A transition metal doped ceria-three-dimensional graphene composite material and a preparation method thereof

Abstract

The application discloses a transition metal doped cerium oxide-three-dimensional graphene composite material rich in oxygen vacancies and a preparation method. 2‑x The chemical formula of the composite material is TM-CeO 2‑x / 3D Gr, wherein x is in the range of 0.09-0.56, and TM is one of Fe, Co, Ni, Mn or Cr. The transition metal doping can introduce a large number of oxygen vacancies in CeO2 by using the difference in valence states, thereby optimizing the electronic structure of the material, improving the redox activity, and enhancing the conductivity of CeO2. The TM-CeO 2‑x / 3D Gr composite material has significantly improved electrochemical performance. When the composite material is assembled into a flexible supercapacitor and subjected to performance testing, the supercapacitor exhibits excellent electrochemical performance and mechanical properties.

Description

Technical Field

[0001] This invention belongs to the field of inorganic composite materials technology, and relates to a transition metal-doped cerium oxide-three-dimensional graphene composite material rich in oxygen vacancies and its preparation method. Background Technology

[0002] Rare earth oxides, as electrode materials, possess numerous advantages such as high stability, long cycle life, and abundant oxygen vacancies. Cerium oxide (CeO2), a common rare earth oxide, exhibits unique redox properties, abundant resources, and environmental friendliness. However, as an electrode material for supercapacitors, cerium oxide has a low intrinsic conductivity, leading to a significant increase in charge transport impedance. According to Joule's law, under high current density operating conditions, resistive polarization within the electrode generates substantial Joule heat, which in turn affects the cycle life, rate performance, and coulombic efficiency of the cerium oxide electrode. These factors collectively limit the practical application of cerium oxide-based supercapacitors in high-power scenarios.

[0003] For example, Chinese invention patent CN111320197 A discloses a cerium dioxide / graphene supercapacitor composite material and its preparation method. The composite material is prepared by a hydrothermal reaction of cerium nitrate hexahydrate and graphene oxide under the action of a silane coupling agent. The resulting electrode material has a specific capacitance of only 114 F / g at a current density of 0.5 A / g, and retains 87.4% of its capacitance after 1000 cycles. While this invention method is simple to operate and produces little pollution, it also suffers from a relatively low capacitance retention rate. This is because the pseudocapacitance of pure cerium oxide is limited, and its redox reaction mainly depends on Ce. 3+ and Ce 4+ The valence state transitions between these components and the limited number of reaction sites ultimately make it difficult to improve the overall electrochemical performance of the composite material.

[0004] Chinese invention patent CN106847545 A discloses a method for preparing a cerium oxide-doped electrode. The method involves preparing an electrodeposition mixture containing soluble trivalent cerium salts, transition metal (such as Fe, Co, Ni) salts, and organic acid salts. Constant current deposition is then performed at 20 °C to obtain a cerium oxide deposition layer doped with metals. Finally, the deposition layer is heat-treated with a current collector to obtain the cerium oxide-doped electrode. In this invention, divalent metal ions introduced during electrodeposition are oxidized to trivalent ions. Subsequent heat treatment introduces defects into the cerium oxide, improving the material's conductivity and electrochemical performance. However, the specific capacitance of the resulting Co-doped cerium oxide electrode is only 249.1 F / g. This is because it lacks a three-dimensional network carrier with high specific surface area and high conductivity, such as graphene, resulting in a limited specific surface area. Furthermore, the reliance on the bonding between the electrodeposited layer and the current collector leads to limited electron transport channels, high internal resistance, and significant ion transport resistance, thus limiting the improvement in specific capacitance.

[0005] Therefore, it is necessary to develop a novel preparation strategy that balances high performance, low cost, and environmental friendliness to achieve synergistic improvement in electrochemical and mechanical properties. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention aims to provide a transition metal-doped cerium oxide-three-dimensional graphene composite material rich in oxygen vacancies and its preparation method. This composite material is synthesized using a one-step hydrothermal method and has the chemical formula TM-CeO. 2-x / 3DGr, where x ranges from 0.09 to 0.56, and TM is one of Fe, Co, Ni, Mn, or Cr; transition metal doping can introduce a large number of oxygen vacancies into CeO2 by utilizing valence state differences, which not only optimizes the electronic structure of the material and improves redox activity, but also enhances the conductivity of CeO2, making TM-CeO 2-x The electrochemical performance of the 3D Gr composite material was significantly improved; when the composite material was assembled into a flexible supercapacitor and its performance was tested, it showed excellent electrochemical and mechanical properties.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A transition metal-doped cerium oxide-three-dimensional graphene composite material rich in oxygen vacancies, wherein the transition metal-doped cerium oxide-three-dimensional graphene composite material is TM-CeO 2-x / 3D Gr composite material, where: x ranges from 0.09 to 0.56, and TM is one of Fe, Co, Ni, Mn or Cr.

