A Ni-based Co-MOF derivative x Co 3-x O4 oxygen evolution catalyst and preparation method thereof

Abstract

The present invention discloses a Ni-based Co-MOF derivative x Co 3‑x O4 oxygen evolution catalyst and preparation method thereof, 2-methylimidazole and cobalt salt are added to a methanol solution, stirred and reacted to obtain a nano-diamond precursor Co-MOF, then the Co-MOF is dispersed in a solution containing a nickel source, stirred and reacted, centrifuged and washed to obtain Co-Ni MOF, and finally the Co-Ni MOF is calcined in an air atmosphere, heated to 300-375°C for annealing, and cooled to obtain Ni x Co 3‑ x O4 oxygen evolution catalyst, control Ni x Co 3‑x The atomic fraction of Ni in the O4 oxygen evolution catalyst is 4%-10%.

Description

Technical Field

[0001] The present invention belongs to the technical field of alkaline water electrolysis hydrogen production, and in particular relates to a Ni-based Co-MOF derivative. x Co 3-x O4 oxygen evolution catalyst and preparation method thereof. Background Art

[0002] The large-scale use of fossil fuels has triggered energy crises and ecological damage, posing a serious threat to sustainable development. Exploring efficient renewable energy systems has become a global consensus, and hydrogen, with its ultra-high energy density and zero-emission characteristics, is considered one of the most promising clean energy solutions. Among the many hydrogen production technologies, water electrolysis has become a research focus in the energy sector due to its green and sustainable potential. Proton / anion exchange membrane electrolyzers (PEM / AEM) offer significant advantages over traditional alkaline water electrolyzers. Currently, PEM water electrolysis catalysts primarily use precious metal catalysts such as platinum (Pt), ruthenium (Ru), and iridium (Ir). However, their high cost severely limits the large-scale application of PEM water electrolysis technology. Therefore, for AEM water electrolysis, which can utilize non-precious metals, it is particularly important to identify high-performance, low-cost transition metal-based catalysts to replace precious metal-based catalysts.

[0003] Metal-organic frameworks (MOFs) are multidimensional porous structures constructed from metal nodes (ions or clusters) and organic ligands. They have attracted considerable attention due to their tunable pore structure, high specific surface area, and abundant unsaturated sites. Due to the multivalent nature and electrical conductivity of cobalt (Co), Co-MOFs also exhibit good electrochemical activity, but their catalytic performance and durability still require further improvement through doping, structural engineering, or defect engineering. Among many transition metals, the coupling of Ni's 3d orbital with Co's 3d orbital can adjust the d-band center position, weaken the adsorption energy of *OOH intermediates, and significantly reduce the reaction energy barrier. Chinese patent application CN118904360A immerses a nickel foam substrate in a reaction solution to produce a nickel foam-supported Co-MOF material (ZIF-67 / NF). Subsequently, after calcination and hydrothermal treatment, the resulting nickel foam self-supported cobalt-nickel bimetallic sulfide heterojunction electrocatalytic composite, Co3S4 / Ni3S2 / NF, exhibits excellent catalytic performance and high stability due to its stable structure, large specific surface area, and abundant vacancies, significantly outperforming the unsupported Co-MOF-supported Ni3S2 / NF. This indicates that the combined and synergistic effect of metallic Co and Ni can have a beneficial effect on the catalyst. However, self-supported oxygen evolution catalysts using nickel foam substrates often suffer from limitations in corrosion resistance, loading process, and mass transfer efficiency. Consequently, the prior art has primarily focused on powder catalysts, which suffer from insufficient performance and poor stability.

[0004] Chinese Patent Document CN117587440A discloses a cobalt-copper-based oxygen evolution electrocatalyst and its preparation method. A cobalt-copper metal-organic framework compound is obtained through solution blending for ion exchange, and a non-self-supporting cobalt-copper MOF-derived oxide high-efficiency oxygen evolution electrocatalyst with a low oxygen evolution potential and excellent stability is prepared through an air annealing process. However, its oxygen evolution catalytic activity is relatively low and further optimization is still needed. At the same time, copper is prone to migration and aggregation during high-temperature treatment or electrochemical cycling, the morphology of the catalyst is prone to collapse during the preparation process, and there is also a problem of poor uniformity in the size of the nanosheets. Summary of the Invention

[0005] To overcome the problems in the prior art, the present invention provides a Ni x Co 3-x O4 oxygen evolution catalyst based on Co-MOF derivatives and its preparation method, and a powder catalyst is prepared to improve the oxygen evolution reaction (OER) performance and stability of the catalyst.

