A method for preparing hollow multi-shell CeO2 / Co3O4 composite nanospheres based on ionic liquids

Abstract

This invention utilizes an ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate) as a dopant and morphology guide, trimesic acid as an organic ligand, and cobalt nitrate and cerium nitrate as metal sources. A cobalt-cerium bimetallic organic framework precursor doped with the ionic liquid is constructed via a solvothermal reaction, and hollow multi-shell CeO2 / Co3O4 composite nanospheres are prepared using gradient-temperature controlled pyrolysis technology. This invention provides a simple, universal method that does not rely on traditional soft / hard templates, enabling the controllable design of composite materials with hollow multi-shell structures, which exhibit significantly enhanced catalytic activity in the oxygen evolution reaction (OER). This invention provides a new approach for morphology control and performance optimization of rare-earth-based composite catalysts, and has significant application value in clean energy fields such as water electrolysis for hydrogen production and fuel cells.

Description

Technical Field

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

[0002] With the increasing severity of the energy crisis and environmental pollution, hydrogen has attracted much attention as a clean energy carrier. Electrocatalytic water splitting technology is an important route for hydrogen production, and the oxygen evolution reaction (OER) in this process consumes a huge amount of energy. While traditional precious metal catalysts exhibit excellent activity, their limited production and high cost severely restrict their large-scale application. Therefore, the development of novel, low-cost, and highly active non-precious metal OER catalysts is particularly urgent.

[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 suffer from poor conductivity, limited composition, and difficulties in the controllable synthesis of composite materials with specific structural morphologies in electrocatalysis, which greatly restricts their application potential in water electrolysis. Currently, the main synthesis methods for cerium oxide-based materials include sol-gel methods, co-precipitation methods, hydrothermal / solvothermal methods, and template-directed synthesis. Although these methods have certain versatility, they often rely on specific templates, and how to achieve precise composites of cerium oxide with other transition metal heteromaterials to improve its inherent conductivity remains a challenge for current research. Summary of the Invention

[0004] To address the shortcomings of existing cerium oxide-based composite nanocatalyst synthesis methods, this invention proposes a method for preparing CeO2 / Co3O4 composite nanospheres with a hollow multi-shell structure. On one hand, the ionic liquid acts as a structure-directing template, influencing the morphology and size of the precursor and facilitating the formation of the hollow multi-layer structure. On the other hand, the ionic liquid, as a heteroatom dopant, provides more active sites and defects. The spherical morphology of this composite catalyst facilitates contact between contact points, effectively preventing grain sintering and aggregation. 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] To achieve the above objectives, the present invention first provides a method for preparing CeO2 / Co3O4 composite nanospheres with a hollow multi-shell structure based on ionic liquids, comprising the following steps:

[0006] (1) Dissolve cerium salt and cobalt salt in N,N-dimethylformamide (DMF) solution to obtain a transparent solution;

[0007] (2) The organic ligand and ionic liquid are added to the above transparent solution in sequence, and the solution is subjected to ultrasonic treatment and stirring until completely dissolved to obtain a mixed solution;

[0008] (3) The mixture was transferred to a polytetrafluoroethylene autoclave and reacted at 150 °C for 6 h. After the autoclave was naturally cooled to room temperature, the reaction solution was separated into solid and liquid. The solid was washed with anhydrous ethanol, and after centrifugation and vacuum drying, the cobalt cerium-based metal-organic framework precursor doped with ionic liquid was obtained.

[0009] (4) The cobalt-cerium-based metal-organic framework precursor doped with ionic liquid is pyrolyzed by controlling the temperature pyrolysis gradient to obtain CeO2 / Co3O4 composite nanospheres with a hollow multi-shell structure.

[0010] In some embodiments, the cerium salt and cobalt salt are cerium nitrate and cobalt nitrate, respectively.

[0011] In some embodiments, the molar ratio of the cobalt salt and the 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.

