CN117374313B - A gas diffusion layer of a proton exchange membrane fuel cell and its preparation method and application - Google Patents

Abstract

The invention relates to a gas diffusion layer of a proton exchange membrane fuel cell, a preparation method and application thereof. The gas diffusion layer of the invention is composed of a macroporous carbon substrate and a microporous layer. The microporous layer adopts a pore-forming agent to form a porous structure, which is beneficial to the water vapor transmission in the fuel cell. According to the invention, siO ₂ with different diameters is used as a hard template to prepare a series of porous carbon materials with uniform pore diameters, then a chemical grafting method is used to graft hydrophobic silane onto the surface of the porous carbon, and finally the modified materials are uniformly sprayed or knife-coated on a carbon paper substrate by an ultrasonic spraying or knife-coating instrument to form a microporous layer, so that the pore diameters of the microporous layer are uniformly distributed and have good hydrophobicity. According to the invention, porous carbon materials with different apertures are sprayed or scraped in a layered manner, the directional gradient aperture can be formed through simple operation, and compared with the single aperture, the performance of layered samples is obviously improved, the discharge of cathode product water is facilitated, the water vapor transmission can be effectively enhanced, and the battery performance is improved.

Description

A gas diffusion layer of a proton exchange membrane fuel cell and its preparation method and application

Technical Field

The present invention relates to the technical field of fuel cells, and in particular to a gas diffusion layer of a proton exchange membrane fuel cell and a preparation method and application thereof.

Background Art

One of the core components of the proton exchange membrane fuel cell (PEMFC) is the membrane electrode, which consists of a proton exchange membrane (PEM), a catalyst layer (CL) and a gas diffusion layer (GDL) with a microporous layer (MPL). The gas diffusion layer is located between the catalyst layer and the gas flow field, supporting the catalyst layer and collecting current. It is also a necessary transmission channel for the reaction gas and product water. Its specific function is to evenly distribute the reaction gas to the surface of the catalyst layer and discharge the reaction product liquid water. During the operation of PEMFC, on the one hand, a certain amount of water must be maintained to improve the wettability of the proton exchange membrane and reduce the ohmic overpotential of the membrane; on the other hand, excessive liquid water content will cause liquid water to occupy the pores of the gas diffusion layer and cover the surface of the catalyst, greatly increasing the transmission resistance of the reaction gas, causing the electrode "flooding" phenomenon, and causing serious concentration polarization losses. In order to improve the mass transfer of reaction gas and liquid water in GDL, carbon paper or carbon cloth is usually treated with hydrophobicity to construct a hydrophobic gas phase channel. At the same time, a microporous layer (MPL) made of a physical mixture of conductive carbon black and polytetrafluoroethylene (PTFE) is added between the carbon paper or carbon cloth and the catalyst layer to improve the water-gas transport in PEMFC. Pore-forming agents are usually used to regulate the pore size of MPL, such as high-temperature decomposition type (NH ₄ ) ₂ CO ₃ and (NH ₄ ) C ₂ O ₄ , dissolved CaCO ₃ , Li ₂ CO ₃ , NaCl and NH ₄ NO ₃ , etc. These pore-forming agents are simple to use, can form through holes and are easy to remove.

The traditional method uses porous carbon powder and PTFE to physically mix to prepare MPL, which can easily affect the pore size distribution and even cause partial pore blockage. At the same time, PTFE needs to be heat treated at around 350°C to make it melt, which increases the production cost to a certain extent, and the water resistance also needs to be improved. Studies have shown that the use of pore-forming agents to prepare MPL with graded porosity and multi-pore size distribution can improve the water management ability of fuel cells. At the same time, under a certain hydrophobicity, the directional gradient pore size can generate additional driving force from small pores to large pores, accelerate the discharge rate of product water, and significantly improve the battery performance under high current density. Therefore, it is of great significance to develop a new microporous layer preparation process to improve stability and mass transfer efficiency.

Summary of the invention

In order to solve the above technical problems, the present invention provides a gas diffusion layer of a proton exchange membrane fuel cell and a preparation method and application thereof, specifically a gradient pore microporous layer for a proton exchange membrane fuel cell and a preparation method and application thereof. The present invention uses sucrose, glucose, fructose, flour, biomass, resin, etc. as carbon sources, adopts _SiO2 template method to prepare a series of porous carbon materials, adopts chemical grafting method to uniformly graft molecular hydrophobic agent on the surface of the material, and sprays or scrapes it on the carbon substrate in a certain order to prepare the microporous layer in the gas diffusion layer.

