A high power density cathode closed air-cooled flat tube bipolar plate, its preparation method and stack structure

Abstract

This invention provides a high power density cathode-enclosed air-cooled flat tube bipolar plate, its fabrication method, and its stack structure. Microchannel flat tubes are disposed inside the substrate of the bipolar plate. The microchannels within the flat tubes form cooling channels. The microchannel flat tubes are arranged parallel to each other inside the substrate, and microchannel heat dissipation ports are provided at both ends of the flat tubes, located on the side of the plate. This invention not only significantly increases the specific surface area for heat dissipation, providing high heat exchange efficiency while maintaining excellent mechanical strength, but also improves the temperature uniformity of the plate. This allows the enclosed cathode air-cooled fuel cell stack to meet higher power density requirements and improve the power-to-weight ratio of the stack. The design and supply chain of the microchannel flat tubes are well-established, with low batch costs and easy processing, making them suitable as a substrate for bipolar plates for both small-batch and large-batch production.

Description

Technical Field

[0001] This invention belongs to the field of fuel cells and relates to electrode plates and stack structures, specifically to a high power density cathode enclosed air-cooled flat tube bipolar plate and stack structure. Background Technology

[0002] Hydrogen energy is an important component of the energy system, and fuel cells, as a hydrogen energy conversion device, are being promoted in various application scenarios. Air-cooled proton exchange membrane fuel cells (PEMFCs) have broad application prospects in portable power supplies, drones, and other fields due to their advantages such as system simplicity and fast start-up. Their bipolar plates not only need to distribute the reactant gases but also play a role in heat dissipation. However, due to limitations in heat dissipation capacity, the power density of air-cooled fuel cell stacks has remained relatively low, significantly lagging behind water-cooled fuel cell stacks. Air-cooled stacks can be structurally divided into two main categories: open-type air-cooled stacks, where the cathode reaction flow field and stack heat dissipation are designed together, with the cathode undertaking both electrochemical reactions and heat dissipation; and closed-type air-cooled stacks, where the cathode reaction flow field and stack heat dissipation are separate, with the cathode responsible for the electrochemical reaction and heat dissipation having dedicated channels, ensuring that the two do not interfere with each other.

[0003] As a core component of fuel cell stacks, bipolar plates play crucial roles in current collection, gas distribution, and thermal management. Their performance directly impacts and determines the power density, lifespan, and reliability of the fuel cell. Existing air-cooled fuel cell bipolar plate technologies still face numerous bottlenecks in practical applications. While traditional graphite bipolar plates offer excellent corrosion resistance and conductivity, their brittleness makes it difficult to process them into thinner layers, and their limited heat dissipation area significantly restricts the improvement of stack power density, making it difficult for stacks to meet the demands of high-power-density applications. Metal bipolar plates, while offering high mechanical strength, can be processed into thinner layers and ensure a larger heat dissipation area, but their high production costs and development difficulties make them unsuitable for small-batch and scenario-specific applications. Regarding thermal management, both structures, being multi-plate bipolar plates (graphite bipolar plates consisting of anode and cathode plates, and metal bipolar plates consisting of anode, cathode, and heat sink), exhibit poor temperature uniformity, resulting in uneven temperature distribution within the stack and negatively impacting the performance of air-cooled fuel cell stacks. Summary of the Invention

[0004] One of the core innovations of this invention addresses the above-mentioned problems by achieving an integrated design of materials and structure. By using microchannel flat tubes as the bipolar plate substrate, the flow field function and air cooling function are cleverly integrated into a single component. Unlike traditional bipolar plates, this design no longer treats the cooling channel as an additional structure, but rather as an integral part of the bipolar plate. This structure not only significantly increases the specific surface area for heat dissipation, providing high heat exchange efficiency while maintaining excellent mechanical strength, but also improves the temperature uniformity of the plate. This allows closed-cathode air-cooled fuel cell stacks to meet higher power density requirements and improve the power-to-weight ratio of the stack. The design and supply chain of microchannel flat tubes are well-established, with low batch costs and easy processing, making them suitable as a substrate for bipolar plates for both small-batch and large-batch production needs.

[0005] The technical solution of this invention is as follows.

