A solid oxide fuel cell composite cathode and its preparation method

Abstract

The present invention belongs to the field of solid oxide fuel cell technology and discloses a solid oxide fuel cell composite cathode and its preparation method. The preparation method comprises the following steps: mixing lanthanum nitrate, strontium nitrate, and ferric nitrate with a solvent to obtain a precursor solution; mixing Co3O4 nanopowder with the precursor solution to obtain a spinning solution; electrospinning the spinning solution to obtain a composite body; and drying and calcining the composite body to obtain an LSF-Co3O4 composite cathode material. The preparation method of the present invention can improve the electrocatalytic performance of the cathode material while ensuring that the thermal expansion coefficient of LSF remains substantially unchanged.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid oxide fuel cells, and in particular relates to a composite cathode of a solid oxide fuel cell and a preparation method thereof. Background Art

[0002] Solid oxide fuel cell (SOFC) is a green and clean energy conversion device with the advantages of rich fuel variety, low operating noise, low or zero emissions and high power generation efficiency. It has attracted much attention in the field of new energy.

[0003] As a SOFC cathode material, strontium-doped lanthanum ferrite (LSF) boasts high electronic conductivity and moderate ionic conductivity, making it widely used in medium- and low-temperature SOFCs. However, the electrochemical performance of LSF materials is still far inferior to that of common cobalt-based cathode materials. Therefore, to enhance the catalytic activity of LSF cathodes and enable their application, cobalt is introduced during the LSF material preparation process to improve their electrochemical performance.

[0004] However, the addition of cobalt increases the thermal expansion coefficient of the material, leading to a thermal mismatch between the cathode and electrolyte. During actual battery operation, this thermal expansion mismatch between the cathode and electrolyte materials can cause the electrolyte to crack, induce thermal stress, and thus reduce the long-term stability of the battery. Summary of the Invention

[0005] To address the above issues, the present invention provides a solid oxide fuel cell and a method for preparing the same. To maintain the thermal expansion coefficient of the LSF while improving the electrocatalytic performance of the material, the present invention introduces cobalt oxide onto the surface of the LSF material rather than into the material's lattice.

[0006] The present invention provides a method for preparing a composite cathode of a solid oxide fuel cell, comprising the following steps: mixing lanthanum nitrate, strontium nitrate, and ferric nitrate with a solvent to obtain a precursor solution; mixing Co3O4 nanopowder with the precursor solution to obtain a spinning solution; electrostatically spinning the spinning solution to obtain a composite green body; and drying and calcining the composite green body to obtain an LSF-Co3O4 composite cathode material.

[0007] In one embodiment of the present invention, the molar ratio of lanthanum, strontium and iron in the precursor solution is x:(1-x):1, wherein the value of x is 0.5-0.8.

[0008] In one embodiment of the present invention, the solvent includes one or more of dimethylformamide, dichloroethane, tetrachloroethane, chlorobenzene, and cyclohexanone.

[0009] In one embodiment of the present invention, the particle size of the Co3O4 nanopowder is 20 to 50 nm.

[0010] In one embodiment of the present invention, the electrospinning conditions are: a voltage of 12 to 18 kV, a distance between the needle of the syringe and the receiving device of 10 to 15 cm, and a propulsion speed of the syringe of 0.2 to 0.6 mL / h.

[0011] In one embodiment of the present invention, the composite green body is calcined at 600-800° C. for 1-3 hours.

[0012] In one embodiment of the present invention, the LSF-Co3O4 composite cathode material is mixed with an impregnation solution and kept warm at 350-400°C for 2-4 hours to obtain a LSF-Co3O4-BCS composite cathode material; wherein the impregnation solution includes barium nitrate, cerium nitrate, samarium nitrate, an additive, and water.

[0013] In one embodiment of the present invention, the molar ratio of barium, cerium and samarium in the impregnation solution is 1:0.8:0.2.

[0014] In one embodiment of the present invention, the auxiliary agent is one or more of citric acid, oxalic acid, and phosphoric acid.

