A bipolar plate with a multi-flow field structure and a method for preparing the same

Abstract

The present invention provides a bipolar plate with a multi-flow field structure and a preparation method thereof, relating to the field of fuel cells. The reaction flow field structure of the bipolar plate is composed of an upper direct current section, a middle barrier section, a lower variable flow section, and a bottom barrier section, each section occupying a different proportion of the total length of the plate; the upper direct current section is a parallel flow field structure, the middle barrier section is a specific boss structure, the lower variable flow section is a variable flow field structure with variable flow channel ridges, a contraction portion, and a widening portion, and the bottom barrier section is a staggered frustum structure; the preparation method includes metal plate surface pretreatment and rubber pad stamping forming processes. By changing the flow field structure, the present invention enables the bipolar plate structure to simultaneously help increase the reactant flow rate, promote reactant diffusion, and promote gas transmission and water discharge in the membrane electrode assembly.

Description

Technical Field

[0001] The present invention relates to the field of fuel cell technology, and in particular to a bipolar plate with a multi-flow field structure and a preparation method thereof. Background Art

[0002] Fuel cells primarily consist of a proton exchange membrane, a catalyst layer, an air diffusion layer, and bipolar plates. As a core component, the bipolar plate plays many important roles in fuel cells, and its performance is largely dependent on the flow field structure. However, there are currently some technical issues with the flow field in fuel cells.

[0003] Since the advent of fuel cell technology, extensive research has been conducted on flow fields. This research can be divided into two aspects: the optimization of traditional flow fields (such as parallel flow fields, serpentine flow fields, and interdigitated flow fields) and the design of novel flow fields. For traditional flow fields, on the one hand, cell performance is improved by optimizing channel parameters and adjusting flow field geometry. However, research has found that while reducing channel depth and width can increase reactant flow rates and thus improve cell performance, it also increases pressure drop and pump parasitic power, affecting the cell's net output power. On the other hand, flow field geometry is being studied. While flow fields with "trap" structures can promote reactant diffusion into the MEA, which is beneficial for improving cell performance, and "convergent-divergent" variable-path flow fields can promote gas transport and water removal within the membrane electrode assembly (MEA) due to the pressure difference between adjacent channel grooves, thereby improving fuel cell output power, these traditional flow field optimization methods still have certain limitations, which are urgent technical issues that need to be addressed in the current development of fuel cell technology. Summary of the Invention

[0004] To address the aforementioned technical challenges of improving fuel cell performance and output power, a bipolar plate with a multi-flow field structure and a method for fabricating the same are provided. By modifying the flow field structure, the present invention simultaneously increases reactant flow rates, promotes reactant diffusion, and facilitates gas transport and water removal within the membrane electrode assembly.

[0005] The technical means adopted in the present invention are as follows:

[0006] A bipolar plate with a multi-flow field structure includes a reaction flow field region disposed on the plate. Along the length of the bipolar plate, the reaction flow field region is composed of an upper direct flow section, a middle barrier section, a lower variable flow section, and a bottom barrier section. Taking the length of the bipolar plate as the total length, the upper direct flow section, the middle barrier section, the lower variable flow section, and the bottom barrier section account for 25%, 15%, 50%, and 5% of the total length of the plate, respectively.

[0007] The upper direct current section is a parallel flow field structure;

[0008] The middle barrier area is a boss structure, which is composed of a transverse ridge and a plurality of longitudinal ridges perpendicular to the transverse ridge. The height of the boss structure is lower than that of the parallel flow field structure.

[0009] The lower variable diameter flow section is a variable diameter flow field structure with the same height as the parallel flow field structure;

[0010] The bottom barrier region is composed of multiple rows of frustums arrayed along the width direction of the bipolar plate, with each row of frustums being staggered, and the upper surface of the frustums being flush with the upper surface of the variable-diameter flow field structure;

[0011] The parallel flow field structure is composed of a plurality of straight flow channel ridges, and a straight flow channel groove of the bipolar plate is formed between each two adjacent straight flow channel ridges;

[0012] The variable diameter flow field structure is composed of a plurality of variable diameter flow channel ridges, and a variable diameter flow channel groove of the bipolar plate is formed between every two adjacent variable diameter flow channel ridges.

