A method for preparing a bipolar plate and its application

Abstract

This application provides a method for preparing and applying a bipolar plate, comprising: (1) processing stainless steel to obtain a primary plate; (2) alloying the primary plate with a composite material in a hydrogen atmosphere to obtain a composite plate; (3) laser welding and shaping the composite plate to obtain a bipolar plate; wherein the composite material comprises a chromium source (chromium, chromium chloride), a magnesium-aluminum eutectic alloy, and a dispersant. This application generates a composite plate with good corrosion resistance by performing powder surface alloying on the surface of the bipolar plate in a hydrogen atmosphere; simultaneously, during the preparation of the bipolar plate, it will not detach or corrode due to welding and shaping; furthermore, after shaping, the two plates will be fused together to form a whole, avoiding gas and liquid leakage.

Description

Technical Field

[0001] This application relates to the field of bipolar plate technology, specifically to a method for preparing and applying a bipolar plate. Technical Background

[0002] The bipolar plate, also known as the flow field plate, is stacked with the membrane electrode assembly (MEA) to form a fuel cell stack. In a fuel cell, it serves multiple functions, including support, current collection, providing channels for the coolant, and separating the oxidant and reductant. Simultaneously, the bipolar plate must also possess excellent heat dissipation, strong corrosion resistance, and good shock resistance.

[0003] Fuel cells commonly use three types of bipolar plates: graphite carbon plates, metal bipolar plates, and composite bipolar plates. Currently, graphite carbon plates are the most mature and widely used technology. However, graphite carbon plates have problems such as thick thickness and poor shock resistance, so they can only be installed in fuel cell stacks of large vehicles such as public transportation and heavy trucks, and cannot be used in ordinary small passenger cars.

[0004] Metal bipolar plates can be made from thin stainless steel sheets through stamping, offering advantages such as low thickness, light weight, good shock resistance, and low cost. However, plain stainless steel bipolar plates cannot meet the corrosion resistance requirements of fuel cells, which is the biggest challenge limiting the use of metal bipolar plates.

[0005] Chromium, as a key corrosion-resistant alloying element in metals such as stainless steel and high-temperature alloys, possesses extremely strong corrosion resistance. Diffusion of a chromium layer onto the surface of stainless steel can increase its corrosion resistance by tens of times. Furthermore, chromium has superior electrical and thermal conductivity compared to stainless steel; after diffusion of a chromium layer onto the surface of stainless steel, the overall thermal and electrical conductivity of the stainless steel bipolar plate does not decrease. Traditional chromium diffusion processes on stainless steel surfaces use ammonium chloride as a catalyst, which leads to increased surface roughness due to powder adhesion, ultimately resulting in a surface finish that fails to meet usage requirements. Simultaneously, the decomposition of ammonium chloride releases large amounts of ammonia and hydrogen chloride gas, making the chromium diffusion process highly susceptible to safety accidents. Summary of the Invention

[0006] To address the aforementioned technical limitations, this application proposes a method for preparing a bipolar plate. This method involves applying a powder surface alloy to the surface of the bipolar plate material in a hydrogen atmosphere to create a composite material with good corrosion resistance. Furthermore, during the preparation of the bipolar plate, it prevents detachment and corrosion during welding and shaping with the frame. After shaping, the two plates are fused together to form a single unit, preventing gas and liquid leakage.

[0007] To achieve the above objectives, this application adopts the following technical solution:

[0008] The invention of this application is to provide a method for preparing a bipolar plate, comprising: (1) processing stainless steel to obtain a primary plate; (2) alloying the primary plate with a composite material in a hydrogen atmosphere to obtain a composite plate; (3) laser welding and shaping the composite plate with a frame to obtain a bipolar plate; wherein the composite material comprises chromium, chromium chloride, magnesium-aluminum eutectic alloy and a dispersant.

[0009] Optionally, the composite material is a powder; the particle size of the powder is 50 to 500 mesh.

[0010] Optionally, the composite material comprises, by mass, 20-60 parts of chromium, 5-20 parts of chromium chloride, 30-70 parts of dispersant, and 0.1-5 parts of magnesium-aluminum eutectic alloy.

