in the carbon matrix. On the one hand, the amino group in POSS plays a role in nitrogen doping. As a non-metallic element incorporated into the carbon nanomaterial, its size and electronegativity are different from those of carbon atoms, which will lead to changes in electron modulation, charge distribution, and electronic properties, greatly changing the chemical properties of the carbon nanomaterial, thereby improving the performance of the carbon nanomaterial. On the other hand, the unique hollow closed cage-like structure of POSS undergoes volume shrinkage during the calcination process, introducing a porous structure. In addition, the SiOC (SiO 2Structures such as (etc.) will be corroded by hydrofluoric acid during the cleaning process, further improving the porous structure of carbon. It should be noted that the dosage of POSS needs to be controlled. When the mass of amino-containing POSS exceeds 5 wt% of the sum of the monomer masses, it not only is not conducive to the progress of the polymerization reaction, but also affects the overall structure of the polyimide, resulting in a decrease in mechanical strength and causing the collapse of the internal porous structure during the heating and carbonization process, which is not conducive to the formation of conductive pathways and affects the performance of the carbon material.

[0018] Furthermore, in step (1), the molar ratio of the dianhydride monomer to the diamine monomer is 1:(1 - 1.05).

[0019] Furthermore, in steps (3) and (4), the inert gas is at least one of argon, nitrogen, and helium.

[0020] Furthermore, in steps (3) and (4), the acid etching is carried out using a hydrofluoric acid solution, and the mass concentration of the hydrofluoric acid solution is 5 - 15 wt%.

[0021] Furthermore, in steps (3) and (4), the cleaning is first carried out by washing with deionized water 2 - 4 times, and then washing with absolute ethanol 1 - 3 times.

[0022] Furthermore, in step (3), the heating rate of the primary pyrolysis is 5 - 10 °C / min. A faster heating rate can promote the rapid formation of the basic structure and prevent the shrinkage and deformation of the pore structure.

[0023] Furthermore, in step (4), the heating rate of the secondary pyrolysis is 1 - 5 °C / min.

[0024] Furthermore, the primary pyrolysis temperature is 950 - 1100 °C and the time is 1.3 - 2 h; the secondary pyrolysis temperature is 700 - 800 °C and the time is 2.5 - 4.5 h. A higher pyrolysis temperature and a longer pyrolysis time are beneficial to the formation of a large specific surface area and the development of a porous structure of the prepared material. However, excessive pyrolysis may also cause the collapse of the pore structure of the material, thereby reducing its specific surface area and lowering its electrical properties. The present invention prepares a carbon material by a two-step pyrolysis method. First, polyimide is carbonized at a higher heating rate and a higher temperature. On the one hand, it promotes the rapid carbonization and shaping of polyimide, especially the POSS structure, and prevents the collapse of the structure during the subsequent carbonization process; on the other hand, the higher temperature promotes the pyrolysis of the POSS structure and promotes the formation of the SiOC (SiO 2 etc.) structure. Then, the temperature is reduced from a higher temperature to a lower carbonization temperature to further carbonize the material and promote the formation of a porous structure. The POSS-modified polyimide carbon material prepared by the two-step method has a large specific surface area and a rich pore structure, which is beneficial to the improvement of the electrical conductivity of the carbon material.

[0025] On the other hand, the present invention also provides an electrode material for a fuel cell. The electrode material prepared by the present invention has a relatively high specific surface area, which enables the reactants to fully contact the active sites; in addition, the electrode material has a good graphite structure and a rich pore structure, which can ensure good conductivity of the material while allowing ions and electrons to rapidly transfer within the pores; at the same time, the introduction of non-metallic nitrogen heteroatoms can increase the active sites and significantly improve the electrochemical activity of the material, making it suitable as an electrode material for fuel cells, especially microbial fuel cells.

[0026] Beneficial effects: The use of polyimide as a precursor material realizes the preparation of self-doped carbon materials. Polyimide is a low-cost engineering plastic with a rigid aromatic skeleton, which is easy to carbonize, has a high carbon yield, is easier in the doping process, and has a more uniform doping effect. The amino group in POSS plays a role in nitrogen doping, greatly changing the chemical properties of the carbon nanomaterials, thereby improving the performance of the carbon nanomaterials; at the same time, the unique hollow closed cage structure of POSS undergoes volume shrinkage during the calcination process, introducing a porous structure. The SiOC (SiO 2 etc.) structure formed by the transformation of POSS therein will be corroded by hydrofluoric acid, further improving the porous structure of carbon. The POSS-modified polyimide carbon material prepared by the two-step method has a large specific surface area and a rich pore structure, which is beneficial to improving the conductivity of the carbon material.

