Oxidation composite coating system and preparation, bipolar plate with the oxidation composite coating system and hydrogen fuel cell with the bipolar plate

Abstract

The present application relates to an oxidation composite coating system (20) and a bipolar plate (30) having the same, and a hydrogen fuel cell having the bipolar plate (30). The oxidation composite coating system (20) comprises a bottom layer (21) containing a metal element selected from at least one of titanium, niobium, chromium, tantalum and zirconium; a top layer (23) containing a carbon element; and a symbiotic layer (22) containing the metal element and the carbon element formed between the bottom layer (21) and the top layer (23); wherein at least one of the bottom layer (21), the top layer (23) and the symbiotic layer (22) contains an oxide formed by doping an oxygen element with the metal element and / or the carbon element, so as to provide high corrosion resistance while maintaining good electrical conductivity, thereby achieving the best balance between electrical conductivity and corrosion resistance of the coating.

Description

TECHNICAL FIELD

[0001] The present application generally relates to an oxidation composite coating system formed on a substrate, a method for preparing the oxidation composite coating system on the substrate using a magnetron sputtering device, a bipolar plate having the oxidation composite coating system, and a hydrogen fuel cell having the bipolar plate. BACKGROUND

[0002] The bipolar plate is a key component of a hydrogen fuel cell, and its functions include conducting electricity, separating gases, transporting reactants and products, and providing structural support. The performance of the bipolar plate is crucial to the overall efficiency and life of the fuel cell. However, since the bipolar plate needs to work in a corrosive environment for a long time, its surface must have excellent corrosion resistance, electrical conductivity and stability.

[0003] Currently, the materials of the bipolar plate mainly include metals, graphite and composite materials. Among them, metal bipolar plates have become a research and application hotspot due to their excellent mechanical properties, good electrical conductivity and high processability. However, metal bipolar plates are prone to corrosion in acidic environments, which in turn affects the efficiency and life of the fuel cell. In order to solve this problem, researchers have proposed various surface protection technologies, such as plating and coating, to improve the corrosion resistance and electrical conductivity of metal bipolar plates.

[0004] However, the corrosion and peeling of the carbon layer on the surface of the metal bipolar plate at high potential has always been a difficult bottleneck problem. The root cause is the imbalance of the potential distribution at the interface between the inside and outside of the surface carbon layer, which is manifested as the coating entering the "overpassivation region" at high potential. By increasing the band gap width between the lower edge of the Fermi level and the top of the valence band, the energy band bending induced by high polarization potential is resisted, that is, the overpassivation potential value of the coating is improved, which is an effective measure to alleviate carbon corrosion.

[0005] However, how to prepare a composite coating with high adhesion, excellent corrosion resistance and electrical conductivity on a metal substrate is still a key technical problem to be solved. SUMMARY

[0006] The purpose of the present application is to provide an oxidation composite coating system and its preparation, a bipolar plate having the oxidation composite coating system, and a hydrogen fuel cell having the bipolar plate, which provides high corrosion resistance while maintaining good electrical conductivity, to achieve the best balance between the coating in terms of electrical conductivity and corrosion resistance.

[0007] Other characteristics and advantages of the present application will become apparent from the following detailed description, or will be learned by practice of the present application.

[0008] According to a first aspect of the present application, there is provided an oxidic composite coating system formed on a substrate, comprising: a bottom layer comprising a metal element, wherein the metal element is selected from at least one of titanium, niobium, chromium, tantalum, zirconium; a top layer comprising a carbon element; and a paragenetic layer comprising the metal element and the carbon element formed between the bottom layer and the top layer; wherein at least one of the bottom layer, the top layer and the paragenetic layer comprises an oxide formed by doping an oxygen element with the metal element and / or the carbon element.

[0009] As a preferred embodiment of the first aspect, wherein the carbon element of the top layer is in the form of amorphous carbon (a-C), SP 2 The hybrid ratio is 50% to 70%.

[0010] As a preferred embodiment of the first aspect, wherein the thickness of the bottom layer is 20 nm to 150 nm, the thickness of the paragenetic layer is 20 nm to 150 nm, and the thickness of the top layer is 20 nm to 80 nm.

[0011] As a preferred embodiment of the first aspect, wherein the oxygen content of the bottom layer when containing an oxide is 0 to 20 at%; the oxygen content of the top layer when containing an oxide is 0 to 15 at%; and the oxygen content of the paragenetic layer when containing an oxide is 0 to 20 at%.

[0012] As a preferred embodiment of the first aspect, wherein the metal element is titanium.

[0013] As a preferred embodiment of the first aspect, wherein the atomic ratio of carbon to titanium in the paragenetic layer is 1:3 to 5:3.

[0014] As a preferred embodiment of the first aspect, wherein the bottom layer contains titanium oxide and / or the top layer contains carbon oxide.

