Preparation method of perovskite type solid oxide fuel cell cathode material

Abstract

The invention discloses a preparation method of a perovskite type solid oxide fuel cell cathode material, and relates to the technical field of solid oxide fuel cells. According to the method, the problem that the molar ratio of each element in the product LSCF does not accord with a design value due to the difference of crystal growth speeds in the precipitation process of different cations is solved through a step-by-step precipitation method, and the high-activity LSCF powder which is uniform in component, excellent in microstructure and excellent in electrochemical performance is obtained to serve as a cathode material to meet the high-performance requirement of an SOFC (Solid Oxide Fuel Cell).

Description

Technical Field

[0001] This invention relates to the field of solid oxide fuel cell technology, and specifically to a method for preparing a perovskite-type solid oxide fuel cell cathode material. Background Technology

[0002] Solid oxide fuel cells (SOFCs), as a highly efficient and clean energy conversion device, can directly convert the chemical energy in fuel into electrical energy, offering advantages such as wide fuel adaptability, high power generation efficiency, and environmental friendliness. The cathode, as a crucial component of the SOFC, directly affects the overall performance and lifespan of the battery.

[0003] La x Sr 1-x Co y Fe 1-y O 3-δ LSCF (sulfurized carbon dioxide) is a composite oxide with a perovskite structure. Due to its excellent oxygen ion conductivity, high catalytic activity for oxygen reduction reactions, and good thermochemical stability in the mid-temperature range (600-800℃), it has become one of the most promising SOFC cathode materials. However, LSCF cathode materials prepared by traditional methods have shortcomings in microstructure, particle size, and uniformity, resulting in underdeveloped electrochemical performance. For example, while the solid-state reaction method is relatively simple to operate, it requires high-temperature sintering (generally 1200℃), which easily leads to raw material volatilization and particle agglomeration, resulting in a small specific surface area and insufficient active sites. The sol-gel method, although it can improve the microstructure to some extent, is complex, costly, and difficult to scale up for mass production. The co-precipitation method uses sodium carbonate as a precipitant, but sodium ions cannot be completely washed away, often resulting in a residual amount of up to 5 wt% in the material, affecting the output performance and service life of the SOFC. Using ammonium carbonate as a precipitant results in cobalt ions forming soluble complexes (such as [Co(NH3)6)). 2+ The inability to completely precipitate the perovskite material alters the stoichiometric ratio of the product, thus affecting the stability of the perovskite structure and the catalytic activity of the cathode. Therefore, developing a method for preparing highly active LSCF cathode materials with excellent microstructure, stable performance, and suitability for industrial production is of great significance. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for preparing LSCF powder. By using a stepwise precipitation method, the problem that the molar ratio of each element in the LSCF product does not match the design value due to the difference in crystal growth rate during the precipitation of different cations is solved. The method obtains highly active LSCF powder with uniform composition, excellent microstructure and excellent electrochemical performance, which can be used as a cathode material to meet the high performance requirements of SOFC.

[0005] The technical problem to be solved by this invention is achieved by the following technical solution: One objective of this invention is to provide a method for preparing LSCF powder, comprising the following steps: S1. Dissolve lanthanum salt, strontium salt and iron salt in deionized water, then add precipitant. After lanthanum, strontium and iron are completely precipitated, filter, wash with water and dry to obtain precipitate I. S2. Dissolve the cobalt salt in deionized water, then add a precipitant. After the cobalt has completely precipitated, filter, wash with water, and dry to obtain precipitate II. S3. Mix precipitate I and precipitate II evenly, calcine, and crush to obtain LSCF powder.

[0006] Furthermore, the lanthanum salt includes, but is not limited to, one or more of lanthanum chloride, lanthanum nitrate, lanthanum sulfate, and their hydrates.

[0007] Furthermore, the strontium salt includes, but is not limited to, one or more of strontium chloride, strontium nitrate, and their hydrates.

[0008] Furthermore, the iron salt includes, but is not limited to, one or more of ferric chloride, ferric nitrate, ferric sulfate, and their hydrates.

[0009] Furthermore, the cobalt salt includes, but is not limited to, one or more of cobalt chloride, cobalt nitrate, cobalt sulfate, and their hydrates.

