Solid oxide fuel cell two-phase composite cathode material and preparation method thereof
Technical Field
The invention belongs to the technical field of intermediate-temperature Solid Oxide Fuel Cells (SOFC), and particularly relates to a novel dual-phase composite cathode material (1-x)Ca3Co2O6/xCe1.8Sm0.2O1.9(0 ≤x< 1) and a process for producing the same.
Technical Field
A Solid Oxide Fuel Cell (SOFC) is a power generation device that directly converts hydrocarbon fuel into electric energy, and has the advantages of high efficiency, low pollution, flexible fuel and the like. The traditional SOFC has the operation temperature as high as about 1000 ℃, which puts high requirements on electrode materials, battery components and accessory equipment, and the construction, operation and maintenance costs of the battery are high. Reducing the operating temperature will help improve the matching between the various components of the cell, reducing operating costs. However, once the operating temperature is lowered, the ohmic resistance of the electrolyte and the interfacial resistance of the electrodes are increased. With the application of the anode-supported cell structure and the perfection of the electrolyte membrane preparation process, the polarization resistance in the oxygen reduction process on the SOFC cathode becomes the most important impedance source of the cell, and the polarization resistance plays a decisive role in the output characteristics of the cell. Therefore, the selection of a suitable catalytic component is one of the fundamental measures to improve the electrochemical performance of the cathode.
In medium and low temperature SOFCs, ABO3Perovskite structureHave been studied in large numbers. The oxide has good catalytic activity of oxygen reduction reaction and higher 'ion-electron' mixed conductivity, is one of the current medium-low temperature SOFC cathode materials which are widely concerned, and mainly comprises La x1-Sr x CoO δ3-(δOxygen vacancy, the same shall apply hereinafter), Ba x1-Sr x Co y1-Fe y O δ3-、Sr x1-RE x CoO δ3-(RE is rare earth element), REBaCo2O δ5+And derivatives thereof, and the like. However, the Thermal Expansion Coefficient (TEC) of such materials is mostly very high and is much different from the TEC of the mainstream SOFC electrolyte material, such as Y x2Zr x1-2O x2-(YSZ)、Ce x1-Sm x O δ2-(SDC) and La x1-Sr x Ga y1-Mg y O δ3-(LSGM), etc., thereby increasing the sintering difficulty of the battery components and also being not beneficial to the stable operation of the battery. In addition, many of the cathode materials have problems of low conductivity, poor thermal stability of crystal lattice, and the like.
Therefore, a novel cobalt-based oxide Ca having a relatively small thermal expansion coefficient is used3Co2O6The material has obvious advantages as the SOFC cathode material. However, the thermoelectric cathode material also has a great challenge, and is limited by the hexagonal lattice structure and the oxygen ion transport property of the cathode material and the cubic or quasi-cubic ABO structure when being used as a cathode only3Cobalt-based perovskite is relatively poor, resulting in poor catalytic performance. Ca can be improved to a certain extent by means of doping, compounding other cobalt-based perovskite compounds and the like3Co2O6The electrochemical performance of the cathode material is simple, but the conventional methods have the limitations. For example, doping has limited improvement on the intrinsic properties of the material, and other cobalt-based perovskites are compounded to introduce more cobalt element, so that the cathode thermal expansion coefficient is improvedThe number will increase.
Disclosure of Invention
Oxide Ca for further developing hexagonal lattice structure3Co2O6Cathode catalytic potential of (2), increasing Ca3Co2O6The invention adopts the introduction of a fast ion conductor Ce0.8Sm0.2O1.9(SDC) method for overcoming the shortage of oxygen ion transport property of the material to expand Ca3Co2O6The three-phase interface during working designs a SOFC two-phase composite cathode material with novel structure and composition.
The solid oxide fuel cell two-phase composite cathode material prepared by the invention comprises the following chemical components: (1-x)Ca3Co2O6/xCe0.8Sm0.2O1.9(xNominal mole fraction of SDC in the complex phase composition), wherein Ca3Co2O6Is of hexagonal structure and space groupR-3C;Ce1.8Sm0.2O1.9Is of cubic structure, space groupFM3-M。
Two-phase composite cathode material (1-x)Ca3Co2O6/xCe1.8Sm0.2O1.9The preparation method comprises the following steps.
