An Al-doped transition metal nitride composite coating, a preparation method thereof and an application thereof

Abstract

The present invention discloses an Al-doped transition metal nitride composite coating, a preparation method and an application thereof, belonging to the technical field of surface engineering protection. The present invention provides an Al-doped transition metal nitride composite coating, which is a titanium nitride coating and a titanium aluminum nitride coating sequentially deposited from bottom to top on a substrate; the thickness of the Al-doped transition metal nitride composite coating is 240 nm to 270 nm. The Al-doped transition metal nitride composite coating of the present invention does not need to use precious metals, reduces costs, and at the same time has excellent electrical conductivity and corrosion resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of surface engineering protection, and more particularly to an Al-doped transition metal nitride composite coating, a preparation method and an application thereof. Background Art

[0002] Hydrogen energy has advantages such as high energy density, water as the combustion product, and no harmful substance emissions. At present, in the hydrogen production industry, electrolysis of water to produce hydrogen accounts for about 3% of the annual hydrogen production scale, which is the most environmentally friendly and efficient preparation method with rich raw materials and environmental friendliness.

[0003] The proton exchange membrane water electrolyzer has increasingly obvious advantages of high efficiency, small volume, flexible control, fast response, compact system design and extended dynamic operation range, and has become the focus of research and development in the field of green hydrogen production.

[0004] As a key component of the proton exchange membrane water electrolyzer, the bipolar plate not only provides mechanical support and current distribution for the membrane electrode assembly, but also provides necessary gas-liquid channels to ensure the normal transmission and uniform distribution of water and gas, and also occupies most of the volume and cost, accounting for about 70% of the overall mass and 30% of the price.

[0005] Due to the high oxygen potential at the anode of the electrolyzer, the oxidative reactive oxygen generated during the water electrolysis process, and the chemical and electrochemical corrosion in the acidic environment, the proton exchange membrane water electrolysis bipolar plate must have high mechanical strength, high corrosion resistance, low interfacial contact resistance, light weight and effective manufacturability. At present, graphite, metal and polymer blends with carbon are three candidate materials for bipolar plates. Dense graphite can meet most of the requirements of the bipolar plate. However, it has challenges such as toughness, corrosion at high potentials >1.5V in the water electrolysis mode, and poor manufacturability. Polymers blended with carbon have advantages in effective manufacturability, but still suffer from poor electron conductivity. Therefore, metal is a good alternative candidate for bipolar plates because of its excellent manufacturability, gas and water impermeability, high thermal conductivity and electrical conductivity, and cost effectiveness.

[0006] In the working environment of a proton exchange membrane water electrolyzer, due to anodic oxidation, a semi-conductive oxide will form on the surface of the metal bipolar plate, which has a negative impact on the performance and durability of the electrolyzer. Once corrosion occurs, metal ions that may poison the catalyst and the proton exchange membrane will be released, reducing the output power and service life of the fuel cell. At the same time, the surface of the metal bipolar plate reacts with oxygen to form a passivation oxide layer. This layer increases the contact resistance between the bipolar plate and the electrode, and the battery performance is significantly reduced. Therefore, it is necessary to modify the surface of the metal bipolar plate with a conductive and corrosion-resistant material, and surface coating is the most commonly used modification method; among them, in order to have both high conductivity and high corrosion resistance, researchers introduce precious metals into the surface coating, and the loading range of the precious metals is still 1mg·cm -2 ~3mg·cm -2 , and the cost is relatively high. Summary of the Invention

[0007] Aiming at the above problems, the present invention provides an Al-doped transition metal nitride composite coating, a preparation method and an application thereof. The Al-doped transition metal nitride composite coating of the present invention does not require the use of precious metals, reduces costs, and at the same time has excellent electrical conductivity and corrosion resistance.

[0008] The first object of the present invention is to provide an Al-doped transition metal nitride composite coating, and the Al-doped transition metal nitride composite coating is a titanium nitride coating and a titanium aluminum nitride coating sequentially deposited from bottom to top on a substrate; the thickness of the Al-doped transition metal nitride composite coating is 240nm~270nm.