[0006] To solve the above technical problems, the technical solution proposed by the present invention is as follows:

[0007] The present invention provides a preparation method of a Ni x Co 3-x O4 oxygen evolution catalyst based on Co-MOF derivatives, comprising the following steps:

[0008] S1. Add 2-methylimidazole and cobalt salt to a solvent, stir and react, then let it stand, and obtain a nano-rhombic precursor Co-MOF after centrifugal washing and drying.

[0009] S2. Disperse the Co-MOF obtained in step S1 into a solution containing a nickel source, stir and react, and obtain Co-Ni MOF after centrifugal washing and drying.

[0010] S3. Slowly heat up the Co-Ni MOF obtained in step S2 in an air atmosphere to maintain the morphology of Co-MOF in step S1 for the product, and then slowly heat up to 300 - 375 °C, and obtain Ni x Co 3-x O4 oxygen evolution catalyst after cooling; where 0 < x < 3; the atomic fraction of Ni in the Ni x Co 3-x O4 oxygen evolution catalyst is 4% - 10%.

[0011] In the present invention, a nano-rhombic precursor Co-MOF is prepared by reacting 2-methylimidazole and cobalt salt. After ion exchange with Ni ions, a hetero-metal node (Co-Ni MOF) is formed, changing the local charge distribution. During this process, the coordination bonds in the Co-MOF structure will be cleaved by protons and Co will be released during the ion exchange process.2+ At this time, the dodecahedral structure of Co-MOF will collapse to form nanosheets or nanorods. In the present invention, the morphology of the precursor Co-Ni MOF is regulated by controlling the content of doped Ni to obtain a Co-Ni MOF precursor with a hexagonal nanosheet morphology, which effectively increases the contact area between the catalyst and the electrolyte. After heat treatment, the metal node Co in the MOF is converted into a porous oxide (such as ), inheriting the nanosheet or spherical morphology of the original MOF, 2-methylimidazole is carbonized into graphitized carbon, leaving a hollow carbon framework, achieving morphology replication and enhancing oxygen evolution activity. In addition, the stability of the catalyst is greatly improved after heat treatment.

[0012] As an optional embodiment, in the preparation method provided by the present invention, in step S3, Ni x Co 3-x The atomic fraction of Ni in the O4 oxygen evolution catalyst is 8%.

[0013] As an optional embodiment, in the preparation method provided by the present invention, in step S3, the temperature is raised to 350° C. for reaction, and the reaction time is >5 h.

[0014] As an optional embodiment, in the preparation method provided by the present invention, in step S1, 2-methylimidazole and cobalt salt are respectively added to a methanol solution, and the methanol solution containing the cobalt salt is dripped into the methanol solution containing 2-methylimidazole at a uniform rate while stirring.

[0015] In the present invention, 2-methylimidazole and cobalt salt are added to the methanol solution respectively, and then the cobalt salt is added with stirring, which is beneficial to the contact between the cobalt ions and the organic ligands and improves the efficiency of the reaction.

[0016] As an optional embodiment, in the preparation method provided by the present invention, in step S2, the nickel source is dissolved in a mixed solution of ethanol and water, with the volume ratio of ethanol to water being 4:1.

[0017] As an optional embodiment, in the preparation method provided by the present invention, in step S2, the stirring reaction temperature is 40-60° C., and the stirring time is 10-30 min.

[0018] In the present invention, controlling the stirring temperature is beneficial to promoting the hydrolysis reaction of Ni ions and Co ions and promoting NiCo ion exchange. Controlling the temperature within the above range is beneficial to controlling the morphology and performance of the product.

[0019] As an optional embodiment, in the preparation method provided by the present invention, the drying temperature in step S1 and step S2 is 50-60°C.

[0020] As an optional embodiment, in the preparation method provided by the present invention, in step S3, the calcination temperature is 150-300° C., and the calcination time is 1.5-2.5 h.

[0021] As an optional embodiment, in the preparation method provided by the present invention, in step S3, the heating rate is 5°C·min -1 .

[0022] Based on the same technical concept, the present invention also provides the above-mentioned Ni based on Co-MOF derivatives x Co 3-x Ni prepared by the preparation method of O4 oxygen evolution catalyst x Co 3-x O4 oxygen evolution catalyst.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) In the present invention, the room temperature reaction utilizes chemical potential to drive the direct synthesis of Co-MOF with a rhombic dodecahedron structure, thus avoiding the high temperature, high pressure and high energy consumption of the hydrothermal method and reducing production costs.

[0025] (2) The present invention prepares a Co-Ni MOF precursor with hexagonal nanosheet morphology by exchanging Ni ions and optimizing the composition, effectively increasing the contact area between the catalyst and the electrolyte, and then annealing treatment makes Ni x Co 3-x The O4 catalyst maintains the morphology of the original MOF, enhances the oxygen evolution activity, and the stability of the catalyst is greatly improved after heat treatment.

