A corrosion-resistant and hydrogen embrittlement-resistant composite coating for titanium-based bipolar plates and its preparation method

Abstract

The present invention discloses a corrosion-resistant and hydrogen embrittlement-resistant composite coating for a titanium-based bipolar plate and a preparation method thereof. A titanium transition layer, a titanium suboxide hydrogen-blocking layer, a titanium sealing layer, and a noble metal conductive layer are sequentially coated on the surface of the titanium-based substrate. The titanium transition layer is a single-element titanium layer with a thickness of 10-30 nm. The material of the titanium suboxide hydrogen-blocking layer is Magneli-phase titanium suboxide with a molecular formula of TinO2n-1 where 4 ≤ n ≤ 10, and the thickness is 100-150 nm. The titanium sealing layer is a single-element titanium layer with a thickness of 10-50 nm. The material of the noble metal conductive layer is at least one of platinum, gold, ruthenium, and iridium, and the thickness is 20-50 nm. The corrosion-resistant and hydrogen embrittlement-resistant composite coating of the present invention can effectively block the diffusion and penetration of hydrogen in the cathode environment of a PEM water electrolyzer while ensuring the corrosion resistance and electrical conductivity, greatly improving the hydrogen embrittlement resistance on the cathode side of the bipolar plate, and reducing the coating processing cost and process complexity.

Description

Technical Field

[0001] The present invention belongs to the technical field of bipolar plates for PEM water electrolyzers in hydrogen production by water electrolysis, and particularly relates to a corrosion-resistant and hydrogen embrittlement-resistant composite coating for a titanium-based bipolar plate and a preparation method thereof. Background Art

[0002] Hydrogen is one of the most abundant elements in nature and plays an important role in the fields of energy chemistry, energy storage and power generation, food processing, etc. Proton exchange membrane electrolysis of water (PEM electrolysis of water) is a green hydrogen production method that has developed rapidly in recent years and has the advantages of high current density, high working efficiency, high hydrogen purity, etc.

[0003] Hydrogen production by water electrolysis is essentially an energy conversion process of converting electricity into gas. The PEM water electrolyzer uses a solid electrolyte to make it have a zero-gap structure. This structure is more flexible and efficient than the alkaline electrolyzer, but also puts higher requirements on the conductivity of components and the interfacial contact resistance between components. Precious metals (especially titanium materials), due to their extremely excellent conductivity, high specific strength, corrosion resistance and chemical stability, are the preferred coating materials for the bipolar plates of PEM water electrolyzers.

[0004] The cathode side of the PEM water electrolyzer is the place where the hydrogen evolution reaction occurs. However, due to the smallest atomic radius of hydrogen atoms, hydrogen atoms have a strong diffusion ability in metals. When the metal material surface cannot effectively inhibit the dissociation of hydrogen molecules into atomic hydrogen (hydrogen atoms H, hydrogen ions H + / H - ), hydrogen is very likely to penetrate into the interior of the metal material and dissolve in it. When hydrogen enters the metal material, it will reduce the tensile strength, fatigue strength and fracture toughness of the metal material, causing the occurrence of hydrogen embrittlement. Figure 2 FIG. is a schematic diagram of three stages of hydrogen dissolution in hydrogen embrittlement. The first stage is the reversible physical adsorption on the metal surface, due to the van der Waals force interaction between hydrogen molecules and the metal surface. The second stage is the chemical adsorption after the dissociation of hydrogen molecules, due to short-range chemical interactions and occurring within a single atomic layer. The third stage is the diffusion of atomic hydrogen into the interior of the metal material due to the existence of a hydrogen concentration gradient, that is, the permeation and dissolution of hydrogen occur.

[0005] The conventional precious metal coating on the titanium-based material for the bipolar plate of the PEM water electrolyzer cannot effectively inhibit the dissociation of hydrogen adsorbed on the cathode, resulting in poor hydrogen embrittlement resistance and being extremely vulnerable to hydrogen penetration. Generally, when the solubility of hydrogen in titanium exceeds several hundred ppm, it will cause a significant decrease in the mechanical properties such as the toughness and plasticity of titanium materials, and there is a risk of cracking under stress conditions.