[0006] A high power density cathode closed-loop air-cooled flat tube bipolar plate includes a microchannel flat tube disposed inside the substrate of the bipolar plate. The microchannels of the microchannel flat tube inside the substrate form cooling channels. The microchannel flat tubes are arranged in parallel inside the substrate, and microchannel heat dissipation ports are provided at both ends of the microchannel flat tubes. The microchannel heat dissipation ports are opened on the side of the plate. A reaction gas flow field, a distribution cavity, a bridging region, a gas distribution region, and a sealing structure are integrated on the surface of the bipolar plate. The distribution cavity is connected to the reaction gas flow field through the bridging region and the gas distribution region. The sealing structure surrounds the reaction gas flow field and the distribution cavity in a complete circle.

[0007] More preferably, the equivalent diameter of the microchannel is between 0.2 mm and 2 mm, and the channel wall thickness is between 0.1 mm and 0.5 mm.

[0008] More preferably, the base material is a metallic material such as stainless steel, aluminum, or titanium; the aluminum alloy is selected from AA3003 or AA5052. The stainless steel is 316 stainless steel, and the titanium is TA1 (Gr1).

[0009] More preferably, the microchannel flat tube is provided with a microchannel structure support inside.

[0010] More preferably, the distribution cavity on the electrode plate includes an air inlet, a hydrogen inlet, an air outlet, and a hydrogen outlet; the air inlet and air outlet are connected to the air active region via an air inlet bridge area and a gas distribution area, respectively; the hydrogen inlet and hydrogen outlet are connected to the hydrogen active region via a hydrogen inlet bridge area and a gas distribution area, respectively. In this invention, the distribution cavity, also called a common channel, functions to provide gas supply to each single cell or bipolar plate.

[0011] More preferably, the sealing structure is a sealing groove and a flat gasket sealing structure. Other sealing methods that can be used include dispensing, screen printing, injection molding, and compression molding, adapting to common sealing methods for fuel cell plates. Dispensing involves applying liquid sealant to seal the fuel cell stack.

[0012] A fuel cell stack structure employing the aforementioned high power density cathode closed-loop air-cooled flat tube bipolar plate, wherein the bipolar plate and membrane electrode assembly (MEA) are alternately stacked; at the cooling air inlet and outlet ends of the fuel cell stack, the cooling air passes through the inlet end of the fuel cell stack, guides the cooling air to the inlet and outlet of all the microchannels of the electrode plates, and then discharges from the outlet end of the fuel cell stack, forming a closed-loop forced convection cooling system.

[0013] The specific structure of the aforementioned fuel cell stack consists of, from top to bottom, a front end plate, an anode current collector plate, an anode tail plate, an alternating stacked structure of one or more bipolar plates and membrane electrode assembly (MEA), a cathode tail plate, a cathode current collector plate, and a rear end plate.

[0014] In the above-mentioned fuel cell stack structure, the front end plate, anode current collector plate, anode tail plate, one or more bipolar plates and membrane electrode assembly (MEA) alternating stack structure, cathode tail plate, cathode current collector plate and rear end plate are fixedly connected by fuel cell stack fasteners, which are screws.

[0015] Compared with the prior art, the advantages of the present invention are:

[0016] 1. Excellent heat dissipation performance: The microchannel structure provides a huge specific surface area, making the heat exchange efficiency between the cooling air and the plate much higher than that of traditional heat dissipation fins, which greatly improves the heat dissipation capacity and temperature uniformity of the plate.

[0017] 2. Simple structure and high reliability: It adopts a single-plate integrated structure, which avoids the leakage risk caused by the traditional two-plate composite liquid cooling plate, making the structure more compact and more reliable.

[0018] 3. Simplified process and reduced cost: It directly uses mature industrial products (microchannel flat tubes) as the base material, and the subsequent processing is mainly milling. The process is simple, which is conducive to large-scale production. The manufacturing cost is significantly lower than that of graphite bipolar plates, and the production process is simpler than that of metal or composite plates.

[0019] 4. Enhanced electrical and thermal conductivity: The microchannel flat tube employs a thin-walled design, providing a larger heat dissipation area for the same electrode size. This results in significantly higher heat dissipation capacity compared to traditional electrodes using graphite plate heat sinks or composite structures. The improved temperature uniformity enhances the overall performance of the fuel cell stack and increases the power-to-weight ratio. This makes it suitable for applications requiring high power-to-weight ratios, such as drones. Attached Figure Description

[0020] Figure 1 A schematic diagram of the structure of a microchannel flat tube substrate;

[0021] Figure 2 This is a schematic diagram of a flat tube bipolar plate structure;

[0022] Figure 3 This is a cross-sectional view of a flat tube bipolar plate.

