Preparation method and application of low-temperature sintered iron oxide doped 8YSZ electrolyte

Abstract

The invention discloses a preparation method and application of a low-temperature sintered iron oxide doped 8YSZ electrolyte, and relates to the technical field of inorganic materials. The preparation method comprises the following steps: dissolving yttrium nitrate hexahydrate, zirconium oxychloride octahydrate and ferric nitrate nonahydrate into distilled water to enable the concentration of metal ions to be 0.5 mol / L; adding polyethylene glycol; then, dropwise adding a concentrated ammonia water precipitator with the concentration of 13 mol / L into the solution, and stirring until the pH value of the solution is equal to 8; and standing the mixed solution and aging for 4 hours. Carrying out centrifugal treatment, water washing and centrifugation on the aged product; adding absolute ethyl alcohol into the washed solid, carrying out alcohol washing, and centrifuging; drying at 80 DEG C for 48 hours; putting the dried powder into an agate mortar, and grinding, so as to obtain FeO < 1.5-8 > YSZ precursor powder; treating the precursor at 800 DEG C for 2 hours, and grinding; and carrying out compression molding on the powder by using a dry pressing method, and sintering to obtain the electrolyte.

Description

Technical Field

[0001] The present invention relates to the technical field of inorganic materials, and in particular to a zirconium oxide (Y2O3) that reduces the stability of yttrium oxide, an oxygen ion conducting electrolyte. 0.08 (ZrO2) 0.92 (8YSZ) Sintering temperature method and application. Background Art

[0002] Solid oxide fuel cells are highly efficient and clean energy conversion devices. The performance optimization of their core electrolyte materials is the key to industrialization. The device adopts a sandwich structure design, consisting of a porous electrode and a dense electrolyte. The electrolyte layer has the dual functions of ion conduction and gas barrier. Its performance index directly affects the output efficiency and durability of the battery. The ideal electrolyte material must meet four-dimensional characteristics: (i) excellent pure oxygen ion conductivity, (ii) zero electronic conductivity, (iii) reliable atmosphere stability, and (iv) mechanical strength. The current mainstream electrolyte system presents a ternary pattern: zirconium dioxide (ZrO2)-based, cerium dioxide (CeO2)-based and lanthanum gallium oxide (LaGaO3)-based materials have their own characteristics. Although LaGaO3-based electrolytes have excellent conductivity characteristics, they are limited by the high cost of lanthanide elements; although CeO2-based electrolytes have good ionic conductivity, they have inherent defects such as valence instability and increased electronic conductivity under reducing atmosphere. Both electrolytes are rarely used in commercial applications.

[0003] In commercial SOFC, 8mol% yttria-stabilized zirconia (8YSZ) is the most commonly used electrolyte material. By doping a small amount of Y in the zirconium dioxide matrix, the structure of ZrO2 is stabilized in a cubic fluorite structure at room temperature. It has high stability, low electronic conductivity and high mechanical strength. Compared with LaGaO3-based and CeO2-based electrolytes, the cost of ZrO2 is significantly reduced. However, the literature Densification behavior of yttria-stabilizedzirconia powders for solid oxide fuel cell electrolytes (D. Panthi, N.Hedayat, Y. Du. Journal of Advanced Ceramics 7 (2018) 325-335) reported that 8YSZ electrolyte faces a bottleneck in the sintering process: the traditional sintering densification temperature is above 1450℃, which not only leads to excessive energy consumption, but also easily induces crystal phase transformation and leads to conductivity decay. In order to solve these shortcomings of 8YSZ, the academic community has mainly made breakthroughs in two dimensions: optimizing the powder preparation process and doping sintering aids. The former is to prepare powders with higher sintering activity by hydrothermal method, and the latter is to add transition metal oxides (such as NiO, Co2O3, CuO) as sintering aids to reduce its densification temperature. According to the literature Cubic yttriastabilized zirconia sintering additive impacts: A comparative study (A.Flegler, T.Burye, Q. Yang, J. Nicholas. Ceramics International 40 (2014)16323–16335), the most effective additives for reducing the sintering temperature of 8YSZ are Ni, Zn, Mn, Co, Li and Bi and their oxides. Fe2O3, as a transition metal oxide, can be dissolved in 8YSZ and reduce the sintering densification temperature of the electrolyte by solid phase sintering. In addition, Fe element is cheap and easy to obtain, and the preparation and addition of sintering aids are simple, which can significantly reduce the commercialization cost of solid oxide fuel cells and has good application potential. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing an iron oxide-doped 8YSZ electrolyte and to reduce the densification temperature of the electrolyte.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: The invention provides a preparation method of low-temperature sintered electrolyte iron oxide doped 8YSZ. The preparation method comprises weighing yttrium nitrate hexahydrate, zirconium oxychloride octahydrate and iron nitrate nonahydrate raw materials according to a molar ratio of Y(NO3)3·6H2O:ZrOCl2·8H2O:Fe(NO3)3·9H2O=16:92:x.