[0006] To solve the problem of hydrogen embrittlement, researchers usually coat the surface of titanium bipolar plates with noble metal coatings such as platinum / gold to ensure high electrical conductivity and corrosion resistance, and block the penetration of hydrogen on the cathode side. However, the anti-hydrogen embrittlement performance of single noble metal coatings is limited, and hydrogen often penetrates through the coating from the coating defects into the interior of the titanium substrate, causing hydrogen embrittlement. Increasing the thickness of the noble metal coating can form a dense coverage of the noble metal coating, thereby alleviating the penetration of hydrogen, but this will lead to an increase in the overall manufacturing cost of the electrolyzer.

[0007] Magneli-phase titanium suboxide is the general term for non-stoichiometric titanium oxides with the molecular formula Ti n O 2n-1 (where 4 ≤ n ≤ 10). Magneli-phase titanium suboxide has the advantages of corrosion resistance to various acids and bases, high electrochemical stability, and good electrical conductivity, and has been gradually applied to fields such as fuel cells, zinc-air batteries, lead-acid batteries, and sewage treatment.

[0008] Patent document CN110071302A discloses a titanium substrate titanium suboxide bipolar plate and its preparation method. The titanium substrate is placed in a micro-arc oxidation electrolyte for micro-arc oxidation treatment to in-situ grow a carbon-containing titanium dioxide ceramic layer; then the titanium substrate obtained after micro-arc oxidation treatment is subjected to carbothermal reduction treatment until the titanium dioxide ceramic layer on the surface of the titanium substrate is transformed into a titanium suboxide (Ti4O7) ceramic layer with a conductive function. However, the titanium substrate titanium suboxide bipolar plate in this document is used for lead-acid flow batteries and has no noble metal conductive layer protection on the surface, so it cannot be used in PEM water electrolyzers. Summary of the Invention

[0009] The purpose of the present invention is to provide a corrosion-resistant and hydrogen embrittlement-resistant composite coating for a titanium substrate bipolar plate and its preparation method to solve the following problems existing in PEM water electrolysis bipolar plates in the prior art: ① large corrosion damage of metal materials in the harsh corrosion environment of high anodic potential and low pH value; ② passivation / oxidation of anodic metal materials, forming a large contact resistance with the gas diffusion layer; ③ hydrogen embrittlement of metal materials is likely to occur in the cathode hydrogen environment; ④ ion precipitation caused by corrosion or hydrogen embrittlement of anodic and cathodic metal materials, thus poisoning the proton membrane and causing a decrease in water electrolysis efficiency.

[0010] The purpose of the present invention is achieved through the following technical solutions:

[0011] A corrosion-resistant and hydrogen embrittlement-resistant composite coating for a titanium substrate bipolar plate of the present invention is coated with a titanium transition layer, a titanium suboxide hydrogen barrier layer, a titanium sealing layer, and a noble metal conductive layer on the surface of the titanium substrate in sequence;

[0012] The titanium transition layer is a single-element titanium layer with a thickness of 10 - 30 nm; its function is to enhance the interfacial matching between the titanium substrate and the titanium suboxide hydrogen barrier layer and strengthen the film-substrate bonding force;

[0013] The material of the titanium suboxide hydrogen barrier layer is titanium with a molecular formula of Ti n O 2n-1 (where 4 ≤ n ≤ 10) of Magneli phase titanium suboxide, with a thickness of 100 - 150 nm; its function is to improve the corrosion resistance and hydrogen embrittlement resistance of the titanium substrate without sacrificing the electrical conductivity of the titanium substrate; the Magneli phase titanium suboxide is preferably one or more of Ti4O7, Ti5O9, Ti6O 11 ;

[0014] The titanium sealing layer is a single - element titanium layer with a thickness of 10 - 50 nm; its function is to enhance the interfacial matching between the titanium suboxide hydrogen barrier layer and the noble metal conductive layer, and to seal and cover the through - type defects such as pinholes and nodules that may appear in the hydrogen barrier layer and the conductive layer, thereby hindering the diffusion and penetration of hydrogen from the coating defects into the substrate interior;

[0015] The material of the noble metal conductive layer is at least one of platinum, gold, ruthenium, and iridium, with a thickness of 20 - 50 nm; its function is to ensure the corrosion - resistant and conductive performance and reduce the interfacial contact resistance between the titanium bipolar plate and the cathode and anode gas diffusion layers.

