CN118465564B - Method for predicting and optimizing service life of solid oxide fuel cell - Google Patents

Method for predicting and optimizing service life of solid oxide fuel cell Download PDF

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CN118465564B
CN118465564B CN202410926081.1A CN202410926081A CN118465564B CN 118465564 B CN118465564 B CN 118465564B CN 202410926081 A CN202410926081 A CN 202410926081A CN 118465564 B CN118465564 B CN 118465564B
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sofc stack
attenuation
electrochemical
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CN118465564A (en
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蒋文春
郑红祥
罗云
石亚洲
宋明
李少华
曾碗莹
张秀成
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China University of Petroleum East China
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Abstract

The invention discloses a service life prediction and optimization method for a solid oxide fuel cell, and belongs to the technical field of solid oxide fuel cells. According to the invention, a mechanical property test of a cell stack material and a cold-hot cycle and continuous operation test of the SOFC cell stack are carried out, electrochemical and mechanical property parameters and attenuation rules of the SOFC cell stack under different operation conditions are obtained, a SOFC cell stack life prediction model based on mechanical property and electrical property attenuation is established, and optimization design is carried out on single cell materials, cell stack structures and operation conditions based on life expectancy targets, so that long service life of the SOFC cell stack is finally realized; the method is based on mechanical property test of SOFC pile materials, electrochemical property test of pile and multi-physical field coupling modeling calculation, so that life prediction and optimal design of SOFC pile are carried out, influencing factors of SOFC pile life are comprehensively considered in the design stage, service life of SOFC is guaranteed from the design and manufacturing level, and the method has important significance for promoting commercial application of SOFC pile.

Description

Method for predicting and optimizing service life of solid oxide fuel cell
Technical Field
The invention belongs to the technical field of solid oxide fuel cells, and particularly relates to a service life prediction and optimization method of a solid oxide fuel cell.
Background
The Solid Oxide Fuel Cell (SOFC) is an energy conversion device with high efficiency and low emission, and has wide application prospect in the fields of distributed power generation and cogeneration. SOFC durability refers to the ability of SOFCs to resist performance degradation during long-term operation. In particular to the capability of maintaining the performance unchanged in the continuous operation and the cold-hot cycle service process of the SOFC, namely the service life and the reliability of the SOFC. SOFC durability includes mainly durability of the stack material and durability of the stack structural components, and is mainly affected by material degradation, mechanical stress, microstructure degradation, and operating conditions. Service life is a core parameter that characterizes SOFC durability. The service life of SOFC is mainly affected by electrochemical performance attenuation and mechanical structure damage. The electrochemical performance attenuation of the SOFC stack is affected by factors such as carbon deposition on the anode, coarsening of nickel, volatilization of Cr on the cathode, diffusion of Sr, electrolyte phase change and the like. On the one hand, when the SOFC electric pile continuously operates, the stress can be generated due to uneven internal temperature of the electric pile; on the other hand, stresses are also generated during start-up and shut-down of the SOFC stack and temperature fluctuations. Due to the inconsistent thermal expansion coefficients and creep rates between the materials comprising the galvanic pile, the deformation is inconsistent, and finally the galvanic pile is subject to creep and mechanical structural damage caused by creep-fatigue.
The life design refers to comprehensively considering the influence of various factors on the life of the SOFC in the design stage so as to achieve the set target life, namely the design life in the service stage. This concept is widely used in equipment design in industries such as petrochemical and nuclear power. However, the current SOFC related units focus mainly on how to manufacture SOFC products with higher power generation performance, and the design life of SOFC stacks and cogeneration systems is less considered in the design stage. Therefore, to advance the commercial application of SOFC stacks, it is necessary to consider the service life of the SOFC stack from both mechanical and electrochemical properties at the design stage. By revealing the decay mechanism of the mechanical and electrochemical properties of the SOFC stack and the coupling relation between the two, a life prediction model of the SOFC stack is established, and further, design indexes and manufacturing requirements of the SOFC stack for long-life operation are respectively provided for single cell materials, stack structures and system processes, and the service life of the SOFC is ensured from the design and manufacturing level. This is of great importance for improving the service life of SOFCs.
Disclosure of Invention
Aiming at the technical problems in the prior art, the invention provides a method for predicting and optimizing the service life of a solid oxide fuel cell, which has reasonable design, overcomes the defects in the prior art and has good effect.
In order to achieve the above purpose, the present invention adopts the following technical scheme: aiming at the technical problems in the prior art, the invention provides a method for predicting and optimizing the service life of a solid oxide fuel cell, which has reasonable design, overcomes the defects in the prior art and has good effect.
In order to achieve the above purpose, the present invention adopts the following technical scheme: a service life prediction and optimization method for a solid oxide fuel cell comprises the following steps: s1: determining a service life target of continuous operation and cold-hot cycle service conditions of the SOFC stack; s2: carrying out a mechanical test of SOFC stack constituent materials, continuous operation of SOFC stacks and cold-hot circulation test by utilizing an SOFC test platform, analyzing microstructure degradation conditions before and after SOFC stack service, and analyzing attenuation mechanisms of the SOFC stack mechanical properties and electrochemical properties; s3: establishing a mechanical property attenuation model and an electrochemical property attenuation model of the SOFC electric pile, associating a coupling relation between the mechanical property and the electrochemical property attenuation of the SOFC electric pile, and establishing a SOFC electric pile life prediction model based on the mechanical property and the electrochemical property attenuation; s4: analyzing influence factors of electrochemical performance and mechanical performance attenuation during continuous operation and cold-hot cycle service of the SOFC stack; s5: modeling calculation is carried out aiming at the actual structure, material parameters and operation conditions of the SOFC electric pile, and the change rule of the mechanical property and the electrochemical property of the SOFC electric pile is analyzed; s6: judging whether the SOFC stack can reach the expected life target; if so, setting design indexes and manufacturing requirements of the SOFC stack under the target service life according to SOFC single cell materials, stack structure parameters and operating conditions; if not, carrying out the next step; s7: and (3) carrying out optimal design aiming at influencing factors of SOFC single cell materials, cell stack structures and operation conditions in the step (S4), and returning to the step (S5) to carry out modeling calculation and life prediction on the SOFC cell stack after the optimal design.
Preferably, in step S1, determining a life target of continuous operation and cold-hot cycle service conditions of the SOFC stack, and defining a failure threshold of the SOFC stack life according to the service conditions; the service life target range of the SOFC stack continuous operation working condition is 20000 to 100000 hours, and the service life target range of the cold and hot circulation service working condition is 10 to 100 times.
Preferably, in step S2, the SOFC test platform includes an SOFC electrochemical test device, a mechanical test device, an electrochemical workstation, and a data control terminal, where the SOFC electrochemical test device includes an SOFC stack, a heating furnace, a fuel processing module, a cathode air module, and an electronic load controller; the SOFC electric pile comprises an electric pile core unit, a packaging material, a top plate and a base, wherein the electric pile core unit comprises a bipolar plate, a sealing material and a single cell, and the single cell comprises a cathode, a barrier layer, an electrolyte, an anode functional layer and an anode supporting layer; the heating furnace is used for heating and preserving heat of the SOFC electric pile, the heating mode is electric heating, and a thermometer is arranged in the heating furnace and used for monitoring the running temperature of the SOFC electric pile; the fuel processing module is used for supplying fuel gas and maintaining the flow and pressure of the fuel gas required by the electric pile in the test process; when the input fuel is hydrogen, the fuel processing module is mainly used for heating the hydrogen; when the input fuel is natural gas, methanol or ethanol fuel, the fuel processing module is mainly used for desulfurizing, reforming and heating the natural gas, methanol or ethanol fuel; the cathode air module is used for supplying air and maintaining the flow and pressure of the air required by the galvanic pile in the test process; flow, pressure and temperature detection sensors are arranged in the fuel processing module and the cathode air module and are used for monitoring the flow, pressure and temperature of fuel gas and air; the electronic load controller is used for adjusting the load of the SOFC electric pile, and recording the voltage response under different currents by changing the current of the SOFC electric pile; the electrochemical workstation comprises a signal generator for generating Alternating Current (AC) signals required for EIS testing, and measuring impedance changes of the galvanic pile at different frequencies; when the continuous operation and the cold and hot circulation voltage test are carried out, the current load of the SOFC stack is regulated by an electronic load controller, and the voltage response of the SOFC stack is recorded at a data control terminal; when an electrochemical impedance spectrum test is carried out, a signal generator of an electrochemical workstation can apply a small-amplitude alternating current signal to the SOFC pile, simultaneously measure an impedance response signal of the SOFC pile, and then obtain an electrochemical impedance spectrum through electrochemical analysis software in a data control terminal; the mechanical test equipment is multifunctional test equipment, and can be used for carrying out mechanical property tests of stretching, bending, creeping, fatigue, creep fatigue tests, small punch rods, three-point bending, four-point bending and nano indentation tests by replacing different types of clamps to obtain the strength, hardness and elastic modulus of the SOFC galvanic pile composition material; the method comprises the steps that electrodes of an SOFC stack are connected to an electronic load controller and an electrochemical workstation through cables, and a heating furnace, a fuel processing module, a cathode air module, the electronic load controller and the electrochemical workstation are connected with a data control terminal through cables; the temperature of the heating furnace, the flow and the pressure of fuel gas and air are controlled by adopting programs in a data control terminal and monitored by data, and the electronic load controller, the electrochemical workstation and the mechanical testing equipment are controlled remotely and data synchronized by the data control terminal.
