A method for preparing a cathode material for a solid oxide fuel cell

Abstract

This invention relates to the field of solid oxide fuel cells, specifically disclosing a method for preparing a cathode material for solid oxide fuel cells, comprising the following steps: mixing raw materials including lanthanum metal salt, nickel metal salt, a complexing agent, and a solvent to obtain an LNO impregnation solution; mixing the LNO impregnation solution with LSCF and then performing a solvothermal reaction to obtain the cathode material. The preparation method of this invention controls parameters such as the concentration of the LNO impregnation solution, the solvent ratio, and the temperature of the solvothermal reaction to regulate the particle size and distribution of La2NiO4 modified on the LSCF surface, thereby shortening the electron and ion transport distance, accelerating the charge transfer process, reducing the cathode polarization resistance, and improving chemical stability.

Description

Technical Field

[0001] This invention relates to the field of solid oxide fuel cells, and more specifically to a method for preparing a cathode material for solid oxide fuel cells. Background Technology

[0002] Solid oxide fuel cells (SOFCs) possess characteristics such as high energy conversion efficiency, low carbon emissions, and flexibility, making them significant in areas such as distributed power generation and regional centralized power supply. Perovskite-type La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ LSCF (Laminated Sr Carbon Fiber) is the most commonly used cathode material. However, due to its surface asymmetry, there is a difference in chemical environment between the crystal surface and the bulk phase. During application, under long-term high-temperature operation, Sr migrates from the cathode and accumulates on the LSCF surface, forming a low-conductivity secondary phase (i.e., an insulating phase). This insulating phase reduces the contact area between the cathode and oxygen, hindering the transfer of electrons from the bulk phase to the oxygen molecules adsorbed on the surface, thus weakening the ORR (oxygen reduction reaction) activity. As Sr segregates to the surface, the Sr content in the lattice gradually decreases, leading to a gradual reduction in the oxygen vacancy concentration and conductivity of the bulk LSCF, resulting in cathode performance degradation and poor long-term stability.

[0003] Existing methods can suppress Sr segregation through doping and surface modification, but the types and quality of elements required for doping are difficult to select and control, and the preparation process is cumbersome, time-consuming, and subject to many limitations. Furthermore, the wet impregnation method commonly used for surface modification of SOFC cathode materials requires repeated impregnation or increasing the concentration of the impregnation solution to form a certain loading of modified phase on the cathode surface. Repeated impregnation is cumbersome, time-consuming, and may cause irreversible damage to the electrode due to repeated calcination. High-concentration solutions are difficult to penetrate into the electrode pores and easily lead to uneven local dispersion of the modified phase. Therefore, there is an urgent need to develop a method for preparing SOFC cathode materials to suppress Sr segregation in LSCF cathode materials and improve the ORR catalytic performance and long-term stability of LSCF cathodes. Summary of the Invention

[0004] In order to overcome at least one of the technical problems existing in the prior art, one of the objectives of the present invention is to provide a method for preparing a cathode material.

[0005] The second objective of this invention is to provide the application of the above-mentioned cathode material preparation method in the preparation of solid oxide fuel cells.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The first aspect of the present invention provides a method for preparing a cathode material, comprising the following steps: A raw material comprising lanthanum metal salt, nickel metal salt, complexing agent and solvent is mixed to obtain an LNO impregnation solution; The cathode material is prepared by mixing the LNO impregnation solution and LSCF and then carrying out a solvothermal reaction. The total molar concentration of lanthanum ions and nickel ions in the LNO impregnation solution is 0.5~2 mol / L; The solvent comprises water and alcohol in a volume ratio of (0.4~0.8):1; The temperature of the solvothermal reaction is 100~150℃; The cathode material contains LSCF and La2NiO4; the molar ratio of LSCF to La2NiO4 is 1:(1~4).

[0007] In this invention, LSCF is a solid oxide fuel cell cathode material with a single-phase perovskite structure.

