Method for improving high-temperature operation life and cold-heat cycle times of SOFC stack

Abstract

The application belongs to the technical field of fuel cells, and specifically discloses a method for improving the high-temperature operation life and the number of cold and hot cycles of an SOFC stack. In the structural design, the single cell adopts an anode-supported structure and a barrier layer is additionally arranged, a reforming and temperature equalizing integrated cooling channel is introduced between adjacent single cells, and a structure in which cross-flow channels and reverse-flow channels are alternately stacked is adopted in the stack. In the material design, the anode of the single cell is of a gradient pore structure, a composite spinel coating layer is introduced on the surface of the bipolar plate, and a material with a smaller creep strength than the bipolar plate is used for the sealing layer. In the manufacturing process, a multiple progressive continuous stamping method is used to prepare a flexible connector, and the structure of the flexible connector is a fin type with a fin angle of 60° and a fillet radius of 10 μm. In the operation method, the sealing property and the insulation property of the stack are detected, and three-step continuous cooling is used in the cooling stage. The application comprehensively reduces the stress in the manufacturing and service processes, and improves the service life of the SOFC stack.

Description

Technical Field

[0001] This invention belongs to the field of fuel cell technology, and in particular relates to a method for improving the high-temperature operating life and the number of thermal cycling cycles of SOFC stacks. Background Technology

[0002] Solid oxide fuel cells (SOFCs) are the most efficient way to utilize hydrogen energy for power generation. Their principle is to directly convert the chemical energy of fuel into electrical energy and generate heat through an electrochemical reaction. Because an SOFC stack consists of multiple overlapping layers, including multiple single-cell layers (anode, electrolyte, cathode), sealing layers (cell-bipolar sealing layer, bipolar-bipolar sealing layer), and bipolar plates, the mechanical properties of these components differ significantly. On one hand, under long-term steady-state operation at high temperatures, the electrode materials of an SOFC stack will change, inevitably resulting in high-temperature creep damage. Furthermore, the creep damage is inconsistent across different layers, leading to steady-state degradation. On the other hand, due to repeated dynamic start-ups and shutdowns, SOFCs undergo multiple thermal cycling loads, causing thermal fatigue damage to various components. The inconsistent expansion and contraction deformation between different materials also contributes to thermal cycling degradation.

[0003] The long-term steady-state lifespan and the number of thermal cycling cycles of SOFC stacks are key factors determining the stack's service life and are also crucial technical indicators for the future commercialization of SOFCs. Therefore, improving the high-temperature operating lifespan and the number of thermal cycling cycles of SOFC stacks is of paramount importance. Summary of the Invention

[0004] The purpose of this invention is to provide a method for improving the high-temperature operating life and thermal cycling number of SOFC stacks, effectively solving the problem of short service life of SOFC stacks.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0006] A method for improving the high-temperature operating life and thermal cycling number of SOFC stacks, wherein the SOFC stack includes multiple single cells, a sealing layer, bipolar plates, and flexible connectors.

[0007] The single cell adopts an anode-supported structure, including an anode layer, an electrolyte layer, a cathode layer, and a barrier layer. The anode layer is a gradient hole structure prepared by phase inversion casting and includes a support layer and a fuel electrode in contact with the electrolyte. The barrier layer is located between the cathode layer and the electrolyte layer. The barrier layer is prepared by magnetron sputtering onto the electrolyte layer that has been sintered at high temperature and then sintering it at high temperature.

[0008] An integrated cooling channel for reforming and temperature equalization is introduced between adjacent single cells, and the surface of the cooling channel is impregnated with a reforming catalyst material.

[0009] The anode layer and the flexible connector form a fuel channel, and the cathode layer and the flexible connector form an air channel. The fuel channel and the air channel adopt an alternating superposition of cross-flow channels and reverse flow channels.

[0010] The surface of the bipolar plate is coated with a composite spinel. The sealing layer is made of a material with a creep strength coefficient and creep failure strain smaller than that of the bipolar plate. The flexible connector is prepared by a multi-step progressive continuous stamping method. The flexible connector has a finned structure with a fin angle of 60° and a corner radius of 10μm.

[0011] The methods for improving the high-temperature operating life and thermal cycling life of the SOFC stack include:

[0012] ① Test the sealing and insulation properties of the SOFC stack;

[0013] ② Control the heating rate of the SOFC stack to 0.5-1.0℃ / min, and control the nitrogen flow rate of each cell to 0.2L / min;

[0014] ③ Reduce the SOFC stack with pure hydrogen at 800℃ for 2-3 hours;

[0015] ④ During the cooling stage, the SOFC stack is cooled in three consecutive steps to reduce the shrinkage and deformation of various components of the SOFC stack.

[0016] Furthermore, the support layer is NiO-3YSZ, the fuel layer is NiO-8YSZ, the electrolyte layer is 8YSZ, and the cathode layer is LSCF.

