Preparation Method of Biomass Carbon Cloth and Membrane Electrode

Abstract

The present invention provides a method for preparing a biomass carbon cloth, comprising the following steps: A) Pretreating a biomass cotton cloth to obtain a precursor biomass cotton cloth; B) Soaking the precursor biomass cotton cloth in a transition metal salt solution and drying; C) Carbonizing and annealing the biomass cotton cloth obtained in step B); D) Passing a carbon source gas into the biomass cotton cloth obtained in step C) in an inert atmosphere and heating; E) Acid-treating the carbon cloth obtained in step D) to obtain a biomass carbon cloth. The biomass carbon cloth material provided by the present invention can be used as a good gas diffusion layer for fuel cells. It has extremely high electrical conductivity and porosity. As a gas diffusion layer for fuel cells, the cost and preparation process are simple, and its performance can meet the standards of commercially available carbon cloths. In view of the high cost problem of current fuel cells, it can be used as a substitute for commercially available carbon cloths to save battery costs.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cells, and particularly to a preparation method of biomass carbon cloth and a membrane electrode. Background Art

[0002] Since the Industrial Revolution, the fossil fuels required for industry have greatly promoted the development of human society. However, for the thorny problems of the gradual depletion of fossil fuels and the deteriorating ecological environment due to environmental pollution, people must find a new energy technology to replace fossil fuels as the source of industrial energy. Compared with traditional fossil fuels, fuel cells can use hydrogen and oxygen as raw materials, and the products of the battery are pollution-free. Proton exchange membrane fuel cells (PEMFCs) belong to low-temperature fuel cells, which not only have a low operating temperature, high energy conversion efficiency, but also a relatively long service life. Therefore, proton exchange membrane fuel cells are one of the most promising devices to replace traditional energy equipment.

[0003] The heart of a proton exchange membrane fuel cell is the membrane electrode, which is composed of a gas diffusion layer, a catalyst layer, and a proton exchange membrane, and its cost accounts for about 75% of the cost of the fuel cell stack. The gas diffusion layer is usually made of a highly conductive and highly porous material. An ideal diffusion layer should meet three conditions: good drainage, good air permeability, and good electrical conductivity. Carbon fiber paper and carbon fiber cloth are widely used diffusion layer materials in fuel cells on the market today, with a thickness of about 100-400 μm. However, carbon fiber paper is very brittle and not flexible, and is easily damaged during the preparation of the electrode. Therefore, carbon fiber cloth is mostly used as the substrate of the gas diffusion layer of proton exchange membrane fuel cells; it does not have the mechanical brittleness of carbon fiber paper and has good compressibility and flexibility. According to the different fiber structures and weaving processes, carbon fiber cloth also has elasticity in the thickness direction, can obtain certain compression performance, and helps to improve the resistance between the electrolyte or catalyst layer by applying a certain pressure.

[0004] Currently, the main component of carbon fiber is polyacrylonitrile. The carbon fiber paper used is prepared by the papermaking process of sheet forming and hot pressing of carbon fiber rovings; the carbon fiber cloth is made by weaving carbon fibers. Polyacrylonitrile is a polymer with interconnected carbon chains and is a material with hardness, keratin, relative insolubility, and high melting point. First, the formed polyacrylonitrile fibers are heated in an air atmosphere at 180 - 300 °C. This step is mainly to fix the carbon skeleton, and the pre-oxidation stage is one of the most complex and time-consuming stages in the preparation of carbon fiber. Secondly, the carbon fiber is carbonized at high temperature (1000 - 1600 °C) in a nitrogen atmosphere. This process requires controlling the heating temperature and heating rate to obtain higher modulus and strength. Finally, in order to further improve the performance, the carbonized fiber must be graphitized in an argon atmosphere. Graphitization is the transformation of the carbon structure into a graphite structure through heat treatment and thermal decomposition under high temperature treatment. This process often reaches a temperature as high as 3000 °C. At this stage, up to 99% of the PAN polymer is converted into a graphite carbon structure, thus preparing carbon fiber with high conductivity and strength. If the optimization process of the preparation is not properly controlled, the fiber is also prone to embrittlement. The carbon fiber obtained through these steps can be used as raw materials to prepare carbon fiber paper and carbon fiber cloth through specific processes.

