Flaky spinel cobalt ferrite and its preparation method and application

Abstract

This application provides a sheet-like spinel cobalt ferrite, its preparation method, and its application, belonging to the field of solid oxide battery technology. In this application, a Co source and an Fe source are dissolved in deionized water, citric acid is added and stirred until homogeneous, then heated in a water bath until the solution becomes a reddish-brown transparent gel. The gel is then dried and ground to obtain a first powder. The first powder is then subjected to two CO2 laser-induced oxidation processes in air at a laser power of x to obtain a second powder. Wherein, 4W < x ≤ 10W. Finally, the second powder is washed and dried to obtain a sheet-like spinel cobalt ferrite. Compared with ordinary spinel cobalt ferrite, using the aforementioned sheet-like spinel cobalt ferrite as a cathode material in SOFC can reduce the polarization impedance of the battery by 0.023 Ωcm. 2 The maximum power density increased by 0.38 W / cm². ‑2 This improves the oxygen reduction activity and stability of SOFCs. Furthermore, using CO2 laser-induced methods simplifies the preparation process, reduces time costs, and increases production efficiency.

Description

Technical Field

[0001] This application relates to the field of solid oxide battery technology, specifically to a sheet-like spinel cobalt ferrite, its preparation method, and its application. Background Technology

[0002] Developing sustainable materials and technologies is a crucial solution to today's energy and environmental problems, particularly the conflict between traditional fossil fuel energy and environmental protection. In the battery field, solid oxide fuel cells (SOFCs) inherit the high efficiency and all-solid-state structure of fuel cells. Compared to rechargeable batteries that require charging and discharging, SOFCs can directly convert chemical energy into electrical energy in an environmentally friendly way, making them a hot research topic. However, SOFCs typically operate at 800-1000℃, and prolonged operation at high temperatures can easily lead to particle coarsening and performance degradation. Some researchers have attempted to lower the operating temperature, but found that this adjustment delays the oxygen reduction reaction (ORR) kinetics at the cathode, thus reducing the overall efficiency of the SOFC. Replacing the cathode material with a suitable one might effectively lower the operating temperature of the SOFC.

[0003] Perovskite oxide materials possess high oxygen ion transport performance and fast surface oxygen exchange kinetics, making them highly promising cathode candidates. However, the segregation effect of alkaline earth metals, their large coefficient of thermal expansion, and high cost hinder their application and development. Compared to perovskite-based cathodes, spinel materials are typically free of alkaline earth metals, effectively preventing performance degradation due to carbonate formation during preparation and operation. Furthermore, spinel materials are currently frequently used as protective layers for metal interconnects in SOFCs, exhibiting excellent stability. Therefore, using spinel materials as cathode materials may contribute to improving the stability of SOFCs.

[0004] Spinel cobalt ferrite is one of the common spinel materials. Currently, the common preparation methods are co-precipitation, hydrothermal method, and sol-gel method. The spinel morphology prepared is mostly irregular nanoparticle. These preparation methods are not only relatively complex, but also require high temperature and high pressure environment for reaction, or sintering at high temperature (around 1000℃). The preparation time is long and the cost is high. Prolonged high temperature calcination may also produce adverse chemical reactions, affecting the quality of the product.

[0005] In conclusion, it is necessary to develop a plate-like spinel cobalt ferrite, its preparation method, and its applications to solve the above problems. Summary of the Invention

[0006] In view of the technical problems existing in the background art, this application provides a sheet-like spinel cobalt ferrite, its preparation method and application, aiming to solve the technical problem of unstable performance of SOFCs at high temperatures over a long period of time by preparing a suitable cathode material. This application uses a CO2 laser-induced method to prepare a sheet-like spinel cobalt ferrite (CoFe2O4), and adjusts the size and fragmentation of the sheet-like morphology of the spinel CoFe2O4 by changing the laser power, thereby giving it a higher specific surface area. Compared with ordinary granular spinel CoFe2O4, the SOFC prepared using this sheet-like spinel CoFe2O4 has superior oxygen reduction activity, lower polarization impedance and higher maximum power density. Furthermore, the CO2 laser-induced method simplifies the preparation process of spinel CoFe2O4, reducing time costs and improving production efficiency.

