Composite coating, bipolar plate and porous diffusion layer

Abstract

The application relates to a composite coating and a bipolar plate and a porous diffusion layer, the composite coating comprising a bottom layer arranged on the surface of a substrate, the material of the bottom layer comprising a non-noble metal element; and a composite material surface layer arranged on the surface of the bottom layer, the material of the composite material surface layer comprising a MAX material, a MXene material and a MAX-MXene material, the chemical formula of the MAX material being M-A-X, the chemical formula of the MXene material being M-X, and the MAX-MXene material having at least two crystal units sharing at least one M atom, wherein M comprises at least one of the elements in the ⅢB-ⅦB elements of the periodic table, A comprises at least one of the ⅦB-ⅥA elements in the second and third periods of the periodic table, and X comprises at least one of B, C and N, the composite material surface layer has pores, and the porosity of the composite material surface layer is 5%-50%. The composite coating can strengthen the corrosion resistance and stability of the substrate in a strong acid environment, effectively prolong the service life of a PEM electrolytic cell, and reduce the manufacturing cost of the PEM electrolytic cell.

Description

Technical Field

[0001] This application relates to the field of proton exchange membrane electrolyzer coating technology, specifically to a composite coating, bipolar plate and porous diffusion layer. Background Technology

[0002] Proton exchange membrane water electrolysis (PEMWE) is considered the most promising hydrogen production technology due to its compact structure and high hydrogen production efficiency. PEMWE utilizes an applied potential and a catalyst to induce hydrogen evolution (HER) at the cathode and oxygen evolution (OER) at the anode, producing high-purity hydrogen energy.

[0003] The main components of a PEM water electrolyzer, from the inside out, are the proton exchange membrane, anode and cathode catalyst layers, anode and cathode gas diffusion layers, and anode and cathode plates. The anode and cathode plates provide the electrical, thermal, gas, and fluid transport medium for the PEM electrolyzer and ensure the transfer of electrons to the catalyst under applied potential, thus promoting water electrolysis at the membrane electrode. The anode and cathode gas diffusion layers are porous media between the proton exchange membrane and the electrode plates. Gas-liquid two-phase fluids are transported to the catalyst layer through the gas diffusion layer. Since the anode of the PEM electrolyzer is in a strongly acidic environment (pH≈2) and the electrolysis voltage is 1.4~2.0 V, the coating materials involved in the PEM electrolyzer are currently metals. In a strongly acidic environment, most non-precious metals will be corroded and may combine with sulfonate ions in PEM, thereby reducing the proton conduction capacity of the PEM electrolyzer. Therefore, at present, the coatings in PEM electrolyzers often use micron-sized precious metals such as ruthenium, platinum and gold to achieve long service life and corrosion resistance. However, the use of precious metals greatly increases the preparation cost of the PEM electrolyzer coating. Summary of the Invention

[0004] In view of this, this application proposes a composite coating, a bipolar plate and a porous diffusion layer. The composite coating can improve the stability of the coating in acidic environments and high potential conditions while reducing costs.

[0005] In a first aspect, embodiments of this application provide a composite coating, the composite coating being applied to the surface of a substrate, the composite coating comprising:

[0006] A base layer applied to the surface of the substrate, wherein the material of the base layer includes non-precious metal elements;

[0007] A composite material surface layer is applied to the surface of the underlying layer. The material of the composite material surface layer includes MAX material, MXene material, and MAX-MXene material. The chemical formula of MAX is MAX, the chemical formula of MXene is MX, and the MAX-MXene material has at least two crystal units sharing at least one M atom. M includes at least one element from IIIB to VIIB in the periodic table, A includes at least one element from VIIB to VIA in the second and third periods of the periodic table, and X includes at least one element from B, C, and N. The composite material surface layer has pores, and the porosity of the composite material surface layer is 5% to 50%.

[0008] In some embodiments, the porosity of the composite material surface layer is distributed in a stepped manner along the direction from the bottom layer to the surface layer.

[0009] In some implementations, the MAX material is disposed between the underlying layer and the MXene material.

[0010] In some embodiments, the composite coating includes at least one of the following features (1) to (3):

[0011] (1) M includes at least one of Ti, Nb, Ta, Hf and Zr;

[0012] (2) The A includes at least one of Co, P, S, Si, Au and Ir;

[0013] (3) The surface of the composite material is provided with non-metallic elements, including at least one of O, F and N.

[0014] In some embodiments, the composite coating includes at least one of the following features (1) to (3):

[0015] (1) The material of the bottom layer includes at least one of a first non-precious metal and an oxide containing a second non-precious metal;

[0016] (2) The material of the bottom layer includes at least one of a first non-precious metal and an oxide containing a second non-precious metal, wherein the first non-precious metal includes at least one of Ti, Nb, Ta, Hf and Zr;

[0017] (3) The material of the bottom layer includes at least one of a first non-precious metal and an oxide containing a second non-precious metal, wherein the second non-precious metal includes at least one of Ti, Nb, Ta, Hf and Zr.

[0018] In some embodiments, the bottom layer contains at least one non-precious metal element; and / or the bottom layer has at least two layers.

[0019] In some embodiments, the composite coating has a contact resistance of less than 2 mΩ / cm under 1.4 MPa conditions. 2 .

[0020] In some embodiments, the contact angle of the composite coating is 20° to 140°.

[0021] Secondly, embodiments of this application provide a bipolar plate for use in a PEM electrolytic cell, the bipolar plate comprising:

[0022] Substrate and

[0023] A coating applied to the surface of the substrate, the coating comprising the composite coating described in the first aspect, wherein the contact resistance of the bipolar plate is less than 4 mΩ / cm under a pressure of 1.4 MPa. 2 .

[0024] Thirdly, embodiments of this application provide a porous diffusion layer, the porous diffusion layer comprising:

[0025] Substrate and

[0026] A coating applied to the surface of the substrate, the coating including the composite coating described in the first aspect, the composite coating having a contact angle of 20° to 60°.

