CN103199287A - Method for promoting densification of silicon-based apatite through doping Cu - Google Patents

Abstract

The invention relates to a method for promoting the densification of silicon-based apatite through doping Cu, belonging to the field of solid oxide fuel cells. According to the method, the silicon-based apatite (the molecular formula is La9.33+xSi6O26+1.5x, wherein x is equal to 0-0.67) is prepared by adopting a citric acid-nitrate method, the sintering activity of powder can be effectively improved through doping Cu at Si site, the densification of the material is promoted, the relative density can be improved by more than 6% under the condition of sintering at equal temperature, and the problem that the silicon-based apatite electrolyte material is difficult to sinter and densify can be solved.

Description

A method of Cu doping to promote the densification of silicon-based apatite electrolyte

the

technical field

The invention relates to a method for promoting the densification of a silicon-based apatite electrolyte by Cu doping, and belongs to the field of solid oxide fuel cells.

Background technique

As the earth's environmental pollution and energy shortage become increasingly severe, seeking new energy technologies with high energy conversion efficiency and environmental friendliness has become an important direction of scientific and technological research. Solid oxide fuel cell (SOFC) has the advantages of high energy utilization rate, clean and pollution-free, strong fuel adaptability, and all-solid-state structure, and is recognized as one of the most potential energy technologies in the 21st century.

Solid oxide fuel cells are mainly composed of four parts: anode, cathode, electrolyte and connecting materials. SOFCs based on the traditional electrolyte material, yttria-stabilized zirconia (YSZ), require relatively high operating temperatures (800-1000 ^o C). Such a high operating temperature has brought about a series of problems, such as reactions between battery components, electrode sintering, and difficulty in sealing the battery stack. Therefore, in order to reduce the cost and improve the stability and reliability of the battery system, it is an inevitable trend to develop medium temperature SOFC (500-750 ^o C). Electrolyte materials are the key to reducing the operating temperature of SOFCs. Due to the low conductivity of YSZ under medium temperature conditions, the battery efficiency is greatly reduced, so the development of electrolyte materials that meet the requirements under medium temperature conditions is one of the focuses of current research. Silicon-based apatite electrolyte material has become one of the important substitutes for YSZ due to its high electrical conductivity and oxygen ion migration number, mild thermal expansion coefficient, good doping characteristics and chemical stability under medium temperature conditions.

The electrolyte material of SOFC needs to have high density firstly, in order to prevent the mutual shuttling of fuel gas and oxygen, guarantee the high open-circuit voltage of the battery. The densification temperature of silicon-based apatite electrolyte materials prepared by traditional solid-state reaction method often needs to be above 1650 ^o C (Yoshioka H, Nojiri Y, Tanase S. Ionic conductivity and fuel cell properties of apatite-type lanthanum silicates doped with Mg and containing excess oxide ions. Solid State Ionics. 2008;179:2165-2169. Nojiri Y, Tanase S, Iwasa M, et al. Ionic conductivity of apatite-type solid electrolyte material, La _10?x Ba _x Si ₆ O _27?x/2 (x=0–1), and its fuel cell performance. Journal of Power Sources. 2010;195:4059-4064). Such a high preparation temperature not only increases the waste of energy and requires high requirements for equipment, but also brings difficulties to the preparation of batteries with electrode support structures. The use of more advanced sintering technology can effectively reduce the densification temperature of silicon-based apatite materials. For example, Panteix et al. used the traditional solid-state method to prepare silicon-based apatite powder materials, and used hot-press sintering to prepare ceramic sheets with a density of more than 95% under the conditions of 35 MPa and 1400 ^o C (Panteix P J , Julien I, Assollant D B, et al. Synthesis and characterization of oxide ions conductors with the apatite structure for intermediate temperature SOFC [J]. Materials Chemistry and Physics, 2006;95:313-320), but the advanced sintering technology has great influence on the equipment The requirements are higher, which increases the preparation cost. Preparation of nanopowder materials by liquid phase method is another way to reduce the densification temperature of silicon-based apatite electrolyte materials, such as sol-gel method (Celerier S, Laberty C, Ansart F, et al. New chemical route based on sol–gel process for the synthesis of oxyapatite La _9.33 Si ₆ O ₂₆ [J]. Ceramics International, 2006, 32(3):271-276), citric acid-nitrate method (Zhou J, Ye X F, Li J L , et al. Synthesis and characterization of apatite-type La _9.67 Si _6-x Al _x O _26.5-x/2 electrolytematerials and compatible cathode materials[J]. Solid State Ionics, 2011;201:81–86. Jothinathan E, Vanmeensel K, Vleugels J, et al. Synthesis of nano-crystalline apatite type electrolyte powders for solid oxide fuel cells. Journal of the European Ceramic Society. 2010; 30:1699-1706. ) and so on. However, the degree to which these methods promote densification is still limited, thus affecting the practical application of silicon-based apatite electrolyte materials. Therefore, it is necessary to continue to explore new methods to effectively reduce the densification temperature of silicon-based apatite electrolyte materials.

