Carbon-supported CeO2 / Co heterojunction active site electrocatalysts, preparation methods and applications

Abstract

A method for preparing a carbon-supported CeO2 / Co heterojunction electrocatalyst with active sites includes the following steps: Step 1: Preparing a Zn-containing... 2+ Co 2+ and Ce 2+ The process involves three steps: first, preparing a chitosan hydrogel; second, using the chitosan hydrogel to prepare a solid CeO2 / Co active site electrocatalyst precursor; and third, subjecting the CeO2 / Co active site electrocatalyst precursor to heat treatment and cooling to obtain a carbon-supported CeO2 / Co heterojunction active site electrocatalyst. The obtained carbon-supported CeO2 / Co heterojunction active site electrocatalyst is applied as a catalyst in the cathode of a lithium-sulfur battery. The heterojunction enables the adsorption and catalysis of polysulfide compounds, significantly reducing the shuttle effect of lithium polysulfides. Simultaneously, the presence of the carbon framework increases electron and ion transport channels, improving conductivity. Its application in lithium-sulfur batteries can improve sulfur utilization, increase coulombic efficiency, and enhance battery cycle stability.

Description

Technical Field

[0001] This invention relates to the field of electrochemistry, and in particular to a carbon-supported CeO2 / Co heterojunction active site electrocatalyst, its preparation method, and its application. Background Technology

[0002] As we all know, the energy crisis is becoming increasingly serious, and the huge demand for energy storage systems has driven the exploration of high-energy-density batteries. However, the commercial lithium-ion batteries based on traditional insert cathodes and graphite anodes are almost close to their theoretical energy density, and there is an urgent need to develop other new battery systems with high energy density. Therefore, developing next-generation rechargeable battery systems with high specific energy is a key direction for energy storage batteries. Lithium-sulfur batteries, due to their low cost, high theoretical capacity and environmental friendliness, can meet the human demand for higher energy density rechargeable batteries, and are also one of the key directions for new energy development in the future of various countries. To realize the commercialization of lithium-sulfur batteries, the problems of sulfur cathodes must be solved first: (1) the shuttle effect of lithium polysulfides leads to the dissolution of electrode active materials and capacity decay; (2) the low conductivity of lithium sulfide products leads to low reaction kinetics and reduced rate performance of the battery; (3) the electrode volume expansion affects the cycle stability of the battery.

[0003] To address the problems existing in the cathode of lithium-sulfur batteries, researchers have proposed various strategies, such as using porous carbon materials to support catalysts, developing novel binders and electrolyte additives, and modifying traditional separators. Among the reported strategies, porous carbon materials supporting catalysts are considered the most effective method: porous carbon can both physically confine polysulfides and enhance electrode conductivity to facilitate electron transport; the catalyst can both chemically adsorb polysulfides and catalyze the interconversion of polysulfides, thus improving kinetics. In catalyst research, heterojunction catalysts can combine various solid materials with independent properties, generating synergistic effects at the interface; some heterojunction interfaces will generate new electronic structures based on the different energy bands of the components, accelerating charge transfer. Rationally designed multiphase interfaces can obtain stronger catalytic active sites, which is beneficial for the rapid conversion of lithium polysulfides to solid-liquid-solid states, alleviating the problem of slow reaction kinetics of sulfur species. For example, in metal oxide / metal heterojunction nanoparticle catalysts, the strong polarity of the metal oxide is responsible for the chemical adsorption of lithium polysulfides, while the high conductivity of the metal is responsible for the catalytic conversion between lithium polysulfides. The preparation of heterojunction materials generally includes chemical hydrothermal methods, chemical vapor deposition, and electrochemical deposition. However, chemical hydrothermal methods are limited to temperatures below 100 degrees Celsius and the morphology and material uniformity of the products are difficult to control; chemical vapor deposition and electrochemical deposition are difficult to implement for powder materials and have extremely low yields.