[0023] Figure 4 It is a cathode-enclosed flat tube electrode stack structure.

[0024] The components in the figure are as follows: 1. Microchannel heat dissipation port; 2. Flat tube smooth surface; 3. Air inlet port; 4. Hydrogen inlet port; 5. Air inlet bridge area; 6. Cathode active area; 7. Gas distribution area; 11. Front end plate; 12. Anode current collector; 13. Anode tail plate; 14. Membrane electrode (MEA); 15. Cathode tail plate; 16. Cathode current collector; 17. Rear end plate; 18. Stack fasteners; 19. Hydrogen exhaust port; 20. Air exhaust port.

[0025] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0026] Example 1

[0027] A high power density cathode closed-type air-cooled flat tube bipolar plate, such as Figure 1 As shown, a microchannel flat tube is disposed inside the substrate of the bipolar plate. The microchannels of the microchannel flat tube inside the substrate form a cooling channel. The microchannel flat tubes are arranged in parallel inside the substrate. Microchannel heat dissipation ports 1 are provided at both ends of the microchannel flat tubes. The microchannel heat dissipation ports 1 are opened on the side of the plate. In this example, the microchannel heat dissipation ports 1 extend all the way to the other side of the substrate of the bipolar plate. The shape can be changed according to design requirements. A reaction gas flow field, a distribution cavity, a bridging area, a gas distribution area, and a sealing structure are integrated on the surface of the bipolar plate. The distribution cavity is connected to the reaction gas flow field through the bridging area and the gas distribution area 7. The sealing structure surrounds the reaction gas flow field and the distribution cavity in a complete circle 21. In this embodiment, the distribution cavity includes an air inlet (common channel) 3, a hydrogen inlet (common channel) 4, an air exhaust (common channel) 20, and a hydrogen exhaust (common channel) 19. In this embodiment, the bridging area is divided into an air inlet bridging area 5 and a hydrogen inlet bridging area (e.g., Figure 2 As shown, the hydrogen inlet bridge area is on the other side. The air inlet 3 and air outlet 20 are connected to the cathode active area (air active area) 6 through the air inlet bridge area 5 and the gas distribution area 7, respectively; the hydrogen inlet 4 and hydrogen outlet 19 are connected to the anode active area (hydrogen active area) through the hydrogen inlet bridge area and the gas distribution area 7, respectively; it should be noted that Figure 2Both the anode plate and cathode plate are located in the gas distribution zone 7; the anode active zone (hydrogen active zone) is in... Figure 2 The back side of the cathode active region of the electrode plate is shown.

[0028] In this embodiment, the equivalent diameter of the microchannel flat tube is between 0.2 mm and 2 mm, and the channel wall thickness is between 0.1 mm and 0.5 mm. Its base material is stainless steel, aluminum, titanium, or other metallic materials; the aluminum alloy is selected from AA3003 or AA5052. The stainless steel is 316 stainless steel, and the titanium is TA1 (Gr1). A microchannel structure support is provided inside the microchannel flat tube.

[0029] In this embodiment, the sealing structure is a sealing groove, a flat gasket sealing structure, or the application of liquid sealant to seal the fuel cell stack.

[0030] After testing, using the same electrode plate heat dissipation size for comparison, the electrode plate in this invention has a heat dissipation specific surface area that is more than 30% larger than that of the existing conventional electrode plate, a heat dissipation capacity that is more than 20% higher, and an electrode plate thickness that is 15% smaller than that of traditional graphite electrode plates or metal air-cooled electrode plates.

[0031] Example 2

[0032] The core of the bipolar plate in this embodiment lies in using a microchannel flat tube as a substrate, and integrating the reactive gas flow field, distribution cavity, and sealing structure on it through a series of machining processes. The main process is as follows:

[0033] Substrate – Microchannel Flat Tube. Structure and Material: This flat tube is a long, extruded part containing multiple parallel microchannels. Air inlets for the electrode plates are pre-formed on both axial sides of the microchannels; in this embodiment, the air inlets are integrally formed. The equivalent diameter of the microchannels is between 0.2mm and 2mm, and the channel wall thickness is between 0.1mm and 0.5mm. The substrate material is corrosion-resistant stainless steel, aluminum, titanium, or other metal materials; the aluminum alloy is selected from AA3003 or AA5052. The stainless steel is 316 stainless steel, and the titanium is TA1 (Gr1). After the sheet metal is processed and formed, the electrode plate surface can undergo anti-corrosion treatment such as anodizing or galvanizing. Function: These microchannels themselves constitute efficient heat dissipation channels for the electrode plates. After the fuel cell stack is assembled, one end of these microchannels converges at the cooling air inlet of the fuel cell stack, and the other end converges at the outlet. Cooling air flows through these channels under the drive of a fan, directly carrying away heat.

