Ultrathin composite carbon paper for portable hydrogen fuel cell and preparation process of ultrathin composite carbon paper

Abstract

The invention discloses ultrathin composite carbon paper for a portable hydrogen fuel cell and a preparation process of the ultrathin composite carbon paper, and belongs to the technical field of fuel cell materials, the carbon paper comprises a composite fiber substrate layer and a microporous layer, the substrate layer is formed by compounding viscose-based and polyacrylonitrile-based carbon fibers, and is doped with carbon nanotubes and a phenolic resin carbonization phase; the microporous layer contains conductive carbon black, graphene and polytetrafluoroethylene; and the preparation process comprises the following steps: manufacturing raw paper by using ultralow-concentration slurry, pre-compounding and reinforcing the carbon nano tube and resin, performing slow-release carbonization and constructing the microporous layer. Through material design and fine process regulation and control, the problem that the strength, conductivity and gas diffusion performance of the ultrathin carbon paper are difficult to synergistically improve is solved, and the ultrathin carbon paper is high in yield, excellent in comprehensive performance and suitable for a portable power supply.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of fuel cell materials, carbon fiber composites and paper-based functional materials, in particular to a kind of ultra-thin composite carbon paper for portable hydrogen fuel cell and its preparation process, especially suitable for portable hydrogen fuel cell power supply sensitive to volume and weight. BACKGROUND

[0002] The gas diffusion layer is a key component of the hydrogen fuel cell membrane electrode assembly, which bears the functions of conducting electrons, transporting reaction gas and discharging product water. As the core substrate of the gas diffusion layer, the performance of carbon paper is crucial. The rapid development of portable hydrogen fuel cells has put unprecedented comprehensive performance requirements on carbon paper: while maintaining high porosity to ensure gas transmission, ultra-thin (usually ≤100 μm) is required to reduce the volume and weight of the stack; it must have extremely high surface resistance to reduce ohmic loss and improve power density; and it must maintain sufficient mechanical strength and flexibility in an ultra-thin state to adapt to the stress during assembly and operation.

[0003] Currently, commercial carbon paper is mainly based on polyacrylonitrile (PAN) carbon fibers, which have good mechanical strength and electrical conductivity, but the fibers are stiff, making it difficult to control the uniformity of the fiber network when making ultra-thin base paper (such as face density <60 g / m 2 ) and prone to defects, and the paper is not flexible enough. Although viscose-based carbon fibers are easy to make thin and flexible, their graphitization degree is low, which often makes the electrical conductivity of the final carbon paper a shortcoming. A single fiber system cannot achieve a balance between strength, conductivity and flexibility in the ultra-thin dimension. In addition, there are two major bottlenecks in the traditional preparation process: first, during the resin carbonization stage, rapid heating (usually 5~10℃ / min) causes the resin to decompose rapidly, generating a large amount of gas and concentrated thermal stress, which makes the ultra-thin blank body prone to cracking and curling, resulting in low yield; second, the microporous layer (MPL) is usually attached using spraying and other processes, which has limited bonding strength, large interface resistance, and difficulty in accurately controlling the thickness uniformity.

[0004] Therefore, it is of great practical significance and industrial value to develop a new type of carbon paper and its preparation process that can comprehensively balance ultra-thin, high conductivity, strength and durability for portable applications. SUMMARY

[0005] The purpose of the present application is to provide an ultra-thin composite carbon paper for portable hydrogen fuel cells and its preparation process, which has low thickness, high surface resistance, excellent gas diffusion capacity and mechanical strength. The process can achieve uniform shaping, low damage carbonization and integrated functional layer construction of ultra-thin materials, and is suitable for large-scale production.

[0006] The present application is realized by the following technical solutions: An ultra-thin composite carbon paper for portable hydrogen fuel cell, comprising a reinforced composite fiber base layer and a microporous layer constructed on at least one surface of the base layer: The composite fiber base layer is made of viscose-based carbon fibers and polyacrylonitrile-based carbon fibers by hybridization, phenolic resin reinforcement and carbon nanotube reinforcement; The microporous layer is made of MPL composite slurry containing conductive carbon black, graphene nanosheet and polytetrafluoroethylene.

