A method for improving the stability of a solid oxide fuel cell

Abstract

The present application relates to the technical field of fuel cell, in particular to a method for improving the stability of solid oxide fuel cell. The solid oxide fuel cell comprises two electrodes, and a functional barrier layer, an electrolyte and a functional barrier layer are sequentially arranged between the two electrodes; the functional barrier layer comprises zinc oxide; and the electrolyte is a semiconductor-ion conductor composite material. The electrodes are laid in a mold, and then the functional barrier layer, the electrolyte, the functional barrier layer and the electrode are sequentially laid on the surface of the electrodes; the obtained fuel cell element is pressed, pretreated and then densified to improve the stability of the solid oxide fuel cell. The present application constructs a dense barrier layer on the surface or inside of the electrolyte by using the in-situ densification characteristics of zinc oxide under specific temperature and reducing atmosphere. The dense layer can effectively block the porous channels in the electrolyte, and prevent the molten carbonate from migrating and losing to the electrode side during long-term operation.

Description

Technical Field

[0001] This invention relates to the field of fuel cell technology, and in particular to a method for improving the stability of solid oxide fuel cells. Background Technology

[0002] Solid oxide fuel cells (SOFCs) are electrochemical devices that directly convert the chemical energy of fuel into electrical energy, offering advantages such as high energy conversion efficiency, wide fuel adaptability, and environmental friendliness. To reduce the high material costs and slow start-up caused by high-temperature operation, low-temperature SOFCs have become a research hotspot in recent years. Among these, electrolyte systems based on semiconductor-ion conductor composite materials (e.g., samarium-doped cerium dioxide (SDC) combined with nickel-cobalt-aluminum lithium oxide (NCAL)) have attracted significant attention due to their excellent ionic conductivity and output performance at low temperatures. Studies have shown that in these composite material systems, the lithium component in the electrode material (e.g., NCAL) will generate carbonate derivatives such as lithium carbonate in situ under battery operating conditions. Since the melting point of lithium carbonate is typically between 460-500°C, these carbonates are in a molten state when the battery operates in the low-temperature range (e.g., 450-550°C). The molten carbonates not only fill the pores between ceramic particles but also provide a rapid channel for proton transport, which is one of the key factors for the high performance of this type of low-temperature SOFC. However, this mechanism of proton transport relying on molten carbonates also brings significant stability issues. During long-term battery operation, molten carbonates, due to their fluidity, are prone to migration, loss, or volatilization, leading to damage to proton transport channels within the electrolyte and consequently causing performance degradation and decreased stability. Existing technologies often struggle to effectively confine molten carbonates while maintaining high conductivity, or their preparation processes are complex and costly. Therefore, designing a simple and effective structure or method that retains the conductive advantages of molten carbonates while effectively preventing their loss to improve long-term battery stability has become a pressing technical challenge in this field. Summary of the Invention

[0003] To address the performance degradation problem caused by lithium carbonate loss during long-term operation of low-temperature solid oxide fuel cells, this invention provides a method for improving the stability of solid oxide fuel cells. This invention introduces a zinc oxide layer into the electrolyte system and densifies it under specific process conditions, thereby effectively preventing lithium carbonate loss and optimizing interfacial proton transport.

[0004] To achieve the above objectives, the present invention provides the following solution: One of the technical solutions of the present invention is a solid oxide fuel cell, comprising two electrodes; a functional barrier layer, an electrolyte, and a functional barrier layer are sequentially disposed between the two electrodes; The functional barrier layer includes zinc oxide; The electrolyte is a semiconductor-ion conductor composite material.

[0005] In a preferred embodiment of the present invention, the electrode comprises nickel cobalt aluminum lithium oxide.

[0006] In a preferred embodiment of the present invention, the electrode is made by coating a nickel cobalt aluminum lithium oxide onto a nickel foam surface.

[0007] In a preferred embodiment of the present invention, the functional barrier layer further includes an electrolyte; the mass ratio of zinc oxide to electrolyte in the functional barrier layer is 8:2 to 9:1.

[0008] In a preferred embodiment of the present invention, the electrolyte is a mixture of samarium-doped cerium dioxide and nickel-cobalt-aluminum lithium oxide in a mass ratio of 7:3.

[0009] In a preferred embodiment of the present invention, the mass ratio of the functional barrier layer, the electrolyte, and the functional barrier layer sequentially disposed between the two electrodes is (0.01~0.1):0.2:(0.01~0.1).

[0010] In this invention, the function of the barrier layer is to prevent the loss of molten carbonate (lithium carbonate) in the electrolyte or electrode.