[0007] In a first aspect, embodiments of this application provide a method for preparing plate-like spinel cobalt ferrite, which is prepared using a CO2 laser-induced method, including the following steps:

[0008] S1, dissolve the Co source and Fe source in deionized water, stir thoroughly, add citric acid, stir evenly, and obtain the precursor solution.

[0009] S2, the precursor solution obtained in step S1 is heated in a water bath until it turns into a reddish-brown transparent gel, and then the reddish-brown transparent gel is dried and ground to obtain the first powder.

[0010] S3, the first powder obtained in step S2 is evenly spread and subjected to CO2 laser induction twice in an air atmosphere to obtain the second powder. The power of the CO2 laser induction is x, and 4W < x ≤ 10W.

[0011] S4. After the second powder obtained in step S3 is cooled to room temperature, the second powder is washed and dried to obtain the plate-like spinel cobalt ferrite.

[0012] In some embodiments, in step S1, the concentration of metal ions in the precursor solution is 0.1 mol / L; the molar ratio of the metal ions to the citric acid is 1:(1.2-1.5); further, the molar ratio of Co ions to Fe ions in the metal ions is 1:2.

[0013] In some embodiments, in step S3, the CO2 laser-induced scanning speed is 100-150 mm / s. -1 The power induced by the CO2 laser is 6-8W.

[0014] In some embodiments, in step S1, the Co source is a cobalt salt and the Fe source is an iron salt; further, the cobalt salt is cobalt nitrate and the iron salt is ferric nitrate.

[0015] In some embodiments, in step S2, the temperature of the water bath heating is 60-90°C.

[0016] In some embodiments, in step S2, the drying method is blower drying; the temperature of blower drying is 70-90℃, and the time is 10-12h.

[0017] In some embodiments, in step S4, the drying temperature is 70-90°C and the time is 10-12 hours.

[0018] In some embodiments, in step S4, the washing refers to washing with distilled water 2-3 times, and then washing with ethanol 2-3 times.

[0019] Secondly, embodiments of this application provide a sheet-like spinel cobalt ferrite, which is prepared by any of the aforementioned methods, wherein the stoichiometric ratio of Co to Fe in the sheet-like spinel cobalt ferrite is 1:2; and the sheet-like spinel cobalt ferrite has a sheet-like morphology.

[0020] Thirdly, this application provides an application of sheet-like spinel cobalt ferrite, using the sheet-like spinel cobalt ferrite prepared in the aforementioned scheme as a cathode material for a solid oxide fuel cell.

[0021] The beneficial effects of this application are:

[0022] This application provides a lamellar spinel cobalt ferrite, its preparation method, and its application. This application utilizes a CO2 laser-induced method to modify the morphology of the spinel cobalt ferrite, increasing its specific surface area and effectively enhancing its oxygen reduction activity, resulting in excellent performance at 750-800℃. Compared to traditional sol-gel preparation methods, CO2 laser induction significantly reduces the time and cost required for cathode material preparation, simplifies the preparation process, and improves production efficiency.

[0023] (1) This application uses a CO2 laser-induced method to prepare sheet-like spinel cobalt ferrite. Compared with the slow and energy-intensive traditional high-temperature calcination method, this method has a simple preparation process, fast reaction speed, and low energy consumption. By adjusting the CO2 laser power, the synthesized spinel cobalt ferrite can have a suitable sheet-like structure, thereby improving the oxygen reduction reaction activity. In particular, when the laser power is 8W, the product prepared maintains a good nano-layer sheet shape, and the embedded nanoparticles are small. The product as a whole exhibits a fine and well-separated sheet-like morphology.

[0024] (2) The lamellar spinel cobalt ferrite has a higher specific surface area than the granular spinel cobalt ferrite prepared by high-temperature solid-state processing. It can provide a longer three-phase reaction interface, increase the number of surface active sites, and give the lamellar spinel cobalt ferrite superior electrochemical performance. Compared with the performance of ordinary granular spinel cobalt ferrite, its polarization resistance at 750℃ is reduced by 0.023 Ωcm. 2 The maximum power density increased by 0.38 W / cm². -2 .

