Preparation method of hollow multi-shell CeO2 / Co3O4 composite nanospheres based on ionic liquid

Abstract

According to the preparation method, ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate) is taken as a doping agent and a morphology guiding agent, trimesic acid is taken as an organic ligand, cobalt nitrate and cerium nitrate are taken as metal sources, and an ionic liquid doped cobalt-cerium bimetallic organic framework precursor is constructed through solvothermal reaction; and the hollow multi-shell CeO2 / Co3O4 composite nanosphere is prepared based on a gradient temperature control pyrolysis technology. The invention provides a method which is simple and universal and does not depend on the use of a traditional soft / hard template, the controllable design of the composite material with a hollow multi-shell structure is realized, and the composite material shows remarkably enhanced catalytic activity in oxygen evolution reaction (OER). A new thought is provided for morphology regulation and performance optimization of the rare earth-based composite catalyst, and the preparation method has important application value in the field of clean energy such as hydrogen production by electrolysis of water and fuel cells.

Description

Technical Field

[0001] The present invention belongs to the technical field of functional materials, and in particular relates to a method for preparing hollow multi-shell CeO2 / Co3O4 composite nanospheres based on ionic liquids and an application thereof in electrocatalytic oxygen evolution reaction (OER). Background Art

[0002] As energy crisis and environmental pollution become increasingly serious, hydrogen has attracted much attention as a clean energy carrier. Electrocatalytic water splitting technology is an important way to produce hydrogen, and the oxygen evolution reaction (OER) consumes a lot of energy in the process of water electrolysis. Although traditional precious metal catalysts have excellent activity, their limited output and high cost seriously restrict their large-scale application. Therefore, it is particularly urgent to develop new low-cost, highly active non-precious metal OER catalysts.

[0003] Cerium oxide (CeO2)-based catalysts have attracted widespread attention in the field of catalysis due to their high cost-effectiveness and resistance to alkali corrosion. However, traditional cerium oxide materials have problems in the field of electrocatalysis, such as poor conductivity, single components, and difficulty in the controllable synthesis of composite materials with specific structural morphology, which greatly limits their application potential in water electrolysis. At present, the synthesis methods of cerium oxide-based materials mainly include sol-gel method, co-precipitation method, hydrothermal / solvothermal method and template-directed synthesis. Although these methods have certain versatility, they often need to rely on specific templates, and how to achieve precise composites of cerium oxide and other transition metal heterogeneous materials to improve their inherent conductivity is still a difficulty in current research. Summary of the invention

[0004] In view of the shortcomings of the existing synthesis of cerium oxide-based composite nanocatalysts, the present invention proposes a method for preparing CeO2 / Co3O4 composite nanospheres with a hollow multi-shell structure. On the one hand, the ionic liquid is used as a structural guide template to affect the morphology and size of the precursor, which is conducive to the formation of a hollow multi-layer hollow structure; on the other hand, the ionic liquid is used as a heteroatom dopant to provide more active sites and defects. The spherical morphology of the composite catalyst facilitates mutual contact between contact points, effectively preventing the sintering and aggregation of grains; its porous shell and cavity structure provide more material transport channels, significantly improving the diffusion efficiency of reactants and products between the inner and outer shells.

[0005] In order to achieve the above object, the present invention first provides a method for preparing CeO2 / Co3O4 composite nanospheres with a hollow multi-shell structure based on ionic liquid, comprising the following steps: (1) dissolving a metal cerium salt and a metal cobalt salt in an N,N-dimethylformamide (DMF) solution to obtain a transparent solution; (2) adding the organic ligand and the ionic liquid to the above transparent solution in sequence, and subjecting the mixture to ultrasonic treatment and stirring until the mixture is completely dissolved to obtain a mixed solution; (3) transferring the mixed solution to a polytetrafluoroethylene autoclave, reacting at 150° C. for 6 hours, and then naturally cooling the autoclave to room temperature. The reaction solution is subjected to solid-liquid separation, and the solid is washed with anhydrous ethanol. After centrifugal washing and vacuum drying, an ionic liquid-doped cobalt-cerium-based metal organic framework precursor is obtained; (4) The ionic liquid-doped cobalt-cerium-based metal organic framework precursor is pyrolyzed by controlling the temperature pyrolysis gradient to obtain CeO2 / Co3O4 composite nanospheres with a hollow multi-shell structure.

