A perovskite oxygen electrode material co-doped with alkaline earth metal and lanthanide element at A position and preparation method thereof

Abstract

A perovskite oxygen electrode material co-doped with alkaline earth metal and lanthanide elements at the A position and a preparation method thereof, wherein the structural formula is Bi 0.8‑ x Ln x Ca 0.2 FeO 3‑δ , where 0<x≤0.1, δ is the content of oxygen vacancies, and Ln is selected from one of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, and Yb. Metal nitrates of Bi, Ln, Ca, and Fe are used as initial raw materials, each raw material is poured into a container, deionized water is added, and stirred until the solution is clear, and then citric acid and ammonia water are added in sequence, the pH value of the solution is adjusted, and the solution is stirred to form a gel, and then the oxygen electrode material is obtained after drying, grinding, and calcining in sequence. The method has a low sintering temperature and a simple preparation process. The obtained oxygen electrode material can obtain excellent oxygen exchange capacity and high catalytic activity, and can also have good electrochemical properties and stability, and can be used as an oxygen electrode material for solid oxide batteries.

Description

Technical Field

[0001] The invention relates to the field of solid oxide batteries, and in particular to a perovskite oxygen electrode material co-doped with alkaline earth metals and lanthanide elements at the A position and a preparation method thereof. Background Art

[0002] Solid oxide cells (SOC) have attracted attention as a highly efficient energy conversion device. On the one hand, they operate in solid oxide fuel cell mode (SOFCs) using H 2 On the other hand, it operates in solid oxide electrolysis cells (SOECs) to generate H 2 O or CO 2 Converted to H 2 Or fuel gas such as CO for energy storage.

[0003] At present, solid oxide batteries face some problems that hinder their commercial development. For example, the thermal expansion coefficient of oxygen electrode materials does not match that of commonly used electrolyte materials. During the temperature rise and fall test, they will gradually peel off from the electrolyte surface due to the presence of thermal stress, resulting in a decrease in the electrochemical performance and stability of the battery. Although the reaction between battery components can be slowed down by lowering the operating temperature and stabilizing the microstructure of the oxygen electrode and the electrolyte, thereby extending the battery life, as the operating temperature decreases, the oxygen reduction reaction (ORR) activity of the oxygen electrode decreases significantly, and the performance also decreases accordingly. Therefore, it is crucial to develop oxygen electrode materials with excellent performance. Summary of the invention

[0004] The purpose of the present invention is to provide a perovskite oxygen electrode material co-doped with alkaline earth metals and lanthanide elements at the A position and a preparation method thereof. The method has a low sintering temperature and a simple preparation process. The prepared oxygen electrode material can obtain excellent oxygen exchange capacity and high catalytic activity, and also has good electrochemical properties and good stability, and can be used as an oxygen electrode material for solid oxide batteries.

[0005] To achieve the above object, the present invention provides a perovskite oxygen electrode material co-doped with alkaline earth metal and lanthanide element at A position, wherein the structural formula of the oxygen electrode material is Bi 0.8-x Ln x Ca 0.2 FeO 3-δ , where 0<x≤0.1, δ is the content of oxygen vacancies, and Ln is selected from one of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, and Yb.

[0006] To achieve the above object, the present invention also provides a method for preparing a perovskite oxygen electrode material co-doped with an alkaline earth metal and a lanthanide element at the A position, comprising the following steps:

[0007] (1) Using metal nitrates of Bi, Ln, Ca, and Fe as the initial raw materials, according to the structural formula Bi 0.8-x Ln x Ca 0.2 FeO 3-δ Weigh each raw material according to the stoichiometric ratio of the corresponding elements, where 0<x≤0.1, δ is the content of oxygen vacancies, and Ln is selected from one of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, and Yb; then weigh an appropriate amount of citric acid;

[0008] (2) Pour various raw metal nitrates into a container, add deionized water, stir at 60-100° C. until the solution becomes clear, then add citric acid and ammonia water in sequence to adjust the pH value of the solution to 6-8, and stir until the water evaporates to form a gel;

[0009] (3) placing the gel obtained in step (2) in a high-temperature drying oven and drying until the gel becomes dry to obtain a precursor;

[0010] (4) Grinding the precursor obtained in step (3), placing it in a high-temperature muffle furnace, and calcining it in an air atmosphere to obtain an oxygen electrode material.

