A highly breathable flexible gas diffusion layer and its preparation method and application

Abstract

The present invention provides a highly breathable flexible gas diffusion layer and a preparation method thereof. Using microcrystalline cellulose as a template, carbon paper slurry is added to the template. After the moisture of the carbon paper slurry is dried by vacuum filtration, the gas diffusion layer is obtained by high-temperature calcination. For the gas diffusion layer prepared by the technical solution of the present invention, carbon nanotubes are used as the filling of carbon fibers, and the porosity of the gas diffusion layer is regulated by adjusting the addition amount and particle size of microcrystalline cellulose. The obtained gas diffusion layer carbon paper has the advantages of high breathability and flexibility. At the same time, since the gas diffusion layer is completely prepared from carbon materials, the carbon paper has good electrical conductivity and can well meet the requirements of flexible fuel cells.

Description

Technical Field

[0001] The present invention relates to the field of energy and clean technology, and particularly relates to a highly breathable flexible gas diffusion layer, a preparation method thereof, and an application thereof. Background Art

[0002] The rapid development of flexible devices has accelerated our demand for flexible, stretchable, and bendable energy production and storage devices. Among them, the flexible proton exchange membrane fuel cell (PEMFC) is considered a promising new energy conversion device due to its high efficiency, low pollution, fast startup, and other advantages. Compared with other devices, the flexible proton exchange membrane fuel cell has advantages such as high energy density and high energy conversion efficiency. Moreover, in the power generation process of the proton exchange membrane fuel cell (PEMFC) that uses only hydrogen and oxygen as fuels, only water is produced as a byproduct, and a small amount of waste heat is released. Compared with the huge gas emissions, waste heat, and cooling requirements in traditional power generation systems, the flexible PEMFC has great advantages.

[0003] In traditional proton exchange membrane fuel cells, the gas diffusion layer (GDL) is a key component of the fuel cell, which is a passage for fuel, air, and water. Therefore, certain requirements are imposed on the gas diffusion layer. It needs to have good electrical conductivity, good porosity, and appropriate pore size to transfer reaction gases and remove moisture in a timely manner, and it also needs to be flexible to meet the requirements of flexible devices. In general PEMFCs, carbon paper is used as the gas diffusion layer in the battery, and carbon paper is made of carbon fibers, which are usually very brittle and not suitable for flexible proton exchange membrane fuel cells. And the general method of making carbon paper flexible, that is, using carbon nanotubes, will greatly affect the mass transfer ability of the gas diffusion layer, resulting in a dense structure of the gas diffusion layer, uneven pore size distribution, and discontinuous internal pores.

[0004] CN113066995A discloses a highly tough porous carbon paper and a preparation method thereof. The metal fibers are pretreated with a citric acid-ammonium bifluoride solution, and carbon nanotubes are deposited on the pretreated metal fibers as catalysts. The pretreated metal fibers are subjected to carbon deposition treatment by a gaseous carbon deposition process to obtain carbon-deposited metal fibers. Next, a porous carbon paper embryo is prepared by using the carbon-deposited metal fibers and polyvinyl acetal, and finally, the porous carbon paper embryo is impregnated with an N-methylpyrrolidone solution containing bisphenol A phthalonitrile and is prepared into a highly tough porous carbon paper through high-temperature carbonization treatment. The production method of the carbon paper is similar to that of traditional carbon paper. Although the problem of porosity regulation is further solved, the relatively brittle characteristic of carbon fibers is still retained and cannot be applied to flexible devices.

[0005] CN112310413A discloses a method for preparing a gas diffusion layer, which uses two materials, carbon nanotubes and carbon fibers, with the carbon fibers as the base framework and the carbon nanotubes as the filler in the framework, to obtain a relatively thin and high-strength gas diffusion layer. However, because carbon nanotubes are used as the filler, the internal structure of the diffusion layer is dense. Although laser drilling is used to create pores, the internal pores are not continuous, resulting in poor mass transfer performance.

[0006] In order to make the carbon paper for fuel cell gas diffusion layer have flexibility, good electrical conductivity, strength and a pore structure that meets the requirements of fuel cells, it is urgent for us to develop a new type of carbon paper for gas diffusion layer on the basis of the existing technology to improve the performance of fuel cell gas diffusion layer, and at the same time ensure that the preparation process is simple and can be industrially produced. Summary of the Invention

[0007] In view of this, to solve the above problems, the present invention provides a highly breathable flexible gas diffusion layer, its preparation method and application. Using microcrystalline cellulose as a template, by means of vacuum filtration and heat treatment, and using carbon fibers, carbon nanofibers and / or carbon nanotubes as raw materials, the preparation process is simple and energy consumption is low, and a gas diffusion layer with flexibility and high breathability performance is prepared.

