Air electrode chromium poisoning resisting method based on surface component regulation and control

Abstract

The invention discloses a method for resisting chromium poisoning of an air electrode based on surface component regulation and control. The method comprises the following steps: (1) manufacturing cation vacancies on the surface of La1-xSrxCo1-yFeyO3 by utilizing acid etching; (2) mixing the powder obtained in the step (1) with a precursor solution containing surface modification elements, and carrying out gelation and drying processes to obtain a precursor mixture; and (3) carrying out heat treatment on the precursor mixture to promote surface modification elements to diffuse to powder near-surface lattice sites through the cation vacancies so as to obtain the chromium poisoning resistant composite nano air electrode powder based on surface component regulation and control. According to the invention, the nano-sized composite air electrode powder can be prepared at low cost, and the composite air electrode powder shows outstanding chromium poisoning resistance.

Description

Technical Field

[0001] This invention belongs to the field of fuel cell catalytic material preparation technology, specifically relating to an air electrode anti-chromium poisoning method based on surface composition regulation. Background Technology

[0002] Solid oxide batteries (SOCs) are considered a promising technology for addressing the growing energy crisis and global climate change due to their clean and efficient energy conversion characteristics. In fuel cell mode, SOCs can efficiently convert fuel into electricity, and in electrolysis mode, they can store renewable electrical energy as chemical energy by converting greenhouse gases. However, the Fe-Cr stainless steel connectors in the stack release gaseous CrO3 under high temperatures and oxidizing atmospheres, which interacts with the air electrode and deposits, leading to performance degradation of the air electrode and hindering the commercial application of SOCs.

[0003] Perovskite materials La 1-x Sr x Co 1-y Fe y O3 (LSCF) possesses excellent mixed ionic-electronic conductivity and oxygen catalytic activity, thus it is considered an ideal air electrode material for SOC. However, during SOC operation, due to elastic and electrostatic interactions, SrO tends to segregate on the LSCF surface and react with CrO3 vapor from the metal interconnect to generate insulating phases such as SrCrO4 and Cr2O3. These secondary phases severely impair the electrochemical performance of LSCF. To improve the operational stability of LSCF, some researchers have used Nb doping to successfully suppress Sr segregation; however, the initial performance remains low (Journal of Materials Chemistry A, 2016, 4(45): 17678-17685). On the other hand, some researchers have used Ca doping to dope LaCo 0.2 Fe 0.8 O 3-δ It can maintain good stability while exhibiting excellent electrolytic performance (ACS Appl Mater Interfaces, 2023, 15(37): 43732-43744). However, some scholars have reported that Ca doping of LaFeO3 leads to a decrease in conductivity (Journal of The Electrochemical Society, 2008, 155(7): B660-B665). Therefore, developing a composite nano-air electrode that combines high electrochemical performance with long-term operational stability is a major challenge for realizing the commercial application of SOC. Summary of the Invention

[0004] The purpose of this invention is to provide an air electrode method for resisting chromium poisoning based on surface composition regulation, utilizing acid etching on La 1-x Sr x Co 1-y Fe y By creating cation vacancies on the O3 surface and doping with surface-modifying elements without altering the bulk properties, and then using heat treatment to induce these elements to diffuse through the cation vacancies to near-surface lattice sites of the powder, excellent electrochemical performance and resistance to chromium poisoning are simultaneously achieved by reducing the driving force of Sr segregation.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A method for preventing chromium poisoning in air electrodes based on surface composition modulation: The initial composition of the electrode material is La. 1- x Sr x Co 1-y Fe y O3, 0.4≤x≤0.8, 0.2≤y≤0.8, through an acid etching-thermal diffusion step, partially replaces the cations on the electrode material surface with surface-modifying elements, which are one or more of Ca, Ba, Pr, and Gd.

[0006] The preparation steps of this electrode are as follows: (1) Using acid etching on La 1-x Sr x Co 1-y Fe y O3 creates cation vacancies on its surface; (2) The powder obtained in step (1) is mixed with a precursor solution containing surface-modifying elements, and then subjected to gelation and drying processes to obtain a precursor mixture; (3) The precursor mixture is heat-treated to promote the diffusion of surface-modifying elements to near-surface lattice sites of the powder through the cation vacancies, thereby obtaining anti-chromium poisoning composite nano air electrode powder based on surface composition regulation.

[0007] Further, in step (1), the acidic solution used for acid etching is one of citric acid, nitric acid, and glacial acetic acid, with a pH value of 1 to 5, an etching time of 5 to 60 min, a temperature of 25 to 60 °C, and a magnetic stirrer speed of 250 to 300 r / min.

[0008] Furthermore, in step (1), the acid used reacts with La 1-x Sr x Co 1-y Fe y The total molar ratio of O3 metal cations is 0.02:1 to 2:1.

[0009] Further, in step (1), the etched powder is collected by centrifugation or filtration and then dried at 60~80 °C for 12~20 h.

[0010] Further, in step (2), the surface-modifying element precursor solution is composed of citric acid, metal salt and deionized water, wherein the metal salt is one or more of calcium nitrate, barium nitrate, praseodymium nitrate and gadolinium nitrate, and the molar ratio of citric acid to metal salt is 1:1.

