CN108695532B - High-stability doped strontium cerate/zirconium cerate-alkali metal salt composite electrolyte and preparation method thereof - Google Patents

High-stability doped strontium cerate/zirconium cerate-alkali metal salt composite electrolyte and preparation method thereof Download PDF

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CN108695532B
CN108695532B CN201710233110.6A CN201710233110A CN108695532B CN 108695532 B CN108695532 B CN 108695532B CN 201710233110 A CN201710233110 A CN 201710233110A CN 108695532 B CN108695532 B CN 108695532B
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cerate
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王洪涛
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Hefei Longzhi Electromechanical Technology Co ltd
Fuyang Normal University
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/10—Fuel cells with solid electrolytes
    • H01M8/1016—Fuel cells with solid electrolytes characterised by the electrolyte material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/10—Fuel cells with solid electrolytes
    • H01M8/12—Fuel cells with solid electrolytes operating at high temperature, e.g. with stabilised ZrO2 electrolyte
    • H01M2008/1293—Fuel cells with solid oxide electrolytes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0065—Solid electrolytes
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Abstract

The invention provides a doped strontium cerate/zirconium cerate-alkali metal salt composite electrolyte, which is prepared by further doping rare earth cations into a strontium cerate/zirconium cerate solid solution material to obtain a high-stability high-conductivity doped SrCeO3/SrZrO3The solid solution is prepared by a sol-gel method and then is compounded with alkali metal salt at a medium and low temperature to obtain the composite electrolyte with excellent chemical stability and conductivity, the working temperature of the solid fuel oxide battery manufactured by the solid solution is greatly reduced, and the stable output power density can be maintained for a long time.

Description

High-stability doped strontium cerate/zirconium cerate-alkali metal salt composite electrolyte and preparation method thereof
Technical Field
The invention belongs to the field of development of solid oxide fuel cell materials, and relates to a high-stability doped strontium cerate/zirconium cerate-alkali metal salt composite electrolyte suitable for a solid oxide fuel cell and a preparation method thereof.
Background
Solid Oxide Fuel Cells (SOFC) are widely studied by researchers by efficiently and cleanly converting chemical energy into electrical energy. The current SOFC electrolyte material makes the SOFC work at high temperature, generally above 1000 ℃, and such high temperature brings a series of problems to the commercialization of SOFC: (1) the selection of key materials of the battery has greater limitation; (2) difficulty in sealing the stack; (3) under the high-temperature condition, the microstructure of the electrode material is easy to change, so that the performance of the electrode material is failed, and the performance of the battery is rapidly degraded. The low-temperature (600-800 ℃) operation trend of SOFC becomes inevitable. However, as the operation temperature of the battery is lowered, the conductivity of the electrolyte material is reduced, the ohmic loss of the battery is increased, and the electrochemical performance of the battery is seriously influenced.
Researches find that the SrCeO doped with the trivalent positive rare earth element is expected to be used as the SOFC electrolyte3Or BaCeO3Has excellent proton conductivity at high temperature, but the conductivity is usually 10 at medium and low temperature-4～10-3S·cm-1. Simultaneously, positive trivalentRare earth element doped SrCeO3Or BaCeO3The electrolyte and carbon dioxide are easy to decompose in reaction, the chemical stability is not high, and the commercial application of the SOFC can not be met.
Therefore, it is highly desirable to develop an electrolyte for a solid oxide fuel cell, which has good electrochemical properties and stable performance under medium and low temperature conditions, and the preparation method is simple and easy.
Disclosure of Invention
In order to solve the above problems, the present inventors have conducted intensive studies and, as a result, have found that: strontium cerate (SrCeO) doped with trivalent rare earth elements and zirconium (Zr)3) The present invention has been completed by the fact that the composite obtained by compounding with a eutectic of alkali metal salts can significantly lower the operating temperature of a solid fuel cell when used as an electrolyte for an SOFC, and the SOFC assembled from the composite has significantly increased and stably sustained output power density, current density and electrical conductivity over a long period of time (at least 40 hours).
The object of the present invention is to provide the following:
in a first aspect of the present invention, there is provided a doped strontium cerate-alkali metal salt composite electrolyte, wherein the doped strontium cerate is an orthotrivalent rare earth element doped strontium cerate, and the alkali metal salt is an alkali metal salt.
