A Co3O4@IrO x Catalysts, preparation methods and applications

Abstract

This invention discloses a Co3O4@IrO x This invention relates to the catalyst, its preparation method, and its application, belonging to the technical field of catalyst materials for hydrogen production through water electrolysis. The Co3O4@IrO catalyst... x The catalyst was prepared as follows: ZIF-67 was used as the core, and quaternary ammonium salt surfactants and imidazole organic ligands were added. The ZIF-67@ZIF-8 core-shell material was obtained by reacting it with a zinc source. This material was then coated onto carbon paper to obtain ZIF-67@ZIF-8 electrode sheets. Pyrolysis yielded Co3O4@defective ZIF-8 electrode sheets. Using a standard three-electrode system, with the Co3O4@defective ZIF-8 electrode sheet as the working electrode, pulse potential etching was performed in potassium hydroxide solution to obtain Co3O4@vacancy-type ZIF-8 electrode sheets. Electrochemical deposition was then performed in iridium-containing potassium hydroxide solution to obtain Co3O4@IrO3. x Catalyst. Co3O4@IrO x The catalyst has excellent hydrogen production capacity through water electrolysis.

Description

Technical Field

[0001] This invention relates to the field of catalyst materials for hydrogen production through water electrolysis, and more specifically to a Co3O4@IrO catalyst. x Catalysts, their preparation methods, and applications. Background Technology

[0002] Electrolysis of water is the only zero-carbon emission method for hydrogen production, which can solve the problem of intermittent wind and solar power generation, enabling continuous and stable long-term energy storage. The oxygen evolution reaction in water electrolysis, due to its higher overpotential, is the main source of energy consumption. Therefore, synthesizing higher-performance catalytic materials to reduce the overpotential of the oxygen evolution reaction can significantly reduce the energy consumption of water electrolysis for hydrogen production, thereby improving the efficiency of industrial production.

[0003] Proton exchange membrane electrolyzers are a commonly used type of electrolyzer in oxygen evolution reactions (OER), offering lower OER overpotentials. However, they typically rely on materials such as IrO2 and RuO2, with Ir's 5d... 7 Its electronic configuration places the d-band center at a suitable position, balancing the adsorption strengths of reaction intermediates *OH, *O, and *OOH, avoiding excessively strong or weak adsorption. Furthermore, the electronic structure of IrO2 allows it to stabilize the high-valence state of Ir during the oxygen evolution reaction. 4+ / Ir 5+ This provides active sites for the reaction. However, the reliance on precious metal materials makes the catalyst expensive, which is currently a bottleneck in water electrolysis.

[0004] To address this challenge, reducing Ir dosage and improving catalytic efficiency are of significant research value. Current common methods, such as single-atom dispersion, have high matching requirements for Ir anchoring on supports like Co3O4 and NC, and involve complex post-processing procedures such as acid washing and electrochemical activation. This can easily lead to cluster formation, resulting in a narrow process window and poor reproducibility. Alloying Ir with transition metals such as Co and Ni can improve atom utilization, but it also presents challenges such as separation difficulties and uncontrollable particle size. Non-precious metal doping suffers from low current density applicability, compositional inhomogeneity, and low long-cycle stability. Therefore, there is a lack of a simple, easy-to-implement, and scalable method for preparing Ir-doped oxygen evolution electrocatalysts. Summary of the Invention

[0005] To address the above problems, this invention provides a Co3O4@IrO x Catalyst, preparation method and application: Co3O4@IrO prepared by this invention x The catalyst has excellent hydrogen production capacity through water electrolysis.

[0006] The first objective of this invention is to provide a Co3O4@IrO xThe method for preparing the catalyst includes the following steps:

[0007] Using ZIF-67 as the core, a quaternary ammonium salt surfactant and an imidazole organic ligand were added to coordinate with a zinc source to prepare ZIF-67@ZIF-8 core-shell material.

[0008] During the reaction, ZIF-67 serves as the core, and the quaternary ammonium salt surfactant can control the morphology of the nanoparticles, modify the surface of ZIF-67, reduce its interfacial energy with imidazole organic ligands, promote the uniform nucleation and growth of ZIF-8, and at the same time alleviate the lattice mismatch problem between ZIF-67 and ZIF-8. The generated ZIF-8 serves as the shell, forming a ZIF-67@ZIF-8 core-shell material.

