Air-cooled fuel cell cathode flow field plate

Abstract

An air-cooled fuel cell cathode flow field plate is disclosed. The air-cooled fuel cell cathode flow field plate includes a plurality of flow channels extending along the air flow direction and a plurality of flow field ridges extending along the air flow direction. The flow channels and the flow field ridges are alternately arranged in a direction perpendicular to the air flow direction. The flow channels include a flow channel inlet, a flow channel outlet, and a plurality of tapered sections distributed along the air flow direction between the flow channel inlet and the flow channel outlet. The tapered sections are staggered between adjacent flow channels. A plurality of slots are distributed along the air flow direction on the side surface of the flow field ridge, and the slots penetrate the air-cooled fuel cell cathode flow field plate in a direction perpendicular to the air flow direction.

Description

Technical Field

[0001] The present invention belongs to the technical field of air-cooled fuel cells, and particularly relates to an air-cooled fuel cell cathode flow field plate. Background Art

[0002] Proton exchange membrane fuel cells fueled by hydrogen have witnessed significant development in recent years. Proton exchange membrane fuel cells have a wide range of applications in many fields, such as new energy vehicles, stationary power plants, and unmanned aerial vehicles, etc.

[0003] Proton exchange membrane fuel cells can be classified into air cooling, liquid cooling, radiator cooling, and phase change cooling, etc. according to the cooling method. The air cooling method, also known as air cooling, is mainly applied to small-power fuel cells, and powers from 100W to 2kW can all adopt it. The main means of air cooling is to use a large cathode flow rate to take away the excess heat in the battery to ensure that the battery operates in an ideal temperature range. Its main advantages are simple structure and no need for additional cooling components, which greatly simplifies the air supply, cooling and other subsystems of traditional fuel cells, significantly reduces the total system mass, improves the power density and mass power density, and has great application potential in the field of portable mobile power, especially in the field of unmanned aerial vehicles.

[0004] For air-cooled fuel cells, most of the cathode air flow is used to take away the excess heat, and a small part of the air is used to provide oxygen for the electrode reaction. In addition, compared with liquid water, the thermal conductivity coefficient and specific heat capacity of air are both lower. Therefore, to ensure that the battery operates in an ideal temperature range, an excessive amount of air needs to be supplied to the cathode. If the air flow rate is too low, the battery cannot be effectively cooled, and the excessively high temperature inside the battery will cause rapid water loss in the membrane electrode assembly, which may cause the exchange membrane to lose water, increase the proton transfer resistance, and reduce the battery performance. On the other hand, if the air flow rate is too high, although the heat dissipation performance can be guaranteed, due to the generally low atmospheric humidity and the extremely high air flow rate, a large amount of water will also be taken away, ultimately resulting in dehydration of the membrane electrode assembly, increased proton transfer resistance, and reduced battery performance. The contradiction between the cooling effect and water retention is one of the technical problems that need to be urgently solved in air-cooled proton exchange membrane fuel cells.

[0005] As a typical application scenario of air-cooled fuel cells, unmanned aerial vehicles are more sensitive to the mass of the battery. Compared with liquid-cooled fuel cells, air-cooled fuel cells can significantly improve the endurance by reducing the self-weight and parasitic power, and are the optimal solution to solve the endurance problem of traditional lithium battery unmanned aerial vehicles. Since the cathode air flow source of air-cooled fuel cells is generally the atmospheric environment, under the operating conditions of unmanned aerial vehicles, the physical properties of air will change with the change of altitude, thereby affecting the performance of air-cooled fuel cells. One of the main factors is that the oxygen content decreases significantly with the increase of altitude. At this time, if the fuel cell operates in a high current density range, large mass transfer losses may occur due to insufficient oxygen supply.

[0006] However, the existing technologies cannot effectively and comprehensively solve the technical problems of the heat dissipation and water retention contradiction in the field of air-cooled fuel cells and the change of air components with altitude. Patent (Publication No.: CN 114695912 A) proposes a design of a flow field plate with staggered tapered sections, which is mainly applied to the field of liquid-cooled fuel cells and solves the technical problem of low drainage efficiency of the flow channels in liquid-cooled fuel cells. This is contradictory to the high water retention technical requirements of air-cooled fuel cells and cannot be applied. Patent (Publication No.: CN 211428275 U) proposes a design of a fuel cell bipolar plate with slots on the spine, which is also applied to the field of liquid-cooled fuel cells. The main design intention is to solve the problem of uneven distribution of reaction gases. Due to its small slot size, it cannot effectively meet the requirements of improving the mass power density of air-cooled fuel cells. Compared with the applied patents, a flow field plate structure including staggered tapered sections and slot designs proposed by the present invention can increase the heat dissipation area and improve the flow velocity of the cooling air flow to achieve the purpose of enhancing the heat dissipation effect, thereby improving the water retention of the proton exchange membrane. At the same time, the combination of the staggered tapered sections and the slot designs can promote the transmission and uniform distribution of components to the reaction sites, effectively solving the technical problems of heat dissipation and water retention and the change of air components with altitude in the field of air-cooled fuel cells. In addition, the slot design alleviates the problem of increased battery mass caused by the arrangement of tapered sections and improves the mass power density of air-cooled fuel cells.

