阅读说明：本技术 一种气体扩散层的制备方法 (Preparation method of gas diffusion layer ) 是由 刘冬安 关春红 张运搏 漆海龙 苏金权 于 2021-09-08 设计创作，主要内容包括：本发明公开了一种气体扩散层的制备方法,属于燃料电池的技术领域。所述气体扩散层中基材层的制备方法为将疏水性靶材通过磁控溅射的方法转移到导电多孔基材上。通过磁控溅射方法溅射聚四氟乙烯在导电多孔基材表面,能够在以少量的聚四氟乙烯达到很好的疏水性能。由于聚四氟乙烯含量少,因此对导电率和透气率的影响不大,适合用于燃料电池的气体扩散层。(The invention discloses a preparation method of a gas diffusion layer, and belongs to the technical field of fuel cells. The preparation method of the base material layer in the gas diffusion layer is to transfer the hydrophobic target material to the conductive porous base material by a magnetron sputtering method. The polytetrafluoroethylene is sputtered on the surface of the conductive porous substrate by a magnetron sputtering method, so that good hydrophobic property can be achieved by using a small amount of polytetrafluoroethylene. Since the polytetrafluoroethylene content is small, the influence on the electrical conductivity and the air permeability is not large, and the polytetrafluoroethylene is suitable for a gas diffusion layer of a fuel cell.)

1. The preparation method of the gas diffusion layer comprises a substrate layer and a preparation method of a microporous layer, and is characterized in that the preparation method of the substrate layer is to transfer a hydrophobic target material to a conductive porous substrate by a magnetron sputtering method.

2. The preparation method according to claim 1, wherein the mass of the hydrophobic target material is 2-6% of the mass of the conductive porous substrate.

3. The production method according to claim 1, wherein the conductive porous substrate is carbon paper or carbon cloth composed of carbon fibers; the hydrophobic target material is polytetrafluoroethylene.

4. The method according to claim 1, wherein the method for preparing the substrate layer specifically comprises the steps of:

s1, placing the conductive porous substrate in a magnetron sputtering instrument, vacuumizing and setting the pressure to be 1 x 10^-6~2×10^-3Pa，

S2, introducing inert gas and reaction gas, wherein the working pressure is 0.5-2.0 Pa;

s3, heating to enable the temperature of the conductive porous base material to be 25-300 ℃;

s4, adopting magnetron sputtering to sputter the hydrophobic target material on the conductive porous substrate to form a film, wherein the sputtering conditions are as follows: the sputtering power is 10-100W, and the sputtering time is 15-60 minutes.

5. The method of claim 4, wherein the inert gas is argon; the reaction gas is carbon tetrafluoride.

6. The method according to claim 5, wherein the volume ratio of the inert gas to the reaction gas is 10: 1-100: 1, said pressure is 2 x 10^-5~6×10^-5Pa。

7. The method according to claim 6, wherein the volume ratio of the inert gas to the reaction gas is 20: 1-50: 1, said pressure is 4X 10^-5Pa。

8. The method according to claim 7, wherein the volume of the inert gas and the reaction gas is 30: 1.

9. the method of claim 5, wherein the temperature of the electrically conductive porous substrate is 60 ℃ to 250 ℃; the working air pressure is 1-1.5 Pa; the sputtering power is 10-100W, and the sputtering time is 20-50 minutes.

10. The method of claim 9, wherein the temperature of the electrically conductive porous substrate is 150 ℃; the working air pressure is 1.2 Pa; the sputtering power is 40W, and the sputtering time is 35 minutes.

Technical Field

The invention belongs to the technical field of fuel cells, and particularly relates to a preparation method of a gas diffusion layer of a fuel cell.

