Bipolar plate composite coating structure, preparation method thereof and electrolytic bath

Abstract

The invention relates to the technical field of battery materials, in particular to a bipolar plate composite coating structure, a preparation method thereof and an electrolytic bath, and the bipolar plate composite coating structure comprises the following elements: Ti element, Si element, Zr element, W element and C element. In terms of the total atomic number being 100%, the percentage of the atomic number of the Ti element is 15%-25%, the percentage of the atomic number of the Zr element is 25%-35%, the percentage of the atomic number of the Si element is 10%-20%, the percentage of the atomic number of the W element is 10%-20%, and the percentage of the atomic number of the C element is 5%-10%. The invention aims to provide the bipolar plate which is low in cost and excellent in conductivity and corrosion resistance.

Description

Technical Field

[0001] This invention relates to the technical field of battery materials, and more specifically, to a bipolar plate composite coating structure, its preparation method, and an electrolytic cell. Background Technology

[0002] The PEM (proton exchange membrane) electrolyzer is the core component of a water electrolysis hydrogen production device. Its core structure consists of stacked components such as membrane electrodes, bipolar plates, gas diffusion layers, and seals. The bipolar plates are made of conductive materials and have flow field channels etched on their surfaces to conduct current, distribute reactants (water), and collect product gases (hydrogen / oxygen).

[0003] Generally, bipolar plates need to maintain a service life of 20 years or more under strong acid (pH=2-3) and high pressure (30 bar) environments. Currently, the industry commonly uses a process of plating precious metals (such as platinum) onto the surface of titanium-based bipolar plates, but there are the following technical bottlenecks: First, the cost is high. The thickness of traditional electroplated platinum coating needs to reach more than 100nm, with a cost of up to 700 yuan per square meter, accounting for more than 50% of the total cost of the bipolar plate; second, the related performance is not good. For example, under 80℃ conditions, the hydrogen permeability increases over time, leading to an increase in contact resistance and thus a decrease in conductivity; and the exposed metal bipolar plates have poor corrosion resistance under high potential, strong oxidation, and strong corrosion working conditions. Summary of the Invention

[0004] The present invention aims to provide a low-cost bipolar plate with excellent conductivity and corrosion resistance.

[0005] To solve or partially solve the above problems, a bipolar plate composite coating structure is proposed, the composition of which includes the following elements: Ti, Si, Zr, W and C.

[0006] Optionally, based on the total number of atoms being 100%, the atomic percentage of Ti is 15% to 25%, the atomic percentage of Zr is 25% to 35%, the atomic percentage of Si is 10% to 20%, the atomic percentage of W is 10% to 20%, and the atomic percentage of C is 5% to 10%. And / or, the thickness of the bipolar plate composite coating structure is 0.5 to 1.2 μm.

[0007] Optionally, the bipolar plate composite coating structure includes a transition layer, an intermediate buffer layer, and a functional layer sequentially disposed from the surface of the bipolar plate substrate outwards. The transition layer is composed of Ti, the intermediate buffer layer is composed of Ti, Si, Zr, and W, and the functional layer is composed of Ti, Si, Zr, W, and C.

[0008] Optionally, the thickness of the transition layer is 30 to 80 nm, the thickness of the intermediate buffer layer is 100 to 350 nm, and the thickness of the functional layer is 250 to 800 nm.

[0009] As a second aspect, the present invention also provides a method for preparing a bipolar plate composite coating structure, used to prepare the bipolar plate composite coating structure as described in the first aspect, the method comprising: Turn on the Ti target current to deposit a transition layer on the surface of the bipolar substrate; Maintain the Ti target current while simultaneously turning on the Zr target current, Si target current, and W target current to deposit an intermediate buffer layer on the surface of the transition layer. Maintain Ti target current, Zr target current, Si target current and W target current, while simultaneously introducing C flow rate to deposit a functional layer on the surface of the intermediate buffer layer.