[0004] It should be noted that the information disclosed in the background section above is only for understanding the background of this application, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0005] The main objective of this invention is to overcome the deficiencies of the aforementioned background technology and provide a carbon-supported CeO2 / Co heterojunction active site electrocatalyst, its preparation method, and its application.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing a carbon-supported CeO2 / Co heterojunction active site electrocatalyst includes the following steps:

[0008] Step 1: Preparation of Zn-containing 2+ Co 2+ and Ce 2+ Chitosan hydrogel;

[0009] Step 2: Prepare a solid CeO2 / Co active site electrocatalyst precursor using the chitosan hydrogel;

[0010] Step 3: The CeO2 / Co active site electrocatalyst precursor is subjected to heat treatment and cooled to obtain carbon-supported CeO2 / Co heterojunction active site electrocatalyst.

[0011] Furthermore, the first step specifically includes the following steps:

[0012] (1.1) Prepare an aqueous solution of chitosan of appropriate concentration;

[0013] (1.2) Prepare an appropriate concentration of Zn 2+ Co 2+ and Ce 2+ Aqueous solution;

[0014] (1.3) Pour the aqueous solution obtained in step (1.2) into the chitosan aqueous solution obtained in step (1.1) to form a solution containing Zn. 2+ Co 2+ and Ce 2+ Chitosan hydrogel.

[0015] In the first step, one or more of the following conditions must be met:

[0016] In step (1.1), the chitosan molecules used have a deacetylation degree greater than 80% and a viscosity of 100-300 mPa·s;

[0017] In step (1.1), the concentration of the chitosan aqueous solution used is 10-40 mg / ml;

[0018] In step (1.2), the Zn 2+ Co 2+ and Ce 2+ Nitrates, sulfates, phosphates, chlorides, acetates, Any one of the acid salts can be the source;

[0019] In step (1.2), the Zn 2+ Co 2+ and Ce 2+ The molar ratio is 50-100:1:1;

[0020] In step (1.2), a Zn-containing solution is formed in the chitosan aqueous solution. 2+ Co 2+ and Ce 2+ The time for chitosan hydrogel formation is 10-40 minutes.

[0021] The second step specifically includes the following steps:

[0022] (1.4) Containing Zn 2+ Co 2+ and Ce 2+ Chitosan hydrogel was frozen into a solid precursor;

[0023] (1.5) The solid precursor is freeze-dried to remove moisture from the solid and maintain the three-dimensional structure of the solid precursor.

[0024] In step (1.5), the solid precursor is placed in a freeze dryer for 12-24 hours.

[0025] The third step specifically includes:

[0026] (1.6) The CeO2 / Co active site electrocatalyst precursor is placed in a tube furnace and heated from room temperature to 250℃-300℃ in an inert atmosphere and maintained for 0.5-1.5 hours to fix the three-dimensional structure of the precursor. Then it is heated to 800-1000℃ for 1.5-3 hours and then naturally cooled to room temperature to obtain the carbon-supported CeO2 / Co heterojunction active site electrocatalyst.

[0027] In step (1.6), the inert atmosphere is argon, nitrogen, or a vacuum.

[0028] A carbon-supported CeO2 / Co heterojunction active site electrocatalyst prepared by the aforementioned preparation method.

[0029] An application of the carbon-supported CeO2 / Co heterojunction active site electrocatalyst in a lithium-sulfur cathode.

[0030] The present invention has the following beneficial effects:

[0031] This invention provides a carbon-supported CeO2 / Co heterojunction electrocatalyst with active sites, its preparation method, and its application. The process successfully constructs the CeO2 / Co heterojunction. This invention utilizes the Zn generated during the heat treatment of a freeze-dried hydrogel. 2+ Volatilization creates vacancies, Co 2+ and Ce 2+ Diffusion to vacancy bonding, due to different metallic properties, Co 2+ and Ce 2+ In the presence of oxygen in chitosan molecules, CeO2 / Co heterojunction active centers are formed in situ, and the process is simple and can be prepared on a large scale.