[0007] A preparation process of the ultra-thin composite carbon paper for portable hydrogen fuel cell according to claim 1, comprising: S1, composite fiber base paper preparation: disperse viscose-based carbon fibers and polyacrylonitrile-based carbon fibers in an aqueous solution containing a dispersing agent according to a proportion to form a mixed slurry, then shape the mixed slurry by papermaking, press and dry to obtain a composite fiber base paper; S2, CNT-resin synergistic reinforcement treatment: disperse carbon nanotubes in a high-residual carbon phenolic resin solution to form a uniform composite reinforcing agent; then uniformly apply the composite reinforcing agent to the composite fiber base paper, and then solidify to obtain a resin-reinforced base paper; S3, temperature-controlled carbonization and graphitization: place the resin-reinforced base paper in an inert atmosphere for carbonization and catalytic graphitization to obtain a composite fiber base layer; S4, microporous layer construction: prepare MPL composite slurry containing conductive carbon black, graphene nanosheet and polytetrafluoroethylene emulsion, uniformly coat the MPL composite slurry on the surface of the carbonized paper by slit coating, and then sequentially dry and sinter to form an ultra-thin composite carbon paper with a microporous layer.

[0008] Preferably, in S1, the mass ratio of viscose-based carbon fibers to polyacrylonitrile-based carbon fibers is (6:4)~(8:2), and the concentration of the mixed slurry is 0.01%~0.05%; the areal density of the composite fiber base layer is 40~60 g / m², and the thickness is 50~100 μm.

[0009] Preferably, in S2, the doping amount of carbon nanotubes is 3%~8% of the dry fiber mass in the composite fiber base layer, the carbon nanotubes account for 10%~20% of the solid amount of phenolic resin, and the solid loading amount of phenolic resin is 20%~35% of the dry weight of the composite fiber base paper.

[0010] Preferably, in S2, the temperature during solidification is 80~120℃, and the time is 25~45min.

[0011] Preferably, in S3, the carbonization process comprises: firstly, increasing the temperature to 300℃ at a rate of 1~2℃ / min, then slowly increasing the temperature from 300℃ to 600℃ at a rate of 0.3~0.8℃ / min and keeping the temperature for 20~40min, and finally increasing the temperature to 1000~1200℃ at a rate of 2~5℃ / min.

[0012] Preferably, in S3, the catalytic graphitization is to heat treat the carbonized paper at 1800~2200℃ for 30~60min under the condition of a catalyst; the catalyst is a compound of boron, iron or nickel.

[0013] Preferably, in S4, in the MPL composite slurry, the mass ratio of the conductive carbon black, graphene nanosheet and polytetrafluoroethylene solid is (2~4):1:(4~6), and the solid content of the MPL composite slurry is 8~12%; when slot coating, the slot gap is 80~150μm, and the thickness of the microporous layer is 15~30μm.

[0014] Preferably, in S4, when drying, the temperature is 80~100℃, and the time is 15~30min.

[0015] Preferably, in S4, when sintering, the temperature is 340~360℃, and the time is 25~30min.

[0016] Compared with the prior art, the application has the following beneficial effects: The portable ultra-thin composite carbon paper for hydrogen fuel cells of the application is composed of viscose-based (flexible and easy to graphitize) and PAN-based (high strength and good conductive path) carbon fibers, which is not a simple mixture. In the ultra-thin network, the flexible viscose-based fibers play a buffering and connecting role, which can reduce brittleness; and the PAN-based fibers act as a rigid skeleton, which can provide main support points, and the synergistic effect of the two can achieve rigid and flexible in mechanics, and can construct more diverse conductive path prototypes in electricity.

[0017] The preparation process of the portable hydrogen fuel cell ultra-thin composite carbon paper first uses viscose-based carbon fibers and polyacrylonitrile-based carbon fibers to form a composite fiber base paper, then uses CNT and phenolic resin to further strengthen it, then uses a heat treatment system including carbonization and catalytic graphitization to obtain a composite fiber base layer, then uses a slot coating method to coat MPL composite slurry which can form a microporous layer on the composite fiber base layer, and then dries and sinters to obtain an ultra-thin composite carbon paper with a microporous layer. Disperse CNT in the resin precursor, so that it is welded between the micron fibers and the phenolic resin pyrolytic carbon in situ during the subsequent carbonization process. CNT, as a one-dimensional nanometer conductor, can effectively bridge adjacent carbon fibers, greatly reducing the contact resistance, and also acts as a nanometer reinforcing agent, forming an interpenetrating network with the phenolic carbon, thereby strengthening the brittle glass carbon bonding phase and improving the overall strength and toughness of the matrix.

