CN110797540A - Preparation method of gas diffusion layer suitable for high temperature and low humidity - Google Patents

Abstract

The invention provides a preparation method of a gas diffusion layer suitable for high temperature and low humidity, which comprises the following steps: preparing a high-conductivity material, a carbon nano tube, a hydrophilic agent and a dispersion liquid into slurry with uniform components in a stirring manner; wherein, the carbon nano tube adopts VGCF-H; uniformly distributing the slurry on the support material in a screen printing mode; and spraying a Nafion solution on the surface of the support material distributed with the slurry by a spraying mode to form the gas diffusion layer. The invention solves the technical problems that the complexity and the energy consumption of a fuel cell system are increased by additionally humidifying in an external humidification or internal humidification mode in the prior art.

Description

A kind of preparation method of gas diffusion layer suitable for high temperature and low humidity

technical field

The invention relates to the technical field of fuel cells, in particular, to a method for preparing a gas diffusion layer suitable for high temperature and low humidity.

Background technique

Membrane electrode (MEA), as the core component of proton exchange membrane fuel cell, plays a decisive role in cell performance. In MEA, the Nafion membrane needs to have sufficient water to maintain good proton conductivity of the membrane. There is a proportional relationship between the proton conductivity and the water content in the membrane. The higher the water content, the faster the proton conduction rate. When the water content is insufficient, the membrane will be The proton conductivity drops sharply. Therefore, the key to ensure the stable operation of PEMFC is to maintain sufficient water content of Nafion resin in the proton exchange membrane and catalytic layer. The fuel cell will generate a lot of moisture during the operation, but this moisture is generated at the cathode and will be taken away by the excess air, and this moisture cannot guarantee the sufficient moisture content of the proton exchange membrane; therefore, in the current fuel cell technology application, Both external humidification or internal humidification are required to additionally humidify the gas before entering the cell to maintain the wetting degree of the Nafion membrane and the anode catalytic layer, and the additional humidification equipment brought by this increases the fuel cell. The complexity and energy consumption of the system, the reduction of the power density of the fuel cell, the increase of the cost of the fuel cell, and the difficulty of hydrothermal management have seriously hindered the commercialization of the fuel cell.

The patent with the application number CN105742666A discloses a preparation method and application of a carbon nanotube gas diffusion layer. The gas diffusion layer prepared by the mentioned CVD method does not need to add an additional hydrophobic agent. Because the carbon nanotubes have strong hydrophobicity, Therefore, the inner side of the gas diffusion layer where the carbon nanotubes are concentratedly grown is hydrophobic, and the contact angle is 130-150° without the addition of a hydrophobic binder. Good hydrophobic, conductive and mass transfer capabilities.

The carbon nanotube gas diffusion layer prepared in the patent exhibits anisotropy, and the density of carbon nanotubes in the direction perpendicular to the plane of the gas diffusion layer increases from outside to inside; in the direction parallel to the plane of the gas diffusion layer, the density of carbon nanotubes is uniform, with Good mass transfer and electrical conductivity can effectively solve the flooding problem of PEM fuel cells at high current density.

The gas diffusion layer is prepared by in-situ growth of carbon nanotubes on a macroporous carbon substrate. Due to the strong van der Waals force between the grown carbon nanotubes, it is easy to entangle and agglomerate after growth. The effective aspect ratio is significantly reduced, resulting in the phenomenon of slippage between tubes, and it is difficult to uniformly disperse them by conventional dispersion methods. The gas diffusion layer prepared by the method of directly adding carbon nanotubes by CVD has unstable properties. The complete process of CVD is relatively complex, and various parameters in the process, such as carbon source gas, temperature, catalyst, time, etc., have a great influence on the distribution, morphology and structure of the grown carbon nanotubes, and the operation repeatability is low. In addition, the surface uniformity of the carbon nanotube gas diffusion layer prepared by CVD is poor, so the performance of the prepared MEA will be affected by the uniformity.

SUMMARY OF THE INVENTION

According to the above-mentioned methods of external humidification or internal humidification in the prior art, the gas before entering the cell is additionally humidified to maintain the wettability of the Nafion membrane and the anode catalytic layer, which increases the complexity and energy of the fuel cell system. consumption, reduced power density, increased cost, difficult water and heat management and other technical problems, and provided a method for preparing a gas diffusion layer suitable for high temperature and low humidity. The present invention can improve the performance of MEA under high temperature and low humidity conditions by adding appropriate amount of VGCF-H and Nafion without adding hydrophobic agent and pore-forming agent to the original ingredients of the microporous layer, and is also conducive to optimizing the water management of MEA ability.

