A fuel cell metal bipolar plate protective coating and its preparation method and application

Abstract

The application discloses a fuel cell metal bipolar plate protective coating and a preparation method and application thereof. The fuel cell metal bipolar plate protective coating comprises a corrosion barrier layer, a plasma oxidation layer and a conductive functional layer which are stacked in sequence; the corrosion barrier layer is Hf; the plasma oxidation layer is HfO2, and the thickness of the plasma oxidation layer is 2-4 nm. The fuel cell metal bipolar plate protective coating has high conductive corrosion resistance, the corrosion current density is less than 1 muA / cm 2 , the contact resistance is less than 10 m omega*cm 2 . Moreover, the coating is difficult to peel off after corrosion for 7200 min under the condition of a constant potential of 1.2 V.

Description

Technical Field

[0001] This invention relates to the field of metal bipolar plates for fuel cells, and more specifically, to a protective coating for metal bipolar plates for fuel cells, its preparation method, and its application. Background Technology

[0002] A proton exchange membrane fuel cell (PEMFC) is an energy conversion device that uses hydrogen as a feedstock and oxygen from the air as an oxidant. It features high energy conversion efficiency, high power density, and zero emissions. Bipolar plates are a crucial component of a PEMFC, primarily serving to separate reactants (H2 and O2), collect current, support electrodes, and connect individual cells in series.

[0003] Traditional fuel cell bipolar plates often use graphite as a raw material. However, graphite and its composites are brittle and have high processing costs, making them unsuitable for large-scale commercial applications. In contrast, stainless steel has higher strength, is easier to process and form, has lower gas permeability, and is less expensive, making it a preferred material for fuel cell stacks. However, in the acidic and high-temperature operating environment of fuel cells, metal ions precipitated inside the stainless steel can reduce catalyst activity, and a passivation film can form on the stainless steel surface, increasing the contact resistance between the bipolar plate and the gas diffusion layer, leading to reduced battery efficiency. Currently, the common approach is to add a protective coating to the stainless steel bipolar plate to improve its corrosion resistance without increasing its contact resistance.

[0004] To address the aforementioned issues, existing technologies often deposit single-layer or multi-layer protective coatings on the surface of metal bipolar plates. These coatings are typically composed of nitrides, carbides, or amorphous carbon. Due to the inherent characteristics of physical vapor deposition (PVD) processes, single-layer protective coatings often contain defects such as cracks and pores. Corrosive solutions can penetrate these pores and corrode the underlying corrosion barrier layer. If the corrosion potential exceeds the pitting potential, it can cause the loss of elements from the underlying layer, leading to the peeling off of the surface carbon coating and ultimately causing corrosion of the bipolar substrate, thus failing to provide effective corrosion protection. Multi-layer composite coatings can effectively block corrosion pathways, but even in long-term testing under simulated fuel cell operating conditions, the multi-layer structure cannot be completely prevented from being penetrated by the corrosive solution, resulting in substrate corrosion. Existing technology discloses a protective coating for fuel cell metal bipolar plates, its preparation method, and its application. Using a metal bipolar plate as the substrate, a Ti or Cr metal transition layer and an amorphous carbon layer are deposited sequentially. The lowest contact resistance can be as low as 1.125 mΩ·cm. 2 At the cathode potential (+0.6V vs) Ag / AgCl The lowest corrosion current density can be as low as 0.1 μA / cm. 2 Although the protective coating has low contact resistance and low corrosion current density, it does not solve the technical problem of coating peeling off under high potential conditions. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects and shortcomings of existing multilayer protective coatings for metal bipolar plates, which are prone to peeling off under high potential conditions, and to provide a protective coating for metal bipolar plates of fuel cells, which has the characteristics of high conductivity, corrosion resistance and non-peeling.

[0006] Another object of the present invention is to provide a method for preparing the protective coating of the metal bipolar plate of the fuel cell.

[0007] Another object of the present invention is to provide a fuel cell.

[0008] The above-mentioned objective of this invention is achieved through the following technical solution:

[0009] A protective coating for a metal bipolar plate of a fuel cell, the protective coating comprising a corrosion barrier layer, a plasma oxidation layer and a conductive functional layer stacked sequentially;

[0010] The corrosion barrier layer is Hf;

[0011] The plasma oxide layer is HfO2, and its thickness is 2-4 nm.

