A three-layer coating for metal bipolar plates used in fuel cells and its preparation method

Abstract

This invention discloses a three-layer coating for metal bipolar plates used in fuel cells and its preparation method, specifically relating to the field of fuel cell technology. The three-layer coating is (Ti... 0.67 Cr 0.33 ) 1‑x N x / Ru 0.99 C 0.01 The three-layer coating includes an inner coating layer (Ti). 0.67 Cr 0.33 ) 1‑x N x and outer coating Ru 0.99 C 0.01 The coating obtained by this invention has the advantages of uniformity, density, and high adhesion, and can effectively improve the corrosion resistance and electrical conductivity of the stainless steel substrate; this invention combines the characteristics of the substrate and the inner and outer coating systems to design (Ti 0.67 Cr 0.33 ) 1‑x N x The transition layer can reduce the thermal expansion mismatch between the substrate and the coating, while improving the elemental compatibility of each layer and increasing the adhesion of the coating.

Description

Technical Field

[0001] This invention relates to the field of fuel cell technology, specifically to a three-layer coating for a metal bipolar plate used in fuel cells and its preparation method, and more specifically to a coating for a stainless steel metal bipolar plate used in proton exchange membrane fuel cells and its preparation method. Background Technology

[0002] Proton exchange membrane fuel cells (PEMFCs) are considered an ideal clean power generation method due to their compact structure, small size, high energy density, high efficiency, rapid start-up, low-temperature operation, and zero emissions. In PEMFCs, bipolar plates, as a core component, are responsible for connecting individual cells in series, parallel, or in combination to form a stack, supporting the overall stack structure, isolating the reactant gases at the cathode and anode, and removing heat and water generated by the stack. They are crucial to the stack's performance. Currently, bipolar plates are mainly classified into three types: graphite bipolar plates, metal bipolar plates, and composite bipolar plates. Metal bipolar plates have the advantages of high strength and ease of processing; their ultra-thin design facilitates mass production, thereby improving the specific power of fuel cells. However, various corrosive ions, such as SO42-, exist in the working environment. 2- and F - These ions easily corrode the metal bipolar plate material, forming a passivation layer. This increases the contact resistance between the bipolar plate and the diffusion layer, significantly affecting the output power and durability of the fuel cell stack. Therefore, to achieve commercial application, surface coating modification is necessary to reduce the surface contact resistance of the metal bipolar plate and improve its conductivity and corrosion resistance.

[0003] Existing bipolar plate coatings mainly include carbon-based coatings, noble metal coatings, conductive polymer coatings, hydrophobic coatings, and transition metal ceramic compounds. Carbon-based coatings offer excellent corrosion resistance, electrical conductivity, and thermal conductivity at a relatively low cost, but their low deposition efficiency limits their large-scale application. Noble metal coatings provide superior corrosion resistance and conductivity, but are expensive. Conductive polymer coatings such as polyaniline (PANI) and polypyrrole (PPy) provide good protection for bipolar plates, exhibiting excellent corrosion resistance and conductivity, but their adhesion to the substrate is weak. Hydrophobic coatings reduce corrosion rates by increasing hydrophobicity, but maintaining long-term stability is difficult. Transition metal ceramic compounds possess excellent physical, chemical, and mechanical properties, providing good corrosion resistance and stability in bipolar plate operating environments while maintaining high conductivity, making them ideal coating materials. However, large particles in the coating may accelerate localized corrosion, and columnar crystals may penetrate the liquid, thus affecting long-term service life.

[0004] Chinese patent CN115663224A discloses a metal composite coating for a proton exchange membrane fuel cell bipolar plate and its preparation method. The coating comprises, from the inside out, a composite metal layer and a nano-conductive layer covering the surface of the composite metal layer on the surface of the metal plate substrate. The thickness of the composite metal layer is 5–3000 nm, and from the inside out, it comprises a metal corrosion-resistant layer, a metal self-healing layer, and a metal catalyst layer. The thickness of the nano-conductive layer is 5–500 nm, and it is selected from one or more carbon-based materials such as graphite, amorphous carbon, graphene, carbon fiber, and carbides. After plasma cleaning of the metal substrate, a metal corrosion-resistant layer is first deposited on the surface of the metal substrate, and then multiple layers of a metal self-healing layer and a metal catalyst layer are alternately deposited on the surface of the metal corrosion-resistant layer, resulting in a nano-conductive layer deposited on the surface of the composite metal layer. However, this patent still includes a carbon-based material layer, which affects the deposition efficiency.