[0005] Although the current commercial carbon fiber cloth and carbon fiber paper have excellent performance and can well adapt to the gas diffusion layer of proton exchange membrane fuel cells, however, their preparation process requires 2500 - 3000 °C. A large amount of energy consumption and extremely high production conditions make it difficult to further reduce the industrial cost. Therefore, the market price of carbon fiber cloth and carbon fiber paper is about 4000 - 6000 yuan per square meter, significantly increasing the cost of fuel cells. In addition, the core technology for producing graphitized carbon furnaces (2500 - 3000 °C) in China is still relatively limited. The production of high-quality carbon fiber is restricted by foreign countries, and the supply time and supply volume are often unstable, greatly restricting the production of carbon fiber paper and carbon fiber cloth in China, thus significantly slowing down the development speed of fuel cells in China. Summary of the Invention

[0006] The technical problem solved by the present invention is to provide a method for preparing a biomass carbon cloth, and the biomass carbon cloth prepared by the present application has high conductivity and air permeability.

[0007] In view of this, the present application provides a method for preparing a biomass carbon cloth, including the following steps:

[0008] A) Pretreat the biomass cotton cloth to obtain a precursor biomass cotton cloth;

[0009] B) Immerse the precursor biomass cotton cloth in a transition metal salt solution and dry it;

[0010] C) Carbonize and anneal the biomass cotton cloth obtained in step B).

[0011] D) Pass a carbon source gas into the biomass cotton cloth obtained in step C) in an inert atmosphere and heat it.

[0012] E) Acid-treat the carbon cloth obtained in step D) to obtain a biomass carbon cloth.

[0013] Preferably, before the carbonization, it further includes: heating the biomass carbon cloth obtained in step B) in air at a heating rate of 2 - 5 °C / min to 180 - 250 °C and holding for 1 - 2 h.

[0014] Preferably, the pretreatment is specifically:

[0015] Wash the biomass cotton cloth with deionized water, then soak the washed biomass cotton cloth in an alkaline solution, and then wash the biomass cotton cloth with deionized water and dry it.

[0016] Soak the obtained biomass cotton cloth in an acid solution, then wash and dry it.

[0017] Preferably, in step B), the concentration of the transition metal salt solution is 1 - 25 wt%, and the transition metal salt is selected from one or more of nitrates, ferric chloride, porphyrin iron, and ferric sulfate; the temperature of the soaking is 50 - 80 °C, and the time is 2 - 12 h; the temperature of the drying is 30 - 100 °C, and the time is 6 - 12 h.

[0018] Preferably, the process of the carbonization is specifically:

[0019] Heat the biomass cotton cloth obtained in step B) at a heating rate of 1 - 4 °C / min to 300 - 500 °C, hold for 20 - 60 min, then introduce a reducing atmosphere, and heat it at a heating rate of 5 - 10 °C / min to 800 - 1200 °C, hold for 30 - 60 min.

[0020] Preferably, the temperature of the annealing is 1000 - 2000 °C, and the time is 1 - 5 h.

[0021] Preferably, step C) is specifically:

[0022] Put the biomass carbon cloth obtained in step C) into a heating furnace, introduce argon, hydrogen, and methane, heat it at a heating rate of 5 - 15 °C / min to 500 - 1000 °C, hold for 20 - 50 min, and then heat it at a heating rate of 5 - 15 °C / min to 1000 - 1200 °C, hold for 10 - 60 min.

[0023] Preferably, the volume ratio of argon, hydrogen, and methane is 9:1:(0.2 - 1).

[0024] Preferably, in step E), the acid solution for the acid treatment is sulfuric acid or hydrochloric acid, the concentration of the acid solution is 0.2 - 0.5 M, and the temperature is 30 - 80 °C.

[0025] The present application also provides a membrane electrode, which consists of a gas diffusion layer, a catalytic layer, and a proton exchange membrane. It is characterized in that the gas diffusion layer is the biomass carbon cloth prepared by the preparation method described above.

[0026] The present application provides a preparation method of biomass carbon cloth. First, the biomass carbon cloth is pretreated to achieve the cleaning and preliminary pore formation of the biomass carbon cloth. Then, the biomass carbon cloth is soaked in a transition metal salt to form a graphitized structure subsequently. Then, carbonization and annealing are carried out to convert the carbon cloth into a graphite carbon material and generate carbon nanotubes on the surface. Then, it is heated in a carbon source gas to grow graphite carbon on the surface of the cotton cloth. Finally, acid washing is carried out to remove the metal ions therein, and the biomass carbon cloth is obtained. According to the principle of transition element-catalyzed graphitization, the preparation method of the biomass carbon cloth provided by the present application catalyzes the conversion of the biomass carbon material into a graphite carbon material, significantly increasing the lateral and longitudinal conductivity of the carbon material, improving the conductivity. During the preparation process of the carbon cloth, a lot of carbon nanotubes grow on the surface. These carbon nanotubes complicate the internal pore structure of the carbon cloth, and at the same time, these carbon nanotubes greatly increase the conductivity between the carbon cloths, strengthening the connection between the biomass carbon fibers and enhancing the conductivity of the carbon cloth. Description of the Drawings