[0008] In this invention, transition metal doping promotes the formation of oxygen vacancies in CeO2 and inserts additional donor levels between the valence bands. Simultaneously, the hybridization of the d-orbital electrons of the transition metal with the 4f / 5d orbitals of CeO2 further reduces the band gap of the CeO2 crystal structure. This significantly improves the intrinsic conductivity and charge transfer kinetics of the material. In TM-CeO 2-x In the preparation of 3D Gr composite materials, the number of oxygen vacancies directly affects the band structure and conductivity of the composite material, which in turn affects the capacitance and cycle stability.

[0009] The TM-CeO prepared by this invention 2-x There are two sources of oxygen vacancies in 3D Gr composite materials: one is the doping of transition metal ions in the formed cerium oxide lattice, where the transition metal ions replace part of the Ce in the CeO2 lattice. 4+ Because the valence state of transition metal ions is often lower than +4, some Ce... 4+ Need to be converted to Ce 3+To compensate for the lattice charge imbalance caused by transition metal substitution, oxygen atoms in the lattice will carry electrons out to maintain charge balance, forming oxygen vacancies; secondly, the addition of a reducing agent will partially remove Ce. 4+ Restored to Ce 3+ This process generates oxygen vacancies. Higher oxygen vacancy concentrations result in more reactive sites and a greater capacity for charge storage. More importantly, the lattice distortion induced by transition metal ion doping lowers the diffusion barrier of ions, synergistically promoting ion embedding and accelerating ion diffusion. This highly active structure on the distorted lattice surface undergoes strong interfacial electronic coupling and chemical anchoring with graphene, forming a high-speed, low-resistance microscopic charge transfer channel. This allows the lattice-distorted material to exhibit excellent electrochemical storage performance, facilitating electrolyte penetration, improving the accessibility and utilization of interlayer electroactive sites, accelerating charge transfer kinetics, thereby increasing conductivity and providing greater electrochemical storage space. Therefore, lattice distortion induced by transition metal doping provides a structural driving force for the efficient construction of oxygen vacancies, optimizing charge storage and transport kinetics.

[0010] This invention also provides a method for preparing a transition metal-doped cerium oxide-three-dimensional graphene composite material rich in oxygen vacancies, which is carried out in the following order: S1. Cerium salt is dispersed in deionized water to obtain an aqueous solution of cerium salt, and then a transition metal salt is added to the solution to obtain a mixed solution; S2. Slowly add the mixed solution dropwise to the graphene oxide solution and stir for 3-8 hours. Then add KOH solution and reducing agent separately, stir evenly, and place in a reaction vessel for hydrothermal reaction. After the reaction is complete, wash and remove impurities from the product, and freeze-dry to obtain TM-CeO. 2-x / 3D Gr composite material.

[0011] As a limitation of the preparation method of the present invention, in step S1, the cerium salt is one of Ce(NO3)3·6H2O, CeCl3·7H2O or Ce2(SO4)3·7H2O; and the transition metal salt is one of Fe(NO3)3·9H2O, Co(NO3)2·6H2O, CoSO4·7H2O, Ni(NO3)2·6H2O, Mn(NO3)2·4H2O or Cr(NO3)3·9H2O.

[0012] As another limitation of the preparation method of the present invention, in step S1, the mass ratio of the cerium salt to the transition metal salt is 1:(0.02~0.08).

[0013] In this invention, the mass ratio of cerium salt to transition metal salt affects the formation of oxygen vacancy defects. When this mass ratio is achieved, it will lead to the formation of Co-CeO. 2-x / 3D Gr composite material has a stable structure and high conductivity. If the mass ratio is greater than this, the excessive doping of transition metals will destroy the cubic fluorite structure of CeO2, and the parent (i.e., CeO2) lattice structure will easily collapse during long-term electrochemical charge and discharge. If the mass ratio is less than this, the doping amount is insufficient, fewer oxygen vacancies are formed, and the improvement in conductivity is limited.

[0014] As a third limitation of the preparation method of the present invention, in step S2, the dropping rate of the mixed solution is 1~4 mL / min.

[0015] As a fourth limitation of the preparation method of the present invention, in step S2, the concentration of the graphene oxide solution is 5.3~7.26 mg / mL; the mass-to-volume ratio of the cerium salt to the graphene oxide solution is (0.7~1.75):(15.3~28.3) mg / mL.

[0016] As a fifth limitation of the preparation method of the present invention, in step S2, the concentration of the KOH solution is 1~3 M; the mass-volume ratio of the cerium salt to the KOH solution is (0.7~1.75):(2~7) mg / mL.

[0017] As a sixth limitation of the preparation method of the present invention, in step S2, the reducing agent is one of hydrazine hydrate, sodium borohydride, ascorbic acid or sodium ascorbate; the mass ratio of the cerium salt to the reducing agent is (0.7~1.75):(0.5~1.2).