[0009] In the structure of the Al-doped transition metal nitride composite coating of the present invention, the titanium nitride coating is the coating relatively close to the bipolar plate, and the titanium aluminum nitride coating is the coating relatively far from the bipolar plate. Specifically exemplary, the transition metal compound composite coating is deposited on the surface of the bipolar plate, and the material of the bipolar plate is titanium alloy or stainless steel; for explanatory purposes, when the material is titanium alloy, the titanium nitride coating in the transition metal compound composite coating is the first layer coating deposited on the surface of the metal substrate, and the titanium aluminum nitride coating is deposited after the titanium nitride coating; the titanium nitride coating is considered to be the reinforcement layer in the double-layer coating because titanium nitride may provide self-healing characteristics for the entire coating. Therefore, the oxidation of the metal substrate inside the coating can solve the defects in other coatings.

[0010] During the deposition process, the double-layer coating structure can truncate the growth of columnar crystals, improve the dislocation of defects such as pores in the single-layer coating, improve the coating density, and adjust the pore defect matching degree between the coatings by changing the modulation ratio of the titanium nitride coating and the titanium aluminum nitride coating to improve the electrical conductivity and corrosion resistance of the bipolar plate.

[0011] In a preferred embodiment of the present invention, the preferred crystal plane orientation of the titanium nitride coating is (200), and the thickness of the titanium nitride coating is 90 nm to 180 nm.

[0012] In a preferred embodiment of the present invention, the preferred crystal plane orientation of the titanium aluminum nitride coating is (200), and the thickness of the titanium aluminum nitride coating is 90 nm to 180 nm.

[0013] The second object of the present invention is to provide a method for preparing the above-mentioned Al-doped transition metal nitride composite coating, comprising the following steps:

[0014] Under a protective gas atmosphere, using a titanium nitride target as the target, a first pulsed laser deposition is performed on the surface of the substrate to form a titanium nitride coating.

[0015] Under a protective gas atmosphere, using a titanium aluminum nitride target as the target, a second pulsed laser deposition is performed on the surface of the titanium nitride coating to form a titanium aluminum nitride coating, obtaining an Al-doped transition metal nitride composite coating.

[0016] In a preferred embodiment of the present invention, in the first pulsed laser deposition, the pressure in the reaction chamber is 2 Pa to 4 Pa, the deposition temperature is 400 °C, and the deposition time is 800 s to 1000 s.

[0017] In a preferred embodiment of the present invention, in the second pulsed laser deposition, the pressure in the reaction chamber is 2 Pa to 4 Pa, the deposition temperature is 400 °C, and the deposition time is 1000 s to 1200 s.

[0018] In a preferred embodiment of the present invention, the titanium aluminum nitride target is composed of the following components by mass percentage: 6% aluminum and 94% titanium nitride.

[0019] In a preferred embodiment of the present invention, the purity of the titanium nitride target is 99.9%, and the purity of the titanium aluminum nitride target is 99.9%.

[0020] The third object of the present invention is to provide the application of the above-mentioned Al-doped transition metal nitride composite coating in a proton exchange membrane fuel cell or a proton exchange membrane water electrolyzer.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The Al-doped transition metal nitride composite coating provided by the present invention is composed of a titanium nitride coating and a titanium aluminum nitride coating deposited in sequence, forming a composite double-layer structure, which improves the denseness of the coating; titanium nitride and titanium aluminum nitride form a double-layer structure, and when deposited on a substrate, it can effectively reduce the probability that corrosive media in the electrolyte penetrate the coating through pore defects and other channels, and then corrode the substrate, ultimately leading to coating failure; the Al-doped transition metal nitride composite coating of the present invention has excellent electrical conductivity and corrosion resistance when deposited, avoids the use of precious metals, reduces the manufacturing cost, and significantly extends the service life of the substrate.