[0011] The second technical solution of the present invention is a method for preparing the above-mentioned solid oxide fuel cell, comprising the following steps: Electrodes are laid in a mold; then, a functional barrier layer, electrolyte, another functional barrier layer, and another electrode are laid on the electrode surface in sequence; and pressed to obtain a fuel cell preform. The fuel cell preform is first pretreated and then densified to obtain the solid oxide fuel cell.

[0012] In a preferred embodiment of the present invention, the pressing pressure is 7~10 MPa.

[0013] In a preferred embodiment of the present invention, the pretreatment temperature is 450~500℃ and the pretreatment time is 30 minutes to 2 hours; the densification temperature is 525℃~550℃ and the densification time is 10 minutes to 30 minutes; both the pretreatment and densification require a reducing atmosphere.

[0014] The reducing atmosphere is a hydrogen atmosphere, maintained by introducing hydrogen. Simultaneously, oxygen (usually air) needs to be introduced on one side during fuel cell operation. Its core purpose is to act as an oxidant, reacting electrochemically with the fuel (such as hydrogen) introduced on the other side to continuously generate electricity, water, and heat. ZnO undergoes a densification transformation at a specific temperature (525℃~550℃) and in a reducing atmosphere (hydrogen), forming a dense ZnO protective layer (i.e., a functional barrier layer) in situ on the electrolyte surface, thereby sealing the pores.

[0015] To prevent the pure ZnO layer from densifying too quickly, which could lead to a decrease in electrode performance or interface peeling, ZnO is mixed with electrolytes (SDC and NCAL) at a predetermined mass ratio (e.g., ZnO:electrolyte = 9:1 or 8:2) to prepare a composite functional barrier layer.

[0016] By sealing the carbonate loss channels through a dense layer formed in situ, and by using the dense ZnO layer to block the migration and volatilization of molten lithium carbonate to the electrode side, the stability of the electrolyte composition is maintained during long-term battery operation.

[0017] The electrode NCAL of a solid oxide fuel cell is easily reduced in a hydrogen atmosphere, Ni 3+ Reduced to Ni 2+ During the process, excess oxygen ions will be generated, and metallic lithium ions will be released. In the fuel cell atmosphere, lithium ions will combine with water produced by the battery reaction and carbon dioxide in the air to form Li2CO3. Since Li2CO3 has a melting point of 460-500℃, it will melt during fuel cell operation. The molten carbonate provides a fast channel for proton transport, which may be a key factor in improving battery performance.

[0018] The densification conditions for zinc oxide are related to hydrogen gas, temperature, time, the presence of electrodes, and whether the battery is discharged. Densification occurs at 525°C with electrodes (NCAL) applied and hydrogen gas introduced for 10 minutes. Adding a discharge step, densification also occurs at 500°C with electrodes (NCAL) applied and hydrogen gas introduced for 30 minutes. Without electrodes (NCAL) or without hydrogen gas introduction, zinc oxide sheets cannot be densified at 450°C-550°C.

[0019] Comparative experiments revealed that batteries without a zinc oxide dense layer (functional barrier layer) exhibited stability of only 2-4 hours, while the addition of a zinc oxide dense layer improved stability tenfold. Stability refers to the battery's performance at 550°C and 100 mA / cm². -2 The duration of holding voltage above 0.7V under current density discharge test.

[0020] After the stability test of the solid oxide fuel cell was completed, X-ray diffraction analysis was performed on its zinc oxide material (functional barrier layer). Meanwhile, under hydrogen and air conditions, XPS analysis showed that the peaks of ZnO did not change due to hydrogen or air treatment, further demonstrating that the ZnO single-phase material is stable under both hydrogen and air conditions.

[0021] The third technical solution of the present invention is a method for improving the stability of a solid oxide fuel cell. The solid oxide fuel cell is prepared by the above-mentioned preparation method, thereby improving the stability of the solid oxide fuel cell.

[0022] The purpose of pretreatment is to ensure that the generated lithium carbonate fully enters the electrolyte; the purpose of densification treatment is to densify the zinc oxide in the functional barrier layer in situ, blocking the channels for lithium carbonate loss, thereby improving the stability of the fuel cell.

[0023] This invention utilizes zinc oxide to achieve in-situ densification of the electrolyte to improve the stability of fuel cells, and is suitable for preparing high-performance, long-life low-temperature solid oxide fuel cell electrolytes.

[0024] Experiments show that rapid densification of zinc oxide semiconductors can be achieved by processing in a hydrogen atmosphere at 525℃, and the resulting dense layer exhibits good chemical stability in both hydrogen and air environments. This invention further significantly improves the discharge performance and long-term operational stability of the battery at 450–550℃ by optimizing the preheating temperature, time, and electrolyte recombination ratio. This method is simple and effective, providing an efficient material solution for stabilizing the electrolyte structure and improving the performance of low-temperature solid oxide fuel cells.

