A method for preparing a modified composite coating for a fuel cell metal connector

Abstract

The present invention discloses a modified composite coating for a fuel cell metal connector. The coating is Ti3SiC2 doped with V and Zr at the Ti position and Al doped at the Si position. The chemical formula of the coating phase is: (Ti 1‑x N x )3(Si,Al)C2, N is one of V and Zr, and is pre-oxidized before depositing the coating to form a nano-layer oxide inner coating on the surface of the metal connector, thereby increasing the bonding strength between the deposited coating and the substrate, reducing the coating deposition temperature, and optimizing the overall antioxidant and conductive properties of the modified coating. The present invention increases the inner coating layer through pre-oxidation, increases the bonding strength between the overall coating and the substrate, optimizes the overall antioxidant and conductive properties of the modified coating; improves the antioxidant properties and conductivity of the material and the density of the coating, effectively solves the problem of cathode poisoning, and can reduce the growth rate of the Cr2O3 film, reduce the working resistance of the connector, and improve the comprehensive working performance of the stainless steel connector. The large-scale application of the present invention can further promote the commercialization of solid oxide fuel cells.

Description

Technical Field

[0001] The present invention belongs to the technical field of fuel cell materials, and in particular relates to a modified composite coating of a fuel cell metal connector and a preparation method thereof. Background Art

[0002] Solid Oxide Fuel Cell (SOFC) has broad application prospects in distributed power stations and power supply fields due to its advantages such as the use of carbon-containing fuels, high power generation efficiency and low power generation cost. Although there are some battery stacks in demonstration operation around the world, their large-scale commercial application is still restricted by the materials of each component. Among them, the interconnect material is one of the bottlenecks in the development of SOFC. The interconnect (also called connecting plate or bipolar plate) is a key component in the assembly of flat-plate SOFC stacks. On the one hand, it electrically connects adjacent single cells; on the other hand, it isolates the gas at the anode and the air at the cathode. Its performance directly affects the output power and service life of the SOFC stack. The alloy connector Cr of the existing solid oxide fuel cell has the problem of volatilization and the metal bipolar plate of the proton exchange membrane fuel cell is easily corroded. To solve these problems, application number 202110692108.1 is a double-layer coating for the metal connector of the fuel cell, in which the inner layer of the coating is a TiC coating and the outer layer is a Ti3SiC2 ceramic or a doped modified solid solution material (Ti, M)3SiC2, wherein M is selected from one of Nb, Ta, W and V materials. The double-layer coating is uniform, dense and has high adhesion. It can effectively inhibit the outward migration of the Cr element contained in the metal connector for a long time, solve the problem of cathode poisoning, and at the same time reduce the growth rate of the Cr2O3 film, reduce the working resistance of the connector, and improve the comprehensive working performance of the stainless steel connector; it can also be used for the metal bipolar plate of the proton exchange membrane fuel cell, effectively improving the corrosion resistance and conductivity of the proton exchange membrane fuel cell bipolar plate. In addition, application number 2021106920888 discloses a metal connector coating for a fuel cell, wherein the coating is Ti3SiC2 or a doped modified solid solution material (Ti, M)3SiC2, wherein M is selected from one of Nb, Ta, W and V materials.

[0003] However, subsequent research revealed that this technology still has some shortcomings. For example, the adhesion between the deposited coating and the substrate is insufficient, the deposition temperature is high, and the overall oxidation resistance and electrical conductivity of the coating are not ideal. The deposited coating material has insufficient oxidation resistance, a high oxidation rate, and insufficient coating density. Further research and breakthroughs are needed. Summary of the Invention

[0004] In order to solve the above problems, the present invention provides a modified composite coating for a fuel cell metal connector and discloses a preparation method thereof.

[0005] The present invention is achieved through the following technical solutions:

[0006] A modified composite coating for a fuel cell metal connector, wherein the composite coating has a double-layer structure, wherein the outer layer is Ti3SiC2 doped with V and Zr at the Ti position, and Al doped at the Si position, and the chemical formula of the coating phase is: (Ti 1-x N x )3(Si,Al)C2, N is one of V and Zr, the inner layer of the composite coating is a nano-oxide layer, and the substrate is pre-oxidized to generate a nano-layer oxide on the surface of the metal connector. The inner oxide layer can increase the bonding force between the outer deposited coating and the substrate, reduce the temperature of the coating deposition, optimize the overall oxidation resistance and conductivity of the modified coating, and at the same time reduce the mutual diffusion of elements between the outer coating and the substrate, thereby increasing the service life of the coating.