[0012] In some embodiments, the concentration of the DMF solution of the cobalt metal salt is 0.15 mol / L, and the concentration of the DMF solution of the cerium metal salt is 7.5 mmol / L-37.5 mmol / L.

[0013] In some embodiments, the organic ligand is pyromellitic acid; the molar ratio of the organic ligand to the total amount of cobalt salt and cerium salt is 1:3.

[0014] In some embodiments, the ionic liquid is 1-butyl-3-methylimidazolium hexafluorophosphate.

[0015] In some embodiments, the total amount of the cobalt salt and cerium salt is in a mass ratio of 1:2 to the ionic liquid.

[0016] In some embodiments, in step (3), the centrifugally washed solid is dried at 60°C in a vacuum oven with a pressure of 0.5 MPa.

[0017] 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 hold it for 2 hours, and then allow it to cool naturally to room temperature to obtain hollow multi-shell CeO2 / Co3O4 composite nanospheres based on ionic liquid.

[0018] In a second aspect, the present invention provides hollow multi-shell CeO2 / Co3O4 composite nanospheres obtained by the above preparation method.

[0019] In some embodiments, the hollow multi-shell CeO2 / Co3O4 composite nanospheres have a clear porous shell and a large cavity structure, with uniform size and a diameter generally around 500 nanometers.

[0020] In a third aspect, the present invention provides the application of the hollow multi-shell CeO2 / Co3O4 composite nanospheres in the oxygen evolution reaction (OER) of water electrolysis.

[0021] Beneficial effects

[0022] This invention uses an ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate) as a dopant and morphology guide, trimesic acid as a ligand, and cobalt nitrate and cerium nitrate as metal salts to prepare an ionic liquid-doped cobalt-cerium-based metal-organic framework precursor via a solvothermal method. Subsequently, hollow multi-shell CeO2 / Co3O4 composite nanospheres are prepared using a controlled temperature pyrolysis gradient. This invention provides a simple, universal method that does not rely on traditional soft / hard templates. It innovatively employs a dual functionalization strategy of ionic liquids to prepare CeO2 / Co3O4 composite nanospheres with a hollow multi-shell structure. The ionic liquid acts both as a soft template to guide the formation of the hollow multi-shell structure and as a dopant source to introduce structural defects and active sites. The doping of the ionic liquid introduces heteroatoms into the composite material and generates abundant wrinkles during calcination, 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. They have a clear porous shell and a large cavity structure, which allows them to have full contact with the electrolyte during the catalytic process.

[0023] This invention successfully integrates the advantages of CeO2 and Co3O4 components. The hollow multi-shell CeO2 / Co3O4 composite nanospheres prepared by this invention exhibit better activity, lower reaction overpotential, lower Tafel slope, and superior stability as an OER catalyst in catalytic experiments on the electrolysis of water compared to single-component catalysts. This invention provides a new approach to controlling the morphology and structure of cerium oxide-based composite nanocatalysts to improve electrocatalytic performance, and is of great significance for achieving efficient water electrolysis for hydrogen production and addressing the environmental crisis. Attached Figure Description

[0024] Figure 1 These are scanning electron microscope images of the cobalt-cerium-based metal-organic framework precursor doped with ionic liquid in Example 1 of this invention;

[0025] Figure 2This 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;

[0026] Figure 3 The image shown is a scanning electron microscope image of the hollow multi-shell CeO2 / Co3O4 composite nanospheres in Example 1 of this invention.

[0027] Figure 4 The image is a transmission electron microscope image of the hollow multi-shell CeO2 / Co3O4 composite nanospheres in Example 1 of this invention.

