CN113451589A

CN113451589A - Gas diffusion layer, preparation method thereof, membrane electrode assembly and fuel cell

Info

Publication number: CN113451589A
Application number: CN202010222617.3A
Authority: CN
Inventors: 余俊良; 周飞鲲; 袁述; 田冬伟; 贾风; 许永亮
Original assignee: Guangzhou Automobile Group Co Ltd
Current assignee: Guangzhou Automobile Group Co Ltd
Priority date: 2020-03-25
Filing date: 2020-03-25
Publication date: 2021-09-28
Anticipated expiration: 2040-03-25
Also published as: CN113451589B

Abstract

The invention discloses a gas diffusion layer with a multi-layer microporous structure, which comprises a flow channel interface layer, a buffer layer, a fluid guide layer and an ultramicropore layer which are sequentially stacked and arranged in the flow guide direction of reaction gas in a fuel cell; wherein the porosity of the flow channel interface layer is smaller than the porosity of the fluid guiding layer and larger than the porosity of the ultramicropores, and a porosity gradient with gradually increased porosity along the first direction is arranged on the buffer layer; the buffer layer with porosity gradient is arranged, so that water generated by the fuel cell during electrochemical reaction is drained in a relatively soft form, the problem of 'membrane dryness' is effectively avoided, and meanwhile, the problem of 'water flooding' is also avoided when the problem of 'membrane dryness' of the fuel cell is avoided through the combined porosity gradient formed by the ultramicropore layer, the fluid guide layer, the buffer layer and the flow channel interface layer, so that the water balance of the fuel cell is effectively maintained, and the performance of the fuel cell is improved.

Description

Gas diffusion layer, preparation method thereof, membrane electrode assembly and fuel cell

Technical Field

The invention relates to the technical field of hydrogen fuel cells, in particular to a gas diffusion layer, a preparation method of the gas diffusion layer, a membrane electrode assembly and a fuel cell.

Background

The fuel cell is also called as a proton exchange membrane fuel cell, is currently recognized as one of energy conversion devices for realizing low emission or zero emission, and has the working principle of converting chemical energy of hydrogen and oxygen into electric energy through electrochemical catalytic reaction and providing a driving device for electric power; the energy-saving device has the advantages of low working temperature, quick start, high energy conversion efficiency, environmental friendliness, simple structure, convenience in operation and the like, is known as a preferred energy source of the electric automobile, and becomes a mainstream power source of the current fuel cell automobile.

The core component of the fuel cell is membrane electrode material, which is compounded and synthesized by proton exchange membrane, catalyst layer and gas diffusion layer through hot pressing process, and combined with polar plate to form the basic structure of the fuel cell. During the operation of the fuel cell, the reaction gas is guided by the polar plate and then diffused to the surface of the catalyst by the gas diffusion layer to react, and the water of the reaction product passes out of the gas diffusion layer and is merged into the gas flow to be discharged. The gas diffusion layer is the most important component of the fuel cell, is made of a conductive porous material, plays multiple roles of supporting a catalyst layer, collecting current, conducting gas, discharging water and the like, realizes redistribution of reaction gas and product water between a flow field and the catalyst layer, is one of key components influencing the performance of an electrode, directly influences the working efficiency of the fuel cell, and particularly influences the reliability and the service life of the fuel cell while influencing the performance of the fuel cell under variable or extreme working environments.

However, the design of the gas diffusion layer is more simplified at present, for example, the invention patent with the application number of 201010524791.X discloses a gas diffusion layer with a gradient pore structure and the preparation and application thereof, the gas diffusion layer is formed by laminating a macroporous carbon-based support body and a microporous layer, the forming material of the microporous layer is embedded into the clamping control carbon-based support body from one side of the macroporous carbon-based support body far away from the battery flow field to form a transition hole layer, the curvature of the reaction gas transmission in the gas diffusion layer from the side adjacent to the flow field to the side adjacent to the catalytic layer is in a gradient increasing trend, the single structure effectively increases the mass transfer curvature of water and gas in the gas diffusion layer, is favorable for maintaining liquid water in the battery, however, the water balance in the fuel cell cannot be guaranteed, and the fuel cell is easily flooded, so that the performance of the fuel cell is reduced.