[0027] The technical solution of this application has at least the following beneficial effects:

[0028] The composite coating of this application includes a base layer and a composite material surface layer. The composite material surface layer is made of three materials: MAX material, MXene material, and MAX-MXene material. Among them, the MAX material is a nano-layered compound with a hexagonal crystal structure. The unit cell of MAX is formed by alternating stacking of MX units and A atomic planes. This special crystal structure gives the MAX phase the excellent properties of both ceramics and metals. It has strong strength, high temperature resistance, and corrosion resistance. The presence of the MAX material and the base layer of this application can significantly improve the mechanical strength and corrosion resistance of the composite coating. The MXene phase is MXene, which corresponds to MAX. MXene is a graphite-like two-dimensional layered material with a unique interface effect. It has good electrical and thermal conductivity and can also improve the stability of the composite coating in high temperature and acidic environments. MAX-MXene material contains at least two crystal units sharing at least one M atom, making it a novel material different from MAX and MXene materials, formed by MAX and MXene structural units sharing at least one M atom. On one hand, due to the significant morphological differences between MAX and MXene materials, the presence of MAX-MXene material enhances their bonding. On the other hand, the new structure of at least two crystal units sharing at least one M atom in MAX-MXene material results in a lower A element content, reducing the proportion of ionic bonds in the entire composite surface layer, which is beneficial for electron conduction and thus improves the conductivity of the composite surface layer. In this application, MAX material, MXene material, and MAX-MXene material form the surface layer of a composite material with a loose and porous structure. The presence of this porous structure improves the diffusivity of water in the PEM electrolyzer, while the dense MAX material prevents water from diffusing to the underlying layer and substrate. In addition, the composite coating of this application also includes a base layer, the coefficient of thermal expansion of which contains non-precious metal elements is between that of the composite material surface layer and the substrate on which the composite coating is loaded, which can improve the adhesion of the composite material surface layer to the substrate and make the composite coating less likely to fall off. Attached Figure Description

[0029] To more clearly illustrate the technical solutions of the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of the composite coating structure of this application.

[0031] In the picture:

[0032] 1- Composite material surface layer;

[0033] 2- Bottom layer;

[0034] 3- Substrate. Detailed Implementation

[0035] To better understand the technical solution of this application, the embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0036] It should be understood that the described embodiments are only some, not all, of the embodiments in this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0037] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0038] It should be understood that the term "and / or" used in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0039] The applicant proposes a composite coating applied to the surface of a substrate, such as... Figure 1 The diagram shown is a schematic representation of the composite coating provided in an embodiment of this application, including:

[0040] The underlayer is applied to the surface of the substrate, and the material of the underlayer includes non-precious metal elements;

[0041] A composite material surface layer is applied to the surface of the base layer. The material of the composite material surface layer includes MAX material, MXene material and MAX-MXene material. The chemical formula of MAX is MAX, the chemical formula of MXene is MX, and the MAX-MXene material has at least two crystal units sharing at least one M atom. M includes at least one of IIIB to VIIB in the periodic table, A includes at least one of VIIB to VIA in the second and third periods of the periodic table, and X includes at least one of B, C and N. The composite material surface layer has pores and the porosity of the composite material surface layer is 5% to 50%.

[0042] In the above scheme, the composite coating of this application includes a base layer and a composite material surface layer. The materials of the composite material surface layer include three types: MAX material, MXene material, and MAX-MXene material. Among them, MAX material is a nano-layered compound with a hexagonal crystal structure. The unit cell of MAX is formed by alternating stacking of MX units and A atomic planes. This special crystal structure gives the MAX phase the excellent properties of both ceramics and metals. It has strong strength, high temperature resistance, and corrosion resistance. The presence of MAX material and the base layer of this application can significantly improve the mechanical strength and corrosion resistance of the composite coating. The MXene phase is MXene, which corresponds to MAX. MXene is a graphite-like two-dimensional layered material. It has a unique interface effect, good electrical and thermal conductivity, and can also improve the stability of the composite coating in high temperature and acidic environments. MAX-MXene material contains at least two crystal units sharing at least one M atom, making it a novel material different from MAX and MXene materials, formed by MAX and MXene structural units sharing at least one M atom. On one hand, due to the significant morphological differences between MAX and MXene materials, the presence of MAX-MXene material enhances their bonding. On the other hand, the new structure of at least two crystal units sharing at least one M atom in MAX-MXene material results in a lower A element content, reducing the proportion of ionic bonds in the entire composite surface layer, which is beneficial for electron conduction and thus improves the conductivity of the composite surface layer. In this application, MAX material, MXene material, and MAX-MXene material form the surface layer of a composite material with a loose and porous structure. The presence of this porous structure improves the diffusivity of water in the PEM electrolyzer, while the dense MAX material prevents water from diffusing to the underlying layer and substrate. In addition, the composite coating of this application also includes a base layer, the coefficient of thermal expansion of which contains non-precious metal elements is between that of the composite material surface layer and the substrate on which the composite coating is loaded, which can improve the adhesion of the composite material surface layer to the substrate and make the composite coating less likely to fall off.

[0043] In some implementations, the MAX material is placed between the underlying layer and the MXene material to act as a transition, preventing the water environment of the electrolytic cell from penetrating the surface of the composite material and corroding the underlying layer, which can significantly improve the mechanical strength and corrosion resistance of the composite coating.

[0044] In the preparation method of the composite material surface layer of this application, a MAX material layer is first prepared, and then the MAX layer is etched with hydrofluoric acid. The etched material is placed in a reaction vessel for reaction, so that the MAX material on the surface layer forms MXene material and MAX-MXene material. Since the MXene material is generated in situ from the MAX material, MAX and MXene sharing at least one M atom can be generated during the reaction, which is the MAX-MXene material. For example, if the MAX material is CrAlC, the CrAlC-MAX phase in the corresponding composite material surface layer has a characteristic peak of 1120 crystal plane at about 65° in the XRD spectrum. Through SEM and TEM analysis, it was found that there is a layered CrC-MXene phase structure in the composite material surface layer, and a new material with a volume much larger than the CrC-MXene phase structure can also be seen, which can effectively prove the formation of the composite material surface layer of this application.

[0045] If the surface material of the composite material is only MAX material, it cannot maintain good stability in a high-temperature acidic environment and is prone to corrosion and loss in such an environment.

[0046] If the surface material of the composite material is only MXene, due to the loose porous structure of MXene, its bonding strength with the underlying layer is low, and the coating is prone to peeling off during high and low temperature alternation.

[0047] In some embodiments, the porosity of the composite material surface layer is 5% to 50%, specifically 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%, etc., and of course, other values ​​within the above range are also possible; this application does not impose any limitations on this. If the porosity is greater than 50%, the corrosive medium in the PEM electrolytic cell environment can easily penetrate into the underlying surface, accelerating the corrosion of the underlying layer and reducing the corrosion resistance of the composite coating. If the porosity is less than 5%, it leads to a decrease in electrical conductivity.

[0048] In some embodiments, M includes at least one of Ti, Nb, Ta, Hf, and Zr. These elements are suitable for use in electrolytic cells, which helps reduce preparation costs while improving the stability of the composite coating at high potentials.

[0049] In some embodiments, A includes at least one of Co, P, S, Si, Au, and Ir.

[0050] In some embodiments, the MAX material can be a ceramic material formed by M being selected from at least one of Ti, Nb, Ta, Hf and Zr, A being selected from at least one of Co, P, S, Si, Au and Ir, and X being selected from at least one of C, B and N.