A cerium nitrate and calcium nitrate are used as a two-phase composite cathode material of a solid oxide fuel cell (1-x)Ca3Co2O6/xCe1.8Sm0.2O1.9The respective molar ratio of the medium calcium to the cerium is prepared into a mixed solution of calcium nitrate and cerium nitrate, and the concentration of the cerium nitrate and the calcium nitrate solution is 2-3 mol/L.
B preparing cobalt acetate or cobalt nitrate as a two-phase composite cathode material (1-x)Ca3Co2O6/xCe1.8Sm0.2O1.9Adding the molar ratio of the medium cobalt element into the calcium cerium nitrate mixed solution prepared in the step A, and stirring to obtain a metal cation mixed solutionWherein the concentration of the cobalt acetate or cobalt nitrate solution is 2-3 mol/L.
Sm is a compound of general formula (I)2O3Two-phase composite cathode material (1-x)Ca3Co2O6/xCe1.8Sm0.2O1.9Adding the samarium element into the concentrated nitric acid solution according to the molar ratio of the samarium element, and slightly heating, stirring and dissolving to obtain a samarium nitrate solution, wherein the concentration of the samarium nitrate solution is 2-3 mol/L.
D, mixing the samarium nitrate solution obtained in the step C with the metal cation mixed solution obtained in the step B to obtain the composite cathode material (1-x)Ca3Co2O6/xCe1.8Sm0.2O1.9All metal ion sources in the desired molar ratio.
E, adding Ethylene Diamine Tetraacetic Acid (EDTA) and citric acid into the solution obtained in the step D as complexing agents, and adding the following metal ions in mass ratio: ethylene diamine tetraacetic acid: citric acid = 1: 1: 1 (molar ratio) with constant stirring.
F, adding concentrated ammonia water into the mixture obtained in the step E until the ethylenediamine tetraacetic acid is completely dissolved and the solution is clear, and adjusting the pH value of the solution to 8-9 by using the concentrated ammonia water and dilute nitric acid to finally obtain a tan solution.
And G, putting the brown solution obtained in the step F into an oven at 100 ℃ for evaporation to obtain viscous gel, and putting the viscous gel into an oven at 150 ℃ for completely drying the water to obtain dry gel.
And H, putting the dried gel obtained in the step G into a muffle furnace with the temperature of 450 ℃ for combustion and decomposition for 5H to obtain a black ash-burning-shaped product.
I, grinding the black ash-burning products in the step H, and putting the ground black ash-burning products into a high-temperature air furnace at the temperature of 960-x)Ca3Co2O6/xCe1.8Sm0.2O1.9. The temperature control process of the high-temperature air furnace comprises the following steps: heating the mixture from room temperature to 960 ℃ and 1020 ℃ at the heating speed of 2 ℃/min, then preserving the heat for 10h, and then cooling the mixture at the cooling speed of 3 ℃/minAnd cooling to room temperature.
The invention has the beneficial effects that: the invention discloses a novel solid oxide fuel cell cathode catalytic component (1-x)Ca3Co2O6/xCe1.8Sm0.2O1.9Wherein 0 is less than or equal toxThe two-phase composite material prepared synchronously by one pot by the sol-gel method has uniform particle size distribution and no generation of any other impurity phase, and simultaneously, compared with the preparation process of the conventional composite component, the preparation process of the material can be greatly simplified by synchronously preparing the one pot. Compared with single-phase cathode material Ca3Co2O6The two-phase composite cathode material has less thermal expansion, interface resistance (area specific resistance,ASR) Lower; at 800 ℃, taking hydrogen as fuel and composition asxWhen the composite material of = 0.5 is used as a cathode, the peak value of the output power of the electrolyte-supported single cell is 620 mW · cm-2Left and right. The invention has low requirements on synthesis equipment, simple operation and no special requirements on a battery sintering process. The synthesized material has stable structure and better comprehensive performance of the electrode.
Drawings
FIG. 1 is an SEM image of the product of example 1 of the present invention.