[0013] Furthermore, along the length direction of the bipolar plate, a plurality of contraction portions are uniformly arrayed on the variable diameter flow channel ridge, and the contraction portions of adjacent variable diameter flow channel ridges are aligned; and the variable diameter flow channel ridge and the contraction portion both have corresponding widening portions.

[0014] Furthermore, the width of the straight flow channel groove is 1-5 mm; the width of the variable diameter flow channel groove is 1-5 mm; the width of the widened portion of the variable diameter flow channel groove is 2-6 mm;

[0015] The depth of the linear flow channel groove and the variable diameter flow channel groove is 0.8-3mm;

[0016] The first row of the frustums in the bottom partition area adjacent to the lower variable-radius flow section are all located at the center between two straight flow channel ridges, and the diameter of the frustum is 1-3 mm.

[0017] Furthermore, in the flow field area, the width direction of the flow field area is the total width, the distance range from the two side edges of the bipolar plate and accounting for one quarter of the total width is the edge area of ​​the flow field area, and the rest is the middle area. The flow channel ridge spacing in the middle area is 0.5-2mm; the flow channel ridge spacing in the edge area is 2.5-5mm; the spacing between two adjacent flow channel ridges in the middle area and the edge area is 1-3mm.

[0018] Furthermore, the boss structure is composed of a transverse ridge and three longitudinal ridges in a uniform array and perpendicular to the transverse ridge. The height of the boss structure is 1 mm lower than the parallel flow field structure. The length of the transverse ridge is flush with the two ends of the upper direct current section. The width of the transverse ridge and the width of the longitudinal ridge are both equal to the width of the straight flow channel ridge.

[0019] Furthermore, in the boss structure, the intersection of the transverse ridge and the longitudinal ridge is low-lying.

[0020] Furthermore, when the middle barrier zone is located in the middle position of the lower variable flow section, the lower variable flow section is divided by the middle barrier zone to form two variable flow field structures, and the reaction flow field structure is composed of the upper direct flow section, the lower variable flow section A, the middle barrier zone, the lower variable flow section B and the bottom barrier zone from top to bottom.

[0021] A method for preparing a bipolar plate with a multi-flow field structure comprises the following steps:

[0022] S1. Use metal sheets and perform surface pretreatment on them;

[0023] S2. A rubber pad stamping process is used to stamp or etch the surface of the metal plate to form a parallel flow field structure, a boss structure, a variable diameter flow field structure, and a truncated cone structure.

[0024] Furthermore, the surface pretreatment in S1 includes grinding, removing the passivation layer, and coating the surface with an anti-corrosion protective layer; grinding uses 50-200 mesh sandpaper; removing the passivation layer uses a weak acid with a pH of 6.6-6.9 for immersion for 1-5 hours; and coating the surface with an anti-corrosion protective layer uses a PVD method to sputter precious metals such as Pt and C.

[0025] Due to the adoption of the above technical solution, the present invention has the following advantages compared with the prior art:

[0026] 1. The present invention provides a bipolar plate with a multi-flow field structure and a preparation method thereof. By combining a straight flow channel groove with a boss turbulence design, the contact opportunity between the gas and the reactants can be increased while ensuring smooth flow of the airflow. The function of the straight flow channel groove is to ensure the stability and low-resistance flow of the airflow, while the boss will induce turbulence of the airflow through the turbulence effect, causing the gas flow rate to fluctuate in a local area, generating turbulence, and more complete mixing of the reactants and the gas. Especially at higher flow rates or high reaction temperatures, the probability of collision between reactant molecules is increased, and the reaction rate is accelerated. Specifically, the position and size of the boss can accurately control the degree of turbulence of the airflow, thereby optimizing the reaction efficiency and avoiding incomplete coverage of the reaction area caused by uneven gas flow.

