Carbon fiber paper with gradient pore structure and preparation method and preparation device thereof

Abstract

The invention relates to the field of fuel cells, and in particular to a carbon fiber paper with a gradient pore structure, and a preparation method and a preparation device thereof; in the process of impregnating the carbon fiber paper with a binder, the invention adopts a hydrophobic drying method to hinder the diffusion speed of the binder in the carbon fiber paper, resulting in different binder amounts in the drainage direction of the carbon fiber paper, thereby forming a continuous gradient pore structure in the carbon fiber paper; due to the effect of gradient capillaries, liquid water is more likely to move from a small-diameter flow channel to a large-diameter flow channel and be discharged, the carbon fiber paper effectively improves the drainage, ensures the smooth flow of the pore flow channel, and realizes the effective mass transfer of the reaction gas; so that the fuel cell can effectively prevent the battery from being flooded under the power generation condition of a large current density, and improve the battery power density; the invention adds a thickener to the binder to increase the viscosity of the binder, effectively slow down the diffusion speed of the binder in the carbon fiber paper, and maintain the gradient pore structure of the carbon fiber paper.

Description

Technical Field

[0001] The invention relates to the field of fuel cells, and in particular to a carbon fiber paper with a gradient pore structure and a preparation method and a preparation device thereof. Background Art

[0002] The core structure of a hydrogen fuel cell stack is a membrane electrode, which is a "seven-in-one" structure consisting of a proton exchange membrane, a catalyst, a gas diffusion layer, and a bipolar plate. The gas diffusion layer is made of a porous carbon paper material as a base layer, and a microporous layer is coated on one side of the surface. The gas diffusion layer provides gas channels, drainage channels, and effective carrier channels for electrode reactions on the one hand; on the other hand, it can support the catalyst and stabilize the electrode structure.

[0003] Carbon paper is usually a paper-like material made from carbon fiber or other carbon-containing materials through a special process. It is used as a multi-functional composite integrated material for fuel cells, especially in proton exchange membrane fuel cells, where it can support catalysts, conduct electrons, drain water and diffuse gases, which is crucial to improving the performance of fuel cells.

[0004] As the base material of the gas diffusion layer, the porous structure of carbon paper mainly serves as a channel for gas mass transfer and reaction water removal. Normally, the pore structure of carbon paper is uniform, with pore sizes ranging from a few microns to tens of microns. In such a structure, the reaction product water may stay in larger pores due to surface tension, causing flooding and having a greater impact on mass transfer. From the structure of the gas diffusion layer, since the carbon paper layer is made of short fibers overlapped, its pore size is tens of microns, and the microporous layer is prepared by mixing carbon black and a hydrophobic binder, coating, and sintering, and its average pore size is less than 1 micron. The membrane electrode generates water on the cathode catalyst side, and then discharges the water to the carbon paper side through the microporous layer. If the microporous layer is effectively discharged through structural regulation, the pore size will mutate at the interface, and liquid water is easy to accumulate here. If it cannot be quickly removed, it is difficult to achieve effective conduction of the reaction gas, resulting in a decrease in the power generation performance of the fuel cell.

[0005] At present, carbon paper with gradient pore structure has been reported, such as patent CN113322713A, which discloses a method for preparing carbon paper with gradient pore structure, the key points of which are to layer carbon fiber slurry in order of aspect ratio from high to low, and form a slant net to obtain a carbon felt precursor with a three-dimensional network structure; the carbon felt precursor is immersed in a resin solution, taken out and dried to obtain carbon felt. Although this invention can form a gradient pore structure, there will still be obvious pore layered structure between the multilayer carbon paper, which may cause problems such as discontinuous drainage pressure due to sudden changes in the capillary pore structure when used in a fuel cell. Summary of the invention

[0006] The purpose of the present invention is to address the deficiencies in the prior art and provide a gradient pore structure with a uniform transition in the drainage direction of carbon fiber paper, which is more conducive to the removal of water from fuel cell reaction products, prevents flooding, and improves the reaction gas conduction efficiency.

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] The first aspect of the present invention is to provide a method for preparing carbon fiber paper having a gradient pore structure, the steps comprising:

[0009] S1, after short-cutting the carbon fibers, the short-cut carbon fibers are mixed and formed into carbon fiber paper;

[0010] S2, spraying a binder on one side of the carbon fiber paper for impregnation treatment, and laying the carbon fiber paper on a drying device coated with a hydrophobic coating for drying treatment, and controlling the diffusion speed of the binder in the carbon fiber paper by the hydrophobic coating, thereby regulating the distribution of the binder in the carbon fiber paper;

[0011] S3, curing the impregnated carbon fiber paper to obtain the carbon fiber paper with a gradient pore structure.

