Medium-temperature solid oxide fuel cell cathode material as well as preparation method and application thereof

Abstract

The invention relates to a medium-temperature solid oxide fuel cell cathode material as well as a preparation method and application thereof, and belongs to the technical field of methods or devices for directly converting chemical energy into electric energy. The chemical general formula of the cathode material of the medium-temperature solid oxide fuel cell is LaxBaySrzCoaFebO3, wherein the ratio of x to y to z is (0.45 to 0.65) to (0.01 to 0.2) to (0.3 to 0.4), and the ratio of (y + z) to (a + b) is 0.35 to 0.55. The cathode material of the medium-temperature solid oxide fuel cell has high conductivity and good oxygen catalytic activity, and can endow the fuel cell with excellent cell performance.

Description

Technical Field

[0001] The present invention relates to the technical field of methods or devices for directly converting chemical energy into electrical energy, and in particular to a cathode material for a medium-temperature solid oxide fuel cell and a preparation method and application thereof. Background Art

[0002] A fuel cell is a power generation device that can directly convert the chemical energy in hydrogen and various hydrocarbons into electrical energy. Compared with traditional thermal power generation, it has a high energy conversion efficiency because it does not need to go through intermediate processes such as combustion. It is also environmentally friendly, has flexible fuel types, and has sustainable fuel supply. According to the type of electrolyte, it is mainly divided into alkaline fuel cells, proton exchange membrane fuel cells, phosphoric acid fuel cells, molten carbonate fuel cells, and solid oxide fuel cells; among them, solid oxide fuel cells have the highest energy conversion efficiency and have broad application prospects in small household cogeneration systems, distributed power generation, transportation, large power stations, and reverse electrolysis hydrogen production.

[0003] The operating temperature of solid oxide fuel cells can reach thousands of degrees during actual operation. The high temperature environment accelerates the aging rate of its components, which in turn greatly affects the stability and service life of the battery. Therefore, reducing the operating temperature of solid oxide fuel cells has gradually become a research and development trend in recent years. For example, the operating temperature range of medium-temperature solid oxide fuel cells (IT-SOFC) is 600-800°C, which can not only effectively relieve the thermal stress of the ceramic structure to improve the operating stability of the battery, but also extend the service life of the battery while reducing manufacturing and maintenance costs. However, ABO3-type perovskite oxides (such as Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ (BSCF), La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF)) As the operating temperature decreases, the catalytic activity of the oxygen reduction reaction decreases, resulting in an increase in resistivity and a significant increase in internal resistance, which in turn limits the output efficiency of the battery and causes the battery performance to decline, making it unsuitable for use as a cathode material for IT-SOFC.

[0004] In view of the above problems, the existing technology mainly develops new material systems to replace traditional cathode materials, or dopes and modifies traditional cathode materials to improve them. However, in actual use, it is found that the conductivity of new structural materials (such as A2BO4 structural materials) is still far lower than that of ABO3 and the catalytic activity is not good; and doping oxygen ion conductor materials (such as Pr, Bi, etc.) can increase the oxygen vacancy concentration in traditional cathode materials to accelerate the oxygen ion conduction rate, but the doped composite cathode material is still easy to interact with zirconium-based electrolyte materials, resulting in Sr element segregation and then generating highly insulating impurities, which leads to poor stability and conductivity of the composite material. In addition, the connectors between the various structures of IT-SOFC are usually made of Fe-Cr alloy, which is easy to generate high-resistance SrCrO4 phase after long-term operation, which will also cause the battery voltage output to decay, resulting in a decrease in the battery life. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a medium-temperature solid oxide fuel cell cathode material and a preparation method and application thereof.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] In a first aspect, the present invention provides a medium-temperature solid oxide fuel cell cathode material, wherein the chemical formula of the medium-temperature solid oxide fuel cell cathode material is La x Ba y Sr z Co a Fe b O3;

[0008] Among them, x:y:z=(0.45~0.65):(0.01~0.2):(0.3~0.4), and (y+z) / (a+b)=0.35~0.55.

