Metal pole plate coating for fuel cell and preparation method of metal pole plate coating

Abstract

The invention relates to the technical field of fuel cells, in particular to a fuel cell metal bipolar plate coating and a preparation method thereof. Comprising a bipolar plate, a corrosion-resistant layer and an alloy layer are sequentially arranged on the surface of the bipolar plate, the corrosion-resistant layer comprises a plurality of stacked laminated layers, and each laminated layer comprises a non-noble metal coating and a non-noble metal nitride layer which are sequentially stacked. Compared with the prior art, the technical problems that in the prior art, a fuel cell metal bipolar plate is poor in conductivity and corrosion resistance, and a coating is not high in durability in an acid environment of a fuel cell are solved.

Description

Technical Field

[0001] The invention relates to the technical field of fuel cells, in particular to a metal plate coating for fuel cells and a preparation method thereof. Background Art

[0002] A hydrogen fuel cell is a device that reacts hydrogen with oxygen to generate electricity, heat and water. The bipolar plate in the battery is a key component that connects each unit. Its functions include conducting electricity, distributing gas, transmitting fluids and resisting corrosion. The performance of the bipolar plate directly affects the efficiency, life and cost of the hydrogen fuel cell. Therefore, selecting the right material and optimizing its design and manufacturing process are one of the keys to improving the performance of hydrogen fuel cells.

[0003] Currently, mature bipolar plate surface coatings mainly include precious metal coatings and carbon-based coatings. The graphite-like carbon-based coatings in carbon-based coatings have good conductivity and corrosion resistance, but the carbon coating has poor durability, which is generally more than 50% shorter than the metal coating, especially in acidic environments, resulting in corrosion changes in the film structure and a rapid increase in contact resistance. However, the use of metal coatings (such as platinum, gold, iridium, molybdenum, and tantalum) has good stability and conductivity and is suitable for fuel cell environments. Under the same requirements, the use of electroplating methods requires that the film thickness be maintained at least above 200nm, which results in high costs and is not conducive to reducing overall benefits. Summary of the invention

[0004] In order to overcome the deficiencies of the prior art, the present invention provides a fuel cell metal plate coating and a preparation method thereof. Based on the metal coating, the vacuum coating method is used and an alloy film layer is added to significantly improve the film performance and reduce the cost.

[0005] To achieve the above-mentioned purpose, a coating for a metal plate of a fuel cell is designed, including a bipolar plate, wherein a corrosion-resistant layer and an alloy layer are sequentially arranged on the surface of the bipolar plate, wherein the corrosion-resistant layer comprises a plurality of stacked layers, and each stack comprises a non-precious metal coating and a non-precious metal nitride layer stacked sequentially.

[0006] The number of layers of the stacked layers is 2 or more.

[0007] The material of the non-precious metal coating includes one or more of Cr, Ti, Nb, and W, and is doped with Ta and Ni; the material of the non-precious metal nitride layer includes one or more of Cr, Ti, Nb, and W, and corresponding Cr, Ti, Nb, and W nitrides, and is doped with Mg and Ni; the material of the alloy layer includes one or more of Pt, Au, and Ir, and is doped with Rh.

[0008] The surfaces of the non-precious metal coating and the non-precious metal nitride layer are microporous structures, and the surface of the alloy layer is a honeycomb structure.

[0009] The thickness of the non-noble metal coating is 1-100nm, the thickness of the non-noble metal nitride layer is 1-100nm, and the thickness of the alloy layer is 1-50nm.

[0010] To achieve the above purpose, a method for preparing a metal bipolar plate coating for a fuel cell is designed, comprising the following steps: S1, providing a bipolar plate, and vacuum coating a surface of one side of the bipolar plate to form a non-precious metal coating; S2, introducing nitrogen into the vacuum chamber and performing vacuum coating to form a non-precious metal nitride layer formed of non-precious metal and its nitride; S3, repeating steps S1 and S2 until the required number of stacked layers is formed; S4, vacuum coating is performed on the surface of one side of the non-precious metal nitride layer to form an alloy layer.

[0011] In the step S1, the temperature is controlled at 300-350°C and the vacuum pressure is maintained at 0.1Pa-0.5Pa; in the step S2, the temperature is controlled at 450°C-500°C and the vacuum pressure is maintained at 0.2Pa-0.45Pa; in the step S4, the temperature is controlled at 700°C-750°C and the vacuum pressure is maintained at 0.2Pa-0.7Pa.

