Metal bipolar plate for fuel cell and preparation method of metal bipolar plate

Abstract

The invention discloses a metal bipolar plate for a fuel cell and a preparation method thereof.The metal bipolar plate comprises a metal substrate and a functional layer covering the metal substrate, the metal substrate is made of 316L stainless steel, and the functional layer sequentially comprises a sputtering layer, a transition layer and a ternary composite layer from the bottom layer close to the metal substrate to the surface layer, the sputtering layer is composed of a Cr element, the transition layer is composed of two elements of Cr and Ti, the ternary composite layer is composed of three elements of Cr, Ti and C. The preparation technology of the functional layer is a combination of a magnetron sputtering technology and a chemical vapor deposition technology. The metal bipolar plate prepared by the method has excellent conductivity and corrosion resistance.

Description

Technical Field

[0001] This invention belongs to the field of fuel cells, specifically relating to a metal bipolar plate for fuel cells and its preparation method. Technical Background

[0002] A proton exchange membrane fuel cell (PEMFC) is a device that directly converts the chemical energy of hydrogen and an oxidant into electrical energy. Overcoming the limitations of the Carnot cycle, it significantly improves energy conversion efficiency and boasts advantages such as high energy conversion rate, no environmental pollution, rapid start-up, long lifespan, and high power density. It has broad application prospects in power plants, automobiles, military, aerospace, and many other fields. Currently, fuel cells have attracted widespread attention worldwide, with countries investing heavily in their research and development and application.

[0003] Bipolar plates are a key component of PEMFCs, serving to support, current collector, and separate the oxidant and reductant, guiding their flow across the electrode surfaces within the battery and facilitating current conduction. Based on their materials, bipolar plates can be categorized into graphite bipolar plates, composite material bipolar plates, and metal-based bipolar plates. Graphite bipolar plates, as a traditional material, possess excellent electrical conductivity and corrosion resistance; however, their brittleness and the high costs associated with graphitization and machining processes significantly limit their practical application. Composite material bipolar plates primarily use highly conductive graphite, incorporating resins, reinforcing fibers, and other substances. By sacrificing some conductivity, they achieve higher mechanical properties, reducing processing difficulty and costs to some extent. However, a balance between conductivity and mechanical performance remains challenging.

[0004] Metal bipolar plates possess advantages such as thinness, high mechanical strength, high air resistance, good processability, and high resource recyclability, making them the current trend in bipolar plate selection and possessing the greatest commercial potential. Thinning bipolar plates can significantly improve mass and volumetric power density while reducing costs. However, their corrosion resistance is the biggest obstacle in the development process. To improve the corrosion resistance of metal bipolar plates while maintaining good electrical conductivity, surface modification technology has become the mainstream research direction for improving the corrosion resistance of fuel cell metal bipolar plates. The industry generally believes that stainless steel is an ideal material for automotive fuel cell bipolar plates and an inevitable choice for industrialization. However, stainless steel bipolar plates are prone to corrosion, generating metal ions that adversely affect components such as the membrane electrode assembly (MEA) of the fuel cell stack. Summary of the Invention

[0005] The purpose of this invention is to provide a metal bipolar plate for fuel cells and a method for preparing the same, which gives the metal bipolar plate excellent conductivity and corrosion resistance.

[0006] The above-mentioned technical objective of the present invention is achieved through the following technical solution: a metal bipolar plate for a fuel cell, comprising a metal substrate and a functional layer covering the metal substrate, wherein the metal substrate is 316L stainless steel, and the functional layer consists of a sputtering layer, a transition layer and a ternary composite layer from the bottom layer near the metal substrate to the surface layer, wherein the sputtering layer is composed of Cr, the transition layer is composed of Cr and Ti, and the ternary composite layer is composed of Cr, Ti and C.

[0007] The present invention is further configured such that: the thickness of the metal substrate is 0.2-0.7 mm, the thickness of the sputtered layer is 0.5-1.5 μm, the thickness of the transition layer is 0.2-1 μm, and the thickness of the ternary composite layer is 0.5-3 μm.

[0008] The present invention is further configured such that the percentage of Cr atoms in the transition layer is 55-75%; In the ternary composite layer, the percentage of C atoms is 30%-65%, and the ratio of Cr atoms to Ti atoms is (0.5-3):1.