Preferably, the doped strontium cerate is also doped with zirconium;
the trivalent rare earth element is expressed by M and is selected from Y3+、Lu3+、Eu3+And Tm3+Any one of the above-mentioned strontium cerate-doped chemical compositions is SrCe(1-x-y)ZrxMyO3-αWherein x is more than or equal to 0.20 and less than or equal to 0.60, y is more than or equal to 0 and less than or equal to 0.20, and alpha is more than or equal to 0 and less than or equal to 0.1.
In a second aspect of the present invention, there is also provided a method for preparing the above-mentioned doped strontium cerate-alkali metal salt composite electrolyte, wherein the method comprises the steps of:
1) mixing doped strontium cerate and alkali metal salt, and pressing to obtain a composite precursor;
2) calcining the composite precursor obtained in the step 1) to prepare the doped strontium cerate-alkali metal salt composite electrolyte.
According to the high-stability doped strontium cerate/zirconium cerate-alkali metal salt composite electrolyte and the preparation method thereof provided by the invention, the high-stability doped strontium cerate/zirconium cerate-alkali metal salt composite electrolyte has the following beneficial effects:
(1) in the invention, the doped strontium cerate is doped with zirconium, and the doping of SrCeO can be improved by partially replacing Ce with Zr3Chemical stability of the material, thereby obtaining a proton conductor with higher conductivity and good chemical stability.
(2) The doped strontium cerate is prepared by a sol-gel method, reactants are dissolved in the solution and can reach the dispersion of molecular or atomic level, the calcination temperature is greatly reduced compared with the traditional solid phase reaction method, and the prepared powder has the characteristics of high purity, fine and uniform granularity, low calcination temperature and the like, and is beneficial to improving the conductivity or chemical stability.
(3) The composite electrolyte prepared by the method has high compactness, no holes, air and water impermeability and uniform and consistent particle size, and is beneficial to improving the safety performance of the battery.
(4) The conductivity of the composite electrolyte prepared by the method of the invention reaches 1.27 multiplied by 10-1S.cm-1(ii) a H assembled therefrom2/O2The open circuit voltage of the fuel cell is 1.07V at the temperature of 700 ℃, and the output power density of the fuel cell can reach 0.57-0.58W-cm in a long time-2The current density can reach 0.89-0.90 A.cm-2The voltage is maintained at 0.63-0.65V.
Drawings
FIG. 1 shows the XRD pattern of a sample prepared in example 1;
FIG. 2 shows an electron micrograph of the surface topography of a sample prepared in example 1;
FIG. 3 shows an electron micrograph of the cross-sectional morphology of the sample prepared in example 1;
FIG. 4 shows the results of the conductivity in an air atmosphere at 700 ℃ for the samples prepared in example 1;
FIG. 5 shows the assembly of the composite electrolyte prepared in example 1 into H2/O2Fuel cell, I-V-P relationship at 700 ℃.
Detailed Description
The features and advantages of the present invention will become more apparent and appreciated from the following detailed description of the invention.
Research shows that SrCeO is doped3Has proton conductivity in hydrogen or water vapor containing atmosphere at higher temperature, and is prepared by dry pressing-co-firing method or high temperature solid phase method3The low conductivity of proton conductors limits their application to H-SOFCs. In the doping of SrCeO3The inorganic salt is introduced, so that the ionic conductivity of the material can be effectively improved, and the excellent conductivity can be obtained at a lower temperature. However, the variety of inorganic salts is very wide, and the selection of the inorganic salt and the addition amount thereof affects the doping of SrCeO3Important factors for the electrical properties of the salt composite electrolyte.
Accordingly, in a first aspect of the present invention, there is provided a doped strontium cerate-alkali metal salt composite electrolyte, wherein the doped strontium cerate is an orthotrivalent rare earth element doped strontium cerate, and the alkali metal salt is an alkali metal salt.
