A fuel cell bipolar plate and a fuel cell stack

Abstract

The application relates to the technical field of proton exchange membrane fuel cells (PEMFC), and discloses a fuel cell bipolar plate and a fuel cell stack, which comprise a bipolar plate body, a reaction gas flow field is arranged on one side of the bipolar plate body, and a cooling flow field is arranged on the other side of the bipolar plate body; the main innovation is that the flow channel of the reaction gas flow field is gradually changed in section, the flow channel of the cooling flow field is a wave-shaped cooling flow channel with peaks and valleys, the peak position of the wave-shaped cooling flow channel corresponds to the ridge of the flow channel of the reaction gas flow field; in this way, the heat dissipation can be matched according to the heat production intensity of the ridge, the ridge part is a heat production concentration area, the fluid disturbance is enhanced at the peak, the local heat exchange coefficient is significantly improved, the reaction flow channel is gradually shrunk to increase the gas flow speed of the downstream, the heat conduction to the ridge part is enhanced, the cooling flow channel forms positive cooperation, and flow-heat-force multi-physical field cooperation is realized.

Description

Technical Field

[0001] This invention relates to the field of proton exchange membrane fuel cell (PEMFC) technology, specifically to a fuel cell bipolar plate and fuel cell stack. The bipolar plate integrates the reaction gas flow field, cooling flow field, and encapsulation mechanics into a single spatial coupling, making it suitable for automotive, energy storage, and portable fuel cell stacks. Background Technology

[0002] Bipolar plates are the core components of fuel cell stacks, undertaking functions such as electrical conductivity, thermal conductivity, gas distribution, support, and sealing. Common reaction flow fields of bipolar plates are mainly serpentine flow fields, parallel flow fields, and gradually changing cross-section flow fields. Among them, the gradually changing cross-section flow field has received increasing research and attention due to its ability to improve gas mass transfer characteristics, make liquid water flow more smoothly, and prevent flooding under high current density; such as the bipolar plates described in Chinese patent documents with publication numbers CN217444438U and CN114824348A.

[0003] However, the gradient design of the flow channel will cause changes in the heat distribution of the bipolar plate. The existing bipolar plate cooling structure is still an independent cooling plate or a straight microchannel set in the bipolar plate body. It does not address the coupling and matching problem between the cooling flow field structure and the new heat generation distribution under the ridge, which can easily lead to an increase in the temperature difference and thermal stress of the bipolar plate. Summary of the Invention

[0004] The purpose of this invention is to provide a fuel cell bipolar plate that integrates a gradually varying cross-section flow field and wave-shaped targeted cooling, thereby spatially coupling the reaction gas flow field, cooling flow field, and encapsulation mechanics in an integrated manner; and to solve one or more technical problems in the prior art, at least provide a beneficial option or create conditions.

[0005] The fuel cell bipolar plate provided by this invention is suitable for automotive, energy storage, and portable fuel cell stacks.

[0006] To achieve the above objectives, the present invention adopts the following technical solution.

[0007] A fuel cell bipolar plate includes a bipolar plate body, a reactant gas flow field on one side of the bipolar plate body, and a cooling flow field on the other side of the bipolar plate body. Its main innovation lies in the fact that the flow channel of the reactant gas flow field has a gradually changing cross-section, and the flow channel of the cooling flow field is a wave-shaped cooling flow channel with peaks and valleys. The peak position of the wave-shaped cooling flow channel corresponds to the ridge of the flow channel of the reactant gas flow field. This allows for matching heat dissipation to the heat generation intensity of the flow channel ridge, which is a concentrated heat generation area. The enhanced fluid turbulence at the peak significantly improves the local heat transfer coefficient. The gradually contracting reactant flow channel increases the downstream gas velocity, enhances heat conduction to the ridge, and forms a positive synergy with the cooling flow channel, achieving synergy of multiple physical fields including flow, heat, and force.

[0008] In this invention, the enhanced fluid disturbance at the crest is caused by the difference in boundary conditions resulting from the coupling of the geometry of the wave-shaped cooling channel with the specific spatial location of the ridge of the reaction flow field. Since the crest is located directly below the heat source (ridge), the thermal expansion micro-convection brought by the high-temperature wall and the larger heat transfer temperature difference work together to significantly enhance the heat transfer coefficient in this region, ultimately achieving precise targeted cooling of the hot spot under the ridge.

