Modified SOFC electrolyte ceramic material and preparation method thereof

Abstract

The invention discloses a modified SOFC (solid oxide fuel cell) electrolyte ceramic material and a preparation method thereof, and the preparation method comprises the following steps: S1, adding sintering-assisting elements into a fluorite phase matrix by using a grain boundary preferred segregation or lattice solid solution mode, and preparing corresponding powder; s2, drying the powder prepared in the step S1 in a drying box; and S3, mixing the powder dried in the step S2 with a binder, carrying out dry pressing molding, and sintering in a high-temperature muffle furnace to obtain a final sintered sample. While the sintering performance is improved, the electric conduction behavior is further differentially regulated and controlled through micro regulation and control of a grain boundary and a lattice structure.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrolyte ceramic materials, and in particular relates to a modified SOFC electrolyte ceramic material and a preparation method thereof. Background Art

[0002] Due to good oxygen ion conductivity and chemical stability, fluorite-structured materials such as SDC are widely used in the oxygen ion conduction phase of oxygen permeable membranes and SOFC electrolytes. However, the densification sintering temperature of SDC is too high (1400 °C - 1600 °C), making it difficult to co-fire with other materials. Reducing its sintering temperature has become a common need in the industry. At the same time, different target requirements also vary for the electrolyte conductance behavior. In addition to the common need to improve the total conductivity, different target products have different requirements for mixed ion-electron conduction ability, grain boundary and grain conductance, etc. Therefore, it is of great significance to improve the sintering performance of fluorite-structured materials such as SDC and simultaneously regulate their conductance behavior. Summary of the Invention

[0003] In view of this, the present invention aims to provide a modified SOFC electrolyte ceramic material and a preparation method thereof to solve at least one technical problem in the background art.

[0004] To achieve the above object, the technical solution of the present invention is realized as follows: A modified SOFC electrolyte ceramic material, in which a sintering aid element is added to the fluorite-phase matrix, and the sintering aid element includes one or more of Cu, Co, or Fe.

[0005] Further, the addition method of the sintering aid element to the fluorite-phase matrix is one of grain boundary preferred segregation or lattice solid solution; And / or, the fluorite-phase matrix includes SDC.

[0006] Further, the addition content of the sintering aid element is 1 mol% - 5 mol%.

[0007] The preparation method of the above-mentioned modified SOFC electrolyte ceramic material includes the following steps: S1: Add the sintering aid element to the fluorite-phase matrix by grain boundary preferred segregation or lattice solid solution, and prepare the corresponding powder; S2: Dry the powder prepared in step S1 in a drying oven; S3: Mix the dried powder in step S2 with a binder, press it into a shape by dry pressing, and obtain the final sintered sample after sintering in a high-temperature muffle furnace.

[0008] Further, the powder preparation method for grain boundary preferred segregation in step S1 includes: Put the nitrate of the sintering aid elements into an ethanol solution, grind to accelerate its dissolution, then immerse the prepared fluorite-phase matrix in the salt solution, stir and grind for 0.8 - 1.2 h, place it in a drying oven and dry at 70 - 80 °C for 9 - 11 h. Grind the dried powder again for 0.8 - 1.2 h, and finally put it into a low-temperature muffle furnace, keep it warm for 4 - 6 h with the same calcination regime as the SDC powder, and grind it again for 0.8 - 1.2 h to ensure the uniform distribution of the sintering aid elements.

[0009] Further, the preparation method of the lattice solid solution powder in step S1 includes the following steps: Put the nitrate of the sintering aid elements, cerium salt, and samarium salt into deionized water, heat and stir. After complete dissolution, add ethylenediaminetetraacetic acid and citric acid monohydrate, adjust the pH, heat and stir, dry, and then put it into a low-temperature muffle furnace to keep it warm to obtain the final required powder; The cerium salt is cerium nitrate hexahydrate, and the samarium salt is samarium nitrate hexahydrate; The nitrate of the sintering aid elements includes one or more of copper salt using copper nitrate, cobalt salt using cobalt nitrate hexahydrate, and iron salt using iron nitrate nonahydrate.