[0015] As a preferred embodiment of the first aspect, wherein the paragenetic layer contains titanium oxide and / or titanium oxide carbide.

[0016] According to a second aspect of the present application, there is provided a metal bipolar plate comprising a substrate and at least one oxidic composite coating system according to any one of the first aspect formed on the substrate.

[0017] According to a third aspect of the present application, there is provided a hydrogen fuel cell comprising a metal bipolar plate according to the second aspect.

[0018] According to a fourth aspect of the present application, there is provided a method for preparing an oxide composite coating system on a substrate by using a magnetron sputtering device, the method comprising: depositing a bottom layer containing a metal element on the substrate, wherein the metal element is selected from at least one of titanium, niobium, chromium, tantalum, and zirconium; depositing a symbiotic layer containing the metal element and a carbon element on the bottom layer; and depositing a top layer containing the carbon element on the symbiotic layer, to obtain the oxide composite coating system; and during the deposition, doping oxygen element into at least one of the bottom layer, the symbiotic layer, and the top layer to form an oxide generated by reacting with the metal element and / or the carbon element.

[0019] As a preferred embodiment of the fourth aspect, the oxygen content of the bottom layer containing the oxide is 0-20 at%; the oxygen content of the top layer containing the oxide is 0-15 at%; and the oxygen content of the symbiotic layer containing the oxide is 0-20 at%.

[0020] As a preferred embodiment of the fourth aspect, the doping of the oxygen element comprises introducing oxygen into the vacuum chamber during the deposition of at least one of the bottom layer, the symbiotic layer, and the top layer.

[0021] As a preferred embodiment of the fourth aspect, the doping of the oxygen element further comprises controlling the flow rate of oxygen or oxygen-argon mixed gas during the deposition of at least one of the bottom layer, the symbiotic layer, and the top layer.

[0022] It should be understood that the general description above and the detailed description below are only exemplary and explanatory, and cannot limit the present application. BRIEF DESCRIPTION OF DRAWINGS

[0023] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate one or more embodiments of the present application and, together with the description, serve to explain the principles of the present application and to enable a person skilled in the relevant art to make and use the present application.

[0024] Figure 1 is an exemplary structural diagram of an oxide composite coating system formed on a substrate according to an embodiment of the present application;

[0025] Figure 2 is an exemplary flowchart of a method for preparing an oxide composite coating system on a substrate according to an embodiment of the present application;

[0026] Figure 3 is an exemplary flowchart of a method for preparing an oxide composite coating system on a substrate according to an embodiment of the present application, wherein (a1)-(a4) are C / TiC x O y(b1)-(b3) are TiC with different oxidation degrees x O y The expected composition and crystal structure of the coating

[0027] Figure 4 (a) of FIG. 1 is a FIB-TEM image of the cross section of the oxidation composite coating system (C / Ti-O coating) of the embodiment of the present application, Figure 4 (b) of FIG. 1 is the corresponding element line scanning image of the C / Ti-O coating;

[0028] Figure 5 is the XPS narrow spectrum image of the oxidation composite coating system (C / Ti-O coating) of the embodiment of the present application;

[0029] Figure 6 (a) of FIG. 2 is the potentiodynamic polarization curve of the oxidation composite coating system (C / Ti-O coating) of the embodiment of the present application, Figure 6 (b) of FIG. 2 is the column chart of the interfacial contact resistance ICR of the oxidation composite coating system (C / Ti-O coating) of the embodiment of the present application under different pressures;

[0030] Figure 7 is the valence band bending and coating interfacial potential distribution diagram of the symbiotic layer (TiC x O y ) of the embodiment of the present application under different potentials. DETAILED DESCRIPTION

[0031] Example implementations will now be described more fully with reference to the accompanying drawings. Example implementations may, however, be implemented in many different forms and should not be construed as limited to the examples set forth herein; rather, these implementations are provided so that this disclosure will be thorough and complete, and will fully convey the scope of example implementations to those skilled in the art. The described features, structures, or characteristics can be combined in any suitable manner in one or more implementations. In the following description, numerous specific details are provided to give a thorough understanding of implementations of the present application.

[0032] Improving the corrosion resistance of the coating while maintaining good electrical conductivity is crucial for the application in fuel cells, especially in proton exchange membrane fuel cell (PEMFC) metal bipolar plates. In response to this need, embodiments of the present application provide a coating system with high corrosion resistance and high electrical conductivity. The coating system significantly improves its corrosion resistance while ensuring excellent electrical conductivity. It should be understood that although the coating system of the present application is mainly designed for application to metal bipolar plates of fuel cells, its application scope is not limited thereto. The coating system is also applicable to other devices / components with high requirements for corrosion resistance and electrical conductivity. Specific application scenarios include, but are not limited to, applicable devices / components in the fields of energy, marine engineering, aerospace, electronic and electrical equipment, automobile industry, building infrastructure, chemical equipment, and medical equipment, etc.