[0015] The present invention also provides a solid oxide fuel cell composite cathode obtained by applying the above method.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] (1) The present invention adds Co3O4 nanopowder to a precursor solution containing La, Sr, and Fe, and uses an electrospinning method to obtain an LSF-Co3O4 composite cathode material in which the Co3O4 nanopowder is attached to the surface of LSF fibers. This allows cobalt oxide to be introduced into the surface of the LSF material instead of being incorporated into the material's lattice, thereby ensuring that the thermal expansion coefficient of the LSF remains essentially unchanged while improving the material's electrocatalytic performance.

[0018] (2) The present invention also impregnates CeO2-based BaCe on the surface of the LSF-Co3O4 composite cathode material. 0.8 Sm 0.2 O 3-δ The LSF-Co3O4 composite cathode material, containing a 1.5-μm (BCS) electrolyte (where δ represents oxygen vacancies), forms a coating structure that addresses the volatilization and easy reduction of the Co element in the LSF-Co3O4 composite cathode material. This further improves the thermal expansion coefficients of the cathode material and the barrier layer, enhancing the long-term stability of the battery. Furthermore, the introduction of BCS significantly enhances oxygen ion conduction, further improving battery performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is an SEM image of the LSF-Co3O4 composite cathode material prepared in Example 1;

[0020] Figure 2 Graph showing cell voltage and power density of a single cell including the cathode layer prepared in Example 1 at 700° C.;

[0021] Figure 3 Graph showing cell voltage and power density at 700° C. for a single cell including the cathode layer prepared in Example 4;

[0022] Figure 4 Graph showing the cell voltage and power density of a single cell including the cathode layer prepared in Comparative Example 1 at 700°C. DETAILED DESCRIPTION

[0023] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0024] The present invention provides a method for preparing a composite cathode of a solid oxide fuel cell, comprising the following steps:

[0025] (1) Lanthanum nitrate, strontium nitrate, and ferric nitrate are mixed with a solvent to obtain a precursor solution.

[0026] The molar ratio of lanthanum, strontium and iron in the precursor solution is x:(1-x):1, wherein the value of x is 0.5-0.8.

[0027] The solvent includes one or more of dimethylformamide (DMF), dichloroethane, tetrachloroethane, chlorobenzene, and cyclohexanone.

[0028] The ratio of nitrate (the sum of lanthanum nitrate, strontium nitrate and ferric nitrate) to solvent in the precursor solution is 2 g: (10-15 mL).

[0029] (2) Mixing the Co3O4 nanopowder with the precursor solution to obtain a spinning solution.

[0030] Wherein, the particle size of the Co3O4 nanopowder is 20 to 50 nm.

[0031] The mass ratio of the Co3O4 nanopowder to LSF is 2:8, wherein the mass of LSF (strontium-doped lanthanum ferrite) can be calculated based on the mass of nitrate in the precursor solution.

[0032] (3) The spinning solution is subjected to electrostatic spinning to obtain a composite body.

[0033] The electrospinning conditions are as follows: a voltage of 12 to 18 kV, a distance between the syringe needle and the receiving device of 10 to 15 cm, and a syringe propulsion speed of 0.2 to 0.6 mL / h. Preferably, the syringe is rotated while being propulsed to ensure a more uniform dispersion of the Co3O4 nanopowder.

[0034] (4) After drying the composite body at 55-65° C., heating it to 600-800° C. and keeping it at that temperature for 1-3 hours to achieve calcination to obtain a LSF-Co 3 O 4 composite cathode material.

[0035] (5) Mixing the LSF-Co3O4 composite cathode material with the impregnation solution, and keeping the mixture at 350-400°C for 2-4 hours to obtain the LSF-Co3O4-BCS composite cathode material.

[0036] The impregnation solution includes barium nitrate, cerium nitrate, samarium nitrate, an additive, and water. The additive is one or more of citric acid, oxalic acid, and phosphoric acid.

[0037] The molar ratio of barium, cerium and samarium in the impregnation solution is 1:0.8:0.2.

[0038] The total metal ion (including barium ions, cerium ions and samarium ions) concentration in the impregnation solution is 0.5-0.8 mol / L.

[0039] The molar ratio of the auxiliary agent to the total metal ions (including barium ions, cerium ions and samarium ions) in the impregnation solution is (1.5-2):1.