[0010] Further, the heating and stirring temperature in step S1 is 85 °C - 90 °C, and the stirring speed is 100 - 200 rpm. The molar ratio of the total metal ions, EDTA, and citric acid in the preparation process is 1:1:1.2 - 1.7; Use ammonia water to adjust the pH to 6 - 8, the drying oven temperature is 140 - 160 °C, the muffle furnace holding temperature is 500 - 600 °C, and the time is 4 - 6 h.

[0011] Further, the drying temperature in step S2 is 75 °C - 85 °C, and the time is 7 - 12 h.

[0012] Further, the powder in step S3 is mixed with a PVA binder, dry-pressed into a green compact, sintered in a high-temperature muffle furnace to obtain the final sintered sample, pressed and sintered with the fired SDC sheet, and finally polished with 400 - 600 mesh SiC sandpaper; The dry-pressing pressure in step S3 is 150 - 200 MPa, the pressure holding time is 2 - 3 min, the high-temperature muffle furnace holding temperature is 1250 °C - 1500 °C, and the time is 5 - 10 h.

[0013] Compared with the prior art, the modified SOFC electrolyte ceramic material and its preparation method of the present invention have the following advantages: The present invention adds Co, Cu, and Fe sintering aid elements to the SDC fluorite phase in the form of grain boundary preferred segregation and lattice solid solution. While improving its sintering performance, through the microscopic regulation of the grain boundary and lattice structure, its conductivity behavior is further differentially regulated. It can be applied to specific target products such as solid oxide fuel cell electrolytes and oxygen ion conducting phases of biphasic oxygen permeable membranes according to different purposes. The present invention provides an innovative idea for the modification of the fluorite structure, especially the introduction of the grain boundary preferred segregation method, as well as the two addition methods of lattice solid solution and solid solution, and the differential regulation of the SDC fluorite phase by different sintering aid elements and contents. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings: Figure 1 is the XRD pattern of the modified SDC powder and partial sintered tablets prepared by the SS and GBS methods; Figure 2 are the morphologies, element distributions, and particle size statistics of some samples prepared according to the method of the present invention; Figure 3 are the high-resolution and internal grain strain distribution images of the representative samples prepared by the SS method according to the method of the present invention; Figure 4 are the high-resolution and internal grain strain distribution images of the representative samples prepared by the GBS method according to the method of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0015] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0016] The present invention will be described in detail below with reference to the drawings and in combination with the embodiments.

[0017] A modified SOFC electrolyte ceramic material and its preparation method are as follows: According to the chemical formula of the material, calculate and accurately weigh the required cerium nitrate hexahydrate (Ce(NO3)3·6H2O) and samarium nitrate hexahydrate (Sm(NO3)3·6H2O). According to the ratio of total metal ion mass of the material in the preparation process: mass of EDTA acid: mass of citric acid = 1:1:1.5, slowly add EDTA acid and citric acid, and adjust the pH of the solution to 6~8 with ammonia water. Continue to heat and stir at 85℃-90℃ until the solution becomes gel-like, then place it in a drying oven at 150℃ for 12 hours. After it becomes black and fluffy, take out the sample and heat it in a flat furnace to burn off the organic matter. After stirring without sparks, put it in a low-temperature muffle furnace and keep it at 550℃ for 5 hours to obtain the final required SDC fluorite phase powder; Weigh the corresponding content of copper nitrate (Cu(NO3)2), cobalt nitrate hexahydrate (Co(NO3)2·6H2O) or iron nitrate nonahydrate (Fe(NO3)3·9H2O), put it into an ethanol solution, and grind it to accelerate its dissolution. Then soak the prepared SDC powder in the nitrate solution, 1 g SDC powder corresponds to 1~1.5 mL solution. The resulting mixture is stirred and ground in an agate mortar for 1 h to mix it evenly, then placed in a drying oven at 75 ° C for 10 h, and the dried powder is ground again for 1 h. Finally, it is placed in a low-temperature muffle furnace, kept warm for 5 h using the same calcination system as the SDC powder, and ground again for 1 h to ensure the uniform distribution of the sintering elements; The prepared powder is placed in a drying oven at 75°C-85°C for 7-12 hours for drying; The powder and binder PVA were mixed at 1 wt% and placed in an agate mortar for uniform grinding. After drying in a drying oven, the mixture was re-ground to fineness. A certain amount of powder was weighed according to the thickness of the membrane and placed in a stainless steel mold. After being evenly spread, the powder was placed in an infrared tablet press at 150-200MPa for 2-3min to obtain a formed blank. The blank was then placed on an alumina plate and placed in a muffle furnace for 5 h at 1250℃-1500℃ in an air atmosphere. Finally, it was polished with 500-mesh sandpaper to obtain the final densified oxygen-permeable membrane. Considering the effect of rapid temperature rise and fall on the membrane, the sintering system was selected in a segmented form. Within the range of 200℃ before the temperature rise and fall time, the temperature rise and fall rate was set to 1℃·min -1 In the rest of the temperature range, the heating and cooling rate is set to 2℃·min -1 In this process, in order to prevent cracking and deformation, the fired SDC sheet is pressed and fired.