Contents of the invention

The purpose of the present invention is to provide a simple, low-cost method that can effectively promote the densification of silicon-based apatite electrolyte materials. The invention prepares the Cu-doped silicon-based apatite electrolyte material through the citric acid-nitrate method. The doping of Cu can effectively improve the sintering activity of the material and promote the densification of the material. The technical scheme is as follows:

_a ) Weigh _{the required} La ₂ O ₃ , tetraethyl orthosilicate ( _TEOS ) and Cu(NO ₃ ) ₂ ·3H ₂ O. Dissolve La ₂ O ₃ and Cu(NO ₃ ) ₂ ·3H ₂ O in deionized water and a certain amount of nitric acid, and the ratio of deionized water to metal ions (including Si ⁴⁺ ) is 10~50:1 , the substance molar ratio of nitric acid and metal ions is 5-20:1; the citric acid and ethylene glycol with a substance molar ratio of 1:1 are added as complexing agents, and the substance molar ratios of complexing agents and metal ions are 1~3:1; add ammonia water with a concentration of 28% to adjust the pH value to 2~7; dissolve TEOS in a certain amount of absolute ethanol and add the above solution, the ratio of absolute ethanol to TEOS is 30~80 : 1; Stir continuously to make the solution fully mixed, then move it into a water bath at 70~90 ^o C to evaporate until the wet gel is formed, then move it into an oven to dry at 70~120 ^o C to form a xerogel, and then heat the xerogel to its Combustion, fluffy precursor powder is formed after combustion.

b) Move the above precursor powder into a muffle furnace for calcination for 5-10 hours, then grind and sieve (160 mesh), dry press and shape, and then sinter at high temperature in air for 4-10 hours to obtain a dense material.

The doping amount y of Cu is between 0 and 0.7; the calcination temperature of the precursor is 800-1000 ^o C; the sintering temperature of the powder material is 1400-1600 ^o C.

The present invention utilizes citric acid-nitrate method to prepare Cu-doped silicon-based apatite electrolyte material La _9.33+x Si _6-y Cu _y O _26+1.5xy (0≤x≤0.67, 0<y≤0.7) , the obtained powder material has good sintering activity, which effectively promotes the densification of the material.

the

Description of drawings

Fig. 1 is the cross-sectional scanning electron microscope picture of the sample obtained in Example 1 of the present invention.

Fig. 2 is a cross-sectional scanning electron microscope image of the sample obtained in Example 2 of the present invention.

Fig. 3 is a scanning electron micrograph of a section of a sample obtained in Example 3 of the present invention.

Fig. 4 is the X-ray electron diffraction pattern of the samples obtained in Examples 1, 2 and 3 of the present invention.

Detailed ways

    The present invention will be further described below in conjunction with examples, but it is not limited to the protection scope of the present invention.

Example 1:

In order to compare the promotion effect of Cu doping on material densification, an undoped sample is specially made, namely this example. Preparation of La _9.67 Si ₆ O _26.5 :

a) Dissolve 3.937 g La ₂ O ₃ in 20 ml deionized water and 30 ml mixed solution of 65 wt% nitric acid. After the dissolution is complete, add 13.922 g citric acid and 4.112 g ethylene glycol, and magnetically stir the solution until it becomes clear.

b) Adjust the pH to 2-3 with 28 wt% ammonia water.

c) After dissolving 3.125 g TEOS in 60 ml of absolute ethanol, add the above solution; magnetically stir for 3 h and then transfer to 80 ^o C water bath until the gel appears; transfer the gel to an oven at 80 ^o C and dry it at 250 ^o C is ignited to obtain the precursor powder.

d) The precursor powder was calcined at 900 ^o C for 9 h, and the calcined powder was ground and sieved (160 mesh), dry-pressed and formed into an electric furnace, and sintered at 1550 ^o C for 6 h in an air atmosphere to obtain the final As for the material, the density of the material measured by the Archimedes drainage method is 87.6%. The phase of the material detected by XRD is a single apatite phase.