[0018] As a seventh limitation of the preparation method of the present invention, in step S2, the temperature of the hydrothermal reaction is 150~200℃ and the time is 10~20 h.

[0019] As an eighth limitation of the preparation method of the present invention, in step S2, the freeze-drying process is carried out according to the following procedure: (a) First stage: Cooling from room temperature to -80 to -60 ℃ at a cooling rate of 0.8 ℃ / s, and holding frozen for 8 to 16 h; (b) Second stage: First, the temperature is increased from -80~-60 ℃ to 0 ℃ at a heating rate of 0.4 ℃ / s, and then increased from 0 ℃ to 10~20 ℃ at a heating rate of 0.2 ℃ / s, and held for 12~36 h.

[0020] In this invention, the freeze-drying process ensures the removal of water while maintaining the integrity of the material's morphology. In the first stage, the temperature is lowered from room temperature to -80 to -60 °C at a rate of 0.8 °C / s, causing the liquid water in the sample to transform into solid ice. Holding this temperature for 8 to 16 hours ensures uniform freezing temperature and complete crystallization. In the second stage, the temperature is first raised from -80 to -60 °C to 0 °C at a rate of 0.4 °C / s to allow the solid ice to sublimate under vacuum, directly transforming into water vapor while preserving the original 3D Gr structure. Then, the temperature is raised from 0 °C to 10 to 20 °C at a rate of 0.2 °C / s to remove any remaining bound water. Holding this temperature for 12 to 36 hours ensures the sample is thoroughly dried at this temperature, facilitating subsequent storage and use.

[0021] The above-described technical solution of this invention, as a whole, involves interconnected and mutually influential steps, which collectively determine the morphological characteristics and properties of the product. This invention employs a hydrothermal method to prepare TM-CeO. 2-x The preparation of 3D Gr composite materials involves the evolution of microstructure morphology and interfacial interactions. First, a mixed solution containing transition metal ions and cerium ions is thoroughly mixed with a graphene oxide solution. The oxygen-containing functional groups (hydroxyl, carboxyl, and epoxy groups) on the graphene oxide surface can form weak coordination with cerium ions, promoting the nucleation of cerium oxide on the graphene surface under subsequent hydrothermal conditions. Potassium hydroxide is added to the reaction system to provide an alkaline environment. - With Ce 3+ The reaction occurs, forming Ce-O bonds, laying the foundation for the formation of the more thermodynamically stable CeO2; simultaneously, a small amount of transition metal ions dope into the cerium dioxide lattice, replacing cerium ion sites to form a substitutional solid solution, thereby inducing lattice distortion. The reducing agent added to the system can reduce graphene oxide to reduced graphene oxide, while also removing some of the Ce... 4+ Restored to Ce 3+ Under hydrothermal conditions, graphene sheets self-assemble through π-π stacking and van der Waals forces to form a three-dimensional porous network structure, providing a large number of highly active sites for the anchoring of cerium ions.

[0022] Three-dimensional graphene is the core foundation for achieving large capacitance in composite materials: its large specific surface area provides a nucleation substrate and efficient conductive channels for cerium oxide, while its porous surface structure accelerates ion transport during electrochemical processes. Furthermore, transition metal doping combined with a chemical activation strategy effectively inhibits the recombination of graphene nanosheets and guides the formation of a hierarchical three-dimensional network structure through a template effect. The hydrothermal reaction environment significantly enhances reaction kinetics, and the resulting unique three-dimensional porous architecture drastically shortens ion transport paths, providing efficient mass transport channels for electrochemical processes. In addition, this invention can be applied to TM-CeO... 2-xThe oxygen vacancy content in the crystal lattice can be controlled. An appropriate amount of oxygen vacancies can significantly improve the conductivity of cerium oxide, while excessive oxygen vacancies will exacerbate lattice distortion, shorten charge lifetime, and worsen interface dynamics. The formation process of oxygen vacancies is shown in the formula: .

[0023] The above technical solution has the following advantages or beneficial effects: 1. This invention uses graphene oxide, cerium salts, and transition metal salts as precursors to prepare oxygen-vacancy-rich TM-CeO via a hydrothermal method. 2-x / 3D Gr composite materials have simple processing steps, high efficiency, and low cost; 2. The TM-CeO prepared by this invention 2-x / 3D Gr composite materials promote the formation of oxygen vacancies through doping, and transition metal ions react with Ce. 4+ The substitution and conversion between them maintain charge balance, enhance redox kinetics, increase reactive sites, and finally obtain a composite material with stable structure, adjustable loading rate, and good conductivity. 3. The TM-CeO prepared by this invention 2-x / 3D Gr composite material, with a mass specific capacitance of up to 706.5 F / g at a current density of 0.5 A / g; 4. TM-CeO prepared using this invention 2-x The flexible supercapacitor assembled from 3D Gr composite materials can withstand various mechanical tests such as bending and nailing, and its electrochemical performance does not show significant attenuation during deformation, indicating that it has excellent mechanical flexibility and deformation resistance, and can be adapted to diverse application scenarios.

