MICROPOROUS LAYER STRUCTURE OF FUEL CELL AND PREPARATION METHOD THEREFOR, AND FUEL CELL CATHODE ASSEMBLY

Abstract

The present invention provides a microporous layer structure of a fuel cell, comprising: a microporous layer having high water vapor transmission rate and a microporous layer having low water vapor transmission rate that are sequentially stacked. In the direction of an air flow path, the thickness of the microporous layer having high water vapor transmission rate increases progressively, the thickness of the microporous layer having low water vapor transmission rate decreases progressively, and the total thickness of the microporous layer structure keeps consistent. At an air inlet, the thickness of the microporous layer having high water vapor transmission rate is smaller than that of the microporous layer having low water vapor transmission rate. At an air outlet, the thickness of the microporous layer having high water vapor transmission rate is greater than that of the microporous layer having low water vapor transmission rate. The present application also provides a preparation method for the microporous layer structure and a membrane electrode assembly of a fuel cell. The microporous layer structure of a fuel cell provided in the present application can balance water content of a gas inlet area and a gas outlet area of the fuel cell, and finally improves the stability of the fuel cell at different temperatures and humidity levels, thereby implementing functions such as improving durability.

Claims

1. A microporous layer structure of a fuel cell, comprising: a microporous layer having high water vapor permeability and a microporous layer having low water vapor permeability that are sequentially stacked, wherein in the direction of air flow, the thickness of the microporous layer having high water vapor permeability increases progressively, and the thickness of the microporous layer having low water vapor permeability decreases progressively, and the microporous layer structure has a uniform total thickness; at an air inlet, the microporous layer having high water vapor permeability is thinner than the microporous layer having low water vapor permeability; and at an air outlet, the microporous layer having high water vapor permeability is thicker than the microporous layer having low water vapor permeability.

2. The microporous layer structure according to claim 1, wherein the thickness of the microporous layer structure ranges from 30 μm to 60 μm.

3. The microporous layer structure according to claim 1, wherein the microporous layer having high water vapor permeability has a thickness ranging from 0 μm to 30 μm at the air inlet and has a thickness ranging from 30 μm to 60 μm at the air outlet; and the microporous layer having low water vapor permeability has a thickness ranging from 30 μm to 60 μm at the air inlet and has a thickness ranging from 0 μm to 30 μm at the air outlet.

4. The microporous layer structure according to claim 1, wherein the microporous layer having high water vapor permeability has a porosity ranging from 40% to 55%; and the microporous layer having low water vapor permeability has a porosity ranging from 30% to 45%.

5. A method for preparing the microporous layer structure according to claim 1, comprising: A), preparing a first slurry mixture and a second slurry mixture, wherein the first slurry mixture and the second slurry mixture each consists of carbon powder, adhesive agent, dispersant and solvent, wherein water vapor permeability of the first slurry mixture is higher than that of the second slurry mixture; and B), coating on surface of a gas diffusion layer subjected to hydrophobic treatment with the first slurry mixture to obtain the microporous layer having high water vapor permeability after heat treatment, then coating with the second slurry mixture to obtain the microporous layer having low water vapor permeability; or coating on surface of a gas diffusion layer subjected to hydrophobic treatment with the second slurry mixture to obtain the microporous layer having low water vapor permeability after heat treatment, then coating with the first slurry mixture to obtain the microporous layer having high water vapor permeability, wherein by controlling coating process, in the direction of air flow, the thickness of the microporous layer having high water vapor permeability increases progressively, the thickness of the microporous layer having low water vapor permeability decreases progressively, and the microporous layer structure has a uniform total thickness; at the air inlet, the microporous layer having high water vapor permeability is thinner than the microporous layer having low water vapor permeability; and at the air outlet, the microporous layer having high water vapor permeability is thicker than the microporous layer having low water vapor permeability.

