CN111477880B

CN111477880B - CeOx/RuO2(iii) MC and CeOx/RuO2Preparation and application of composite nanosheet material

Info

Publication number: CN111477880B
Application number: CN202010148483.5A
Authority: CN
Inventors: 苏利伟; 陈思远; 赵宜哲; 吴昊; 王连邦
Original assignee: Zhejiang University of Technology ZJUT
Current assignee: Zhejiang University of Technology ZJUT
Priority date: 2020-03-05
Filing date: 2020-03-05
Publication date: 2021-07-27
Anticipated expiration: 2040-03-05
Also published as: CN111477880A

Abstract

The invention discloses CeO_x/RuO₂Composite nano-sheet of/MC and CeO_x/RuO₂Preparation and application of composite nanosheet material. The preparation method comprises the following steps: (1) removing hard shells of waste corn straws, crushing the waste corn straws into small particles, performing acid treatment, washing the small particles to be neutral by deionized water, filtering and drying to obtain a biomass carbon raw material; (2) preparing a mixed solution of cerium salt and ruthenium salt; (3) soaking the biomass carbon raw material in the mixed solution, sequentially carrying out ultrasonic treatment, vacuum treatment and ultrasonic treatment again in the soaking process, and then filtering and fully drying; (4) roasting the dried product in argon to obtain CeO_xa/Ru/MC composite nanosheet; (5) adding CeO_xRoasting the/Ru/MC composite nanosheet in the air to obtain CeO_x/RuO₂Composite nano-sheet of/MC or CeO_x/RuO₂And (3) compounding the nanosheet material. The present invention provides the CeO_x/RuO₂Composite nano sheet material of/MC or CeO_x/RuO₂The composite nanosheet material is applied as a lithium-oxygen battery anode catalyst material, has high catalytic activity, and can greatly reduce the overpotential of the OER reaction.

Description

CeOx/RuO2(iii) MC and CeOx/RuO2Preparation and application of composite nanosheet material

Technical Field

The invention relates to CeO_x/RuO₂Composite nano-sheet of/MC and CeO_x/RuO₂A preparation method of the composite nanosheet material and application of the nanosheet material as a lithium-oxygen battery anode catalyst material.

Background

Lithium ion batteries, as the main energy storage devices of today, have become increasingly difficult to meet people's living and production needs. The search for the next generation of energy storage system with higher energy density is becoming more and more gradual, and the theoretical energy density of the rechargeable lithium-oxygen battery is the highest of the currently known battery systems, which is more than ten times higher than that of any currently used lithium ion battery, so the rechargeable lithium-oxygen battery is researched and paid attention to by broad scholars and enterprises. The major problems that currently impede the development of li-o batteries are their excessive overpotential, low cycle life, low round-trip efficiency, and poor rate capability. The fundamental solution to these problems is to develop a positive electrode catalyst material having excellent performance. The discharge process occurs primarily through the Oxygen Reduction Reaction (ORR), where the primary reason for limiting cell performance is the low concentration of oxygen in the cell system and slow transport. CeO (CeO)₂Because lattice oxygen has high activity and fluidity, oxygen vacancies are easily caused. Thus, in most cases, CeO₂In fact as CeO_xIn the form of (1.5)<x<2) Which has a higher oxygen transfer capacity and more importantly, oxygen vacancies can provide additional catalytically active sites. So CeO_xIs an ideal ORR catalyst in a lithium-oxygen battery. However, in addition to the limitation of the slow ORR process on lithium oxygen batteries, the excessive overpotential of the OER process is more challenging for the stable cycling of the battery. Too high an OER overpotential can lead to many side reactions, such as decomposition of the electrolyte, carbon-mediated side reactions in some materials, and the like. The existence of these side reactions is the main cause of short cycle life and poor reciprocating efficiency of the lithium-oxygen battery. A large number of studies have shown that the noble metal Ru, in particular its oxide RuO₂The catalyst has excellent capability of reducing the reaction overpotential of the lithium-oxygen battery OER and has been actively explored to be applied as a catalyst material. It is not difficult to imagine that CeO_xAnd RuO₂The combination of the catalyst and the catalyst for the lithium-oxygen battery has great advantages. In addition to these metals or metal oxides, carbon materials are also frequently used for research on lithium-oxygen battery positive electrode catalysts because of their excellent electrical conductivity, and are mainly used as support carriers to reach dispersion levelsThe surface nano-particles and the function of enhancing the conductivity of the material. However, some research results show that carbon materials are an important part of the occurrence of side reactions in lithium-oxygen batteries, and thus the rationality of the presence of carbon remains to be considered. The invention provides a novel preparation method, which can be used for preparing CeO_xAnd RuO₂And the carbon material, and whether the carbon substrate is reserved or partially reserved can be selected according to the situation. The method is environment-friendly and pollution-free, adopts biomass as a raw material, has a simple process, and is very suitable for large-scale production. The invention also provides the application of the catalyst material in a lithium-oxygen battery.