[0006] In some embodiments, the metal cerium salt and the metal cobalt salt are cerium nitrate and cobalt nitrate, respectively.

[0007] In some embodiments, the molar ratio of the metal cobalt salt to the metal cerium salt is: Ce:Co = (2.5-25):100, for example, 2.5:100, 5:100, 7.5:100, 10:100, 12.5:100, 15:100, 25:100, preferably, Ce:Co = 10:100.

[0008] In some embodiments, the concentration of the DMF solution of the metal cobalt salt is 0.15 mol / L, and the concentration of the DMF solution of the metal cerium salt is 7.5 mmol / L-37.5 mmol / L.

[0009] In some embodiments, the organic ligand is trimesic acid; and the molar ratio of the organic ligand to the total amount of the metal cobalt salt and the metal cerium salt is 1:3.

[0010] In some embodiments, the ionic liquid is 1-butyl-3-methylimidazolium hexafluorophosphate.

[0011] In some embodiments, the mass ratio of the total amount of the metal cobalt salt and the metal cerium salt to the ionic liquid is 1:2.

[0012] In some embodiments, in step (3), the solid washed by centrifugation is dried in a vacuum oven at a pressure of 0.5 MPa at a temperature of 60°C.

[0013] In some embodiments, in step (4), the temperature pyrolysis gradient is to increase the temperature to 300°C at a rate of 2°C / min and maintain it for 2 hours, and then naturally cool it to room temperature to obtain hollow multi-shell CeO2 / Co3O4 composite nanospheres based on ionic liquid.

[0014] In a second aspect, the present invention provides hollow multi-shell CeO2 / Co3O4 composite nanospheres obtained by the above preparation method.

[0015] In some embodiments, the hollow multi-shell CeO2 / Co3O4 composite nanospheres have a clear porous shell and a large cavity structure, and are uniform in size, with a diameter generally being about 500 nanometers.

[0016] In a third aspect, the present invention provides an application of the hollow multi-shell CeO2 / Co3O4 composite nanospheres in oxygen evolution reaction (OER) by water electrolysis.

[0017] Beneficial Effects The present invention uses ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate) as a dopant and morphology directing agent, trimesic acid as a ligand, cobalt nitrate and cerium nitrate as metal salts, and prepares an ionic liquid-doped cobalt-cerium-based metal organic framework precursor by a solvent thermal method, and then uses a controlled temperature pyrolysis gradient to prepare hollow multi-shell CeO2 / Co3O4 composite nanospheres. The present invention provides a simple, universal method that does not rely on the use of traditional soft / hard templates. The dual functionalization strategy of ionic liquids is used to prepare CeO2 / Co3O4 composite nanospheres with hollow multi-shell structures. It not only serves as a soft template to guide the formation of hollow multi-shell structures, but also serves as a doping source to introduce structural defects and active sites. The doping of ionic liquids can introduce heteroatoms into the composite material and produce abundant wrinkles during the calcination process, thereby increasing the specific surface area and active sites of the material. The prepared hollow multi-shell CeO2 / Co3O4 composite nanospheres are uniform in size, with a diameter generally around 500 nanometers, and have a clear porous shell and a large cavity structure, which enables them to fully contact with the electrolyte during the catalytic process.