[0027] Figure 1 It is the X-ray diffraction characterization diagram of the carbon cloth prepared in Example 1 of the present invention;

[0028] Figure 2 It is the Raman spectrum characterization diagram of the carbon cloth prepared in Example 1 of the present invention;

[0029] Figure 3 It is the scanning electron microscope characterization diagram of the carbon cloth prepared in Example 1 of the present invention;

[0030] Figure 4 It is the transmission electron microscope characterization diagram of the carbon cloth prepared in Example 1 of the present invention;

[0031] Figure 5 It is the X-ray photoelectron spectroscopy characterization diagram of the carbon cloth prepared in Example 1 of the present invention;

[0032] Figure 6 It is the pore distribution characterization diagram of the carbon cloth prepared in Example 1 of the present invention tested by mercury intrusion porosimetry;

[0033] Figure 7 It is the bar chart of the frequency of the resistivity tested in Table 1 of the present invention;

[0034] Figure 8It is a comparison chart of the polarization curve performance of a single cell composed of the carbon cloth prepared in Example 1 of the present invention and a certain commercial carbon cloth, and a comparison chart of the power performance of the single cell;

[0035] Figure 9 It is the carbon cloth sample of the 20cm*20cm sample prepared in Example 1 of the present invention;

[0036] Figure 10 It is the thickness measurement of the carbon cloth prepared in Example 1 of the present invention;

[0037] Figure 11 It is a photo of the carbon cloth prepared in Example 1 of the present invention after being bent 180°;

[0038] Figure 12 It is the vertical resistivity curve graph of the carbon cloth of Example 1 of the present invention and the commercially available product. Detailed implementation mode

[0039] To further understand the present invention, the preferred implementation modes of the present invention will be described below in conjunction with embodiments. However, it should be understood that these descriptions are only for further explaining the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0040] In view of the problems of complex preparation process and high cost of biomass carbon cloth in the prior art, the present application provides a preparation method of biomass carbon cloth, which can prepare biomass carbon cloth with excellent conductivity and air permeability, and the preparation process is simple and the cost is low. Specifically, the embodiment of the present invention discloses a preparation method of biomass carbon cloth, including the following steps:

[0041] A) Pretreat the biomass cotton cloth to obtain a precursor biomass cotton cloth;

[0042] B) Immerse the precursor biomass cotton cloth in a transition metal salt solution and dry it;

[0043] C) Carbonize and anneal the biomass cotton cloth obtained in step B);

[0044] D) Pass a carbon source gas into the biomass cotton cloth obtained in step C) in an inert atmosphere and heat it;

[0045] E) Acid-treat the carbon cloth obtained in step D) to obtain biomass carbon cloth.

[0046] In the process of preparing biomass carbon cloth, the present application first pretreats the biomass cotton cloth to achieve pore formation and cleaning of the biomass cotton cloth, and obtains a precursor biomass carbon cloth. The specific process of the pretreatment is as follows:

[0047] S1) Wash the biomass cotton cloth with deionized water, then soak the washed biomass cotton cloth in an alkaline solution, and then wash the biomass cotton cloth with deionized water and dry it to obtain an alkali-treated biomass cotton cloth;

[0048] S2) Soak the obtained alkali-treated biomass cotton cloth in an acid solution, then wash and dry it to obtain a precursor biomass cotton cloth.

[0049] In this application, the biomass cotton cloth is first alkali-treated to create pores in the cotton fibers of the cotton cloth and improve the porosity of the cotton cloth. In this process, the alkaline solution is an alkaline solution well-known to those skilled in the art, and specifically, it can be selected from potassium hydroxide, and its concentration is 0.1 - 1.5M. Specifically, the concentration of the alkaline solution is 0.5 - 1.0M; the soaking time is 1 - 6h; the drying temperature is 40 - 80°C, and the time is 6 - 8h.