[0008] To achieve the above object, the present invention provides a method for preparing a highly breathable flexible gas diffusion layer. Specifically, the technical solution includes using microcrystalline cellulose as a template, adding carbon paper slurry to the template, and after drying the moisture of the carbon paper slurry by vacuum filtration, obtaining the gas diffusion layer through heat treatment. The microcrystalline cellulose and other impurities are removed by heat treatment to obtain a gas diffusion layer of pure carbon material.

[0009] Preferably, the particle size of the microcrystalline cellulose is selected according to the requirements of the pores in the gas diffusion layer and configured into a microcrystalline cellulose solution; the microcrystalline cellulose solution is slowly poured on the filter membrane, and after drying the moisture of the microcrystalline cellulose by vacuum filtration to form a network structure, the filter membrane is overlapped with the network structure of the microcrystalline cellulose, thus obtaining the template. Preferably, the pressure of vacuum filtration is 0.01 - 0.1 MPa.

[0010] Preferably, the method for preparing the microcrystalline cellulose solution includes obtaining microcrystalline cellulose with different particle sizes by sedimentation and separation methods. The microcrystalline cellulose raw material is added to water, ultrasonically treated and shaken evenly, then transferred to a graduated cylinder. After standing until the microcrystalline cellulose settles completely according to the particle size, the liquid in the graduated cylinder is taken out in portions according to the same interval scale according to the need of the particle size. By controlling the standing time and the interval of the sampling scale, the particle size and the particle size range are controlled. The samples of the particle size to be used are centrifuged and layered, and the particle size is counted. Finally, the microcrystalline cellulose with different particle sizes is obtained.

[0011] Preferably, the particle size range of the microcrystalline cellulose is 4 to 200 μm; including but not limited to, particle size ranges of 4 μm, 10 μm, 15 μm, 20 μm, 29 μm, 35 μm, 40 μm, 46 μm, 53 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 126 μm, 160 μm, 200 μm. It should be noted that the particle size here is the average particle size. According to the requirement of the porosity of the gas diffusion layer, the standing time and sampling interval are controlled to obtain different particle size ranges and the required average particle size.

[0012] Preferably, the filter membrane is a mixed cellulose (MCE) filter membrane.

[0013] Preferably, the addition proportion of the microcrystalline cellulose poured on the surface of the filter membrane is x (mg·cm -2 ), where x = (0, 6]; including but not limited to, x = 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6.

[0014] Preferably, the addition proportion is x = [3, 6], and most preferably, x = 3.

[0015] Preferably, the preparation of the gas diffusion layer includes: pretreating the carbon paper slurry, dropping it on the microcrystalline cellulose network structure of the template, allowing the carbon paper slurry to penetrate into the template, drying the moisture of the carbon paper slurry by vacuum filtration, and then peeling it off from the MCE filter membrane to obtain a carbon paper precursor; the gas diffusion layer is obtained by high-temperature calcination of the carbon paper precursor.

[0016] Preferably, the pretreatment step of the carbon paper slurry includes adding a water repellent to the carbon paper slurry and performing ultrasonic treatment for 10 to 30 min; preferably, the water repellent is polytetrafluoroethylene; further, the addition amount of the water repellent is 5 to 40 wt% of the carbon paper slurry.

[0017] Preferably, the carbon paper slurry is a mixed slurry of chopped carbon fiber slurry, carbon nanofiber slurry, single-walled carbon nanotube fiber (SWCNT) slurry, and multi-walled carbon nanotube fiber (MWCNT) slurry; preferably, in the carbon paper slurry, the mass ratio of chopped carbon fiber slurry to carbon nanofiber slurry is 4:1; the mass ratio of SWCNT slurry to MWCNT slurry is 1:1. More preferably, the chopped carbon fiber slurry, carbon nanofiber slurry, SWCNT slurry, and MWCNT slurry in the carbon paper slurry are mixed according to a mass ratio of 24:6:5:5. Specifically, the chopped carbon fiber accounts for 60 wt%, the carbon nanofiber accounts for 15 wt%, the single-walled carbon nanotube accounts for 12.5 wt%, and the multi-walled carbon nanotube accounts for 12.5 wt%.

[0018] Preferably, the specific gravity of each component added when the carbon paper slurry is poured into the template is as follows: the specific gravity of the chopped carbon fiber is 0.1-2 mg·cm -2 , preferably 1.6 mg·cm -2 ; the specific gravity of the carbon nanofiber is 0.1-2 mg cm -2 , preferably 0.4 mg·cm -2 ; the specific gravity of the single-walled carbon nanotube is 0.1-2 mg·cm -2 , preferably 0.33 mg cm -2 ; the specific gravity of the multi-walled carbon nanotube is 0.1-2 mg·cm -2 , preferably 0.33 mg·cm -2 .

[0019] Preferably, the porosity of the gas diffusion layer carbon paper is 85-90%, for example, 85%, 86%, 87%, 88%, 89%, 90%, etc.