Research shows that the SrCeO is doped after the alkali metal inorganic salt is added3The conductivity of the conductive paste is improved, and the conductivity is obviously improved when the alkali metal salt is alkali metal hydrochloride compared with other alkali metal salts. Preferably, the alkali metal salt is a eutectic of at least two alkali metal salt salts, more preferably the alkali metal salt is a eutectic of potassium chloride and sodium chloride, the molar amount of potassium chloride and sodium chloride being in a ratio of 1:1, wherein the molar amount of potassium chloride is based on the molar amount of potassium element therein and the molar amount of sodium chloride is based on the molar amount of sodium element therein.
In the invention, the trivalent rare earth element is represented by M3+Is represented by Y3+、Lu3+、Eu3+And Tm3+Any one, preferably Eu3+. Rare earth element doped SrCeO3In, M3+Substituted Ce4+More oxygen vacancies (denoted Vo ″) are generated, thereby enabling the doped strontium cerate to undergo defect reaction with better proton conductivity.
In the present invention, the chemical composition of the doped strontium cerateIs SrCe(1-y)MyO3-αWherein y is more than or equal to 0 and less than or equal to 0.20, alpha is more than or equal to 0 and less than or equal to 0.1, and y is a positive trivalent rare earth element M3+The doping amount to form a solid solution, and alpha represents the number of oxygen vacancies per doped strontium cerate unit. For doped SrCe(1-y)MyO3-αThe larger y is, the more oxygen vacancies are, and the better the conductivity is; however, as y increases, when y > 0.2, a diffraction peak of a hetero phase begins to appear, indicating that the doped rare earth element is not completely dissolved into SrCeO3In the lattice of (a), an electrolyte of a single crystal phase, SrCe, cannot be obtained(1-y)MyO3-αThe stability of (2) is low and the sintering temperature is high. The smaller y is, the less oxygen vacancies are generated in the doped strontium cerate, which is not favorable for SrCe(1-y)MyO3-αTherefore, 0 < y.ltoreq.0.20 is preferable, and 0.01. ltoreq. y.ltoreq.0.15 is more preferable. The inventors have found that when the rare earth element (especially Eu) is used3+) When the doping amount of (a) is 0.1, electrochemical properties such as conductivity, output power density, and stability time of the electrolyte obtained therefrom are optimal.
In the present invention, the weight ratio of the doped strontium cerate to the alkali metal salt is (3-8): 1, preferably (4-5): 1. When the weight ratio of the doped strontium cerate to the alkali metal salt is less than 3:1, the structural stability of the composite electrolyte is reduced due to excessive doping amount of the alkali metal salt; and when the weight ratio of the doped strontium cerate to the alkali metal salt is more than 8:1, the doping amount of the alkali metal salt is small, and the improvement of the conductivity of the composite electrolyte is limited.
Doping with SrCeO3The composite electrolyte formed with the alkali metal salt is excellent in conductivity, and if the doping amount of SrCeO is further increased3Or the chemical stability and mechanical properties of the composite electrolyte formed therefrom, is advantageous in improving the reliability of the final battery product.
Therefore, in the present invention, zirconium is also doped in the doped strontium cerate. SrZrO3Has better chemical stability as a proton conductor, and can improve the doping of SrCeO by partially replacing Ce with Zr3Chemical stability of the material, thereby obtaining a proton conductor with higher conductivity and good chemical stability.
However, the addition of Zr not only reduces the electrical conductivity of the material, but also increases the sintering temperature (more than 1700 ℃) of the material, so that the sintering is difficult to obtain a compact electrolyte structure, and the co-firing process of the battery anode and the electrolyte is also influenced. Because the porosity is greatly reduced due to easy burning of the anode structure of the battery at an excessively high co-firing temperature, a porous anode structure cannot be obtained, thereby affecting the normal transportation of the fuel gas of the battery and reducing the output performance of the battery. Therefore, the selection of the doping amount of Zr is also important.
SrCeO doped with Zr and positive trivalent rare earth element3The chemical composition of the material is SrCe(1-x-y)ZrxMyO3-αWhich is doped with SrCeO3/SrZrO3Wherein 0.10. ltoreq. x.ltoreq.0.60, 0. ltoreq. y.ltoreq.0.20, 0. ltoreq. alpha.ltoreq.0.1, preferably 0.20. ltoreq. x.ltoreq.0.30, 0.01. ltoreq. y.ltoreq.0.15, 0.005. ltoreq. alpha.ltoreq.0.05. The trivalent rare earth element is represented by M, and x is Zr4+Doping amount for forming solid solution, y is positive trivalent rare earth element M3+The doping amount to form a solid solution, and alpha represents the number of oxygen vacancies per doped strontium cerate unit.