[0024] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0025] Figure 1 The Co-CeO prepared in Example 1 of this invention 2-x Scanning electron microscope (SEM) images of the / 3D Gr (x=0.32) composite material, where: (a) and (b) are Co-CeO3 and 3D Gr (x=0.32) composite materials, respectively. 2-x Morphology images of the 3D Gr (x=0.32) composite material at different resolutions; Figure 2 The Co-CeO prepared in Example 1 of this invention 2-x Cyclic voltammetry curves and constant current charge-discharge curves of the 3D Gr (x=0.32) composite material, where: (a) is the cyclic voltammetry curve and (b) is the constant current charge-discharge curve; Figure 3 The Co-CeO prepared in Example 1 of this invention 2-xEPR test diagram of / 3D Gr (x=0.32) composite material; Figure 4 The Co-CeO prepared in Example 1 of this invention 2-x A schematic diagram of bending and pinning of a flexible supercapacitor assembled from 3D Gr (x=0.32) composite materials, where: (a) is the original state of the flexible supercapacitor, and (b) and (c) are the bending and pinning of the flexible supercapacitor by 90 degrees respectively. ° and 180 ° The state diagrams are shown in (d) and (e), which are state diagrams of a flexible supercapacitor with one and two nails respectively. Figure 5 The Co-CeO prepared in Example 1 of this invention 2-x Comparison of CV curves of flexible supercapacitors assembled from 3D Gr (x=0.32) composite materials under bending and pinning conditions at a scanning rate of 100 mV / s, where: (a) under bending conditions and (b) under pinning conditions; Figure 6 The graph shows a comparison of the constant current charge-discharge curves of the composite materials prepared in Example 1 and Comparative Examples 1-2 of this invention at a current density of 0.5 A / g. Detailed Implementation

[0026] The following embodiments are merely some, not all, of the embodiments of the present invention. Therefore, the detailed descriptions of the embodiments provided below are not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0027] In this invention, unless otherwise specified, all equipment and raw materials are commercially available or commonly used in the industry. The methods described in the following embodiments are conventional methods in the art, unless otherwise specified.

[0028] This embodiment prepares a Co-CeO 2-x / 3D Gr (x=0.32), its preparation process and steps are as follows: S1. Disperse 1.75 g Ce(NO3)3·6H2O in 20 mL of deionized water to obtain a cerium nitrate solution, and then add 0.058 g Co(NO3)2·6H2O to the solution to obtain a mixed solution; S2. The mixed solution was added dropwise to 28.3 mL of a 5.3 mg / mL graphene oxide solution at a dropping rate of 1.3 mL / min. The mixture was stirred for 6 h. Then, 5 mL of 2 M KOH solution and 1 mL of hydrazine hydrate were added, and the mixture was stirred thoroughly. The mixture was then placed in a reaction vessel and reacted at 180 °C for 20 h. After the reaction, the product was washed with deionized water and freeze-dried. The freeze-drying process was as follows: First, the temperature was lowered from room temperature to -80 °C at a cooling rate of 0.8 °C / s and held for 10 h. Then, the temperature was increased from -80 °C to 0 °C at a heating rate of 0.4 °C / s. Finally, the temperature was increased from 0 °C to 10 °C at a heating rate of 0.2 °C / s and held for 18 h to obtain Co-CeO. 2-x / 3D Gr (x=0.32) composite material. Co-CeO at a current density of 0.5 A / g. 2-x The 3D Gr (x=0.32) composite material exhibits a specific capacitance of up to 706.5 F / g.

[0029] Co-CeO 2-x The 3D Gr (x=0.32) composite material was cut into sheets and pressed onto nickel sheets using a tablet press. A flexible supercapacitor was assembled using PVA / KOH as the solid electrolyte (the preparation method of PVA / KOH solid electrolyte is: dissolve 10 g of polyvinyl alcohol PVA powder in 90 mL of deionized water, then add 45 mL of 6 M KOH solution, and stir at room temperature). The supercapacitor was then tested.