[0017] Furthermore, the barrier layer is formed by sintering Ag-doped cerium oxide at 1300°C.

[0018] Furthermore, the anode layer is prepared using a phase inversion casting method, which includes: preparing a phase inversion casting slurry according to a casting slurry ratio of ceramic powder: polyethersulfone: N-methylpyrrolidone: polyvinylpyrrolidone = 10:1:4:0.1; setting the casting blade height to 1mm; using a special mold to prevent insufficient slurry from spreading on the casting panel and causing uneven thickness; placing a stainless steel mesh 0.5mm from the bottom surface before casting; using a method of preparing YSZ electrolyte films on both sides to eliminate the problem of sintering shrinkage mismatch; after sintering, finely polishing one side of the electrolyte until the finger-shaped holes are exposed; and then using ultrasonic treatment to shake out the powder blocking the channels by vibration.

[0019] Furthermore, the flexible connector is formed by stamping in three stages. The first stage is mechanical stamping, in which a prefabricated stamping die is used to initially press the flexible connector into a fin shape. The second stage is hydraulic forming, in which a hydraulic die is used to stamp the flexible connector to a specific height and width. The third stage is rounded corner forming, in which a mechanical rounded corner stamping die is used to finish stamping the flexible connector to its final shape.

[0020] Furthermore, the method for testing the sealing performance of the SOFC stack is as follows: a hydraulic cylinder is used to apply a pressure of 0.1-0.2 MPa to the stack at room temperature, and the pressure at the exhaust end is detected to determine whether there is any leakage or cross-contamination.

[0021] Furthermore, the insulation testing method for the SOFC stack is as follows: before heating, use a multimeter to check the resistance value of the SOFC stack and observe whether the positive and negative lines are short-circuited.

[0022] The beneficial technical effects of this invention are:

[0023] This invention comprehensively reduces stress during manufacturing and service, improves stress-deformation mismatch between different components of the SOFC stack, and enhances temperature uniformity during service by improving the structural design, material design, manufacturing process design, and SOFC stack operation control methods. This results in increased high-temperature service life and thermal cycling cycles of the SOFC stack. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the improvement method of the present invention;

[0025] Figure 2 This is an I / Vt curve of the fuel cell stack within 1000 hours in the embodiments and comparative examples of the present invention. Detailed Implementation

[0026] The English abbreviations of the chemical substances involved in this invention are as follows:

[0027] NiO-3YSZ: Nickel oxide-yttrium oxide stabilized zirconium oxide;

[0028] NiO-8YSZ: Nickel oxide-yttrium oxide stabilized zirconium oxide;

[0029] 8YSZ: Yttrium 8-stabilized zirconium oxide;

[0030] LSCF: Lanthanum-Strontium-Cobalt-Iron;

[0031] Ag: Silver;

[0032] YSZ: Yttrium-stabilized zirconium oxide.

[0033] The present invention provides a method for improving the high-temperature operating life and thermal cycling cycles of SOFC stacks. This method comprehensively reduces stress during manufacturing and service by addressing the structural design, material design, manufacturing process design, and SOFC stack operation control methods, thereby ensuring the service life of the SOFC stack. Specific improvement methods are as follows: Figure 1 As shown.

[0034] (1) SOFC stack structure design.

[0035] The SOFC stack includes multiple individual cells, a sealing layer, bipolar plates, and flexible connectors. Each individual cell adopts an anode-supported structure and includes an anode layer, an electrolyte layer, a cathode layer, and a barrier layer. The anode layer comprises two layers: a support layer and a fuel electrode in contact with the electrolyte. The support layer is made of NiO-3YSZ, and the fuel electrode is made of NiO-8YSZ.

[0036] The electrolyte layer is 8YSZ, the cathode layer is LSCF, and a barrier layer is applied between the cathode layer and the electrolyte layer to improve the density of the cathode material and prevent gas leakage.

[0037] An integrated cooling channel for reforming and temperature equalization is introduced between adjacent single cells. The surface of the cooling channel is impregnated with reforming catalyst material, which removes heat from the battery through internal reforming, preventing the stack temperature from becoming too high and maintaining the overall temperature uniformity of the stack.

[0038] The anode layer and the flexible connector form a fuel channel, and the cathode layer and the flexible connector form an air channel. The fuel channel and the air channel adopt an alternating superposition of cross-flow channels and reverse flow channels to ensure the uniformity of air intake and the uniformity of stack temperature.

[0039] (2) SOFC stack material design.