[0026] (3) Compared with self-supporting oxygen evolution catalysts based on substrates such as nickel foam and carbon cloth, the powdered oxygen evolution catalyst prepared by the present invention has greater flexibility and designability. In an AEM electrolyzer, the powder can be coated onto an anion exchange membrane or a current collector of any shape or material (nickel felt, titanium felt, nickel foam), adapting to the modular design of industrial electrolyzers and possessing greater potential for large-scale application. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0028] Figure 1SEM images of the precursor Co MOF at different magnifications, where (a) is a SEM image at 50,000 times, and (b) is a SEM image at 30,000 times;

[0029] Figure 2 The Co MOF prepared in Example 1-4 was subjected to Ni 2+ SEM images of the Co-Ni MOF series precursors after ion exchange, including (a) 4-Co-Ni MOF, (b) 6-Co-Ni MOF, (c) 8-Co-Ni MOF, and (d) 10-Co-NiMOF;

[0030] Figure 3 8-Ni prepared in Example 3 x Co 3-x SEM images of the O4 catalyst at different magnifications, where (a) is a 70,000x SEM image and (b) is a 100,000x SEM image;

[0031] Figure 4 4-Ni prepared in Example x Co 3-x O4、6-Ni x Co 3-x O4、10-Ni x Co 3-x SEM images of O4 catalysts, where (a) is 4-Ni x Co 3-x O4, (b) is 6-Ni x Co 3-x O4, (c) is 10-Ni x Co 3-x O4;

[0032] Figure 5 4-Ni prepared in Example x Co 3-x O4、6-Ni x Co 3-x O4、8-Ni x Co 3-x O4、10-Ni x Co 3-x EDS spectrum of O4, where (a) is 4-Ni x Co 3-x O4, (b) is 6-Ni x Co 3-x O4, (c) is 8-Ni x Co 3-x O4, (d) is 10-Ni x Co 3-x O4;

[0033] Figure 6 Co MOF, Co-Ni MOF and Ni prepared in the examples x Co 3-x XRD patterns of O4, where (a) is the XRD pattern of CoMOF and the Co MOF pattern simulated by VESTA, (b) is the XRD pattern of 4-Co-Ni MOF, 6-Co-Ni MOF, 8-Co-Ni MOF and 10-Co-Ni MOF and the comparative Co-MOF and Ni MOF (CCDC 1494751) patterns, (c) is a partial enlargement of (b), and (d) is the XRD pattern of 4-Ni x Co 3-x O4、6-Ni x Co 3-x O4、8-Ni x Co 3-x O4、10-Ni x Co 3-x XRD spectrum of O4;

[0034] Figure 7 8-Ni x Co 3-x TEM test results of O4, where (a) is the TEM image at a magnification of 50k, and (b) is the TEM image at a magnification of 800k;

[0035] Figure 8 8-Ni x Co 3-x The full XPS spectrum of O4 and the high-resolution spectra of Ni, Co, and O, where (a) is 8-Ni x Co 3-x The full XPS spectrum of O4, (bd) are the high-resolution spectra of Ni, Co, and O, respectively;

[0036] Figure 9 4-Ni prepared in Example x Co 3-x O4、6-Ni x Co 3-x O4、10-Ni x Co 3-x Oxygen evolution catalytic activity results of O4 catalysts, where (a) 4-Ni x Co 3-x O4、6-Ni x Co 3-x O4、10-Ni x Co 3-x Anodic polarization (LSV) curve of O4 catalyst, (b) is the Tafel slope diagram obtained by fitting the polarization curve;

[0037] Figure 10 Anodic polarization curves of 8-Co-Ni MOF catalyst products at different annealing temperatures;

[0038] Figure 11 Figure 2 is the anodic polarization curve after 8-Co-Ni MOF catalyst was loaded onto nickel foam and nickel felt;

[0039] Figure 12 8-Ni prepared in Example 3 x Co 3-x Electrochemical detection results of O4, where (a) is 8-Ni x Co 3-x O4 at a constant current density of 10 mA·cm -2 (b) is the long-term electrolysis curve, and (c) is the comparative polarization curve before and after 5000 cycles of CV accelerated decay.

[0040] Figure 13 4-Ni x Co 3-x O4、6-Ni x Co 3-x O4、10-Ni x Co 3-x O4 catalyst at a constant current density of 10 mA·cm -2 Long-term electrolysis curve under the following conditions, where (a) is 4-Ni x Co 3-x O4, (b) is 6-Ni x Co 3-x O4, (c) is 10-Ni x Co 3-x O4. DETAILED DESCRIPTION

[0041] To facilitate understanding of the present invention, the present invention will be described in more comprehensive and detailed form below in conjunction with the accompanying drawings and preferred embodiments. However, the protection scope of the present invention is not limited to the following specific embodiments.