[0009] ZIF-67@ZIF-8 electrode sheets were prepared by coating ZIF-67@ZIF-8 core-shell material onto carbon paper.

[0010] In an air atmosphere, ZIF-67@ZIF-8 electrode sheets are pyrolyzed at 300℃~400℃. During pyrolysis, ZIF-67 collapses into Co3O4, resulting in Co3O4@defect-type ZIF-8 electrode sheets. Specifically, during pyrolysis, ZIF-67 is unstable, and the dodecahedral structure collapses first, being oxidized to Co3O4. The ZIF-8 core-shell material framework remains intact, with some Zn being oxidized, forming defects on the dodecahedral surface. The ZIF-67@ZIF-8 core-shell material is transformed into Co3O4@defect-type ZIF-8.

[0011] A standard three-electrode system was used, with a carbon rod as the counter electrode, an Hg / HgO electrode as the reference electrode, and a Co3O4@defective ZIF-8 electrode sheet as the working electrode. The Co3O4@defective ZIF-8 electrode sheet was subjected to pulsed potential etching in potassium hydroxide solution. During the pulsed potential etching process, zinc ions on the surface of the defective ZIF-8 were etched out into the solution, resulting in a Co3O4@vacancy-type ZIF-8 electrode sheet.

[0012] A standard three-electrode system was used, with a carbon rod as the counter electrode, an Hg / HgO electrode as the reference electrode, and a Co3O4@defect-type ZIF-8 electrode as the working electrode. Iridium was deposited onto the zinc ion vacancies of the Co3O4@vacancy-type ZIF-8 electrode in an iridium-containing potassium hydroxide solution via electrochemical deposition, resulting in a Co3O4@Ir-deposited ZIF-8 electrode, which is the Co3O4@IrO electrode required in this invention. x catalyst.

[0013] In a preferred embodiment of the present invention, during the pulsed potential etching process, short pulses of cathode potential and short pulses of anode potential are repeated. The cathode potential is -2V and the time is 1s~2s; the anode potential is 2V and the time is 1s~2s. This process is repeated 150 times to form one activation cycle.

[0014] The activation cycle is 3 to 4 times.

[0015] In a preferred embodiment of the present invention, during the electrochemical deposition process, short pulses of cathode potential and short pulses of anode potential are repeated. The cathode potential is -6V and the duration is 1s to 2s; the anode potential is 6V and the duration is 1s to 2s. This process is repeated 500 times to form one activation cycle.

[0016] The activation cycle is 5 to 10 times.

[0017] In a preferred embodiment of the present invention, the concentration of iridium in the potassium hydroxide solution containing iridium is 100 μmol / L.

[0018] In a preferred embodiment of the present invention, the pyrolysis time is 0.5 h.

[0019] In a preferred embodiment of the present invention, the mass ratio of quaternary ammonium salt surfactant to imidazole organic ligand is 15:1135~1136.

[0020] The mass ratio of quaternary ammonium salt surfactant to zinc source is 15:72~73.

[0021] In a preferred embodiment of the present invention, the ratio of ZIF-67 to quaternary ammonium salt surfactant is 6.9~7.4:15.

[0022] In a preferred embodiment of the present invention, the quaternary ammonium salt surfactant is hexadecyltrimethylammonium bromide and the imidazole organic ligand is 2-methylimidazole.

[0023] A second objective of this invention is to provide Co3O4@IrO prepared by the above-described preparation method. x catalyst.

[0024] A third objective of this invention is to provide the aforementioned Co3O4@IrO x Application of catalysts in oxygen evolution electrocatalysis.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The Co3O4@Ir deposited ZIF-8 material prepared by the method of this invention exhibits excellent catalytic performance in the oxygen evolution reaction, demonstrating low overpotential and outstanding cycling stability. It maintains good redox performance and energy storage capacity during long-term electrochemical reactions exceeding 1500 hours. Its performance is significantly superior to traditional noble metal catalysts and single metal oxides. This material achieves triple synergistic catalytic enhancement by anchoring atomically dispersed Ir active centers onto a nitrogen-doped porous carbon framework derived from ZIF-8 and forming a strong coupling interface with Co3O4 nanoparticles: the ZIF-67@ZIF-8 synthesized by this method itself has a high specific surface area; further, air calcination forms Co3O4@defective ZIF-8, introducing defects to enhance conductivity; and subsequent pulse activation etches Zn atoms from their intrinsic hexahedral organic framework, creating further defects in the original 3D ordered porous structure without collapsing the hexahedral structure. This defective structure not only provides abundant active sites but also significantly enhances electron transfer efficiency. Furthermore, the Co3O4 formed by the collapse of ZIF-67 is rich in Co. 2+ / Co 3+ Redox pairs can serve as active sites in the proton-electron transfer process of the oxygen evolution reaction (OER). By anchoring Ir atoms onto a ZIF-8-derived porous carbon matrix, the utilization rate of Ir is significantly improved, the dosage is reduced, the OER reaction kinetics are accelerated, and the catalytic activity of the material is greatly enhanced.