[0033] The coating system and its application related to embodiments of the present application are further described below in conjunction with the accompanying drawings.

[0034] Oxidation composite coating system

[0035] Figure 1 is an exemplary structural diagram of the oxidation composite coating system formed on the substrate provided by embodiments of the present application. As shown in Figure 1 , the oxidation composite coating system 20 includes a bottom layer 21 disposed on the substrate 10, a symbiotic layer 22 disposed on the bottom layer 21, and a top layer 23 disposed on the symbiotic layer 22. For example, in any one plane, the bottom layer 21 can cover part or all of the surface of the substrate 10, the symbiotic layer 22 can cover part or all of the surface of the bottom layer 21, and the top layer 23 can cover part or all of the surface of the symbiotic layer 22.

[0036] The substrate 10 serves as the construction carrier of the oxidation composite coating system 20, and its material is selected to be stainless steel, for example, SS 316L with high corrosion resistance and oxidation resistance. In other embodiments, the substrate 10 can also be selected from other materials, such as aluminum alloy, titanium alloy, copper and copper alloy, cobalt-based alloy, zirconium alloy, tungsten and tungsten alloy, molybdenum and molybdenum alloy, magnesium and magnesium alloy, etc.

[0037] The bottom layer 21 is disposed on the substrate 10 and contains a metal element selected from at least one of titanium, niobium, chromium, tantalum, and zirconium. The bottom layer has a thickness of about 20 nm to 150 nm, for example, a thickness of about 25 nm to 140 nm, about 30 nm to 130 nm, about 35 nm to 120 nm, about 40 nm to 110 nm, about 45 nm to 100 nm, about 50 nm to 90 nm, about 55 nm to 80 nm.

[0038] The symbiotic layer 22 is disposed above the bottom layer 21, i.e. between the bottom layer 21 and the top layer 23, and contains a symbiotic structure of metal elements and carbon elements. The metal elements are selected from at least one of titanium, niobium, chromium, tantalum, zirconium, and preferably are the same as the metal elements selected for the bottom layer 21, e.g. when the bottom layer 21 contains titanium, the metal elements contained in the symbiotic layer 22 are also selected to be titanium. Alternatively, the metal elements of the symbiotic layer 22 can also be different from the bottom layer 21. The symbiotic layer 22 has a thickness of about 20 nm to 150 nm, e.g. a thickness of about 25 nm to 140 nm, about 30 nm to 130 nm, about 35 nm to 120 nm, about 40 nm to 110 nm, about 45 nm to 100 nm, about 50 nm to 90 nm, about 55 nm to 80 nm. The atomic ratio of carbon elements to metal elements in the symbiotic layer 22 can be regulated, e.g. 1:3 to 5:3.

[0039] The top layer 23 is disposed above the symbiotic layer 22 and contains carbon elements, and the top layer 23 has a thickness of about 20 nm to 80 nm, e.g. a thickness of about 25 nm to 70 nm, about 30 nm to 60 nm, about 35 nm to 50 nm. The carbon elements are in the form of amorphous carbon (a-C), for example, and the a-C has a sp3 content of about 20% to 80%, e.g. about 25% to 75%, about 30% to 70%, about 35% to 65%, about 40% to 60%. 2 The hybrid ratio is about 50% to 70%.

[0040] The oxide composite coating system 20 contains oxides formed by doping oxygen elements with metal elements and / or carbon elements. The doping layer of oxygen elements can be one or more of the bottom layer 21, the top layer 23 and the symbiotic layer 22. When the bottom layer 21 is doped with oxygen elements, the oxygen reacts with at least one of titanium, niobium, chromium, tantalum, zirconium to generate the corresponding oxides. When the top layer 23 is doped with oxygen elements, the oxygen reacts with carbon to generate the corresponding oxides. When the symbiotic layer 22 is doped with oxygen elements, the oxygen reacts with carbon and at least one of titanium, niobium, chromium, tantalum, zirconium to generate the corresponding oxides. The bottom layer 21 containing oxides has an oxygen content of about 0 to 20 at%; the top layer 23 containing oxides has an oxygen content of about 0 to 15 at%; the symbiotic layer 22 containing oxides has an oxygen content of about 0 to 20 at%.