[0042] Unless otherwise defined, all technical terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0043] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0044] The following reagents used in the present invention and tests were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China): cobalt nitrate hexahydrate (Co(NO₃)₂·6H₂O), nickel chloride hexahydrate (NiCl₂·6H₂O), 2-methylimidazole (C₅H₂N₂), methanol (C₄O), sodium hydroxide (NaOH), nitric acid (HNO₃), sulfuric acid (H₂SO₄), potassium chloride (KCl), and 5 wt.% Nafion (DuPont D520). All chemical reagents were of analytical grade and used without further purification. Deionized (DI) water was purified using a Millipore system.

[0045] Example 1

[0046] A Ni-based Co-MOF derivative x Co 3-x The preparation method of an O4 oxygen evolution catalyst comprises the following steps:

[0047] (1) Preparation of Co-MOF

[0048] First, 4.50 g of 2-methylimidazole and 2.00 g of cobalt nitrate hexahydrate were added to 160 mL and 100 mL of methanol, respectively, designated as Solution 1 and Solution 2. The mixture was then magnetically stirred until completely dissolved. While Solution 1 was continuously magnetically stirred at room temperature, Solution 2 was uniformly added dropwise to Solution 1, mixing the two. After stirring for 30 minutes, the mixture was sealed and allowed to stand for 12 hours. The supernatant was discarded, washed three times by centrifugation with methanol, and dried under vacuum at 60°C for 6 hours to obtain the Co MOF.

[0049] (2) Preparation of Co-Ni MOF

[0050] 0.35 g Co MOF was dispersed in 75 mL of ethanol / water mixed solution (ethanol-water volume ratio 4:1) containing 150 mg of nickel chloride hexahydrate and stirred at 50 °C for 20 min. The product was washed three times with pure water and ethanol by centrifugation and dried in vacuum at 60 °C for 6 h to obtain 8-Co-Ni MOF.

[0051] (3) Ni x Co 3-x Preparation of O4

[0052] Co-Ni MOF was heated in air at 5 °C·min -1 The temperature was raised to 200 °C and maintained for 2 h, and then heated at 5 °C·min -1 The temperature was raised to 350 °C at a rate of 100 °C and maintained for 2 h, and Ni x Co 3-x O4.

[0053] The difference between Examples 2-7 and Example 1 lies in the different amounts of nickel chloride hexahydrate added and the different annealing temperatures. For specific parameters, see Table 1.

[0054] Table 1: Addition amount of nickel chloride hexahydrate and annealing temperature in Examples 1-7

[0055]

[0056] By controlling the addition amount of nickel chloride hexahydrate, Examples 1-4 obtained final products with Ni atomic fractions of 4%, 6%, 8% and 10%, respectively, and named 4-Ni x Co 3-x O4、6-Ni x Co 3-x O4、8-Ni x Co 3-x O4 and 10-Ni x Co 3-x O4. By controlling the final annealing temperature at 300 ℃, 325 ℃, and 375 ℃, the catalyst products of the precursor 8-Co-Ni MOF at different temperatures were obtained and named 8-Ni x Co 3-x O4-300、8-Ni x Co 3-x O4-325 and 8-Ni x Co 3-x O4-375.

[0057] Performance testing

[0058] The precursor Co MOF prepared in the example was tested, and the SEM images at different magnifications were as follows: Figure 1 As shown, Figure 1 (a) is a SEM image at 50,000 times magnification. Figure 1 (b) is a SEM image at 30,000x magnification. As shown in the figure, the precursor Co MOF is shaped like nano-rhombic dodecahedrons, which are evenly distributed and uniform in size, with a relatively smooth surface and no obvious agglomeration.

[0059] Co MOF via Ni 2+ SEM images of the precursors 4-Co-Ni MOF, 6-Co-Ni MOF, 8-Co-Ni MOF and 10-Co-Ni MOF after ion exchange at 50,000 times, where Figure 2 (a) Figure 4 -Co-Ni MOF, Figure 2 (b) is 6-Co-Ni MOF, Figure 2 (c) is 8-Co-Ni MOF, Figure 2 (d) is 10-Co-Ni MOF. As shown in the figure, when Ni is exchanged 2+ At low Ni content, the nano-rhombic dodecahedral structure of Co MOF begins to dissolve and gradually transforms into nano-spherical particles. As the Ni content increases, the dodecahedral structure almost completely transforms into a nano-spherical structure and simultaneously begins to transform into a hexagonal nano-sheet structure. As the Ni content continues to increase, the hexagonal sheet structure begins to dissolve, forming a nano-rod-like structure.