[0051] In some implementations, the MXene material can be Ti3C2, Ti2C, Nb2C, (Ti 0.5 Nb 0.5 At least one of )2C and Ti3CN.

[0052] In some embodiments, the surface of the composite material layer is provided with non-metallic elements, including at least one of O, F, and N, which are covalently bonded to M. The non-metallic elements can be incorporated into the surface of the composite material layer through acid etching and oxidation. The presence of these non-metallic elements, when increasing the O and N content on the surface of the composite material layer, can reduce the contact angle of the composite coating, thus adjusting its hydrophilicity; conversely, increasing the F content on the surface of the composite material layer can regulate the hydrophobicity of the composite coating.

[0053] In some embodiments, the underlying material includes at least one of a first non-precious metal and an oxide containing a second non-precious metal.

[0054] In some embodiments, the first non-noble metal includes at least one of Ti, Nb, Ta, Hf, and Zr.

[0055] In some embodiments, the second non-noble metal includes at least one of Ti, Nb, Ta, Hf and Zr, and the oxide containing the second non-noble metal may be, for example, NbO2, TiO2, NbO5 and Ti4O7.

[0056] The aforementioned first non-precious metal and oxide containing the second non-precious metal are metallic materials with stable oxides, capable of forming a dense film layer. This film layer, positioned between the substrate and the composite material surface, acts as a barrier, preventing acid from easily penetrating the porous composite material surface and directly contacting the substrate, thus further enhancing the corrosion resistance of the composite coating. Furthermore, the presence of this underlayer reduces the difference in thermal expansion coefficients between the substrate and the composite material surface, achieving stable bonding with the substrate and improving the bonding strength of the composite coating.

[0057] In some embodiments, the substrate contains at least one non-precious metal element. That is, the substrate of this application may be a coating formed by a single non-precious metal or a single non-precious metal oxide, or a coating formed by two or more non-precious metals, a coating formed by two or more non-precious metal oxides, or a coating formed by at least one non-precious metal and at least one non-precious metal oxide.

[0058] In some implementations, at least two layers are provided as the bottom layer. The provision of multiple layers of bottom layer material can improve the density of the coating material, reduce the passage of corrosive media, and improve the corrosion resistance of the composite coating.

[0059] In some embodiments, the total thickness of the bottom layer is 100 nm to 2000 nm, specifically 100 nm, 300 nm, 500 nm, 800 nm, 1000 nm, 1500 nm, 1800 nm or 2000 nm, etc., and of course, other values ​​within the above range are also possible, which are not limited in this application.

[0060] In some embodiments, the thickness of the composite material surface layer is 200 nm to 5000 nm, specifically 200 nm, 500 nm, 1000 nm, 1500 nm, 2000 nm, 2500 nm, 3000 nm, 3500 nm, 4000 nm, 4500 nm or 5000 nm, etc., and of course, other values ​​within the above range are also possible, which are not limited in this application.

[0061] In some embodiments, the contact angle of the composite coating is 20°~140°, specifically 20°, 30°, 40°, 50°, 60°, 70°, 80°, 90°, 100°, 110°, 120°, 130°, or 140°, or other values ​​within the above range. This application can control the contact angle of the composite coating by adjusting the porosity of the composite material surface layer. The contact angle of the composite coating is positively correlated with the porosity. Furthermore, the hydrophilicity and hydrophobicity can be further adjusted by modifying the composite material surface layer. When the O and N content of the composite material surface layer increases, the contact angle of the coating can be reduced, achieving hydrophilicity control. The aforementioned composite coating can be applied to porous diffusion layers to meet the hydrophilicity requirements of the porous diffusion layer, which is beneficial for improving the wettability of liquids such as water to the porous diffusion layer. When the F content of the composite material surface layer increases, the contact angle of the composite coating can be increased, achieving hydrophobicity control. The aforementioned composite coating can be applied to bipolar plates.

[0062] In some embodiments, the composite coating exhibits a contact resistance of less than 2 mΩ / cm under 1.4 MPa conditions. 2 Specifically, it could be 0.2 mΩ / cm 2 0.5 mΩ / cm 2 0.8 mΩ / cm 2 1 mΩ / cm 2 1.3 mΩ / cm 2 1.5 mΩ / cm 2 1.8 mΩ / cm 2 Or 1.9 mΩ / cm 2 Of course, other values ​​within the above range are also possible, and this application does not impose any limitations on them. Within the above range, it is indicated that the composite coating of this application has excellent electrical conductivity.

[0063] In some embodiments, the porosity of the composite coating can be adjusted according to the ratio of the MAX phase and the MXene phase, thereby controlling the contact angle of the composite coating and giving it tunable hydrophilicity / hydrophobicity.

[0064] The composite coating of this application can be applied to the bipolar plates of a PEM electrolyzer. The hydrophilicity / hydrophobicity of the composite coating is not required, but the contact resistance of the bipolar plate must be less than 4 @ 1.4 MPa. When the composite coating is applied to the bipolar plate, the substrate is a bipolar plate substrate, and the material of the bipolar plate substrate includes, but is not limited to, stainless steel, titanium alloy, and their composite substrates.

[0065] The composite coating of this application can also be applied to the porous diffusion layer of a PEM electrolytic cell. In this case, the composite coating needs to have excellent hydrophilicity, i.e., the contact angle of the composite coating is 20°~60°, specifically 20°, 30°, 40°, 50°, 55° or 60°, etc., and of course, other values ​​within the above range are also possible, which are not limited here. Within the above-defined range, the wettability of the porous diffusion layer to water can be improved, which is beneficial to improving the water transport capacity of the porous diffusion layer. It is understood that when the composite coating is applied to the porous diffusion layer, the substrate is a porous diffusion layer substrate. In some embodiments, the porous diffusion layer substrate is titanium, titanium alloy or stainless steel, etc.

[0066] In some embodiments, this application provides a method for preparing the above-mentioned composite coating, comprising the following steps:

[0067] S100, providing substrate.

[0068] In some embodiments, the substrate can be a porous diffusion layer substrate or a bipolar plate substrate. It is understood that the bipolar plate substrate and the porous diffusion layer substrate can be the same substrate, but different processes are used to prepare them based on different functions.

[0069] In some embodiments, after providing the substrate, a pretreatment step is included, which includes, but is not limited to, methods such as acid oxidation, electropolishing, and alkaline cleaning to clean the surface oil stains of the bipolar plate.

[0070] S200: Deposit the underlying material onto the surface of the substrate to form the underlying layer.

[0071] S200 specifically includes the following steps: fixing the substrate obtained in S100 on a hanger, moving it to a closed reaction chamber and evacuating its interior; when the vacuum reaches 10... -3When the pressure reaches Pa, the heater is turned on for heating; when the temperature in the reaction chamber reaches the specified temperature, it is kept at that temperature for a period of time, and then Ar is introduced into the chamber through the gas path and gas hole to maintain a vacuum of 0.6 Pa. At least one of Ti, Nb, Ta, Hf and Zr metal or metal oxide target material is used for deposition treatment to obtain the bottom layer.

