Titanium metal matrix surface oxygen gradient composite oxide coating and preparation method and application thereof

Abstract

The invention relates to the technical field of surface protection of metal bipolar plates for fuel cells, in particular to a titanium metal matrix surface oxygen gradient composite oxide coating and a preparation method and application thereof. The oxygen gradient composite oxide coating on the surface of the titanium metal matrix is a coating growing on the titanium metal matrix in situ, in the coating, from the titanium metal matrix to the outside, the oxygen concentration is firstly increased in a gradient mode and then decreased in a gradient mode, and the structure is TiOx-TiO2-TiOx, and 2, the coating is combined with a titanium metal matrix, so that a continuous Ti-TiOx-TiO-TiOx composite structure is formed. The oxygen gradient composite oxide coating on the surface of the titanium metal matrix has corrosion resistance and electrical conductivity, the interface contact resistance is smaller than 10 m omega.cm < 2 >, and the corrosion current density t in a simulated fuel cell environment is achieved; the method is suitable for surface protection of the titanium metal bipolar plate of the proton exchange membrane fuel cell.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal bipolar plate surface protection for fuel cells, in particular to a titanium metal substrate surface oxygen gradient composite oxide coating and a preparation method and application thereof. BACKGROUND

[0002] As one of the key components of proton exchange membrane fuel cells, the bipolar plate accounts for about 80% of the weight of the cell stack, almost accounts for the entire volume of the cell stack, and accounts for about 18-28% of the cost of the battery pack. It plays an important role in electron conduction, chemical fuel distribution, membrane electrode support, and water management in the cell. The bipolar plate not only needs to have good electrical conductivity to reduce internal resistance, but also needs to have excellent electrochemical corrosion resistance to maintain long-term stable operation. Although the metal bipolar plate has good mechanical properties and good electrical conductivity, it is easy to form a passivation layer on the surface in the acidic and high potential working environment of the fuel cell, which leads to the increase of the contact resistance between the bipolar plate and the gas diffusion layer interface, affecting the power output and efficiency of the cell.

[0003] In order to solve the above problems, researchers have developed various metal bipolar plate modification coating technologies, such as noble metal coating, amorphous carbon coating, and metal oxide. Among them, although the noble metal coating has good corrosion resistance and conductivity, the high cost limits its large-scale use. The amorphous carbon coating currently used in commercial applications has high electrical conductivity and chemical stability, but its adhesion to the titanium metal substrate is poor, and interface peeling easily occurs, and oxidation failure problem occurs at high potential. For titanium metal plates, although titanium oxide TiO2 has good chemical stability and corrosion resistance, its electrical conductivity is poor, and the contact resistance is large, which will affect the performance of the fuel cell if it is directly used as a bipolar plate coating. SUMMARY

[0004] Based on the deficiencies of the prior art, the present application provides a titanium metal substrate surface oxygen gradient composite oxide coating and a preparation method and application thereof. The titanium metal substrate surface oxygen gradient composite oxide coating is an in-situ grown coating on the titanium metal substrate. From the titanium metal substrate outward, the oxygen concentration first increases and then decreases, and the structure is TiO x -TiO2-TiO x (x<2), and after being combined with the titanium metal substrate, the structure is Ti-TiO x -TiO2-TiO x (x<2). On the one hand, it utilizes the excellent corrosion resistance of TiO2, and on the other hand, it utilizes the excellent electrical conductivity of the non-stoichiometric oxide TiO X (x<2), and the titanium metal substrate surface oxygen gradient composite oxide coating prepared has corrosion resistance and electrical conductivity, and is suitable for surface protection of metal bipolar plates of proton exchange membrane fuel cells.

[0005] To achieve the above technical purposes, the present application adopts the following technical solutions: The present application protects a titanium metal matrix surface oxygen gradient composite oxide coating, which is an in-situ grown coating on a titanium metal matrix. x -TiO2-TiO x Wherein x<2; in the titanium metal matrix surface oxygen gradient composite oxide coating, the TiO x As a transition phase from metal Ti to insulating TiO2, its thermal expansion coefficient is between that of metal Ti and TiO2, which is used to relieve interface stress caused by thermal expansion difference; TiO2 is used for corrosion resistance; the outer layer of TiO x There are oxygen vacancies and oxygen defects for electrical conduction, and the outer layer of TiO x is wrapped by TiO2.