[0018] like Figure 1As shown in the figure, this embodiment uses a modified SOFC electrolyte ceramic material and its preparation method to prepare SDC electrolytes modified with different sintering aid element contents and different addition methods. The characteristic diffraction peaks corresponding to the cubic fluorite structure of all samples are basically formed, and the positions of the diffraction peaks match well with those of face-centered cubic fluorite-structured CeO2 (PDF#34-0394, a = b = c = 5.411 Å), and they respectively belong to the (111), (200), (220), (311), (222), (400), (331), and (420) crystal planes, and the corresponding 2θ values are located at 28.5°, 33.1°, 47.5°, 56.3°, 59.1°, 69.4°, 76.7°, and 79.1°. No impurity peaks of the second phase are found, indicating that the CeO2 solid solution with the space group Fm-3m has been formed.

[0019] As Figure 2 shown, for the sample morphology, element distribution, and particle size statistics of some samples prepared in this embodiment, the grain sizes are concentrated between 10 nm and 35 nm, and the average grain sizes are 25.02 nm and 24.29 nm respectively, which are roughly equivalent to the XRD calculation results. The matrix elements Ce and Sm and the added sintering aid elements are evenly distributed.

[0020] As Figure 3 shown, the high-resolution and grain internal strain distribution images of the representative samples prepared by the SS method according to the method of the present invention. Figure (b) is the diffraction pattern obtained by performing a Fast Fourier Transform (FFT) on (a). According to the calibration results, it can be known that this grain is the SDC fluorite phase, and the interplanar spacing of its (111) crystal plane is 3.07 Å. Compared with the standard PDF card (PDF#75-0158), the interplanar spacing has a slight decrease, which is mainly caused by the sintering aid elements added by the SS method entering the SDC lattice and substituting Sm3+, further confirming the XRD result analysis. At the same time, as shown in the atomic signal intensity distribution along the L line direction in Figure (d), some atoms with weak signal intensities are observed, which may be due to the solid solution of the sintering aid elements into the grain interior or the existence of vacancies.

[0021] As Figure 4 shown, the high-resolution and grain internal strain distribution images of the representative samples prepared by the GBS method according to the method of the present invention. After FFT and calibration, in addition to the matrix SDC with a face-centered cubic fluorite structure (space group: Fm-3m), grains of hexagonal Co2O3 (PDF#02-0770) are also found to exist. For the samples added by the GBS method, the sintering aid elements mainly exist in the form of oxides at low temperatures at the grain boundaries. The change in the grain boundary distribution by the sintering aid has a significant impact on the reduction of the grain boundary resistance and the ion and electron conduction.

[0022] This material is based on cerium-doped fluorite Ce 0.8 Sm 0.2 O 2-δ (SDC). Different amounts of sintering aid elements such as Co, Cu or Fe are introduced in the form of lattice solid solution (SS) or grain boundary preferred segregation (GBS). While significantly reducing the sintering temperature, the conductance behavior is improved through the microscopic regulation of the grain boundary and lattice structure. Since the types, contents and addition methods of the sintering aids have different effects and influence mechanisms on the total conductivity, grain / grain boundary conductance and ionic / electronic conductance of SDC, their sintering performance and conductance behavior are different, and they can be applied to specific target products such as the electrolyte of solid oxide fuel cells (SOFC) and the oxygen ion conduction of the dual-phase oxygen permeable membrane according to different purposes.