[0012] In the steps S1, S2, S3 and S4, before each coating process, a reaction gas is introduced into the vacuum chamber and ionized to generate plasma. The plasma bombards the surface of the bipolar plate or the film layer of the previous coating process under the action of the electric field to clean the surface and form a microporous structure on the surface of the film layer; wherein the vacuum pressure is maintained at 0.3-1 Pa and the time is controlled at 1-500 seconds.

[0013] After the coating in step S4 is completed, the reaction gas is introduced into the vacuum chamber and ionized to generate plasma. The plasma bombards the surface of the alloy layer under the action of the electric field to remove the non-precious metal substances remaining on the surface of the alloy layer, and finally forms a honeycomb structure on the surface of the alloy layer, wherein the vacuum pressure is controlled at 0.5-1.5Pa and the time is controlled at 1-30 seconds.

[0014] It also includes step S5, after the surface treatment of the membrane layer is completed, annealing is carried out in an independent chamber, after the annealing is completed, air is introduced into the chamber to break the air, and the bipolar plate is waited for gradual cooling; wherein the annealing temperature is controlled at 200-800°C, the annealing time is 0.2-0.5h, and the vacuum during the annealing process is maintained at 1-10Pa.

[0015] Compared with the prior art, the present invention solves the technical problems in the prior art that the metal bipolar plates of fuel cells have poor electrical conductivity and corrosion resistance, and the coating has low durability in the acidic environment of the fuel cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a structural diagram of embodiment 1 of the present invention.

[0017] Figure 2 This is a schematic diagram of the process of Embodiment 1 of the present invention.

[0018] Figure 3 This is the corrosion curve obtained by the present invention.

[0019] Figure 4 It is a structural diagram of embodiment 2 of the present invention. DETAILED DESCRIPTION

[0020] The present invention will be further described below with reference to the accompanying drawings.

[0021] like Figure 1 to Figure 2 As shown, the surface of the bipolar plate 1 is provided with a corrosion-resistant layer and an alloy layer 4 in sequence, wherein the corrosion-resistant layer comprises a plurality of stacked layers, each of which comprises a non-precious metal coating 2 and a non-precious metal nitride layer 3 stacked in sequence. The alloy layer 4 plays a conductive role.

[0022] The corrosion-resistant layer is formed by combining multiple layers of film. Each film layer has the same elements, and the binding force of the same elements is stronger, thereby enhancing the binding force between the film layers, and when used specifically, the thickness of the single layer and the number of stacking layers can be changed as needed to meet the corrosion resistance requirements of different bipolar plates. The number of stacked layers is 2 or more. In this embodiment, the number of stacked layers is 3.

[0023] The material of the non-precious metal coating 2 includes one or more of Cr, Ti, Nb, and W, and is doped with Ta and Ni, and the mass ratio of the doped elements to the non-precious metal element is less than 2%.

[0024] The material of the non-precious metal nitride layer 3 includes one or more of Cr, Ti, Nb, and W, and corresponding Cr, Ti, Nb, and W nitrides, and is doped with Mg and Ni. The mass ratio of the corresponding Cr, Ti, Nb, and W nitrides to the non-precious metals Cr, Ti, Nb, and W is 1%-80%.

[0025] The material of the alloy layer 4 includes one or more of Pt, Au, and Ir, and is doped with Rh, wherein the mass ratio of Rh to the alloy elements Pt, Au, and Ir is 0.5%-1.5%.

[0026] The surfaces of the non-precious metal coating 2 and the non-precious metal nitride layer 3 are microporous structures, and the surface of the alloy layer 4 is a honeycomb structure.

[0027] The thickness of the non-precious metal coating layer 2 is 1-100 nm, the thickness of the non-precious metal nitride layer 3 is 1-100 nm, and the thickness of the alloy layer 4 is 1-50 nm.

[0028] like Figure 2 As shown, a method for preparing a fuel cell metal bipolar plate coating in this embodiment includes the following steps: S1, providing a bipolar plate 1, and vacuum coating a surface of one side of the bipolar plate 1 to form a non-precious metal coating 2; S2, introducing nitrogen into the vacuum chamber and performing vacuum coating to form a non-precious metal nitride layer 3 formed of non-precious metal and its nitride; S3, repeating steps S1 and S2 until the required number of stacked layers is formed; S4, vacuum coating is performed on one side of the non-precious metal nitride layer 3 to form an alloy layer 4.