[0028] Figure 5 This is an X-ray powder diffraction pattern of the hollow multi-shell CeO2 / Co3O4 composite nanospheres in Example 1 of the present invention;

[0029] Figure 6 This refers to the ordinary CeO2 / Co3O4 composite nanospheres prepared without the addition of ionic liquid in Comparative Example 1 of this invention;

[0030] Figure 7 These are scanning electron microscope images and transmission electron microscope images of Co3O4 in Comparative Example 2 of this invention;

[0031] Figure 8 These are scanning electron microscope images and transmission electron microscope images of CeO2 in Comparative Example 3 of this invention;

[0032] Figure 9 The following are schematic diagrams of the catalytic performance of the catalysts prepared in Example 1 and Comparative Examples 1-3 in the oxygen evolution reaction of water electrolysis: (a) LSV polarization curves; (b) overpotential of each catalyst at 10 mA / cm; (c) Tafel slope; (d) stability test; (e) function graph of different scan rates versus capacitance current; (f) electrochemical impedance spectroscopy.

[0033] Figure 10 This is a comparison of the LSV polarization curves of water electrolysis catalysts with different Ce:Co ratios prepared in Examples 1-7 of this invention.

[0034] Specific implementation methods

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0036] Example 1:

[0037] (1) Co(NO3)2‧6H2O and Ce(NO3)3‧6H2O were dissolved in 30 mL of N,N-dimethylformamide (DMF) with the aid of stirring and ultrasound in a molar ratio (Ce:Co=10:100). The total molar amount of metal salt was 2 mmol, and a transparent solution was obtained.

[0038] (2) Add 150 mg of pyromellitic acid and 400 mg of ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate) to the transparent solution in sequence, and stir until completely dissolved to obtain a mixed solution;

[0039] (3) The above mixed solution was transferred into a polytetrafluoroethylene autoclave and kept at 150°C for 6 hours. After the autoclave was naturally cooled to room temperature, the product after the hydrothermal reaction was separated by vacuum filtration. The obtained solid was washed multiple times with anhydrous ethanol and then centrifuged at 8000 r / s for two minutes. The upper layer of solution was discarded, and the lower precipitate was retained and dried in a vacuum oven at 60°C with a pressure of 0.5 MPa to obtain the ion liquid-doped cobalt cerium-based metal-organic framework precursor.

[0040] (4) Place the above-mentioned cobalt cerium-based metal-organic framework precursor powder sample doped with ionic liquid in a muffle furnace, heat it from room temperature to 300°C at a heating rate of 2°C / min, hold it at 300°C for 2 hours, and then cool it down to room temperature at a cooling rate of 2°C / min to obtain hollow multi-shell CeO2 / Co3O4 composite nanospheres after cooling.

[0041] Scanning electron microscope images of cobalt-cerium-based metal-organic framework precursors doped with ionic liquids ( Figure 1 The precursors are shown as uniform nanospheres with sizes ranging from ~500 nm; X-ray powder diffraction pattern of the cobalt-cerium-based metal-organic framework precursor doped with ionic liquid ( Figure 2 The hollow multi-shell CeO2 / Co3O4 composite nanospheres show good crystallization; scanning electron microscope image (SEM image). Figure 3 The image shows that after controlled-temperature calcination, the morphology of the material was maintained, and due to the introduction of ionic liquid, wrinkles appeared on the surface, and a hollow structure was observed. The image is a transmission electron microscope image of hollow multi-shell CeO2 / Co3O4 composite nanospheres. Figure 4 The structure exhibits a uniform multilayer hollow structure, typically with 3-4 layers and uniform size; X-ray powder diffraction pattern of hollow multilayer CeO2 / Co3O4 composite nanospheres ( Figure 5 The results show that the precursor is converted into CeO2 / Co3O4 after oxidation and calcination. The diffraction peaks correspond well with the standard card of Co3O4 (JCPDS No. 09-0418) and the standard card of CeO2, indicating that the material is successfully composited and has high purity.

[0042] Comparative Example 1:

[0043] (1) Co(NO3)2‧6H2O and Ce(NO3)3‧6H2O were dissolved in 30 mL of N,N-dimethylformamide (DMF) with the assistance of stirring and ultrasound in a molar ratio (Ce:Co=1:9). The total molar amount of metal salt was 2 mmol, and a transparent solution was obtained.