[0009] In one embodiment, the reaction flow field employs a multi-stage distribution and gradually varying cross-section parallel flow field, comprising: a gradually expanding inlet manifold, several parallel sub-channels, and a gradually contracting outlet manifold. The cross-sectional area of ​​each parallel sub-channel decreases linearly along the gas flow direction, with a decrease rate of 8%-30%.

[0010] The advantage of this design is that the large cross-sectional area of ​​the inlet section reduces air intake resistance and ensures sufficient oxygen supply; the small cross-sectional area of ​​the outlet section increases flow velocity and enhances liquid water carrying capacity; thus achieving a synergistic effect of "low pressure drop at the inlet and strong drainage at the outlet".

[0011] In one embodiment, a plurality of recesses communicating with the flow channel are provided at the bottom of the flow channel of the reaction flow field, and the reaction fluid is brought closer to the cooling flow field through the recesses.

[0012] In one embodiment, the recess is a concave circle.

[0013] In one embodiment, the wave-shaped cooling channel is a wave-shaped microchannel structure, preferably a sine wave, with a hydraulic diameter of 0.3 mm to 1.2 mm. The crests of the wave-shaped cooling channel are directly below the channel ridge of the reaction flow field in the thickness direction, and the troughs are directly below the channel of the reaction flow field.

[0014] In one embodiment, the wave-shaped cooling channel is a trapezoidal wave or a triangular wave.

[0015] In one embodiment, the wavy cooling channel is a non-uniform periodic waveform. The amplitude and / or wavelength of the wavy cooling channel are non-uniformly distributed along the flow direction, with larger amplitudes or higher peak densities corresponding to high heat generation regions.

[0016] In one embodiment, the fuel cell bipolar plate is an anode plate and / or a cathode plate.

[0017] In one embodiment, the fuel cell bipolar plate is made of graphite, stainless steel, titanium alloy, or composite material.

[0018] In one embodiment, during the design process, the amplitude, wavelength, and peak position of the wave-shaped cooling channel, as well as the decrease rate, ridge width, and heat generation intensity distribution of the gradually changing cross section of the reaction channel, are optimized through multiphysics simulation to establish a function mapping relationship, thereby achieving integrated matching between structural parameters and physical fields.

[0019] In one embodiment, the amplitude and wavelength of the wave channel are optimized through finite element simulation to match its stress distribution with the pressure field of the gradually changing flow channel, thereby suppressing local stress concentration.

[0020] In one embodiment, the contact pressure in the active area is made uniform by optimizing the sealing structure and assembly preload of the anode and cathode plates.

[0021] Specifically, a sealing groove is set on one of the anode plate and the cathode plate. The sealing gasket adopts a D-shaped cross-section, with the flat side of the sealing gasket adhering to the bottom surface of the sealing groove and the arc side of the sealing gasket facing the opposite electrode plate. The compression rate of the sealing gasket is controlled at 20%±5%. The width of the sealing groove is 1.0-1.3 times the width of the sealing gasket, and the depth is 75%-85% of the original height of the sealing gasket. In this way, after the sealing gasket is compressed, it deforms into the reserved space in the sealing groove, reducing the interference of the sealing reaction force on the contact pressure of the active area.

[0022] When assembling and tightening, a step-by-step, cross-symmetrical tightening strategy is adopted. First, all bolts are pre-tightened with the first target torque and then tightened in a cross-diagonal sequence. Then, the second round of tightening is performed with the second target torque. Finally, the final tightening is completed with 100% of the target torque to ensure uniform assembly pre-tightening force.

[0023] This invention has at least the following beneficial effects: I. The fuel cell bipolar plate provided by this invention organically combines a gradually changing reaction flow field channel and a corrugated cooling flow field. The crests of the corrugated cooling flow field correspond to the ridges of the reactant gas flow field, and the troughs correspond to the flow paths of the reactant gas flow field. Simulation tests show a significant improvement in overall mass transfer compared to bipolar plates with straight cooling flow fields (non-corrugated channels): cathode voltage drop is reduced by 54.2%, current density uniformity index is increased by 27.8%, and limiting current density is reduced from 2.15 A / cm². 2 Increased to 2.45 A / cm 2 This represents an increase of 14.0%.