Disclosure of Invention

The invention provides CeO which has simple process flow, wide raw material source and low cost and is very suitable for large-scale production_x/RuO₂Composite nano sheet material of/MC and CeO with extremely low MC content_x/RuO₂Preparation method of composite nanosheet material and prepared CeO_x/RuO₂Composite nano-sheet of/MC and CeO_x/RuO₂The composite nano sheet material has higher catalytic activity and can greatly reduce the overpotential of OER reaction.

It is a second object of the present invention to provide the CeO_x/RuO₂Composite nano-sheet material of/MC and CeO_x/RuO₂The composite nanosheet material is applied as a lithium-oxygen battery anode catalyst material.

In order to achieve the purpose, the invention adopts the following technical scheme:

in a first aspect, the present invention provides a CeO_x/RuO₂Composite nano-sheet material of/MC and CeO_x/RuO₂The preparation method of the composite nanosheet material comprises the following steps:

(1) removing hard shells of waste corn straws, crushing the waste corn straws into small particles, placing the small particles in an acid solution, fully stirring, washing the small particles to be neutral by using deionized water, filtering and drying to obtain a biomass carbon raw material;

(2) weighing a proper amount of cerium salt and ruthenium salt, dissolving the cerium salt and the ruthenium salt in deionized water, and fully stirring the cerium salt and the ruthenium salt to completely dissolve the cerium salt and the ruthenium salt to obtain a mixed solution with the total concentration of 5-50mM, wherein the molar ratio of the cerium salt to the ruthenium salt is 1: 0.02-1;

(3) dipping the biomass carbon raw material in the step (1) in the mixed solution prepared in the step (2), sequentially performing ultrasonic treatment, vacuum treatment and ultrasonic treatment again in the dipping process, then filtering, and fully drying the filtered product;

(4) roasting the product dried in the step (3) at the temperature of 600-900 ℃ in an argon atmosphere to obtain CeO_xa/Ru/MC composite nanosheet material;

(5) the CeO obtained in the step (4) is added_xRoasting the/Ru/MC composite nano-sheet for 1-3 hours at the temperature of 200-450 ℃ in air atmosphere to obtain CeO_x/RuO₂Composite nano sheet material of/MC or CeO_x/RuO₂And (3) compounding the nanosheet material.

According to the preparation method, the adsorption of the functional groups on the surfaces of the corn straws on the cerium ions and the ruthenium ions is utilized to realize the thin-layer adhesion of the cerium ions and the ruthenium ions on the surfaces of the functional groups, so that the serious agglomeration of excessive cerium ions and ruthenium ions in the roasting process is avoided, and the ultra-small particle size and the high loading capacity are realized. The concentration of cerium ions and ruthenium ions in the impregnation liquid is crucial: excessive concentration of Ru and CeO_xExcessive generation and serious agglomeration; too low concentration of Ru and CeO_xToo small an amount, the catalytic action is greatly impaired. The second core of the invention is the roasting temperature in the step (4): the particles are easy to agglomerate due to the overhigh temperature; too low a temperature tends to result in incomplete carbonization of the biomass. The third core of the invention is the baking temperature and the baking time of the last step, and the combination of the two can adjust the oxidation degree of Ru and the removal degree of the carbon substrate.

Preferably, the acid solution in step (1) is sulfuric acid, hydrochloric acid or nitric acid with a concentration of 0.5 to 5 wt%; stirring at 70-100 deg.C for 1-3 hr; the drying temperature after filtration is 35-60 ℃.