[0007] Furthermore, in the chemical formula of the outer phase of the composite coating, x is 0.01 to 0.25; the atomic percentage of Al replacing Si is 3 at.%. 1-x N x )3(Si,Al)C2 (N is one of V and Zr, x is 0.01-0.25; the atomic percentage of Al replacing Si is 3at.%), N-doped Ti can improve the material's antioxidant properties, reduce the oxidation rate, and increase the conductivity of the generated oxide, and Al replacing 3at.% Si can increase the density of the coating.

[0008] Furthermore, the inner layer of the composite coating is mainly nano-oxide, which is obtained through pre-oxidation treatment of the metal connector. The inner layer coating can improve the bonding strength between the outer layer coating and the metal substrate, and can reduce the diffusion of elements between the two, prevent phase degradation, and increase the service life of the coating system.

[0009] Furthermore, the pretreatment method of the metal connector is: first, the metal connector is ground and polished, and polished step by step with 400#, 600#, 800#, 1000#, and 1200# metallographic sandpaper, and then the polished metal connector is ultrasonically cleaned with acetone, alcohol, and deionized water for 10 to 30 minutes respectively, and then blown dry in the air for use.

[0010] Furthermore, the preparation method of the nano-oxide inner layer coating is: the pre-treated metal connector is placed in a tube furnace for heating and pre-oxidation, the heating temperature is: 600-800℃, the holding time is 2-20 hours, and a nano-oxide layer with a thickness of 50-500nm is obtained.

[0011] Furthermore, the outer layer of the modified composite coating is deposited on the surface of the metal connector by pre-treating the metal connector and then pre-oxidizing it to form a nano-layer oxide inner coating on the surface of the metal connector, and then (Ti 1-x N x )3(Si,Al)C2 is the coating block target material, and the target material is deposited onto the surface containing nano-metal connectors by magnetron sputtering.

[0012] Furthermore, a magnetron sputtering device is used to deposit a coating on the alloy surface. When depositing the coating, the sample plate is attached to a frame plate, and the frame plate is heated to adjust the coating temperature.

[0013] Furthermore, the magnetron sputtering method means that before the coating is prepared, the vacuum is firstly pre-evacuated to 5×10 -4 Pa, in order to minimize the contamination of residual gas during the sputtering process, after reaching the required vacuum degree, high-purity Ar gas with a flow rate of 50ml / min is introduced, and the working gas pressure is adjusted to be maintained at 0.20~0.40Pa. Before the deposition begins, Ar is first used to + Clean the target material to remove contaminants on the target surface. The cleaning time is 5 to 10 minutes. Then heat the metal connector to 50 to 200°C and keep it warm for 15 minutes. After the temperature of the entire metal connector is uniform, start sputtering to prepare the coating. The sputtering power is 0.08 to 1.5 kW and the sputtering time is 1 to 8 hours. After the deposition is completed, cool it to room temperature at a rate of 10°C / min under the original vacuum conditions, and then stop vacuuming and releasing the pressure.

[0014] Furthermore, the metal connector is ferritic stainless steel: any one of SUS430, Crofer22APU, Fe-10Cr, 1.4724, Fe-17Cr-0.2Y, 1.4016, Ferrotherm (1.4742), Fe-18Cr-9W, Fe-20Cr-7W, Fe-20Cr, AL 453, 1.4763 (446), FeCrMn (LaTi), Fe-Cr-Mn, Fe-25Cr-DIN 50049, Fe-25Cr-0.1Y-2.5Ti, Fe-25Cr-0.2Y-1.6Mn, Fe-25Cr-0.4La, Fe-25Cr-0.3Zr, Fe26CrTiY, Fe26CrTiNbY, Fe26CrMoTiY, E-Brite, Al29-4C or Fe-30Cr.

[0015] Furthermore, the (Ti 1-x N xThe preparation method of )3(Si,Al)C2 bulk target is as follows: take Ti powder, one of V or Zr, silicon powder, aluminum powder and graphite powder, and sinter them in a hot pressing furnace by hot pressing / solid-liquid reaction method. The sintering temperature is 1400℃~1750℃, and the heat preservation is carried out for 25~90 minutes. The hot pressing pressure is 8~90MPa, and flowing argon is used as the protective gas.