[0023] The lattice parameters of titanium nitride and aluminum nitride are 0.424 nm and 0.412 nm respectively. The substitution of Al atoms for Ti atoms results in changes in the internal stress and lattice deformation of the titanium aluminum nitride coating, causing the overall right shift of the X-ray diffraction peak of the titanium aluminum nitride coating. After doping a third element Al into the titanium nitride hard coating, due to the formation of Al2O3, excellent temperature, oxidation resistance and mechanical properties, the corrosion resistance of titanium aluminum nitride can be improved. The titanium nitride coating with relatively low hardness and high corrosion resistance is considered as an adhesive coating between the metal substrate and the outermost layer. The titanium nitride coating is the reinforcement layer in the coating because titanium nitride may provide self-healing characteristics for the entire coating. Therefore, the oxidation of the metal substrate inside the coating can solve the defects in other coatings. Due to the hardness, good electrical conductivity and excellent corrosion resistance of the titanium aluminum nitride, it can be used as the outer layer.

[0024] The present invention prepares an Al-doped transition metal nitride composite coating with both high conductivity and high corrosion resistance through a pulsed laser deposition process. This coating adopts the pulsed laser deposition process, which ensures the homogeneity of the phase and improves the denseness of the coating at the same time. In the pulsed laser deposition of the present invention, after changing the coating process, parameters such as nitrogen gas pressure, substrate temperature, and deposition time, a single-layer coating with uniform composition and phase is obtained, avoiding the generation of multiple phases in the single layer, reducing the influence of impurity phases, and ensuring the corrosion resistance of the coating; in addition, a double-layer structure of an Al-doped transition metal compound composite coating is prepared by sequentially depositing a titanium nitride coating and a titanium aluminum nitride coating. Through the double-layer design, the pores and other defects in each layer are effectively misaligned, improving the denseness of the coating and effectively reducing the probability that corrosive media in the electrolyte penetrate the coating through pores and other defects to corrode the substrate, thereby causing coating failure. Description of the Drawings

[0025] Figure 1 It is a schematic diagram of the Al-doped transition metal nitride composite coating in the present invention.

[0026] Figure 2 It is a surface scan of the Al-doped transition metal nitride composite coating prepared in Example 1 of the present invention.

[0027] Figure 3 It is a cross-sectional scanning image of the Al-doped transition metal nitride composite coating prepared in Example 1 of the present invention.

[0028] Figure 4 It is a comparison graph of the potentiodynamic scanning test results of Example 1 to Example 2 and Comparative Example 1 - Comparative Example 2 of the present invention.

[0029] Figure 5 It is a comparison graph of the interface contact resistance test results of Example 1 to Example 2 and Comparative Example 2 of the present invention. The inset is Figure 5 a partial enlarged view of.

[0030] Reference numerals: 1 - substrate, 2 - titanium nitride coating, 3 - titanium aluminum nitride coating. Detailed implementation manners

[0031] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0032] In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units does not necessarily have to be limited to those clearly listed steps or units, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0033] In the market, by modifying the surface of the metal bipolar plate by coating with noble metals, the corrosion current density of the obtained metal bipolar plate is basically lower than 1×10 -7 A·cm -2 . However, the presence of noble metals results in high preparation costs. Based on this, the present invention provides an Al-doped transition metal nitride composite coating that takes into account high conductivity and high corrosion resistance. Please refer to Figure 1 The Al-doped transition metal nitride composite coating provided by the present invention has a bilayer structure, including a titanium nitride coating and a titanium aluminum nitride coating deposited in sequence.

[0034] The Al-doped transition metal nitride composite coating provided by the present invention is used to be deposited on the surface of a substrate. It is composed of a titanium nitride coating and a titanium aluminum nitride coating deposited in sequence to form a double-layer structure, thereby improving the density of the coating. In the coating provided by an embodiment of the present invention, titanium nitride and titanium aluminum nitride are selected to form a double-layer structure, which is deposited on the bipolar plate. This can effectively reduce the probability that the corrosive medium in the electrolyte penetrates the coating through pore defects and the like as channels, thereby corroding the substrate and ultimately causing coating failure. In this way, the bipolar plate can have both excellent electrical conductivity and corrosion resistance, which not only reduces the manufacturing cost of the bipolar plate, but also significantly extends the service life of the bipolar plate. The improvement measures of the present invention are of great significance for improving the performance, stability and economy of the overall equipment.