The present invention is achieved through the following technical solutions:

The first object of the present invention is to provide a gas diffusion layer of a proton exchange membrane fuel cell, comprising a substrate, a silane-modified porous carbon material and a binder; the silane-modified porous carbon material is composed of silane-modified porous carbon materials with different pore sizes, and the silane-modified porous carbon materials are layered and coated on the substrate in descending order of pore size. In the present invention, the pore size of the silane-modified porous carbon material is controllable and uniform, and has strong water scouring resistance.

In one embodiment of the present invention, the size of the pore is 20nm-400nm; for example, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm.

In one embodiment of the present invention, the silane-modified porous carbon material is prepared by the following method:

(1) Preparation of porous carbon materials using _SiO2 template method;

(2) performing a hydroxylation treatment on the surface of the obtained porous carbon material to obtain a carbon material with hydroxyl groups on the surface;

(3) The obtained carbon material with hydroxyl groups on the surface is mixed with a dispersant and silane, and heated and stirred to obtain a silane-modified porous carbon material.

In one embodiment of the present invention, in step (1), the carbon source for preparing the porous carbon material is selected from one or more of sucrose, glucose, fructose, flour, biomass and resin.

In one embodiment of the present invention, in step (2), the hydroxylation treatment method is to hydroxylate the material with Fenton's reagent, specifically, to treat the porous carbon material with a certain concentration of hydrogen peroxide solution and iron salt to obtain a hydroxylated carbon material. Wherein, the ratio of iron salt, hydrogen peroxide and porous carbon material is (0.5-1) g: 30 mL: (0.1-0.2) g. Alternatively, the hydroxylation treatment method is to treat the carbon material with a strong oxidant, typically concentrated nitric acid or potassium permanganate; specifically, 1 g of carbon material is dispersed in (50-150) mL of 65% nitric acid solution, refluxed and stirred at 80°C for 4h-8h, then washed with deionized water for multiple times, and dried to obtain the carbon material with hydroxyls on the surface.

In one embodiment of the present invention, in step (3), the silane is selected from one or more of vinyl silanes, chloroalkyl silanes, aminoalkyl silanes, epoxyalkyl silanes, methacryloxyalkyl silanes, sulfur-containing hydrocarbon silanes, pseudohalogen silanes and alkane silanes.

In one embodiment of the present invention, in step (3), the dispersant is selected from one or more of isopropanol, ethanol and deionized water; the stoichiometric ratio of the carbon material with hydroxyl groups on the surface, silane and the dispersant is 1g: (5-10)mL: 50mL.

In one embodiment of the present invention, the substrate is selected from carbon paper and/or carbon cloth.

In one embodiment of the present invention, the binder is selected from one or more of Nafion solution, PTFE and PVDF.

The second object of the present invention is to provide a method for preparing a gas diffusion layer of a proton exchange membrane fuel cell, comprising the following steps:

The silane-modified porous carbon materials with different pore sizes are mixed with a dispersant and a binder respectively to obtain microporous layer slurries with different pore sizes;

The obtained microporous layer slurry with different pore diameters is sprayed or scraped on the substrate in order of pore diameter from large to small, and the gas diffusion layer of the proton exchange membrane fuel cell is obtained after drying.

In one embodiment of the present invention, the dispersant is selected from one or more of isopropanol, ethanol and deionized water; the ratio of the silane-modified porous carbon material, the dispersant and the adhesive is (0.1-0.2) g: 10 mL: (0.1-0.2) mL.

In one embodiment of the present invention, the loading amount of the microporous layer carbon material on the substrate is 0.5 mg/cm ² -2.0 mg/cm ² ; the mass of the hydrophobic agent in the microporous layer slurry accounts for 1% -20% of the carbon material.

The third object of the present invention is to provide the use of the gas diffusion layer of the proton exchange membrane fuel cell in the preparation of the fuel cell membrane electrode.

The above technical solution of the present invention has the following advantages compared with the prior art:

1. The gas diffusion layer of the present invention is composed of a macroporous carbon substrate and a microporous layer. The microporous layer usually uses a pore-forming agent to form a porous structure. Studies have shown that this structure is conducive to water vapor transmission in fuel cells. The present invention first uses _SiO2 of different diameters as a hard template to prepare a series of porous carbon materials with uniform pore sizes; the porous carbon materials prepared in the present invention have uniform and controllable pore sizes, and the combination of different pore sizes is conducive to quantitative analysis of the effect of pore size on fuel cell performance.