[0020] Specifically, the preparation method of the highly breathable flexible gas diffusion layer provided by the present invention includes the following steps:

[0021] S1. Preparation of carbon paper slurry; the chopped carbon fiber, carbon nanofiber, single-walled carbon nanotube fiber (SWCNT) and multi-walled carbon nanotube fiber (MWCNT) are dispersed and mixed in proportion respectively, and a hydrophobic agent is added, and the carbon paper slurry is obtained by ultrasonic treatment;

[0022] S2. Preparation of the template; select the particle size of microcrystalline cellulose according to needs, configure it into a microcrystalline cellulose solution and slowly pour it on the filter membrane, and the water of the microcrystalline cellulose solution is dried by vacuum filtration to form a network structure, and the filter membrane is overlapped with the network structure of the microcrystalline cellulose, and the template is obtained;

[0023] S3. Preparation of the gas diffusion layer; the carbon paper slurry prepared in S1 is slowly dropped on the template prepared in S2, the carbon paper slurry penetrates into the internal network structure of the microcrystalline cellulose, the carbon paper slurry is dried by vacuum filtration, and after drying, it is peeled off from the MCE filter membrane and placed in a muffle furnace for high-temperature calcination at 200-500 °C for 10-60 min to remove the microcrystalline cellulose and other impurities, and the gas diffusion layer with pure carbon material is obtained.

[0024] The gas diffusion layer prepared by the above technical solution does not undergo graphitization treatment. Only simple methods such as vacuum filtration and heat treatment are required. Using carbon fiber, carbon nanofiber, and carbon nanotube as raw materials, aiming at the problem of the dense internal structure of the gas diffusion layer caused by the addition of carbon nanotubes, the particle size of microcrystalline cellulose is used to regulate the inside of the carbon paper. By optimizing parameters such as porosity and pore size, its pore structure is optimized, and a gas diffusion layer with high flexibility, high air permeability and suitable for fuel cells is obtained.

[0025] At the same time, the method of high-temperature heat treatment is adopted. Finally, microcrystalline cellulose and other impurities are removed, making the gas diffusion layer a complete carbon material structure, providing good electrical conductivity, and laying a foundation for its good electrical properties after being applied to fuel cells.

[0026] The beneficial technical effects obtained by the present invention are as follows:

[0027] 1. The gas diffusion layer prepared by the technical solution of the present invention uses carbon nanotubes as the filling of carbon fiber. The obtained gas diffusion layer carbon paper has the advantages of high air permeability and flexible bendability. At the same time, the method of high-temperature heat treatment is adopted to remove microcrystalline cellulose and other impurities, making the gas diffusion layer completely prepared from carbon materials. The carbon paper has good electrical conductivity and can well meet the needs of flexible fuel cells.

[0028] 2. The gas diffusion layer prepared by the technical solution of the present invention uses microcrystalline cellulose as a template, and can adjust the void size inside the gas diffusion layer according to the particle size and addition ratio of microcrystalline cellulose, so as to increase the porosity of the internal structure of the gas diffusion layer, thereby improving the mass transfer performance of the gas diffusion layer, and thus improving the electrical properties of the battery.

[0029] 3. By adopting the technical solution of the present invention, the problems of dense internal structure and discontinuous internal pores of the carbon paper caused by directly filling with the carbon nanotube itself in the prior art are avoided. After using microcrystalline cellulose to create pores in the present invention, the particle size and addition ratio of microcrystalline cellulose added can be quantitatively controlled, and the internal pores of the carbon paper can be quantitatively regulated. And the method is simple, ensuring the electrical conductivity and at the same time enhancing the mass transfer ability of the gas diffusion layer carbon paper.

[0030] 4. By adopting the technical solution of the present invention, the process is simple, the raw materials are simple, the energy consumption is low, and it is suitable for mass production and promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of the sedimentation separation simulation of microcrystalline cellulose in Example 1 of the present invention.

[0032] Figure 2 Schematic diagram of the preparation process in Example 1 of the present invention.

[0033] Figure 3a SEM image of the cross-section of the carbonaceous structure when preparing the gas diffusion layer without adding microcrystalline cellulose in Comparative Example 1 of the present invention.

[0034] Figure 3b SEM image of the cross-section of the carbonaceous structure when preparing the gas diffusion layer in Example 1 of the present invention with a microcrystalline cellulose addition ratio of 3 mg·cm -2 of.

[0035] Figure 3c SEM image of the cross-section of the carbonaceous structure when preparing the gas diffusion layer in Example 1 of the present invention with a microcrystalline cellulose addition ratio of 6 mg·cm -2 of.

[0036] Figure 4 Comparison chart of the performance of fuel cells prepared with the gas diffusion layers respectively prepared in Example 1 and Comparative Example 1 of the present invention.

