An ordered structure gas diffusion layer with pore gradient and hydrophobic gradient and its processing method

Abstract

The present invention provides an ordered structure gas diffusion layer with pore gradient and hydrophobic gradient and a processing method thereof. A spherical pore structure is provided in the gas diffusion layer, and adjacent spherical pore structures are interconnected; the gas diffusion layer is divided into a ridge region gas diffusion layer and a flow channel region gas diffusion layer; the flow channel region gas diffusion layer is located between two ridge region gas diffusion layers; the pore diameter of the spherical pore structure shows a gradient decreasing distribution from the flow channel region gas diffusion layer to the ridge region gas diffusion layer; the hydrophobicity of the ridge region gas diffusion layer is higher than that of the flow channel region gas diffusion layer. The present invention can reduce the liquid water transport resistance and regulate the breakthrough position of liquid water, effectively prevent the accumulation of liquid water under the bipolar plate ridge to solve the flooding problem, and increase the contact area between the gas diffusion layer and other components of the membrane electrode, enhancing the conductivity.

Description

Technical Field

[0001] The present invention relates to the field of fuel cells, and particularly to an ordered structure gas diffusion layer with pore gradient and hydrophobic gradient and a processing method thereof. Background Art

[0002] The gas diffusion layer is the base layer that supports the catalyst layer, stabilizes the electrode structure, and provides gas, electron, and drainage channels for the electrode reaction. During the operation of a fuel cell, a large amount of liquid water is generated. If excessive liquid water accumulates in the gas diffusion layer, it will block the gas transport channels, resulting in a flooding phenomenon, which will damage the performance, stability, and lifespan of the fuel cell. The gas diffusion layer in the area below the bipolar plate ridge cannot directly contact the flow channel, so the liquid water cannot be purged, and thus the flooding problem is more serious. Traditional gas diffusion layers are mainly made of porous materials such as carbon paper and carbon cloth. The carbon fiber distribution is disordered, and the pore distribution is random. Therefore, the resistance to water transport is large, and the breakthrough position of liquid water cannot be controlled. Therefore, the optimized design of the pore distribution and hydrophobicity of the gas diffusion layer has become an important method to improve the liquid water transport efficiency and solve the flooding problem.

[0003] The prior art discloses a structural design and manufacturing method of an ordered gas diffusion layer. A three-dimensional structure template is manufactured through a two-photon microfabrication system, and then the ordered gas diffusion layer structure is manufactured using the micro-transfer molding technology. This structure provides an optimal path for gas and electron transport, improving the performance of the fuel cell. However, the micropores in this structure are evenly distributed, and the gas diffusion layer area below the bipolar plate ridge has not been structurally optimized. The generated liquid water is likely to accumulate below the ridge, resulting in a flooding phenomenon. Moreover, the contact area between the gas diffusion layer and the other components of the fuel cell membrane electrode is small, increasing the contact resistance.

[0004] The prior art discloses a stepped hydrophobic gas diffusion layer and a preparation method thereof. By strengthening the hydrophobic treatment of the gas diffusion layer below the bipolar plate ridge, the gas diffusion layer is divided into a common hydrophobic area and a strengthened hydrophobic area, thereby reducing the flooding problem of the gas diffusion layer below the bipolar plate ridge. However, this design only optimizes the hydrophobicity of the gas diffusion layer. Due to the disordered structure of the traditional gas diffusion layer, the breakthrough position of liquid water still cannot be effectively controlled. Therefore, its effect on solving the flooding problem below the ridge is very limited. Summary of the Invention

[0005] In view of the deficiencies in the prior art, the present invention provides an ordered structure gas diffusion layer with pore gradient and hydrophobic gradient and its processing method. It not only designs the pore gradient of the ordered gas diffusion layer by using the method of spherical cavity array, but also strengthens the hydrophobic design of the area under the ridge to form a hydrophobic gradient. Such a design can not only reduce the liquid water transport resistance and regulate the breakthrough position of liquid water, effectively prevent the accumulation of liquid water under the bipolar plate ridge and solve the flooding problem, but also increase the contact area between the gas diffusion layer and other membrane electrode components and enhance the conductivity.

[0006] The present invention achieves the above technical objectives through the following technical means.

