Surface coating of a fuel cell metal flow field plate and preparation method thereof

Abstract

The present invention discloses a surface coating of a metal flow field plate of a fuel cell and a preparation method thereof. The preparation method of the surface coating of the metal flow field plate of the fuel cell comprises the following steps: (1) performing multi-arc target deposition and reactive sputtering deposition on the surface of the flow field plate substrate to obtain a transition layer; (2) depositing a protective layer on the transition layer; the protective layer includes but is not limited to a noble metal layer or a carbon-based coating; (3) applying a bias voltage of ‑300 to ‑1500 V under an inert atmosphere until the plasma is extinguished. The preparation method solves the problems of poor coating adhesion, coating micropores, and dust pollution on the coating surface through an online post-processing method, simplifies the process flow and the pollution problem introduced by post-processing after the furnace is opened, improves the quality of the coating, and increases the electrochemical performance and stability of the PEM fuel cell.

Description

Technical Field

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

[0002] In the prior art, the preparation methods of the coating of the fuel cell flow field plate include physical vapor deposition, chemical vapor deposition, electrochemical deposition, plasma spraying, screen printing and many other methods. Among them, the physical vapor deposition (PVD) process is widely used because of its advantages of uniformity and good density of the coating, high deposition efficiency and low environmental pollution. The flow field plate has a large area and a stamped groove structure on the surface, which easily leads to uneven thickness of the coating, localized pitting caused by the non-density of the local coating, and thus causes local heating of the battery unit or contamination of the membrane electrode, which directly affects the electrochemical performance and stability of the battery stack.

[0003] The performance of films deposited on metal flow field plates by PVD depends on four factors that affect film growth and performance: (1) substrate surface conditions, such as surface morphology (roughness, inclusions, particle contamination), surface chemistry (surface composition, contaminants), surface defects, degassing, preferential nucleation sites, and surface stability; (2) detailed information about the deposition process and system geometry, such as incident angle distribution, depositing atom flux, substrate temperature, deposition rate, gas contamination, and concurrent energetic particle bombardment; (3) details of film growth on the substrate surface, such as surface mobility of depositing atoms, nucleation, interface formation, interface defect generation, energy input to the growing film, simultaneous bombardment, film growth morphology, gas entrapment, reaction with the deposition environment (including reactive deposition processes), and changes in film and interface properties during deposition; and (4) post-deposition treatments and reactions, such as reaction of the film surface with the environment, thermal or mechanical cycling, corrosion, interface degradation, soft surface deformation (e.g., polishing, shot peening), and coatings ("topcoats").

[0004] However, the film deposited on the surface of the flow field plate has residual stress, which is mainly due to the following reasons: stress caused by the different coefficients of thermal expansion (CTE) of the film and substrate when deposited at high temperature; growth stress caused by atoms not being in their most favorable energy position; and stress caused by phase changes in the film material after deposition. These stresses are stored in the coating film-substrate system and are prone to cause cracks or wrinkles in the coating film.

[0005] Moreover, the PVD process itself will generate a lot of nano-dust, which will be directly deposited on the surface of the flow field plate, making it difficult to clean up later. Some dust will even enter the entrance or water channel of the water channel, directly causing the conductivity of the cooling water to increase, affecting the insulation of the battery stack.

[0006] The general solution to the above problems is to take out the flow field plate after coating and heat the system. However, since the film and substrate have different expansion coefficients, the thermal cycle will exert stress on the interface and cause defects, resulting in cracking of the film. At the same time, the composition of the gas environment will affect the diffusion of the interface material away from the interface, and heating will also cause the film material to agglomerate on the surface.

[0007] Therefore, there is an urgent need to provide a surface coating of a fuel cell metal flow field plate having good coating bonding strength and no dust pollution on the coating surface, and a preparation method thereof. Summary of the invention

[0008] The present invention is to solve the problems of poor adhesion and density of the surface coating of the metal flow field plate of the fuel cell, and the presence of a lot of surface particle precipitation and dust pollution, thereby providing a surface coating of the metal flow field plate of the fuel cell and a preparation method thereof. The preparation method solves the problems of poor coating adhesion, coating micropores, and coating surface dust pollution through online post-processing, simplifies the process flow and the pollution problem introduced by post-processing after the furnace is opened, improves the quality of the coating, and increases the electrochemical performance and stability of the PEM fuel cell.