Preferably, in step S2, (1) for the bipolar plate material, tensile, bending, creep, fatigue and creep fatigue tests are performed by using a mechanical test device, so as to obtain the mechanical properties of the bipolar plate material; aiming at single cells and sealing materials, carrying out small punch, three-point bending, four-point bending and nano indentation tests by using mechanical testing equipment to obtain the mechanical properties of the single cell materials and glass sealing materials; (2) Carrying out continuous operation and cold and hot cycle testing of the SOFC stack by using SOFC electrochemical testing equipment, collecting a change curve of temperature, voltage and current along with operation time, and collecting a polarization curve and an electrochemical impedance spectrum EIS of the stack every 100-500 h when an electrochemical workstation is continuously operated, or testing and collecting the polarization curve and the electrochemical impedance spectrum EIS of the stack when each cold and hot cycle is carried out; (3) Analyzing and processing Nyquist data of electrochemical impedance spectrum EIS of the SOFC stack by using relaxation time distribution, namely a DRT method, calculating ohmic impedance generated by pure electric charge transfer and polarization impedance generated by diffusion and electrochemical reaction, determining change rules of different electrode reaction processes based on DRT curve distribution rules, and providing reasonable initial values for ECM accessories of an equivalent circuit model; (4) Calculating voltage loss caused by each electrode reaction process in the continuous operation and the cold and hot circulation of the SOFC stack by using an equivalent circuit model ECM, and determining contribution values of different electrode reaction processes in the continuous operation and the cold and hot circulation to voltage attenuation by using an ECM fitting result; (5) And dismantling the SOFC pile after the continuous operation or the cold and hot circulation test is finished, and testing the microstructure of the SOFC pile before and after the continuous operation or the cold and hot circulation test by utilizing a scanning electron microscope SEM, an X-ray spectrometer EDS, an X-ray photoelectron spectroscopy technology XPS and an electron probe X-ray microscopic analyzer EPMA, so as to analyze the attenuation mechanism of the mechanical property and the electrochemical property of the SOFC pile.
Preferably, in step S3, a calculation formula of a predicted lifetime T f of the SOFC stack during continuous operation and cold-hot cycle service is as follows: In the formula (1), T f is the predicted service life of the SOFC stack, deltaU is the attenuation amplitude, v is the voltage attenuation rate of the SOFC stack per thousand hours, and K p is the voltage attenuation coefficient caused by the microstructure degradation and mechanical property attenuation of the SOFC stack; the calculation formula of the voltage attenuation rate of the SOFC stack comprises the following steps: v=v T+vd(2);vT represents the voltage attenuation rate of the SOFC stack during the cold-hot cycle and variable load working condition operation, and v d represents the voltage attenuation rate of the SOFC stack during the steady working condition operation; when the SOFC stack runs in the stable running stage, the SOFC stack and the auxiliary system working conditions thereof do not fluctuate, the voltage is attenuated linearly, and the attenuation rate is constant; the calculation formula of the voltage attenuation rate in the stable operation stage: in the formula (3), v d represents a voltage decay rate per thousand hours of stable operation of the SOFC stack, The porosity is represented, and Fu represents the fuel utilization rate under a stable working condition; t represents the average temperature inside the stack in Kelvin (K); t 0 represents the reduction temperature of the galvanic pile in Kelvin (K); i represents the current density under the stable working condition, the unit is ampere per square centimeter (A.cm -2);A1、A2 is a constant related to the anode material property, C 1、C2 is a constant related to the cathode material property, the calculation formula of the voltage attenuation coefficient caused by the deterioration of the SOFC stack microstructure and the mechanical property attenuation is K p =1+ρ (4), wherein ρ is the damage parameter of the microcrack.
In the damage attenuation stage, microstructure degradation and mechanical property attenuation simultaneously occur in the SOFC stack, wherein the microstructure degradation continuously leads to voltage attenuation, and the mechanical property attenuation accelerates the voltage attenuation; in addition, when the voltage attenuation of the SOFC stack is only affected by the microstructure degradation, the voltage attenuation caused by the mechanical property attenuation can be ignored, and at this time K p =1; in terms of mechanical property attenuation, the expression of the microcrack damage parameter rho relative to damage omega in the SOFC stack is as follows: wherein ρ is the damage parameter of the microcracks, n is the material constant (creep stress index), and d is the average diameter of the microcracks; n is the creep stress index, ω is the damage variable of conventional damage mechanics, i.e. creep-fatigue induced structural damage.
When the SOFC stack is continuously operated and is in service in a cold-hot cycle mode, ohmic resistance degradation caused by YSZ electrolyte phase change and anode Ni particles coarsening is most serious in the influence of cathode concentration polarization degradation caused by cathode Cr poisoning and anode Ni particles coarsening on voltage attenuation caused by anode side TPB charge transfer reaction and ion transmission degradation; thus, a theoretical model of Ni grain coarsening, cr poisoning, and phase change of the electrolyte is established; the coarsening of Ni reduces the conductivity and TPB length of the anode, and the calculation formula of the radius r Ni of Ni particles is shown as formula (8); the calculation formula of the electronic conductivity sigma e,an of the Ni coarsening-influenced composite anode is shown as formula (9); wherein, The initial radius of the Ni particles is indicated,Λ refers to the fitting parameters of the Ni coarsening model, λ=2.5e-04 h -1, t refers to run time, C is a constant; is the intrinsic conductivity of the anode Ni material, phi is the anode porosity, phi Ni is the volume fraction of Ni in the anode, phi Ni = 0.4, Is the percolation threshold of the anode nickel particles.
The electrochemical reaction due to Cr poisoning in cathode TPB is as follows ：2CrO2(OH)2(g)+6e-(LSM)→CrO3(s)+2H2O(g)+3O2-(YSZ) (15).
Cr poisoning in TPB was simulated using a Cr poisoning model, with a charge transfer current density for Cr oxide deposition of i D: Wherein i 0,D is the intrinsic exchange current density of the Cr-poisoned (deposited) TPB; And The mole fractions of CrO 2(OH)2 and water vapor in the gas phase, respectively; F. r and T are Faraday constant, gas constant and temperature, respectively; η act,TPB is the local activation overpotential at TPB.Representing the local exchange current density, in relation to the material parameters; i 0,D is defined as 6.74A/m 2.
At SOFC operating temperatures, the crystal structure of the 8YSZ electrolyte material may gradually change from cubic to tetragonal phase, resulting in a decrease in its ionic conductivity, a time-dependent expression of 8YSZ ionic conductivity: wherein, Is the initial ion conductivity of 8YSZ and t is the operating time in hours.
Preferably, in step S4, the influencing factors of the SOFC stack life include, but are not limited to, cell materials including cathode, anode, barrier layer, material composition of electrolyte, stack structural parameters including geometry and material parameters of the cell, bipolar plate and sealing materials, and operating conditions including operating conditions parameters of the stack and stack auxiliary components; factors affecting cell materials and stack structure include, but are not limited to, creep fatigue strain accumulation rate, failure probability accumulation rate, adjacent material thermal expansion coefficient difference, area resistivity increase rate, stack component assembly tolerances, and SOFC operating conditions include, but are not limited to, stack operating temperature, fuel flow, air flow, stack internal temperature difference, stack internal monolithic cell voltage uniformity, air excess coefficient, fuel utilization, reforming efficiency.
Preferably, in step S5, a multi-physical field coupling SOFC stack model including electrochemical reaction-substance transfer-gas flow-charge transfer-heat transfer-solid mechanics is built in finite element simulation software according to the actual structure, material parameters and operation conditions of the SOFC stack in step S2, and the change rule of current, voltage, temperature, creep-fatigue damage and failure probability of the SOFC stack along with the service time and the service times in the continuous operation and the cold-hot circulation processes is solved respectively.
Preferably, in step S6, according to the failure threshold value of the SOFC stack in step S1 and the change rule of the mechanical property and the electrochemical property of the SOFC stack obtained by modeling calculation in step S5, it is determined whether the continuous operation and the cold-hot cycle life of the SOFC stack reach the expected target life.