2. The present invention adopts a chemical grafting method to graft hydrophobic silane onto the porous carbon surface, and finally the modified material is evenly sprayed or scraped onto the carbon paper substrate by ultrasonic spraying or scraping to form a microporous layer. This method avoids the influence of high-temperature heat treatment on the carbon material and improves the hydrophobic stability of the material by chemically grafting the hydrophobic agent.

3. The present invention adopts layered spraying or scraping of porous carbon materials with different pore sizes, and a directional gradient pore size can be formed through simple operation. Compared with a single pore size, the performance of the directional gradient pore size sample is significantly improved. Studies have shown that the directional gradient pore size is more conducive to the discharge of cathode product water, which can effectively enhance water vapor transmission and improve battery performance.

4. The preparation method of the present invention can avoid the pore blocking phenomenon similar to the traditional PTFE physical mixing and coating.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein

FIG1 is a cross-sectional schematic diagram of Embodiment 1 of the present invention;

Figure 2 is a scanning electron microscope image of the porous carbon materials in Comparative Example 1, Comparative Example 2, Comparative Example 3, Comparative Example 4, Comparative Example 5, and Comparative Example 6; wherein a is a porous carbon with a pore size of 20 nm (Comparative Example 1), b is a porous carbon with a pore size of 60 nm (Comparative Example 2), c is a porous carbon with a pore size of 100 nm (Comparative Example 3), d is a porous carbon with a pore size of 200 nm (Comparative Example 4), e is a porous carbon with a pore size of 400 nm (Comparative Example 5), and f is a porous carbon with a mixed pore size of 100 nm, 200 nm, and 400 nm (Comparative Example 6);

FIG3 is a scanning electron microscope image of Comparative Example 5 of the present invention before and after chemical modification; wherein a is porous carbon without hydrophobic modification; b is porous carbon after hydrophobic modification;

FIG4 is an infrared comparison diagram of porous carbon before and after chemical modification in Comparative Example 5 of the present invention;

FIG5 is a comparison diagram of the contact angles of the microporous layer obtained before and after chemical modification in Comparative Example 5 of the present invention; wherein a and b are the contact angles of the non-hydrophobic modified material tested at 0 seconds and 30 seconds, respectively; c and d are the contact angles of the hydrophobic modified material tested at 0 seconds and 30 seconds, respectively;

6 is a performance curve comparison diagram of a fuel cell assembled with a cathode gas diffusion layer prepared in Example 1 of the present invention and a fuel cell assembled with a cathode gas diffusion layer prepared in Comparative Example 1;

7 is a performance curve comparison diagram of a fuel cell assembled with a cathode gas diffusion layer prepared in Example 2 of the present invention and a fuel cell assembled with a cathode gas diffusion layer prepared in Comparative Example 2;

8 is a performance curve comparison diagram of a fuel cell assembled with a cathode gas diffusion layer prepared in Example 3 of the present invention and a fuel cell assembled with a cathode gas diffusion layer prepared in Comparative Example 3;

9 is a performance curve comparison diagram of a fuel cell assembled with a cathode gas diffusion layer prepared in Example 3 of the present invention and a fuel cell assembled with a cathode gas diffusion layer prepared in Comparative Example 4;

10 is a performance curve comparison diagram of a fuel cell assembled with a cathode gas diffusion layer prepared in Example 3 of the present invention and a fuel cell assembled with a cathode gas diffusion layer prepared in Comparative Example 5;

11 is a performance curve comparison diagram of a fuel cell assembled with a cathode gas diffusion layer prepared in Example 3 of the present invention and a fuel cell assembled with a cathode gas diffusion layer prepared in Comparative Example 6;

12 is a performance curve comparison diagram of a fuel cell assembled with a cathode gas diffusion layer prepared in Example 2 of the present invention and a fuel cell assembled with a cathode gas diffusion layer prepared in Comparative Example 7;

13 is a comparison chart of the performance curves of fuel cells assembled with cathode gas diffusion layers prepared in Example 1, Example 2, Example 3, and Example 4 of the present invention.

