Co3O4 and CoO-based heat storage material with high sintering resistance and uniform doping and preparation method of Co3O4 and CoO-based heat storage material

Abstract

The invention discloses a Co3O4 and CoO-based heat storage material with high sintering resistance and uniform doping and a preparation method thereof.The preparation method comprises the steps that cobalt salt and alkaline earth metal salt are dissolved in a mixed solvent composed of water and alcohol, a carbon source and an organic ligand are added, stirring is conducted for dissolution, and uniform sol is formed; evaporating a solvent from the sol to form viscous gel, and drying to obtain a xerogel precursor; performing first heat treatment on the xerogel precursor in an inert atmosphere to obtain metal oxide / carbon composite powder; and performing secondary heat treatment on the metal oxide / carbon composite powder in an oxygen-containing atmosphere to obtain the heat storage material. According to the preparation method, a cobalt source, a doped metal source and a carbon precursor are uniformly mixed on a molecular level through a novel porous carbon matrix assisted-sol-gel composite process, and a three-dimensional porous carbon network formed in a subsequent carbonization process is used as a nano reactor and a spatial isolator; the obtained heat storage material has high specific surface area and excellent cycle performance.

Description

Technical Field

[0001] This invention belongs to the field of thermochemical energy storage technology, specifically relating to a Co3O4 and CoO-based thermal storage material with high sintering resistance and uniform doping and its preparation method. Background Technology

[0002] With the increasing global demand for efficient utilization of renewable energy and industrial waste heat, thermochemical energy storage technology has attracted widespread attention due to its high energy density and the ability to achieve long-term, non-destructive energy storage. Among various thermal storage materials, systems based on the redox reaction of metal oxides, especially the cobalt oxide (Co3O4 / CoO) cycle, are considered a promising high-temperature thermal storage material due to their suitable reaction temperature, high enthalpy change, and good reversibility. Its energy storage (endothermic) and energy release (exothermic) reactions can be expressed as follows: 2Co3O4⇌6CoO + O2; However, this technology still faces many challenges in practical applications. In existing technologies, to suppress sintering, improve cycle stability, and regulate reaction temperature, the method of doping with metal ions (such as Mg²⁺, Zn²⁺, Ni²⁺, etc.) is often employed. However, traditional solid-state mixing methods and other preparation methods struggle to achieve atomically uniform distribution of dopant elements in the cobalt oxide matrix. Non-uniform doping leads to localized performance differences, forms reactive inert regions, and can even introduce defects that become crack initiation points, thus reducing the overall cycle stability and heat storage performance of the material—the problem of doping uniformity.

[0003] Therefore, developing a method for producing Co3O4 / CoO thermal storage materials that is simple to process, scalable, and can simultaneously achieve high sintering resistance and excellent doping uniformity is of great practical significance and application value. Summary of the Invention

[0004] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of the invention, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0005] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0006] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing a Co3O4 and CoO-based thermal storage material with high sintering resistance and uniform doping.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: including, Cobalt salts and alkaline earth metal salts are dissolved in a mixed solvent of water and alcohol, and a carbon source and organic ligands are added. The mixture is stirred and dissolved to form a homogeneous sol. After evaporating the solvent from the sol to form a viscous gel, it is dried to obtain a dry gel precursor. The dry gel precursor was subjected to a first heat treatment under an inert atmosphere to obtain metal oxide / carbon composite powder. The metal oxide / carbon composite powder is subjected to a second heat treatment in an oxygen-containing atmosphere to obtain the heat storage material described above. The molar ratio of organic ligands to the total amount of all metal ions is 1.5~3:1; The alkaline earth metal salt has a doping amount of 1 to 10 mol relative to cobalt atoms.

[0008] In a preferred embodiment of the preparation method described in this invention, the cobalt salt includes one of cobalt nitrate and cobalt acetate.

[0009] In a preferred embodiment of the preparation method described in this invention, the alkaline earth metal salt includes one or more of magnesium nitrate and zinc nitrate.

[0010] In a preferred embodiment of the preparation method described in this invention, the carbon source includes one of glucose and sucrose.

[0011] In a preferred embodiment of the preparation method described in this invention, the organic ligand includes one of citric acid, tartaric acid, and oxalic acid.

[0012] In a preferred embodiment of the preparation method described in this invention, when the organic ligand is citric acid, the molar ratio of the citric acid organic ligand to the total amount of all metal ions is 2:1.

[0013] In a preferred embodiment of the preparation method described in this invention, the volume ratio of water to alcohol in the mixed solvent composed of water and alcohol is 2~3:1.