[0030] Figure 1 and Figure 2 In this embodiment, Co-CeO are respectively 2-x Scanning electron microscope image, cyclic voltammetry curve, and constant current charge-discharge curve of / 3D Gr (x=0.32). From Figure 1 In (a) and (b), it can be clearly observed that a large number of nanoscale particles are uniformly loaded on the surface of the graphene sheets, and the particles are well dispersed. CeO 2-x The spheres are approximately 15–20 nm in size, indicating successful construction of Co-CeO₂. 2-x / 3D Gr composite structure, in which nanoscale CeO 2-x It can provide a rich number of active sites. For example... Figure 2 As shown in (a), with the increase of scan rate, the CV curve becomes wider, the anodic peak potential shifts positively, and the cathode peak potential shifts negatively. The CV curve exhibits obvious redox peaks, which clearly indicates that the nanocomposite material has excellent pseudocapacitive properties. Figure 2In (b), the constant current charge-discharge curves all have obvious plateaus, which means that the capacitance of the composite material is mainly controlled by the redox reaction. Moreover, the constant current charge-discharge curves also show symmetrical characteristics, which indicates that the composite material has good electrochemical capacitance behavior and good reversibility. Figure 3 This is an EPR test graph, from which Co-CeO can be clearly seen. 2-x The / 3D Gr (x=0.32) composite material exhibits significant oxygen vacancy generation.

[0031] Figure 4 and Figure 5 Co-CeO prepared in this embodiment 2-x A schematic diagram of the pinning of a flexible supercapacitor assembled from 3D Gr (x=0.32) composite materials and a comparison of CV curve changes at a scan rate of 100 mV / s. Figure 4 (a) in the diagram represents the initial state of the assembled flexible capacitor. Figure 4 (b) and Figure 4 (c) Bending 90 degrees to the assembled flexible capacitor respectively ° 180 ° The images, Figures (d) and (e), show flexible capacitors with one and two nails respectively. Figure 5 (a) and Figure 5 As can be seen in (b), the CV curve did not change significantly. Different bending angles and pin numbers showed similar capacitive behavior, indicating a good combination of flexibility and capacitive behavior.

[0032] Example 2 This embodiment prepares a Co-CeO 2-x / 3D Gr (x=0.09), its preparation process and steps are as follows: S1. Disperse 0.87 g Ce(NO3)3·6H2O in 20 mL of deionized water to obtain a cerium nitrate solution, and then add 0.041 g Co(NO3)2 6H2O to the solution to obtain a mixed solution; S2. The mixed solution was added dropwise to 18.9 mL of a 5.3 mg / mL graphene oxide solution at a dropping rate of 1 mL / min. The mixture was stirred for 4 h. Then, 2 mL of 2 M KOH solution and 1 mL of hydrazine hydrate were added, and the mixture was stirred thoroughly. The mixture was then placed in a reaction vessel and reacted at 180 °C for 18 h. After the reaction was completed, the product was washed with deionized water and freeze-dried. The freeze-drying process was as follows: First, the temperature was lowered from room temperature to -80 °C at a cooling rate of 0.8 °C / s and held for 10 h. Then, the temperature was raised from -80 °C to 0 °C at a heating rate of 0.4 °C / s. Finally, the temperature was raised from 0 °C to 10 °C at a heating rate of 0.2 °C / s and held for 18 h to obtain Co-CeO. 2-x / 3D Gr (x=0.09) composite material. Co-CeO at a current density of 0.5 A / g. 2-x The 3D Gr (x=0.09) composite material exhibits a specific capacitance of up to 482.7 F / g.

[0033] Example 3 This embodiment prepares a Co-CeO 2-x / 3D Gr (x=0.25), its preparation process and steps are as follows: S1. Disperse 1.75 g Ce(NO3)3·6H2O in 20 mL of deionized water to obtain a cerium nitrate solution, and then add 0.034 g CoSO4·7H2O to the solution to obtain a mixed solution; S2. The mixed solution was added dropwise to 18.9 mL of a 5.3 mg / mL graphene oxide solution at a dropping rate of 4 mL / min. The mixture was stirred for 5 h. Then, 7 mL of 3 M KOH solution and 1.2 g of ascorbic acid were added to the mixture, and after thorough stirring, it was placed in a reaction vessel and reacted at 160 °C for 16 h. After the reaction, the product was washed with deionized water and freeze-dried. The freeze-drying process was as follows: First, the temperature was lowered from room temperature to -80 °C at a cooling rate of 0.8 °C / s and held for 12 h. Then, the temperature was raised from -80 °C to 0 °C at a heating rate of 0.4 °C / s. Finally, the temperature was raised from 0 °C to 10 °C at a heating rate of 0.2 °C / s and held for 24 h to obtain Co-CeO. 2-x / 3D Gr (x=0.25) composite material. Co-CeO at a current density of 0.5 A / g. 2-x The 3D Gr (x=0.25) composite material exhibits a specific capacitance of up to 639.4 F / g.