[0027] 2. The present invention provides a bipolar plate with a multi-flow field structure and a preparation method thereof. The design of the straight flow channel optimizes the mainstream path of the airflow, reduces the fluid friction resistance caused by bends or sudden cross-sections, and ensures an overall low pressure drop. The boss spoiler design can produce a certain flow disturbance in the local area to prevent the airflow from generating dead zones or local flow rates being too low in the flow channel. The function of the boss is mainly to periodically disrupt the airflow so that the airflow maintains a relatively uniform distribution, and to increase the disturbance of the airflow through local turbulence, thereby preventing the possible occurrence of low-speed zones. Combining these two, while maintaining a low overall pressure drop, it is possible to avoid extreme phenomena of too fast or too slow airflow, thereby ensuring the stability of the gas flow and the efficient operation of the system.

[0028] 3. The present invention provides a bipolar plate with a multi-flow field structure and a preparation method thereof. The combination of the straight flow channel groove and the boss spoiler design makes the system more adaptable to changes in operating conditions such as flow rate, temperature, and reactant composition. The boss structure divides the lower variable diameter flow section into two variable diameter flow field structures, so that the flow field structure of the bipolar plate is formed from top to bottom into an upper straight flow section, a lower variable diameter flow section area A, a middle barrier area, a lower variable diameter flow section area B, and a bottom barrier area. That is, at this time, the straight flow field structure of the upper straight flow section is directly the same as the variable diameter flow field structure of the lower variable diameter flow section area A. At this time, the middle barrier area can re-collect and redistribute the gas, reduce the difference in gas usage in different flow channel grooves, and redistribute it into the next area after collection, increase the gas distribution, and improve performance. Such a design is conducive to the enlargement of the bipolar plate to a large size, can increase the number of intermediate barrier areas, and increase the consistency of large-area bipolar plates.

[0029] 4. The present invention provides a bipolar plate with a multi-flow field structure and a preparation method thereof, in which the intersection of the transverse ridges and the longitudinal ridges in the boss structure is designed to be low-lying, so that the reactants that pass through the straight flow field structure directly and directly connect with the lower variable diameter flow section A in sequence will have a certain "flow convergence" effect again in the low-lying structure, effectively avoiding the reaction weakening phenomenon, thereby further increasing the gas distribution effect and allowing the gas to flow evenly into the variable diameter flow field in the rear section.

[0030] Based on the above reasons, the present invention can be promoted in the field of fuel cell technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0032] Figure 1Schematic diagram I of a bipolar plate structure with a multi-flow field structure according to the present invention;

[0033] Figure 2 Schematic diagram II of a bipolar plate structure with a multi-flow field structure according to the present invention;

[0034] Figure 3 Schematic diagram III of a bipolar plate structure with a multi-flow field structure according to the present invention;

[0035] Figure 4 This is a schematic diagram showing a depression at the intersection of the transverse ridges and the longitudinal ridges in a bipolar plate boss structure with a multi-flow field structure according to the present invention;

[0036] Figure 5 This is a flow chart of a method for preparing a bipolar plate with a multi-flow field structure described in the present invention.