[0016] Preferably, the total thickness of the corrosion - resistant and hydrogen - embrittlement - resistant composite coating is 160 - 260 nm.

[0017] Preferably, the titanium substrate bipolar plate is one of a pure titanium flat plate with a metal stretching / stamping mesh, a pure titanium plate with etched flow channels, and a stamping - formed pure titanium bipolar plate; preferably, the titanium substrate bipolar plate is made of pure titanium of grade TA1 or TA2, and preferably has a thickness of 0.5 - 2 mm.

[0018] The present invention also provides a method for preparing the corrosion - resistant and hydrogen - embrittlement - resistant composite coating for the titanium substrate bipolar plate, including the following steps:

[0019] S1, Pretreatment of the titanium substrate: First, the titanium substrate is ground step by step, then mirror - polished, and then ultrasonically cleaned in acetone and ethanol respectively, and dried with cold air;

[0020] S2, Preparation of the composite coating: Deposit a titanium transition layer, a titanium suboxide hydrogen barrier layer, a titanium sealing layer, and a noble metal conductive layer on the surface of the titanium substrate in sequence.

[0021] Preferably, the step - by - step grinding uses 400 - 1200 - mesh sandpaper, and the mirror - polishing uses diamond grinding paste.

[0022] It should be noted that although the present invention takes magnetron sputtering as an example only, the preparation process of the composite coating includes one or more of physical vapor deposition methods such as magnetron sputtering, multi-arc ion plating, and / or electron beam evaporation. The output mode of the magnetron sputtering power supply can also be one or more of direct current, direct current pulse, and / or high power pulse; the pretreated titanium substrate is placed in the sputtering deposition equipment, and the background vacuum degree of the deposition chamber is lower than 1×10 -3 Pa. The titanium transition layer and the titanium sealing layer use titanium metal single-element target as the sputtering target; the titanium suboxide hydrogen barrier layer uses Magneli phase titanium suboxide target as the sputtering target; the noble metal conductive layer uses noble metal single-element target as the sputtering target.

[0023] Preferably, before depositing the composite coating, the surface of the titanium substrate needs to be etched by glow plasma. The main component of the glow plasma is Ar ions, and the etching time is 20 - 60 min.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] The present invention uses Magneli phase titanium suboxide as the hydrogen barrier layer. Due to its unique lattice stacking structure, it has both conductive and corrosion-resistant properties and a low hydrogen diffusion coefficient. Compared with noble metal coatings, it has better hydrogen embrittlement resistance and cost advantages, ensuring that the corrosion-resistant and hydrogen embrittlement-resistant composite coating of the present invention can effectively block the diffusion and penetration of hydrogen in the cathode environment of PEM water electrolyzers while ensuring corrosion-resistant and conductive properties, greatly improving the hydrogen embrittlement resistance on the cathode side of the bipolar plate, and reducing the coating processing cost and process complexity.

[0026] Generally speaking, there will inevitably be defects such as droplets, pinholes, impurities, and nodules in the coating of the bipolar plate, and through-type defects such as pinholes and nodules will form favorable channels for hydrogen diffusion and penetration. The present invention adds a titanium sealing layer between the hydrogen barrier layer and the conductive layer, which not only seals and covers the coating defects of both, further improving the overall hydrogen embrittlement resistance of the composite coating; but also can enhance the interfacial bonding force between the compound hydrogen barrier layer and the elemental metal conductive layer, ensuring that the corrosion-resistant and hydrogen embrittlement-resistant composite coating can withstand the harsh high potential and low pH value corrosion environment on the anode of the PEM water electrolyzer and has the same good conductive and corrosion-resistant properties as the pure noble metal coating.

[0027] The anode side and the cathode side of the PEM water electrolyzer have different service environments. The anode side focuses on the requirement that the bipolar plate material is conductive and corrosion-resistant, while the cathode side focuses on the requirement that the bipolar plate material is conductive and hydrogen embrittlement-resistant. Since the corrosion-resistant and hydrogen embrittlement-resistant composite coating of the present invention has both excellent conductive and corrosion-resistant properties and hydrogen embrittlement resistance, it is not necessary to adopt two different coating systems or coating processes on both sides of the bipolar plate of the present invention, which greatly reduces the process complexity of the bipolar plate coating. Description of the Drawings

[0028] Figure 1 It is a schematic diagram of the corrosion-resistant and hydrogen embrittlement-resistant composite coating on the titanium substrate bipolar plate of the present invention.