[0011] Optionally, the conditions for alloying are: temperature 850–980℃, time 2–20 hours.

[0012] Optionally, the shaping temperature is 880–1050℃, and the shaping time is greater than 10 minutes.

[0013] Optionally, the material of the primary plate includes at least one of 304 stainless steel, 304L stainless steel, 310 stainless steel, 310L stainless steel, 316 stainless steel, 316L stainless steel, and 347 stainless steel; the dispersant includes at least one of alumina, silicon oxide, and magnesium oxide.

[0014] Another inventive point of this application is to provide a bipolar plate obtained according to the above preparation method.

[0015] Optionally, the composite plate includes a primary plate and an alloy layer located on the surface of the primary plate; the thickness of the alloy layer is 0.1 μm to 30 μm.

[0016] Optionally, the alloy layer comprises, by mass, 35%–85% chromium, 10%–50% iron, 1%–10% nickel, 1%–10% aluminum, and 0%–5% trace metal elements.

[0017] Another inventive point of this application is to provide an application of the bipolar plate as described above in a fuel cell.

[0018] Compared with the prior art, this application has the following advantages:

[0019] (1) This application uses a hydrogen atmosphere to alloy the bipolar plate material. Under the reduction effect of hydrogen, the oxide film on the surface of the composite material and the primary plate is removed, which produces a cleaning effect and facilitates the subsequent penetration of chromium and aluminum. At the same time, magnesium also has a cleaning effect on the surface of the primary plate, and the departure of magnesium causes a large number of voids in the magnesium-aluminum eutectic alloy, exposing more aluminum. Chromium chloride also acts as an activator and a source of some chromium. Under high temperature, it decomposes to generate a large number of active chloride ions, which promotes the activation of chromium and aluminum and accelerates the penetration of chromium and aluminum. This allows chromium and aluminum to be embedded into the surface of the bipolar plate and become part of the bipolar plate. There is no interface problem between different metals, which can effectively avoid problems such as coating peeling.

[0020] (2) Furthermore, the composite plates generated by the above method do not crack or fall off even during subsequent laser welding and shaping processes. During laser welding, the composite plate first contacts the surface of the frame, that is, the alloy layer of the composite plate contacts the surface. Due to the high content of chromium and aluminum in the alloy layer, local fine-tuning of the chromium and aluminum composition occurs, thus naturally fusing the two plates into a whole, thereby enhancing the welding effect. During shaping, secondary alloying is achieved, allowing chromium metal in the stainless steel surface alloy layer to diffuse with elements such as iron and nickel, ultimately making the alloy layer composition more uniform and the performance more stable. Due to the interaction force between chromium, iron and aluminum, the damage to the alloy layer caused by the high temperature of shaping is reduced, avoiding problems such as gas and liquid leakage of bipolar plates that reduce service life. Moreover, through this high-temperature shaping, the content of chromium, iron and aluminum is further homogenized, and the fusion is more complete. Attached Figure Description

[0021] Figure 1 This is a scanning electron microscope image of the magnesium-aluminum eutectic alloy used in Test Example 1 of this application;

[0022] Figure 2 This is a scanning electron microscope image of the magnesium-aluminum eutectic alloy after magnesium evaporation used in Experimental Example 1 of this application;

[0023] Figure 3 An external view of the bipolar plate provided in Test Example 1 of this application;

[0024] Figure 4 A scanning electron microscope image of the cross-section of the composite plate provided in Test Example 1 of this application;

[0025] Figure 5 for Figure 4 A magnified view of the area outlined in the frame;

[0026] Figure 6 A scanning electron microscope image of the cross-section of the composite plate provided in Test Example 2 of this application;

[0027] Figure 7for Figure 5 A magnified view of the area outlined in the frame;

[0028] Figure 8 A scanning electron microscope image of the cross-section of the composite plate provided in Test Example 3 of this application;

[0029] Figure 9 for Figure 6 A magnified view of the area within the framed region. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this application clearer, a more detailed description is provided below. However, it should be understood that the description herein is merely for explaining this application and is not intended to limit its scope.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. All reagents and instruments used herein are commercially available, and the characterization methods involved can be found in relevant descriptions in the prior art, and will not be repeated here.