[0044] (2) Add 150 mg of pyromellitic acid to the clear solution and stir until completely dissolved to obtain a mixed solution;

[0045] (3) The above mixed solution was transferred into a polytetrafluoroethylene autoclave and kept at 150°C for 6 hours. After the autoclave was naturally cooled to room temperature, the product after the hydrothermal reaction was separated by vacuum filtration. The obtained solid was washed multiple times with anhydrous ethanol and then centrifuged at 8000 r / s for two minutes. The upper layer of solution was discarded, and the lower precipitate was retained and dried in a vacuum oven at 60°C with a pressure of 0.5 MPa to obtain the cobalt cerium-based metal-organic framework precursor.

[0046] (4) Place the above cobalt-cerium-based metal-organic framework precursor powder sample in a muffle furnace, heat it from room temperature to 300°C at a heating rate of 2°C / min, hold it at 300°C for 2 hours, and then cool it down to room temperature at a cooling rate of 2°C / min to obtain ordinary CeO2 / Co3O4 composite nanospheres.

[0047] Comparative Example 2:

[0048] (1) Co(NO3)2‧6H2O (2 mmol) was dissolved in 30 mL of N,N-dimethylformamide (DMF) with the aid of stirring and ultrasound to obtain a transparent solution;

[0049] (2) Add 150 mg of pyromellitic acid to the clear solution and stir until completely dissolved to obtain a mixed solution;

[0050] (3) The above mixed solution was transferred into a polytetrafluoroethylene autoclave and kept at 150°C for 6 hours. After the autoclave was naturally cooled to room temperature, the product after the hydrothermal reaction was separated by vacuum filtration. The obtained solid was washed multiple times with anhydrous ethanol and then centrifuged at 8000 r / s for two minutes. The upper layer of solution was discarded, the lower precipitate was retained, and dried in a vacuum oven at 60°C with a pressure of 0.5 MPa to obtain the cobalt-based metal-organic framework precursor.

[0051] (4) Place the above cobalt-based metal-organic framework precursor powder sample in a muffle furnace, heat it from room temperature to 300 ℃ at a heating rate of 2 ℃ / min, hold it at 300 ℃ for 2 hours, and then cool it down to room temperature at a cooling rate of 2 ℃ / min to obtain Co3O4 nanospheres.

[0052] Comparative Example 3:

[0053] (1) Ce(NO3)3‧6H2O (2 mmol) was dissolved in 30 mL of N,N-dimethylformamide (DMF) with the aid of stirring and ultrasound to obtain a transparent solution;

[0054] (2) Add 150 mg of pyromellitic acid to the clear solution and stir until completely dissolved to obtain a mixed solution;

[0055] (3) The above mixed solution was transferred into a polytetrafluoroethylene autoclave and kept at 150°C for 6 hours. After the autoclave was naturally cooled to room temperature, the product after the hydrothermal reaction was separated by vacuum filtration. The obtained solid was washed multiple times with anhydrous ethanol and then centrifuged at 8000 r / s for two minutes. The upper layer of solution was discarded, the lower precipitate was retained, and dried in a vacuum oven at 60°C with a pressure of 0.5 MPa to obtain the cerium-based metal-organic framework precursor.

[0056] (4) Place the above cerium-based metal-organic framework precursor powder sample in a muffle furnace and heat it from room temperature to 300°C at a heating rate of 2°C / min. Hold it at 300°C for 2 hours and then cool it down to room temperature at a cooling rate of 2°C / min to obtain CeO2 solid powder.

[0057] Example 2:

[0058] The procedure was carried out according to the method in Example 1, except that in step 1, Co(NO3)2‧6H2O and Ce(NO3)3‧6H2O were in a molar ratio (Ce:Co=2.5:100) with a total molar amount of 2 mmol, and CeO2 / Co3O4 (Ce:Co=2.5%) composite nanospheres were finally obtained.