[0050] Then, the alkali-treated biomass cotton cloth is pickled in this application to remove surface contaminants and neutralize the alkaline solution. In this process, the acid solution can be selected from hydrochloric acid or sulfuric acid, and the concentration of the acid solution is 0.2 - 0.8M. Specifically, the concentration of the acid solution is 0.3 - 0.5M. The soaking temperature is 20 - 60°C, and the time is 1 - 3h; the drying temperature is 40 - 80°C, and the time is 6 - 8h.

[0051] Then, the precursor biomass cotton cloth is soaked in a transition metal salt solution and dried in this application; after the above treatment, the transition metal salt is loaded on the precursor biomass carbon cloth to catalyze the graphitization of the carbon cloth. The transition metal salt is specifically selected from one or more of nitrates, iron chloride, porphyrin iron, and iron sulfate; the concentration of the transition metal salt solution is 1 - 25wt%, specifically, the concentration of the transition metal salt solution is 5 - 20wt%. The mass ratio of the precursor biomass cotton cloth to the transition metal salt is (2 - 5):1, specifically 3:1. The soaking temperature is 50 - 80°C, and the time is 2 - 12h; specifically, the soaking temperature is 60 - 70°C, and the time is 8 - 10h. The drying temperature is 30 - 100°C, and the time is 6 - 12h; specifically, the drying temperature is 50 - 80°C, and the time is 8 - 10h.

[0052] This application preferably pre-oxidizes the cotton cloth obtained above to enhance the strength of the final carbon cloth. Specifically, the cotton cloth is placed in the air and heated, and the temperature is raised to 180 - 250°C at a heating rate of 2 - 5°C / min and maintained for 1 - 2h; more specifically, the above heating rate is 3 - 4°C / min, and the temperature is 200 - 230°C.

[0053] According to the present invention, then the pre-oxidized cotton cloth is carbonized to generate carbon nanotubes. The specific steps of the carbonization are as follows:

[0054] Heat the carbon cloth obtained in step B) at a heating rate of 1 - 4 °C / min to 300 - 500 °C, hold for 20 - 60 min, then introduce a reducing atmosphere, and heat at a heating rate of 5 - 10 °C / min to 800 - 1200 °C, hold for 30 - 60 min.

[0055] In the above process, the reducing atmosphere is specifically ammonia or hydrogen.

[0056] This application then anneals the obtained carbon cloth to further catalyze the graphitization of the carbon material and enhance the conductivity. The annealing temperature is 1000 - 2000 °C, and the time is 1 - 5 h; specifically, the annealing temperature is 1300 - 1800 °C, and the time is 2 - 4 h.

[0057] According to the present invention, put the above - obtained carbon cloth into a heating furnace, introduce argon, hydrogen and additive, heat at a heating rate of 5 - 15 °C / min to 500 - 1000 °C, hold for 20 - 50 min, and then heat at a heating rate of 5 - 15 °C / min to 1000 - 1200 °C, hold for 10 - 60 min. The above is specifically a chemical vapor deposition process to deposit graphene on the surface of the carbon cloth to further increase the conductivity of the carbon cloth. More specifically, put the above - obtained carbon cloth into a plasma heating furnace, introduce an atmosphere with an argon:hydrogen ratio of 9:1, heat to 700 °C at a heating rate of 10 °C / min, hold for 20 - 40 min, during which methane gas is introduced, and keep the gas ratio of argon:hydrogen:methane at 9:1:(0.2 - 1), then heat to 1000 - 1050 °C at 10 °C / min, hold for 10 - 60 min.

[0058] According to the present invention, finally, the above - obtained carbon cloth is subjected to acid treatment to obtain a biomass carbon cloth. The above acid treatment is to remove iron elements because the presence of iron elements will have a negative impact on the membrane electrode of the fuel cell. The acid solution for the acid treatment is sulfuric acid or hydrochloric acid, the concentration of the acid solution is 0.2 - 0.5 M, the temperature is 30 - 80 °C, and the time is 1 - 5 h. Specifically, the concentration of the acid solution is 0.3 - 0.4 M, the temperature is 40 - 60 °C, and the time is 2 - 4 h.

[0059] This application also provides a membrane electrode, which consists of a gas diffusion layer, a catalytic layer and a proton exchange membrane. It is characterized in that the gas diffusion layer is the biomass carbon cloth prepared by the preparation method described in the above solution.