[0009] In order to achieve the above object, the present invention provides the following technical solutions:

[0010] One of the technical solutions provided by the present invention is: a method for preparing a surface coating of a metal flow field plate of a fuel cell, which comprises the following steps:

[0011] (1) performing multi-arc target deposition and reactive sputtering deposition on the surface of the flow field plate substrate to obtain a transition layer;

[0012] (2) depositing a protective layer on the transition layer; the protective layer includes but is not limited to a noble metal layer or a carbon-based coating;

[0013] (3) Under an inert atmosphere, apply a bias voltage of -300 to -1500 V until the plasma is extinguished.

[0014] In step (1) of the present invention, the multi-arc target deposition can be conventional multi-arc ion plating in the art, which generally refers to a method of directly evaporating metal on a solid cathode target material by an arc discharge method, and the evaporated material is the ions of the cathode material emitted from the cathode arc bright point, thereby depositing a thin film on the surface of the substrate. The target material of the multi-arc target deposition can be conventional in the art, such as one or more of a Ti target, a Cr target, an Al target, a Nd target, a V target, a Cr target, a Mo target and a Ta target; preferably a Ti target or a Cr target.

[0015] The temperature of the multi-arc target deposition may be 50-500°C, preferably 100-300°C, such as 150-170°C.

[0016] The current of the multi-arc target deposition may be 50-200A, preferably 50-150A, such as 80-85A.

[0017] The bias voltage used in the multi-arc target deposition process may be -100 to -1000V, preferably -200 to -900V, such as -300V.

[0018] The multi-arc target deposition time may be 50 to 700 s, preferably 100 to 500 s, and more preferably 200 to 300 s.

[0019] According to the conventional art, after the multi-arc target deposition is completed, a primer layer is formed on the surface of the flow field plate substrate. The primer layer is generally a Ti layer or a Cr layer.

[0020] In step (1) of the present invention, the reactive sputtering deposition may be conventional in the art, generally referring to the process of introducing a reactive gas such as oxygen or nitrogen into the sputtering of a pure metal or alloy target to reactively deposit a compound film. Preferably, in the reactive sputtering deposition of step (1), the reactive gas introduced is nitrogen.

[0021] The temperature of the reactive sputtering deposition may be 50-500°C, preferably 100-300°C, for example 200°C.

[0022] The current of the reactive sputtering deposition may be 30-200A, preferably 50-150A, for example 80A.

[0023] The bias voltage of the reactive sputtering deposition may be -100 to -1000V, preferably -200 to -500V, for example -270V.

[0024] The reactive sputtering deposition time may be 1 to 50 min, preferably 6 to 25 min, more preferably 8 to 17 min, for example 13 min.

[0025] In step (1) of the present invention, the flow field plate substrate can be conventional in the art, for example, after cleaning the flow field plate obtained by the conventional coating procedure in the art.

[0026] The flow field plate may be a stainless steel stamped flow field plate, and the thickness of the flow field plate may be 0.05 to 0.2 mm, preferably 0.1 mm.

[0027] The cleaning method can be a conventional cleaning method in the art that can remove the oxide layer on the surface of the substrate, such as one or more of ultrasonic cleaning, bias cleaning, ion source cleaning and radio frequency cleaning; preferably ultrasonic cleaning and bias cleaning. Removing the oxide layer on the surface of the substrate is more conducive to the surface resistance of the obtained surface coating meeting the requirements of the fuel cell bipolar plate.

[0028] The bias cleaning may be conventional in the art, and may generally be transferred to the furnace chamber through customized tooling for bias cleaning.

[0029] In step (1) of the present invention, the transition layer may be a TiN over-plating layer or a CrN over-plating layer.

[0030] In step (2) of the present invention, the protective layer preferably comprises a noble metal layer, a carbon-based coating or other coating that meets the requirements.