[0010] Furthermore, the molar ratio of lanthanum, strontium, iron, and cobalt in the lanthanum salt, strontium salt, iron salt, and cobalt salt is 6:4:8:2.

[0011] This invention uses water-soluble lanthanum salts, strontium salts, iron salts and cobalt salts as raw materials and water as a solvent, thereby reducing solvent costs and improving the environmental friendliness of the process.

[0012] Further, the precipitant is at least one selected from ammonium carbonate, ammonium bicarbonate, sodium hydroxide, and potassium hydroxide. The precipitant is added dropwise to the metal salt solution in the form of an aqueous solution, reacting with the metal ions to form a precipitate that is insoluble in water. In step S1, ammonium carbonate or ammonium bicarbonate is preferred as the precipitant because strontium hydroxide, formed by the reaction of sodium hydroxide or potassium hydroxide with strontium salt, has high solubility in water.

[0013] Further, in step S1, the molar ratio of the anions in the precipitant to the metal cations in the lanthanum, strontium, and iron salts is ≥1.5:1, wherein the metal cations include lanthanum ions, strontium ions, and iron ions; in step S2, the molar ratio of the anions in the precipitant to the cobalt ions in the cobalt salt is ≥1:1.

[0014] Furthermore, the mixing method is ball milling, preferably wet ball milling.

[0015] Furthermore, the calcination temperature is 700~1000℃, and the holding time is 1~3 h. Calcination transforms the composite metal carbonate into an LSCF perovskite structure.

[0016] The second objective of this invention is to provide an LSCF powder obtained by the aforementioned preparation method.

[0017] Furthermore, the molecular formula of the LSCF is La. 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-σ .

[0018] Furthermore, the LSCF powder has a particle size of D50 of 0.2±0.05 μm and a specific surface area of ​​7~9 m2 / g.

[0019] A third objective of this invention is to provide the application of the LSCF powder in SOFC.

[0020] The fourth objective of this invention is to provide a SOFC that uses the LSCF powder as the cathode material.

[0021] The beneficial effects of this invention are as follows: By separately precipitating the LCF precursor and the cobalt precursor, this invention avoids the problem of incomplete cobalt precipitation, ensuring that the molar ratio of each element in the product LSCF matches the design value; at the same time, the minimum calcination temperature required for LSCF phase formation is 700℃, which is significantly lower than the 1200℃ required by the solid-state method, thus minimizing cobalt volatilization and helping to ensure the stability of the element ratio in the product; furthermore, the prepared LSCF, due to its small particle size and high specific surface area, increases oxygen reduction active sites and has lower polarization resistance, making it suitable as a cathode material to meet the high-performance requirements of SOFC. Attached Figure Description

[0022] Figure 1 SEM image of the LSCF powder prepared in Example 1; Figure 2 The image shows the XRD pattern of the LSCF powder prepared in Example 1. Figure 3 SEM image of the LSCF powder prepared in Comparative Example 1; Figure 4 The image shows the XRD pattern of the LSCF powder prepared in Comparative Example 1. Detailed Implementation

[0023] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific embodiments and illustrations.

[0024] Example 1 Preparation of LSCF powder: S1. Ammonium carbonate (259.2 g, 2.7 mol) was dissolved in 1000 mL of deionized water by stirring to obtain an ammonium carbonate solution. Lanthanum nitrate hexahydrate (259.8 g, 0.6 mol), strontium nitrate (84.4 g, 0.4 mol), and ferric nitrate nonahydrate (323.2 g, 0.8 mol) were dissolved in 1000 mL of deionized water by stirring. Then, the ammonium carbonate solution was added dropwise. After the addition was completed, the mixture was stirred for 2 h to form a precipitate. The precipitate was filtered, and the residue was washed with deionized water and anhydrous ethanol in sequence. The residue was dried in a vacuum environment at 80 °C for 12 h to obtain lanthanum-strontium-iron composite carbonate.

[0025] S2. Dissolve 19.2 g, 0.2 mol of ammonium carbonate in 80 mL of deionized water to obtain an ammonium carbonate solution. Dissolve 58.2 g, 0.2 mol of cobalt nitrate hexahydrate in 100 mL of deionized water, then add the ammonium carbonate solution dropwise. After the addition is complete, continue stirring for 2 h to form a precipitate. Filter the solution, wash the residue with deionized water and anhydrous ethanol in sequence, and dry it under vacuum at 80 °C for 12 h to obtain cobalt carbonate.