[0005] Chinese patent CN110797545A mainly employs the following technical solution: a metal bipolar plate includes a metal substrate and a carbon-based coating; wherein the carbon-based coating is deposited on the metal substrate, and the carbon-based coating includes at least two carbon films deposited sequentially; wherein each carbon film is any one of laser pulse deposited carbon film, magnetron sputtered carbon film, multi-arc ion plating deposited carbon film, and chemical vapor deposition carbon film; the carbon-based coating includes at least two of the following carbon films: laser pulse deposited carbon film, magnetron sputtered carbon film, multi-arc ion plating deposited carbon film, and chemical vapor deposition carbon film. However, in the bilayer structure, the high etching current density and high contact resistance will reduce its service life.

[0006] Further research is needed on how to select materials to achieve rapid preparation and easy-to-control processes, while maintaining high corrosion resistance and conductivity to extend the service life of fuel cells. Summary of the Invention

[0007] Therefore, the present invention provides a three-layer coating for a metal bipolar plate used in fuel cells and a method for preparing the same, in order to solve the above-mentioned problems.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] According to a first aspect of the present invention, a three-layer coating for a metal bipolar plate used in a fuel cell is provided, wherein the three-layer coating is (Ti 0.67 Cr 0.33 ) 1-x N x / Ru 0.99 C 0.01 The three-layer coating includes an inner coating layer (Ti). 0.67 Cr 0.33 ) 1-x N x and outer coating Ru 0.99 C 0.01 .

[0010] The inner layer Ti of the coating of the present invention 0.67 Cr 0.33 、(Ti 0.67 Cr 0.33 ) 1-x N x As a transition layer, it is used to reduce interlayer thermal expansion mismatch, improve the elemental compatibility of each layer, and increase the adhesion of the coating; the outer layer of the coating, Ru 0.99 C 0.01 The composition coating is used to improve the corrosion resistance and electrical conductivity of the substrate.

[0011] Furthermore, the inner layer of the coating (Ti) 0.67 Cr 0.33 ) 1-x N x Including the first inner layer Ti 0.67 Cr 0.33 With the second inner layer (Ti) 0.67 Cr 0.33 ) 1-x N x In this case, nitrogen (N) is incorporated in the gas phase.

[0012] Furthermore, the ratio of Ti to the doped Cr is (1.5-2.5):1.

[0013] The Ti of the present invention 0.67 Cr 0.33 This is a modified material for binary layered ceramic titanium-chromium, in which Cr is doped at Ti sites in a specific ratio. As an example, the preferred ratio of Ti to Cr is approximately 2:1. The corrosion resistance and electrical conductivity of the doped titanium-chromium are significantly improved. 0.67 Cr 0.33 The coating thickness is approximately 100 nm, the corrosion current density decreases by 40%, the self-corrosion potential increases by approximately 0.1 V, and the contact resistance decreases by approximately 30%.

[0014] Furthermore, the N element doping ratio is 40–55 at.%.

[0015] Furthermore, the first inner layer Ti 0.67 Cr 0.33 The thickness is 50-500 nm, and the second inner layer (Ti) 0.67 Cr 0.33 ) 1-x N x The thickness is 50-500 nm, and the thickness of the outer Ru-C composite coating is 2-100 nm.

[0016] A method for preparing a three-layer coating for a metal bipolar plate used in a fuel cell, according to a second aspect of the present invention, includes:

[0017] Step 1, inner coating layer (Ti) 0.67 Cr 0.33 ) 1-x N x Preparation

[0018] Ti powder and Cr powder were prepared by sintering in a hot press furnace using a hot pressing / solid-liquid phase reaction method; wherein, flowing argon gas was used as a protective gas to prepare Ti. 0.67 Cr 0.33 Ti was prepared using flowing nitrogen as a protective gas. 0.67 Cr 0.33 ) 1-x N x ;

[0019] Step 2, apply the outer Ru coating 0.99 C 0.01 Preparation

[0020] A mixture of ruthenium and carbon was used to apply an electric arc discharge to a ruthenium target, generating high-temperature plasma. Ruthenium was evaporated, and a carbon-containing gas was introduced as a carbon source. Carbon was introduced into the coating through plasma reaction. By adjusting the evaporation rates of ruthenium and carbon, the Ru / C ratio of the coating was controlled to be 0.99 / 0.01, resulting in a Ru-rich outer layer. 0.99 C 0.01 .