[0007] The above information disclosed in the background art section is only used to enhance the understanding of the background of the present invention, and therefore may include information that does not constitute the prior art known to those of ordinary skill in the art. Summary of the Invention

[0008] Aiming at the problems existing in the prior art, the present invention proposes a cathode flow field plate for an air-cooled fuel cell, which solves the technical problem that it is difficult to balance cooling and water retention in the cathode flow field of the existing air-cooled fuel cell, alleviates the problem of insufficient oxygen supply that may occur under conditions such as high altitude, and at the same time enhances the applicability of the air-cooled fuel cell in application scenarios such as unmanned aerial vehicles that are sensitive to weight.

[0009] The object of the present invention is achieved through the following technical solutions. A cathode flow field plate for an air-cooled fuel cell includes a plurality of flow channels extending along the air flow direction and a plurality of flow field spines extending along the air flow direction. The flow channels and the flow field spines are alternately arranged in a direction perpendicular to the air flow direction. The flow channels include a flow channel inlet, a flow channel outlet, and a plurality of tapered sections distributed along the air flow direction between the flow channel inlet and the flow channel outlet. The tapered sections are staggered between adjacent flow channels. A plurality of slots are distributed along the air flow direction on the side surface of the flow field spine, and the slots penetrate the cathode flow field plate of the air-cooled fuel cell in a direction perpendicular to the air flow direction.

[0010] In the air-cooled fuel cell cathode flow field plate described above, the slotted openings are aligned with the tapered section in a direction perpendicular to the air flow direction.

[0011] In the air-cooled fuel cell cathode flow field plate described above, the length of the tapered section is 3 mm - 8 mm, and the width in the direction perpendicular to the air flow direction accounts for 30% - 70% of the width of the flow channel.

[0012] In the air-cooled fuel cell cathode flow field plate described above, the contraction angle of the tapered section in the air flow direction is 15° - 75°.

[0013] In the air-cooled fuel cell cathode flow field plate described above, the number of tapered sections in each flow channel is 3 - 10.

[0014] In the air-cooled fuel cell cathode flow field plate described above, the distance between adjacent tapered sections on the flow channel is the length of the tapered section of the adjacent flow channel.

[0015] In the air-cooled fuel cell cathode flow field plate described above, the height of the slotted openings located on the side of the flow field ridge is 30% - 70% of the height of the flow channel, and the length of the slotted openings is the same as the length of the tapered section.

[0016] In the air-cooled fuel cell cathode flow field plate described above, the number of slotted openings is the same as the number of tapered sections, and the spacing distance of the slotted openings in the air flow direction is the length of the tapered section.

[0017] In the air-cooled fuel cell cathode flow field plate described above, the slotted openings are rectangular or trapezoidal.

[0018] In the air-cooled fuel cell cathode flow field plate described above, the flow channels are parallel straight flow channels, and the cross-section of the flow channels is rectangular or trapezoidal.

[0019] Compared with the prior art, the present invention has the following advantages: By increasing the flow velocity of the cooling air flow and the contact area between the flow field plate and the cooling air flow, the present invention improves the heat exchange rate, can improve the cooling performance without increasing the intake air flow, and thus achieves the purpose of increasing the membrane water content. At the same time, the staggered arrangement of the tapered sections and the slotted opening design helps to promote the transport of oxygen to the reaction site, and at the same time improves the uniformity of the oxygen distribution at the reaction site, and can significantly reduce the mass transfer loss of the air-cooled fuel cell under oxygen-deficient conditions such as high altitude. Finally, through the slotted opening design, the mass of the flow field plate can be reduced, the problem of the increase in the mass of the flow field plate caused by the arrangement of the tapered sections can be alleviated, the mass power density of the air-cooled fuel cell can be improved, and the endurance of the mobile device can be enhanced. Description of the Drawings

[0020] By reading the detailed description of the preferred specific embodiments below, various other advantages and benefits of the present invention will become clear to those of ordinary skill in the art. The accompanying drawings are only for the purpose of showing the preferred embodiments and are not considered to be a limitation of the present invention. Obviously, the drawings described below are only some embodiments of the present invention, and those of ordinary skill in the art can obtain other drawings based on these drawings without creative efforts. Moreover, throughout the drawings, the same reference numerals are used to represent the same components.