[0025] The preparation method provided by this invention can construct a barrier layer through in-situ densification technology, effectively suppressing the loss of molten carbonates (such as lithium carbonate), thereby significantly improving the stability of the battery during long-term operation.

[0026] Compared with the prior art, the present invention has the following beneficial effects: This invention utilizes the in-situ densification property of zinc oxide (ZnO) under specific temperatures and reducing atmospheres to construct a dense barrier layer on or inside the electrolyte surface. This dense layer effectively seals the porous channels in the electrolyte, preventing molten carbonates (especially Li2CO3) from migrating and leaking towards the electrode side during long-term operation.

[0027] Furthermore, to address the potential interface matching issues or increased resistance caused by excessively rapid densification of the pure ZnO layer, this invention employs a composite barrier layer design combining ZnO and the electrolyte. This design maintains the function of preventing carbonate loss while improving interfacial contact and charge transport capabilities by introducing an ion conductor (SDC) and a catalytic material (NCAL). Experimental results demonstrate that, after the in-situ densification treatment of this invention, the battery exhibits potential for regulation in terms of IVP performance at high current densities and long-term stability, effectively mitigating performance degradation caused by carbonate loss. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a structural diagram of the five-layer battery and the single-layer battery of the present invention.

[0030] Figure 2 This is an X-ray derived image of the electrolyte material of the present invention.

[0031] Figure 3 This is a scanning electron microscope image of the zinc oxide material after densification in Example 3 of the present invention.

[0032] Figure 4 This is a scanning electron microscope image of the zinc oxide material of the present invention before densification.

[0033] Figure 5 This is a graph showing the IVP test results of a fuel cell at different temperatures with the same preheating time.

[0034] Figure 6 This is a scanning electron microscope image of zinc oxide material treated at 550°C for 4 hours without hydrogen gas, electrodes (NCAL), or discharge.

[0035] Figure 7 This is a scanning electron microscope image of zinc oxide material treated at 550°C for 30 minutes without electrodes (NCAL) and without discharge under hydrogen gas.

[0036] Figure 8 This is a scanning electron microscope image of zinc oxide material after being treated at 500°C for 30 minutes without discharge using a hydrogen-filled electrode (NCAL).

[0037] Figure 9 The image shows a scanning electron microscope (SEM) image of zinc oxide material after treatment at 525°C for 30 minutes without discharge using a hydrogen-filled electrode (NCAL).

[0038] Figure 10 This is a scanning electron microscope image of zinc oxide material after being treated with hydrogen gas and electrode discharge (NCAL) at 500°C for 30 minutes.

[0039] Figure 11 Stability test results of a single-layer battery without a zinc oxide dense layer, preheated to 450℃ and tested at 550℃.

[0040] Figure 12 The stability test diagram of the five-layer structure battery of the present invention is shown in the figure, which is preheated to 450℃ and tested at 550℃.

[0041] Figure 13 This is the X-ray diffraction pattern of zinc oxide material after fuel cell stability testing.

[0042] Figure 14 This is an XPS analysis graph of zinc oxide material under hydrogen and oxygen conditions after fuel cell stability testing.

[0043] Figure 15 The image shows the IVP (left) and stability test results (right) of the battery after the dense layer was replaced with a mixture of zinc oxide and electrolyte (mass ratio 9:1).

[0044] Figure 16 This is a stability test diagram of a low-temperature solid oxide fuel cell in Example 2. Detailed Implementation

[0045] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0046] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0047] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0048] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0049] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0050] Unless otherwise specified, the technical solutions described in this invention are all conventional solutions in the field, and the reagents or raw materials used are all purchased from commercial channels or are publicly available unless otherwise specified.

[0051] This invention provides a low-temperature in-situ electrolyte densification method and its application in improving fuel cell stability, comprising the following steps: (1) Step 1 of zinc oxide densification conditions: Step 1 of this invention aims to systematically study the microstructure evolution of pure zinc oxide material after heat treatment at different temperatures and times in a static air atmosphere, and to clarify its intrinsic sintering characteristics.

[0052] Weigh 1.0 g of commercial high-purity zinc oxide powder (particle size approximately 100 nm) and place it in a circular mold (mold cross-sectional area 0.064 cm²). 2 The ZnO blanks were prepared by uniaxial pressing at 7 MPa for 3 minutes on a tablet press. The pressed ZnO blanks were then placed in a muffle furnace and heat-treated in a static air atmosphere. The specific process was as follows: the temperature was increased to 450℃, 500℃, 525℃ and 550℃ at a rate of 10℃ / min. At each target temperature, four holding times were set for 30 minutes, 60 minutes, 120 minutes and 240 minutes, for a total of 16 sets of experiments. After the holding time was completed, all samples were cooled to room temperature with the furnace.