[0040] For the electrode material: the anode layer is a gradient pore structure prepared by phase inversion casting, which reduces redox stress and improves thermal cycling stability. The phase inversion casting method includes: preparing a phase inversion casting slurry according to the casting slurry ratio of ceramic powder: polyethersulfone: N-methylpyrrolidone: polyvinylpyrrolidone = 10:1:4:0.1; setting the casting blade height to 1mm; using a special mold to avoid insufficient slurry spreading on the casting panel and causing uneven thickness; placing a stainless steel mesh 0.5mm from the bottom surface before casting; using a method of preparing YSZ electrolyte films on both sides to eliminate the problem of sintering shrinkage mismatch; after sintering, finely polishing one side of the electrolyte until the finger-like holes are exposed; and then using ultrasonic treatment to shake out the powder blocking the channels by vibration.

[0041] For bipolar plates: A composite spinel coating is introduced on the surface of the bipolar plate to reduce the thermal stress mismatch between the bipolar plate and the sealing layer, and to improve the conductivity, oxidation resistance and chemical stability of the bipolar plate (inhibiting chromium volatilization).

[0042] For the sealing layer: The sealing layer is made of a material with a creep strength coefficient and creep failure strain smaller than that of the bipolar plate, which can greatly reduce the creep damage and failure probability of the sealing layer and improve the service life of the sealing layer.

[0043] (3) SOFC stack manufacturing process design.

[0044] The flexible connector has a finned structure with an angle of 60° and a fin radius of 10μm. It is fabricated using a multi-stage progressive continuous stamping method, consisting of three stamping processes. The first is mechanical stamping, where a pre-fabricated stamping die initially presses the flexible connector into a finned shape. The second is hydroforming, where a hydraulic die stamps the flexible connector to a specific height and width. The third is rounded corner forming, where a mechanical rounded corner stamping die refines and finalizes the flexible connector. This multi-stage progressive continuous stamping method reduces residual stress in the bipolar plate and ensures forming accuracy and thickness uniformity.

[0045] The barrier layer is prepared by magnetron sputtering onto an electrolyte layer that has already been sintered at high temperature, followed by high-temperature sintering. Further research by the applicant revealed that the product obtained by sintering Ag-doped cerium oxide at 1300℃ has the same density as cerium oxide obtained by sintering at 1500℃ without sintering aids, but with smaller grains.

[0046] (4) SOFC stack operation control methods.

[0047] include:

[0048] ① Test the sealing and insulation properties of the SOFC fuel cell stack. The sealing property test method is as follows: apply a pressure of 0.1-0.2 MPa to the stack at room temperature using a hydraulic cylinder, and test the pressure at the exhaust end to determine if there is any leakage or cross-contamination. The insulation property test method is as follows: before heating, use a multimeter to check the resistance value of the SOFC fuel cell stack and observe whether the positive and negative wires are short-circuited.

[0049] ② Control the heating rate of the SOFC stack to 0.5-1.0℃ / min, and control the nitrogen flow rate of each cell to 0.2L / min.

[0050] ③ Reduce the SOFC stack with pure hydrogen at 800℃ for 2-3 hours.

[0051] ④ During the cooling stage, the SOFC stack is cooled in three consecutive steps to reduce the shrinkage and deformation of various components of the SOFC stack.

[0052] The above-mentioned SOFC stack operation process control scheme reduces the demand for air and the power consumption of the air compressor, which to some extent helps to improve the power generation efficiency of the stack. At the same time, it avoids uneven temperature distribution in the stack, thereby improving the stack's lifespan and safety factor.

[0053] The present invention will now be described in conjunction with embodiments and comparative examples. Example

[0054] Based on the present invention, a method for improving the high-temperature operating life and thermal cycling number of SOFC stacks is designed to use methane as fuel. The stack has a flat plate structure with an effective electrode area of ​​10*10cm, contains 30 single cells, and operates at a temperature of 800℃.

[0055] Comparative Example

[0056] A 1.5kW SOFC (Solar-to-Fuel Cell) stack using methane as fuel was designed based on existing technology. The stack has a planar structure with an effective electrode area of ​​10*10cm, containing 30 individual cells. The stack operates at 800℃. The individual cells have no obstruction layer, and the anode has a through-hole structure. There is no integrated cooling channel for reforming and homogenization within the stack. The individual cells are manufactured using a thin-film casting + screen printing + sintering method. Connectors are prepared by etching, with an angle of 90°, and are formed in a single etching step. The SOFC stack employs a single-stage cooling process during the cooling phase.

[0057] The basic performance and dynamic / static degradation performance of the fuel cell stacks in the test examples and comparative examples were tested using IV curve testing according to the GB / T 34582-2017 standard. The test conditions were: heating rate: 0.5-1.0℃ / min, reduction with pure hydrogen at 800℃ for 2-3 hours, and test temperature: 750℃. Peak power density, power generation efficiency, fuel utilization rate, and internal reforming efficiency were obtained. The expected lifespan and expected number of thermal cycles of the fuel cell stack were obtained through numerical simulation of high-temperature and thermal cycling. The test results are shown in Table 1. It can be seen that the peak power density, power generation efficiency, fuel utilization rate, internal reforming efficiency, expected lifespan, and expected number of thermal cycles of the test examples are all superior to those of the comparative examples.