[0018] The present invention successfully combines the advantages of CeO2 and Co3O4. In the catalytic experiment of oxygen evolution in electrolysis of water, the hollow multi-shell CeO2 / Co3O4 composite nanospheres prepared by the present invention have better activity, lower reaction overpotential, lower Tafel slope and excellent stability as OER catalysts compared with single-component catalysts. This invention provides a new idea for controlling the morphology and structure of cerium oxide-based composite nanocatalysts to improve electrocatalytic performance, which is of great significance for achieving efficient hydrogen production by electrolysis of water and coping with environmental crises. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a scanning electron microscope image of the cobalt-cerium-based metal organic framework precursor doped with an ionic liquid in Example 1 of the present invention; Figure 2 is an X-ray powder diffraction pattern of the cobalt-cerium-based metal organic framework precursor doped with ionic liquid in Example 1 of the present invention; Figure 3 This is a scanning electron microscope image of the hollow multi-shell CeO2 / Co3O4 composite nanospheres in Example 1 of the present invention; Figure 4 This is a transmission electron microscope image of the hollow multi-shell CeO2 / Co3O4 composite nanospheres in Example 1 of the present invention; Figure 5 is the X-ray powder diffraction pattern of the hollow multi-shell CeO2 / Co3O4 composite nanospheres in Example 1 of the present invention; Figure 6 The ordinary CeO2 / Co3O4 composite nanospheres prepared without adding ionic liquid in Comparative Example 1 of the present invention; Figure 7 The scanning electron microscope image and the transmission electron microscope image of Co3O4 in Comparative Example 2 of the present invention are shown; Figure 8 The scanning electron microscope image and the transmission electron microscope image of CeO2 in Comparative Example 3 of the present invention are shown; Fig. 9 Schematic diagram of the catalytic performance of the catalysts prepared in Example 1 and Comparative Examples 1-3 of the present invention in the electrolytic water oxygen evolution reaction: (a) LSV polarization curve; (b) overpotential of each catalyst at 10 mA / cm; (c) Tafel slope; (d) stability test; (e) function graph of different scan rates versus capacitive current; (f) electrochemical impedance spectroscopy.

[0021] Fig.10 This is a comparison of the LSV polarization curves for water electrolysis of catalysts with different Ce:Co ratios prepared in Examples 1-7 of the present invention.

[0022] Specific embodiment In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments.

[0023] Embodiment 1: (1) Co(NO3)2‧6H2O and Ce(NO3)3‧6H2O were dissolved in 30 mL of N,N-dimethylformamide (DMF) in a molar ratio (Ce:Co=10:100) with stirring and ultrasonic assistance. The total molar amount of the metal salt was 2 mmol to obtain a transparent solution. (2) Add trimesic acid (150 mg) and ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate, 400 mg) to the transparent solution in sequence, stir evenly until completely dissolved, and obtain a mixed solution; (3) The mixed solution was transferred into a polytetrafluoroethylene autoclave and kept reacting at 150°C for 6 hours. After the autoclave was naturally cooled to room temperature, the product after the hydrothermal reaction was filtered to separate the solid and liquid, and the obtained solid was washed with anhydrous ethanol for multiple times, and then centrifuged at a speed of 8000r / s for two minutes, the upper solution was discarded, and the precipitate below was retained and dried at 60°C in a vacuum oven with an air pressure of 0.5Mpa to obtain an ionic liquid-doped cobalt-cerium-based metal organic framework precursor; (4) The ionic liquid-doped cobalt-cerium-based metal organic framework precursor powder sample is placed in a muffle furnace, heated from room temperature to 300°C at a heating rate of 2°C / min, maintained at 300°C for 2 hours, and then cooled to room temperature at a cooling rate of 2°C / min. After cooling, hollow multi-shell CeO2 / Co3O4 composite nanospheres can be obtained.

[0024] Scanning electron microscopy image of ionic liquid-doped Co-Ce-based metal-organic framework precursor ( Figure 1 ) shows a uniform nanosphere morphology with a size of ~500 nm; X-ray powder diffraction pattern of ionic liquid-doped cobalt-cerium-based metal-organic framework precursor ( Figure 2 ) shows good crystallization; scanning electron microscope image of hollow multi-shell CeO2 / Co3O4 composite nanospheres ( Figure 3 ) shows that after temperature-controlled calcination, the material morphology is maintained, and due to the introduction of ionic liquid, wrinkles appear on the surface and there is a hollow structure. The transmission electron microscope image of the hollow multi-shell CeO2 / Co3O4 composite nanospheres ( Figure 4 ) shows a uniform multi-layer hollow structure, with 3 to 4 layers and uniform size; X-ray powder diffraction pattern of hollow multi-shell CeO2 / Co3O4 composite nanospheres ( Figure 5 ) shows that the precursor is converted into CeO2 / Co3O4 after oxidation calcination, and the diffraction peaks correspond well to the standard card of Co3O4 (JCPDS No. 09-0418) and the standard card of CeO2, indicating that the material is successfully composited and has a high purity.