[0018] Further, the slurry concentration is strictly controlled at 0.01%~0.05%, which is much lower than conventional papermaking (>0.1%), so as to reduce the mutual interference and flocculation probability of fibers during the settling process, follow the probability statistics law, and enable the fibers to be randomly and uniformly distributed to the maximum extent, thereby avoiding uneven thickness, density spots and weak conductive areas caused by fiber aggregation from the source, and forming a physical basis for obtaining high-performance ultra-thin substrates.

[0019] Further, the present application has a unique 300~600℃ interval 0.3~0.8℃ / min slow-release heating and holding process, which is a precise intervention for the pyrolysis kinetics of phenolic resin. This temperature range is the main reaction zone where the resin undergoes a large number of chemical bond breakage, polycondensation aromatization and release of small molecule gas. Traditional rapid heating leads to violent reaction and explosive escape of gas, resulting in high pressure in the limited pores of the ultra-thin blank and causing defects. By extremely slowing down the heating rate, the concentrated thermochemical stress is thinned in time and space, making the decomposition reaction approach quasi-steady state, the gas diffuses and releases smoothly, and the resin is orderly converted into continuous and dense glass carbon, thereby perfectly preserving the structural integrity of the ultra-thin blank.

[0020] Further, the advantages of using slot coating instead of traditional spraying or blade coating are: (1) the coating thickness is accurately determined by the mechanical slot gap, enabling the high-precision and high-repeatability preparation of 15~30 μm ultra-thin MPL; (2) the shear force makes the sheet-shaped graphene nanosheet have a certain orientation, which is beneficial to in-plane conduction; (3) the slurry is transferred in a continuous and stable fluid form, the obtained MPL layer has uniform pore structure and clear and firm bonding interface with the substrate, effectively reducing the interface contact resistance.

[0021] Finally, the ultra-thin composite carbon paper of the present application is a composite structure of micron fiber skeleton (composite base layer) - nano enhanced conductive network (CNT / phenolic carbon) - microporous layer (carbon black / graphene / PTFE). The structure realizes the functional gradient distribution of gas diffusion, electron conduction, mechanical support and waterproof drainage from macro to micro, and is tightly combined between layers through chemical bonds and physical interlocking, which together gives the carbon paper excellent comprehensive performance under extreme thinness. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The schematic diagram of the overall process of the preparation process of the present application is shown in the figure. Figure 2 The microstructure diagram of the carbon paper base obtained in Comparative Example 1 is shown in the figure. DETAILED DESCRIPTION

[0023] The present application will be further described below in conjunction with specific examples, but the protection scope of the present application is not limited thereto.

[0024] The present application provides an ultra-thin composite carbon paper for portable hydrogen fuel cells, comprising a reinforced composite fiber base layer and a microporous layer constructed on at least one surface of the base layer: The composite fiber base layer is made of viscose-based carbon fibers and polyacrylonitrile-based carbon fibers by hybridization, phenolic resin reinforcement and carbon nanotube reinforcement. Specifically, the composite fiber base layer is doped with carbon nanotubes (CNT) and impregnated with a continuous glassy carbon bonding phase formed by carbonization of high residual carbon phenolic resin, which is used to form a multi-level conductive reinforcement network.

[0025] The microporous layer is made of MPL composite slurry containing conductive carbon black, graphene nanosheets and polytetrafluoroethylene.

[0026] The present application also provides a preparation process of an ultra-thin composite carbon paper, referring to Figure 1 , comprising the following steps: S1. Composite fiber base paper preparation: mix viscose-based and PAN-based carbon fiber chopped filaments in proportion, disperse them in an aqueous solution containing a dispersing agent to form an ultra-low concentration slurry with a concentration of 0.01%-0.05%. Dynamic papermaking is carried out using a square paper page former, and after pressing and drying, a composite fiber base paper with uniform fiber distribution is obtained.

[0027] The mass ratio of viscose-based carbon fibers to polyacrylonitrile-based carbon fibers is (6:4)~(8:2), and the concentration of the mixed slurry is 0.01%-0.05%. The areal density of the composite fiber base layer is 40-60 g / m², and the thickness is 50-100 μm.