[0006] Preferably, 0.5≤x≤5.

[0007] The metal salt raw material was dissolved in distilled water to make the concentration of metal ions 0.5 mol / L; polyethylene glycol 1000 (PEG1000) equivalent to 5% of the mass of the metal salt was added thereto; then, concentrated ammonia water precipitant with a concentration of 13 mol / L was added dropwise to the above solution and stirred until the solution pH = 8; the mixed solution was allowed to stand for aging for 4 hours.

[0008] The aged product was centrifuged at a speed of 4500 r / min for 5 minutes; deionized water was added to the solid obtained by centrifugation, washed with water, and centrifuged; anhydrous ethanol was then added to the washed solid, washed with alcohol, and centrifuged; dried at 80 °C for 48 hours; the dried powder was ground in an agate mortar to obtain FeO 1.5 -8YSZ precursor powder.

[0009] The FeO obtained by the above method 1.5 -8YSZ powder was treated at 800 °C for 2 hours and then ground; the obtained powder was pressed into shape by dry pressing at a pressure of 300 MPa for 5 minutes. After molding, it was sintered in a muffle furnace to obtain the electrolyte.

[0010] In the present invention, the high temperature sintering temperature is 1350°C, the sintering time is 5 hours, and the heating rate is 3°C / min.

[0011] The present invention provides an application of an oxygen ion conductive electrolyte with a low densification temperature in an SOFC electrolyte material. Based on the electrolyte material provided by the present invention, an SOFC with a low sintering temperature, low cost and high stability can be obtained.

[0012] Compared with the prior art, in the preparation method provided by the present invention, a new nominal component of x% FeO is formed by doping transition metal oxide iron oxide into the matrix 8YSZ. 1.5-8YSZ (x=0.5, 1, 2,5 mol); moreover, the introduction of the above-mentioned Fe has a positive significance for the regulation of the densification temperature, electrical conductivity and thermal expansion coefficient of 8YSZ, which reduces the densification temperature of the material, improves the sintering density, improves the electrical conductivity, makes the thermal expansion coefficient adjustable, and makes the obtained oxygen ion conducting electrolyte have a low densification temperature and high electrical conductivity, which can be used as an electrolyte layer in the research of SOFC and has important value.

[0013] The experimental results show that the 0.5% FeO 1.5 The linear shrinkage of the -8YSZ oxygen ion conducting electrolyte during sintering is 23.6%. After sintering at 1350 °C for 5 h, the total ionic conductivity at 800 °C is 2.52×10 -2 S / cm; At 700 °C, the total ionic conductivity is 1.04×10 -2 S / cm; At 600 °C, the total ionic conductivity is 3.03×10 -3 S / cm; At 500 °C, the total ionic conductivity is 4.93×10 -4 S / cm; At 400 °C, the total ionic conductivity is 4.06×10 -5 S / cm; At 300 °C, the total ionic conductivity is 1.32×10 -6 S / cm; Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is the X-ray diffraction spectrum of the product obtained in Example 1; Figure 2 This is a scanning electron microscope image of the product obtained in Example 1; Figure 3 The total conductivity curve of the product obtained in Example 1 between 550 and 800 °C; Figure 4 This is a sintering shrinkage curve of the product obtained in Example 2; Figure 5 is a first-order differential curve of the sintering shrinkage curve of the product obtained in Example 2 versus temperature; Figure 6 This is the thermal expansion curve of the product obtained in Example 2. DETAILED DESCRIPTION