[0006] Preferably, TiO x Not limited to one oxide, it is a general term for multiple oxides, including but not limited to TiO 3 / 2 , TiO, TiO 1 / 2 , TiO 1 / 3 , TiO 1 / 6 .

[0007] The present application also protects a preparation method of a titanium metal matrix surface oxygen gradient composite oxide coating, comprising the following steps: S1, cleaning the titanium metal matrix.

[0008] S2, placing the cleaned titanium metal matrix in a heating furnace and performing in-situ oxidation heat treatment in an oxygen environment to perform in-situ oxidation on the surface of the titanium metal matrix, forming a TiO2 coating on the outer surface of the titanium metal matrix, and there will be some incomplete oxidation oxide phase TiO x between the outer surface and the titanium metal matrix (i.e. between the TiO2 layer and the titanium metal matrix). x -TiO2 film, TiO x -TiO2 film, the main phase of which is TiO2, and the titanium oxide alloy matrix is obtained through this step.

[0009] The TiO x -TiO2 film is partially reduced by using a hydrogen plasma reduction method or a Ti powder thermal reduction method, forming an oxide phase TiO x outside the TiO2, obtaining a structure of TiO x -TiO2-TiO xThe titanium metal matrix surface oxygen gradient composite oxide coating.

[0010] Preferably, the oxygen environment is oxygen with purity ≥99% or dry air.

[0011] Preferably, the in-situ oxidation heat treatment is performed at 500-700℃ for 1-7h.

[0012] Preferably, the hydrogen plasma reduction method is performed as follows: the titanium oxide metal matrix is placed in a device equipped with a plasma generator and a heating device, and first, a mixture of argon and hydrogen is filled in under a vacuum degree ≤10 -3 Pa, and when the heating device is heated to 500-800℃, the plasma generator is used to discharge plasma to ionize hydrogen into hydrogen ion groups, and the hydrogen ion groups reduce part of TiO2 into TiO x (x<2), the power of the plasma generator is 200-400W, and the discharge plasma treatment time is 5-60min.

[0013] Preferably, the hydrogen plasma reduction method is performed as follows: the titanium oxide metal matrix is placed in a device equipped with a plasma generator and a heating device, and first, a mixture of argon and hydrogen is filled in under a vacuum degree ≤10

[0014] Preferably, the Ti powder reduction method is performed as follows: the titanium oxide alloy matrix is placed in a mixed powder composed of Ti and TiO2, and the TiO2 powder is added to control the reduction degree of the Ti powder to the surface TiO2, and then the crucible containing the titanium oxide alloy matrix and the mixed powder is covered and placed in a heating furnace, and calcined at 800-900℃ for 5-60min under a vacuum degree <10 -3 Pa.

[0015] Preferably, the Ti powder reduction method is performed as follows: the titanium oxide alloy matrix is placed in a mixed powder composed of Ti and TiO2, and the TiO2 powder is added to control the reduction degree of the Ti powder to the surface TiO2, and then the crucible containing the titanium oxide alloy matrix and the mixed powder is covered and placed in a heating furnace, and calcined at 800-900℃ for 5-60min under a vacuum degree <10

[0016] Preferably, the titanium metal matrix is cleaned as follows: the titanium metal matrix is placed in ultrapure water for ultrasonic treatment for 10-30min, and then dried in an oven at 60-90℃ for 10-30min.

[0017] The application also protects the use of the titanium metal matrix surface oxygen gradient composite oxide coating in the preparation of a metal bipolar plate surface protective coating for a fuel cell.