[0009] The cathode material of the medium-temperature solid oxide fuel cell of the present invention is an ABO3 type perovskite oxide, and the A-position element is occupied / substituted by a cation having a different radius or oxidation state, so that the trivalent cation La in the cathode material 3+ 、Divalent alkali metal ion Sr 2+ And Ba 2+They work together to change the oxidation state of the B-site cation and the oxygen vacancy concentration, accelerate the rate of the oxygen ion transfer process in the reaction and the adsorption / dissociation process of oxygen on the cathode surface, and enhance the catalytic activity for the oxygen reduction reaction; at the same time, the ratio of x, y, and z is controlled within the above range to obtain high catalytic activity and high oxygen diffusion coefficient and surface exchange coefficient to increase the electronic and ionic conductivity, thereby giving the fuel cell high conductivity, high oxygen catalytic activity, low impedance value, high battery output power and low voltage decay rate, thereby significantly extending the actual service life of the fuel cell; satisfying the relationship between y, z and a, b can be appropriately doped with low-valent cations in the cathode material, introducing an appropriate amount of oxygen vacancies, and improving the oxygen ion conduction rate while ensuring the stability of the crystal structure.

[0010] The study found that when Sr 2+ When the proportion is too high, it is easy to cause serious Sr segregation during the use of the fuel cell, and react with the zirconium-based electrolyte to generate highly insulating SrZrO3, which increases the ohmic impedance of the fuel cell and reduces the battery output power. 2+ When the ratio is too low, the electrical conductivity and oxygen catalytic activity of the cathode material will decrease.

[0011] At the same time, it was found that if Ba 2+ If the proportion of Ba is too high, it will cause serious lattice distortion, making the stability of the perovskite structure worse, and then causing the polarization impedance of the fuel cell to be too large; if Ba 2+ If the ratio is too low, it will be difficult to effectively alleviate the interface diffusion reaction and segregation without affecting the electrochemical performance of the fuel cell, resulting in an increase in the ohmic impedance of the fuel cell, and excessive battery output power and voltage attenuation rate. 3+ If the proportion is too low, excessive Sr will be introduced 2+ and Ba 2+ , which will affect its cubic structure and even cause lattice distortion; if La 3+ If the proportion is too high, Sr 2+ And Ba 2+ The proportion is too low, resulting in the above-mentioned adverse effects.

[0012] As a preferred embodiment of the medium-temperature solid oxide fuel cell cathode material of the present invention, in terms of molar parts, the x:y:z=(0.5-0.6):(0.08-0.15):(0.32-0.35).

[0013] As a preferred embodiment of the intermediate temperature solid oxide fuel cell cathode material of the present invention, x is 0.45 to 0.65; and / or, y is 0.01 to 0.2; and / or, z is 0.3 to 0.4. Optionally, x can be 0.46, 0.48, 0.50, 0.52, 0.54, 0.56, 0.58, 0.6, 0.62, 0.64; y can be 0.03, 0.05, 0.07, 0.09, 0.11, 0.13, 0.15, 0.17, 0.19; z can be 0.31, 0.32, 0.33, 0.34, 0.35, 0.36, 0.37, 0.38, 0.39.

[0014] As a preferred embodiment of the intermediate temperature solid oxide fuel cell cathode material of the present invention, a is 0.1 to 0.3; and / or b is 0.7 to 0.9. Optionally, a can be 0.12, 0.14, 0.16, 0.18, 0.2, 0.22, 0.24, 0.26, 0.28; b can be 0.72, 0.74, 0.76, 0.78, 0.8, 0.82, 0.84, 0.86, 0.88.