Therefore, how to ensure the water balance in the fuel cell to improve the performance of the fuel cell is a problem which needs to be solved urgently in the field of the fuel cell at present.

Disclosure of Invention

In view of the above-mentioned shortcomings of the prior art, the main object of the present invention is to provide a gas diffusion layer applied to a fuel cell, a method for preparing the same, a membrane electrode assembly using the gas diffusion layer, and a fuel cell, and the present invention aims to ensure water balance in the fuel cell and improve the performance of the fuel cell.

A gas diffusion layer is applied to a fuel cell, is of a multi-layer microporous structure and comprises a flow channel interface layer, a buffer layer, a fluid guide layer and a super-microporous layer which are sequentially stacked and arranged in a first direction;

wherein the first direction is a flow guiding direction of reactant gas in the fuel cell, a porosity of the flow channel interface layer is smaller than a porosity of the fluid guiding layer and larger than a porosity of the ultramicropores, and a porosity gradient in which the porosity gradually increases along the first direction is provided on the buffer layer.

Specifically, the buffer layer includes a plurality of first fiber layers arranged in layers in the first direction,

wherein the porosity of each first fiber layer of the buffer layer gradually increases in the first direction.

Preferably, each first fibre layer of the buffer layer is provided with a first coating,

wherein the first contact angle of the first coating layer of each first fiber layer of the cushioning layer tapers in the first direction.

Preferably, the fluid guiding layer is formed by mixing carbon nano-particles and carbon nano-tubes,

wherein the carbon nanotubes penetrate the fluid guiding layer in the first direction for guiding water entering the fluid guiding layer from the ultra-microporous layer into the buffer layer.

Preferably, the average particle diameter of the carbon nano-particles is 5-6 μm, and the average tube diameter of the carbon nano-tubes is 10-12 μm.

Preferably, the flow channel interface layer includes a plurality of second fiber layers stacked in the first direction,

and a second coating is coated on each second fiber layer of the flow channel interface layer, and a second contact angle of the second coating of each second fiber layer is gradually increased along the first direction.

Preferably, the ultra-microporous layer is a porous medium formed by sintering carbon particles, wherein the average particle size of the carbon particles is 2-3 μm, and the average pore size of the ultra-microporous layer is 5-6 μm.

Preferably, the thickness of the ultramicropore layer is smaller than that of the flow guiding layer, the thickness of the flow guiding layer is smaller than that of the buffer layer, and the thickness of the buffer layer is smaller than that of the flow channel interface layer.

Preferably, the microporous layer, the fluid guiding layer, the buffer layer and the flow channel interface layer are processed separately and then laminated together.

A membrane electrode assembly comprises a cathode gas diffusion layer, a cathode catalyst layer, a proton exchange membrane, an anode catalyst layer and an anode gas diffusion layer which are sequentially stacked;

wherein the cathode gas diffusion layer is a gas diffusion layer as described above.

A fuel cell comprising a membrane electrode assembly as described above.

Compared with the prior art, the gas diffusion layer provided by the invention is of a multi-layer microporous structure and comprises a flow channel interface layer, a buffer layer, a fluid guide layer and a super-microporous layer which are sequentially stacked and arranged in the flow guide direction of reaction gas in the fuel cell; wherein the porosity of the flow channel interface layer is smaller than the porosity of the fluid guiding layer and larger than the porosity of the ultramicropores, and a porosity gradient with gradually increased porosity along the first direction is arranged on the buffer layer; the buffer layer with porosity gradient is arranged, so that water generated by the fuel cell during electrochemical reaction is drained in a relatively soft form, the problem of 'membrane dryness' is effectively avoided, and meanwhile, the problem of 'water flooding' is also avoided when the problem of 'membrane dryness' of the fuel cell is avoided through the combined porosity gradient formed by the ultramicropore layer, the fluid guide layer, the buffer layer and the flow channel interface layer, so that the water balance of the fuel cell is effectively maintained.