[0027] Furthermore, the preparation method of the present invention is simple to operate, has low equipment requirements, and the operation process is highly controllable. A high-performance oxygen evolution reaction catalyst can be obtained with a relatively small amount of Ir doping required, which is very suitable for large-scale production and has significant value. Attached Figure Description

[0028] Figure 1 This is a field emission scanning electron microscope image of ZIF-67@ZIF-8 synthesized in Example 1 of this invention.

[0029] Figure 2 This is a field emission scanning electron microscope image of ZIF-67@ZIF-8 synthesized in Example 2 of this invention.

[0030] Figure 3 This is a field emission scanning electron microscope image of ZIF-67@ZIF-8 synthesized in Example 3 of this invention.

[0031] Figure 4 This is a real-energy filtered transmission electron microscope image of ZIF-67@ZIF-8 synthesized in Example 1 of this invention.

[0032] Figure 5This is a field emission scanning electron microscope image of ZIF-67@ZIF-8 synthesized in Example 1 of this invention after calcination at 350°C in air.

[0033] Figure 6 These are the ZIF-67@ZIF-8 raw materials synthesized in Example 1 of this invention and their powder X-ray diffraction patterns after electrochemical etching and electrochemical deposition, respectively.

[0034] Figure 7 The X-ray photoelectron spectra of cobalt in the Co3O4@defect type ZIF-8, Co3O4@vacancy type ZIF-8, and Co3O4@Ir deposition type ZIF-8 synthesized in Example 1 of this invention are shown.

[0035] Figure 8 The X-ray photoelectron spectra of zinc in Co3O4@defective ZIF-8, Co3O4@vacancy ZIF-8, and Co3O4@Ir deposition ZIF-8 synthesized in Example 1 of this invention are shown.

[0036] Figure 9 The X-ray photoelectron spectra of iridium in Co3O4@defect type ZIF-8, Co3O4@vacancy type ZIF-8, and Co3O4@Ir deposition type ZIF-8 synthesized in Example 1 of this invention are shown.

[0037] Figure 10 The image shows the inductively coupled plasma (ICP) detection results of three electrodes: the etching solution for the Co3O4@defect type ZIF-8 electrode, the deposition solution for the Co3O4@Ir type ZIF-8 electrode, and the Co3O4@Ir type ZIF-8 electrode.

[0038] Figure 11 This is a transmission electron microscope image of the core-shell surface of the Co3O4@Ir deposited ZIF-8 synthesized in Example 1 of this invention at 0 nm defocus.

[0039] Figure 12 This is a transmission electron microscope image of the core-shell interior of the Co3O4@Ir deposited ZIF-8 synthesized in Example 1 of this invention at a defocused wavelength of 58 nm.

[0040] Figure 13 This is an electrochemical active surface area diagram of the three types of ZIF-8 synthesized in Example 1 of this invention: Co3O4@defective ZIF-8, Co3O4@vacancy ZIF-8, and Co3O4@Ir deposition ZIF-8.

[0041] Figure 14This is a linear sweep voltammetry curve of Co3O4@defect type ZIF-8, Co3O4@vacancy type ZIF-8, Co3O4@Ir deposition type ZIF-8 synthesized in Example 1 of this invention, Co3O4@Ir deposition type ZIF-8-2 synthesized in Example 2, and Co3O4@Ir deposition type ZIF-8-3 synthesized in Example 3.

[0042] Figure 15 This is a Tafel slope diagram of Co3O4@defect type ZIF-8, Co3O4@vacancy type ZIF-8, Co3O4@Ir deposition type ZIF-8 synthesized in Example 1 of this invention, Co3O4@Ir deposition type ZIF-8-2 synthesized in Example 2, and Co3O4@Ir deposition type ZIF-8-3 synthesized in Example 3.