[0029] Figure 2 It is a schematic diagram of three stages of hydrogen dissolution occurring in the hydrogen embrittlement phenomenon of the present invention.

[0030] Figure 3 It is the grazing incidence XRD pattern of the hydrogen-blocking layer in Example 1, and the main phase of the hydrogen-blocking layer is Ti4O7.

[0031] Figures 4 - 6 It is the glow discharge optical emission spectroscopy (GD-OES) diagram of the cathode side of Examples 1 to 3.

[0032] Figure 7 It is the glow discharge optical emission spectroscopy (GD-OES) diagram of the cathode side of Comparative Example 1. Specific embodiments

[0033] Those of ordinary skill in the art of this technology should recognize that this embodiment is only used to illustrate the present invention and is not used to limit the present invention. As long as changes and modifications are made to the embodiment within the scope of the implementation of the present invention, they can be within the scope of the claims of the present invention.

[0034] Example 1

[0035] A TA1 pure titanium bipolar plate with a thickness of 0.5 mm is used as the titanium substrate. The preparation method of the corrosion-resistant and hydrogen embrittlement-resistant composite coating on the titanium substrate bipolar plate includes the following steps:

[0036] S1, pretreatment of the titanium substrate: The titanium substrate is gradually polished with 400-1200 mesh sandpaper, then mirror-polished with diamond polishing paste, and finally the polished substrate is ultrasonically cleaned in acetone and ethanol for 15 minutes each and dried with cold air;

[0037] S2, preparation of the composite coating: Ar + ion glow etching is carried out on the surface of the titanium substrate to remove oxides and impurities on the substrate surface and activate the surface. The bias voltage of Ar + glow etching is set to -350 V, and the etching time is 30 minutes; The high power impulse magnetron sputtering (HiPIMS) technology is used to deposit a titanium transition layer, a sub-oxide hydrogen-blocking layer, a titanium sealing layer, and a noble metal conductive layer on the surface of the titanium substrate in sequence:

[0038] The preparation process parameters of the titanium transition layer are: the power of the power supply is constant at 1 kW, the pulse duty cycle is 2%, the deposition temperature is 200 °C, the substrate bias voltage is -150 V, and the deposition time is 2 minutes; The deposition thickness of the coating is about 10 nm;

[0039] The process parameters for preparing the titanium dioxide hydrogen barrier layer are as follows: a Ti4O7 compound target is used as the sputtering target, a constant power supply of 1.5kW, a pulse duty cycle of 5%, a deposition temperature of 200°C, a substrate bias of -150V, a deposition time of 50min, and a coating thickness of approximately 150nm.

[0040] The preparation process parameters of the titanium sealing layer are as follows: constant power of 1 kW, pulse duty cycle of 2%, deposition temperature of 200°C, substrate bias of -150 V, deposition time of 2 minutes, and coating thickness of about 10 nm.

[0041] The preparation process parameters of the precious metal conductive layer are as follows: Pt target is used as the precious metal sputtering target, the power supply is constant at 1kW, the pulse duty cycle is 2%, the deposition temperature is 200℃, the substrate bias is -150V, the deposition time is 5min, and the coating deposition thickness is about 50nm.

[0042] The total thickness of the corrosion-resistant and hydrogen-embrittlement-resistant composite coating of the titanium-based bipolar plate of Example 1 is about 220 nm.

[0043] Example 2

[0044] A 0.5 mm thick TA2 pure titanium bipolar plate is used as a titanium substrate. The method for preparing a corrosion-resistant and hydrogen-embrittlement-resistant composite coating for a titanium substrate bipolar plate comprises the following steps:

[0045] S1, titanium substrate pretreatment: the titanium substrate was polished step by step using 400-1200 grit sandpaper, then mirror-polished using diamond paste, and finally the polished substrate was ultrasonically cleaned in acetone and ethanol for 15 min each, and then dried with cold air;