[0060] 8-Ni prepared in Example 3 x Co 3-x The O4 catalyst was tested, and the SEM images at different magnifications were as follows Figure 3 As shown, Figure 3 (a) is a SEM image at 70,000 times magnification. Figure 3 (b) is a 100,000x SEM image. Figure 2 (c) Comparison shows that 8-Ni after annealing x Co 3-x O4 retains the hexagonal nanosheet structure of 8-Co-Ni MOF and obtains a rougher surface.

[0061] Figure 4 4-Ni prepared in Examples 1-2 and 4 x Co 3-x O4、6-Ni x Co 3-x O4 and 10-Ni x Co 3-x SEM image of O4, where Figure 4 (a) is 4-Co-Ni MOF, Figure 4 (b) is 6-Co-Ni MOF, Figure 4 (c) shows a 10-Co-Ni MOF. As shown in the figure, when the Ni content in the catalyst is low, the nanospheres aggregate to form a cellular structure. As the Ni content increases, the number of nanosheets increases, and the sheet-like structures stack. As the Ni content continues to increase, the formed nanosheets begin to dissolve, forming abundant ellipsoidal and rod-like structures.

[0062] 4-Ni prepared in Example 1-4 x Co 3-x O4、6-Ni x Co 3-x O4、8-Ni x Co 3-x O4、10-Ni x Co 3-x O4 was tested by EDS, and the spectrum was as follows Figure 5 As shown, it is confirmed that Ni x Co3-x The elemental composition of the O4 catalyst, when performing EDS analysis, the catalyst is loaded on a silicon substrate, which results in a strong silicon peak in the energy spectrum. Figure 5 (a) Figure 4 -Co-Ni MOF, Figure 5 (b) is 6-Co-NiMOF, Figure 5 (c) is 8-Co-Ni MOF, Figure 5 (d) is 10-Co-Ni MOF.

[0063] The Co MOF, Co-Ni MOF and Ni x Co 3-x O4 was tested by XRD, and the results were as follows Figure 6 As shown, Figure 6 (a) shows the XRD pattern of Co MOF and the simulated Co MOF pattern (ZIF-67, CCDC-671073) calculated using VESTA. As can be seen from the figure, the XRD pattern of the Co MOF in the present invention matches the simulated pattern well. The diffraction peaks at 7.37°, 10.43°, and 12.78° correspond to the (011), (002), and (112) crystal planes of the simulated Co-MOF (CCDC 671073), respectively. The above results indicate that the Co MOF with a rhombic dodecahedral structure was successfully synthesized. Figure 6 (b) is the Ni 2+ XRD spectra of the precursors 4-Co-Ni MOF, 6-Co-Ni MOF, 8-Co-Ni MOF and 10-Co-Ni MOF after ion exchange, and the comparative Co-MOF and computationally simulated Ni MOF (CCDC 1494751) spectra. It can be seen from the figure that, first, when the Ni content is low, the XRD spectrum of 4-Co-Ni MOF basically maintains the peak shape of Co MOF, and the diffraction peak intensities at 7.37°, 10.43° and 12.78° are all weakened to a certain extent. As the Ni content increases, the peak intensities of the three main peaks belonging to Co MOF gradually weaken, until no obvious Co MOF peak is observed in the XRD spectrum of 10-Co-Ni MOF. The diffraction peak at 11.84° in the simulated Ni MOF spectrum corresponds to the (200) crystal plane, while this diffraction peak shifts to 11.06°, 11.10°, and 11.20° in the XRD spectra of 6-Co-Ni MOF, 8-Co-Ni MOF, and 10-Co-Ni MOF, respectively. Figure 6(c) This is because the Ni ion radius (0.69 Å) is slightly larger than that of Co (0.65 Å). According to the Bragg equation, as the Ni content in the lattice increases, the lattice distorts and gradually expands, causing the diffraction peak to shift toward smaller angles. Simultaneously, with the addition of Ni ions, the Co-Ni MOF spectrum begins to exhibit amorphous diffuse scattering peaks, indicating a certain degree of amorphization. Figure 6 (d) is 4-Ni x Co 3-x O4、6-Ni x Co 3-x O4、8-Ni x Co 3-x O4、10-Ni x Co 3-x The XRD spectra of O4 were analyzed by jade software. The PDF cards with the best correspondence to the four XRD spectra were Co3O4 (JCPDS 43-1003), Co2NiO4 (JCPDS 02-1074) and Co 1.29 Ni 1.71 O4 (JCPDS 40-1191), the main peaks of the three PDF cards corresponding to the (311) crystal plane are located at 36.85°, 36.65° and 36.60° respectively. Correspondingly, because the 4-Co-Ni MOF precursor still basically maintains the peak shape of Co MOF, the 4-Ni x Co 3-x The main peak in the O4 spectrum is closer to the main peak of the Co3O4 card, while the 10-Ni x Co 3-x The main peak in the O4 spectrum and the Co 1.29 Ni 1.71 The main peak of the O4 card is closer, Figure 6 This change can be observed in the inset of (d), where the red and blue lines correspond to Co3O4 and Co 1.29 Ni 1.71 The main peak of the O4 card. At the same time, the spectra of the four samples are relatively close, and the degree of amorphization is high. The reason is that Ni x Co 3-x O4 is formed by annealing Co-Ni MOF with a high degree of amorphousness in air, and has a relatively low degree of crystallinity. Low crystallinity is conducive to exposing more catalytic active sites, accelerating the charge transfer between reaction intermediates and active sites to reduce electrochemical impedance and improve the activity per unit site.