[0008] The crystal structure of La2NiO4 (LNO) consists of alternating perovskite and rock salt layers, with interstitial oxygen present in the rock salt layers. Therefore, La2NiO4 exhibits an overall stoichiometric ratio of excess oxygen. According to the surface oxygen vacancy mechanism of Sr segregation, the positively charged oxygen vacancies on the LSCF surface exert an electrostatic attraction on the negatively charged Sr'La in the bulk phase, thus promoting Sr segregation to the surface. By covering the LSCF surface with La2NiO4 particles, the excess oxygen causes the LSCF surface to become negatively charged, which cancels out the positively charged oxygen vacancies, thereby suppressing Sr segregation. After long-term heat treatment, La2SrO forms on the surface of the cathode material. x This phase prevents the formation of the surface insulating phase, thereby improving the long-term stability of the cathode.

[0009] In some embodiments of the present invention, the total molar concentration of lanthanum ions and nickel ions in the LNO impregnation solution (i.e., the LNO impregnation solution concentration) is any value selected from 0.5 mol / L, 0.7 mol / L, 0.9 mol / L, 1.0 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L, and 2.0 mol / L, or a range formed by any combination of both. In some preferred embodiments of the present invention, the total molar concentration of lanthanum ions and nickel ions in the LNO impregnation solution is 1 to 1.5 mol / L. The concentration of LNO impregnation solution determines the loading and particle size of the modified phase La2NiO4 (which is the product of a solvothermal reaction of lanthanum metal salt, nickel metal salt and complexing agent). If the LNO impregnation solution concentration is too low, the amount of La2NiO4 generated will be too small, and a continuous La2NiO4 phase will not be formed. This will not enhance the surface exchange processes such as oxygen adsorption dissociation and reduction of LSCF. Instead, it will promote the enrichment of Sr on the surface during the solvothermal process, generating a surface Sr secondary phase, which will lead to the degradation of LSCF performance. On the other hand, if the LNO impregnation solution concentration is too high, the impregnation amount will be too large, which will reduce the electrode porosity and increase the gas phase diffusion resistance. At the same time, it will cause the agglomeration of LNO nanoparticles (i.e., La2NiO4), reduce the three-phase / two-phase reaction area, weaken the cathode electrocatalytic performance and increase the cathode polarization resistance.

[0010] In some embodiments of the present invention, the volume ratio of water to alcohol solvent is any value or a range formed by any two of 0.4:1, 0.5:1, 0.6:1, 0.7:1, and 0.8:1. In some preferred embodiments of the present invention, the volume ratio of water to alcohol solvent is (0.5~0.6):1. Different volume ratios of water and alcohol solvents result in varying wettability of the LSCF matrix. When the volume ratio of water to alcohol solvent is too large (i.e., more water and less alcohol solvent), the LSCF matrix surface is hydrophobic, resulting in excessive surface tension and an inability to uniformly coat the nanoparticles. This leads to a large exposed area of ​​the LSCF matrix, which fails to suppress Sr precipitation and causes a high polarization attenuation rate. As the proportion of alcohol solvent increases, i.e., the volume ratio of water to alcohol solvent decreases, the contact angle between the solvent and the LSCF matrix decreases, indicating lower surface tension and better wettability between the alcohol solvent and LSCF, which helps to obtain more uniformly distributed La2NiO4 nanoparticles. However, when the volume ratio is too small (i.e., less deionized water and more alcohol solvent), the interaction force between the La2NiO4 nanoparticles and the LSCF matrix is ​​too weak, resulting in too many growth points and making it difficult to control the reaction rate. This leads to severe aggregation of the La2NiO4 nanoparticles, reducing the three-phase reaction area and increasing polarization resistance.

[0011] In some embodiments of the present invention, the alcohol solvent includes at least one selected from ethanol, propanol, butanol, isopropanol, propylene glycol, glycerol, and butanediol.

[0012] In some embodiments of the present invention, the water is deionized water.

[0013] In some embodiments of the present invention, the ratio between the total molar amount of lanthanum ions and nickel ions in the LNO impregnation solution and the volume of the solvent is 1 mol: 0.5~2 L.