[0037] Figure 5 Comparison chart of the gas permeability of the gas diffusion layers obtained with different microcrystalline cellulose particle sizes in the examples and comparative examples of the present invention.

[0038] Figure 6 Comparison chart of the performance of fuel cells prepared with the gas diffusion layers obtained with different microcrystalline cellulose particle sizes in the examples and comparative examples of the present invention. Detailed implementation manners

[0039] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of this application. Apparently, the described embodiments are some, but not all, of the embodiments of this application.

[0040] The present invention provides a gas diffusion layer with high air permeability and flexibility. A microcrystalline cellulose with a network structure is formed as a template by a vacuum filtration method, carbon nanotubes are filled into the network structure as carbon fibers, and finally the microcrystalline cellulose is removed by a high-temperature heat treatment method to form a gas diffusion layer carbon paper with an obvious pore structure, improving the problem of dense pores in the gas diffusion layer in the prior art. Among them, the conditions for the heat treatment include high-temperature calcination at 200 - 500 °C for 10 - 60 min.

[0041] In particular, by adopting the technical solution of the present invention, the porosity of the gas diffusion layer can be regulated by adjusting the particle size and addition ratio of microcrystalline cellulose. The excellent pore structure can maintain the mass transfer performance of other diffusion layers, thereby maintaining the electrical conductivity of the carbon paper. At the same time, by adopting the technical solution of the present invention, the air permeability of the gas diffusion layer can also be adjusted, so as to obtain an air diffusion layer with both air permeability and flexibility. It should be noted that in the present invention, the addition ratio of microcrystalline cellulose specifically refers to the mass of microcrystalline cellulose added per unit area. Under the conditions of the same thickness and the same particle size of microcrystalline cellulose, the homogenization of microcrystalline cellulose added per unit area can be ensured, so as to finally obtain a uniform and continuous pore structure and achieve more excellent mass transfer performance.

[0042] Further, the particle size of microcrystalline cellulose is selected according to the requirements of the pores in the gas diffusion layer and configured into a microcrystalline cellulose solution; the microcrystalline cellulose solution is slowly poured on the filter membrane, and the moisture of the microcrystalline cellulose is dried by vacuum filtration to form a network structure, and the filter membrane is overlapped with the network structure of the microcrystalline cellulose, thus obtaining a microcrystalline cellulose template. Preferably, the vacuum filtration conditions are that the pressure of vacuum filtration is 0.01-0.1 MPa, and the vacuum filtration of the present invention is carried out in a vacuum filter. The pore size of the filter membrane is selected according to actual needs, and the present invention does not make specific limitations.

[0043] Further, the raw materials selected in the preparation method of the present invention are simple, and only include microcrystalline cellulose, carbon paper slurry, and a hydrophobic agent. Preferably, the hydrophobic agent is polytetrafluoroethylene. After high-temperature heat treatment, microcrystalline cellulose and other impurities are calcined and removed, and the obtained gas diffusion layer is made of carbon material with excellent electrical conductivity, thus providing an excellent electrical performance basis for the application of the present invention in fuel cells.

[0044] Preferably, the addition ratios of the components in the carbon paper slurry poured into the template are as follows: the proportion of chopped carbon fibers is 0.1-2 mg·cm -2 , preferably 1.6 mg·cm -2 ; the proportion of carbon nanofibers is 0.1-2 mg cm -2 , preferably 0.4 mg·cm -2 ; the proportion of single-walled carbon nanotubes is 0.1-2 mg·cm -2 , preferably 0.33 mg cm -2 ; the proportion of multi-walled carbon nanotubes is 0.1-2 mg·cm -2 , preferably 0.33 mg·cm -2 . The technical solution of the present invention may select the mass ratio of the addition of each carbon fiber in the carbon paper slurry through the preferred addition ratio.

[0045] The technical solution of the present invention will be further described in detail through specific embodiments below. The prepared gas diffusion layer carbon paper will be applied to the preparation of fuel cells, and its electrical properties and air permeability will be tested.

[0046] Example 1

[0047] 1. Separation of microcrystalline cellulose

[0048] Prepare an aqueous solution of microcrystalline cellulose at 10 mg·mL -1 , treat it with an ultrasonic cleaner for 5 min, shake and mix it evenly, then transfer it to a 250 mL graduated cylinder and let it stand for 15 min. Refer to Figure 1 . The microcrystalline cellulose in the graduated cylinder is dispersed in water. Since particles of the same substance with different particle sizes have different sedimentation rates in the liquid, large-particle-size particles have a fast sedimentation rate in the solution, and small-particle-size particles have a slow sedimentation rate. According to Stokes' sedimentation principle, microcrystalline cellulose is dispersed in water layer by layer from small to large according to the particle size.