[0025] Comparative Example 1: (1) Co(NO3)2‧6H2O and Ce(NO3)3‧6H2O were dissolved in 30 mL of N,N-dimethylformamide (DMF) in a molar ratio (Ce:Co=1:9) with stirring and ultrasonic assistance. The total molar amount of the metal salt was 2 mmol to obtain a transparent solution. (2) Add trimesic acid (150 mg) into the transparent solution and stir until completely dissolved to obtain a mixed solution; (3) The mixed solution was transferred into a polytetrafluoroethylene autoclave and kept reacting at 150°C for 6 hours. After the autoclave was naturally cooled to room temperature, the product after the hydrothermal reaction was filtered to separate the solid and liquid, and the obtained solid was washed with anhydrous ethanol for multiple times, and then centrifuged at a speed of 8000r / s for two minutes, the upper solution was discarded, and the precipitate below was retained and dried at 60°C in a vacuum oven with an air pressure of 0.5Mpa to obtain a cobalt-cerium-based metal organic framework precursor; (4) The cobalt-cerium-based metal organic framework precursor powder sample is placed in a muffle furnace, heated from room temperature to 300°C at a heating rate of 2°C / min, maintained at 300°C for 2 hours, and then cooled to room temperature at a cooling rate of 2°C / min to obtain ordinary CeO2 / Co3O4 composite nanospheres.

[0026] Comparative Example 2: (1) Co(NO3)2‧6H2O (2 mmol) was dissolved in 30 mL of N,N-dimethylformamide (DMF) under stirring and ultrasonication to obtain a transparent solution; (2) Add trimesic acid (150 mg) into the transparent solution and stir evenly until completely dissolved to obtain a mixed solution; (3) The mixed solution was transferred into a polytetrafluoroethylene autoclave and kept reacting at 150°C for 6 hours. After the autoclave was naturally cooled to room temperature, the product after the hydrothermal reaction was filtered to separate the solid and liquid, and the obtained solid was washed with anhydrous ethanol for multiple times, and then centrifuged at a speed of 8000r / s for two minutes, the upper solution was discarded, and the precipitate below was retained and dried at 60°C in a vacuum oven with an air pressure of 0.5Mpa to obtain a cobalt-based metal organic framework precursor; (4) The cobalt-based metal organic framework precursor powder sample is placed in a muffle furnace, and the temperature is increased from room temperature to 300 °C at a heating rate of 2 °C / min, maintained at 300 °C for 2 hours, and then cooled to room temperature at a cooling rate of 2 °C / min to obtain Co3O4 nanospheres.

[0027] Comparative Example 3: (1) Ce(NO3)3‧6H2O (2 mmol) was dissolved in 30 mL of N,N-dimethylformamide (DMF) under stirring and ultrasonication to obtain a transparent solution; (2) Add trimesic acid (150 mg) into the transparent solution and stir evenly until completely dissolved to obtain a mixed solution; (3) The mixed solution was transferred into a polytetrafluoroethylene autoclave and kept reacting at 150°C for 6 hours. After the autoclave was naturally cooled to room temperature, the product after the hydrothermal reaction was filtered to separate the solid and liquid, and the obtained solid was washed with anhydrous ethanol for multiple times, and then centrifuged at a speed of 8000r / s for two minutes, the upper solution was discarded, and the precipitate below was retained and dried at 60°C in a vacuum oven with an air pressure of 0.5Mpa to obtain a cerium-based metal organic framework precursor; (4) The cerium-based metal organic framework precursor powder sample is placed in a muffle furnace, and the temperature is increased from room temperature to 300°C at a heating rate of 2°C / min, maintained at 300°C for 2 hours, and then cooled to room temperature at a cooling rate of 2°C / min to obtain CeO2 solid powder.

[0028] Embodiment 2: The method in Example 1 was followed, except that the molar ratio of Co(NO3)2‧6H2O and Ce(NO3)3‧6H2O in step 1 was (Ce:Co=2.5:100), with a total molar amount of 2 mmol, to finally obtain CeO2 / Co3O4 (Ce:Co= 2.5%) composite nanospheres.

[0029] Embodiment 3: The method in Example 1 was followed, except that the molar ratio of Co(NO3)2‧6H2O and Ce(NO3)3‧6H2O in step 1 was (Ce:Co=5:100), with a total molar amount of 2 mmol, to finally obtain CeO2 / Co3O4 (Ce:Co=5%) composite nanospheres.

