A kind of carbon paper prepared with reduced cost and its manufacturing method and application

Abstract

The present invention discloses a carbon paper prepared at a reduced cost, a manufacturing method thereof and an application thereof, and belongs to the technical field of porous electrode material preparation. In view of the problems that the temperature during graphitization of carbon paper is high, the processing time is long, and the equipment loss is large, the preparation cost is high, and the uneven distribution of thermal stress caused by excessive temperature easily causes cracking, resulting in a decrease in the mechanical properties of carbon paper, the present invention provides a low-cost carbon paper manufacturing method, which can significantly reduce the graphitization temperature of carbon paper, and reduce the graphitization temperature from 2200°C to about 1500°C; shorten the graphitization processing time, reduce the loss of graphitization equipment, and thus reduce the manufacturing cost of carbon paper; in addition, compared with the prior art, the present invention can achieve the reduction of carbon paper cracking while ensuring the high electrical conductivity and thermal conductivity of carbon paper, effectively improve the tensile strength, bending strength and other mechanical properties of carbon paper, and avoid the problems of low electrical conductivity, low thermal conductivity and poor corrosion resistance of carbon paper caused by conventional low-temperature processes.

Description

Technical Field

[0001] The invention belongs to the technical field of porous electrode material preparation, and in particular relates to low-cost prepared carbon paper and a manufacturing method and application thereof. Background Art

[0002] Carbon paper is the core key material of fuel cell membrane electrode. It is usually composed of carbon fiber and resin carbon, with uniform porous structure, good strength and excellent electrical conductivity. As a supporting material for the gas diffusion layer in fuel cells, it can support the catalytic layer and provide electron channels, heat transfer channels, gas channels and drainage channels for electrode reactions. In order to meet the electrical and heat transfer requirements of carbon paper for high current density fuel cell electrodes, electrical conductivity and thermal conductivity are particularly important.

[0003] In order to achieve high electrical conductivity and high thermal conductivity of carbon paper, the prior art often needs to increase the graphitization temperature to more than 2000°C, even to 2500°C or extend the graphitization treatment time to several hours. Patent CN115262265 discloses a carbon paper and a preparation method thereof, characterized in that the carbon fiber felt is impregnated with resin and then laminated and hot-pressed to obtain a carbon paper preform; and the carbon paper preform is sequentially carbonized and graphitized to obtain carbon paper. The temperature of the carbonization treatment is 700°C to 1600°C, and the temperature of the graphitization treatment is 1800°C to 2800°C. Patent CN114808536 discloses a carbon paper and a preparation method thereof, characterized in that a carbon paper skeleton layer is placed in a boron-containing impregnation solution to form a carbon paper precursor, which is then graphitized, the graphitization temperature is in the range of 1800°C to 2200°C, and the graphitization time is in the range of 10min to 2h. There are some inherent problems in the high-temperature heat treatment process, such as long cycle, high energy consumption, and difficulty in high-temperature heating. The high heat treatment temperature has a great impact on equipment and products. For example, high temperature puts forward more stringent requirements on the insulation and heating elements of graphitization equipment. If the graphitization temperature can be lowered, energy consumption can be reduced, the cycle can be shortened, and damage and frequent maintenance of insulation refractory materials and heating elements can be reduced, thereby extending the life of the graphitization furnace and reducing costs.

[0004] The thermal expansion coefficient and elastic modulus of carbon fiber and resin carbon do not match. For example, the thermal expansion coefficient of Toray T300 carbon fiber is 0.74×10 -6 / K, elastic modulus 216GPa, and the thermal expansion coefficient of thermosetting phenolic resin is 8-20.5×10 -6 / K, elastic modulus 30 ~ 60Mpa, the large difference between the interface of the two during high temperature heat treatment will cause excessive thermal stress in the product and lead to cracking. If the structural defects such as cracking and interface peeling of carbon paper can be reduced, its structural performance can be better exerted. How to achieve a good level of electrical conductivity and thermal conductivity of carbon paper at a lower temperature, taking into account the multiple properties of electrical conductivity, thermal conductivity and mechanical strength, is a major problem in the carbon paper manufacturing process. Summary of the invention

[0005] In view of the problems that the temperature of carbon paper is high and the processing time is long during graphitization, which leads to large equipment loss and high preparation cost, and the uneven distribution of thermal stress caused by excessively high temperature easily causes cracking, resulting in a decrease in the mechanical properties of carbon paper, the present invention provides a low-cost carbon paper manufacturing method, which can significantly reduce the graphitization temperature of carbon paper, shorten the graphitization processing time, reduce the loss of graphitization equipment, and thus reduce the manufacturing cost of carbon paper; in addition, compared with the prior art, the present invention can reduce the cracking phenomenon of carbon paper and improve the mechanical properties of carbon paper such as tensile strength while ensuring the high electrical conductivity and thermal conductivity of carbon paper.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for preparing carbon paper with reduced cost comprises the following steps:

[0008] Step 1, electrolytic treatment of carbon fiber base paper: using carbon fiber base paper as raw material, fixing the carbon fiber base paper on a paper placing device, pulling it through an electrolytic cell containing a boron catalyst solution at a certain speed by a guide roller, connecting a DC power supply electrode to the carbon paper and a graphite electrode respectively, electrolyzing the carbon fiber base paper, and then drying it in a drying furnace to achieve the purpose of loading the boron catalyst on the carbon fiber base paper;

[0009] Step 2, impregnation and curing treatment of base paper: the carbon fiber base paper prepared in step 1 is pulled by a guide roller through a dipping tank, the solvent of the dipping solution in the dipping tank is methanol or water, the main component of the dipping solution is a resin binder, and the additive is a boron catalyst. The carbon fiber base paper is impregnated with the dipping solution, and the excess dipping solution is removed by squeezing with a pressure roller, and then the carbon fiber base paper is cured and formed at high temperature in a heat curing furnace to form a carbon paper prepreg;

[0010] Step 3, graphitization molding of carbon paper prepreg: The carbon paper prepreg prepared in step 2 is pulled by a guide roller through a low-temperature graphitization furnace at a certain speed for low-temperature graphitization treatment to obtain carbon paper. The graphitization furnace body is equipped with an atmosphere protection system and a furnace mouth air sealing structure. Finally, the carbon paper is introduced into a winding device for collection.

[0011] Boron-catalyzed graphitization reduces the cracking of carbon paper caused by thermal stress distribution at extremely high temperatures, which can effectively improve the mechanical properties of carbon paper such as tensile strength and flexural strength, while avoiding the problems of low electrical conductivity, low thermal conductivity and poor corrosion resistance of carbon paper caused by conventional low-temperature processes.

[0012] Furthermore, the boron catalyst includes one or more of boron powder, boric acid, boron oxide, boric acid ester, and boron carbide.

[0013] Furthermore, the carbon fiber base paper in step 1 is a continuous porous mesh thin layer paper-like material formed by dispersing, dehydrating and papermaking 3-6 mm short chopped carbon fibers. The short chopped fibers are too short to form a carbon fiber base paper with poor mechanical properties, while the short chopped fibers are too long to be dispersed and papered into a uniform carbon fiber base paper; its surface density is 10-200 g / m 2 If the surface density is too small, the tear strength of the carbon fiber base paper is poor and it is difficult to be processed by guide roller traction. If the surface density is too large, the thickness of the prepared carbon paper is too large, which will directly affect the gas conduction and drainage efficiency of the membrane electrode, and further affect the volume power density of the fuel cell.

[0014] Furthermore, during the electrolytic treatment in step 1, the DC power supply loading method includes: continuous treatment, pulse treatment, and positive and negative electrode alternating treatment. The use of different treatment methods helps to make the mass transfer of the boric acid electrolyte and the catalyst loading more uniform; the current density is 0.1-2.5A / cm 2 If the current density is too small, the catalyst loading is too low and the catalytic effect is difficult to exert. If the current density is too large, it may cause excessive etching of the carbon fiber surface, resulting in performance degradation. The drying furnace temperature is 120℃.

[0015] In the step 1, the carbon fiber base paper is connected to the positive electrode of the DC power supply, the graphite electrode in the electrolytic cell is connected to the negative electrode of the DC power supply, and the graphite electrodes in the electrolytic cell are respectively located above and below the carbon fiber paper;

[0016] The electrolyte in the electrolytic cell is 0.5-5wt% boron catalyst (boric acid), 1.5wt% sodium sulfate and 2wt% citric acid. If the amount of boron catalyst added in the electrolyte is too low, the catalyst loading is too small, and the catalytic effect is difficult to exert. If the amount of boron catalyst added is too large, the electrolytic reaction is too intense, which may cause excessive etching of the carbon fiber surface and lead to performance degradation.

[0017] Furthermore, the conveying speed of the carbon fiber base paper during the preparation process is 0.5m / min to 5m / min. If the conveying speed is too low, the production efficiency of the carbon paper will be affected, while if the conveying speed is too high, the residence time of the carbon fiber base paper will be short and it will be difficult to fully load the boron catalyst, thus affecting the degree of graphitization.