[0016] Compared with the prior art, the advantages of the present invention are as follows:

[0017] 1. Due to the increase of the inner layer of nano-oxide layer between the coating and the metal connector through pre-oxidation, the bonding force between the deposited coating and the substrate is increased, and the temperature of coating deposition can be reduced (the deposited coating can obtain a dense and highly bonded coating at a lower temperature), thereby optimizing the overall oxidation resistance and conductivity of the modified coating, reducing the element diffusion between the outer coating and the substrate, preventing phase degradation, and improving the life of the coating system;

[0018] 2. The outer coating is modified by doping Ti and Si at the same time (Ti 1-x N x )3(Si,Al)C2, N is one of V and Zr, and x is 0.01-0.25; the atomic percentage of Al replacing Si is 3 at.%, and N-doped Ti can improve the material's oxidation resistance, reduce the oxidation rate, and increase the conductivity of the generated oxide. Al replacing 3 at.% Si can increase the density of the coating, improve the coating's ability to block the diffusion of oxygen and Cr ions, and improve the coating's oxidation resistance and conductivity;

[0019] 3. Metal interconnects with modified composite coatings can effectively solve the problem of outward migration of Cr elements and cathode poisoning. At the same time, they can reduce the growth rate of Cr2O3 films, reduce the working resistance of the interconnects, and improve the overall working performance of stainless steel interconnects. The large-scale application of metal interconnects with modified coatings can further promote the commercialization of solid oxide fuel cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The TiO2 prepared by pre-oxidation and magnetron sputtering in Example 1 is 0.9 Zr 0.2 )3(Si,Al)C2 coating surface morphology;

[0021] Figure 2 The TiO2 prepared by pre-oxidation and magnetron sputtering in Example 1 is 0.9 Zr 0.2 )3(Si,Al)C2 coating surface morphology after oxidation;

[0022] Figure 3 The TiO2 prepared by pre-oxidation and magnetron sputtering in Example 1 is0.9 Zr 0.2 )3(Si,Al)C2 coating cross-sectional morphology after oxidation;

[0023] Figure 4 The TiO2 prepared by pre-oxidation and magnetron sputtering in Example 2 is 0.99 V 0.01 )3(Si,Al)C2 coating surface microstructure; DETAILED DESCRIPTION

[0024] The present invention is further described in detail below with reference to specific embodiments and accompanying drawings.

[0025] The metal connector materials used in the following examples are ferritic stainless steel alloys purchased from the market, including SUS430, Crofer22APU, Fe-10Cr, 1.4724, Fe-17Cr-0.2Y, 1.4016, Ferrotherm (1.4742), Fe-18Cr-9W, Fe-20Cr-7W, Fe-20Cr, AL 453, 1.4763 (446), FeCrMn (LaTi), Fe-Cr-Mn, and Fe-25Cr-DIN. Any one of 50049, Fe-25Cr-0.1Y-2.5Ti, Fe-25Cr-0.2Y-1.6Mn, Fe-25Cr-0.4La, Fe-25Cr-0.3Zr, Fe26CrTiY, Fe26CrTiNbY, Fe26CrMoTiY, E-Brite, Al29-4C or Fe-30Cr.

[0026] Deposition (Ti 1-x N x The preparation method of the )3(Si,Al)C2 (N is one of V and Zr, x is 0.01-0.25, and the atomic percentage of Al replacing Si is 3 at.%) target is as follows:

[0027] The raw powder includes Ti powder, one of V or Zr, silicon powder, aluminum powder and graphite powder, and is prepared by sintering in a hot pressing furnace using a hot pressing / solid-liquid phase reaction method. The sintering temperature is 1400°C to 1750°C, and the heat preservation time is 25 to 90 minutes. The hot pressing pressure is 8 to 90 MPa, and flowing argon is used as the protective gas.

[0028] Example 1

[0029] (Ti 0.9 Zr 0.2 )3(Si,Al)C2 coating was deposited on the surface of the pre-oxidized SUS430 stainless steel connector to obtain Cr2O3 / (Ti 0.9 Zr 0.2)3(Si,Al)C2 composite coating.

[0030] First, prepare (Ti 0.9 Zr 0.2 )3(Si,Al)C2 bulk target, the process used is: first select the stoichiometric ratio of the elements used in the molecular formula to prepare the powder, then use 10MPa cold pressing, and finally put it into the hot pressing furnace for sintering, the sintering temperature is 1550℃, and the hot pressing pressure is 75MPa. Prepare SUS430 metal block 10*10*2mm 3 The alloy substrate was polished step by step with 400#, 600#, 800#, and 1000# metallographic sandpaper, and then the polished metal connector samples were ultrasonically cleaned with acetone, alcohol, and deionized water for 15 minutes respectively, and then blown dry in the air for use.

[0031] The treated metal connector sample was placed in a tube furnace for heating and pre-oxidation. The heating temperature was set to 700° C. and the holding time was 5 hours to obtain a 108 nm thick nano-oxide layer.