[0018] Compared with the prior art, the application has the following beneficial effects: 1、The present application is first in-situ oxidation on the titanium metal substrate, forming a TiO x 2 film on the outer surface of the titanium metal substrate, and then using a controllable partial reduction process (hydrogen plasma reduction method or Ti powder hot reduction method) to form a TiO x 2-TiO x x<2) coating, that is, to build an oxygen gradient composite oxide coating with an increasing and then decreasing oxygen concentration on the surface of the titanium metal substrate, the coating and the titanium metal substrate are combined to form a continuous Ti-TiO x 2-TiO x 2-TiO x 2 film, which has good adhesion with the titanium metal substrate, the TiO x 2 in the inner layer is a transition phase from metal Ti to insulating TiO2, and its thermal expansion coefficient is between metal Ti (titanium metal substrate) and TiO2, which can effectively relieve the interface stress caused by the difference in thermal expansion, such as the thermal expansion coefficient of α-Ti is 8.6×10 -6 K -1 , the calculated thermal expansion coefficient of TiO2 is 6.55×10 -6 K -1 , the thermal expansion coefficients of TiO, TiO 1 / 2 (Ti2O) and TiO 1 / 3 (Ti3O) are 8.22×10 -6 K -1 , 8.01×10 - 6 K -1 and 6.81×10 -6 K -1 , respectively, disclosed in Tang, S. L., Li, Y. F., Wang, Y. R., Gao, Y. M., Zheng, Q. L., &Yi, D. W. (2018). Theoretical study of mechanical and thermodynamic properties of titanium oxides TixOy. Materials Chemistry and Physics, 213 , 538-547. TiO2 with excellent corrosion resistance provides a corrosion-resistant barrier, and non-stoichiometric TiO x obtained by hydrogen plasma reduction method or Ti powder hot reduction method on the surface of TiO x 2 film has good electrical conductivity, effectively reduces the interface contact resistance of the gradient coating, and at the same time, the TiO x 2 in the surface layer wraps the TiOx Further oxidation.

[0019] 2. The contact resistance of the oxygen gradient composite oxide coating on the titanium metal substrate prepared by this invention is reduced by two-thirds compared to the contact resistance of the titanium metal substrate, and is less than 10 mΩ·cm. 2 Furthermore, the contact resistance is significantly lower than that of the TiO2-based coating on the surface of titanium after in-situ oxidation. Electrochemical tests conducted under simulated fuel cell conditions (80℃, 0.5 mmol / L H2SO4 solution + 5 ppm HF solution) showed that the corrosion current density of the oxygen gradient composite oxide coating on the titanium substrate surface was <0.2 μA·cm⁻¹. -2 The corrosion current is reduced by at least an order of magnitude compared to that of titanium metal substrates.

[0020] 3. The preparation method of the present invention is simple and efficient, and can significantly improve the conductivity of titanium metal plates and their corrosion resistance in fuel cell environments. Attached Figure Description

[0021] Figure 1 The image shows the XRD phase diagram of the oxygen gradient composite oxide coating on the surface of the titanium metal substrate in Example 1.

[0022] Figure 2 This is a cross-sectional EDS line scan of the oxygen gradient composite oxide coating on the surface of the titanium metal substrate in Example 1.

[0023] Figure 3 The image shows the XRD phase diagram of the oxygen gradient composite oxide coating on the surface of the titanium metal substrate in Example 2.

[0024] Figure 4 This is a cross-sectional EDS line scan of the oxygen gradient composite oxide coating on the surface of the titanium metal substrate in Example 2.

[0025] Figure 5 The interface contact resistance diagrams are for the oxygen gradient composite oxide coating on the surface of the titanium metal substrate in Examples 1 and 2, the titanium metal substrate in Comparative Example 1, and the titanium oxide alloy substrate in Comparative Example 2.

[0026] Figure 6 The graphs show the potentiodynamic polarization curves of the titanium metal substrate surface with oxygen gradient composite oxide coating in Examples 1 and 2, and the titanium metal substrate in Comparative Example 1, under a simulated fuel cell environment. Detailed Implementation

[0027] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. Unless otherwise specified, the experimental methods described in the embodiments of the present invention are conventional methods.