[0011] Preferably, in step (1), the metal nitrates of Bi, Ln, Ca and Fe are respectively Bi(NO 3 ) 3 ·5H 2 O、Ln(NO 3 ) 3 6H 2 O, Ca(NO 3 ) 2 ·4H 2 O, Fe(NO 3 ) 3 9H 2 O.

[0012] Preferably, in step (1), citric acid is weighed so that the molar ratio between metal ions and citric acid is 1:1.5.

[0013] Preferably, in step (2), the pH value of the solution is adjusted to 6 and the stirring temperature is 80°C.

[0014] Preferably, in step (3), the temperature of the high temperature drying oven is 150-300° C., and the drying time is 5-12 hours.

[0015] Preferably, in step (4), the calcination temperature is 800-1000° C. and the calcination time is 5-10 hours.

[0016] In the present invention, the matrix material BiFeO 3 Co-doping alkaline earth metals and lanthanide elements at the A position can improve the oxygen vacancy concentration and reaction activity of the perovskite oxygen electrode material; doping with alkaline earth metal Ca elements can improve the conductivity of the perovskite material and improve the oxygen exchange performance; in addition, doping with lanthanide elements is beneficial to enhancing the catalytic activity of the oxygen electrode material. The present invention adopts the citrate combustion method for preparation, with low sintering temperature and simple preparation process. The key properties of the material (thermal expansion coefficient, polarization impedance, etc.) are regulated by co-doping. The prepared oxygen electrode material has excellent oxygen exchange capacity and high catalytic activity, and also has good electrochemical performance and good stability, and can be used as an oxygen electrode material for solid oxide batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is the XRD pattern of the oxygen electrode material prepared in Example 1;

[0018] Figure 2 is the XRD pattern of the oxygen electrode material prepared in Example 2;

[0019] Figure 3 is a SEM image of the oxygen electrode material prepared in Example 2;

[0020] Figure 4 is a schematic diagram of the relationship between the thermal expansion coefficient and temperature of a dense sample strip prepared from the oxygen electrode material prepared in Example 2;

[0021] Figure 5 It is a schematic diagram of the impedance curve of the oxygen electrode material prepared in Example 2. DETAILED DESCRIPTION

[0022] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] Embodiment 1

[0024] A perovskite oxygen electrode material co-doped with alkaline earth metal and lanthanide element at A position, wherein the structural formula of the oxygen electrode material is Bi 0.7 La 0.1 Ca 0.2 FeO 3-δ , where δ is the content of oxygen vacancies.

[0025] The method for preparing the above oxygen electrode material comprises the following steps:

[0026] (1) According to the structural formula Bi 0.7 La0.1 Ca 0.2 FeO 3-δ The stoichiometric ratio of the corresponding elements in the mixture is 0.7:0.1:0.2:1. Weigh 33.9549 g of Bi(NO 3 ) 3 ·5H 2 O, 4.3301 g of La(NO 3 ) 3 6H 2 O, 4.723 g of Ca(NO 3 ) 2 ·4H 2 O, 40.3997 g of Fe(NO 3 ) 3 9H 2 O, where δ is the content of oxygen vacancies; then 63.042 g of citric acid is weighed according to the molar ratio between metal ions and citric acid being 1:1.5;

[0027] (2) Pour various raw metal nitrates into a beaker, add 200 mL of deionized water, place the mixed solution on a magnetic stirrer, stir at 80° C. until the solution becomes clear, then add citric acid and ammonia water in sequence to adjust the pH value of the solution to 6, and keep the solution stirred at 80° C. until the water evaporates and a gel is formed;