DETAILED DESCRIPTION

The gas diffusion layer of the proton exchange membrane fuel cell plays the role of transmitting reaction gases, conducting heat, and mechanically supporting the membrane electrode and the timely discharge of product water. Therefore, it is of great significance to explore the appropriate pore size in water management. The present invention adopts the _SiO2 template method to prepare a series of porous carbon materials with uniform pore size, and at the same time adopts the chemical grafting method to graft the hydrophobic agent to the surface of the carbon material through chemical bonds, and then sprays or scrapes the carbon materials with different pore sizes on the carbon substrate in a certain order to form a composite microporous layer in the gas diffusion layer. The porous carbon material prepared in the present invention has uniform pore size, which is conducive to the qualitative analysis of the influence of directional gradient pore size distribution on the performance of fuel cells.

As an example, the method for preparing the gas diffusion layer of the proton exchange membrane fuel cell disclosed in the present invention is as follows:

1) Using _SiO2 hard template method, one or more of glucose, sucrose, fructose, biomass, flour, resin, etc. are used as carbon source, one or more of deionized water and ethanol are used as dispersant, the mass ratio of _SiO2 , carbon source, and dispersant is (0.5-2):1:50, stirring and ultrasonicating for several hours, then placing in a 60℃ forced air oven to slowly dry for several hours, and then calcining at 800℃ to carbonize it, and a series of porous carbon materials are obtained by changing _SiO2 with different diameters;

2) _SiO2 was removed by conventional HF etching method, with HF and deionized water as dispersants, the mass ratio of carbon material to dispersant being (0.1-0.5):50, stirring for several hours, and centrifugation washing several times to obtain a porous carbon material with uniform pore size.

3) The surface of the porous carbon material is hydroxylated to make it have functional groups such as -OH on the surface. The dispersant is one or more of deionized water, ethanol, methanol or isopropanol, and FeCl ₂ ·4H ₂ O or FeSO ₄ ·6H ₂ O is used as a catalyst. A 0.1M hydrochloric acid solution is used to adjust the pH of the dispersant to 3-4, and a 30wt% H ₂ O ₂ solution is diluted in a ratio of 1:3 and added dropwise, stirred at room temperature for 2h-3h, filtered, washed and dried to obtain a porous carbon material with a large number of functional groups such as hydroxyl groups on the surface. The mass ratio of carbon powder, dispersant and catalyst is (0.1-0.5):(20-50):(0.5-1).

4) dispersing the hydroxylated carbon material in a mixed solution of deionized water and ethanol or ethylene glycol or isopropanol, wherein the mass ratio of the material, water and alcohol is (0.1-0.5):5:(25-50), and adding acetic acid or 0.1M hydrochloric acid solution to adjust the pH of the solution to 4-5;

5) Add silane to the above solution, the mass ratio of carbon material to silane is 1:(1-5), the water bath temperature is controlled at 50°C-70°C, the speed is set to 300rpm, and mechanical stirring is performed for 1h-6h, and then centrifugally filtered and washed with water and ethanol for several times, and the obtained silane-modified porous carbon material is placed in a 60°C oven to dry for standby use;

6) dispersing the prepared silane-modified porous carbon material in one or more mixed solutions of isopropanol, ethanol or water, adding a binder Nafion, wherein the content of Nafion accounts for 1wt%-20wt% of the carbon material, and ultrasonically dispersing for 2h-8h to form a microporous layer slurry;

7) The microporous layer slurry is composited onto the carbon paper substrate by spraying or blade coating, dried and weighed, and then the steps are repeated until the carbon loading reaches 0.5 mg/cm ² -2.0 mg/cm ² , finally obtaining the gas diffusion layer of the proton exchange membrane fuel cell.

8) Test method: The prepared gas diffusion layer was used as the cathode gas diffusion layer, and assembled with a commercial membrane electrode (Pt content of 20 wt%) and a commercial anode gas diffusion layer into a fuel cell for testing. The cell was operated at a temperature of 80°C, 40% relative humidity, a stoichiometric ratio of _H2 to air of 1.5:3, a back pressure of 1 atm, and a test area of 25 ^cm2 . The test was conducted using a fuel cell test system made in the United States (Scribner Associates, Inc, 850 Fuel Cell Test System).

In order to facilitate the understanding of the present invention, the present invention lists the following embodiments. Those skilled in the art should understand that the examples are only to help understand the present invention, and the present invention is not limited to the scope of the examples. The raw materials involved in the present invention are all conventional products for batteries, and the specific preparation operations and testing methods are all conventional methods.