[0014] In some embodiments of the present invention, the molar ratio of LSCF to La2NiO4 is any one of 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.4, 1:4, or any range formed by both; in some embodiments of the present invention, the molar ratio of LSCF to La2NiO4 is 1:(1~2). The uniform and continuous distribution of La2NiO4 on the LSCF surface can effectively promote the ORR process and reduce the polarization resistance and activation energy of the LSCF cathode at 600~750℃. When the molar ratio of LSCF to La2NiO4 is too high, La2NiO4 cannot achieve continuous coating, and cannot effectively utilize the increased surface exchange processes such as oxygen adsorption dissociation and reduction; when the molar ratio of LSCF to La2NiO4 is too low, it easily leads to the aggregation of La2NiO4 nanoparticles, reducing the three-phase / two-phase reaction area, ultimately resulting in weakened cathode electrocatalytic performance.

[0015] In some embodiments of the present invention, the temperature of the solvothermal reaction is any value or a range formed by any two of 100°C, 105°C, 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C, and 150°C; in some preferred embodiments of the present invention, the temperature of the solvothermal reaction is 100~120°C. The temperature of the solvothermal reaction affects the content of the Sr secondary phase on the surface of the LSCF cathode. When the solvothermal reaction temperature is too high, the content of the surface Sr secondary phase is low. Although the initial polarization resistance is low, after long-term heat preservation operation, the increase of the Sr secondary phase on the surface of the LSCF cathode after high-temperature solvothermal treatment is the greatest, and the degree of Sr segregation is large, thus leading to an excessively high decay rate. When the solvothermal reaction temperature is too low, the content of the surface Sr secondary phase is high. At this time, the initial polarization resistance is high, and the initial performance is poor. It can be seen that the solvothermal reaction temperature affects the initial surface Sr secondary phase content and its increase. An appropriate temperature is required to ensure a low initial polarization resistance and low decay performance.

[0016] In some embodiments of the present invention, the solvothermal reaction time is 2 to 4 hours; in some embodiments of the present invention, the solvothermal reaction time is any value of 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, or a range formed by any two of them.

[0017] In some embodiments of the present invention, the solvothermal reaction is carried out in a polytetrafluoroethylene (PTFE) liner, which is encapsulated in a reaction vessel.

[0018] In some embodiments of the present invention, the molar ratio of the lanthanum metal salt to the nickel metal salt is (1~2):1; in some embodiments of the present invention, the molar ratio of the lanthanum metal salt to the nickel metal salt is any value or a range formed by any two of the following: 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2:1.

[0019] In some embodiments of the present invention, the ratio of the total molar number of lanthanum ions and nickel ions in the LNO impregnation solution to the molar number of the complexing agent is 1:(0.5~2); in some embodiments of the present invention, the ratio of the total molar number of lanthanum ions and nickel ions in the LNO impregnation solution to the molar number of the complexing agent is any value of 1:0.5, 1:0.7, 1:0.9, 1:1, 1:1.2, 1:1.4, 1:1.6, 1:1.8, 1:2 or a range formed by any two of these values.

[0020] In some embodiments of the present invention, the chemical formula of the LSCF is La. 1-x Sr x Co 1-y Fe y O3, 0 < x < 1; 0 < y < 1.

[0021] In some embodiments of the present invention, x can be selected from any value of 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.95 or a range of values ​​formed by any two of them.

[0022] In some embodiments of the present invention, y can be selected from any value of 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.95 or a range of values ​​formed by any two of them.

[0023] In some embodiments of the present invention, the chemical formula of the LSCF is La. 0.6 Sr 0.4 Co 0.2 Fe 0.8 O3, La 0.5 Sr 0.5 Co 0.8 Fe 0.2 O3 or La 0.8 Sr 0.2 Co 0.5 Fe 0.5 O3.

[0024] In some embodiments of this invention, the particle size of the La2NiO4 is 45-65 nm. By controlling the size of the La2NiO4 nanoparticles, this invention can better suppress Sr element segregation in the LSCF cathode material, thereby obtaining a SOFC cathode material with good catalytic performance and chemical stability. This invention uses nanoscale La2NiO4 particles as a surface modification phase material. Their small size shortens the electron and ion transport distance and accelerates the charge transfer process. Furthermore, the large specific surface area of ​​La2NiO4 nanoparticles increases the three-phase interface (TPB) and enhances the ORR capability. La2NiO4 (LNO) is a layered perovskite phase material with a higher oxygen exchange coefficient and bulk diffusion coefficient than LSCF, exhibiting excellent ORR capability. Therefore, the cathode material in this invention has a lower initial polarization resistance than LSCF.