[0049] Take one portion from each 50 mL scale of the liquid in the graduated cylinder. By controlling the standing time and the sampling scale interval, control the particle size and particle size range of each sample. Centrifuge and layer the obtained samples to obtain microcrystalline cellulose with particle sizes of 4 μm, 29 μm, 53 μm, and 126 μm respectively. It should be noted that the particle size here is the average particle size obtained from the microcrystalline cellulose particles within the sampling scale.

[0050] 2. Dispersion of carbon materials

[0051] (1) Dispersion of carbon fibers: Weigh 500 mg of short-cut carbon fibers and measure 500 mL of deionized water. Disperse 500 mg of short-cut carbon fibers in 500 mL of deionized water. First, stir evenly with a glass rod, and then clean with a 500 W ultrasonic cleaner for 20 min to obtain a short-cut carbon fiber slurry of 1 mg·mL -1 .

[0052] (2) Dispersion of carbon nanofibers: Weigh 100 mg of carbon nanofibers and measure 200 mL of deionized water. Disperse 100 mg of carbon nanofibers in 200 mL of deionized water, stir evenly with a glass rod, and then clean with a 500 W ultrasonic cleaner for 10 min to obtain a carbon nanofiber slurry of 0.5 mg·mL -1 .

[0053] (3) Dispersion of single-walled carbon nanotubes (SWCNT): Weigh 500 mg of single-walled carbon nanotubes and measure 100 mg·mL -50 mL of a 1% sodium dodecylbenzenesulfonate (SDBS) solution was measured, 950 mL of deionized water was measured, and the mass ratio of carbon nanotubes to sodium dodecylbenzenesulfonate was 1:10. The single-walled carbon nanotubes, SDBS, and deionized water were mixed evenly and sonicated with a cell crusher for 3 h to obtain a black, uniformly dispersed liquid that could be stored for up to several weeks without obvious precipitation, resulting in an SWCNT slurry.

[0054] (4) Dispersion of multi-walled carbon nanotubes (MWCNT): Weighed 500 mg of multi-walled carbon nanotubes, measured 50 mL of a 1% sodium dodecylbenzenesulfonate (SDBS) solution, and measured 950 mL of deionized water. The multi-walled carbon nanotubes, SDBS, and deionized water were mixed evenly and sonicated with a cell crusher for 2 h to obtain a black, uniformly dispersed liquid that could be stored for up to several weeks without obvious precipitation, resulting in an MWCNT slurry. -1 50 mL of a 1% sodium dodecylbenzenesulfonate (SDBS) solution was measured, 950 mL of deionized water was measured. The multi-walled carbon nanotubes, SDBS, and deionized water were mixed evenly and sonicated with a cell crusher for 2 h to obtain a black, uniformly dispersed liquid that could be stored for up to several weeks without obvious precipitation, resulting in an MWCNT slurry.

[0055] 3. Preparation of the gas diffusion layer

[0056] Refer to Figure 2 , including the following steps:

[0057] (1) The chopped carbon fiber slurry, carbon nanofiber slurry, SWCNT slurry, and MWCNT slurry processed in step 2 were mixed according to a mass ratio of 24:6:5:5. Among them, the chopped carbon fibers accounted for 60 wt%, the carbon nanofibers accounted for 15 wt%, the single-walled carbon nanotubes accounted for 12.5 wt%, and the multi-walled carbon nanotubes accounted for 12.5 wt%. Finally, a polytetrafluoroethylene (PTFE) solution accounting for 25 wt% of the total slurry was added as a water repellent and mixed to obtain the final carbon paper slurry, which was sonicated with an ultrasonic cleaner for 20 min and set aside.

[0058] (2) A mixed fiber (MCE) filter membrane with a pore size of 0.45 μm was placed on a suction filtration device, and microcrystalline cellulose with a particle size of 4 μm separated in step 1 was configured into a solution, and the microcrystalline cellulose solution was slowly poured onto the MCE filter membrane at an addition ratio of 3 mg·cm -2 . The water was drained through vacuum filtration to obtain a network structure of overlapping microcrystalline cellulose on the filter membrane, forming a microcrystalline cellulose template.

[0059] (3) The carbon paper slurry prepared in step 3-(1) was slowly dropped onto the microcrystalline cellulose network structure on the MCE filter membrane, and the proportion of the carbon paper slurry was controlled by controlling the added thickness. Among them, the proportion of chopped carbon fibers was 1.6 mg cm -2 ; the proportion of carbon nanofibers was 0.4 mg cm -2 ; the proportion of single-walled carbon nanotubes was 0.33 mg cm -2; The specific gravity of multi-walled carbon nanotubes is 0.33 mg / cm -2 .