Preferably, in the step (2), the cerium salt is cerium acetate, and the ruthenium salt is ruthenium trichloride, ruthenium acetate or ruthenium sulfate.

Preferably, in the step (2), the total concentration of the mixed solution is 20mM, and the molar ratio of the cerium salt to the ruthenium salt is 1: 0.2.

Preferably, the first ultrasonic treatment time in the step (3) is 20-60 minutes of ultrasonic treatment, the vacuum treatment time is 20-60 minutes, the second ultrasonic treatment time is 20-60 minutes, and the drying temperature is 35-80 ℃.

Preferably, the calcination temperature in step (4) is 600-900 deg.C (more preferably 600 deg.C), the time is 3-6 hours (more preferably 4 hours), and the temperature rise rate is 2-20 deg.C/min (more preferably 5 deg.C/min).

Preferably, the roasting temperature in the step (5) is 250-350 ℃, and the time is 2-2.5 hours; more preferably, the calcination temperature is 250 ℃ and the calcination time is 2 hours.

CeO prepared by the method of the invention_x/RuO₂Composite nano-sheet material of/MC and CeO_x/RuO₂The composite nanosheet material has high catalytic activity, and the invention provides application of the composite nanosheet material as a lithium-oxygen battery anode catalyst material.

Compared with the prior art, the invention has the following advantages:

(1) realization of small-size RuO by adopting corn straws for the first time₂And CeO_xIn situ growth on mesoporous carbon.

(2) In the known CeO_x/RuO₂RuO of the invention in/MC Material₂And CeO_xThe particle size is smaller and the distribution is more uniform.

(3) Realize RuO₂And CeO_xThe loading capacity of the nano-crystal on the mesoporous carbon and the controllable adjustment of the grain diameter of the crystal.

(4) Firstly adopts a sacrificial biomass template method to prepare CeO_x/RuO₂The composite nano sheet can keep the sheet structure from collapsing after the carbon substrate is removed.

(5) The raw materials are rich and renewable, the process is simple, green and pollution-free, and the large-scale production is easy.

(6)CeO_x/RuO₂(MC) nanosheet and CeO_x/RuO₂The composite nanosheets all show good catalytic performance of the lithium-oxygen battery, and particularly the reaction overpotential in the OER process is greatly reduced.

Drawings

The accompanying drawings, which are included to provide a further understanding of the embodiments of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principles of the invention.

FIG. 1 is a CeO prepared in example 1_x/RuO₂TG pattern of/MC nanoplates.

FIG. 2 is CeO prepared in example 1_x/RuO₂TEM and SEM images of/MC nanosheets.

FIG. 3 is CeO prepared in example 1_x/RuO₂A lithium-oxygen battery limit charge-discharge curve graph and a limited capacity charge-discharge curve graph with/MC nanosheets as the positive electrode.

FIG. 4 is CeO prepared in example 2_x/RuO₂TG profile of nanoplates.

FIG. 5 is CeO prepared in example 2_x/RuO₂TEM images of the nanoplates.

FIG. 6 is CeO prepared in example 2_x/RuO₂The lithium-oxygen battery with the nanosheet as the positive electrode has a limit charge-discharge curve diagram and a limited capacity charge-discharge curve diagram.

FIG. 7 is CeO prepared in example 3_x/RuO₂TG profile of nanoplates.

FIG. 8 is CeO prepared in example 3_x/RuO₂TEM images of the nanoplates.

FIG. 9 is CeO prepared in example 3_x/RuO₂The lithium-oxygen battery with the nanosheet as the positive electrode has a limit charge-discharge curve diagram and a limited capacity charge-discharge curve diagram.

FIG. 10 is CeO prepared in example 4_x/RuO₂TEM images of the nanoplates.

FIG. 11 is CeO prepared in example 4_x/RuO₂The lithium-oxygen battery with the nanosheet as the positive electrode has a limit charge-discharge curve diagram and a limited capacity charge-discharge curve diagram.

FIG. 12 is CeO prepared in example 5_x/RuO₂TEM images of the nanoplates.

FIG. 13 is CeO prepared in example 5_x/RuO₂Lithium-oxygen battery limit charge and discharge with nanosheet as positive electrodeGraph and defined capacity charge and discharge graph.

FIG. 14 is CeO prepared in example 6_x/RuO₂TEM images of the nanoplates.