[0027] The electrode material has a relatively high specific surface area, which enables the reactants to fully contact the active sites; in addition, the electrode material has a good graphite structure and a rich pore structure, which can ensure good conductivity of the material while allowing ions and electrons to rapidly transfer within the pores; at the same time, the introduction of non-metallic nitrogen heteroatoms can increase the active sites and significantly improve the electrochemical activity of the material, making it suitable as an electrode material for fuel cells, especially microbial fuel cells. Detailed implementation manners

[0028] To better understand the technical content of the present invention, specific examples are provided below to further illustrate the present invention.

[0029] The experimental methods used in the embodiments of the present invention are all conventional methods unless otherwise specified.

[0030] The materials, reagents, etc. used in the embodiments of the present invention can be obtained from commercial channels unless otherwise specified.

[0031] Example 1 A preparation method of an electrode material for a fuel cell includes the following steps: (1) Add diamine monomers into an organic solvent. Under continuous stirring, add dianhydride monomers into the organic solvent in three portions at intervals of 5 minutes each. After the addition of dianhydride monomers is completed, stir and react for 3.2 h, then add amino-POSS and continue to react for 7.5 h to form a polyamic acid solution; the mass of amino-POSS is 2.5 wt% of the sum of the masses of dianhydride monomers and diamine monomers; the stirring rate is 200 r / min; The dianhydride monomer is selected from pyromellitic dianhydride; the diamine monomer is selected from 4,4'-diaminodiphenyl ether; the amino-POSS is octaaminophenylcage silsesquioxane; the organic solvent is N,N-dimethylacetamide; the molar ratio of dianhydride monomer to diamine monomer is 1:1.01; (2) Drop the polyamic acid solution into deionized water to precipitate polyamic acid powder, and obtain polyimide after gradient temperature-rising thermal imidization; The process of gradient temperature-rising thermal imidization is as follows: the heating rate is 4 °C / min, heat from room temperature to 75 °C and hold for 0.5 h, then heat to 100 °C and hold for 1.4 h, then heat to 130 °C and hold for 1.2 h, then heat to 180 °C and hold for 1.3 h, then heat to 230 °C and hold for 1.3 h, then heat to 260 °C and hold for 1.2 h; (3) Carry out primary pyrolysis of the polyimide in an argon atmosphere. The product is successively etched with acid, washed, and dried to obtain primary carbonized polyimide; the heating rate of primary pyrolysis is 5 °C / min; the primary pyrolysis temperature is 950 °C and the time is 2 h; the acid etching is carried out with a hydrofluoric acid solution with a mass concentration of 8 wt%, and the washing is to wash 3 times with deionized water first, and then wash 2 times with absolute ethanol; (4) Grind the primary carbonized polyimide and then pyrolyze it again in an argon atmosphere. The product is successively etched with acid, washed, and dried to obtain the electrode material for fuel cells; the heating rate of the second pyrolysis is 3 °C / min, the second pyrolysis temperature is 700 °C and the time is 4.5 h; the acid etching is carried out with a hydrofluoric acid solution with a mass concentration of 8 wt%, and the washing is to wash 3 times with deionized water first, and then wash 2 times with absolute ethanol. Test the specific surface area and pore volume of the product through nitrogen adsorption experiment, and test its conductivity through a four-probe tester. The specific surface area is 924 m 2 g -1 , the pore volume is 0.53 cm 3 g -1 ; the conductivity is 12.2 Scm -1 .