[0041] In some embodiments, the metal elements are selected to be titanium, the bottom layer 21 and the symbiotic layer 22 both contain titanium, and the atomic ratio of carbon to titanium in the symbiotic layer 22 is about 1:3 to 5:3. On this basis, by introducing oxygen elements, the performance of each layer can be further optimized, so as to significantly improve its corrosion resistance while ensuring excellent electrical conductivity. For example, when the bottom layer 21 is doped with oxygen elements, the bottom layer 21 contains titanium (Ti) and titanium oxide (TiO y ); when the top layer 23 is doped with oxygen elements, the top layer 23 contains carbon (C) and carbon oxide (CO y) ; when symbiotic layer 22 introduces oxygen element, symbiotic layer 22 contains titanium oxide (TiO x ) and / or titanium oxide carbide (TiC y ) in addition to titanium carbide (TiC x O y ). Wherein, x represents the atomic ratio of carbon, y represents the atomic ratio of oxygen, which are used to describe the relative atomic number of each element in a specific compound in the oxidation composite coating system 20. Titanium carbide is a conductor, titanium oxide is an insulator, and titanium oxide carbide is a semiconductor nanocrystal. In the above layer structure, the bottom layer 21, the symbiotic layer 22 and the top layer 23 each provide different functions and work together to improve the overall performance of the oxidation composite coating system 20.

[0042] Preparation of oxidation composite coating system

[0043] The embodiment of the present application uses a method of magnetron sputtering to prepare the oxidation composite coating system 20. Magnetron sputtering is a physical vapor deposition (PVD) technology that uses magnetic field control plasma to make target material (target material) atoms sputter onto the substrate surface to form a thin film. The magnetron sputtering equipment used is, for example, a closed field unbalanced magnetron sputtering equipment, which applies an electric field and a magnetic field between the target material and the substrate to improve the plasma density and ionization efficiency, thereby improving the deposition rate and quality of the thin film.

[0044] Figure 2 is an exemplary flowchart of the method for preparing the oxidation composite coating system on the substrate provided by the embodiment of the present application. As Figure 2 shown, the method 40 generally involves steps 41 (depositing a bottom layer 21 containing at least one metal element of titanium, niobium, chromium, tantalum, zirconium on the substrate 10), step 42 (depositing a symbiotic layer 22 containing at least one metal element of titanium, niobium, chromium, tantalum, zirconium and carbon element on the bottom layer 21) and step 43 (depositing a top layer 23 containing carbon element on the symbiotic layer 22), and during the deposition of at least one of the bottom layer 21, the symbiotic layer 22 and the top layer 23, at least one of the bottom layer 21, the symbiotic layer 22 and the top layer 23 contains oxides generated by reacting with metal elements and / or carbon elements by doping oxygen elements. The method 40 further implements the following steps:

[0045] (Pretreatment and installation of the substrate)

[0046] A substrate 10 is obtained, for example, using SS 316L stainless steel as the material of the substrate 10. The surface of the substrate 10 is cleaned and pretreated. For example, it involves using a solvent to clean the surface of the substrate 10 to remove grease and dirt, then mechanically polishing to remove the oxide layer and surface unevenness, and then using ultrasonic cleaning to further remove small particles and impurities, to ensure that the surface of the substrate 10 is clean and conducive to the subsequent adhesion of the coating. The treated substrate 10 is installed in a magnetron sputtering device, and the substrate 10 is fixed firmly to ensure that it can uniformly receive the deposition of sputtered materials during the sputtering process.

[0047] (bottom layer deposition)

[0048] According to the design, at least one material selected from titanium, niobium, chromium, tantalum, and zirconium is used as the target material of the metal target (it should be understood that when two or more materials are selected, an alloy target containing the corresponding elements can be used as the target material). Start the magnetron sputtering device, set the sputtering power and gas (argon) flow, and usually perform sputtering in a low vacuum environment. By controlling the sputtering parameters, the atoms of the metal target are deposited onto the surface of the substrate 10 at an appropriate rate, forming a uniform bottom layer 21. By adjusting the deposition time and sputtering power, the thickness of the bottom layer is precisely controlled to be in the range of about 20 nm to 150 nm. For example, the thickness can be controlled in the thickness interval of about 25 nm to 140 nm, about 30 nm to 130 nm, about 35 nm to 120 nm, about 40 nm to 110 nm, about 45 nm to 100 nm, about 50 nm to 90 nm, about 55 nm to 80 nm, to meet the needs of different applications.

[0049] (syngenetic layer deposition)

[0050] The same metal target as the deposition of the bottom layer 21 is used, and a carbon target is used. Start the magnetron sputtering device to sputter the metal target and the carbon target at the same time. By controlling the sputtering power and gas (argon) flow, ensure that the atoms of metal and carbon are uniformly deposited on the bottom layer 21 to form a syngenetic structure of metal and carbon elements. By adjusting the deposition time and sputtering parameters, the thickness of the syngenetic layer 22 is controlled to be in the range of about 20 nm to 150 nm. For example, the thickness can be controlled in the thickness interval of about 25 nm to 140 nm, about 30 nm to 130 nm, about 35 nm to 120 nm, about 40 nm to 110 nm, about 45 nm to 100 nm, about 50 nm to 90 nm, about 55 nm to 80 nm, and ensure that the atomic ratio of carbon to metal elements in the syngenetic layer 22 is between 1:3 and 5:3, to achieve excellent electrical conductivity and corrosion resistance.