[0028] S2. CNT-resin synergistic reinforcement treatment: Carbon nanotubes (CNT) are pre-dispersed in a high-residual carbon phenolic resin solution to form a uniform composite reinforcement. The composite reinforcement is uniformly applied to the surface of the base paper and penetrates into the interior by precise spraying. Then, it is cured in a vacuum oven at 80-120°C for 25-45 min to form a resin-reinforced base paper. The solid loading of phenolic resin is 20-35% of the dry weight of the base paper, and the CNT accounts for 10-20% of the solid content of the phenolic resin (i.e., the total loading of CNT is about 2-7% of the dry weight of the base paper); the doping amount of carbon nanotubes is 3-8% of the dry fiber mass in the composite fiber base layer.

[0029] S3. Temperature-controlled carbonization and graphitization: The cured base paper is placed in an inert atmosphere (such as nitrogen or argon) for programmed temperature heat treatment, with the following specific stages: First, the temperature is raised from room temperature to 300°C at a slow rate of 1-2°C / min to slowly release residual water and low molecular weight substances.

[0030] Then, the temperature is raised from 300°C to 600°C at a very slow release rate of 0.3-0.8°C / min, and held at 600°C for 20-40 min. The slow heating and holding at 600°C ensures the gradual release of pyrolysis gas, which helps to alleviate the stress concentration in the ultra-thin material caused by the instantaneous generation of gas and uneven thermal shrinkage, which is the key to avoiding cracking, warping, and obtaining a complete carbon skeleton.

[0031] Subsequently, the temperature is raised to 1000-1200°C at a rate of 2-5°C / min to complete carbonization, obtaining carbonized paper.

[0032] Finally, to further improve the degree of graphitization and electrical conductivity, the carbonized paper is subjected to catalytic graphitization treatment at 1800-2200°C in the presence of a catalyst (such as compounds of boron, iron, and nickel).

[0033] S4. Micro-porous layer construction: MPL composite slurry with a solid content of 8-12% is prepared, with a composition of conductive carbon black, graphene nanosheet, and PTFE emulsion (solid mass ratio (2-4):1:(4-6)), and the solid content of the MPL composite slurry is 8-12%. Then, the MPL composite slurry is uniformly coated on the surface of the base layer treated in step S3 using a slot coating technique with a wet film thickness of 80-150 μm. Then, it is dried at 80-100°C for 15-30 min and sintered at 340-360°C for 25-30 min, respectively, to fiberize the PTFE and form a hydrophobic network, finally obtaining an ultra-thin composite carbon paper.

[0034] Example 1 S1, viscose base and PAN-based carbon fibers were mixed in a mass ratio of 7:3, and a slurry with an ultra-low concentration of 0.025% was prepared in an aqueous solution containing 0.1 wt% dispersant. The composite fiber base paper was obtained by square sheet former, pressing, drying, and the basis weight was about 45 g / m².

[0035] S2, CNT was ultrasonically dispersed in a phenolic resin ethanol solution (solid content 25%) accounting for 15% of the solid mass of the phenolic resin. The composite solution was precisely sprayed on the base paper, and the total load of the phenolic resin solid was controlled to be 28% of the dry weight of the base paper, and then cured at 100°C for 2 hours to obtain a resin reinforced base paper.

[0036] S3, under nitrogen atmosphere, the temperature was raised to 300°C at 1.5°C / min, then raised to 600°C at a slow release rate of 0.5°C / min and kept for 30 min, finally raised to 1100°C at 3°C / min and kept for 1 hour to obtain the composite fiber base layer.

[0037] The carbonized paper was immersed in a 5 wt% boric acid ethanol solution (catalyst) and dried, and then placed in an argon atmosphere and heated to 2000°C at 5°C / min for catalytic graphitization treatment for 30 min.

[0038] S4, prepare a slurry with conductive carbon black: graphene nanosheet: PTFE solid = 3:1:5 (solid content 10%). Coating was carried out by slot coating (gap 120 μm), dried at 80°C, sintered at 350°C for 30 min to obtain finished carbon paper A.

[0039] Comparative Example 1 S1, viscose base and PAN-based carbon fibers were mixed in a mass ratio of 7:3, and a slurry with an ultra-low concentration of 0.025% was prepared in an aqueous solution containing 0.1 wt% dispersant. The composite fiber base paper was obtained by square sheet former, pressing, drying, and the basis weight was about 45 g / m².