[0007] An ordered structure gas diffusion layer with pore gradient and hydrophobic gradient, in which spherical pore structures are provided in the gas diffusion layer, and adjacent spherical pore structures are interconnected; the gas diffusion layer is divided into a ridge area gas diffusion layer and a flow channel area gas diffusion layer; the ridge area gas diffusion layer is located under the bipolar plate; the flow channel area gas diffusion layer is located under the flow channel; the flow channel area gas diffusion layer is located between two ridge area gas diffusion layers; the pore diameter of the spherical pore structure shows a gradient decrease distribution from the flow channel area gas diffusion layer to the ridge area gas diffusion layer, which is used to actively regulate the breakthrough of liquid water from the flow channel; the hydrophobicity of the ridge area gas diffusion layer is higher than that of the flow channel area gas diffusion layer to prevent flooding in the ridge area gas diffusion layer of the bipolar plate and accelerate the transport of water in the gas diffusion layer.

[0008] Furthermore, the pore diameter of the spherical pore structure shows a distribution of first gradient increase and then gradient decrease in the ridge area gas diffusion layer - flow channel area gas diffusion layer - ridge area gas diffusion layer. Through the design of the spherical pore structure, the appearance of sharp pore structures is avoided, the liquid water flow resistance is reduced, and the liquid water transport is accelerated.

[0009] Furthermore, the sphere diameter of the pores in the spherical pore structure of the ridge area gas diffusion layer is 20 - 50 μm; the sphere diameter of the pores in the spherical pore structure of the flow channel area gas diffusion layer is 50 - 80 μm.

[0010] Furthermore, the porosity of the spherical pore structures in the gas diffusion layer gradually decreases from the flow channel area gas diffusion layer to the ridge area gas diffusion layer. Since a smaller porosity has a greater capillary pressure, it drives the liquid water to move along the pore gradient direction, that is, from the ridge area gas diffusion layer to the flow channel area gas diffusion layer, thereby regulating the breakthrough of liquid water in the flow channel area gas diffusion layer. The breakthrough occurs in the flow channel and is directly purged by the gas, so the flooding phenomenon in the ridge area is avoided and the water discharge is accelerated.

[0011] Furthermore, the porosity of the gas diffusion layer in the rib region is 0.5 - 0.65; the porosity of the gas diffusion layer in the flow channel region is 0.65 - 0.85.

[0012] Furthermore, the hydrophobicity of the gas diffusion layer shows a distribution of first decreasing in gradient and then increasing in gradient in the rib region gas diffusion layer - flow channel region gas diffusion layer - rib region gas diffusion layer, so as to prevent the occurrence of waterlogging in the rib region gas diffusion layer of the bipolar plate and accelerate the transportation of water in the gas diffusion layer.

[0013] Furthermore, the contact angle of the gas diffusion layer in the rib region is 130° - 160°; the contact angle of the gas diffusion layer in the flow channel region is 100° - 130°.

[0014] A processing method for an ordered structure gas diffusion layer with pore gradient and hydrophobic gradient includes the following steps:

[0015] Print the gas diffusion layer layer by layer along the thickness direction;

[0016] Coat the surface of the printed gas diffusion layer with a PTFE solution of the first concentration;

[0017] Separate the rib region gas diffusion layer from the flow channel region gas diffusion layer by using a metal sheet;

[0018] Coat the surface of the rib region gas diffusion layer with a PTFE solution of the second concentration, and the value of the second concentration is greater than that of the first concentration.

[0019] The beneficial effects of the present invention are as follows:

[0020] 1. For the ordered structure gas diffusion layer with pore gradient and hydrophobic gradient described in the present invention, by showing a distribution of first increasing in gradient and then decreasing in gradient in the rib region gas diffusion layer - flow channel region gas diffusion layer - rib region gas diffusion layer, the transportation of liquid water inside the gas diffusion layer can be actively regulated, guiding the liquid water in the gas diffusion layer below the rib of the bipolar plate to break through from the flow channel region and solving the waterlogging problem.

[0021] 2. For the ordered structure gas diffusion layer with pore gradient and hydrophobic gradient described in the present invention, by showing a distribution of first decreasing in gradient and then increasing in gradient in the rib region gas diffusion layer - flow channel region gas diffusion layer - rib region gas diffusion layer, the hydrophobicity of the gas diffusion layer region below the rib of the bipolar plate is strengthened, reducing the aggregation phenomenon of liquid water in this region, lowering the saturation of liquid water, and solving the waterlogging problem.