[0072] In some implementations, at least two layers are deposited at the bottom layer. The process parameters can be adjusted and repeated according to the above steps based on the required number of layers at the bottom layer.

[0073] S300: A composite material surface layer is formed on a substrate with an underlayer.

[0074] S301. Mix raw material powders containing M, A and X, press the resulting mixture with a substrate having a bottom layer into a blank, and sinter the resulting blank to obtain a pre-treated layer, which is the MAX material layer.

[0075] Alternatively, S301, raw materials containing M and A are prepared into pure M and pure A targets, which are introduced through an organic X source. Under high vacuum, the sputtering current of the target is adjusted, and the X and Ar gas volumes are optimized. A MAX material layer is deposited on the bottom layer through a co-deposition reaction.

[0076] In some embodiments, M includes at least one element from IIIB to VIIB of the periodic table, preferably at least one element from Ti, Nb, Ta, Hf, and Zr. These elements are suitable for use in electrolytic cells, which helps reduce preparation costs while improving the stability of the composite coating at high potentials.

[0077] In some embodiments, A includes at least one of VIIB to VIA from the second and third periods of the periodic table. Preferably, A includes at least one of Co, P, S, Si, Au, and Ir.

[0078] In some implementations, X includes at least one of B, C, and N.

[0079] This application does not impose any restrictions on the proportions of M, A, and X elements in raw material powders containing M, A, and X; however, specific proportion restrictions can be imposed based on actual needs.

[0080] In some embodiments, the mesh size of the raw material powder containing M, A and X is less than or equal to 500 mesh, for example, it can be 100 mesh, 150 mesh, 200 mesh, 250 mesh, 300 mesh, 350 mesh, 400 mesh or 450 mesh, etc. Of course, it can also be other values ​​within the above range, which are not limited here.

[0081] In some embodiments, the method of pressing the mixture and the substrate with the bottom layer into a blank can be, for example, cold pressing, specifically by placing the mixture and the substrate with the bottom layer in a cold press to press into a blank.

[0082] In some embodiments, the temperature for cold pressing into a billet is -1200℃ to -800℃, specifically -1200℃, -1100℃, -1000℃, -900℃ or -800℃, etc., and of course, other values ​​within the above range are also possible, which are not limited here.

[0083] In some embodiments, the pressure for cold pressing is 30 MPa to 50 MPa, specifically 30 MPa, 33 MPa, 35 MPa, 38 MPa, 40 MPa, 43 MPa, 46 MPa, 48 MPa or 50 MPa, etc. Of course, it can also be other values ​​within the above range, which are not limited here.

[0084] In some embodiments, the sintering equipment may be, for example, a vacuum sintering furnace, but of course, other sintering equipment may also be used, and this application does not limit the scope of the application.

[0085] In some embodiments, the sintering temperature is >500°C, specifically 550°C, 600°C, 700°C, 800°C, 900°C, or 1000°C, etc., and of course, other values ​​within the above range are also possible, which are not limited herein.

[0086] In some embodiments, the sintering pressure is 1×10⁻⁶. -3 Pa~2×10 -3 Pa can specifically be 0.001 Pa, 0.0015 Pa, or 0.002 Pa, or other values ​​within the above range. This application does not impose any restrictions on these values.

[0087] In some embodiments, the sintering time is 36 h to 50 h, specifically 36 h, 42 h, 48 h or 50 h, etc., and of course other values ​​within the above range are also possible. This application does not limit this.

[0088] S302. The pretreatment layer is immersed in an acidic solution for treatment to obtain the surface layer of the composite material.

[0089] In the above steps, by etching the MAX material in an acid solution, MXene is generated in situ from the MAX material on the surface. Inside the composite material surface layer, MAX-MXene material is generated in situ from the MAX material inside the surface layer. In the MAX-MXene material, at least two crystal units share at least one M atom. By setting a composite material surface layer composed of three materials, this application can, on the one hand, facilitate the bonding between the composite material surface layer and the underlying layer, and on the other hand, improve the conductivity of the composite coating while enhancing the electron conduction, thereby improving the stability of the composite material surface layer in high potential and acidic environments, and improving the liquid diffusion of the composite coating in the electrolytic cell, thus extending the service life of the electrolytic cell using the composite coating.

[0090] In some embodiments, the acidic solution includes a hydrofluoric acid solution.

[0091] In some embodiments, the concentration of the hydrofluoric acid solution is 15 wt% to 40 wt%, specifically 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, or 40 wt%, etc., and of course, other values ​​within the above range are also possible, which are not limited herein. Within the above-defined range, when other conditions (temperature and time) are constant, the lower the concentration of hydrofluoric acid, the higher the oxygen / nitrogen content in the surface layer of the composite material, resulting in a smaller contact angle and enhanced hydrophilicity of the composite material surface layer; when other conditions (temperature and time) are constant, the higher the concentration of hydrofluoric acid, the faster the etching rate and the higher the covalent ratio of F ions, resulting in an increased contact angle and enhanced hydrophobicity of the composite coating.

[0092] In some embodiments, the acid solution treatment further includes: encapsulating the material obtained from the acid solution treatment with silica gel, the presence of which can coat the cross-sectional area of ​​the material obtained from the acid solution treatment, and reacting it in a reaction vessel to obtain a composite material surface layer.

[0093] In some embodiments, the pressure in the reactor is 0.1 MPa to 5 MPa, specifically 0.1 MPa, 0.3 MPa, 0.5 MPa, 1 MPa, 2 MPa, 3 MPa, 4 MPa or 5 MPa, etc. Of course, it can also be other values ​​within the above range. This application does not limit it here. This application carries out the treatment of the material obtained by acid solution in the reactor, which is beneficial to the generation of MAX-MXene material on the one hand, and can reduce the temperature of the reaction treatment and the reaction time by pressurizing, thereby improving the etching effect.

[0094] In some embodiments, the reaction temperature in the reactor is 60℃~90℃, specifically 60℃, 70℃, 80℃, or 90℃, or other values ​​within the above range; this application does not impose any limitations on this. The lower reaction temperature in this application serves two purposes: firstly, it reduces the reaction of the underlying material in an aqueous environment, thus minimizing the reduction in the coating's corrosion resistance; secondly, it avoids excessively high temperatures that could lead to excessively high acid solution concentrations, affecting the etching effect.

[0095] In some embodiments, the reaction time in the reactor is 24h to 200h, specifically 24h, 36h, 48h, 60h, 72h, 84h, 96h, 120h, 150h, 180h or 200h, etc., and of course other values ​​within the above range are also possible, which are not limited in this application.