[0012] Preferably, in step S1, the surface density of the carbon fiber paper is 15-120 g / m 2 , thickness is 150-500μm.

[0013] Preferably, in step S2, the hydrophobic coating comprises: at least one of a silane-modified hydrophobic coating, a wax hydrophobic coating, a fluorocarbon hydrophobic coating, and a polysiloxane hydrophobic coating.

[0014] Preferably, in step S2, the binder comprises: phenolic resin and solvent; and the viscosity of the binder is 15-80 cps.

[0015] More preferably, the solvent comprises: 80% to 95% methanol and 5% to 20% thickener; the thickener comprises: glycerol.

[0016] Preferably, in step S2, the spraying amount of the adhesive is 35-200 g / m 2 .

[0017] Preferably, in step S2, the temperature of the drying process is 80-110°C.

[0018] Preferably, in step S3, the curing treatment comprises: sequentially performing curing preheating treatment, hot pressing treatment and cold pressing treatment on the carbon fiber paper;

[0019] Wherein, the temperature of the curing preheat treatment is 130-160°C, and the temperature of the hot pressing treatment is 160-180°C.

[0020] More preferably, the curing preheating treatment comprises: heating the carbon fiber paper while vacuum adsorbing it along the thickness direction of the carbon fiber paper.

[0021] More preferably, the vacuum degree of the vacuum adsorption is -2~-5Pa.

[0022] Preferably, in step S3, the thickness of the carbon fiber paper with a gradient pore structure is 98-450 μm.

[0023] The second aspect of the present invention is to provide a preparation device for carbon fiber paper with a gradient pore structure, which is used to prepare the carbon fiber paper prepared by the above preparation method, including: an unwinding device, a spraying and dipping device, a three-roll curing device and a winding device;

[0024] The spraying and dipping equipment includes: a guide roller, an adhesive storage tank, an atomizing nozzle and a drying roller; the adhesive storage tank is connected to the atomizing nozzle pipeline; the atomizing nozzle is located at the tangent point between the carbon fiber paper and the drying roller; the drying roller is provided with a first electric heating component;

[0025] The three-roll curing equipment includes: a vacuum pump, a vacuum adsorption hot roller, a hot pressure roller and a cold pressure roller; the vacuum adsorption hot roller is provided with an adsorption chamber and a second electric heating component, and the vacuum pump is connected to the adsorption chamber; the surface of the vacuum adsorption hot roller is provided with a plurality of adsorption holes.

[0026] Preferably, the gap between the hot pressing roller and the vacuum adsorption hot roller is the hot pressing gap, and the gap between the cold pressing roller and the vacuum adsorption hot roller is the cold pressing gap; the hot pressing gap and the cold pressing gap are both the thickness of the carbon fiber paper before spraying the binder × the curing compression ratio;

[0027] The curing compression ratio is the ratio of the thickness of the carbon fiber paper after complete curing to the thickness of the carbon fiber paper before spraying the binder, and the curing compression ratio is 0.65-0.9.

[0028] The third aspect of the present invention is to provide a carbon fiber paper, comprising: a plurality of gradient pores; the pore sizes of the gradient pores increase from small to large along the drainage direction of the carbon fiber paper.

[0029] The present invention adopts the above technical solution, and has the following technical effects compared with the prior art:

[0030] (1) In the process of impregnating the carbon fiber paper with the binder, the present invention adopts a hydrophobic drying method to hinder the diffusion speed of the binder in the carbon fiber paper, resulting in different binder amounts in the drainage direction of the carbon fiber paper, thereby forming a continuous gradient pore structure in the carbon fiber paper; due to the gradient capillary effect, liquid water is more likely to move from the small-diameter flow channel to the large-diameter flow channel and be discharged, and the carbon fiber paper effectively improves the drainage, ensures the smooth flow of the pore flow channel, and realizes the effective mass transfer of the reaction gas; so that the fuel cell can effectively prevent the battery from being flooded under the condition of high current density power generation, thereby improving the battery power density.

[0031] (2) The present invention adds a thickener to the binder to increase the viscosity of the binder, effectively slow down the diffusion rate of the binder in the carbon fiber paper, and maintain the gradient pore structure of the carbon fiber paper.