[0025] (3) Using CO2 laser-induced preparation can reduce the number of sintering times and sintering time, avoid adverse chemical reactions that may occur due to long-term high-temperature calcination, and make the powder prepared by CO2 laser-induced preparation finer and more regular in morphology. No grinding is required, which further shortens the electrode preparation time.

[0026] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, specific embodiments of this application are given below. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0028] Figure 1 SEM images of the products prepared in Examples 1-3 and Comparative Examples 1-3 of this application at 6Kx magnification;

[0029] Figure 2 These are SEM images of the products prepared in Examples 1-3 and Comparative Examples 1-3 of this application, magnified 2K times.

[0030] Figure 3 The XRD patterns of the products prepared in Examples 1-3 and Comparative Examples 1-3 of this application;

[0031] Figure 4 Electrochemical impedance spectroscopy of symmetric cells CFO-4W-S, CFO-6W-S, CFO-8W-S and CFO-10W-S prepared for application examples of this application at 750 °C.

[0032] Figure 5 Electrochemical impedance spectroscopy of the symmetric cell CFO-SG-S prepared for the application example of this application at 750 °C;

[0033] Figure 6 This is a relaxation time distribution diagram of the symmetric cells CFO-6W-S, CFO-8W-S, CFO-10W-S and CFO-SG-S prepared by the application examples of this application at 750℃.

[0034] Figure 7 These are the electrochemical impedance spectroscopy diagrams of the symmetric cell CFO-8W-S prepared in the application example of this application at 700℃ and 800℃, respectively;

[0035] Figure 8 This is a comparison chart of the output power of the full cells CFO-6W-F, CFO-8W-F, CFO-10W-F and CFO-SG-F prepared in the application examples of this application at 750°C;

[0036] Figure 9 These are output power diagrams of the full cell CFO-8W-F prepared in the application example of this application at 700℃ and 800℃, respectively;

[0037] Figure 10 The O1s spectrum is obtained by X-ray photoelectron spectroscopy (XPS) testing of the products prepared in Examples 1-2 of this application. Detailed Implementation

[0038] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0040] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0041] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0042] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0043] SOFCs typically operate at 800-1000℃. Prolonged operation at high temperatures can lead to particle coarsening and performance degradation. Using spinel as the cathode material may help improve the stability of SOFCs. Spinel cobalt ferrite is one of the common spinel materials. Currently, its common preparation methods are co-precipitation, hydrothermal methods, and sol-gel methods, producing spinel morphologies that are mostly irregular nanoparticles. These preparation methods are not only complex but also often require high-temperature and high-pressure reactions or sintering at high temperatures (around 1000℃), resulting in long preparation times and high costs. Prolonged high-temperature calcination may also produce adverse chemical reactions, affecting product quality.

[0044] To address the technical problem of unstable performance of SOFCs under long-term high-temperature operation, this application provides a sheet-like spinel cobalt ferrite, its preparation method, and its application. Specifically, a sheet-like spinel cobalt ferrite (CoFe2O4) is prepared using a CO2 laser-induced method, simplifying the preparation process, reducing time, and lowering costs. By adjusting the laser power to control the sheet size and fragmentation degree of the spinel CoFe2O4, a higher specific surface area is achieved, thereby increasing the electrochemical performance of the spinel CoFe2O4. Furthermore, by using this spinel CoFe2O4 as a cathode material in SOFCs, the stability of SOFC performance during high-temperature operation is improved.

[0045] In a first aspect, embodiments of this application provide a method for preparing plate-like spinel cobalt ferrite, comprising the following steps:

[0046] S1, dissolve the Co source and Fe source in deionized water, stir thoroughly, add citric acid, stir evenly, and obtain the precursor solution.

[0047] In some embodiments, the concentration of metal ions in the precursor solution is 0.1 mol / L.

[0048] In some embodiments, the molar ratio of metal ions to citric acid is 1:(1.2-1.5). Further, the molar ratio of Co ions to Fe ions in the metal ions is 1:2.

