Bipolar plate and gas diffusion layer integrated structure

Abstract

The invention provides an integrated structure of a bipolar plate and a gas diffusion layer. A main body of the integrated structure is made of a porous material; a plurality of conical holes are formed in the side face of the integrated structure, a plurality of injection holes parallel to the side face are formed in the end face perpendicular to the side face, and the injection holes penetrate through the integrated structure. And each injection hole is communicated with the adjacent conical hole or / and pores of the porous material through a communicating runner. According to the invention, the functions of a traditional bipolar plate and a gas diffusion layer can be replaced, the structure and the material are innovated, the mass transfer efficiency is ensured, the problem of large contact resistance in the traditional structure is solved, and the power upper limit of the fuel cell is broken through.

Description

Technical Field

[0001] The present invention relates to the field of fuel cells, and particularly to an integrated structure of a bipolar plate and a gas diffusion layer. Background Art

[0002] A proton exchange membrane fuel cell is a device that directly converts the chemical energy of fuel into electrical energy, and has the advantages of high energy conversion efficiency, low operating temperature, fast dynamic response speed, etc. Therefore, it is currently widely used in vehicles such as automobiles and ships.

[0003] A proton exchange membrane fuel cell mainly consists of four main components: a bipolar plate, a gas diffusion layer, a catalyst layer, and a proton exchange membrane. Hydrogen and oxygen are respectively transported through flow channels, and diffuse through the gas diffusion layer to the catalyst layer to participate in the reaction. Water is generated in the cathode catalyst layer, and most of it is discharged from the cathode flow channel with the gas through the cathode gas diffusion layer.

[0004] Currently, the fuel cell adopts a stacked assembly method to improve the energy density and space utilization rate. However, due to different materials of the bipolar plate and the gas diffusion layer, the contact between the surfaces will cause a relatively high contact resistance, and the unevenness of the flow channels of the bipolar plate will cause protrusions and depressions of the gas diffusion layer, affecting the battery performance. The accumulation of liquid water in the contact area will cause local flooding, resulting in an increase in local temperature and shortening the service life.

[0005] Therefore, many scholars have turned their attention to the promising integrated bipolar plate / electrode fuel cell. The prior art discloses an integrated sintered bipolar plate. This invention only realizes the integration of the bipolar plate and the GDL from the aspects of materials and assembly processes, solves the interface effects such as deformation and poor contact, but does not essentially change the structure of the traditional fuel cell. Another integrated sintered bipolar plate with a metal fiber flow field and a metal fiber gas diffusion layer can construct a three-dimensional flow field and eliminate the contact resistance, and to a certain extent increase the mass transfer and heat transfer capabilities, but the drainage performance is still poor under the condition of low flow rate and cannot adapt to the complex and diverse working conditions of the fuel cell. Summary of the Invention

[0006] In view of the deficiencies in the prior art, the present invention provides an integrated structure of a bipolar plate and a gas diffusion layer. The integrated structure can replace the functions of the traditional bipolar plate and gas diffusion layer, and innovate in terms of structure and materials, ensuring the mass transfer efficiency while solving the problem of large contact resistance in the traditional structure, and breaking through the power limit of the fuel cell.

[0007] The present invention achieves the above technical objectives through the following technical means.

[0008] An integrated structure of a bipolar plate and a gas diffusion layer, the main body of the integrated structure is composed of a porous material; several conical holes are provided on the side surface of the integrated structure, and several ejection holes parallel to the side surface are provided on the end surface perpendicular to the side surface, and the ejection holes penetrate through the integrated structure; each ejection hole is communicated with the conical hole or / and the pores of the porous material nearby through a connecting flow channel.

[0009] Furthermore, the main body of the integrated structure is composed of a metal foam porous material with circular pores, and there are several pores in the integrated structure of the porous material; the pores communicate with each other; the porosity gradient increases from the side surface to the direction away from the side surface.

[0010] Furthermore, the integrated structure of the porous material is a low-porosity region at the side surface, the porosity of the low-porosity region is 30%-40%, and the pore diameter of the low-porosity region is 15-25 μm; the other side surface opposite to the side surface is a high-porosity region, the porosity of the high-porosity region is 80%-90%, and the pore diameter of the low-porosity region is 50-80 μm.