[0060] The present application provides a method for preparing biomass carbon cloth. According to the principle of transition element-catalyzed graphitization, it catalyzes the conversion of biomass carbon materials into graphite carbon materials, significantly increasing the lateral and longitudinal conductivity of the carbon materials. The conductive performance is excellent, and it does not require the long-time high-temperature treatment at 2000-3000 °C in traditional graphitization production, saving industrial production costs and simplifying the production steps. The prepared carbon cloth has a uniform structure and a high internal porosity. In addition to the rich pore structure inside the raw material biomass cloth, a large number of micropores are added to the internal structure through the gas-phase corrosion method, increasing the internal air permeability and the internal porosity of the carbon cloth. And during the preparation of the carbon cloth, a lot of carbon nanotubes grow on the surface. These carbon nanotubes complicate the internal pore structure of the carbon cloth. At the same time, these carbon nanotubes greatly increase the conductivity between the carbon cloths, strengthen the connection between the biomass carbon fibers, and improve the conductivity of the carbon cloth. The prepared carbon cloth is flexible and will not break when bent by 90-180°. And it has a rich internal pore structure, good air permeability, and a high porosity. The thickness and internal structure of the carbon cloth as the gas diffusion layer of the present invention depend on the thickness and structure of the original cotton cellulose cloth. The thickness and internal pore structure of the prepared carbon cloth can both be adjusted by weaving different cotton fiber carbon cloths as precursors. The raw material source of the gas diffusion layer prepared by the method of the present invention is wide, the preparation cost is low, and it has extremely high economic benefits. The present invention, like traditional carbon cloth, is suitable for large-scale production. The production steps are simple, and it also uses a two- to three-step carbonization process. And the temperature used in the carbonization process is low, and each step of the treatment process is simple.

[0061] To further understand the present invention, the following examples are used to illustrate in detail the method for preparing biomass carbon cloth provided by the present invention. The protection scope of the present invention is not limited by the following examples.

[0062] It should be noted that the experimental methods used in the following examples are all conventional methods unless otherwise specified. The materials, reagents, equipment, etc. used in the following examples can all be obtained from commercial channels unless otherwise specified.

[0063] Example 1

[0064] S1. Wash the biomass cotton cloth with deionized water, then soak the biomass cotton cloth in 0.1 M potassium hydroxide solution for 5 h, then rinse the biomass cotton cloth with deionized water, and then dry it at 60 °C for 7 h to obtain the alkali-treated biomass cloth.

[0065] S2. Immerse the carbon cloth obtained in the above S1 step in 0.5 M sulfuric acid solution at 60 °C for 3 h, then rinse the carbon cloth with deionized water to remove the acid on the surface, and then dry it at 80 °C for 8 h to obtain the precursor biomass cotton cloth.

[0066] S3. Ultrasonically treat the above 10 g of treated biomass cotton fabric substrate in an aqueous solution of iron nitrate with a mass fraction of 20 wt% for 30 min, then soak it at 70 °C for 10 h, then take out the cotton fabric substrate and then dry it at 80 °C for 12 h;

[0067] S4. Place the above-treated biomass cotton fabric in the air and heat it to 250 °C at a heating rate of 2 °C / min and hold for 2 h;

[0068] S5. Place the carbon cloth prepared in S4 above in a plasma heating furnace, heat it to 400 °C at a heating rate of 2 °C / min, hold for 60 min, then introduce an H2 atmosphere, and at the same time heat it to 1000 °C at a heating rate of 5 °C / min, hold for 60 min, and then cool down;

[0069] S6. Anneal the carbon cloth prepared in S5 at 1500 °C for 5 h;

[0070] S7. Place the material prepared in S6 into a plasma heating furnace, introduce an atmosphere with an argon:hydrogen ratio of 9:1, heat it to 700 °C at a heating rate of 10 °C / min, hold for 40 min, and introduce methane gas during this period, maintaining the gas ratio of argon:hydrogen:methane at 9:1:1, and then heat it to 1050 °C at a heating rate of 10 °C / min and hold for 60 min;

[0071] S8. Immerse the sample described in S7 in a 0.5 M acid solution at 60 °C for 1 - 3 h, then wash the carbon cloth with deionized water and dry it to obtain the target carbon cloth.