[0049] Adding citric acid to the precursor solution facilitates better binding of Co and Fe ions. The addition of citric acid effectively controls the morphology and particle size of the material, resulting in a more uniform distribution and reducing agglomeration. However, the amount of citric acid added should not exceed the aforementioned molar ratio range. Excessive citric acid addition leads to excessive binding of Co and Fe ions, resulting in stronger binding between some metal ions and the formation of a second impurity phase. Insufficient citric acid addition leads to unstable material structure, which is detrimental to the synthesis of the material.

[0050] In some embodiments, the Co source is a cobalt salt and the Fe source is an iron salt; further, the cobalt salt is cobalt nitrate and the iron salt is ferric nitrate.

[0051] S2, the precursor solution obtained in step S1 is heated in a water bath until it turns into a reddish-brown transparent gel. Then the reddish-brown transparent gel is dried and ground to obtain the first powder, which is the precursor powder.

[0052] In some embodiments, the water bath heating temperature is 60-90°C, and the time is 15-25 hours.

[0053] In some embodiments, the drying method is forced air drying. The forced air drying temperature is 70-90°C, and the time is 10-12 hours.

[0054] S3, the first powder obtained in step S2 is evenly spread and subjected to CO2 laser induction twice in an air atmosphere to obtain the second powder. The power of CO2 laser induction is x, and 4W < x ≤ 10W. Further, the power of CO2 laser induction is 6-8W. Even further, the power of CO2 laser induction is 8W.

[0055] The product prepared by the CO2 laser-induced method exhibits a sheet-like morphology. The power of the CO2 laser affects the temperature at the moment of laser emission, thus influencing the formation and final morphology of the spinel cobalt ferrite. Specifically, firstly, sheet-like spinel cobalt ferrite could not be prepared with a laser power of 4W, while it was successfully prepared with a laser power of 6-10W. Secondly, as the laser power increased, the sheet-like morphology of the product showed varying degrees of fragmentation, resulting in the inclusion of a small number of fine nanoparticles within the sheet-like morphology. Specifically, the product prepared by a laser power of 4-8W maintained a good nanolayer sheet-like morphology with relatively small nanoparticles. Specifically, the product prepared by a laser power of 4-6W exhibited a large, adherent sheet-like morphology, while the product prepared by a laser power of 8W exhibited a fine and well-separated sheet-like morphology. The product prepared by a laser power of 10W showed a higher degree of fragmentation in its sheet-like morphology, with a greater number of fine nanoparticles and a small amount of agglomeration.

[0056] In some embodiments, the CO2 laser-induced scan rate is 100-150 mm / s. -1 .

[0057] S4. After the second powder obtained in step S3 is cooled to room temperature, the second powder is washed and dried to obtain plate-shaped spinel cobalt ferrite with the chemical formula CoFe2O4.

[0058] In some embodiments, the drying temperature is 70-90°C and the drying time is 10-12 hours. Further, the drying method is forced-air drying.

[0059] In some embodiments, washing refers to washing with distilled water 2-3 times, followed by washing with ethanol 2-3 times.

[0060] The platy spinel cobalt ferrite powder prepared in this application is relatively fine and does not require grinding, thus effectively shortening the preparation time.

[0061] Secondly, embodiments of this application provide a sheet-like spinel cobalt ferrite, which has a sheet-like morphology and a stoichiometric ratio of Co to Fe of 1:2.

[0062] Thirdly, embodiments of this application provide an application of sheet-like spinel cobalt ferrite, including using the sheet-like spinel cobalt ferrite as a cathode material for SOFC. SOFCs prepared using this sheet-like spinel cobalt ferrite exhibit excellent performance at 750-800°C, and their oxygen reduction activity, polarization resistance, and maximum power density are all higher than those of ordinary granular spinel cobalt ferrite.

[0063] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0064] Example 1

[0065] This embodiment provides a method for preparing plate-like spinel cobalt ferrite, including the following steps:

[0066] S1, at room temperature, 0.873g Co(NO3)2·6H2O and 2.424g Fe(NO3)2·9H2O were dissolved in 30mL of deionized water and stirred thoroughly on a magnetic stirrer until clear and transparent. Then, 2.836g citric acid was added and stirred evenly to obtain the precursor solution.