Background

The fuel cell directly converts chemical energy stored in fuel (such as hydrogen, natural gas and the like) and oxidant (such as air, oxygen) into electric energy through electrochemical reaction, and is a high-efficiency and environment-friendly power generation device. The PEMFC has the advantages of quick start, low working temperature, no noise, no pollution and the like, and has wide application prospect in automobiles, household residences, small and medium-sized power stations and portable devices. The main body of a typical proton exchange membrane fuel cell is a repetition of bipolar plates, Membrane Electrode Assemblies (MEAs) and corresponding sealing elements, and the outermost sides are end plates. The membrane electrode assembly is generally prepared from a gas diffusion layer, a catalyst layer and a proton exchange membrane by a hot-pressing process.

The Gas Diffusion Layer (GDL) is composed of two parts, namely a substrate layer (GDB) and a microporous layer (MPL). The substrate layer is the main body skeleton of gas diffusion layer, and different GDB raw materials have multiple different pore structure. The transmission structure of the gas diffusion layer is mainly used for uniform conduction and water management of reaction gas and is jointly borne by GDB and MPL, and the GDB layer is built by a pore structure generated by overlapping carbon fibers of a base body. The gas diffusion layer is made of an electric-conductive and heat-conductive porous material, plays a role in supporting the catalyst layer, collecting current, conducting reaction gas, discharging water and the like, realizes redistribution of the reaction gas and product water between the flow field and the catalyst layer, and is one of key components influencing the performance of the electrode. Due to the electrochemical reaction of the fuel gas and the oxidant gas, a large amount of water (water vapor) is generated at a large current density. If the water vapor condenses into water drops at low temperature, the pores of the gas diffusion electrode layer are blocked, and the phenomenon of electrode flooding occurs, so that the mass transfer resistance of the reaction gas is increased. A good gas diffusion layer should satisfy the dynamic balance between hydrophilicity and hydrophobicity in order to prevent excessive water from blocking the pores of the diffusion layer to reduce the efficiency of the cell.

The gas diffusion layer is generally prepared by uniformly dispersing conductive carbon black in deionized water to which a dispersant is added, adding a water repellent emulsion thereto to form a uniform microporous layer slurry, and uniformly coating the slurry on a conductive substrate such as a carbon paper or carbon cloth substrate to form a gas diffusion layer having a microporous layer.

In order to increase the hydrophobicity of these gas diffusion layer substrates, it is common to immerse the conductive porous substrate in polytetrafluoroethylene emulsion or the like to perform a hydrophobic treatment. Further, a slurry of polytetrafluoroethylene and conductive carbon black is applied to the hydrophobic-treated conductive porous substrate, and dried and sintered to form a hydrophobic microporous layer.

When the conductive porous substrate is immersed in the polytetrafluoroethylene emulsion for hydrophobic treatment, in order to obtain good hydrophobicity, polytetrafluoroethylene is required in an amount of 8 wt% or more of the conductive substrate. However, since ptfe is non-conductive, if ptfe is excessive, the resistance of the gas diffusion layer increases and the contact resistance with the bipolar plate increases, which in turn decreases the power generation performance. In addition, when the polytetrafluoroethylene content is too high, the pores of the gas diffusion layer become small, and the gas diffusion property is lowered.

Disclosure of Invention

The present invention provides a method for preparing a gas diffusion layer for a fuel cell, which solves the technical problems in the background art.

The invention adopts the following technical scheme: a preparation method of a gas diffusion layer comprises a substrate layer and a preparation method of a microporous layer, wherein the preparation method of the substrate layer is to transfer a hydrophobic target material to a conductive porous substrate by a magnetron sputtering method.

The mass of the hydrophobic target material is 2-6% of that of the conductive porous base material, and the contact angle of the gas diffusion layer is 100-140 degrees.

Wherein the conductive porous substrate is carbon paper or carbon cloth consisting of carbon fibers. The hydrophobic target material is polytetrafluoroethylene.

By adopting the technical scheme: the matrix has basic pores and does not influence the diffusion of gas.