FIG. 15 is CeO prepared in example 6_x/RuO₂The lithium-oxygen battery with the nanosheet as the positive electrode has a limit charge-discharge curve diagram and a limited capacity charge-discharge curve diagram.

Detailed Description

The technical solution of the present invention is further illustrated by the following specific examples, but is not limited thereto:

the preparation method of the nano sheet comprises the following steps: the adsorption of the functional groups on the surface of the corn straws on cerium ions and ruthenium ions is utilized to realize the attachment of the two ions on a thin layer on the surface of the corn straws, and the thin layer of the ions is decomposed into small-size Ru and small-size CeO in the roasting process_xThe nanometer crystal is loaded on the surface of the mesoporous carbon evenly to avoid serious agglomeration, and finally the nanometer crystal is roasted in the air to achieve the purposes of oxidizing Ru and removing the carbon substrate, so that CeO can be obtained_x/RuO₂/MC nanosheet or CeO_x/RuO₂Nanosheets.

The assembly and test method of the battery in the embodiment of the invention is as follows: adding CeO_x/RuO₂/MC or CeO_x/RuO₂Mixing PVDF according to a mass ratio of 9:1, adding NMP as a solvent, stirring into a slurry, coating the slurry on carbon paper, and drying the carbon paper for 12 hours in vacuum at 120 ℃ to obtain a positive electrode material; the method comprises the steps of taking metal lithium as a negative electrode, taking glass fiber filter paper as a diaphragm, taking dimethyl sulfoxide (DMSO) solution of 1M lithium bis (trifluoromethylsulfonyl) imide (LiTFSI) as electrolyte, assembling the battery in a glove box under the protection of argon, and testing the performance of the battery in pure oxygen atmosphere.

Example 1:

(1) removing hard shells from corn straws recovered from farms, crushing into small particles, placing the small particles in a 0.5 wt.% sulfuric acid solution, stirring at 70 ℃ for 1 hour, washing with deionized water to neutrality, and drying the filtered product at 35 ℃ to obtain a biomass carbon raw material.

(2) Weighing cerium acetate and ruthenium trichloride, dissolving in deionized water, stirring to completely dissolve the cerium acetate and ruthenium trichloride to obtain a 5mM solution, wherein the molar ratio of cerium salt to ruthenium salt is 1: 0.02.

(3) and (2) soaking the biomass carbon raw material in the step (1) in the solution prepared in the step (2), performing ultrasonic treatment for 20 minutes, performing vacuum treatment for 20 minutes, performing ultrasonic treatment for 20 minutes again, filtering, and fully drying the filtered product at the drying temperature of 35 ℃.

(4) Roasting the product dried in the step (3) for 6 hours at 600 ℃ in an argon atmosphere at the heating rate of 2 ℃/min to obtain CeO_xthe/Ru/MC nanosheet material.

(5) The CeO obtained in the step (4) is added_xRoasting the/Ru/MC nanosheet in air atmosphere at the roasting temperature of 200 ℃ for 1 hour to obtain CeO_x/RuO₂an/MC nano-sheet.

FIG. 1 shows CeO prepared in example 1_x/RuO₂TG diagram of/MC nano-sheet, it can be seen that the carbon content of the nano-sheet is only about 25%, and the rest is CeO_xAnd RuO₂And (4) forming. FIG. 2 shows CeO prepared in example 1_x/RuO₂TEM image and SEM image of/MC nano sheet, and the material can be observed to be in a sheet structure in the whole, CeO_xAnd RuO₂The nano-crystals are uniformly distributed, and the particle size is fine and uniform and is about 3-4 nm. FIG. 3 is CeO prepared in example 1_x/RuO₂The limit charge-discharge curve diagram and the constant-capacity charge-discharge curve diagram of the lithium-oxygen battery assembled by taking the/MC nanosheet as the positive electrode (the capacity is limited to 500mAh/g, the current density is 200mA/g, and the voltage range is 2.25-4.5V). It can be seen that the material can contribute a specific discharge capacity in excess of 5500mAh/g with a higher coulombic efficiency. The lithium-oxygen battery assembled by the cathode material can stably cycle for more than 27 weeks, and has better cycle performance.