All the batteries in the following examples and comparative examples have the same components except for the cathode gas diffusion layer.

Spherical _SiO2 with uniform diameter refers to the ready-made synthesis scheme, and the specific operation is as follows:

20nm _SiO2 : 14.5mL dodecane, 139mL deionized water, 0.146g lysine were fully stirred, then 11.5mL tetraethyl orthosilicate (TEOS) was added, heated and stirred at 60℃ for 24h, then placed in a 100℃ oven for 20h, then placed in a tube furnace and heated to 600℃ at a rate of 2℃/min and annealed in air atmosphere for 3h.

60nm _SiO2 : 100mL ethanol, 10mL deionized water, 2.74mL ammonia water were fully stirred, then 2.5mL tetraethyl orthosilicate (TEOS) was added, stirred at 300rpm for 4h at room temperature, centrifuged at high speed, then washed with deionized water for several times, and dried in a 60℃ forced air oven for use.

100nm _SiO2 : 25mL ethanol, 25mL deionized water, 4mL ammonia water were stirred evenly, then 1mL tetraethyl orthosilicate (TEOS) was added, stirred at 300rpm for 7h at room temperature, centrifuged at high speed, then washed with deionized water for several times, and dried in a 60℃ forced air oven for use.

200nm SiO ₂ : 50mL ethanol, 4mL ammonia water were fully stirred, then 1mL tetraethyl orthosilicate was added, stirred at 300rpm for 7h at room temperature, centrifuged at high speed, then washed with deionized water for several times, and dried in a 60°C forced air oven for use.

400nm SiO ₂ : 65mL ethanol, 14.7mL deionized water, 80mL ammonia water were fully stirred, then 6.94mL tetraethyl orthosilicate was added, stirred at 300rpm for 4h at room temperature, centrifuged at high speed, then washed with deionized water for several times, and dried in a 60°C forced air oven for use.

(a) Initial porous material synthesis:

Weigh 1.25g _SiO2 (one of the diameters of 20nm, 60nm, 100nm, 200nm, and 400nm), 1g glucose, disperse in 30mL deionized water and 10mL ethanol, ultrasonicate for 1h, stir for 1h, alternate several times, until _SiO2 is fully dispersed in the solution. Let stand for 24h, then transfer to a 60℃ oven, slowly dry the dispersant to form a tightly packed cake-like mixture of glucose and _SiO2 . Then, put the obtained product into a 800℃ tube furnace and anneal at a heating rate of 5℃/min for 2 hours in a nitrogen atmosphere. Disperse the carbonized material in 20mL HF and 30mL deionized water, stir at a constant speed for more than 6h, and finally, wash it with water and ethanol by centrifugation several times until the solution is neutral, put it in a 60℃ oven to dry for standby use, and obtain the initial porous carbon material. The scanning electron microscope image corresponding to each pore size material is shown in Figure 2. It can be seen from Figure 2 that the pore size distribution of the initial porous carbon material prepared by the present invention is uniform and controllable.

(b) Preparation of hydroxylated porous carbon materials:

Weigh 0.2g of the initial porous carbon material and disperse it in 40mL of deionized water. Adjust the pH to about 3.5 with 0.1M hydrochloric acid solution, stir and heat to 35°C. Then weigh 0.98g of _FeCl2 · _4H2O and add it to the dispersion, and ultrasonicate for 30min to completely dissolve it. Dilute 30wt% hydrogen peroxide solution with deionized water in a volume ratio of 1:3. Take 100mL of the diluted hydrogen peroxide solution and add it dropwise to the above dispersion through a separatory funnel and react for 2h. Filter and wash the reaction product with 0.1M hydrochloric acid solution to remove the residual iron ions in the product, and then wash it with a large amount of deionized water until it is neutral. Finally, the obtained hydroxylated carbon material is placed in a vacuum oven at 40°C and dried for 24h.