[0034] Example 4 This embodiment prepares a Fe-CeO2-x / 3D Gr (x=0.23), its preparation process and steps are as follows: S1. Disperse 1.75 g CeCl3·7H2O in 20 mL of deionized water to obtain a cerium nitrate solution, and then add 0.133 g Fe(NO3)3·9H2O to the solution to obtain a mixed solution; S2. The mixed solution was added dropwise to 27.5 mL of a 7.26 mg / mL graphene oxide solution at a dropping rate of 2 mL / min. The mixture was stirred for 8 h. Then, 3 mL of 3 M KOH solution and 1 g of sodium ascorbate were added to the mixture. After stirring thoroughly, the mixture was placed in a reaction vessel and reacted at 160 °C for 20 h. After the reaction was completed, the product was washed with deionized water and freeze-dried. The freeze-drying process was as follows: First, the temperature was lowered from room temperature to -70 °C at a cooling rate of 0.8 °C / s and held for 14 h. Then, the temperature was raised from -70 °C to 0 °C at a heating rate of 0.4 °C / s. Finally, the temperature was raised from 0 °C to 10 °C at a heating rate of 0.2 °C / s and held for 18 h to obtain Fe-CeO. 2-x / 3D Gr (x=0.23) composite material. Fe-CeO at a current density of 0.5 A / g. 2-x The 3D Gr (x=0.23) composite material exhibits a specific capacitance of up to 625.1 F / g.

[0035] Example 5 This embodiment prepares a Ni-CeO 2-x / 3D Gr (x=0.28), its preparation process and steps are as follows: S1. Disperse 0.87 g CeCl3·7H2O in 20 mL of deionized water to obtain a cerium nitrate solution, and then add 0.029 g Ni(NO3)2·6H2O to the solution to obtain a mixed solution; S2. The mixed solution was added dropwise to 15.3 mL of a 6.54 mg / mL graphene oxide solution at a dropping rate of 1 mL / min. The mixture was stirred for 3 h. Then, 5 mL of 1 M KOH solution and 0.5 g of sodium borohydride were added, and the mixture was stirred thoroughly. The mixture was then placed in a reaction vessel and reacted at 180 °C for 16 h. After the reaction, the product was washed with deionized water and freeze-dried. The freeze-drying process was as follows: First, the temperature was lowered from room temperature to -60 °C at a cooling rate of 0.8 °C / s and held for 16 h. Then, the temperature was increased from -60 °C to 0 °C at a heating rate of 0.4 °C / s. Finally, the temperature was increased from 0 °C to 20 °C at a heating rate of 0.2 °C / s and held for 12 h to obtain Ni-CeO. 2-x / 3D Gr (x=0.28) composite material. Ni-CeO at a current density of 0.5 A / g. 2-x The 3D Gr (x=0.28) composite material exhibits a specific capacitance of up to 679.1 F / g.

[0036] Example 6 This embodiment prepares a Mn-CeO 2-x / 3D Gr (x=0.21), its preparation process and steps are as follows: S1. Disperse 0.7 g Ce2(SO4)3·7H2O in 20 mL of deionized water to obtain a cerium nitrate solution, and then add 0.021 g Mn(NO3)2·4H2O to the solution to obtain a mixed solution; S2. The mixed solution was added dropwise to 22.9 mL of a 6.54 mg / mL graphene oxide solution at a dropping rate of 1.5 mL / min. The mixture was stirred for 4 h. Then, 3 mL of 1 M KOH solution and 0.9 g of ascorbic acid were added, and the mixture was stirred thoroughly. The mixture was then placed in a reaction vessel and reacted at 200 °C for 12 h. After the reaction was completed, the product was washed with deionized water and freeze-dried. The freeze-drying process was as follows: First, the temperature was lowered from room temperature to -80 °C at a cooling rate of 0.8 °C / s and held for 8 h. Then, the temperature was raised from -80 °C to 0 °C at a heating rate of 0.4 °C / s. Finally, the temperature was raised from 0 °C to 10 °C at a heating rate of 0.2 °C / s and held for 36 h to obtain Mn-CeO. 2-x / 3D Gr (x=0.21) composite material. Mn-CeO at a current density of 0.5 A / g. 2-x The 3D Gr (x=0.21) composite material exhibits a specific capacitance of up to 608.9 F / g.

[0037] Example 7 This embodiment prepares a Cr-CeO 2-x The preparation process and steps of / 3D Gr (x=0.56) are as follows: S1. Disperse 1.25 g Ce2(SO4)3·7H2O in 20 mL of deionized water to obtain a cerium nitrate solution, and then add 0.026 g Cr(NO3)3·9H2O to the solution to obtain a mixed solution; S2. The mixed solution was added dropwise to 22.9 mL of a 6.54 mg / mL graphene oxide solution at a dropping rate of 2 mL / min. The mixture was stirred for 6 h. Then, 5 mL of 1 M KOH solution and 1 g of ascorbic acid were added, and the mixture was stirred thoroughly. The mixture was then placed in a reaction vessel and reacted at 150 °C for 10 h. After the reaction, the product was washed with deionized water and freeze-dried. The freeze-drying process was as follows: First, the temperature was lowered from room temperature to -80 °C at a cooling rate of 0.8 °C / s and held for 16 h. Then, the temperature was increased from -80 °C to 0 °C at a heating rate of 0.4 °C / s. Finally, the temperature was increased from 0 °C to 15 °C at a heating rate of 0.2 °C / s and held for 36 h to obtain Cr-CeO. 2-x / 3D Gr (x=0.56) composite material. Cr-CeO at a current density of 0.5 A / g. 2-x The 3D Gr (x=0.56) composite material exhibits a specific capacitance of up to 522.3 F / g.