[0025] In some embodiments of the present invention, the La2NiO4 is distributed on the LSCF surface.

[0026] In some embodiments of the present invention, the complexing agent is selected from at least one of citric acid, glycine, and gluconic acid.

[0027] In some embodiments of the present invention, the lanthanum metal salt is selected from La(NO3)3, La(NO3)3 At least one of 6H2O and LaCl3.

[0028] In some embodiments of the present invention, the nickel metal salt is selected from Ni(NO3)2. At least one of 6H2O, Ni(NO3)2, NiCl2, and Ni(CH3COO)2.

[0029] In some embodiments of the present invention, the preparation method further includes a washing and drying step; the washing and drying step is performed after the solvothermal reaction step.

[0030] In some embodiments of the present invention, the washing is performed using water. In some embodiments of the present invention, the washing is performed using deionized water.

[0031] The second aspect of the present invention provides the application of the method for preparing the cathode material described in the first aspect of the present invention in the preparation of solid oxide fuel cells.

[0032] The beneficial effects of this invention are as follows: The preparation method of this invention controls parameters such as the concentration of the LNO impregnation solution, the solvent ratio, and the temperature of the solvothermal reaction, thereby regulating the particle size and distribution of La2NiO4 modified on the LSCF surface, shortening the electron and ion transport distance, accelerating the charge transfer process, reducing the cathode polarization resistance, and improving chemical stability. Specifically, the initial polarization resistance of the cathode measured at 650℃ is <1.5Ω·cm. 2 The initial polarization resistance measured at 750℃ was 0.20~0.27 Ω·cm. 2 The polarization resistance measured after holding at 750℃ for 1000 hours was 0.209~0.27 Ω·cm. 2 The polarization resistance attenuation rate is ≤5% / kh, and the content of Sr secondary phase on the surface is kept at a low level, thus improving the overall performance of the cathode. Attached Figure Description

[0033] Figure 1 This is a SEM image of the symmetrical battery cathode in Example 1.

[0034] Figure 2 This is a SEM image of the cathode of the symmetrical cell in Comparative Example 4. Detailed Implementation

[0035] The specific implementation of the present invention will be further described in detail below with reference to the accompanying drawings and examples, but the implementation and protection of the present invention are not limited thereto. It should be noted that any processes not specifically described in detail below are those that can be implemented or understood by those skilled in the art by referring to the prior art. Reagents or instruments used without specified manufacturers are all conventional products that can be purchased commercially.

[0036] Example 1 This example provides a method for preparing a cathode material for SOFCs, including the following steps: S1: La(NO3)3 6H2O, Ni(NO3)2 6H2O, deionized water, ethanol, and citric acid are mixed and stirred to dissolve, yielding an LNO impregnation solution; Among them, La(NO3)3 6H2O and Ni(NO3)2 The molar ratio of 6H2O is 2:1; La in LNO impregnation solution 3+ and Ni 2+ The total ion concentration (i.e., LNO impregnation solution concentration) is 1.2 mol / L; the volume ratio of deionized water to ethanol is 0.55:1; The concentration of citric acid is 1.8 mol / L, and the molar amount of citric acid is: La 3+ and Ni2+ The total number of moles = 1.5:1; S2: Weigh 50g of commercial LSCF (La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O3) powder was poured into the LNO impregnation solution obtained in S1. The molar ratio of nickel ions in the LSCF powder and LNO impregnation solution (i.e., the molar ratio of LSCF to LNO) was 1:1.5. After stirring evenly, the solution was transferred to a polytetrafluoroethylene liner, and then the liner was sealed in a stainless steel reactor. The reaction was carried out at a solvothermal reaction temperature of 110℃ for 3 hours (i.e., the solvothermal reaction time was 3 hours). After the temperature naturally decreased to room temperature, the liner was removed, and the solution was centrifuged, washed, and dried with deionized water. Finally, LNO nanoparticle powder modified on the surface of LSCF cathode powder was obtained, which is the cathode material for SOFCs in this example, denoted as LNO@LSCF-1. LNO refers to La2NiO4. In the cathode material for SOFCs, the molar ratio of LSCF to LNO is 1:1.5.