[0064] In order to analyze 8-Ni x Co 3-x The microstructure and organization structure of O4 were tested by TEM. The results are as follows: Figure 7 As shown, from Figure 7(a) and 7(b) show that 8-Ni x Co 3-x The nanosheet structure of O4 presents a regular hexagonal structure and is formed by the combination of nanocrystals with a width of 5-10 nm. It has good uniformity. This highly dispersed nanoparticle is conducive to providing more catalytic active sites. x Co 3-x The regular hexagonal structure of the O4 nanosheet structure also confirms the view that the MOF-derived material in the present invention can retain the original MOF morphology, indicating that the morphology of the material does not collapse during the preparation process.

[0065] Figure 8 8-Ni x Co 3-x The full XPS spectrum of O4 and the high-resolution spectrum of Ni, Co, and O. Figure 8 8-Ni shown in (a) x Co 3- x The XPS full spectrum of O4 shows that the sample mainly contains Co, Ni, O and C elements, among which the C signal may come from the calibration C. Figure 8 (b) is the high-resolution spectrum of Ni element, where two spin-orbit peaks can be fitted near 855.4 and 872.3 eV, corresponding to Ni 2p 3 / 2 and Ni 2p 1 / 2 , where the peaks at binding energies of 853.8 and 872.1 eV are attributed to Ni 2+ , while the peaks at 855.5 and 874.1 eV are attributed to Ni 3+ The two peaks at 861.0 and 879.5 eV are Ni 2p 3 / 2 and Ni2p 1 / 2 Satellite peaks (labeled as Sat.). Figure 8 The Co 2p spectrum shown in (c) can also be fitted with two spin-orbit doublets, where the peaks at 780.5 eV and 795.5 eV correspond to the Co 2+ 2p 3 / 2 and 2p 1 / 2 , the peaks at 781.7 eV and 797.2 eV correspond to Co 3+ 2p 3 / 2 and 2p 1 / 2 , and the peak at 805.7 eV is Co 2p 1 / 2 characteristic satellite peaks. Figure 8(d) shows the high-resolution spectrum of O 1s, where the peak at 529.3 eV corresponds to the typical Metal-O binding energy, the peak at 531.1 eV corresponds to the vacancy oxygen binding energy, and the peak at 533.0 eV corresponds to the CO bond binding energy. 3+ and Ni 3+ The valence electrons of 8-Ni are more abundant than those of low valence states, and their presence endows the prepared nanostructure with excellent catalytic activity in OER. x Co 3-x The surface chemical state of O4 is mainly Co 2+ 、Co 3+ 、Ni 2+ and Ni 3+ The existence of various Co / Ni nodes with different metal valence states promotes the synergistic effect of the bimetallic structure, thereby effectively improving the performance of 8-Ni x Co 3- x Electrocatalytic performance of O4.

[0066] To evaluate the OER performance of the catalyst, a standard three-electrode system was used to conduct the OER of a series of Ni x Co 3-x The O4 catalyst was electrochemically tested.

[0067] The electrochemical test method is as follows:

[0068] All electrochemical tests were performed in a standard three-electrode system on a CHI660B electrochemical workstation at 25 °C with a 1 mol·L -1 The reaction was carried out in KOH solution. A commercial glassy carbon electrode (GCE, with a bottom diameter of 6 mm and a central effective area diameter of 3 mm) was used as the modified electrode to load the catalyst as the working electrode, a saturated calomel electrode (SCE), and a graphite electrode as the reference electrode and counter electrode, respectively.