[0046] S2, composite coating preparation: Ar + Ion glow etching to remove oxides and impurities on the substrate surface and activate the surface, Ar + The glow etching bias voltage was set to -350V, and the etching time was 30 minutes. Direct current magnetron sputtering (DCMS) technology was used to sequentially deposit a titanium transition layer, a titanium suboxide hydrogen barrier layer, a titanium sealing layer, and a noble metal conductive layer on the surface of the titanium substrate:

[0047] The preparation process parameters of the titanium transition layer are as follows: deposition current of 1.5A, deposition temperature of 200°C, substrate bias of -100V, deposition time of 6min, and coating deposition thickness of about 30nm;

[0048] The preparation process parameters of the titanium dioxide hydrogen barrier layer are as follows: using a Ti4O7 compound target as a sputtering target, a deposition current of 2A, a deposition temperature of 200°C, a substrate bias of -100V, a deposition time of 30min, and a coating deposition thickness of approximately 120nm;

[0049] The preparation process parameters of the titanium sealing layer are as follows: the deposition current is 1.5 A, the deposition temperature is 200 °C, the substrate bias voltage is -100 V, the deposition time is 4 min, and the coating deposition thickness is about 20 nm;

[0050] The preparation process parameters of the noble metal conductive layer are as follows: an Au target is used as the noble metal sputtering target, the deposition current is 1.2 A, the deposition temperature is 200 °C, the substrate bias voltage is -100 V, the deposition time is 4 min, and the deposition thickness is about 30 nm.

[0051] The total thickness of the corrosion-resistant and hydrogen embrittlement-resistant composite coating for the titanium substrate bipolar plate in Example 2 is about 200 nm.

[0052] Example 3

[0053] A 0.8 mm thick TA1 pure titanium bipolar plate is used as the titanium substrate. The preparation method of the corrosion-resistant and hydrogen embrittlement-resistant composite coating for the titanium substrate bipolar plate includes the following steps:

[0054] S1. Pretreatment of the titanium substrate: The titanium substrate is gradually polished with 400-1200 mesh sandpaper, then mirror-polished with diamond grinding paste, and finally the polished substrate is ultrasonically cleaned in acetone and ethanol for 15 min each, and dried with cold air;

[0055] S2. Preparation of the composite coating: Ar + ion glow etching is performed on the surface of the titanium substrate to remove oxides and impurities on the substrate surface and activate the surface. The Ar + glow etching bias voltage is set to -350 V, and the etching time is 30 min; First, the high-power pulsed magnetron sputtering (HiPIMS) technology is used to deposit a titanium transition layer and a titanium suboxide hydrogen barrier layer on the surface of the titanium substrate in sequence, and then the direct current magnetron sputtering (DCMS) technology is used to deposit a titanium sealing layer and a noble metal conductive layer on the surface of the hydrogen barrier layer in sequence:

[0056] The preparation process parameters of the titanium transition layer are as follows: the power of the power supply is kept constant at 1.2 kW, the pulse duty cycle is 3%, the deposition temperature is 250 °C, the substrate bias voltage is -150 V, the deposition time is 5 min, and the coating deposition thickness is about 20 nm;

[0057] The preparation process parameters of the titanium suboxide hydrogen barrier layer are as follows: a Ti4O7 compound target is used as the sputtering target, the power of the power supply is kept constant at 1.2 kW, the pulse duty cycle is 3%, the deposition temperature is 250 °C, the substrate bias voltage is -150 V, the deposition time is 30 min, and the coating deposition thickness is about 100 nm;

[0058] The preparation process parameters of the titanium sealing layer are as follows: the deposition current is 1.2 A, the deposition temperature is 200 °C, the substrate bias voltage is -120 V, the deposition time is 2 min, and the coating deposition thickness is about 10 nm;

[0059] The preparation process parameters of the noble metal conductive layer are as follows: using a Pt target as the noble metal sputtering target, the deposition current is 1.2 A, the deposition temperature is 200 °C, the substrate bias voltage is -120 V, the deposition time is 4 min, and the deposition thickness is about 30 nm.

[0060] The total thickness of the corrosion-resistant and hydrogen embrittlement-resistant composite coating on the titanium substrate bipolar plate in Example 3 is about 160 nm.