Preferably, in step S7, a threshold condition and an optimization strategy for continuous operation and long service life of the cold and hot cycle are respectively proposed for the SOFC single cell material, the stack structure and the operation condition, and the optimization design of the SOFC stack constituent material, the structure and the operation condition includes the following contents: (1) development of gradient layer composite single cell materials: the gradient layer composite cathode cell of the NiO-3YSZ anode support layer/NiO-8 YSZ anode functional layer/YSZ electrolyte/GDC barrier layer/GDC-LSC transition layer/LSC-GDC composite cathode composition structure is researched and developed, compared with the original cell of the NiO-3YSZ anode support layer/NiO-8 YSZ anode functional layer/YSZ electrolyte/GDC barrier layer/LSC cathode composition structure, the gradient layer composite cathode cell is adopted to replace the original cell in the SOFC stack, and the heat treatment process at 1000 ℃ is utilized after the preparation of the cell is completed, so that the mechanical property of the gradient layer composite cathode cell is improved, and the stability of the SOFC cell and the stack is improved; (2) structural design and preparation of flexible bipolar plate: the problems of high rigidity, high stress and short service life of the traditional connector are solved by developing the design of a flow passage of the flexible connector and the research of a hydraulic forming technology; (3) optimization of sealing material: the fiber reinforced phase is added into the glass ceramic material, so that the thermal stress of the sealing material in continuous operation and cold-hot cycle service is reduced, and the leakage of the sealing interface between the sealing material and the battery piece and between the sealing material and the bipolar plate is slowed down; (4) optimization of SOFC operating conditions: and comparing the output voltages of the SOFC single cells, the electric pile and the system under different operation conditions, and further determining the optimal operation condition of the SOFC under continuous operation and service of the cold-hot circulation working condition.
The invention has the beneficial technical effects that: the invention provides a method for predicting and optimizing the service life of a solid oxide fuel cell, which comprehensively considers influencing factors of the service life of an SOFC (solid oxide fuel cell) stack in a design stage by establishing a service life prediction model of the SOFC stack, and ensures the service life of the SOFC from the design and manufacturing level, thereby having important significance for improving the service life of the SOFC and promoting the commercial application of the SOFC stack; the invention has the main advantages that: 1. according to the invention, a mechanical property test of the SOFC electric pile material and a cold and hot cycle and continuous operation test of the SOFC electric pile are carried out, electrochemical and mechanical property parameters and attenuation rules of the SOFC electric pile under different operation conditions are obtained, contributions of different electrode reaction processes of the SOFC electric pile to voltage attenuation in the cold and hot cycle and continuous operation service process are quantitatively analyzed, and a SOFC electric pile service life prediction model based on the mechanical property and the electrical property attenuation is established.
2. According to the invention, by combining multiple physical field coupling numerical simulation analysis of the mechanical property and electrical property attenuation law of each layer in the cooling and heating cycle and continuous operation service process of the galvanic pile, weak positions and failure modes, where the galvanic pile is easy to fail, are disclosed. Further, theoretical guidance is provided for optimizing single cell materials, a galvanic pile structure and operation parameters according to a life prediction model, a gradient layer composite cathode cell is developed, a flexible bipolar plate is designed and prepared, a sealing material is optimized, and the optimal operation condition of the SOFC in continuous operation and cold-hot cycle working condition service is determined. In the invention, the influencing factors of the service life of the SOFC stack are comprehensively considered in the design stage, and the service life of the SOFC is ensured from the design and manufacturing level. This has important significance for improving the service life of SOFC and promoting the commercial application of SOFC stacks.
Drawings
FIG. 1 is a flow chart of a solid oxide fuel cell service life prediction and optimization method; FIG. 2 is a schematic diagram of a SOFC test platform; FIG. 3 is a schematic structural view of an SOFC stack; FIG. 4 is a schematic structural diagram of a cross section of a core unit of the SOFC stack; FIG. 5 is a schematic diagram of a voltage variation curve at 300mA/cm 2 during SOFC stack operation; fig. 5 (a) is a graph showing the voltage change with time at 300mA/cm 2 during continuous operation of the SOFC stack; (b) The change curve of voltage along with time in the cold-hot cycle process of the SOFC stack; FIG. 6 is a schematic diagram showing the percentage contribution of each electrode reaction process to voltage decay after SOFC stack service; FIG. 7 is a schematic view of SEM microstructure after PEN service of the SOFC stack; fig. 7 (a) is a voltage versus time curve of 2500h of continuous operation of the SOFC stack; (b) A voltage variation curve of 10 times of cold and hot cycles of the SOFC stack along with the cycle times; FIG. 8 is a schematic diagram showing the voltage decay curve of the SOFC stack; FIG. 9 is a graph showing numerical simulation results of a three-layer SOFC stack; fig. 9 (a) shows the temperature distribution of each region of the three-layer SOFC stack after 5000 hours of continuous operation; (b) stress distribution for the top portion of the SOFC stack; FIG. 10 is a schematic diagram of the measured voltage values and the predicted model values of the continuous operation of the optimized SOFC stack; fig. 11 is a schematic diagram of the actual measured voltage values and the model predicted values of the cold and hot cycles of the optimized SOFC stack.
Detailed Description
The invention is described in further detail below with reference to the attached drawings and detailed description: the invention establishes a method for predicting and optimizing the service life of a solid oxide fuel cell, develops a mechanical property test of an SOFC (solid oxide fuel cell) pile material, obtains mechanical property parameters such as creep deformation, creep fatigue and the like of the pile material, and establishes a constitutive model of creep deformation-fatigue damage of the SOFC pile material. A large number of cold-hot circulation and continuous operation tests are carried out, and electrochemical performance parameters and attenuation rules of the SOFC stack under different operation conditions are obtained. The SOFC electric pile life prediction model based on mechanical property and electric property attenuation is established, and weak positions and failure modes of the electric pile, where failure is easy to occur, are revealed by combining multiple physical field coupling numerical simulation analysis of electric pile cooling and heating cycle and mechanical property and electric property attenuation rules of each layer in the continuous operation service process. Furthermore, theoretical guidance is provided for optimizing single cell materials, cell stack structures and operation parameters according to a life prediction model, and high-temperature long-life operation of the SOFC cell stack is realized. In the invention, the influencing factors of the service life of the SOFC stack are comprehensively considered in the design stage, and the service life of the SOFC is ensured from the design and manufacturing level. This has important significance for improving the service life of SOFC and promoting the commercial application of SOFC stacks.
In the embodiment, the SOFC stack is required to realize the operation life of 80000h and the cold and hot cycle life of 100 times in commercial operation, and the operation life of 80000h means that the SOFC stack can be in service for 10 years under the condition of 8000h operation per year; the lifetime of 100 cold and hot cycles means that the device can be used for 10 years under the condition that 10 start-stops occur each year. This means that under the condition that the mechanical strength of the cell stack is not destroyed after long-term high-temperature service and startup and shutdown conditions, the electrochemical performance of the SOFC cell stack is slowly attenuated, namely the output voltage of the SOFC cell stack is still 80% of the initial voltage after the service time reaches 80000h or 100 times of thermal cycles.
A service life prediction and optimization method of a solid oxide fuel cell, the flow of which is shown in figure 1, comprises the following steps: s1, determining a service life target of continuous operation and cold-hot circulation service conditions of the SOFC stack.
Determining a service life target of continuous operation and cold-hot circulation service conditions of the SOFC stack, and defining a failure threshold value of the service life of the SOFC stack according to the service conditions; the service life target of the SOFC stack under the continuous operation condition is generally 20000-100000 h, and the service life target of the cold-hot circulation service condition is generally 10-100 times.
SOFC stack life definition: under the conditions of constant current density and fuel utilization, the voltage is degraded to an operation duration corresponding to 50% -90% of the initial voltage according to the fuel composition specified by the galvanic pile manufacturer. When the failure threshold is 80%, the operating life of the SOFC stack corresponds to an operating duration for which the voltage is degraded to 80% of the initial voltage.
According to the failure threshold value of 80%, the voltage attenuation rate corresponding to the service 60000h operation life of the SOFC stack is 0.33%/kh, and the voltage attenuation rate corresponding to the 80000h operation life is 0.25%/kh.
When the SOFC electric pile runs, the change of the mechanical property cannot be monitored in real time, so that the output voltage of the SOFC electric pile is used as the standard of the electric pile property. When the electrochemical performance of the SOFC is lower than 80%, the low power generation efficiency may reduce the economic benefit of the SOFC device, so that the failure threshold of the electrochemical performance of the SOFC stack is defined as 80%. Taking the output voltage of 300mA/cm 2 as an example, the electrochemical performance life of the SOFC stack is considered to be terminated when the output voltage of 300mA/cm 2 is attenuated to 80% of the output voltage of the first cold and hot cycle.