[0015] In a second aspect, the present invention provides a method for preparing the above-mentioned medium-temperature solid oxide fuel cell cathode material, which comprises the following steps:

[0016] S1, wet-mixing, drying, and once sintering the La-containing compound, the Sr-containing carbonate, and the Ba-containing carbonate to obtain a primary premixed compound;

[0017] S2, uniformly mixing the primary premixed compound, the Co-containing compound and the Fe-containing compound in S1, performing secondary sintering treatment, crushing and sieving to obtain a medium-temperature solid oxide fuel cell cathode material;

[0018] The ratio of the specific surface area of ​​the Sr-containing carbonate to the specific surface area of ​​the Ba-containing carbonate in S1 is 0.5 to 4.5;

[0019] The temperature of the primary sintering treatment in S1 is less than 1000°C (the temperature of the primary sintering needs to ensure that the Sr-containing carbonate and the Ba-containing carbonate can be decomposed), and the temperature of the secondary sintering treatment in S2 is greater than or equal to 1000°C.

[0020] Preferably, the La-containing compound in the above preparation method may specifically be La2O3; the Sr-containing carbonate may specifically be SrCO3; and the Ba-containing carbonate may specifically be BaCO3.

[0021] Compared with the preparation method of the traditional cathode material by mixing and sintering all raw material powders at one time, the present invention first prepares a premixed compound containing La, Sr and Ba by sintering at a lower temperature, and then sintering it with a Co-containing compound and an Fe-containing compound at a higher temperature. The low temperature sintering can be used to promote the decomposition of the carbonate compound, so as to achieve a more uniform solid solution of the A-site element. When the premixed compound is evenly mixed with the Co-containing and Fe-containing compounds by ball milling and then sintered at a higher temperature, the free energy of the solid solution reaction from the B site to the A site is greatly reduced due to the reduced diffusion resistance of the elements, so that the reaction is more complete, and La can be finally obtained. x Ba y Sr z Co a Fe b O3.

[0022] In addition, the above preparation method uses Ba-containing carbonate as raw material instead of other barium-containing compounds (such as Ba(NO3)2, BaCl2, Ba(OH)2, etc.) as raw materials, which can effectively avoid the loss of raw materials such as Ba(NO3)2 or Ba(OH)2 in wet mixing and the segregation of raw materials during the drying process, and will not produce the poisonous effect of Cl element on the battery. Moreover, since the atomic free energy of carbonate increases during the decomposition process, diffusion movement is more likely to occur; the present invention preferentially forms a mixed oxide combination by pre-sintering La-containing compounds, Sr-containing carbonates and Ba-containing carbonates, which can ensure the uniform solid solution of each element in the whole process.

[0023] Further, when the ratio of the specific surface area of ​​the Sr-containing carbonate to the specific surface area of ​​the Ba-containing carbonate is 0.5 to 4.5, the raw material powders of the Sr-containing carbonate and the Ba-containing carbonate can be more evenly mixed in the decomposition reaction and have good sintering activity. Optionally, the ratio of the specific surface area of ​​the Sr-containing carbonate to the specific surface area of ​​the Ba-containing carbonate can be specifically 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, or any two of the range values.

[0024] As a preferred embodiment of the method for preparing the cathode material of the medium-temperature solid oxide fuel cell of the present invention, the ratio of the specific surface area of ​​the Sr-containing carbonate to the specific surface area of ​​the Ba-containing carbonate in S1 is 1 to 2.5.

[0025] As a preferred embodiment of the method for preparing the cathode material of the medium-temperature solid oxide fuel cell of the present invention, the specific surface area of ​​the Sr-containing carbonate in S1 is 4 to 18 m 2 / g; and / or, the specific surface area of ​​the Ba-containing carbonate in S1 is 4 to 8m 2 / g. Optionally, the specific surface area of ​​the Sr-containing carbonate can be 4m2 / g, 6m 2 / g, 8m 2 / g, 10m 2 / g, 12m 2 / g, 14m 2 / g, 16m 2 / g, 18m 2 / g or any two of them; the specific surface area of ​​the Ba-containing carbonate can be 4m 2 / g, 5m 2 / g, 6m 2 / g, 7m 2 / g, 8m 2 / g or both.