[0032] To further understand this application, the following detailed description is provided in conjunction with the preferred embodiments.

[0033] Example 1

[0034] This embodiment provides a method for preparing a bipolar plate, including: (1) processing stainless steel to obtain a primary plate; (2) mixing the primary plate with a composite material in a hydrogen atmosphere to alloy the plate to obtain a composite plate; (3) laser welding and shaping the composite plate with a frame to obtain a bipolar plate; wherein the composite material includes chromium chloride, magnesium-aluminum eutectic alloy and dispersant.

[0035] Step (1) can be: based on the internal space flow channel structure design of the bipolar plate, the primary plate is processed by stamping; or any process commonly available on the market can be used, and there is no limitation on this.

[0036] The primary sheet material includes at least one of the following: 304 stainless steel, 304L stainless steel, 310 stainless steel, 310L stainless steel, 316 stainless steel, 316L stainless steel, and 347 stainless steel.

[0037] The main component of stainless steel is iron, which has good compatibility with chromium and aluminum, forming chromium-iron-aluminum alloys.

[0038] Step (2) In a hydrogen atmosphere, the primary plate is mixed with the composite material to alloy and obtain the composite plate.

[0039] The composite material is in powder form. If there are lumps or large particles, they need to be ground into powder before use. Small powder particles help to occur more uniformly during the alloying process and can promote the fusion of the alloy and stainless steel more quickly and effectively.

[0040] The particle size of the composite material is less than 50 mesh, preferably 50-500 mesh, and more preferably 80-200 mesh. This range ensures that the powder can fully contact and react with the stainless steel surface, while avoiding the sintering and agglomeration of excessively fine powder particles, which would affect its use.

[0041] To ensure the composite material meets the aforementioned particle size requirements, each raw material must also meet these requirements. If lumpy or large particles are present, they must be ground into powder before use. Small, powdery particles facilitate more uniform alloying and promote faster and greater fusion between the alloy and stainless steel.

[0042] Chromium chloride in the composite material acts as both an activator and a partial chromium provider; the magnesium-aluminum eutectic alloy provides magnesium and aluminum, with magnesium acting as a reducing agent; the dispersant is used to disperse the above materials and prevent adhesion from affecting the alloying process.

[0043] The composite material includes, by mass, 20-60 parts of chromium, 5-20 parts of chromium chloride, 30-70 parts of dispersant, and 0.1-5 parts of magnesium-aluminum eutectic alloy. The components are: chromium (20 parts, 25 parts, 30 parts, 35 parts, 40 parts, 45 parts, 50 parts, 55 parts, 60 parts, or any value between any two values); chromium chloride (5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts, 11 parts, 12 parts, 13 parts, 14 parts, 15 parts, 16 parts, 17 parts, 18 parts, 19 parts, 20 parts, or any value between any two values); dispersant (30 parts, 35 parts, 40 parts, 45 parts, 50 parts, 55 parts, 60 parts, 65 parts, 70 parts, or any value between any two values); and magnesium-aluminum eutectic alloy (0.1 parts, 0.2 parts, 0.3 parts, 0.4 parts, 0.5 parts, 0.6 parts, 0.7 parts, 0.8 parts, 0.9 parts, 1 part, 2 parts, 3 parts, 4 parts, 5 parts, or any value between any two values).

[0044] The dispersant includes at least one of alumina, silicon dioxide, and magnesium oxide.

[0045] The conditions for alloying are: temperature 850~980℃, which can be 850℃, 880℃, 900℃, 950℃ or 980℃; time 2~20 hours, which can be 2 hours, 5 hours, 10 hours, 15 hours or 20 hours.