[0032] Example 2 A preparation method of an electrode material for fuel cells, comprising the following steps: (1) Add the diamine monomer into an organic solvent. Under continuous stirring, add the dianhydride monomer into the organic solvent in three portions at intervals of 5 minutes each. After the addition of the dianhydride monomer is completed, stir and react for 4 h, then add amino-POSS and continue to react for 6 h to form a polyamic acid solution; the mass of amino-POSS is 5 wt% of the sum of the masses of the dianhydride monomer and the diamine monomer; the stirring rate is 200 r / min; The dianhydride monomer is selected from 3,3',4,4'-biphenyltetracarboxylic dianhydride; the diamine monomer is selected from 4,4'-diaminodiphenylmethane; the amino-POSS is octaaminophenylcage silsesquioxane; the organic solvent is N,N-dimethylformamide; the molar ratio of the dianhydride monomer to the diamine monomer is 1:1.05; (2) Drop the polyamic acid solution into deionized water to precipitate polyamic acid powder, and obtain polyimide after gradient heating thermal imidization; The process of gradient heating thermal imidization is as follows: the heating rate is 4 °C / min, heat up from room temperature to 75 °C and hold for 0.5 h, then heat up to 100 °C and hold for 1.4 h, then heat up to 150 °C and hold for 1.2 h, then heat up to 200 °C and hold for 1.3 h, then heat up to 250 °C and hold for 1.3 h, then heat up to 270 °C and hold for 1.2 h; (3) Carry out primary pyrolysis of the polyimide in an argon atmosphere. The product is successively etched with acid, washed, and dried to obtain primary carbonized polyimide; the heating rate of primary pyrolysis is 6 °C / min; the primary pyrolysis temperature is 1100 °C and the time is 1.3 h; the acid etching is carried out with a hydrofluoric acid solution with a mass concentration of 8 wt%, and the washing is first carried out with deionized water 3 times, and then with absolute ethanol 2 times; (4) Grind the primary carbonized polyimide and then pyrolyze it again in an argon atmosphere. The product is successively etched with acid, washed, and dried to obtain the electrode material for fuel cells; the heating rate of the second pyrolysis is 3 °C / min, the second pyrolysis temperature is 800 °C and the time is 2.5 h; the acid etching is carried out with a hydrofluoric acid solution with a mass concentration of 8 wt%, and the washing is first carried out with deionized water 3 times, and then with absolute ethanol 2 times. Test the specific surface area and pore volume of the product through nitrogen adsorption experiments, and test its conductivity through a four-probe tester. The specific surface area is 1024 m 2 g -1 , the pore volume is 0.62 cm 3 g -1 ; the conductivity is 17.1 S cm -1 .

[0033] Example 3 A preparation method of an electrode material for fuel cells, comprising the following steps: (1) Add the diamine monomer to an organic solvent. Under continuous stirring, add the dianhydride monomer to the organic solvent in 3 portions at intervals of 5 minutes. After the addition of the dianhydride monomer is completed, stir and react for 3.2 h, then add amino-POSS and continue to react for 6 h to form a polyamic acid solution; the mass of amino-POSS is 3 wt% of the sum of the masses of the dianhydride monomer and the diamine monomer; the stirring rate is 200 r / min; The dianhydride monomer is selected from a mixture of 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride and 2,2'-bis(3,4-dicarboxylic acid) hexafluoropropane dianhydride with a molar ratio of 1:1; the diamine monomer is selected from 4,4'-diaminodiphenyl ether; the amino-POSS is octaaminophenylcage silsesquioxane; the organic solvent is N,N-dimethylacetamide; the molar ratio of the dianhydride monomer to the diamine monomer is 1:1.03; (2) Drop the polyamic acid solution into deionized water to precipitate polyamic acid powder, and obtain polyimide after gradient heating and thermal imidization; The process of gradient heating and thermal imidization is as follows: the heating rate is 4 °C / min, heat from room temperature to 75 °C and hold for 0.5 h, then heat to 100 °C and hold for 1.4 h, then heat to 135 °C and hold for 1.2 h, then heat to 185 °C and hold for 1.3 h, then heat to 245 °C and hold for 1.3 h, then heat to 262 °C and hold for 1.2 h; (3) Carry out primary pyrolysis of the polyimide in an argon atmosphere. The product is successively etched with acid, washed, and dried to obtain primary carbonized polyimide; the heating rate of primary pyrolysis is 6 °C / min; the primary pyrolysis temperature is 1050 °C and the time is 1.5 h; the acid etching is carried out with a hydrofluoric acid solution with a mass concentration of 8 wt%, and the washing is to wash 3 times with deionized water first, and then wash 2 times with absolute ethanol; (4) After grinding the primary carbonized polyimide, pyrolyze it again in an argon atmosphere. The product is successively etched with acid, washed, and dried to obtain the electrode material for fuel cells; the heating rate of the second pyrolysis is 3 °C / min, the second pyrolysis temperature is 730 °C, and the time is 3.1 h; the acid etching is carried out with a hydrofluoric acid solution with a mass concentration of 8 wt%, and the washing is to wash 3 times with deionized water first, and then wash 2 times with absolute ethanol. The specific surface area and pore volume of the product are tested by nitrogen adsorption experiment, and its conductivity is tested by a four-probe tester. The specific surface area is 1147 m 2 g -1 , the pore volume is 0.63 cm 3 g -1 ; the conductivity is 19.2 S cm -1 .