[0026] The study found that the Sr-containing carbonate and Ba-containing carbonate with the above specific surface area have moderate sintering activity, which can better ensure the uniform diffusion of various elements during the sintering process.

[0027] As a preferred embodiment of the method for preparing the medium-temperature solid oxide fuel cell cathode material of the present invention, the temperature of the first sintering treatment in S1 is 800-980°C and the time is 2-4 hours; and / or, the temperature of the second sintering treatment in S2 is 1000-1300°C and the time is 4-8 hours.

[0028] Optionally, the temperature of the primary sintering treatment can be 850°C, 900°C, or 950°C, and the time can be 2.5h, 3h, or 3.5h; the temperature of the secondary sintering treatment can be 1050°C, 1100°C, 1150°C, 1200°C, or 1250°C, and the time can be 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, or 7.5h.

[0029] In a third aspect, the present invention provides the use of the above-mentioned medium-temperature solid oxide fuel cell cathode material in the preparation of a fuel cell.

[0030] In a fourth aspect, the present invention provides a solid oxide fuel cell, which includes a cathode, and the cathode contains the above-mentioned medium-temperature solid oxide fuel cell cathode material.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] The cathode material of the medium-temperature solid oxide fuel cell of the present invention is an ABO3 type perovskite oxide, and the A-position element is occupied / substituted by a cation having a different radius or oxidation state, so that the trivalent cation La in the cathode material 3+ 、Divalent alkali metal ion Sr 2+ And Ba2+ They work together to change the oxidation state of the B-site cation and the oxygen vacancy concentration, accelerate the rate of the oxygen ion transfer process in the reaction and the adsorption / dissociation process of oxygen on the cathode surface, and enhance the catalytic activity for the oxygen reduction reaction; at the same time, the ratio of the three is controlled to obtain high catalytic activity and high oxygen diffusion coefficient and surface exchange coefficient to increase the electronic and ion conductivity, thereby giving the fuel cell high conductivity, high oxygen catalytic activity, low impedance value, high battery output power and low voltage decay rate, thereby significantly extending the actual service life of the fuel cell. DETAILED DESCRIPTION

[0033] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0034] Unless otherwise specified, other materials, reagents, etc. used in the examples and comparative examples can be obtained from commercial sources.

[0035] Examples 1 to 10 and Comparative Examples 1 to 3

[0036] Table 1 La in Examples 1 to 10 and Comparative Examples 1 to 3 x Ba y Sr z Co a Fe b The specific surface area of ​​O3, SrCO3 is S1, and the specific surface area of ​​BaCO3 is S2

[0037]

[0038]

[0039] The method for preparing the intermediate temperature solid oxide fuel cell cathode material of the embodiments 1 to 10 and comparative examples 1 to 3 comprises the following steps:

[0040] S1. According to the ratio in Table 1, La2O3, SrCO3 and BaCO3 were mixed by pure water wet method for 2 hours, dried at 80°C and then sintered once (atmosphere: air, temperature: 900°C, time: 3 hours) to obtain a premixed compound;

[0041] S2. The primary premixed compound in S1 is evenly mixed with the Co-containing compound (Co3O4) and the Fe-containing compound (Fe3O4), and then subjected to secondary sintering treatment (the atmosphere is air, the temperature is 1200°C, and the time is 6 hours). After the sintering is completed, the medium-temperature solid oxide fuel cell cathode material is obtained by crushing and sieving.

[0042] Comparative Example 4

[0043] A comparative example of the medium-temperature solid oxide fuel cell cathode material of the present invention. The preparation method of the medium-temperature solid oxide fuel cell cathode material in this comparative example is basically the same as that in Example 1, except that BaCO3 in step S1 is replaced by Ba(NO3)2.