[0012] The metal bipolar plate substrate is made of 304 stainless steel and / or Ti-6Al-4V titanium alloy. The corrosion barrier layer directly covers the surface of the metal bipolar plate substrate.

[0013] The protective coating for fuel cell metal bipolar plates of this invention utilizes a metal Hf coating with excellent corrosion resistance, dense structure, and excellent toughness as a corrosion barrier layer to protect the metal bipolar plate substrate, enabling it to adapt to rapid oxidation and self-heal cracks.

[0014] The protective coating for the metal bipolar plate of the fuel cell of the present invention constructs a plasma oxide layer between the corrosion barrier layer and the conductive functional layer. The pitting potential of the plasma oxide layer is higher than that of the pure metal Hf layer, which can prevent the coating from peeling off caused by pitting corrosion of pure metal Hf at high potential. It can also regulate the diffusion of corrosive media, ions and electrons, block the corrosive solution in the corrosion channel of carbon layer, and control the corrosion rate. With a plasma oxide layer of a specific thickness, the corrosion rate can be reduced without significantly increasing the contact resistance of the coating, thereby improving the corrosion resistance of the coating and providing high conductivity and corrosion resistance.

[0015] Moreover, the protective coating of the metal bipolar plate of the fuel cell of the present invention has long-term corrosion resistance because the plasma oxidation layer increases the pitting potential of the corrosion barrier layer, so the coating does not show any peeling marks in the constant potential test.

[0016] The conductive functional layer in the protective coating of the fuel cell metal bipolar plate of the present invention helps to reduce the surface contact resistance of the coating.

[0017] Furthermore, the protective coating for the metal bipolar plate of the fuel cell of the present invention can reduce corrosion current, which indicates that it has an adaptive repair function.

[0018] Preferably, the thickness of the corrosion barrier layer is 550–600 nm.

[0019] Preferably, the conductive functional layer is an amorphous carbon coating. The high sp content in the amorphous carbon coating... 2 The higher bond content can reduce contact resistance and improve conductivity. Moreover, carbon's chemical stability can protect the corrosion barrier layer.

[0020] Preferably, the thickness of the conductive functional layer is 100–150 nm.

[0021] This invention also protects a method for preparing the protective coating for the metal bipolar plate of a fuel cell according to any one of the preceding claims, comprising the following steps:

[0022] S1. Deposition of corrosion barrier layer: High-power pulsed magnetron sputtering (HiPIMS) technology is used to deposit metal Hf on the surface of the metal bipolar plate substrate to obtain a corrosion barrier layer;

[0023] S2. Preparation of plasma oxide layer: Using ion beam modification process, oxygen plasma is generated by ion source to construct plasma oxide layer on the surface of corrosion barrier layer in S1;

[0024] S3. Deposition of conductive functional layer: Using DC magnetron sputtering technology, with graphite as the sputtering target, an amorphous carbon layer is deposited on the surface of the plasma oxide layer in S2;

[0025] Wherein, the deposition corrosion barrier layer in S1 is a metal Hf coating; the plasma oxide layer in S2 is an HfO2 plasma oxide layer.

[0026] This invention uses the PVD method to prepare a metal Hf coating with excellent corrosion resistance, dense structure, and excellent toughness using HiPIMS technology as a corrosion barrier layer to protect the metal bipolar plate substrate. Then, an ion beam modification process is used to introduce oxygen-containing plasma into the furnace cavity through an ion source. The oxygen-containing plasma bombards and modifies the metal Hf corrosion barrier layer to generate an HfO2 plasma oxide layer. Finally, an amorphous carbon conductive functional layer is constructed on the oxide layer using magnetron sputtering (DCMS) technology to achieve the preparation of a composite structure coating.

[0027] Preferably, in step S1, when depositing the corrosion barrier layer using HiPIMS technology, metal Hf is used as the sputtering target, the output pulse width is 50μs, the frequency is 500Hz, the target power is 4kW, and the gas pressure is 0.55~0.6Pa.

[0028] The purity of metallic Hf is 99.9% or higher.