[0010] Optionally, the C flow rate is C2H2 gas, and the C2H2 gas flow rate is 100 to 150 sccm.

[0011] Optionally, the magnitude of the Ti target current is 10 to 15 A, the magnitude of the Zr target current is 5 to 15 A, the magnitude of the W target current is 5 to 15 A, and the magnitude of the Si target current is 5 to 10 A.

[0012] Optionally, the deposition time of the transition layer is 5 to 15 minutes, and the deposition time of the intermediate buffer layer and the functional layer is 20 to 30 minutes, respectively.

[0013] Optionally, the deposition temperature of the transition layer, the intermediate buffer layer, and the functional layer is 150 to 250°C, and the deposition pressure is 0.3 to 0.5 Pa.

[0014] As a third aspect, the present invention provides an electrolytic cell comprising a bipolar plate, the bipolar plate comprising a bipolar plate composite coating structure as described in the first aspect, or a bipolar plate composite coating structure prepared by a method for preparing a bipolar plate composite coating structure as described in the second aspect.

[0015] The advantages of this invention compared to related technologies include: In the bipolar plate composite coating structure of this invention, carbon (C) provides a dispersed matrix for other elements, jointly constructing the composite structure. Metallic elements (Ti, Zr, W) typically exist in the amorphous carbon matrix as carbides, nitrides, or solid solutions. Ti has a strong affinity for C, preferentially forming ultra-hard TiC nanocrystals, which significantly improves the coating's hardness and wear resistance. Furthermore, TiC itself is a good conductor, and its formation helps establish conductive bridges, thus improving conductivity. Zr carbides exhibit excellent chemical stability in acidic environments containing fluoride ions (such as PEMFC environments). Therefore, the addition of Zr further enhances the coating's passivation ability, making it more resistant to pitting corrosion. Moreover, Zr's large atomic size contributes to the formation of a denser and more stable amorphous structure, reducing rapid corrosion channels such as grain boundaries. W carbides are also excellent conductors. In the composite coating structure, W or WC nanoparticles can form a highly efficient conductive effect, thereby significantly reducing the surface resistance and contact resistance of the entire coating. Furthermore, their extremely high melting point improves the stability of the coating at higher temperatures. Si effectively promotes and stabilizes the amorphous carbon network structure and inhibits the growth of graphite grains, resulting in a more uniform, amorphous, and dense coating structure that effectively blocks the penetration channels of corrosive media. On the coating surface, Si is preferentially oxidized to form an extremely dense SiO2 or silicate glassy protective layer. This protective film effectively prevents oxygen from diffusing inward, thus significantly improving the coating's oxidation resistance. Through the synergistic combination of these elements, the bipolar plate composite coating of this invention possesses the characteristics of low cost, ultra-high corrosion resistance, high conductivity, high adhesion, and good wear resistance, effectively improving the stability and service life of bipolar plates in fuel cell environments. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the bipolar plate composite coating structure in an exemplary embodiment of the present invention; Figure 2 This is a comparison diagram of the interface contact resistance of Embodiment 1 and Comparative Examples 1 and 2 of the present invention; Figure 3 This is a comparison diagram of the corrosion potential of Example 1 of the present invention and Comparative Examples 1 and 2. Explanation of reference numerals in the attached diagram: 1. Bipolar plate substrate; 2. Transition layer; 3. Intermediate buffer layer; 4. Functional layer. Detailed Implementation

[0017] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below.

[0018] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in the description of this application is for the purpose of describing particular embodiments only and is not intended to limit this application. The term "comprising" and its variations as used herein are open-ended, meaning "including but not limited to"; the term "based on" means "at least partially based on"; the term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; the term "some embodiments" means "at least some embodiments"; and the term "optionally" means "optional embodiments". Definitions of other terms will be given in the description below. It should be noted that the concepts of "first," "second," etc., mentioned in this invention are used to distinguish different objects, not to describe a specific order or hierarchy. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "a plurality of" means two or more.