[0015] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further explained below in conjunction with specific embodiments and drawings.

[0016] Unless otherwise specified, the experimental materials and reagents used in the following examples can be obtained from commercial sources. If no specific techniques or conditions are specified in the examples, they can be carried out according to the techniques or conditions described in the literature in the field or according to the product instructions.

[0017] As mentioned above, the present invention provides a method for preparing a low-temperature sintered iron oxide-doped 8YSZ oxygen ion conductive electrolyte, characterized in that: Weigh the raw materials of yttrium nitrate hexahydrate, zirconium oxychloride octahydrate, and ferric nitrate nonahydrate according to the molar ratio of Y(NO3)3·6H2O:ZrOCl2·8H2O:Fe(NO3)3·9H2O =16:92:x. Preferably, 0.5≤x≤5.

[0018] The metal salt raw material was dissolved in distilled water to make the concentration of metal ions 0.5 mol / L; polyethylene glycol 1000 (PEG1000) equivalent to 5% of the mass of the metal salt was added thereto; then, concentrated ammonia water precipitant with a concentration of 13 mol / L was added dropwise to the above solution and stirred until the solution pH = 8; the mixed solution was allowed to stand for aging for 4 hours.

[0019] The aged product was centrifuged at a speed of 4500 r / min for 5 minutes; deionized water was added to the solid obtained by centrifugation, washed with water, and centrifuged; anhydrous ethanol was then added to the washed solid, washed with alcohol, and centrifuged; dried at 80 °C for 48 hours; the dried powder was ground in an agate mortar to obtain FeO 1.5 -8YSZ precursor powder.

[0020] The FeO obtained by the above method 1.5 -8YSZ powder was treated at 800 °C for 2 hours and ground; the powder was pressed into shape by dry pressing at a pressure of 300 MPa for 5 minutes. After forming, it was sintered in a muffle furnace to obtain an electrolyte.

[0021] In the present invention, the high temperature sintering temperature is 1350°C, the sintering time is 5 hours, and the heating rate is 3°C / min.

[0022] The inventors of the present application have found that by doping iron oxide into the matrix 8YSZ, a new nominal composition of x% FeO is formed. 1.5-8YSZ (x=0.5, 1, 2,5 mol) electrolyte; moreover, the introduction of the above iron oxide components has a positive significance for reducing the densification temperature of 8YSZ, significantly improving the sintering shrinkage, reducing the densification temperature, and improving the electrical conductivity. Compared with the current 8YSZ electrolyte material, its densification temperature is significantly reduced. It is of great value for the development of low-cost SOFC. It can be used as an electrolyte material with good application potential in SOFC.

[0023] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0024] In the following examples, the raw materials used are all commercially available analytically pure commodities, specifically, yttrium nitrate hexahydrate (Y(NO3)3·6H2O), zirconium oxychloride octahydrate (ZrOCl2·8H2O), ferric nitrate nonahydrate (Fe(NO3)3·9H2O), and polyethylene glycol 1000 (PEG1000) were provided by Sinopharm Group; The tablet press used was a 40-ton manual tablet press provided by Hefei Kejing Company, the molding pressure was 300 MPa, and the molded sample was a 13 mm × 1 mm round tablet sample. The sintering furnace used was a muffle furnace provided by Hefei Kejing Company.