[0034] Example 4 A preparation method of an electrode material for fuel cells, comprising the following steps: (1) Add diamine monomers into an organic solvent. Under continuous stirring, add dianhydride monomers into the organic solvent in three portions at intervals of 5 minutes. After the addition of dianhydride monomers is completed, stir and react for 3.7 h, then add amino-POSS and continue to react for 7 h to form a polyamic acid solution; the mass of amino-POSS is 3.2 wt% of the sum of the masses of dianhydride monomers and diamine monomers; the stirring rate is 200 r / min; The dianhydride monomers are selected from a mixture of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 3,3',4,4'-diphenylethertetracarboxylic dianhydride with a molar ratio of 1:1; the diamine monomers are selected from 4,4'-diaminodiphenylmethane; the amino-POSS is octaaminophenylcage silsesquioxane; the organic solvent is N,N-dimethylformamide; the molar ratio of dianhydride monomers to diamine monomers is 1:1.04; (2) Drop the polyamic acid solution into deionized water to precipitate polyamic acid powder, and obtain polyimide after gradient temperature-rising thermal imidization; The process of gradient temperature-rising thermal imidization is as follows: the heating rate is 4 °C / min, heat from room temperature to 75 °C and hold for 0.5 h, then heat to 100 °C and hold for 1.4 h, then heat to 142 °C and hold for 1.2 h, then heat to 193 °C and hold for 1.3 h, then heat to 248 °C and hold for 1.3 h, then heat to 266 °C and hold for 1.2 h; (3) Carry out primary pyrolysis of the polyimide in an argon atmosphere. The product is sequentially etched with acid, washed, and dried to obtain primary carbonized polyimide; the heating rate of primary pyrolysis is 6 °C / min; the primary pyrolysis temperature is 990 °C and the time is 1.7 h; the acid etching is carried out using a hydrofluoric acid solution with a mass concentration of 8 wt%, and the washing is to wash 3 times with deionized water first, and then wash 2 times with absolute ethanol; (4) Grind the primary carbonized polyimide and then pyrolyze it again in an argon atmosphere. The product is sequentially etched with acid, washed, and dried to obtain the electrode material for fuel cells; the heating rate of the second pyrolysis is 3 °C / min, the second pyrolysis temperature is 770 °C and the time is 4.1 h; the acid etching is carried out using a hydrofluoric acid solution with a mass concentration of 8 wt%, and the washing is to wash 3 times with deionized water first, and then wash 2 times with absolute ethanol. Test the specific surface area and pore volume of the product through nitrogen adsorption experiments, and test its conductivity through a four-probe tester. The specific surface area is 1068 m 2 g -1 , the pore volume is 0.57 cm 3 g -1 ; the conductivity is 14.8 S cm -1 .

[0035] Example 5 A preparation method of an electrode material for fuel cells, comprising the following steps: (1) Add diamine monomers into an organic solvent. Under continuous stirring, add dianhydride monomers into the organic solvent in three portions at intervals of 5 minutes. After the addition of dianhydride monomers is completed, stir and react for 3.6 h, then add amino-POSS and continue to react for 6 h to form a polyamic acid solution; the mass of amino-POSS is 3.4 wt% of the sum of the masses of dianhydride monomers and diamine monomers; the stirring rate is 200 r / min; The dianhydride monomers are selected from a mixture of pyromellitic dianhydride and 3,3',4,4'-biphenyltetracarboxylic dianhydride with a molar ratio of 2:1; the diamine monomers are selected from 4,4'-diaminodiphenyl ether; the amino-POSS is octaaminophenylcage silsesquioxane; the organic solvent is N,N-dimethylformamide; the molar ratio of dianhydride monomers to diamine monomers is 1:1.03; (2) Drop the polyamic acid solution into deionized water to precipitate polyamic acid powder, and obtain polyimide after gradient temperature rise thermal imidization; The process of gradient temperature rise thermal imidization is as follows: the heating rate is 4 °C / min, heat up from room temperature to 75 °C and hold for 0.5 h, then heat up to 100 °C and hold for 1.4 h, then heat up to 140 °C and hold for 1.2 h, then heat up to 193 °C and hold for 1.3 h, then heat up to 241 °C and hold for 1.3 h, then heat up to 267 °C and hold for 1.2 h; (3) Carry out primary pyrolysis of the polyimide in an argon atmosphere. The product is sequentially etched with acid, washed, and dried to obtain primary carbonized polyimide; the heating rate of primary pyrolysis is 3 °C / min; the primary pyrolysis temperature is 1000 °C and the time is 1.7 h; the acid etching is carried out with a hydrofluoric acid solution with a mass concentration of 8 wt%, and the washing is carried out by first washing 3 times with deionized water and then washing 2 times with absolute ethanol; (4) Grind the primary carbonized polyimide and then pyrolyze it again in an argon atmosphere. The product is sequentially etched with acid, washed, and dried to obtain the electrode material for fuel cells; the heating rate of the second pyrolysis is 3 °C / min, the second pyrolysis temperature is 780 °C and the time is 3.8 h; the acid etching is carried out with a hydrofluoric acid solution with a mass concentration of 8 wt%, and the washing is carried out by first washing 3 times with deionized water and then washing 2 times with absolute ethanol. Test the specific surface area and pore volume of the product through nitrogen adsorption experiments, and test its conductivity through a four-probe tester. The specific surface area is 973 m 2 g -1 , the pore volume is 0.55 cm 3 g -1 ; the conductivity is 18.1 S cm -1 .