[0040] S2, CNT was ultrasonically dispersed in a phenolic resin ethanol solution (solid content 25%) accounting for 15% of the solid mass of the phenolic resin. The composite solution was precisely sprayed on the base paper, and the total load of the phenolic resin solid was controlled to be 28% of the dry weight of the base paper, and then cured at 100°C for 2 hours to obtain a resin reinforced base paper.

[0041] S3, under nitrogen atmosphere, the temperature was raised to 300°C at 1.5°C / min, then raised to 600°C at a slow release rate of 0.5°C / min and kept for 30 min, finally raised to 1100°C at 3°C / min and kept for 1 hour to obtain the composite fiber base layer.

[0042] S4, slurry was prepared with conductive carbon black: graphene nanoplatelets: PTFE solids = 3:1:5 (10% solid content). Coating was performed by slot coating (gap 120 pm), dried at 80 °C, and sintered at 350 °C for 30 min to obtain the finished carbon paper B. From Figure 2 It can be seen that the carbon paper has built a uniform three-dimensional reinforcing network, which is the basis for good air permeability and electrical conductivity.

[0043] Comparative Example 2 S1, S2, S3 and Comparative Example 1 are exactly the same, using the same batch of carbonized paper.

[0044] S4. MPL construction: no graphene nanoplatelets were added to the MPL slurry, and the formulation was adjusted to conductive carbon black: PTFE solids = 4:5 (keeping the PTFE content equivalent to Example 1), with a solid content of 10%. The coating and sintering processes were the same as in Comparative Example 1 to obtain the finished carbon paper C.

[0045] Comparative Example 3 S1, same as Comparative Example 1.

[0046] S2, CNT-resin synergistic reinforcement: a "two-step method" was used. First, the same amount of CNT as in Example 1 was dispersed in an ethanol / water solution (without resin) and applied to the base paper by immersion, and then dried. Then, the same amount of pure phenolic resin solution (without CNT) as in Comparative Example 1 was immersed and cured at 100 °C for 2 hours.

[0047] S3, S4 steps: exactly the same as Comparative Example 1, to obtain the finished carbon paper D.

[0048] Comparative Example 4: S1: only PAN-based carbon fibers were used, with a total mass equal to the sum of the two fibers in Example 1, and the slurry concentration was still 0.025%, and the base paper was made by papermaking.

[0049] S2, S3, S4: exactly the same as Comparative Example 1, to obtain the comparative carbon paper E.

[0050] Comparative Example 5: S1, S2 steps: exactly the same as Comparative Example 1.

[0051] S3: a traditional rapid carbonization program was used. Under a nitrogen atmosphere, the temperature was directly raised from room temperature to 1100 °C at a rate of 8 °C / min, and held for 1 hour.

[0052] S4 step: exactly the same as Comparative Example 1, to obtain the comparative carbon paper F.

[0053] Table 1 Performance of Examples and Comparative Examples

[0054] Table 1 is the key technical parameters of the composite carbon paper prepared in the examples and comparative examples, and the analysis can be obtained: (1) The sample of Comparative Example 2 appears serious curling and cracking, which leads to unreliable mechanical strength. This directly proves that for the ultra-thin composite material of the present application, if the slow-release carbonization is not used to release the thermal stress gently in the key temperature range of resin decomposition (300-600℃), it will lead to disastrous structural damage, so that the advantages of other material design cannot be reflected.

[0055] (2) Comparative Example 1 is superior to Comparative Example 1 in flexibility, product uniformity and comprehensive performance, which shows that the composite fiber system is more suitable for ultra-thin structure with extremely high uniformity requirement through the design of rigidity and flexibility.

[0056] (3) The interfacial bonding force of Comparative Example 1 is significantly better than that of Comparative Example 2, which shows that the introduction of graphene nanosheet is not only adding a conductive agent, but also forming a point-surface interconnected mixed conductive network with carbon black, and at the same time enhancing the physical and chemical combination with the substrate, producing a synergistic optimization effect.

[0057] (4) The conductivity and mechanical strength of Comparative Example 1 are better than those of Comparative Example 3, which confirms that the pre-combination of carbon nanotubes and phenolic resin in solution state is the optimal process path to realize the uniform dispersion in the subsequent carbonized matrix, which is effectively welded and fixed, so as to build a stable three-dimensional reinforcing network.