[0021] Furthermore, the inner coating (Ti) 0.67 Cr 0.33 ) 1-x N x The Ru and C combined coating is deposited on a metal bipolar plate using a magnetron sputtering device; the coating is deposited using an arc ion plating device.

[0022] As an example, the coating target of the inner coating is (Ti 0.67 Cr 0.33 ) 1-x N x The target material is prepared using Ti powder and Cr powder, which are sintered in a hot press furnace using a hot pressing / solid-liquid phase reaction method. The sintering temperature is 1000℃~1600℃, the holding time is 20~100min, and the hot pressing pressure is 15~75MPa. Flowing argon and nitrogen are used as protective gases to obtain Ti. 0.67 Cr 0.33 Target material and (Ti 0.67 Cr 0.33 ) 1-x N xTarget material. The target material for the outer coating is a mixture of ruthenium and carbon. An electric arc discharge is applied to the ruthenium target to generate high-temperature plasma, which evaporates the ruthenium and introduces carbon-containing gases (such as ethylene, methane, etc.) as a carbon source. Carbon elements are introduced into the coating through plasma reaction. By adjusting the evaporation rate of ruthenium and carbon, the Ru / C ratio of the coating is controlled to be 0.99 / 0.01.

[0023] Furthermore, the method for depositing on a metal bipolar plate using the magnetron sputtering equipment includes: adjusting and maintaining the chamber temperature, turning on the DC power supply to the target, controlling the sputtering power and sputtering time for deposition, and after deposition, cooling to room temperature, stopping the vacuuming, and depressurizing. In this invention, two sputtering power supplies are arranged in one chamber. During coating deposition, the sample is suspended on the sample holder of the equipment, and the column suspending the sample rotates on its own axis while simultaneously revolving with the rotary table to obtain a uniform coating.

[0024] As an example, the method for depositing on a metal bipolar plate using a magnetron sputtering device is as follows: First, adjust the chamber temperature to 200–500°C and hold for 10–40 minutes, then turn on the Ti... 0.67 Cr 0.33 The target was powered by a DC power supply, with a sputtering power of 0.1–2 kW and a sputtering time of 15–45 min. After deposition, the material was cooled to room temperature at a rate of 10 °C / min under the original vacuum conditions. Then, the vacuum was stopped and the pressure was released, finally yielding Ti. 0.67 Cr 0.33 Coating. Prepared using the same process after changing the target material (Ti). 0.67 Cr 0.33 ) 1-x N x coating.

[0025] Furthermore, the deposition method of the arc ion plating equipment includes: first removing contaminants and oxide layers from the substrate surface; controlling the working gas pressure in the vacuum chamber by adjusting the pumping speed of the molecular pump; heating the chamber; turning on the DC power supply to the target material; and controlling the arc current, bias voltage, and sputtering time. In this invention, an arc ion plating device with a high deposition rate is used to deposit on a metal bipolar plate to improve the adhesion of the outer coating and increase the compatibility between the coating and the substrate.

[0026] As an example, the deposition method in an arc ion plating equipment is as follows: before coating preparation, the vacuum chamber is pre-evacuated to 4 × 10⁻⁶. -3 After Pa, a 500V negative pulse bias voltage is applied to the substrate for backsplash cleaning for 3–15 min to remove contaminants and oxide layers from the substrate surface. Then, the Ar flow valve is opened, with a gas flow rate of 50 mL / min. The working gas pressure in the vacuum chamber is controlled by adjusting the pumping speed of the molecular pump to maintain it at 0.4 Pa. The chamber heating temperature is set to 100–200℃. The Ru... 0.99C 0.01 The target material is supplied with a DC power supply, an arc current of 40–80A, a bias voltage of -200–-400V, and a sputtering time of 1–15 minutes.