[0035] Example 1

[0036] This embodiment provides a method for preparing an Al-doped transition metal nitride composite coating that has both high conductivity and high corrosion resistance. The specific preparation steps are as follows:

[0037] S1. TA1 commercial titanium plate was selected as the substrate. The substrate was polished with SiC paper with particle sizes of 240#, 600#, 1000#, 2000# and 3000# in sequence, and then polished to a mirror finish with diamond polishing paste with a particle size of 0.5µm. The polished substrate was ultrasonically cleaned with acetone, alcohol and deionized water for 15 minutes respectively, and finally the substrate was naturally air-dried.

[0038] S2, the air-dried substrate is fixed on the sample stage and transferred into the deposition chamber. The substrate is heated to 400 ° C and the vacuum degree of the chamber is less than 2 × 10 -4 After 4 Pa, high-purity nitrogen is introduced and the nitrogen flow rate is adjusted to keep the nitrogen pressure at around 4 Pa; the deposition target is set to a titanium nitride target with a purity of 99.9%, the laser frequency is set to 8 Hz, the laser energy is 3342 mJ, the deposition time is 1000 s, and the laser switch is turned on to start depositing the titanium nitride coating.

[0039] S3. After the deposition of the titanium nitride coating is completed, the thickness of the titanium nitride coating is 127.67 nm. Turn off the laser switch and set the deposition target to a titanium aluminum nitride target with a purity of 99.9%. In the titanium aluminum nitride target, the mass percentage of Al is 6%, and the mass percentage of titanium nitride is 94%. The substrate temperature, nitrogen pressure, laser frequency and laser energy remain unchanged. The deposition time is 1000 s and the laser is turned on.

[0040] S4. Turn off the laser switch, cool naturally to room temperature, and take it out from the chamber. The thickness of the titanium aluminum nitride coating is 132.98 nm. Finally, an Al-doped transition metal nitride composite coating is deposited on the surface of the TA1 commercial titanium plate. The total thickness of the Al-doped transition metal nitride composite coating is 260.65 nm.

[0041] Figure 2 The surface scanning test results of the Al-doped transition metal nitride composite coating in Example 1 show that the surface of the prepared coating is complete and uniform. Figure 3 The cross-section scanning test results of the Al-doped transition metal nitride composite coating in Example 1 show that the prepared coating presents a columnar crystal structure.

[0042] The self-corrosion current density of this composite coating sample is about 1.0×10 -8 A·cm -2 , and at a working voltage of 2.0 V, its corrosion current density is less than 1×10 -7 A·cm -2 , comparable to or even better than noble metal coatings on the market; the interface contact resistance is about 8.55 mΩ·cm 2 . While maintaining high corrosion resistance, it also greatly improves the conductivity of the substrate, taking into account both high corrosion resistance and conductivity, and without the need to load noble metals.

[0043] Example 2

[0044] This example provides a preparation method for an Al-doped transition metal nitride composite coating that takes into account both high conductivity and high corrosion resistance. The specific preparation steps are as follows:

[0045] S1. Select a TA1 commercial titanium plate as the substrate. Polish the substrate successively with SiC papers of particle sizes 240#, 600#, 1000#, 2000# and 3000#, and then polish the surface of the substrate into a mirror state with diamond polishing paste of particle size 0.5 µm; ultrasonically clean the polished substrate with acetone, alcohol and deionized water, and the cleaning times are 15 min respectively. Finally, let the substrate air dry naturally.

[0046] S2. Fix the air-dried substrate on the sample stage and transfer it into the deposition chamber. Heat the substrate to 400 °C. After the chamber vacuum is less than 2×10 -4 Pa, introduce high-purity nitrogen gas, and adjust the nitrogen gas flow rate so that the nitrogen gas pressure remains at about 4 Pa; set the deposition target as a titanium nitride target with a purity of 99.9%, set the laser frequency to 8 Hz, the laser energy to 3342 mJ, the deposition time to 800 s, and turn on the laser switch to start depositing the titanium nitride coating.