[0036] Example 6 A preparation method of an electrode material for fuel cells, comprising the following steps: (1) Add diamine monomers into an organic solvent. Under continuous stirring, add dianhydride monomers into the organic solvent in three portions at 5-minute intervals. After the addition of dianhydride monomers is completed, directly add amino-POSS and continue the reaction for 9.6 h to form a polyamic acid solution; the mass of amino-POSS is 3.4 wt% of the sum of the masses of dianhydride monomers and diamine monomers; the stirring rate is 200 r / min; The dianhydride monomers are selected from a mixture of pyromellitic dianhydride and 3,3',4,4'-biphenyltetracarboxylic dianhydride with a molar ratio of 2:1; the diamine monomers are selected from 4,4'-diaminodiphenyl ether; the amino-POSS is octaaminophenylcage silsesquioxane; the organic solvent is N,N-dimethylformamide; the molar ratio of dianhydride monomers to diamine monomers is 1:1.03; (2) Drop the polyamic acid solution into deionized water to precipitate polyamic acid powder, and obtain polyimide after gradient temperature-rising thermal imidization; The process of gradient temperature-rising thermal imidization is as follows: the heating rate is 4 °C / min, heat from room temperature to 75 °C and hold for 0.5 h, then heat to 100 °C and hold for 1.4 h, then heat to 140 °C and hold for 1.2 h, then heat to 193 °C and hold for 1.3 h, then heat to 241 °C and hold for 1.3 h, then heat to 267 °C and hold for 1.2 h; (3) Carry out primary pyrolysis of the polyimide in an argon atmosphere. The product is successively etched with acid, washed, and dried to obtain primary carbonized polyimide; the heating rate of primary pyrolysis is 6 °C / min; the primary pyrolysis temperature is 1000 °C and the time is 1.7 h; the acid etching is carried out with a hydrofluoric acid solution with a mass concentration of 8 wt%, and the washing is to wash 3 times with deionized water first, and then wash 2 times with absolute ethanol; (4) Grind the primary carbonized polyimide and pyrolyze it again in an argon atmosphere. The product is successively etched with acid, washed, and dried to obtain the electrode material for fuel cells; the heating rate of the second pyrolysis is 3 °C / min, the second pyrolysis temperature is 780 °C, and the time is 3.8 h; the acid etching is carried out with a hydrofluoric acid solution with a mass concentration of 8 wt%, and the washing is to wash 3 times with deionized water first, and then wash 2 times with absolute ethanol. Test the specific surface area and pore volume of the product through nitrogen adsorption experiments, and test its conductivity through a four-probe tester. The specific surface area is 1035 m 2 g -1 , the pore volume is 0.59 cm 3 g -1 ; the conductivity is 15.4 S cm -1 .