[0014] As a preferred embodiment of the preparation method described in this invention, the first heat treatment includes heating to 400-600°C at a rate of 2-5°C / min and holding at that temperature for 1-3 hours.

[0015] As a preferred embodiment of the preparation method described in this invention, the second heat treatment includes a first stage of calcination and a second stage of calcination; The first stage of calcination includes heating to 300-400°C at a rate of 1-3°C / min and holding at that temperature for 0.5-1h; The second stage of calcination includes heating to 500-700°C at a rate of 1-3°C / min and holding at that temperature for 1-2 hours.

[0016] Another objective of this invention is to overcome the shortcomings of the prior art and provide a method for preparing Co3O4 and CoO-based thermal storage materials with high sintering resistance and uniform doping.

[0017] Beneficial effects of this invention: (1) This invention uses a novel “porous carbon matrix-assisted sol-gel” composite process to uniformly mix cobalt source, doped metal source and carbon precursor at the molecular level, and uses the three-dimensional porous carbon network formed by the subsequent carbonization process as “nanoreactor” and “spatial isolation body”. Finally, a Co3O4 / CoO thermal storage material with high sintering resistance and uniform doping is obtained through controlled calcination.

[0018] (2) In the sol-gel stage, metal ions achieve uniform molecular-level dispersion in the polymer network, laying the foundation for the subsequent formation of a uniform solid solution. During calcination, the in-situ generated three-dimensional porous carbon framework effectively blocks and restricts the growth space of cobalt oxide grains, thereby greatly inhibiting sintering and agglomeration at high temperatures. The entire process is based on mature sol-gel and heat treatment technologies, making it easy to scale up and industrialize. The resulting thermal storage material has a higher specific surface area and superior cycle performance compared to materials obtained by traditional methods. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the preparation process of the thermal storage material in Embodiment 1 of the present invention.

[0021] Figure 2 This is a morphological image of the thermal storage material of Comparative Example 1 of the present invention after 30 redox cycles.

[0022] Figure 3 This is a morphology diagram of the thermal storage material of Comparative Example 2 of the present invention after 30 redox cycles. Detailed Implementation

[0023] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0024] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0025] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0026] Example 1 This embodiment provides a method for preparing a Co3O4 and CoO-based thermal storage material with high sintering resistance and uniform doping, specifically as follows: (1) Weigh 9.5 mmol cobalt nitrate, 0.4 mmol magnesium nitrate and 0.1 mmol calcium nitrate, dissolve them in 40 mL deionized water and 20 mL ethanol, add 10 mL of 1 mol / L glucose solution and 20 mmol citric acid, stir in a 60℃ water bath until completely dissolved, and obtain a clear pink sol; wherein, the molar ratio of citric acid organic ligand to all metal ions is 2:1; (2) The sol obtained in step (1) is continuously heated at 80°C to evaporate the solvent until a purple viscous gel is formed. Then, it is placed at 110°C and dried for 12 hours to obtain a fluffy purple dry gel precursor. (3) The dry gel obtained in step (2) was placed in a tube furnace, heated to 500°C at 3°C / min under a nitrogen atmosphere and kept at that temperature for 2 hours, and then cooled to room temperature to obtain black Co-Mg-O / carbon composite powder. (4) The composite powder obtained in step (3) is heated to 300°C in air at a slow heating rate of 2°C / min and kept at that temperature for 0.5h. Then, it is heated to 500°C and kept at that temperature for 1h to obtain the heat storage material of this embodiment.

[0027] Figure 1 A flowchart illustrating the preparation process of the thermal storage material in Example 1 is shown.

[0028] Example 2 The difference between this embodiment and Embodiment 1 is that calcium nitrate was not added in step (1), specifically: Weigh 9.5 mmol of cobalt nitrate and 0.5 mmol of magnesium nitrate, and dissolve them in a mixed solvent of 40 mL of deionized water, 20 mL of ethanol, and 10 mL of 1 mol / L glucose. Then add 20 mmol of citric acid and stir in a 60°C water bath until completely dissolved to obtain a clear pink sol. The molar ratio of citric acid organic ligand to all metal ions is 2:1. The remaining preparation methods are the same as in Example 1, resulting in the thermal storage material of this example.

[0029] Comparative Example 1 The difference between this comparative example and Example 1 is that calcium nitrate and glucose solution were not added in step (1), specifically: Weigh out 9.5 mmol of cobalt nitrate and 0.5 mmol of magnesium nitrate, dissolve them in a mixed solvent of 50 mL of deionized water and 20 mL of ethanol, then add 20 mmol of citric acid, and stir in a 60°C water bath until completely dissolved to obtain a clear pink sol; wherein the molar ratio of citric acid organic ligand to all metal ions is 2:1. The remaining preparation methods are the same as in Example 1, and the thermal storage material of this comparative example is obtained.

