Method for preparing solid oxide fuel cell (SOFC) material from molten salt

Abstract

The invention relates to a method for preparing an SOFC (solid oxide fuel cell) material from molten salt, which comprises the following steps: by taking alkali metal mixed salt as a reaction medium and cerium salt and gadolinium salt as reactants, carrying out high-temperature treatment at the eutectic point temperature (550-700 DEG C) of the reaction medium, cooling, washing the product with deionized water, washing the reaction medium, and filtering to obtain the reaction product SOFC material. The preparation method has the advantages that the preparation process is simpler through a molten salt method, the electrolyte powder with higher sintering activity can be obtained, the electrolyte powder is more environmentally friendly, the particle size of the powder is smaller than 500 nm, the sintering density at 1250 DEG C is larger than or equal to 95%, no impurity phase exists in an X-ray diffraction (XRD) test, and the conductivity is larger than or equal to 0.04 S / cm at the temperature of 750 DEG C through the test.

Description

Technical Field

[0001] The invention relates to the technical field of solid oxide fuel cell materials, and in particular to a method for preparing SOFC materials with molten salt. Background Art

[0002] At present, the commonly used methods for synthesizing gadolinium-doped cerium oxide (GDC) and other solid oxide fuel cells (SOFC), SOFC electrolyte powders can be divided into solid phase method and liquid phase method (combustion method, co-precipitation method and sol-gel method, etc.).

[0003] Among them, the solid-phase method is the most commonly used method for large-scale preparation of powders, that is, the metal oxide raw materials are ground and mixed, and then directly subjected to solid-phase reaction at high temperature to obtain the desired product. However, the powder prepared by the solid-phase method has a large particle size, uneven distribution, high sintering temperature and low electrical conductivity.

[0004] The glycine combustion method is similar to the sol-gel method, in that the corresponding metal salt solution is dried and high-temperature solidified to obtain a precursor, and then high-temperature calcination is performed to prepare the desired product. The advantages are that the prepared powder has a small particle size, uniform distribution, and good sintering activity, but the yield is low, and the use of organic solvents causes cost and environmental pressure.

[0005] The coprecipitation powder is a coprecipitation of water and organic solvent. A precipitant is added to a metal salt solution to form a precipitate, and then the precipitate is separated from the liquid phase and dried to obtain a precursor. The precursor is calcined at high temperature to obtain the desired product. The advantages are similar to those of the combustion method and the sol-gel method, but the precipitated particles have poor dispersibility and fluidity and are easy to agglomerate.

[0006] Moreover, the powders prepared by the above-mentioned liquid phase method are all precursors, which require further high-temperature calcination to obtain the desired products.

[0007] The liquid phase method has not been widely used due to the complicated preparation process, high cost, and the environmental risks caused by the use of organic solvents. In addition, GDC prepared by conventional methods requires a high temperature of more than 1400°C to be sintered densely.

[0008] The molten salt method has been studied in the synthesis of ceramic powders with certain special morphologies, but it has hardly been used in the preparation of SOFC / SOEC powders. The performance of the GDC powders prepared by the method, especially the conductivity, has not yet been studied.

[0009] Therefore, it is of great significance to develop a method for preparing electrolyte powder that is more environmentally friendly, has a simpler preparation process, and has higher sintering activity. Summary of the invention

[0010] The task of the present invention is to overcome the deficiencies of the prior art and propose a method for preparing SOFC materials using molten salt, which can not only make the preparation process simpler through the molten salt method, but also obtain electrolyte powder with higher sintering activity and is more environmentally friendly.

[0011] The method for preparing SOFC materials by molten salt uses alkali metal mixed salt as the reaction medium, cerium salt and gadolinium salt as the reactants, performs high temperature treatment in the range of low eutectic temperature of the reaction medium (550-700°C), rinses the product with deionized water after cooling, rinses the reaction medium clean, and obtains the reaction product after filtering. The specific process steps and conditions are as follows:

[0012] A. According to Ce x G 1-x O y Weighing cerium salt and gadolinium salt in a stoichiometric ratio and uniformly mixing them to form salt 1;

[0013] B. Sodium chloride and potassium chloride are used as reaction medium, the molar ratio of sodium chloride to potassium chloride is 1:1-1:1.5, and they are evenly mixed to obtain salt 2;

[0014] C. Salt 1 and Salt 2 are uniformly mixed in a mass ratio of 1:5-1:10, and calcined at 550-750°C;

[0015] D. Rinse the calcined frit with deionized water, filter it, and dry it to obtain GDC powder.