[0009] The present invention is further configured such that: in the ternary composite layer, its composition changes in a continuous gradient from near the transition layer to the surface layer, with the percentage of Ti atoms gradually decreasing and the percentage of C atoms gradually increasing; In the ternary composite layer, the percentage of C atoms is 30%-65%, and the ratio of Cr atoms to Ti atoms is (0.5-3):1.

[0010] The present invention further provides a method for preparing a metal bipolar plate as described above, wherein the functional layer is formed by combining magnetron sputtering with chemical vapor deposition.

[0011] The present invention is further configured such that: the sputtering layer is formed by sputtering with a Cr target, the transition layer is formed by sputtering with a high-purity Cr target and a Ti target, and the ternary composite layer is formed by sputtering with a high-purity Cr target and a Ti target and introducing high-purity methane gas, wherein the purity of the high-purity Ti target is ≥99.5%, the purity of the high-purity Cr target is ≥99.5%, and the purity of the high-purity methane is ≥99.99%.

[0012] The present invention is further configured such that: the sputtering layer uses a high-purity Cr target, the sputtering power is 300-600W, and the deposition time is 3-5min; The transition layer is co-sputtered using a high-purity Cr target and a high-purity Ti target. During the sputtering process, the Cr target power is 300-600W, the Ti target power is 100-300W, and the deposition time is 3-5 minutes. During the sputtering process of the ternary composite layer, high-purity Cr and high-purity Ti targets are co-sputtered and high-purity methane gas is introduced. The sputtering power of the high-purity Cr target is 200-500W, the sputtering power of the high-purity Ti target is 100-300W, the gas flow rate of high-purity methane is 5-15 sccm, the deposition temperature is ≤200℃, and the sputtering time is 5-10min.

[0013] The present invention is further configured such that: during the sputtering process of the ternary composite layer, the sputtering power of the Ti target and the flow rate of methane gas are dynamically adjusted simultaneously, the flow rate of methane gas increases linearly, the power of the Ti target decreases linearly with the increase of the carbon source gas flux, and the power of the Cr target increases linearly with the decrease of the Ti target power.

[0014] The present invention is further configured such that: the growth rate of the methane gas flow rate is 0.5-1 sccm / min, the linear decrease rate of the Ti target power is 10-20 w / min, and the linear increase rate of the Cr target power is 15-25 w / min; The initial sputtering power of the high-purity Cr target is 200-250W, the initial sputtering power of the high-purity Ti target is 250-300W, and the initial gas flow rate of high-purity methane is 3-5 sccm.

[0015] The present invention is further configured as follows: the substrate is formed by polishing and grinding the surface of the 316L stainless steel substrate, immersing and cleaning in dilute sulfuric acid solution, cleaning with anhydrous ethanol, and drying. During the immersion and cleaning process in dilute sulfuric acid solution, the concentration of sulfuric acid is 10-30%, the time is 5-25 minutes, the temperature is 50-80℃, and the sputtering time is 5-10 minutes.

[0016] In summary, the present invention has the following beneficial effects: 1. This invention targets bipolar plates with stainless steel substrates. First, a dense chromium layer is prepared on the surface using magnetron sputtering to "seal" the micropores of the stainless steel and prevent acid from penetrating and corroding the substrate. The surface layer uses a more economical chromium-titanium-carbon composite with a high carbon content. Under the controlled composition and process parameters of this invention, Cr-Ti-C compounds can be generated in situ, exhibiting chemical inertness far exceeding that of metals, further reducing acid corrosion in fuel cells. In addition, the surface Cr-Ti-C compounds can form a conductive grain boundary network, meaning that the amplitude and structure of the surface layer contribute to corrosion resistance and high conductivity. Furthermore, this invention designs a Cr-Ti alloy layer between the pure chromium layer and the surface layer, forming a buffer transition layer with a certain degree of elasticity. This effectively alleviates the problem of large thermal expansion and contraction differences between the pure chromium layer and the surface carbides, buffering thermal stress and preventing coating cracking. Moreover, since the Cr-Ti alloy layer contains Cr and Ti atoms, it has good atomic-level bonding force with both the sputtered pure chromium layer and the surface layer. In other words, the Cr-Ti alloy layer is an adhesive transition layer that combines the sputtered layer and the ternary composite layer.