6. The method according to claim 5, wherein the carbon powder in the first slurry mixture is large particle carbon powder with a particle size ranging from 30 nm to 60 nm; and the carbon powder in the second slurry mixture is small particle carbon powder with a particle size ranging from 20 nm to 50 nm.

7. The method according to claim 5, wherein a coating tool for performing the coating process is a coater with a slit or a spray head, or a scraper.

8. A membrane electrode assembly of a fuel cell, comprising an electrolyte membrane, a catalytic electrode layer, a microporous layer and a gas diffusion layer that are sequentially stacked, wherein the microporous layer has the microporous layer structure according to claim 1.

9. The membrane electrode assembly of a fuel cell according to claim 8, wherein the microporous layer having high water vapor permeability of the microporous layer structure is arranged on a side of the gas diffusion layer.

10. The membrane electrode assembly of a fuel cell according to claim 8, wherein the microporous layer comprises at least one layer.

11. The membrane electrode assembly of a fuel cell according to claim 8, wherein the thickness of the microporous layer structure ranges from 30 μm to 60 μm.

12. The membrane electrode assembly of a fuel cell according to claim 8, wherein the microporous layer having high water vapor permeability has a thickness ranging from 0 μm to 30 μm at the air inlet and has a thickness ranging from 30 μm to 60 μm at the air outlet; and the microporous layer having low water vapor permeability has a thickness ranging from 30 μm to 60 μm at the air inlet and has a thickness ranging from 0 μm to 30 μm at the air outlet.

13. The membrane electrode assembly of a fuel cell according to claim 8, wherein the microporous layer having high water vapor permeability has a porosity ranging from 40% to 55%; and the microporous layer having low water vapor permeability has a porosity ranging from 30% to 45%.

14. The membrane electrode assembly of a fuel cell according to claim 8, wherein the microporous layer structure is prepared by a method comprising the following steps: A), preparing a first slurry mixture and a second slurry mixture, wherein the first slurry mixture and the second slurry mixture each consists of carbon powder, adhesive agent, dispersant and solvent, wherein water vapor permeability of the first slurry mixture is higher than that of the second slurry mixture; and B), coating on surface of a gas diffusion layer subjected to hydrophobic treatment with the first slurry mixture to obtain the microporous layer having high water vapor permeability after heat treatment, then coating with the second slurry mixture to obtain the microporous layer having low water vapor permeability; or coating on surface of a gas diffusion layer subjected to hydrophobic treatment with the second slurry mixture to obtain the microporous layer having low water vapor permeability after heat treatment, then coating with the first slurry mixture to obtain the microporous layer having high water vapor permeability, wherein by controlling coating process, in the direction of air flow, the thickness of the microporous layer having high water vapor permeability increases progressively, the thickness of the microporous layer having low water vapor permeability decreases progressively, and the microporous layer structure has a uniform total thickness; at the air inlet, the microporous layer having high water vapor permeability is thinner than the microporous layer having low water vapor permeability; and at the air outlet, the microporous layer having high water vapor permeability is thicker than the microporous layer having low water vapor permeability.

15. The membrane electrode assembly of a fuel cell according to claim 14, wherein the carbon powder in the first slurry mixture is large particle carbon powder with a particle size ranging from 30 nm to 60 nm; and the carbon powder in the second slurry mixture is small particle carbon powder with a particle size ranging from 20 nm to 50 nm.

16. The membrane electrode assembly of a fuel cell according to claim 14, wherein a coating tool for performing the coating process is a coater with a slit or a spray head, or a scraper.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG. 1 shows a microporous layer structure of a fuel cell according to the present disclosure;

[0028] FIG. 2 is a schematic diagram showing comparison of performances of a cell formed by a microporous layer structure prepared according to an example of the present disclosure under a low humidity condition; and

[0029] FIG. 3 is a schematic diagram showing comparison of performances of a cell formed by a microporous layer structure prepared according to an embodiment of the present disclosure under a high humidity condition.