[0032] The obtained carbon-supported CeO2 / Co heterojunction electrocatalyst was used as a catalyst in the cathode of a lithium-sulfur battery. The heterojunction enables the adsorption and catalysis of polysulfide compounds, which can greatly reduce the shuttle effect of lithium polysulfides. At the same time, the presence of the carbon framework can increase the electron and ion transport channels and improve conductivity. Its application in lithium-sulfur batteries can improve sulfur utilization, increase coulombic efficiency, and enhance the cycle stability of the battery.

[0033] Compared with traditional technologies, the main advantages of this invention include:

[0034] (1) The carbon-supported CeO2 / Co heterojunction nanomaterials prepared by the method described in this invention have a uniform particle size distribution with particles of approximately 10 nm in diameter. Due to the high specific surface area of ​​the carbon skeleton obtained by maintaining it at low temperature for a certain time followed by high-temperature carbonization, it can support more sulfur as a sulfur host and improve the volume expansion of the cathode during lithiation in lithium-sulfur batteries. As a catalyst, the active catalytic center of the CeO2 / Co heterojunction can effectively promote the catalytic conversion between lithium polysulfides, which greatly reduces the shuttle effect, improves sulfur utilization, and has a good yield effect.

[0035] (2) Compared with heterojunction materials prepared by other methods, the present invention adopts a simple and convenient one-step process, which does not involve complex equipment or operation processes. Moreover, the raw material, the biopolymer chitosan, is easy to obtain, inexpensive, and can be prepared on a large scale. At the same time, the technical solution has certain guiding significance for the design and preparation of other types of metal oxide / metal heterojunctions and has good benefits.

[0036] Other beneficial effects of the embodiments of the present invention will be further described below. Attached Figure Description

[0037] Figure 1 This is a diagram illustrating the CeO2 / Co heterojunction formation process according to an embodiment of the present invention.

[0038] Figure 2 These are transmission electron microscope (TEM) images of a carbon-supported CeO2 / Co heterojunction and a heterojunction, respectively, representing embodiments of the present invention.

[0039] Figure 3 The image shows the XRD pattern of the carbon-supported CeO2 / Co heterojunction in an embodiment of the present invention, compared with the PDF standard card.

[0040] Figure 4 The figure shows the discharge cycle diagram at 0.1C when the carbon-supported CeO2 / Co heterojunction material of this invention is used as a cathode material in a lithium-sulfur battery.

[0041] Figure 5 The diagram shows the charge / discharge rate performance of the carbon-supported CeO2 / Co heterojunction material used as a cathode material in a lithium-sulfur battery according to an embodiment of the present invention. Detailed Implementation

[0042] The embodiments of the present invention will be described in detail below. It should be emphasized that the following description is merely exemplary and not intended to limit the scope and application of the present invention.

[0043] This invention provides a method for preparing a carbon-supported CeO2 / Co heterojunction active site electrocatalyst, comprising the following steps:

[0044] Step 1: Preparation of Zn-containing 2+ Co 2+ and Ce 2+ Chitosan hydrogel;

[0045] Step 2: Prepare a solid CeO2 / Co active site electrocatalyst precursor using the chitosan hydrogel;

[0046] Step 3: The CeO2 / Co active site electrocatalyst precursor is subjected to heat treatment and cooled to obtain carbon-supported CeO2 / Co heterojunction active site electrocatalyst.

[0047] In this preparation method, metal ions are uniformly fixed around chitosan molecules by forming a hydrogel; subsequently, Zn is heated during the heat treatment process. 2+ Volatilization creates vacancies, Co 2+ and Ce 2+ Diffusion to vacancy bonding, due to different metallic properties, Co 2+ and Ce 2+ In the presence of oxygen molecules in chitosan, CeO2 / Co active centers are eventually formed in situ. The metal oxide CeO2 provides strong adsorption for polysulfides, while the metal Co provides strong catalytic conversion between polysulfides. The carbon skeleton provides both conductivity and adsorption for polysulfides.