Drawings

FIG. 1 is a schematic cross-sectional view of a gas diffusion layer according to an embodiment of the present invention;

FIG. 2 is a graph of contact angle and porosity for each layer structure of a gas diffusion layer according to an example of the present invention;

FIG. 3 is a schematic cross-sectional view of a fluid conducting layer of the present invention;

reference numerals:

10-gas diffusion layer, 11-flow passage interface layer, 12-buffer layer, 13-fluid guiding layer, 131-carbon nano particle, 132-carbon nano tube and 14-ultramicropore layer.

The implementation, functional features and advantages of the objects of the present invention will be further explained with reference to the accompanying drawings.

Detailed Description

In order to make the aforementioned objects, features and advantages of the present invention more comprehensible, embodiments of the present invention are described in detail below with reference to the accompanying drawings; it should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. Various substitutions and alterations can be made by those skilled in the art and by conventional means without departing from the spirit of the method of the invention described above.

At present, the basic components of a fuel cell include a proton exchange membrane, a catalyst layer, a gas diffusion layer, and a plate. The proton exchange membrane and the catalyst layer are used as main fields of electrochemical reaction in the fuel cell, and the generated energy which can be theoretically reached by the fuel cell is determined; the polar plate is divided into a unipolar plate and a bipolar plate, is applied to a fuel cell stack, has the functions of conducting all monocells in the stack, conveying electrochemical reactants to a gas diffusion layer through channels on the monocells, dredging products of electrochemical reaction, and meanwhile has high conductivity and is used for outputting electric energy to the outside.

The gas diffusion layer is positioned between the proton exchange membrane and the catalyst layer, is the outermost layer of the membrane electrode assembly, provides contact for the membrane electrode assembly and the polar plate, conveys reactants to the catalyst layer, and allows water of a reaction product to leave the surface of the electrode to allow the water to pass between the electrode and the flow channel; and functions of current conduction, mechanical support of the proton exchange membrane, porous media attached with the catalyst, reaction channels of the catalyst layer, product water removal and the like. The performance of the fuel cell is directly affected by the performance of the fuel cell, and particularly, the reliability and the service life of the fuel cell are affected by the gas diffusion layer under variable or extreme operating environments. An ideal gas diffusion layer should satisfy 3 conditions: good drainage, good air permeability and good electrical conductivity.

In view of the above requirements, most of the materials currently used for the gas diffusion layer of the fuel cell are porous carbon materials such as carbon paper (carbon fiber paper) or carbon cloth (carbon fiber cloth), and a microporous layer is coated on one side surface thereof, so that the product water can be rapidly discharged, preventing the "flooding" problem peculiar to the fuel cell; however, the design route of the gas diffusion layer is single, and only the water drainage function is considered, so that the product water of the electrochemical reaction is rapidly discharged, so that the proton exchange membrane which can work efficiently only by maintaining a certain humidity originally becomes very easy to enter the low-humidity working environment, and the water balance of the fuel cell is caused to be a problem, namely another specific problem in the fuel cell: "film dry". In the existing fuel cell system, in order to solve the problem of 'dry membrane', humidification equipment is usually added for use, an additional humidifier is expensive, the accessory cost of the fuel cell is increased, and the volume of the fuel cell is increased, so that the volume power density of the fuel cell system is reduced, and the system power is also consumed, that is, the accessory energy consumption of the fuel cell is increased. Therefore, how to utilize the product water of the electrochemical reaction of the fuel cell to realize the water balance of the fuel cell without an additional humidifying device is a research focus of the current fuel cell.

The invention designs the gas diffusion layer with a certain buffer effect from the gas diffusion layer of the fuel cell, so that the product water of the electrochemical reaction of the fuel cell is dredged out in a relatively soft form, the water balance of the fuel cell is achieved as far as possible, the problems of 'water logging' and 'membrane dryness' are effectively avoided, the use requirement that the fuel cell needs to be matched with humidifying equipment is fundamentally reduced, and the auxiliary part cost and the auxiliary part energy consumption of the fuel cell system are reduced. The structure of the gas diffusion layer will be described in further detail below.