[0067] S2, the precursor solution obtained in step S1 is heated in a water bath at 60°C for 20 hours to obtain a reddish-brown transparent gel. Then, the reddish-brown transparent gel is placed in an oven and dried in a forced-air dryer at 80°C for 10 hours. After grinding, the first powder (i.e., precursor powder) is obtained.

[0068] S3, the first powder obtained in step S2 is evenly spread out, and the laser power is 8W and the scanning speed is 150mms. -1 Under certain conditions, the first powder was subjected to CO2 laser induction twice in an air atmosphere to obtain the second powder.

[0069] S4. After the second powder obtained in step S3 is cooled to room temperature, the second powder is washed with distilled water 2-3 times, then washed with ethanol 2-3 times, and then placed in an oven and dried at 80°C for 10 hours to obtain a plate-like spinel cobalt ferrite, which is named CFO-8W with the chemical formula CoFe2O4.

[0070] Example 2-3

[0071] The difference between Examples 2 and 3 and Example 1 is that in step S3, the power induced by the CO2 laser is changed to 6W and 10W respectively. The other contents are roughly the same as in Example 1, and will not be repeated here.

[0072] Comparative Example 1

[0073] Comparative Example 1 provides a method for preparing spinel cobalt ferrite using the sol-gel method, comprising the following steps:

[0074] S1, at room temperature, 0.873g Co(NO3)2·6H2O and 2.424g Fe(NO3)2·9H2O were dissolved in 30mL of deionized water and stirred thoroughly on a magnetic stirrer until clear and transparent. Then, 2.836g citric acid and 3g polyethylene glycol were added as complexing agent and combustion aid, respectively, to obtain the precursor solution.

[0075] S2, after adjusting the pH of the precursor solution obtained in step S1 to 7 with ammonia, the precursor solution was placed on a magnetic stirrer and stirred continuously for 30 minutes (room temperature), and then heated in a water bath at 60°C for 20 hours to obtain CoFe2O4 gel.

[0076] S3. The CoFe2O4 gel obtained in step S2 is heated to 600℃ until combustion (i.e., pre-calcination) to remove organic matter and moisture, resulting in powder. Next, the pre-calcined powder is pressed into discs under a pressure of 15 MPa, and the discs are sintered at 1000℃ for 5 hours. The discs are then ground to improve particle uniformity and fineness, yielding spinel cobalt ferrite, denoted as CFO-SG.

[0077] Comparative Example 2

[0078] The difference between Comparative Example 2 and Example 1 is that the power induced by the CO2 laser in step S3 is changed to 4W. The other contents are roughly the same as those in Example 1, and will not be repeated here. The product prepared in Comparative Example 2 is denoted as CFO-4W.

[0079] Comparative Example 3

[0080] The difference between Comparative Example 3 and Example 1 is that the amount of citric acid used in step S1 is changed to 3.782 g, that is, the molar ratio of metal ions to citric acid in the precursor solution is changed to 1:2. Other aspects are largely the same as in Example 1 and will not be repeated here. The product prepared in Comparative Example 3 is designated as CFO-8W. 1：2 .

[0081] For ease of understanding, the differences between Examples 1-3 and Comparative Examples 1-3 are shown in the table below:

[0082]

[0083]

[0084] The morphology of the products prepared in Examples 1-3 and Comparative Examples 1-3 was characterized using scanning electron microscopy (SEM).

[0085] See also Figures 1 to 2 As shown, where, Figure 1 These are morphological images of the products prepared in Examples 1-3 and Comparative Examples 1-3 at 6Kx magnification. Figure 2The images show the morphology of the products prepared in Examples 1-3 and Comparative Examples 1-3 at 2Kx magnification. It can be seen that the products prepared by the sol-gel method exhibit granular morphology of varying sizes, with some showing aggregation. In contrast, the products prepared by the CO2 laser-induced method exhibit a sheet-like morphology, and with increasing laser power, the sheet-like morphology shows varying degrees of fragmentation, resulting in the inclusion of a small number of fine nanoparticles. CFO-4W, CFO-6W, and CFO-8W maintain good nanosheet-like morphology with relatively small nanoparticles. CFO-4W and CFO-6W exhibit large, adhered sheet-like morphologies, while CFO-8W shows fine and well-separated sheet-like morphologies. CFO-10W, however, shows a higher degree of fragmentation in its sheet-like morphology and contains a greater number of fine nanoparticles. Figure 1 A small amount of agglomeration can be observed. This demonstrates that the CO2 laser-induced preparation method alters the morphology of the material.