[0030] Embodiment 4: The method in Example 1 was followed, except that the molar ratio of Co(NO3)2‧6H2O and Ce(NO3)3‧6H2O in step 1 was (Ce:Co=7.5:100), with a total molar amount of 2 mmol, to finally obtain CeO2 / Co3O4 (Ce:Co=7.5%) composite nanospheres.

[0031] Embodiment 5: The method in Example 1 was followed, except that the molar ratio of Co(NO3)2‧6H2O and Ce(NO3)3‧6H2O in step 1 was (Ce:Co=12.5:100), with a total molar amount of 2 mmol, to finally obtain CeO2 / Co3O4 (Ce:Co=12.5%) composite nanospheres.

[0032] Embodiment 6: The method in Example 1 was followed, except that the molar ratio of Co(NO3)2‧6H2O and Ce(NO3)3‧6H2O in step 1 was (Ce:Co=15:100), with a total molar amount of 2 mmol, to finally obtain CeO2 / Co3O4 (Ce:Co=15%) composite nanospheres.

[0033] Embodiment 7: The method in Example 1 was followed, except that the molar ratio of Co(NO3)2‧6H2O and Ce(NO3)3‧6H2O in step 1 was (Ce:Co=25:100), with a total molar amount of 2 mmol, to finally obtain CeO2 / Co3O4 (Ce:Co=25%) composite nanospheres.

[0034] Figure 1 is a scanning electron microscope image of the cobalt-cerium-based metal organic framework precursor doped with ionic liquid in Example 1 of the present invention, such as Figure 1 As shown, it is a nanosphere with uniform size. Figure 2 Shows good crystallinity, Figure 3 is a scanning electron microscope image of the hollow multi-shell CeO2 / Co3O4 composite nanospheres in Example 1 of the present invention, which shows that the uniform nanospheres are well maintained after temperature gradient pyrolysis. Figure 4 (Transmission electron microscope image of the hollow multi-shell CeO2 / Co3O4 composite nanospheres in Example 1 of the present invention) shows a uniform multilayer structure. Figure 5 The X-ray powder diffraction of the hollow multi-shell CeO2 / Co3O4 composite nanospheres in Example 1 of the present invention further shows that the prepared hollow multi-shell CeO2 / Co3O4 composite nanospheres have high purity and are in good agreement with the standard card.

[0035] Meanwhile, in the comparative example, the transmission electron microscope image of the ordinary CeO2 / Co3O4 composite nanospheres prepared without adding ionic liquid in comparative example 1 ( Figure 6 ), transmission electron microscope image of Co3O4 in comparative example 2 ( Figure 7 ) and the scanning electron microscope image of CeO2 in Comparative Example 3 ( Figure 8 ) show that no uniform hollow multi-shell structure appears.

[0036] Examples 2-7 demonstrate that Ce:Co within the above range can be prepared to have uniform size, generally with a diameter of about 500 nanometers, a clear porous shell and a large cavity structure.

[0037] Test Example 1 In a 1.0M potassium hydroxide solution, a traditional three-electrode system was used to investigate the oxygen evolution performance of the hollow multi-shell CeO2 / Co3O4 composite nanospheres of Example 1, the ordinary CeO2 / Co3O4 composite nanospheres of Comparative Example 1, the Co3O4 catalyst of Comparative Example 2 and the CeO2 catalyst of Comparative Example 3 in electrolysis of water, wherein the counter electrode, the working electrode and the reference electrode were a Pt sheet, a catalyst-loaded glassy carbon electrode and a Hg / HgO electrode, respectively, and the electrolyte was a 1.0M KOH aqueous solution. The applied potential was corrected for interference (i.e., iR) to compensate for the influence of the solution resistance and calibrated to the RHE scale (relative to Hg / HgO). The polarization curve test range was 0.1 to 0.8V (vsHg / HgO), and the scanning rate was 2mV / s.

[0038] Tafel plots were drawn using the logarithmic current (log[J]) of the overpotential. The stability was evaluated under constant current conditions at 10 mA / cm. The electrochemically active surface area (ECSA) was determined by CV curves in the potential range where no reduction process occurred, and the double layer capacitance (C dl ) at scan rates of 1, 2, 3, 4 and 5 mV / s.