[0032] The coating was deposited by magnetron sputtering. First, the vacuum was pre-evacuated to 5×10 -4 Pa, in order to minimize the contamination of residual gas during the sputtering process. After reaching the vacuum required for the experiment, high-purity Ar gas with a flow rate of 50ml / min was introduced, and the working pressure was adjusted to maintain at 0.3Pa. Before the deposition began, the target was first cleaned with Ar+ to remove contaminants on the target surface. The cleaning time was 7min. The sample was then heated to 100℃ and kept warm for 30min. After the temperature of the entire sample was uniform, sputtering and coating preparation began. Open (Ti 0.9 Zr 0.2 )3(Si,Al)C2 target power supply, sputtering power of 0.1kw, sputtering time of 4h. After deposition, the temperature was cooled to room temperature at a rate of 10℃ / min under the original vacuum conditions, and then the vacuum and pressure were stopped. After sputtering, the surface and cross-sectional micromorphology of the deposited coating were observed by scanning electron microscopy. After deposition, it was found that the coating was dense, smooth, without holes, and the coating particles were tightly bonded to the substrate (such as Figure 1 As shown). The metal connector sample with coating was then oxidized at 800℃, and a dense and continuous oxide film structure was formed on the surface. The oxide was dense and without holes, and the coating suppressed the outward diffusion of Cr (as shown). Figure 2 and 3 This effectively blocks Cr volatilization, addressing the SOFC cathode poisoning problem. Furthermore, compared to the same coating without pre-oxidation to form a nanocrystalline oxide layer, the sample's oxidation rate constant is reduced by 12% and its surface resistivity is reduced by 9%.

[0033] Example 2

[0034] (Ti 0.99V 0.01 )3(Si,Al)C2 coating was deposited on the surface of Crofer 22APU.

[0035] First, prepare (Ti 0.99 V 0.01 )3(Si,Al)C2 bulk target, the process used is: first select the stoichiometric ratio of the elements used in the molecular formula to prepare the powder, then use 8MPa cold pressing, and finally put it into the hot pressing furnace for sintering, the sintering temperature is 1450℃, and the hot pressing pressure is 50MPa. Prepare SUS430 metal block 10*10*2mm 3 The alloy substrate was polished step by step with 400#, 600#, 800#, and 1000# metallographic sandpaper, and then the polished metal connector samples were ultrasonically cleaned with acetone, alcohol, and deionized water for 10 minutes respectively, and then blown dry in the air for later use.

[0036] The treated metal connector sample was placed in a tube furnace for heating and pre-oxidation. The heating temperature was set to 800° C. and the holding time was 3 hours to obtain a 213 nm thick nano-oxide layer.

[0037] The coating was deposited by magnetron sputtering. First, the vacuum was pre-evacuated to 5×10 -4 Pa, in order to minimize the contamination of residual gas during the sputtering process. After reaching the vacuum required for the experiment, high-purity Ar gas with a flow rate of 50ml / min was introduced, and the working pressure was adjusted to maintain at 0.35Pa. Before the deposition began, the target was first cleaned with Ar+ to remove contaminants on the target surface. The cleaning time was 10min. The sample was then heated to 50℃ and kept warm for 30min. After the temperature of the entire sample was uniform, sputtering and coating preparation began. Open (Ti 0.99 V 0.01 )3(Si,Al)C2 target power supply, sputtering power of 0.12kw, sputtering time of 6h. After deposition, the temperature was cooled to room temperature at a rate of 10℃ / min under the original vacuum conditions, and then the vacuum and pressure were stopped. After sputtering, the surface and cross-sectional micromorphology of the deposited coating were observed with a scanning electron microscope. After deposition, it was found that the coating was dense, flat, without holes, and the coating particles were tightly packed and well bonded to the substrate. The metal connector sample with the coating was then oxidized at 700℃, and a dense and continuous oxide film structure (such as Figure 4 The oxide is dense and pore-free, and the coating inhibits the outward diffusion of Cr, effectively preventing its volatilization and addressing SOFC cathode poisoning. Furthermore, compared to the same coating without pre-oxidation to form a nanocrystalline oxide layer, the sample exhibits a 10% lower oxidation rate constant and an 8% lower surface resistivity.

[0038] Comparative Example

[0039] The (Ti, W) 3 SiC 2 coating was deposited on the surface of the Crofer 22APU stainless steel connector. The coating was deposited on the alloy surface using a magnetron sputtering device, and then the sample was heated to 700 ° C and kept warm for 15 minutes. After the temperature of the entire sample was uniform, sputtering was started to prepare the coating. During the coating preparation process, the sputtering power was 0.2 kW and the sputtering time was 5 hours. After the deposition was completed, the temperature was cooled to room temperature at a rate of 10 ° C / min under the original vacuum conditions, and then the vacuum and pressure were stopped. Finally, the surface and cross-sectional micromorphology of the deposited coating were observed using a scanning electron microscope. After deposition, it was found that the (Ti, W) 3 SiC 2 coating was dense, smooth, without holes, and well bonded to the substrate. Under these conditions, the thickness of the coating was about 4.5 μm. It can be seen from the comparative example that the deposition temperature of this process is much higher than that of the embodiment of the present invention.