[0051] (top layer deposition)

[0052] The carbon target is magnetron sputtered alone to form the top layer 23. The sputtering power and gas (argon) flow are adjusted to ensure uniform deposition of carbon atoms onto the symbiotic layer 22. By controlling the deposition time and parameters, the thickness of the top layer 23 is between about 20 nm and 80 nm. For example, the thickness can be controlled in a thickness interval of about 25 nm to 70 nm, about 30 nm to 60 nm, about 35 nm to 50 nm. The carbon element in the top layer 23 mainly exists in the form of amorphous carbon (a-C), and the SP 2 The hybrid ratio is controlled between 50% and 70% to ensure that the top layer has good electrical conductivity and mechanical properties.

[0053] (oxygen element doping)

[0054] During the deposition of at least one of the bottom layer 21, the symbiotic layer 22 and the top layer 23, oxygen element doping is introduced into the corresponding coating by introducing oxygen or oxygen-argon mixed gas into the vacuum chamber and controlling the gas flow. The oxygen element introduced into the coating reacts with the metal element and / or the carbon element to form an oxide. For example, the bottom layer 21 can contain titanium oxide (TiO y ), the top layer 23 can contain carbon oxide (CO y ), and the symbiotic layer 22 can contain titanium oxide (TiO y ) and / or titanium oxide carbide (TiC x O y During the oxygen introduction process, the oxygen content in each layer is accurately controlled by adjusting the flow rate of oxygen or oxygen-argon mixed gas. For example, the oxygen content of the bottom layer 21 is in the range of 0 to 20 at%, the oxygen content of the top layer 23 is in the range of 0 to 15 at%, and the oxygen content of the symbiotic layer 22 is in the range of 0 to 20 at%.

[0055] In the oxidation composite coating system 20, by accurately adjusting the oxygen content, the performance of each layer can be optimized to meet the specific application requirements. Not only is the high electrical conductivity of the coating ensured, but its corrosion resistance is also significantly improved. The key to regulating the oxygen content is that it has a high degree of controllability, which can effectively manage the oxidation process, not only limited to the surface or easily oxidized metal layer to achieve the introduction of oxide, but also avoids excessive oxidation, thereby achieving a long-term balance between electrical conductivity and corrosion resistance. This high-precision oxygen content regulation technology ensures the stability and reliability of the coating in various harsh environments.

[0056] The following takes titanium as the metal element and oxygen element doping in the symbiotic layer as an example to further illustrate the preparation of the oxidation composite coating system. Figure 3 is an exemplary flowchart of the method for preparing an oxidation composite coating system with titanium as the metal element on a substrate provided by the embodiments of the present application, wherein (a1)-(a4) are C / TiC x O y / Schematic diagram of Ti coating preparation process, (b1)-(b3) are TiC with different oxidation degrees x O y A schematic diagram of the expected composition and crystal structure of the coating. (e.g.) Figure 3 As shown, C / TiC was prepared using a thin SS 316L stainless steel substrate (300 × 150 × 0.1 mm) 10 and a closed-field unbalanced magnetron sputtering apparatus. x O y / Ti coating. First, a Ti target is sputtered to deposit Ti atoms onto the surface of the substrate 10 to form the underlayer 21. On the underlayer 21, O (with controlled flow of oxygen or an oxygen-argon mixture), C, and Ti are co-deposited to prepare a substrate composed mainly of elemental C and Ti, with locally distributed conductive TiC. x TiO2 insulator y and semiconductor nanocrystalline TiC x O y A mixed layer (symbiotic layer 22) is formed. During the deposition of symbiotic layer 22, the oxygen content in symbiotic layer 22 is precisely controlled by adjusting the flow rate of oxygen or oxygen-argon mixture, resulting in TiC with different contents and forms. x TiO y and TiC x O y The composite structure yields a symbiotic layer 22 with a wide valence band gap and a narrow conduction band gap, thereby improving the overpassivation potential while ensuring the conductivity of the coating. Finally, a C target is sputtered onto the symbiotic layer 22 to deposit C atoms onto the surface of the symbiotic layer 22 to form a top layer 23, ultimately forming a C / TiC composite layer. x O y / Ti coating. Through the above steps, a C / TiC coating is finally formed. x O y / Ti coating.