[0061] Comparative Example 1

[0062] The pretreatment of the titanium substrate and the Ar + The parameters of the glow lithography cleaning are exactly the same as those in Example 1. Using high-power pulsed magnetron sputtering (HiPIMS) technology, a titanium transition layer and a noble metal conductive layer are sequentially deposited on the surface of the titanium substrate:

[0063] The preparation process parameters of the titanium transition layer are as follows: the power of the power supply is constant at 1 kW, the pulse duty cycle is 2%, the deposition temperature is 200 °C, and the deposition time is 3 min. The thickness of the deposited coating is about 10 nm;

[0064] The preparation process parameters of the noble metal conductive layer are as follows: using a Pt target as the noble metal sputtering target, the power of the power supply is constant at 1 kW, the pulse duty cycle is 2%, the deposition temperature is 200 °C, the substrate bias voltage is -150 V, the deposition time is 21 min, and the deposition thickness is about 210 nm.

[0065] The total thickness of the coating on the titanium substrate bipolar plate in Comparative Example 1 is about 220 nm.

[0066] The coating bipolar plate samples of Examples 1 to 3 and Comparative Example 1 are respectively subjected to contact resistance testing, corrosion performance testing and adhesion measurement to evaluate the corrosion resistance and adhesion performance of the coating samples. The corrosion test includes potentiodynamic polarization testing (measuring the corrosion current density by Tafel extrapolation) and 1.6 V constant potential polarization testing (measuring the contact resistance values before and after corrosion and the ion precipitation amount in the corrosion solution); the corrosion solution is 0.5 M H2SO4 + 0.1 ppm HF, the holding time is 80 °C, and the duration of the 1.6 V constant potential polarization test is 24 h.

[0067] According to GB / T 20042.6-2011 "Proton Exchange Membrane Fuel Cells - Part 6: Test Methods for Bipolar Plate Characteristics", the contact resistance with carbon paper is tested at a pressure of 2.4 MPa.

[0068] The ion precipitation amount during 24 h of constant potential polarization is measured and calculated by a professional third-party institution using ICP-MS.

[0069] The adhesion of the coating is tested by the cross-cut method according to GB / T 9286-2021, and the test results are shown in Table 1.

[0070] Table 1 Test Results of Examples 1-3 and Comparative Example 1

[0071] Test item Example 1 Example 2 Example 3 Comparative example 1 <![CDATA[Corrosion current density (μA / cm 2 ).]]> 2.79 3.26 3.10 3.47 <![CDATA[Contact resistance with carbon paper before corrosion (mΩ·cm 2 )]]> 1.21 1.17 1.19 1.09 <![CDATA[Contact resistance with carbon paper after corrosion (mΩ·cm 2 )]]> 1.52 1.63 1.59 1.48 <![CDATA[Total Pt / Au / Ti precipitation per unit area (μg / cm 2 )]]> ＜0.05 ＜0.05 ＜0.05 ＜0.05 Coating adhesion (Cross - cut test) Grade 0 Grade 0 Grade 0 Grade 0

[0072] At present, there is no unified and standardized performance index in the field of PEM water electrolysis. Referring to the index requirements of the bipolar plates of the US Department of Energy (DOE) in the fuel cell field, by 2025, the contact resistance between the bipolar plate and the carbon paper should be < 10 mΩ·cm 2 . It can be seen from the test results in Table 1 that although the noble metal loading of the composite coatings in Examples 1-3 is reduced, resulting in a slightly higher contact resistance with the carbon paper before and after corrosion than that of the pure noble metal coating, the difference is not obvious and is still far lower than the 10 mΩ·cm 2 standard, and it has comparable electrical conductivity, corrosion resistance and coating adhesion to the pure noble metal coating. Therefore, the coating processing cost is effectively reduced without sacrificing the electrical conductivity and corrosion resistance performance.

[0073] The titanium substrate bipolar plates of Examples 1-3 and Comparative Example 1 were respectively placed in a tank for 1000 h durability test, and then glow discharge optical emission spectroscopy (GD-OES) test was carried out on the cathode side to characterize the change of the hydrogen element signal intensity with the coating depth to evaluate the hydrogen permeation situation, that is, its hydrogen embrittlement resistance performance. The results are shown in Figures 4 - 7 . It can be clearly seen that in Examples 1-3, the H element is effectively blocked and does not enter the titanium substrate. The detected H signal is only the impurity component in the metal, and the coating has excellent hydrogen embrittlement resistance performance; while in Comparative Example 1, due to the lack of a hydrogen barrier layer, the relatively thick noble metal layer cannot block the penetration of the H element either. The H penetrates through the coating and enters the titanium substrate and dissolves inside the titanium substrate. The detected H signal is strong and stably exists within a certain depth range of the titanium substrate, and the coating has poor hydrogen embrittlement resistance performance. It is proved that the composite coatings of Examples 1-3 of the present invention have excellent hydrogen embrittlement resistance performance.