S2, carrying out a mechanical test of SOFC pile constituent materials and continuous operation and cold-hot circulation test of the SOFC pile by utilizing the SOFC test platform, analyzing the microstructure degradation condition of the SOFC pile after service, and analyzing the attenuation mechanism of the SOFC pile mechanical property and electrochemical property.
As shown in fig. 2, the SOFC test platform comprises an SOFC electrochemical test device, a mechanical test device, an electrochemical workstation and a data control terminal, wherein the SOFC electrochemical test device comprises an SOFC stack, a heating furnace, a fuel processing module, a cathode air module and an electronic load controller; the SOFC electric pile comprises an electric pile core unit, a packaging material, a top plate and a base, wherein the electric pile core unit comprises a bipolar plate, a sealing material and a single cell, and the single cell consists of a cathode, a barrier layer, an electrolyte, an anode functional layer and an anode supporting layer.
The heating furnace is used for heating and preserving heat of the SOFC electric pile, the heating mode is electric heating, and a thermometer is arranged in the heating furnace and used for monitoring the running temperature of the SOFC electric pile; the fuel processing module is used for supplying fuel gas and maintaining the flow and pressure of the fuel gas required by the electric pile in the test process; when the input fuel is hydrogen, the fuel processing module is mainly used for heating the hydrogen; when the input fuel is natural gas, methanol or ethanol fuel, the fuel processing module is mainly used for desulfurizing, reforming and heating the natural gas, methanol or ethanol fuel; the cathode air module is used for supplying air and maintaining the flow and pressure of the air required by the galvanic pile in the test process; flow, pressure and temperature detection sensors are arranged in the fuel processing module and the cathode air module and are used for monitoring the flow, pressure and temperature of fuel gas and air.
The electronic load controller is used for adjusting the load of the SOFC electric pile, and recording the voltage response under different currents by changing the current of the SOFC electric pile; the electrochemical workstation comprises a signal generator for generating Alternating Current (AC) signals required for EIS testing, and measuring impedance changes of the galvanic pile at different frequencies; and when the continuous operation and the cold and hot circulation voltage test are carried out, the current load of the SOFC stack is regulated by the electronic load controller, and the voltage response of the SOFC stack is recorded at the data control terminal. When the electrochemical impedance spectrum test is carried out, the signal generator of the electrochemical workstation can apply a small-amplitude alternating current signal to the SOFC pile, meanwhile, the impedance response signal of the SOFC pile is measured, and then the electrochemical impedance spectrum is obtained through electrochemical analysis software in the data control terminal.
The mechanical test equipment is multifunctional test equipment, and can be used for carrying out mechanical property tests of stretching, bending, creep deformation, fatigue, creep deformation fatigue tests, small punch rods, three-point bending, four-point bending and nano indentation tests by replacing different types of clamps, so that the strength, hardness and elastic modulus of the SOFC galvanic pile composition material are obtained.
The method comprises the steps that electrodes of an SOFC stack are connected to an electronic load controller and an electrochemical workstation through cables, and a heating furnace, a fuel processing module, a cathode air module, the electronic load controller and the electrochemical workstation are connected with a data control terminal through cables; the temperature of the heating furnace, the flow and the pressure of fuel gas and air are controlled by adopting programs in a data control terminal and monitored by data, and the electronic load controller, the electrochemical workstation and the mechanical testing equipment are controlled remotely and data synchronized by the data control terminal.
The specific study content of step S2 is as follows: (1) Aiming at the bipolar plate material, carrying out stretching, bending, creep, fatigue and creep fatigue tests by using mechanical testing equipment to obtain the mechanical properties of the bipolar plate material; aiming at single cells and sealing materials, carrying out small punch, three-point bending, four-point bending and nano indentation tests by using mechanical testing equipment to obtain the mechanical properties of the single cell materials and glass sealing materials; (2) Carrying out continuous operation and cold and hot cycle testing of the SOFC stack by using SOFC electrochemical testing equipment, collecting a change curve of temperature, voltage and current along with operation time, and collecting a polarization curve and an Electrochemical Impedance Spectrum (EIS) of the stack every 100-500 h when an electrochemical workstation is continuously operated, or collecting the polarization curve and the Electrochemical Impedance Spectrum (EIS) of the test stack during cold and hot cycle; determining the structure composition of the SOFC electric pile and preparing the SOFC electric pile, wherein the SOFC electric pile consists of an anode supporting type flat plate type single cell, a sealing material, a bipolar plate, a fuel gas inlet and outlet, an air inlet and outlet, a top plate and a base, and the anode supporting type flat plate type single cell, the sealing material and the bipolar plate are core units of the SOFC electric pile. The anode supporting type flat plate single cell provided by the invention is characterized in that NiO-3YSZ, niO-8YSZ, YSZ, GDC, LSC, siO-SrO-MgO-B2O 3 and SUS 430 ferrite stainless steel materials are respectively used as an anode supporting layer, an anode functional layer, electrolyte, a barrier layer, a cathode, a sealing material and a bipolar plate, so that a Solid Oxide Fuel Cell (SOFC) stack consisting of 3 single cells is prepared. Wherein, cell and sealing material in SOFC stack belong to ceramic material, bipolar plate belongs to metal material. The structure of the SOFC stack is shown in fig. 3, and the structure of the cross section of the core unit of the SOFC stack is shown in fig. 4. The dimensions and parameters of the individual constituent materials of the cell stack are shown in table 1. After the SOFC stack is assembled, the SOFC stack is installed in an SOFC test system, the heating and cooling rates of the SOFC stack and the gas supply procedures of the cathode and anode sides are set, and test preparation work is completed.
TABLE 1
After the SOFC electric pile test preparation work is finished, the SOFC electric pile is heated from room temperature to the reduction temperature of 800 ℃ for reduction, the electric pile is cooled to the working temperature of 750 ℃ after the reduction is finished, and the SOFC electric pile is started. Pure hydrogen and dry air are used as fuel and oxidant, respectively, and nitrogen is used as shielding gas. During the heating, dry nitrogen was supplied to the anode at a flow rate of 1.5L/min. After the temperature reached 750 ℃, 1.5L/min of hydrogen was supplied to the anode, and dry air was supplied to the cathode at a flow rate of 4.5L/min, and the SOFC stack was set to perform continuous operation and thermal cycling tests at a current density of 300mA/cm 2. After the test is completed, it is cooled to room temperature at a rate of 0.5 ℃ per minute 1 ℃.
The change curves of temperature, voltage and current along with the operation time are collected in the continuous operation and the cold and hot cycle test of the SOFC electric pile, and the polarization curve and the Electrochemical Impedance Spectrum (EIS) of the electric pile are collected every 100-500 h in the continuous operation, or the polarization curve and the Electrochemical Impedance Spectrum (EIS) of the electric pile are collected in each cold and hot cycle.
The voltage profile of the SOFC stack at a current density of 300mA/cm 2 at 750℃operating temperature over time during continuous operation is shown in FIG. 5 (a). The voltage of the electric pile at the initial moment in the activation stage decays fast, the voltage at the initial moment is about 2.63V, and the fuel utilization rate is 43.35%. After 400.25 hours of operation time, the stable operation stage is started, the initial voltage of the stable operation stage is 2.05V, then gradually drops to 1.60V at the end of 2494.25 hours, the voltage attenuation rate of the stable operation stage is 10.48%/kh, and the total voltage attenuation rate is 15.70%/kh. The voltage profile varies approximately linearly throughout the test, which indicates that no catastrophic failure has occurred during this period.
The curve of the voltage of the SOFC stack at a working temperature of 750 ℃ and a current density of 300mA/cm 2 according to the cycle times during the cold and hot cycles is shown in FIG. 5 (b). The voltage at 300mA/cm 2 at the first thermal cycle of the SOFC stack was 2.43V and the fuel utilization was 43.35%. When the SOFC stack is subjected to 10 th thermal cycles, the voltage at 300mA/cm 2 is 2.09V, and the attenuation rate reaches 13.99%.
(3) And analyzing and processing Nyquist data of an Electrochemical Impedance Spectrum (EIS) of the SOFC stack by using a relaxation time Distribution (DRT) method, calculating ohmic impedance generated by pure electric charge transfer and polarization impedance generated by diffusion, electrochemical reaction and the like, determining change rules of different electrode reaction processes based on the DRT curve distribution rules, and providing reasonable initial values for Equivalent Circuit Model (ECM) accessories.
And collecting electrochemical impedance spectrum and Nyquist data of the SOFC stack under 3-5 current densities in different continuous operation and cold-hot cycle service processes by using an electrochemical workstation. Ohmic resistance R ohm generated by pure electric charge transfer and polarization resistance R pol generated by diffusion, electrochemical reaction, or the like are calculated from Nyquist data.