Example 2:

(1) removing hard shells from corn straws recovered from farms, crushing the corn straws into small particles, placing the corn straws in a 1.5 wt.% nitric acid solution, stirring the corn straws for 1 hour at 70 ℃, washing the corn straws to be neutral by deionized water, and drying the filtered corn straws at 45 ℃ to obtain a biomass carbon raw material.

(2) Weighing cerium acetate and ruthenium sulfate, dissolving in deionized water, stirring to completely dissolve the cerium acetate and ruthenium sulfate to obtain a 20mM solution, wherein the molar ratio of cerium salt to ruthenium salt is 1: 0.2.

(3) and (2) soaking the biomass carbon raw material in the step (1) in the solution prepared in the step (2), performing ultrasonic treatment for 30 minutes, performing vacuum treatment for 30 minutes, performing ultrasonic treatment for 30 minutes again, filtering, and fully drying the filtered product at the drying temperature of 60 ℃.

(4) Roasting the product dried in the step (3) for 4 hours at the temperature of 600 ℃ in the argon atmosphere, and obtaining CeO at the heating rate of 5 ℃/min_xthe/Ru/MC nanosheet material.

(5) The CeO obtained in the step (4) is added_xRoasting the/Ru/MC nanosheets in air atmosphere at the roasting temperature of 250 ℃ for 2 hours to obtain CeO_x/RuO₂Nanosheets.

FIG. 4 shows CeO prepared in example 2_x/RuO₂TG pattern of nanosheets, from which it is apparent that the material consists essentially of CeO_xAnd RuO₂Composition, carbon is only about 5.5%. FIG. 5 shows CeO prepared in example 2_x/RuO₂TEM images of the nanoplates show a morphology similar to that of the material in example 1, but with a marked increase in particle size due to crystal growth caused by firing in air. FIG. 6 is CeO prepared in example 2_x/RuO₂The limit charge-discharge curve and the constant-capacity charge-discharge curve chart (the capacity is limited to 500mAh/g, the current density is 200mA/g, and the voltage range is 2.25-4.5V) of the lithium-oxygen battery assembled by the nanosheet as the positive electrode. It can be seen that the material can contribute a specific discharge capacity in excess of 6000mAh/g with a higher coulombic efficiency. The lithium-oxygen battery assembled by the cathode material can stably cycle for more than 50 weeks, and has good cycle performance.

Example 3:

(1) removing hard shells from corn straws recovered from farms, crushing into small particles, placing the small particles in a 2 wt.% sulfuric acid solution, stirring for 1 hour at 90 ℃, washing with deionized water to be neutral, and drying a product obtained by filtering at 50 ℃ to obtain a biomass carbon raw material.

(2) Weighing cerium acetate and ruthenium trichloride, dissolving in deionized water, stirring to completely dissolve the cerium acetate and ruthenium trichloride to obtain a 10mM solution, wherein the molar ratio of cerium salt to ruthenium salt is 1: 0.1.

(5) The CeO obtained in the step (4) is added_xRoasting the/Ru/MC nanosheets in air atmosphere at the roasting temperature of 300 ℃ for 2 hours to obtain CeO_x/RuO₂Nanosheets.

FIG. 7 shows CeO prepared in example 3_x/RuO₂TG pattern of nanosheets, from which it is apparent that the material consists essentially of CeO_xAnd RuO₂Composition, carbon is only about 4.5%. FIG. 8 is a CeO prepared in example 3_x/RuO₂TEM image of the nanoplatelets, it can be seen that the morphology is similar to the material in example 2, but the particle size is slightly increased due to crystal growth caused by firing in air, and the contrast between the particles and the background is increased in this image because the amount of carbon is small, so the background color appears weaker in TEM. FIG. 9 is CeO prepared in example 3_x/RuO₂The lithium-oxygen battery assembled by the nanosheet as the positive electrode has a limit charge-discharge curve and a cycling stability curve (constant-capacity charge-discharge test is adopted, the capacity is limited to 500mAh/g, the current density is 200mA/g, and the voltage range is 2.25-4.5V), so that the material can contribute to the specific discharge capacity of more than 5500mAh/g, and has higher coulombic efficiency. The lithium-oxygen battery assembled by the cathode material can stably cycle for more than 45 weeks, and has good cycle performance.