[0028] In this invention, the oxygen gradient composite oxide coating on the titanium metal substrate surface exhibits an oxygen gradient distribution characteristic along the coating growth direction. From the titanium metal substrate to the coating, the oxygen concentration first increases and then decreases, resulting in a TiO₂ concentration. x -TiO2-TiO x (x<2, TiO) x Not limited to one type of oxide, but a general term for a variety of oxides, including but not limited to TiO2. 3 / 2 That is, Ti2O3, TiO, TiO 1 / 2 That is, Ti2O and TiO 1 / 3 That is, Ti3O, TiO 1 / 6 That is, Ti6O), the coating bonds with the titanium metal substrate to form a continuous Ti-TiO. x -TiO2-TiO x Composite structure. This invention also provides a method for preparing an oxygen gradient composite oxide coating on a titanium metal substrate surface: firstly, TiO2 is prepared on the titanium metal substrate surface using a high-temperature in-situ oxidation method. x - A TiO2 film was formed, and then TiO2 was partially reduced to TiO2 using hydrogen plasma reduction or Ti partial thermal reduction. X TiO x -TiO2-TiO x The composite coating. The TiO2 in the composite coating has excellent corrosion resistance, and the inner TiO2 layer... x As a transition phase from metallic Ti to insulating TiO2, its coefficient of thermal expansion lies between that of metallic Ti (titanium metal matrix) and TiO2. This effectively alleviates interfacial stress caused by differences in thermal expansion, allowing for the in-situ oxidation of TiO2. x - The TiO2 film exhibits good adhesion to the titanium metal substrate, and the TiO2 on the surface of the composite coating... x The presence of oxygen vacancies results in excellent electrical conductivity, and the incomplete reduction of TiO2 leads to the formation of high conductivity in TiO2. x TiO2 is encapsulated in TiO2. x This creates conductive pathways, enhancing the conductivity of the composite coating while also preventing the formation of Ti. 2+ and Ti 3+ Further oxidation.

[0029] The following exemplarily illustrates a method for preparing a corrosion-resistant conductive gradient oxide coating.

[0030] Step 1: In-situ high-temperature oxidation of titanium metal substrate: The cleaned titanium metal substrate is subjected to high-temperature holding treatment in an air or oxygen atmosphere to form TiO2 in-situ on the titanium metal surface. x -TiO2 oxide film, to obtain titanium oxide metal matrix.

[0031] Step 2: Partial reduction of TiO2 using hydrogen plasma or Ti powder: For partial reduction using plasma, the titanium oxide metal matrix is ​​placed in a device equipped with a plasma generator and heating apparatus. Hydrogen and carrier gas are introduced, and the plasma generator activates the hydrogen to form hydrogen plasma. Then, the hydrogen plasma reacts with TiO2... x The TiO2 oxide film undergoes a reduction reaction, with the surface oxide film reduced by a high concentration of hydrogen plasma, resulting in a low oxygen content. The oxide film closer to the titanium substrate is partially reduced by a small amount of diffused plasma, resulting in a high oxygen content. When using Ti powder for partial reduction, the titanium oxide substrate is placed in a mixture of Ti powder and TiO2 powder, and calcined at high temperature under high vacuum. The oxide film on the surface of the titanium substrate is thermally reduced by the Ti powder at high temperature. The powder ratio and calcination time control the degree of reduction. The oxygen gradient composite oxide coating on the titanium substrate surface obtained by these two methods exhibits good electrical conductivity due to the high concentration of oxygen defects on the surface, while the incompletely reduced TiO2 also provides good corrosion resistance.

[0032] The oxygen gradient composite oxide coating on the surface of the titanium metal substrate prepared by this invention can be used alone as a conductive and corrosion-resistant coating for the titanium metal substrate, or as a transition layer for composite coatings, such as a transition layer between a carbon coating and a titanium metal substrate, because the in-situ oxidation and reduction of TiO2... x - The TiO2 oxide film has good adhesion to the substrate, and the oxygen vacancy defect layer on the surface has high activity, which greatly improves the adhesion of the carbon-coated titanium substrate.

[0033] The technical solution of the present invention will be studied below using examples and comparative examples. The specific research methods and results are shown below: Example 1 A method for preparing an oxygen gradient composite oxide coating on a titanium metal substrate includes the following steps: S1. Clean the metal substrate. The metal substrate is a TA1 titanium metal substrate (size 50mm×50mm×0.1mm). The metal substrate is ultrasonically cleaned with ultrapure water for 10 minutes. After cleaning, the metal substrate is placed in an oven at 80℃ and dried for 20 minutes to obtain a clean and dry titanium metal substrate.

[0034] S2. Place the titanium metal substrate in a tube furnace, introduce air, and heat at 700℃ for 3 hours to form TiO2 in situ oxidation on the surface of the titanium metal substrate. x -TiO2 film was obtained to obtain titanium oxide alloy substrate.