[0018] Furthermore, the resin binder includes: one or more of alcohol-soluble phenolic resin, water-soluble phenolic resin, water-soluble polyvinyl pyrrolidone (PVP), or other high-residual carbon resins.

[0019] Furthermore, in step 2, the mass ratio of the solvent, the resin binder and the boron catalyst is 100:(5-20):(0.02-0.4). Boron, as an electron-deficient atom, can form a substitutional solid solution with carbon. The trace addition of boron atoms will not affect the destruction of the graphite lattice structure; the substitution of boron for carbon is structurally stable at low-temperature graphitization temperature and will not have a negative impact. After boron-catalyzed graphitization, the crystal structure is more dense and ordered. The addition of an appropriate amount of boron has a positive effect on the graphitization process of carbon paper, can effectively repair structural defects, promote the growth of graphite crystals, and improve the degree of graphitization.

[0020] Furthermore, the temperature of high temperature curing molding in step 2 is 80-200°C.

[0021] Furthermore, in step 3, the temperature of the low-temperature graphitization treatment is 1300° C. to 1600° C., and the time of the low-temperature graphitization treatment is 1 min to 10 min. If the treatment temperature is too low and the time is too short, the carbon paper cannot be converted into a graphitized crystalline structure. If the treatment temperature is too high and the time is too long, it will undoubtedly increase energy consumption, reduce production efficiency, and cause unnecessary waste.

[0022] Furthermore, in step 3, the atmosphere protection system includes a protective atmosphere and a boron-containing catalyst atmosphere; the protective atmosphere includes: nitrogen, argon; the boron-containing catalyst atmosphere is: diborane, butane; and the boron-containing catalyst atmosphere accounts for 0.02% to 0.5% of the volume of the protective atmosphere. If the proportion of the boron catalyst atmosphere is too low, the degree of graphitization of the carbon paper will be affected, and if the proportion is too high, it will not only cause waste of resources, but also may cause pollution of the atmosphere.

[0023] A carbon paper prepared by the above preparation method.

[0024] Application of the carbon paper prepared by the above preparation method in a fuel cell.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] The present invention introduces a boron active catalyst to achieve solid solution replacement, effectively reducing the activation energy of the conversion of amorphous carbon to crystalline carbon, thereby reducing the graphitization temperature, shortening the graphitization treatment time, achieving low-temperature graphitization of carbon paper, avoiding various negative problems caused by high-temperature graphitization, reducing graphitization equipment losses (such as reducing graphitization furnace heating component losses, insulation layer losses, water cooling system losses), and significantly reducing carbon paper manufacturing costs. While ensuring high porosity, high electrical conductivity, and high thermal conductivity of carbon paper, the mechanical properties of carbon paper are improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram of the preparation process of the method of the present invention;

[0028] Figure 2 Schematic diagram of part of the electrolytic cell.

[0029] Among them: 1 paper placing device, 2 carbon fiber base paper, 3 guide roller, 4 graphite electrode, 5 electrolyte, 6 DC power supply, 7 electrolytic cell, 8 drying furnace, 9 dipping solution, 10 dipping tank, 11 pressing roller, 12 thermal curing furnace, 13 carbon paper prepreg, 14 low-temperature graphitization furnace, 15 atmosphere protection system, 16 carbon paper, 17 paper collecting device. DETAILED DESCRIPTION

[0030] Carbon paper supports the catalytic layer in fuel cells and provides electron channels, heat transfer channels, gas channels and drainage channels for electrode reactions. It is required to have high electrical and thermal conductivity, rich pore structure and strong mechanical properties. In order to improve the power generation performance of fuel cells, the traditional technology to improve the electrical and thermal conductivity of carbon paper is to increase the graphitization temperature and extend the graphitization time. However, the process will cause problems such as long time, high energy consumption, and great damage to graphitization equipment. At the same time, due to the uneven distribution of thermal stress caused by excessively high temperature, it is easy to cause cracking, resulting in a decrease in the mechanical properties of carbon paper.

[0031] Boron is the only element that can form a substitutional solid solution with carbon. After adding a trace amount of boron, boron atoms preferentially enter the disordered or layered carbon structure through diffusion during the heat treatment process, replacing carbon atoms to form hexagonal layers, without destroying the regular graphite structure; and boron atoms can attract the electrons of carbon atoms, resulting in the breaking of covalent bonds between carbon atoms and structural rearrangement. In this way, the defects between the carbon fiber layered graphite structure can be eliminated first, and the transformation to the graphite structure can be achieved. In addition, the transformation of amorphous resin carbon (binder) to a three-dimensional ordered graphite structure can be accelerated, and an effective covalent bond connection structure can be formed between the carbon fiber and the resin carbon, which can effectively improve the tensile strength, bending strength and other mechanical properties of carbon paper, while avoiding the problems of low electrical conductivity, low thermal conductivity and poor corrosion resistance of carbon paper caused by conventional low-temperature processes. The application of the method of the present invention solves the problem that carbon paper is difficult to use in high current density fuel cell electrodes.