[0027] Furthermore, the method also includes pretreatment: first, the metal bipolar plate is ground and polished, then the ground metal bipolar plate is ultrasonically cleaned with acetone, alcohol and deionized water respectively, and finally dried in nitrogen for later use. As an example, the cleaning time is 10-20 minutes.

[0028] According to a third aspect of the present invention, a three-layer coating for a metal bipolar plate used in a fuel cell is applied to a proton exchange membrane fuel cell metal bipolar plate.

[0029] The present invention has the following advantages:

[0030] This invention first employs magnetron sputtering technology to form two transition metal-ceramic compound layers in the inner layer, and then uses arc ion plating technology to deposit Ru in the outer layer. 0.99 C 0.01 The composition is coated to modulate the gradient structure of the three-layer coating. The coating of the present invention is characterized by uniformity, density and strong adhesion, which can effectively improve the corrosion resistance and conductivity of the stainless steel substrate; the overall coating is prepared quickly and the process is easy to control, thereby significantly improving the performance of the bipolar plate and extending the service life of the fuel cell.

[0031] This invention deposits (Ti) on a metal bipolar plate using two sputtering methods. 0.67 Cr 0.33 ) 1-x N x / Ru 0.99 C 0.01 The three-layer coating results in a coating with advantages of uniformity, density, and high adhesion. This invention combines the characteristics of the substrate and the inner and outer coating systems to design (Ti) 0.67 Cr 0.33 ) 1-x N x The transition layer can reduce the thermal expansion mismatch between the substrate and the coating, while improving the elemental compatibility of each layer and increasing the adhesion of the coating; Ru 0.99 C 0.01 The coating, a Ru-C composition, significantly improves the coating's corrosion resistance and electrical conductivity. Results show that compared to Ti... 0.67 Cr 0.33 / Ru 0.99 C 0.01 Double-layer coating, the present invention (Ti) 0.67 Cr 0.33 ) 1-x N x / Ru 0.99 C0.01 The three-layer coating structure can reduce the corrosion current density by 28%, increase the self-corrosion potential by 0.08V, and reduce the contact resistance by 50%, which can significantly improve the performance of the bipolar plate and thus extend the service life of the fuel cell.

[0032] The coating preparation method of this invention is easy to control and efficient. It uses high-efficiency arc ion plating technology to prepare the intermediate transition layer and magnetron sputtering technology to prepare the outer coating, which can obtain a dense, flat and uniform coating with uniform composition and structure. It is easy to promote industrialization. Attached Figure Description

[0033] To more clearly illustrate the embodiments of the present invention or the technical solutions in 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 merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0034] The structures, proportions, sizes, etc. illustrated in this specification are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed herein, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportions, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0035] Figure 1 This is a schematic diagram of the three-layer coating structure provided in Embodiment 1 of the present invention; wherein, 1-metal substrate; 2-Ti 0.67 Cr 0.33 ;3-(Ti 0.67 Cr 0.33 ) 1-x N x ;4-Ru 0.99 C 0.01 ;

[0036] Figure 2 A scanning electron microscope cross-sectional image of the coating prepared according to Example 1 of the present invention;

[0037] Figure 3 The image shown is a scanning electron microscope (SEM) image of the coating prepared according to Example 1 of this invention.

[0038] Figure 4 The electrochemical test-potential motion scan diagram of the coating prepared in Example 1 of the present invention. Detailed Implementation

[0039] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] The metal substrate used in the following examples is a metal bipolar plate. The Ti deposited... 0.67 Cr 0.33 Target material and (Ti 0.67 Cr 0.33 ) 1-x N x The target material is prepared by hot pressing / solid-liquid phase reaction sintering in a hot press furnace. The sintering temperature is 1000℃~1600℃, held for 20~100 minutes, and the hot pressing pressure is 15~75MPa. Flowing argon and nitrogen are used as protective gases. The raw powder used in the preparation includes Ti powder and Cr powder, and the ratio is determined by the Ti content. 0.67 Cr 0.33 In this process, the raw material powder is prepared with a Ti:Cr ratio of 2:1, and wet-mixed in a ball mill for 24–50 hours. Afterward, it is removed, air-dried, and sieved for later use. The target material obtained in argon atmosphere is Ti. 0.67 Cr 0.33 The target material obtained in nitrogen is (Ti 0.67 Cr 0.33 ) 1-x N x .