[0044] Comparative Example 5

[0045] A comparative example of the medium-temperature solid oxide fuel cell cathode material of the present invention. The preparation method of the medium-temperature solid oxide fuel cell cathode material in this comparative example is basically the same as that in Example 1, except that: BaCO3 in step S1 is replaced by BaCl2.

[0046] Comparative Example 6

[0047] A comparative example of the medium-temperature solid oxide fuel cell cathode material of the present invention. The preparation method of the medium-temperature solid oxide fuel cell cathode material in this comparative example is basically the same as that in Example 1, except that: BaCO3 in step S1 is replaced by Ba(OH)2.

[0048] Comparative Example 7

[0049] A comparative example of the intermediate temperature solid oxide fuel cell cathode material of the present invention, the chemical formula of the intermediate temperature solid oxide fuel cell cathode material of this comparative example is La 0.45 Ba 0.2 Sr 0.35 Co 0.2 Fe 0.8 O3, the preparation method thereof comprises the following steps:

[0050] According to La 0.45 Ba 0.2 Sr 0.35 Co 0.2 Fe 0.8 O3, La2O3, SrCO3, BaCO3, Co3O4 and Fe3O4 are mixed evenly and then subjected to high-temperature sintering treatment only once (the atmosphere is air, the temperature is 1200°C, and the time is 6h). After the sintering is completed, it is crushed to obtain the medium-temperature solid oxide fuel cell cathode material (the raw material formula and specific surface area are the same as those in Example 1).

[0051] Performance Testing

[0052] The intermediate temperature solid oxide fuel cell cathode material (1 g) in each embodiment and comparative example was mixed with 10 mL of isopropanol, 2 mL of ethylene glycol and 0.6 mL of glycerol, and zirconium oxide grinding balls were added, and the mixture was ball-milled at a speed of 400 rpm for 1 h to obtain a cathode slurry;

[0053] 2 g of NiO-YSZ anode raw material mixed powder (NiO-YSZ anode raw material mixed powder is composed of NiO and YSZ in a mass ratio of 1:1, wherein YSZ is 8 mol% of stable ZrO2) is weighed and placed in a mold, and a tablet press is used to press and mold the anode layer (Ni-YSZ, thickness is 10 μm) at 150 MPa; then 1 g of YSZ electrolyte powder is laid on the anode layer, and the powder is placed in a mold and pressed at 300 MPa, and then sintered at 1500° C. in a muffle furnace for 5 h to obtain a half-cell structure of anode layer | electrolyte layer (Ni-YSZ | YSZ, thickness is 30 μm);

[0054] The cathode slurry is uniformly printed on the electrolyte layer of the anode half-cell structure to form a single cell structure anode layer | electrolyte layer | cathode layer (Ni-YSZ | YSZ | La x Ba y Sr z Co a Fe b O3, thickness is 50 μm); and then sintered at 1000°C for 2 h to obtain a single cell.

[0055] The intermediate temperature solid oxide fuel cell cathode materials and the above-mentioned single cell in each embodiment and comparative example were tested as shown in 2. The test results are shown in Table 3.

[0056] Table 2 Summary of test contents and their standards

[0057]

[0058]

[0059] Table 3 Performance test data

[0060]

[0061]

[0062] According to the data in Table 3, the conductivity of the intermediate temperature solid oxide fuel cell cathode materials prepared in Examples 1 to 10 is greater than or equal to 108 S·cm -1 , and the polarization impedance is less than or equal to 0.189Ω·cm 2 , and the ohmic impedance is less than or equal to 0.4Ω·cm 2 At the same time, the output power of the prepared medium-temperature solid oxide fuel cell cathode material after being made into a single cell reaches 400mW·cm 2The above values, and the voltage decay rate is below 0.05%, indicate that the medium-temperature solid oxide fuel cell cathode material of the present invention has both high electrical conductivity and low impedance, which can effectively improve the battery output power of the fuel cell and reduce its voltage decay rate, thereby significantly extending the actual service life of the fuel cell.