[0040] The proportion of BCS in the LSF-Co3O4-BCS composite cathode material is 12wt% to 18wt%, wherein BCS (BaCe 0.8 Sm 0.2 BiO 3-δ ) can be calculated based on the mass of nitrate in the impregnation solution.

[0041] (6) The LSF-Co3O4-BCS composite cathode material and the pinene alcohol solution containing ethyl cellulose are stirred and mixed evenly to obtain a cathode slurry, and the obtained cathode slurry is screen-printed on the barrier layer. After drying, the temperature is increased to 900-950°C at a heating rate of 2-4°C and kept warm for 2-3 hours to obtain a cathode layer.

[0042] Wherein, the mass ratio of the terpineol solution to the LSF-Co3O4-BCS composite cathode material is 8:10 to 9:10.

[0043] The mass ratio of ethyl cellulose to terpineol in the terpineol solution is 2:98 to 8:92.

[0044] The present invention also provides a solid oxide fuel cell composite cathode obtained by applying the above preparation method.

[0045] Example 1

[0046] This embodiment provides a method for preparing a composite cathode of a solid oxide fuel cell, comprising the following steps:

[0047] (1) Lanthanum nitrate, strontium nitrate, and ferric nitrate were mixed with DMF and stirred for 10 hours to obtain a precursor solution. The molar ratio of lanthanum, strontium, and iron in the precursor solution was 0.7:0.3:1. The ratio of nitrate (the sum of lanthanum nitrate, strontium nitrate, and ferric nitrate) to DMF in the precursor solution was 2 g:13 mL.

[0048] (2) Co3O4 nanopowder was mixed with the precursor solution and stirred for 2 hours to obtain a spinning solution. The mass ratio of the Co3O4 nanopowder to LSF was 2:8. The particle size of the Co3O4 nanopowder was 30 nm.

[0049] (3) Electrospinning the spinning solution to obtain a composite body. The electrospinning conditions are: voltage of 15 kV, distance between the needle of the syringe and the receiving device of 10 cm, and syringe propulsion speed of 0.4 mL / h.

[0050] (4) After drying the composite body at 60°C, the temperature was raised to 800°C and kept at this temperature for 2 hours to achieve calcination to obtain a LSF-Co3O4 composite cathode material.

[0051] (5) The LSF-Co3O4 composite cathode material is mixed with an impregnation solution, and the mixture is kept at 380°C for 3 hours to obtain an LSF-Co3O4-BCS composite cathode material. The impregnation solution includes barium nitrate, cerium nitrate, samarium nitrate, citric acid, and water. The molar ratio of barium, cerium, and samarium in the impregnation solution is 1:0.8:0.2. The total metal ion concentration in the impregnation solution (i.e., the sum of the concentrations of barium ions, cerium ions, and samarium ions) is 0.6 mol / L. The molar ratio of citric acid to total metal ions (including barium ions, cerium ions, and samarium ions) in the impregnation solution is 1.5:1. The proportion of BCS in the LSF-Co3O4-BCS composite cathode material is 15 wt%.

[0052] (6) The LSF-Co3O4-BCS composite cathode material and the pinene alcohol solution containing ethyl cellulose were stirred and mixed evenly to obtain a cathode slurry, and the obtained cathode slurry was screen-printed on the barrier layer. After drying, the temperature was increased to 930°C at a heating rate of 3°C and kept at this temperature for 2.5 hours to obtain a cathode layer.

[0053] The mass ratio of the terpineol solution to the LSF-Co3O4-BCS composite cathode material is 8:10. The mass ratio of ethyl cellulose to terpineol in the terpineol solution is 2:98.

[0054] This embodiment also provides a solid oxide fuel cell composite cathode obtained by applying the above preparation method. Figure 2 Graph showing the cell voltage and power density of a single cell including the cathode layer of this embodiment at 700°C.

[0055] Example 2

[0056] This embodiment provides a method for preparing a composite cathode of a solid oxide fuel cell, comprising the following steps:

[0057] (1) Lanthanum nitrate, strontium nitrate, and ferric nitrate are mixed with cyclohexanone and stirred for 10 hours to obtain a precursor solution. The molar ratio of lanthanum, strontium, and iron in the precursor solution is 0.5:0.5:1. The ratio of nitrate (the sum of lanthanum nitrate, strontium nitrate, and ferric nitrate) to cyclohexanone in the precursor solution is 2 g:10 mL.