[0019] Bipolar plates are a key component of PEM electrolyzers, accounting for more than 50% of the stack cost. Exposed metal bipolar plates are prone to corrosion under high-potential, strong-oxidizing, and highly corrosive operating conditions, leading to significant power losses in the electrolyzer. Therefore, developing low-cost, highly conductive, and highly corrosion-resistant composite coatings for bipolar plate surfaces has become an urgent problem to be solved.

[0020] Reference Figure 1 As shown, an embodiment of the present invention provides a bipolar plate composite coating structure, the composition of which includes the following elements: Ti, Si, Zr, W and C.

[0021] In the bipolar plate composite coating structure, carbon (C) provides a dispersed matrix for other elements, collectively constructing the composite structure. Metallic elements (Ti, Zr, W) typically exist in the amorphous carbon matrix as carbides, nitrides, or solid solutions. Ti has a strong affinity for C, preferentially forming ultra-hard TiC nanocrystals, which significantly improves the coating's hardness and wear resistance. Furthermore, TiC itself is a good conductor, and its formation helps establish conductive bridges, enhancing conductivity. Zr carbides exhibit excellent chemical stability in acidic environments containing fluoride ions (such as PEMFC environments). Therefore, the addition of Zr further improves the coating's passivation ability, enhancing its resistance to pitting corrosion. Additionally, Zr's large atomic size contributes to the formation of a denser and more stable amorphous structure, reducing rapid corrosion pathways such as grain boundaries. W carbides are also excellent conductors of light. In the coating, W or WC nanoparticles can form a highly efficient conductive effect, thereby significantly reducing the surface resistance and contact resistance of the entire coating. Furthermore, their extremely high melting point improves the stability of the coating at higher temperatures. Si effectively promotes and stabilizes the amorphous carbon network structure and inhibits the growth of graphite grains, resulting in a more uniform, amorphous, and dense coating structure. This effectively blocks the penetration channels of corrosive media. On the coating surface, Si is preferentially oxidized to form an extremely dense SiO2 or silicate glassy protective layer. This protective film effectively prevents oxygen from diffusing inward, thus significantly improving the coating's oxidation resistance. Through the synergistic combination of these elements, the bipolar plate composite coating of this invention possesses the characteristics of low cost, ultra-high corrosion resistance, high conductivity, high adhesion, and good wear resistance, effectively improving the stability and service life of bipolar plates in fuel cell environments.

[0022] Specifically, in some optional embodiments, the atomic percentage of Ti is 15 to 25%, the atomic percentage of Zr is 25 to 35%, the atomic percentage of Si is 10 to 20%, the atomic percentage of W is 10 to 20%, and the atomic percentage of C is 5 to 10%. The thickness of the bipolar plate composite coating structure is 0.5 to 1.2 μm.

[0023] By rationally controlling the proportions of each element, we can maximize the synergistic effect of each element and keep the total cost to a minimum.

[0024] In some alternative embodiments, such as Figure 1 As shown, the bipolar plate composite coating structure includes a transition layer 2, an intermediate buffer layer 3, and a functional layer 4 arranged sequentially from the surface of the bipolar plate substrate 1. The transition layer 2 is composed of Ti, the intermediate buffer layer 3 is composed of Ti, Si, Zr, and W, and the functional layer 4 is composed of Ti, Si, Zr, W, and C.