[0037] In the figure: 1. Upper direct flow section; 2. Middle barrier section; 3. Lower variable runoff section; 31. Lower variable runoff section area A; 32. Lower variable runoff section area B; 4. Bottom barrier section; 5. Horizontal ridge; 6. Longitudinal ridge. DETAILED DESCRIPTION

[0038] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments of the present invention can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0039] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0040] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0041] Unless otherwise specifically stated, the relative arrangement of the parts and steps, numerical expressions and numerical values ​​described in these embodiments do not limit the scope of the present invention. At the same time, it should be clear that, for ease of description, the sizes of the various parts shown in the drawings are not drawn according to the actual proportional relationship. The techniques, methods and equipment known to ordinary technicians in the relevant fields may not be discussed in detail, but where appropriate, the techniques, methods and equipment should be considered as part of the authorization specification. In all examples shown and discussed here, any specific value should be interpreted as merely exemplary and not as a limitation. Therefore, other examples of the exemplary embodiments may have different values. It should be noted that similar numbers and letters represent similar items in the following figures, so once an item is defined in one figure, it does not need to be further discussed in subsequent figures.

[0042] In the description of the present invention, it should be understood that the directions or positional relationships indicated by directional words such as "front, back, up, down, left, right", "horizontal, vertical, vertical, horizontal" and "top, bottom" are usually based on the directions or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description. Unless otherwise specified, these directional words do not indicate or imply that the device or element referred to must have a specific direction or be constructed and operated in a specific direction. Therefore, they cannot be understood as limiting the scope of protection of the present invention: the directional words "inside and outside" refer to the inside and outside relative to the outline of each component itself.

[0043] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used herein to describe the spatial positional relationship of a device or feature to other devices or features as shown in the figures. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figures. For example, if the device in the drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below their position devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0044] In addition, it should be noted that the use of terms such as "first" and "second" to limit components is only for the convenience of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore cannot be understood as limiting the scope of protection of the present invention.

[0045] Example 1

[0046] like Figure 1 As shown, the present invention provides a bipolar plate with a multi-flow field structure, including a reaction flow field region provided on the plate. Along the length direction of the bipolar plate, the reaction flow field region is composed of an upper straight flow section 1, a middle barrier region 2, a lower variable flow section 3, and a bottom barrier region 4. Taking the length direction of the bipolar plate as the total length, the upper straight flow section 1, the middle barrier region 2, the lower variable flow section 3, and the bottom barrier region 4 account for 25%, 15%, 50%, and 5% of the total length of the plate, respectively.

[0047] The upper DC section 1 is a parallel flow field structure, which is composed of multiple straight flow ridges. The straight flow grooves of the bipolar plate are formed between each two adjacent straight flow ridges. The width of the straight flow grooves is 1 mm, and the depth of the straight flow grooves is 0.8 mm.

[0048] The middle barrier area 2 is a boss structure, such as Figure 4 As shown, the boss structure consists of a transverse ridge 5 and three longitudinal ridges 6 in a uniform array and perpendicular to the transverse ridge 5. The height of the boss structure is 1 mm lower than the parallel flow field structure. The length of the transverse ridge 5 is flush with the two ends of the upper direct current section 1. The width of the transverse ridge 5 and the width of the longitudinal ridge 6 are both equal to the width of the straight flow channel ridge. The intersection of the transverse ridge 5 and the longitudinal ridge 6 is low-lying.

[0049] The lower variable diameter flow section 3 is a variable diameter flow field structure with the same height as the straight flow ridge. The variable diameter flow field structure is composed of multiple variable diameter flow ridges. The variable diameter flow channel groove of the bipolar plate is formed between each two adjacent variable diameter flow ridges. Along the length direction of the bipolar plate, multiple contractions are evenly arrayed on the variable diameter flow ridge. The variable diameter flow channel groove and the contraction portion each have a widening portion corresponding to the widening portion. The width of the variable diameter flow channel groove is 1 mm, the width of the widening portion of the variable diameter flow channel groove is 2 mm, and the depth of the variable diameter flow channel groove is 0.8 mm.

[0050] The bottom barrier area 4 is composed of two rows of cones arrayed along the width direction of the bipolar plate. The spacing between each row of cones is 1 mm, and the cones in each row are staggered. The cones adjacent to the parallel flow field structure are located at the center between the two straight flow channel ridges. The upper surface of the cone is flush with the upper surface of the variable diameter flow field structure, and the diameter of the cone is 1 mm.