[0096] The porosity of the surface layer of the composite material is related to temperature, pressure and time. Within the scope defined in this application, the higher the temperature, the higher the porosity, the higher the pressure, and the longer the time, the higher the porosity.

[0097] In some embodiments, the reaction in the reactor is followed by a step of placing the resulting material in a vacuum chamber and treating it with nitrogen and / or oxygen.

[0098] In some embodiments, the process parameters of the above treatment are: temperature of 200℃~350℃, time of 20min~40min, and vacuum degree of -0.2pa~-0.5pa. Within the above range, the content of oxygen atoms in the surface layer of the composite material is greater than 20%, and / or the content of nitrogen atoms in the surface layer of the composite material is 1%~15%, thereby making the contact angle of the composite coating between 20° and 60° and improving the hydrophilicity of the bipolar plate.

[0099] The above preparation method can sequentially generate a bottom layer containing non-precious metal elements and a composite material surface layer on the surface of the substrate. The composite coating composed of the two layers can enhance the corrosion resistance, conductivity and stability of the substrate in a strong acid environment, effectively improve the service life of the PEM electrolyzer, reduce the manufacturing cost of the PEM electrolyzer, and improve the economic efficiency of the PEM electrolyzer.

[0100] The embodiments of this application will be further described below with reference to several examples. However, the embodiments of this application are not limited to the specific embodiments described below.

[0101] Example 1

[0102] (1) Select a porous diffusion layer with pure titanium as the substrate and uniform thickness, and perform ultrasonic cleaning in ethanol and water to remove surface grease and surface debris.

[0103] (2) Fix the titanium substrate to the bracket, move it to the closed reaction chamber and evacuate its interior. When the vacuum reaches 10... -3 At a pressure of Pa, the heater is turned on for heating. When the temperature in the reaction chamber reaches the specified temperature, it is kept at that temperature for a period of time. Then, Ar is introduced into the chamber through the gas path and gas vent to maintain a vacuum of 0.6 Pa. The sputtering current of the Nb target is controlled and the bias voltage is adjusted. The deposition time is 10 min to obtain the first layer. After the first layer is completed, Ar and O2 in a ratio of 3:1 are introduced to maintain a vacuum of 0.3 Pa. The sputtering current of the Nb target is controlled and the bias voltage is adjusted. The deposition time is 15 min to obtain the second layer. After the second layer is completed, Ar and O2 are introduced to maintain a vacuum of 0.6 Pa. The sputtering current of the Nb target is controlled and the bias voltage is adjusted. The deposition time is 15 min to complete the deposition of the third layer, resulting in a three-layer corrosion-resistant Nb underlayer.

[0104] (3) A certain proportion of Ti, graphite and SiC mixed powder with a mesh size of less than 500 is hot-pressed onto the corrosion-resistant substrate and cold-pressed with the pre-deposited titanium substrate at 30 MPa to form a billet. The cold-pressing parameters are: pressure of 40 MPa and temperature of -1000℃. The cold-pressed billet is placed in a vacuum sintering furnace at 1.2 × 10⁻⁶ ℃. -3 The pressure of Pa was applied to the pre-deposited titanium substrate, and the sintering time was 48 h to obtain the MAX phase layer Ti3SiC2.

[0105] (4) The material obtained in (3) is wrapped with silicone and immersed in 20wt% hydrofluoric acid solution. The reaction is carried out in a reactor at 0.1MPa and 60℃ for 72h to finally obtain the surface layer of MAX-MXene composite material.

[0106] In this embodiment, a porous diffusion layer containing a composite coating is prepared. The composite coating includes a titanium porous substrate and a Ti-Si-C-Ti-C material layer stacked sequentially. The Ti-Si-C-Ti-C material layer is a mixture of MAX material (Ti3SiC2), MXene material (Ti3C2), and MAX-MXene material (Ti-Si-C).

[0107] Example 2

[0108] (1) Select a bipolar plate with pure titanium as the substrate and uniform thickness, and perform ultrasonic cleaning in ethanol and water to remove surface grease and surface debris.

[0109] (2) Fix the titanium substrate to the bracket, move it to the closed reaction chamber and evacuate its interior. When the vacuum reaches 10... -3At a pressure of Pa, the heater is turned on for heating. When the temperature in the reaction chamber reaches the specified temperature, it is kept at that temperature for a period of time. Then, Ar is introduced into the chamber through the gas path and gas vent to maintain a vacuum of 0.2 Pa. The sputtering current of the Ti target is controlled and the bias voltage is adjusted. The deposition time is 10 min to obtain the first layer. After the first layer is completed, Ar is introduced to maintain a vacuum of 0.1 Pa. The sputtering current of the Nb target is controlled and the bias voltage is adjusted. The deposition time is 15 min to obtain the second layer. After the second layer is completed, Ar is introduced to maintain a vacuum of 0.2 Pa. The sputtering current of the Ti target is controlled and the bias voltage is adjusted. The deposition time is 15 min to obtain the third layer. After the third layer is completed, Ar is introduced to maintain a vacuum of 0.1 Pa. The sputtering current of the Nb target is controlled and the bias voltage is adjusted. The deposition time is 15 min to form the fourth layer, resulting in a four-layer corrosion-resistant underlayer.

[0110] (3) A certain proportion of ZrH2, graphite and SiC mixed powder with a mesh size of less than 500 is hot-pressed onto the corrosion-resistant substrate and cold-pressed with the pre-deposited titanium substrate at 60 MPa to form a billet. The billet is then placed in a vacuum sintering furnace at 20 MPa and a temperature of -1200℃ at a pressure of 1.2 × 10⁻⁶. -3 The pressure of Pa was applied to the pre-deposited titanium substrate, and the sintering time was 30 h to obtain the MAX phase layer Zr2SiC.

[0111] (4) The material obtained in (3) was wrapped with silicone and immersed in a 30wt% hydrofluoric acid solution. The reaction was carried out in a reactor at 0.1MPa and 60℃ for 72h to finally obtain the MAX-MXene composite material surface layer.

[0112] In this embodiment, a porous diffusion layer containing a composite coating is prepared. The composite coating includes a titanium porous substrate and a Zr-Si-C-Zr-C material layer stacked sequentially. The Zr-Si-C-Zr-C material layer is a mixture of MAX material (Zr2SiC), MXene material (Zr2C), and MAX-MXene material (Zr-Si-C).

[0113] Example 3

[0114] (1) Select a bipolar plate with pure titanium as the substrate and uniform thickness, and perform ultrasonic cleaning in ethanol and water to remove surface grease and surface debris.