In a further embodiment, the thickness of the film formed on the conductive porous substrate by the hydrophobic target material is 20-60 nm.

In a further embodiment, the method specifically comprises the following steps:

s1, placing the conductive porous substrate in a magnetron sputtering instrument, vacuumizing and controlling the pressure to be 1 x 10^-6～2×10^{- 3}Pa, further 2X 10^-5～6×10^-5Pa, most preferably 4X 10^-5Pa. Wherein the conductive porous substrate is carbon paper or carbon cloth consisting of carbon fibers.

And S2, introducing inert gas and reaction gas, wherein the working pressure is 0.5-2.0 Pa, further 1-1.5 Pa, and optimally 1.2 Pa. The inert gas is argon; the reaction gas is carbon tetrafluoride.

S3, heating to make the temperature of the conductive porous base material be 25-300 ℃, further 60-250 ℃, and optimally 150 ℃.

S4, sputtering a hydrophobic target on the conductive porous substrate by magnetron sputtering to form a film, wherein the sputtering conditions are as follows: the sputtering power is 10-100W, further 30-60W, and optimally 40W; the sputtering time is 15 to 60 minutes, further 20 to 50 minutes, and most preferably 35 minutes. The hydrophobic target material is polytetrafluoroethylene.

By adopting the technical scheme: the polytetrafluoroethylene is a non-conductive polymer, and during magnetron sputtering, fluorocarbon gas contains fluorine, so that the plasma density can be improved, active sites with high activity can be promoted, and the deposition rate and the fluorine content can be improved.

In a further embodiment, the volume ratio of the inert gas to the reaction gas is 10: 1-100: 1 is further 20: 1-50: 1, more preferably 30: 1.

the preparation method of the microporous layer (MPL) comprises the steps of uniformly mixing and dispersing conductive carbon, a hydrophobic agent and a solvent for a pore-forming agent to obtain viscous pasty slurry. And (3) coating the obtained product on the surface of the GDB by adopting a screen printing, spraying or coating mode, and curing at high temperature to obtain the MPL.

The preparation method of the microporous layer comprises the steps of uniformly dispersing conductive carbon black in deionized water added with a dispersing agent, adding a water repellent emulsion into the deionized water to form uniform microporous layer slurry, and uniformly coating the uniform microporous layer slurry on a conductive substrate such as carbon paper or carbon cloth substrate to form the microporous layer.

The invention has the beneficial effects that: ultrathin polytetrafluoroethylene is formed on the surface of the conductive porous substrate by a magnetron sputtering method, and the material consumption of the polytetrafluoroethylene is reduced. The polytetrafluoroethylene has little influence on the conductivity and the air permeability because of low content, and is suitable for a gas diffusion layer of a fuel cell.

Detailed Description

In the prior art, when the conductive porous substrate is immersed in the polytetrafluoroethylene emulsion for hydrophobic treatment, in order to obtain good hydrophobicity, polytetrafluoroethylene is required in an amount of 8 wt% or more of the conductive substrate. However, since ptfe is non-conductive, if ptfe is excessive, the resistance of the gas diffusion layer increases and the contact resistance with the bipolar plate increases, which in turn decreases the power generation performance. In addition, when the polytetrafluoroethylene content is too high, the pores of the gas diffusion layer become small, and the gas diffusion property is lowered. It is difficult to simultaneously provide good hydrophobicity, conductivity, and gas diffusion properties. Therefore, the applicant selects a magnetron sputtering method to sputter polytetrafluoroethylene on the conductive porous substrate, and the mass of the polytetrafluoroethylene used in the method is 2-6 wt% of the conductive porous substrate, so that the gas diffusion layer with good hydrophobicity can be obtained, and the air permeability and the conductivity of the gas diffusion layer are not influenced.