[0026] S3. 122.7 g of lanthanum-strontium-iron composite carbonate and 14.4 g of cobalt carbonate were mixed evenly by wet ball milling and dried under vacuum at 80°C for 12 h. Then, the mixture was calcined in a muffle furnace at 800°C for 2 h, followed by wet ball milling with zirconium beads (particle size of 2 mm). Finally, the mixture was dried under vacuum at 80°C for 12 h to obtain LSCF powder.

[0027] Preparation of symmetric cells: (1) Take 2.5 g of GDC powder (molecular formula (Ce) 0.90 Gd 0.10 )O 1.95 Particles with a D50 of 0.2 μm were packed into a cylindrical mold (13 mm in diameter) and pressed into circular blanks under a pressure of 400 MPa. The blanks were then calcined in a muffle furnace at 1400 °C for 4 h to obtain GDC electrolyte sheets.

[0028] (2) The LSCF powder prepared in Example 1 was mixed with terpineol, anhydrous ethanol and PVB in a mass ratio of 10:12:3:0.5 and ball-milled to obtain LSCF slurry.

[0029] (3) Coat one side of the GDC electrolyte sheet with LSCF slurry to a thickness of 100 μm and dry at 80°C. Then repeat the coating process on the other side of the GDC electrolyte sheet.

[0030] (4) The coated sample was calcined in a muffle furnace at 1250°C for 2 h and then cooled to obtain a symmetrical cell.

[0031] Polarization impedance test: The symmetrical cell prepared in Example 1 was placed in a tube furnace and heated to 700°C in air atmosphere for 30 min to ensure uniform temperature. The electrochemical impedance spectroscopy (EIS) method was used, with a 10 mV AC signal applied using a frequency response analyzer, and the frequency range set to 1 MHz to 0.01 Hz. The impedance spectrum was recorded. The polarization impedance (Ro) of the cell was calculated by fitting an equivalent circuit. p A higher polarization impedance indicates increased resistance to the reduction reaction at the cathode, requiring additional voltage to drive the reaction and thus reducing the battery's actual output voltage. Furthermore, polarization impedance leads to energy loss during charging and discharging, reducing the battery's energy conversion efficiency.

[0032] Examples 2-5 and Comparative Examples 1-2 LSCF powder was prepared according to the method in Example 1, except that the calcination temperature and holding time in step S3 were adjusted, as shown in Table 1.

[0033] Symmetric cells were prepared according to the method in Example 1 and their polarization impedance was tested. The results are shown in Table 1.

[0034] Table 1 As can be seen from Table 1, the polarization resistance of Comparative Examples 1-2 increased significantly after calcination at 650℃. The main reason is that the calcination temperature was too low, the raw materials could not react completely, and unreacted substances were present in the product.

[0035] Examples 6-7 LSCF powder was prepared according to the method in Example 1, except that the types of lanthanum salt, strontium salt, cobalt salt, and iron salt were adjusted, as shown in Table 2.

[0036] Symmetric cells were prepared according to the method in Example 1 and their polarization impedance was tested. The results are shown in Table 2.

[0037] Table 2 As can be seen from Table 2, using different types of water-soluble lanthanum salts, strontium salts, cobalt salts, and iron salts as raw materials for the preparation of LSCF powder will not have a significant impact on the polarization impedance of the battery.

[0038] Example 8 and Comparative Examples 3-4 LSCF powder was prepared according to the method in Example 1, except that the type of precipitant was adjusted, as shown in Table 3.

[0039] Symmetric cells were prepared according to the method in Example 1 and their polarization impedance was tested. The results are shown in Table 3.

[0040] Table 3 As shown in Table 3, compared to ammonia and sodium carbonate, using ammonium carbonate or ammonium bicarbonate as a precipitant can significantly reduce the polarization impedance of the battery. This is because strontium hydroxide has higher solubility, with a Ksp of 3.2 × 10⁻⁶ at 25 °C. -4 When ammonia is used as a precipitant, strontium cannot be completely precipitated, and the unprecipitated strontium will be lost during washing. When sodium carbonate is used as a precipitant, sodium is difficult to wash away completely, and a large number of sodium ions are present in the product, which leads to poor LSCF tolerance and increased LSCF polarization resistance.