[0022] 3. The ordered structure gas diffusion layer with pore gradient and hydrophobic gradient according to the present invention greatly reduces the resistance during the transportation of liquid water by using the spherical cavity pore structure design. Moreover, it ensures the contact area between the ordered gas diffusion layer and other components of the membrane electrode, reduces the contact resistance, and improves the conductivity.

[0023] 4. The processing method of the ordered structure gas diffusion layer with pore gradient and hydrophobic gradient according to the present invention uses the surface projection type photopolymerization micro-nano 3D printing technology with a nano-silver / photosensitive resin composite material as the raw material, which greatly improves the conductivity of the material and enhances the performance of the gas diffusion layer. And the photopolymerization micro-nano 3D printing technology method can precisely manufacture complex ordered gas diffusion layer structures.

[0024] 5. The processing method of the ordered structure gas diffusion layer with pore gradient and hydrophobic gradient according to the present invention uses a hydrophobic gradient treatment method with a simple process flow, easy to operate, and can be widely applied to the hydrophobic treatment of ordered gas diffusion layers. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. The drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, it is obvious that other drawings can also be obtained based on these drawings.

[0026] Figure 1 It is the front view of the gas diffusion layer described in the present invention.

[0027] Figure 2 It is the top view of the gas diffusion layer described in the present invention.

[0028] Figure 3 It is the schematic diagram of the spherical pore structure.

[0029] Figure 4 It is the schematic diagram of the regional division of the gas diffusion layer described in the present invention.

[0030] Figure 5 It is the flow chart of the gas diffusion layer processing method described in the present invention.

[0031] Figure 6 It is the change of the porosity of the gas diffusion layer at different positions described in the present invention.

[0032] Figure 7 It is the water saturation at different positions described in the present invention.

[0033] Figure 8 It is the influence of different GDL structures on the polarization curve of the fuel cell described in the present invention.

[0034] In the figure:

[0035] 1 - Gas diffusion layer; 2 - Spherical pore structure; 3 - Gas diffusion layer in the left ridge region; 4 - Gas diffusion layer in the flow channel region; 5 - Gas diffusion layer in the right ridge region; 6 - Bipolar plate; 7 - Flow channel. Detailed implementation manners

[0036] The embodiments of the present invention will be described in detail below. Examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals indicate the same or similar elements or elements with the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and are intended to explain the present invention, and should not be construed as a limitation to the present invention.

[0037] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by terms such as "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "axial", "radial", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "a plurality" means two or more unless otherwise specifically defined.

[0038] In the present invention, unless otherwise clearly specified and defined, terms such as "installed", "connected", "connected to", "fixed" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0039] Such as Figure 1 , Figure 2 and Figure 3As shown in the figure, the ordered structure gas diffusion layer with pore gradient and hydrophobic gradient of the present invention has spherical pore structures 2 provided in the gas diffusion layer 1, and adjacent spherical pore structures 2 are interconnected; the gas diffusion layer 1 is divided into a left ridge region gas diffusion layer 3, a right ridge region gas diffusion layer 5, and a flow channel region gas diffusion layer 4; the left ridge region gas diffusion layer 3 and the right ridge region gas diffusion layer 5 are located below the ridges on both sides of the bipolar plate 6; the flow channel region gas diffusion layer 4 is located below the flow channel 7, as Figure 4 shown; the flow channel region gas diffusion layer 4 is located between the left ridge region gas diffusion layer 3 and the right ridge region gas diffusion layer 5; the pore diameter of the spherical pore structure 2 shows a gradient decrease distribution from the flow channel region gas diffusion layer 4 to the ridge region gas diffusion layer, that is, the pore diameter of the spherical pore structure 2 shows a gradient decrease distribution from the flow channel region gas diffusion layer 4 to the left ridge region gas diffusion layer 3, and the pore diameter of the spherical pore structure 2 shows a gradient decrease distribution from the flow channel region gas diffusion layer 4 to the right ridge region gas diffusion layer, which can actively regulate the transport of liquid water inside the gas diffusion layer, guide the liquid water in the gas diffusion layer below the bipolar plate ridge to break through from the flow channel region, and solve the flooding problem. The hydrophobicity of the left ridge region gas diffusion layer 3 and the right ridge region gas diffusion layer 5 is higher than that of the flow channel region gas diffusion layer 4. It can not only reduce the liquid water transport resistance and regulate the breakthrough position of liquid water, effectively prevent the accumulation of liquid water below the bipolar plate ridge and solve the flooding problem, but also increase the contact area between the gas diffusion layer and other membrane electrode components and enhance the conductivity.