[0037] Example 7 A preparation method of an electrode material for fuel cells, comprising the following steps: (1) Add the diamine monomer to an organic solvent. Under continuous stirring, add the dianhydride monomer to the organic solvent in three portions, with a 5-minute interval between each addition. After the addition of the dianhydride monomer is complete, stir and react for 3.6 h, then add amino-POSS and continue to react for 6 h to form a polyamic acid solution; the mass of amino-POSS is 3.4 wt% of the sum of the masses of the dianhydride monomer and the diamine monomer; the stirring rate is 200 r / min; The dianhydride monomer is selected from a mixture of pyromellitic dianhydride and 3,3',4,4'-biphenyltetracarboxylic dianhydride with a molar ratio of 2:1; the diamine monomer is selected from 4,4'-diaminodiphenyl ether; the amino-POSS is octaaminophenyl silsesquioxane; the organic solvent is N,N-dimethylformamide; the molar ratio of the dianhydride monomer to the diamine monomer is 1:1.03; (2) Drop the polyamic acid solution into deionized water to precipitate polyamic acid powder, and obtain polyimide after gradient temperature thermal imidization; The process of gradient temperature thermal imidization is as follows: the heating rate is 4 °C / min, heat from room temperature to 75 °C and hold for 0.5 h, then heat to 100 °C and hold for 1.4 h, then heat to 140 °C and hold for 1.2 h, then heat to 193 °C and hold for 1.3 h, then heat to 241 °C and hold for 1.3 h, then heat to 267 °C and hold for 1.2 h; (3) Carry out primary pyrolysis of the polyimide in an argon atmosphere. The product is successively etched with acid, washed, and dried to obtain primary carbonized polyimide; the heating rate of primary pyrolysis is 6 °C / min; the primary pyrolysis temperature is 1000 °C and the time is 1.7 h; the acid etching is carried out using a hydrofluoric acid solution with a mass concentration of 8 wt%, and the washing is carried out by first washing 3 times with deionized water and then washing 2 times with absolute ethanol; (4) After grinding the primary carbonized polyimide, pyrolyze it again in an argon atmosphere. The product is successively etched with acid, washed, and dried to obtain the electrode material for fuel cells; the heating rate of the second pyrolysis is 3 °C / min, the second pyrolysis temperature is 780 °C, and the time is 3.8 h; the acid etching is carried out using a hydrofluoric acid solution with a mass concentration of 8 wt%, and the washing is carried out by first washing 3 times with deionized water and then washing 2 times with absolute ethanol. Test the specific surface area and pore volume of the product through nitrogen adsorption experiments, and test its conductivity through a four-probe tester. The specific surface area is 1242 m 2 g -1 , the pore volume is 0.67 cm 3 g -1 ; the conductivity is 19.5 S cm -1 .

[0038] Comparative Example 1 A preparation method of an electrode material for fuel cells, comprising the following steps: (1) Add diamine monomers into an organic solvent. Under continuous stirring, add dianhydride monomers into the organic solvent in three portions at intervals of 5 minutes each. After the addition of dianhydride monomers is completed, stir and react for 3.6 h, then add amino-POSS and continue to react for 6 h to form a polyamic acid solution; the mass of amino-POSS is 3.4 wt% of the sum of the masses of dianhydride monomers and diamine monomers; the stirring rate is 200 r / min; The dianhydride monomers are selected from a mixture of pyromellitic dianhydride and 3,3',4,4'-biphenyltetracarboxylic dianhydride with a molar ratio of 2:1; the diamine monomers are selected from 4,4'-diaminodiphenyl ether; the amino-POSS is octaaminophenylcage silsesquioxane; the organic solvent is N,N-dimethylformamide; the molar ratio of dianhydride monomers to diamine monomers is 1:1.03; (2) Drop the polyamic acid solution into deionized water to precipitate polyamic acid powder, and obtain polyimide after gradient heating thermal imidization; The process of gradient heating thermal imidization is as follows: the heating rate is 4 °C / min, heat from room temperature to 75 °C and hold for 0.5 h, then heat to 100 °C and hold for 1.4 h, then heat to 140 °C and hold for 1.2 h, then heat to 193 °C and hold for 1.3 h, then heat to 241 °C and hold for 1.3 h, then heat to 267 °C and hold for 1.2 h; (3) Carry out primary pyrolysis of the polyimide in an argon atmosphere. The product is successively etched with acid, washed, and dried to obtain primary carbonized polyimide; the heating rate of primary pyrolysis is 3 °C / min; the primary pyrolysis temperature is 780 °C and the time is 3.8 h; the acid etching is carried out using a hydrofluoric acid solution with a mass concentration of 8 wt%, and the washing is to wash 3 times with deionized water first, and then wash 2 times with absolute ethanol; (4) Grind the primary carbonized polyimide and then pyrolyze it again in an argon atmosphere. The product is successively etched with acid, washed, and dried to obtain the electrode material for fuel cells; the heating rate of the second pyrolysis is 6 °C / min, the second pyrolysis temperature is 1000 °C and the time is 1.7 h; the acid etching is carried out using a hydrofluoric acid solution with a mass concentration of 8 wt%, and the washing is to wash 3 times with deionized water first, and then wash 2 times with absolute ethanol. Test the specific surface area and pore volume of the product through nitrogen adsorption experiments, and test its conductivity through a four-probe tester. The specific surface area is 423 m 2 g -1 , the pore volume is 0.25 cm 3 g -1 ; the conductivity is 5.6 S cm -1 .