[0057] In existing technologies, the presence of oxygen in the bipolar plate coating is typically avoided during the coating process to prevent oxide formation. This approach is based on several considerations: First, oxides are usually insulators or semiconductors with poor conductivity; a high oxide content in the coating significantly reduces its conductivity. Second, excessive oxide formation can increase the coating's brittleness, thereby reducing its mechanical properties and impact resistance. In contrast to existing technologies, this application employs a reverse approach: doping the coating with oxygen and precisely controlling its content. Introducing an appropriate amount of oxide into the coating not only maintains good conductivity but also significantly improves its corrosion resistance. This unexpected technical effect significantly enhances the coating's performance and lifespan in various applications.

[0058] It is understood that the main purpose of oxygenation is to improve the corrosion resistance of the coating, but too much oxide will deteriorate the conductivity. During the deposition process, the most important thing is that the oxygen content is highly controllable, and the oxidation is not just concentrated on the surface or the layer of easily oxidizable metal. In this way, both the oxide is introduced and the over-oxidation is avoided, so as to achieve a long-term balance between high corrosion resistance and conductivity.

[0059] In addition, in the prior art, there is also a means of preparing an oxide layer on the surface of the corrosion-resistant coating. This oxide layer is formed on the surface of the coating and its main function is to block the penetration of corrosive media by forming a dense oxide layer, thereby improving the corrosion resistance of the coating. However, the formation of the surface oxide layer often brings some limitations and deficiencies, for example: the surface oxide layer is usually an insulator or a semiconductor, and the conductivity is poor. When the oxide layer is concentrated on the surface of the coating, it will significantly reduce the overall conductivity of the coating, affecting the performance of the coating in conductive applications. The surface oxide layer is brittle and easy to peel off or break under external force, reducing the overall mechanical properties and durability of the coating. The protective effect of the surface oxide layer is limited to the outer layer of the coating. Once the surface oxide layer is damaged or worn, the metal material inside the coating is easily exposed to the corrosion environment, reducing the overall corrosion resistance.

[0060] By contrast, the embodiments of the present application introduce oxygen elements into the interior of the coating, for example, in the symbiotic layer 22, which has the following advantages: by introducing an appropriate amount of oxide into the symbiotic layer 22 and accurately controlling the oxygen content, a mixed layer structure of locally distributed conductor TiC x , insulator TiO y and semiconductor nanocrystalline TiC x O y is formed. This internal oxide layer not only improves the corrosion resistance, but also performs excellently in ensuring the overall conductivity of the coating. The oxide in the symbiotic layer 22 is distributed in the interior of the coating, reducing the brittleness problem of the surface oxide layer. The nanocrystalline structure of TiC x O y has good mechanical properties, enhancing the overall durability and impact resistance of the coating. The oxide in the symbiotic layer 22 forms a uniform internal protective layer. Even if the surface is damaged, the internal oxide can still provide effective protection, significantly improving the long-term corrosion resistance of the coating. The oxide in the symbiotic layer 22 has good corrosion resistance throughout the thickness of the coating by regulating the oxygen content and distribution. Through the design of the oxide composite structure in the symbiotic layer 22, a wider valence band gap and a narrower conduction band gap are provided, which improves the overpassivation potential value of the coating. Within the passivation interval, the coating can resist higher potential drop, improving the electrochemical stability and further enhancing the corrosion resistance. Compared with the prior art of forming a dense oxide layer only on the surface, the oxide in the symbiotic layer 22 of the present application can work cooperatively with the surface layer to provide multi-level protection and enhance the overall corrosion resistance of the coating.

[0061] Performance characterization of oxidation composite coating system

[0062] Figure 4 (a) is the FIB-TEM image of the cross section of the oxidation composite coating system (C / Ti-O coating) of the embodiment of the present application, Figure 4 (b) is the corresponding element line scanning image of the C / Ti-O coating. The total thickness of the prepared C / Ti-O coating is about 185 nm. The coating mainly comprises three parts, namely a Ti layer (bottom layer) of 70 nm at the bottom, a C-Ti composite layer (paragenetic layer) of 70 nm in the middle, and an a-C layer (top layer) of 45 nm on the surface. The proportion of oxygen atoms in the bottom layer Ti is about 15%; the proportion of oxygen atoms in the paragenetic layer is about 12%, and the atomic ratio of Ti to C decreases from 5:3 to 1:1; the proportion of oxygen atoms in the top layer is about 8%, the surface is amorphous carbon structure, and the bottom layer and the paragenetic layer are mostly nanocrystalline structure, and there is local amorphous.