[0035] S3. Place the titanium oxide alloy substrate into a heating furnace equipped with a DC plasma generator, and evacuate to a vacuum level of 6×10⁻⁶. -4 After Pa, hydrogen and argon were introduced as reactant gases, with a flow rate of 40 sccm and a flow rate of 20 sccm. The temperature was then increased to 600°C. The DC plasma generator was then turned on with a power setting of 200W. After the gas ionization produced a noticeable glow, reduction began. After 30 minutes of treatment, the DC plasma generator was turned off and the temperature was lowered to room temperature. At this point, the previously formed TiO2 was partially reduced, forming an oxygen gradient composite oxide coating on the surface of the titanium metal substrate.

[0036] XRD tests were performed on the oxygen gradient composite oxide coating (metal bipolar plate coating) on ​​the titanium metal substrate surface obtained in Example 1, and the results are as follows: Figure 1 As shown, the detected oxides are TiO2 and Ti3O (corresponding to TiO2). x Writing TiO 1 / 3 ) and Ti6O (corresponding to TiO) x Writing TiO 1 / 6 ).like Figure 2 The energy dispersive spectroscopy (EDS) results show that the oxygen content gradually increases and then gradually decreases from the substrate to the surface, exhibiting a gradient distribution characteristic of oxygen concentration. Therefore, the actual structure of the oxygen gradient composite oxide coating on the titanium metal substrate surface should be (TiO2) 1 / 3 TiO 1 / 6 )-TiO2-(TiO 1 / 3 TiO 1 / 6 The interfacial contact resistance of the oxygen gradient composite oxide coating on the titanium substrate surface in Example 1 was tested at a pressure of 1.4 MPa. Figure 5 As shown, the obtained surface contact resistance is 6.78 mΩ·cm. 2 The electrodynamic polarization curve was tested in a simulated environment of 0.5 mmol / L H2SO4 solution + 5 ppm HF solution at 80℃, and the corrosion current density was found to be 0.11 μA·cm. -2 The corrosion current density of the titanium metal matrix is ​​2.5 μA·cm. -2 Reduce by an order of magnitude, such as Figure 6 As shown.

[0037] Example 2 A method for preparing an oxygen gradient composite oxide coating on a titanium metal substrate includes the following steps: S1. Clean the metal substrate. The metal substrate is a TA1 titanium metal substrate (size 50mm×50mm×0.1mm). The metal substrate is ultrasonically cleaned with ultrapure water for 10 minutes. After cleaning, the metal substrate is placed in an oven at 80℃ and dried for 20 minutes to obtain a clean and dry titanium metal substrate.

[0038] S2. Place the titanium metal substrate in a tube furnace, introduce air, and heat at 700℃ for 3 hours to form TiO2 in situ oxidation on the surface of the titanium metal substrate. x -TiO2 film was obtained to obtain titanium oxide alloy substrate.

[0039] S3. Place the titanium oxide alloy matrix into a mixture of Ti powder and TiO2 powder, with a mass ratio of Ti powder to TiO2 powder of 1:6. After weighing, grind and mix the mixture evenly using a mortar and pestle. Pour the mixture into an alumina crucible, and spread the mixed powder evenly on both the upper and lower surfaces of the titanium oxide alloy matrix. Use an alumina pad to compact and fix the top of the crucible, and then seal the top of the crucible. Place the crucible in a heating furnace and evacuate it to a vacuum level of <10. -3 After Pa, argon gas is introduced for protection, the temperature is raised to 880℃ and held for 10 minutes, and then cooled. At this time, the previously formed TiO2 is partially reduced, forming an oxygen gradient composite oxide coating on the surface of the titanium metal substrate.

[0040] XRD tests were performed on the oxygen gradient composite oxide coating (metal bipolar plate coating) on ​​the titanium metal substrate surface obtained in Example 2, and the results are as follows: Figure 3 As shown, the detected oxides are TiO2 and Ti3O (corresponding to TiO2). x Writing TiO 1 / 3 ).like Figure 4 The energy dispersive spectroscopy (EDS) results show that the oxygen content gradually increases and then gradually decreases from the substrate to the surface, exhibiting a gradient distribution characteristic of oxygen concentration. Therefore, the actual structure of the oxygen gradient composite oxide coating on the titanium metal substrate surface should be TiO2. 1 / 3 -TiO2-TiO 1 / 3 The interfacial contact resistance of the oxygen gradient composite oxide coating on the titanium substrate surface in Example 2 was tested at a pressure of 1.4 MPa. Figure 5 As shown, the obtained surface contact resistance is 7.23 mΩ·cm. 2 The electrodynamic polarization curve was tested in a simulated environment of 0.5 mmol / L H2SO4 solution + 5 ppm HF solution at 80℃, and the corrosion current density was found to be 0.2 μA·cm. -2 The corrosion current density of the titanium metal matrix is ​​2.5 μA·cm. -2 Reduce by an order of magnitude, such as Figure 6 As shown.