Example 4:

(1) removing hard shells from corn straws recovered from farms, crushing into small particles, placing the small particles in a 3 wt.% sulfuric acid solution, stirring for 1 hour at 90 ℃, washing with deionized water to be neutral, and drying a product obtained by filtering at 45 ℃ to obtain a biomass carbon raw material.

(2) Weighing cerium acetate and ruthenium trichloride, dissolving in deionized water, stirring to completely dissolve the cerium acetate and ruthenium trichloride to obtain a 20mM solution, wherein the molar ratio of cerium salt to ruthenium salt is 1: 0.5.

(3) and (2) soaking the biomass carbon raw material in the step (1) in the solution prepared in the step (2), performing ultrasonic treatment for 40 minutes, performing vacuum treatment for 40 minutes, performing ultrasonic treatment for 40 minutes again, filtering, and fully drying the filtered product at the drying temperature of 70 ℃.

(4) Roasting the product dried in the step (3) for 4 hours at 700 ℃ in an argon atmosphere at the heating rate of 10 ℃/min to obtain CeO_xthe/Ru/MC nanosheet material.

(5) The CeO obtained in the step (4) is added_xRoasting the/Ru/MC nanosheet in air atmosphere at 350 ℃ for 2 hours to obtain CeO_x/RuO₂Nanosheets.

FIG. 10 shows CeO prepared in example 4_x/RuO₂TEM images of the nanoplates, it can be seen that the morphology is similar to the material in example 3. FIG. 11 is a CeO prepared in example 4_x/RuO₂The lithium-oxygen battery assembled by the nanosheet as the positive electrode has a limit charge-discharge curve and a cycling stability chart (constant-capacitance charge-discharge test is adopted, the capacity is limited to 500mAh/g, the current density is 200mA/g, and the voltage range is 2.25-4.5V), so that the material can contribute to the specific discharge capacity of more than 7000mAh/g and has higher coulombic efficiency. The lithium-oxygen battery assembled by the cathode material can stably cycle for more than 40 weeks, and has good cycle performance.

Example 5:

(1) removing hard shells from corn straws recovered from farms, crushing into small particles, placing the small particles in a 4 wt.% sulfuric acid solution, stirring at 80 ℃ for 1 hour, washing with deionized water to neutrality, and drying the filtered product at 50 ℃ to obtain a biomass carbon raw material.

(2) Weighing cerium acetate and ruthenium trichloride, dissolving in deionized water, stirring to completely dissolve the cerium acetate and ruthenium trichloride to obtain a 40mM solution, wherein the molar ratio of cerium salt to ruthenium salt is 1: 0.5.

(3) and (2) soaking the biomass carbon raw material in the step (1) in the solution prepared in the step (2), performing ultrasonic treatment for 30 minutes, performing vacuum treatment for 30 minutes, performing ultrasonic treatment for 30 minutes again, filtering, and fully drying the filtered product at the drying temperature of 80 ℃.

(4) Roasting the product dried in the step (3) for 4 hours at 800 ℃ in an argon atmosphere, and obtaining CeO at the heating rate of 5 ℃/min_xthe/Ru/MC nanosheet material.

(5) The CeO obtained in the step (4) is added_xRoasting the/Ru/MC nanosheets in an air atmosphere at the roasting temperature of 400 ℃ for 2 hours to obtain CeO_x/RuO₂Nanosheets.

FIG. 12 is a CeO prepared in example 5_x/RuO₂TEM images of the nanosheets, it can be seen that the morphology is similar to the material in example 4, with a slight increase in particle size. FIG. 13 is CeO prepared in example 5_x/RuO₂The lithium-oxygen battery assembled by the nanosheet as the positive electrode has a limit charge-discharge curve and a cycling stability curve (constant-capacity charge-discharge test is adopted, the capacity is limited to 500mAh/g, the current density is 200mA/g, and the voltage range is 2.25-4.5V), so that the material can contribute to the specific discharge capacity of over 4500mAh/g and has higher coulomb efficiency. The lithium-oxygen battery assembled by the cathode material can stably cycle for more than 39 weeks, and has good cycle performance.

Example 6:

(1) removing hard shells from corn straws recovered from farms, crushing into small particles, placing the small particles in a 5 wt.% hydrochloric acid solution, stirring for 3 hours at 100 ℃, washing with deionized water to be neutral, and drying a product obtained by filtering at 60 ℃ to obtain a biomass carbon raw material.