[0032] (3) During the curing process, vacuum adsorption is performed while heating to prevent the binder from flowing, stabilize the gradient pore structure, and complete the curing of the binder to form stable carbon fiber paper pores. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a schematic diagram of the basic structure of a device for preparing carbon fiber paper with a gradient pore structure in Example 1 of the present invention;

[0034] Figure 2 This is a schematic diagram of the gradient structure of carbon fiber paper after being impregnated with a binder in one embodiment of the present invention;

[0035] Figure 3 This is a microscope image of the macroporous side of carbon fiber paper in one embodiment of the present invention;

[0036] Figure 4 This is a microscope image of the small pore side of carbon fiber paper in one embodiment of the present invention.

[0037] Reference numerals in the figures include:

[0038] Unwinding device 1; spraying and dipping device 2; guide roller 21; adhesive storage tank 22; atomizing nozzle 23; drying roller 24; three-roller curing device 3; vacuum pump 31; vacuum adsorption hot roller 32; hot pressing roller 34; cold pressing roller 35; winding device 4; carbon fiber paper 5; short chopped carbon fiber 51; adhesive 52. DETAILED DESCRIPTION

[0039] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0041] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

[0042] Example 1

[0043] like Figure 1 As shown, this embodiment provides a preparation device for carbon fiber paper with a gradient pore structure, comprising: an unwinding device 1, a spraying and dipping device 2, a three-roller curing device 3 and a winding device 4;

[0044] The spraying and dipping device 2 comprises: a guide roller 21, a binder storage tank 22, an atomizing nozzle 23 and a drying roller 24; the binder storage tank 22 is connected to the atomizing nozzle 23 by a pipeline; the atomizing nozzle 23 is located at the tangent point of the carbon fiber paper 5 and the drying roller 24; the drying roller 24 is provided with a first electric heating component;

[0045] The three-roll curing device 3 includes: a water ring vacuum pump 31, a vacuum adsorption hot roller 32, a hot pressure roller 34 and a cold pressure roller 35; the vacuum adsorption hot roller 32 is provided with an adsorption chamber and a second electric heating component, and the water ring vacuum pump 31 is connected to the adsorption chamber; the surface of the vacuum adsorption hot roller 32 is provided with a plurality of adsorption holes;

[0046] The gap between the hot pressing roller 34 and the vacuum adsorption hot roller 32 is a hot pressing gap, and the gap between the cold pressing roller 35 and the vacuum adsorption hot roller 32 is a cold pressing gap; both the hot pressing gap and the cold pressing gap are calculated by the thickness of the carbon fiber paper before spraying the adhesive × the curing compression ratio;

[0047] The curing compression ratio is the ratio of the thickness of the carbon fiber paper after complete curing to the thickness of the carbon fiber paper before spraying the binder, and the curing compression ratio is 0.65-0.9.

[0048] Here’s how it works:

[0049] The operator puts the adhesive into the adhesive storage tank 22 in advance, and sprays Teflon on the surface of the drying roller 24 to form a hydrophobic coating; the carbon fiber paper 5 is introduced from the unwinding device 1 into the guide roller 21 and runs vertically downward, and is pulled into the drying roller 24, and the atomizing nozzle 23 located at the tangent point of the carbon fiber paper 5 and the drying roller 24 sprays the adhesive onto the surface of the carbon fiber paper 5 so that the adhesive is immersed in the carbon fiber paper 5, and then the carbon fiber paper 5 is dried by the drying roller 24;

[0050] like Figure 2As shown, when the binder 52 diffuses in the direction of outer surface-interior-interior surface and impregnates the entire carbon fiber paper 5, due to the presence of the hydrophobic coating and the fact that the carbon fiber paper 5 is a thin layer of porous material, under the action of a large surface tension, it is difficult for the binder 52 to completely impregnate the inner surface of the carbon fiber paper 5, and then the binder 52 will be unevenly distributed in the drainage direction, that is, the binder 52 is more distributed on the outside of the carbon fiber paper 5 and less distributed on the inside, and this binder gradient distribution is a continuous transition structure without an obvious dividing line, and the pore structure formed between the short chopped carbon fibers 51 where the binder 52 is less infiltrated is larger, and the pore structure formed between the short chopped carbon fibers 51 where the binder 52 is more infiltrated is smaller; after subsequent carbonization and graphitization of the carbon fiber paper 5, the carbon fiber paper 5 forms a gradient pore structure in the drainage direction due to the difference in resin carbon distribution;

[0051] The impregnated and dried carbon fiber paper 5 is pulled into the vacuum adsorption hot roller 32, and the vacuum pump 31 is turned on, so that the vacuum adsorption hot roller 32 forms a negative pressure suction effect on the carbon fiber paper on its surface, effectively preventing the gradient pore structure from being destroyed due to the flow of resin during the curing process of the binder resin;

[0052] The hot pressing gap and the cold pressing gap are adjusted according to the curing compression ratio set in advance, and the carbon fiber paper 5 is cured and shaped after passing through the hot pressing roller 34 and the cold pressing roller 35, and finally the carbon fiber paper 5 is introduced into the winding device 4 to complete the winding.