[0024] II. The fuel cell bipolar plate provided by this invention solves the hot spot problem that existing technologies cannot solve: Through simulation testing, compared with bipolar plates with straight cooling channels (non-wavy channels), after adding the spatial targeted coupling design of wavy microchannels, the maximum temperature difference of the membrane electrode decreased from 16.1℃ to 7.6℃, a reduction of 52.8%, thus eliminating local hot spots from a mechanistic perspective.

[0025] III. The fuel cell bipolar plate provided by this invention achieves multi-physics field synergistic optimization of reaction flow field, temperature field, and stress. Simulation tests show that, compared with bipolar plates with straight cooling channels (non-wavy channels), the maximum thermal stress of the membrane electrode is reduced by 57.3%; contact pressure uniformity is improved by 54%; and high-frequency resistance is reduced from 8.9 mΩ•cm. 2 Reduced to 8.2 mΩ•cm 2 The decrease was 7.9%.

[0026] IV. The fuel cell bipolar plate structure provided by this invention is highly integrated and improves power density: by eliminating the independent cooling plate, simulation tests show that compared with bipolar plates with straight cooling channels (non-wavy channels), the 0.6V current density is increased by 10.7% and the peak power density is increased by 11.8%.

[0027] V. The durability of the fuel cell bipolar plate provided by this invention is greatly improved: through simulation testing, the voltage decay rate is reduced by 53.5% in a 500-hour dynamic cycle test, which is particularly suitable for the high current density and frequent load changes of automotive fuel cells. Attached Figure Description

[0028] Figure 1 The diagram shown is a schematic diagram of the overall structure of the bipolar plate in this invention.

[0029] Figure 2 The image shown is a perspective view of the bipolar plate in this invention.

[0030] Figure 3 The diagram shows a cooling channel for the bipolar plate in this invention.

[0031] Figure 4 The diagram shows a comparison of flow field transport characteristics (left: pressure distribution of the control group; right: pressure distribution of the present invention).

[0032] Figure 5 The figure shown is a comparison of temperature field distribution and maximum temperature difference (left: temperature distribution in the comparison figure; right: temperature distribution of the wave-shaped targeted cooling of the present invention).

[0033] Figure 6 The figure shows a comparison of durability under 500 hours of dynamic working conditions (the attenuation rate of the control group is 1.01% / 100h, the attenuation rate of the present invention is 0.47% / 100h, and the attenuation is reduced by 53.5%).

[0034] Figure 7 The figure shown is a cloud diagram of the stress distribution of the bipolar plate assembly in Example 1.

[0035] Explanation of reference numerals in the attached figures:

[0036] 1: Bipolar plate body, 2: Reaction flow field, 3: Cooling flow field.

[0037] 201: Ridge, 202: Flow channel, 203: Depression.

[0038] 301: Peak position, 302: Trough position. Detailed Implementation

[0039] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings, making the technical solution and beneficial effects of the present invention clearer and more explicit. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, but should not be construed as limiting the present invention.

[0040] Additional aspects and advantages of the invention will become apparent in the following description or may be learned by practice of the invention.

[0041] Example 1.

[0042] See Figures 1-3 As shown, a fuel cell bipolar plate includes a bipolar plate body 1, a reactant gas flow field 2 on one side of the bipolar plate body 1, and a cooling flow field 3 on the other side of the bipolar plate body. Its main innovation lies in the fact that the flow channel of the reactant gas flow field 2 is a gradually changing cross-section flow channel, and the flow channel of the cooling flow field 3 is a wave-shaped cooling flow channel with peaks and valleys. The peak position 301 of the wave-shaped cooling flow channel corresponds to the ridge 201 of the reactant gas flow field 2, and the trough position 302 of the wave-shaped cooling flow channel corresponds to the flow channel 202 of the reactant gas flow field 2. This allows for matching heat dissipation to the heat generation intensity of the flow channel ridge. The flow channel ridge is a heat generation concentration area, and the enhanced fluid disturbance at the peak significantly improves the local heat transfer coefficient. The gradually contracting reactant flow channel increases the downstream gas velocity, enhancing heat conduction to the ridge, forming a positive synergy with the cooling flow channel, and achieving multi-physics field synergy of flow, heat, and force.