The doped SrCeO3The smaller x is, the higher the conductivity is, but when x is less than 0.10, the improvement of the chemical stability of the material is limited; the larger x is, the larger the inhibition of the conductivity is, and when x is more than 0.6, good chemical stability can be obtained, but the sintering temperature is obviously increased, and the inhibition of the conductivity is obvious. Thus, when Zr is selected to dope SrCeO3When is Zr4+The doping amount of x is more than or equal to 0.10 and less than or equal to 0.60.
Experiments show that after the doped strontium cerate is compounded with the alkali metal salt, the conductivity of the prepared composite electrolyte is obviously increased, and the conductivity of the composite electrolyte can reach 1.27 multiplied by 10 at the temperature of 700 DEG C-1S.cm-1. Meanwhile, the SOFC assembled by the composite electrolyte provided by the invention can obviously reduce the working temperature, the working temperature of the SOFC in the prior art is at least over 1000 ℃, and the working temperature of the SOFC assembled by the composite electrolyte provided by the invention is only 700 ℃, and is reduced by at least 300 ℃ compared with the SOFC in the prior art. More importantly, because ofThe composite electrolyte provided by the invention has high chemical stability, so that the cell performance of the SOFC assembled by the composite electrolyte is improved.
The doped strontium cerate-alkali metal salt composite electrolyte is a solid composite with high crystallinity, uniform grain size and high compactness, and particularly Eu is adopted3+、Zr4+Doped strontium cerate, sodium chloride and potassium chloride eutectic compound compact homogeneous electrolyte (SrCe)0.7Zr0.2M0.1O3-αAssembly of-NaCl-KCl) into H2/O2The fuel cell has an open circuit voltage of 1.07V at 700 deg.C and an output power density of 0.57-0.58W-cm for at least 40 hours-2The corresponding current density is maintained at 0.89-0.90A-cm-2The voltage is maintained at 0.63-0.65V.
In a second aspect of the present invention, there is also provided a method for preparing the above-mentioned doped strontium cerate-alkali metal salt composite electrolyte, wherein the method comprises the steps of:
1) mixing doped strontium cerate and alkali metal salt, and pressing to obtain a composite precursor;
2) calcining the composite precursor obtained in the step 1) to prepare the doped strontium cerate-alkali metal salt composite electrolyte.
In the step 1), the doped strontium cerate and the alkali metal salt are mixed and pressed to obtain a composite precursor.
In the invention, SrCeO is doped3Has a chemical composition of SrCe(1-x-y)ZrxMyO3-αWhich is doped with SrCeO3/SrZrO3Wherein 0.10. ltoreq. x.ltoreq.0.60, 0. ltoreq. y.ltoreq.0.20, 0. ltoreq. alpha.ltoreq.0.1, preferably 0.20. ltoreq. x.ltoreq.0.30, 0.01. ltoreq. y.ltoreq.0.15, 0.005. ltoreq. alpha.ltoreq.0.05. The trivalent rare earth element is represented by M, and x is Zr4+Doping amount for forming solid solution, y is trivalent rare earth element M3+The doping amount to form a solid solution, and alpha represents the number of oxygen vacancies per doped strontium cerate unit.
The alkali metal salt is an alkali metal salt, preferably a eutectic of at least two alkali metal salts, more preferably the alkali metal salt is a eutectic of potassium chloride and sodium chloride, the molar ratio of potassium chloride to sodium chloride being 1: 1.
The weight ratio of the doped strontium cerate to the alkali metal salt is (3-8): 1, preferably (4-5): 1.
In the invention, the doped strontium cerate and the alkali metal salt are mixed by using a grinding method, so that the particle size of each raw material is reduced, the raw materials are mixed more fully and uniformly, and the finally obtained sheet-shaped electrolyte is more uniform.
In the present invention, the time for grinding is not particularly limited, and it is determined that the raw materials are sufficiently and uniformly mixed.