[0041] Example 1

[0042] This embodiment provides a coating suitable for the metal bipolar plate of a proton exchange membrane fuel cell (structural diagram shown below). Figure 1 Preparation method (as shown):

[0043] Step 1: Prepare a stainless steel bipolar plate. Polish the bipolar plate step by step with metallographic sandpaper of 200#, 400#, 600#, 800#, 1000#, 1500#, and 2000#. After polishing, ultrasonically clean the bipolar plate with acetone, alcohol, and deionized water for 20 minutes each, and then air dry it for later use.

[0044] Step 2: Deposit Ti using magnetron sputtering. 0.67 Cr 0.33 With (Ti) 0.67 Cr 0.33 ) 1-x Nx Inner coating:

[0045] First, adjust the chamber temperature to 300℃ and maintain it for 20 minutes, then open the Ti... 0.67 Cr 0.33 The target was powered by a DC power supply, the sputtering power was 1 kW, and the sputtering time was 30 min. After deposition, the temperature was lowered to room temperature at a rate of 10 °C / min under the original vacuum conditions, then the vacuum was stopped and the pressure was released to obtain Ti. 0.67 Cr 0.33 .

[0046] After changing the target material, the same process was repeated to finally obtain (Ti). 0.67 Cr 0.33 ) 1-x N x (x = 0.4 ~ 0.55) Coating.

[0047] Step 3: Deposit Ru using arc ion plating. 0.99 C 0.01 Before the coating layer is prepared, the vacuum chamber is pre-evacuated to a back-bottom vacuum of 4 × 10⁻⁶. -3 After Pa, a 500V negative pulse bias voltage was applied to the substrate for backsplash cleaning for 10 min to remove contaminants and oxide layers from the substrate surface. Then, the Ar flow valve was opened, and the Ar gas flow rate was 50 mL / min. The working pressure in the vacuum chamber was controlled by adjusting the pumping speed of the molecular pump to maintain it at approximately 0.4 Pa, and the chamber heating temperature was 100℃. The DC power supply for the TiC target was turned on, with an arc current of 50 A, a bias voltage of -200 V, and a sputtering time of 2 min.

[0048] After the experiment, the surface and cross-sectional microstructure of the deposited coating were observed using a scanning electron microscope. It was found that the obtained three-layer coating was smooth, dense, and well-bonded to the substrate. Figure 2 and Figure 3 As shown. In a fuel cell simulation environment, as... Figure 4 As shown, in a solution with H₂SO₄ concentration of 0.5 mol / L and HF concentration of 2 ppm, a potentiodynamic test was performed at 80 °C, and the corrosion current density was 0.65 μA / cm². 2 At an assembly force of 150 N / cm 2 Under these conditions, the contact resistance is approximately 2 mΩ·cm 2 .

[0049] Example 2

[0050] This embodiment provides a method for preparing a coating suitable for metal bipolar plates in proton exchange membrane fuel cells:

[0051] Step 1: Prepare a stainless steel bipolar plate. Polish the bipolar plate step by step with metallographic sandpaper of 200#, 400#, 600#, 800#, 1000#, 1500#, and 2000#. After polishing, ultrasonically clean the bipolar plate with acetone, alcohol, and deionized water for 20 minutes each, and then air dry it for later use.

[0052] Step 2: Deposit Ti using magnetron sputtering. 0.67 Cr 0.33 With (Ti) 0.67 Cr 0.33 ) 1-x N x Inner coating:

[0053] First, adjust the chamber temperature to 500℃ and maintain it for 15 minutes, then open the Ti... 0.67 Cr 0.33 The target was powered by DC, the sputtering power was 0.1 kW, and the sputtering time was 45 min. After deposition, the target was cooled to room temperature at a rate of 10 °C / min under the original vacuum conditions, then the vacuum was stopped and the pressure was released. The same process was repeated after changing the target material, ultimately yielding (Ti) 0.67 Cr 0.33 ) 1-x N x (x = 0.4 ~ 0.55) Coating.