[0046] Chromium chloride reacts with hydrogen to generate active chloride ions, which further enhance the activity of chromium. These active chloride ions can also react rapidly with oxides on the surface of the stainless steel under high-temperature conditions and are released with the flowing hydrogen. At this point, active chromium is easily adsorbed onto the stainless steel surface. As the holding time increases, it undergoes a diffusion reaction with the stainless steel, thus forming a high-chromium alloy layer on the surface. Simultaneously, aluminum can vaporize with magnesium to become aluminum with a high surface area ratio and high activity, while removing the oxide film adhering to the aluminum surface, further promoting the activity of aluminum. Aluminum has a face-centered cubic crystal structure, and its atomic radius is similar to that of chromium and iron. Furthermore, at this high temperature, aluminum can melt, forming a certain "molten mixture" with chromium and iron. Then, under the action of active chloride ions, it and chromium undergo diffusion alloying with the stainless steel.

[0047] After chromium infiltration, during the cooling process, the iron undergoes a transformation from a face-centered cubic structure to a body-centered cubic structure, resulting in volume expansion. Due to the "anchoring" effect of chromium atoms, this volume expansion during cooling is limited, resulting in a uniform and dense infiltrated layer. This prevents water and water vapor from penetrating into the matrix and reacting with free iron ions, thus exhibiting good corrosion resistance. Furthermore, since aluminum is a good conductor of heat (three times greater than iron), the addition of aluminum enhances the heat dissipation of the prepared bipolar plate.

[0048] Magnesium-aluminum alloy powder is a eutectic powder, such as Figure 1 As shown, its melting point is much lower than that of elemental magnesium and aluminum, starting to melt at around 450℃. In a hydrogen atmosphere, when the temperature exceeds 850℃, the magnesium in the magnesium-aluminum alloy begins to vaporize. Since the vaporization temperature of aluminum is as high as 1200℃, the aluminum does not vaporize. The vaporized magnesium reacts with oxygen on the aluminum surface, exposing the highly reactive aluminum. Simultaneously, the vaporization of magnesium in the powder leaves behind numerous pores, such as... Figure 2 As shown, this significantly increases the specific surface area of ​​the powder, accelerating the aluminum infiltration process. On the other hand, the vaporized magnesium reacts with the chromium oxide on the chromium surface, removing the chromium oxide film that would hinder the infiltration process. Under the catalytic action of active chloride ions, chromium and aluminum simultaneously infiltrate into the stainless steel matrix.

[0049] In addition, aluminum has a certain reducing property. During the chromium diffusion process, aluminum undergoes a micro-reaction with the chromium surface, and the reaction is exothermic. This process promotes the diffusion of chromium while also introducing a certain amount of aluminum. The small amount of aluminum in the diffusion layer can improve its overall corrosion resistance, mainly because aluminum can promote a denser layer structure.

[0050] Aluminum is obtained through magnesium-aluminum eutectic alloy powder (containing 45wt%–55wt% aluminum). This alloy has a melting point of around 450℃, which is lower than that of the constituent aluminum and magnesium, and it is also more reactive. After the magnesium-aluminum alloy melts, the magnesium in it turns into a gaseous state as the temperature rises. This not only reduces the chromium oxide film on the surface of the chromium powder, but also provides reactive aluminum, ensuring that aluminum penetrates into the matrix at the same time as chromium.

[0051] The stamped portion of the stainless steel bipolar plate is relatively thin, but the edges need to have a certain thickness during assembly. Therefore, it is welded to the metal frame.

[0052] Edge sealing is performed by laser welding. Laser welding process parameters: power 20-500W, speed 10-200m / S.

[0053] The shaping temperature is 880–1050℃, and the shaping time is greater than 10 minutes, preferably 20–60 minutes. The flatness of the shaped stainless steel bipolar plate is less than 0.2. Shaping improves the bonding between chromium and aluminum and stainless steel, while also promoting weldability and resulting in stronger welds. Furthermore, welding can damage the alloy layer at the weld joint, and shaping can redistribute the damaged alloy elements evenly, reforming the alloy layer. Simultaneously, shaping can adjust the surface content of chromium and aluminum in the composite plate, making the overall content more consistent, thus making the bipolar plate a unified whole and avoiding air and liquid leaks caused by poor sealing.