[0028] (3) placing the gel obtained in step (2) in a high temperature drying oven and drying at 200° C. for 10 h until the gel becomes dry to obtain a precursor;

[0029] (4) The precursor obtained in step (3) was ground and placed in a high-temperature muffle furnace, and calcined at 900° C. for 5 h in an air atmosphere to obtain Bi 0.7 La 0.1 Ca 0.2 FeO 3-δ Oxygen electrode material, the XRD spectrum of the prepared oxygen electrode powder is as follows Figure 1 As shown. Figure 1 It can be seen that the prepared material does not have any impurities, confirming that the prepared material is a pure phase perovskite oxygen electrode material.

[0030] Embodiment 2

[0031] A perovskite oxygen electrode material co-doped with alkaline earth metal and lanthanide element at A position, wherein the structural formula of the oxygen electrode material is Bi 0.7 Pr 0.1 Ca 0.2 FeO 3-δ , where δ is the content of oxygen vacancies.

[0032] The method for preparing the above oxygen electrode material comprises the following steps:

[0033] (1) According to the structural formula Bi 0.7 La 0.1 Ca 0.2 FeO 3-δ The stoichiometric ratio of the corresponding elements in the mixture is 0.7:0.1:0.2:1. Weigh 33.9549 g of Bi(NO 3 ) 3 ·5H 2 O, 4.3501g of Pr(NO 3 ) 3 6H 2 O, 4.723 g of Ca(NO 3 ) 2 ·4H 2 O, 40.3997 g of Fe(NO 3 ) 3 9H 2 O, where δ is the content of oxygen vacancies; then 63.042 g of citric acid is weighed according to the molar ratio between metal ions and citric acid being 1:1.5;

[0034] (2) Pour various raw metal nitrates into a beaker, add 200 mL of deionized water, place the mixed solution on a magnetic stirrer, stir at 80° C. until the solution becomes clear, then add citric acid and ammonia water in sequence to adjust the pH value of the solution to 7, and keep the solution stirred at 80° C. until the water evaporates and a gel is formed;

[0035] (3) placing the gel obtained in step (2) in a high temperature drying oven and drying at 250° C. for 12 h until the gel becomes dry to obtain a precursor;

[0036] (4) The precursor obtained in step (3) was ground and placed in a high-temperature muffle furnace, and calcined at 900° C. for 5 h in an air atmosphere to obtain Bi 0.7 Pr 0.1 Ca 0.2 FeO 3-δ Oxygen electrode material, XRD spectrum and SEM image of the prepared oxygen electrode powder are shown as follows Figure 2 and Figure 3 As shown. Figure 2 It can be seen that the prepared material does not have any impurities, confirming that the prepared material is a pure phase perovskite oxygen electrode material. Figure 3 It can be seen that the oxygen electrode material grains are closely arranged and the grain size is uniform.

[0037] Weigh 2g of Bi prepared in Example 2 0.7 Pr 0.1 Ca 0.2 FeO 3-δThe oxygen electrode material was placed in a stripping mold and maintained at a pressure of 300 MPa for 5 minutes to form a rectangular sample strip, which was then placed in a muffle furnace and calcined at 950°C for 5 hours to obtain a dense sample strip (with a specification of approximately 0.44 cm × 0.5 cm × 1.9 cm). The prepared dense sample strip was placed in a thermal expansion instrument to test the thermal expansion coefficient at a test temperature of 30-900°C. The test results are shown in FIG. Figure 4 As shown. Figure 4 It can be seen that the thermal expansion coefficient is 16.7638×10 -6 K -1 , which is lower than the thermal expansion coefficient of commonly used Co-based materials by 20×10 -6 K -1 The low thermal expansion coefficient of the oxygen electrode material prepared in this embodiment matches the thermal expansion coefficient of common electrolyte materials. The oxygen electrode material with a low thermal expansion coefficient can ensure that the battery will not fall off from the electrolyte during the test, thereby ensuring the stability of the battery during the test.