And analyzing and fitting Electrochemical Impedance Spectroscopy (EIS) data of the SOFC stack by using a relaxation time Distribution (DRT) method and an Equivalent Circuit Model (ECM), and calculating voltage loss caused by the reaction process of each electrode in continuous operation and cold and hot circulation of the SOFC stack.
And distinguishing the peaks on the DRT graph according to the characteristics of different electrochemical reaction processes of the SOFC stack. And (3) distinguishing the change rule of different electrode reaction processes based on the electrode reaction process determined by the DRT curve distribution rule, and providing a reasonable initial value for the ECM fittings. And determining the contribution of different electrode reaction processes to the voltage attenuation in the cold and hot cycles by using ECM fitting results, and determining the contribution value and the sequence of each electrode reaction process to the voltage attenuation.
(4) And calculating voltage loss caused by each electrode reaction process in the continuous operation and the cold and hot circulation of the SOFC electric pile by using an Equivalent Circuit Model (ECM), and determining the contribution value of different electrode reaction processes in the continuous operation and the cold and hot circulation to voltage attenuation by using an ECM fitting result.
The ECM fitting results were used to determine the contribution of the different electrode reactions of the SOFC stack to voltage decay during continuous operation and cold and hot cycling, as shown in fig. 7 (a), 7 (b). When the SOFC stack is in continuous operation service, degradation of R s (ohmic resistance) is dominant in voltage decay of the SOFC stack, and its contribution rate is 68.90%. The second largest contribution comes from R A1 (anode side TPB charge transfer reaction and ion transport), with a contribution of 66.70%. The contribution of R C1(O2 surface exchange kinetics and O 2- diffusion at the cathode was 21.90% and the contribution of R C2 (cathode gas phase diffusion and conversion) was 8.48%. The contribution of R A2 (anode gas phase diffusion and conversion) is negative (-66.00%). The order in which each electrode reaction process contributes to the voltage decay is R S>RA1>RC1>RC2>RA2.
When the SOFC stack is in service in a cold and hot cycle, degradation of R s (ohmic resistance) is dominant in voltage decay of the SOFC stack, and its contribution rate is 57.13%. The second largest contribution comes from R A1 (anode side TPB charge transfer reaction and ion transport) with a contribution of 37.38%. The contribution of R C1(O2 surface exchange kinetics and O 2- diffusion at the cathode was 6.99% and the contribution of R C2 (cathode gas phase diffusion and conversion) was 6.58%. The contribution of R A2 (anode gas phase diffusion and conversion) is negative (-8.08%). The order in which each electrode reaction process contributes to the voltage decay is R S>RA1>RC1>RC2>RA2.
(5) And dismantling the SOFC pile after continuous operation or cold and hot cycle test, and testing the microstructure of the SOFC pile before and after the continuous operation and cold and hot cycle test by using a Scanning Electron Microscope (SEM), an X-ray energy spectrometer (EDS), an X-ray photoelectron spectroscopy technology (XPS) and an electron probe X-ray microscopic analyzer (EPMA), so as to analyze the attenuation mechanism of the mechanical property and the electrochemical property of the SOFC pile.
After continuous operation or cold and hot cycling service, the SOFC stack was disassembled to analyze the mechanical properties and microstructure of the cell, bipolar plate and seal material. And testing the microstructure of the material before and after continuous operation and cold and hot circulation test of the SOFC electric pile by using a Scanning Electron Microscope (SEM), an X-ray energy spectrometer (EDS), an X-ray photoelectron spectroscopy (XPS) and an electron probe X-ray microscopic analyzer (EPMA), and calculating the content of various elements and the average diameter of particles in the SOFC electric pile. SEM microstructure of the SOFC stack PEN after 1772h of continuous operation and 10 service cycles is shown in fig. 6.
The size of elemental particles in each electrode before and after continuous operation and thermal cycling was calculated from SEM and EDS images obtained in S7 using image processing software ImageJ. And calculating by using an area weighting algorithm to obtain the average equivalent circle diameter of element particles in each electrode in the sample before and after continuous operation and cold and hot circulation.
S3, establishing a mechanical property attenuation model and an electrochemical property attenuation model of the SOFC electric pile, associating the coupling relation of the SOFC electric pile mechanical property and the electrochemical property attenuation, and establishing a SOFC electric pile service life prediction model based on the mechanical property and the electrochemical property attenuation.
The characteristic division of the SOFC stack voltage decay curve is shown in fig. 8, and the curve can be divided into three stages of activation, stable operation and damage destruction according to the decay characteristic of the stack voltage, and the characteristic influencing factors and the dominant factors of the voltage decay of each stage are listed in table 2.
TABLE 2
Calculating a predicted life T f calculation formula of the SOFC stack in the continuous operation and cold-hot cycle service process: (1) ; in formula (1), T f is the predicted lifetime of the SOFC stack, Δu is the attenuation amplitude, v is the voltage attenuation rate per thousand hours of the SOFC stack, and K p is the voltage attenuation coefficient due to the deterioration of the microstructure and the mechanical property attenuation of the SOFC stack.
The calculation formula of the voltage attenuation rate of the SOFC stack comprises the following steps: v=v T+vd(2);vT represents the voltage decay rate of the SOFC stack during the cold-hot cycle and variable load operation, and v d represents the voltage decay rate of the SOFC stack during the steady operation.
When the SOFC stack is in the running process of the stable running stage, the SOFC stack and the auxiliary system working condition of the SOFC stack do not fluctuate, the voltage is attenuated linearly, and the attenuation rate is constant. At this time, the voltage decay rate and the average current density show a positive correlation of an exponential relationship, the voltage decay rate and the fuel utilization rate show a positive correlation of a linear relationship, and the voltage decay rate and the operating temperature show a negative correlation of an exponential relationship. The three parameters of current density, fuel utilization rate and running temperature are easy to test and can be regulated and controlled, so that the verification of a model is facilitated. Therefore, a calculation model of the operating temperature-current density-fuel utilization and the voltage decay rate is established by fitting experimental data. The calculation formula of the voltage attenuation rate in the stable operation stage: in the formula (3), v d represents a voltage decay rate per thousand hours of stable operation of the SOFC stack, The porosity is represented, and Fu represents the fuel utilization rate under a stable working condition; t represents the average temperature inside the stack in Kelvin (K); t 0 represents the reduction temperature of the galvanic pile in Kelvin (K); i represents the current density in amperes per square centimeter under steady state conditions (a/cm 2);A1、A2 is a constant related to the properties of the anode material and C 1、C2 is a constant related to the properties of the cathode material.
The calculation formula of the voltage attenuation coefficient caused by the deterioration of the microstructure and the mechanical property attenuation of the SOFC stack is as follows: k p =1+ρ (4); wherein ρ is the damage parameter of the microcrack.
In the damage attenuation stage, microstructure degradation and mechanical property attenuation simultaneously occur in the SOFC stack, wherein the microstructure degradation continuously causes voltage attenuation, and the mechanical property attenuation accelerates voltage attenuation. In addition, when the voltage attenuation of the SOFC stack is only affected by the microstructure degradation, the voltage attenuation caused by the mechanical property attenuation can be ignored, and K p =1.
In the aspect of mechanical property attenuation, the ceramic material in the SOFC stack is easy to generate defects in the manufacturing process, and is suitable for a damage constitutive model containing a small amount of micro-defect materials, and the calculation equation of the microcrack damage parameter rho is shown as follows: Where ρ is the damage parameter of the microcracks, N is the material constant (creep stress index), N is the number of microcracks per unit volume, and d is the average diameter of the microcracks.
In order to correlate the microcrack parameter ρ with the damage variable ω of conventional damage mechanics, it is assumed that microcracks of small cylindrical shape with diameter d are contained in a cylindrical unit cell of both diameter and high dimension L. As a reduction in effective cross-sectional area within the unit cell, the damage ω can be defined as: This means that the variable ω is only a function of the damaged microstructure (length and density of the microstructure), unlike the microcrack parameter ρ, which is independent of the deformation characteristics (e.g., material constant n). The expression of the microcrack damage parameter ρ with respect to the damage ω is: where n is the creep stress index and ω is the damage variable of conventional damage mechanics, i.e. creep-fatigue induced structural damage.