[0069] The working electrode preparation process is as follows: 8 mg of catalyst powder is mixed with 80 μL of 5 wt.% Nafion, 460 μL of anhydrous ethanol, and 460 μL of deionized water. The mixture is then sonicated in a cold water bath for 1 h to obtain a uniform ink. Subsequently, the ink is evenly applied to the GCE surface, placed horizontally under an infrared lamp, and dried for 3-5 minutes before measurement. A glassy carbon electrode is used as the working electrode, with a surface catalyst loading of 1 mg cm -2 .

[0070] At 10 mA cm -2 The overpotential of was used as the evaluation standard for oxygen evolution catalytic activity. Figure 9 As shown. Figure 9(a) shows the anodic polarization curve of 8-Ni x Co 3-x The overpotential of O4 is only 320 mV, slightly lower than that of 4-Ni x Co 3-x O4 (331 mV), 6-Ni x Co 3-x O4 (321 mV), 10-Ni x Co 3-x O4 (329 mV) at the same current density; when the current density increases, 8-Ni x Co 3-x O4 only requires an overpotential of 391 mV to reach 50 mA cm -2 The current density is significantly better than that of 4-Ni x Co 3-x O4 (430 mV), 6-Ni x Co 3-x O4 (408 mV) and 10-Ni x Co 3-x O4 (413 mV). Combined with the above results, it can be inferred that when the Ni atomic ratio is 8%, the synergistic effect between Ni and Co atoms maximizes the catalyst's OER activity gain, thereby enhancing the catalyst's intrinsic catalytic activity. Combined with the SEM results, when the Ni content is low, the catalyst surface appears as irregular spheres and flakes. At higher Ni content, the formed nanosheet structure begins to dissolve. It can be inferred that the regular hexagonal nanosheet morphology possesses more active sites, which is beneficial for OER performance. Figure 9 (b) is the Tafel slope diagram obtained by fitting the polarization curve, 8-Ni x Co 3-x The Tafel slope of O4 is only 61.5 mV·dec -1 , should be lower than 4-Ni x Co 3-x O4 (74.4 mV·dec -1 )、6-Ni x Co 3-x O4 (67.0 mV·dec -1 ) and 10-Ni x Co 3-x O4 (70.3 mV·dec -1 ), indicating that the Ni prepared by the present invention x Co 3-x O4 catalyst has excellent OER kinetics, while 8-Ni x Co 3-x O4 has the best performance.

[0071] The catalyst products prepared from the same precursor 8-Co-Ni MOF prepared in Examples 5-7 at different annealing temperatures were tested, and the anodic polarization curves thereof are shown in FIG. Figure 10 As shown, at the same current density (10 mA cm -2 ), 8-Ni x Co 3-x O4-350 has the lowest overpotential (320 mV), which is better than 8-Ni x Co 3-x O4-300 (330 mV), 8-Ni x Co 3-x O4-325 (327mV), 8-Ni x Co 3-x Performance of O4-375 (333 mV).

[0072] The 8-Ni prepared in Example 3 x Co 3-x O4 catalyst was loaded onto nickel foam and nickel felt to prepare working electrodes, and their oxygen evolution performance was tested.

[0073] The electrochemical test method is as follows:

[0074] All electrochemical tests were performed in a standard three-electrode system on a CHI660B electrochemical workstation at 25 °C with a 1 mol·L -1 The reaction was carried out in KOH solution. Nickel foam and nickel felt were used as modified electrodes to load catalysts as working electrodes, saturated calomel electrode (SCE) and graphite electrode were used as reference electrode and counter electrode, respectively.

[0075] The working electrode preparation process is as follows: 8 mg of catalyst powder is mixed with 80 μL 5 wt.% Nafion, 460 μL anhydrous ethanol and 460 μL deionized water. The mixture is then ultrasonicated in a cold water bath for 1 h to obtain a uniform ink. Subsequently, the ink is evenly applied to nickel foam or nickel felt, placed horizontally under an infrared lamp, and measured after drying for 3-5 min. Among them, the pretreatment steps of the nickel foam / nickel felt substrate are: cutting the substrate into a size of 1 cm*1 cm and reserving a 0.5 cm*1 cm tab, followed by ultrasonic washing with acetone, hydrochloric acid, and deionized water for 15 min, and then vacuum drying at 60 °C and storing for later use. Referring to the loading amount of non-precious metals in the AEM electrolytic cell, the catalyst loading on the surface of nickel foam / nickel felt is 2 mg·cm -2 .

[0076] The test results are as follows Figure 11 As shown, 8-Ni x Co 3-x O4 / Foam Nickel and 8-Nix Co 3-x O4 / nickel felt at 10 mA cm -2 The overpotentials at these current densities were 231 and 243 mV, respectively, significantly improving performance compared to that achieved on glassy carbon electrodes. This is due to the larger surface area of ​​the nickel foam and nickel felt substrates, which increases the contact area between the catalyst powder and the electrolyte, exposing more active sites and improving oxygen evolution efficiency. This is also due to the increased catalyst loading.