FIG. 2 shows the product (1-x)Ca3Co2O6/xCe1.8Sm0.2O1.9XRD spectrum of (1).
FIG. 3 is an electrochemical impedance spectrum of the product of example 1 of the present invention.
Fig. 4 is a graph showing the variation trend of the operating voltage and the power density of a single cell of the product of example 1 of the invention with the current density at different temperatures.
FIG. 5 is an SEM image of the product of example 2 of the present invention.
FIG. 6 is an electrochemical impedance spectrum of the product of example 2 of the present invention.
Fig. 7 is a graph showing the variation trend of the operating voltage and the power density with the current density of a single cell of the product of example 2 of the invention at different temperatures.
FIG. 8 is an SEM image of the product of example 3 of the present invention.
FIG. 9 is an electrochemical impedance spectrum of the product of example 3 of the present invention.
Fig. 10 is a graph showing the variation of the operating voltage and the power density with the current density of a single cell of the product of example 3 of the present invention at different temperatures.
Detailed Description
The present invention will be further described with reference to the following examples.
Example 1
Single-phase cathode material Ca for solid oxide fuel cell3Co2O6(i.e. thex= 0) and weighing calcium nitrate and cobalt acetate to prepare a mixed solution; adding Ethylene Diamine Tetraacetic Acid (EDTA) and citric acid into the calcium-cobalt mixed ion solution as complexing agents, wherein the mass ratio of the EDTA to the citric acid is as follows: ethylene diamine tetraacetic acid: citric acid = 1: 1: 1 (molar ratio), continuously stirring, simultaneously adding concentrated ammonia water until the ethylenediamine tetraacetic acid is completely dissolved and the solution is clear, and adjusting the pH value of the solution to 8-9 to obtain a brownish red solution; putting the brownish red solution into an oven, baking at 100 ℃, evaporating most of water to obtain viscous gel, baking at 150 ℃, and completely drying the water in the viscous gel to obtain dry gel; putting the dried gel into a muffle furnace with the temperature of 450 ℃ for combustion and decomposition for 5 hours to obtain a black ash-burning-shaped product; taking out black ash-burning products, grinding, and then putting the products into an air furnace with the temperature of 960 ℃ for annealing for 10 hours to obtain the single-phase cathode material Ca of the solid oxide fuel cell3Co2O6。
SEM appearance analysis was performed on the synthesized positive electrode material, and Ca shown in FIG. 13Co2O6Is similar to a fruit commonly called Hovenia dulcis, and has relatively large particles. XRD diffraction is carried out on the prepared anode material, and the test result is shown in figure 2x= 0, and comparison of standard spectral lines in the figure shows that the synthesized sample is pure, has no impurity peak and Ca3Co2O6Has a hexagonal structure and space groups ofR-3C. Electrochemical impedance spectroscopy is carried out on the interface of the sample cathode material and the electrolyteThe results are shown in FIG. 3, and it can be seen that the interface impedance is about 0.28. omega. cm2. The results of the tests performed on the single cell using the sample material as the cathode are shown in fig. 4, and the peak value of the output power of the single cell at 800 ℃ is 410 mw.cm-2Left and right.