[0058] (5) On the basis of maintaining the integrity of the material, the surface resistance of Example 1 is more than 30% higher than that of Comparative Example 1, which shows that on the premise of solving the forming of ultra-thin substrate and low-damage carbonization, the catalytic graphitization process can effectively improve the graphitization degree of carbon material.

[0059] The above-described examples are only the preferred embodiments of the present application, and do not limit the technical solutions of the present application in any way. Those skilled in the art should understand that without departing from the spirit and principles of the present application, the technical solutions can be modified and replaced in several simple ways, and these modifications and replacements also belong to the protection scope covered by the claims.

Claims

1. An ultra-thin composite carbon paper for portable hydrogen fuel cells, characterized by, It includes a reinforced composite fiber substrate layer and a microporous layer constructed on at least one surface of the substrate layer: The composite fiber substrate is made of viscose-based carbon fiber and polyacrylonitrile-based carbon fiber through mixing, phenolic resin reinforcement and carbon nanotube reinforcement. The microporous layer is formed by coating an MPL composite slurry containing conductive carbon black, graphene nanosheets and polytetrafluoroethylene.

2. A preparation process for ultrathin composite carbon paper for portable hydrogen fuel cells as described in claim 1, characterized in that, include: S1. Preparation of composite fiber base paper: Viscose-based carbon fiber and polyacrylonitrile-based carbon fiber are dispersed in an aqueous solution containing a dispersant in a certain proportion to form a mixed slurry. The mixed slurry is then formed by papermaking, pressing and drying to obtain composite fiber base paper. S2, CNT-resin synergistic strengthening treatment: Carbon nanotubes are dispersed in a phenolic resin solution with high carbon residue to form a uniform composite reinforcing agent; the composite reinforcing agent is then uniformly applied to the composite fiber base paper, and subsequently cured to obtain resin-reinforced base paper; S3. Temperature-controlled carbonization and graphitization: The resin-reinforced base paper is carbonized and catalytically graphitized under an inert atmosphere to obtain a composite fiber base layer. S4. Microporous layer construction: MPL composite slurry containing conductive carbon black, graphene nanosheets and polytetrafluoroethylene emulsion is prepared. The MPL composite slurry is uniformly coated on the surface of carbonized paper by slit coating. Then, it is dried and sintered to form an ultra-thin composite carbon paper with a microporous layer.

3. The ultra-thin composite carbon paper of claim 2, wherein, In S1, the mass ratio of viscose-based carbon fiber to polyacrylonitrile-based carbon fiber is (6:4) to (8:2), the concentration of the mixed slurry is 0.01% to 0.05%, the areal density of the composite fiber substrate is 40 to 60 g / m², and the thickness is 50 to 100 μm.

4. The ultra-thin composite carbon paper of claim 2, wherein, In S2, the amount of carbon nanotubes doped is 3% to 8% of the dry fiber mass in the composite fiber substrate layer, the carbon nanotubes account for 10% to 20% of the solid content of phenolic resin, and the solid loading of phenolic resin is 20% to 35% of the dry weight of the composite fiber base paper.

5. The ultrathin composite carbon paper of claim 2, wherein, In S2, the curing temperature is 80~120℃ and the time is 25~45min.

6. The ultrathin composite carbon paper of claim 2, wherein, In S3, the carbonization process includes: first, heating to 300℃ at a rate of 1~2℃ / min, then slowly heating from 300℃ to 600℃ at a rate of 0.3~0.8℃ / min and holding at that temperature for 20~40min, and finally heating to 1000~1200℃ at a rate of 2~5℃ / min.

7. The process of claim 2, wherein, In S3, catalytic graphitization involves heat-treating carbonized paper at 1800~2200℃ for 30~60 min under catalytic conditions; the catalyst is a compound of boron, iron, and nickel.

8. The ultra-thin composite carbon paper of claim 2, wherein, In S4, the mass ratio of conductive carbon black, graphene nanosheets and polytetrafluoroethylene solid in the MPL composite slurry is (2~4):1:(4~6), and the solid content of the MPL composite slurry is 8~12%; when slit coating is applied, the slit gap is 80~150μm, and the thickness of the microporous layer is 15~30μm.

9. The ultrathin composite carbon paper of claim 2, wherein, In S4, the drying temperature is 80~100℃ and the time is 15~30 min.

10. The ultra-thin composite carbon paper of claim 2, wherein, In S4, the sintering temperature is 340~360℃ and the time is 25~30 min.

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