[0115] (2) Fix the titanium substrate to the bracket, move it to the closed reaction chamber and evacuate its interior. When the vacuum reaches 10... -3At Pa, the heater is turned on for heating; when the temperature in the reaction chamber reaches the specified temperature, it is kept at that temperature for a period of time, and then Ar is introduced into the chamber through the gas path and gas hole to maintain a vacuum of 0.2 Pa. The sputtering current of the Ti target is controlled and the bias voltage is adjusted. The deposition time is 10 min to obtain the first layer. After the first layer is completed, Ar is introduced and the vacuum is maintained at 0.3 Pa. The sputtering current of the Hf target is controlled and the bias voltage is adjusted. The deposition time is 15 min to obtain the second layer. After the second layer is completed, Ar is introduced and the vacuum is maintained at 0.2 Pa. The sputtering current of the Nb target is controlled and the bias voltage is adjusted. The deposition time is 15 min to obtain the third layer. Ar and O2 are introduced and the vacuum is maintained at 0.3 Pa. The sputtering current of the Nb target is controlled and the bias voltage is adjusted. The deposition time is 15 min to complete the fourth layer, forming a four-layer corrosion-resistant underlayer.

[0116] (3) A certain proportion of Ti, graphite and SiC mixed powder with a mesh size of less than 500 is hot-pressed onto the corrosion-resistant substrate and cold-pressed with the pre-deposited titanium substrate at 30 MPa to form a billet. The billet is then placed in a vacuum sintering furnace at 40 MPa and a temperature of -1100℃ and sintered at 1.2 × 10⁻⁶ ℃. -3 The pressure of Pa was applied to the pre-deposited titanium substrate, and the sintering time was 50 h to obtain the MAX phase layer Ti3SiC2.

[0117] (4) The MAX phase layer was immersed in a 40wt% hydrofluoric acid solution, the substrate was wrapped with silicone, and the reaction was carried out in a reactor at 0.1MPa pressure and 60℃ for 72h to obtain the Ti3SiC2 surface layer of the MAX-MXene composite material.

[0118] In this embodiment, a porous diffusion layer containing a composite coating is prepared. The composite coating includes a titanium porous substrate and a Ti-Si-C-Ti-C material layer stacked sequentially. The Ti-Si-C-Ti-C material layer is a mixture of MAX material (Ti3SiC2), MXene material (Ti3C2), and MAX-MXene material (Ti-Si-C).

[0119] Example 4

[0120] (1) Select a porous diffusion layer with pure titanium as the substrate and uniform thickness, and perform ultrasonic cleaning in ethanol and water to remove surface grease and surface debris.

[0121] (2) Fix the titanium substrate to the bracket, move it to the closed reaction chamber and evacuate its interior. When the vacuum reaches 10... -3At a pressure of Pa, the heater is turned on for heating. When the temperature in the reaction chamber reaches the specified temperature, it is kept at that temperature for a period of time. Then, Ar is introduced into the chamber through the gas path and gas vent to maintain a vacuum of 0.2 Pa. The sputtering current of the Ti target is controlled and the bias voltage is adjusted. The deposition time is 10 min to obtain the first layer. After the first layer is completed, Ar is introduced to maintain a vacuum of 0.1 Pa. The sputtering current of the Nb target is controlled and the bias voltage is adjusted. The deposition time is 15 min to obtain the second layer. After the second layer is completed, Ar is introduced to maintain a vacuum of 0.2 Pa. The sputtering current of the Ti target is controlled and the bias voltage is adjusted. The deposition time is 15 min to obtain the third layer. After the third layer is completed, Ar is introduced to maintain a vacuum of 0.1 Pa. The sputtering current of the Nb target is controlled and the bias voltage is adjusted. The deposition time is 15 min to form the fourth layer, resulting in a four-layer corrosion-resistant underlayer.

[0122] (3) A certain proportion of ZrH2, graphite and SiC mixed powder with a mesh size of less than 500 is hot-pressed onto the corrosion-resistant substrate and cold-pressed with the pre-deposited titanium substrate at 60 MPa to form a billet. The billet is then placed in a vacuum sintering furnace at 20 MPa and a temperature of -1200℃ at a pressure of 1.2 × 10⁻⁶. -3 The pressure of Pa was applied to the pre-deposited titanium substrate, and the sintering time was 30 h to obtain the MAX phase layer Zr2SiC.

[0123] (4) The MAX phase layer was immersed in a 25wt% hydrofluoric acid solution, the substrate was wrapped with silicone, and the reaction was carried out in a reactor at 0.1MPa and 60℃ for 72h to finally obtain the MAX-MXene composite material surface layer.

[0124] In this embodiment, a porous diffusion layer containing a composite coating is prepared. The composite coating includes a titanium porous substrate and a Zr-Si-C-Zr-C material layer stacked sequentially. The Zr-Si-C-Zr-C material layer is a mixture of MAX material (Zr2SiC), MXene material (Zr2C), and MAX-MXene material (Zr-Si-C).

[0125] Example 5

[0126] Unlike Example 1, the substrate in step (4) where the MAX phase layer was immersed in a 15wt% hydrofluoric acid solution was wrapped with silicone and reacted in a reactor at 60°C for 72 hours.

[0127] In this embodiment, a porous diffusion layer containing a composite coating is prepared. The composite coating includes a titanium porous substrate and a Ti-Si-C-Ti-C material layer stacked sequentially. The Ti-Si-C-Ti-C material layer is a mixture of MAX material (Ti3SiC2), MXene material (Ti3C2), and MAX-MXene material (Ti-Si-C).

[0128] Example 6

[0129] Unlike Example 3, in step (4): the MAX phase layer is immersed in a 40wt% hydrofluoric acid solution, the substrate is wrapped with silicone, and the pressure in the reactor is 0.5MPa.

[0130] In this embodiment, a porous diffusion layer containing a composite coating is prepared. The composite coating includes a titanium porous substrate and a Ti-Si-C-Ti-C material layer stacked sequentially. The Ti-Si-C-Ti-C material layer is a mixture of MAX material (Ti3SiC2), MXene material (Ti3C2), and MAX-MXene material (Ti-Si-C).

[0131] Example 7

[0132] Unlike Example 3, in step (4): the MAX phase layer is immersed in a 40wt% hydrofluoric acid solution, the substrate is wrapped with silicone, and the pressure in the reactor is 1MPa.

[0133] In this embodiment, a porous diffusion layer containing a composite coating is prepared. The composite coating includes a titanium porous substrate and a Ti-Si-C-Ti-C material layer stacked sequentially. The Ti-Si-C-Ti-C material layer is a mixture of MAX material (Ti3SiC2), MXene material (Ti3C2), and MAX-MXene material (Ti-Si-C).

[0134] Example 8

[0135] Unlike Example 3, in step (4): the MAX phase layer is immersed in a 40wt% hydrofluoric acid solution, the substrate is wrapped with silicone, and the pressure in the reactor is 5MPa.