[0053] The running direction of the drying roller 24 is counterclockwise, the running direction of the vacuum adsorption hot roller 32 is clockwise, and the running directions of the hot pressing roller 34 and the cold pressing roller 35 are counterclockwise; in the whole device, the drying roller 24, the vacuum adsorption hot roller 32, the hot pressing roller 34, and the cold pressing roller 35 are all equipped with a transmission device, and the running speed of the carbon fiber paper 5 is 0.2-1.2m / min.

[0054] Example 2

[0055] This embodiment provides a method for preparing carbon fiber paper with a gradient pore structure, the steps comprising:

[0056] S1, after short-cutting the carbon fibers, the short-cut carbon fibers are mixed and formed into carbon fiber paper;

[0057] S2. Spray a binder on one side of the carbon fiber paper for impregnation (the binder includes phenolic resin, methanol and glycerol, with a solid content of 8% and a viscosity of 55 cps). The amount of the binder sprayed (the weight gain per unit area of ​​the carbon fiber paper impregnated with the binder after drying) is 95 g / m 2 ; At the same time, the carbon fiber paper is laid on a drying device coated with a hydrophobic coating and dried at 85°C; the diffusion rate of the binder in the carbon fiber paper is controlled by the hydrophobic coating, thereby regulating the distribution of the binder in the carbon fiber paper.

[0058] S3, vacuum adsorbing the carbon fiber paper along the thickness direction of the carbon fiber paper, the vacuum degree is -5Pa, and heating is performed at 135°C; then the carbon fiber paper is subjected to hot pressing at 165°C, and finally cold pressing, so as to obtain a carbon fiber paper with a gradient pore structure ( Figure 2 ); During hot pressing and cold pressing, the curing compression ratio of the carbon fiber paper is 0.75.

[0059] Embodiment 3-8

[0060] By adjusting the solid content, viscosity, spraying amount of the binder, the temperature of the drying treatment, the vacuum degree of the vacuum adsorption, the temperature of the hot pressing treatment and other parameters, Examples 3-8 were obtained. The specific parameters are shown in Table 1.

[0061] Table 1

[0062]

[0063] Comparative Example 1

[0064] This comparative example provides another method for preparing carbon fiber paper. In step S2, no hydrophobic coating is applied to the drying device. The rest is the same as in Example 2.

[0065] Comparative Example 2

[0066] This comparative example provides another method for preparing carbon fiber paper. The binder in step S2 does not contain a thickener, and the rest is the same as in Example 2.

[0067] Comparative Example 3

[0068] This comparative example provides another method for preparing carbon fiber paper. In step S3, vacuum adsorption is not performed, and the rest is the same as in Example 2.

[0069] Detection Example

[0070] The carbon fiber paper prepared by the preparation method described in Examples 2-8 and Comparative Examples 1-3 was tested for air permeability, porosity by drainage method, and bubble point pressure of deionized water passing through the carbon fiber paper by bubble point method. The carbon fiber paper was coated with a microporous layer on the side with smaller pores, and a gas diffusion layer was formed after sintering. The gas diffusion layer was installed in the membrane electrode for power generation performance test, and its limiting current density, i.e., the current density at a voltage of 0.1V, was determined. The test results are shown in Table 2.

[0071] Table 2

[0072]

[0073] Compared with Comparative Examples 1-3, the air permeability of the carbon fiber paper prepared in Example 2 is slightly smaller than that of the carbon fiber paper prepared in Comparative Examples 1-3, which reflects that the effective mass transfer area of ​​Example 2 is smaller in the drainage direction. From the perspective of porosity, since the amount of binder sprayed and the curing compression ratio are consistent, the overall porosity of the material remains unchanged. Since the effective mass transfer area is determined by the layer with the smallest pore area, under the premise of the same overall porosity, the effective mass transfer area of ​​Example 2 is smaller, indicating that Example 2 has a different pore size distribution, that is, the formation of a gradient pore structure, Figure 3-4 It is also clear that there are different pore structures on both sides of the carbon fiber paper.