[0054] Step 3: Deposit Ru using arc ion plating. 0.99 C 0.01 Before the coating layer is prepared, the vacuum chamber is pre-evacuated to a back-bottom vacuum of 4 × 10⁻⁶. -3 After Pa, a 500V negative pulse bias voltage was applied to the substrate for backsplash cleaning for 10 min to remove contaminants and oxide layers from the substrate surface. Then, the Ar flow valve was opened, and the Ar gas flow rate was 50 mL / min. The working pressure in the vacuum chamber was controlled by adjusting the pumping speed of the molecular pump to maintain it at approximately 0.4 Pa, and the chamber heating temperature was 200℃. The DC power supply for the TiC target was turned on, with an arc current of 80 A, a bias voltage of -200 V, and a sputtering time of 15 min.

[0055] Example 3

[0056] This embodiment provides a method for preparing a coating suitable for metal bipolar plates in proton exchange membrane fuel cells:

[0057] Step 1: Prepare a stainless steel bipolar plate. Polish the bipolar plate step by step with metallographic sandpaper of 200#, 400#, 600#, 800#, 1000#, 1500#, and 2000#. After polishing, ultrasonically clean the bipolar plate with acetone, alcohol, and deionized water for 20 minutes each, and then air dry it for later use.

[0058] Step 2: Deposit Ti using magnetron sputtering. 0.67 Cr 0.33 With (Ti) 0.67 Cr 0.33 ) 1-x N x Inner coating:

[0059] First, adjust the chamber temperature to 200℃ and maintain it for 30 minutes, then open the Ti... 0.67 Cr 0.33 The target was powered by DC, the sputtering power was 0.1 kW, and the sputtering time was 45 min. After deposition, the target was cooled to room temperature at a rate of 10 °C / min under the original vacuum conditions, then the vacuum was stopped and the pressure was released. The same process was repeated after changing the target material, ultimately yielding (Ti) 0.67 Cr 0.33 ) 1-x N x (x = 0.4 ~ 0.55) Coating.

[0060] Then, Ru was deposited using an arc ion plating method. 0.99 C 0.01 Before the coating layer is prepared, the vacuum chamber is pre-evacuated to a back-bottom vacuum of 4 × 10⁻⁶. -3 After Pa, a 500V negative pulse bias voltage was applied to the substrate for backsplash cleaning for 10 min to remove contaminants and oxide layers from the substrate surface. Then, the Ar flow valve was opened, and the Ar gas flow rate was 50 mL / min. The working pressure in the vacuum chamber was controlled by adjusting the pumping speed of the molecular pump to maintain it at approximately 0.4 Pa, and the chamber heating temperature was 150℃. The DC power supply for the TiC target was turned on, with an arc current of 40 A, a bias voltage of -200 V, and a sputtering time of 10 min.

[0061] Comparative Example 1

[0062] This comparative example provides a method for preparing a coating suitable for metal bipolar plates in proton exchange membrane fuel cells:

[0063] In step two of this comparative example, only Ti is used. 0.67 Cr 0.33 No longer proceeding (Ti) 0.67 Cr 0.33 ) 1-x N xPreparation, otherwise identical to Example 1, yielded Ti 0.67 Cr 0.33 / Ru 0.99 C 0.01 Double coating.

[0064] After the experiment, the surface and cross-sectional microstructure of the deposited coating were observed using scanning electron microscopy. The results showed that the obtained three-layer coating was smooth, dense, and well-bonded to the substrate. Potentiodynamic testing was conducted in a fuel cell simulation environment (0.5 mol / L H₂SO₄ and 2 ppm HF solution) at 80℃, with a corrosion current density of 0.95 μA / cm². 2 At an assembly force of 150 N / cm 2 Under these conditions, the contact resistance is approximately 4 mΩ·cm. 2 .

[0065] Compared to Ti 0.67 Cr 0.33 / Ru 0.99 C 0.01 Double-layer coating, the present invention (Ti) 0.67 Cr 0.33 ) 1-x N x / Ru 0.99 C 0.01 The three-layer coating structure can reduce the corrosion current density by 28%, increase the self-corrosion potential by 0.08V, and reduce the contact resistance by 50%, which can significantly improve the performance of the bipolar plate and thus extend the service life of the fuel cell.