The technical means adopted in the present invention are as follows:

A method for preparing a gas diffusion layer suitable for high temperature and low humidity, comprising:

The highly conductive material, carbon nanotubes, hydrophilic agent and dispersion liquid are prepared into a slurry with uniform composition by stirring; wherein, the carbon nanotubes are VGCF-H;

The slurry is evenly distributed on the support material by screen printing;

The gas diffusion layer is formed by spraying the Nafion solution on the surface of the support material distributed with the slurry by spraying.

Further, the dispersion medium of the dispersion liquid adopts isopropanol to which carbon black is added.

Further, the mass ratio of carbon black to VGCF-H is 1:0.5 to 1:1.5.

Further, the dispersion liquid is a Nafion water dispersion liquid; the content of Nafion in the Nafion water dispersion liquid is 6 g to 14 g; and Nafion is used as a binder of the slurry.

Further, the supporting material is hydrophobic treated carbon paper; the screen printing thickness of the screen printing is 20 μm to 50 μm.

Compared with the prior art, the present invention has the following advantages:

In the method for preparing a gas diffusion layer suitable for high temperature and low humidity provided by the invention, an appropriate amount of VGCF-H and Nafion are added to the original ingredients of the microporous layer without adding a hydrophobic agent or a pore-forming agent; With the characteristics of larger size and larger pore volume, the MEA prepared by using the gas diffusion layer can not only improve the performance of the MEA under high temperature and low humidity conditions, but also help to optimize the water management capability of the MEA.

To sum up, applying the technical solution of the present invention can improve the performance of MEA under high temperature and low humidity conditions by adding an appropriate amount of VGCF-H and Nafion without adding hydrophobic agents and pore-forming agents to the original ingredients of the microporous layer. Helps to optimize the water management capabilities of the MEA. Therefore, the technical solution of the present invention solves the external humidification or internal humidification used in the prior art to additionally humidify the gas before entering the cell, maintains the wettability of the Nafion membrane and the anode catalytic layer, and increases the fuel cell performance. The complexity and energy consumption of the system reduces the power density, increases the cost and technical issues such as difficult hydrothermal management.

Based on the above reasons, the present invention can be widely applied in the fields of fuel cells and the like.

Description of drawings

In order to illustrate the embodiments of the present invention or the technical solutions in the prior art more clearly, the following briefly introduces the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description These are some embodiments of the present invention, and for those of ordinary skill in the art, other drawings can also be obtained from these drawings without any creative effort.

FIG. 1 is a schematic structural diagram of the gas diffusion layer according to the present invention.

FIG. 2 is the surface morphology of the microporous layer according to the present invention.

FIG. 3 is the contact angle of the gas diffusion layer according to the present invention.

FIG. 4 shows the polarization curves of the single cells of Example 1 and Comparative Example 1 under the operating conditions of 80° C.-RH 60% high temperature and low humidity.

FIG. 5 shows the polarization curves of single cells of Example 1 and Comparative Example 1 under the operating conditions of 80° C.-RH 40% high temperature and low humidity.

In the figure: 1. Carbon paper substrate; 2. Microporous layer.

Detailed ways

It should be noted that the embodiments of the present invention and the features of the embodiments may be combined with each other under the condition of no conflict. The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments.

In order to make the purposes, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments It is only a part of the embodiments of the present invention, but not all of the embodiments. The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

It should be noted that the terminology used herein is for the purpose of describing specific embodiments only, and is not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly dictates otherwise, the singular is intended to include the plural as well, furthermore, it is to be understood that when the terms "comprising" and/or "including" are used in this specification, it indicates that There are features, steps, operations, devices, components and/or combinations thereof.

The relative arrangement of the components and steps, the numerical expressions and numerical values set forth in these embodiments do not limit the scope of the invention unless specifically stated otherwise. Meanwhile, it should be understood that, for convenience of description, the dimensions of various parts shown in the accompanying drawings are not drawn in an actual proportional relationship. Techniques, methods, and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the authorized specification. In all examples shown and discussed herein, any specific values should be construed as illustrative only and not limiting. Accordingly, other examples of exemplary embodiments may have different values. It should be noted that like numerals and letters refer to like items in the following figures, so once an item is defined in one figure, it does not require further discussion in subsequent figures.