[0037] The concentration of the LNO impregnation solution, the volume ratio of water to ethanol, the molar ratio of LSCF to LNO, the solvothermal reaction temperature, and the solvothermal reaction time parameters in this example are all recorded in Table 1 below.

[0038] Examples 2-5 The only difference between the preparation methods of the cathode materials for SOFCs in Examples 2-5 and Example 1 is that the concentration of LNO impregnation solution is different, as shown in Table 1 below.

[0039] Examples 6-9 The only difference between the preparation methods of the cathode materials for SOFCs in Examples 6-9 and Example 1 is that the volume ratio of water to ethanol is different, as shown in Table 1 below.

[0040] Examples 10-12 The only difference between the preparation methods of the cathode materials for SOFCs in Examples 10-12 and those in Example 1 is that the molar ratio of LSCF and LNO is different, as shown in Table 1 below.

[0041] Examples 13-15 The only difference between the preparation methods of the cathode materials for SOFCs in Examples 13-15 and those in Example 1 is that the solvothermal reaction temperature is different, as shown in Table 1 below.

[0042] Examples 16-17 The only difference between the preparation methods of the cathode materials for SOFCs in Examples 16 and 17 and those in Example 1 is the solvothermal reaction time, as shown in Table 1 below.

[0043] Comparative Examples 1-2 The only difference between the preparation methods of the cathode materials for SOFCs in Comparative Examples 1 and 2 and those in Example 1 is the concentration of the LNO impregnation solution, as shown in Table 1 below.

[0044] Comparative Examples 3-4 The only difference between the preparation methods of the cathode materials for SOFCs in Comparative Examples 3 and 4 and those in Example 1 is the volume ratio of water to ethanol, as shown in Table 1 below.

[0045] Comparative Examples 5-6 The only difference between the preparation methods of the cathode materials for SOFCs in Comparative Examples 5 and 6 and those in Example 1 is that the molar ratio of LSCF and LNO is different, as shown in Table 1 below.

[0046] Comparative Examples 7-8 The only difference between the preparation methods of the cathode materials for SOFCs in Comparative Examples 7 and 8 and those in Example 1 is that the solvothermal reaction temperature is different, as shown in Table 1 below.

[0047] Comparative Example 9 The only difference between the preparation method of the cathode material for SOFCs in this example and that in Example 1 is that an equal amount of propionic acid is used instead of citric acid in Example 1.

[0048] Table 1. Preparation parameters for Examples 1-17 and Comparative Examples 1-8

[0049] Performance testing: The cathode materials obtained in Examples 1-17 and Comparative Examples 1-9 were used to prepare the cells required for testing. The specific preparation steps are as follows: (1) Preparation of cathode slurry: 8g of cathode material, 10mL of isopropanol, 2mL of ethylene glycol, 0.6mL of glycerol and 0.4mL of binder (96% terpineol and 4% ethyl cellulose) were added to a zirconia high-energy ball mill jar and ball milled at 400 rpm for 1h to obtain cathode slurry.

[0050] (2) Preparation of symmetrical battery: The electrolyte sheet is a commercial product (its composition is: 8% by mass Y2O3 stabilized ZrO2, 8YSZ), with a diameter of about 10 mm and a thickness of about 3 mm. GDC (i.e., gadolinium-doped cerium oxide) paste is screen-printed on both sides of the electrolyte sheet and calcined at 1300℃ for 300 min as a GDC barrier layer to prevent the cathode material from reacting with 8YSZ. The sintered GDC electrolyte sheet is double-sided polished with 600-mesh sandpaper, and then the cathode paste prepared in step (1) is uniformly printed on both sides of the GDC electrolyte sheet, with a coating area of ​​50 mm. 2 A circular region was formed to create a symmetrical cell with the structure LNO@LSCF|GDC|YSZ|GDC|LNO@LSCF. The cell was calcined at 1080℃ for 180 min at a heating rate of 5°C / min to ensure tight adhesion between the material and the electrolyte, resulting in a cathode|electrolyte|cathode symmetrical cell. Before testing, platinum paste was uniformly coated onto the cell surface and sintered at 900℃ to serve as the current collector, with four platinum wires connected as conductors.