[0031] In step (2) of the present invention, when the protective layer includes a noble metal layer, the noble metal layer is an Au coating.

[0032] In step (2) of the present invention, the method for depositing the protective layer on the transition layer can be conventional in the art, such as magnetron sputtering or arc method; preferably, magnetron sputtering.

[0033] In step (3) of the present invention, the inert atmosphere may be any conventional atmosphere in the art, and is preferably an Ar gas atmosphere.

[0034] In step (3) of the present invention, preferably, plasma is generated by bias discharge, and the regulating valve is opened until the plasma is extinguished.

[0035] In step (3) of the present invention, preferably a bias voltage of -600 to -1200 V is applied, and more preferably a bias voltage of -700 to -800 V is applied.

[0036] In step (3) of the present invention, after extinguishing the plasma, a vacuum breaking step is generally included to take out the coated sample.

[0037] The vacuum breaking generally refers to destroying the vacuum state. The vacuum breaking method may be conventional in the art, such as opening a valve of a vacuumed container and filling the container with air.

[0038] In the present invention, preferably, steps (1) to (3) are all completed in a vacuum furnace chamber, wherein the arrangement of the gas pipes can be conventional in the art.

[0039] In the present invention, the bias voltage generally refers to a negative voltage applied during the coating process according to the conventional art. Preferably, the bias voltage is applied in the form of a direct current bias voltage or a pulse bias voltage.

[0040] The second technical solution provided by the present invention is: a surface coating of a metal flow field plate of a fuel cell, which is prepared by the preparation method of the surface coating of a metal flow field plate of a fuel cell as described above.

[0041] In the present invention, the structure of the surface coating of the fuel cell metal flow field plate can be flow field plate substrate, transition layer and protective layer from bottom to top; preferably, flow field plate substrate, primer layer, transition layer and protective layer.

[0042] Wherein, the thickness of the flow field plate substrate may be 0.05-0.2 mm, preferably 0.1 mm.

[0043] The primer layer is preferably a Ti layer or a Cr layer.

[0044] The thickness of the transition layer may be 0.1 to 100 μm, preferably 1 to 20 μm, such as 10 to 15 μm.

[0045] The protective layer preferably comprises a noble metal layer or a carbon-based coating. When the protective layer comprises a noble metal layer, the noble metal layer is preferably an Au coating.

[0046] The thickness of the protective layer may be 1 to 10 nm, preferably 2 to 5 nm, such as 3 to 4 μm.

[0047] In the present invention, preferably, the coating thickness uniformity of the surface coating of the fuel cell metal flow field plate is ≥95%.

[0048] In the present invention, during the metal flow field plate coating process of steps (1) to (2), and during the post-processing process of step (3), the duty cycle of the bias power supply is preferably 20% to 95%.

[0049] The third technical solution provided by the present invention is: application of a surface coating of a metal flow field plate of a fuel cell in a fuel cell.

[0050] A fourth technical solution provided by the present invention is: a fuel cell, which includes the surface coating of the fuel cell metal flow field plate as described above.

[0051] On the basis of being in accordance with the common sense in the art, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0052] The reagents and raw materials used in the present invention are commercially available.

[0053] The positive and progressive effects of the present invention are:

[0054] By depositing a transition layer and an Au coating on the surface of the flow field plate substrate, in conjunction with an "online" post-processing method, that is, a post-processing method in which a bias voltage is directly applied in a vacuum furnace chamber after the deposition of the transition layer and the Au coating is completed, there is no need to take the sample out of the vacuum furnace chamber and then perform post-processing processes such as high-temperature treatment. This solves the problems of poor coating adhesion, coating micropores, and dust contamination on the coating surface, simplifies the process flow and the pollution problem introduced by post-processing after the furnace is opened, improves the quality of the coating, and increases the performance and stability of PEM fuel cells, which is beneficial to the large-scale promotion and application of metal bipolar plates. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 It is a comparison diagram of the corrosion current curves of the surface coating of the metal flow field plate of the fuel cell in Example 1 and Comparative Example 2.