[0029] Preferably, in step S2, when preparing the plasma oxide layer using an ion beam modification process, the plasma modification time is 10s to 20s; the ion source power is 1kW, the O2 flow rate is 300sccm, and the bias voltage is -200V.

[0030] Reducing the plasma oxidation time can decrease the thickness of the oxide layer, thereby affecting the overall corrosion rate of the coating.

[0031] Preferably, in step S3, when preparing the amorphous carbon coating using DC magnetron sputtering technology, graphite is used as the target material, argon gas is introduced, and the current and bias voltage of the arc evaporation graphite target are set, the gas pressure is 0.4 Pa, and the bias voltage applied to the metal bipolar plate substrate is -50 to -100 V.

[0032] This invention also protects the application of the protective coating for the metal bipolar plate of the fuel cell described in any of the preceding claims in the preparation of fuel cells.

[0033] The present invention also protects a fuel cell comprising the protective coating for the metal bipolar plate of the fuel cell as described in any of the preceding claims.

[0034] Compared with the prior art, the beneficial effects of the present invention are:

[0035] This invention provides a protective coating for a fuel cell metal bipolar plate. The protective coating comprises a corrosion barrier layer, a plasma oxidation layer, and a conductive functional layer stacked sequentially. The corrosion barrier layer is Hf; the plasma oxidation layer is HfO2, and its thickness is 2–4 nm. The protective coating for the fuel cell metal bipolar plate of this invention exhibits high conductivity and corrosion resistance, with a corrosion current density of less than 1 μA / cm². 2 Contact resistance less than 10 mΩ·cm 2 Furthermore, the coating is difficult to peel off after 7200 minutes of corrosion under a constant potential of 1.2V. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the protective coating structure of the metal bipolar plate of the fuel cell in Example 1. In the figure, 1-corrosion barrier layer, 2-plasma oxidation layer, 3-conductive functional layer, and 4-metal bipolar plate substrate.

[0037] Figure 2 The graphs show the potentiodynamic polarization curves of the protective coatings for the metal bipolar plates of fuel cells in Examples 1-4 and Comparative Examples 1-3.

[0038] Figure 3 This is an electron microscope image of the sample surface after corrosion of the protective coating on the metal bipolar plate of the fuel cell in Example 1.

[0039] Figure 4 Examples 1-4 and Comparative Examples 1-3 were subjected to constant potential testing at 1.2V for 7200 min. Detailed Implementation

[0040] The present invention will be further described below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise stated, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents.

[0041] Example 1

[0042] like Figure 1 As shown, a protective coating for a metal bipolar plate of a fuel cell includes a metal bipolar plate substrate 4 and a protective coating covering the surface of the metal bipolar plate substrate 4. The protective coating includes a corrosion barrier layer 1, a plasma oxidation layer 2 and a conductive functional layer 3 stacked sequentially.

[0043] The corrosion barrier layer 1 is Hf with a thickness of 550 nm;

[0044] The plasma oxide layer 2 is HfO2, and its thickness is 2 nm;

[0045] The conductive functional layer 3 is an amorphous carbon layer with a thickness of 150 nm.

[0046] The aforementioned protective coating for fuel cell metal bipolar plates can be prepared using the following methods:

[0047] Substrate pretreatment: The 304 stainless steel substrate was mechanically ground and polished, then ultrasonically cleaned for 10 minutes with a metal cleaner and deionized water, followed by ultrasonic cleaning for 10 minutes with an anhydrous ethanol solution with a volume fraction ≥99.8%. After removal, it was ultrasonically cleaned for 3 minutes with ultrapure water. Finally, the metal substrate underwent glow discharge treatment. Glow discharge cleaning treatment: The substrate was cleaned for 30 minutes using an Ar gas ion source at a furnace chamber pressure of 1.5 Pa; the substrate bias voltage was -900 V, and the duty cycle was 70%.

[0048] S1. Deposition of corrosion barrier layer: The metal Hf coating was prepared by adjusting the output pulse width of the high-power pulsed magnetron power supply to 50μs, the frequency to 500Hz, the target power to 4kW, and the air pressure to 0.6pa.