[0011] Furthermore, in step (2), the metal salt reacts with La 1-x Sr x Co 1-y Fe y The total molar ratio of O3 metal cations is 0.02:1 to 2:1.

[0012] Furthermore, in step (2), the gelation process temperature is 50~300 °C.

[0013] Furthermore, in step (2), the drying temperature is 50~300 °C and the drying time is 2~20 h.

[0014] Furthermore, in step (3), the calcination temperature of the heat treatment is 750~950 °C, and the calcination time is 1~20 h.

[0015] Furthermore, an anti-chromium poisoning composite nano air electrode powder based on surface composition regulation was prepared by the method described above.

[0016] This invention has the following advantages: 1. The composite nano air electrode disclosed in this invention not only has a fine nanostructure, but also achieves a synergistic improvement in electrochemical performance and anti-chromium poisoning ability.

[0017] 2. The composite nano air electrode preparation method disclosed in this invention has the advantages of simple process, low cost and high stability, and has excellent prospects for industrial application. Attached Figure Description

[0018] Figure 1 These are the XRD spectra of the composite nano air electrode powder obtained in Example 1 and Comparative Example 1, and commercial LSCF.

[0019] Figure 2 This is a comparison of the polarization resistance of the composite nano-air polarimetric cell obtained in Example 1 and Comparative Example 1 and the commercial LSCF polarimetric cell at 750 °C.

[0020] Figure 3The graph shows the polarization resistance changes of the composite nano-air polarimetric cell and the commercial LSCF polarimetric cell obtained in Example 1 and Comparative Example 1 at 750 °C in a humid air environment containing chromium pollutants.

[0021] Figure 4 The graph shows the ohmic resistance changes of the composite nano-air electrode symmetric cell and the commercial LSCF symmetric cell obtained in Example 1 and Comparative Example 1 at 750 °C in a humid air environment containing chromium pollutants.

[0022] Figure 5 The images show the surface Raman spectra of the composite nano-air electrode symmetric cell and the commercial LSCF symmetric cell obtained in Example 1 after 100 h at 750 °C in a humid air environment containing chromium pollutants. Detailed Implementation

[0023] The present invention will be further illustrated by the following specific embodiments, but its scope of protection is not limited to the following embodiments.

[0024] Example 1: (1) La is added according to the molar ratio of the total metal cations to citric acid of 1:0.02. 0.6 Sr 0.4 Co 0.2 Fe 0.8 O3 and citric acid solution were added to a beaker and mixed. The pH of the citric acid solution was 2.8. The magnetic stirrer was set to 25 °C and 260 r / min. After stirring for 10 min, the pH of the solution was neutral. The powder was washed three times with deionized water using a centrifuge and then dried in an oven at 80 °C for 12 h to obtain air electrode powder with surface Sr defects.

[0025] (2) Mix calcium nitrate, citric acid and 25 mL of deionized water. Set the magnetic stirrer speed to 260 r / min and stir continuously to dissolve it completely. Set the magnetic stirrer temperature to 260 °C and evaporate some of the water. After obtaining the colloid, add air electrode powder with surface Sr defects. The molar ratio of the sum of metal cations of citric acid, calcium nitrate and surface Sr defect air electrode powder is 0.02:0.02:1. Continue heating and stirring until the water is completely evaporated to obtain the mixture gel.

[0026] (3) The mixture gel was dried in an oven at 180 °C for 12 h, and then calcined at 750 °C for 3 h to obtain anti-chromium poisoning composite nano air electrode powder based on surface composition regulation.

[0027] Example 2: (1) La is added according to the molar ratio of the total metal cations to citric acid of 1:0.02. 0.6Sr 0.4 Co 0.2 Fe 0.8 O3 and citric acid solution were added to a beaker and mixed. The pH of the citric acid solution was 2.8. The magnetic stirrer was set to 25 °C and 260 r / min. After stirring for 10 min, the pH of the solution was neutral. The powder was washed three times with deionized water using a centrifuge and then dried in an oven at 80 °C for 12 h to obtain air electrode powder with surface Sr defects.

[0028] (2) Mix calcium nitrate, citric acid and 25 mL of deionized water. Set the magnetic stirrer speed to 260 r / min and stir continuously to dissolve it completely. Set the magnetic stirrer temperature to 260 °C and evaporate some of the water. After obtaining the colloid, add air electrode powder with surface Sr defects. The molar ratio of the sum of metal cations of citric acid, calcium nitrate and surface Sr defect air electrode powder is 0.02:0.02:1. Continue heating and stirring until the water is completely evaporated to obtain the mixture gel.

[0029] (3) The mixture gel was dried in an oven at 180 °C for 12 h, and then calcined at 950 °C for 3 h to obtain anti-chromium poisoning composite nano air electrode powder based on surface composition regulation.

[0030] Comparative Example 1: (1) La is added according to the molar ratio of the total metal cations to citric acid of 1:0.02. 0.6 Sr 0.4 Co 0.2 Fe 0.8 O3 and citric acid solution were added to a beaker and mixed. The pH of the citric acid solution was 2.8. The magnetic stirrer was set to 25 °C and 260 r / min. After stirring for 10 min, the pH of the solution was neutral. The powder was washed three times with deionized water using a centrifuge and then dried in an oven at 80 °C for 12 h to obtain air electrode powder with surface Sr defects.