[0056] Figure 2 A comparison chart of polarization curves obtained by assembling the fuel cell metal flow field plates in Example 1 and Comparative Example 2 into batteries.

[0057] Figure 3 Comparison diagram of electrochemical impedance spectra obtained by assembling batteries using the metal flow field plates of the fuel cell in Example 1 and Comparative Example 2. DETAILED DESCRIPTION

[0058] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods in the following examples without specifying specific conditions are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0059] Example 1

[0060] 1. Ultrasonic cleaning and drying of the 0.1mm stainless steel stamped flow field plate;

[0061] 2. Transfer to the furnace chamber through customized tooling for bias cleaning;

[0062] 3. Use Ti target material to prime through multi-arc target; wherein, the temperature of multi-arc target is 150°C, arc target current is 80A, bias voltage is -300V, and time is 5min;

[0063] 4. N2 was introduced for reactive sputtering to generate a TiN overcoat (thickness of 10-15 μm); wherein the reactive sputtering temperature was 200°C, the arc target current was 80A, the bias voltage was -270V, and the time was 13min;

[0064] 5. Nano Au coating (thickness of 3-4 nm) is plated on the TiN overcoat by magnetron sputtering;

[0065] 6. Introduce Ar, generate plasma by bias voltage -800V discharge mode, and open the regulating valve at the same time until the plasma is extinguished;

[0066] 7. Break the vacuum and take out the coated samples.

[0067] Example 2

[0068] 1. Ultrasonic cleaning and drying of the 0.1mm stainless steel stamped flow field plate;

[0069] 2. Transfer to the furnace chamber through customized tooling for bias cleaning;

[0070] 3. Use Cr target material to prime through multi-arc target; wherein, the temperature of multi-arc target is 170°C, arc target current is 85A, bias voltage is -300V, and time is 5min;

[0071] 4. N2 was introduced for reactive sputtering to generate a CrN overcoat (thickness of 10-15 μm); wherein the reactive sputtering temperature was 200°C, the arc target current was 80A, the bias voltage was -270V, and the time was 13min;

[0072] 5. Plating a nano Au coating (thickness of 3-4 nm) on the CrN over-plating layer by magnetron sputtering;

[0073] 6. Introduce Ar, generate plasma by bias voltage -700V discharge mode, and open the regulating valve at the same time until the plasma is extinguished;

[0074] 7. Break the vacuum and take out the coated samples.

[0075] Comparative Example 1

[0076] Step 6 is: introducing Ar, generating plasma by discharge at a bias voltage of -1700 V, and opening the regulating valve until the plasma is extinguished;

[0077] The other steps are the same as those in Example 1.

[0078] The bias voltage in Comparative Example 1 is too high (>1500 V), which causes coating damage during high-energy ion bombardment, resulting in a rough coating on the surface of the sample obtained in Comparative Example 1.

[0079] Comparative Example 2

[0080] Comparative Example 2 does not include step 6, and the other steps are the same as those in Example 1.

[0081] Effect Example

[0082] (1) The corrosion current curve comparison of the surface coating of the metal flow field plate of the fuel cell in Example 1 and Comparative Example 2 is shown in FIG. Figure 1 shown.

[0083] Depend on Figure 1 It can be seen that the corrosion current of the sample after post-treatment in Example 1 is lower (~3.6*10 -6 A / cm 2 ), and remained essentially unchanged over a 4-hour period, whereas the corrosion current of the sample without post-treatment in Comparative Example 2 was ~2*10 -5 A / cm 2 , indicating that the surface coating after bias treatment in Example 1 has better corrosion resistance.

[0084] (2) The metal flow field plates of the fuel cell in Example 1 and Comparative Example 2 were respectively assembled into batteries, and the polarization curves were measured as follows: Figure 2 shown.

[0085] The flow field plates with bias and without bias were assembled into a battery, and the polarization curves were tested using the Chino FC5100 fuel cell test system. H2 was introduced into the anode and Air was introduced into the cathode. The battery temperature was 80°C, the humidity of the anode and cathode was 100%, the hydrogen utilization rate was 68%, and the air utilization rate was 40%.