[0038] Comparative Example To investigate the influence of different raw materials on the performance of the product during the preparation process of this invention, the following comparative experiments were conducted. Different composite electrode materials were prepared in the following comparative examples, as detailed below: Comparative Example 1 This comparative example prepares a composite electrode material. The preparation process is similar to that of Example 1, except that in step S2, the temperature of the hydrothermal reaction is replaced with 140 °C and the reaction time is replaced with 8 h. The remaining steps and parameters are the same as in Example 1. Finally, a Co-CeO2 / 3D Gr composite material is obtained. The composite material has a specific capacitance of 423.1 F / g at a current density of 0.5 A / g.

[0039] Compared with Example 1, the temperature and reaction time in the hydrothermal process of this comparative example were insufficient, which did not ensure the complete occurrence of the reduction process. Therefore, the Co-CeO2 / 3D Gr composite material obtained did not have obvious oxygen vacancies, resulting in a lower specific capacitance than that of Example 1.

[0040] Comparative Example 2 This comparative example prepares a composite electrode material. The preparation process is similar to that of Example 1, except that in step S2, 1 mL of hydrazine hydrate is replaced with 4 mL. The remaining steps and parameters are the same as in Example 1, and Co-CeO is finally obtained. 2-x / 3DGr (x=1) composite material, which has a specific capacitance of 492.5 F / g at a current density of 0.5 A / g.

[0041] Compared with Example 1, this comparative example used an excessive amount of hydrazine hydrate. The addition of excessive hydrazine hydrate will destroy the carbon skeleton structure of graphene. Although the number of oxygen vacancies increases, when the oxygen vacancy content is too high, the lattice structure is prone to collapse during long-term electrochemical charge and discharge, which ultimately leads to a decline in material performance.

[0042] Figure 6 The Co-CeO prepared in Example 1 of this invention 2-x / 3D Gr (x=0.32), Co-CeO2 / 3D Gr prepared in Comparative Example 1 and Co-CeO2 prepared in Comparative Example 2 2-x A comparison of the galvanostatic charge-discharge curves of the 3D Gr (x=1) composite material at a current density of 0.5 A / g. (This is achieved through...) Figure 6 It can be seen that, at the same current density, the constant current charge-discharge curve of Co-CeO2 / 3D Gr without oxygen vacancies is significantly smaller than that of Co-CeO containing oxygen vacancies. 2-x Constant current charge-discharge curves of / 3D Gr (x=0.32 and 1); Co-CeO when oxygen vacancies are present. 2-x The specific capacitance of the 3D Gr (x=1) composite material in its constant current charge-discharge curve is smaller than that of Co-CeO. 2-x The specific capacitance of the / 3D Gr (x=0.32) composite material indicates that Co-CeO 2-x The / 3D Gr (x=0.32) composite material exhibits optimal capacitance.

[0043] Comparative Example 3 This comparative example prepares a composite electrode material. The preparation process is similar to that of Example 1, except that in step S2, 0.058 g Co(NO3)2·6H2O is replaced with 0.034 g AgNO3. The remaining steps and parameters are the same as in Example 1, and Ag-CeO is finally obtained. 2-x / 3D Gr (x=0.11) composite material, which has a specific capacitance of 491.9 F / g at a current density of 0.5 A / g.

[0044] Compared with Example 1, this comparative example uses the noble metal silver for doping. However, the ionic radius of silver is much larger than that of other transition metals, which leads to excessive lattice distortion, making it difficult to form a stable doped structure. This is not conducive to the uniform distribution of oxygen vacancies and ultimately leads to a decline in the performance of the material.

[0045] Comparative Example 4 This comparative example prepares a composite electrode material. The preparation process is similar to that of Example 1, except that in step S1, 28.3 mL of graphene oxide solution is replaced with 0.15 g of activated carbon. The remaining steps and parameters are the same as in Example 1, and Co-CeO is finally obtained.2-x / AC (x=0.05) composite material, which has a specific capacitance of 362.5 F / g at a current density of 0.5 A / g.

[0046] Compared to Example 1, this comparative example uses activated carbon as the substrate material, with cobalt-doped cerium oxide attached to it. However, its specific capacitance is lower than that of reduced graphene oxide as the substrate material. This is mainly because although activated carbon has a high specific surface area, its conductivity is lower than that of graphene. Excessive interfacial contact increases the electron transport resistance. In contrast, reduced graphene oxide has excellent intrinsic conductivity, enabling the construction of a highly efficient conductive network. It is also easily combined with active materials, coated, or used as a supporting framework. Therefore, the material obtained in Example 1 performs better than that in this comparative example.