[0043] Figure 16 This is a constant potential long-cycle test diagram of the Co3O4@Ir deposition type ZIF-8 synthesized in Example 1 of this invention. Detailed Implementation

[0044] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0045] Under alkaline conditions, the equilibrium potential of the oxygen evolution reaction (OER) is approximately 0.401 V relative to the reversible hydrogen electrode, while under acidic conditions, it is approximately 1.23 V. The alkaline condition provides a lower equilibrium potential for OER and offers a higher concentration of OH⁻ directly participating in the rate-determining step of the OER reaction, which is beneficial for the reaction. However, in an alkaline environment, higher requirements are placed on the chemical stability of the catalyst, such as its resistance to oxidation and alkaline corrosion. Furthermore, the alkaline OER reaction involves OH⁻ adsorption or H₂O dissociation, resulting in a higher energy barrier and requiring a catalyst with high intrinsic activity. Therefore, this invention utilizes Co₃O₄@IrO₂. x The catalyst has a high specific surface area. Defects are introduced through calcination, which enriches the active sites. Furthermore, the atomic dispersion doping of Ir achieves economical and efficient oxygen evolution catalysis.

[0046] In this invention, unless otherwise specified, all raw materials used are commercially available products in the art, and all operations are performed at room temperature.

[0047] Example 1

[0048] This embodiment provides a Co3O4@IrO x The specific steps for preparing the catalyst are as follows:

[0049] Step 1: Weigh 11.75 mg of cobalt nitrate hexahydrate and 27.5 mg of 2-methylimidazole into two beakers, respectively, according to a molar ratio of 1:8.3. Add 1 ml of methanol to each beaker and sonicate for 10 min to fully dissolve and disperse. Then mix the two solutions and transfer them to a magnetic stirrer at 500 rpm for 3 h. After the reaction time is complete, centrifuge the mixture at 5000 rpm for 10 min to obtain 7.2 mg of ZIF-67. Sonicate this solution in 3 ml of fresh methanol and label it as solution 1 for later use.

[0050] Dissolve 15 mg of cetyltrimethylammonium bromide in 1 ml of methanol and 1135.03 mg of 2-methylimidazole in 17.5 ml of methanol. Sonicate each solution for 10 min and then mix them. Stir magnetically at 500 rpm for 20 min. Label this solution as the second solution and set aside for later use.

[0051] Dissolve 72.5 mg of zinc nitrate hexahydrate in 2.5 ml of methanol by sonication for 10 min, and label it as the third solution.

[0052] Step 2: Take the first solution into a 100ml reaction vessel, sonicate for 3 minutes, then pour the second solution into the sonicated first solution, continue sonicating for 5 minutes, pour in the third solution, and continue sonicating for 5 minutes. Then close the reaction vessel and let it stand at room temperature for 24 hours. After the reaction, separate the products by centrifugation at 5000 rpm for 3 minutes. Wash the obtained products with methanol. Sonicate the products for 5 minutes to disperse them in methanol solution, then centrifuge at 5000 rpm for 3 minutes. Repeat this process three times. After the final product is separated, dry it under vacuum at 80℃ for 12 hours. After drying, allow it to cool naturally to room temperature, then remove the dried sample and grind it in an agate grinding mortar for 15 minutes to obtain ZIF-67@ZIF-8 core-shell material.

[0053] Step 3: Weigh 0.3 mg of ZIF-67@ZIF-8 core-shell material and dissolve it in 0.5 ml of ethanol using ultrasonication. Then, drop the solution onto carbon paper that has been ultrasonically cleaned with ethanol. The carbon paper should be 0.5 × 0.5 cm in size. After drying with an infrared lamp, ZIF-67@ZIF-8 electrode sheets are obtained.

[0054] The ZIF-67@ZIF-8 electrode sheets were placed inside a quartz boat, which was then placed in a tube furnace for pyrolysis in air. The pyrolysis temperature was 350℃, and the heating rate was 5℃·min.-1 After maintaining a constant temperature of 350℃ for 0.5 hours, the electrode was naturally cooled to obtain a Co3O4@defect type ZIF-8 electrode sheet.