[0047] S3. After the deposition of the titanium nitride coating is completed, the thickness of the titanium nitride coating is 121.64 nm. Turn off the laser switch, and set the deposition target as a titanium aluminum nitride target with a purity of 99.9%. Among them, in the titanium aluminum nitride target, the mass percentage of Al is 6% and the mass percentage of titanium nitride is 94%. Keep the substrate temperature, nitrogen gas pressure, laser frequency and laser energy unchanged, the deposition time is 1200 s, and turn on the laser.

[0048] S4. Turn off the laser switch, naturally cool to room temperature, take it out of the chamber. The thickness of the titanium aluminum nitride coating is 123.94 nm. Finally, an Al-doped transition metal nitride composite coating deposited on the surface of TA1 commercial titanium plate is obtained. The total thickness of the Al-doped transition metal nitride composite coating is 245.58 nm.

[0049] The self-corrosion current density of this coating sample is about 1.18×10 -8 A·cm -2 , and at a working voltage of 2.0 V, its corrosion current density is less than 5×10 -7 A·cm -2 , comparable to or even better than precious metal coatings on the market; the interface contact resistance is about 13.28 mΩ·cm 2 . While maintaining high corrosion resistance, it also greatly improves the conductivity of the substrate, taking into account both high corrosion resistance and conductivity, and without the need to load precious metals.

[0050] Compared with Example 1, in this example, after changing the deposition time, the modulation ratio of the titanium nitride coating and the titanium aluminum nitride coating changes, and the thicknesses of the two coatings change, which affects the matching degree of the coating pore defects.

[0051] Example 3

[0052] This example provides a preparation method of an Al-doped transition metal nitride composite coating that takes into account both high conductivity and high corrosion resistance. The specific preparation steps are as follows:

[0053] S1. Select a TA1 commercial titanium plate as the substrate. Polish the substrate successively with SiC papers with particle sizes of 240#, 600#, 1000#, 2000# and 3000#, and then polish the surface of the substrate into a mirror state with diamond polishing paste with a particle size of 0.5 µm; ultrasonically clean the polished substrate with acetone, alcohol and deionized water, and the cleaning times are 15 min respectively. Finally, let the substrate dry naturally.

[0054] S2. Fix the air-dried substrate on the sample stage and transfer it into the deposition chamber. Heat the substrate to 400 °C. After the chamber vacuum is less than 2×10 -4 Pa, introduce high-purity nitrogen, adjust the nitrogen flow rate to keep the nitrogen pressure at about 2 Pa; set the deposition target as a titanium nitride target with a purity of 99.9%, set the laser frequency to 8 Hz, the laser energy to 3342 mJ, the deposition time to 1000 s, and turn on the laser switch to start depositing the titanium nitride coating.

[0055] S3. After the deposition of the titanium nitride coating is completed, the thickness of the titanium nitride coating is 99.09 nm. Turn off the laser switch, and set the deposition target to a titanium aluminum nitride target with a purity of 99.9%. Among them, in the titanium aluminum nitride target, the mass percentage of Al is 6%, and the mass percentage of titanium nitride is 94%. The substrate temperature, laser frequency, and laser energy remain unchanged. The nitrogen gas pressure is 2 Pa, the deposition time is 1000 s, and turn on the laser.

[0056] S4. Turn off the laser switch, naturally cool to room temperature, take it out of the chamber. The thickness of the titanium aluminum nitride coating is 103.39 nm. Finally, an Al-doped transition metal nitride composite coating deposited on the surface of a TA1 commercial titanium plate is obtained. The total thickness of the Al-doped transition metal nitride composite coating is 202.48 nm.

[0057] The self-corrosion current density of this coating sample is about 1.04×10 -8 A·cm -2 , at a working voltage of 2.0 V, its corrosion current density is less than 5×10 -7 A·cm -2 , comparable to or even better than noble metal coatings on the market; the interface contact resistance is about 13.84 mΩ·cm 2 , while maintaining high corrosion resistance, it also greatly improves the conductivity of the substrate, taking into account both high corrosion resistance and conductivity, and without the need to load noble metals.

[0058] Compared with Example 1, in this example, the nitrogen gas pressure is changed. The influence of the nitrogen gas pressure on corrosion resistance is mainly caused by the influence on the surface morphology and crystallinity of the coating.