[0021] In the drawings:

[0022] Figure 1 is a schematic structural diagram of an air-cooled fuel cell cathode flow field plate according to an embodiment of the present invention;

[0023] Figure 2 is a polarization curve and mass power density curve graph of an air-cooled fuel cell cathode flow field plate according to an embodiment of the present invention and an existing parallel flow field plate under different operating conditions;

[0024] Figure 3 is an oxygen content cloud map at the cathode catalyst layer-gas diffusion layer interface of an air-cooled fuel cell cathode flow field plate according to an embodiment of the present invention and an existing parallel flow field plate under high altitude conditions;

[0025] Figure 4 is an average temperature curve graph at the catalyst layer-gas diffusion layer interface of an air-cooled fuel cell cathode flow field plate according to an embodiment of the present invention and an existing parallel flow field plate under low cathode gas flow velocity;

[0026] Figure 5 is a membrane water content cloud map of an air-cooled fuel cell cathode flow field plate according to an embodiment of the present invention and an existing parallel flow field plate under low cathode gas flow velocity.

[0027] The present invention will be further explained below with reference to the accompanying drawings and embodiments. Specific Embodiments

[0028] The following will refer to the attached Figures 1 to 5 Describe the specific embodiments of the present invention in more detail. Although the specific embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided so that the present invention can be more thoroughly understood and the scope of the present invention can be completely conveyed to those skilled in the art.

[0029] It should be noted that in the description and claims, certain terms are used to refer to specific components. Those skilled in the art should understand that technicians may use different nouns to refer to the same component. The description and claims in this specification do not use the difference in nouns as a way to distinguish components, but use the difference in the functions of components as the criterion for distinction. For example, the terms "comprising" or "including" mentioned throughout the description and claims are open-ended terms, so they should be interpreted as "including but not limited to". The subsequent description in the specification is the preferred implementation manner for implementing the present invention, but the description is for the purpose of the general principles of the specification and is not used to limit the scope of the present invention. The protection scope of the present invention shall be determined by the scope defined by the appended claims.

[0030] To facilitate the understanding of the embodiments of the present invention, the following will further explain with specific embodiments in conjunction with the drawings, and each drawing does not constitute a limitation to the embodiments of the present invention.

[0031] For better understanding, in one embodiment, as Figure 1 shown, the air-cooled fuel cell cathode flow field plate includes a plurality of flow channels 1 and flow field ridges 2, the flow channels 1 and the flow field ridges 2 are arranged alternately, the flow channels 1 include a flow channel 1 inlet and an outlet. The flow channels 1 are arranged with a tapered section 3 along the air flow direction, and the tapered sections 3 are arranged staggeredly between adjacent flow channels 1. The flow field ridges 2 are arranged with slots 4 along the air flow direction, and the slots 4 are perpendicular to the air flow direction and horizontally penetrate the flow field plate.

[0032] The length of the tapered section 3 is approximately 3 mm - 8 mm, and it occupies approximately 30% - 70% of the width of the flow channel 1 perpendicular to the air flow direction, and the number is 3 - 10. This design can increase the flow velocity of the cooling air flow and increase the contact area between the cooling air flow and the flow field plate, thereby achieving the purpose of improving the cooling effect.

[0033] The contraction angle of the tapered section 3 along the air flow direction is approximately 15° - 75°, and each tapered section 3 is evenly distributed along the air flow direction.

[0034] The staggered distance of the tapered section 3 between the adjacent flow channels 1 is the length of one tapered section 3 to ensure sufficient intensity of the transverse flow is induced between adjacent flow channels 1 to enhance mass transfer.

[0035] The slot 4 is located between the top and the bottom of the flow channel 1, and the height is approximately 30% - 70% of the height of the flow channel 1, and the length is the same as the length of the tapered section 3. This design can significantly reduce the mass of the flow field plate, and at the same time enable material exchange between adjacent flow channels 1 to ensure the uniformity of component distribution.

[0036] The number of the slots 4 is the same as the number of the tapered sections 3, and the interval distance along the air flow direction is the length of the tapered section 3.

[0037] The slot 4 is rectangular or trapezoidal.

[0038] The battery flow channel 1 is a parallel direct flow channel 1, and the cross-section of the flow channel 1 is rectangular or trapezoidal.