[0017] 2. Compared with the direct sputtering of pure Cr + pure Ti + pure C to form a coating, this invention uses pure Cr and pure Ti sputtering with methane introduced simultaneously. In this way, the introduction of methane during sputtering can be easily controlled and allows for a full and uniform reaction with pure Cr and pure Ti. In this process, methane can act as the dominant gaseous reaction, that is, the gaseous active carbon generated by plasma cracking of CH4 undergoes a controlled Eley-Rideal reaction with high-kinetic-energy metal ions to form a (Ti,Cr)C solid solution coating. This method can achieve atomic-level miscibility of elements, reduce the energy barrier of the reaction path, suppress in-situ defects, and has the advantages of dynamic composition controllability.

[0018] 3. In the ternary composite layer of this invention, the percentage of Ti atoms decreases while the percentage of C atoms increases, forming a compositional gradient interface. Due to the differences in composition between layers in traditional multilayer coatings, such as the abrupt change in thermal expansion coefficient / crystal structure at the interface between a pure Ti layer and a pure C layer, problems such as interface peeling occur. The gradient design of this invention enables a continuous transition of interface composition. The high Ti content in the inner layer forms a metallurgical bond with the transition layer (Cr-Ti alloy), further enhancing interlayer stress. Moreover, the high Ti content has passivation properties, thus further improving corrosion resistance in acidic environments. Furthermore, the high C content on the surface can effectively improve conductivity, and when the C atom content is >50%, an amorphous carbon + nano-chromium carbide / titanium composite phase is formed, thereby reducing contact resistance and providing surface hardness and a corrosion barrier.

[0019] 4. The gradient structure in the invented ternary composite layer also possesses excellent hydrophobicity. As the C atom content increases from the gradient in the ternary composite layer, a carbon-rich region is formed on the outermost layer. Carbon has low surface energy, and the gradient formation results in a composite structure with amorphous carbon as the continuous phase on the surface, further reducing surface energy. Furthermore, the high-purity methane deposition process of this invention generates nano-carbides on the surface and embeds them into the amorphous carbon matrix, thus forming a micro-nano rough structure similar to the surface of a lotus leaf, further improving hydrophobicity. Additionally, the sputtered layer of this invention, i.e., the pure Cr layer, densely covers the 316L stainless steel substrate. The highly dense passivation film blocks the diffusion of metal ions from the substrate to the surface, thus... To prevent Fe oxidation and the formation of hydrophilic oxides, the transition layer, with its high Ti atom content of 40-80%, forms a strongly bonded Cr-Ti intermetallic compound, creating a barrier layer. This prevents excessive diffusion of Cr from the bottom layer to the surface, which could affect the continuity of the amorphous carbon on the surface. It also prevents C from penetrating into the substrate, reducing the C content in the outermost layer and causing an increase in surface energy. In addition, the transition layer acts as a stress gradient buffer layer, preventing crack formation and further ensuring the hydrophobic effect. In summary, while traditional hydrophobic coatings (such as PTFE) increase hydrophobicity, they sacrifice conductivity. This solution achieves integrated hydrophobicity and conductivity through a nano-carbide / amorphous carbon composite phase, solving the existing problems.

[0020] 5. The three-layer corrosion-resistant composite coating design of this invention significantly reduces the contact resistance between the titanium-based metal bipolar plate and the carbon paper. The (Cr,Ti) / C coating has good corrosion resistance and hydrophobicity. The coating is inexpensive, which can reduce the cost of proton exchange membrane fuel cells and is suitable for large-scale applications. Attached Figure Description

[0021] Figure 1 The following are contact angle test diagrams of the surface layers of Comparative Example 1, Comparative Example 2, and Example 2, respectively. Figure 2 This is a schematic diagram of the layer structure of the metal bipolar plate in the embodiment; In the figure: 1. Metal substrate; 2. Sputtered layer; 3. Transition layer; 4. Ternary composite layer. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to the accompanying drawings.