[0025] In this embodiment, by further setting a progressively layered composite coating structure, the problem of matching the physicochemical properties between the coating and the substrate is systematically solved, ultimately achieving optimal overall performance. Specifically, the Ti element in the transition layer 2 has good miscibility and affinity with the metal elements in the bipolar plate substrate 1, and can form a strong metallurgical bond with the substrate surface. This provides an ideal and firmly bonded deposition surface for subsequent coatings, promoting their uniform nucleation and dense growth. At the same time, the metallic Ti layer has certain plasticity and toughness, which can absorb some of the thermal stress caused by the mismatch in the thermal expansion coefficients between the substrate and the outer coating. The intermediate buffer layer 3 contains all the metal elements, forming a compositional gradient from pure metal (transition layer 2) to carbon-based composite ceramic (functional layer 4). This gradient can maximize the elimination of interfacial stress and effectively inhibit crack propagation at different structural interfaces. The outermost functional layer 4 is the working surface that directly faces the harsh environment of the fuel cell (acidity, high potential, water), and can provide excellent corrosion resistance, low contact resistance, and good wear resistance. The addition of carbon element in this layer provides a good bonding matrix for metal elements, and the resulting metal carbide particles have strong wear resistance and electrical conductivity.

[0026] Specifically, the thickness of transition layer 2 is 30 to 80 nm, the thickness of intermediate buffer layer 3 is 100 to 350 nm, and the thickness of functional layer 4 is 250 to 800 nm. Further, the atomic percentages of each element in intermediate buffer layer 3 are: Ti: 20 to 30%, Si: 5 to 10%, Zr: 20 to 35%, W: 10 to 25%. The atomic percentages of each element in functional layer 4 are: Ti: 10 to 20%, Si: 5 to 10%, Zr: 20 to 35%, W: 10 to 25%, C: 5 to 15%.

[0027] Another embodiment of the present invention provides a method for preparing a bipolar plate composite coating structure, used to prepare the bipolar plate composite coating structure as described above. The preparation method includes: Step S1: Turn on the Ti target current to deposit a transition layer 2 on the surface of the bipolar substrate 1. In this step, the substrate bias voltage is controlled at -200V.

[0028] In some optional embodiments, before step S1, the method further includes: sequentially performing ultrasonic cleaning and ion bombardment cleaning on the surface of the bipolar plate substrate 1 to obtain a clean surface of the bipolar plate substrate 1. Specifically, the ultrasonically cleaned and dried bipolar plate substrate 1 is placed into a medium-frequency magnetron sputtering furnace cavity, and a vacuum is drawn until the vacuum degree of the furnace cavity is lower than 2.0 × 10⁻⁶. -3 The substrate is subjected to ion bombardment cleaning at Pa. The substrate bias voltage can be controlled at around -1000V, and the sputtering cleaning time is 10 to 15 minutes.

[0029] Step S2: Maintain the Ti target current while simultaneously turning on the Zr, Si, and W target currents to deposit an intermediate buffer layer 3 on the surface of transition layer 2. In this step, the substrate bias is controlled at -150V.

[0030] Step S3: Maintain the Ti target current, Zr target current, Si target current, and W target current while simultaneously introducing a C flow rate to deposit the functional layer 4 on the surface of the intermediate buffer layer 3. In this step, the substrate bias is controlled at -150V. Optionally, the C flow rate can be C2H2 gas, with a flow rate of 100 to 150 sccm. In other embodiments, graphite can also be used as the target material for C deposition.

[0031] In some optional embodiments, in steps S1 to S3, the Ti target current is 10 to 15 A, the Zr target current is 5 to 15 A, the W target current is 5 to 15 A, and the Si target current is 5 to 10 A. The deposition time for the transition layer 2 is 5 to 15 min, and the deposition times for the intermediate buffer layer 3 and the functional layer 4 are 20 to 30 min, respectively. The deposition temperature for the transition layer 2, the intermediate buffer layer 3, and the functional layer 4 is 150 to 250 °C, and the deposition gas pressure is 0.3 to 0.5 Pa.

[0032] This embodiment utilizes multi-arc combined magnetron sputtering deposition technology to sequentially deposit a transition layer 2, an intermediate buffer layer 3, and a functional layer 4 on the surface of a bipolar substrate 1. By adjusting process parameters such as target current and deposition time, the composition and thickness of each coating are adjusted, significantly improving the film-substrate adhesion of the bipolar plate, further enhancing corrosion resistance, and reducing contact resistance. Precise control of the proportions of each element in the composite coating is achieved by regulating the target current and reactive gas flow rate, ensuring the uniformity and density of the coating structure. Another embodiment of the present invention provides an electrolytic cell comprising a bipolar plate, the bipolar plate comprising the bipolar plate composite coating structure as described above, or comprising the bipolar plate composite coating structure prepared by the method described above.