[0051] The symmetrical cell prepared according to the above method was subjected to electrochemical impedance spectroscopy (EIS) using a CHI604C electrochemical workstation. The specific test method is as follows: (a) Initial polarization resistance @ 650℃ Symmetrical batteries were subjected to electrochemical impedance spectroscopy (EIS) testing under open-circuit voltage conditions. The AC disturbance voltage was 10 mV, the test frequency was 0.1 Hz to 500 kHz, and the test temperature was 650℃. According to the Nyquist plot of AC impedance, the intercept of the semicircle at low frequencies with the horizontal axis represents the polarization resistance Rp of the battery. The obtained impedance data Rp was divided by two to obtain the true polarization resistance. The compliance standard is: initial polarization resistance @ 650℃ < 1.5 Ω·cm. 2 ; (b) Initial polarization resistance @ 750℃ Symmetrical cells were subjected to AC impedance testing (EIS) in air atmosphere and open circuit voltage. The AC disturbance voltage during the test was 10mV, the test frequency was 0.1 Hz~500 kHz, and the test temperature was 750℃. (c) Polarization resistance at 750℃ and polarization resistance decay rate over 1000 hours After the symmetrical battery is kept at 750℃ for 1000h, its polarization resistance is tested according to the same treatment method. Then, it is compared with the initial polarization resistance to calculate the corresponding attenuation rate. Attenuation rate = (1000h polarization resistance@750℃ - initial polarization resistance@750℃) / initial polarization resistance@750℃ × 100%, and the standard is ≤5% / kh.

[0052] The performance data of the symmetrical cells assembled from the cathode materials of Examples 1-17 and Comparative Examples 1-9, obtained according to the above test methods, are shown in Table 2 below.

[0053] Table 2 Performance data of symmetric cells

[0054] As shown in Table 2, compared with Comparative Examples 1-9, the cathode materials used in Examples 1-17, when used to prepare symmetrical cells, exhibited an initial polarization resistance of 1.09-1.48 Ω·cm at 650℃. 2 The initial polarization resistance at 750℃ is 0.208~0.265 Ω·cm. 2 The polarization resistance at 750℃ over 1000 hours is 0.209~0.269 Ω·cm. 2 The polarization resistance attenuation rate is 0.48~4.27% / kh. The following analysis is based on specific examples and comparative examples: By comparing Examples 1-5 with Comparative Examples 1-2, it can be seen that as the concentration of LNO impregnation solution increases, the polarization resistance gradually decreases. When the concentration of LNO impregnation solution is 1.2 mol / L, the polarization resistance reaches its lowest value, reaching 1.09 Ω·cm at 650°C. 2 This indicates that modifying nano-LNO can promote the cathode ORR process, thereby reducing cathode resistance. However, when the LNO impregnation solution concentration continued to increase to 1.5 mol / L and 2 mol / L, the polarization resistance actually increased. This is because the excessive impregnation amount led to a decrease in electrode porosity and an increase in gas phase diffusion resistance. At the same time, the excessively high LNO impregnation solution concentration caused the aggregation of LNO nanoparticles, reducing the three-phase / two-phase reaction area, ultimately resulting in a weakening of the cathode electrocatalytic performance.

[0055] By comparing Examples 1, 6-9 with Comparative Examples 3-4, it can be seen that a higher water / ethanol ratio (i.e., more deionized water and less ethanol) results in a hydrophobic LSCF substrate surface with excessive surface tension, hindering uniform coating of nanoparticles. As the ethanol ratio increases, the contact angle between the solvent and the LSCF substrate gradually decreases, improving wettability. This allows the solution to easily penetrate the pores of the LSCF cathode, enabling uniform in-situ growth of nanoparticles on the LSCF surface. To verify this conclusion, scanning electron microscopy (SEM) was used to examine the surface morphology of the cathode materials in Examples 1 and 4 at 10K magnification, as shown below. Figure 1 and Figure 2 As shown. By Figure 1 and Figure 2It can be seen that, compared with the surface of the cathode material in Comparative Example 1, the modified LSCF cathode material in Example 1 has LNO nanoparticles uniformly attached to both the surface and the interior of the cavities. Moreover, the nanoparticles are uniform in size, ranging from 45 to 65 nm, and there is no aggregation. This indicates that when the solvothermal reaction is carried out at a water / ethanol volume ratio of 0.55:1, LNO nanoparticles are grown in situ on the surface of the LSCF cathode material, resulting in well-dispersed nanoparticles with uniform particle size. Since LNO has a higher oxygen exchange coefficient and bulk diffusion coefficient than LSCF, it greatly improves the ORR performance.