[0051] Example 2

[0052] like Figure 2As shown, the present invention also provides a bipolar plate with a multi-flow field structure, including a reaction flow field region provided on the plate. Along the length direction of the bipolar plate, the reaction flow field region is composed of an upper straight flow section 1, a middle barrier region 2, a lower variable flow section 3, and a bottom barrier region 4. Taking the length direction of the bipolar plate as the total length, the upper straight flow section 1, the middle barrier region 2, the lower variable flow section 3, and the bottom barrier region 4 respectively account for 25%, 15%, 50%, and 5% of the total length of the plate.

[0053] The upper DC section 1 is a parallel flow field structure, which is composed of multiple straight flow ridges. The straight flow grooves of the bipolar plate are formed between each two adjacent straight flow ridges. The width of the straight flow grooves is 1 mm, and the depth of the straight flow grooves is 0.8 mm.

[0054] The middle barrier area 2 is a boss structure, such as Figure 4 As shown, the boss structure consists of a transverse ridge 5 and three longitudinal ridges 6 in a uniform array and perpendicular to the transverse ridge 5. The height of the boss structure is 1 mm lower than the parallel flow field structure. The length of the transverse ridge 5 is flush with the two ends of the upper direct current section 1. The width of the transverse ridge 5 and the width of the longitudinal ridge 6 are both equal to the width of the straight flow channel ridge. The intersection of the transverse ridge 5 and the longitudinal ridge 6 is low-lying.

[0055] The lower variable diameter flow section 3 is a variable diameter flow field structure with the same height as the straight flow ridge. The variable diameter flow field structure is composed of multiple variable diameter flow ridges. The variable diameter flow channel groove of the bipolar plate is formed between each two adjacent variable diameter flow ridges. Along the length direction of the bipolar plate, multiple contractions are evenly arrayed on the variable diameter flow ridge. The variable diameter flow channel groove and the contraction portion each have a widening portion corresponding to the widening portion. The width of the variable diameter flow channel groove is 1 mm, the width of the widening portion of the variable diameter flow channel groove is 2 mm, and the depth of the variable diameter flow channel groove is 0.8 mm.

[0056] The middle barrier zone 2 is located in the middle of the lower variable flow section 3. The lower variable flow section 3 is divided by the middle barrier zone 2 to form two variable flow field structures. The reaction flow field structure is composed of the upper straight flow section 1, the lower variable flow section A section 31, the middle barrier zone 2, the lower variable flow section B section 32 and the bottom barrier zone 4 from top to bottom.

[0057] The bottom barrier area 4 is composed of two rows of cones arrayed along the width direction of the bipolar plate. The spacing between each row of cones is 1 mm, and the cones in each row are staggered. The cones adjacent to the parallel flow field structure are located at the center between the two straight flow channel ridges. The upper surface of the cone is flush with the upper surface of the variable diameter flow field structure, and the diameter of the cone is 1 mm.

[0058] Example 3

[0059] like Figure 3As shown, the present invention also provides a bipolar plate with a multi-flow field structure, including a reaction flow field region provided on the plate. Along the length direction of the bipolar plate, the reaction flow field region is composed of an upper straight flow section 1, a middle barrier region 2, a lower variable flow section 3, and a bottom barrier region 4. Taking the length direction of the bipolar plate as the total length, the upper straight flow section 1, the middle barrier region 2, the lower variable flow section 3, and the bottom barrier region 4 respectively account for 25%, 15%, 50%, and 5% of the total length of the plate.