[0086] from Figure 2 The comparison of the polarization curve test results in the embodiment 1 shows that the battery performance of the flow field plate with bias treatment is better than that of the flow field plate battery without bias treatment in the comparative example 2. For example, the current density is 1000 mA·cm -2 When the voltage of the flow field plate battery with and without bias treatment is 0.697V and 0.661V respectively. See Table 1 for details.

[0087] Table 1

[0088]

[0089] (3) The fuel cell metal flow field plates in Example 1 and Comparative Example 2 were assembled into batteries, and their electrochemical impedance spectra were tested. The results are as follows: Figure 3 shown.

[0090] The EIS spectrum was measured using a KIKUSUI KFM2150 impedance meter. H2 was introduced into the anode of the single cell, and Air was introduced into the cathode. The cell temperature was 80°C, and the humidification temperature of the anode gas and cathode gas was 80°C. The EIS test frequency was 10kHz-100mHz, and the operating current density of the PEMFC was 1200mA·cm -2 , the amplitude of the sinusoidal current is 1.5A.

[0091] Depend on Figure 3It can be seen that the ohmic resistance of the battery composed of the flow field plate with bias treatment in Example 1 is lower than that of the flow field plate battery without bias treatment in Comparative Example 2. The ohmic resistance of the battery composed of the flow field plate with bias treatment and the battery without bias treatment is 50.9 mohm·cm 2 and 69.2mohm·cm 2 (AC impedance value at the start of the semicircle curve). Since all other components of the battery are identical except for the difference in the flow field plate, the difference in battery ohmic resistance is caused by whether the coating is biased. It can be determined that the ohmic resistance of the biased coated flow field plate is lower than that of the unbiased flow field plate.

[0092] The corrosion current curve of the surface coating of the fuel cell metal flow field plate in Example 2, the polarization curve and the electrochemical impedance spectrum measured after the fuel cell metal flow field plate is assembled into a battery are comparable to those in Example 1. However, the toughness of the surface coating of the fuel cell metal flow field plate in Example 2 is not as good as that in Example 1.

[0093] In addition, the inventors discovered through experiments that:

[0094] (1) By replacing the Ti target or Cr target in the embodiment with an Al, V, Cr, Mo, W or Nb target, the obtained surface coating can also achieve the same technical effect as the surface coating in the embodiment.

[0095] (2) If the bias voltage in step 6 of the above embodiment is too low (<300 V), a lot of dust will accumulate on the surface of the prepared sample. During the preparation process, atoms will not have time to migrate and diffuse to the lattice point position, and new grains will be generated, resulting in structural defects such as vacancies and interstitial atoms. This will cause greater stress inside the coating, seriously affecting the bonding performance between the coating and the substrate; thus resulting in poor coating density and high residual stress, which will in turn affect battery performance and life.

Claims

1. A method for preparing a surface coating of a metal flow field plate of a fuel cell, It is characterized in that The method for preparing the surface coating of the fuel cell metal flow field plate comprises the following steps: (1) performing multi-arc target deposition and reactive sputtering deposition on the surface of the flow field plate substrate to obtain a transition layer; (2) depositing a protective layer on the transition layer; the protective layer comprises a noble metal layer or a carbon-based coating; (3) Under an inert atmosphere, apply a bias voltage of -300 to -1500 V until the plasma is extinguished.

2. The method for preparing the surface coating of the metal flow field plate of a fuel cell according to claim 1, It is characterized in that The method for preparing the surface coating of the metal flow field plate of the fuel cell meets one or more of the following conditions ① to ④: ①, in step (3), the inert atmosphere is Ar gas atmosphere; ② In step (3), plasma is generated by bias discharge, and the regulating valve is opened until the plasma is extinguished; ③. In step (3), a bias voltage of -600 to -1200 V is applied; ④. In step (3), after the plasma is extinguished, a vacuum breaking step is also included to take out the coated sample.

3. The method for preparing the surface coating of the metal flow field plate of a fuel cell according to claim 2, It is characterized in that In step (3), a bias voltage of -700 to -800 V is applied.