[0011] Furthermore, the contact angle in the integrated structure of the porous material decreases gradually from the side surface to the direction away from the side surface.

[0012] Furthermore, the contact angle of the integrated structure of the porous material at the side surface is 120-140° after hydrophobic treatment; the contact angle of the other side surface opposite to the side surface is 80-100° after hydrophilic treatment.

[0013] Furthermore, the conical holes are arranged in a staggered manner on the side surface of the integrated structure, and the diameter of the conical holes gradually decreases in the direction away from the side surface; the increasing gradient of the contact angle on the inner surface of the conical holes decreases along the direction of gradual reduction; the large-end diameter of the conical holes is 70-90 μm; the small-end diameter of the conical holes is 30-40 μm; the height of the conical holes is 200-300 μm.

[0014] Furthermore, the conical holes are inserted into the low-porosity region, and the ejection holes are located above the low-porosity region; at least one ejection region with a cross-sectional mutation is provided on each ejection hole, and the ejection regions on adjacent ejection holes are distributed in a staggered manner.

[0015] Furthermore, the effective cross-sectional diameter of the ejection region with a cross-sectional mutation is 40%-60% of the diameter of the ejection hole; the diameter of the ejection hole is 150-250 μm; one ejection region is provided on each ejection hole every 250-300 μm.

[0016] Furthermore, the ejection hole adjacent to the conical hole makes the ejection region communicate with the small end of the conical hole through a connecting flow channel.

[0017] Furthermore, the ejection region of each ejection hole communicates with the pores of the nearby porous material through a connecting flow channel.

[0018] The beneficial effects of the present invention are as follows:

[0019] 1. The integrated structure of the bipolar plate and the gas diffusion layer according to the present invention can replace the functions of the traditional bipolar plate and gas diffusion layer, and innovate in terms of structure and materials. While ensuring the mass transfer efficiency, it solves the problem of relatively large contact resistance in the traditional structure and breaks through the power upper limit of the fuel cell.

[0020] 2. The integrated structure of the bipolar plate and the gas diffusion layer according to the present invention can achieve gas-liquid separation. On side 1 (considered as the reaction side), hydrophobic treatment is used to force the generated water to enter the larger-diameter conical holes rather than the pores of the porous medium, and the reaction gas is transported through the pores, realizing the directional transport of the reaction gas and liquid water, avoiding the blockage of the reaction gas by liquid water, and improving the supply efficiency of the reaction gas, thereby improving the working efficiency of the battery.

[0021] 3. The integrated structure of the bipolar plate and the gas diffusion layer according to the present invention designs a void gradient and a wetting gradient, drives the transport of liquid water under the action of capillary force and gradient contact angle, enhances the drainage performance of the fuel cell applying a three-dimensional flow field under low-speed conditions, improves the adverse effects of local flooding on the fuel cell, and improves the working stability of the fuel cell while greatly extending the service life of the battery.

[0022] 4. The integrated structure of the bipolar plate and the gas diffusion layer according to the present invention has the volume advantage of being thinner compared with the traditional structure, can greatly improve the energy density of the stack, and meets the development goal of efficient energy utilization while improving the space utilization rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] 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 following drawings 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 according to these drawings.

[0024] Figure 1 It is a three-dimensional view of the integrated structure of the bipolar plate and the gas diffusion layer according to the present invention.

[0025] Figure 2 It is Figure 1 A sectional view in the XOY plane.

[0026] Figure 3 It is Figure 2 The A-A sectional view of

[0027] Figure 4 For Figure 2 Flow direction diagram of surface gas-liquid

[0028] In the figure:

[0029] 1 - Side; 2 - Low porosity area; 3 - High porosity area; 4 - Tapered hole; 5 - Ejector hole; 6 - Small end; 7 - Large end; 8 - Tapered hole height; 9 - Ejector hole diameter; 10 - Ejector area; 11 - Connecting flow channel; 12 - Oblique angle. Specific implementation manner

[0030] The embodiments of the present invention will be described in detail below. The examples of the embodiments are shown in the drawings, where the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the drawings are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0031] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "axial", "radial", "vertical", "horizontal", "inner", "outer", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. They are 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 limiting the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and should not be construed 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 of" means two or more unless otherwise specifically defined.

[0032] In the present invention, unless otherwise clearly specified and defined, the terms "installed", "connected", "connected", "fixed", etc. 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.