[0054] The purpose of high-temperature forming is twofold: first, to remove residual surface stress after chromium plating, restoring its overall shape to a stress-free state; and second, to achieve secondary alloying, allowing chromium metal in the stainless steel surface alloy layer to diffuse secondary with elements such as iron and nickel, ultimately resulting in a more uniform alloy layer composition and more stable performance.

[0055] Example 2

[0056] This embodiment provides a bipolar plate, which is prepared by the same method as the bipolar plate in Embodiment 1, and therefore will not be described in detail here.

[0057] The composite sheet comprises a primary sheet and an alloy layer on the surface of the primary sheet; the thickness of the alloy layer is 0.1 μm to 30 μm. For example, it can be 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 30 μm, or any value between any two values.

[0058] If the thickness is less than 0.1 micrometers, it is difficult to form a completely continuous alloy layer. Once the alloy layer is discontinuous, gaps will appear, allowing acidic substances to enter the bipolar plate, causing corrosion of the substrate and rendering the bipolar plate unusable. If the thickness is greater than 30 micrometers, on the one hand, the surface brittleness will increase rapidly, leading to a decrease in the overall material toughness. On the other hand, an excessively thick alloy layer will affect the conductivity in the fuel cell.

[0059] The alloy layer comprises, by mass, 35%–85% chromium, 10%–50% iron, 1%–10% nickel, 1%–10% aluminum, and 0%–5% trace metal elements.

[0060] Trace metal elements include one or more of molybdenum, manganese, vanadium, titanium, cobalt, and barium.

[0061] The chromium content in stainless steel is generally less than 30%. When the chromium content is less than 30%, it is difficult to form a sufficiently dense chromium passivation film, thus failing to provide adequate protection. However, in the composite bipolar plate of this application, there is a chromium alloy layer with a chromium content of ≥35%, which is the main element in the alloy layer. This allows chromium to bond with each other, forming a sufficiently dense passivation film. Furthermore, aluminum is also doped. Chromium and iron have a body-centered cubic structure, while aluminum is a face-centered cubic crystal with a more compact packing. The addition of aluminum can fill the gaps between chromium and iron, and through structural space constraints, it also prevents the slippage of nickel and aluminum, keeping the entire structure stable and preventing external gases or solvents from entering the structure, thus providing better corrosion resistance.

[0062] It exhibits high corrosion resistance in acidic or alkaline environments, which can extend the service life of composite bipolar plates; it also improves high-temperature resistance, and can maintain its original shape without deformation during subsequent use.

[0063] Example 3

[0064] Based on the content of this application, the preparation method of Example 1 and the bipolar plate of Example 2 are described in detail below:

[0065] Experimental Example 1

[0066] (1) Purchase 60-micron-thick 304 stainless steel from the market, stamp it into the required shape, and obtain the primary plate.

[0067] (2) The primary sheet material and the 80-mesh composite material were mixed together and placed in a furnace. The alloy material was used to embed the entire surface of the stainless steel sheet. The composite material consisted of 30 parts chromium powder, 5 parts chromium chloride powder, 35 parts alumina powder, and 1 part magnesium-aluminum eutectic alloy (of which aluminum accounted for 45 wt%). Then, the mixture was heated to 920°C under a hydrogen flow rate of 0.2 L / min and maintained at this temperature for 4 hours to obtain the composite sheet material.

[0068] (3) The composite plate is then laser-welded to the frame (power 100W, speed 200m / S), followed by high-temperature shaping at 950℃ for 30 minutes to obtain the bipolar plate, as shown below. Figure 3 As shown.

[0069] Alloy layer composition: 38% chromium, 50% iron, 8% nickel, 2% aluminum, and 2% trace elements (manganese, etc.).

[0070] like Figure 4 and Figure 5 As shown, the alloy layer is the surface of the stainless steel substrate, and its composition is significantly different from that of the stainless steel substrate; moreover, the alloy layer has a dense structure. The thickness of the alloy layer was measured at seven locations, which were 12.437 μm, 13.295 μm, 13.581 μm, 10.579 μm, 11.580 μm, 10.722 μm, and 11.008 μm, respectively. After calculation, the average thickness of the alloy layer is approximately 11.29 μm.