[0053] This invention does not limit the amount of zinc oxide powder used or the size of the circular mold, as long as it allows for clear observation.

[0054] The present invention preferably uses a tablet press at 7MPa, but can be pressed at 8~10MPa; there is no special limitation on the pressing time.

[0055] The present invention does not impose any special limitations on the optical sheet pressing method; adjustments can be made according to actual needs.

[0056] This invention does not impose any special limitations on the heating rate of the muffle furnace; it is sufficient to reach the desired temperature.

[0057] This invention does not have a specific limitation on the heat preservation comparison time; it is sufficient to achieve a comparative effect, such as 40, 80, 160, 320 minutes, etc.

[0058] The present invention does not have any special limitations on the cooling operation; cooling to room temperature is sufficient.

[0059] Scanning electron microscopy (SEM) was performed on the surface and cross-sectional morphology of all 16 heat-treated ZnO wafers. The results showed that the microstructure of the ZnO wafers treated at all temperatures (450-550℃) and for all holding times (30-240 minutes) remained porous with clear particle boundaries. No significant grain growth or a significant decrease in porosity was observed. The SEM image of the wafer treated at 550℃ for 240 minutes (4 hours) is shown below. Figure 6 As shown.

[0060] The results indicate that heat treatment in a simple air atmosphere, even at a temperature of 550°C and with a holding time of 4 hours, cannot achieve effective densification of the ZnO layer.

[0061] The present invention also tested the case of holding at 550℃ with hydrogen gas for 30 minutes, and the results are as follows. Figure 7 As shown. By Figure 7 It can be seen that the microstructure of the zinc oxide particles has changed significantly compared to the samples without hydrogen. The originally clear and independent near-spherical or short columnar particle outlines have become blurred, exhibiting obvious fragmentation and loose, porous, lamellar characteristics. Comparison reveals that the addition of hydrogen disrupts the original smooth surface of the particles, making the material distribution in the images appear more chaotic and layered, with numerous fine debris and micron-sized pore structures appearing between the particles. The main reason for this morphological difference is the strong reducing property of hydrogen. Under high-temperature conditions, hydrogen will capture oxygen atoms from the zinc oxide lattice to generate water vapor, leading to a large number of lattice defects (such as oxygen vacancies). This reduction process induces chemical etching, causing the originally dense particles to peel off or collapse. Simultaneously, the presence of hydrogen actually acts as a sintering aid; the oxygen vacancies it induces greatly increase the diffusion rate of lattice atoms. This enhanced mass transport effect results in the material exhibiting morphological characteristics equivalent to those sintered at higher temperatures at the same nominal temperature, accelerating material migration and structural rearrangement between particles. The stress generated by the local reduction reaction and the accelerated diffusion under the hydrogen-assisted combustion effect jointly promote the transformation of large particles into smaller, more irregular fragments with higher surface roughness, thus forming a unique microstructure that is different from the air-atmosphere heat-treated samples.

[0062] (2) Step 2 of the zinc oxide densification conditions: Study on the rapid densification behavior of ZnO layer with electrode and reaction atmosphere.

[0063] a: To simulate the electrolyte / electrode interface environment, a three-layer structure of "NCAL+ZnO+NCAL electrode" was used for research.

[0064] The preparation process is as follows: In an area of ​​0.064 cm² 2 In a circular mold, an NCAL electrode (prepared by coating a circular nickel foam with a mixture of NCAL powder and pine resin (pure turpentine) in a mass ratio of 3:1, then drying it in a drying oven at 120°C for 3 minutes, ensuring the mixture is opaque after drying, about 1~2 mm) is first laid in as a substrate.

[0065] Then accurately weigh 0.30g of ZnO powder and spread it evenly on the NCAL electrode. Add another layer of NCAL electrode and press it into a “NCAL / ZnO / NCAL” three-layer sheet under a pressure of 8MPa and dry it.

[0066] This invention does not impose any particular restrictions on the porosity, conductivity, areal density, or thickness of the nickel foam used, nor does it impose any particular restrictions on the source of the nickel foam, which can be obtained through commercial channels.

[0067] This invention does not have special limitations on drying time; the goal is to achieve a drying time that is neither powdery nor wet.

[0068] The preferred amount of electrolyte used in the battery of the present invention is 0.3g, and it only needs to have a certain thickness (the electrolyte is located in the middle of the two electrodes).

[0069] In this step of the invention, a tablet press is preferably used at 8 MPa, but 7~10 MPa can be used for pressing, and there is no special limitation on the pressing time.

[0070] b: Atmosphere treatment experiment under non-electrical conditions: The dried three-layer sheet was placed in a battery fixture and then placed in a muffle furnace. Hydrogen gas was introduced into the anode side at a flow rate of 150 mL / min, and air was introduced into the other side. The experiment was conducted according to the following procedure: The temperature was increased to 500℃ at a rate of 10℃ / min, and then kept at that temperature for 10 minutes, 20 minutes, and 30 minutes, respectively, followed by cooling and sampling.

