A defect-rich cobalt hydroxide-cerium dioxide heterojunction material with high-efficiency oxygen evolution electrocatalytic performance and preparation method

Abstract

The present invention discloses a defect-rich cobalt hydroxide-cerium dioxide heterojunction material with high-efficiency oxygen evolution electrocatalytic performance and a preparation method, belonging to the technical field of new materials. The cobalt hydroxide-cerium dioxide heterojunction belongs to a p-n heterojunction, CeO 2 When the cobalt hydroxide working electrode with cerium ions contacts the electrolyte, it can be generated in situ. 2 Can activate inert Co(OH) 2 The nanosheet plane produces a large number of lattice-mismatched active centers and oxygen vacancies at the interface, which show excellent electrocatalytic activity in the OER reaction. This invention realizes the preparation of in-situ heterojunctions in the process of making working electrodes for the first time. The preparation strategy is simple and efficient, and the heterojunctions are evenly dispersed, which is not only conducive to improving the performance of the catalyst, but also expected to provide guidance for the directional design of other metal heterojunction catalysts.

Description

Technical Field

[0001] The present invention belongs to the technical field of new materials, and in particular relates to a defect-rich cobalt hydroxide-cerium dioxide heterojunction material with high-efficiency oxygen evolution electrocatalytic performance and a preparation method thereof. Background Art

[0002] The development of energy conversion and storage technology has greatly promoted the development and efficient utilization of intermittent renewable energy such as solar energy and wind energy. The development of low-energy energy conversion and storage systems such as electrocatalytic water splitting and metal secondary batteries is crucial, but the inert oxygen evolution reaction (OER) involved greatly limits their practical application. Therefore, the development of efficient, stable and low-cost OER catalysts is the key to improving equipment efficiency and increasing cost-effectiveness. See (Amiinu IS, Pu Z, Liu X, et al. [J]. Advanced Functional Materials, 2017, 27 (44): 1702300. Li D, Qin Y, Liu J, et al. [J]. Advanced Functional Materials, 2021, 32 (7): 2107056. Sui Y, Ji X. [J]. Chemical Reviews, 2021, 121 (11): 6654-6695. Chia X, Pumera M. Nat. Catal. [J]. 2018, 1, 909–921.). The size and surface properties of the catalyst play a crucial role in the preparation of the final catalytic site. Two-dimensional (2D) first-row transition metal hydroxide electrocatalysts have been widely used in the OER field due to their strong mechanical structure, large surface area and tunable electronic structure. However, due to anisotropy, the heterogeneous electron transfer rate of the inert basal plane is significantly lower than that of the coordination-unsaturated active edge positions. Typical 2D nanomaterials, such as Co(OH)2 nanosheets, have a larger edge-to-surface ratio, which makes their intrinsic activity weaker and has fewer active centers, resulting in poor OER performance. However, these 2D materials are reported to be highly sensitive to lattice strain. See (Chemical Reviews, 2021, 121(11): 6654-6695. Chia X, Pumera M. Nat. Catal. [J]. 2018, 1, 909–921. Gu LF, Li CF, Zhao JW, et al. [J]. Journal of Materials Chemistry A, 2021, 9(22): 13279-13287. J, Ollár T, Vancsó P, et al. [J]. Nature chemistry, 2018, 10 (12): 1246-1251.). Therefore, carefully and cleverly designing the lattice-mismatched heterojunction structure to activate the inert planes of Co(OH)2 nanosheets plays a significant role in improving the OER catalytic performance. Summary of the invention

[0003] The object of the present invention is to provide a hydroxide-oxide heterojunction material and a preparation method thereof, and the OER catalyst prepared based on the material has good catalytic activity and cyclability.