[0029] In step S1, the temperature is controlled at 300-350°C to ensure that the deformation of the bipolar plate 1 is within a reasonable range, and the vacuum pressure of the coating is maintained at 0.1Pa-0.5Pa, so as to strictly control the amount of gas introduced and form a dense film layer. In step S2, the temperature is controlled at 450°C-500°C, and the vacuum pressure is maintained at 0.2Pa-0.45Pa to form a stable film layer structure; in step S4, the temperature is controlled at 700°C-750°C, and the vacuum pressure is maintained at 0.2Pa-0.7Pa.

[0030] In step S1, step S2, S3, and S4, before each coating, a reaction gas is introduced into the vacuum chamber and ionized to generate plasma. The plasma bombards the surface of the bipolar plate 1 or the film layer of the previous coating under the action of the electric field, and the dirt falls off under the bombardment to achieve the effect of cleaning the surface. Furthermore, the vacuum pressure of the bombardment of the bipolar plate 1 is maintained at 0.3-1Pa, and the cleaning time is in the range of 1-500 seconds. When used specifically, Ar is selected as the reaction gas.

[0031] When bombarding the surface of the film layer of the previous coating, it also plays a role in activating the surface. At this time, the vacuum pressure is maintained at 0.3-1Pa, the time is controlled at 1-100 seconds, and the bombardment time is accurately controlled to completely clean the surface after the previous coating. At the same time, micropores are generated on the surface after plasma bombardment, which helps to improve the bonding strength of this coating.

[0032] After the coating is completed in step S4, a reaction gas is introduced into the vacuum chamber and ionized to generate plasma. The plasma bombards the surface of the alloy layer 4 under the action of the electric field to remove the non-precious metal substances remaining on the surface of the alloy layer 4, and finally forms a honeycomb structure on the surface of the alloy layer 4, wherein the vacuum pressure is controlled at 0.5-1.5 Pa and the time is controlled at 1-30 seconds. When used specifically, CF4 is selected as the reaction gas.

[0033] It also includes step S5, after the surface treatment of the membrane layer is completed, annealing is performed in an independent chamber, after the annealing is completed, air is introduced into the chamber to break the air, and the bipolar plate is gradually cooled down; wherein the annealing temperature is controlled at 200-800°C, the annealing time is 0.2-0.5h, and the vacuum during the annealing process is maintained at 1-10Pa. The annealing treatment is to eliminate the voids left by the etching treatment and improve the bonding strength of the outer layer of precious metal.

[0034] Steps S1 to S4 are performed in a high vacuum environment, and the background vacuum of the cavity is required to be less than 10-4Pa.

[0035] The coating of the present invention is composed of a non-precious metal coating, a non-precious metal nitride layer 3, and an alloy layer from the inside to the outside. The outermost alloy layer is formed into a honeycomb shape after plasma action and annealing. Since the alloy layer is a precious metal, the conductive performance of the coating can be guaranteed. The coating thickness is between 1-100nm.

[0036] Among them, the composition of the non-precious metal coating 2 and the non-precious metal nitride layer 3 is similar. On the one hand, it ensures the basic material continuity between the two film layers, thereby enhancing the bonding strength. On the other hand, this type of coating material has strong corrosion resistance and enhances the corrosion resistance of the film layer.

[0037] The coating method from step S1 to step S4 is performed by using a physical vapor coating method such as multi-arc ion plating, magnetron sputtering, etc.