[0060] The carbon paper slurry penetrates into the network structure of the microcrystalline cellulose template, and then the carbon paper slurry is dried by vacuum filtration. The pressure of vacuum filtration is 0.1 MPa. After drying, it is peeled off from the MCE membrane to obtain a carbon paper precursor; the carbon paper precursor is placed in a muffle furnace and calcined at 350 °C for 30 min to remove the microcrystalline cellulose and other impurities in the carbon paper precursor, and a gas diffusion layer with flexibility and high air permeability is obtained.

[0061] Example 2

[0062] The difference between this example and Example 1 is that the particle size of the microcrystalline cellulose used in step 3-(2) is 29 μm.

[0063] Example 3

[0064] The difference between this example and Example 1 is that the particle size of the microcrystalline cellulose used in step 3-(2) is 53 μm.

[0065] Example 4

[0066] The difference between this example and Example 1 is that the particle size of the microcrystalline cellulose used in step 3-(2) is 126 μm.

[0067] Example 5

[0068] The difference between this example and Example 1 is that the addition ratio of the microcrystalline cellulose solution in step 3-(2) is 1.5 mg / cm -2 .

[0069] Example 6

[0070] The difference between this example and Example 1 is that the addition ratio of the microcrystalline cellulose solution in step 3-(2) is 4.5 mg / cm -2 .

[0071] Example 7

[0072] The difference between this example and Example 1 is that the addition ratio of the microcrystalline cellulose solution in step 3-(2) is 6 mg / cm -2 .

[0073] The specific gravity of the chopped carbon fiber is 0.1 - 2 mg / cm -2 , preferably 1.6 mg / cm -2 ; The specific gravity of the carbon nanofiber is 0.1 - 2 mg / cm -2 , preferably 0.4 mg / cm -2 ; The specific gravity of the single-walled carbon nanotube is 0.1 - 2 mg / cm -2, preferably 0.33 mg / cm -2 ; the specific gravity of the multi-walled carbon nanotubes is 0.1 - 2 mg / cm -2 , preferably 0.33 mg / cm -2 .

[0074] Comparative Example 1

[0075] The difference between this example and Example 1 lies in that microcrystalline cellulose is not added in step 3-(2), that is, the addition ratio of the microcrystalline cellulose solution is 0. The carbon paper slurry is directly dropped on the MCE filter membrane and the gas diffusion layer is obtained through vacuum filtration and high-temperature heat treatment.

[0076] Characterize the air permeability and electrical properties of the above examples and comparative examples.

[0077] Performance characterization method:

[0078] 1. Air permeability characterization: One of the most important functions of the gas diffusion layer in a fuel cell is to conduct gas transfer. Therefore, the gas permeability of the gas diffusion layer and its magnitude are crucial. Here, we use a self-made detection device. (1) Fix the gas diffusion layer in the fixture and connect the device. (2) Turn on the air pump so that the gas flows in from the air pump and flows out from the air flowmeter after passing through the fixture. (3) Adjust the flow valve on the device to increase the air flow rate from slow to fast, and record the pressure reading (unit: Kpa) and the flow rate of the flowmeter (unit: mL·min -1 ·cm -2 ) to make the pressure and flow rate data correspond one by one. (4) Repeat each set of data 2 - 3 times and record at least 7 sets of data to finally obtain the result.

[0079] 2. Conductive performance: As a gas diffusion electrode, the gas diffusion layer plays a role in transferring electrons in a fuel cell, and its conductivity is also an aspect we need to investigate. We measure the sheet resistance (R □ ) of the gas diffusion layer to measure its conductive performance.

[0080] In the experiment, a four-probe resistance meter is used. Take out the gas diffusion layer sample, sample at different points, measure 20 points and then take the average value to obtain the sheet resistance (R □ ) of the gas diffusion layer. Since the sheet resistance is also called the film resistance, its magnitude is independent of the sample size, and the unit is ohm / sq. This unit is directly translated as sheet resistance or surface resistance. Therefore, the smaller its value, the faster the electrons transfer within the diffusion layer. The calculation formula for the sheet resistance is: Rs = ρ / t (where ρ is the resistivity of the material and t is the material thickness).

[0081] 3. Battery performance: Assemble the prepared gas diffusion layer into a fuel cell: Coat a microporous layer on the prepared diffusion layer, dry it at 350 °C, then coat a platinum-carbon catalyst, dry it at 105 °C for 2 hours, then place a proton exchange membrane (DuPont) between the anode and cathode, and hot-press it at 130 °C for two minutes to obtain an MEA for encapsulation. Perform performance tests on the obtained fuel cell. At normal temperature and pressure, use an electrochemical workstation to perform linear voltammetry, test the linear sweep curve at a potential of 0 V (relative to the open circuit) - 0.2 V (relative to the reference electrode), and obtain its peak power density.

[0082] Results of performance characterization:

[0083] Observe and compare the pore structures of the cross-sections of the gas diffusion layer carbon papers prepared in Example 1, Example 7, and Comparative Example 1 through an electron microscope.