[0041] Example 3 A method for preparing an oxygen gradient composite oxide coating on a titanium metal substrate includes the following steps: S1. Clean the metal substrate. The metal substrate is a TA1 titanium metal substrate (size 50mm×50mm×0.1mm). The metal substrate is ultrasonically cleaned with ultrapure water for 20 minutes. After cleaning, the metal substrate is placed in an oven at 60℃ and dried for 30 minutes to obtain a clean and dry titanium metal substrate.

[0042] S2. Place the titanium metal substrate in a tube furnace, introduce air, and heat at 500℃ for 7 hours to form TiO2 in situ on the surface of the titanium metal substrate. x -TiO2 film was obtained to obtain titanium oxide alloy substrate.

[0043] S3. Place the titanium oxide alloy substrate into a heating furnace equipped with a DC plasma generator, and evacuate to a vacuum level of 6×10⁻⁶. -4 After Pa, hydrogen and argon were introduced as reaction gases, with a flow rate of 20 sccm and a flow rate of 50 sccm. The temperature was then increased to 500°C. The DC plasma generator was then turned on and set to 300W. After the gas ionization produced a noticeable glow, reduction began. After 10 minutes of treatment, the DC plasma generator was turned off and the temperature was lowered to room temperature. At this point, the previously formed TiO2 was partially reduced, forming an oxygen gradient composite oxide coating on the surface of the titanium metal substrate.

[0044] Example 4 A method for preparing an oxygen gradient composite oxide coating on a titanium metal substrate includes the following steps: S1. Clean the metal substrate. The metal substrate is a TA1 titanium metal substrate (size 50mm×50mm×0.1mm). The metal substrate is ultrasonically cleaned with ultrapure water for 30 minutes. After cleaning, the metal substrate is placed in an oven at 90℃ and dried for 10 minutes to obtain a clean and dry titanium metal substrate.

[0045] S2. Place the titanium metal substrate in a tube furnace, introduce air, and heat at 600℃ for 5 hours to form TiO2 in situ on the surface of the titanium metal substrate. x -TiO2 film was obtained to obtain titanium oxide alloy substrate.

[0046] S3. Place the titanium oxide alloy substrate into a heating furnace equipped with a DC plasma generator, and evacuate to a vacuum level of 6×10⁻⁶. -4After Pa, hydrogen and argon were introduced as reactant gases, with a flow rate of 40 sccm and a flow rate of 100 sccm. The temperature was then increased to 800°C. The DC plasma generator was then turned on with a power setting of 400W. After the gas ionization produced a noticeable glow, reduction began. After 5 minutes of treatment, the DC plasma generator was turned off and the temperature was lowered to room temperature. At this point, the previously formed TiO2 was partially reduced, forming an oxygen gradient composite oxide coating on the surface of the titanium metal substrate.

[0047] Example 5 A method for preparing an oxygen gradient composite oxide coating on a titanium metal substrate includes the following steps: S1. Clean the metal substrate. The metal substrate is a TA1 titanium metal substrate (size 50mm×50mm×0.1mm). The metal substrate is ultrasonically cleaned with ultrapure water for 20 minutes. After cleaning, the metal substrate is placed in an oven at 60℃ and dried for 30 minutes to obtain a clean and dry titanium metal substrate.

[0048] S2. Place the titanium metal substrate in a tube furnace, introduce air, and heat at 500℃ for 7 hours to form TiO2 in situ on the surface of the titanium metal substrate. x -TiO2 film was obtained to obtain titanium oxide alloy substrate.