[0038] The present invention innovatively designs a metal coating specifically for fuel cell metal bipolar plates. The corrosion-resistant layer of the metal coating adopts a multi-layer structure, composed of non-precious metals and their nitrides, and has performance advantages in corrosion resistance: the outer layer adopts a precious metal alloy layer, which has high conductivity in terms of electrical conductivity, and can effectively meet the performance requirements of fuel cells. At the same time, the metal coating exhibits good bonding strength and the internal stress is at a low level. This means that during long-term operation and use, the undesirable phenomenon of coating shedding will not occur, which fundamentally guarantees the durability of the metal bipolar plate, greatly prolongs its service life, and reduces maintenance costs and replacement frequency. Compared with traditional electroplating processes and physical sputtering methods of coating precious metal films, the unique coating structure proposed in the present invention and the matching preparation process have significant economic advantages. Embodiment 1

[0039] The structure of this embodiment is as follows Figure 1 As shown, in this embodiment, a non-precious metal layer 2 with a thickness of 20 nm is first plated on the bipolar plate 1; then a non-precious metal nitride layer 3 with a thickness of 50 nm is plated; the non-precious metal layer 2 and the non-precious metal nitride layer 3 are stacked and plated three times; finally, an alloy layer 4 with a thickness of 2 nm is plated to form a complete coating structure of this embodiment.

[0040] The method for preparing the coating in this embodiment comprises the following steps: S1: Pre-place the metal bipolar plates 1 into a carbon-based ultrasonic cleaning device to remove oil stains, impurities and other pollutants on the product surface, improve the cleanliness of the sample surface, and prevent oil stains from affecting subsequent coating. Then dry and wait to be loaded into the furnace chamber.

[0041] S2: Place the carbon-based cleaned metal bipolar plate 1 product into the vacuum coating chamber for plasma cleaning, and heat the chamber at the same time so that the chamber temperature reaches 350-450°C to remove the oxide layer and adsorbed gas on the surface of the sample and enhance the adhesion of the coating.

[0042] S3: A mixed layer of metals Ti, Nb, and W is plated on the surface of the cleaned metal bipolar plate 1, doped with Ni, with a thickness of 20 nm. Then, a nitride of the above metals is plated with a thickness of 50 nm, and the plating is repeated 3 times to form a corrosion-resistant layer.

[0043] S4: Ar is introduced, and ions are formed after Ar is ionized. Under the condition of electric field, the surface of the corrosion-resistant layer is cleaned. Then, an alloy layer 3 formed by Pt, Ir, and Rh is plated on the surface of the cleaned corrosion-resistant layer. The plating pressure is 0.25Pa, and the thickness of the plating coating is 2nm, which is the conductive layer.

[0044] S5: CF4 gas is introduced to form plasma through ionization, and the non-precious metal coating on the surface is removed under the action of the electric field for 20 seconds.

[0045] S6: Vacuum annealing, placing the coated bipolar plate 1 in a vacuum chamber, maintaining the temperature range between 350°C and 450°C, for 0.3 hours, and maintaining the vacuum degree at 1-2.5Pa.

[0046] .S7: Annealing is completed, wait for the bipolar plate 1 to cool down, take out the bipolar plate 1, and complete the preparation process.

[0047] After obtaining the bipolar plate 1 of this embodiment, a rapid evaluation method of constant potential polarization is used. The corrosion solution simulates the acidic environment of the fuel cell, and H2SO4 with pH 3 and 0.1ppm HF are selected. The temperature is +80°C, the applied potential is 0.84VSHE and 1.6VSHE, and the contact resistance test pressure is 0.6MPa. The obtained corrosion curve is as follows: Figure 3 As shown, the corrosion resistance current decreases rapidly, reaching 2uA in about 1h; then due to the increase in ion concentration in the solution, the current rises slightly at 7.8h, at this time 3.4uA; it rises to a maximum of 6.17uA at 27h. As the test continues, after the ions in the solution reach equilibrium, the corrosion current gradually decreases until it stabilizes; after more than 60h of testing, the current stabilizes at around 2-2.5uA. It can be concluded from the figure that the corrosion resistance of the bipolar plate obtained in this embodiment is good.

[0048] In a preferred embodiment of the present invention, the contact resistance of the nano-metal coating after the constant potential 1.6V-5h and 0.84V-100h polarization tests was between 2-3mΩcm2, without significant changes, and the results of the solution ion concentration test after corrosion showed that the concentration of each ion was much lower than that of other coating processes. Therefore, the nano-metal coating proposed in the present invention can effectively improve the durability of metal bipolar plates. Embodiment 2

[0049] This embodiment only describes the differences from the first embodiment, and the similarities are not described again.

[0050] The difference between this embodiment and the first embodiment is that Figure 4 As shown, in this embodiment, a non-precious metal layer 2 with a thickness of 30 nm is firstly plated on the bipolar plate 1; then a non-precious metal nitride layer 3 with a thickness of 40 nm is plated, the plating is stacked 4 times, and finally an alloy layer 4 with a thickness of 3 nm is plated.