[0060] The upper DC section 1 is a parallel flow field structure, which is composed of multiple straight flow channel ridges. The straight flow channel groove of the bipolar plate is formed between each two adjacent straight flow channel ridges. The width of the straight flow channel groove is 1mm, and the depth of the straight flow channel groove is 0.8mm. The width direction of the bipolar plate is the total width, and the distance from the two sides of the bipolar plate to one-quarter of the total width is the edge area of ​​the bipolar plate, and the rest is the middle area. The straight flow channel ridges of the upper DC section 1 are dense in the middle area and sparse in the edge area. Figure 3 As shown, the distance between the flow channel ridges in the middle area is 0.5 mm; the distance between the flow channel ridges in the edge area is 2.5 mm; the distance between two adjacent flow channel ridges in the middle area and the edge area is 1 mm;

[0061] The middle barrier area 2 is a boss structure, such as Figure 4 As shown, the boss structure consists of a transverse ridge 5 and three longitudinal ridges 6 in a uniform array and perpendicular to the transverse ridge 5. The height of the boss structure is 1 mm lower than the parallel flow field structure. The length of the transverse ridge 5 is flush with the two ends of the upper direct current section 1. The width of the transverse ridge 5 and the width of the longitudinal ridge 6 are both equal to the width of the straight flow channel ridge. The intersection of the transverse ridge 5 and the longitudinal ridge 6 is low-lying.

[0062] The lower variable diameter flow section 3 is a variable diameter flow field structure with the same height as the straight flow ridge. The variable diameter flow field structure is composed of multiple variable diameter flow ridges. The variable diameter flow channel groove of the bipolar plate is formed between each two adjacent variable diameter flow ridges. Along the length direction of the bipolar plate, multiple contractions are evenly arrayed on the variable diameter flow ridge. The variable diameter flow channel groove and the contraction portion each have a widening portion corresponding to the widening portion. The width of the variable diameter flow channel groove is 1 mm, the width of the widening portion of the variable diameter flow channel groove is 2 mm, and the depth of the variable diameter flow channel groove is 0.8 mm.

[0063] The bottom barrier area 4 is composed of two rows of cones arrayed along the width direction of the bipolar plate. The spacing between each row of cones is 1 mm, and the cones in each row are staggered. The cones adjacent to the parallel flow field structure are located at the center between the two straight flow channel ridges. The upper surface of the cone is flush with the upper surface of the variable diameter flow field structure, and the diameter of the cone is 1 mm.

[0064] like Figure 5 As shown, the present invention also provides a method for preparing a bipolar plate with a multi-flow field structure, comprising the following steps:

[0065] S1. Two 280×500mm metal plates were subjected to surface pretreatment, including grinding, removing the passivation layer, and coating the surface with an anti-corrosion protective layer. 200-grit sandpaper was used for grinding. The passivation layer was removed by soaking in a weak acid with a pH of 6.6 for 5 hours. The surface anti-corrosion protective layer was coated with Pt precious metal by sputtering using the PVD method.

[0066] S2. Use a rubber pad stamping process to stamp or etch the surface of the metal plate to form a parallel flow field structure, a boss structure, a variable diameter flow field structure and a truncated cone structure, wherein the total length of the parallel flow field structure is 100 mm, the total length of the boss structure is 60 mm, the total length of the variable diameter flow field structure is 200 mm, the total length of the truncated cone structure is 20 mm, and the total length of the remaining parts is 100 mm, thereby forming the anode plate and the cathode plate.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A bipolar plate with a multi-flow field structure, characterized in that: The reaction flow field region is provided on the bipolar plate. Along the length direction of the bipolar plate, the reaction flow field region is composed of an upper straight flow section, a middle barrier section, a lower variable flow section, and a bottom barrier section. Taking the length direction of the bipolar plate as the total length, the upper straight flow section, the middle barrier section, the lower variable flow section, and the bottom barrier section account for 25%, 15%, 50%, and 5% of the total length of the bipolar plate, respectively. The upper direct current section is a parallel flow field structure; The middle barrier area is a boss structure, which is composed of a transverse ridge and a plurality of longitudinal ridges perpendicular to the transverse ridge. The height of the boss structure is lower than that of the parallel flow field structure. The lower variable diameter flow section is a variable diameter flow field structure with the same height as the parallel flow field structure; The bottom barrier region is composed of multiple rows of frustums arrayed along the width direction of the bipolar plate, with each row of frustums being staggered, and the upper surface of the frustums being flush with the upper surface of the variable-diameter flow field structure; The parallel flow field structure is composed of a plurality of straight flow channel ridges, and a straight flow channel groove of the bipolar plate is formed between each two adjacent straight flow channel ridges; The variable diameter flow field structure is composed of a plurality of variable diameter flow channel ridges, and a variable diameter flow channel groove of the bipolar plate is formed between every two adjacent variable diameter flow channel ridges.