[0071] The temperature was increased to 525℃ at a rate of 10℃ / min, and held for 10 minutes, 20 minutes, and 30 minutes respectively, followed by cooling and sampling.

[0072] The preferred hydrogen flow rate in this invention is 150 mL / min. A flow rate that is too high will cause the temperature inside the muffle furnace to decrease.

[0073] The preferred heat preservation time of this invention is 10, 20, and 30 minutes, but 5-minute intervals can also be used, in order to better compare the changes in density.

[0074] The present invention does not have any special limitations on the cooling operation; cooling to room temperature is sufficient.

[0075] The present invention does not have a special limitation on the heating rate of the muffle furnace in this step, as long as the desired temperature is reached.

[0076] SEM observation of all samples revealed that at 525℃, samples held for only 10 minutes exhibited significant densification of the ZnO layer, with interparticle porosity essentially disappearing. Extending the holding time to 20 and 30 minutes resulted in even more pronounced densification. However, at 500℃, even with a holding time extended to 30 minutes, the ZnO layer maintained a porous structure and did not show significant densification (SEM image of samples held at 500℃ for 30 minutes is shown below). Figure 8 As shown; Scanning electron microscope image after incubation at 525℃ for 30 minutes. Figure 9 (As shown).

[0077] c: Atmosphere treatment experiment under energized (discharged) conditions: The only difference from "b: Atmosphere treatment experiment under no-power conditions" above is that the temperature is increased to 500℃ at 10℃ / min, and while holding at that temperature for 30 minutes, the battery is subjected to an IVP discharge test—by systematically changing the operating load of the fuel cell (manifested as output current), the corresponding output voltage is measured.

[0078] After the experiment, the sample was cooled and taken for SEM observation, which showed that... Figure 10 The results showed that, under a discharge process at 500℃ and in an H2 / air atmosphere, significant densification was also observed in the ZnO layer after 30 minutes of heat preservation.

[0079] This result indicates that the electrochemical process (discharge) can further promote the densification of the ZnO layer and lower the temperature threshold for densification.

[0080] In this step of the invention, the heat preservation time is preferably 30 minutes, but any time longer than 30 minutes is acceptable.

[0081] (3) Preparation and performance of composite electrolytes and fuel cells based on in-situ densified ZnO protective layers: (i) Preparation of raw materials and composite powders: a: SDC (Sm 0.2 Ce 0.8 O 1.9 Powder synthesis: The sol-gel method was employed. Ce(NO3)3·6H2O and Sm(NO3)3·6H2O were weighed at a Ce:Sm molar ratio of 4:1 and dissolved in deionized water. Citric acid was added as a complexing agent (metal ion:citric acid molar ratio = 1:1.5), and the mixture was stirred in an 80°C water bath to form a wet gel. After drying at 120°C for 12 hours, the gel was ground and calcined at 800°C for 4 hours in air at a rate of 10°C / min. After cooling, the gel was ground for 30 minutes and passed through a 400-mesh sieve to obtain SDC powder.

[0082] b: NCAL (Ni 0.8 Co 0.15 Al 0.05 Li 0.2 O 2-δ Powder synthesis: A co-precipitation method was employed. A mixed solution (1.0 mol / L) of metal nitrates (nickel nitrate, cobalt nitrate, aluminum nitrate, and lithium nitrate) was prepared according to a Ni:Co:Al:Li molar ratio of 0.8:0.15:0.05:0.2. This solution was added dropwise with 2 mol / L NaOH solution at 50°C with continuous stirring, maintaining the pH at 11.0 ± 0.2. After reacting for 4 hours, the solution was filtered, washed, and dried. The resulting precursor was sintered in air at 750°C at a rate of 3°C / min for 8 hours, cooled, and then ground to obtain NCAL powder.

[0083] The present invention does not have any special limitations on the cooling operation; cooling to room temperature is sufficient.

[0084] The present invention does not impose any special limitations on the grinding operation; adjustments can be made according to actual needs.

[0085] The present invention does not impose any special limitations on the specific operation of the sol-gel method and co-precipitation method, as long as the solid electrolyte of the battery is obtained.

[0086] c: Preparation of SDC-NCAL composite powder: SDC and NCAL powders were weighed and mixed at a mass ratio of 7:3, anhydrous ethanol was added, and the mixture was ball-milled at 300 rpm for 6 hours. The slurry was dried at 80℃ and then passed through a 200-mesh sieve to obtain a uniform SDC-NCAL (7:3) composite powder. Figure 2 This is an X-ray diffraction pattern.