[0043] In this embodiment, a plurality of recesses 203 are provided at the bottom of the flow channel 202. These recesses 203 allow the reaction fluid to be closer to the cooling flow field 3 at the bottom, thus improving heat dissipation. Preferably, the recesses 203 are concave circles, which minimizes structural defects caused by their placement. In some embodiments, the shape of the recesses 203 can be adjusted appropriately according to actual needs, and is not limited to this embodiment.

[0044] In this embodiment, the bipolar plate body 1 is made of high-purity graphite material with a resistivity ≤1.5mΩ•cm and a single-cell active area of ​​300 cm². 2 It is rectangular in shape with a length-to-width ratio of 3:1. One side of the bipolar plate is the cathode reaction flow field, and the other side is the cooling flow field, forming the cathode plate.

[0045] The cathode flow field adopts a multi-stage distribution-gradient cross-section parallel flow field structure, specifically including: a gradually expanding inlet manifold, 30 parallel direct-flow channels, and a gradually contracting outlet manifold. The flow channel geometry parameters are: inlet width 1.0 mm, outlet width 0.8 mm, flow channel depth 0.8 mm (constant ridge height), ridge width: 0.8 mm, cross-sectional area reduction rate 20% (linearly decreasing along the flow direction), and a micro-groove structure with a depth of 0.05 mm at the bottom of the flow channel to disrupt the boundary layer and promote liquid water discharge.

[0046] The cooling flow field is located on the back of the bipolar plate and employs a sinusoidal wave-shaped microchannel structure. The hydraulic diameter of the cooling channel is 0.7 mm, the amplitude is 0.3 mm, and the wavelength is 4 mm. The spatial correspondence is as follows: the crest of the wave-shaped cooling channel is directly below the ridge of the reaction flow field in the thickness direction, with a alignment deviation not exceeding 0.1 mm (achieved through CNC precision machining). Connecting holes are opened inside the cooling channel, forming a single loop in series.

[0047] Simulation Test: The above-mentioned cathode plate, anode plate, and proton exchange membrane were assembled into a fuel cell stack. A simplified parallel constant cross-section flow field was adopted for the anode flow field, and a silicone rubber gasket was used for sealing. The assembly preload was 2.5-3.5 MPa. The contact resistance of the assembled fuel cell stack was ≤10 mΩ·cm. 2 Pressure rating ≥3 bar.

[0048] In this embodiment, a sealing groove is provided on the anode plate; the sealing gasket adopts a D-shaped cross-section, with its flat side conforming to the bottom surface of the sealing groove and its arc side facing the counter-electrode plate. The compression rate of the sealing gasket is controlled at 20%±5%; the width of the sealing groove is 1.0-1.3 times the width of the sealing gasket, and the depth is 75%-85% of the original height of the sealing gasket, so that the sealing gasket leaves deformation space in the groove after compression, reducing the interference of the sealing reaction force on the contact pressure of the active area. When assembling the anode plate and cathode plate, a step-by-step cross-symmetrical tightening strategy is adopted: first, all bolts are pre-tightened with 28% of the target torque (0.70-1.00MPa), and then tightened in a cross-diagonal sequence; then, a second round of tightening is performed with 55% of the target torque (1.2-1.8MPa); finally, the final tightening is completed with 100% of the target torque (2.0-3.0MPa). By optimizing the sealing structure and assembly pre-tightening force of the anode plate and cathode plate, the contact pressure of the active area is made uniform. See Figure 7 As shown, from Figure 7 From the perspective of the contact pressure distribution in the low-stress and high-stress areas, the stress distribution in this embodiment is matched and suppresses local concentration.

[0049] To better demonstrate the progressiveness of the present invention, a control group was also set up and simulation tests were conducted. The cathode plate of the control group was a bipolar plate with the same active area and material, but the cooling flow field was an independent flat DC channel. Everything else was the same as in Example 1.

[0050] The performance comparison between Example 1 and the control group of the present invention is shown in Table 1 and... Figures 4-6 As shown.

[0051] Table 1. Performance comparison between Example 1 of the present invention and the control group.

[0052]

[0053] From Table 1 and Figures 4-6 It can be seen that the performance of each phase in this invention is significantly better than that of the control group, demonstrating a clear technological advancement.

[0054] It should also be noted that in the description of this invention, directional terms such as "center," "lateral," "longitudinal," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise" indicate the orientation and positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. They should not be construed as limiting the specific protection scope of this invention.