[0048] This invention also provides an application of a carbon-supported CeO2 / Co active site electrocatalyst, in which the catalyst prepared by the method is applied to a lithium-sulfur cathode.

[0049] In a preferred embodiment, the specific operation steps are as follows:

[0050] Step 1: Preparation of sulfur / carbon supported heterojunction cathode

[0051] Sublimed sulfur and carbon-supported heterojunctions were ground thoroughly at a mass ratio of 7:3, and then heated to 155°C at a rate of 2°C per minute under an Ar atmosphere and maintained for 12 hours. The resulting powder was then mixed and ground thoroughly with carbon nanotubes and PVDF at a mass ratio of 8:1:1, and NMP was added and stirred for 12 hours. The resulting uniform slurry was coated onto carbon-coated aluminum foil and dried at 60°C for 12 hours.

[0052] Step 2: Assemble the lithium-sulfur battery

[0053] The prepared sulfur / carbon supported heterojunction cathode, separator, and lithium sheet were assembled into a lithium-sulfur battery. 25 μL of electrolyte was added to each of the positive and negative electrode sides, with a sulfur loading of ~1.0 mg / cm³. 2 .

[0054] The following describes specific embodiments of the present invention.

[0055] Example 1

[0056] The carbon-supported CeO2 / Co heterojunction active site electrocatalyst and its preparation method include the following steps:

[0057] Step 1: Preparation of Zn 2+ / Co 2+ / Ce 2+ Chitosan hydrogel

[0058] (1.1) Prepare a 40 mg / ml chitosan aqueous solution;

[0059] (1.2) Prepare aqueous solutions of 0.25M ZnAc2 (zinc acetate), 0.02M Co(NO3)2 (cobalt nitrate) and 0.02M Ce(NO3)2 (cerium nitrate);

[0060] (1.3) Pour the aqueous solution in (1.2) into the chitosan aqueous solution in (1.1) to form a hydrogel;

[0061] Step 2: Preparation of CeO2 / Co active site electrocatalyst precursor

[0062] (1.4) Take the Zn obtained in step (1.3) 2+ / Co2+ / Ce 2+ / The chitosan hydrogel was frozen in the refrigerator for 12 hours;

[0063] (1.5) The frozen Zn obtained in step (1.4) 2+ / Co 2+ / Ce 2+ The chitosan hydrogel was placed in a freeze dryer and kept for 12 hours.

[0064] Step 3: Preparation of CeO2 / Co active site electrocatalyst;

[0065] (1.6) The freeze-dried CeO2 / Co active site electrocatalyst precursor obtained in step (1.5) is placed in a tube furnace and heated from room temperature to 250°C at a rate of 5°C / min and held for 0.5 hours in an inert atmosphere. Then, it is heat-treated to 900°C at a rate of 5°C / min for 2 hours. After natural cooling to room temperature, the product obtained is the carbon-supported CeO2 / Co active site electrocatalyst.

[0066] Example 2

[0067] Repeat the steps of Example 1, except that the concentration of chitosan in step (1.1) is changed to 30 mg / ml.

[0068] Example 3

[0069] Repeat the steps of Example 1, except that in step (1.2), cobalt nitrate and cerium nitrate are replaced with cobalt acetate and cerium acetate, respectively.

[0070] Example 4

[0071] Repeat the steps of Example 1, except that the freezing and holding time in step (1.4) is changed from 12 hours to 24 hours.

[0072] Example 5

[0073] Repeat the steps of Example 1, except that the freeze dryer is kept in the freeze dryer for 24 hours instead of 12 hours in step (1.5).

[0074] Example 6

[0075] Repeat the steps of Example 1, except that the heating rate of 5°C / minute to 250°C in step (1.6) is changed to a heating rate of 2°C / minute to 250°C.

[0076] Example 7

[0077] Repeat the steps of Example 1, except that in step (1.6), the temperature is kept at 250°C for 0.5 hours, which is changed to 250°C for 1 hour.