[0016] Compared with the prior art, the present invention has the following advantages or effects:

[0017] Because the raw materials react in a molten salt medium, compared with ordinary solid-phase reactions and calcination of precursors, the mass transfer and heat transfer processes are faster and more complete, and the primary particle size of the powder is less than 500nm, so the sintering activity can be effectively improved; at the same time, due to the small primary particle size of the powder, the sintering activity is high, the sintering density at 1250℃ is ≥95%, and there is no impurity phase in the X-ray diffraction (XRD) test, so the medium salt is completely removed, the gadolinium doping is good, and there are no obvious impurities; in addition, due to the influence of powder particle size, density and doping conditions (oxygen vacancies), the tested conductivity at 750℃ is greater than or equal to 0.04S / cm.

[0018] The % mentioned in the application documents refers to mass percentage. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the method for preparing SOFC materials using molten salt proposed in the present invention.

[0020] Figure 2 for Figure 1Schematic diagram of XRD of GDC powder prepared by solid phase method.

[0021] Figure 3 Schematic diagram of XRD of GDC powder prepared by sol-gel method.

[0022] Figure 4 SEM schematic diagram of GDC powder prepared by solid phase method.

[0023] Figure 5 Schematic diagram of SEM (20000×) of GDC powder prepared by nitrate at different temperatures.

[0024] Figure 6 SEM schematic diagram of GDC powder prepared by molten salt at different temperatures.

[0025] Figure 7 SEM schematic diagram of GDC powder prepared by sol-gel method.

[0026] Figure 8 SEM schematic diagram of GDC powder prepared by sol-gel method.

[0027] The present invention is further described in detail below in conjunction with the accompanying drawings. DETAILED DESCRIPTION

[0028] like Figures 1 to 8 As shown in the figure, the method for preparing SOFC materials by molten salt aims at the problem of high sintering temperature and low conductivity of GDC powder. Alkali metal mixed salt is used as reaction medium, cerium salt and gadolinium salt are used as reactants, and high temperature treatment is performed in the range of low eutectic temperature of reaction medium (550-700℃). After cooling, the product is rinsed with deionized water, the reaction medium is rinsed clean, and the reaction product is obtained after filtering. The specific process steps and conditions are as follows:

[0029] A. According to Ce x G 1-x O y Weighing cerium salt and gadolinium salt in a stoichiometric ratio and uniformly mixing them to form salt 1;

[0030] B. Sodium chloride and potassium chloride are used as reaction medium, the molar ratio of sodium chloride to potassium chloride is 1:1-1:1.5, and they are evenly mixed to obtain salt 2;

[0031] C. Salt 1 and Salt 2 are uniformly mixed in a mass ratio of 1:5-1:10, and calcined at 550-750°C;

[0032] D. Rinse the calcined frit with deionized water, filter it, and dry it to obtain GDC powder.

[0033] The process of the present invention may further be:

[0034] The cerium salt and gadolinium salt may be nitrate, sulfate, acetate and chloride of cerium and gadolinium;

[0035] The reaction medium salt may also be a nitrate or sulfate of sodium, potassium or lithium;

[0036] The method is also applicable to the preparation of other electrolyte and electrode materials in SOFC.

[0037] Example 1

[0038] According to the stoichiometric ratio of Ce0.9Gd0.1O1.95, cerium nitrate and gadolinium nitrate were weighed and mixed to form salt 1; sodium chloride and potassium chloride were weighed in a molar ratio of 0.506:0.494 to form salt 2. Salt 1:Salt 2 was mixed in a mass ratio of 1:3 and placed in a crucible, and calcined at 550°C for 3h. After calcination, the frit was rinsed with deionized water and filtered to obtain light yellow GDC powder.

[0039] Example 2

[0040] According to the stoichiometric ratio of Ce0.9Gd0.1O1.95, cerium nitrate and gadolinium nitrate were weighed and mixed to form salt 1; sodium chloride and potassium chloride were weighed in a molar ratio of 0.506:0.494 to form salt 2. Salt 1:Salt 2 was mixed in a mass ratio of 1:3 and placed in a crucible, and calcined at 600°C for 3h. After calcination, the frit was rinsed with deionized water and filtered to obtain light yellow GDC powder.

[0041] Example 3

[0042] According to the stoichiometric ratio of Ce0.9Gd0.1O1.95, cerium nitrate and gadolinium nitrate were weighed and mixed to form salt 1; sodium chloride and potassium chloride were weighed in a molar ratio of 0.506:0.494 to form salt 2. Salt 1:Salt 2 was mixed in a mass ratio of 1:3 and placed in a crucible, and calcined at 650°C for 3h. After calcination, the frit was rinsed with deionized water and filtered to obtain light yellow GDC powder.