[0039] Arranging the tapered section 3 and the slot 4 structure along the air flow direction is beneficial to enhancing the cooling effect, increasing the water content of the proton exchange membrane, thereby reducing the proton conduction loss and improving the performance of the air-cooled fuel cell. In addition, arranging the tapered section 3 in a staggered manner and arranging the slot 4 structure helps to promote the transmission and uniform distribution of reaction components to the reaction position. At the same time, the slot 4 structure reduces the battery mass, can further improve the mass power density, and enhances its applicability in weight-sensitive application scenarios such as unmanned aerial vehicles.

[0040] As an embodiment, the length of the cathode flow field plate is 70 mm, the width is 7 mm, and the thickness is 1.25 mm. The length of the flow channel 1 is 70 mm, the width is 1 mm, and the height is 1 mm. The width of the ridge is 1 mm. The length of the tapered section 3 is 5 mm, the contraction angle along the air flow direction is 45°, and it occupies 50% of the width of the flow channel 1 along the direction perpendicular to the air flow. The number of the tapered sections 3 is 6. The slot 4 is rectangular. The lower surface of the slot 4 is flush with the lower surface of the flow channel 1, and the height is 70% of the height of the flow channel 1. The battery flow channel 1 has a rectangular cross-section.

[0041] To compare the implementation effects, the embodiment uses 2 air-cooled proton exchange membrane fuel cells. One of them has the cathode flow field adopting the structure proposed by the present invention, and the other uses an unoptimized traditional parallel flow field structure. These two cells are completely the same in terms of structure and materials except for the different cathode flow field structure forms. In addition, the length, width, height, and channel-to-rib ratio of the flow channel 1 of the cathode flow channel 1 are all kept consistent.

[0042] The two cells are tested under the same working conditions: the embodiment includes three working conditions. The first working condition simulates the ground working conditions, and the cathode inlet stoichiometric ratio is 80. The second working condition simulates the high-altitude working conditions. The altitude is 8 km. According to the international standard atmosphere model, the partial pressure of oxygen in the atmosphere at this altitude is 0.07 standard atmospheric pressure, which is a 66.7% decrease compared to the horizontal plane. Therefore, if the cell operates in the high current density region at this time, relatively large mass transfer losses may occur. The third working condition simulates the working conditions of low cathode air flow velocity, and the cathode inlet stoichiometric ratio is 50. At this time, the cathode flow velocity is small, and the heat dissipation efficiency may be insufficient and the proton exchange membrane may lose water. The embodiments all operate in a constant current mode, adopt adiabatic boundary conditions, the humidity of the air introduced into the cathode is 40%, the humidity of the hydrogen introduced into the anode is 0, the anode stoichiometric ratio is 2, and the outlet pressures of both the anode and the cathode are the local atmospheric pressure.

[0043] Appendix Figure 2The polarization curves and mass power density curves of the air-cooled fuel cell with the cathode flow field plate using the traditional parallel flow field plate and the lightweight flow field plate proposed by the present invention are given. It can be seen that in the high current density region, the new flow field designs proposed by the present invention can significantly improve the performance of the air-cooled fuel cell under different working conditions. Taking the current density of 1.1 A cm -2 as an example, under the three working conditions of ground, high altitude and low cathode flow rate, when using the flow field plate proposed by the present invention, the output voltages are increased by 12.26%, 20.49% and 15.8% respectively compared with the traditional parallel direct flow channel 1 flow field plate. This is mainly because the arrangement of the tapered section 3 and the slotted design 4 strengthens the cooling ability, increases the water content of the proton exchange membrane of the air-cooled fuel cell, and thus reduces the mass transfer loss. This conclusion can be corroborated by the internal temperature curve of the battery and the contour map of the water content distribution of the proton exchange membrane under low cathode gas flow rate, as shown in Appendix Figure 4 and Appendix Figure 5 respectively. Among them, Appendix Figure 4 shows the relationship between the average internal temperature of the battery and the current density under low cathode gas flow rate. It can be seen that when using the new flow field plate, the internal temperature of the battery is significantly reduced, and the reduction amplitude increases with the increase of the battery density. Because as the battery density increases, the electrode reaction rate accelerates and the heat generation increases, the advantage of the new design proposed by the present invention in strengthening heat dissipation is highlighted. Appendix Figure 5 corresponds to the contour map of the water content in the middle part of the proton exchange membrane at 1.1 A cm -2 under low cathode gas flow rate. It can be seen that when using the new flow field, the water content of the proton exchange membrane is significantly increased. Moreover, the staggered arrangement of the tapered section 3 and the slotted design 4 helps to enhance the transport of air to the catalytic layer, and thus improves the oxygen concentration in the catalytic layer. This conclusion can be corroborated by the contour map of the oxygen concentration distribution at the interface between the catalytic layer and the gas diffusion layer under high altitude conditions in Appendix Figure 3 . The current density in the attached figure is 1.1 A cm -2 . It can be seen from the attached figure that when using the traditional flow field, the oxygen concentration decreases along the gas flow direction, while when using the new flow field, this decreasing trend is alleviated, and there is still a large oxygen concentration at the end of the flow field, and the average oxygen concentration is increased by 4.17%. In addition, due to the slotted design 4 reducing the mass of the air-cooled fuel cell, when using the design of the present invention, the mass power density of the air-cooled fuel cell is significantly improved, and it is increased by 15.21%, 23.61% and 18.88% respectively under the three working conditions.