[0049] S2. Preparation of plasma oxide layer: Control the ion source power to 1kW, bias voltage to -200V, introduce oxygen into the furnace cavity through the ion source, oxygen flow rate to 300sccm, etching time to 10s, and use oxygen-containing plasma to bombard the metal Hf thin film coating to construct a plasma oxide layer on the surface of the metal Hf coating.

[0050] S3. Deposition of conductive functional layer: A graphite target is sputtered using DC magnetron sputtering technology, with the DC power supply controlled at 2kW, the deposition pressure at 0.4Pa, and the bias voltage adjusted to -50V. An amorphous carbon coating is deposited on the surface of the plasma oxide in an Ar atmosphere.

[0051] Example 2

[0052] A protective coating for a metal bipolar plate of a fuel cell includes a metal bipolar plate and a protective coating covering the surface of the metal bipolar plate. The protective coating includes a corrosion barrier layer, a plasma oxidation layer and a conductive functional layer stacked sequentially.

[0053] The corrosion barrier layer is Hf with a thickness of 550 nm;

[0054] The plasma oxide layer is HfO2, and its thickness is 4 nm;

[0055] The conductive functional layer is an amorphous carbon layer with a thickness of 150 nm.

[0056] The preparation method of the protective coating for the metal bipolar plate of the fuel cell is basically the same as that in Example 1, except that the etching time in step S2 is 20s.

[0057] Example 3

[0058] A protective coating for a metal bipolar plate of a fuel cell includes a metal bipolar plate and a protective coating covering the surface of the metal bipolar plate. The protective coating includes a corrosion barrier layer, a plasma oxidation layer and a conductive functional layer stacked sequentially.

[0059] The corrosion barrier layer is Hf with a thickness of 550 nm;

[0060] The plasma oxide layer is HfO2, and its thickness is 2 nm;

[0061] The conductive functional layer is an amorphous carbon layer with a thickness of 150 nm.

[0062] Unlike Example 1, the metal bipolar plate substrate is a Ti-6Al-4V titanium alloy.

[0063] The rest is the same as in Example 1, and will not be repeated here.

[0064] Example 4

[0065] A protective coating for a metal bipolar plate of a fuel cell includes a metal bipolar plate and a protective coating covering the surface of the metal bipolar plate. The protective coating includes a corrosion barrier layer, a plasma oxidation layer and a conductive functional layer stacked sequentially.

[0066] The corrosion barrier layer is Hf with a thickness of 550 nm;

[0067] The plasma oxide layer is HfO2, and its thickness is 2 nm;

[0068] The conductive functional layer is an amorphous carbon layer with a thickness of 150 nm.

[0069] The preparation method of the protective coating for the metal bipolar plate of the fuel cell is basically the same as that in Example 1, except that in step S3, the bias voltage is adjusted to -100V.

[0070] Comparative Example 1

[0071] A protective coating for a metal bipolar plate of a fuel cell includes a metal bipolar plate and a protective coating covering the surface of the metal bipolar plate. The protective coating includes a corrosion barrier layer and a conductive functional layer stacked sequentially.

[0072] The protective coating has a thickness of 700 nm; the corrosion barrier layer is Hf with a thickness of 550 nm; and the conductive functional layer is an amorphous carbon layer with a thickness of 150 nm.

[0073] The preparation method of the protective coating for the metal bipolar plate of the fuel cell described above is basically the same as that in Example 1, except that step S2, the preparation of the plasma oxide layer, is not included.

[0074] Comparative Example 2

[0075] A protective coating for a metal bipolar plate of a fuel cell includes a metal bipolar plate and a protective coating covering the surface of the metal bipolar plate. The protective coating includes a corrosion barrier layer, a plasma oxidation layer and a conductive functional layer stacked sequentially.

[0076] The corrosion barrier layer is Hf with a thickness of 550 nm;

[0077] The plasma oxide layer is HfO2, and its thickness is 1 nm;

[0078] The conductive functional layer is an amorphous carbon layer with a thickness of 150 nm.

[0079] The preparation method of the protective coating for the metal bipolar plate of the fuel cell is basically the same as that in Example 1, except that the etching time in step S2 is 5s.