[0025] Example 1: x%FeO 1.5 Preparation of -8YSZ (x=0.5, 1, 2, 5 mol) electrolyte 1.1 Weigh the raw materials of yttrium nitrate hexahydrate, zirconium oxychloride octahydrate, and ferric nitrate nonahydrate according to the molar ratio of Y(NO3)3·6H2O:ZrOCl2·8H2O:Fe(NO3)3·9H2O =16:92:x. Preferably, 0.5≤x≤5.

[0026] The metal salt raw material was dissolved in distilled water to make the concentration of metal ions 0.5 mol / L; polyethylene glycol 1000 (PEG1000) equivalent to 5% of the mass of the metal salt was added thereto; then, concentrated ammonia water precipitant with a concentration of 13 mol / L was added dropwise to the above solution and stirred until the solution pH = 8; the mixed solution was allowed to stand for aging for 4 hours.

[0027] The aged product was centrifuged at a speed of 4500 r / min for 5 minutes; deionized water was added to the solid obtained by centrifugation, washed with water, and centrifuged; anhydrous ethanol was then added to the washed solid, washed with alcohol, and centrifuged; dried at 80 °C for 48 hours; the dried powder was ground in an agate mortar to obtain FeO 1.5-8YSZ precursor powder.

[0028] The FeO obtained by the above method 1.5 -8YSZ powder was treated at 800 °C for 2 hours and ground; the powder was pressed into shape by dry pressing at a pressure of 300 MPa for 5 minutes. After forming, it was sintered in a muffle furnace to obtain an electrolyte.

[0029] In the present invention, the high temperature sintering temperature is 1350°C, the sintering time is 5 hours, and the heating rate is 3°C / min.

[0030] 1.2 Product Characterization: The product obtained in 1.1 was cut, and a part of it was ground into powder. The phase analysis was performed using a RigakuSmartlab (9kW) X-ray diffractometer from Rigaku Electric Co., Ltd.; the unground electrolyte fragment surface was photographed using a Hitachi SU8200 field emission scanning electron microscope. The results were as follows: Figure 1 and 2 As shown (where Figure 1 is the X-ray diffraction pattern of the product obtained in this example; Figure 2 ) is a scanning electron microscope image of the cross section of the product obtained in this example.

[0031] Depend on Figure 1 It can be seen that the main crystal structure of the obtained product is still 8YSZ. 1.5 When the doping ratio is not higher than 5%, FeO 1.5 It can form a uniform solid solution with the 8YSZ matrix.

[0032] Depend on Figure 2 It can be seen that after sintering at 1350 °C for 5h, the 8YSZ product is not dense and presents a porous structure. With the increase of iron oxide content, the cross-section porosity continues to decrease and the grain size continues to increase. 1.5 -8YSZ samples can be observed with obvious large-sized grains and grain boundaries. This indicates that with the increase of iron oxide content, the x%FeO 1.5 -8Densification of YSZ electrolyte samples.

[0033] 1.3 Performance test: The product obtained in 1.1 was polished on both sides, and a layer of platinum slurry was evenly coated as a current collecting layer. It was placed in a muffle furnace and heated to 950 °C at a rate of 3 °C / min, and kept at this temperature for 30 minutes, and then cooled to room temperature at a rate of 3 °C / min. The conductivity test was performed using an AMETEK Solartron 1260 frequency analyzer. The results are shown in the figure. Figure 3 shown by Figure 3 It can be seen that the total conductivity of the 8YSZ sample at 750 °C is 1.16×10 -2 S / cm. 0.5%FeO 1.5 The total conductivity of the -8YSZ sample at 750 °C is 1.73×10 -2 S / cm. 1%FeO 1.5 The total conductivity of the -8YSZ sample at 750 °C is 1.55×10 -2 S / cm. 2%FeO 1.5 The total conductivity of the -8YSZ sample at 750 °C is 1.32×10 -2 S / cm. 5%FeO 1.5 The total conductivity of the -8YSZ sample at 750 °C is 1.06×10 -2 It is worth noting that after adding a small amount of Fe2O3, the overall conductivity of the electrolyte increased significantly, which is mainly due to the improvement of material density by Fe; when the Fe doping amount is further increased, the reduction reaction at high temperature prevents the improvement of ionic conductivity.