[0077] 4-Ni prepared in Example x Co 3-x O4、6-Ni x Co 3-x O4 and 10-Ni x Co 3-x O48-Ni x Co 3-x O4 was detected at a constant current density of 10 mA·cm -2 The long-term electrolysis curve under the condition of CV acceleration decay and the comparative polarization curve before and after 5000 cycles are shown in the figure. Figure 12 and 13 shown.

[0078] like Figure 12 As shown, 8-Ni x Co 3-x After 32 h of constant current electrolysis, the overpotential decay rate of the O4 catalyst was only about 1.2%, and the electrolysis curve was relatively stable. After 5000 CV cycles of aging, its polarization curve was compared with the initial polarization curve at 10 mA·cm -2 The overpotential change at 50 mA·cm -2 The potential decay rate at is only 0.8%. Figure 13 As shown, after 32 h of constant current electrolysis, Figure 13 (a)4-Ni x Co 3-x The O4 overpotential decay rate is about 2.7%; after 32 h of constant current electrolysis, Figure 13 (b)6-Ni x Co 3-x The overpotential decay rate of O4 is about 2.0%; after 32 h of constant current electrolysis, Figure 13 (c)10-Ni x Co 3-x The O4 overpotential decay rate is about 2.9%. The above results show that the electrochemical oxygen evolution stability of the catalyst prepared in the present invention is good, and the 8-Ni x Co 3-x O4 is the best.

[0079] The above is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. For those skilled in the art to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, and all of these should be considered to fall within the scope of protection of the present invention.

Claims

1. A Ni based on Co-MOF derivative x Co 3-x The preparation method of O4 oxygen evolution catalyst is characterized in that: The following steps are involved: S1. Add 2-methylimidazole and cobalt salt to a solvent, stir the reaction, let it stand, centrifuge, wash, and dry to obtain a nano-rhombus precursor Co-MOF; S2, dispersing the Co-MOF obtained in step S1 into a solution containing a nickel source, stirring the reaction at 40-60° C., centrifuging, washing, and drying to obtain Co-Ni MOF; S3. Slowly heat up the Co-Ni MOF obtained in step S2 in an air atmosphere to maintain the morphology of the Co-MOF in step S1, and then slowly heat up to 300 - 375 °C. After cooling, Ni x Co 3-x O4 oxygen evolution catalyst; wherein, 0 < x < 3, the Ni x Co 3-x In the O4 oxygen evolution catalyst, the atomic fraction of Ni is 4% - 10%.

2. Ni based on Co-MOF derivatives according to claim 1 x Co 3-x The preparation method of O4 oxygen evolution catalyst is characterized in that: In step S3, Ni x Co 3-x The atomic fraction of Ni in the O4 oxygen evolution catalyst is 8%.

3. Ni based on Co-MOF derivatives according to claim 1 x Co 3-x The preparation method of O4 oxygen evolution catalyst is characterized in that: In step S3, the temperature is raised to 350° C. for reaction, and the reaction time is >5 h.

4. Ni based on Co-MOF derivatives according to claim 1 x Co 3-x The preparation method of O4 oxygen evolution catalyst is characterized in that: In step S1, 2-methylimidazole and cobalt salt are added to a methanol solution respectively, and the methanol solution containing the cobalt salt is dripped into the methanol solution containing 2-methylimidazole at a uniform speed while stirring.

5. Ni based on Co-MOF derivatives according to claim 1 x Co 3-x The preparation method of O4 oxygen evolution catalyst is characterized in that: In step S2, the nickel source is dissolved in a mixed solution of ethanol and water, with the volume ratio of ethanol to water being 4:

1.

6. Ni based on Co-MOF derivative according to claim 1 x Co 3-x The preparation method of O4 oxygen evolution catalyst is characterized in that: In step S2, the stirring time is 10-30 min.

7. Ni based on Co-MOF derivatives according to claim 1 x Co 3-x The preparation method of O4 oxygen evolution catalyst is characterized in that: The drying temperature in step S1 and step S2 is 50-60°C.

8. The Ni based Co-MOF derivative according to claim 1 x Co 3-x The preparation method of O4 oxygen evolution catalyst is characterized in that: In step S3, the heating rate is 5°C·min -1 .

9. Ni based on Co-MOF derivatives according to any one of claims 1 to 8 x Co 3-x Ni prepared by the preparation method of O4 oxygen evolution catalyst x Co 3-x O4 oxygen evolution catalyst.

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