[0058] Table 1. Basic performance and dynamic / static attenuation performance of the fuel cell stack

[0059]

[0060] The test examples and comparative examples show the 1000-hour high-temperature stable operation curves, and the test results are as follows: Figure 2As shown, the fuel cell stack in this embodiment exhibits a smaller steady-state degradation rate compared to the comparative example.

[0061] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for improving the high-temperature operating life and thermal cycling cycles of an SOFC stack, wherein the SOFC stack comprises multiple single cells, a sealing layer, bipolar plates, and flexible connectors; The single cell adopts an anode-supported structure, including an anode layer, an electrolyte layer, a cathode layer, and a barrier layer. The anode layer is a gradient hole structure prepared by phase inversion casting and includes a support layer and a fuel electrode in contact with the electrolyte. The barrier layer is located between the cathode layer and the electrolyte layer. The barrier layer is prepared by magnetron sputtering onto the electrolyte layer that has been sintered at high temperature and then sintering it at high temperature. An integrated cooling channel for reforming and temperature equalization is introduced between adjacent single cells, and the surface of the cooling channel is impregnated with a reforming catalyst material; The anode layer and the flexible connector form a fuel channel, and the cathode layer and the flexible connector form an air channel. The fuel channel and the air channel adopt a structure in which cross-flow channels and reverse flow channels are alternately superimposed. The surface of the bipolar plate is coated with a composite spinel. The sealing layer is made of a material with a creep strength coefficient and creep failure strain smaller than that of the bipolar plate. The flexible connector is prepared by a multi-step progressive continuous stamping method. The flexible connector has a finned structure with a fin angle of 60° and a corner radius of 10μm. Its features are, The methods for improving the high-temperature operating life and thermal cycling life of the SOFC stack include: ① Test the sealing and insulation properties of the SOFC stack; ② Control the heating rate of the SOFC stack to 0.5-1.0℃ / min, and control the nitrogen flow rate of each cell to 0.2L / min; ③ Reduce the SOFC stack with pure hydrogen at 800℃ for 2-3 hours; ④ During the cooling stage, the SOFC stack is cooled in three consecutive steps to reduce the shrinkage and deformation of various components of the SOFC stack.

2. The method for improving the high-temperature operating life and thermal cycling number of SOFC stacks according to claim 1, characterized in that, The support layer is NiO-3YSZ, the fuel layer is NiO-8YSZ, the electrolyte layer is 8YSZ, and the cathode layer is LSCF.

3. The method for improving the high-temperature operating life and thermal cycling number of SOFC stacks according to claim 2, characterized in that, The barrier layer is formed by sintering Ag-doped cerium oxide at 1300°C.

4. The method for improving the high-temperature operating life and thermal cycling number of SOFC stacks according to claim 3, characterized in that, The anode layer is prepared using a phase inversion casting method, which includes: preparing a phase inversion casting slurry according to the casting slurry ratio of ceramic powder: polyethersulfone: N-methylpyrrolidone: polyvinylpyrrolidone = 10:1:4:0.1; setting the casting blade height to 1mm; using a special mold to prevent insufficient slurry from spreading on the casting panel and causing uneven thickness; placing a stainless steel mesh 0.5mm from the bottom surface before casting; using a double-sided YSZ electrolyte film preparation method to eliminate the problem of sintering shrinkage mismatch; after sintering, finely polishing one side of the electrolyte until the finger-shaped holes are exposed; and then using ultrasonic treatment to shake out the powder blocking the channels by vibration.

5. The method for improving the high-temperature operating life and thermal cycling number of SOFC stacks according to claim 1, characterized in that, The flexible connector is formed by stamping in three stages. The first stage is mechanical stamping, in which a prefabricated stamping die is used to initially press the flexible connector into a fin shape. The second stage is hydraulic forming, in which a hydraulic die is used to stamp the flexible connector to a specific height and width. The third stage is rounded corner forming, in which a mechanical rounded corner stamping die is used to finish stamping the flexible connector to its final shape.

6. The method for improving the high-temperature operating life and thermal cycling number of SOFC stacks according to claim 4 or 5, characterized in that, The method for testing the sealing performance of the SOFC stack is as follows: a hydraulic cylinder is used to apply a pressure of 0.1-0.2 MPa to the stack at room temperature, and the pressure at the exhaust end is detected to determine whether there is any leakage or cross-contamination.

7. The method for improving the high-temperature operating life and thermal cycling number of SOFC stacks according to claim 6, characterized in that, The insulation testing method for the SOFC stack is as follows: before heating, use a multimeter to check the resistance value of the SOFC stack and observe whether the positive and negative lines are short-circuited.

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