After the doped strontium cerate and the alkali metal salt are fully and uniformly mixed, the mixture is pressed into a specific shape under the action of larger pressure according to the requirements of different fuel cells so as to be prepared into the solid electrolyte in the solid fuel cell. Tabletting is required before raw material synthesis to improve the density and uniformity of the calcined electrolyte.
In the present invention, the pressure and pressing time for pressing the mixture are not particularly limited, and it is preferable that the pressure when pressing the electrolyte having a specific shape is 8 to 10MPa, and the pressing time is 2 to 3 min; the thickness of the pressed electrolyte film is 1-3 mm, and the density of the composite electrolyte is 3.0-4.5 g-cm-3Preferably 4.0 to 4.2 g/cm-3. The dense electrolyte film has the function of isolating fuel gas and oxidizing gas, and can effectively prevent the gas leakage in the SOFC structure caused by the rupture of the electrolyte within the thickness range of the film.
In the invention, the doped strontium cerate is strontium cerate doped with trivalent rare earth element, preferably strontium cerate doped with trivalent rare earth element and zirconium element. The doped strontium cerate can be commercially available or prepared, preferably prepared, on its own.
Preferably, the preparation method of the doped strontium cerate comprises the following steps:
1-1), weighing a strontium source, a cerium source, a zirconium source and a compound containing rare earth elements according to a set molar ratio, dissolving the strontium source, the cerium source, the zirconium source and the compound containing rare earth elements in concentrated nitric acid, and adding a ligand compound;
1-2), adjusting the pH value of the system to form sol, and heating to form gel;
1-3) calcining the gel to obtain the doped strontium cerate.
In the invention, the preparation method of the doped strontium cerate is a sol-gel method, which has the following advantages: in the method, reactants are dissolved in a solution, the dispersion at a molecular or atomic level can be achieved, the calcination temperature is greatly reduced compared with that of the traditional solid phase reaction method, the uniformity is higher, the stoichiometric ratio is accurate, and other metal ion impurities which are difficult to remove are not introduced except organic components in the whole preparation process, so that the prepared powder has the characteristics of high purity, fine and uniform granularity, low calcination temperature and the like, and is beneficial to the improvement of the conductivity or the chemical stability.
Step 1-1), weighing a strontium source, a cerium source, a zirconium source and a rare earth element compound according to a set molar ratio, dissolving the strontium source, the cerium source, the zirconium source and the rare earth element compound in concentrated nitric acid, adding a ligand compound, wherein,
the strontium source is selected from strontium oxide, strontium acetate or strontium nitrate and other strontium-containing compounds soluble in nitric acid, preferably strontium acetate;
the cerium source is selected from cerium-containing compounds soluble in nitric acid, such as cerium oxide, cerium carbonate, cerium nitrate or ammonium cerium nitrate, preferably ammonium cerium nitrate;
the zirconium source is selected from zirconium carbonate, zirconium nitrate and other zirconium-containing compounds soluble in nitric acid, preferably zirconium nitrate;
the rare earth element compound is selected from oxide, acetate or nitrate of rare earth element, and preferably oxide of rare earth element.
In the invention, the weight fraction of the concentrated nitric acid is more than 65%. When one or more of the strontium source, the cerium source and the rare earth element compound is selected from oxides, the oxides are preferably dissolved in concentrated nitric acid, and then the non-oxide compound is added into the concentrated nitric acid to be dissolved, so that the concentrated nitric acid is prevented from being diluted and the oxides cannot be rapidly dissolved.
In the invention, a ligand is introduced into the system through a ligand compound, so that cerium element, strontium element, zirconium element and rare earth element in the system are matched with the ligand compound to form a complex, and the complex which is easy to age can be formed after the pH value of the system is adjusted. The complex is not limited, but is preferably citric acid and/or ethylenediaminetetraacetic acid (EDTA) based on its ability to complex the above elements.
The citric acid is a bidentate ligand, each citric acid molecule can be matched with two metal atoms, and in order to fully perform the matching reaction of the citric acid and the metal atoms, the addition amount of the citric acid is preferably 3-4 times of the total mole number of metal ions; the EDTA is a hexadentate ligand and can chelate various metal ions, the EDTA and the metal ions are usually chelated in a ratio of 1:1 or 1:2, and in order to enable the coordination reaction of the EDTA and the metal atoms to be fully carried out, the addition amount of the EDTA is preferably 5-6 times of the mole number of the total metal ions.