(2) Weighing cerium acetate and ruthenium acetate, dissolving in deionized water, stirring to completely dissolve the cerium acetate and the ruthenium acetate to obtain a 50mM solution, wherein the molar ratio of cerium salt to ruthenium salt is 1: 1.

(3) and (2) soaking the biomass carbon raw material in the step (1) in the solution prepared in the step (2), performing ultrasonic treatment for 60 minutes, performing vacuum treatment for 60 minutes, performing ultrasonic treatment for 60 minutes again, filtering, and fully drying the filtered product at the drying temperature of 80 ℃.

(4) Roasting the product dried in the step (3) for 3 hours at 900 ℃ in an argon atmosphere at the heating rate of 20 ℃/min to obtain CeO_xthe/Ru/MC nanosheet material.

(5) The CeO obtained in the step (4) is added_xRoasting the/Ru/MC nanosheet in air atmosphere at the roasting temperature of 450 ℃ for 3 hours to obtain CeO_x/RuO₂Nanosheets.

FIG. 14 shows CeO prepared in example 6_x/RuO₂TEM images of the nanoplates show a morphology similar to that of the material in example 5, but with a significant increase in particle size and little background visible, indicating that the material has a very low carbon content. FIG. 15 is CeO prepared in example 6_x/RuO₂The limit charge-discharge curve diagram and the circulation stability diagram of the lithium-oxygen battery assembled by the nanosheet as the positive electrode (constant-capacity charge-discharge test is adopted, the capacity is limited to 500mAh/g, the current density is 200mA/g, and the voltage range is 2.25-4.5V), so that the material can contribute to the discharge capacity exceeding 4500mAh/g and has higher coulomb efficiency. The lithium-oxygen battery assembled by the cathode material can stably cycle for more than 36 weeks, and has good cycle performance.

The above-mentioned embodiments are only a part of the preferred embodiments of the present invention, not all embodiments, and are not intended to limit the scope of the present invention, and any modifications, substitutions, etc. made under the concept and principle of the present invention should be included in the scope of the present invention.

Claims

1. CeO (CeO)_x/RuO₂Composite nano-sheet material of/MC and CeO_x/RuO₂The preparation method of the composite nanosheet material comprises the following steps:

(1) removing hard shells of waste corn straws, crushing the waste corn straws into small particles, and fully stirring the small particles in an acid solution, wherein the acid solution is sulfuric acid, hydrochloric acid or nitric acid with the concentration of 0.5-5 wt%, and the stirring temperature is 70-100 ℃ and the stirring time is 1-3 hours; washing the biomass carbon raw material with deionized water to be neutral, filtering and drying to obtain a biomass carbon raw material;

2. The method of claim 1, wherein: in the step (1), the drying temperature is 35-60 ℃ after filtration.

3. The method of claim 1, wherein: in the step (2), the cerium salt is cerium acetate, and the ruthenium salt is ruthenium trichloride, ruthenium acetate or ruthenium sulfate.

4. The method of claim 1, wherein: in the step (2), the total concentration of the mixed solution is 20mM, and the molar ratio of the cerium salt to the ruthenium salt is 1: 0.2.

5. The method of claim 1, wherein: in the step (3), the ultrasonic treatment time is 20-60 minutes, the vacuum treatment time is 20-60 minutes, the ultrasonic treatment time is 20-60 minutes again, and the drying temperature is 35-80 ℃.

6. The method of claim 1, wherein: in the step (4), the roasting temperature is 600-900 ℃, the time is 3-6 hours, and the heating rate is 2-20 ℃/min.

7. The method of claim 1, wherein: in the step (4), the roasting temperature is 600 ℃, the time is 4 hours, and the heating rate is 5 ℃/min.

8. The method of claim 1, wherein: in the step (5), the roasting temperature is 250-350 ℃, and the time is 2-2.5 hours.

9. The method of claim 1, wherein: in the step (5), the roasting temperature is 250 ℃, and the roasting time is 2 hours.

10. CeO produced by the production method according to claim 1_x/RuO₂Composite nano sheet material of/MC or CeO_x/RuO₂The composite nanosheet material is applied as a lithium-oxygen battery anode catalyst material.