[0039] Comparative Example 2 A preparation method of an electrode material for fuel cells, comprising the following steps: (1) Add diamine monomers into an organic solvent. Under continuous stirring, add dianhydride monomers into the organic solvent in three portions at 5-minute intervals. After the addition of dianhydride monomers is completed, stir and react for 3.6 h, then add amino-POSS and continue to react for 6 h to form a polyamic acid solution; the mass of amino-POSS is 3.4 wt% of the sum of the masses of dianhydride monomers and diamine monomers; the stirring rate is 200 r / min; The dianhydride monomers are selected from a mixture of pyromellitic dianhydride and 3,3',4,4'-biphenyltetracarboxylic dianhydride with a molar ratio of 2:1; the diamine monomers are selected from 4,4'-diaminodiphenyl ether; the amino-POSS is octaaminophenylcage silsesquioxane; the organic solvent is N,N-dimethylformamide; the molar ratio of dianhydride monomers to diamine monomers is 1:1.03; (2) Drop the polyamic acid solution into deionized water to precipitate polyamic acid powder, and obtain polyimide after gradient heating thermal imidization; The process of gradient heating thermal imidization is as follows: the heating rate is 4 °C / min, heat up from room temperature to 75 °C and hold for 0.5 h, then heat up to 100 °C and hold for 1.4 h, then heat up to 140 °C and hold for 1.2 h, then heat up to 193 °C and hold for 1.3 h, then heat up to 241 °C and hold for 1.3 h, then heat up to 267 °C and hold for 1.2 h; (3) Carry out primary pyrolysis of the polyimide in an argon atmosphere. The product is washed and dried in sequence to obtain primary carbonized polyimide; the heating rate of primary pyrolysis is 6 °C / min; the primary pyrolysis temperature is 1000 °C and the time is 1.7 h; the washing is to wash 3 times with deionized water first, and then wash 2 times with absolute ethanol; (4) Grind the primary carbonized polyimide and pyrolyze it again in an argon atmosphere. The product is etched with acid, washed and dried in sequence to obtain the electrode material for fuel cells; the heating rate of the second pyrolysis is 3 °C / min, the second pyrolysis temperature is 780 °C and the time is 3.8 h; the acid etching is carried out with a hydrofluoric acid solution with a mass concentration of 8 wt%, and the washing is to wash 3 times with deionized water first, and then wash 2 times with absolute ethanol. Test the specific surface area and pore volume of the product through nitrogen adsorption experiment, and test its conductivity through a four-probe tester. The specific surface area is 652 m 2 g -1 , the pore volume is 0.41 cm 3 g -1 ; the conductivity is 10.3 S cm -1 .

[0040] As can be seen from the above embodiments, the use of polyimide as a precursor material enables the preparation of self-doped carbon materials. Polyimide is a low-cost engineering plastic with a rigid aromatic backbone, which is easy to carbonize, has a high carbon yield, and is easier to dope with a more uniform doping effect. The amino group in POSS plays a role in nitrogen doping, greatly changing the chemical properties of carbon nanomaterials, thereby improving the performance of carbon nanomaterials; at the same time, the unique hollow closed cage structure of POSS undergoes volume shrinkage during calcination, introducing a porous structure. The SiOC (SiO 2 etc.) structure formed by the transformation of POSS therein will be corroded by hydrofluoric acid, further improving the porous structure of carbon. A two-step pyrolysis method is used to prepare carbon materials. First, polyimide is carbonized at a higher temperature. On the one hand, it promotes the rapid carbonization and shaping of polyimide, especially the POSS structure, preventing the collapse of the structure during subsequent carbonization; on the other hand, the higher temperature promotes the pyrolysis of the POSS structure and the formation of the SiOC (SiO 2 etc.) structure. After acid etching, the temperature is reduced from a higher temperature to a lower carbonization temperature to further carbonize the material and promote the formation of a porous structure. The POSS-modified polyimide carbon material prepared by the two-step method has a large specific surface area and a rich pore structure, which is beneficial to improving the electrical conductivity of the carbon material. Compared with Example 7, in Comparative Example 1, a conventional stepwise heating process is used for carbonization. The stepwise heating process cannot quickly form the structure of POSS and is prone to collapse during the heating process, which is not conducive to the increase of the specific surface area and conductivity of the carbon material. Comparative Example 2 shows that, compared with the common one-step acid etching process in the art, the first acid etching can promote the exposure of internal silicon oxides, which is not only beneficial to the second acid etching but also promotes the low-temperature carbonization process and is beneficial to the increase of the specific surface area.