[0058] (2) Co3O4 nanopowder was mixed with the precursor solution and stirred for 2 hours to obtain a spinning solution. The mass ratio of the Co3O4 nanopowder to LSF was 2:8. The particle size of the Co3O4 nanopowder was 20 nm.

[0059] (3) Electrospinning the spinning solution to obtain a composite body. The electrospinning conditions are: voltage of 12 kV, distance between the needle of the syringe and the receiving device of 13 cm, and syringe propulsion speed of 0.2 mL / h.

[0060] (4) After drying the composite body at 55°C, the temperature was raised to 700°C and kept at this temperature for 1 hour to achieve calcination to obtain a LSF-Co3O4 composite cathode material.

[0061] (5) The LSF-Co3O4 composite cathode material is mixed with an impregnation solution, and the mixture is kept at 350°C for 4 hours to obtain an LSF-Co3O4-BCS composite cathode material. The impregnation solution includes barium nitrate, cerium nitrate, samarium nitrate, phosphoric acid, and water. The molar ratio of barium, cerium, and samarium in the impregnation solution is 1:0.8:0.2. The total metal ion concentration in the impregnation solution (i.e., the sum of the concentrations of barium ions, cerium ions, and samarium ions) is 0.6 mol / L. The molar ratio of phosphoric acid to total metal ions (including barium ions, cerium ions, and samarium ions) in the impregnation solution is 1.6:1. The proportion of BCS in the LSF-Co3O4-BCS composite cathode material is 18 wt%.

[0062] (6) The LSF-Co3O4-BCS composite cathode material and a terpineol solution containing ethyl cellulose were stirred and mixed to obtain a cathode slurry, and the obtained cathode slurry was screen-printed onto a barrier layer. After drying, the temperature was increased to 900°C at a heating rate of 2°C and kept at this temperature for 3 hours to obtain a cathode layer. The mass ratio of the terpineol solution to the LSF-Co3O4-BCS composite cathode material was 8.5:10. The mass ratio of the ethyl cellulose to the terpineol in the terpineol solution was 5:95.

[0063] This embodiment also provides a solid oxide fuel cell composite cathode obtained by applying the above preparation method.

[0064] Example 3

[0065] This embodiment provides a method for preparing a composite cathode of a solid oxide fuel cell, comprising the following steps:

[0066] (1) Lanthanum nitrate, strontium nitrate, and ferric nitrate are mixed with dichloroethane and stirred for 10 hours to obtain a precursor solution. The molar ratio of lanthanum, strontium, and iron in the precursor solution is 0.8:0.2:1. The ratio of nitrate (the sum of lanthanum nitrate, strontium nitrate, and ferric nitrate) to dichloroethane in the precursor solution is 2 g:15 mL.

[0067] (2) Co3O4 nanopowder was mixed with the precursor solution and stirred for 2 hours to obtain a spinning solution. The mass ratio of the Co3O4 nanopowder to LSF was 2:8. The particle size of the Co3O4 nanopowder was 50 nm.

[0068] (3) Electrospinning the spinning solution to obtain a composite body. The electrospinning conditions are: voltage of 18 kV, distance between the needle of the syringe and the receiving device of 15 cm, and syringe propulsion speed of 0.6 mL / h.

[0069] (4) After drying the composite body at 65°C, the temperature was raised to 600°C and kept at this temperature for 3 hours to achieve calcination to obtain a LSF-Co3O4 composite cathode material.

[0070] (5) The LSF-Co3O4 composite cathode material is mixed with an impregnation solution, and the mixture is kept warm at 400°C for 2 hours to obtain an LSF-Co3O4-BCS composite cathode material. The impregnation solution includes barium nitrate, cerium nitrate, samarium nitrate, oxalic acid, and water. The molar ratio of barium, cerium, and samarium in the impregnation solution is 1:0.8:0.2. The total metal ion concentration in the impregnation solution (i.e., the sum of the concentrations of barium ions, cerium ions, and samarium ions) is 0.8 mol / L. The molar ratio of oxalic acid to total metal ions (including barium ions, cerium ions, and samarium ions) in the impregnation solution is 2:1. The proportion of BCS in the LSF-Co3O4-BCS composite cathode material is 12 wt%.