[0023] Example 1: A 0.7mm thick 316L stainless steel substrate was sequentially ultrasonically cleaned with acetone and ethanol for 15 minutes each, followed by argon ion sputtering to remove surface oxides. The treated substrate was then placed vertically on the vacuum chamber rack of a magnetron sputtering apparatus. The vacuum chamber door was closed, and a mechanical pump was used to evacuate the system to 5 Pa. The specific sputtering steps are as follows: S1. Using a 99.5% pure Cr target, sputtering power of 600W, argon flow rate of 30sccm, deposition temperature of 150℃, and deposition time of 3min, a 1.4μm thick pure Cr sputtered layer 2 was obtained. S2. A Cr target with a purity of 99.5% and a Ti target with a purity of 99.5% were co-sputtered. The sputtering power of the Cr target was 600W, the sputtering power of the Ti target was 300W, the argon flow rate was 40sccm, and the deposition time was 3min. A transition layer 3 with a Cr atomic content of 67% and a Ti atomic content of 33% and a thickness of 1μm was obtained. S3. A 99.5% pure Cr target and a 99.5% pure Ti target were co-sputtered, and 8 sccm of 99.9% pure high-purity CH4 was simultaneously introduced. The sputtering power of the Cr target was 350W and the sputtering power of the Ti target was 300W. During this sputtering process, the argon flow rate was 25 sccm, the deposition temperature was 200℃, the sputtering pressure was 0.5Pa, and the deposition time was 8min, resulting in a ternary composite layer 4 with a C atom content of 33% + Cr atom content of 45% + Ti atom content of 22% and a thickness of 2.2μm. A schematic diagram of the layer structure of the metal bipolar plate fabricated in Example 1 is shown below. Figure 2 As shown.

[0024] Example 2: A 0.5mm thick 316L stainless steel substrate was sequentially ultrasonically cleaned with acetone and ethanol for 15 minutes each, followed by argon ion sputtering to remove surface oxides. The treated substrate was then placed vertically on the vacuum chamber rack of a magnetron sputtering apparatus. The vacuum chamber door was closed, and a mechanical pump was used to evacuate the system to 5 Pa. The specific sputtering steps are as follows: S1. A pure Cr sputtered layer 2 with a thickness of 1.1 μm was obtained by using a 99.5% pure Cr target, sputtering power of 450W, argon flow rate of 25sccm, deposition temperature of 100℃ and deposition time of 4min. S2. A transition layer 3 with a purity of 99.5% Cr target and a purity of 99.5% Ti target was co-sputtered. The sputtering power of the Cr target was 450W, the sputtering power of the Ti target was 200W, the argon flow rate was 30sccm, and the deposition time was 4min. A transition layer 3 with a Cr atomic content of 71% + Ti atomic content of 29% and a thickness of 0.6μm was obtained. S3. A 99.5% pure Cr target and a 99.5% pure Ti target were co-sputtered, while simultaneously introducing 5 sccm of high-purity CH4 (99.9% pure). The sputtering power of the Cr target was 200W, and the sputtering power of the Ti target was 300W. During this sputtering process, the argon flow rate was 5 sccm, and the deposition temperature was 150℃. After 1 min, a ternary composite inner layer with a C atom content of 30% + Cr atom content of 27% + Ti atom content of 53% was obtained. Subsequently, the methane flow rate increased by 1 sccm / min, the Ti target power decreased by 15W / min, and the Cr target power increased by 20W / min. After 5 min, a ternary composite inner layer with a C atom content of 33% + Cr atom content of 38% + Ti atom content of 29% was obtained. After 10 min, an outer layer 4 of the ternary composite layer with a C atom content of 59% + Cr atom content of 30% + Ti atom content of 11% was obtained. The total thickness of this ternary composite layer was 2.8 μm.

[0025] Example 3: A 0.2mm thick 316L stainless steel substrate was sequentially ultrasonically cleaned with acetone and ethanol for 15 minutes each, followed by argon ion sputtering to remove surface oxides. The treated substrate was then placed vertically on the vacuum chamber rack of a magnetron sputtering apparatus. The vacuum chamber door was closed, and a mechanical pump was used to evacuate the system to 5 Pa. The specific sputtering steps are as follows: S1. A pure Cr sputtered layer 2 with a thickness of 0.6 μm was obtained by using a 99.5% pure Cr target, sputtering power of 300W, argon flow rate of 20sccm, deposition temperature of 80℃, and deposition time of 5min. S2. A transition layer 3 with a purity of 99.5% Cr target and a purity of 99.5% Ti target was co-sputtered. The sputtering power of the Cr target was 300W, the sputtering power of the Ti target was 100W, the argon flow rate was 30sccm, and the deposition time was 5min. A transition layer 3 with a Cr atomic content of 75% + Ti atomic content of 25% and a thickness of 0.3μm was obtained. S3. A 99.5% pure Cr target and a 99.5% pure Ti target were co-sputtered, and high-purity CH4 with a purity of 99.9% was simultaneously introduced at 15 sccm. The sputtering power of the Cr target was 300W and the sputtering power of the Ti target was 100W. During this sputtering process, the argon flow rate was 15 sccm, the deposition temperature was 130℃, the sputtering pressure was 0.5Pa, and the deposition time was 10min, resulting in a ternary composite layer 4 with a C atom content of 58% + Cr atom content of 31% + Ti atom content of 11% and a thickness of 1.8μm.