[0084] Refer to Figure 3a 、 3b 、3c, which are Comparative Example 1, Example 1, and Example 7 respectively. The specific gravity of microcrystalline cellulose added is 0, 3 mg cm -2 and 6 mg cm -2 SEM images of the cross-sections of the gas diffusion layer carbon papers obtained under the conditions. It can be seen that after adding microcrystalline cellulose, the pores in the cross-section of the obtained carbon paper are obviously changed from a dense structure to a structure with obvious pores. Obviously, by increasing the specific gravity of microcrystalline cellulose added, the porosity of the carbon paper can be significantly increased.

[0085] The specific gravity of microcrystalline cellulose added in Comparative Example 1, Example 5, Example 1, Example 6, and Example 7 is 0, 1.5 mg·cm -2 、3 mg·cm -2 、6 mg·cm -2 , and the porosities of the gas diffusion layer carbon papers are 76.5%, 85.2%, 86.4%, 87.5%, and 88.3% respectively. As the amount of microcrystalline cellulose added increases, the porosity changes regularly in a positive direction with the content of microcrystalline cellulose. Therefore, we can control the pore changes by changing the content of microcrystalline cellulose.

[0086] See Table 1 for the comparison of the air permeability, sheet resistance, and battery peak power of different specific gravities of microcrystalline cellulose added in Comparative Example 1, Example 5, Example 1, Example 6, and Example 7. The results show that after adding microcrystalline cellulose to form pores, the air permeability of the carbon paper increases significantly; in terms of electrical conductivity, the sheet resistance of Example 1 and Example 6 increases slightly, but the change is not obvious; in terms of battery performance (at room temperature and pressure), when the added specific gravity is 3 mg·cm -2 (Example 1), there is an optimization of the mass transfer of microcrystalline cellulose, that is, the optimal pore structure can optimize the mass transfer performance of the gas diffusion layer.

[0087] Refer to Figure 4 , the battery performance obtained from the carbon paper prepared by adding microcrystalline cellulose with a specific gravity of 3 mg·cm -2 is compared with that of the carbon paper prepared without adding microcrystalline cellulose. When the added specific gravity is 3 mg·cm -2 , the electrical performance is significantly improved, that is, adding microcrystalline cellulose can significantly improve the battery performance.

[0088] Table 1 Comparison of air permeability, sheet resistance and battery peak power with different addition specific gravities of microcrystalline cellulose

[0089]

[0090] When the addition specific gravity of microcrystalline cellulose is 3 mg·cm -2 , the particle size of microcrystalline cellulose is changed. In Examples 1-4, the particle sizes of the added microcrystalline cellulose are 4 μm, 29 μm, 53 μm and 126 μm respectively. With the change of the particle size of the added microcrystalline cellulose, the pore size of the carbon paper can be adjusted. As the particle size of microcrystalline cellulose increases, the air permeability of the carbon paper increases sharply. Refer to Figure 5 , from 10.5 mL·min -1 ·kPa -1 ·cm -2 at 4 μm to 220 mL·min -1 kPa -1 ·cm -2 at 126 μm at most. As the air permeability increases.

[0091] Furthermore, refer to Figure 6 , for the battery performance comparison between Comparative Example 1 and Example 4 respectively, the battery performance obtained from the carbon paper prepared with microcrystalline cellulose of 126 μm size is also significantly improved, that is, adjusting the size of microcrystalline cellulose can control the pore size inside the carbon paper, thereby changing the gas transmission situation inside it to improve the battery performance.

[0092] In summary, the gas diffusion layer prepared by the present invention meets the requirements of high air permeability and flexibility, and also has good electrochemical performance. Moreover, the preparation method is simple, the porosity is easy to control, the cost is low, and it is suitable for large-scale popularization and production.

[0093] The above are only the preferred embodiments of the present invention, and it does not limit the protection scope of the present invention. For those skilled in the art, the present invention can have various changes and modifications. All changes, modifications, substitutions, integrations and parameter changes made to these embodiments by conventional substitutions or capable of achieving the same functions without departing from the principle and spirit of the present invention fall within the protection scope of the present invention.

Claims

1. A preparation method of a gas diffusion layer with high air permeability and flexibility, characterized in that, Using microcrystalline cellulose as a template, adding carbon paper slurry into the template, draining the water of the carbon paper slurry by vacuum filtration, and then performing heat treatment to obtain the gas diffusion layer; The particle size of the microcrystalline cellulose is selected according to the requirements of the pores in the gas diffusion layer and is configured into a microcrystalline cellulose solution; the microcrystalline cellulose solution is slowly poured onto a filter membrane, and the water of the microcrystalline cellulose is drained by vacuum filtration to form a network structure, and the filter membrane is overlapped with the network structure of the microcrystalline cellulose to obtain the template; The particle size of the microcrystalline cellulose is in the range of 4 to 200 μm; The heat treatment condition is high temperature calcination at 200-500° C. for 10-60 min.