[0041] Comparative Example 5 The raw materials were weighed according to the proportions in Example 1, except that LSCF powder was prepared by co-precipitation.

[0042] S1. Ammonium carbonate (278.4 g, 2.9 mol) was dissolved in 1080 mL of deionized water by stirring to obtain an ammonium carbonate solution. Lanthanum nitrate hexahydrate (259.8 g, 0.6 mol), strontium nitrate (84.4 g, 0.4 mol), ferric nitrate nonahydrate (323.2 g, 0.8 mol), and cobalt nitrate hexahydrate (58.2 g, 0.2 mol) were dissolved in 1100 mL of deionized water by stirring. Then, the ammonium carbonate solution was added dropwise. After the addition was completed, stirring was continued for 2 h to form a precipitate. The precipitate was filtered, and the residue was washed successively with deionized water and anhydrous ethanol. It was then dried in a vacuum environment at 80 °C for 12 h to obtain lanthanum-strontium-iron-cobalt composite carbonate.

[0043] S2. The lanthanum-strontium-iron-cobalt composite carbonate was mixed evenly by wet ball milling and dried in a vacuum environment at 80°C for 12 hours. Then it was calcined in a muffle furnace at 800°C for 2 hours, followed by wet ball milling with zirconium beads (particle size of 2 mm). Finally, it was dried in a vacuum environment at 80°C for 12 hours to obtain LSCF powder.

[0044] Symmetric cells were prepared according to the method in Example 1 and their polarization impedance was tested. The results are shown in Table 4.

[0045] Table 4 As shown in Table 4, the polarization impedance of LSCFs prepared by co-precipitation of La, Sr, Co, and Fe is significantly increased. This is because Co cannot be completely precipitated in ammonium salts (forming a cobalt-ammonia solution), while cobalt mainly enhances the oxygen reduction catalytic activity in LSCFs.

[0046] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing an LSCF powder, characterized by, The preparation method comprises the following steps: S1, dissolving lanthanum salt, strontium salt and iron salt in deionized water, then adding a precipitant, filtering after lanthanum-strontium-iron precipitates completely, washing with water, drying to obtain precipitate I; S2, dissolving cobalt salt in deionized water, then adding a precipitant, filtering after cobalt precipitates completely, washing with water, drying to obtain precipitate II; S3, mixing precipitate I and precipitate II uniformly, calcining, crushing to obtain LSCF powder.

2. The method of claim 1, wherein: The lanthanum salt is one or more of lanthanum chloride, lanthanum nitrate, lanthanum sulfate and hydrates thereof; The strontium salt is one or more of strontium chloride, strontium nitrate and hydrates thereof; The iron salt is one or more of iron chloride, iron nitrate, iron sulfate and hydrates thereof; The cobalt salt is one or more of cobalt chloride, cobalt nitrate, cobalt sulfate and hydrates thereof.

3. The method of claim 1, wherein: The element molar ratio of lanthanum, strontium, iron and cobalt in the lanthanum salt, strontium salt, iron salt and cobalt salt is 6:4:8:

2.

4. The method of claim 1, wherein: The precipitant is at least one of ammonium carbonate, ammonium bicarbonate, sodium hydroxide and potassium hydroxide.

5. The method of claim 1, wherein: In step S1, the molar ratio of acid radical ions in the precipitant to metal cations in the lanthanum salt, strontium salt and iron salt is ≥1.5:1, wherein the metal cations include lanthanum ions, strontium ions and iron ions; In step S2, the molar ratio of acid radical ions in the precipitant to cobalt ions in the cobalt salt is ≥1:

1.

6. The method of claim 1, wherein: The calcination temperature is 700-1000°C, and the holding time is 1-3 h.

7. LSCF powder obtained by the preparation method of any one of claims 1-6.

8. The LSCF powder of claim 7, wherein: The molecular formula of the LSCF is La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-σ ; Preferably, the particle size of the LSCF powder is D50 of 0.2±0.05 μm, and the specific surface area is 7-9 m2 / g.

9. Application of the LSCF powder of claim 7 or 8 in SOFC.

10. A SOFC taking the LSCF powder of claim 7 or 8 as a cathode material.

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