[0056] Comparing Examples 1, 10-12 with Comparative Examples 5-6, it is evident that when the molar ratio of LSCF to LNO is too high, LNO fails to provide continuous coating; when the molar ratio is too low, LNO nanoparticles tend to agglomerate, reducing the three-phase / two-phase reaction area and ultimately weakening the cathode electrocatalytic performance. When the molar ratio of LSCF to LNO is 1:1.5, LNO nanoparticles are uniformly and continuously distributed on the LSCF surface, reducing the polarization resistance and activation energy of the LSCF cathode, effectively promoting the ORR process, and achieving the lowest polarization resistance, reaching 1.09 Ω·cm at 650℃ and 750℃. 2 and 0.208Ω·cm 2 .

[0057] Comparing Examples 1, 13-15 with Comparative Examples 7-8 reveals that the solvothermal reaction temperature affects the content of Sr secondary phase on the LSCF cathode surface. Generally, the higher the solvothermal reaction temperature, the lower the content of Sr secondary phase on the surface, and the lower the initial polarization resistance. However, after long-term heat treatment, the Sr secondary phase on the LSCF cathode surface increased the most after high-temperature solvothermal treatment, indicating the greatest degree of Sr segregation and the highest decay rate. Therefore, the solvothermal reaction temperature affects the initial surface Sr secondary phase content and its increase, and an appropriate solvothermal reaction temperature is required to ensure both initial and decay performance.

[0058] Long-term stability tests were conducted on Examples 1 and Comparative Examples 7-8 by holding them at 750°C for 1000 hours, and the change in polarization resistance over time was observed. The results showed that after holding, the polarization resistance of Comparative Example 7 decreased from its initial value of 0.264 Ω·cm. 2 Increased to 0.284 Ω·cm 2 The performance degraded by 7.58% / kh. In Comparative Example 8, after heat preservation, the polarization resistance decreased from the initial 0.226 Ω·cm. 2 Increased to 0.249 Ω·cm 2 The performance degraded by 10.18% / kh. In Example 1, after heat preservation, the polarization resistance decreased from the initial 0.208 Ω·cm. 2 Increased to 0.209 Ω·cm2 The attenuation was 0.48% / kh, indicating that impregnation with LNO can improve the stability of the LSCF cathode.

[0059] Comparing Example 1 and Comparative Example 9, it can be seen that when propionic acid is used instead of citric acid as a complexing agent, propionic acid, being a monodentate ligand, has weak chelating ability and is only suitable for low-valence metal ions. This results in a significant increase in the polarization resistance decay of the prepared cathode material after being kept at 750°C for 1000 hours, with a decay rate as high as 12.55%. In contrast, the complexing agents used in this invention—citric acid, glycine, and gluconic acid—are multidentate, bidentate, and soft embryo ligands, respectively. Their chelating abilities are all of medium strength, and they function under neutral and alkaline conditions. They can form an LNO coating layer on the surface of the LSCF cathode, thereby significantly reducing the polarization resistance decay rate of the cathode material after being kept at 750°C for 1000 hours and improving the stability of the cathode material at high temperatures.

[0060] The Sr secondary phase content on the cathode surface in Examples 1 and Comparative Examples 7-8 was tested using the XPS semi-quantitative method. Based on the XPS fitting results of Sr 3d before and after 1000 h of heat treatment at 750℃ for the LSCF cathode, the Sr 3d content was determined to consist of two parts: surface Sr and bulk Sr. The pair of peaks with low binding energy (~133.5 eV and ~132 eV) belong to the 3d³ / ² and 3d⁵ / ² of the bulk Sr in the LSCF, respectively; while the pair of peaks with high binding energy (~135.5 eV and ~133.9 eV) belong to the 3d³ / ² and 3d⁵ / ² of the surface Sr, respectively, representing Sr precipitated from the LSCF lattice to form the secondary phase. The content of the surface Sr secondary phase was calculated after fitting, as shown in Table 3.