2. The bipolar plate with a multi-flow field structure according to claim 1, characterized in that: Along the length direction of the bipolar plate, a plurality of contraction portions are evenly arrayed on the variable diameter flow channel ridge, and the contraction portions of adjacent variable diameter flow channel ridges are aligned; the variable diameter flow channel ridge and the contraction portion both have corresponding widening portions.

3. The bipolar plate with a multi-flow field structure according to claim 1, characterized in that: The width of the straight channel groove is 1-5 mm; the width of the variable diameter channel groove is 1-5 mm; the width of the widened portion of the variable diameter channel groove is 2-6 mm; The depth of the linear flow channel groove and the variable diameter flow channel groove is 0.8-3mm; A row of frustums adjacent to the lower variable-diameter flow section is located at the center between two variable-diameter flow channel ridges, and the diameter of the frustum is 1-3 mm.

4. The bipolar plate with a multi-flow field structure according to claim 1, characterized in that: In the flow field area, the width direction of the flow field area is the total width, and the distance range from the two sides of the bipolar plate and accounting for one quarter of the total width is the edge area of ​​the flow field area, and the rest is the middle area. The flow channel ridge spacing in the middle area is 0.5-2mm; the flow channel ridge spacing in the edge area is 2.5-5mm; the spacing between two adjacent flow channel ridges in the middle area and the edge area is 1-3mm.

5. The bipolar plate with a multi-flow field structure according to claim 1, characterized in that: The boss structure consists of a transverse ridge and three longitudinal ridges in a uniform array and perpendicular to the transverse ridge. The height of the boss structure is 1 mm lower than the parallel flow field structure. The length of the transverse ridge is flush with the two ends of the upper direct current section. The width of the transverse ridge and the width of the longitudinal ridge are both equal to the width of the straight flow channel ridge.

6. The bipolar plate with a multi-flow field structure according to claim 5, characterized in that: In the boss structure, the intersection of the transverse ridge and the longitudinal ridge is low-lying.

7. The bipolar plate with a multi-flow field structure according to any one of claims 1 to 6, characterized in that: When the middle barrier zone is located in the middle position of the lower variable flow section, the lower variable flow section is divided by the middle barrier zone to form two variable flow field areas, and the reaction flow field areas are, from top to bottom, the upper direct flow section, the lower variable flow section A, the middle barrier zone, the lower variable flow section B and the bottom barrier zone.

8. A method for preparing a bipolar plate with a multi-flow field structure, based on the bipolar plate according to claim 1, characterized in that: The following steps are involved: S1. Use metal sheets and perform surface pretreatment on them; S2. A rubber pad stamping process is used to stamp or etch the surface of the metal plate to form a parallel flow field structure, a boss structure, a variable diameter flow field structure, and a truncated cone structure.

9. The method for preparing a bipolar plate with a multi-flow field structure according to claim 8, characterized in that: The surface pretreatment in S1 includes grinding, removing the passivation layer, and coating the surface with an anti-corrosion protective layer; grinding uses 50-200 mesh sandpaper; removing the passivation layer uses a weak acid with a pH of 6.6-6.9 for immersion for 1-5 hours; and coating the surface with an anti-corrosion protective layer uses PVD sputtering of precious metals such as Pt and C.

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