[0034] Machining process. Blanking and leveling: First, the microchannel flat tube is precisely cut to the required electrode length (e.g., wire cutting). Then, leveling is performed to ensure the substrate has high flatness, forming a shape like... Figure 1The smooth surface 2 of the flat tube shown is used for machining the flow field and the inlet cavity. Machining the reactive gas flow field: On a wide face (front side) of the microchannel flat tube, the reactive gas flow field (such as a serpentine flow field, parallel flow field, or interdigitated flow field) is etched using precision machining techniques such as CNC milling, etching, or femtosecond laser machining. The machining depth must be precisely controlled to ensure that the flat tube wall is not penetrated and that it does not connect with the internal microchannels. Specifically, as shown... Figure 3 As shown, the anode machining surface does not interfere with the microchannel heat dissipation space (mainly illustrating that the electrode machining will not open up to the heat dissipation). Figure 3 The mark 8 in the diagram indicates that a minimum thickness of 0.1-0.5mm is reserved; the cathode machining surface does not interfere with the microchannel heat dissipation space, such as... Figure 3 Mark 9 indicates a minimum thickness of 0.1-0.5mm; the microchannel structure support 10 has a thickness of 0.2-1mm. Processing the fluid distribution chambers and sealing structure: At both ends of the electrode plate along its length, inlet and outlet distribution chambers for the reactant gases are milled, specifically air inlet 3, hydrogen inlet 4, air exhaust port 20, and hydrogen exhaust port 19. Simultaneously, sealing grooves are machined around the electrode plate and around the distribution chambers for sealing. Surface treatment: All machined surfaces are cleaned and coated with a carbon-based coating (a common surface treatment for metal electrodes to enhance corrosion resistance) or a PVD nano-coating, primarily to improve corrosion resistance.

[0035] Example 3

[0036] A fuel cell stack structure employing the aforementioned high power density cathode closed-loop air-cooled flat tube bipolar plate, wherein the bipolar plates and membrane electrode assembly (MEA) 14 are alternately stacked; at the cooling air inlet and outlet ends of the fuel cell stack, cooling air is guided through the inlet end to the inlet and outlet of all electrode microchannels, and then discharged from the outlet end (in this embodiment, the inlet and outlet ends can be interchanged), forming a closed-loop forced convection cooling system. The cooling of the fuel cell stack is achieved by... Figure 1 The flat tube itself has a built-in heat dissipation channel, which is cooled by a fan installed on the fuel cell stack casing. In this embodiment, the gas for the cathode and anode is provided by a common channel of the electrode plates. The cooling of the fuel cell stack is achieved by the cooling fan providing positive or negative pressure to guide air from the inlet end of the microchannel for heat exchange and then exhausting it from the outlet end. The cathode, anode and heat dissipation gas of the fuel cell stack are all separated into separate paths, forming a closed forced convection cooling system.

[0037] The specific structure, from top to bottom, consists of a front-end plate 11 (non-metallic or insulating material), an anode current collector 12, an anode tail plate 13, an alternating stacked structure of one or more bipolar plates and membrane electrode assembly (MEA) 14, a cathode tail plate 15, a cathode current collector 16, and a rear-end plate 17 (non-metallic or insulating material). The front-end plate 11, anode current collector 12, anode tail plate 13, the alternating stacked structure of one or more bipolar plates and MEA 14, the cathode tail plate 15, the cathode current collector 16, and the rear-end plate 17 are fixedly connected by electrode stack fasteners 18 (screws in this embodiment).

[0038] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A high power density cathode enclosed air-cooled flat tube bipolar plate, characterized in that, Microchannel flat tubes are provided inside the substrate of the bipolar plate. The microchannels of the microchannel flat tubes inside the substrate form cooling channels. The microchannel flat tubes are arranged in parallel inside the substrate. Microchannel heat dissipation ports (1) are provided at both ends of the microchannel flat tubes. The microchannel heat dissipation ports (1) are opened on the side of the plate.