(c) Preparation of silane-modified porous carbon materials:

Weigh 0.2g of hydroxylated carbon material and disperse it in a mixed solution of 45mL ethanol and 5mL deionized water, and ultrasonically disperse it for 30min. Adjust the pH to about 4.5 with 0.1M hydrochloric acid solution, add 1mL perfluorotrimethoxysilane, stir in a water bath at 60℃ for 4h, filter and wash the product with water and ethanol several times, and then put it in a 60℃ oven to dry to obtain a silane-modified porous carbon material. The scanning electron microscope image of the carbon material is shown in Figure 3. It can be seen from Figure 3 that the chemical grafting hydrophobic modification retains the initial structure well. The Fourier transform infrared spectroscopy (FTIR) results of the carbon material are shown in Figure 4. From Figure 4, it can be seen that the peaks of the silane-modified porous carbon material at 1239.69 cm ^-1 and 1208.05 cm ^-1 are fluorine-containing functional groups, the peak at 1150.03 cm ^-1 is the Si-OC bond, and the peaks at 1068.28 cm ^-1 and 964.98 cm ^-1 are the Si-O bonds. These results indicate that silane is successfully grafted onto the porous carbon material.

(d) Preparation of microporous layer slurry and spraying or scraping:

0.1g of silane-modified porous carbon material and 0.1g of Nafion solution (5wt%) were weighed and dispersed in 10mL of isopropanol solution, and ultrasonic dispersion was performed for a total of 8h to form a uniform microporous layer slurry. The microporous layer slurry was sprayed or scraped on a carbon paper substrate using an ultrasonic spray or scraper, and dried at 80°C to obtain a gas diffusion layer, wherein the porous carbon material loading was 1.0mg/ ^cm2 . The contact angle of the obtained gas diffusion layer was 148° as shown in FIG5, showing super-hydrophobic characteristics, while the contact angle of the surface without surface hydrophobic treatment was only about 85°, which decreased to 0° after 30 seconds.

Example 1

Weigh the same mass of hydrophobic porous carbon materials with pore sizes of 20nm, 60nm, and 100nm, respectively, prepare slurries according to the above steps, and spray or scrape the slurries of 100nm, 60nm, and 20nm on the surface of carbon paper in turn, so as to obtain directional gradient graded pores with pore sizes from large pores to catalyst layers. The carbon loading is accurately weighed and calculated to reach 1mg/ ^cm2 . The cross section of the sample can be clearly shown in Figure 1. The actual thickness of each microporous layer is about several microns, and the actual thickness of the carbon paper is about 190μm. The prepared gas diffusion layer is used as the cathode gas diffusion layer, and is assembled into a fuel cell with a commercial membrane electrode (Pt content is 20wt%) and a commercial anode gas diffusion layer for testing. The battery is operated at a temperature of 80℃, a relative humidity of 40%, a stoichiometric ratio of _H2 and air of 1.5:3, and a back pressure of 1atm, and the test area is ^25cm2 . The test was conducted using a fuel cell test system made in the United States (Scribner Associates, Inc, 850 Fuel Cell Test System). As shown in FIG6 , the peak output power of the battery was 1054.59 mW/cm ² .

Example 2

Weigh the same mass of hydrophobic porous carbon materials with pore sizes of 60nm, 100nm, and 200nm, respectively, prepare slurries according to the above steps, and spray or scrape the slurries of 200nm, 100nm, and 60nm on the surface of carbon paper in sequence to obtain directional gradient graded pores with pore sizes from large pores to small pores in the catalytic layer. The subsequent steps are consistent with Example 1. As shown in Figure 7, the peak output power of the battery is 1288.95mW/ ^cm2 .

Example 3

Weigh the same mass of hydrophobic porous carbon materials with pore sizes of 100nm, 200nm, and 400nm, respectively, prepare slurries according to the above steps, and spray or scrape the slurries of 400nm, 200nm, and 100nm on the surface of carbon paper in turn to obtain directional gradient graded pores with pore sizes from large pores to small pores in the catalytic layer. The subsequent steps are consistent with Example 1. As shown in Figure 8, the peak output power of the battery is 1242.69mW/ ^cm2 .

Example 4

Weigh the same mass of hydrophobic porous carbon materials with pore sizes of 20nm, 60nm, 100nm, 200nm, and 400nm, respectively, prepare slurries according to the above steps, and spray or scrape the slurries of 400nm, 200nm, 100nm, 60nm, and 20nm on the surface of carbon paper in sequence to obtain directional gradient graded pores with pore sizes from large pores to small pores from the macroporous diffusion substrate to the catalytic layer. The subsequent steps are consistent with Example 1. As shown in Figure 13, the peak output power of the battery is 1113.18mW/ ^cm2 .