[0071] Experimental Example 2

[0072] (1) Purchase 316 stainless steel with a thickness of 80 micrometers from the market, process or stamp it into the required shape to obtain the primary plate.

[0073] (2) The primary sheet material and the 80-mesh composite material were mixed together and placed in a furnace. The alloy material was used to embed the entire surface of the stainless steel sheet. The composite material consisted of 40 parts chromium powder, 10 parts chromium chloride powder, 40 parts alumina powder, and 2 parts magnesium-aluminum eutectic alloy (of which aluminum accounted for 45 wt%). Then, the mixture was heated to 950°C under a hydrogen flow rate of 0.3 L / min and maintained at this temperature for 6 hours to obtain the composite sheet material.

[0074] (3) The composite plate is then laser welded to the frame (power 150W, speed 100m / S) and then high temperature shaped at 980℃ for 60 minutes to obtain the bipolar plate.

[0075] Alloy layer composition: 62% chromium, 26% iron, 6% nickel, 5% aluminum, and 1% trace elements (molybdenum, manganese, etc.).

[0076] like Figure 6 and Figure 7 As shown, eight length measurements were taken at the following locations: 15.583 μm, 17.584 μm, 13.009 μm, 14.010 μm, 13.295 μm, 13.581 μm, 14.296 μm, 14.868 μm, and 17.155 μm. After calculation, the average thickness of the alloy layer is approximately 16.67 μm.

[0077] Experimental Example 3

[0078] (1) Purchase 100-micron-thick 316L stainless steel from the market, process or stamp it into the required shape to obtain primary sheet material.

[0079] (2) The primary sheet material and the 80-mesh composite material were mixed together and placed in a furnace. The alloy material was used to embed the entire surface of the stainless steel sheet. The composite material consisted of 60 parts chromium powder, 20 parts chromium chloride powder, 60 parts alumina powder, and 2 parts magnesium-aluminum eutectic alloy (of which aluminum accounted for 45 wt%). Then, the mixture was heated to 980°C under a hydrogen flow rate of 0.4 L / min and maintained at this temperature for 10 h to obtain the composite sheet material.

[0080] (3) The composite plate is then laser welded to the frame (power 220W, speed 80m / S) and then high temperature shaped. The shaped temperature is 1020℃ and the shaped time is 120 minutes to obtain the bipolar plate.

[0081] Alloy layer composition: 78% chromium, 10% iron, 4% nickel, 7% aluminum, balance of trace elements (molybdenum, manganese) 1%.

[0082] like Figure 8 and Figure 9 As shown, eight length measurements were taken at the following locations: 26.733μm, 28.878μm, 29.593μm, 27.448μm, 26.305μm, 26.733μm, 26.447μm, and 28.878μm. After calculation, the average thickness of the alloy layer is approximately 27.63μm.

[0083] Comparative Example 1

[0084] It only includes steps (1) and (3) of Experimental Example 1, that is, there is no alloying step.

[0085] Comparative Example 2

[0086] The comparison example is a common graphite bipolar plate on the market. Graphite bipolar plates are currently the most commonly used bipolar plates in proton exchange membrane fuel cells (PEMFCs) in China. They have good electrical conductivity, thermal conductivity, stability and corrosion resistance, but they have problems such as relatively poor mechanical properties, brittleness, and difficulty in machining, which leads to higher costs.

[0087] The process involves mixing carbon powder or graphite powder with a graphitizable resin, pressing the mixture into shape, and then performing graphitization at high temperature (usually 2200℃) under a reducing atmosphere or vacuum. The graphite plate is then impregnated and sealed, and the required gas flow channels are machined on its surface using a CNC machine tool.

[0088] Performance testing

[0089] The bipolar plates of the experimental and comparative examples were tested to measure parameters such as resistivity, compressive strength, contact resistance, corrosion current density, and hardness. The test results are shown in Table 1.

[0090] Table 1 Performance parameters of bipolar plates prepared for each experimental example and comparative example.