DETAILED DESCRIPTION OF EMBODIMENTS

[0030] For a further understanding of the present disclosure, preferred embodiments of the present disclosure are described below in conjunction with examples. However, it should be understood that these descriptions are only for further describing features and advantages of the present disclosure rather than limiting the claims of the present disclosure.

[0031] In view of the problem of poor water management in a fuel cell in the prior art, a microporous layer structure of a fuel cell is provided according to the present disclosure. The microporous layer structure comprises microporous layers having different water vapor permeabilities. In a direction of air flow, each single layer of the microporous layer has a gradient distribution of thickness and the microporous layer has a uniform total thickness. At the air inlet, the microporous layer having low water vapor permeability is thicker than the microporous layer having high water vapor permeability. At an air outlet, the microporous layer having low water vapor permeability is thinner than the microporous layer having high water vapor permeability. The microporous layer structure according to the present disclosure can balance water content of a fuel cell at the air inlet and the air outlet, thus distribution of current density of a fuel cell with a big size can be improved, stability of the fuel cell under various temperature and humidity conditions can be improved, and durability can be improved. Specifically, the present disclosure provides a microporous layer structure of a fuel cell, comprising: a microporous layer having high water vapor permeability and a microporous layer having low water vapor permeability that are sequentially stacked, wherein in the direction of air flow, the thickness of the microporous layer having high water vapor permeability increases progressively, and the thickness of the microporous layer having low water vapor permeability decreases progressively, and the microporous layer structure has a uniform total thickness; at an air inlet, the microporous layer having high water vapor permeability is thinner than the microporous layer having low water vapor permeability; and at an air outlet, the microporous layer having high water vapor permeability is thicker than the microporous layer having low water vapor permeability.

[0032] The present disclosure provides a microporous layer structure of a fuel cell with a gradient variation, consisting of a microporous layer having high water vapor permeability and a microporous layer having low water vapor permeability. In actual application, the microporous layer having high water vapor permeability and the microporous layer having low water vapor permeability form a set and the microporous layer structure may comprises one or more sets, which is not limited herein. In the direction of air flow, that is, a direction from the air inlet to the air outlet, the thickness of the microporous layer having high water vapor permeability increases in a gradient manner, and the thickness of the microporous layer having low water vapor permeability decreases in a gradient manner. Though thicknesses of the microporous layer having high water vapor permeability and the thickness of the microporous layer having low water vapor permeability both change in a gradient manner, the microporous layer structure has a uniform total thickness in the direction of air flow. The gradient distribution in progressively increasing thickness or progressively decreasing thickness of the microporous layer can make water more uniformly distributed in the direction from the air inlet to the air outlet, and the effect is better.

[0033] In specific embodiments, the thickness of the microporous layer structure ranges from 30 μm to 60 μm. Specifically, the microporous layer having high water vapor permeability has a thickness ranging from 0 μm to 30 μm at the air inlet and has a thickness ranging from 30 μm to 60 μm at the air outlet. In an specific embodiment, the microporous layer having high water vapor permeability has a thickness ranging from 10 μm to 20 μm at the air inlet and has a thickness ranging from 30 μm to 50 μm at the air outlet; the microporous layer having low water vapor permeability has a thickness ranging from 30 μm to 60 μm at the air inlet and has a thickness ranging from 0 μm to 30 μm at the air outlet. In specific embodiments, the microporous layer having low water vapor permeability has a thickness ranging from 30 μm to 50 μm at the air inlet and has a thickness ranging from 10 μm to 20 μm at the air outlet.