Comparative Example 1

Weigh a hydrophobic porous carbon material with a pore size of 20 nm, prepare a slurry according to the above steps, spray or scrape a 20 nm slurry on the surface of carbon paper, and accurately weigh and calculate that the carbon loading reaches 1 mg/cm ² . The test conditions are the same as those in Example 1. As shown in FIG6 , the peak output power of the battery is 980.93 mW/cm ² .

Comparative Example 2

Weigh a hydrophobic porous carbon material with a pore size of 60 nm, prepare a slurry according to the above steps, spray or scrape the 60 nm slurry on the surface of carbon paper, and accurately weigh and calculate the carbon loading to reach 1 mg/cm ² . The test conditions are consistent with Example 1. As shown in Figure 7, the peak output power of the battery is 981.06 mW/cm ² .

Comparative Example 3

Weigh a hydrophobic porous carbon material with a pore size of 100 nm, prepare a slurry according to the above steps, spray or scrape a 100 nm slurry on the surface of carbon paper, and accurately weigh and calculate the carbon loading to reach 1 mg/cm ² . The test conditions are the same as those in Example 1. As shown in FIG8 , the peak output power of the battery is 1070.45 mW/cm ² .

Comparative Example 4

Weigh a hydrophobic porous carbon material with a pore size of 200 nm, prepare a slurry according to the above steps, spray or scrape a 200 nm slurry on the surface of carbon paper, and accurately weigh and calculate the carbon loading to reach 1 mg/cm ² . The test conditions are the same as those in Example 1. As shown in FIG9 , the peak output power of the battery is 1124.81 mW/cm ² .

Comparative Example 5

Weigh a hydrophobic porous carbon material with a pore size of 400nm, prepare a slurry according to the above steps, spray or scrape the slurry of 400nm on the surface of carbon paper, and accurately weigh and calculate the carbon loading to reach 1mg/ ^cm2 . The test conditions are consistent with Example 1. As shown in Figure 10, the peak output power of the battery is 1071.56mW/ ^cm2 .

Comparative Example 6

Weigh 0.4g 100nm SiO ₂ , 0.4g 200nm SiO ₂ , 0.45g 400nm SiO ₂ , 1g glucose, add 30mL deionized water and 10mL ethanol, ultrasonicate for 1h, stir for 1h, alternate several times, until SiO ₂ is fully dispersed in the solution. Let it stand for 24h, then transfer it to a 60℃ oven, slowly dry the dispersant until a thin and hard cake-like mixture of glucose and SiO ₂ is formed. Then, put the obtained product into a 800℃ tube furnace and anneal it at a heating rate of 5℃/min for 2 hours under a nitrogen atmosphere. Disperse the carbonized material in 20mL HF and 30mL deionized water, stir at a constant speed for more than 6h, and finally, centrifuge and wash it with ethanol and water several times until the solution is neutral, put it in a 60℃ oven to dry for use, and the scanning electron microscope image is shown in Figure 2. Hydroxylation, hydrophobization, and spraying or scraping work are consistent with the above.

Weigh a mixture of hydrophobic porous carbon materials with pore sizes of 100 nm, 200 nm, and 400 nm, prepare a slurry according to the above steps, spray or scrape the slurry on the surface of carbon paper, and accurately weigh and calculate the carbon loading to reach 1 mg/cm ² . The test conditions are consistent with those in Example 1. As shown in FIG11 , the peak output power of the battery is 1171.77 mW/cm ² .

Comparative Example 7

Weigh the same mass of hydrophobic porous carbon materials with pore sizes of 20nm, 60nm, and 100nm, respectively, prepare slurries according to the above steps, and spray or scrape the slurries of 20nm, 60nm, and 100nm on the surface of carbon paper in sequence to obtain directional gradient graded pores with pore sizes from large pore diffusion substrate to catalytic layer from small to large. Accurately weigh and calculate the carbon loading to reach 1mg/ ^cm2 . The test conditions are consistent with Example 1. As shown in Figure 12, the peak output power of the battery is 969.78mW/ ^cm2 .

The present invention successfully prepares porous carbon materials with uniform pore size by using _SiO2 sacrificial template with controllable diameter, grafts hydrophobic silane substances by chemical grafting to achieve super-hydrophobic effect, well retains the original pore structure, and composites the material with a carbon substrate by ultrasonic spraying or scraping. At the same time, materials with different pore sizes are sprayed or scraped in sequence to achieve the purpose of directional gradient, thereby successfully enhancing battery performance.