Referring to fig. 1, fig. 1 is a schematic structural diagram of a gas diffusion layer 10 according to an embodiment of the present invention, where the gas diffusion layer 10 is applied to a fuel cell and has a multi-layer microporous structure, and the multi-layer microporous structure includes a flow channel interface layer 11, a buffer layer 12, a fluid guide layer 13, and a microporous layer 14, which are sequentially stacked in a first direction; wherein the first direction a is a flow direction of the reactant gas in the fuel cell, as indicated by arrow a in fig. 1, which is opposite to a flow direction of the product water in the fuel cell (i.e., a second direction B), as indicated by arrow B in fig. 1; in addition, the porosity of the flow channel interface layer 11 is smaller than the porosity of the fluid guiding layer 13 and larger than the porosity of the microporous layer 14, and a porosity gradient in which the porosity gradually increases along the first direction a is provided on the buffer layer 12.

It should be noted that the determination of the porosity in this embodiment can be based on the existing porosity testing method, and is not emphasized here. By performing gradient design on the porosity of the multi-layer microporous structure of the gas diffusion layer 10, when the porosity of the flow channel interface layer 11 is smaller than the porosity of the fluid guide layer 13 and the buffer layer 12 is provided with a porosity gradient in which the porosity gradually increases along the first direction a, the siphon force of the corresponding flow channel interface layer 11 is greater than the siphon force of the fluid guide layer 13, and the siphon force gradually increases from the fluid guide layer 13 to the buffer layer 12 to the flow channel interface layer 11; when the porosity of the runner interface layer 11 is greater than that of the ultramicropore layer 14, the siphon force corresponding to the runner interface layer 11 is less than the siphon force of the ultramicropore layer 14; that is, the siphon force of the fluid guiding layer 13 in the middle of the multi-layer microporous structure of the gas diffusion layer 10 is greater than the siphon force of the microporous layers 14 and the channel interface layer 11 on both sides, and the siphon force of the channel interface layer 11 is greater than the siphon force of the microporous layers 14, while the siphon force is gradually increased from the fluid guiding layer 13 to the buffer layer 12 to the channel interface layer 11; thus, when the product water of the fuel cell is discharged through the gas diffusion layer 10, the flow rate of the product water entering the ultra-microporous layer 14 is the fastest, but after entering the ultra-microporous layer 14, the flow rate of the product water entering the fluid guiding layer 13 is slowed down due to the difference of the siphon force of the fluid guiding layer 13 compared with that of the ultra-microporous layer 14, and the flow rate of the product water entering the buffer layer 13 is slowly increased until the flow rate of the product water entering the flow channel interface layer 11 is slower than that of the product water entering the ultra-microporous layer 14, so that the reaction product water of the fuel cell can rapidly enter the gas diffusion layer 10 from the catalyst layer but can not be rapidly discharged from the gas diffusion layer 10, and the gas diffusion layer 10 can better keep the reaction product water in the multi-layer microporous structure thereof, thereby maintaining the water balance of the fuel cell and preventing the problems of 'water flooding' and 'dry film'.

Further, the buffer layer 12 comprises a plurality of first fiber layers stacked in the first direction a, wherein the porosity of each first fiber layer of the buffer layer 12 gradually increases in the first direction, i.e. the buffer layer 12 is provided with a porosity gradient along the first direction a. In practical implementation, each first fiber layer of the buffer layer 12 may be a carbon fiber layer woven by carbon fibers, and each first fiber layer may be woven by carbon fibers with different diameters, wherein the number of carbon fibers used in weaving each first fiber layer is the same, but the diameters of the carbon fibers used in weaving are different; specifically, the diameter of the carbon fiber used in each carbon fiber layer is regularly woven layer by layer from large to small in the first direction, and then the porosity of each first fiber layer forming the buffer layer 12 gradually increases in the first direction, as shown in fig. 2, the porosity of each first fiber layer in the buffer layer 12 decreases from 0.9 to 0.7 in the flow direction of the reaction product water (i.e., the second direction B). The plurality of first fiber layers of the buffer layer 12 form a gradient due to porosity, such that a positive gradient of siphon force in the second direction B is generated in the buffer layer 12, and water generated from the electrochemical reaction of the fuel cell is more easily discharged out of the gas diffusion layer 10 by the siphon force gradient.