[0033] Such as Figure 1As shown in the figure, the integrated structure of the bipolar plate and the gas diffusion layer in the present invention has a main body made of porous material; several conical holes 4 are provided on the side surface 1 of the integrated structure, and several injection holes 5 parallel to the side surface 1 are provided on the end surface perpendicular to the side surface 1, and the injection holes 5 penetrate through the integrated structure; each injection hole 5 is connected to the conical hole 4 and / or the pores of the porous material nearby through a communication channel 11. Generally, the side surface 1 of the integrated structure is close to the catalytic layer of the fuel cell during use.

[0034] The main body of the integrated structure is made of a metal foam porous material with circular pores, and there are several pores in the integrated structure of the porous material; generally, metal foam (such as nickel or stainless steel foam) is used as the matrix material and integrally formed into a cube shape by 3D printing technology, with an overall thickness of 600–1000 μm. The pore shape is circular, and the pore diameter and porosity are distributed in a gradient manner, that is, the porosity and pore diameter increase gradually from the side surface 1 to the direction away from the side surface 1. The pores are connected through flow channels, and the width of the flow channels is 20–50 μm to ensure smooth gas diffusion and liquid water drainage paths.

[0035] As Figure 2 shown in the figure, the integrated structure of the porous material is a low-porosity region 2 at the side surface 1, the porosity of the low-porosity region 2 is 30% - 40%, and the pore diameter of the low-porosity region is 15 - 25 μm, which is used to enhance the contact with the catalytic layer; at the other side opposite to the side surface 1 is a high-porosity region 3, the porosity of the high-porosity region 3 is 80% - 90%, and the pore diameter of the high-porosity region is 50 - 80 μm, which improves the gas transmission efficiency. The porosity increases linearly along the thickness direction, and the pore diameter is adjusted layer by layer through 3D printing parameters (such as laser power, scanning speed).

[0036] The contact angle inside the integrated structure of the porous material decreases gradually from the side surface 1 to the direction away from the side surface 1. The contact angle of the integrated structure of the porous material at the side surface 1 is 120 - 140° after hydrophobic treatment (achieved by a high-concentration PTFE coating); the contact angle at the other side opposite to the side surface 1 is 80 - 100° after hydrophilic treatment (achieved by a low-concentration PTFE or hydrophilic oxide coating). First, the whole metal foam is impregnated in a PTFE suspension (concentration 10wt%), and a basic hydrophobic layer is formed after curing. Then, the layer-by-layer impregnation method is used, and the other side away from the side surface 1 is impregnated with low-concentration PTFE (2–5wt%) to reduce the hydrophobicity; the side surface 1 is repeatedly impregnated with high-concentration PTFE (15–20wt%) to enhance the hydrophobicity.

[0037] As Figure 2 and Figure 3As shown, tapered holes 4 are arranged in a staggered pattern on side 1 of the integrated structure. The diameter of the tapered holes 4 tapers off in the direction away from side 1. The diameter of the large end 7 of the tapered holes 4 is 70 - 90 μm. The diameter of the small end 6 of the tapered holes 4 is 30 - 40 μm, and the height of the tapered holes 4 is 200 - 300 μm. Or it satisfies that the tapered hole bevel angle 13 is 80°–87°, or the cross-sectional area ratio of the large end 7 diameter to the small end 6 diameter is 0.2–0.3. As long as 3 of these conditions are met, the tapered holes 4 can be determined. On side 1, the spacing between adjacent tapered holes 4 is 250–300 μm. In the longitudinally arranged tapered holes from top to bottom, the adjacent rows are vertically offset by 130–180 μm and horizontally misaligned by 120–160 μm, forming a staggered structure. Along the tapering direction, the increasing gradient of the contact angle on the inner surface of the tapered holes 4 decreases; the gradient change of the contact angle on the inner surface of the tapered holes 4 is consistent with the gradient change of the contact angle inside the integrated structure of the porous material.

[0038] The tapered holes 4 are inserted into the low-porosity region 2, and the ejection holes 5 are located above the low-porosity region 2. The ejection holes 5 are used to convey gas. The diameter 9 of the ejection holes is 150–250 μm. At least one ejection region 10 with a cross-sectional mutation is provided on each ejection hole 5, and the ejection regions 10 on adjacent ejection holes 5 are staggered.