[0004] The present invention includes a hydroxide-oxide heterojunction OER catalyst, represented as Co(OH)2@CeO2. The material belongs to a pn heterojunction, wherein the morphology of Co(OH)2 is a micron-scale sheet structure, and CeO2 is a nano-scale particle structure. The inert surface of Co(OH)2 is activated by constructing a pn heterojunction electrocatalyst with CeO2. The Co(OH)2@CeO2 pn heterojunction can be generated in situ after the working electrode contacts the electrolyte. After the generated CeO2 activates the inert Co(OH)2 nanosheet plane, the discrete distribution of CeO2 particles on the Co(OH)2 layer leads to abundant interfacial oxygen vacancies and achieves a surge in catalytic active sites.

[0005] The preparation of the Co(OH)2@CeO2p-n heterojunction electrocatalyst in the present invention mainly includes the following steps:

[0006] (1) Preparation of lamellar structure Co(OH)2: A certain amount of cobalt acetate was dissolved in deionized water, and then a certain proportion of hydrazine hydrate and ammonia solution were added to the above solution. The suspension was refluxed at 95°C for 90 minutes, cooled to room temperature and washed with distilled water several times, and the collected product was dried at 80°C to obtain pink Co(OH)2 powder. The volume ratio of ammonia water to hydrazine hydrate was 28.6:1.

[0007] (2) Preparation of Co(OH)2-Ce electrode sheet: A certain amount of Co(OH)2 powder was added to 10 mL of a mixture of cerium nitrate, ethanol and water, and a certain amount of naphthol solution was added and ultrasonicated to obtain a pink electrode slurry. Then a certain amount of the slurry was taken out and dripped twice onto a 1 cm -2 The carbon paper was dried by a hair dryer to obtain a catalytic Co(OH)2-Ce electrode sheet. The mass of the Co(OH)2 powder was 3 mg, the volume ratio of the mixed solution of ethanol to water was 6:4, the volume ratio of the mixed solution to naphthol was 29:1, and the concentration of cerium nitrate in the mixed solution was 0.02 mol L -1 .

[0008] (3) Preparation of Co(OH)2@CeO2p-n heterojunction: The Co(OH)2-Ce electrode sheet was soaked in alkaline KOH at room temperature for a certain period of time, then taken out, rinsed with distilled water and dried with a hair dryer to obtain the target catalyst. The concentration of the KOH solution was 1.0 mol L -1 The room temperature is 20°C to 25°C, and the certain time is 30min to 60min.

[0009] The outstanding advantages of the present invention are: the Co(OH)2@CeO2p-n heterojunction can be generated in situ after the working electrode contacts the electrolyte, and after the generated CeO2 activates the inert Co(OH)2 nanosheet plane, a large number of lattice-mismatched active centers and oxygen vacancies are generated at the interface, which can be used in the OER reaction to exhibit outstanding catalytic activity and excellent stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 The Zeta potential curve of the Co(OH)2@CeO2p-n heterojunction electrocatalyst

[0011] Figure 2 This is the X-ray diffraction pattern of the Co(OH)2@CeO2p-n heterojunction electrocatalyst

[0012] Figure 3 The model Schottky curve of the Co(OH)2@CeO2p-n heterojunction electrocatalyst

[0013] Figure 4 This is a scanning electron microscope image of the Co(OH)2@CeO2p-n heterojunction electrocatalyst.

[0014] Figure 5 This is a transmission electron microscope image of the Co(OH)2@CeO2p-n heterojunction electrocatalyst.

[0015] Figure 6 The linear sweep voltammetric curve of the Co(OH)2@CeO2p-n heterojunction electrocatalyst for OER

[0016] Figure 7 is the double layer capacitance curve of the Co(OH)2@CeO2p-n heterojunction electrocatalyst DETAILED DESCRIPTION

[0017] The features of the present invention are further described below by way of examples, but the present invention is not limited to the following examples.

[0018] The present invention provides a defect-rich cobalt hydroxide-cerium dioxide heterojunction material with high-efficiency oxygen evolution electrocatalytic performance and a preparation method. The specific steps of synthesizing the catalyst are shown in Example 1, and the catalyst is evaluated using OER catalytic oxidation as a reaction model, as shown in Example 2.