[0041] In this specification, the various embodiments are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The same or similar parts among the embodiments can be referred to each other. For the solutions disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the description in the method part. The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing an electrode material for a fuel cell, characterized in that: The following steps are involved: (1) adding dianhydride monomer and diamine monomer to an organic solvent, stirring and reacting for a period of time, adding amino-containing POSS, and continuing the reaction to generate a polyamic acid solution; the mass of amino-containing POSS is 0.1-5wt% of the sum of the mass of dianhydride monomer and diamine monomer; (2) dropping the polyamic acid solution into deionized water to precipitate polyamic acid powder, and performing thermal imidization by gradient heating to obtain polyimide; (3) The polyimide is subjected to primary pyrolysis in an inert gas atmosphere, and the product is successively acid-etched, cleaned, and dried to obtain primary carbonized polyimide; the primary pyrolysis temperature is 900-1200°C, and the time is 0.5-2h; (4) After the primary carbonized polyimide is ground, it is pyrolyzed again in an inert gas atmosphere. The product is acid-etched, cleaned, and dried in sequence to obtain an electrode material for a fuel cell. The pyrolysis temperature is 500-800°C and the time is 2-5 hours.

2. The method for preparing a fuel cell electrode material according to claim 1, characterized in that: In step (1), the dianhydride monomer is selected from pyromellitic anhydride, 3,3',4,4'-diphenyl ether tetracarboxylic anhydride, 3,3',4,4'-biphenyl tetracarboxylic anhydride, 2,3,3',4'-biphenyl tetracarboxylic anhydride, diphenyl sulfone-3,4,3',4'-tetracarboxylic anhydride, bis(3,4-dicarboxyphenyl) sulfide dianhydride, 2,2'-bis(3,4-dicarboxylic acid) hexafluoropropane dianhydride, 4,4'-hexafluoroisopropyl phthalic anhydride, 2,3,3',4'-benzophenone tetracarboxylic anhydride, 3,3',4,4'-benzophenone tetracarboxylic anhydride, bis(3,4-dicarboxyphenyl) sulfide dianhydride One or more of 1,3-bis(3,4-dicarboxyphenoxy)phthalic anhydride, 1,4-bis(3,4-dicarboxyphenoxy)phthalic anhydride, 1,4-bis(3,4-dicarboxyphenoxy)biphenyl dianhydride, 2,2-bis(3,4-dicarboxyphenoxy)phenyl)propane dianhydride, 2,3,6,7-naphthalenetetracarboxylic anhydride, and 1,4,5,8-naphthalenetetracarboxylic anhydride.

3. The method for preparing a fuel cell electrode material according to claim 1, characterized in that: The diamine monomer in step (1) is selected from p-phenylenediamine, m-phenylenediamine, 3,3'-dimethylbenzidine, 2,2'-dimethylbenzidine, 2,4-diaminotoluene, 2,6-diaminotoluene, 3,5-diaminobenzoic acid, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 3,3'-dimethyl-4,4'-diaminobiphenyl, 2,2'-dimethyl-4,4'-diaminobiphenyl, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 3,3'-dicarboxy-4,4'-diaminodiphenylmethane, 3,3',5, One or more of 5'-tetramethyl-4,4'-diaminodiphenylmethane, 4,4'-diaminobenzanilide, 3,3'-dimethoxybenzidine, 2,2'-dimethoxybenzidine, 3,3'-diaminodiphenyl ether, 3,3'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminobenzophenone, 4,4'-diaminobenzophenone, 3,3'-diamino-4,4'-dichlorobenzophenone, and 3,3'-diamino-4,4'-dimethoxybenzophenone.

4. The method for preparing a fuel cell electrode material according to claim 1, characterized in that: The amino-containing POSS in step (1) is one or more of octaaminophenyl cage silsesquioxane, octaaminopropyl cage silsesquioxane, aminopropyl isobutyl cage silsesquioxane, and aminopropyl isooctyl cage silsesquioxane.

5. The method for preparing a fuel cell electrode material according to claim 1, characterized in that: In step (1), the molar ratio of the dianhydride monomer to the diamine monomer is 1:(1-1.05).

6. The method for preparing a fuel cell electrode material according to claim 1, characterized in that: In step (3) and step (4), the inert gas is at least one of argon, nitrogen and helium.

7. The method for preparing a fuel cell electrode material according to claim 1, characterized in that: In step (3) and step (4), the acid etching is performed using a hydrofluoric acid solution, and the mass concentration of the hydrofluoric acid solution is 5-15wt%.

8. The method for preparing a fuel cell electrode material according to claim 1, characterized in that: In step (3) and step (4), the cleaning is first performed with deionized water for 2-4 times, and then with anhydrous ethanol for 1-3 times.

9. The method for preparing a fuel cell electrode material according to claim 1, characterized in that: The heating rate of the primary pyrolysis in step (3) is 5-10°C / min; the heating rate of the secondary pyrolysis in step (4) is 1-5°C / min.

10. A fuel cell electrode material, characterized in that: The fuel cell electrode material is prepared by the method for preparing the fuel cell electrode material according to any one of claims 1 to 9.