[0071] (6) The LSF-Co3O4-BCS composite cathode material and the terpineol solution containing ethyl cellulose were stirred and mixed to obtain a cathode slurry, and the obtained cathode slurry was screen-printed onto the barrier layer. After drying, the temperature was increased to 950°C at a heating rate of 4°C and kept at this temperature for 2 hours to obtain a cathode layer. The mass ratio of the terpineol solution to the LSF-Co3O4-BCS composite cathode material was 9:10. The mass ratio of the ethyl cellulose to the terpineol in the terpineol solution was 8:92.

[0072] This embodiment also provides a solid oxide fuel cell composite cathode obtained by applying the above preparation method.

[0073] Example 4

[0074] The difference between this embodiment and embodiment 1 is that step (5) is not performed in this embodiment, and the LSF-Co3O4 composite cathode material obtained in step (4) is directly mixed into a cathode slurry to prepare a cathode layer. Other conditions are the same as those in embodiment 1. Figure 3 Graph showing the cell voltage and power density of a single cell including the cathode layer of this embodiment at 700°C.

[0075] Comparative Example 1

[0076] The difference between this comparative example and Example 1 is that step (2) is not performed in this comparative example, and the precursor solution obtained in step (1) is directly subjected to electrospinning. Other conditions are the same as those in Example 1. Figure 4 Graph showing the cell voltage and power density of a single cell including the cathode layer of this comparative example at 700°C.

[0077] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in this field can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. These modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and description of the present invention.

Claims

1. A method for preparing a composite cathode of a solid oxide fuel cell, characterized in that: The following steps are involved: mixing lanthanum nitrate, strontium nitrate, ferric nitrate and a solvent to obtain a precursor solution; Mixing Co3O4 nanopowder with the precursor solution to obtain a spinning solution; The spinning solution is subjected to electrostatic spinning to obtain a composite body, The composite green body is dried and calcined to obtain a LSF-Co3O4 composite cathode material.

2. The method for preparing a composite cathode of a solid oxide fuel cell according to claim 1, wherein: The molar ratio of lanthanum, strontium and iron in the precursor solution is x:(1-x):1, wherein the value of x is 0.5-0.

8.

3. The method for preparing a composite cathode of a solid oxide fuel cell according to claim 1, wherein: The solvent includes one or more of dimethylformamide, dichloroethane, tetrachloroethane, chlorobenzene, and cyclohexanone.

4. The method for preparing a composite cathode of a solid oxide fuel cell according to claim 1, wherein: The particle size of the Co3O4 nanopowder is 20 to 50 nm.

5. The method for preparing a composite cathode of a solid oxide fuel cell according to claim 1, wherein: The electrospinning conditions are as follows: voltage of 12-18 kV, distance between the needle of the syringe and the receiving device of 10-15 cm, and propulsion speed of the syringe of 0.2-0.6 mL / h.

6. The method for preparing a composite cathode of a solid oxide fuel cell according to claim 1, wherein: The composite green body is calcined at 600-800° C. for 1-3 hours.

7. The method for preparing a composite cathode of a solid oxide fuel cell according to claim 1, wherein: The following steps are also included: The LSF-Co3O4 composite cathode material is mixed with an impregnation solution, and kept at 350-400° C. for 2-4 hours to obtain a LSF-Co3O4-BCS composite cathode material; The impregnation solution includes barium nitrate, cerium nitrate, samarium nitrate, additives and water.

8. The method for preparing a composite cathode of a solid oxide fuel cell according to claim 7, wherein: The molar ratio of barium, cerium and samarium in the impregnation solution is 1:0.8:0.

2.

9. The method for preparing a composite cathode of a solid oxide fuel cell according to claim 7, wherein: The auxiliary agent is one or more of citric acid, oxalic acid and phosphoric acid.

10. A composite cathode for a solid oxide fuel cell obtained by the preparation method according to any one of claims 1 to 9.

Images