[0026] Comparative Example 1, without sputtering layer: A 0.5mm thick 316L stainless steel plate was sequentially ultrasonically cleaned with acetone and ethanol for 15 minutes each, and then argon ion sputtering was used to remove surface oxides. After that, the treated substrate was placed on the vacuum chamber rack of the magnetron sputtering equipment, placed vertically, the vacuum chamber door was closed, and a mechanical pump was used to evacuate to 5 Pa. The specific sputtering steps are as follows: S1. A transition layer with a purity of 99.5% Cr target and a purity of 99.5% Ti target was co-sputtered. The sputtering power of the Cr target was 450W, the sputtering power of the Ti target was 200W, the argon flow rate was 30sccm, and the deposition time was 4min. A transition layer with a Cr atomic content of 71% + Ti atomic content of 29% and a thickness of 0.6μm was obtained. S2. A 99.5% pure Cr target and a 99.5% pure Ti target were co-sputtered, while simultaneously introducing 5 sccm of high-purity CH4 (99.9% pure). The sputtering power of the Cr target was 200W, and the sputtering power of the Ti target was 300W. During this sputtering process, the argon flow rate was 5 ccm, and the deposition temperature was 150℃. After 1 min, a ternary composite inner layer with a C atom content of 30% + Cr atom content of 27% + Ti atom content of 53% was obtained. Subsequently, the methane flow rate increased by 1 sccm / min, the Ti target power decreased by 15W / min, and the Cr target power increased by 20W / min. After 5 min, a ternary composite inner layer with a C atom content of 33% + Cr atom content of 38% + Ti atom content of 29% was obtained. After 10 min, a ternary composite outer layer with a C atom content of 59% + Cr atom content of 30% + Ti atom content of 11% was obtained. The total thickness of this ternary composite layer was 2.8 μm.

[0027] Comparative Example 2, without a transition layer: A 0.5mm thick 316L stainless steel plate was sequentially ultrasonically cleaned with acetone and ethanol for 15 minutes each, followed by argon ion sputtering to remove surface oxides. The treated substrate was then placed vertically on the vacuum chamber rack of a magnetron sputtering equipment, the vacuum chamber door was closed, and a mechanical pump was used to evacuate the vacuum to 5 Pa. The specific sputtering steps are as follows: S1. A 1.1 μm thick pure Cr layer was obtained by using a 99.5% high-purity Cr target, sputtering power of 450W, argon flow rate of 25 sccm, deposition temperature of 100℃, and deposition time of 4 min. S2. A 99.5% pure Cr target and a 99.5% pure Ti target were co-sputtered, while simultaneously introducing 5 sccm of high-purity CH4 (99.9% pure). The sputtering power of the Cr target was 200W, and the sputtering power of the Ti target was 300W. During this sputtering process, the argon flow rate was 5 ccm, and the deposition temperature was 150℃. After 1 min, a ternary composite inner layer with a C atom content of 30% + Cr atom content of 27% + Ti atom content of 53% was obtained. Subsequently, the methane flow rate increased by 1 sccm / min, the Ti target power decreased by 15W / min, and the Cr target power increased by 20W / min. After 5 min, a ternary composite inner layer with a C atom content of 33% + Cr atom content of 38% + Ti atom content of 29% was obtained. After 10 min, a ternary composite outer layer with a C atom content of 59% + Cr atom content of 30% + Ti atom content of 11% was obtained. The total thickness of this ternary composite layer was 2.8 μm.

