A fuel cell and its application

Abstract

This invention discloses a fuel cell and its application. The bipolar plate includes a connecting structure with a cross-flow channel and a narrowing structure. The hydraulic diameter of the narrowing structure is smaller than that of the non-narrowing structure. The non-narrowing structure of the flow channel has a connecting structure corresponding to at least one of two adjacent ridges. Furthermore, the resistance of the gas in the first direction through the narrowing structure is R1, and the resistance in the second direction through the connecting structure is R2, where R1 / R2 ≥ 20. The first direction is the flow direction of the gas entering the flow field, and the second direction is perpendicular to the first direction. Therefore, the fuel cell bipolar plate provided by this invention can more fully utilize the pressure drop generated by the narrowing structure to create a larger pressure difference between adjacent flow channels. This allows a smaller flow field pressure drop to create the same or higher level of under-ridge gas convection and permeation effect within the gas diffusion layer or membrane electrode, thereby improving the under-ridge mass transfer and drainage performance of the fuel cell.

Description

Technical Field

[0001] This application relates to the field of fuel cells, specifically to a fuel cell and its applications. Background Technology

[0002] A proton exchange membrane fuel cell (PEMFC) mainly consists of bipolar plates and membrane electrode assemblies (MEAs). The bipolar plates function as gas guides and distributes gas flow, conducts electrons, transfers heat, and provide structural support. The flow field region of the bipolar plate typically consists of multiple channels and ridges; the channels are responsible for gas mass transfer and drainage, while the ridges are responsible for electrical conductivity and heat transfer. The working principle of a fuel cell is the electrochemical reaction between hydrogen and oxygen, which generates electrons, produces water, and releases heat. Therefore, the effective removal of water is crucial for the rapid flow of reactant gases through the bipolar plate to the electrochemical reaction site in the catalyst layer. According to numerous research reports, the generated water within the MEA of a fuel cell mainly accumulates under the ridges. Therefore, effectively removing the liquid water under the bipolar plate ridges to improve gas reaction mass transfer has become an important issue in reducing mass transfer polarization losses in fuel cells.

[0003] To increase gas convection flow within the membrane electrode assembly (MEA) surface, thereby reducing residual water content and improving power generation performance, related patents propose setting staggered constriction structures within any two adjacent flow channels in the reaction gas flow field. By creating these staggered constriction structures in adjacent channels, a pressure difference can be formed between them. Driven by this pressure difference, more gas will pass through the MEA or gas diffusion layer, generating alternating convection permeation within the MEA surface, effectively improving mass transfer. However, according to Darcy's law of permeability, the amount of convection permeation is related to the permeability of the porous medium and the pressure difference; the higher the permeability of the porous medium, the greater the amount of convection permeation. However, electrical conductivity, thermal conductivity, and structural strength limit the permeability of the porous medium. Furthermore, while a larger pressure difference leads to greater convection permeation, it also increases the work done by the gas, i.e., the power consumption of the fuel cell system, such as the air compressor and blower, also increases. Therefore, there is room for further improvement in the amount of convection permeation. Summary of the Invention

[0004] The purpose of this invention is to provide a fuel cell and its application, which has a bipolar plate with a cross-channel interconnection structure and a reduced diameter structure, in order to solve the problems existing in the prior art. The cross-channel interconnection structure can make fuller use of the pressure drop generated by the reduced diameter structure to form a larger pressure difference between adjacent channels. This allows a smaller flow field pressure drop to form the same or higher level of under-ridge gas convection and permeation effect in the gas diffusion layer or membrane electrode, thereby improving the under-ridge mass transfer and drainage performance of the fuel cell.

[0005] This invention provides a fuel cell comprising at least two fuel cell units, each fuel cell unit comprising a membrane electrode assembly, a gas diffusion layer, and a flow field plate arranged sequentially. The flow field plate comprises parallel ridges and flow channels located between two adjacent ridges. The flow channels contain a narrowing structure 14 and a non-narrowing structure 20, wherein the hydraulic diameter of the narrowing structure 14 is smaller than the hydraulic diameter of the non-narrowing structure 20. The non-narrowing structure 20 is connected to at least one of the two adjacent ridges by a connecting structure 15, the extending direction of the connecting structure 15 being perpendicular to the extending direction of the ridge.

[0006] Furthermore, the resistance of the gas in the first direction after passing through the aforementioned narrowing structure 14 is R1, and the resistance in the second direction after passing through the aforementioned connecting structure 15 is R2. R1 and R2 satisfy: R1 / R2≥20, and the flow direction of the gas when entering the flow field in the first direction is perpendicular to the first direction.