[0059] Example 3:

[0060] The procedure was carried out according to the method in Example 1, except that the total molar amount of Co(NO3)2‧6H2O and Ce(NO3)3‧6H2O in step 1 was 2 mmol in a molar ratio (Ce:Co=5:100), and CeO2 / Co3O4 (Ce:Co=5%) composite nanospheres were finally obtained.

[0061] Example 4:

[0062] The procedure was carried out according to the method in Example 1, except that in step 1, Co(NO3)2‧6H2O and Ce(NO3)3‧6H2O were in a molar ratio (Ce:Co=7.5:100) with a total molar amount of 2 mmol, and CeO2 / Co3O4 (Ce:Co=7.5%) composite nanospheres were finally obtained.

[0063] Example 5:

[0064] The procedure was carried out according to the method in Example 1, except that in step 1, Co(NO3)2‧6H2O and Ce(NO3)3‧6H2O were in a molar ratio (Ce:Co=12.5:100) with a total molar amount of 2 mmol, and CeO2 / Co3O4 (Ce:Co=12.5%) composite nanospheres were finally obtained.

[0065] Example 6:

[0066] The procedure was carried out according to the method in Example 1, except that the total molar amount of Co(NO3)2‧6H2O and Ce(NO3)3‧6H2O in step 1 was 2 mmol (Ce:Co=15:100), and CeO2 / Co3O4 (Ce:Co=15%) composite nanospheres were finally obtained.

[0067] Example 7:

[0068] The procedure was carried out according to the method in Example 1, except that the total molar amount of Co(NO3)2‧6H2O and Ce(NO3)3‧6H2O in step 1 was 2 mmol (Ce:Co=25:100), and CeO2 / Co3O4 (Ce:Co=25%) composite nanospheres were finally obtained.

[0069] Figure 1 These are scanning electron microscope images of the cobalt-cerium-based metal-organic framework precursor doped with ionic liquid in Example 1 of this invention, such as... Figure 1 As shown, it consists of nanospheres with uniform morphology and size. Figure 2 It shows good crystallinity. Figure 3 This is a scanning electron microscope image of the hollow multi-shell CeO2 / Co3O4 composite nanospheres in Example 1 of this invention. It shows that the uniform nanospheres remain well-preserved after temperature gradient pyrolysis. Figure 4 (The transmission electron microscope image of the hollow multi-shell CeO2 / Co3O4 composite nanospheres in Example 1 of this 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 this invention further shows that the prepared hollow multi-shell CeO2 / Co3O4 composite nanospheres have high purity and match well with the standard card.

[0070] Meanwhile, in the comparative examples, transmission electron microscopy images of ordinary CeO2 / Co3O4 composite nanospheres prepared without the addition of ionic liquid in Comparative Example 1 are shown ( Figure 6 ), Transmission electron microscope image of Co3O4 in Comparative Example 2 ( Figure 7 Images of CeO2 from Comparative Example 3 (using scanning electron microscopy). Figure 8 The results showed that no uniform hollow multi-shell structure was observed.

[0071] Examples 2-7 demonstrate that Ce:Co within the above range can be prepared to obtain uniform size, with a diameter generally around 500 nanometers, and a clear porous shell and large cavity structure.

[0072] Test Example 1

[0073] In a 1.0 M potassium hydroxide solution, a conventional three-electrode system was used to investigate the oxygen evolution performance of hollow multi-shell CeO2 / Co3O4 composite nanospheres from Example 1, ordinary CeO2 / Co3O4 composite nanospheres from Comparative Example 1, Co3O4 catalyst from Comparative Example 2, and CeO2 catalyst from Comparative Example 3 in water electrolysis. The counter electrode, working electrode, and reference electrode were a Pt sheet, a glassy carbon electrode with a supported catalyst, and a Hg / HgO electrode, respectively. The electrolyte was a 1.0 M KOH aqueous solution. The applied potential was corrected for interference immunity (i.e., iR) to compensate for the influence of solution resistance and calibrated to the RHE scale (relative to Hg / HgO). The polarization curve was measured in the range of 0.1 to 0.8 V (vs Hg / HgO) at a scan rate of 2 mV / s.