[0087] The present invention does not impose any special limitations on the ball milling and drying operation; adjustments can be made according to actual needs.

[0088] The optimal performance of this invention is achieved by mixing SDC and NCAL powders at a mass ratio of 7:3.

[0089] (ii) Fabrication of sandwich-structured composite electrolyte fuel cells: In an area of ​​0.064 cm 2 Spread the powder in the mold in the following order: a: Bottom layer: Lay in foamed nickel NCAL electrodes and gently press them flat.

[0090] b: Dense layer: Accurately weigh 0.05 g of ZnO powder and spread it evenly.

[0091] c: Electrolyte layer: Accurately weigh 0.20 g of SDC-NCAL (7∶3) composite powder and spread it evenly.

[0092] d: Dense layer: Accurately weigh 0.05 g of ZnO powder and spread it evenly.

[0093] e: Top layer: Lay in foamed nickel NCAL electrodes and gently press them flat.

[0094] A composite fuel cell preform with a structure of "NCAL / ZnO / SDC-NCAL / ZnO / NCAL" was obtained by uniaxial pressing at 8 MPa for 3 minutes. Figure 1 This is a structural diagram of a battery.

[0095] The present invention does not impose any special limitations on the battery pressing method; adjustments can be made according to actual needs.

[0096] (iii) Battery assembly and electrochemical testing: The composite fuel cell preform prepared in step (ii) is placed in the test system. Hydrogen gas is introduced at a rate of 150 mL / min at the anode, and air is introduced at the cathode. The preferred hydrogen rate in this step is 150 mL / min, and the air flow rate should not be too high, as excessive flow will cause a decrease in the temperature inside the muffle furnace. The temperature is increased to 450, 475, 500, 525, and 550 °C at a rate of 10 °C / min, held for 30 minutes, and then either increased further or directly at 550 °C for IVP and EIS tests. The IVP test results are as follows: Figure 5 As shown.

[0097] The present invention does not have any special restrictions on the 25°C temperature step in this step; it is sufficient to achieve a step comparison effect.

[0098] Test results show that the power generated by discharging at 550℃ after preheating at 450℃, 475℃, and 500℃ is significantly higher than that generated by discharging at 525℃ and 550℃ after preheating.

[0099] Combining the above (1) and (2), it can be seen that zinc oxide does not become dense below 525°C, but becomes dense at 525°C and above, blocking Li ions from entering the electrolyte layer. This indicates that carbonates cannot enter the battery electrolyte at high temperatures to provide channels for proton transport, thus resulting in power loss.

[0100] Therefore, in the process of in-situ electrolyte densification to improve the stability of fuel cells, it is necessary to first maintain the temperature at a relatively low temperature (450~500℃) while ventilating to allow lithium carbonate to fully enter the electrolyte, and then raise the temperature to the densification temperature (525~550℃) to densify zinc oxide in situ, blocking the channels for lithium carbonate loss, thereby improving the stability of the fuel cell.

[0101] The preferred temperature range of 450-500°C in this invention is the lower temperature range, but there are no specific limitations on the specific implementation.

[0102] The preferred temperature for densification in this invention is 525~550℃, but there are no specific limitations on the specific implementation.

[0103] (4) Comparison of battery stability with zinc oxide dense layer: (i): Two batteries are made using the same method, one of which is a common single-layer battery: "electrode (NCAL) + electrolyte (SDC:NCAL 7:3) + electrode (NCAL)"; The other one is a five-layer structure with a dense zinc oxide layer: "electrode (NCAL) + dense layer (zinc oxide) + electrolyte (SDC:NCAL=7:3) + dense layer (zinc oxide) + electrode (NCAL)"; Both batteries were preheated under the same conditions, and then simultaneously discharged under a constant current of 0.064A during the test. The results were observed as follows. Figure 11 , 12.

[0104] The results show that the addition of a zinc oxide dense layer significantly improves the stability of fuel cells.

[0105] In this invention, the preferred conditions for this step are: hydrogen gas is introduced at 450°C, air is preheated for 30 minutes, the temperature is raised to 550°C and held for 30 minutes, and stability is tested after IVP and EIS tests using an IT8511 electronic load. The stability test mode is a constant current discharge of 0.064A.

[0106] This invention simultaneously performed X-ray diffraction and XPS tests on the tested zinc oxide layer, and the results are as follows: Figure 13 14. The results demonstrate the single-phase stability of zinc oxide.

[0107] This invention innovatively develops a method for rapidly densifying semiconductor zinc oxide at low temperatures and applies it to the field of fuel cells, which is of great significance for improving the stability of fuel cells.