[0033] The present invention will be described in detail below through specific embodiments and comparative examples: Example 1 Step (1): The titanium bipolar plate substrate is placed in an ultrasonic cleaning device to remove dust, impurities, oil and other contaminants from the product surface. Then it is dried in a vacuum oven and placed in a magnetron sputtering furnace. The furnace is evacuated until the vacuum level is below 2.0 × 10⁻⁶. -3 Ion bombardment cleaning was performed using Pa. The substrate bias voltage could be controlled at -1000V, and the sputtering cleaning time was 10 minutes.

[0034] Step (2): Turn on the intermediate frequency Ti target current, keep the working gas pressure at 0.3 Pa, the deposition temperature at 200 °C, the substrate bias voltage at -200 V, the Ti target current at 10 A, deposit Ti atoms on the surface of the bipolar substrate, the deposition time is 15 min, and a transition layer is obtained with a thickness of 50 nm.

[0035] Step (3): Maintain the Ti target current, and simultaneously turn on the Si target current, Zr target current, and W target current. The current of the Si target is 10A, the current of the Zr target is 15A, the current of the W target is 15A, the substrate bias voltage is -150V, the deposition time is 20min, and an intermediate buffer layer is deposited on the transition layer. The deposition gas pressure is 0.3Pa, the deposition temperature is 200℃, and the thickness of the intermediate buffer layer is 250nm.

[0036] Step (4): Maintain the target currents for Ti, Si, Zr, and W, control the substrate bias voltage to -150V, and simultaneously introduce 150 sccm of C2H2 gas. Deposit for 30 min, and deposit a functional layer on the surface of the intermediate buffer layer obtained in step (3). The deposition temperature is 200℃, the deposition pressure is 0.3 Pa, and the thickness of the functional layer is 300 nm.

[0037] In the bipolar plate composite coating structure prepared in this embodiment, the atomic percentage of Ti is 20%, the atomic percentage of Zr is 30%, the atomic percentage of Si is 20%, the atomic percentage of W is 20%, and the atomic percentage of C is 10%.

[0038] Example 2 The difference between this embodiment and embodiment 1 is that in step (2), the Ti target current is 15A, in step (3), the Zr target current is 5A, the Si target current is 10A, the W target current is 5A, and in step (4), the C2H2 gas flow rate is 100sccm.

[0039] Comparative Example 1 The difference between this comparative example and Example 1 is that the elements (Ti-Si-Zr-W) in the intermediate buffer layer are replaced with a TiSiW coating, wherein the atomic ratio of Ti, Si, and W is 3:2:5.

[0040] Comparative Example 2 The difference between this comparative example and Example 1 is that the elements (Ti-Si-Zr-WC) of the functional layer are replaced with a TiSiZrW coating, wherein the atomic ratio of Ti, Si, Zr and W is 3:1:3:3.

[0041] The prepared metal plates were subjected to contact resistance measurement and electrochemical corrosion performance evaluation in a PEM electrolytic cell simulation environment.

[0042] The interface contact resistance test was conducted according to national standards GB / T20042.6 and GB / T20042.7, with a test pressure range of 0.2 to 3.0 MPa and a test pressure interval of 0.2 MPa. Figure 2 As shown, compared to Comparative Examples 1 and 2, the bipolar plate prepared in Example 1 of this invention has a lower contact resistance; specifically, the contact resistance under a pressure of 1.5 MPa is less than 2 mΩ / cm. 2 .