[0039] Fig. 9 Schematic diagram of the catalytic performance of the hollow multi-shell CeO2 / Co3O4 composite nanospheres of Example 1 of the present invention, the ordinary CeO2 / Co3O4 composite nanospheres of Comparative Example 1, the Co3O4 catalyst in Comparative Example 2, and the CeO2 catalyst obtained in Comparative Example 3 in the electrolytic water oxygen evolution reaction. Fig. 9 As shown: Hollow multi-shell CeO2 / Co3O4 composite nanospheres have the best LSV polarization curve ( Fig. 9 a) and the lowest reaction overpotential ( Fig. 9 b), the lowest Tafel slope ( Fig. 9 c), good stability ( Fig. 9 d), the highest electrochemically active area ( Fig. 9 e), and the lowest charge transfer resistance ( Fig. 9 f), in addition, the hollow multi-shell CeO2 / Co3O4 composite nanospheres of Example 1 have the best reaction activity and the lowest reaction overpotential ( Fig.10 ). This shows that the electrocatalyst activity and reaction kinetics of the hollow multi-shell CeO2 / Co3O4 composite nanospheres obtained by the method of the present invention are significantly improved, and the long-term stability is good in practical applications.

[0040] Therefore, the hollow multi-shell CeO2 / Co3O4 composite nanospheres obtained according to the method of the present invention have the advantages of uniform morphology and size, rich hierarchical pores, large cavities and multi-layer hollow carbon shells. This material also has good practical value as an electrocatalyst in the field of water electrolysis and oxygen evolution.

[0041] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for preparing CeO2 / Co3O4 composite nanospheres with hollow multi-shell structure based on ionic liquid, comprising the following steps: Dissolving a metal cerium salt and a metal cobalt salt in an N,N-dimethylformamide solution to obtain a transparent solution; (2) adding the organic ligand and the ionic liquid to the above transparent solution in sequence, and subjecting the mixture to ultrasonic treatment and stirring until the mixture is completely dissolved to obtain a mixed solution; (3) transferring the mixed solution to a polytetrafluoroethylene autoclave, reacting at 150° C. for 6 hours, and then naturally cooling the autoclave to room temperature. The reaction solution is subjected to solid-liquid separation, and the solid is washed with anhydrous ethanol. After centrifugal washing and vacuum drying, an ionic liquid-doped cobalt-cerium-based metal organic framework precursor is obtained; (4) The ionic liquid-doped cobalt-cerium-based metal organic framework precursor is pyrolyzed by controlling the temperature pyrolysis gradient to obtain CeO2 / Co3O4 composite nanospheres with a hollow multi-shell structure.

2. The preparation method according to claim 1, wherein The metal cerium salt and the metal cobalt salt are cerium nitrate and cobalt nitrate respectively.

3. The preparation method according to claim 1, wherein The molar ratio of the metal cobalt salt to the metal cerium salt is: Ce:Co= (2.5-25):

100.

4. The preparation method according to claim 1, wherein The organic ligand is trimesic acid.

5. The preparation method according to claim 1, wherein The molar ratio of the organic ligand to the total amount of the metal cobalt salt and the metal cerium salt is 1:

3.

6. The preparation method according to claim 1, wherein The ionic liquid is 1-butyl-3-methylimidazolium hexafluorophosphate.

7. The preparation method according to claim 1, wherein The mass ratio of the total amount of the metal cobalt salt and the metal cerium salt to the ionic liquid is 1:

2.

8. The preparation method according to claim 1, wherein In step (4), the temperature pyrolysis gradient is to increase the temperature to 300°C at a rate of 2°C / min and maintain it for 2 hours, and then naturally cool it to room temperature to obtain hollow multi-shell CeO2 / Co3O4 composite nanospheres based on ionic liquid.

9. Hollow multi-shell CeO2 / Co3O4 composite nanospheres obtained by the preparation method according to any one of claims 1 to 8.

10. Use of the hollow multi-shell CeO2 / Co3O4 composite nanospheres according to claim 9 in oxygen evolution reaction by water electrolysis.

Images