[0063] At the same time, according to Comparative Examples 1 to 3, it can be seen that when La in the cathode material of the medium-temperature solid oxide fuel cell is 3+ , Sr 2+ And Ba 2+ When the proportion is not appropriate, it is difficult to effectively improve the conductivity while reducing the polarization impedance and ohmic impedance, and thus it is difficult to improve the output power and voltage decay rate of the single cell; according to Comparative Examples 4, 5 and 6, it can also be found that when Ba(NO3)2, BaCl2 or Ba(OH)2 is used as the source of Ba in the cathode material of the medium-temperature solid oxide fuel cell, the prepared cathode material not only has a significantly decreased conductivity, but also a significantly increased polarization impedance value; According to Comparative Example 7, it can be seen that the conductivity, polarization impedance, ohmic impedance of the cathode material obtained by mixing and sintering all the raw material powders at one time, as well as the output power and voltage decay rate of the single cell cannot meet the application requirements.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A medium-temperature solid oxide fuel cell cathode material, characterized in that: The chemical formula of the intermediate temperature solid oxide fuel cell cathode material is La x Ba y Sr z Co a Fe b O3; Among them, x:y:z=(0.45~0.65):(0.01~0.2):(0.3~0.4), and (y+z) / (a+b)=0.35~0.

55.

2. The intermediate temperature solid oxide fuel cell cathode material according to claim 1, characterized in that: The x:y:z=(0.5~0.6):(0.08~0.15):(0.32~0.35).

3. The intermediate temperature solid oxide fuel cell cathode material according to claim 1, characterized in that: The x is 0.45 to 0.65; and / or, the y is 0.01 to 0.2; and / or, the z is 0.3 to 0.

4.

4. The intermediate temperature solid oxide fuel cell cathode material according to claim 1, characterized in that: The a is 0.1 to 0.3; and / or the b is 0.7 to 0.

9.

5. The method for preparing the cathode material of the intermediate temperature solid oxide fuel cell according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1, wet-mixing, drying, and once sintering the La-containing compound, the Sr-containing carbonate, and the Ba-containing carbonate to obtain a primary premixed compound; S2, uniformly mixing the primary premixed compound, the Co-containing compound and the Fe-containing compound in S1, performing secondary sintering treatment, crushing and sieving to obtain a medium-temperature solid oxide fuel cell cathode material; The ratio of the specific surface area of ​​the Sr-containing carbonate to the specific surface area of ​​the Ba-containing carbonate in S1 is 0.5 to 4.5; The temperature of the primary sintering process in S1 is less than 1000°C, and the temperature of the secondary sintering process in S2 is greater than or equal to 1000°C.

6. The preparation method according to claim 5, characterized in that: The ratio of the specific surface area of ​​the Sr-containing carbonate to the specific surface area of ​​the Ba-containing carbonate in S1 is 1 to 2.

5.

7. The preparation method according to claim 5, characterized in that: The specific surface area of ​​the Sr-containing carbonate in S1 is 4 to 18 m 2 / g; And / or, the specific surface area of ​​the Ba-containing carbonate in S1 is 4 to 8 m 2 / g.

8. The preparation method according to claim 5, characterized in that: The temperature of the primary sintering treatment in S1 is 800-980°C and the time is 2-4h; And / or, the temperature of the secondary sintering treatment in S2 is 1000-1300° C. and the time is 4-8 hours.

9. Use of the intermediate temperature solid oxide fuel cell cathode material according to any one of claims 1 to 4 in the preparation of a fuel cell.

10. A solid oxide fuel cell, characterized in that: It comprises a cathode, wherein the cathode comprises the intermediate-temperature solid oxide fuel cell cathode material according to any one of claims 1 to 4.

Images