[0038] In order to characterize the catalytic performance of oxygen electrode material samples, a symmetrical cell method was used to measure the Bi 0.7 Pr 0.1 Ca 0.2 FeO 3-δ The polarization impedance (ASR) of Bi 0.7 Pr 0.1 Ca 0.2 FeO 3-δ The sample was placed in air atmosphere and tested for ASR at 700-800°C to obtain the impedance curve fitted by EIS, as shown in Figure 5 As shown. Figure 5 It can be seen that Bi 0.7 Pr 0.1 Ca 0.2 FeO 3-δ The ASR of the oxygen electrode sample shows a gradually decreasing trend with increasing temperature. Oxygen electrode materials with low polarization impedance are an effective way to improve the electrochemical performance and long-term stability of the battery. This shows that the oxygen electrode material prepared in this example has good electrochemical performance and good stability.

Claims

1. A perovskite oxygen electrode material co-doped with alkaline earth metal and lanthanide element at the A position, characterized in that: The structural formula of the oxygen electrode material is Bi 0.8-x Ln x Ca 0.2 FeO 3-δ , where 0< x ≤0.1, δ is the content of oxygen vacancies, and Ln is selected from La or Pr.

2. The method for preparing a perovskite oxygen electrode material co-doped with alkaline earth metal and lanthanide element at A position according to claim 1, characterized in that: The following steps are involved: (1) Using metal nitrates of Bi, Ln, Ca, and Fe as the initial raw materials, according to the structural formula Bi 0.8-x Ln x Ca 0.2 FeO 3-δ Weigh each raw material according to the stoichiometric ratio of the corresponding elements, where 0 < x ≤0.1, δ is the content of oxygen vacancies, Ln is selected from La or Pr; (2) Pour various raw metal nitrates into a container, add deionized water, stir at 60-100°C until the solution becomes clear, then add citric acid and ammonia water in sequence, adjust the pH value of the solution to 6-8, and stir until the water evaporates to form a gel; (3) placing the gel obtained in step (2) in a high-temperature drying oven and drying until the gel becomes dry to obtain a precursor; (4) The precursor obtained in step (3) is ground, placed in a high-temperature muffle furnace, and calcined in an air atmosphere to obtain an oxygen electrode material.

3. The method for preparing a perovskite oxygen electrode material co-doped with alkaline earth metal and lanthanide element at A position according to claim 2, characterized in that: In step (1), the metal nitrates of Bi, Ln, Ca and Fe are Bi(NO3)3·5H2O, Ln(NO3)3·6H2O, Ca(NO3)2·4H2O and Fe(NO3)3·9H2O respectively.

4. The method for preparing a perovskite oxygen electrode material co-doped with alkaline earth metal and lanthanide element at A position according to claim 2 or 3, characterized in that: In step (1), citric acid is weighed so that the molar ratio of metal ion to citric acid is 1:1.

5.

5. The method for preparing a perovskite oxygen electrode material co-doped with alkaline earth metal and lanthanide element at A position according to claim 2 or 3, characterized in that: In step (2), the pH value of the solution is adjusted to 6 and the stirring temperature is 80°C.

6. The method for preparing a perovskite oxygen electrode material co-doped with alkaline earth metal and lanthanide element at A position according to claim 2 or 3, characterized in that: In step (3), the temperature of the high temperature drying oven is 150-300°C, and the drying time is 5-12 hours.

7. The method for preparing a perovskite oxygen electrode material co-doped with alkaline earth metal and lanthanide element at A position according to claim 2 or 3, characterized in that: In step (4), the calcination temperature is 800-1000° C. and the calcination time is 5-10 hours.

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