[0061] Table 3. XPS semi-quantitative test results of Sr secondary phase content on cathode surface

[0062] As shown in Table 3, before high-temperature treatment, the Sr secondary phase content on the cathode surface of Comparative Example 7 was 30.57%. After being kept at 750℃ for 1000 hours, the Sr secondary phase content on the cathode surface of Comparative Example 7 was 57.52%, which was 26.95% higher than that of the uninsulated LSCF cathode. This is because after long-term insulation, Sr segregates to the surface of the LSCF to form an insulating phase, which is the main reason for the performance degradation of the LSCF. Before high-temperature treatment, the Sr secondary phase content on the cathode surface of Comparative Example 8 was 26.89%, while after high-temperature insulation treatment, the Sr secondary phase content on the cathode surface increased the most. Before high-temperature treatment, the Sr secondary phase content on the cathode surface of Example 1 was 41.95%, which was higher than that of Comparative Example 7. This may be because during the solvothermal reaction, Sr segregated to form more Sr secondary phase on the cathode of Example 1. However, after 1000 h of heat preservation, the Sr secondary phase content on the cathode surface of Example 1 actually decreased to 38.29%, a reduction of 3.66% compared to before heat preservation. This is because some of the surface Sr combined with La elements in LNO to form La2SrO. x This prevents the formation of the surface insulating phase, thus the cathode material prepared in Example 1 has superior stability.

[0063] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A method for preparing a cathode material, characterized in that: Includes the following steps: A raw material comprising lanthanum metal salt, nickel metal salt, complexing agent and solvent is mixed to obtain an LNO impregnation solution; The cathode material is prepared by mixing the LNO impregnation solution and LSCF and then carrying out a solvothermal reaction. The total molar concentration of lanthanum ions and nickel ions in the LNO impregnation solution is 0.5~2 mol / L; The solvent comprises water and alcohol in a volume ratio of (0.4~0.8):1; The temperature of the solvothermal reaction is 100~150℃; The cathode material contains LSCF and La2NiO4; the molar ratio of LSCF to La2NiO4 is 1:(1~4). The LSCF is a cathode material for solid oxide fuel cells.

2. The method for preparing the cathode material according to claim 1, characterized in that: The solvothermal reaction takes 2-4 hours.

3. The method for preparing the cathode material according to claim 1, characterized in that: The molar ratio of the lanthanum metal salt to the nickel metal salt is (1~2):

1.

4. The method for preparing the cathode material according to claim 1, characterized in that: The ratio of the total molar number of lanthanum and nickel ions in the LNO impregnation solution to the molar number of the complexing agent is 1:(0.5~2).

5. The method for preparing the cathode material according to claim 1, characterized in that: The chemical formula of the LSCF is La. 1- x Sr x Co 1-y Fe y O3, 0 < x < 1; 0 < y < 1.

6. The method for preparing the cathode material according to claim 5, characterized in that: The chemical formula of the LSCF is La. 0.6 Sr 0.4 Co 0.2 Fe 0.8 O3, La 0.5 Sr 0.5 Co 0.8 Fe 0.2 O3 or La 0.8 Sr 0.2 Co 0.5 Fe 0.5 O3.

7. The method for preparing the cathode material according to claim 1, characterized in that: The particle size of the La2NiO4 is 45~65nm.

8. The method for preparing the cathode material according to claim 7, characterized in that: The La2NiO4 is distributed on the LSCF surface.

9. The method for preparing the cathode material according to any one of claims 1 to 8, characterized in that: The complexing agent is selected from at least one of citric acid, glycine, and gluconic acid; And / or, the lanthanum metal salt is selected from La(NO3)3, La(NO3)3 At least one of 6H2O and LaCl3; And / or, the nickel metal salt is selected from Ni(NO3)2. At least one of 6H2O, Ni(NO3)2, NiCl2, and Ni(CH3COO)2.

10. The application of the method for preparing the cathode material according to any one of claims 1 to 9 in the preparation of solid oxide fuel cells.

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