[0043] Meanwhile, the bipolar plates in Example 1 and Comparative Examples 1 and 2 were subjected to external electrochemical tests under simulated electrolytic hydrogen production conditions (the reference electrode for the electrochemical test potential was a RO305 silver-silver chloride electrode, and the test solution was 0.5 mol H2SO4 + 5.6 x 10⁻⁶ at pH=0). -6 Using molHF, oxygen at a flow rate of 20 ml / min, and a test temperature of 80℃ (with constant potential polarization of 2V>96H), it was found that after a long-term accelerated test, the coating morphology remained intact without corrosion marks, and the contact resistance after corrosion remained essentially unchanged. The test results are as follows... Figure 3 As shown, from Figure 3 It can be seen that under constant potential polarization 2V test potential, the corrosion current of Example 1 is slightly less than that of Comparative Example 1 and significantly less than that of Comparative Example 2, indicating that the corrosion resistance of Example 1 is superior.

[0044] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and all such changes and modifications will fall within the scope of protection of the present invention.

Claims

1. A bipolar plate composite coating structure, characterized in that, Its components include the following elements: The elements are Ti, Si, Zr, W, and C.

2. The bipolar plate composite coating structure according to claim 1, characterized in that, Based on a total atomic percentage of 100%, the atomic percentage of Ti is 15% to 25%, the atomic percentage of Zr is 25% to 35%, the atomic percentage of Si is 10% to 20%, the atomic percentage of W is 10% to 20%, and the atomic percentage of C is 5% to 10%. And / or, the thickness of the bipolar plate composite coating structure is 0.5 to 1.2 μm.

3. The bipolar plate composite coating structure according to claim 1, characterized in that, It includes a transition layer (2), an intermediate buffer layer (3) and a functional layer (4) arranged sequentially from the surface of the bipolar plate substrate (1). The transition layer (2) is composed of Ti, the intermediate buffer layer (3) is composed of Ti, Si, Zr and W, and the functional layer (4) is composed of Ti, Si, Zr, W and C.

4. The bipolar plate composite coating structure according to claim 3, characterized in that, The thickness of the transition layer (2) is 30 to 80 nm, the thickness of the intermediate buffer layer (3) is 100 to 350 nm, and the thickness of the functional layer (4) is 250 to 800 nm.

5. A method for preparing a bipolar plate composite coating structure, characterized in that, The method for preparing the bipolar plate composite coating structure as described in any one of claims 1 to 4 includes: Turn on the Ti target current to deposit a transition layer (2) on the surface of the bipolar substrate (1); Maintain the Ti target current while simultaneously turning on the Zr target current, Si target current and W target current to deposit an intermediate buffer layer (3) on the surface of the transition layer (2). Maintain Ti target current, Zr target current, Si target current and W target current, while introducing C flow rate to deposit a functional layer (4) on the surface of the intermediate buffer layer (3).

6. The method for preparing the bipolar plate composite coating structure according to claim 5, characterized in that, The C flow rate is C2H2 gas, and the C2H2 gas flow rate is 100 to 150 sccm.

7. The method for preparing the bipolar plate composite coating structure according to claim 5, characterized in that, The Ti target current is 10 to 15 A, the Zr target current is 5 to 15 A, the W target current is 5 to 15 A, and the Si target current is 5 to 10 A.

8. The method for preparing the bipolar plate composite coating structure according to claim 5, characterized in that, The deposition time of the transition layer (2) is 5 to 15 minutes, and the deposition time of the intermediate buffer layer (3) and the functional layer (4) is 20 to 30 minutes, respectively.

9. The method for preparing the bipolar plate composite coating structure according to claim 5, characterized in that, The deposition temperature of the transition layer (2), the intermediate buffer layer (3) and the functional layer (4) is 150 to 250°C, and the deposition pressure is 0.3 to 0.5 Pa.

10. An electrolytic cell, characterized in that, The bipolar plate includes a bipolar plate composite coating structure as described in any one of claims 1 to 4, or a bipolar plate composite coating structure prepared by a method for preparing a bipolar plate composite coating structure as described in any one of claims 5 to 9.

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