[0047] Comparative Example 5 This comparative example prepares a composite electrode material. The preparation process is similar to that of Example 1, except that KOH solution is not added in step S2. The remaining steps and parameters are the same as in Example 1, and Co-CeO is finally obtained. 2-x / 3D Gr (x=0.07) composite material, which has a specific capacitance of 408.9 F / g at a current density of 0.5 A / g.

[0048] Compared with Example 1, this comparative example does not add KOH solution during the preparation process. Without KOH solution, the reaction system lacks an alkaline environment, which prevents the cerium precursor from being effectively hydrolyzed. This reduces the number of oxygen vacancies, causing a sharp drop in active sites and ultimately degrading its performance.

[0049] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A transition metal-doped cerium oxide-three-dimensional graphene composite material rich in oxygen vacancies, characterized in that, The transition metal-doped cerium oxide-three-dimensional graphene composite material rich in oxygen vacancies is TM-CeO. 2-x / 3D Gr composite material, where: x ranges from 0.09 to 0.56, and TM is one of Fe, Co, Ni, Mn or Cr.

2. The method for preparing a transition metal-doped cerium oxide-three-dimensional graphene composite material rich in oxygen vacancies according to claim 1, characterized in that, Follow these steps in sequence: S1. Cerium salt is dispersed in deionized water to obtain an aqueous solution of cerium salt, and then a transition metal salt is added to the solution to obtain a mixed solution; S2. Slowly add the mixed solution dropwise to the graphene oxide solution and stir for 3-8 hours. Then add KOH solution and reducing agent separately, stir evenly, and place in a reaction vessel for hydrothermal reaction. After the reaction is complete, wash and remove impurities from the product, and freeze-dry to obtain TM-CeO. 2-x / 3D Gr composite material.

3. The method for preparing a transition metal-doped cerium oxide-three-dimensional graphene composite material rich in oxygen vacancies according to claim 2, characterized in that, In step S1, the cerium salt is one of Ce(NO3)3·6H2O, CeCl3·7H2O, or Ce2(SO4)3·7H2O; and the transition metal salt is one of Fe(NO3)3·9H2O, Co(NO3)2·6H2O, CoSO4·7H2O, Ni(NO3)2·6H2O, Mn(NO3)2·4H2O, or Cr(NO3)3·9H2O.

4. The method for preparing a transition metal-doped cerium oxide-three-dimensional graphene composite material rich in oxygen vacancies according to claim 2, characterized in that, In step S1, the mass ratio of the cerium salt to the transition metal salt is 1:(0.02~0.08).

5. The method for preparing a transition metal-doped cerium oxide-three-dimensional graphene composite material rich in oxygen vacancies according to claim 2, characterized in that, In step S2, the dropping rate of the mixed solution is 1~4 mL / min.

6. The method for preparing a transition metal-doped cerium oxide-three-dimensional graphene composite material rich in oxygen vacancies according to claim 2, characterized in that, In step S2, the concentration of the graphene oxide solution is 5.3~7.26 mg / mL; the mass-to-volume ratio of the cerium salt to the graphene oxide solution is (0.7~1.75):(15.3~28.3) mg / mL.

7. The method for preparing a transition metal-doped cerium oxide-three-dimensional graphene composite material rich in oxygen vacancies according to claim 2, characterized in that, In step S2, the concentration of the KOH solution is 1~3 M; the mass-to-volume ratio of the cerium salt to the KOH solution is (0.7~1.75):(2~7) mg / mL.

8. The method for preparing a transition metal-doped cerium oxide-three-dimensional graphene composite material rich in oxygen vacancies according to claim 2, characterized in that, In step S2, the reducing agent is one of hydrazine hydrate, sodium borohydride, ascorbic acid, or sodium ascorbate; the mass ratio of the cerium salt to the reducing agent is (0.7~1.75):(0.5~1.2).

9. The method for preparing a transition metal-doped cerium oxide-three-dimensional graphene composite material rich in oxygen vacancies according to claim 2, characterized in that, In step S2, the temperature of the hydrothermal reaction is 150~200 ℃ and the time is 10~20h.

10. The method for preparing a transition metal-doped cerium oxide-three-dimensional graphene composite material rich in oxygen vacancies according to claim 2, characterized in that, In step S2, the freeze-drying process is carried out according to the following procedure: (a) First stage: Cooling from room temperature to -80 to -60 ℃ at a cooling rate of 0.8 ℃ / s, and holding frozen for 8 to 16 h; (b) Second stage: First, the temperature is increased from -80~-60 ℃ to 0 ℃ at a heating rate of 0.4 ℃ / s, and then increased from 0 ℃ to 10~20 ℃ at a heating rate of 0.2 ℃ / s, and held for 12~36 h.

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