[0007] The gas in the adjacent flow channel of the above-mentioned flow field plate is mixed in the above-mentioned connecting structure 15 and then enters the adjacent flow channel downstream of the connecting structure 15.

[0008] The reduced diameter structure 14 of the aforementioned flow field plate is arranged in a staggered manner within adjacent flow channels.

[0009] The present invention also provides a power generation system comprising the aforementioned fuel cell.

[0010] The present invention also provides an electrical device comprising the aforementioned fuel cell.

[0011] The present invention has the following advantages:

[0012] 1. In a fuel cell containing the above-mentioned flow field plate, a hydraulically reduced diameter structure is provided in the flow field plate. The reduced diameter structure is respectively located upstream and downstream of the ridge. The pressure drop generated by the reduced diameter structure creates a pressure difference on both sides of the ridge. Under the action of the pressure difference, the gas passes through the gas diffusion layer under the ridge, thereby improving mass transfer and drainage under the ridge.

[0013] 2. Along the flow direction, a cross-channel connecting structure is set between the ridges. The connecting structure allows the pressure upstream and downstream of the ridge to be reconstructed, and the flow channels on both sides of the ridge can maximize the use of the pressure drop generated by the narrowing to build a pressure difference.

[0014] 3. Regarding the technical characteristic that R1 and R2 satisfy R1 / R2≥20, its beneficial effect lies in ensuring that the high pressure reduction generated by the narrowed diameter structure can be rapidly constructed between adjacent flow channels using a low-resistance interconnected structure through optimized matching of the resistance ratio. This design greatly enhances the gas convection and permeation capacity across the ridge without increasing the total power consumption of the system, effectively suppresses concentration polarization under high current density, and significantly improves the drainage efficiency and mass transfer performance in the region below the ridge, ensuring the stability of fuel cell operation.

[0015] The innovative flow field plate provided by this invention is suitable for the anode hydrogen flow field, cathode air flow field, and cooling flow field of fuel cells. Furthermore, the flow channels are not limited to direct-flow channels, but also include corrugated flow channels and serpentine flow channels.

[0016] The innovative flow field plate provided by this invention is a typical characteristic structure of flow fields and is applicable to other flow fields that include this typical characteristic structure. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of the bipolar plate of the proton exchange membrane fuel cell of the present invention, wherein: 1-air inlet common channel; 2-air outlet common channel; 3-hydrogen inlet common channel; 4-hydrogen outlet common channel; 5-cooling medium inlet common channel; 6-cooling medium outlet common channel; 7-reaction zone; 8-distribution zone; 9-air.

[0018] Figure 2 This is a schematic diagram of the flow field structure of a conventional fuel cell bipolar plate with a reduced diameter structure used in the comparative example, where 11-first flow channel; 13-second flow channel; 14-reduced diameter structure; 20-non-reduced diameter structure.

[0019] Figure 3 The diagram shows the pressure distribution curves of adjacent channels in the first direction of the bipolar plate flow field of a conventional fuel cell with a reduced diameter structure used in the comparative example, where A represents the pressure drop point.

[0020] Figure 4 This is a schematic diagram of the flow field structure of the bipolar plate of the fuel cell in Example 1, wherein 10-first ridge; 11-first flow channel; 12-second ridge; 13-second flow channel; 14-reduced diameter structure; 15-connected structure; 16-additional first ridge; 17-additional first flow channel; 18-additional second ridge; 19-additional second flow channel; 20-non-reduced diameter structure.

[0021] Figure 5 The graph shows the pressure distribution curves of adjacent flow channels in the bipolar plate flow field of the fuel cell in Example 1 in the first direction, where A is the pressure drop point.

[0022] Figure 6The relationship between the pressure difference ratio R1 / R2 and the pressure difference and concentration difference overpotential is given, where R1 is the resistance of the narrowing structure 14 in the first direction of gas flow; R2 is the resistance of the connecting structure 15 in the second direction of gas flow, wherein the flow direction of the reactant gas when entering the flow field is the first direction, and the second direction is perpendicular to the first direction mentioned above.

[0023] Figure 7 This is a schematic diagram of the flow field structure of the bipolar plate of the fuel cell in Example 2, wherein 10-first ridge; 11-first flow channel; 12-second ridge; 13-second flow channel; 14-reduced diameter structure; 15-connected structure; 16-additional first ridge; 17-additional first flow channel; 18-additional second ridge; 19-additional second flow channel; 20-non-reduced diameter structure.