[0034] The microporous layer having high water vapor permeability described herein is relative to the microporous layer having low water vapor permeability. The microporous layer having high water vapor permeability means that water easily escapes therethrough and the microporous layer having low water vapor permeability means that water is difficult to escape therethrough. Specifically, the water vapor permeability may be adjusted by adjusting porosity and density of the microporous layer having high water vapor permeability and the microporous layer having low water vapor permeability. Specifically, the porosity of the microporous layer having high water vapor permeability ranges from 40% to 55%, and preferably ranges from 45% to 55%; the porosity of the microporous layer having low water vapor permeability ranges from 30% to 45%, and preferably ranges from 30% to 40%.

[0035] The present disclosure further provides a method for preparing the microporous layer structure of a fuel cell, comprising the following steps:

[0036] A), preparing a first slurry mixture and a second slurry mixture, wherein the first slurry mixture and the second slurry mixture each consists of carbon powder, adhesive agent, dispersant and solvent, wherein water vapor permeability of the first slurry mixture is higher than that of the second slurry mixture; and

[0037] B), coating on surface of a gas diffusion layer subjected to hydrophobic treatment with the first slurry mixture to obtain the microporous layer having high water vapor permeability after heat treatment, then coating with the second slurry mixture to obtain the microporous layer having low water vapor permeability; or

[0038] coating on surface of a gas diffusion layer subjected to hydrophobic treatment with the second slurry mixture to obtain the microporous layer having low water vapor permeability after heat treatment, then coating with the first slurry mixture to obtain the microporous layer having high water vapor permeability, wherein

[0039] by controlling coating process, in the direction of air flow, the thickness of the microporous layer having high water vapor permeability increases progressively, the thickness of the microporous layer having low water vapor permeability decreases progressively, and the microporous layer structure has a uniform total thickness;

[0040] at the air inlet, the microporous layer having high water vapor permeability is thinner than the microporous layer having low water vapor permeability; and

[0041] at the air outlet, the microporous layer having high water vapor permeability is thicker than the microporous layer having low water vapor permeability.

[0042] In a process of preparing the microporous layer structure, two slurry mixtures are firstly prepared, which are distinguished into a first slurry mixture and a second slurry mixture. The first slurry mixture and the second slurry mixture each may consist of carbon powder, adhesive agent, dispersant and solvent. The carbon powder, adhesive agent, dispersant and solvent are well known to those skilled in the art, and are not limited herein. In the present disclosure, the water vapor permeability of the first slurry mixture is greater than that of the second slurry mixture. In order to achieve this, the carbon powder in the first slurry mixture may be large particle carbon powder with a particle size ranging from 30 nm to 60 nm, preferably ranging from 40 nm to 60 nm, and more preferably ranging from 45 nm to 60 nm; and in some specific embodiments, the particle size ranges from 40 nm to 50 nm, which leads to high porosity and low density of the microporous layer having high water vapor permeability. The carbon powder in the second slurry mixture may be small particle carbon powder with a particle size ranging from 20 nm to 50 nm, preferably ranging from 20 nm to 45 nm, and more preferably ranging from 20 nm to 40 nm; and in some specific embodiments, the particle size ranges from 30 nm to 40 nm, which leads to low porosity and high density of the microporous layer having low water vapor permeability. Similarly, the adhesive agent in the first slurry mixture may be reduced to change contact angles of pores in the microporous layer so as to increase the water vapor permeability, and the adhesive agent in the second slurry mixture may be increased so as to reduce the water vapor permeability.

[0043] Then, the surface of the gas diffusion layer subjected to hydrophobic treatment is coated with the first slurry mixture, after heat treatment, the microporous layer having high water vapor permeability after heat treatment is obtained, then coated with the second slurry mixture, to obtain the microporous layer having low water vapor permeability. Alternatively, the surface of the gas diffusion layer subjected to hydrophobic treatment is coated with the second slurry mixture, after heat treatment, the microporous layer having low water vapor permeability is obtained, then coated with the first slurry mixture, to obtain the microporous layer having high water vapor permeability. In the present disclosure, by controlling the coating process, the microporous layer having high water vapor permeability and the microporous layer having low water vapor permeability meet requirements for the above microporous layer structure. Specifically, in a coating process, a coating tool may be a scraper, or a coater with a slit, or a coater with a spray head. In the case of using a scraper, the thickness gradient may be controlled by changing heights of two ends of the scraper. For example, the microporous layer having high water vapor permeability can be coated by making the scraper on one end higher than the other end. The inclination direction of the scraper is changed when coating the second slurry mixture, which is opposite to that when coating the first slurry mixture. In this way, the two microporous layers prepared have a uniform total thickness. In the case of using a coater with a slit, coating thicknesses of different slurry mixtures may be controlled by adjusting the slit at one end to be wider than that at the other end.