And 1-2), adjusting the pH value of the system to form sol, and heating to form gel.
In the invention, the pH value of the system is adjusted to 8-9, so that metal ions in the system and ligands are subjected to a coordination reaction to generate a stable complex.
Preferably, the pH of the system is adjusted using ammonia or an organic base (e.g., triethylamine). Ammonia or an organic base can remove residual base in the system by subsequent calcination without remaining heteroatoms in the system. If inorganic alkali is used, alkali metal or alkaline earth metal in the inorganic alkali can remain in the system and cannot be effectively removed, so that the prepared product is mixed with miscellaneous metal elements, thereby changing the chemical composition of the product and influencing the mechanical property or electrochemical property of the product.
In the present invention, the pH adjustment is accompanied by a stirring process. Heating the system after pH adjustment at 70-90 ℃ for 10-20 h to form transparent sol.
Heating the sol at 100-130 ℃ for 5-20 h to form a gel
And step 1-3), calcining the gel to obtain doped strontium cerate.
In the invention, the gel is calcined for the first time at 1150-1250 ℃ to remove organic impurities, and is calcined for the second time at 1500-1600 ℃ to obtain the doped strontium cerate. Through twice calcination, the purity of the doped strontium cerate is further improved, and the crystallinity and the compactness of the doped strontium cerate are better. Preferably, the time for the first calcination of the gel is 4-6 hours, and the time for the second calcination is 4-8 hours.
And (3) crushing the calcined doped strontium cerate to obtain a powder material, so that the subsequent processing is facilitated.
In the present invention, when the alkali metal salt is a co-melt of potassium chloride and sodium chloride, the co-melt is prepared by the following method:
step 2-1, weighing each alkali metal salt according to a set proportion, and carrying out primary calcination;
and 2-2, crushing the calcined product, and carrying out secondary calcination.
And 2-1, weighing the alkali metal hydrochloride according to a set proportion, grinding, uniformly mixing and calcining.
The grinding and mixing can be carried out sequentially or simultaneously, and the mixing effect is achieved through co-grinding.
In the invention, the temperature of the first calcination is selected from 600-800 ℃, preferably 650-750 ℃; the calcination time is selected from 20-60 min, preferably 30-40 min; at this temperature and time, sodium chloride and potassium chloride can form a stable eutectic body.
And 2-2, crushing the calcined product and calcining again.
The inventor finds that the eutectic body with more uniform element distribution can be obtained by crushing the primary calcined product and then carrying out secondary calcination.
In the invention, the temperature of the second calcination is selected to be 600-800 ℃, preferably 650-750 ℃; the calcination time is selected from 20 to 60min, preferably 30 to 40 min.
After the second calcination, the mixture was cooled to room temperature, taken out, ground into fine powder and passed through a 200 mesh sieve.
And 2) calcining the compound precursor obtained in the step 1) to prepare the doped strontium cerate-alkali metal salt compound electrolyte.
In the invention, the solid electrolyte is subjected to green forming, has certain shape and strength, but is only loose combination of powder essentially, and the strength and the performance can not meet the requirements, so the solid electrolyte also needs to be subjected to sintering treatment. The purpose of sintering is to transform a powder material into a bulk material, giving the material its characteristic properties, resulting in a bulk polycrystalline material.
Preferably, the composite precursor obtained in step 1) is calcined at 700-800 ℃ for 1-2 hours, so that the doped strontium cerate and the alkali metal salt can be compounded to form a uniform electrolyte.
Examples
Example 1
Preparation of doped strontium cerate
Weighing 0.05moL of europium oxide, dissolving in concentrated nitric acid, weighing 1moL of strontium acetate, 0.7moL of ammonium ceric nitrate and 0.2moL of zirconium nitrate, dissolving, adding 6moL of citric acid, adjusting the pH value to 9 with ammonia water, fully stirring, and heating at 80 ℃ to form transparent sol. Placing in an oven, and keeping the temperature at 110 ℃ for 10h to form gel. Ashing the gel, burning at 1200 deg.C for 5h, sintering at 1540 deg.C for 5h, and pulverizing to obtain SrCe0.7Zr0.2Eu0.1O3-αPowder (SCZE-SG).