Example 1

The preparation method of the gas diffusion layer specifically comprises the following steps:

placing the conductive porous carbon paper substrate on an objective table of a magnetron sputtering instrument, selecting a polytetrafluoroethylene plate as a hydrophobic target material, and vacuumizing to 6 x 10^-5Pa, introducing argon and carbon tetrafluoride with the volume ratio of 20:1, wherein the working pressure is 1.0 Pa; regulating the sputtering power to 80W, the temperature of the conductive porous carbon paper substrate to 80 ℃, and the sputtering time to 15 minutes to ensure that the weight of the polytetrafluoroethylene sputtered on the carbon paper substrate is 2% of the weight of the polytetrafluoroethylene, wherein the thickness of the polytetrafluoroethylene formed film is 20nm, and preparing the gas diffusion layer substrate layer.

In this embodiment, the magnetron sputtering apparatus may be selected from JCPY500 and JZCK-6400S.

65mg of acetylene black and 5ml of ethanol were ultrasonically dispersed for 40 minutes to form a uniform mixed solution, and then 500mg of PTFE emulsion (5 wt%) was added thereto and stirred uniformlyAnd (4) homogenizing to obtain microporous layer slurry. Uniformly coating the microporous layer slurry on one side of the carbon paper to ensure that the loading amount of the carbon black reaches 0.5mg/cm². Finally, the obtained product is placed in a nitrogen-filled oven to be sintered for 30 minutes at the temperature of 240 ℃ and 350 ℃ respectively, and the gas diffusion layer with the microporous layer is obtained.

The resistivity of the gas diffusion layer obtained in this example was measured: the resistivity is measured according to the national standard GBT20042.7-2014 part 7 of a proton exchange membrane fuel cell: carbon paper characteristic test method, test at 1MPa pressure.

The contact angle of the gas diffusion layer obtained in this example was measured: a contact angle tester model is OCA40Micro video contact angle tester for testing, and the used liquid is distilled water.

The gas permeability of the gas diffusion layer obtained in this example was tested: the test is carried out by using an American Gurley-4110N air permeability tester.

The results of the above tests are shown in Table 1.

Example 2

Placing the conductive porous carbon paper substrate on an objective table of a magnetron sputtering instrument, selecting a polytetrafluoroethylene plate as a hydrophobic target material, and vacuumizing with the pressure of 2 x 10^-5Pa, introducing argon and carbon tetrafluoride with the gas volume ratio of 30:1, wherein the working pressure is 0.5 Pa; and regulating the sputtering power to be 100W, the temperature of the conductive porous carbon paper substrate to be 150 ℃, and the sputtering time to be 60 minutes, so that the weight of the polytetrafluoroethylene sputtered on the carbon paper substrate is 4% of the weight of the polytetrafluoroethylene, and the thickness of the polytetrafluoroethylene film is 40nm, thus preparing the gas diffusion layer substrate.

In this embodiment, the magnetron sputtering apparatus may be selected from JCPY500 and JZCK-6400S. The microporous layer was prepared as in example 1.

The gas diffusion layer prepared in this example was subjected to the resistivity, contact angle and air permeability tests in the same manner as in example 1, and the results are also shown in table 1.

Example 3

Placing the conductive porous carbon paper substrate on an objective table of a magnetron sputtering instrument, and selecting a polytetrafluoroethylene plateIs hydrophobic target material, and the vacuum pressure is 1 x 10^-6Pa, introducing argon and carbon tetrafluoride with the gas volume ratio of 50:1, wherein the working pressure is 2 Pa; regulating the sputtering power to be 10W, the temperature of the conductive porous carbon paper substrate to be 60 ℃, and the sputtering time to be 40 minutes, so that the weight of the polytetrafluoroethylene sputtered on the carbon paper substrate is 6% of the weight of the polytetrafluoroethylene, and the thickness of the polytetrafluoroethylene film formed at the moment is 60nm, thereby preparing the gas diffusion layer substrate. In this embodiment, the magnetron sputtering apparatus may be selected from JCPY500 and JZCK-6400S. The microporous layer was prepared as in example 1.