[0066] Comparative Example 2

[0067] This comparative example provides a method for preparing a metal composite coating for the bipolar plate of a proton exchange membrane fuel cell:

[0068] (1) Under vacuum conditions, the metal substrate on the sample holder is cleaned by radio frequency plasma to remove impurities and oxides from the surface of the metal substrate.

[0069] (2) A metal corrosion-resistant layer is deposited on the cleaned metal substrate surface by magnetron sputtering. The sputtering target is titanium metal and the thickness of the metal corrosion-resistant layer is 100 nm.

[0070] (3) A metal self-healing layer is deposited on the metal corrosion-resistant layer by magnetron sputtering. The sputtering target is metallic silver and the thickness of the metal self-healing layer is 50 nm.

[0071] (4) A metal catalyst layer is deposited on the surface of the metal self-healing layer by reactive magnetron sputtering. The sputtering target is lanthanum metal, the reaction gas is oxygen, the thickness of the metal catalyst layer is 50 nm, and the atomic ratio of lanthanum metal in lanthanum oxide is 20%.

[0072] (5) A layer of amorphous carbon nanotube conductive layer was deposited on the surface of the metal catalyst layer by magnetron sputtering. The sputtering target was a graphite target and the thickness of the nanotube conductive layer was 100 nm.

[0073] Potentiodynamic testing was conducted in a fuel cell simulation environment, specifically in a solution with H₂SO₄ concentration of 0.5 mol / L and HF concentration of 2 ppm, at a temperature of 80 °C, with a corrosion current density of 1.2 μA / cm². 2 At an assembly force of 150 Ncm -2 Under these conditions, the contact resistance is approximately 4.3 mΩ·cm. 2 .

[0074] Therefore, it can be seen that the coating of the stainless steel metal bipolar plate of the proton exchange membrane fuel cell of the present invention significantly reduces the corrosion current density and contact resistance, which can greatly improve the performance of the bipolar plate and thus improve the service life of the fuel cell.

[0075] Comparative Example 3

[0076] This comparative example provides a method for preparing a coating suitable for metal bipolar plates in proton exchange membrane fuel cells:

[0077] In step three, the Ru and C layers are changed to Pt and C layers, but everything else is exactly the same as in Example 1.

[0078] Potentiodynamic testing was conducted in a fuel cell simulation environment, specifically in a solution with H₂SO₄ concentration of 0.5 mol / L and HF concentration of 2 ppm, at a temperature of 80 °C, with a corrosion current density of 1.2 μA / cm². 2 At an assembly force of 150 N / cm 2 Under these conditions, the contact resistance is approximately 3 mΩ·cm. 2 .

[0079] Comparative Example 4

[0080] This comparative example provides a method for preparing a coating suitable for metal bipolar plates in proton exchange membrane fuel cells:

[0081] In step three, the Ru and C layers are changed to Ag and C layers, but everything else is exactly the same as in Example 1.

[0082] In a fuel cell simulation environment, specifically a solution with H₂SO₄ concentration of 0.5 mol / L and HF concentration of 2 ppm, at a temperature of 80 °C, potentiodynamic testing was conducted, with a corrosion current density of 1.9 μA / cm². 2 At an assembly force of 150 N / cm 2 Under these conditions, the contact resistance is approximately 3.7 mΩ·cm. 2 .

[0083] Therefore, changing the elemental composition of the outer layer of the coating will significantly increase the corrosion current density and contact resistance. Thus, Ru and C are the best choices for the outer layer of the coating.