[0055] Step 4: Using a standard three-electrode system, a carbon rod is used as the counter electrode, an Hg / HgO electrode as the reference electrode, and the Co3O4@defective ZIF-8 electrode sheet prepared above is used as the working electrode. The Co3O4@defective ZIF-8 working electrode is activated by pulsed potential in a 1 mol / L potassium hydroxide solution. During the pulsed potential activation process, the cathode potential is -2V for 1 s, and the anode potential is 2V for 1 s. This short cathode potential pulse followed by the anode potential is repeated 150 times for 300 s. This activation process is repeated 4 times, and the total holding time for oxidation and reduction activation is 1200 s. This process is used to activate Zn. 2+ Ions are etched from the organic ligands on 2-methylimidazole, further creating defects in the organic framework, resulting in Co3O4@vacancy type ZIF-8.

[0056] Step 5: Replace with a fresh 1M potassium hydroxide solution and add 100 μmol / L IrCl4·H2O. Perform electrochemical deposition in the same three-electrode system. The cathode potential is -6V for 1 s, and the anode potential is 6V for 1 s. Repeat the short pulse at the anode potential 500 times for 1000 s. Repeat this deposition process 10 times. The total holding time for oxidation and reduction activation is 10000 s. This deposits Ir ions onto the vacancies of Co3O4@vacancy-type ZIF-8, completing the electrochemical atomic exchange between Zn and Ir in the MOF material, resulting in a Co3O4@Ir deposition-type ZIF-8 electrode, i.e., Co3O4@IrO. x catalyst.

[0057] Example 2

[0058] This embodiment provides a Co3O4@IrO x The specific steps for preparing the catalyst are as follows:

[0059] Step 1: Weigh 11.3 mg of cobalt nitrate hexahydrate and 28 mg of 2-methylimidazole into two beakers, respectively, according to a molar ratio of 1:8.8. Add 1 ml of methanol to each beaker and sonicate for 10 min to fully dissolve and disperse. Then mix the two solutions and transfer them to a magnetic stirrer at 500 rpm for 3 h. After the reaction time is complete, centrifuge the mixture at 5000 rpm for 10 min to obtain 6.93 mg of ZIF-67. Sonicate this solution into 3 ml of fresh methanol and label it as solution 1 for later use.

[0060] Dissolve 15 mg of cetyltrimethylammonium bromide in 1 ml of methanol and 1135 mg of 2-methylimidazole in 17.5 ml of methanol. Sonicate each solution for 10 min and then mix them together. Stir magnetically at 500 rpm for 20 min. Label this solution as the second solution and set aside for later use.

[0061] Dissolve 72 mg of zinc nitrate hexahydrate in 2.5 ml of methanol by sonication for 10 min, and label it as the third solution.

[0062] Step 2: Take the first solution into a 100ml reaction vessel, sonicate for 3 minutes, then pour the second solution into the sonicated first solution, continue sonicating for 5 minutes, pour in the third solution, and continue sonicating for 5 minutes. Then close the reaction vessel and let it stand at room temperature for 26 hours. After the reaction, separate the products by centrifugation at 5000 rpm for 3 minutes. Wash the obtained products with methanol. Sonicate the products for 5 minutes to disperse them in methanol solution, then centrifuge at 5000 rpm for 3 minutes. Repeat this process three times. After the final product is separated, dry it under vacuum at 80℃ for 12 hours. After drying, allow it to cool naturally to room temperature, then remove the dried sample and grind it in an agate grinding mortar for 15 minutes to obtain ZIF-67@ZIF-8 core-shell material.

[0063] Step 3: Weigh 0.3 mg of ZIF-67@ZIF-8 core-shell material and dissolve it in 0.5 ml of ethanol using ultrasonication. Then, drop the solution onto carbon paper that has been ultrasonically cleaned with ethanol. The carbon paper should be 0.5 × 0.5 cm in size. After drying with an infrared lamp, ZIF-67@ZIF-8 electrode sheets are obtained.

[0064] The ZIF-67@ZIF-8 electrode sheets were placed inside a quartz boat, which was then placed in a tube furnace for pyrolysis in air. The pyrolysis temperature was 400℃, and the heating rate was 5℃·min. -1 After maintaining a constant temperature of 400℃ for 0.5 hours, the electrode was naturally cooled to obtain a Co3O4@defect type ZIF-8-2 electrode sheet.