[0024] Figure 8 This is a schematic diagram of the flow field structure of the bipolar plate of the fuel cell in Example 3, wherein 10-first ridge; 11-first flow channel; 12-second ridge; 13-second flow channel; 14-reduced diameter structure; 15-connecting structure; 17-additional first flow channel; 18-additional second ridge; 19-additional second flow channel. Detailed Implementation

[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] Figure 1 The diagram shows a schematic of the bipolar plate of a proton exchange membrane fuel cell provided by this invention. The fuel cell bipolar plate typically consists of a hydrogen inlet common channel 3, a hydrogen outlet common channel 4, an air inlet common channel 1, an air outlet common channel 2, a cooling medium inlet common channel 5, a cooling medium outlet common channel 6, a distribution zone 8, a reaction zone 7, and a sealing zone. Taking air 9 as an example, air 9 first enters the bipolar plate through the air inlet common channel 1. After entering through the air inlet common channel 1, the air enters the distribution zone 8. Under the uniform distribution effect of the distribution zone 8, the air 9 evenly enters each gas flow channel of the reaction zone 7. Within the reaction zone 7, the air 9 diffuses and convections into the membrane electrode to participate in the electrochemical reaction. Unreacted gases and water vapor are discharged from the reaction zone 7, then pass through the distribution zone 8 and enter the air outlet common channel 2, exiting the fuel cell stack.

[0027] It should be noted that this invention is not limited to liquid-cooled fuel cell bipolar plates, but also includes air-cooled fuel cell bipolar plates. In an open-cathode air-cooled fuel cell bipolar plate, the bipolar plate typically has only a hydrogen inlet common channel 3 and a hydrogen outlet common channel 4; in a closed-cathode air-cooled fuel cell bipolar plate, the bipolar plate typically has a hydrogen inlet common channel 3, a hydrogen outlet common channel 4, an air inlet common channel 1, and an air outlet common channel 2.

[0028] The innovative flow field structure of the fuel cell bipolar plate proposed in this invention mainly refers to the reaction zone 7, which will be referred to as the flow field in the following text and will not be elaborated further. For ease of description, the flow direction of the reactant gas entering the flow field is defined as the first direction, and the second direction is perpendicular to the first direction mentioned above.

[0029] Figure 2 This is a schematic diagram of the flow field of a conventional fuel cell bipolar plate with a reduced diameter structure used in a comparative example. To improve mass transfer of the reactant gas and efficient drainage, a patent proposes using a reduced diameter structure 14 to force the reactant gas to convectively permeate from under the ridge, thereby enhancing the flow of the reactant gas and drainage. The aforementioned reduced diameter structure 14 is located on the first flow channel 11 and the adjacent second flow channel 13, and the hydraulic diameter of the flow channel of the reduced diameter structure 14 is smaller than the hydraulic diameter of the flow channel at the non-reduced diameter structure 20, and the cross-sectional area of ​​the flow channel of the reduced diameter structure 14 is smaller than the cross-sectional area of ​​the flow channel at the non-reduced diameter structure 20. Furthermore, the aforementioned reduced diameter structures 14 are spaced apart on the first flow channel 11 and the second flow channel 13, staggered from each other. The advantage of this structure is that it creates alternating pressures between adjacent flow channels, specifically... Figure 3 This means that the reactant gas is forced to cross the gas diffusion layer under the ridge under the pressure difference between two adjacent flow channels, which enhances the mass transfer and drainage of the reactant gas.

[0030] Figure 3 This example illustrates the pressure distribution curves in the second flow channel 13 and the first flow channel 11 in the first direction within the bipolar plate flow field of a fuel cell with a reduced diameter structure, as described in the comparative example above. Specifically, the pressure distribution curves are obtained by simulating the pressure along the centerline of the gas flow direction in two adjacent flow channels using computer CFD tools.

[0031] The results of the pressure distribution curve are as follows: the pressure on the first flow channel 11 and the second flow channel 13 forms a pressure drop point A after passing through the aforementioned narrowing structure, thereby generating alternating pressure changes in the first direction, and thus forming an alternating pressure difference on both sides of the ridge. Under the action of the alternating pressure difference, the gas passes through the gas diffusion layer under the ridge more effectively, thereby improving mass transfer and drainage under the ridge.