[0074] Tafel plots were plotted using the logarithmic overpotential current (log[J]). Stability assessments were performed under a constant current condition of 10 mA / cm. The electrochemical active surface area (ECSA) was determined by CV curves over the potential range without reduction, and the double-layer capacitance (C0) was extracted. dl The scan rates are 1, 2, 3, 4 and 5 mV / s.

[0075] Figure 9 This is a schematic diagram illustrating the catalytic 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 obtained in Comparative Example 3 in the oxygen evolution reaction of water electrolysis. Figure 9 As shown: Hollow multi-shell CeO2 / Co3O4 composite nanospheres exhibit the optimal LSV polarization curve ( Figure 9 a) and the lowest reaction overpotential ( Figure 9 b), the lowest Tafel slope ( Figure 9c), good stability ( Figure 9 d), the highest electrochemical active area ( Figure 9 e), and the lowest charge transfer resistance ( Figure 9 f), in addition, the hollow multi-shell CeO2 / Co3O4 composite nanospheres of Example 1 have the best reactivity and the lowest reaction overpotential (f). Figure 10 This indicates that the hollow multi-shell CeO2 / Co3O4 composite nanosphere electrocatalyst obtained according to the method of the present invention exhibits significantly improved activity and reaction kinetics, and good long-term stability in practical applications.

[0076] Therefore, the hollow multi-shell CeO2 / Co3O4 composite nanospheres obtained by the method of the present invention have advantages such as uniform morphology and size, abundant hierarchical pores, large cavities and multi-layered hollow carbon shells. This material also has good practical value as an electrocatalyst in the field of oxygen evolution through water electrolysis.

[0077] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing CeO2 / Co3O4 composite nanospheres with a hollow multi-shell structure based on ionic liquids, comprising the following steps: (1) Dissolve cerium salt and cobalt salt in N,N-dimethylformamide solution to obtain a transparent solution; (2) The organic ligand and the ionic liquid are added to the above transparent solution in sequence, and the solution is subjected to ultrasonic treatment and stirring until completely dissolved to obtain a mixed solution; the organic ligand is pyromellitic acid; the ionic liquid is 1-butyl-3-methylimidazolium hexafluorophosphate; (3) The mixture was transferred to a polytetrafluoroethylene autoclave and reacted at 150 °C for 6 h. After the autoclave was naturally cooled to room temperature, the reaction solution was separated into solid and liquid. The solid was washed with anhydrous ethanol, and after centrifugation and vacuum drying, the cobalt cerium-based metal-organic framework precursor doped with ionic liquid was obtained. (4) The cobalt-cerium-based metal-organic framework precursor doped with ionic liquid is pyrolyzed by controlling the temperature pyrolysis gradient. The temperature pyrolysis gradient is to raise the temperature to 300℃ at a rate of 2℃ / min and hold it for 2h, and then let it cool naturally to room temperature to obtain CeO2 / Co3O4 composite nanospheres with hollow multi-shell structure based on ionic liquid.

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

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

100.

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

3.

5. The preparation method according to claim 1, wherein, The total amount of the cobalt salt and cerium salt is in a mass ratio of 1:2 to the ionic liquid.

6. Hollow multi-shell CeO2 / Co3O4 composite nanospheres obtained by the preparation method according to any one of claims 1-5.

7. The application of the hollow multi-shell CeO2 / Co3O4 composite nanospheres as described in claim 6 in the oxygen evolution reaction of water electrolysis.

Images