In terms of microstructure degradation, according to the analysis result of the voltage decay mechanism in the step S5, when the SOFC stack is continuously operated and is in service in a cold-hot cycle, the deterioration of ohmic resistance caused by YSZ electrolyte phase change and anode Ni particle coarsening, the deterioration of cathode concentration polarization caused by LSC cathode Cr poisoning and the deterioration of anode side TPB charge transfer reaction and ion transport caused by anode Ni particle coarsening can be obtained, and the influence of the three electrode reaction processes on voltage decay is most serious; therefore, when modeling the SOFC microstructure degradation, the effect of three degradation processes, i.e., ni particle coarsening of the anode electrode, cr poisoning of the cathode electrode, and phase change of the electrolyte, on the SOFC stack voltage degradation was mainly analyzed.
(1) Theoretical model of anode electrode Ni particle coarsening.
Coarsening of Ni particles is a degradation mechanism of the Ni-YSZ anode, and Ni coarsening reduces the conductivity and TPB length of the anode; the increase in radius of the Ni particles can be described by a theoretical model; radius r Ni of Ni particles: The initial radius of the Ni particles is indicated, Λ refers to the fitting parameters of the Ni coarsening model, λ=2.5x -4h-1, t refers to run time, C is a constant; ni roughening affects the electron conductivity σ e,an of the composite anode: is the intrinsic conductivity of the anode Ni material, Is the anode porosity, and is Ni is the volume fraction of Ni in the anode, ψ Ni =0.4,Is the percolation threshold of the anode nickel particles; wherein the average particle coordination number And also with the agglomeration of Ni particles.
Average particle coordination numberAlso with the agglomeration of Ni particles; Z YSZ,YSZ represents the coordination number between YSZ particles, and Z YSZ,YSZ has a value of 6; psi YSZ is the volume fraction of YSZ in the anode, r YSZ represents the radius of the YSZ particles.
Coarsening of Ni particles also affects the anode effective volume TPB length lambda TPB,eff can be calculated as:
coarsening of Ni particles also affects the anode effective volume TPB length lambda TPB,eff can be calculated as:
θ is the contact angle between Ni and YSZ particles, assuming θ=15°.
(2) Theoretical model of cathode Cr poisoning degradation.
Electrochemical deposition due to oxidation of volatile chromium species at the cathode TPB is considered to be a major cause of Cr poisoning degradation.
The electrochemical reaction of Cr poisoning in TPB is as follows ：2CrO2(OH)2(g)+6e-(LSM)→CrO3(s)+2H2O(g)+3O2-(YSZ) (15).
The decrease in cathode TPB due to Cr oxide deposition was modeled by empirical relationship, based on the Cr oxidation reaction rate obtained by the Butler-Volmer equation.
Cr poisoning in TPB was modeled using Cr poisoning model equation (18). The charge transfer current density for Cr oxide deposition is i D: i 0,D is the intrinsic exchange current density of the Cr-poisoned (deposited) TPB; And The mole fractions of CrO 2(OH)2 and water vapor in the gas phase, respectively; F. r and T are Faraday constant, gas constant and temperature, respectively; η act,TPB is the local activation overpotential at TPB; Representing the local exchange current density, in relation to the material parameters.
The material-dependent exchange current density is denoted as i m: Wherein i 0,D is defined as 6.74A/m 2.
(3) Theoretical model of electrolyte phase change degradation.
At SOFC operating temperatures, the crystal structure of the 8YSZ electrolyte material may gradually change from a cubic phase to a tetragonal phase, resulting in a decrease in its ionic conductivity.
At t=800 ℃, experiments found that the conductivity of 8YSZ decreased from 5.45s·m -1 to 4.29s·m -1 in 500 hours, after which it remained stable.
8YSZ ion conductivity over time: is the initial ion conductivity of 8YSZ and t is the operating time in hours.
S4, analyzing influence factors of electrochemical performance and mechanical performance attenuation during continuous operation and cold-hot cycle service of the SOFC stack.
Factors affecting SOFC stack life include, but are not limited to, cell materials including cathode, anode, barrier layer, material composition of electrolyte, stack structural parameters including geometry and material parameters of cell, bipolar plate and seal materials, SOFC operating conditions including operating conditions parameters of stack and stack auxiliary components; factors affecting cell materials and stack structure include, but are not limited to, creep fatigue strain accumulation rate, failure probability accumulation rate, adjacent material thermal expansion coefficient difference, area resistivity increase rate, stack component assembly tolerances, and SOFC operating conditions include, but are not limited to, stack operating temperature, fuel flow, air flow, stack internal temperature difference, stack internal monolithic cell voltage uniformity, air excess coefficient, fuel utilization, reforming efficiency.
By analyzing the pile life prediction model, the influence rule of single cell materials, pile structural parameters and operation conditions of the SOFC on the pile life can be obtained.
Further, based on the material mechanics test and the electrochemical performance durability test of the SOFC stack, the actual values of the mechanical and electrochemical performance parameters of the SOFC stack constituent materials are obtained, as shown in Table 3.
Wherein cold start means a cold and hot cycle test mode from room temperature to 750 ℃.
TABLE 3 Table 3
And S5, modeling calculation is carried out aiming at the actual structure, material parameters and operation conditions of the SOFC electric pile, and the change rule of the mechanical property and the electrochemical property of the SOFC electric pile is analyzed.
According to the pile material and the SOFC pile actual structure in the step S2, establishing an SOFC pile model with multiple physical field coupling such as electrochemical reaction, substance transfer, gas flow, charge transfer, heat transfer, solid mechanics and the like in finite element simulation software, and respectively solving the change rule of current, voltage, temperature, creep-fatigue damage and failure probability of the SOFC pile along with the service time and the service times in the continuous operation and cold-hot circulation process.
The temperature distribution of each region of the three-layer SOFC stack after 5000 hours of continuous operation is shown in fig. 9 (a), and the stack temperature is 750 ℃ at the minimum and 770 ℃ at the maximum.
The stress distribution at the top of the SOFC stack is shown in FIG. 9 (b), and the maximum stress reaches 17.9MPa.
S6, judging whether the SOFC stack can reach the expected life target; if so, setting design indexes and manufacturing requirements of the SOFC stack under the target service life according to SOFC single cell materials, stack structure parameters and operating conditions; if not, the next step is carried out.
And judging whether the service life of the SOFC stack reaches the expected service life according to the failure threshold of the SOFC stack in the step S1, the actual structure of the SOFC stack and the predicted continuous operation and cold-hot cycle service life of the material parameters.
When the failure threshold of the SOFC stack is defined as 80%, the continuous operation life under the current density of 300mA/cm 2 is predicted to be only 7200h according to the actual structure and material parameters of the SOFC stack, and is far less than the expected life of 80000h continuous operation.
The error between the model predicted value and the actual value of the output voltage of the pile at 5000h is 6.103%, and the maximum error between the voltage predicted value and the actual value of the stable operation stage in the 5000h operation process is 8.64%.
The voltage attenuation rate of the SOFC stack in the cold and hot circulation process under the current density of 300mA/cm 2 is 0.403 percent/time, the cold and hot circulation times of the SOFC stack are about 50 times, and the life expectancy of the SOFC stack is far less than 100 times of heat circulation.
And S7, carrying out optimal design aiming at influencing factors of SOFC single cell materials, cell stack structures and operation conditions in the step S4, and returning to the step S5 to carry out modeling calculation and life prediction on the SOFC cell stack after the optimal design.
In order to realize the expected service life of the SOFC electric pile with continuous operation of more than or equal to 80000h and cold-hot cycle of more than or equal to 100 times, the influence factors and the service life prediction model of the SOFC electric pile are combined, and the threshold conditions and the optimization strategies of continuous operation and long-service life of the cold-hot cycle are respectively provided for SOFC single cell materials, electric pile structural parameters and operation conditions.
Design indexes of continuous operation 80000h and 100 times of cold and hot circulation of the SOFC single cell material, cell stack structural parameters, operating conditions and other SOFC cell stack core influencing factors are shown in table 4.
TABLE 4 Table 4
In order to realize the core influencing factor design indexes of the SOFC stack, which are presented in table 4, the invention respectively develops an optimal design aiming at SOFC single cell materials, stack structural parameters and operation conditions, and specific optimizing measures comprise the following four contents: (1) development of gradient layer composite single cell materials: the gradient layer composite cathode cell of the NiO-3YSZ anode support layer/NiO-8 YSZ anode functional layer/YSZ electrolyte/GDC barrier layer/GDC-LSC transition layer/LSC-GDC composite cathode composition structure is developed, compared with the original cell of the NiO-3YSZ anode support layer/NiO-8 YSZ anode functional layer/YSZ electrolyte/GDC barrier layer/LSC cathode composition structure, the gradient layer composite cathode cell is adopted to replace the original cell in the SOFC stack, and the heat treatment process at 1000 ℃ is utilized after the preparation of the cell is completed, so that the mechanical property of the gradient layer composite cathode cell is improved, and the stability of the SOFC cell and the stack is improved.