In the description of the present invention, it should be understood that the orientations indicated by orientation words such as "front, rear, top, bottom, left, right", "horizontal, vertical, vertical, horizontal" and "top, bottom" etc. Or the positional relationship is usually based on the orientation or positional relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, and these orientation words do not indicate or imply the indicated device or element unless otherwise stated. It must have a specific orientation or be constructed and operated in a specific orientation, so it should not be construed as a limitation on the scope of protection of the present invention: the orientation words "inside and outside" refer to the inside and outside relative to the contour of each component itself.

For ease of description, spatially relative terms, such as "on", "over", "on the surface", "above", etc., may be used herein to describe what is shown in the figures. The spatial positional relationship of one device or feature shown to other devices or features. It should be understood that spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as "above" or "over" other devices or features would then be oriented "below" or "over" the other devices or features under its device or structure". Thus, the exemplary term "above" can encompass both an orientation of "above" and "below." The device may also be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptions used herein interpreted accordingly.

In addition, it should be noted that the use of words such as "first" and "second" to define components is only for the convenience of distinguishing corresponding components. Unless otherwise stated, the above words have no special meaning and therefore cannot be understood to limit the scope of protection of the present invention.

Example 1

The invention provides a method for preparing a gas diffusion layer suitable for high temperature and low humidity, comprising:

The highly conductive material, carbon nanotubes, hydrophilic agent and dispersion liquid are prepared into a slurry with uniform composition by stirring; wherein, the carbon nanotubes are VGCF-H;

The slurry is evenly distributed on the support material by screen printing;

The gas diffusion layer is formed by spraying Nafion solution on the surface of the support material distributed with the slurry by spraying, forming a gas diffusion layer with a special pore structure and appropriate hydrophilicity and hydrophobicity. The gas diffusion layer has the characteristics of large pore size and large pore volume. The gas diffusion layer itself has certain advantages in water retention, so that the proton exchange membrane can be well kept wet, the gas can better contact the catalyst, and the electrical properties of the MEA are improved.

Further, the dispersion medium of the dispersion liquid adopts isopropanol to which carbon black is added.

Further, the mass ratio of carbon black to VGCF-H is 1:0.5 to 1:1.5.

Further, the dispersion liquid is a Nafion water dispersion liquid; the content of Nafion in the Nafion water dispersion liquid is 6 g to 14 g; and Nafion is used as a binder of the slurry.

Further, the supporting material is hydrophobic treated carbon paper; the screen printing thickness of the screen printing is 20 μm to 50 μm. The viscosity of the slurry is low, which is also suitable for the coating method of screen printing. It is also necessary to control the thickness of the slurry penetrated into the carbon paper.

The preparation method provided by the invention has simple operation process, few kinds of required raw materials and low equipment requirements.

Commonly used carbon nanotubes include CNT, CF, VGCF-H, etc. The carbon nanotubes used in the present invention are VGCF-H. Carbon nanotubes are hydrophobic. No hydrophobic agent is required after the microporous layer contains carbon nanotubes. The contact angle of MPL in the microporous layer ranges from 150° to 170°. The hydrophobicity affects the discharge rate of generated water. The hydrophobicity of MPL It needs to be determined according to the operating conditions of the proton exchange membrane fuel cell.

When preparing the MEA, the gas diffusion layer GDL does not need to be fired, and the catalyst-coated proton exchange membrane (CCM), the gas diffusion layer and the polyester frame are pressed together to make the MEA. The pressure during the pressing process is 40kg/cm ² -100kg/cm ² .

Further, observe or test the gas diffusion layer prepared by the method of the present invention, and then use the gas diffusion layer to prepare MEA and perform performance test. The specific operation process is as follows:

1) Dilute the Nafion concentrate with a mass fraction greater than 5% to 5% with deionized water, and stir evenly;

2) Weigh 3g of carbon black, 1g of VGCF-H, 13.16g of 5% Nafion aqueous dispersion and pour it into a certain amount of isopropanol, stir to make a slurry with a viscosity between 80cp-150cp;

3) using the method of screen printing to coat the above-mentioned slurry on the hydrophobic treated carbon paper to form a microporous layer with a coating thickness of 20 μm;

The schematic diagram of the prepared gas diffusion layer is shown in Figure 1;

4) Observe the surface morphology of the microporous layer of the gas diffusion layer, as shown in Figure 2;

5) Roughness test is carried out on the surface of the microporous layer; wherein, Comparative Example 1 is the production diffusion layer of the prior art, in the experimental process, the slurry is not added with VGCF, and the whole proportion is carbon black, and the total amount is the same; without adding Nafion, use PTFE Do replacement, the consumption is the same, and other process parameters are the same as in Example 1; the test results are as shown in Table 1;