4. The method for preparing the surface coating of the metal flow field plate of a fuel cell according to claim 1, It is characterized in that The method for preparing the surface coating of the metal flow field plate of the fuel cell satisfies one or more of the following conditions a to f: a. In step (1), the target material for multi-arc target deposition is one or more of a Ti target, a Cr target, an Al target, a Nd target, a V target, a Cr target, a Mo target and a Ta target; b. In step (1), the temperature of the multi-arc target deposition is 50-500° C.; c. In step (1), the current of the multi-arc target deposition is 50 to 200 A; d. In step (1), the bias voltage used in the multi-arc target deposition process is -100 to -1000 V; e. In step (1), the multi-arc target deposition time is 50 to 700 seconds; f. In step (1), after the multi-arc target deposition is completed, a primer layer is formed on the surface of the flow field plate substrate.

5. The method for preparing the surface coating of the metal flow field plate of a fuel cell according to claim 4, It is characterized in that In step (1), the target material for the multi-arc target deposition is a Ti target or a Cr target.

6. The method for preparing the surface coating of the metal flow field plate of a fuel cell according to claim 4, It is characterized in that In step (1), the temperature of the multi-arc target deposition is 100-300°C.

7. The method for preparing the surface coating of the metal flow field plate of a fuel cell according to claim 6, It is characterized in that In step (1), the temperature of the multi-arc target deposition is 150-170°C.

8. The method for preparing the surface coating of the metal flow field plate of a fuel cell according to claim 4, It is characterized in that In step (1), the bias voltage used in the multi-arc target deposition process is -200 to -900V.

9. The method for preparing the surface coating of the metal flow field plate of a fuel cell according to claim 4, It is characterized in that In step (1), the multi-arc target deposition time is 100 to 500 seconds.

10. The method for preparing the surface coating of the metal flow field plate of a fuel cell according to claim 9, It is characterized in that In step (1), the multi-arc target deposition time is 200 to 300 seconds.

11. The method for preparing the surface coating of the metal flow field plate of a fuel cell according to claim 4, It is characterized in that The primer layer is a Ti layer or a Cr layer.

12. The method for preparing the surface coating of the metal flow field plate of a fuel cell according to claim 4, It is characterized in that In step (1), the method for preparing the surface coating of the metal flow field plate of the fuel cell satisfies conditions a to f at the same time.

13. The method for preparing the surface coating of the metal flow field plate of a fuel cell according to claim 4, It is characterized in that The method for preparing the surface coating of the metal flow field plate of the fuel cell satisfies one or more of the following conditions g to k: g. In step (1), the reactive gas introduced in the reactive sputtering deposition is nitrogen; h. In step (1), the temperature of the reactive sputtering deposition is 50 to 500° C.; i. In step (1), the current of the reactive sputtering deposition is 30 to 200 A; j. In step (1), the bias voltage of the reactive sputtering deposition is -100 to -1000 V; k. In step (1), the reaction sputtering deposition time is 1 to 50 minutes.

14. The method for preparing the surface coating of the metal flow field plate of a fuel cell according to claim 13, It is characterized in that In step (1), the temperature of the reactive sputtering deposition is 100 to 300°C.

15. The method for preparing the surface coating of the metal flow field plate of a fuel cell according to claim 13, It is characterized in that In step (1), the current of the reactive sputtering deposition is 50 to 150A.

16. The method for preparing the surface coating of the metal flow field plate of a fuel cell according to claim 13, It is characterized in that In step (1), the bias voltage of the reactive sputtering deposition is -200 to -500V.

17. The method for preparing the surface coating of the metal flow field plate of a fuel cell according to claim 13, It is characterized in that In step (1), the reaction sputtering deposition time is 6 to 25 minutes.

18. The method for preparing the surface coating of the metal flow field plate of a fuel cell according to claim 17, It is characterized in that In step (1), the reaction sputtering deposition time is 8 to 17 minutes.

19. The method for preparing the surface coating of the metal flow field plate of a fuel cell according to claim 13, It is characterized in that The method for preparing the surface coating of the metal flow field plate of the fuel cell satisfies conditions g to k at the same time.