The gas diffusion layer prepared in this example was subjected to the resistivity, contact angle and air permeability tests in the same manner as in example 1, and the results are also shown in table 1.

Example 4

Putting a conductive porous carbon cloth substrate on an objective table of a magnetron sputtering instrument, wherein the target material is a polytetrafluoroethylene plate, and the preparation conditions are as follows: evacuation 2 x 10^-3Pa, introducing argon gas and carbon tetrafluoride in a volume ratio of 100: 1, working pressure is 1.5Pa, sputtering power is 60W, base temperature is 250 ℃, and sputtering time is controlled, so that the amount of polytetrafluoroethylene sputtered on the carbon cloth substrate is 3% of the weight of the carbon cloth substrate, and the thickness of the polytetrafluoroethylene film is 30 nm. The microporous layer was prepared as in example 1. The resistivity, contact angle and air permeability test methods were the same as in example 1, and the test results are shown in table 2.

Example 5

Putting a conductive porous carbon cloth substrate on an objective table of a magnetron sputtering instrument, wherein the target material is a polytetrafluoroethylene plate, and the preparation conditions are as follows: evacuation 4 x 10^-5Pa, introducing argon gas and carbon tetrafluoride in a volume ratio of 10: 1, working pressure is 1.2Pa, sputtering power is 40W, base temperature is 25 ℃, and sputtering time is controlled, so that the amount of polytetrafluoroethylene sputtered on the carbon cloth substrate is 5% of the weight of the carbon cloth substrate, and the thickness of the polytetrafluoroethylene film is 50 nm. The microporous layer was prepared as in example 1. The resistivity, contact angle and air permeability test methods were the same as in example 1, and the test results are shown in table 2.

Comparative example 1

And (3) depositing the polytetrafluoroethylene emulsion on the conductive porous carbon paper in a soaking mode to prepare the gas diffusion layer, wherein the polytetrafluoroethylene content of the polytetrafluoroethylene on the carbon paper substrate is 10% of the weight of the polytetrafluoroethylene, and the deposition thickness is 100 nm. The microporous layer was prepared as in example 1.

The gas diffusion layer prepared in this example was subjected to the resistivity, contact angle and air permeability tests in the same manner as in example 1, and the results are also shown in table 1.

Comparative example 2

Putting the conductive porous carbon paper substrate on an objective table of a magnetron sputtering instrument, wherein the target material is a polytetrafluoroethylene plate, and the preparation conditions are as follows: vacuum pumping 6 x 10^-5Pa, introducing argon gas and carbon tetrafluoride in a volume ratio of 20:1, working pressure is 1.0Pa, sputtering power is 80W, base temperature is 80 ℃, sputtering time is controlled, the amount of polytetrafluoroethylene sputtered on the carbon paper base material is 1 percent of the weight of the carbon paper base material, the thickness of a polytetrafluoroethylene film is 10nm, and the gas diffusion layer base material is prepared. The microporous layer was prepared as in example 1.

The resistivity, contact angle and air permeability test methods were the same as in example 1, and the test results are shown in table 1.

Comparative example 3

Putting the conductive porous carbon paper substrate on an objective table of a magnetron sputtering instrument, wherein the target material is a polytetrafluoroethylene plate, and the preparation conditions are as follows: evacuation 2 x 10^-5Pa, introducing argon gas and carbon tetrafluoride in a volume ratio of 50:1, working pressure is 1.0Pa, sputtering power is 100W, base temperature is 150 ℃, sputtering time is controlled, the amount of polytetrafluoroethylene sputtered on the carbon paper substrate is 8% of the weight of the carbon paper substrate, and the polytetrafluoroethylene forms a film with the thickness of 80nm at the moment, so that the gas diffusion layer substrate is prepared. The microporous layer was prepared as in example 1. The resistivity, contact angle and air permeability test methods were the same as in example 1, and the test results are shown in table 1.