[0059] Comparative Example 1

[0060] In this comparative example, a TA1 commercial titanium plate without any treatment is used.

[0061] After testing, the self-corrosion current density of this coating sample is about 2.4×10 -4 A·cm -2 , at a working voltage of 2.0 V, its corrosion current density is about 1×10 -4 A·cm -2 , and the corrosion resistance is poor.

[0062] Comparative Example 2

[0063] In this comparative example, a single-layer titanium nitride coating prepared by magnetron reactive sputtering with optimized process parameters is used. The preparation method is as follows:

[0064] S1. Select a commercial TA1 titanium plate as the substrate. Polish the substrate successively with SiC papers of particle sizes 240#, 600#, 1000#, 2000#, and 3000#, and then polish the surface of the substrate into a mirror state with diamond polishing paste of particle size 0.5 µm. Ultrasonically clean the polished substrate with acetone, alcohol, and deionized water for 15 minutes each, and finally air-dry the substrate naturally.

[0065] S2. Fix the air-dried substrate on the sample stage and transfer it into the deposition chamber. Heat the substrate to 300 °C. After the chamber vacuum is less than 5×10 -4 Pa, introduce high-purity argon gas, and adjust the argon gas flow rate to keep it at about 20 sccm. Introduce high-purity nitrogen gas and adjust the nitrogen gas flow rate to keep it at about 6 sccm.

[0066] S3. Use a 99.99% pure titanium target as the target material, block the target with a target baffle, set the sputtering power to 100 W, and pre-sputter for 15 minutes to remove impurities such as oxides on the surface of the target.

[0067] S4. After the pre-sputtering is completed, remove the target baffle and start the formal sputtering deposition. During the deposition process, keep the sample stage rotating at a constant speed to make the deposition more uniform. The deposition time is 150 minutes, and the thickness of the deposited titanium nitride coating is 372.88 mm.

[0068] S5. Naturally cool to room temperature and take out the sample from the chamber.

[0069] After testing, the self-corrosion current density of this coating sample is about 5.9×10 -7 A·cm -2 , and at a working voltage of 2.0 V, its corrosion current density is about 1×10 -5 A·cm -2 , with good corrosion resistance. The interface contact resistance is about 261.56 mΩ·cm 2 , with poor conductivity. The noble metal loading is 0 mg·cm -2 .

[0070] Comparative Example 3

[0071] This comparative example provides a preparation method for an Al-doped transition metal nitride composite coating that takes into account both high conductivity and high corrosion resistance. The specific preparation steps are as follows:

[0072] S1. Select a commercial TA1 titanium plate as the substrate. Polish the substrate successively with SiC papers of particle sizes 240#, 600#, 1000#, 2000#, and 3000#, and then polish the surface of the substrate into a mirror state with diamond polishing paste of particle size 0.5 µm. Ultrasonically clean the polished substrate with acetone, alcohol, and deionized water, with the cleaning time being 15 min respectively, and finally air-dry the substrate naturally.

[0073] S2. Fix the air-dried substrate on the sample stage and transfer it into the deposition chamber. Heat the substrate to 400 °C. After the chamber vacuum is less than 2×10 -4 Pa, introduce high-purity nitrogen, and adjust the nitrogen flow rate so that the nitrogen pressure remains at about 2 Pa. Set the deposition target as a titanium nitride target with a purity of 99.9%, set the laser frequency to 8 Hz, the laser energy to 3342 mJ, and the deposition time to 125 s. Turn on the laser switch to start depositing the titanium nitride coating.

[0074] S3. Turn off the laser switch. Set the deposition target as a titanium aluminum nitride target with a purity of 99.9%, where the mass percentage of Al in the titanium aluminum nitride target is 6% and the mass percentage of titanium nitride is 94%. Keep the substrate temperature, laser frequency, and laser energy unchanged, with the nitrogen pressure being 4 Pa and the deposition time being 125 s. Turn on the laser.