[0080] Comparative Example 3

[0081] A protective coating for a metal bipolar plate of a fuel cell includes a metal bipolar plate and a protective coating covering the surface of the metal bipolar plate. The protective coating includes a corrosion barrier layer, a plasma oxidation layer and a conductive functional layer stacked sequentially.

[0082] The corrosion barrier layer is Hf with a thickness of 550 nm;

[0083] The plasma oxide layer is HfO2, and its thickness is 6 nm;

[0084] The conductive functional layer is an amorphous carbon layer with a thickness of 150 nm.

[0085] The preparation method of the protective coating for the metal bipolar plate of the fuel cell is basically the same as that in Example 1, except that the etching time in step S2 is 30s.

[0086] Performance testing

[0087] The performance of the protective coatings for the metal bipolar plates prepared in the above embodiments and comparative examples was tested, and the specific test methods are as follows:

[0088] (1) Potentiodynamic polarization test: The test conditions were pH=3, H2SO4 + 2ppm HF solution, and the temperature was maintained at 70℃. The test method was a potentiodynamic scanning of -0.6V to 0.6V. The corrosion current density and corrosion potential were obtained. The test results are as follows: Figure 2 As shown in Table 1.

[0089] (2) Contact resistance: Tested using a Merrick RK2514 precision resistance meter and a Tsushima AGS-X 50KN electronic universal testing machine (manufactured by Tsushima Corporation, Japan). The test conditions were an applied pressure of 1.4 MPa. The test method was to measure the total resistance R1 of the test model under a pressure of 1.4 MPa, where R1 = 2(R... B +R BC +R C +R CD )+R D (R B To test the resistance of the copper sheet; R BC R is the contact resistance between the copper sheet and the carbon paper. C R is the resistance of Toray carbon paper. CD For the contact resistance being tested, R D (This refers to the resistance of the substrate itself). Then, under the same pressure of 1.4 MPa, the sample was removed, leaving only a piece of carbon paper. The total resistance R2 = 2R was measured. B +2R BC +R C , where R C With R D The resistance is much smaller than R CD Therefore, the contact resistance R can be obtained. CD = (R1-R2) / 2. The test results are shown in Table 1.

[0090] (3) Potential constant test: The test conditions are pH=3, H2SO4+2ppm HF solution, temperature maintained at 70℃, and the test method is to perform a potential constant test for 7200min under a potential constant condition of 1.2V.

[0091] Corrosion current density refers to the intensity of the corrosion current per unit area of ​​a metal surface. In electrochemical corrosion tests of metal bipolar plate protective coatings, a lower corrosion current density indicates a smaller corrosion rate, signifying stronger corrosion resistance. Contact resistance is the resistance between the metal bipolar plate protective coating and the gas diffusion layer; a lower contact resistance value results in less energy loss in practical applications. Corrosion resistance and conductivity together affect the reliability of metal bipolar plates in fuel cells.

[0092] Table 1 Performance Tests

[0093]

[0094]

[0095] The data above show that, at 70℃, pH=3, and in a solution containing H2SO4 + 2ppm HF, the corrosion current density of the protective coatings for the metal bipolar plates in Examples 1-4 is 1μA / cm². 2 Below this, the contact resistance is low, less than 10 mΩ·cm, under a pressure of 1.4 MPa. 2 It meets the 2020 technical specifications given by the U.S. Department of Energy (DOE) and also complies with the national standard GB / T 20042.6-2011. Moreover, after a constant potential test exceeding 0.8V, the coating did not peel off over a large area, and the coating still maintained its stability before corrosion.

[0096] As can be seen from Examples 1, 2, 1, 2, and 3, with the extension of oxygen-containing plasma modification time, the thickness of the plasma oxide layer gradually increases, and the corrosion current density continuously decreases, indicating that the long-term corrosion resistance of the protective coating is improved. This demonstrates that the plasma oxide layer can delay the corrosion process of the metal substrate. However, with the increase of plasma oxide layer thickness, the contact resistance of the metal bipolar plate also increases. When the plasma thickness is 6 nm, although the corrosion resistance is improved, the contact resistance is too high and can no longer meet the technical requirements for bipolar plate installation.