[0023] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A modified SOFC electrolyte ceramic material, characterized in that: A sintering-aiding element is added to the fluorite phase matrix, and the sintering-aiding element includes one or more of Cu, Co or Fe.

2. A modified SOFC electrolyte ceramic material according to claim 1, characterized in that: The addition of sintering aid elements to the fluorite phase base can be divided into one of the following: preferential segregation at grain boundaries or solid solution in the lattice; And / or, the fluorite phase matrix includes SDC.

3. The modified SOFC electrolyte ceramic material according to claim 1, characterized in that: The content of sintering aid elements added is 1 mol%-5 mol%.

4. A method for preparing a modified SOFC electrolyte ceramic material according to any one of claims 1 to 3, characterized in that: The steps include: S1: Add the sintering aid elements to the fluorite phase matrix by using the grain boundary preferential segregation or lattice solid solution method, and prepare the corresponding powder; S2: drying the powder prepared in step S1 in a drying oven; S3: Mix the powder dried in step S2 with a binder, dry-press and form, and sinter in a high-temperature muffle furnace to obtain a final sintered sample.

5. The method for preparing a modified SOFC electrolyte ceramic material according to claim 4, characterized in that: The method for preparing the powder with preferential grain boundary segregation in step S1 includes: The nitrate of the sintering element is placed in an ethanol solution and ground to accelerate its dissolution. The prepared fluorite phase matrix is ​​then immersed in the salt solution, stirred and ground for 0.8-1.2 hours, placed in a drying oven and dried at 70-80°C for 9-11 hours, the dried powder is ground again for 0.8-1.2 hours, and finally placed in a low-temperature muffle furnace, kept warm for 4-6 hours using the same calcination system as the SDC powder, and ground again for 0.8-1.2 hours to ensure uniform distribution of the sintering element.

6. The method for preparing a modified SOFC electrolyte ceramic material according to claim 4, characterized in that: The method for preparing the lattice solid solution powder in step S1 comprises the following steps: Nitrate, cerium salt and samarium salt containing sintering aid elements are placed in deionized water, heated and stirred, and after complete dissolution, ethylenediaminetetraacetic acid and citric acid monohydrate are added, the pH is adjusted, heated and stirred, and after drying, the mixture is placed in a low-temperature muffle furnace for heat preservation to obtain the final desired powder.

7. The method for preparing a modified SOFC electrolyte ceramic material according to claim 6, characterized in that: The cerium salt is cerium nitrate hexahydrate, and the samarium salt is samarium nitrate hexahydrate; The nitrate containing the combustion-aiding element includes one or more of copper salt using copper nitrate, cobalt salt using cobalt nitrate hexahydrate, and iron salt using ferric nitrate nonahydrate.

8. The method for preparing a modified SOFC electrolyte ceramic material according to claim 6, characterized in that: The heating and stirring temperature is 85 ℃-90 ℃, and the stirring speed is 100-200 rpm. During the preparation process, the molar ratio of total metal ions, EDTA, and citric acid in the material is 1:1:1.2-1.7; Use ammonia water to adjust the pH to 6-8, the drying oven temperature is 140-160℃, the muffle furnace insulation temperature is 500-600℃, and the time is 4-6h.

9. The method for preparing a modified SOFC electrolyte ceramic material according to claim 3, characterized in that: The drying temperature in step S2 is 75°C-85°C and the drying time is 7-12 hours.

10. The method for preparing a modified SOFC electrolyte ceramic material according to claim 3, characterized in that: The powder in step S3 is mixed with a PVA binder, and a green blank is obtained by dry pressing. The final sintered sample is obtained after sintering in a high-temperature muffle furnace. The sintered SDC sheet is used for press firing, and the film is finally polished with 400-600 mesh SiC sandpaper; The dry pressing pressure in step S3 is 150-200 MPa, the holding time is 2-3 min, the holding temperature of the high-temperature muffle furnace is 1250° C.-1500° C., and the holding time is 5-10 h.

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