[0075] S4. Turn off the laser switch. Set the deposition target as a titanium nitride target with a purity of 99.9%. Keep the substrate temperature, laser frequency, and laser energy unchanged, with the nitrogen pressure being 4 Pa and the deposition time being 125 s. Turn on the laser.

[0076] S5. Turn off the laser switch. Set the deposition target as a titanium aluminum nitride target with a purity of 99.9%, where the mass percentage of Al in the titanium aluminum nitride target is 6% and the mass percentage of titanium nitride is 94%. Keep the substrate temperature, laser frequency, and laser energy unchanged, with the nitrogen pressure being 4 Pa and the deposition time being 125 s. Turn on the laser.

[0077] S6. Turn off the laser switch. Set the deposition target as a titanium nitride target with a purity of 99.9%. Keep the substrate temperature, laser frequency, and laser energy unchanged, with the nitrogen pressure being 4 Pa and the deposition time being 125 s. Turn on the laser.

[0078] S7. Turn off the laser switch. Set the deposition target as a titanium aluminum nitride target with a purity of 99.9%, where the mass percentage of Al in the titanium aluminum nitride target is 6% and the mass percentage of titanium nitride is 94%. Keep the substrate temperature, laser frequency, and laser energy unchanged, with the nitrogen pressure being 4 Pa and the deposition time being 125 s. Turn on the laser.

[0079] S8. Turn off the laser switch, set the deposition target to a titanium nitride target with a purity of 99.9%, keep the substrate temperature, laser frequency and laser energy unchanged, set the nitrogen gas pressure to 4 Pa, set the deposition time to 125 s, and turn on the laser.

[0080] S9. Turn off the laser switch, set the deposition target to a titanium aluminum nitride target with a purity of 99.9%, where in the titanium aluminum nitride target, the mass percentage of Al is 6% and the mass percentage of titanium nitride is 94%, keep the substrate temperature, laser frequency and laser energy unchanged, set the nitrogen gas pressure to 4 Pa, set the deposition time to 125 s, and turn on the laser.

[0081] S10. Turn off the laser switch, naturally cool to room temperature, take it out of the chamber, and finally obtain an Al-doped transition metal nitride composite coating deposited on the surface of the TA1 commercial titanium plate.

[0082] The self-corrosion current density of this coating sample is about 3.98×10 -5 A·cm -2 , and the interface contact resistance is about 26.44 mΩ·cm 2 . Both the corrosion resistance and conductivity are poor. This is because during the periodic preparation of the multi-layer coating, coating defects will accumulate, resulting in deteriorated performance.

[0083] Please refer to Figure 4 and Figure 5 , and the performance test analysis and comparison of Comparative Example 1 - Comparative Example 2 and Example 1 - Example 2 are as follows:

[0084] The electrochemical performance test of the corrosion resistance of the sample is carried out using a three-electrode system on an Autolab electrochemical workstation. The sample to be tested is the working electrode, with a working area of 1 cm 2 exposed. The counter electrode is a platinum mesh, and the reference electrode is a saturated calomel electrode. Simulate the high-temperature and strong-acid working environment of the bipolar plate of a proton exchange membrane water electrolyzer. The test electrolyte consists of 0.5 mol / L H2SO4 and 5 ppm fluoride ion solution, and the electrolyte temperature is 80 °C. The stable open-circuit voltage is measured after soaking for 1 h under open circuit conditions. A linear voltammetric scan is performed on the specimen in the potential range of -1 V to 2 V (vs. SCE) at a scan rate of 1 mV / s to test the dynamic response of the specimen to the working potential and the influence of the potential on its corrosion resistance. The results are as Figure 4 shown. The corrosion potential and corrosion current and other data can be obtained by performing Tafel fitting on the results.

[0085] The self-corrosion current density of Example 1 is 1.0×10 -8 A·cm -2 , and the self-corrosion current density of Example 2 is 1.15×10 -8 A·cm -2, the self-corrosion current density of Comparative Example 1 is 2.4×10 -4 A·cm -2 , the self-corrosion current density of Comparative Example 2 is 7.7×10 -7 A·cm -2 , the composite coating prepared in the examples of the present invention has better corrosion resistance than the substrate and the single-layer coating.