[0039] The effective cross-sectional diameter of the ejection region 10 with a cross-sectional mutation is 40% - 60% of the diameter of the ejection hole 5. The diameter 9 of the ejection holes is 150 - 250 μm. One ejection region 10 is provided on each ejection hole 5 every 250 - 300 μm. The effective cross-sectional area diameter of the ejection region 10 is 60–150 μm. The row spacing of the ejection holes arranged in parallel longitudinally is 100–150 μm. In the transverse direction, 3–4 columns of ejection holes are arranged in each row, and the horizontal misalignment between columns is 120–160 μm to avoid flow dead zones.

[0040] As Figure 2 shown, the ejection holes 5 adjacent to the tapered holes 4 communicate the ejection region 10 with the small end 6 of the tapered holes 4 through the connecting flow channels 11. The ejection region 10 of each ejection hole 5 communicates with the pores of the porous material nearby through the connecting flow channels 11.

[0041] Example 1

[0042] Using stainless steel foam as the matrix material, it is integrally formed into a cubic shape by means of 3D printing technology, and the overall thickness is precisely set to 800 μm. In terms of pore design, the pore shape is circular, and the pore diameter and porosity show a gradient distribution. The pores are connected by flow channels with a width of 35 μm, which can ensure the smoothness of the gas diffusion and liquid water drainage paths. The entire structure adopts a gradient porosity design. The porosity of the low-porosity region 2 near side 1 is set to 35%, and the pore diameter is 20 μm. Such a design can enhance the contact with the catalytic layer. The porosity of the high-porosity region 3 at the other side opposite to side 1 reaches 85%, and the pore diameter is 65 μm, significantly improving the gas transmission efficiency. The porosity increases linearly along the thickness direction, and the pore diameter is precisely regulated layer by layer through 3D printing parameters, with the laser power set to 240 W and the scanning speed set to 750 mm / s.

[0043] The overall structure is subjected to gradient wettability treatment in the thickness direction. The contact side 1 is treated with hydrophobicity, and the contact angle is precisely controlled at 130°, which is achieved through a high-concentration PTFE coating with a concentration of 18 wt%. The other side opposite to side 1 is treated with hydrophilicity, and the contact angle is 90°, which is achieved by using a low-concentration PTFE (3 wt%) coating.

[0044] There are staggered conical holes 4 on side 1. The large end 7 of the conical hole 4 has a diameter of 80 μm, the small end 6 of the conical hole 4 has a diameter of 35 μm, the small end 6 of the conical hole 4 faces the gas flow field side, and the height of the conical hole 4 is 250 μm. The ejection hole 5 has a circular cross-section with a diameter of 150 μm, and the extension direction is the same as the gas flow direction. Along the extension direction of the hole, an ejection section with a diameter reduced to 90 μm, that is, 60% of the original diameter, is set every 275 μm. The longitudinal spacing of the ejection holes 5 is 125 μm, and three columns of ejection holes are arranged in each row in the transverse direction, with a horizontal misalignment of 140 μm between columns to avoid flow dead zones. The contraction area of the ejection hole 5 is connected to the bottom surface of the small diameter of the conical hole through a flow channel to form a directional flow guiding path, effectively guiding the gas flow and improving the gas transmission efficiency.

[0045] Working principle: The catalytic layer consumes the reaction gas to generate liquid water. After leaving the microporous layer, the water reaches the hydrophobically treated side 1, where it accumulates in the conical holes 4 with a larger diameter under the action of surface tension and does not block the holes in the low-porosity region 2. As the volume increases, the liquid water reaches the small end of the conical hole 4 under the action of gradient wettability and enters the channel communicating with the entrainment region 10. When the reaction gas in the entrainment hole 5 faces the suddenly reduced pipe diameter, a local negative pressure is generated, which attracts the liquid water in the channel and makes it move along the direction of the jet of the entrainment hole 5. After the liquid water moves forward for a certain distance, it reaches near the entrainment region 10 of the adjacent entrainment hole 5 and enters the adjacent entrainment hole 5 under the action of the negative pressure in the entrainment region 10 of the adjacent entrainment hole 5, so that the liquid water moves upward along the thickness direction. The reaction gas in the entrainment hole 5 diffuses around and enters the micropores due to the blocking effect of the entrainment region 10, and finally gradually moves to the side 1 with a lower concentration and finally reaches the catalytic layer to participate in the reaction. Thus, the liquid water with a higher concentration on the side 1 gradually moves away from the side 1. As Figure 4 shown.