Claims

1. A metal bipolar plate coating for a fuel cell, comprising a bipolar plate, characterized in that: The surface of the bipolar plate (1) is provided with a corrosion-resistant layer and an alloy layer (4) in sequence, the corrosion-resistant layer comprising a plurality of stacked layers, each of which comprises a non-precious metal coating (2) and a non-precious metal nitride layer (3) stacked in sequence.

2. The coating for a metal bipolar plate of a fuel cell according to claim 1, characterized in that: The number of layers of the stacked layers is 2 or more.

3. The coating for a metal bipolar plate of a fuel cell according to claim 1, characterized in that: The material of the non-precious metal coating (2) includes one or more of Cr, Ti, Nb, and W, and is doped with Ta and Ni; the material of the non-precious metal nitride layer (3) includes one or more of Cr, Ti, Nb, and W, and corresponding nitrides of Cr, Ti, Nb, and W, and is doped with Mg and Ni; the material of the alloy layer (4) includes one or more of Pt, Au, and Ir, and is doped with Rh.

4. The coating for a metal bipolar plate of a fuel cell according to claim 1, characterized in that: The surfaces of the non-precious metal coating (2) and the non-precious metal nitride layer (3) are microporous structures, and the surface of the alloy layer (4) is a honeycomb structure.

5. The coating for a metal bipolar plate of a fuel cell according to claim 1, characterized in that: The thickness of the non-precious metal coating (2) is 1-100 nm, the thickness of the non-precious metal nitride layer (3) is 1-100 nm, and the thickness of the alloy layer (4) is 1-50 nm.

6. A method for preparing a metal bipolar plate coating for a fuel cell according to any one of claims 1 to 5, characterized in that: The steps include: S1, providing a bipolar plate (1), and vacuum coating a surface of one side of the bipolar plate (1) to form a non-precious metal coating (2); S2, introducing nitrogen into the vacuum chamber and performing vacuum coating to form a non-precious metal nitride layer (3) formed of a non-precious metal and its nitride; S3, repeating steps S1 and S2 until the required number of stacked layers is formed; S4, vacuum coating a film on one side of the non-precious metal nitride layer (3) to form an alloy layer (4).

7. The method for preparing a metal bipolar plate coating for a fuel cell according to claim 1, characterized in that: In the step S1, the temperature is controlled at 300-350°C and the vacuum pressure is maintained at 0.1Pa-0.5Pa; in the step S2, the temperature is controlled at 450°C-500°C and the vacuum pressure is maintained at 0.2Pa-0.45Pa; in the step S4, the temperature is controlled at 700°C-750°C and the vacuum pressure is maintained at 0.2Pa-0.7Pa.

8. The method for preparing a metal bipolar plate coating for a fuel cell according to claim 1, characterized in that: In the steps S1, S2, S3 and S4, before each coating process, a reaction gas is introduced into the vacuum chamber and ionized to generate plasma. The plasma bombards the surface of the bipolar plate (1) or the film layer of the previous coating process under the action of the electric field to clean the surface and form a microporous structure on the surface of the film layer. The vacuum pressure is maintained at 0.3-1 Pa and the time is controlled at 1-500 seconds.

9. A method for preparing a metal bipolar plate coating for a fuel cell according to claim 6 or 8, characterized in that: After the coating in step S4 is completed, a reaction gas is introduced into the vacuum chamber and ionized to generate plasma. The plasma bombards the surface of the alloy layer (4) under the action of the electric field to remove the non-precious metal substances remaining on the surface of the alloy layer (4), and finally forms a honeycomb structure on the surface of the alloy layer (4), wherein the vacuum pressure is controlled at 0.5-1.5 Pa and the time is controlled at 1-30 seconds.

10. The method for preparing a metal bipolar plate coating for a fuel cell according to claim 9, characterized in that: It also includes step S5, after the surface treatment of the membrane layer is completed, annealing is carried out in an independent chamber, after the annealing is completed, air is introduced into the chamber to break the air, and the bipolar plate is waited for gradual cooling; wherein the annealing temperature is controlled at 200-800°C, the annealing time is 0.2-0.5h, and the vacuum during the annealing process is maintained at 1-10Pa.

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