[0032] Example 1

[0033] Figure 4 This is a schematic diagram of the flow field of the bipolar plate in the fuel cell of Embodiment 1 of the present invention.

[0034] As shown in the figure, when viewed along the second direction, a first ridge 10 and a second ridge 12 extending along the first direction are alternately arranged in the flow field. A first flow channel 11 and a second flow channel 13 are alternately formed between the first ridge 10 and the second ridge 12. When viewed along the first direction, both the first flow channel 11 and the adjacent second flow channel 13 are provided with a diameter reduction structure 14. The diameter reduction structures 14 are arranged in a staggered manner in the first direction.

[0035] To further enhance the pressure difference between adjacent flow channels and improve mass transfer, this embodiment of the invention introduces a cross-flow channel connection structure 15. Specifically, viewed along the first direction, an additional first ridge 16 with the same or similar structure as the first ridge 10 is provided downstream of the first ridge 10, thereby forming a cross-flow channel connection structure 15 in the second direction between the first ridge 10 and the additional first ridge 16. Similarly, in the first direction, an additional second ridge 18 with the same or similar structure as the second ridge is provided downstream of the second ridge 12, thereby also forming a cross-flow channel connection structure 15 in the second direction between the second ridge 12 and the additional second ridge 18.

[0036] Viewed along the second direction, additional first flow channels 17 and additional second flow channels 19 are alternately formed between the aforementioned additional first ridge 16 and the adjacent additional second ridge 18. Therefore, the gas within the aforementioned first flow channel 11 and second flow channel 13 can mix in the region of the connecting structure 15 and then enter the aforementioned additional first flow channels 17 and additional second flow channels 19. Similar to the aforementioned first flow channel 11 and second flow channel 13, the aforementioned additional first flow channel 17 and the adjacent additional second flow channel 19 are each provided with a diameter reduction structure 14 at intervals along the first direction.

[0037] It should be noted that in this embodiment, the narrowing structure 14 of the ridge is adjacent to the connecting structure 15 upstream or downstream. The advantage of the structure in the above embodiment is that the narrowing structures are respectively located upstream and downstream of the ridge, and the resulting pressure drop creates a pressure difference on both sides of the ridge. Gas passes through the gas diffusion layer under the ridge under the action of this pressure difference, thereby improving mass transfer and drainage under the ridge. Furthermore, a connecting structure across the flow channel is provided between the ridges along the flow direction. This connecting structure cuts off the ridges that originally isolated the flow channels, allowing the pressure upstream and downstream of the ridge to be reconstructed. Through the combined use of the narrowing structure and the connecting structure, the flow channels on both sides of the ridge can maximize the use of the pressure drop generated by the narrowing to construct a pressure difference.

[0038] Figure 5This example illustrates the pressure distribution curves in the second flow channel 13 and the first flow channel 11 in a first direction within the bipolar plate flow field of a fuel cell simultaneously using a cross-channel connecting structure and a reduced-diameter structure, as shown in Example 1. In the first direction, the pressures in the second flow channel 13 and the first flow channel 11 alternate, forming an alternating pressure difference. Compared to a comparative example, such as... Figure 2 and Figure 3 As shown, Example 1, by setting a cross-channel connecting structure, brings the pressure drop points A of adjacent channels closer together, thereby increasing the pressure difference between adjacent channels. Specifically, computer CFD simulations showed that the inlet and outlet pressure losses of the flow field with the cross-channel connecting structure were reduced by approximately 200 Pa, and the pressure loss between adjacent channels was increased by 96%. Therefore, under the same conditions, the in-surface gas convection permeation effect of the membrane electrode in Example 1 is better, and its performance is superior.

[0039] Furthermore, to enhance the pressure difference of the connected structure, the embodiment introduces the index of the connection pressure difference ratio R1 / R2, such as... Figure 6 As shown. The resistance of the narrowing structure 14 in the first direction of gas flow is represented by R1, and the resistance of the connecting structure 15 in the second direction of gas flow is represented by R2. According to the Darcy-Wiesbach formula in fluid mechanics, the resistance R = ΔP / Q = 32 * μ * L / D^4, where ΔP is the pressure difference, Q is the flow rate, μ is the air viscosity, L represents the length, and D represents the hydraulic diameter. The relationship between R1 and R2 is expressed as follows: R1 / R2 = L1 * D2^4 / (L2 * D1^4). Here, L1 represents the length of the narrowing structure 14, D1 represents the hydraulic diameter of the narrowing structure 14, L2 represents the length of the connecting structure 15, and D2 represents the hydraulic diameter of the connecting structure 15.