[0049] S3. Place the titanium oxide alloy matrix into a mixture of Ti powder and TiO2 powder, with a mass ratio of Ti powder to TiO2 powder of 1:3. After weighing, grind and mix the mixture evenly using a mortar and pestle. Pour the mixture into an alumina crucible, and spread the mixed powder evenly on both the upper and lower surfaces of the titanium oxide alloy matrix. Use an alumina pad to compact and fix the top of the crucible, and then seal the top of the crucible. Place the crucible in a heating furnace and evacuate it to a vacuum level of <10. -3 After Pa, argon gas is introduced for protection, the temperature is raised to 800℃ and held for 60 minutes, and then cooled. At this time, the previously formed TiO2 is partially reduced, forming an oxygen gradient composite oxide coating on the surface of the titanium metal substrate.

[0050] Example 6 A method for preparing an oxygen gradient composite oxide coating on a titanium metal substrate includes the following steps: S1. Clean the metal substrate. The metal substrate is a TA1 titanium metal substrate (size 50mm×50mm×0.1mm). The metal substrate is ultrasonically cleaned with ultrapure water for 30 minutes. After cleaning, the metal substrate is placed in an oven at 90℃ and dried for 10 minutes to obtain a clean and dry titanium metal substrate.

[0051] S2. Place the titanium metal substrate in a tube furnace, introduce air, and heat at 600℃ for 1 hour to form TiO2 in situ on the surface of the titanium metal substrate. x -TiO2 film was obtained to obtain titanium oxide alloy substrate.

[0052] S3. Place the titanium oxide alloy matrix into a mixture of Ti powder and TiO2 powder, with a mass ratio of Ti powder to TiO2 powder of 1:7. After weighing, grind and mix the mixture evenly using a mortar and pestle. Pour the mixture into an alumina crucible, and spread the mixed powder evenly on both the upper and lower surfaces of the titanium oxide alloy matrix. Use an alumina pad to compact and fix the top of the crucible, and then seal the top of the crucible. Place the crucible in a heating furnace and evacuate it to a vacuum level of <10. -3 After Pa, argon gas is introduced for protection, the temperature is raised to 900℃ and held for 5 minutes, and then cooled. At this time, the previously formed TiO2 is partially reduced, forming an oxygen gradient composite oxide coating on the surface of the titanium metal substrate.

[0053] Comparative Example 1 A method for preparing a titanium metal matrix, wherein the titanium metal matrix is ​​prepared by step S1 of Example 1, including the following steps: The metal substrate, a TA1 titanium metal substrate (50mm×50mm×0.1mm in size), was cleaned by ultrasonic cleaning with ultrapure water for 10 minutes. After cleaning, the metal substrate was placed in an oven at 80℃ and dried for 20 minutes to obtain a clean and dry titanium metal substrate.

[0054] Comparative Example 2 The method for preparing a titanium oxide alloy matrix, wherein the titanium oxide alloy matrix is ​​obtained by steps S1 and S2 of Example 1, includes the following steps: S1. Clean the metal substrate. The metal substrate is a TA1 titanium metal substrate (size 50mm×50mm×0.1mm). The metal substrate is ultrasonically cleaned with ultrapure water for 10 minutes. After cleaning, the metal substrate is placed in an oven at 80℃ and dried for 20 minutes to obtain a clean and dry titanium metal substrate.

[0055] S2. Place the titanium metal substrate in a tube furnace, introduce air, and heat at 700℃ for 3 hours to form TiO2 in situ oxidation on the surface of the titanium metal substrate. x -TiO2 film was obtained to obtain titanium oxide alloy substrate.

[0056] Interfacial contact resistance was tested on the titanium dioxide alloy matrix of Comparative Example 2 at a pressure of 1.4 MPa. Figure 5 As shown, the obtained surface contact resistance is 6.53 × 10⁻⁶. 6 mΩ·cm 2The oxygen gradient composite oxide coating on the surface of the titanium metal substrate in Comparative Example 1 is significantly higher than that on the partially reduced titanium metal substrate surface in Examples 1 and 2. This comparison demonstrates that TiO2 is not suitable for direct use as the outermost coating of a metal bipolar plate, and that the outermost TiO2 in the composite oxide structure... x The layer can significantly improve its conductivity.