[0019] Example 1: Preparation of Co(OH)2@CeO2p-n heterojunction electrocatalyst

[0020] (1) Preparation of lamellar structure Co(OH)2: 1.245 g of cobalt acetate tetrahydrate was dissolved in 400 mL of deionized water, and then 350 μL of a mixture of 85% hydrazine hydrate and 10 mL of ammonia water was added. The suspension was refluxed at 95°C for 90 minutes, cooled to room temperature, washed with distilled water three times, and the product was collected by centrifugation and finally dried at 80°C to obtain pink Co(OH)2 powder.

[0021] (2) Preparation of Co(OH)2-Ce electrode sheet: 87 mg of cerium nitrate hexahydrate was added to a 60% ethanol aqueous solution, and ultrasonicated until the nitrate was completely dissolved to obtain a mixed solution. 290 μL of the mixed solution was added with 3 mg of Co(OH)2 nanosheets and 10 μL of naphthol solution (5 wt.%), and ultrasonicated for 10 minutes to obtain a pink electrode slurry. Then 100 μL of the slurry was taken out and dripped twice on a 1 cm×1 cm hydrophilic carbon paper to make the loading amount 1 mg cm -2 , and blow dry with cold air from a hair dryer to obtain a Co(OH)2-Ce catalyst.

[0022] Figure 1 The Zeta potential curves of the Co(OH)2-Ce catalyst prepared by the present invention and pure Co(OH)2 show that the positive shift of the Co(OH)2-Ce potential indicates that the positively charged cerium ions are successfully compounded with Co(OH)2.

[0023] (3) Preparation of Co(OH)2@CeO2p-n heterojunction: 2.8 g potassium hydroxide and 50 mL deionized water were prepared to a concentration of 1.0 mol L -1 The Co(OH)2-Ce electrode sheet obtained above is immersed in the electrolyte for 30 minutes, and the Co(OH)2-Ce can be in situ converted into Co(OH)2@CeO2p-n heterojunction catalyst.

[0024] Figure 2 This is the X-ray diffraction pattern of the Co(OH)2@CeO2 catalyst prepared in the present invention, indicating that CeO2 is generated in situ on the Co(OH)2 nanosheets.

[0025] Figure 3This is the model Schottky curve of the Co(OH)2@CeO2 catalyst prepared in the present invention. The test temperature of the model Schottky is 25°C, the test frequency is 1000 Hz, and the electrolyte solution is 0.2 mol L -1 Anhydrous sodium sulfate solution. This curve shows that the combination of the two compounds is a pn-type heterojunction.

[0026] Figure 4 and Figure 5 The scanning and transmission electron microscope images of the Co(OH)2@CeO2 catalyst prepared by the present invention respectively illustrate that CeO2 is uniformly loaded on large-sized Co(OH)2 nanosheets in the form of nanoparticles.

[0027] Example 2: The Co(OH)2@CeO2p-n heterojunction electrocatalyst described in Example 1 was subjected to an OER performance test. The electrochemical test was performed using a standard three-electrode system test method on a CHI760E workstation produced by Shanghai Chenhua Instrument Co., Ltd. In the three-electrode system used, the working electrode for OER is a carbon paper-supported catalyst, the reference electrode is an Ag / AgCl electrode (the filling liquid is a 1.0M KCl solution), and the counter electrode is a platinum mesh electrode (1cm×1cm) or a carbon rod electrode. In the present invention, linear sweep voltammetry (LSV), constant voltage curve method (VT Curves), etc. are used to perform electrochemical performance tests, and the voltage data in the test curves are converted into the standard reversible hydrogen electrode potential (E RHE ) and then compare the results: E RHE =E Ag / AgCl +0.059×pH+0.2223V.