Claims

1. A corrosion-resistant and hydrogen embrittlement-resistant composite coating for a titanium-based bipolar plate, characterized in that, A titanium transition layer, a titanium suboxide hydrogen barrier layer, a titanium sealing layer, and a noble metal conductive layer are sequentially coated on the surface of the titanium substrate; the titanium transition layer is a single-element titanium layer with a thickness of 10 to 30 nm; the material of the titanium suboxide hydrogen barrier layer is Magneli phase titanium suboxide with a thickness of 100 to 150 nm, and the Magneli phase titanium suboxide is one or more of Ti4O7, Ti5O9, Ti6O 11 ; the titanium sealing layer is a single-element titanium layer with a thickness of 10 to 50 nm; the material of the noble metal conductive layer is at least one of platinum, gold, ruthenium, and iridium, and the thickness is 20 to 50 nm.

2. The corrosion-resistant and hydrogen embrittlement-resistant composite coating for titanium-based bipolar plates according to claim 1, wherein, The total thickness of the corrosion-resistant and hydrogen embrittlement-resistant composite coating is 160 - 260 nm.

3. The corrosion-resistant and hydrogen embrittlement-resistant composite coating for titanium-based bipolar plates according to claim 1, wherein, The titanium substrate bipolar plate is one of a pure titanium flat plate with a metal stretching / stamping mesh, a pure titanium plate with etched flow channels, and a pure titanium bipolar plate formed by stamping.

4. The corrosion-resistant and hydrogen embrittlement-resistant composite coating for titanium-based bipolar plates according to claim 3, wherein The titanium substrate bipolar plate is made of pure titanium with the label TA1 or TA2, and the thickness is 0.5 - 2 mm.

5. The preparation method of the corrosion-resistant and hydrogen embrittlement-resistant composite coating for the titanium-based bipolar plate according to any one of claims 1 to 4, characterized in that, It includes the following steps: S1, Pretreatment of the titanium substrate: First, the titanium substrate is ground step by step, then mirror-polished, and then ultrasonically cleaned in acetone and ethanol respectively, and dried with cold air. S2, Preparation of the composite coating: A titanium transition layer, a titanium suboxide hydrogen barrier layer, a titanium sealing layer, and a noble metal conductive layer are sequentially deposited on the surface of the titanium substrate.

6. The preparation method of the corrosion-resistant and hydrogen embrittlement-resistant composite coating for the titanium-based bipolar plate according to claim 5, characterized in that The step-by-step grinding uses 400 - 1200 mesh sandpaper, and the mirror polishing uses diamond grinding paste.

7. The preparation method of the corrosion-resistant and hydrogen embrittlement-resistant composite coating for the titanium-based bipolar plate according to claim 5, characterized in that The preparation process for the preparation of the composite coating includes one or more of magnetron sputtering, multi-arc ion plating, or / and electron beam evaporation.

8. The preparation method of the corrosion-resistant and hydrogen embrittlement-resistant composite coating for the titanium-based bipolar plate according to claim 7, wherein, The power output mode of the magnetron sputtering is one or more of DC, DC pulse, or / and high-power pulse; the titanium transition layer and the titanium sealing layer use a titanium metal single-element target as the sputtering target; the titanium suboxide hydrogen barrier layer uses a Magneli phase titanium suboxide target as the sputtering target; the noble metal conductive layer uses a noble metal single-element target as the sputtering target.

9. The preparation method of the corrosion-resistant and hydrogen embrittlement-resistant composite coating for the titanium-based bipolar plate according to claim 5, characterized in that, Before depositing the composite coating, the surface of the titanium substrate needs to be etched by glow plasma. The main component of the glow plasma is Ar ions, and the etching time is 20 - 60 min.

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