[0078] Example 8

[0079] Repeat the steps of Example 1, except that the heating rate of 5°C / min to 900°C in step (1.6) is changed to a heating rate of 2°C / min to 900°C.

[0080] Example 9

[0081] Repeat the steps of Example 1, except that the heat treatment at 900°C for 2 hours in step (1.6) is changed to heat treatment at 1000°C for 2 hours.

[0082] Example 10

[0083] Repeat the steps of Example 1, except that the heat treatment at 900°C for 2 hours in step (1.6) is changed to heat treatment at 900°C for 3 hours.

[0084] Experimental Example

[0085] The carbon-supported CeO2 / Co heterojunction material obtained in Example 1 was used as a cathode material for performance testing in lithium-sulfur batteries.

[0086] Depend on Figure 2 , Figure 3 It can be seen that carbon in carbon-supported CeO2 / Co heterojunction materials has a three-dimensional network structure, and CeO2 / Co heterojunctions are uniformly distributed on the three-dimensional carbon framework.

[0087] The carbon-supported CeO2 / Co heterojunction material was tested using X-ray diffraction, such as... Figure 3 As shown, its XRD pattern matches the peaks of the PDF standard card, proving that the synthesized material contains CeO2 and Co. For the sample without heterostructure, it exhibits typical (002) and (101) diffraction peaks of amorphous carbon materials. For the sample containing CeO2 / Co heterostructure, a strong and sharp (002) characteristic diffraction peak appears at 2θ = 25.9°, indicating that the chitosan polymer successfully transforms into graphitized carbon under the catalysis of metal during carbonization, which helps to improve conductivity and facilitates electron transport in lithium-sulfur battery cycling.

[0088] The carbon-supported CeO2 / Co heterojunction material (ZnCeCo sample) was used as the cathode material in a lithium-sulfur battery under electrochemical cycling conditions at a charge-discharge rate of 0.1C. The results are as follows: Figure 4 As shown, the specific capacity reached 900 mAh / g for the first time, which is higher than that of pure carbon material without heterojunction material (Zn sample) (795 mAh / g). This indicates that the presence of heterojunction material effectively promotes the reduction process of lithium polysulfides. Figure 5 The charge-discharge cycle at 1C rate is given. It can be seen that the sample containing the heterojunction CeO2 / Co catalyst performs better than the sample without the heterojunction catalyst, which also highlights the stability of the carbon-supported heterojunction material.

[0089] The same tests were performed on the materials of Examples 2 to 10, and the results were similar to those of Example 1.

[0090] In summary, this invention provides a carbon-supported CeO2 / Co heterojunction electrocatalyst with active sites, its preparation method, and its application. The proposed process successfully constructs a CeO2 / Co heterojunction. This invention utilizes the Zn... 2+ Volatilization creates vacancies, Co 2+ and Ce 2+ Diffusion to vacancy bonding, due to different metallic properties, Co 2+ and Ce 2 + In the presence of oxygen within chitosan molecules, CeO2 / Co heterojunction active centers are formed in situ. This CeO2 / Co heterojunction plays a crucial role in lithium-sulfur batteries, where the metal oxide CeO2 provides strong adsorption for polysulfides, metal Co provides strong catalytic conversion between polysulfides, and the carbon framework simultaneously provides conductivity and polysulfide adsorption. Similarly, this invention provides a reference for the preparation and catalytic applications of other types of metal oxide / metal heterojunctions.

[0091] The background section of this invention may include background information about the problems or environment in which the invention is being developed, and is not necessarily a description of prior art. Therefore, the content included in the background section does not constitute an admission of prior art by the applicant.

[0092] The above description provides a further detailed explanation of the present invention in conjunction with specific / preferred embodiments, and it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various substitutions or modifications can be made to these described embodiments without departing from the concept of the present invention, and all such substitutions or modifications should be considered within the scope of protection of the present invention. In the description of this specification, the reference to terms such as "an embodiment," "some embodiments," "preferred embodiment," "example," "specific example," or "some examples," etc., indicates that the specific features, structures, materials, or characteristics described in connection with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any suitable manner in one or more embodiments or examples. Without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification and the features of different embodiments or examples. Although the embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions, and modifications can be made herein without departing from the scope of protection of the patent application.