[0063] Figure 5 is the XPS narrow spectrum image of the oxidation composite coating system (C / Ti-O coating) of the embodiment of the present application. According to the XPS narrow spectrum analysis, the C-C sp2 bonding in the top layer is mainly in the form of C-C sp2 bonding, which accounts for 55%-60%, which ensures the initial conductivity of the C / Ti-O coating, and a small amount of C-O and C=O bonds are formed, and the proportion of oxide bonding is about 15%. When entering the paragenetic layer, the C peak is all in the form of metal carbide, the proportion of Ti metal peak in the Ti peak gradually increases, the proportion of TiC gradually decreases, and the Ti in the layer mainly exists in the form of metal or carbide, and TiO oxide is formed, which accounts for about 10%. x x

[0064] Figure 6 (a) is the potentiodynamic polarization curve of the oxidation composite coating system (C / Ti-O coating) of the embodiment of the present application. The potentiodynamic polarization curve shows that the C / Ti-O coating has a more positive corrosion potential, a smaller corrosion current density, and a larger passivation potential than the SS316L substrate. The corrosion current at the conventional working potential 0.84 V of the hydrogen fuel cell is only 5.1×10 −8 A / cm 2 , which is much lower than the target value 10 −6 A / cm 2 of DOE. When the potential of the C / Ti-O coating reaches 1.18 V, the current exceeds 10 −6 A / cm 2 , which shows excellent corrosion resistance. Figure 6 ​​(b) is a column chart of the interfacial contact resistance ICR of the oxidation composite coating system (C / Ti-O coating) of the embodiment of the present application at different pressures. As the pressure gradually increases, the contact area between the carbon paper and the sample increases, and the value of the interfacial contact resistance ICR gradually decreases. The original C / Ti-O coating exhibits excellent electrical conductivity, and the ICR at all pressures is less than 3 mΩ·cm 2 At 140 N / cm 2 , the ICR decreases to 1.4 mΩ·cm 2 , which is much lower than the target value of 10 mΩ·cm of the DOE 2 , highlighting the excellent electrical conductivity of the coating.

[0065] Through the above analysis, the C / Ti-O coating prepared in the embodiment of the present application exhibits significant advantages in corrosion resistance and electrical conductivity. Through a reasonable oxygen doping process, not only the good electrical conductivity is maintained, but also the corrosion resistance of the coating is significantly improved.

[0066] Figure 7 is a schematic diagram of the valence band bending and the interfacial potential distribution of the symbiotic layer (TiC x O y ) of the embodiment of the present application at different potentials. According to the energy band bending theory proposed by Norio Sato, when a small anodic potential is applied to the electrode, the Fermi level in the coating will decrease, which is equivalent to the upward bending of the energy band. Within the passivation interval, the Fermi level always remains within the forbidden band of the film. The passivation interval is an important region, during which the coating can effectively resist corrosion without significant electrochemical reaction. When the anodic potential increases to cause the energy band bending so that the valence band top E V exceeds the Fermi level E F , the surface will undergo electron transition, forming positively charged holes on the surface. This process marks the beginning of the overpassivation interval. The overpassivation interval is a critical region, during which the coating can still provide protection, but its performance begins to be affected, and the corrosion process can become more significant.

[0067] From the above process, it can be seen that the electrochemical stability of the coating surface is closely related to the electronic energy band structure in the film. The height of the overpassivation potential depends on the size of the valence band gap in the film. It is known that oxides have a wide valence band gap, and usually exhibit strong corrosion resistance and poor electrical conductivity. Therefore, the valence band gap of the coating containing oxides ∆E 2is greater than the valence band gap of the coating without oxides ∆E 1. In the process of rising anodic polarization potential, the oxide-containing coating has stronger resistance to energy band bending due to its wider valence band gap, and can withstand greater potential drop during polarization. This characteristic makes the double-layer potential ΔEdl reducing the current density in polarization, and improving the passivation potential.

[0068] To achieve the above performance, in the coating design process, the coating can be made to have a proper valence band gap by precisely controlling the content and distribution of oxygen. In this way, the coating can provide high corrosion resistance while maintaining good electrical conductivity. The specific implementation method includes introducing an appropriate amount of oxygen element in the symbiotic layer of the coating, forming a composite structure with different contents and forms of TiC x , TiO y , and TiC x O y by adjusting the flow of oxygen or oxygen-argon mixed gas. The design of such a composite structure not only ensures the initial electrical conductivity of the coating, but also significantly improves its corrosion resistance. It can be seen that, through reasonable coating design and precise control of oxygen elements, the best balance between electrical conductivity and corrosion resistance of the coating can be achieved. By applying the band bending theory, the valence band gap in the coating can be optimized, which can significantly improve the passivation potential of the coating, so that it still maintains excellent protection performance under extreme conditions.