2. The high power density cathode enclosed air-cooled flat tube bipolar plate as described in claim 1, characterized in that, A reaction gas flow field, a distribution cavity, a bridging region, a gas distribution region, and a sealing structure are integrated on the surface of the bipolar plate; the distribution cavity is connected to the reaction gas flow field through the bridging region and the gas distribution region; the sealing structure surrounds the reaction gas flow field and the distribution cavity in a complete circle (21).

3. The high power density cathode enclosed air-cooled flat tube bipolar plate as described in claim 1, characterized in that, The equivalent diameter of the microchannel in the microchannel flat tube is between 0.2 mm and 2 mm, and the channel wall thickness is between 0.1 mm and 0.5 mm. The microchannel flat tube is provided with a microchannel structure support (10).

4. The high power density cathode enclosed air-cooled flat tube bipolar plate as described in claim 1, characterized in that, The substrate is made of stainless steel, aluminum, titanium, or other metallic materials; the aluminum alloy is selected from AA3003 or AA5052. The stainless steel is 316 stainless steel, and the titanium is TA1 (Gr1).

5. The high power density cathode enclosed air-cooled flat tube bipolar plate as described in claim 2, characterized in that, The distribution chamber on the electrode plate includes an air inlet (3), a hydrogen inlet (4), an air outlet (20), and a hydrogen outlet (19); the air inlet (3) and the air outlet (20) are connected to the air active zone (6) through the air inlet bridge area (5) and the gas distribution area (7), respectively; the hydrogen inlet (4) and the hydrogen outlet (19) are connected to the hydrogen active zone through the hydrogen inlet bridge area and the gas distribution area (7), respectively.

6. The high power density cathode enclosed air-cooled flat tube bipolar plate as described in claim 2, characterized in that, The sealing structure is a sealing groove or a flat gasket sealing structure.

7. The method for preparing the high power density cathode closed-type air-cooled flat tube bipolar plate according to any one of claims 1 to 6, characterized in that, Using a microchannel flat tube as a substrate, a reaction gas flow field, distribution cavity, bridging region, gas distribution region, and sealing structure are integrated onto it through a series of machining processes; including the following steps: (1) Take a microchannel flat tube substrate, precisely cut the microchannel flat tube substrate according to the required electrode length, and then perform a leveling process to ensure that the substrate has high flatness and form a smooth surface of the flat tube for processing flow field and air inlet. (2) On a wide surface of the microchannel flat tube substrate after step (1), the reaction gas flow field is processed by CNC milling, etching or femtosecond laser processing technology. The processing depth must be precisely controlled to ensure that the flat tube wall is not penetrated and is not connected to the internal microchannel. (3) Processing fluid distribution cavity and sealing structure: At both ends of the length direction of the microchannel flat tube substrate obtained in step (2), the inlet distribution cavity and outlet distribution cavity of the reaction gas are milled. At the same time, sealing grooves for sealing are processed in the periphery of the microchannel flat tube substrate and around the distribution cavity. (4) Surface treatment: Clean all machined surfaces and apply carbon-based coating or PVD nano coating to improve corrosion resistance.

8. The preparation method according to claim 7, characterized in that, In step (1), the precision cutting is wire cutting; in step (2), the reaction gas flow field is a serpentine flow field, a parallel flow field, or an interdigitated flow field.

9. A fuel cell stack structure employing the high power density cathode enclosed air-cooled flat tube bipolar plate as described in any one of claims 1 to 6, characterized in that, Bipolar plates and membrane electrodes (MEA) (14) are alternately stacked; cooling air passes through the inlet end of the stack, guides the cooling air to the inlet and outlet of all the microchannels of the plates, and then discharges from the outlet end of the stack, forming a closed forced convection cooling system.

10. The fuel cell stack structure according to claim 8, characterized in that, The specific structure consists of, from top to bottom, a front end plate (11), an anode current collector plate (12), an anode tail plate (13), an alternating stacked structure of one or more bipolar plates and a membrane electrode (MEA) (14), a cathode tail plate (15), a cathode current collector plate (16), and a rear end plate (17). The front end plate (11), anode current collector (12), anode tail plate (13), one or more bipolar plates and membrane electrode (MEA) (14) are alternately stacked, and the cathode tail plate (15), cathode current collector (16) and rear end plate (17) are fixedly connected by a stack fastener (18); the stack fastener (18) is a screw.

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