The present invention belongs to the technical field of fuel cells, and specifically discloses a method for preparing a microporous layer in a gas diffusion layer and its application in a proton exchange membrane fuel cell. A controllable and uniform porous carbon material is prepared by a _SiO2 template method, hydrophobic silane is grafted onto the surface by a chemical grafting method, and then the silane-modified porous carbon material is prepared into a slurry, and a microporous layer for a fuel cell is formed by composite on a carbon paper substrate by ultrasonic spraying or scraping. The fuel cell gas diffusion layer disclosed by the present invention has the following advantages: a series of porous carbon materials with uniform pore sizes are prepared by a _SiO2 template method, and hydrophobic silane is grafted onto the surface of the carbon material by chemical bonds by a chemical grafting method to achieve a stable hydrophobic effect, thereby constructing a more stable microporous layer. The gas diffusion layer prepared by the above method can effectively promote water vapor transmission at the three-phase interface, improve the output power of the fuel cell, and open up a promising way to explain the influence of directional gradient pore size on the performance of the fuel cell and the water vapor transmission mechanism.

Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims (10)

1. A gas diffusion layer of a proton exchange membrane fuel cell, comprising a substrate, a silane modified porous carbon material and a binder; the silane modified porous carbon material is prepared by preparing a series of porous carbon materials with uniform pore diameters by adopting a SiO ₂ template method, and then grafting a hydrophobic agent on the surface of the carbon material by adopting a chemical grafting method; the silane modified porous carbon material is sequentially coated on the substrate layer by layer according to the sequence of the pore diameters from large to small.

2. The gas diffusion layer of claim 1, wherein the pore size is from 20 nm to 400 nm.

3. The gas diffusion layer of claim 1, wherein the silane modified porous carbon material is prepared by:

(1) Preparing a porous carbon material by adopting a SiO ₂ template method;

(2) Hydroxylation treatment is carried out on the surface of the obtained porous carbon material, so that the carbon material with hydroxyl on the surface is obtained;

(3) And mixing the obtained carbon material with the hydroxyl on the surface, the dispersing agent and the silane, and heating and stirring to obtain the silane modified porous carbon material.

4. A gas diffusion layer according to claim 3, wherein in step (1), the carbon source from which the porous carbon material is made is selected from one or more of sucrose, glucose, fructose, flour, biomass and resins.

5. A gas diffusion layer according to claim 3, wherein in step (3) the silane is selected from one or more of vinyl-based silanes, chlorohydrocarbyl-based silanes, aminoalkyl-based silanes, epoxyhydrocarbyl-based silanes, methacryloxyalkyl-based silanes, sulphur-containing hydrocarbyl-based silanes, pseudohalogen-based silanes and alkane-based silanes.

6. A gas diffusion layer according to claim 3, wherein in step (3), the dispersing agent is selected from one or more of isopropanol, ethanol and deionized water; the metering ratio of the carbon material with the hydroxyl on the surface, the silane and the dispersing agent is 1 g: (5-10) mL:50 And (3) mL.

7. The gas diffusion layer according to claim 1, wherein the substrate is selected from carbon paper and/or carbon cloth.

8. A method for preparing a gas diffusion layer of a proton exchange membrane fuel cell, comprising the steps of:

Respectively mixing silane modified porous carbon materials with different pore diameters with a dispersing agent and a binder to obtain microporous layer slurry with different pore diameters; the silane modified porous carbon material is prepared by preparing a series of porous carbon materials with uniform pore diameters by adopting a SiO ₂ template method, and then grafting a hydrophobic agent on the surface of the carbon material by adopting a chemical grafting method;

And sequentially spraying or knife-coating the obtained microporous layer slurry with different pore diameters on a substrate according to the sequence from large pore diameters to small pore diameters, and drying to obtain the gas diffusion layer of the proton exchange membrane fuel cell.

9. The method of claim 8, wherein the dispersant is selected from one or more of isopropanol, ethanol, and deionized water; the ratio of the silane modified porous carbon material, the dispersing agent and the adhesive is (0.1-0.2) g:10 mL: (0.1-0.2) mL.

10. Use of a gas diffusion layer of a proton exchange membrane fuel cell according to any one of claims 1 to 7 for the preparation of a fuel cell membrane electrode.