Comparative example 4

And (3) depositing the polytetrafluoroethylene emulsion on the conductive porous carbon cloth base cloth in a soaking mode to prepare the gas diffusion layer, wherein the polytetrafluoroethylene content of the polytetrafluoroethylene on the carbon paper base material is 12% of the weight of the polytetrafluoroethylene, and the deposition thickness is 120 nm. The microporous layer was prepared as in example 1.

The gas diffusion layer prepared in this example was subjected to the resistivity, contact angle and air permeability tests in the same manner as in example 1, and the results are also shown in table 1.

Comparative example 5

Putting a conductive porous carbon cloth substrate on an objective table of a magnetron sputtering instrument, wherein the target material is a polytetrafluoroethylene plate, and the preparation conditions are as follows: vacuum pumping 6 x 10^-5Pa, introducing argon gas and carbon tetrafluoride in a volume ratio of 20:1, working pressure is 1.0Pa, sputtering power is 80W, base temperature is 80 ℃, and sputtering time is controlled, so that the amount of polytetrafluoroethylene sputtered on the carbon cloth substrate is 9% of the weight of the carbon cloth substrate, and the polytetrafluoroethylene forms a film with the thickness of 90 nm. The microporous layer was prepared as in example 1. The resistivity, contact angle and air permeability test methods were the same as in example 1, and the test results are shown in table 2.

TABLE 1 contact angle, TP resistivity, TP permeability results for magnetron sputtered porous carbon papers of different PTFE content

As can be seen from Table 1, the contact angle was over 105 ℃ at 2 wt%, 4 wt%, 6 wt% of the weight of the carbon paper with polytetrafluoroethylene, the hydrophobic property was much higher than that of comparative example 2 (polytetrafluoroethylene was 1 wt% of the weight of the carbon paper), and the TP resistivity and TP gas permeability were not increased much, and thus the polytetrafluoroethylene is very suitable for use as a gas diffusion layer of a fuel cell. Comparative example 1, which was soaked with polytetrafluoroethylene emulsion and had a large polytetrafluoroethylene content (10 wt%), and comparative example 3, which had a large polytetrafluoroethylene content (8 wt%), although the hydrophobic property was good, the TP resistivity increased to more than 7m Ω · cm²When the gas diffusion layer is used for generating electricity by a fuel cell, the gas diffusion layer consumes large power, and the output power is reduced.TP has a long permeability time and poor gas permeability, which is not conducive to gas and water transport.

TABLE 2 contact angle, TP resistivity, TP permeability results for magnetron sputtering porous carbon cloths of different polytetrafluoroethylene contents

As can be seen from table 2, comparative example 4 is soaked with ptfe emulsion and has a high ptfe content (12 wt%), comparative example 1 is soaked with ptfe emulsion and has a high ptfe content (10 wt%), and comparative example 5 has a high ptfe content (9 wt%), has good hydrophobic properties, but the TP resistivity is increased a lot, and when the composition is used for power generation of a fuel cell, the gas diffusion layer consumes much power and the output power is reduced; TP has a long permeability time, poor gas permeability, and is not conducive to gas and water transport.

As can be seen from the comparison between the two examples and the comparative example, when the amount of PTFE exceeds 6 wt%, although the hydrophobic property is good, the TP resistivity increases, and when the PTFE is used for power generation of a fuel cell, the gas diffusion layer consumes much power and the output power decreases. Below 2 wt%, the hydrophobic properties of the diffusion layer are poor, leading to flooding and poor electrode performance.

In conclusion, when polytetrafluoroethylene with a proper content is sputtered on the surface of the carbon paper or the carbon cloth by a magnetron sputtering method, and the content of the polytetrafluoroethylene is 2 wt% -6 wt% of the weight of the carbon paper or the carbon cloth, the carbon paper or the carbon cloth has excellent drainage property, electric conductivity and air permeability.