[0108] This invention utilizes semiconductor zinc oxide material and solid electrolyte as raw materials to conduct in-situ electrolyte densification research. The densification technology employed has the advantages of simple operation, low cost, and rapid processing time. The densification method provided by this invention can reduce the densification temperature of semiconductor zinc oxide to 525℃. This method not only improves the densification rate and reduces costs but also provides a new approach to improving the stability of solid oxide fuel cells. This is of great significance for promoting the application and development of fuel cells.

[0109] This invention offers significant economic benefits and innovative solutions for improving fuel cell stability, substantially enhancing fuel cell stability and providing new insights for the development of solid oxide fuel cells. Furthermore, this method can boost the economy of the fuel cell industry and drive progress in sustainable energy technologies.

[0110] The present invention also provides a dense layer material and an electrolyte material for fuel cells prepared by the preparation method described above.

[0111] The technical solutions provided by the present invention will be described in detail below with reference to specific embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0112] Example 1 A method for improving the stability of low-temperature solid oxide fuel cells by densifying the in-situ electrolyte: This low-temperature solid oxide fuel cell has a five-layer structure: "electrode (NCAL) + dense layer (zinc oxide) + electrolyte (SDC∶NCAL=7∶3) + dense layer (zinc oxide) + electrode (NCAL)". The preparation method is as follows: a: Bottom layer: Lay in foamed nickel NCAL electrodes and gently press them flat.

[0113] b: Dense layer: Accurately weigh 0.05g of ZnO powder and spread it evenly.

[0114] c: Electrolyte layer: Accurately weigh 0.20g of SDC-NCAL (7∶3) composite powder and spread it evenly.

[0115] d: Dense layer: Accurately weigh 0.05g of ZnO powder and spread it evenly.

[0116] e: Top layer: Lay in foamed nickel NCAL electrodes and gently press them flat.

[0117] A five-layer fuel cell was placed in a muffle furnace using a battery clamp and heated to 450°C at a rate of 10°C / min, with hydrogen gas introduced from both sides and held at this temperature for 30 minutes. The muffle furnace was then heated to 550°C and held for 30 minutes to form a dense zinc oxide layer. Subsequently, hydrogen gas was introduced at the anode and oxygen gas at the cathode, and an IT8511 load was connected for reverse discharge testing of the battery performance. In the reverse connection state (hydrogen gas introduced at the cathode and oxygen gas introduced at the anode), a constant current of 0.064A was set for discharge testing of the battery stability. The results are consistent with... Figure 12 Similarly, the stability of the battery has been significantly improved.

[0118] Example 2 A method for improving the stability of low-temperature solid oxide fuel cells by densifying the in-situ electrolyte: This low-temperature solid oxide fuel cell has a five-layer structure: "electrode (NCAL) + dense layer (zinc oxide) + electrolyte (SDC∶NCAL=7∶3) + dense layer (zinc oxide) + electrode (NCAL)". The preparation method is as follows: a: Bottom layer: Lay in foamed nickel NCAL electrodes and gently press them flat.

[0119] b: Dense layer: Accurately weigh 0.05 g of ZnO powder and spread it evenly.

[0120] c: Electrolyte layer: Accurately weigh 0.20 g of SDC-NCAL (7∶3) composite powder and spread it evenly.

[0121] d: Dense layer: Accurately weigh 0.05 g of ZnO powder and spread it evenly.

[0122] e: Top layer: Lay in foamed nickel NCAL electrodes and gently press them flat.

[0123] A five-layer fuel cell was placed in a muffle furnace using a battery clamp and heated to 500°C at a rate of 10°C / min. Hydrogen gas was introduced through both sides and the temperature was maintained for 30 minutes. The muffle furnace was then heated to 550°C and maintained for 30 minutes to form a dense zinc oxide layer. Subsequently, hydrogen gas was introduced through the anode and oxygen gas through the cathode, and an IT8511 load was connected for reverse discharge testing of the battery performance. In the reverse connection state (hydrogen gas through the cathode and oxygen gas through the anode), a constant current of 0.064A was set to discharge the battery to test its stability. The results are as follows. Figure 16 As shown, it can be seen that compared to a single-layer battery ( Figure 11 The stability of the battery has been significantly improved.

[0124] Example 3 A method for low-temperature dense semiconductor zinc oxide: A battery structure comprising "electrode (NCAL) + zinc oxide + electrode (NCAL)" is fabricated. a: Bottom layer: Lay in foamed nickel NCAL electrodes and gently press them flat.

[0125] b: Dense layer: Accurately weigh 0.05 g of ZnO powder and spread it evenly.

[0126] c: Top layer: Lay in foamed nickel NCAL electrodes and gently press them flat.