[0044] The present disclosure further provides a membrane electrode assembly of a fuel cell, comprising an electrolyte membrane, a catalytic electrode layer, a microporous layer and a gas diffusion layer that are sequentially stacked. The microporous layer has the above described microporous layer structure. The microporous layer having high water vapor permeability of the microporous layer structure is arranged on a side of the gas diffusion layer. Reference is made to FIG. 1, which shows a cathode assembly of a fuel cell. A cathode structure and a microporous layer structure of the fuel cell can be seen clearly from FIG. 1. In the present disclosure, the microporous layer having high water vapor permeability may be arranged on the side of the gas diffusion layer. Similarly, the microporous layer having low water vapor permeability may be arranged on the side of the gas diffusion layer. In a specific embodiment, the microporous layer having high water vapor permeability is arranged on the side of the gas diffusion layer.

[0045] In the present disclosure, the microporous layer may comprise multiple layers based on actual requirements, which is not limited herein.

[0046] In order to further understand the present disclosure, the microporous layer structure according to the present disclosure will be described in detail below with reference to examples. The protection scope of the present disclosure is not limited by the following examples.

Example 1

[0047] A first dispersion liquid consisting of carbon powder A, polytetrafluoroethylene emulsion, deionized water and a surfactant was subjected to ultrasonic dispersion and mechanical agitation, to form a uniform slurry, which was coated on the side of the gas diffusion layer. The coating tool was a coater with a scraper. The thickness gradient from the air inlet to the air outlet was formed by changing the height of the scraper at both ends. In this way, the side of the scraper at the air inlet was lower than the other side of the scraper at the air outlet, such that the slurry applied on the side at the air inlet was thinner than that applied on the other side at the air outlet.

[0048] A first layer, that is microporous layer having high water vapor permeability was formed after heat treatment, which had a gradient distribution of thickness from the air inlet to the air outlet. The thickness at the air inlet was 10 μm, which was less than the thickness of 30 μm at the air outlet.

[0049] A second dispersion liquid consisting of carbon powder B, polytetrafluoroethylene emulsion, deionized water and a surfactant was subjected to ultrasonic dispersion and mechanical agitation, to form a uniform slurry for the microporous layer, which was coated on the surface of the first microporous layer. The coating tool was a coater with a scraper. The thickness gradient from the air inlet to the air outlet was formed by changing the height of the scraper at both ends. In this way, the side of the scraper at the air inlet was higher than the other side of the scraper at the air outlet, such that the slurry applied on the side at the air inlet was thicker than that applied on the other side at the air outlet. A second layer, that is microporous layer having low water vapor permeability was formed after heat treatment, which had a gradient distribution of thickness from the air inlet to the air outlet. The thickness at the air inlet was 30 μm, which was higher than the thickness of 10 μm at the air outlet. By adjusting an inclination angle of the scraper to be reverse or consistent from the air inlet to the air outlet when coating the first layer and the second layer of the microporous layer, the total thickness of the first layer and the second layer of the microporous layer was kept to be uniform 40 μm. The carbon powder A used had an average particle size of 50 nm, which was larger than the average particle size of 30 nm of the carbon powder B.