Preparation of sodium (di) chloride-potassium chloride eutectic
Weighing 1moL of sodium chloride and 1moL of potassium chloride, grinding, uniformly mixing, placing in a box-type resistance furnace, heating at 720 ℃ for about 30min, cooling to room temperature, taking out, and grinding into fine powder. And heating the prepared eutectic powder again according to the conditions, cooling to room temperature, taking out, grinding into fine powder, sieving by using a 200-mesh standard sieve, putting into a sealed bag, and labeling for later use.
Preparation of (III) composite electrolyte
Taking 4.0g of SrCe0.7Zr0.2Eu0.1O3-αMixing with 1.0g sodium chloride-potassium chloride eutectic, grinding thoroughly, tabletting under 9MPa for 3min, placing 2-3mm round piece on a gasket, covering with a ceramic crucible, and firing at 750 deg.C for 1 hr to obtain SrCe0.7Zr0.2Eu0.1O3-αNaCl-KCl (SCZE-SG-NK). And then processed into electrolyte wafers with the thickness of 1.0 mm. In the airThe conductivity of the composite electrolyte reaches a maximum of 1.27X 10 in the atmosphere when the temperature is 700 DEG C-1S.cm-1。
Example 2
This example was carried out in a similar manner to example 1 except that (one) was added with 0.05moL of europium oxide, 1moL of strontium acetate, 0.6moL of ceric ammonium nitrate and 0.3moL of zirconium nitrate to obtain a product having a chemical composition of SrCe0.6Zr0.3Eu0.1O3-αWhich is compounded with potassium chloride and sodium chloride to prepare SrCe0.6Zr0.3Eu0.1O3-α-NaCl-KCl composite electrolyte.
The conductivity of the composite electrolyte can reach a maximum value of 1 x 10 in an air atmosphere when the temperature is 700 DEG C- 1S.cm-1. The solid oxide fuel cell assembled by the composite electrolyte prepared in example 2 has an open circuit voltage of 1.07V and a maximum output power density of 450-460 mW-cm at 700 DEG C-2The power density was stable within 40 hours.
Examples of the experiments
Characterization of XRD for samples of Experimental example 1
XRD of the sample obtained in example 1 was measured, and the results are shown in FIG. 1.
As can be seen from fig. 1, the intensity and position of the peaks are consistent with the cubic phase when undoped as seen by comparing this pattern with the standard diffraction pattern, and there are diffraction peaks of the (110), (112), (220) and (224) crystal planes at 20.75 °, 29.48 °, 42.18 ° and 61.13 ° 2 θ, respectively.
It can be seen from the graph that the strongest diffraction peak appears at around 2 θ ═ 30 °, and the peak profile is sharper and the half-peak width is narrower, indicating that the sample has high crystallinity. It can also be seen that the diffraction peaks of NaCl and KCl are newly increased in the sample, indicating that NaCl, KCl and SrCe0.7Zr0.2Eu0.1O3-αNo chemical reaction occurs after the recombination.
Experimental example 2 Electron microscopy analysis of samples
Scanning electron microscopes of the surface and cross-section of the sample prepared in example 1 were respectively tested, and the results are shown in fig. 2 and 3, respectively, wherein,
FIG. 2 shows an electron micrograph of the surface topography of a sample prepared in example 1;
FIG. 3 shows an electron micrograph of the cross-section of the sample prepared in example 1.
As is clear from fig. 2 and 3, the composite electrolyte SrCe obtained in example 10.7Zr0.2Eu0.1O3-αThe NaCl-KCl has high compactness, no holes and uniform and consistent particle size.
Experimental example 3 conductivity analysis of sample
The conductivity of the sample prepared in example 1 was tested at 500-700 ℃ in an air atmosphere, and the results are shown in FIG. 4.