[0127] The zinc oxide was pressed into sheets using a tablet press at 8 MPa. The prepared batteries were then clamped in a fixture and placed in a muffle furnace. The muffle furnace was heated to 550°C at a rate of 10°C / min, and hydrogen gas was introduced and the temperature was maintained for 10 min. The batteries were then removed, allowed to cool, and subjected to scanning electron microscopy (SEM). SEM images of the densified zinc oxide and the zinc oxide raw material (zinc oxide sheets pressed using a tablet press at 8 MPa) are shown below. Figure 3 , Figure 4 As shown. Comparison Figure 3 , Figure 4 It can be seen that, compared with untreated zinc oxide particles, the zinc oxide grains at this time exhibit a distinctly dense ceramic structure.

[0128] Example 4 A method for improving the stability of low-temperature solid oxide fuel cells by densifying the in-situ electrolyte: This low-temperature solid oxide fuel cell has a five-layer structure: "electrode (NCAL) + dense layer + electrolyte (SDC:NCAL 7:3) + dense layer + electrode (NCAL)". The dense layer is a mixture of zinc oxide and electrolyte (SDC:NCAL = 7:3) in a mass ratio of 9:1 or 8:2. The preparation method is as follows: a: Bottom layer: Lay in foamed nickel NCAL electrodes and gently press them flat.

[0129] b: Dense layer: Accurately weigh 0.05 g and spread evenly.

[0130] c: Electrolyte layer: Accurately weigh 0.20 g of SDC-NCAL (7∶3) composite powder and spread it evenly.

[0131] d: Dense layer: Weigh 0.05 g precisely and spread evenly.

[0132] e: Top layer: Lay in foamed nickel NCAL electrodes and gently press them flat.

[0133] The five-layer fuel cell was placed in a muffle furnace using a battery clamp and heated to 450°C at a rate of 10°C / min. Hydrogen was introduced into both sides and the temperature was maintained for 30 minutes. The muffle furnace was then heated to 550°C and maintained for 30 minutes to form a dense zinc oxide layer. Hydrogen was introduced into the anode and oxygen into the cathode. The load IT8511 was connected and the battery performance was tested by reversing the polarity. In the reverse polarity state (hydrogen was introduced into the cathode and oxygen into the anode), the battery stability was tested by setting a constant current of 0.064A.

[0134] The dense layer uses an IVP chart (left) and a stability test chart (right) of a mixture of zinc oxide and electrolyte in a 9:1 mass ratio. Figure 15 As shown; from Figure 15 It can be seen that compared to single-layer batteries ( Figure 11 The stability of the battery has been significantly improved.

[0135] As can be seen from the above embodiments, the steps and preparation method provided by the present invention can improve the stability of fuel cells and the rapid densification of low-temperature electrolytes.

[0136] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A solid oxide fuel cell, characterized in that, It includes two electrodes; between the two electrodes, a functional barrier layer, an electrolyte, and another functional barrier layer are arranged sequentially. The functional barrier layer includes zinc oxide; The electrolyte is a semiconductor-ion conductor composite material.

2. The solid oxide fuel cell according to claim 1, characterized in that, The electrode comprises nickel-cobalt-aluminum-lithium oxide.

3. The solid oxide fuel cell according to claim 1, characterized in that, The functional barrier layer also includes an electrolyte; the mass ratio of zinc oxide to electrolyte in the functional barrier layer is 8:2 to 9:

1.

4. The solid oxide fuel cell according to claim 1, characterized in that, The electrolyte is a mixture of samarium-doped cerium dioxide and nickel-cobalt-aluminum lithium oxide in a mass ratio of 7:

3.

5. The solid oxide fuel cell according to claim 1, characterized in that, The mass ratio of the functional barrier layer, electrolyte, and functional barrier layer arranged sequentially between the two electrodes is (0.01~0.1):0.2:(0.01~0.1).

6. A method for preparing a solid oxide fuel cell according to any one of claims 1 to 5, characterized in that, Includes the following steps: Electrodes are laid in the mold; Then, a functional barrier layer, an electrolyte, another functional barrier layer, and an electrode are sequentially laid on the electrode surface; the electrode is then pressed to obtain a fuel cell preform. The fuel cell preform is first pretreated and then densified to obtain the solid oxide fuel cell.

7. The method for preparing a solid oxide fuel cell according to claim 6, characterized in that, The pressing pressure is 7~10 MPa.

8. The method for preparing a solid oxide fuel cell according to claim 6, characterized in that, The pretreatment temperature is 450~500℃, and the pretreatment time is 30 minutes to 2 hours; the densification temperature is 525℃~550℃, and the densification time is 10 minutes to 30 minutes; both the pretreatment and densification require a reducing atmosphere.

9. A method for improving the stability of a solid oxide fuel cell, characterized in that, Solid oxide fuel cells are prepared using the preparation method described in any one of claims 6 to 8, thereby improving the stability of solid oxide fuel cells.

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