[0032] Carbon fiber base paper is a continuous porous mesh thin layer paper-like material formed by dispersing, dehydrating and papermaking 3-6mm short-cut carbon fibers. Its surface density is 10-200g / m 2 .

[0033] Example 1

[0034] A method for preparing carbon paper with reduced cost, such as Figure 1 As shown, the following steps are included:

[0035] Step 1, electrolytic treatment of carbon fiber base paper: using carbon fiber base paper as raw material, fixing the carbon fiber base paper on a paper placing device, and pulling it through an electrolytic cell containing 1wt% boric acid solution at a speed of 1m / min by a guide roller, the electrolytic cell being as Figure 2 As shown, the DC power supply electrode is connected to the carbon paper and the graphite electrode respectively (the carbon fiber base paper is connected to the positive electrode of the DC power supply, the graphite electrode in the electrolytic cell is connected to the negative electrode of the DC power supply, and the graphite electrodes in the electrolytic cell are located above and below the carbon fiber paper respectively). A continuous treatment method is adopted and the current density is controlled to be 1A / cm 2 , electrolyzing the carbon fiber base paper, and then drying it in a drying furnace to load the boron catalyst on the carbon fiber base paper;

[0036] Step 2, impregnation and curing treatment of carbon fiber base paper: the carbon fiber base paper prepared in step 1 is pulled by a guide roller through a dipping tank, wherein the dipping solution solvent is methanol, the resin binder is phenolic resin, and the boron catalyst is boron oxide, and the mass ratio of the three is (100:10:0.1). The carbon fiber base paper is impregnated with the dipping solution, and the excess dipping solution is removed by squeezing with a pressure roller, and then the carbon fiber base paper is cured and formed at a high temperature of 160°C in a thermal curing furnace to form a carbon paper prepreg;

[0037] Step 3, graphitization molding of carbon paper prepreg: the carbon paper prepreg prepared in step 2 is pulled by a guide roller through a low-temperature graphitization furnace at a speed of 1 m / min for low-temperature graphitization treatment to obtain carbon paper. The graphitization temperature is 1500°C and the treatment time is 5 min. The graphitization furnace body is equipped with an atmosphere protection system and a furnace mouth air sealing structure. The protective atmosphere is nitrogen and diborane (accounting for 0.1% of the volume of the protective atmosphere). Finally, the carbon paper is introduced into a winding device for collection.

[0038] Embodiment 2 to Embodiment 5

[0039] The preparation process is basically the same as that in Example 1, except for the parameters such as the operating speed, current density and treatment method, electrolyte concentration, binder type and mass ratio, curing temperature, protective atmosphere and volume ratio, graphitization temperature and treatment time in the preparation process. The specific conditions are shown in Table 1.

[0040] Comparative Example 1

[0041] The preparation process is basically the same as that in Example 1, except that no boron catalyst is added.

[0042] Comparative Example 2

[0043] The preparation process is basically the same as that in Example 1, except that no boron catalyst is added, but the graphitization treatment temperature is 2200°C.

[0044] Table 1

[0045]

[0046] In order to further illustrate the technical effects of the embodiments of the present invention, the carbon papers prepared by using the embodiments 1 to 5 of the present invention and the comparative examples 1 and 2 were tested. The test results are shown in Table 2.

[0047] Table 2

[0048]

[0049] The energy consumption refers to the electricity consumption for manufacturing unit length of carbon paper.

[0050] The degree of graphitization is calculated using the following formula:

[0051] g=(0.3440-d 002 ) / (0.3440-0.3354)

[0052] Where: g is the degree of graphitization (%); 0.3440nm is the interlayer spacing of completely disordered carbon materials; 0.3354nm is the interlayer spacing of ideal graphite crystals; d 002 is the interlayer spacing of the (002) plane (nm), characterized by X-ray diffraction, according to the Bragg formula: d 002 =λ / (2sinθ), where λ is the wavelength of the incident light (the value is 0.154178nm); θ is the diffraction angle of the (002) plane.

[0053] As can be seen from the above table, the method of the present invention can catalyze graphitization, the degree of catalysis can be controlled, the graphitization temperature can be reduced, the energy consumption can be reduced, the equipment loss can be reduced, and low cost can be achieved; while ensuring the high porosity, high electrical conductivity and high thermal conductivity of the carbon paper, the mechanical properties of the carbon paper are improved.