[0040] Figure 6 The beneficial effects of this invention are explained by interpreting the relationship between the interconnection pressure differential ratio R1 / R2 and the pressure differential and concentration overpotential. Compared to traditional reduced-diameter structures without interchannel interconnection, such as... Figure 2 As shown in the comparative example, the pressure difference between adjacent flow channels with a narrowed diameter and a connecting structure is significantly improved. When R1 / R2 is 110, the pressure difference between adjacent flow channels reaches 383 Pa, which is 96% higher than that of the traditional flow channel without a connecting structure. Based on the relationship between the connecting pressure difference ratio R1 / R2 and the concentration overpotential, it can be seen that when the connecting pressure difference ratio R1 / R2 ≥ 20, the change trend of the concentration overpotential is relatively slow. Conversely, a larger concentration overpotential indicates poorer mass transfer and a lower output voltage of the fuel cell. Therefore, in engineering design, a connecting pressure difference ratio R1 / R2 ≥ 20 is preferred.

[0041] Example 2

[0042] Figure 7 This is a schematic diagram of the flow field of the bipolar plate in the fuel cell of Embodiment 2 of the present invention. Figure 4 The only difference in Example 1 is that, when viewed along the second direction, the positions of the first ridge 10 and the second ridge 12 are interchanged; the rest of the structure is the same as in Example 1. The bipolar plate flow field structure described above achieves a flow field structure similar to that of Example 1, and retains the characteristic of simultaneously using a narrowed diameter structure and a connected structure, thereby generating a pressure difference that is the same as or similar to that of Example 1.

[0043] Example 3

[0044] Figure 8 This is a schematic diagram of the flow field of the bipolar plate in the fuel cell of Embodiment 3 of the present invention. Figure 4 The only difference in Example 1 is that Figure 4 The connecting structure 15 is no longer provided between the first ridge 10 and the additional first ridge 16, from which the and Figure 2 A conventional ridge extending along the first direction with a similar structure is defined as the first ridge 10, and the other structures are the same as in Embodiment 1. The bipolar plate flow field structure described above retains the feature of simultaneously using a reduced-diameter structure and a connected structure, thereby generating a pressure difference that is the same as or similar to that in Embodiment 1.

[0045] It should be noted that the innovative flow field provided by this invention is applicable to the anode hydrogen flow field, cathode air flow field, and cooling flow field of fuel cells. Furthermore, the flow channel is not limited to a direct-flow channel, but also includes corrugated flow channels and serpentine flow channels.

[0046] It should be noted that the innovative flow field structure provided by this invention is a typical characteristic structure of the flow field and is applicable to other flow fields that include this typical characteristic structure.

[0047] 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 fuel cell comprising at least two fuel cell cells, each fuel cell cell comprising a membrane electrode assembly, a gas diffusion layer, and a flow field plate arranged sequentially therefrom, characterized in that, The flow field plate comprises parallel ridges and flow channels located between two adjacent ridges. The flow channel is provided with a narrowing structure (14) and a non-narrowing structure (20), and the hydraulic diameter of the narrowing structure (14) is smaller than the hydraulic diameter of the non-narrowing structure (20) of the flow channel. The non-narrowing flow channel structure (20) is provided with a connecting structure (15) at at least one of the two adjacent ridges. The extending direction of the connecting structure (15) is perpendicular to the extending direction of the ridge. The resistance of the gas in the first direction through the narrowing structure (14) is R1, and the resistance in the second direction through the connecting structure (15) is R2. R1 and R2 satisfy: R1 / R2≥20, and the first direction is the flow direction of the gas entering the flow field, while the second direction is perpendicular to the first direction. The reduced diameter structure (14) of the flow field plate is arranged in a staggered manner in adjacent flow channels.

2. The fuel cell of claim 1, wherein The gas in the adjacent flow channel is mixed in the connecting structure (15) and then enters the adjacent flow channel downstream of the connecting structure (15).

3. The fuel cell according to any one of claims 1-2, characterized in that, The fuel cell includes a liquid-cooled fuel cell bipolar plate or an air-cooled fuel cell bipolar plate.

4. A power generation system, characterized in that, The power generation system includes a fuel cell according to any one of claims 1-2.

5. An electrical appliance, characterized in that, The electrical equipment includes a fuel cell according to any one of claims 1-2.

Images