[0074] Further analysis of the bubble point pressure data shows that the bubble point pressure can directly reflect the difficulty of liquid water breaking through the carbon fiber paper. In Example 2-8, under the action of the capillary gradient pore size, a lower pressure can make the liquid water penetrate the entire carbon fiber paper, thereby enhancing the fuel cell's ability to drain water on the cathode side.

[0075] The power generation performance of the membrane electrode was measured. Under low voltage (0.1V), Example 2 can effectively prevent flooding due to the drainage effect of the gradient pore structure, and its limiting current density reaches 3.78A / cm 2 However, due to the imperfect gradient pore structure and limited drainage effect of comparative examples 1-3, at higher current density, more channels in the pores are occupied by liquid water, making it difficult for the reaction gas to fully enter the membrane electrode catalyst layer, and the degree of reaction is greatly reduced, resulting in a limiting current density of less than 3A / cm 2 .

[0076] The above description is only a preferred embodiment of the present invention, and does not limit the implementation mode and protection scope of the present invention. For those skilled in the art, it should be aware that all solutions obtained by equivalent substitutions and obvious changes made using the description and illustrations of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing carbon fiber paper with a gradient pore structure, characterized in that the steps include: S1, after short-cutting the carbon fibers, the short-cut carbon fibers are mixed and formed into carbon fiber paper; S2, spraying a binder on one side of the carbon fiber paper for impregnation treatment, and laying the carbon fiber paper on a drying device coated with a hydrophobic coating for drying treatment, and controlling the diffusion speed of the binder in the carbon fiber paper by the hydrophobic coating, thereby regulating the distribution of the binder in the carbon fiber paper; the binder includes: phenolic resin and solvent; in terms of mass percentage, the solvent includes: 80%~95% methanol and 5%~20% thickener; the thickener includes: glycerol; S3, curing the impregnated carbon fiber paper to obtain carbon fiber paper with a gradient pore structure; the curing treatment includes: sequentially performing curing preheating treatment, hot pressing treatment and cold pressing treatment on the carbon fiber paper; the curing preheating treatment includes: vacuum adsorption and heating of the carbon fiber paper along the thickness direction of the carbon fiber paper.

2. The preparation method according to claim 1, characterized in that: In step S2, the hydrophobic coating includes at least one of a silane-modified hydrophobic coating, a wax hydrophobic coating, a fluorocarbon hydrophobic coating, and a polysiloxane hydrophobic coating.

3. The preparation method according to claim 1, characterized in that: In step S2, the viscosity of the adhesive is 15-80 cps.

4. The preparation method according to claim 1, characterized in that: In step S2, the temperature of the drying process is 80-110°C.

5. The preparation method according to claim 1, characterized in that: In step S3, the temperature of the curing preheat treatment is 130-160°C, and the temperature of the hot pressing treatment is 160-180°C.

6. A device for preparing carbon fiber paper with a gradient pore structure, characterized in that: Used to prepare carbon fiber paper prepared by the preparation method according to any one of claims 1 to 5, comprising: an unwinding device (1), a spraying and impregnation device (2), a three-roller curing device (3) and a winding device (4); The spraying and dipping device (2) comprises: a guide roller (21), a binder storage tank (22), an atomizing nozzle (23) and a drying roller (24); the binder storage tank (22) is connected to the atomizing nozzle (23) through a pipeline; the atomizing nozzle (23) is located at the tangent point between the carbon fiber paper (5) and the drying roller (24); the drying roller (24) is provided with a first electric heating component; The three-roller curing device (3) comprises: a vacuum pump (31), a vacuum adsorption hot roller (32), a hot pressure roller (34) and a cold pressure roller (35); an adsorption chamber and a second electric heating component are provided in the vacuum adsorption hot roller (32), and the vacuum pump (31) is connected to the adsorption chamber; and a plurality of adsorption holes are provided on the surface of the vacuum adsorption hot roller (32).

7. The preparation device according to claim 6, characterized in that: The gap between the hot pressing roller (34) and the vacuum adsorption hot roller (32) is a hot pressing gap, and the gap between the cold pressing roller (35) and the vacuum adsorption hot roller (32) is a cold pressing gap; the hot pressing gap and the cold pressing gap are both the thickness of the carbon fiber paper before spraying the adhesive×the curing compression ratio; The curing compression ratio is the ratio of the thickness of the carbon fiber paper after complete curing to the thickness of the carbon fiber paper before spraying the binder, and the curing compression ratio is 0.65-0.

9.

8. A carbon fiber paper prepared by the preparation method according to any one of claims 1 to 5, characterized in that: include: A plurality of gradient pores; the pore sizes of the gradient pores increase from small to large along the drainage direction of the carbon fiber paper.

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