[0034] Example 2: x%FeO 1.5 -8Preparation and shrinkage and thermal expansion tests of YSZ electrolyte 2.1 Weigh the raw materials of yttrium nitrate hexahydrate, zirconium oxychloride octahydrate, and ferric nitrate nonahydrate according to the molar ratio of Y(NO3)3·6H2O:ZrOCl2·8H2O:Fe(NO3)3·9H2O =16:92:x. Preferably, 0.5≤x≤5.

[0035] The metal salt raw material was dissolved in distilled water to make the concentration of metal ions 0.5 mol / L; polyethylene glycol 1000 (PEG1000) equivalent to 5% of the mass of the metal salt was added thereto; then, concentrated ammonia water precipitant with a concentration of 13 mol / L was added dropwise to the above solution and stirred until the solution pH = 8; the mixed solution was allowed to stand for aging for 4 hours.

[0036] The aged product was centrifuged at a speed of 4500 r / min for 5 min; deionized water was added to the solid obtained by centrifugation, washed with water, and centrifuged; anhydrous ethanol was then added to the washed solid, washed with alcohol, and centrifuged; dried at 80 °C for 48 hours; the dried powder was ground in an agate mortar to obtain FeO 1.5 -8YSZ precursor powder.

[0037] The FeO obtained by the above method 1.5-8YSZ powder was treated at 800 °C for 2 hours and ground; the powder was pressed into a rectangular mold using a dry pressing method to obtain x% FeO 1.5 -8YSZ strip samples; 2.2 Product Characterization: The two ends of the strip product obtained in 2.1 were ground flat, and the sintering curve was tested using a DIL 402 C thermal expansion instrument from German Netzsch Instruments. The test temperature range was 25~1400 °C, and the heating rate was 10 °C / min. The results were as follows: Figure 4 and 5 As shown (where Figure 4 This is the sintering curve of the product obtained in this example; Figure 5 This is the first-order differential diagram of the sintering curve of the product obtained in this example).

[0038] Depend on Figure 4 It can be seen that the sintering curve of the 8YSZ sample begins to change significantly at 870°C, indicating the beginning of sintering shrinkage. 1.5 The sintering curve of -8YSZ sample starts to shrink at 860 °C. 1%FeO 1.5 The sintering curve of -8YSZ sample starts to shrink at 855 °C. 2%FeO 1.5 The sintering curve of -8YSZ sample starts to shrink at 830 °C. 5%FeO 1.5 The sintering curve of the -8YSZ sample begins to shrink at 805 °C. The shrinkage increases with the increase of Fe2O3 content, which indicates the improvement of sintering activity. When the high temperature section is reached, the sintering curve gradually becomes flat, and the shrinkage rate of the sample can be judged according to the shrinkage amount. The shrinkage rate of 8YSZ is 12.73%. 0.5%FeO 1.5 -8YSZ has a shrinkage of 20.98%. 1%FeO 1.5 -8YSZ has a shrinkage of 21.38%. 2%FeO 1.5 -8YSZ has a shrinkage of 21.78%. 5%FeO 1.5 -8YSZ has a shrinkage of 23.62%. This represents x%FeO 1.5 -8YSZ samples have higher density as the Fe2O3 content increases.