[0069] Metal bipolar plate

[0070] With reference still to Figure 1 , the substrate 10 and the oxide composite coating system 20 deposited on the substrate 10 constitute a metal bipolar plate 30. Through the above-mentioned preparation method 30, a metal bipolar plate 30 with a multilayer structure is constructed, and the precise control of each layer of coating makes the metal bipolar plate 30 achieve the best balance between electrical conductivity and corrosion resistance. In addition, the oxide composite coating system 20 can be deposited on the surface of the substrate 10 in more than one layer. For example, according to the needs, two or more layers of oxide composite coating system 20 can be deposited on the surface of the substrate 10. Such a multilayer structure can be achieved by repeating the target sputtering after the preparation of one layer of oxide composite coating system 20 is completed.

[0071] Hydrogen fuel cell

[0072] In this embodiment, the core components of the hydrogen fuel cell include a proton exchange membrane (PEM), a catalyst layer (CCL), a gas diffusion layer (GDL), and a metal bipolar plate 30. In particular, the metal bipolar plate 30 adopts the bipolar plate design of any structure, composition or preparation process described above, and the focus is on the metal bipolar plate 30 composed of a substrate 10 (such as SS 316L stainless steel) and an oxide composite coating system 20 deposited on the substrate 10.

[0073] Proton exchange membrane (PEM) is a key component of hydrogen fuel cells, for example made of fluoropolymer, which can selectively conduct protons (H+) and prevent the direct passage of electrons and fuel gas, thus enabling the electrochemical reaction of hydrogen and oxygen. Catalyst layer (CCL) for example uses platinum-based catalyst, distributed on both sides of the proton exchange membrane (PEM). The anode catalyst layer catalyzes the decomposition of hydrogen into protons and electrons; the cathode catalyst layer catalyzes the combination of oxygen with protons and electrons to generate water. Gas diffusion layer (GDL) for example is made of carbon fiber paper or carbon cloth, with high porosity and conductivity, ensuring uniform distribution of reaction gas and helping to discharge the water generated by the reaction, preventing water flooding. The hydrogen fuel cell of the embodiments of the present application, by using metal bipolar plates with multi-layer oxidation composite coating system, significantly improves the overall performance and service life of the cell. Especially in terms of electrical conductivity and corrosion resistance, the retention of electrical conductivity and significant improvement of corrosion resistance are achieved, meeting the strict requirements of hydrogen fuel cells in practical applications.

[0074] Other embodiments of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application disclosed herein. It is intended that the specification and examples be considered as exemplary only, with the true scope of the application being indicated by the following claims.

Claims

1. A method for preparing an oxide composite coating system (20) on a substrate (10) for a metal bipolar plate (30) using a magnetron sputtering apparatus, the method comprising: Select at least one of titanium, niobium, chromium, tantalum and zirconium as the target target material, and use magnetron sputtering equipment to deposit the atoms of the metal target material onto the surface of the substrate (10) to form the bottom layer (21); Using the same metal target as the deposited bottom layer (21) and a carbon target, the atoms of the metal target and the carbon target are simultaneously deposited onto the bottom layer (21) using the magnetron sputtering equipment to form a symbiotic layer (22). The carbon target is sputtered separately to form a top layer (23), which is formed on top of the symbiotic layer (22); as well as During the deposition process of at least one of the bottom layer (21), symbiotic layer (22) and top layer (23), oxygen element is doped into at least one of the bottom layer (21), symbiotic layer (22) and top layer (23) by introducing oxygen or oxygen-argon mixture into the vacuum chamber, and reacts with metal element and / or carbon element to generate oxide.

2. The method according to claim 1, wherein the oxygen content of the bottom layer (21) containing oxides is greater than 0 and less than or equal to 20 at; the oxygen content of the top layer (23) containing oxides is greater than 0 and less than or equal to 15 at; and the oxygen content of the symbiotic layer (22) containing oxides is greater than 0 and less than or equal to 20 at.

3. The method according to claim 1, wherein the thickness of the bottom layer (21) is 20 nm to 150 nm, the thickness of the symbiotic layer (22) is 20 nm to 150 nm, and the thickness of the top layer (23) is 20 nm to 80 nm.

4. The method according to claim 1, wherein the carbon element of the top layer (23) is in the form of amorphous carbon (aC), SP 2 The hybridization ratio is 50% to 70%.

5. The method according to claim 1, wherein the metal target is a titanium target.

6. The method according to claim 5, wherein the atomic ratio of carbon to titanium in the symbiotic layer (22) is 1:3 to 5:

3.

7. The method according to claim 5, wherein the bottom layer (21) contains titanium oxide and / or the top layer (23) contains carbon oxide.

8. The method according to claim 5 or 7, wherein the symbiotic layer (22) contains titanium oxide and / or titanium oxide carbide.

9. An oxide composite coating system (20) obtained by the method according to any one of claims 1 to 8.

10. A metal bipolar plate (30) comprising a substrate (10) and at least one oxide composite coating system (20) according to claim 9 formed on said substrate (10).

11. A hydrogen fuel cell comprising a metal bipolar plate (30) according to claim 10.

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