Example 2:

This example is a sample with Cu doping amount y=0.1. Preparation of La _9.67 Si _5.9 Cu _0.1 O _26.4 :

a) Dissolve 3.937 g La ₂ O ₃ in 20 ml deionized water and 30 ml 65wt% nitric acid mixture, add 0.060 g Cu(NO ₃ ) ₂ 3H ₂ O, and add 13.922 g lemon acid and 4.112 g ethylene glycol, and magnetically stir the solution until clear.

b) Adjust the pH to 2-3 with 28 wt% ammonia water.

c) After dissolving 3.073 g TEOS in 60 ml of absolute ethanol, add the above solution; magnetically stir for 3 h and then transfer to 80 ^o C water bath until the gel appears; transfer the gel to an 80 ^o C oven for drying and place at 250 ^o C is ignited to obtain the precursor powder.

d) The precursor powder was calcined at 900 ^o C for 9 h, and the calcined powder was ground and sieved (160 mesh), dry-pressed and formed into an electric furnace, and sintered at 1550 ^o C for 6 h in an air atmosphere to obtain the final As for the material, the density of the material measured by the Archimedes drainage method is 93.8%. The phase of the material detected by XRD is a single apatite phase, and no second phase impurities appear.

Example 3:

This example is a sample with Cu doping amount y=0.5. Preparation of La _9.67 Si _5.5 Cu _0.5 O ₂₆ :

a) Dissolve 3.937 g La ₂ O ₃ in 20 ml deionized water and 30 ml 65wt% nitric acid mixture, add 0.302 g Cu(NO ₃ ) ₂ 3H ₂ O, and add 13.922 g lemon acid and 4.112 g ethylene glycol, and magnetically stir the solution until clear.

b) Adjust the pH to 2-3 with 28 wt% ammonia water.

c) After dissolving 2.865 g TEOS in 60 ml of absolute ethanol, add the above solution; after magnetic stirring for 3 h, transfer to 80 ^o C water bath until the gel appears; transfer the gel to an 80 ^o C oven and dry it at 250 ^o C is ignited to obtain the precursor powder.

d) The precursor powder was calcined at 900 ^o C for 9 h, and the calcined powder was ground and sieved (160 mesh), dry-pressed and formed into an electric furnace, and sintered at 1550 ^o C for 6 h in an air atmosphere to obtain the final As for the material, the compactness of the material measured by the Archimedes drainage method is 95.0%. The phase of the material detected by XRD is a single apatite phase, and no second phase impurities appear.

Claims (2)

1. a Cu mixes and promotes the method for silica-based apatite electrolyte densification, it is characterized in that in Si position doped with Cu, the doping of Cu is 0＜y≤0.7, is expressed as La with molecular formula _9.33+xSi _6-yCu _yO _26+1.5x-y(x=0 ~ 0.67); Electrolytical dense material preparation method is as follows:

A) according to molecular formula La _9.33+xSi _6-yCu _yO _26+1.5x-yIn the stoichiometric proportion of each element take by weighing required La ₂O ₃, tetraethoxysilane is TEOS and Cu (NO ₃) ₂3H ₂O; With La ₂O ₃And Cu (NO ₃) ₂3H ₂O is dissolved in the mixed solution of deionized water and a certain amount of nitric acid, and deionized water and metal ion (comprise Si ⁴⁺) the amount of substance ratio be 10 ~ 50:1, the amount of substance ratio of nitric acid and metal ion is 5 ~ 20:1; Add complexing agent in the mixed solution, add concentration again and be 28% ammoniacal liquor and regulate pH value to 2 ~ 7, adding at last is dissolved with the ethanol solution of TEOS; Constantly stir and make solution fully mix back immigration 70 ~ 90 ^oEvaporation forms until wet gel in the water-bath of C, moves into baking oven then 70 ~ 120 ^oThe dry xerogel that forms of C; Xerogel is heated to its burning, forms fluffy precursor powder after the burning; Wherein the ratio of absolute ethyl alcohol and TEOS is 30 ~ 80:1; Complexing agent is 1 ~ 3:1 with the amount of substance ratio of metal ion; The composition of complexing agent is citric acid and ethylene glycol, and ratio is 1:1;

B) above-mentioned precursor powder is moved into Muffle furnace calcining 5 ~ 10 h and ground 160 mesh sieves, dry-pressing formed afterwards, high temperature sintering 4-10 h obtains fine and close material in air then.

2. mixing according to the described Cu of claim 1 promotes the method for silica-based apatite electrolyte densification, it is characterized in that the calcining heat of described presoma is 800-1000 ^oC; The dense sintering temperature of material is 1400-1600 ^oC.

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