In addition, in order to make the buffer layer 12 function as a fluid buffer, each first fiber layer of the buffer layer 12 is provided with a first coating, and a first contact angle of the first coating of each first fiber layer of the buffer layer 12 gradually decreases along the first direction a to form a first contact angle gradient, that is, the buffer layer 12 is provided with a first contact angle gradient in which the first contact angle gradually decreases along the first direction a, so that water produced by the electrochemical reaction is gently discharged from the gas diffusion layer in a dry and low-humidity operating environment. As shown in fig. 2, specifically, along the flowing direction of the reaction product water (i.e., the second direction B), the first contact angle of the first coating layer of each first fiber layer is transited from 90 ° to 120 °, which forms a fluid surface tension opposite to the flowing direction of the liquid, thereby blocking the flowing of the liquid water and acting as a buffer of the liquid water. The buffer layer 12 solves the problem that the fuel cell is too fast to discharge product water under a low-humidity environment, which causes the problem of 'dry membrane' of the fuel cell by setting a porosity gradient and a first contact angle gradient.

It should be noted that the flow channel interface layer 11 herein includes a plurality of second fiber layers stacked in the first direction a, specifically, since the flow channel interface layer 11 directly contacts with the polar plate of the fuel cell, it will bear a certain compression force from the polar plate, and each second fiber layer of the flow channel interface layer 11 is made of carbon fiber layers, and is formed by weaving and pressing carbon fibers. Wherein, the porosity of each second carbon fiber layer can be the same, specifically, the porosity of each second carbon fiber layer is set to 0.7; which is less than the porosity of the flow guiding layer 13 but greater than the porosity of the microporous layer 14, as shown in fig. 2, forms a continuous gradient with the flow guiding layer 13 through the buffer layer 12, facilitating the drainage of product water. Further, each second fiber layer of the flow channel interface layer 11 is coated with a second coating, and a second contact angle of the second coating of each second fiber layer gradually increases along the first direction a, specifically, a porous structure built by multiple second fiber layers is provided with a second contact angle gradient from large to small along the second direction B, that is, the flow channel interface layer 11 is provided with a second contact angle gradient from small to large along the first direction a; specifically, as shown in fig. 2, the second contact angle of the second fiber layers is gradually changed from 120 ° to 90 ° along the second direction B, and the second contact angle gradient forms a driving force along the flowing direction of the reaction product water (i.e., the second direction B), and the driving force of the water flow in the direction can promote the product water passing through the buffer layer 12 to rapidly leave the whole gas diffusion layer, so as to ensure that the fuel cell does not suffer from the "flooding" problem and the product water is timely discharged out of the gas diffusion layer, while the water retention of the whole gas diffusion layer is considered.

Specifically, as shown in fig. 3, the fluid guiding layer 13 is formed by mixing carbon nanoparticles 131 and carbon nanotubes 132, wherein the average particle diameter of the carbon nanoparticles 131 is 5-6 μm, and the carbon nanotubes 132 are randomly stacked together to form a porous medium, the carbon nanotubes 132 penetrate through the fluid guiding layer 13 in the first direction a, the carbon nanotubes 132 are hollow-filled, and the average diameter of the carbon nanotubes is 10-12 μm, which is twice the particle diameter of the carbon nanoparticles 131, and is used for guiding water entering the fluid guiding layer 13 from the ultra-microporous layer 14 to enter the buffer layer 12. The flow resistance of the product water of the electrochemical reaction of the fuel cell in the carbon nanotube 132 is much smaller than that in the porous medium formed by the carbon nano 131 particles, so that the reaction product water tends to flow through the fluid guiding layer 13 through the carbon nanotube 132, the liquid water of the reaction product can be guided into the buffer layer 12 rapidly at a certain rate and direction, the product water is shortened, and the porous structure formed by the carbon nano 131 can leave sufficient space for the gaseous reactant to flow from the flow channel interface layer 11 to the ultra-microporous layer 14 along the first direction a because of no accumulation of the liquid water; meanwhile, in order to avoid the flow of product water along the direction parallel to the first direction A and shorten the residence time of the water ultramicropore layer 14, the whole fluid guide layer 13 is coated, namely the contact angle is adjusted to 120 degrees through the same hydrophobic material treatment, so that the problem of 'water logging' of the fuel cell is prevented.