As can be seen from fig. 4, the conductivity gradually increases with increasing temperature, indicating that the composite electrolyte has better conductivity. The logarithm of the conductivity of the sample does not have a linear relation with the temperature, the temperature is continuously increased along with the increase of the temperature to the solid melting point of NaCl and KCl, the slope is reduced, the slope is large, the activation energy of the sample is large, the slope is small, the activation energy of the sample is small, the conduction of conduction protons is facilitated, and when the temperature is 700 ℃, the conductivity of the composite electrolyte reaches 1.27 multiplied by 10-1S.cm-1。
Experimental example 4 Performance of Fuel cell
H was assembled from the composite electrolyte prepared in example 1 using hydrogen as fuel gas and oxygen as oxidant, respectively2/O2The fuel cell was tested for I-V-P relationship at 700 ℃ and the results are shown in FIG. 5.
As can be seen from fig. 5, the open circuit voltage was 1.07V, which was close to the theoretical value, indicating that the composite electrolyte was very dense. The open-circuit voltage is gradually reduced, the current density is gradually increased, the power is gradually increased, and the maximum output power density of the fuel cell is maintained at 0.57-0.58W-cm within 40 hours-2The corresponding current density is maintained at 0.89-0.90A-cm-2The voltage is maintained at 0.63-0.65V.
The invention has been described in detail with reference to specific embodiments and illustrative examples, but the description is not intended to be construed in a limiting sense. Those skilled in the art will appreciate that various equivalent substitutions, modifications or improvements may be made to the technical solution of the present invention and its embodiments without departing from the spirit and scope of the present invention, which fall within the scope of the present invention. The scope of the invention is defined by the appended claims.

Claims (2)

1. A method for preparing a doped strontium cerate-alkali metal salt composite electrolyte, comprising the steps of:
1) mixing doped strontium cerate and alkali metal salt, and pressing to obtain a composite precursor;
2) calcining the composite precursor obtained in the step 1) to prepare a doped strontium cerate-alkali metal salt composite electrolyte;
wherein the doped strontium cerate is Eu3+、Zr4+Co-doping strontium cerate, wherein the alkali metal salt is a eutectic body of potassium chloride and sodium chloride; the weight ratio of the doped strontium cerate to the alkali metal salt is (4-5) to 1;
the chemical composition of the doped strontium cerate is SrCe(1-x-y)ZrxEuyO3-αWherein x is more than or equal to 0.20 and less than or equal to 0.30, y is more than 0.01 and less than or equal to 0.15, alpha is more than or equal to 0.005 and less than or equal to 0.05, x is the doping amount of Zr forming solid solution, y is the doping amount of positive trivalent rare earth element Eu forming solid solution, and alpha represents the oxygen vacancy number of each doped strontium cerate unit;
wherein the doped strontium cerate is prepared by the method comprising the following steps:
1-1) weighing a strontium source, a cerium source, a zirconium source and a europium-containing compound according to a set molar ratio, dissolving the strontium source, the cerium source, the zirconium source and the europium-containing compound in concentrated nitric acid, adding a ligand compound,
the strontium source is strontium acetate, and the strontium source is strontium acetate,
the cerium source is cerium ammonium nitrate,
the zirconium source is zirconium nitrate, and the zirconium source is zirconium nitrate,
the europium-containing compound is europium oxide,
the weight fraction of the concentrated nitric acid is more than 65 percent;
1-2) adjusting the pH value of the system to form sol, and heating to form gel; wherein, ammonia water or organic alkali is used for adjusting the pH value of the system;
1-3) calcining the gel to obtain doped strontium cerate;
wherein the co-melt is prepared by the following method:
step 2-1, weighing potassium chloride and sodium chloride according to a set proportion, and carrying out primary calcination at the temperature of 650-750 ℃ for 30-40 min;
and 2-2, crushing the calcined product, and carrying out secondary calcination at 650-750 ℃ for 30-40 min.
2. The method as claimed in claim 1, wherein in the step 1-3), the gel is subjected to a first calcination at 1150-1250 ℃ and a second calcination at 1500-1600 ℃, wherein the first calcination is performed for 4-6 hours and the second calcination is performed for 4-8 hours.
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High-performance intermediate temperature fuel cells of new SrCe0.9Yb0.1O3-α- inorganic salt composite electrolytes;Wenbao Zhang等;《Journal of Alloys and Compounds》;20160330;第677卷;第38-41页 *
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