Example 2

[0050] A first dispersion liquid consisting of carbon powder A, polytetrafluoroethylene emulsion, deionized water and a surfactant was subjected to ultrasonic dispersion and mechanical agitation, to form a uniform slurry for the microporous layer, which was coated on the side of the gas diffusion layer. The coating tool was a coater with a scraper. In this way, the side of the scraper at the air inlet was as high as the other side of the scraper at the air outlet, such that a microporous layer having high water vapor permeability with uniform thickness was formed after heat treatment. The thickness of the microporous layer was equal to the total thickness of the two microporous layers in Example 1, i.e., 40 μm.

Example 3

[0051] A second dispersion liquid consisting of carbon powder B, polytetrafluoroethylene emulsion, deionized water and a surfactant was subjected to ultrasonic dispersion and mechanical agitation, to form a uniform slurry for the microporous layer, which was coated on the side of the gas diffusion layer. The coating tool was a coater with a scraper. In this way, the side of the scraper at the air inlet was as high as the other side of the scraper at the air outlet, such that a microporous layer having low water vapor permeability with uniform thickness was formed after heat treatment. The thickness of the microporous layer was equal to the total thickness of the two microporous layers in Example 1, i.e., 40 μm.

[0052] In Example 1, composite microporous layers with different thickness were prepared by using two kinds of carbon powders, which was respectively used in Example 2 and Example 3. The particle size of the carbon powder A was greater than that of the carbon powder B, so that the microporous layers prepared respectively with the carbon powder A and the carbon powder B have different pore distributions and porosities.

[0053] Water vapor permeability K relates to porosity, average pore size d.sub.pore and tortuosity of the pore, that is, d.sub.pore=(K/ηε).sup.0.5. In addition, capillary force P.sub.c of pores in the microporous layer relates to the difference between gas pressure and liquid pressure, that is, P.sub.c=(P.sub.1−P.sub.g).sup.∞ σ/d.sub.pore, wherein a represents surface energy. For a small pore size d.sub.pore, hydrostatic pressure of the pores is high, thus liquid water is difficult to flow into the pores, resulting in a low water vapor permeability. Based on the above formulas and theoretical analysis, the microporous layer prepared with the carbon powder with large particles has large porosity and large average pore size, thereby having a high water vapor permeability.

[0054] The microporous layers prepared in Example 1 to Example 3 were assembled to form a cathode of a fuel cell, and the performance of the fuel cell was tested. The testing conditions for data shown in FIG. 2 includes: inlet pressure of 200 KPa of the cathode, inlet RH of 30% of an anode, inlet RH of 42% of the cathode, and a stoichiometric ratio of 0.2 of the anode to the cathode. As shown in FIG. 2, the microporous layer had an EMA with gradient performance. At 90° C., the fuel cell showed higher performance of about 30 mV. At 75° C., the fuel cell showed similar performance. The testing conditions for data shown in FIG. 3 includes: inlet pressure of 200 KPa of the cathode, inlet RH of 100% of the anode, inlet RH of 100% of the cathode, and a stoichiometric ratio of 2.0 of the anode to the cathode. As shown in FIG. 3, the microporous layer had an EMA with gradient performance. At 55° C., the fuel cell showed a higher performance of about 20 mV. At 80° C., the fuel cell showed a higher performance of about 10 mV.

[0055] The above description of the examples is only used to facilitate understanding of the method and core concept of the present disclosure. It should be noted that for those skilled in the art, various improvements and modifications may be made without departing from the principle of the present disclosure, and these improvements and modifications should fall within the scope of protection of the present disclosure.

[0056] Based on the above description of the disclosed embodiments, those skilled in the art can implement or carry out the present disclosure. It is apparent for those skilled in the art to make many modifications to these embodiments. The general principle defined herein may be applied to other embodiments without departing from the spirit or scope of the present disclosure. Therefore, the present disclosure is not limited to the embodiments illustrated herein, but should be defined by the widest scope consistent with the principle and novel features disclosed herein.