[0072] Example 2

[0073] S1. Wash the biomass cotton fabric with deionized water, then soak the biomass cotton fabric in a 0.1 M potassium hydroxide solution for 5 h, then rinse the biomass cotton fabric with deionized water, and then dry it at 60 °C for 7 h to obtain an alkali-treated biomass fabric;

[0074] S2. Immerse the carbon cloth obtained in step S1 above in a 0.5 M sulfuric acid solution at 60 °C for 3 h to increase the active groups on the surface of the carbon cloth, then rinse the carbon cloth with deionized water to remove the acid on the surface, and then dry it at 80 °C for 8 h to obtain a precursor biomass cotton fabric;

[0075] S3. Ultrasonically treat the above 10 g of treated biomass cotton fabric substrate in an aqueous solution of iron nitrate with a mass fraction of 15 wt% for 30 min, then soak it at 70 °C for 10 h, then take out the cotton fabric substrate and then dry it at 80 °C for 12 h;

[0076] S4. Place the above-treated biomass cotton fabric in the air and heat it to 250 °C at a heating rate of 2 °C / min and hold for 2 h;

[0077] S5. Place the carbon prepared in S4 above in a plasma heating furnace, heat it to 400 °C at a heating rate of 2 °C / min, hold for 60 min, then introduce an H₂ atmosphere, and at the same time heat it to 1000 °C at a heating rate of 10 °C / min, hold for 60 min, and then cool down;

[0078] S6. Anneal the carbon cloth prepared in S5 at 1300 °C for 5 h;

[0079] S7. Put the material prepared in S6 into a plasma heating furnace, introduce an atmosphere with an argon:hydrogen ratio of 9:1, heat it to 700 °C at a heating rate of 10 °C / min, hold for 40 min, and during this period introduce methane gas to keep the ratio of argon:hydrogen:methane in the gas at 9:1:1, and then heat it to 1050 °C at a heating rate of 10 °C / min and hold for 60 min;

[0080] S8. Immerse the sample described in S7 in a 0.5 M acid solution at 60 °C for 1 - 3 h, then wash the carbon cloth with deionized water and dry it to obtain the target carbon cloth.

[0081] Example 3

[0082] S1. Wash the biomass cotton cloth with deionized water, then soak the biomass cotton cloth in a 0.1 M potassium hydroxide solution for 5 h, then rinse the biomass cotton cloth with deionized water, and then dry it at 60 °C for 7 h to obtain the alkali-treated biomass cloth;

[0083] S2. Immerse the carbon cloth obtained in the above S1 step in a 0.5 M sulfuric acid solution at 60 °C for 3 h, then rinse the carbon cloth with deionized water to remove the acid on the surface, and then dry it at 80 °C for 8 h to obtain the precursor biomass cotton cloth;

[0084] S3. Ultrasonically treat 10 g of the treated biomass cotton cloth substrate in an aqueous solution of ferric nitrate with a mass fraction of 25 wt% for 30 min, then soak it at 70 °C for 10 h, then take out the cotton cloth substrate and then dry it at 80 °C for 12 h;

[0085] S4. Place the treated biomass cotton cloth in the air and heat it to 250 °C at a heating rate of 2 °C / min and hold for 2 h for pre-oxidation to increase the strength of the carbon cloth;

[0086] S5. Place the carbon cloth prepared in S4 above in a plasma heating furnace, heat it to 400 °C at a heating rate of 2 °C / min, hold for 60 min, then introduce an H₂ atmosphere, and at the same time heat it to 1000 °C at a heating rate of 10 °C / min, hold for 60 min, and then cool down;

[0087] S6. Anneal the carbon cloth prepared in S5 at 1300 °C for 5 h;

[0088] S7. Place the material prepared in S6 into a plasma heating furnace, introduce an atmosphere with an argon:hydrogen ratio of 9:1, heat it to 700 °C at a heating rate of 10 °C / min, hold for 40 min, introduce methane gas during this period, maintain the gas ratio of argon:hydrogen:methane at 9:1:1, and then heat it to 1050 °C at a heating rate of 10 °C / min and hold for 60 min;

[0089] S8. Immerse the sample described in S7 in a 0.5 M acid solution at 60 °C for 1 - 3 h, then wash the carbon cloth with deionized water and dry it to obtain the target carbon cloth.