[0040] The pore diameter of the spherical pore structure 2 shows a distribution of first gradient increase and then gradient decrease in the left ridge region gas diffusion layer 3 - flow channel region gas diffusion layer 4 - right ridge region gas diffusion layer. Through the design of the spherical pore structure, the appearance of sharp pore structures is avoided, the liquid water flow resistance is reduced, and the liquid water transport is accelerated. The sphere diameter of the pores in the spherical pore structure 2 of the ridge region gas diffusion layer is 20 - 50 μm; the sphere diameter of the pores in the spherical pore structure 2 of the flow channel region gas diffusion layer 4 is 50 - 80 μm.

[0041] The porosity of the spherical pore structure 2 in the gas diffusion layer 1 gradually decreases along the flow channel region gas diffusion layer 4 to the left ridge region gas diffusion layer 3 and the right ridge region gas diffusion layer. Since a smaller porosity has a greater capillary pressure, it drives the liquid water to move along the pore gradient direction, that is, from the ridge region gas diffusion layer to the flow channel region gas diffusion layer, and then regulates the breakthrough of liquid water in the flow channel region gas diffusion layer. The breakthrough occurs in the flow channel and is directly purged by gas, so the flooding phenomenon in the ridge region is avoided and the water discharge is accelerated. The porosity of the ridge region gas diffusion layer is 0.5 - 0.65; the porosity of the flow channel region gas diffusion layer 4 is 0.65 - 0.85, as Figure 6 shown.

[0042] The hydrophobicity of the gas diffusion layer 1 shows a distribution of first decreasing in gradient and then increasing in gradient in the left ridge region gas diffusion layer 3 - flow channel region gas diffusion layer 4 - right ridge region gas diffusion layer 5. This is to prevent the gas diffusion layer in the bipolar plate ridge region from being flooded and to accelerate the transportation of water in the gas diffusion layer. The contact angle of the ridge region gas diffusion layer is 130° - 160°; the contact angle of the flow channel region gas diffusion layer 4 is 100° - 130°.

[0043] As Figure 5 shown, the processing method of the ordered structure gas diffusion layer with pore gradient and hydrophobic gradient of the present invention includes the following steps:

[0044] Layer - by - layer printing is carried out on the gas diffusion layer along the thickness direction. Specifically: The three - dimensional structure of the ordered gas diffusion layer is sliced by using a host computer control system, and the two - dimensional ordered gas diffusion layer structure is pixelated by using a liquid crystal display device and a digital micromirror array. The resin tank contains liquid nano - silver composite photosensitive resin, and the ultraviolet beam is exposed on the surface of the photosensitive resin according to the sectional information of each layer of the part under the control of a digital light field engine. The resin thin layer in the irradiated area undergoes a photopolymerization reaction and solidifies; after one thin layer of the part is solidified, the workbench moves down a layer thickness distance for the next layer of printing until the entire structure is completed.

[0045] Prepare a 10wt% PTFE solution, and obtain the first hydrophobic agent after ultrasonic oscillation for 2 h. The gas diffusion layer is taken out after being completely immersed in the first hydrophobic agent for 2 h and then dried in a vacuum drying oven for 2 h.

[0046] Use a metal sheet to separate the ridge region gas diffusion layer from the flow channel region gas diffusion layer;

[0047] Prepare a 30wt% PTFE solution, and obtain the second hydrophobic agent 2 after ultrasonic oscillation for 2 h. Use the second hydrophobic agent 2 to coat the surface of the ridge region gas diffusion layer. After standing for 5 h, remove the metal sheet, and place the gas diffusion layer structure in a vacuum drying oven for drying for 2 h to obtain an ordered gas diffusion layer structure with both pore gradient and hydrophobic gradient.