(2) Structural design and preparation of flexible bipolar plate: the problems of high rigidity, high stress and short service life of the traditional connector are solved by developing the design of a flow passage of the flexible connector and the research of the hydraulic forming technology. The flexible connector can reduce the weight by 50% compared with the traditional rigid bipolar plate, and the creep deformation resistance of the bipolar plate can be improved by about 30% by adopting Crofer 22H material to replace 430 stainless steel; meanwhile, a silver-based coating and a manganese cobalt spinel coating are respectively sprayed on the surface of the bipolar plate, so that the oxidation resistance of the bipolar plate during continuous operation and cold-hot cycle service is improved, and the problem of Cr enrichment on the surface of the bipolar plate is solved.
(3) And (3) optimizing a sealing material: the fiber reinforced phase is added into the SiO2-SrO-MgO-B2O3 glass ceramic material to delay the crystallization process of the glass body in the sealing material, reduce the thermal stress of the sealing material during continuous operation and cold-hot cycle service, and slow down the leakage of the sealing interface between the sealing material and the battery plate and between the sealing material and the bipolar plate.
(4) Optimization of SOFC operating conditions: and carrying out electrochemical performance tests of the SOFC single cells, the electric stacks and the system under parameters of different temperatures, fuel gas components, fuel flow rates and the like, comparing output voltage conditions of the SOFC single cells, the electric stacks and the system under different operating conditions, and further determining the optimal operating conditions of the SOFC under continuous operation and service under cold-hot cycle working conditions.
And (3) carrying out optimization on single cell materials, stack structural parameters and operation conditions of the SOFC stack by utilizing the optimization strategy, and then returning to the step (8) to predict the service life of the optimized SOFC stack until the service life reaches the expected requirement.
And carrying out continuous operation and cold-hot cycle testing of the SOFC electric pile by using the optimized SOFC single cell material, electric pile structural parameters and operation conditions. 3 SOFC stacks consisting of single cells are used for testing, the testing condition is set to be 750 ℃ in operation temperature, the current density during continuous operation and cold-hot cycle discharge is 300mA/cm 2, the fuel gas introduced into the anode is hydrogen, and the flow rate of the fuel gas is 1500 mL/min -1; the cathode gas was air, and the gas flow rate was 4500 mL/min -1. The expected continuous operation life of the optimized SOFC stack at the current density of 300mA/cm 2 is 82755 hours, as shown in FIG. 10; the expected number of cold and hot cycles was 106 as shown in fig. 11.
It should be understood that the above description is not intended to limit the invention to the particular embodiments disclosed, but to limit the invention to the particular embodiments disclosed, and that the invention is not limited to the particular embodiments disclosed, but is intended to cover modifications, adaptations, additions and alternatives falling within the spirit and scope of the invention.

Claims (5)

1. A service life prediction and optimization method for a solid oxide fuel cell is characterized by comprising the following steps of: the method comprises the following steps:
S1: determining a service life target of continuous operation and cold-hot cycle service conditions of the SOFC stack;
S2: carrying out a mechanical test of SOFC stack constituent materials, continuous operation of SOFC stacks and cold-hot circulation test by utilizing an SOFC test platform, analyzing microstructure degradation conditions before and after SOFC stack service, and analyzing attenuation mechanisms of the SOFC stack mechanical properties and electrochemical properties;
S3: establishing a mechanical property attenuation model and an electrochemical property attenuation model of the SOFC electric pile, associating a coupling relation between the mechanical property and the electrochemical property attenuation of the SOFC electric pile, and establishing a SOFC electric pile life prediction model based on the mechanical property and the electrochemical property attenuation;
s4: analyzing influence factors of electrochemical performance and mechanical performance attenuation during continuous operation and cold-hot cycle service of the SOFC stack;
S5: modeling calculation is carried out aiming at the actual structure, material parameters and operation conditions of the SOFC electric pile, and the change rule of the mechanical property and the electrochemical property of the SOFC electric pile is analyzed;
S6: judging whether the SOFC stack can reach the expected life target; if so, setting design indexes and manufacturing requirements of the SOFC stack under the target service life according to SOFC single cell materials, stack structure parameters and operating conditions; if not, carrying out the next step;
s7: carrying out optimal design aiming at influencing factors of SOFC single cell materials, cell stack structures and operation conditions in the step S4, returning to the step S5 to carry out modeling calculation and life prediction on the SOFC cell stack after the optimal design;
In step S2, (1) carrying out tensile, bending, creep, fatigue and creep fatigue tests on the bipolar plate material by using mechanical test equipment to obtain the mechanical properties of the bipolar plate material; aiming at single cells and sealing materials, carrying out small punch, three-point bending, four-point bending and nano indentation tests by using mechanical testing equipment to obtain the mechanical properties of the single cell materials and glass sealing materials;
(2) Carrying out continuous operation and cold and hot cycle testing of the SOFC stack by using SOFC electrochemical testing equipment, collecting a change curve of temperature, voltage and current along with operation time, and collecting a polarization curve and an electrochemical impedance spectrum EIS of the stack every 100-500 h when an electrochemical workstation is continuously operated, or testing and collecting the polarization curve and the electrochemical impedance spectrum EIS of the stack when each cold and hot cycle is carried out;
(3) Analyzing and processing Nyquist data of electrochemical impedance spectrum EIS of the SOFC stack by using relaxation time distribution, namely a DRT method, calculating ohmic impedance generated by pure electric charge transfer and polarization impedance generated by diffusion and electrochemical reaction, determining change rules of different electrode reaction processes based on DRT curve distribution rules, and providing reasonable initial values for ECM accessories of an equivalent circuit model;
(4) Calculating voltage loss caused by each electrode reaction process in the continuous operation and the cold and hot circulation of the SOFC stack by using an equivalent circuit model ECM, and determining contribution values of different electrode reaction processes in the continuous operation and the cold and hot circulation to voltage attenuation by using an ECM fitting result;
(5) After the continuous operation or the cold and hot cycle test is finished, removing the SOFC stack, and testing the microstructure of the SOFC stack before and after the continuous operation or the cold and hot cycle test by utilizing a scanning electron microscope SEM, an X-ray spectrometer EDS, an X-ray photoelectron spectroscopy technology XPS and an electron probe X-ray microscopic analyzer EPMA, so as to analyze the attenuation mechanism of the mechanical property and the electrochemical property of the SOFC stack;
In step S3, a calculation formula of a predicted lifetime T f of the SOFC stack in a continuous operation and a cold-hot cycle service process is as follows:
In the formula (1), T f is the predicted service life of the SOFC stack, deltaU is the attenuation amplitude, v is the voltage attenuation rate of the SOFC stack per thousand hours, and K p is the voltage attenuation coefficient caused by the microstructure degradation and mechanical property attenuation of the SOFC stack;
The calculation formula of the voltage attenuation rate of the SOFC stack comprises the following steps:
v＝vT+vd (2)；
v T represents the voltage attenuation rate of the SOFC stack during the cold-hot cycle and variable load working condition operation, and v d represents the voltage attenuation rate of the SOFC stack during the steady working condition operation;
when the SOFC stack runs in the stable running stage, the SOFC stack and the auxiliary system working conditions thereof do not fluctuate, the voltage is attenuated linearly, and the attenuation rate is constant; the calculation formula of the voltage attenuation rate in the stable operation stage:
in the formula (3), v d represents a voltage decay rate per thousand hours of stable operation of the SOFC stack, The porosity is represented, and Fu represents the fuel utilization rate under a stable working condition; t represents the average temperature inside the pile, and the unit is Kelvin, namely K; t 0 represents the reduction temperature of the galvanic pile, and the unit is Kelvin, K; i represents the current density under stable working conditions, the unit is ampere/square centimeter, namely A/cm 2;A1、A2 is a constant related to the property of anode materials, and C 1、C2 is a constant related to the property of cathode materials;
The calculation formula of the voltage attenuation coefficient caused by the deterioration of the microstructure and the mechanical property attenuation of the SOFC stack is as follows:
Kp＝1+ρ (4)；
Wherein ρ is a microcrack damage parameter;
in the damage attenuation stage, microstructure degradation and mechanical property attenuation simultaneously occur in the SOFC stack, wherein the microstructure degradation continuously leads to voltage attenuation, and the mechanical property attenuation accelerates the voltage attenuation; in addition, when the voltage decay of the SOFC stack is affected only by the microstructure degradation, ignoring the mechanical property decay leads to a voltage decay, where K p =1; in terms of mechanical property attenuation, the expression of the microcrack damage parameter rho relative to damage omega in the SOFC stack is as follows:
Wherein ρ is the damage parameter of the microcracks, n is the material constant, namely the creep stress index, and d is the average diameter of the microcracks; n is creep stress index, ω is the damage variable of conventional damage mechanics, i.e., structural damage caused by creep-fatigue;
When the SOFC stack is continuously operated and is in service in a cold-hot cycle mode, ohmic resistance degradation caused by YSZ electrolyte phase change and anode Ni particles coarsening is most serious in the influence of cathode concentration polarization degradation caused by cathode Cr poisoning and anode Ni particles coarsening on voltage attenuation caused by anode side TPB charge transfer reaction and ion transmission degradation; thus, a theoretical model of Ni grain coarsening, cr poisoning, and phase change of the electrolyte is established; the coarsening of Ni reduces the conductivity and TPB length of the anode, and the calculation formula of the radius r Ni of Ni particles is shown as formula (8); the calculation formula of the electronic conductivity sigma e,an of the Ni coarsening-influenced composite anode is shown as formula (9);
wherein, The initial radius of the Ni particles is indicated,Λ refers to the fitting parameters of the Ni coarsening model, λ=2.5e-04 h -1, t refers to run time, C is a constant; is the intrinsic conductivity of the anode Ni material, Is the anode porosity, and is Ni is the volume fraction of Ni in the anode, ψ Ni =0.4,Is the percolation threshold of the anode nickel particles;
the electrochemical reaction due to Cr poisoning in cathode TPB is as follows:
2CrO2(OH)2(g)+6e-(LSM)→CrO3(s)+2H2O(g)+3O2-(YSZ) (15);
Cr poisoning in TPB was simulated using a Cr poisoning model, with a charge transfer current density for Cr oxide deposition of i D:
i 0,D is the intrinsic exchange current density of the Cr-poisoned TPB; And The mole fractions of CrO 2(OH)2 and water vapor in the gas phase, respectively; F. r and T are Faraday constant, gas constant and temperature, respectively; η act,TPB is the local activation overpotential at TPB,Representing the local exchange current density, in relation to the material parameters; i 0,D is defined as 6.74A/m 2;
at the SOFC operating temperature, the crystal structure of the 8YSZ electrolyte material gradually changes from cubic phase to tetragonal phase, resulting in a decrease in ionic conductivity, and the expression of the change in 8YSZ ionic conductivity over time:
is the initial ionic conductivity of 8YSZ, t is the operating time in hours;
In step S7, a threshold condition and an optimization strategy for continuous operation and long service life of a cold-hot cycle are respectively provided for SOFC single cell materials, cell stack structures and operation conditions, and the optimization design of SOFC cell stack constituent materials, structures and operation conditions comprises the following contents:
Gradient layer composite single cell material: a gradient layer composite cathode cell sheet with a structure composed of a NiO-3YSZ anode support layer, a NiO-8YSZ anode functional layer, a YSZ electrolyte, a GDC barrier layer, a GDC-LSC transition layer and a LSC-GDC composite cathode is adopted; compared with a primary cell of a NiO-8YSZ anode support layer NiO-3YSZ anode support layer/NiO-8 YSZ anode functional layer/YSZ electrolyte/GDC barrier layer/LSC cathode composition structure, the gradient layer composite cathode cell is adopted to replace the primary cell in the SOFC stack, and the primary cell is treated by a 1000 ℃ heat treatment process after the preparation of the cell is completed.
2. The solid oxide fuel cell service life prediction and optimization method according to claim 1, wherein: in step S2, the SOFC test platform includes an SOFC electrochemical test device, a mechanical test device, an electrochemical workstation and a data control terminal, where the SOFC electrochemical test device includes an SOFC stack, a heating furnace, a fuel processing module, a cathode air module and an electronic load controller; the SOFC electric pile comprises an electric pile core unit, a packaging material, a top plate and a base, wherein the electric pile core unit comprises a bipolar plate, a sealing material and a single cell, and the single cell comprises a cathode, a barrier layer, an electrolyte, an anode functional layer and an anode supporting layer; the mechanical test equipment is multifunctional test equipment, and mechanical property tests including stretching, bending, creeping, fatigue, creep fatigue tests, small punch, three-point bending, four-point bending and nano indentation tests are carried out by replacing different types of clamps, so that the strength, hardness and elastic modulus of the SOFC galvanic pile composition material are obtained; the method comprises the steps that electrodes of an SOFC stack are connected to an electronic load controller and an electrochemical workstation through cables, and a heating furnace, a fuel processing module, a cathode air module, the electronic load controller and the electrochemical workstation are connected with a data control terminal through cables; the temperature of the heating furnace, the flow and the pressure of fuel gas and air are controlled by adopting programs in a data control terminal and monitored by data, and the electronic load controller, the electrochemical workstation and the mechanical testing equipment are controlled remotely and data synchronized by the data control terminal.
3. The solid oxide fuel cell service life prediction and optimization method according to claim 1, wherein: in step S4, influencing factors of SOFC stack life include single cell materials, stack structural parameters and operating conditions; the single cell material comprises cathode, anode, barrier layer and electrolyte material components, the pile structure parameters comprise geometry and material parameters of single cell, bipolar plate and sealing material, and the SOFC operation conditions comprise operation condition parameters of the pile and pile auxiliary parts; factors affecting cell materials and stack structure include creep fatigue strain accumulation rate, failure probability accumulation rate, adjacent material thermal expansion coefficient difference, surface resistivity increase rate, stack component assembly tolerance, and factors affecting SOFC operating conditions include stack operating temperature, fuel flow, air flow, stack internal temperature difference, stack internal cell voltage uniformity, air excess factor, fuel utilization and reforming efficiency.
4. The solid oxide fuel cell service life prediction and optimization method according to claim 1, wherein: in step S5, according to the actual structure, material parameters and operation conditions of the SOFC stack in step S2, a multi-physical field coupling SOFC stack model comprising electrochemical reaction-substance transfer-gas flow-charge transfer-heat transfer-solid mechanics is built in finite element simulation software, and the change rule of current, voltage, temperature, creep-fatigue damage and failure probability along with service time and service times of the SOFC stack in the continuous operation and cold-hot circulation processes is solved respectively.
5. The solid oxide fuel cell service life prediction and optimization method according to claim 1, wherein: in step S6, according to the failure threshold value of the SOFC stack in step S1 and the change rule of the mechanical property and the electrochemical property of the SOFC stack obtained by modeling calculation in step S5, whether the continuous operation and the cold-hot cycle life of the SOFC stack reach the expected target life is determined.
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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN1667862A (en) * 2005-04-05 2005-09-14 中国矿业大学（北京校区） High reliability long life solid oxide fuel battery and process for preparation
CN117725446A (en) * 2024-02-07 2024-03-19 南昌大学 SOFC (solid oxide fuel cell) stack performance decay prediction method and system based on GA-BP (GAs-liquid-phase reactor)

Family Cites Families (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20170363689A1 (en) * 2016-06-16 2017-12-21 University Of South Carolina Accelerated Testing Protocols For Solid Oxide Fuel Cell Cathode Materials
CN112736268B (en) * 2020-12-17 2022-02-15 华中科技大学 Control optimization method and system for prolonging service life of SOFC (solid oxide fuel cell) system
WO2024055271A1 (en) * 2022-09-16 2024-03-21 华东理工大学 Anti-fatigue and safety regulation and control method for service structure having ultra-long service life in extreme environment
CN116259797A (en) * 2023-02-21 2023-06-13 华中科技大学 Health assessment and prediction method and system for solid oxide fuel cell system
CN116643192B (en) * 2023-06-01 2024-09-27 哈尔滨工业大学(深圳)(哈尔滨工业大学深圳科技创新研究院) Method, device, computer and storage medium for predicting service life of SOFC (solid oxide Fuel cell)/electric pile
CN116879781B (en) * 2023-06-21 2024-07-02 中国石油大学(华东) Life prediction method for electrochemical performance of solid oxide fuel cell stack
CN116959634B (en) * 2023-06-21 2024-08-06 中国石油大学(华东) Service life prediction method for SOFC (solid oxide fuel cell) pile structure damage and electrochemical performance decay
CN116879782B (en) * 2023-06-21 2024-07-02 中国石油大学(华东) Method for predicting creep life of solid oxide fuel cell stack
CN116879783B (en) * 2023-06-21 2024-07-12 中国石油大学(华东) Cold and hot circulation acceleration test method for service life of SOFC (solid oxide Fuel cell) stack
CN117592224B (en) * 2024-01-19 2024-04-30 中国石油大学(华东) Solid oxide fuel cell flexible bipolar plate structure optimization design method

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN1667862A (en) * 2005-04-05 2005-09-14 中国矿业大学（北京校区） High reliability long life solid oxide fuel battery and process for preparation
CN117725446A (en) * 2024-02-07 2024-03-19 南昌大学 SOFC (solid oxide fuel cell) stack performance decay prediction method and system based on GA-BP (GAs-liquid-phase reactor)

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