[0086] The structures of the products prepared in Examples 1-3 and Comparative Examples 1-3 were characterized by X-ray diffraction (XRD), and the results were as follows. Figure 3 The X-ray diffraction patterns shown were analyzed using Jade software. The conclusions are as follows: Comparative Examples 2 and 3 failed to prepare plate-like spinel cobalt ferrite, while Examples 1-3 and Comparative Example 1 successfully prepared plate-like spinel cobalt ferrite. This demonstrates that laser power has a significant impact on the successful preparation of spinel cobalt ferrite and the morphological characteristics of the prepared spinel cobalt ferrite. Furthermore, the XRD pattern of Comparative Example 3 shows that excessive citric acid addition led to impurities in the material, thus preventing the successful preparation of spinel cobalt ferrite.

[0087] Application examples

[0088] This application example includes the fabrication of symmetric cells and full cells. The commercially available anode-supported half-cells used in this application example were purchased from Zhongfu (Wuxi) New Energy Co., Ltd. Furthermore, CFO-4W, CFO-6W, CFO-8W, CFO-10W, and CFO-SG were used as cathode materials, and a mixture of 92% terpineol and 8% ethyl cellulose was used as a binder.

[0089] The specific preparation steps of a symmetric cell are as follows:

[0090] The cathode material and binder are uniformly mixed to obtain a cathode slurry. Then, the cathode slurry is coated onto the electrolyte BaZr. 0.7 Ce 0.1 Y 0.1Symmetrical cells were prepared by sintering O3 (BZCY) on both sides at 1000℃ for 2 hours, and were designated as CFO-4W-S, CFO-6W-S, CFO-8W-S, CFO-10W-S and CFO-SG-S, respectively.

[0091] The specific preparation steps for the full cell are as follows:

[0092] The cathode material and binder were uniformly mixed to obtain a cathode slurry. The prepared cathode slurry was screen-printed onto the electrolyte surface of a commercial anode-supported half-cell, and calcined at 1000℃ for 2 hours to prepare full cells, which were designated as CFO-6W-F, CFO-8W-F, CFO-10W-F, and CFO-SG-F, respectively.

[0093] The electrochemical impedance spectral density (EIT) of the symmetric cells CFO-4W-S, CFO-6W-S, CFO-8W-S, CFO-10W-S, and CFO-SG-S prepared for the corresponding use cases was tested at 750 °C using an electrochemical workstation (Chenhua 660E) at 10 °C. 5 Up to 10 -1 Electrochemical impedance spectroscopy (EIS) data were collected and analyzed in the Hz range. The symmetrical cell was placed in a high-temperature tube furnace, and the temperature was raised to 750°C in an air atmosphere for electrochemical impedance spectroscopy testing.

[0094] The polarization impedance data obtained from the test are shown in the table below.

[0095] project <![CDATA[Polarization impedance (Ωcm 2 )]]> CFO-4W-S 0.082 CFO-6W-S 0.054 CFO-8W-S 0.033 CFO-10W-S 0.067 CFO-SG-S 0.056

[0096] See also Figures 4 to 5 The table shows the electrochemical impedance spectroscopy (EIS) obtained from the tests. As can be seen from the table above, with increasing laser power, the polarization impedance of the symmetric cells prepared using sheet-like spinel cobalt ferrite exhibits a trend of first decreasing and then increasing. Furthermore, the polarization impedances of CFO-8W-S and CFO-6W-S are both lower than that of CFO-SG-S, especially CFO-8W-S, whose polarization impedance is only 0.033 Ωcm. 2 The CFO-4W-S exhibited the highest polarization impedance, and XRD analysis revealed it was not a lamellar spinel cobalt ferrite structure, rendering further testing pointless. This indicates that compared to ordinary granular spinel cobalt ferrite, the lamellar spinel cobalt ferrite prepared using the CO2 laser-induced method in this application exhibits significantly increased oxygen reduction reactivity, with an optimal laser power of 8W. Increasing the laser power to 10W, however, resulted in a decrease in oxygen reduction reactivity.