20. The method for preparing the surface coating of the metal flow field plate of a fuel cell according to claim 1, It is characterized in that In step (1), the flow field plate substrate is obtained by cleaning the flow field plate; And / or, in step (1), the transition layer is a TiN over-plating layer or a CrN over-plating layer.

21. The method for preparing the surface coating of the metal flow field plate of a fuel cell according to claim 20, It is characterized in that In step (1), the flow field plate is a flow field plate stamped from stainless steel.

22. The method for preparing the surface coating of the metal flow field plate of a fuel cell according to claim 21, It is characterized in that In step (1), the thickness of the flow field plate is 0.05 to 0.2 mm.

23. The method for preparing the surface coating of the metal flow field plate of a fuel cell according to claim 1, It is characterized in that In step (2), when the protective layer includes a noble metal layer, the noble metal layer is an Au coating; and / or, in step (2), the method of depositing the protective layer on the transition layer is magnetron sputtering or arc method.

24. The method for preparing the surface coating of the metal flow field plate of a fuel cell according to claim 23, It is characterized in that In step (2), the method of depositing the protective layer on the transition layer is magnetron sputtering.

25. A surface coating for a metal flow field plate of a fuel cell, It is characterized in that The surface coating of the metal flow field plate of a fuel cell is prepared by the method for preparing the surface coating of the metal flow field plate of a fuel cell as described in any one of claims 1 to 24.

26. The surface coating of the fuel cell metal flow field plate according to claim 25, It is characterized in that The surface coating of the fuel cell metal flow field plate satisfies one or more of the following conditions m to o: m. The structure of the surface coating of the fuel cell metal flow field plate is, from bottom to top, a flow field plate substrate, a transition layer and a protective layer; n. The coating thickness uniformity of the surface coating of the fuel cell metal flow field plate is ≥ 95%; o. During the metal flow field plate coating process of steps (1) to (2), and during the post-processing process of step (3), the duty cycle of the bias power supply is 20% to 95%.

27. The surface coating of the fuel cell metal flow field plate according to claim 26, It is characterized in that The structure of the surface coating of the fuel cell metal flow field plate is, from bottom to top, a flow field plate substrate, a primer layer, a transition layer and a protective layer.

28. The surface coating of the fuel cell metal flow field plate according to claim 27, It is characterized in that The thickness of the flow field plate substrate is 0.05-0.2 mm.

29. The surface coating of the fuel cell metal flow field plate according to claim 28, It is characterized in that The thickness of the flow field plate substrate is 0.1 mm.

30. The surface coating of the fuel cell metal flow field plate according to claim 29, It is characterized in that The primer layer is a Ti layer or a Cr layer.

31. The surface coating of the fuel cell metal flow field plate according to claim 27, It is characterized in that The thickness of the transition layer is 0.1-100 μm.

32. The surface coating of the fuel cell metal flow field plate according to claim 31, It is characterized in that The thickness of the transition layer is 1-20 μm.

33. The surface coating of the fuel cell metal flow field plate according to claim 32, It is characterized in that The thickness of the transition layer is 10-15 μm.

34. The surface coating of the fuel cell metal flow field plate according to claim 27, It is characterized in that The protective layer is a noble metal layer or a carbon-based coating.

35. The surface coating of the fuel cell metal flow field plate according to claim 34, It is characterized in that When the protective layer includes a noble metal layer, the noble metal layer is an Au coating.

36. The surface coating of the fuel cell metal flow field plate according to claim 35, It is characterized in that The thickness of the protective layer is 1-10 nm.

37. The surface coating of the fuel cell metal flow field plate according to claim 36, It is characterized in that The thickness of the protective layer is 2-5 nm.

38. The surface coating of the fuel cell metal flow field plate according to claim 26, It is characterized in that The surface coating of the fuel cell metal flow field plate satisfies conditions m to o at the same time.

39. Use of the surface coating of a fuel cell metal flow field plate according to any one of claims 26 to 38 in a fuel cell.

40. A fuel cell, It is characterized in that The fuel cell comprises a surface coating of a fuel cell metal flow field plate as claimed in any one of claims 26 to 38.

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