[0039] from Figure 5 It can be seen that the first-order differential curve of the sintering curve of 8YSZ with respect to temperature has a significant peak, which means that its maximum shrinkage rate is 4.81×10 -3 cm -1 0.5%FeO 1.5 -8The maximum shrinkage rate of YSZ is 8.00×10 -3 cm-1 1%FeO 1.5 -8The maximum shrinkage rate of YSZ is 8.50×10 -3 cm -1 2%FeO 1.5 -8The maximum contraction rate of YSZ is 9.50×10 -3 cm -1 5%FeO 1.5 The maximum shrinkage rate of -8YSZ is 1.27×10 -2 cm -1 The increase in the maximum shrinkage rate indicates that the doping of Fe2O3 significantly promotes the densification of 8YSZ.

[0040] 2.3 Performance Test: The strip product obtained in 2.1 was sintered in a muffle furnace to a high density. The sintering temperature was 1350 °C, the heating rate was 3 °C / min, the temperature was kept for 5 hours, and the cooling rate was 3 °C / min. The two ends of the obtained dense product were ground flat, and the sintering curve was tested using a DIL 402 C thermal expansion instrument from NETZSCH Instruments, Germany. The test temperature range was 200~1000 °C, and the heating rate was 10 °C / min. The results are shown in Figure 2. Figure 6 shown by Figure 6 It can be seen that the thermal expansion coefficient of the 8YSZ sample is 12.0×10 -6 K -1 0.5%FeO 1.5 The thermal expansion coefficient of the -8YSZ sample is 12.3×10 -6 K -1 1%FeO 1.5 The thermal expansion coefficient of the -8YSZ sample is 12.4×10 -6 K -1 2%FeO 1.5 The thermal expansion coefficient of the -8YSZ sample is 13.1×10 -6 K -1 5%FeO 1.5 The thermal expansion coefficient of the -8YSZ sample is 15.8×10 -6 K -1 The thermal expansion coefficient changes linearly with the increase of iron oxide doping content, making the thermal expansion coefficient of the electrolyte adjustable and more compatible with the thermal expansion behavior of the anode and cathode.

[0041] Based on the above data, compared with 8YSZ, the x% FeO 1.5 -8YSZ oxygen ion conducting electrolyte has a lower densification temperature, 0.5% FeO 1.5-8YSZ has higher conductivity and a thermal expansion coefficient that is more compatible with the electrode, and is an electrolyte material with great potential. In addition, the doped electrolyte proposed in the present invention has the advantages of being easy to prepare and can be mass-produced, which is beneficial for application in SOFC.

[0042] The above shows and describes the basic principles, main features and characteristics of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of the present invention to be protected is defined by the attached claims and their equivalents.

Claims

1. A method for preparing a low-temperature sintered iron oxide-doped 8YSZ electrolyte, characterized in that: Weigh the raw materials of yttrium nitrate hexahydrate, zirconium oxychloride octahydrate, and ferric nitrate nonahydrate according to the molar ratio of Y(NO3)3·6H2O:ZrOCl2·8H2O:Fe(NO3)3·9H2O=16:92:x, where 0.5≤x≤5, and dissolve them in distilled water to make the concentration of metal ions 0.5 mol / L; add polyethylene glycol 1000 equivalent to 5% of the mass of the metal salt; then, add concentrated ammonia water with a concentration of 13 mol / L dropwise to the above solution, stir until the solution pH is 7~8; let the mixed solution stand for aging for 4 hours; The aged product was centrifuged at 4500 r / min for 5 minutes; deionized water was added to the solid obtained by centrifugation, washed with water, and centrifuged; Then, anhydrous ethanol was added to the washed solid, and the solid was washed with alcohol and centrifuged; the solid was dried at 80 °C for 48 hours; the dried solid was ground in an agate mortar to obtain FeO 1.5 -8YSZ precursor powder; The obtained FeO 1.5 -8YSZ powder was treated at 800 °C for 2 hours and ground; the ground powder was dry-pressed and then sintered in a muffle furnace at a sintering temperature of 1350-1450 °C for 5 hours to obtain an electrolyte.

2. An electrolyte obtained by the preparation method as claimed in claim 1.

3. Use of the electrolyte obtained by the preparation method as claimed in claim 1 in a solid oxide fuel cell.

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