[0090] Example 4

[0091] S1. Wash the biomass cotton cloth with deionized water, then immerse the biomass cotton cloth in a 0.1 M potassium hydroxide solution for 3 h, then rinse the biomass cotton cloth with deionized water, and then dry it at 60 °C for 7 h to obtain the alkali-treated biomass cloth;

[0092] S2. Immerse the carbon cloth obtained in the above S1 step in a 0.5 M sulfuric acid solution at 60 °C for 3 h, then rinse the carbon cloth with deionized water to remove the acid on the surface, and then dry it at 80 °C for 8 h to obtain the precursor biomass cotton cloth;

[0093] S3. Ultrasonic the above 10 g of treated biomass cotton cloth substrate in an aqueous solution of 5 wt% iron nitrate for 30 min, then immerse it at 70 °C for 10 h, then take out the cotton cloth substrate and then dry it at 80 °C for 12 h;

[0094] S4. Place the treated biomass cotton cloth in the air and heat it to 250 °C at a heating rate of 2 °C / min and hold for 2 h for pre-oxidation to increase the strength of the carbon cloth;

[0095] S5. Place the carbon cloth prepared in the above S4 in a plasma heating furnace, heat it to 400 °C at a heating rate of 2 °C / min and hold for 60 min, then introduce a H2 atmosphere, and at the same time heat it to 1000 °C at a heating rate of 10 °C / min and hold for 60 min, and then cool down;

[0096] S6. Anneal the carbon cloth prepared in S5 at 1300 °C for 5 h;

[0097] S7. Place the material prepared in S6 into a plasma heating furnace, introduce an atmosphere with an argon:hydrogen ratio of 9:1, heat it to 700 °C at a heating rate of 10 °C / min, hold for 40 min, introduce methane gas during this period, maintain the gas ratio of argon:hydrogen:methane at 9:1:1, and then heat it to 1050 °C at a heating rate of 10 °C / min and hold for 60 min;

[0098] S8. Immerse the sample described in S7 in a 0.5 M acid solution at 60 °C for 1 - 3 h, then wash the carbon cloth with deionized water and dry it to obtain the target carbon cloth.

[0099] Figure 1 X-ray diffraction characterization diagram of the carbon cloth prepared in Example 1 of the present invention; Figure 2 Raman spectrum characterization diagram of the carbon cloth prepared in Example 1 of the present invention; Figure 3 Scanning electron microscope characterization diagram of the carbon cloth prepared in Example 1 of the present invention; Figure 4 Transmission electron microscope characterization diagram of the carbon cloth prepared in Example 1 of the present invention; Figure 5 X-ray photoelectron spectroscopy characterization diagram of the carbon cloth prepared in Example 1 of the present invention; Figure 6 Pore size distribution characterization diagram of the carbon cloth prepared in Example 1 of the present invention by mercury intrusion method; As can be seen from the above figure, the porosity of the carbon cloth prepared by the present invention is 77%, and the internal pores are extremely rich, indicating that it is suitable for the gas diffusion layer of fuel cells.

[0100] Table 1 is the surface resistivity test data table of the carbon cloth prepared in Example 1 of the present invention tested by a four-probe resistance meter, and the frequency of resistivity is as Figure 7 shown; Table 2 is the sheet resistance test data table of the carbon cloth prepared in Example 1 of the present invention tested by a four-probe resistance meter; Table 3 is the porosity data table of each example of the present invention determined by mercury intrusion method.

[0101] Table 1 Surface resistivity test data table of the carbon cloth prepared in Example 1 tested by a four-probe resistance meter

[0102]

[0103]

[0104] Table 2 Sheet resistance test data table of the carbon cloth prepared in Example 1 tested by a four-probe resistance meter

[0105]

[0106] Table 3 Porosity data table of each example determined by mercury intrusion method

[0107] Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Porosity 76.94％ 74.96％ 79.65％ 76.26％ 77.35％

[0108] From the above data, it can be seen that the surface resistivity of the carbon cloth is concentrated in the range of 0.030 - 0.046 Ω·cm, the sheet resistance is 0.8 - 1 Ω / sq, and the electrical conductivity is excellent.

[0109] The prepared carbon cloth of Example 1 and the carbon cloth of WOS 1009 from Taiwan Carbon Energy Company were used as the gas diffusion layer substrate of the fuel cell and put into the fuel cell for polarization curve comparison tests. The test conditions were as follows: the battery operating temperature was 70 °C, the cathode oxygen inlet pressure was 0 bar, the gas flow rate was 50 sccm, the relative humidity was 50%, and the catalyst loading was 0.5 mgPt / cm 2 ; the anode hydrogen inlet pressure was 0 bar, the gas flow rate was 80 sccm, the relative humidity was 50%, and the catalyst loading was 0.3 mgPt / cm 2 , and the battery working area was 4 cm 2 . As can be seen from Figure 8 , the polarization curve performance of the prepared carbon cloth and a commercially available carbon cloth (the carbon cloth of WOS1009 from Taiwan Carbon Energy Company) as the gas diffusion layer is almost equivalent. However, the cost of the carbon cloth prepared in the present invention is less than 100 yuan per square meter, and compared with the price of the commercial carbon cloth which is more than 5000 yuan per square meter, it has high economic benefits.