2. The preparation method of the gas diffusion layer with high air permeability and flexibility according to claim 1, wherein The method for preparing a microcrystalline cellulose solution comprises obtaining microcrystalline cellulose of different particle sizes by sedimentation and separation methods, adding a microcrystalline cellulose raw material into water, ultrasonically treating and vibrating the raw material to mix the raw material evenly, and then transferring the raw material into a measuring cylinder, standing the raw material until the microcrystalline cellulose is completely precipitated according to the particle size, taking out the liquid in the measuring cylinder in portions according to the scale with the same interval according to the particle size requirements, controlling the particle size and the particle size range by controlling the standing time and the interval of the sampling scale, centrifuging and stratifying the sample with the particle size to be used, and counting the particle size, so as to finally obtain the microcrystalline cellulose of different particle sizes.

3. The preparation method of the gas diffusion layer with high air permeability and flexibility according to claim 2, wherein The filter membrane is a mixed cellulose filter membrane MCE.

4. The preparation method of the gas diffusion layer with high air permeability and flexibility according to claim 1, characterized in that, The specific gravity of the microcrystalline cellulose poured on the surface of the filter membrane is x mg·cm -2 , where x = (0, 6].

5. The preparation method of the gas diffusion layer with high air permeability and flexibility according to claim 1, characterized in that, The method comprises the following steps: pre-treating the carbon paper slurry, dripping it onto the microcrystalline cellulose mesh structure of the template, allowing the carbon paper slurry to penetrate into the template, draining the water of the carbon paper slurry by vacuum filtration, and then peeling it off from the MCE filter membrane to obtain a carbon paper precursor; and heat-treating the carbon paper precursor to obtain the gas diffusion layer.

6. The preparation method of the gas diffusion layer with high air permeability and flexibility according to claim 5, characterized in that, The pretreatment step of the carbon paper slurry includes adding a hydrophobic agent to the carbon paper slurry and performing ultrasonic treatment for 10 to 30 minutes.

7. The preparation method of the gas diffusion layer with high air permeability and flexibility according to claim 6, characterized in that, The hydrophobic agent is polytetrafluoroethylene.

8. The preparation method of the gas diffusion layer with high air permeability and flexibility according to claim 5, characterized in that, The carbon paper slurry is a mixed slurry of chopped carbon fiber slurry, carbon nanofiber slurry, single-walled carbon nanotube fiber SWCNT slurry and multi-walled carbon nanotube fiber MWCNT slurry.

9. The preparation method of the gas diffusion layer with high air permeability and flexibility according to claim 8, characterized in that, In the carbon paper slurry, the mass ratio of chopped carbon fiber slurry: carbon nanofiber slurry is 4:1; the mass ratio of SWCNT slurry to MWCNT slurry is 1:

1.

10. The preparation method of the gas diffusion layer with high air permeability and flexibility according to claim 8, characterized in that, The chopped carbon fiber slurry, the carbon nanofiber slurry, the SWCNT slurry and the MWCNT slurry were mixed in a mass ratio of 24:6:5:

5.

11. The preparation method of the gas diffusion layer with high air permeability and flexibility according to any one of claims 1-10, characterized in that, The following steps are involved: S1. Preparation of carbon paper slurry; chopped carbon fibers, carbon nanofibers, single-walled carbon nanotube fibers SWCNT and multi-walled carbon nanotube fibers MWCNT are dispersed and mixed according to a proportion, a hydrophobic agent is added, and the carbon paper slurry is obtained by ultrasonic treatment; S2. Preparation of template; The particle size of microcrystalline cellulose is selected according to the need, and a microcrystalline cellulose solution is prepared and then slowly poured onto a filter membrane, and the water of the microcrystalline cellulose solution is drained by vacuum filtration to form a network structure, and the filter membrane is overlapped with the network structure of the microcrystalline cellulose to obtain the template; S3. Preparation of the gas diffusion layer: Slowly drop the carbon paper slurry prepared in S1 onto the template prepared in S2. The carbon paper slurry penetrates into the internal reticular structure of the microcrystalline cellulose. The carbon paper slurry is dried by vacuum filtration. After drying, it is peeled off from the MCE filter membrane and then put into a muffle furnace for heat treatment to remove the microcrystalline cellulose and other impurities, thus obtaining the gas diffusion layer.

12. A gas diffusion layer is prepared by using the preparation method of the gas diffusion layer with high air permeability and flexibility according to any one of claims 1-11.

13. A fuel cell comprises a gas diffusion layer prepared by using the preparation method of the gas diffusion layer with high air permeability and flexibility according to any one of claims 1-11 or the gas diffusion layer according to claim 12.

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