[0054] The contents not described in detail in the specification of the present invention belong to the prior art known to the professional and technical personnel in the field. Although the illustrative specific embodiments of the present invention are described above to facilitate the understanding of the present invention by the technical personnel in the field, it should be clear that the present invention is not limited to the scope of the specific embodiments. For the ordinary technical personnel in the field, as long as various changes are within the spirit and scope of the present invention defined and determined by the attached claims, these changes are obvious, and all inventions and creations using the concept of the present invention are protected.

Claims

1. A method for preparing carbon paper with reduced cost, characterized in that: The following steps are involved: Step 1, electrolytic treatment of carbon fiber base paper: using carbon fiber base paper as raw material, fixing the carbon fiber base paper on a paper placing device, pulling it through an electrolytic cell containing a boron catalyst solution at a certain speed by a guide roller, connecting a DC power supply electrode to the carbon paper and a graphite electrode respectively, electrolyzing the carbon fiber base paper, and then drying it in a drying furnace to achieve the purpose of loading the boron catalyst on the carbon fiber base paper; Step 2, impregnation and curing treatment of base paper: the carbon fiber base paper prepared in step 1 is pulled by a guide roller through a dipping tank, the solvent of the dipping solution in the dipping tank is methanol or water, the main component of the dipping solution is a resin binder, and the additive is a boron catalyst. The carbon fiber base paper is impregnated with the dipping solution, and the excess dipping solution is removed by squeezing with a pressure roller, and then the carbon fiber base paper is cured and formed at high temperature in a heat curing furnace to form a carbon paper prepreg; Step 3, graphitization molding of carbon paper prepreg: the carbon paper prepreg prepared in step 2 is pulled by a guide roller through a low-temperature graphitization furnace at a certain speed for low-temperature graphitization treatment to obtain carbon paper, the graphitization furnace body is equipped with an atmosphere protection system and a furnace mouth air sealing structure, and finally the carbon paper is introduced into a winding device for collection; The boron catalyst includes: one or more of boron powder, boric acid, boron oxide, boric acid ester, and boron carbide; During the electrolytic treatment in step 1, the DC power supply loading method includes: continuous treatment, pulse treatment or positive and negative electrode alternating treatment, and the current density is 0.1~2.5 A / cm 2 ; The electrolyte in the electrolytic cell in step 1 is 0.5-5wt% of a boron catalyst, 1.5wt% of sodium sulfate and 2wt% of citric acid; The temperature of the low-temperature graphitization treatment in step 3 is 1300° C. to 1600° C., and the time of the low-temperature graphitization treatment is 1 min to 10 min; In step 3, the atmosphere protection system includes a protective atmosphere and a boron-containing catalyst atmosphere; the protective atmosphere includes: nitrogen or argon; the boron-containing catalyst atmosphere is: diborane or tetraborane; and the boron-containing catalyst atmosphere accounts for 0.02% to 0.5% of the volume of the protective atmosphere.

2. The method for preparing carbon paper with reduced cost according to claim 1, characterized in that: The carbon fiber base paper in step 1 is a continuous porous mesh thin layer paper-like material formed by dispersing, dehydrating and papermaking 3-6 mm short-cut carbon fibers, and its surface density is 10-200 g / m 2 .

3. The method for preparing carbon paper with reduced cost according to claim 1, characterized in that: The conveying speed of the carbon fiber base paper during the preparation process is 0.5 m / min~5 m / min.

4. The method for preparing carbon paper with reduced cost according to claim 1, characterized in that: The temperature of the drying oven in step 1 is 120°C.

5. The method for preparing carbon paper with reduced cost according to claim 1, characterized in that: In step 1, the carbon fiber base paper is connected to the positive electrode of the DC power supply, and the graphite electrode in the electrolytic cell is connected to the negative electrode of the DC power supply. The graphite electrodes in the electrolytic cell are respectively located above and below the carbon fiber paper.

6. The method for preparing carbon paper with reduced cost according to claim 1, characterized in that: The resin binder includes: one or more of alcohol-soluble phenolic resin, water-soluble phenolic resin or water-soluble polyvinyl pyrrolidone.

7. The method for preparing carbon paper with reduced cost according to claim 1, characterized in that: In step 2, the mass ratio of the solvent, the resin binder and the boron catalyst is 100:(5-20):(0.02-0.4).

8. The method for preparing carbon paper with reduced cost according to claim 1, characterized in that: The temperature of high temperature curing molding in step 2 is 80-200°C.

9. A carbon paper prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the carbon paper prepared by the preparation method according to any one of claims 1 to 8 in a fuel cell.

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