[0030] Comparative Example 2 This comparative example provides a traditional solid-state method for preparing Co3O4 and CoO-based thermal storage materials, specifically: 9.5 mmol cobalt nitrate, 0.4 mmol magnesium nitrate, and 0.1 mmol calcium nitrate were mixed evenly and ball-milled at 400 rpm for 2 hours in air. After being compressed into tablets, the tablets were placed in a muffle furnace and heated to 850°C at 5°C / min. The temperature was maintained for 10 hours, and then ball-milled again at 400 rpm for 2 hours to obtain the heat storage material of this comparative example. The ball-to-material ratio in both ball milling processes was 15:1.

[0031] The initial specific surface area and thermal density of Examples 1-2 and Comparative Examples 1-2, as well as the specific surface area and thermal density after 30 redox cycles, were tested. The results are shown in Table 1.

[0032] Table 1. Effects of different preparation methods on the performance of energy storage materials

[0033] As shown in Table 1, the initial specific surface area of ​​Example 1 reached 60 m². 2 / g, after 30 redox cycles, the specific surface area decreased by only 12%, while the specific surface area of ​​Example 2 decreased by only 16% after 30 redox cycles.

[0034] Comparative Example 1 had an initial specific surface area of ​​only 49 m². 2 / g, after 30 redox cycles, the specific surface area decreased by about 15%, but the particle morphology remained good, such as Figure 2 As shown. However, the thermal storage material prepared by the traditional solid-state method (Comparative Example 2) showed a decrease in specific surface area of ​​over 50% after cycling, and the particles exhibited severe sintering and agglomeration, such as... Figure 3 As shown, its thermal storage density is less than 70%.

[0035] Comparative Example 3 The difference between this comparative example and Example 1 is that the molar ratio of citric acid organic ligand to all metal ions in step (1) is adjusted to 1:1, and the rest of the preparation methods are the same as in Example 1, so as to obtain the heat storage material of this comparative example.

[0036] Comparative Example 4 The difference between this comparative example and Example 1 is that the molar ratio of citric acid organic ligand to all metal ions in step (1) is adjusted to 4:1, while the rest of the preparation methods are the same as in Example 1, thus obtaining the heat storage material of this comparative example.

[0037] The initial specific surface area and thermal storage density of comparative examples 3-4, as well as the specific surface area and thermal storage density after 30 redox cycles, are shown in Table 2.

[0038] Table 2. Effect of Organic Ligand Addition Amount on Energy Storage Material Performance

[0039] As shown in Table 2, the thermal storage material in Comparative Example 3 exhibited sintering and agglomeration, resulting in poor anti-sintering performance and a small specific surface area. In Comparative Example 4, the thermal storage material contained residual carbon, leading to low material purity and a significant decrease in thermal storage density after 30 redox cycles.

[0040] Comparative Example 5 The difference between this comparative example and Example 1 is that the carbonization temperature in step (3) is adjusted to 700°C, while the rest of the preparation methods are the same as in Example 1, thus obtaining the thermal storage material of this comparative example.

[0041] Comparative Example 6 The difference between this comparative example and Example 1 is that in step (4), the temperature is raised to 300°C at a relatively slow heating rate of 1°C / min and held for 0.5h for a short time. The second step of calcination is not performed. The rest of the preparation methods are the same as in Example 1, and the heat storage material of this comparative example is obtained.

[0042] Comparative Example 7 The difference between this comparative example and Example 1 is that the heating rate in step (4) is increased to 5℃ / min, while the rest of the preparation methods are the same as in Example 1, and the heat storage material of this comparative example is obtained.

[0043] The initial specific surface area and thermal density of comparative examples 5-7, as well as the specific surface area and thermal density after 30 redox cycles, were tested. The results are shown in Table 3.

[0044] Table 1. Effect of temperature on the performance of energy storage materials

[0045] As shown in Table 3, excessively high carbonization temperature leads to rapid evaporation, making it difficult for the carbon skeleton to provide support, resulting in no significant increase in specific surface area and poor cycle performance.

[0046] Since the one-step calcination only removes some carbon and initially oxidizes the metal to Co3O4, but does not completely remove the residual carbon and crystallize the Co3O4-based solid solution, the heat storage material prepared in Comparative Example 6 has low purity, which hinders the entry of oxygen and significantly reduces its circulation performance.