[0055] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features. Thus, the use of "first" and "second" to define a feature may explicitly or implicitly include one or more of that feature, and in the description of this invention, "at least" means one or more, unless otherwise explicitly specified.

[0056] In this invention, unless otherwise explicitly specified and limited, the terms "assembly," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can also refer to a mechanical connection; they can refer to a direct connection or a connection through an intermediate medium; or they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0057] In this invention, unless otherwise specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "below," and "over" the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Above," "below," and "below" the second feature includes the first feature being directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0058] Based on the above description of the structure and principles, those skilled in the art should understand that this invention is not limited to the specific embodiments described above. Improvements and substitutions made using techniques known in the art based on this invention all fall within the scope of protection of this invention, which should be defined by the claims and their equivalents. Parts not described in the specific embodiments are all prior art or common knowledge.

Claims

1. A fuel cell bipolar plate, comprising a bipolar plate body, a reactant gas flow field disposed on one side of the bipolar plate body, and a cooling flow field disposed on the other side of the bipolar plate body; characterized in that, The flow channel of the reactive gas flow field is a gradually changing cross section flow channel, and the flow channel of the cooling flow field is a wave-shaped cooling flow channel. The peak position of the wave-shaped cooling flow channel corresponds to the ridge of the reactive gas flow field, and the trough position of the wave-shaped cooling flow channel corresponds to the flow channel of the reactive gas flow field.

2. The fuel cell bipolar plate according to claim 1, characterized in that, The reaction flow field adopts a multi-stage distribution and gradually changing cross-section parallel flow field, including a gradually expanding inlet manifold, several parallel sub-channels and a gradually contracting outlet manifold; the cross-sectional area of ​​each parallel sub-channel decreases linearly along the gas flow direction, with a decrease rate of 8%-30%.

3. A fuel cell bipolar plate according to claim 1 or 2, characterized in that, Several recesses communicating with the flow channel are provided at the bottom of the flow channel of the reaction flow field, and the reaction fluid is brought closer to the cooling flow field through the recesses.

4. A fuel cell bipolar plate according to claim 3, characterized in that, The recessed portion is a concave circle.

5. A fuel cell bipolar plate according to claim 1, characterized in that, The wave-shaped cooling channel is a wave-shaped microchannel structure in the form of a sine wave, trapezoidal wave, or triangular wave, and the hydraulic diameter of the wave-shaped cooling channel is 0.3mm-1.2mm.

6. A fuel cell bipolar plate according to claim 1, characterized in that, The wave-shaped cooling channel is a non-uniform periodic waveform. The amplitude and / or wavelength of the wave-shaped cooling channel are non-uniformly distributed along the flow direction. In the high heat generation region, a larger amplitude or a higher peak density is set accordingly.

7. A fuel cell bipolar plate according to claim 1, characterized in that, The fuel cell bipolar plate is an anode plate and / or a cathode plate, and the fuel cell bipolar plate is made of one of graphite, stainless steel, titanium alloy or composite material.

8. A fuel cell bipolar plate according to claim 1, characterized in that, The amplitude, wavelength, and peak position of the wave-shaped cooling channel, as well as the decrease rate, ridge width, and heat generation intensity distribution of the gradually changing cross section of the reaction channel, are optimized through multiphysics simulation to establish a function mapping relationship, thereby achieving integrated matching between structural parameters and physical fields.

9. A fuel cell stack, characterized in that, A fuel cell bipolar plate as described in any one of claims 1-8.

10. A fuel cell stack according to claim 9, characterized in that, The contact pressure in the active area is made uniform by optimizing the sealing structure and assembly pre-tightening force of the anode and cathode plates. A sealing groove is set on one of the anode and cathode plates. The sealing gasket has a D-shaped cross-section, with the flat side of the sealing gasket adhering to the bottom surface of the sealing groove and the arc side of the sealing gasket facing the opposite plate. The compression rate of the sealing gasket is controlled at 20%±5%. The width of the sealing groove is 1.0-1.3 times the width of the sealing gasket, and the depth is 75%-85% of the original height of the sealing gasket. When assembling and tightening, a step-by-step cross-symmetrical tightening strategy is adopted. First, all bolts are pre-tightened with the first target torque and then tightened in a cross-diagonal sequence. Then, the second round of tightening is performed with the second target torque. Finally, the final tightening is completed with 100% of the target torque to ensure uniform assembly pre-tightening force.

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