[0031] Figure 1 The figures show the XRD patterns of the composite nano-air electrode powder obtained in Example 1 and Comparative Example 1, and commercial LSCF. As shown in the figure, no obvious impurity phase diffraction peaks were observed in any of the samples, indicating the successful preparation of the composite nano-air electrode powder.

[0032] Figure 2 This is a comparison of the polarization resistance of the composite nano-air electrode symmetric cell obtained in Example 1 and Comparative Example 1, and a commercial LSCF symmetric cell at 750 °C. As shown in the figure, the polarization resistance of Example 1 is as low as 0.104 Ω cm. 2 This value is lower than the 0.119 Ω cm of Comparative Example 1. 2This is significantly lower than the 0.270 Ω cm of commercial LSCF symmetric cells. 2 It exhibits excellent electrochemical performance.

[0033] Figure 3 The graph shows the polarization resistance changes of the composite nano-air electrode symmetric cell and the commercial LSCF symmetric cell obtained in Example 1 and Comparative Example 1, respectively, at 750 °C in a humid air environment containing chromium pollutants. As shown in the figure, the polarization resistance increases of Example 1, Comparative Example 1, and the commercial LSCF within 100 h are 0.128 Ω cm. 2 0.351Ω cm 2 and 0.333Ω cm 2 Example 1 showed excellent resistance to chromium poisoning.

[0034] Figure 4 The graph shows the ohmic resistance changes of the composite nano-air electrode symmetric cell and the commercial LSCF symmetric cell obtained in Example 1 and Comparative Example 1, respectively, at 750 °C in a humid air environment containing chromium pollutants. As shown in the figure, the ohmic resistance increases of Example 1, Comparative Example 1, and the commercial LSCF within 100 h are 0.022 Ω cm. 2 0.113 Ω cm 2 and 0.190 Ωcm 2 This further confirms its excellent resistance to chromium poisoning.

[0035] Figure 5 The Raman spectra of the composite nano-air electrode symmetric cell obtained in Example 1 and the commercial LSCF symmetric cell were measured at 750 °C for 100 h in a humid air environment containing chromium pollutants. As shown in the figure, compared with the commercial LSCF, Example 1 only detected a weak SrCrO4 signal, further verifying its excellent resistance to chromium poisoning.

[0036] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A method for preventing chromium poisoning in air based on surface composition regulation, characterized in that: The initial composition of the electrode material is La 1-x Sr x Co 1-y Fe y O3, 0.4≤x≤0.8, 0.2≤y≤0.8, through an acid etching-thermal diffusion step, partially replaces the cations on the electrode material surface with surface-modifying elements, which are one or more of Ca, Ba, Pr, and Gd.

2. The method according to claim 1, characterized in that: Includes the following steps: (1) Using acid etching on La 1-x Sr x Co 1-y Fe y O3 creates cation vacancies on its surface; (2) The powder obtained in step (1) is mixed with a precursor solution containing surface-modifying elements, and then subjected to gelation and drying processes to obtain a precursor mixture; (3) The precursor mixture is heat-treated to promote the diffusion of surface-modifying elements to near-surface lattice sites of the powder through the cation vacancies, thereby obtaining anti-chromium poisoning composite nano air electrode powder based on surface composition regulation.

3. The method according to claim 2, characterized in that: In step (1), the acidic solution used for acid etching is one of citric acid, nitric acid, or glacial acetic acid, with a pH value of 1 to 5, an etching time of 5 to 60 min, a temperature of 25 to 60 °C, and a magnetic stirrer speed of 250 to 300 r / min.

4. The method according to claim 2, characterized in that: In step (1), the acid reacts with La 1-x Sr x Co 1-y Fe y The total molar ratio of O3 metal cations is 0.02:1 to 2:

1.

5. The method according to claim 2, characterized in that: In step (1), the etched powder is collected by centrifugation or filtration and then dried at 60-80 °C for 12-20 h.

6. The method according to claim 2, characterized in that: In step (2), the precursor solution containing surface-modifying elements is composed of citric acid, a metal salt, and deionized water, wherein the metal salt is one or more of calcium nitrate, barium nitrate, praseodymium nitrate, and gadolinium nitrate, and the molar ratio of citric acid to the metal salt is 1:1; the metal salt and La 1-x Sr x Co 1-y Fe y The total molar ratio of O3 metal cations is 0.02:1 to 2:

1.

7. The method according to claim 2, characterized in that: In step (2), the gelation process temperature is 50~300 °C.

8. The method according to claim 2, characterized in that: In step (2), the drying temperature is 50~300 °C and the drying time is 2~20 h.

9. The method according to claim 2, characterized in that: In step (3), the calcination temperature of the heat treatment is 750~950°C and the calcination time is 1~20 h.

10. A composite nano-air electrode powder for resisting chromium poisoning based on surface composition regulation, prepared by the method according to any one of claims 1-9.

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