[0110] Figure 9 This is the carbon cloth sample of the 20 cm * 20 cm sample prepared in Example 1 of the present invention; Figure 10 This is the thickness measurement of the carbon cloth prepared in Example 1 of the present invention; as can be seen from the figure, the thickness of the carbon cloth < 0.5 mm; Figure 11 This is the photo of the carbon cloth prepared in Example 1 of the present invention after being bent 180°. From this, it can be seen that the carbon cloth has flexibility and will not break when bent 90 - 180°.

[0111] Figure 12 This is the resistivity curve graph of the carbon cloth prepared in Example 1 and the commercially available carbon cloth (the carbon cloth of WOS 1009 from Taiwan Carbon Energy Company) measured by the vertical resistivity test method in the national standard "GB / T 20042.7 - 2014 Proton Exchange Membrane Fuel Cells - Part 7: Test Methods for the Characteristics of Carbon Paper".

[0112] In summary, the biomass carbon cloth material provided in the present invention can be used as a good gas diffusion layer of the fuel cell. It has extremely high conductivity and porosity. As the gas diffusion layer of the fuel cell, the cost and the preparation process are simple, and its performance can meet the standards of commercially available carbon cloth. Aiming at the high cost problem of the current fuel cell, it can be used as a substitute for commercially available carbon cloth to save the battery cost.

[0113] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the purpose and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

[0114] The description of the above embodiments is only used to help understand the method and its core idea of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0115] 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, and 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 rather to the broadest scope consistent with the principles and novel features disclosed herein.

Claims

1. A preparation method of biomass carbon cloth, comprising the following steps: A) Cleaning the biomass cotton cloth with deionized water, then soaking the cleaned biomass cotton cloth in an alkaline solution, and then cleaning the biomass cotton cloth with deionized water and drying it; Soaking the obtained biomass cotton cloth in an acid solution, then cleaning and drying it to obtain a precursor biomass cotton cloth; B) Soaking the precursor biomass cotton cloth in a transition metal salt solution and drying it; The transition metal salt is selected from iron nitrate, and the transition metal salt is loaded on the precursor biomass cotton cloth to catalyze the graphitization of the cotton cloth; C) Heating the biomass cotton cloth obtained in step B) at a heating rate of 1-4 °C / min to 300-500 °C, holding for 20-60 min, then introducing a reducing atmosphere, and heating at a heating rate of 5-10 °C / min to 800-1200 °C, holding for 30-60 min for carbonization and annealing; the carbonization is to generate carbon nanotubes, and the annealing is to further catalyze the graphitization of the carbon material, the annealing temperature is 1000-2000 °C, and the time is 1-5 h; D) Introducing argon, hydrogen and methane into the biomass cotton cloth obtained in step C), heating at a heating rate of 5-15 °C / min to 500-1000 °C, holding for 20-50 min, and then heating at a heating rate of 5-15 °C / min to 1000-1200 °C, holding for 10-60 min; to deposit graphene on the surface of the carbon cloth to further increase the conductivity of the carbon cloth; E) Performing acid treatment on the carbon cloth obtained in step D) to obtain biomass carbon cloth.

2. The preparation method according to claim 1, characterized in that, Before the carbonization, it further includes: heating the biomass carbon cloth obtained in step B) in air at a heating rate of 2-5 °C / min to 180-250 °C and holding for 1-2 h.

3. The preparation method according to claim 1 or 2, characterized in that In step B), the concentration of the transition metal salt solution is 1-25 wt%, the soaking temperature is 50-80 °C, and the time is 2-12 h; the drying temperature is 30-100 °C, and the time is 6-12 h.

4. The preparation method according to claim 1, wherein The volume ratio of the argon, hydrogen and methane is 9:1:(0.2-1).

5. The preparation method according to claim 1, characterized in that In step E), the acid solution for the acid treatment is sulfuric acid or hydrochloric acid, the concentration of the acid solution is 0.2-0.5 M, and the temperature is 30-80 °C.

6. A membrane electrode, comprising a gas diffusion layer, a catalytic layer and a proton exchange membrane, characterized in that, The gas diffusion layer is the biomass carbon cloth prepared by the preparation method according to any one of claims 1-5.

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