[0097] As can be seen from Examples 1 and 4, the corrosion current density of Example 4 is lower than that of Example 1, and the contact resistance of Example 4 is higher than that of Example 1. This is because the amorphous carbon sample prepared under a bias voltage of 100V has a lower corrosion current density than that prepared under Example 1. 3 The bond content is higher than that of the -50V bias sample, sp 3 With higher bond content, it exhibits stronger corrosion resistance and can mitigate the corrosive effects of corrosive solutions on the underlying coating. 3 A high bond content will decrease its conductivity.

[0098] Figure 3This is an electron microscope (EM) image of the sample surface of the protective coating on the metal bipolar plate of the fuel cell in Example 1 after corrosion. From... Figure 3 It can be seen that the protective coating of the metal bipolar plate of the fuel cell of the present invention did not show any peeling after corrosion.

[0099] Figure 4 For Example 1 and Comparative Examples 1-2, a constant potential test was conducted at 1.2V for 7200 minutes. Figure 4 It can be seen that, after long-term constant potential polarization, the corrosion resistance of the protective coating of the metal bipolar plate of the fuel cell of the present invention is significantly better than that of the comparative example.

[0100] The above embodiments of the present invention are merely examples for clearly illustrating the present invention and are not intended to limit the implementation of the present invention. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all possible implementations here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A protective coating for a fuel cell metal bipolar plate, characterized in that, The protective coating comprises a corrosion barrier layer, a plasma oxidation layer, and a conductive functional layer stacked sequentially. The corrosion barrier layer is a metal Hf coating prepared using high-power pulsed magnetron sputtering technology; The plasma oxide layer is generated by using an ion beam modification process. Oxygen-containing plasma is introduced into the furnace cavity through an ion source, and the oxygen-containing plasma is used to bombard and modify the metal Hf corrosion barrier layer to form an HfO2 plasma oxide layer. The thickness of the plasma oxide layer is 2~4nm. The conductive functional layer is an amorphous carbon coating.

2. The protective coating for the metal bipolar plate of the fuel cell as described in claim 1, characterized in that, The thickness of the corrosion barrier layer is 550~600nm.

3. The protective coating for the metal bipolar plate of the fuel cell as described in claim 1, characterized in that, The thickness of the conductive functional layer is 100~150nm.

4. The method for preparing the protective coating for the metal bipolar plate of a fuel cell according to any one of claims 1 to 3, characterized in that, Includes the following steps: S1. Deposition of corrosion barrier layer: A corrosion barrier layer is obtained by depositing metal Hf on the surface of the metal bipolar plate substrate using high-power pulsed magnetron sputtering technology; S2. Preparation of plasma oxide layer: Using ion beam modification process, oxygen plasma is generated by ion source to construct plasma oxide layer on the surface of corrosion barrier layer in S1; S3. Deposition of conductive functional layer: Using DC magnetron sputtering technology, with graphite as the sputtering target, an amorphous carbon layer is deposited on the surface of the plasma oxide layer in S2; Wherein, the deposition corrosion barrier layer in S1 is a metal Hf coating; the plasma oxide layer in S2 is an HfO2 plasma oxide layer.

5. The preparation method according to claim 4, characterized in that, In step S1, when depositing the corrosion barrier layer using high-power pulsed magnetron sputtering technology, metal Hf is used as the sputtering target, the output pulse width is 50μs, the frequency is 500Hz, the target power is 4kW, and the gas pressure is 0.55~0.6Pa.

6. The preparation method according to claim 4, characterized in that, In step S2, when preparing the plasma oxide layer using ion beam modification, the plasma modification time is 10s~20s; the ion source power is 1kW, the O2 flow rate is 300sccm, and the bias voltage is -200V.

7. The preparation method according to claim 4, characterized in that, In step S3, when preparing an amorphous carbon coating using DC magnetron sputtering technology, graphite is used as the target material, argon gas is introduced, the deposition pressure is set to 0.4 Pa, and the bias voltage applied to the metal bipolar plate substrate is -50 to -100 V.

8. The application of the protective coating for the metal bipolar plate of the fuel cell according to any one of claims 1 to 3 in the preparation of fuel cells.

9. A fuel cell, characterized in that, Includes the protective coating for the metal bipolar plate of the fuel cell as described in any one of claims 1 to 3.

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