[0028] Comparative Example 3, with a C atom content of 24% in the ternary composite layer (below the lower limit): A 0.2 mm thick 316L stainless steel plate was sequentially ultrasonically cleaned with acetone and ethanol for 15 min each, followed by argon ion sputtering to remove surface oxides. The treated substrate was then placed vertically on the vacuum chamber rack of a magnetron sputtering equipment, the vacuum chamber door was closed, and a mechanical pump was used to evacuate the vacuum to 5 Pa. The specific sputtering steps are as follows: S1. A pure Cr layer with a thickness of 0.6 μm was obtained by using a 99.5% high-purity Cr target, sputtering power of 300W, argon flow rate of 20 sccm, deposition temperature of 80℃, and deposition time of 5 min. S2. Co-sputtering with a 99.5% pure Cr target and a 99.5% pure Ti target was used. The sputtering power of the Cr target was 300W, the sputtering power of the Ti target was 100W, the argon flow rate was 30sccm, and the deposition time was 5min. A transition layer with a Ti atomic content of 75% and a Cr atomic content of 25% and a thickness of 0.3μm was obtained. S3. A 99.5% pure Cr target and a 99.5% pure Ti target were co-sputtered, and 3 sccm of 99.9% pure high-purity CH4 was simultaneously introduced. The sputtering power of the Cr target was 400W and the sputtering power of the Ti target was 280W. During this sputtering process, the argon flow rate was 15 sccm, the deposition temperature was 130℃, the sputtering pressure was 0.5Pa, and the deposition time was 15min, resulting in a ternary composite layer with a C atom content of 22% + Cr atom content of 46% + Ti atom content of 32% and a thickness of 1.4μm.

[0029] Test Example 1: The contact resistance of Examples 1-3 and Comparative Examples 1-2 was measured using the four-probe method under a clamping force of 1.4 MPa, and the data are recorded in Table 1 below. The samples of Examples 1-3 and Comparative Examples 1-3 were placed in a 0.5 M H2SO4 solution and heated to simulate the high temperature and acidic environment inside the PEMFC. Then, a scanning voltage from negative to positive was applied to the sample, and the current response was measured. The corrosion current density was obtained from the curve by the Tafel extrapolation method and recorded in Table 1 below. The three-point bending test of Examples 1-3 and Comparative Examples 1-3 was performed according to ASTM D790 standard, with a loading rate of 0.5 mm / min and a temperature of 80 °C, and the bending strength was recorded in Table 1 below.

[0030] Table 1 sample Contact resistance (mΩ·cm²) Corrosion current (μA / cm²) Flexural strength (MPa) Remark Example 1 6.2 0.71 198 Example 2 7.1 0.53 216 Example 3 7.8 0.69 189 Comparative Example 1 17.7 1.24 112 No sputtering layer Comparative Example 2 12.5 1.6 158 No transition layer Comparative Example 3 8.8 2.1 164 The C content in the ternary composite surface layer is below the lower limit. .

[0031] As can be seen from Table 1, Examples 1-3 are significantly superior. Comparative Example 1 lacks a Cr sputtered layer, and the substrate oxide directly contacts the transition layer. Furthermore, the substrate is directly exposed to an acidic environment, resulting in a significant increase in corrosion current and corrosion products covering the conductive channels.

[0032] Comparative Example 2 lacks a transition layer, and the Cr sputtered layer is in direct contact with the ternary composite layer. The lack of a transition layer leads to corrosion channels caused by internal stress at the interface between the sputtered layer and the ternary composite layer, and the reduced effective conductive area at the interface results in an increase in contact resistance.

[0033] In terms of strength, Example 2 is the best. Its gradient composition design enhances toughness buffering and surface hardness. The gradient layer disperses bending stress through continuous composition changes, avoiding brittle fracture. Therefore, the bending resistance of Example 2 is also significantly better than that of Examples 1 and 3. Comparative Example 1 has no sputtering layer, resulting in weak bonding between the transition layer and the substrate interface. Comparative Example 2 has no transition layer, and its sputtering layer directly contacts the ternary composite layer, which leads to stress concentration.

[0034] The carbon content in the ternary composite layer is the core factor affecting corrosion resistance and conductivity. A high carbon content significantly improves corrosion resistance. As shown in Table 1, when the carbon content is too low, the corrosion resistance drops sharply because it cannot form an effective protective layer.