Specifically, the microporous layer 14 is a porous medium formed by sintering small carbon nanoparticles having an average particle diameter of 2 to 3 μm, which is smaller than the particle diameter of the carbon nanoparticles 11 in the fluid guide layer 13, and an average pore diameter of 5 to 6 μm, so that the porous medium has a superior siphon ability, and water, which is a reaction product, can rapidly flow in and be discharged through the microporous layer by the siphon force. In addition, in order to provide the microporous layer 14 with a certain water retention capability while providing a siphon drainage capability, as shown in fig. 2, the microporous layer is not coated to ensure that the contact angle of the product water therein is equal to the contact angle of water on the carbon substrate, i.e., 90 °.

In addition, the thickness of the ultramicropore layer 14 is smaller than that of the fluid guiding layer 13, the thickness of the fluid guiding layer 13 is smaller than that of the buffer layer 12, and the thickness of the buffer layer 12 is smaller than that of the flow channel interface layer 11; that is, the thickness of the microporous layer, the fluid guiding layer, the buffer layer and the flow channel interface layer, which are sequentially stacked in the second direction B, is gradually increased, wherein the thickness of the buffer layer 12 may be appropriately adjusted according to the humidity of the use environment, and specifically, the thickness of the buffer layer may be set to 1/3 of the thickness of the gas diffusion layer 10, so that the gas diffusion layer 10 may be better optimized, and the water balance of the fuel cell during the electrochemical reaction may be adjusted.

Further, as shown in fig. 2, the present invention provides a gas diffusion layer as a multi-layered integrated porous structure, and the ultra-microporous layer 14 is formed by depositing small carbon nanoparticles having a small pore size to form a carbon nano-porous medium having a porosity of 0.6, and can ensure that the generated liquid water can uniformly pass through the ultra-microporous layer without a special hydrophobic treatment. The fluid guiding layer 13 is formed by mixing carbon nano-particles 131 and carbon nano-tubes 132, the carbon nano-tubes 132 are arranged in a penetrating manner along the flowing direction of liquid water, liquid water generated by the fuel cell is guided to flow to the buffer layer 12 at a certain speed, and in addition, in order to further prevent the occurrence of a flooding phenomenon in the operation process of the fuel cell, the whole fluid guiding layer 13 is processed by the same hydrophobic material, and the contact angle of the whole fluid guiding layer 13 is adjusted to 120 degrees. A plurality of first fiber layers with gradient porosity along the first direction A are arranged on the buffer layer 12, wherein the porosity of the first fiber layer close to the fluid guide layer 13 is relatively high (0.9), and the porosity of the first fiber layer close to the flow channel interface layer 11 is relatively low (0.7); and the plurality of first fiber layers of the buffer layer 12 are treated by the stepped hydrophobic material along the gas flow guiding direction (i.e. the first direction a), the first contact angle of the first coating of the first fiber layer near the fluid guiding layer 13 is small (90 °), and the first contact angle of the first coating of the first fiber layer near the flow channel interface layer 11 is large (120 °). The flow channel interface layer 11 is formed by stacking a plurality of second fiber layers, and is required to have good mechanical ductility and be less prone to mechanical damage; the porosity of the flow channel interface layer 10 is the same as the porosity of the junction of the buffer layer 12 and the flow channel interface layer 11, and is 0.7, and a second coating is arranged on a second fiber layer forming the flow channel interface layer 11, wherein the hydrophilic and hydrophobic integrity of the surfaces of the multiple layers of second fiber layers is distributed in a certain gradient along the gas flow guiding direction (the first direction a), the second contact angle of the second coating of the part of the second fiber layer close to the buffer layer is 120 degrees, and the second contact angle of the second coating of the part of the second fiber layer close to the surface of the gas diffusion membrane is 90 degrees.