[0097] The electrochemical impedance spectroscopy of CFO-6W-S, CFO-8W-S, CFO-10W-S and CFO-SG-S was analyzed using the relaxation time distribution (DRT) method.

[0098] See also Figure 6 The figure shows the relaxation time distribution of CFO-6W-S, CFO-8W-S, CFO-10W-S, and CFO-SG-S. As can be seen, the curves in the figure are divided into low-frequency (LF), mid-frequency (IF), and high-frequency (HF) regions, corresponding to gas diffusion, oxygen adsorption and dissociation at the three-phase boundary (TPB), and charge transfer, respectively. The peak area in each of the three regions is related to the polarization impedance value within the corresponding frequency range. DRT analysis shows that, compared with the other three symmetrical cells, the relaxation time distribution curve of CFO-8W-S has the smallest area for each peak, and the high-frequency and mid-frequency peaks are significantly reduced. This indicates that the change in the morphology of spinel cobalt ferrite effectively promotes the charge transfer and oxygen adsorption and dissociation processes in the oxygen reduction reaction (ORR). The promotion of the charge transfer process is due to the increase in active sites caused by the morphological change, while the promotion of the oxygen adsorption and dissociation process is due to the increase in specific surface area caused by the morphological change. Compared with CFO-SG-S, the high-frequency peaks of all materials prepared by laser methods are significantly reduced, and the mid-frequency peaks are also slightly reduced. The area of ​​the mid-frequency peak in CFO-10W-S is not much different from that in CFO-SG-S, proving that further increases in laser power have an adverse effect on the material morphology, leading to a decrease in material performance.

[0099] Further testing of the polarization impedance of CFO-8W-S at 700℃ and 800℃ yielded electrochemical impedance spectroscopy (see attached diagram). Figure 7 As shown, the polarization impedance of CFO-8W-S at 700℃, 750℃, and 800℃ is 0.087Ωcm. 2 0.033Ωcm 2 and 0.007Ωcm 2 .

[0100] The output power of the full cells CFO-6W-F, CFO-8W-F, CFO-10W-F, and CFO-SG-F prepared for the corresponding use cases was tested at 750°C. Electrochemical impedance spectroscopy (EIS) data were collected and analyzed in the range of 10⁵ to 10⁻¹ Hz using an electrochemical workstation (CHEN ZHHUA 660E). The full cells were placed in a high-temperature tube furnace, using air as the oxidant and H₂ as the fuel, and the output characteristics of the full cells were evaluated at 750°C. Linear sweep voltammetry was tested in the voltage range of 0-1.5V using an electrochemical workstation (CHEN ZHHUA 660E). The maximum power density obtained from the tests is shown in the table below.

[0101] project <![CDATA[Maximum power density (W cm -2 )]]> CFO-6W-F 0.63 CFO-8W-F 0.77 CFO-10W-F 0.45 CFO-SG-F 0.39

[0102] See also Figure 8The table shows the output power of the full cell at 750℃. As can be seen from the table, the power densities of CFO-6W-F, CFO-8W-F, and CFO-10W-F are all higher than those of CFO-SG-S. Among them, CFO-8W-F has the highest maximum power density at 0.77 W / cm². -2 This indicates that the plate-like spinel cobalt ferrite prepared by CO2 laser induction has better electrochemical performance, and the optimal laser power is 8W.

[0103] Further testing of the CFO-8W-F's output power at 700℃ and 800℃ yielded the maximum power density, which can be found in the [reference needed]. Figure 9 As shown, the maximum power density of CFO-8W-F at 700℃ is 0.61 W / cm². -2 The maximum power density at 800℃ is 1.00 W / cm³. -2 .