[0091] Experimental Example 1 Experimental Example 2 Experimental Example 3 Comparative Example 1 Comparative Example 2 Shore hardness - - - - 71 Microhardness 960HV 1180HV 1340HV 210HV - thickness 72um 95um 127um 100um 10mm resistivity 0.95mΩ·mm 0.92mΩ·mm 0.88mΩ·mm 1.02mΩ·mm 9.5mΩ·mm tensile strength 820MPa 880MPa 920MPa 720MPa 150MPa Contact resistance <![CDATA[2.8mΩ·cm 2 ]]> <![CDATA[2.2mΩ·cm 2 ]]> <![CDATA[1.6mΩ·cm 2 ]]> <![CDATA[68mΩ·cm 2 ]]> <![CDATA[6.74mΩ·cm 2 ]]> Corrosion current density <![CDATA[0.68uA·cm -2 ]]> <![CDATA[0.52uA·cm -2 ]]> <![CDATA[0.45uA·cm -2 ]]> <![CDATA[146uA·cm -2 ]]> <![CDATA[0.46uA·cm -2 ]]>

[0092] As shown in Table 1, Comparative Example 2 is a graphite bipolar plate. Although its electrical properties and corrosion resistance meet the requirements, it suffers from problems such as excessive thickness, low hardness, and low tensile strength. This results in the bipolar plate occupying a large volume, requiring vibration damping processes, and is prone to powder shedding. Comparative Example 1 is a 316 stainless steel bipolar plate, which has excellent mechanical properties, but its corrosion resistance falls far short of the requirements for bipolar plate use. Examples 1-3 show the performance data of stainless steel after surface chromium alloying treatment. Its hardness and mechanical properties are significantly improved, while it also exhibits extremely low contact resistance, reducing energy loss, and extremely low corrosion current density, demonstrating high corrosion resistance and fully meeting the requirements for bipolar plate use. Furthermore, stainless steel can be stamped, eliminating the need for machining of graphite bipolar plates, greatly reducing production costs. Furthermore, stainless steel bipolar plates have advantages such as thinness and light weight, which makes them lightweight and miniaturized. Their volume and weight are reduced by about 50% compared to graphite bipolar plates, which can significantly reduce costs and can be widely used in hydrogen fuel cell stack systems.

[0093] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for preparing a bipolar plate, characterized in that, include: (1) The stainless steel is processed to obtain a primary sheet; (2) In a hydrogen atmosphere, the primary plate is mixed with the composite material and alloyed to obtain a composite plate; (3) The composite board and the frame are laser welded and shaped to obtain a bipolar plate; The composite material includes chromium, chromium chloride, magnesium-aluminum eutectic alloy, and dispersant; The alloying conditions are: temperature 850~980℃, time 2~20 hours; The composite material comprises, by mass, 20-60 parts of chromium, 5-20 parts of chromium chloride, 30-70 parts of dispersant, and 0.1-5 parts of magnesium-aluminum eutectic alloy.

2. The preparation method according to claim 1, characterized in that, The composite material is a powder; the particle size of the powder is 50~500 mesh.

3. The preparation method according to claim 1, characterized in that, The temperature for shaping is 880~1050℃, and the shaping time is more than 10 minutes.

4. The preparation method according to claim 1, characterized in that, The primary plate material includes at least one of 304 stainless steel, 304L stainless steel, 310 stainless steel, 310L stainless steel, 316 stainless steel, 316L stainless steel, and 347 stainless steel; the dispersant includes at least one of alumina, silicon oxide, and magnesium oxide.

5. The bipolar plate obtained by the preparation method according to any one of claims 1 to 4.

6. The bipolar plate according to claim 5, characterized in that, The composite board includes a primary board and an alloy layer on the surface of the primary board; the thickness of the alloy layer is 0.1μm to 30μm.

7. The bipolar plate according to claim 6, characterized in that, The alloy layer comprises, by mass, 35%~85% chromium, 10%~50% iron, 1%~10% nickel, 1%~10% aluminum, and 0~5% trace metal elements.

8. The application of the bipolar plate according to any one of claims 5 to 7 in a fuel cell.

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