[0046] Through the above precise design and preparation process, the integrated bipolar plate / gas diffusion layer structure of the present invention exhibits excellent performance in fuel cells. Its gradient porosity and wettability design, as well as the optimized layout of the conical holes and entrainment holes, jointly improve the mass transfer efficiency and stability of fuel cells, providing a strong guarantee for the high-performance operation of fuel cells.

[0047] It should be understood that although this specification is described according to each embodiment, 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.

[0048] 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 integrated structure of a bipolar plate and a gas diffusion layer, characterized in that, The main body of the integrated structure is made of porous material; several conical holes (4) are provided on the side surface (1) of the integrated structure, and several ejection holes (5) parallel to the side surface (1) are provided on the end surface perpendicular to the side surface (1), and the ejection holes (5) penetrate through the integrated structure; each ejection hole (5) is communicated with the conical hole (4) or / and the pores of the porous material nearby through a connecting flow channel (11).

2. The integrated structure of the bipolar plate and the gas diffusion layer according to claim 1, wherein The main body of the integrated structure is made of a metal foam porous material with circular pores, and there are several pores in the integrated structure of the porous material; the pores communicate with each other; the porosity and the pore diameter gradient increase from the side surface (1) to the direction away from the side surface (1).

3. The integrated structure of the bipolar plate and the gas diffusion layer according to claim 2, characterized in that, The integrated structure of the porous material is a low-porosity region (2) at the side surface (1), the porosity of the low-porosity region (2) is 30%-40%, and the pore diameter of the low-porosity region is 15-25 μm; the other side surface opposite to the side surface (1) is a high-porosity region (3), the porosity of the high-porosity region (3) is 80%-90%, and the pore diameter of the high-porosity region is 50-80 μm.

4. The integrated structure of the bipolar plate and the gas diffusion layer according to claim 1, characterized in that, The contact angle inside the integrated structure of the porous material decreases in gradient from the side surface (1) to the direction away from the side surface (1).

5. The integrated structure of the bipolar plate and the gas diffusion layer according to claim 4, wherein The contact angle of the integrated structure of the porous material is 120-140° after hydrophobic treatment at the side surface (1); the contact angle after hydrophilic treatment at the other side surface opposite to the side surface (1) is 80-100°.

6. The integrated structure of the bipolar plate and the gas diffusion layer according to claim 1, characterized in that, The conical holes (4) are arranged in a staggered manner on the side surface (1) of the integrated structure, and the diameter of the conical holes (4) gradually decreases along the direction away from the side surface (1); the increasing gradient of the contact angle on the inner surface of the conical holes (4) decreases along the gradually decreasing direction; the diameter of the large end (7) of the conical holes (4) is 70-90 μm; the diameter of the small end (6) of the conical holes (4) is 30-40 μm; the height of the conical holes (4) is 200-300 μm.

7. The integrated structure of the bipolar plate and the gas diffusion layer according to claim 1, characterized in that, The conical holes (4) are inserted into the low-porosity region (2), and the ejection holes (5) are located above the low-porosity region (2); at least one ejection region (10) with a cross-section mutation is provided on each ejection hole (5), and the ejection regions (10) on the adjacent ejection holes (5) are distributed in a staggered manner.

8. The integrated structure of the bipolar plate and the gas diffusion layer according to claim 7, wherein The effective cross-section diameter of the ejection region (10) with a cross-section mutation is 40%-60% of the diameter of the ejection hole (5); the ejection hole diameter (9) is 150-250 μm; each ejection hole (5) is provided with an ejection region (10) every 250-300 μm.

9. The integrated structure of the bipolar plate and the gas diffusion layer according to claim 7, wherein The ejection hole (5) adjacent to the conical hole (4) makes the ejection region (10) communicate with the small end (6) of the conical hole (4) through a connecting flow channel (11).

10. The integrated structure of the bipolar plate and the gas diffusion layer according to claim 7, characterized in that, The ejection region (10) of each ejection hole (5) communicates with the pores of the porous material nearby through a connecting flow channel (11).

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