[0035] Test Example 2: Contact angle tests for Comparative Example 1, Comparative Example 2, and Example 2 were performed according to ASTM D7334 standard: Samples from Comparative Example 1, Comparative Example 2, and Example 2 were placed sequentially on a 25°C constant temperature platform. Using a 5μL droplet of ultrapure water, the dynamic contact angle was collected over 10 seconds using an optical contact angle meter. The average value at three different locations was taken as the final result. The test results are as follows: Figure 1 As shown, Comparative Example 1 is Figure 1 (2) in the example, comparative example 2 is Figure 1 In (1), Example 2 is Figure 1 (3) in the middle, by Figure 1 It can be seen that the contact angle of Example 2 is significantly better than that of Comparative Examples 1 and 2. In Comparative Example 1, there is no sputtering layer, and the transition layer directly contacts the substrate, which is prone to corrosion and accelerates the peeling of the carbon film at the interface, thereby exposing the hydrophilic metal oxide. In Comparative Example 2, there is no transition layer, and the thermal expansion coefficients of the sputtering layer and the ternary composite layer are mismatched. When cooling, microcracks are generated, which leads to the carbon film peeling off after the corrosive liquid penetrates.

[0036] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A metal bipolar plate for a fuel cell, characterized by: The functional layer comprises a metal base and a functional layer covering the metal base, the metal base is 316L stainless steel, and the functional layer comprises, from the bottom layer close to the metal base to the surface layer, a sputtering layer, a transition layer and a ternary composite layer, the sputtering layer is composed of Cr elements, the transition layer is composed of Cr and Ti elements, and the ternary composite layer is composed of Cr, Ti and C elements.

2. The metal bipolar plate of claim 1, wherein: The thickness of the metal base is 0.2-0.7mm, the thickness of the sputtering layer is 0.5-1.5μm, the thickness of the transition layer is 0.2-1μm, and the thickness of the ternary composite layer is 0.5-3μm.

3. The metal bipolar plate of claim 1, wherein: The atomic percentage of Cr in the transition layer is 55-75%; In the ternary composite layer, the percentage of C atoms is 30%-65%, and the ratio of Cr atoms to Ti atoms is (0.5-3):

1.

4. The metal bipolar plate of claim 3, wherein: In the ternary composite layer, the composition components continuously change in a gradient from the transition layer to the surface layer, the percentage of Ti atoms gradually decreases, and the percentage of C atoms gradually increases. In the ternary composite layer, the percentage of C atoms is 30%-65%, and the ratio of Cr atoms to Ti atoms is (0.5-3):

1.

5. A method of producing a metal bipolar plate as claimed in any one of claims 1 to 4, characterized in that: The functional layer is formed by a magnetron sputtering method combined with chemical vapor deposition.

6. The method of claim 5, wherein: The sputtering layer is formed by sputtering a Cr target, the transition layer is formed by co-sputtering a high-purity Cr target and a Ti target, and the ternary composite layer is formed by co-sputtering the high-purity Cr target and the Ti target and introducing high-purity methane gas, the purity of the high-purity Ti target is ≥99.5%, the purity of the high-purity Cr target is ≥99.5%, and the purity of the high-purity methane is ≥99.99%.

7. The method of claim 5, wherein: The sputtering layer uses a high-purity Cr target, the sputtering power is 300-600W, and the deposition time is 3-5min; The transition layer uses co-sputtering of a high-purity Cr target and a high-purity Ti target, during the sputtering process, the Cr target electric power is 300-600W, the Ti target power is 100-300W, and the deposition time is 3-5min; During the sputtering process of the ternary composite layer, high-purity Cr and Ti targets are co-sputtered and high-purity methane gas is introduced, the sputtering power of the high-purity Cr target is 200-500W, the sputtering power of the high-purity Ti target is 100-300W, the gas flow of the high-purity methane is 5-15sccm, the deposition temperature is ≤200℃, and the sputtering time is 5-10min.

8. The method of claim 7, wherein: During the sputtering process of the ternary composite layer, the sputtering power of the Ti target and the flow rate of the introduced methane gas are synchronously and dynamically adjusted, the flow rate of the introduced methane gas linearly increases, the Ti target power linearly decreases with the increase of the carbon source gas flow, and the Cr target power linearly increases with the decrease of the Ti target power.

9. The method of claim 8, wherein: The growth rate of the flow rate of the introduced methane gas is 0.5-1sccm / min, the linear decrease rate of the Ti target power is 10-20w / min, and the linear increase rate of the Cr target power is 15-25w / min. The high-purity Cr target starts sputtering power is 200-250W, the high-purity Ti target starts sputtering power is 250-300W, high-purity methane gas flow is 3-5sccm, and the sputtering time is 5-10min.

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