[0028] The LSV of the Co(OH)2@CeO2 catalyst OER described in Example 1 is as follows Figure 6 As shown, the double layer capacitance of the Co(OH)2@CeO2 catalyst described in Example 1 is as follows Figure 7 As shown, it can be seen that the overpotential of the Co(OH)2@CeO2 catalyst prepared by the present invention is significantly reduced compared with the original pure Co(OH)2, indicating that the catalytic activity of the catalyst is significantly improved after the heterojunction is constructed. Figure 7 It can be seen that the Co(OH)2@CeO2 catalyst prepared by the present invention has the highest electrochemical active area, that is, the CeO2 nanoparticles successfully activate the originally inert Co(OH)2 plane, thereby increasing the number of effective catalytic sites and thereby enhancing the OER electrocatalytic activity.

[0029] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A defect-rich cobalt hydroxide-cerium dioxide heterojunction material with high-efficiency oxygen evolution electrocatalytic performance, characterized in that: The cobalt oxide-cerium dioxide heterojunction belongs to the pn heterojunction. The Co(OH)2@CeO2 pn heterojunction is generated after the working electrode contacts the electrolyte. After the generated CeO2 activates the inert Co(OH)2, a large number of lattice-mismatched active centers and oxygen vacancies are generated at the interface. The working electrode is a Co(OH)2-Ce electrode sheet; the electrolyte is an alkaline KOH solution; The Co(OH)2-Ce electrode sheet was obtained by the following method: Co(OH)2 powder was added to 10 mL of cerium nitrate ethanol water mixed solution, a certain amount of naphthol solution was added and ultrasonicated to obtain a pink electrode slurry, and then a certain amount of the slurry was taken out and dripped twice onto a 1.0 cm -2 The catalytic Co(OH)2-Ce electrode sheet was obtained by drying on a hydrophilic carbon paper with a hair dryer.

2. The method for preparing the defect-rich Co(OH)2@CeO2p-n heterojunction material with high-efficiency oxygen evolution electrocatalytic performance according to claim 1 comprises the following steps: (1) Preparation of catalyst electrode sheet: Co(OH)2 powder was added to 10 mL of cerium nitrate ethanol water mixed solution, and a certain amount of naphthol solution was added and ultrasonicated to obtain pink electrode slurry. Then, a certain amount of the slurry was taken out and dripped twice onto a 1.0 cm -2 The catalytic Co(OH)2-Ce electrode sheet was obtained by drying with a hair dryer on a hydrophilic carbon paper; (2) Preparation of Co(OH)2@CeO2 pn heterojunction: The Co(OH)2-Ce electrode sheet was soaked in alkaline KOH solution at room temperature, taken out, rinsed with distilled water and dried with a hair dryer to obtain the target catalyst.

3. The method for preparing a defect-rich Co(OH)2@CeO2 heterojunction material with high oxygen evolution electrocatalytic performance according to claim 2, characterized in that: Co(OH)2 powder was obtained by the following method: a certain amount of cobalt acetate was dissolved in deionized water, and then a certain proportion of hydrazine hydrate and ammonia solution were added to the above solution, the suspension was refluxed at 95°C for 90 minutes, cooled to room temperature and washed with distilled water, and the collected product was dried at 80°C to obtain Co(OH)2 powder.

4. The method for preparing a defect-rich Co(OH)2@CeO2 heterojunction material with high-efficiency oxygen evolution electrocatalytic performance according to claim 2, characterized in that: Step (1) Co(OH)2 powder 3.0 mg, cerium nitrate concentration 0.02 mol / L -1 The volume ratio of ethanol to water in the mixed solvent is 6:4, the amount of the mixed solvent in the electrode slurry is 290 μL, the mass percentage concentration of the naphthol solution is 5%, and the amount is 10 μL.

5. The method for preparing a defect-rich Co(OH)2@CeO2 heterojunction material with high-efficiency oxygen evolution electrocatalytic performance according to claim 2, characterized in that: The concentration of KOH solution in step (2) is 1.0 mol / L -1 The electrode sheet immersion time is 30min to 60min, and the room temperature is 20℃ to 25℃.

6. The method for preparing a defect-rich Co(OH)2@CeO2 heterojunction material with high-efficiency oxygen evolution electrocatalytic performance according to claim 3, characterized in that: The volume ratio of the ammonia water to the hydrazine hydrate is 28.6:1.

Images