According to the invention, the gas diffusion layer 10 with a multi-layer microporous structure is reasonably arranged, so that the integration and compatibility of the gas diffusion layer 10 are improved, and the structure of each layer is refined, so that the gas diffusion layer can be compatible with changeable fuel cell operating conditions and covers the operating conditions under different humidities. Specifically, the present invention adopts the structure shown in fig. 1, such as the porosity gradient and the hydrophobic gradient shown in fig. 2, to form the microporous layer 14, the fluid guiding layer 13, the buffer layer 12, and the flow channel interface layer 11, and simultaneously takes effective advantage of the siphon force effect and the liquid surface tension effect in the porous medium, so as to realize the water retention and drainage of the gas permeable membrane of the present invention to liquid water through the two physical gradients; for example, in the flowing direction of the reaction product water, when the porosity is changed from large to small, the siphon force corresponding to the microporous structure is changed from small to large, so that the microporous structure has stronger water retention property, and the risk of 'membrane dry' of the fuel cell is reduced; on the contrary, when the porosity is transited from small to large, the siphon force corresponding to the microporous structure is changed from large to small, so that the microporous structure has stronger hydrophobicity, the drainage capability of generated liquid water is improved, the risk of 'water logging' of the fuel cell is reduced, namely the problems of 'water logging' and 'membrane dryness' of the fuel cell in a low-humidity or dry running environment are balanced, the fuel cell runs under the self-created water balance for a long time, and the influence of the external humidity environment on the fuel cell is eliminated.

The preparation method of the gas diffusion layer can be used for respectively processing the ultramicropore layer 14, the fluid guide layer 13, the buffer layer 12 and the flow channel interface layer 11 and then laminating and pressing the two layers together. Wherein, the ultra-microporous layer 14 forms a porous medium with average porosity of 0.6 through deposition of carbon nano particles, and plating treatment is not carried out, so that the surface contact angle is ensured to be 90 degrees; the fluid guiding layer 13 is formed by penetrating carbon nanotubes 132 into carbon nanoparticles 131 in a first direction a and sintering, and in order to facilitate the attachment of the microporous layer 14 and the fluid guiding layer 13, the porosity of the fluid guiding layer 13 is 0.9, which is greater than that of the microporous layer, and in addition, the contact angle of the whole fluid guiding layer 13 is adjusted to 120 ° by the treatment of the same hydrophobic material; the buffer layer 12 is a plurality of first fiber layers with different porosities, which are formed by weaving a plurality of carbon fibers with different thicknesses layer by layer, wherein the porosity of each first fiber layer increases layer by layer in the first direction a, and simultaneously, different hydrophobic materials are coated on each first fiber layer to form first coatings with different first contact angles, wherein the first contact angle of the first coating of each first fiber layer gradually decreases in the first direction a, namely, the first contact angle gradually changes from 120 degrees to 90 degrees; the flow channel interface layer 11 is also formed by randomly building carbon fibers, and in order to ensure that the second contact angle gradually changes from 120 degrees to 90 degrees along the second direction B, the second fiber layers formed by the carbon fibers are processed layer by layer, different hydrophobic coatings are applied, and finally each layer of the second fiber layers is pressed and combined.