[0104] X-ray photoelectron spectroscopy (XPS) was performed on CFO-8W and CFO-6W prepared in Examples 1-2. The resulting O1s spectra are shown below. Figure 10 As shown, the peak at 529 eV in the spectrum corresponds to lattice oxygen (O). lat The peak at 530V corresponds to adsorbed oxygen (O). ads O ads With O lat The ratio is commonly used to express the relative oxygen vacancy content in different materials. In CFO-6W, O... ads / O lat The value is 1.05, in CFO-8W O ads / O lat A value of 2.38 indicates that within the power range of 6-8W, as the laser power increases, O ads / O lat The value gradually increases. This indicates that changes in laser power can affect the oxygen vacancy concentration of the material. Oxygen vacancies are the active sites for electrochemical reactions. Therefore, cathode materials with higher oxygen vacancy concentrations have better ORR catalytic performance.

[0105] In summary, this application provides a lamellar spinel cobalt ferrite, its preparation method, and its application. A lamellar spinel cobalt ferrite (CoFe2O4) with a specific morphology was prepared using a CO2 laser-induced method, and its application as a cathode material in symmetric and full cells is provided. This application adjusts the size and fragmentation degree of the lamellar morphology of the CoFe2O4 spinel by changing the laser power. SEM images show that CFO-8W prepared with a laser power of 8W exhibits a fine and well-separated lamellar morphology with fewer fragmented nanoparticles, resulting in a higher specific surface area and excellent performance at 750-800℃. Compared to ordinary granular CoFe2O4 spinel, the morphological changes in the lamellar CoFe2O4 spinel prepared in this application result in better electrochemical performance when used as a cathode material, such as lower polarization impedance, higher maximum power density, and superior oxygen reduction activity.

[0106] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for preparing plate-like spinel cobalt ferrite, characterized in that, The preparation method using CO2 laser-induced method includes the following steps: S1, dissolve the Co source and Fe source in deionized water, stir thoroughly, add citric acid, stir evenly to obtain a precursor solution; the metal ions in the precursor solution are Co ions and Fe ions, the molar ratio of Co ions to Fe ions is 1:2, and the molar ratio of the metal ions to the citric acid is 1:(1.2-1.5). S2, the precursor solution obtained in step S1 is heated in a water bath until it turns into a reddish-brown transparent gel, and then the reddish-brown transparent gel is dried and ground to obtain the first powder; S3, the first powder obtained in step S2 is evenly spread and subjected to CO2 laser induction twice in an air atmosphere to obtain the second powder; the power of the CO2 laser induction is x, and 4W < x ≤ 10W; S4. After the second powder obtained in step S3 is cooled to room temperature, the second powder is washed and dried to obtain the plate-shaped spinel cobalt ferrite; the plate-shaped spinel cobalt ferrite has a plate-shaped morphology.

2. The method for preparing platy spinel cobalt ferrite according to claim 1, characterized in that, In step S1, the concentration of metal ions in the precursor solution is 0.1 mol / L.

3. The method for preparing platy spinel cobalt ferrite according to claim 1, characterized in that, In step S3, the scanning speed induced by the CO2 laser is 100-150 mm / s. -1 The power induced by the CO2 laser is 6-8W.

4. The method for preparing platy spinel cobalt ferrite according to claim 2, characterized in that, In step S1, the Co source is a cobalt salt, and the Fe source is an iron salt; the cobalt salt is cobalt nitrate, and the iron salt is ferric nitrate.

5. The method for preparing platy spinel cobalt ferrite according to claim 1, characterized in that, In step S2, the water bath heating temperature is 60-90℃.

6. The method for preparing platy spinel cobalt ferrite according to claim 5, characterized in that, In step S2, the drying method is blower drying; the temperature of blower drying is 70-90℃, and the time is 10-12h.

7. The method for preparing platy spinel cobalt ferrite according to claim 1, characterized in that, In step S4, the drying temperature is 70-90℃ and the time is 10-12h.

8. The method for preparing platy spinel cobalt ferrite according to claim 7, characterized in that, In step S4, the washing refers to washing with distilled water 2-3 times, and then washing with ethanol 2-3 times.

9. A sheet-like spinel cobalt ferrite prepared by the method of any one of claims 1-8, characterized in that, The stoichiometric ratio of Co to Fe in the platy spinel cobalt ferrite is 1:

2.

10. An application of the lamellar spinel cobalt ferrite according to claim 9, characterized in that, The sheet-like spinel cobalt ferrite is used as the cathode material for a solid oxide fuel cell.

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