Claims

1. A method for preparing a carbon-supported CeO2 / Co heterojunction active site electrocatalyst, characterized in that, Includes the following steps: Step 1: Preparation of Zn-containing 2+ Co 2+ and Ce 2+ Chitosan hydrogel, wherein the Zn 2+ Co 2+ and Ce 2+ The molar ratio is 50-100:1:1; Step 2: Prepare a solid CeO2 / Co active site electrocatalyst precursor using the chitosan hydrogel; Step 3: The CeO2 / Co active site electrocatalyst precursor is subjected to heat treatment and cooled to obtain carbon-supported CeO2 / Co heterojunction active site electrocatalyst.

2. The method for preparing the carbon-supported CeO2 / Co heterojunction active site electrocatalyst as described in claim 1, characterized in that, The first step specifically includes the following steps: (1.1) Prepare an aqueous solution of chitosan of appropriate concentration; (1.2) Configure Zn 2+ Co 2+ and Ce 2+ Aqueous solution; (1.3) Pour the aqueous solution obtained in step (1.2) into the chitosan aqueous solution obtained in step (1.1) to form a solution containing Zn. 2+ Co 2+ and Ce 2+ Chitosan hydrogel.

3. The method for preparing the carbon-supported CeO2 / Co heterojunction active site electrocatalyst as described in claim 2, characterized in that, In the first step, one or more of the following conditions must be met: In step (1.1), the chitosan molecules used have a deacetylation degree greater than 80% and a viscosity of 100-300 mPa·s; In step (1.1), the concentration of the chitosan aqueous solution used is 10-40 mg / ml; In step (1.2), the Zn 2+ Co 2+ and Ce 2+ The source can be any one of nitrate, sulfate, phosphate, chloride, acetate, or thiazoline. In step (1.2), a Zn-containing solution is formed in the chitosan aqueous solution. 2+ Co 2+ and Ce 2+ The time for chitosan hydrogel formation is 10-40 minutes.

4. The method for preparing the carbon-supported CeO2 / Co heterojunction active site electrocatalyst according to any one of claims 1 to 3, characterized in that, The second step specifically includes the following steps: (1.4) Containing Zn 2+ Co 2+ and Ce 2+ Chitosan hydrogel was frozen into a solid precursor; (1.5) The solid precursor is freeze-dried to remove moisture from the solid and maintain the three-dimensional structure of the solid precursor.

5. The method for preparing the carbon-supported CeO2 / Co heterojunction active site electrocatalyst as described in claim 4, characterized in that, In step (1.5), the solid precursor is placed in a freeze dryer for 12-24 hours.

6. The method for preparing the carbon-supported CeO2 / Co heterojunction active site electrocatalyst according to any one of claims 1 to 3, characterized in that, The third step specifically includes: (1.6) The CeO2 / Co active site electrocatalyst precursor is placed in a tube furnace and heated from room temperature to 250℃-300℃ in an inert atmosphere and maintained for 0.5-1.5 hours to fix the three-dimensional structure of the precursor. Then it is heated to 800-1000℃ for 1.5-3 hours and then naturally cooled to room temperature to obtain the carbon-supported CeO2 / Co heterojunction active site electrocatalyst.

7. The method for preparing the carbon-supported CeO2 / Co heterojunction active site electrocatalyst as described in claim 6, characterized in that, In step (1.6), the inert atmosphere is argon, nitrogen or vacuum.

8. A carbon-supported CeO2 / Co heterojunction active site electrocatalyst prepared by the preparation method according to any one of claims 1 to 7.

9. An application of the carbon-supported CeO2 / Co heterojunction active site electrocatalyst of claim 8 in a lithium-sulfur cathode.

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