It should be noted that, during the actual preparation of the gas diffusion layer, the thicknesses of the respectively processed ultramicropore layer 14, the fluid guiding layer 13, the buffer layer 12 and the channel interface layer 11 are thicker than the thicknesses of the corresponding layers in the gas diffusion layer 10, specifically, the thickness of the respectively processed ultramicropore layer 14 is increased by 20% than the thickness of the layer laminated in the gas diffusion layer, the thickness of the fluid guiding layer 13 is increased by 20% than the thickness of the layer laminated in the gas diffusion layer, and the same is true for the buffer layer and the channel interface layer, mainly during the preparation of the gas diffusion layer, each layer has both sides processing and compression margins during the lamination and lamination processing, so as to ensure that the obtained thickness parameter of the gas diffusion layer is better, and the processing yield is higher.

Further, the gas diffusion layer is applied to a membrane electrode assembly which comprises a cathode gas diffusion layer, a cathode catalyst layer, a proton exchange membrane, an anode catalyst layer and an anode gas diffusion layer which are sequentially stacked; the cathode gas diffusion layer is the gas diffusion layer, specifically, an ultramicropore layer in the gas diffusion layer is tightly attached to the cathode catalyst layer, and the flow channel interface layer is used for directly contacting with a polar plate flow channel of the fuel cell.

When the membrane electrode assembly is used in a fuel cell, liquid water generated by electrochemical reaction of the fuel cell sequentially passes through the ultramicropore layer, the fluid guide layer, the buffer layer and the flow channel interface layer and is discharged out of the fuel cell along the polar plate flow channel. The gas diffusion layer of the fuel cell balances the water balance of the fuel cell during operation by virtue of the design of the buffer layer and the fluid guide layer, avoids the problems of 'membrane dryness' and 'water flooding' when the fuel cell is used, reduces the addition and the use of humidifying equipment, reduces the accessory cost and the accessory energy consumption in a fuel cell system, and optimizes the performance of the fuel cell. The sequence numbers in the above embodiments of the present invention are merely for description and do not represent the merits of the embodiments.

The above description is only a preferred embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes, which are made by using the contents of the present specification and the accompanying drawings, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.

Claims

1. A gas diffusion layer for use in a fuel cell, comprising: the gas diffusion layer is of a multilayer microporous structure and comprises a flow channel interface layer, a buffer layer, a fluid guide layer and a super-microporous layer which are sequentially stacked and arranged in a first direction;

2. The gas diffusion layer of claim 1, wherein: the cushioning layer includes a plurality of first fiber layers arranged in a stacked manner in the first direction,

3. The gas diffusion layer of claim 2, wherein: each first fiber layer of the buffer layer is provided with a first coating,

4. The gas diffusion layer of claim 1, wherein: the fluid guide layer is formed by mixing carbon nano-particles and carbon nano-tubes,

5. The gas diffusion layer of claim 4, wherein: the average particle diameter of the carbon nano-particles is 5-6 μm, and the average pipe diameter of the carbon nano-tubes is 10-12 μm.

6. The gas diffusion layer of claim 1, wherein: the flow channel interface layer includes a plurality of second fiber layers stacked in the first direction,

7. The gas diffusion layer of claim 1, wherein: the microporous layer is a porous medium formed by sintering carbon particles, wherein the average particle size of the carbon particles is 2-3 mu m, and the average pore size of the microporous layer is 5-6 mu m.

8. The gas diffusion layer of claim 1, wherein: the thickness of the ultramicropore layer is smaller than that of the fluid guide layer, the thickness of the fluid guide layer is smaller than that of the buffer layer, and the thickness of the buffer layer is smaller than that of the flow channel interface layer.

9. A method of preparing a gas diffusion layer according to any of claims 1 to 8, wherein: the ultramicropore layer, the fluid guide layer, the buffer layer and the flow channel interface layer can be respectively processed and then laminated together.

10. A membrane electrode assembly characterized by: the cathode gas diffusion layer, the cathode catalyst layer, the proton exchange membrane, the anode catalyst layer and the anode gas diffusion layer are sequentially stacked;

wherein the cathode gas diffusion layer is a gas diffusion layer according to any one of claims 1 to 8.

11. A fuel cell, characterized by: the fuel cell comprising the membrane electrode assembly according to claim 10.