[0057] Figure 6 To test the potentiodynamic curves of the oxygen gradient composite oxide coatings on the titanium substrates of Examples 1 and 2, and the titanium substrate of Comparative Example 1, under a simulated fuel cell environment (80°C, 0.5 mmol / L H₂SO₄ + 5 ppm HF), the corrosion current densities of the oxygen gradient composite oxide coatings on the titanium substrates of Examples 1 and 2, and the titanium substrate of Comparative Example 1, were obtained by extrapolation from Tafel curves. -2 0.2μA·cm -2 and 2.5 μA·cm -2 That is, the corrosion current density of the oxygen gradient composite oxide coating on the surface of the titanium metal substrate prepared by the method of the present invention is reduced by an order of magnitude compared with the titanium metal substrate, and it has good corrosion resistance.

[0058] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. An oxygen gradient composite oxide coating on a titanium metal substrate surface, characterized in that, The oxygen gradient composite oxide coating on the titanium metal substrate is an in-situ grown coating on the titanium metal substrate. In the coating, the oxygen concentration first increases and then decreases from the titanium metal substrate outwards, and the structure is TiO2. x -TiO2-TiO x , where x < 2.

2. The oxygen gradient composite oxide coating on the titanium metal substrate surface according to claim 1, characterized in that, TiO x TiO 3 / 2 TiO, TiO 1 / 2 TiO 1 / 3 TiO 1 / 6 One or more of them.

3. The oxygen gradient composite oxide coating on the titanium metal substrate surface according to claim 1, characterized in that, In the oxygen gradient composite oxide coating on the surface of a titanium metal substrate, the inner layer of TiO2... x As a transition phase from metallic Ti to insulating TiO2, its coefficient of thermal expansion is between that of metallic Ti and TiO2, which helps to alleviate interfacial stress caused by the difference in thermal expansion. TiO2 is used for corrosion resistance; the outer layer of TiO x The presence of oxygen vacancies and oxygen defects facilitates electrical conductivity, and the outer TiO₂ layer... x Encapsulated by TiO2.

4. A method for preparing an oxygen gradient composite oxide coating on a titanium metal substrate surface as described in claim 1, characterized in that, Includes the following steps: In-situ oxidation heat treatment of titanium metal substrate in an oxygen environment forms TiO2 on the outer surface of the titanium metal substrate. x -TiO2 film, to obtain titanium oxide alloy substrate; TiO2 is reduced using hydrogen plasma reduction or Ti powder thermal reduction. x - The TiO2 on the TiO2 film undergoes partial reduction, forming an oxide phase TiO2 on the outer side of the TiO2 film. x And the outer TiO x Encapsulated by TiO2, resulting in a TiO structure. x -TiO2-TiO x Oxygen gradient composite oxide coating on titanium metal substrate surface.

5. The method for preparing an oxygen gradient composite oxide coating on a titanium metal substrate according to claim 4, characterized in that, The oxygen environment is oxygen with a purity of ≥99% or dry air.

6. The method for preparing an oxygen gradient composite oxide coating on a titanium metal substrate according to claim 4, characterized in that, The conditions for in-situ oxidation heat treatment are: treatment at 500℃~700℃ for 1h~7h.

7. The method for preparing an oxygen gradient composite oxide coating on a titanium metal substrate according to claim 4, characterized in that, The operation of the hydrogen plasma reduction method is as follows: A titanium oxide metal substrate is placed in a device equipped with a plasma generator and heating apparatus, prior to a vacuum degree ≤10... -3 Under Pa conditions, a mixture of argon and hydrogen is introduced. When the heating device is heated to 500℃~800℃, a plasma generator is used for discharge plasma treatment. The power of the plasma generator is 200W~400W, and the discharge plasma treatment time is 5min~60min. The flow rate of argon is 20 sccm to 100 sccm, and the flow rate of hydrogen is 20 sccm to 40 sccm.

8. The method for preparing an oxygen gradient composite oxide coating on a titanium metal substrate according to claim 4, characterized in that, The operation of the Ti powder thermal reduction method is as follows: A titanium oxide alloy matrix is ​​placed in a mixed powder composed of Ti and TiO2, and the mixture is subjected to a vacuum degree <10... -3 Calcination at 800℃~900℃ for 5min~60min; The mass ratio of Ti to TiO2 is 1:3 to 1:

7.

9. The application of the oxygen gradient composite oxide coating on the surface of a titanium metal substrate as described in claim 1 in the preparation of a protective coating for the surface of a metal bipolar plate for fuel cells.

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