[0086] Incorporating a third element Al into the titanium nitride hard coating provides additional benefits. Due to the formation of Al2O3, excellent temperature, oxidation resistance, and superior mechanical properties, the corrosion resistance of aluminum titanium nitride can be improved. The titanium nitride coating with relatively low hardness and high corrosion resistance is considered an adhesive coating between the metal substrate and the outermost layer. The titanium nitride coating is the reinforcing layer in the coating because titanium nitride may provide self-healing properties for the entire coating. Therefore, the oxidation of the metal substrate inside the coating can solve the defects in other coatings. Due to the hardness, good electrical conductivity, and superior corrosion resistance of aluminum titanium nitride, it can be used as the outer layer.

[0087] Apply an assembly pre-tightening force of 1.5 MPa to the sample surface and conduct a contact resistance test. The results are as Figure 5 shown. Under a pre-tightening force of 1.5 MPa, the contact resistance of Example 1 is 8.55 mΩ·cm 2 , the contact resistance of Example 2 is 13.28 mΩ·cm 2 , and the contact resistance of Comparative Example 2 is 261.56 mΩ·cm 2 . Based on the above comparative analysis, it is proved that the products prepared in the examples of the present invention maintain good electrical conductivity while maintaining high corrosion resistance.

[0088] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they know the basic creative concept. Therefore, the appended claims are intended to be construed to include the preferred embodiments as well as all changes and modifications falling within the scope of the present invention.

[0089] Obviously, those skilled in the art can make various changes and deformations to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and deformations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these changes and deformations.

Claims

1. A method for preparing an Al-doped transition metal nitride composite coating, characterized in that, The Al-doped transition metal nitride composite coating is a titanium nitride coating and a titanium aluminum nitride coating sequentially deposited from bottom to top on a substrate; the thickness of the Al-doped transition metal nitride composite coating is 240 nm to 270 nm; The preparation method of the Al-doped transition metal nitride composite coating comprises the following steps: Under a protective gas atmosphere, using a titanium nitride target as the target material, a first pulsed laser deposition is carried out on the surface of the substrate to form a titanium nitride coating; in the first pulsed laser deposition, the air pressure in the reaction chamber is 2 Pa to 4 Pa, the deposition temperature is 400 °C, and the deposition time is 800 s to 1000 s; the laser frequency is 8 Hz, and the laser energy is 3342 mJ; Under a protective gas atmosphere, using a titanium aluminum nitride target as the target material, a second pulsed laser deposition is carried out on the surface of the titanium nitride coating to form a titanium nitride coating, obtaining an Al-doped transition metal nitride composite coating; in the second pulsed laser deposition, the air pressure in the reaction chamber is 2 Pa to 4 Pa, the deposition temperature is 400 °C, and the deposition time is 1000 s to 1200 s; the laser frequency is 8 Hz, and the laser energy is 3342 mJ; The titanium aluminum nitride target consists of the following components by mass percentage: 6% aluminum and 94% titanium nitride.

2. The preparation method of an Al-doped transition metal nitride composite coating according to claim 1, wherein, The preferred crystal plane orientation of the titanium nitride coating is (200), and the thickness of the titanium nitride coating is 90 nm to 180 nm.

3. The preparation method of an Al-doped transition metal nitride composite coating according to claim 1, characterized in that, The preferred crystal plane orientation of the titanium aluminum nitride coating is (200), and the thickness of the titanium aluminum nitride coating is 90 nm to 180 nm.

4. The preparation method of an Al-doped transition metal nitride composite coating according to claim 1, wherein The purity of the titanium nitride target is 99.9%, and the purity of the titanium aluminum nitride target is 99.9%.

5. Application of an Al-doped transition metal nitride composite coating prepared by the preparation method according to any one of claims 1-3 in a proton exchange membrane fuel cell or a proton exchange membrane water electrolyzer.

6. Use of the Al-doped transition metal nitride composite coating according to claim 5 in a proton exchange membrane fuel cell or a proton exchange membrane water electrolyzer, characterized in that, The Al-doped transition metal nitride composite coating is deposited on a metal bipolar plate.

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