[0043] Example 4

[0044] Weigh cerium nitrate and gadolinium nitrate according to the stoichiometric ratio of Ce0.9Gd0.1O1.95 and mix them to form Salt 1; weigh sodium chloride and potassium chloride according to the molar ratio of 0.506:0.494 to form Salt 2. Mix them according to the mass ratio of Salt 1:Salt 2=1:3 and place them in a crucible, calcine at 700℃ for 3h, and after calcination, rinse the frit with deionized water and filter to obtain light yellow GDC powder Comparative Example 1

[0045] Cerium oxide and gadolinium oxide were weighed according to the stoichiometric ratio of Ce0.9Gd0.1O1.95, and appropriate amounts of deionized water and zirconium oxide balls were added for ball milling. Part of the ball-milled GDC slurry was taken out into a beaker and diluted to a solid content of about 30%. The slurry was spray dried using a spray dryer at a feed rate of 200 ml / min and an inlet temperature of 300°C. The dried GDC precursor was then placed in a high-temperature furnace and calcined at 650°C to obtain a light yellow GDC powder.

[0046] Comparative Example 2

[0047] Ce(NO3)4·6H2O and Gd(NO3)3·6H2O were dissolved in deionized water in a stoichiometric ratio. Polyethylene glycol and solid citric acid were added to the mixture at a ratio of 1.5 times that of metal ions under continuous stirring at room temperature to obtain a precursor solution of GDC. The obtained mixture was then dehydrated at a temperature of 75°C to obtain a dry gel, which was calcined at 650°C for 3h in a muffle furnace to obtain GDC powder.

[0048] The test results of the conductivity and density of the samples after sintering show that the conductivity and density of the samples prepared by the molten salt method are higher than those by the solid phase method. The reason may be that the powder particles prepared by the molten salt method are more uniform, the primary particles are fine, and the sintering activity is high. In addition, since the molten salt method has no mechanical mixing and drying process, no external impurities are introduced, and the influence of impurity atoms is small, the conductivity is higher, and the conductivity can reach the level of the sol-gel method.

[0049] Scanning Electron Microscope (SEM) results show that the particle size distribution of GDC powder prepared by the solid phase method is very uneven and the shape is irregular. The GDC powder prepared by the molten salt method at 550-600℃ has good dispersibility, and the primary particles are uniform particles of tens of nanometers. When the preparation temperature reaches above 650℃, the secondary particles are severely agglomerated, reaching more than 10μm.

[0050] XRD see Figure 3 , Figure 4 , Figure 5 It shows that the diffraction peaks of the products prepared by the molten salt method, solid phase method and sol-gel method are consistent with Ce0.9Gd0.1O1.95 (PDF#75-0161), without other impurities and no obvious peak shift.

[0051] In short, the molten salt method has a "dissolution-precipitation" process due to the presence of medium salt, which effectively improves the sintering activity and doping effect of GDC. Compared with the traditional solid phase method, the particle size is small and uniform, and the conductivity is high. Compared with the ordinary liquid phase method, there is no precursor preparation process, and the raw material to GDC powder only needs one calcination. The process is simpler, the reaction conditions are easier to control, and the conductivity and density can also reach the level of the ordinary liquid phase method.

[0052] The comparison of conductivity and sintering density of different methods is shown in the following table:

[0053]

[0054] As described above, the present invention can be better implemented. The above embodiments are only the best implementation methods of the present invention, but the implementation methods of the present invention are not limited by the above embodiments. Other changes, modifications, replacements, combinations, and simplifications made without departing from the spirit and principle of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. The method for preparing SOFC materials with molten salt is to solve the problem of high sintering temperature and low conductivity of GDC powder. It is characterized by Using alkali metal mixed salt as reaction medium, cerium salt and gadolinium salt as reactants, high temperature treatment is performed in the range of low eutectic temperature of the reaction medium (550-700°C), and the product is rinsed with deionized water after cooling, the reaction medium is rinsed clean, and the reaction product is obtained after filtering. The specific process steps and conditions are as follows: A. According to Ce x G 1-x O y Weighing cerium salt and gadolinium salt in a stoichiometric ratio and uniformly mixing them to form salt 1; B. Sodium chloride and potassium chloride are used as reaction medium, the molar ratio of sodium chloride to potassium chloride is 1:1-1:1.5, and they are evenly mixed to obtain salt 2; C. Salt 1 and Salt 2 are uniformly mixed in a mass ratio of 1:5-1:10, and calcined at 550-750°C; D. Rinse the calcined frit with deionized water, filter it, and dry it to obtain GDC powder.

2. The method according to claim 1, characterized in that The cerium salt and gadolinium salt may be nitrates, sulfates, acetates and chlorides of cerium and gadolinium.

3. The method according to claim 1, characterized in that The reaction medium salt may also be a nitrate or sulfate of sodium, potassium or lithium.

4. The method according to claim 1, 2 or 3, characterized in that It is also suitable for preparing other electrolyte and electrode materials in SOFC.

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