[0040] The embodiments described above are merely descriptions of preferred implementations of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should fall within the scope of protection determined by the claims of the present invention.

Claims

1. A method for preparing a modified composite coating for a fuel cell metal interconnect, characterized in that: The following steps are involved: First, the metal connector is pre-treated and then pre-oxidized to form a nano-layer oxide on the surface of the metal connector as the inner layer of the composite coating. 1-x N x )3(Si,Al)C2 is a bulk target material, and magnetron sputtering is used to deposit (Ti 1- x N x )3(Si,Al)C2 target is deposited on the surface of the metal connector covered with a nano-oxide layer to prepare the outer layer of the coating; the outer layer of the composite coating is Ti3SiC2 doped with Zr or V at the Ti position and Al doped at the Si position, and the chemical formula is (Ti 1- x N x )3(Si,Al)C2, N is one of Zr or V, x is 0.01-0.25; the atomic percentage of Al replacing Si is 3 at.%; the target material preparation method is: Ti powder, one of V or Zr powder, silicon powder, aluminum powder and graphite powder are prepared by hot pressing / solid-liquid phase reaction method and sintered in a hot pressing furnace, the sintering temperature is 1400℃~1750℃, the heat is kept for 25-90 minutes, the hot pressing pressure is 8-90MPa, and flowing argon is used as a protective gas; the magnetron sputtering method is: before coating preparation, first pre-vacuum to 5×10 -4 Pa, in order to minimize the contamination of residual gas during the sputtering process, after reaching the required vacuum degree, high-purity Ar gas with a flow rate of 50ml / min was introduced, and the working gas pressure was adjusted to maintain at 0.20~0.40Pa; Before the deposition begins, Ar + The target material is cleaned to remove contaminants on the target surface. The cleaning time is 5 to 10 minutes. The metal connector is then heated to 50°C and kept warm for 15 minutes to make the temperature of the entire metal connector uniform. Then, sputtering is started to prepare the outer coating. The sputtering power is 0.08 to 1.5 kw and the sputtering time is 1 to 8 hours. After the deposition is completed, the target material is cooled to room temperature at a rate of 10°C / min under the original vacuum conditions, and then the vacuum and pressure are stopped.

2. The method for preparing a modified composite coating of a fuel cell metal interconnect according to claim 1, wherein: The metal connector is ferritic stainless steel: any one of SUS430, Crofer22APU, Fe-10Cr, 1.4724, Fe-17Cr-0.2Y, 1.4016, Ferrotherm (1.4742), Fe-18Cr-9W, Fe-20Cr-7W, Fe-20Cr, AL 453, 1.4763 (446), FeCrMn (LaTi), Fe-Cr-Mn, Fe-25Cr-DIN 50049, Fe-25Cr-0.1Y-2.5Ti, Fe-25Cr-0.2Y-1.6Mn, Fe-25Cr-0.4La, Fe-25Cr-0.3Zr, Fe26CrTiY, Fe26CrTiNbY, Fe26CrMoTiY, E-Brite, Al29-4C or Fe-30Cr.

3. The method for preparing the modified composite coating of the fuel cell metal connector according to claim 1, wherein the pretreatment method of the metal connector is: firstly grinding and polishing the metal connector with 400 # , 600 # , 800 # , 1000 # , 1200 # The polished metal connector was polished step by step with metallographic sandpaper, and then ultrasonically cleaned with acetone, alcohol and deionized water for 10 to 30 minutes respectively, and then blown dry in the air for later use.

4. The method for preparing a modified composite coating of a fuel cell metal connector according to claim 3 is characterized in that the pre-oxidation method is: placing the pre-treated metal connector in a tubular furnace for heating and pre-oxidation, the heating temperature is: 600-800°C, the insulation time is 2-20 hours, and a nano-oxide layer with a thickness of 50-500 nm is obtained.

5. The method for preparing a modified composite coating for a fuel cell metal connector according to claim 1 is characterized in that: in the magnetron sputtering method, a magnetron sputtering device is used to prepare the outer layer of the coating on the alloy surface, the sample plate is attached to a rack plate, and the rack plate is heated to adjust the coating temperature.

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