Example 2
Two-phase composite cathode material 0.75Ca according to solid oxide fuel cell3Co2O6/0.25Ce1.8Sm0.2O1.9(i.e. thex= 0.25), weighing calcium nitrate, cerium nitrate and cobalt acetate to prepare a mixed solution; then according to the composite cathode material 0.75Ca of the solid oxide fuel cell3Co2O6/0.25Ce1.8Sm0.2O1.9The molar ratio of the medium samarium element is measured2O3Adding into concentrated nitric acid solution for dissolving, and mixing with solution containing calcium, cerium and cobalt ions after the solution is clarified; adding Ethylene Diamine Tetraacetic Acid (EDTA) and citric acid into the calcium cerium cobalt samarium ion solution as complexing agents, wherein the mass ratio of the EDTA to the citric acid is as follows: ethylene diamine tetraacetic acid: citric acid = 1: 1: 1 (molar ratio), continuously stirring, simultaneously adding concentrated ammonia water until the ethylenediamine tetraacetic acid is completely dissolved and the solution is clear, and adjusting the pH value of the solution to 8-9 to obtain a brownish red solution; putting the brownish red solution into an oven, baking at 100 ℃, evaporating most of water to obtain viscous gel, baking at 150 ℃, and completely drying the water in the viscous gel to obtain dry gel; putting the dried gel into a muffle furnace with the temperature of 450 ℃ for combustion and decomposition for 5 hours to obtain a black ash-burning-shaped product; taking out the black ash-burning products, grinding, and then putting into an air furnace at 990 ℃ for annealing for 10h to obtain the composite cathode material 0.75Ca of the solid oxide fuel cell3Co2O6/0.25Ce1.8Sm0.2O1.9。
SEM morphology analysis of the synthesized anode material shows that the characteristics of the two-phase components are obvious, and one phase is uniformly attached to the other phase, as shown in FIG. 5. XRD diffraction is carried out on the prepared anode material, and the test result is shown in figure 2x= 0.25,As can be seen by comparing the standard spectral lines in the figure, the synthesized sample is pure and has no impurity peak, Ce, of any third party except the target composition phase1.8Sm0.2O1.9Is of cubic structure and space group isFM3-M. Electrochemical impedance spectroscopy measurement was performed on the interface between the cathode material and the electrolyte of the sample, and the result is shown in fig. 6, where it can be seen that the interface impedance was about 0.25 Ω · cm2. The test of the single cell using the sample material as the cathode was carried out, and the result is shown in fig. 7, where the peak value of the output power of the single cell at 800 ℃ was 420 mw-2Left and right.
Example 3
Two-phase composite cathode material 0.5Ca according to solid oxide fuel cell3Co2O6/0.5Ce1.8Sm0.2O1.9(i.e. thex= 0.5), weighing calcium nitrate, cerium nitrate and cobalt acetate to prepare a mixed solution; further according to the composite cathode material 0.5Ca of the solid oxide fuel cell3Co2O6/0.5Ce1.8Sm0.2O1.9The molar ratio of the medium samarium element is measured2O3Adding into concentrated nitric acid solution for dissolving, and mixing with solution containing calcium, cerium and cobalt ions after the solution is clarified; adding Ethylene Diamine Tetraacetic Acid (EDTA) and citric acid into the calcium cerium cobalt samarium ion solution as complexing agents, wherein the mass ratio of the EDTA to the citric acid is as follows: ethylene diamine tetraacetic acid: citric acid = 1: 1: 1 (molar ratio), continuously stirring, simultaneously adding concentrated ammonia water until the ethylenediamine tetraacetic acid is completely dissolved and the solution is clear, and adjusting the pH value of the solution to 8-9 to obtain a brownish red solution; putting the brownish red solution into an oven, baking at 100 ℃, evaporating most of water to obtain viscous gel, baking at 150 ℃, and completely drying the water in the viscous gel to obtain dry gel; putting the dried gel into a muffle furnace with the temperature of 450 ℃ for combustion and decomposition for 5 hours to obtain a black ash-burning-shaped product; taking out the black ash-burning products, grinding, and then putting the black ash-burning products into an air furnace at the temperature of 1020 ℃ for annealing for 10 hours to obtain the composite cathode material 0.5Ca of the solid oxide fuel cell3Co2O6/0.5Ce1.8Sm0.2O1.9。
SEM morphology analysis of the synthesized positive electrode material, as shown in fig. 8, the two-phase composition is characterized in that one phase is uniformly attached to the other phase. XRD diffraction is carried out on the prepared anode material, and the test result is shown in figure 2xAnd = 0.5, and as can be seen by comparing the standard spectral lines in the figure, the synthesized sample is pure, and no impurity peak of a third party is present except the target composition phase. Electrochemical impedance spectroscopy measurement was performed on the interface between the cathode material and the electrolyte of the sample, and the result is shown in fig. 9, where it can be seen that the interface impedance was about 0.12 Ω · cm2. The results of the tests performed on the single cell using the sample material as the cathode are shown in fig. 10, and the peak value of the output power of the single cell at 800 ℃ is 620 mw-2And the electrochemical performance of the cathode is greatly higher than that of a single-phase cathode.