[0048] To verify the mass transfer effect of the ordered structure gas diffusion layer with pore gradient and hydrophobic gradient of the present invention, an ordered two - phase mass transfer model is constructed by using COMSOL5.6 software, and the water saturation at different GDL positions of an ordinary ordered GDL with uniform pores and an ordered GDL with pore gradient is compared. The water saturation results are as Figure 7 shown. The ordered gas diffusion layer with pore gradient can significantly reduce the liquid water saturation in the ridge region (200 - 800 μm), and increase the water saturation in the flow channel region, accelerating water transportation. Figure 8The influence of different GDL structures on the polarization curve of fuel cells. The results show that the ordered GDL structure with pore gradient and hydrophobic gradient significantly enhances the current density under high load conditions and improves the performance of fuel cells. On the one hand, this is because the ordered GDL structure with pore gradient and hydrophobic gradient reduces the liquid water flooding under the ribs and improves the overall water transport performance of the gas diffusion layer; on the other hand, because the spherical pore structure increases the contact area between the gas diffusion layer and the rest of the membrane electrode components and reduces the contact resistance, the performance of fuel cells is improved.

[0049] It should be understood that although this specification is described according to various embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0050] The series of detailed descriptions listed above are only specific descriptions of the feasible embodiments of the present invention, and they are not intended to limit the protection scope of the present invention. Any equivalent embodiments or changes made without departing from the technical spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. An ordered structure gas diffusion layer with pore gradient and hydrophobic gradient, characterized in that, The gas diffusion layer (1) is provided with a spherical pore structure (2), and adjacent spherical pore structures (2) communicate with each other; the gas diffusion layer (1) is divided into a rib region gas diffusion layer and a flow channel region gas diffusion layer (4); the rib region gas diffusion layer is located below the bipolar plate (6); the flow channel region gas diffusion layer (4) is located below the flow channel (7); the flow channel region gas diffusion layer (4) is located between two rib region gas diffusion layers; the pore diameter of the spherical pore structure (2) shows a gradient decreasing distribution from the flow channel region gas diffusion layer (4) to the rib region gas diffusion layer, which is used to actively control the breakthrough of liquid water from the flow channel; the hydrophobicity of the rib region gas diffusion layer is higher than that of the flow channel region gas diffusion layer (4).

2. The ordered structure gas diffusion layer with pore gradient and hydrophobic gradient according to claim 1, characterized in that, The pore diameter of the spherical pore structure (2) shows a distribution of first gradient increasing and then gradient decreasing in the rib region gas diffusion layer - flow channel region gas diffusion layer (4) - rib region gas diffusion layer.

3. The ordered structure gas diffusion layer with pore gradient and hydrophobic gradient according to claim 1, characterized in that, The spherical diameter of the pores in the spherical pore structure (2) of the rib region gas diffusion layer is 20 - 50 μm; the spherical diameter of the pores in the spherical pore structure (2) of the flow channel region gas diffusion layer (4) is 50 - 80 μm.

4. The ordered structure gas diffusion layer with pore gradient and hydrophobic gradient according to claim 1, characterized in that, The porosity of the spherical pore structure (2) in the gas diffusion layer (1) gradually decreases along the flow channel region gas diffusion layer (4) to the rib region gas diffusion layer, which is used to drive the movement of liquid water along the pore gradient direction.

5. The ordered structure gas diffusion layer having a pore gradient and a hydrophobic gradient according to claim 4, characterized in that, The porosity of the rib region gas diffusion layer is 0.5 - 0.65; the porosity of the flow channel region gas diffusion layer (4) is 0.65 - 0.

85.

6. The ordered structure gas diffusion layer with pore gradient and hydrophobic gradient according to claim 1, characterized in that The hydrophobicity of the gas diffusion layer (1) shows a distribution of first gradient decreasing and then gradient increasing in the rib region gas diffusion layer - flow channel region gas diffusion layer (4) - rib region gas diffusion layer.

7. The ordered structure gas diffusion layer having a pore gradient and a hydrophobic gradient according to claim 6, wherein The contact angle of the rib region gas diffusion layer is 130° - 160°; the contact angle of the flow channel region gas diffusion layer (4) is 100° - 130°.

8. A processing method of an ordered structure gas diffusion layer with pore gradient and hydrophobic gradient according to any one of claims 1-7, characterized in that, It includes the following steps: Print the gas diffusion layer (1) layer by layer along the thickness direction; Coat the surface of the printed gas diffusion layer (1) with a PTFE solution of the first concentration; Separate the rib region gas diffusion layer from the flow channel region gas diffusion layer (4) by using a metal sheet; Coat the surface of the rib region gas diffusion layer with a PTFE solution of the second concentration, and the value of the second concentration is greater than that of the first concentration.

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