[0136] In this embodiment, a porous diffusion layer containing a composite coating is prepared. The composite coating includes a titanium porous substrate and a Ti-Si-C-Ti-C material layer stacked sequentially. The Ti-Si-C-Ti-C material layer is a mixture of MAX material (Ti3SiC2), MXene material (Ti3C2), and MAX-MXene material (Ti-Si-C).

[0137] Example 9

[0138] Unlike Example 3, in step (4): the MAX phase layer is immersed in a 40wt% hydrofluoric acid solution, the substrate is wrapped with silicone, and the temperature in the reactor is 70°C.

[0139] In this embodiment, a porous diffusion layer containing a composite coating is prepared. The composite coating includes a titanium porous substrate and a Ti-Si-C-Ti-C material layer stacked sequentially. The Ti-Si-C-Ti-C material layer is a mixture of MAX material (Ti3SiC2), MXene material (Ti3C2), and MAX-MXene material (Ti-Si-C).

[0140] Example 10

[0141] Unlike Example 3, in step (4): the MAX phase layer is immersed in a 40wt% hydrofluoric acid solution, the substrate is wrapped with silicone, and the temperature in the reactor is 80°C.

[0142] In this embodiment, a porous diffusion layer containing a composite coating is prepared. The composite coating includes a titanium porous substrate and a Ti-Si-C-Ti-C material layer stacked sequentially. The Ti-Si-C-Ti-C material layer is a mixture of MAX material (Ti3SiC2), MXene material (Ti3C2), and MAX-MXene material (Ti-Si-C).

[0143] Example 11

[0144] Unlike Example 3, in step (4): the MAX phase layer is immersed in a 40wt% hydrofluoric acid solution, the substrate is wrapped with silicone, and the temperature in the reactor is 90°C.

[0145] In this embodiment, a porous diffusion layer containing a composite coating is prepared. The composite coating includes a titanium porous substrate and a Ti-Si-C-Ti-C material layer stacked sequentially. The Ti-Si-C-Ti-C material layer is a mixture of MAX material (Ti3SiC2), MXene material (Ti3C2), and MAX-MXene material (Ti-Si-C).

[0146] Example 12

[0147] (1) Select a porous diffusion layer with pure titanium as the substrate and uniform thickness, and perform ultrasonic cleaning in ethanol and water to remove surface grease and surface debris.

[0148] (2) Fix the titanium substrate to the bracket, move it to the closed reaction chamber and evacuate its interior. When the vacuum reaches 10... -3At a pressure of Pa, the heater is turned on for heating. When the temperature in the reaction chamber reaches the specified temperature, it is kept at that temperature for a period of time. Then, Ar is introduced into the chamber through the gas path and gas vent to maintain a vacuum of 0.6 Pa. The sputtering current of the Nb target is controlled and the bias voltage is adjusted. The deposition time is 10 min to obtain the first layer. After the first layer is completed, Ar and O2 in a ratio of 3:1 are introduced to maintain a vacuum of 0.3 Pa. The sputtering current of the Nb target is controlled and the bias voltage is adjusted. The deposition time is 15 min to obtain the second layer. After the second layer is completed, Ar and O2 are introduced to maintain a vacuum of 0.6 Pa. The sputtering current of the Nb target is controlled and the bias voltage is adjusted. The deposition time is 15 min to complete the deposition of the third layer, resulting in a three-layer corrosion-resistant underlayer.

[0149] (3) A certain proportion of Ti, graphite and SiC mixed powder with a mesh size of less than 500 is hot-pressed onto the corrosion-resistant substrate and cold-pressed with the pre-deposited titanium substrate at 30 MPa to form a billet. The cold-pressing parameters are: pressure of 40 MPa and temperature of -1000℃. The cold-pressed billet is placed in a vacuum sintering furnace at 1.2 × 10⁻⁶ ℃. -3 The pressure of Pa was applied to the pre-deposited titanium substrate, and the sintering time was 48 h to obtain the MAX phase layer Ti3SiC2.

[0150] (4) The material obtained in (3) was encapsulated in silica gel and then immersed in a 40wt% hydrofluoric acid solution. It was reacted in a reactor at 0.1MPa and 60℃ for 72h to finally obtain the MAX-MXene composite material surface layer. The deposited sample was re-attached and moved into a vacuum chamber, and a certain amount of nitrogen and oxygen were introduced. The treatment lasted for 30min, with a vacuum of -0.3Pa and a temperature of 300℃.

[0151] In this embodiment, a porous diffusion layer containing a composite coating is prepared. The composite coating includes a titanium porous substrate and a Ti-Si-C-Ti-C material layer stacked sequentially. The Ti-Si-C-Ti-C material layer is a mixture of MAX material (Ti3SiC2), MXene material (Ti3C2), and MAX-MXene material (Ti-Si-C).

[0152] Example 13

[0153] (1) Select a titanium bipolar plate with pure titanium as the substrate and uniform thickness, and perform ultrasonic cleaning in ethanol and water to remove surface grease and surface debris.

[0154] (2) Fix the titanium substrate to the bracket, move it to the closed reaction chamber and evacuate its interior. When the vacuum reaches 10... -3At a pressure of Pa, the heater is turned on for heating. When the temperature in the reaction chamber reaches the specified temperature, it is kept at that temperature for a period of time. Then, Ar is introduced into the chamber through the gas path and gas pores to maintain a vacuum of 0.6 Pa. The sputtering current of the Ti target is controlled and the bias voltage is adjusted. The deposition time is 10 min to obtain the first layer. After the first layer is completed, Ar and O2 in a ratio of 3:1 are introduced to maintain a vacuum of 0.3 Pa. The sputtering current of the Nb target is controlled and the bias voltage is adjusted. The deposition time is 15 min to obtain the second layer. After the second layer is completed, Ar and O2 are introduced to maintain a vacuum of 0.6 Pa. The sputtering current of the Nb target is controlled and the bias voltage is adjusted. The deposition time is 15 min to complete the deposition of the third layer, resulting in a three-layer corrosion-resistant underlayer.

[0155] (3) Move the rack to the next chamber. When the temperature in the reaction chamber reaches the specified temperature, keep it warm for a period of time. Then, introduce Ar and C2H2 into the chamber through the gas path and gas hole to maintain the vacuum at 0.3pa. Sputter a certain proportion of Ti target and Si target, adjust the bias voltage and target current, and deposit for 30 minutes to obtain the MAX phase coating material Ti3SiC2.

[0156] (4) The material obtained in (3) was encapsulated in silicone and then immersed in a 40wt% hydrofluoric acid solution. The reaction was carried out in a reactor at 0.1MPa and 60℃ for 72h to finally obtain the MAX-MXene composite material surface layer.