[0084] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A three-layer coating for a metal bipolar plate used in fuel cells, characterized in that, The three-layer coating is (Ti) 0.67 Cr 0.33 ) 1-x N x / Ru 0.99 C 0.01 The three-layer coating includes an inner coating layer (Ti). 0.67 Cr 0.33 ) 1-x N x and outer coating Ru 0.99 C 0.01 The inner layer of the coating (Ti) 0.67 Cr 0.33 ) 1-x N x Including the first inner layer Ti 0.67 Cr 0.33 With the second inner layer (Ti) 0.67 Cr 0.33 ) 1-x N x , 1≥x>0, where N element is incorporated in the gas phase; The method for preparing the three-layer coating of the metal bipolar plate used in fuel cells includes: Step 1, inner coating layer (Ti) 0.67 Cr 0.33 ) 1-x N x Preparation Ti powder and Cr powder were prepared by sintering in a hot press furnace using a hot pressing / solid-liquid phase reaction method; wherein, flowing argon gas was used as a protective gas to prepare Ti. 0.67 Cr 0.33 Ti was prepared using flowing nitrogen as a protective gas. 0.67 Cr 0.33 ) 1-x N x The inner layer of the coating (Ti) 0.67 Cr 0.33 ) 1-x N x Deposited onto a metal bipolar plate using magnetron sputtering equipment; Ti was prepared by sintering in a hot press furnace using a hot pressing / solid-liquid phase reaction method. The sintering temperature was 1000℃~1600℃, the holding time was 20~100min, and the hot pressing pressure was 15~75MPa. Flowing argon and nitrogen were used as protective gases, respectively, to obtain Ti. 0.67 Cr 0.33 Target material and (Ti 0.67 Cr 0.33 ) 1-x N x Target material; Step 2, apply the outer Ru coating 0.99 C 0.01 Preparation A mixture of ruthenium and carbon was used to apply an electric arc discharge to a ruthenium target, generating high-temperature plasma. Ruthenium was evaporated, and a carbon-containing gas was introduced as a carbon source. Carbon was introduced into the coating through a plasma reaction. By adjusting the evaporation rates of ruthenium and carbon, the Ru / C ratio of the coating was controlled to be 0.99 / 0.01, resulting in a Ru... 0.99 C 0.01 The target material; the combined Ru and C coating is deposited using an arc ion plating apparatus; the method for deposition using the arc ion plating apparatus includes pre-evacuating the vacuum chamber to 4 × 10⁻⁶ before coating preparation. - 3 After Pa, a 500V negative pulse bias voltage is applied to the substrate for backsplash cleaning for 3–15 min to remove contaminants and oxide layers from the substrate surface. Then, the Ar flow valve is opened, with a gas flow rate of 50 mL / min. The working gas pressure in the vacuum chamber is controlled by adjusting the pumping speed of the molecular pump to maintain it at 0.4 Pa. The chamber heating temperature is set to 100–200℃. The Ru... 0.99 C 0.01 The target material is supplied with a DC power supply, the arc current is 40–80 A, the bias voltage is -200–-400 V, and the sputtering time is 1–15 min; this yields an outer Ru coating. 0.99 C 0.01 .

2. The three-layer coating for a metal bipolar plate used in a fuel cell according to claim 1, characterized in that, First inner layer Ti 0.67 Cr 0.33 The thickness is 50~500 nm, the second inner layer (Ti) 0.67 Cr 0.33 ) 1-x N x The thickness is 50~500 nm, and the thickness of the outer Ru and C composite coating is 2~100 nm.

3. The three-layer coating for a metal bipolar plate used in a fuel cell according to claim 1, characterized in that, The nitrogen doping ratio is 40-55 at.%.

4. The three-layer coating for a metal bipolar plate used in a fuel cell according to claim 1, characterized in that, The ratio of Ti to doped Cr is (1.5-2.5):

1.

5. The three-layer coating for a metal bipolar plate used in a fuel cell according to claim 1, characterized in that, The method for deposition on a metal bipolar plate using the magnetron sputtering equipment includes: adjusting the chamber temperature and maintaining the temperature, turning on the DC power supply to the target material, controlling the sputtering power and sputtering time for deposition, and after deposition, cooling to room temperature, stopping the vacuum pumping, and depressurizing. The method for deposition using the arc ion plating equipment includes: first removing contaminants and oxide layers from the substrate surface, controlling the working gas pressure in the vacuum chamber by adjusting the pumping speed of the molecular pump, heating the chamber, turning on the DC power supply to the target material, and controlling the arc current, bias voltage, and sputtering time.

6. The three-layer coating for a metal bipolar plate used in a fuel cell according to claim 1, characterized in that, The method also includes pretreatment: first, the metal bipolar plate is polished, then the polished metal bipolar plate is ultrasonically cleaned with acetone, alcohol and deionized water respectively, and finally dried in nitrogen for later use.

7. The application of a three-layer coating for a metal bipolar plate in a proton exchange membrane fuel cell according to any one of claims 1 to 6.

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