Table 1 Test results of surface roughness of microporous layer

sample name Interface expansion area ratio Maximum height difference (μm) Comparative Example 1 4.013 63.7 Example 1 3.163 57.44

6) Pressing the prepared gas diffusion layer, CCM and polyester frame with a force of 100kg/cm through a hydraulic press to form an MEA with an effective reaction area of 25cm ⁽ a total of ² pieces);

7) Assemble the remaining 1 piece of the MEA made in 6) into a single cell, and conduct an initial performance test; the schematic diagram of the single cell structure is shown in Figure 3; The results are shown in Figure 4 under the working condition of 80°C RH 60%, and the results under the working condition of 80°C RH 40% are shown in Figure 5.

Observation and test results:

As shown in Figure 1, on the hydrophobic carbon paper substrate 1 with large pore size, a layer of slurry added with VGCF-H carbon nanotubes was printed on the microporous screen to form a microporous layer 2 with larger pore size and larger pore volume. .

As shown in Figure 2, it can be seen from the surface morphology of the microporous layer that the surface of the microporous layer of Comparative Example 1 is smooth and dense after carbon nanotubes are added, and most of the cracks and pits in the microporous layer disappear.

As shown in Table 1, the thicknesses of Comparative Example 1 and Example 1 are similar. The interface development ratio and the maximum height difference of the sample surface were obtained by using a surface roughness tester. Under the condition of similar thickness, the test values did not change significantly.

As shown in Fig. 3, it can be seen from the experimentally obtained contact angle results of the gas diffusion layer that the surface of the gas diffusion layer after adding carbon nanotubes exhibits hydrophobicity without adding a hydrophobic agent.

As shown in Figure 4, the electrical properties of the polarization curves of the single cells of Example 1 and Comparative Example 1 under high temperature and low humidity conditions (80°C-RH60%) are explained: the total thickness of the microporous layer in Comparative Example 1 and Experimental Example 1 is maintained Consistently, the performance of the proton exchange membrane fuel cell composed of the gas diffusion layer added with carbon nanotubes is better, the water retention capacity of the low electric density region is better than that of the comparative example, and the water management capacity is improved, which can improve the mass transfer performance of the MEA. .

As shown in Figure 5, the electrical properties of the polarization curves of the single cells of Example 1 and Comparative Example 1 under high temperature and low humidity conditions (80°C-RH40%) are explained: Continue to reduce the humidity under the operating conditions, the comparative example and the experimental example are slightly Under the condition that the total thickness of the pore layer remains the same, the performance of the proton exchange membrane fuel cell composed of the gas diffusion layer with carbon nanotubes is better, and the water management ability has obvious advantages, which can improve the mass transfer performance of the MEA.

The single cell polarization curves of Example 1 and Comparative Example 1 show that the gas diffusion layer of the microporous layer structure with a certain amount of VGCF-H added has a certain water retention under high temperature and low humidity conditions, and can effectively increase the protons within a certain humidity range. Electrical properties of exchange membrane fuel cells.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, but not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that it can still be The technical solutions described in the foregoing embodiments are modified, or some or all of the technical features thereof are equivalently replaced; and these modifications or replacements do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.

Claims (5)

1. a high temperature and low humidity applicable gas diffusion layer preparation method, is characterized in that, comprising: The highly conductive material, carbon nanotubes, hydrophilic agent and dispersion liquid are prepared into a slurry with uniform composition by stirring; wherein, the carbon nanotubes are VGCF-H; The slurry is evenly distributed on the support material by screen printing; The gas diffusion layer is formed by spraying the Nafion solution on the surface of the support material distributed with the slurry by spraying. 2 . The method for preparing a gas diffusion layer suitable for high temperature and low humidity according to claim 1 , wherein the dispersion medium of the dispersion adopts isopropyl alcohol added with carbon black. 3 . 3 . The method for preparing a gas diffusion layer suitable for high temperature and low humidity according to claim 2 , wherein the mass ratio of carbon black to VGCF-H is 1:0.5 to 1:1.5. 4 . 4. The method for preparing a gas diffusion layer suitable for high temperature and low humidity according to claim 1, wherein the dispersion is a Nafion water dispersion; the content of Nafion in the Nafion water dispersion is 6g to 14g; Nafion is used as a bonding agent of the slurry agent. 5 . The method for preparing a gas diffusion layer suitable for high temperature and low humidity according to claim 1 , wherein the supporting material is carbon paper treated with hydrophobicity; and the screen printing thickness of the screen printing is 20 μm to 50 μm. 6 .

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