[0157] In this embodiment, a porous diffusion layer containing a composite coating is prepared. The composite coating includes a titanium porous substrate and a Ti-Si-C-Ti-C material layer stacked sequentially. The Ti-Si-C-Ti-C material layer is a mixture of MAX material (Ti3SiC2), MXene material (Ti3C2), and MAX-MXene material (Ti-Si-C).

[0158] Comparative Example 1

[0159] Unlike Example 2, only one corrosion-resistant underlayer is deposited in step (2).

[0160] Comparative Example 2

[0161] Unlike Example 2, step (4) is not performed.

[0162] Comparative Example 3

[0163] (1) Select a titanium bipolar plate with pure titanium as the substrate and uniform thickness, and perform ultrasonic cleaning in ethanol and water to remove surface grease and surface debris.

[0164] (2) Fix the titanium substrate to the bracket, move it to the closed reaction chamber and evacuate its interior. When the vacuum reaches 10... -3At a pressure of Pa, the heater is turned on for heating. When the temperature in the reaction chamber reaches the specified temperature, it is kept at that temperature for a period of time. Then, Ar is introduced into the chamber through the gas path and gas pores to maintain a vacuum of 0.6 Pa. The sputtering current of the Ti target is controlled and the bias voltage is adjusted. The deposition time is 10 min to obtain the first layer. After the first layer is completed, Ar and O2 in a ratio of 3:1 are introduced to maintain a vacuum of 0.3 Pa. The sputtering current of the Nb target is controlled and the bias voltage is adjusted. The deposition time is 15 min to obtain the second layer. After the second layer is completed, Ar and O2 are introduced to maintain a vacuum of 0.6 Pa. The sputtering current of the Nb target is controlled and the bias voltage is adjusted. The deposition time is 15 min to complete the deposition of the third layer, resulting in a three-layer corrosion-resistant underlayer.

[0165] (3) Move the rack to the next chamber. When the temperature in the reaction chamber reaches the specified temperature, keep it warm for a period of time. Then, introduce Ar and C2H2 into the chamber through the gas path and gas hole to maintain the vacuum at 0.3pa. Sputter a certain proportion of Ti target and Si target, adjust the bias voltage and target current, and deposit for 30 minutes to obtain the MAX phase coating material.

[0166] (4) The material obtained in (3) was encapsulated in silicone and then immersed in a 5 wt% hydrofluoric acid solution. The reaction was carried out in a reactor at 0.1 MPa and 60°C for 72 h to finally obtain the MAX-MXene composite material surface layer.

[0167] In this embodiment, a bipolar plate containing a composite coating is prepared. The composite coating includes a titanium substrate and a Ti-Si-C-Ti-C material layer stacked sequentially. The Ti-Si-C-Ti-C material layer is a mixture of MAX material (TiSiC), MXene material (TiC), and MAX-MXene material (TiSiC-TiC).

[0168] Performance testing

[0169] (1) The thickness of each layer in the composite coating was tested by SEM electron microscopy.

[0170] (2) The corrosion conductivity of the composite coatings of each embodiment and comparative example was tested by electrochemical method. The corrosion medium was sulfuric acid environment with pH=3. The test potential was greater than or equal to 2.5 V and the polarization time was greater than or equal to 100 h. The stability of the contact resistance of the coating before and after corrosion was evaluated by surface contact resistance test. The test pressure was 0.6 MPa.

[0171] (3) The contact resistance of the composite coating under a 1.4MPa clamping force was tested using the contact resistance test method in GB / T 20042.6-2011 bipolar plate test.

[0172] (4) The contact angle was tested using a water contact angle meter.

[0173] (5) Porosity was tested using the mercury intrusion porosimetry method: The material sample was immersed in mercury, and the pressure was increased to allow the mercury to fully penetrate the pores. The porosity was calculated by measuring the volume of mercury injected into the sample. The test results are shown in Table 1.

[0174]

[0175] Table 1. Performance tests of composite coatings prepared in each example and comparative example

[0176] As can be seen from the data in Table 1, by setting the bottom layer and the composite material surface layer in Examples 1 to 13 of this application, the bottom layer and the composite material surface layer of this application can work together to reduce the preparation cost and improve the stability of the composite coating in high potential and strong acid environment, thereby improving the service life of the composite coating.

[0177] In Comparative Example 1, the bottom layer of the composite coating is a single layer, which leads to an increase in the composite current density of the composite coating and a decrease in its corrosion resistance.

[0178] In Comparative Example 2, the composite coating only contains MAX material, which cannot maintain good stability in a high-temperature acidic environment and is prone to corrosion and loss in such an environment.

[0179] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A composite coating, said composite coating being applied to the surface of a substrate, characterized in that, The composite coating includes: The bottom layer is disposed on the surface of the substrate, and the material of the bottom layer includes at least one of a first non-precious metal and an oxide containing a second non-precious metal. The first non-precious metal includes at least one of Ti, Nb and Hf, and the second non-precious metal includes at least one of Ti, Nb and Hf. The bottom layer is provided with at least two layers. A composite material surface layer is applied to the surface of the underlying layer. The material of the composite material surface layer includes MAX material, MXene material, and MAX-MXene material. The chemical formula of MAX is MAX, the chemical formula of MXene is MX, and the MAX-MXene material has at least two crystal units sharing at least one M atom, wherein M is at least one of Ti and Zr, A is Si, and X is C. The composite material surface layer has pores, and the porosity of the composite material surface layer is 8% to 29%. By etching the MAX material in an acid solution, MXene is generated in situ from the MAX material on the surface, and MAX-MXene material is generated in situ from the MAX material inside the surface layer of the composite material.

2. The composite coating according to claim 1, characterized in that, Along the direction from the bottom layer to the surface layer of the composite material, the porosity of the surface layer of the composite material is distributed in a stepped manner.

3. The composite coating according to claim 1, characterized in that, The MAX material is disposed between the bottom layer and the MXene material.

4. The composite coating according to claim 1, characterized in that, The surface of the composite material is provided with a non-metallic element, which includes at least one of O and F.

5. The composite coating according to claim 1, characterized in that, The composite coating exhibits a contact resistance of less than 2 mΩ / cm under 1.4 MPa conditions. 2 .

6. The composite coating according to claim 1, characterized in that, The contact angle of the composite coating is 20°~140°.

7. A bipolar plate, characterized in that, The bipolar plate is used in a PEM electrolytic cell, and the bipolar plate includes: Substrate and A coating applied to the surface of the substrate, the coating comprising the composite coating according to any one of claims 1 to 4, wherein the contact resistance of the bipolar plate is less than 4 mΩ / cm under a pressure of 1.4 MPa. 2 .

8. A porous diffusion layer, characterized in that, The porous diffusion layer includes: The substrate and the coating applied to the surface of the substrate, the coating comprising the composite coating according to any one of claims 1 to 4, wherein the contact angle of the composite coating is 20° to 60°.

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