[0047] In addition, the excessively rapid heating rate also leads to excessively fast evaporation, making it difficult for the carbon skeleton to provide support. Ultimately, the specific surface area is not significantly improved compared to traditional methods, and the heat storage density drops drastically after multiple cycles.

[0048] Example 3 This embodiment provides a method for preparing a Co3O4 and CoO-based thermal storage material with high sintering resistance and uniform doping, specifically as follows: (1) Weigh 9.5 mmol cobalt nitrate, 0.4 mmol magnesium nitrate and 0.1 mmol calcium nitrate, dissolve them in 60 mL deionized water and 20 mL ethanol, add 10 mL of 1 mol / L glucose solution and 20 mmol citric acid, stir in a 60℃ water bath until completely dissolved, and obtain a clear pink sol; wherein, the molar ratio of citric acid organic ligand to all metal ions is 2:1; (2) The sol obtained in step (1) is continuously heated at 90°C to evaporate the solvent until a purple viscous gel is formed. Then, it is placed at 120°C and dried for 24 hours to obtain a fluffy purple dry gel precursor. (3) The dry gel obtained in step (2) was placed in a tube furnace, heated to 600°C at 5°C / min under a nitrogen atmosphere and kept at that temperature for 3 hours, and then cooled to room temperature to obtain black Co-Mg-O / carbon composite powder. (4) The composite powder obtained in step (3) is heated to 400°C in air at a slow heating rate of 3°C / min and kept at that temperature for 1 hour. Then, it is heated to 700°C and kept at that temperature for 2 hours to obtain the heat storage material of this embodiment.

[0049] The thermal storage material prepared in Example 5 has similar performance to that in Example 1, but its specific surface area is slightly lower than that in Example 1.

[0050] In summary, the Co3O4 and CoO-based thermal storage material provided by this invention, with high resistance to sintering and uniform doping, exhibits a higher specific surface area and superior cycle performance compared to traditional solid-state methods through comprehensive optimization of the preparation process. Furthermore, the thermal storage material obtained by this invention directly stores thermal energy; during storage, thermal energy is converted into chemical energy, and during release, chemical energy is converted back into thermal energy. Compared to energy storage methods using chemical batteries, cobalt oxides do not require specific electrical conductivity.

[0051] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a Co3O4 and CoO-based thermal storage material with high sintering resistance and uniform doping, characterized in that: The application relates to a Co3O4 and CoO-based heat storage material and a preparation method thereof. A cobalt salt and an alkaline earth metal salt are dissolved in a mixed solvent composed of water and alcohol, a carbon source and an organic ligand are added, stirring and dissolution are carried out, and a uniform sol is formed; After the sol is evaporated to form a viscous gel, drying is carried out to obtain a dry gel precursor; The dry gel precursor is subjected to first heat treatment in an inert atmosphere to obtain a metal oxide / carbon composite powder; The metal oxide / carbon composite powder is subjected to second heat treatment in an oxygen-containing atmosphere to obtain the heat storage material; The molar ratio of the organic ligand to the total amount of all metal ions is 1.5-3:

1. The doping amount of the alkaline earth metal salt to cobalt atoms is 1-10 mol%.

2. The production method according to claim 1, characterized by: The cobalt salt comprises one of cobalt nitrate and cobalt acetate.

3. The production method according to claim 1, wherein: The alkaline earth metal salt comprises one or more of magnesium nitrate and zinc nitrate.

4. The production method according to claim 1, wherein: The carbon source comprises one of glucose and sucrose.

5. The production method according to claim 1, wherein: The organic ligand comprises one of citric acid, tartaric acid and oxalic acid.

6. The production method according to claim 1, wherein: When the organic ligand is citric acid, the molar ratio of the citric acid organic ligand to the total amount of all metal ions is 2:

1.

7. The production method according to claim 1, wherein: In the mixed solvent composed of water and alcohol, the volume ratio of water to alcohol is 2-3:

1.

8. The production method according to claim 1, wherein: The first heat treatment comprises heating at a rate of 2-5 DEG C / min to 400-600 DEG C and keeping for 1-3 h.

9. The production method according to claim 1, wherein: The second heat treatment comprises first stage calcination and second stage calcination. The first stage calcination comprises heating at a rate of 1-3 DEG C / min to 300-400 DEG C and keeping for 0.5-1 h. The second stage calcination comprises heating at a rate of 1-3 DEG C / min to 500-700 DEG C and keeping for 1-2 h.

10. A Co3O4 and CoO-based heat storage material prepared by the preparation method in any one of claims 1-9.

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