[0044] The present invention significantly increases the contact area between the cooling air flow and the flow field plate, thereby effectively reducing the internal temperature of the battery, and thus achieving the purpose of increasing the water content of the proton exchange membrane in the air-cooled fuel cell. The staggered arrangement of the tapered sections 3 induces a pressure difference between adjacent channels 1, thereby generating a lateral flow in the gas diffusion layer and directly and efficiently promoting the transport of the reaction gas to the reaction site. The through slots 4 solve the problems of increased battery mass and uneven component distribution in the channels 1 caused by the staggered arrangement of the tapered sections 3, making it more suitable for the lightweight application scenarios required by air-cooled fuel cells. Compared with the traditional parallel flow field plate, the water retention capacity of the air-cooled fuel cell is improved, the mass transfer capacity is enhanced, and the battery mass power density is increased by reducing the mass of the electrode plate, enhancing the applicability of the air-cooled fuel cell in application scenarios such as unmanned aerial vehicles that are sensitive to weight.

[0045] Although the embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the above specific embodiments and application fields. The above specific embodiments are merely illustrative and guiding, rather than restrictive. Those of ordinary skill in the art can also make many forms under the inspiration of this specification and without departing from the scope protected by the claims of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. Application of a cathode flow field plate in an air-cooled fuel cell, characterized in that, It includes a plurality of flow channels extending in the air flow direction and a plurality of flow field ridges extending in the air flow direction. The flow channels and the flow field ridges are alternately arranged perpendicular to the air flow direction. The flow channel includes a flow channel inlet, a flow channel outlet, and a plurality of tapered sections distributed in the air flow direction between the flow channel inlet and the flow channel outlet. The tapered sections are staggeredly arranged between adjacent flow channels. A plurality of slots are distributed along the air flow direction on the side surface of the flow field ridge, and the slots penetrate through the air-cooled fuel cell cathode flow field plate perpendicular to the air flow direction.

2. The application of the cathode flow field plate according to claim 1 in an air-cooled fuel cell, characterized in that, The slots are aligned with the tapered sections perpendicular to the air flow direction.

3. The application of the cathode flow field plate according to claim 1 in an air-cooled fuel cell, characterized in that, The length of the tapered section is 3 mm - 8 mm, and the width perpendicular to the air flow direction accounts for 30% - 70% of the width of the flow channel.

4. The application of the cathode flow field plate according to claim 1 in an air-cooled fuel cell, characterized in that, The contraction angle of the tapered section in the air flow direction is 15° - 75°.

5. The application of the cathode flow field plate according to claim 1 in an air-cooled fuel cell, characterized in that, The number of tapered sections in each flow channel is 3 - 10.

6. The application of the cathode flow field plate according to claim 1 in an air-cooled fuel cell, characterized in that, The distance between adjacent tapered sections on the flow channel is the length of the tapered section of the adjacent flow channel.

7. The application of the cathode flow field plate according to claim 1 in an air-cooled fuel cell, characterized in that, The height of the slots located on the side surface of the flow field ridge is 30% - 70% of the height of the flow channel, and the length of the slots is the same as the length of the tapered section.

8. The application of the cathode flow field plate according to claim 1 in an air-cooled fuel cell, characterized in that, The number of slots is the same as the number of tapered sections, and the interval distance of the slots in the air flow direction is the length of the tapered section.

9. The application of the cathode flow field plate according to claim 1 in an air-cooled fuel cell, characterized in that, The slots are rectangular or trapezoidal.

10. The application of the cathode flow field plate according to claim 1 in an air-cooled fuel cell, characterized in that, The flow channels are parallel straight flow channels, and the cross-section of the flow channels is rectangular or trapezoidal.

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