[0065] Step 4: Using a standard three-electrode system, a carbon rod is used as the counter electrode, an Hg / HgO electrode as the reference electrode, and the Co3O4@defective ZIF-8 electrode sheet prepared above is used as the working electrode. The Co3O4@defective ZIF-8 working electrode is activated by pulse potential in a 1 mol / L potassium hydroxide solution. During the pulse potential activation process, the cathode potential is -2V for 2 seconds, and the anode potential is 2V for 2 seconds. This is repeated 150 times with short cathode potential pulses immediately following the anode potential, for a total duration of 600 seconds. This activation process is repeated 3 times. The total holding time for oxidation and reduction activation is 1800 seconds. This process is used to activate Zn... 2+Ions are etched from the organic ligands on 2-methylimidazole, further creating defects in the organic framework, resulting in Co3O4@vacancy type ZIF-8.

[0066] Step 5: Replace with a fresh 1M potassium hydroxide solution and add 100 μmol / L IrCl4·H2O. Perform electrochemical deposition in the same three-electrode system. The cathode potential is -6V for 2 s, and the anode potential is 6V for 2 s. Repeat the short pulse at the cathode potential followed by the anode potential 50 times for 200 s. Repeat this deposition process 8 times. The total holding time for oxidation activation and reduction activation is 1600 s. In this way, Ir ions are deposited onto the vacancies of Co3O4@vacancy-type ZIF-8, completing the electrochemical atomic exchange between Zn and Ir in the MOF material, and obtaining the Co3O4@Ir deposition-type ZIF-8-2 electrode, i.e., Co3O4@IrO. x catalyst.

[0067] Example 3

[0068] This embodiment provides a Co3O4@IrO x The specific steps for preparing the catalyst are as follows:

[0069] Step 1: Weigh 12 mg of cobalt nitrate hexahydrate and 27.3 mg of 2-methylimidazole into two beakers according to a molar ratio of 1:8.1. Add 1 ml of methanol to each beaker and sonicate for 10 min to fully dissolve and disperse. Then mix the two and transfer them to a magnetic stirrer at 500 rpm for 3 h. After the reaction time is complete, centrifuge the mixture at 5000 rpm for 10 min to obtain 7.36 mg of ZIF-67. Sonicate this solution into 3 ml of fresh methanol and label it as solution 1 for later use.

[0070] Dissolve 15 mg of cetyltrimethylammonium bromide in 1 ml of methanol and 1136 mg of 2-methylimidazole in 17.5 ml of methanol. Sonicate each solution for 10 min to dissolve them, then mix them together. Stir magnetically at 500 rpm for 20 min. Label this solution as the second solution and set aside for later use.

[0071] Dissolve 73 mg of zinc nitrate hexahydrate in 2.5 ml of methanol by sonication for 10 min, and label it as the third solution.

[0072] Step 2: Take the first solution into a 100ml reaction vessel, sonicate for 3 minutes, then pour the second solution into the sonicated first solution, continue sonicating for 5 minutes, pour in the third solution, and continue sonicating for 5 minutes. Then close the reaction vessel and let it stand at room temperature for 22 hours. After the reaction, separate the products by centrifugation at 5000 rpm for 3 minutes. Wash the obtained products with methanol. Sonicate the products for 5 minutes to disperse them in methanol solution, then centrifuge at 5000 rpm for 3 minutes. Repeat this process three times. After the final product is separated, dry it under vacuum at 80℃ for 12 hours. After drying, allow it to cool naturally to room temperature, then remove the dried sample and grind it in an agate grinding mortar for 15 minutes to obtain ZIF-67@ZIF-8 core-shell material.

[0073] Step 3: Weigh 0.3 mg of ZIF-67@ZIF-8 core-shell material and dissolve it in 0.5 ml of ethanol using ultrasonication. Then, drop the solution onto carbon paper that has been ultrasonically cleaned with ethanol. The carbon paper should be 0.5 × 0.5 cm in size. After drying with an infrared lamp, ZIF-67@ZIF-8 electrode sheets are obtained.

[0074] The ZIF-67@ZIF-8 electrode sheets were placed inside a quartz boat, which was then placed in a tube furnace for pyrolysis in air. The pyrolysis temperature was 300℃, and the heating rate was 5℃·min. -1 After maintaining a constant temperature of 300℃ for 0.5 hours, the electrode was naturally cooled to obtain a Co3O4@defect type ZIF-8 electrode sheet.

[0075] Step 4: Using a standard three-electrode system, a carbon rod is used as the counter electrode, an Hg / HgO electrode as the reference electrode, and the Co3O4@defective ZIF-8 electrode sheet prepared above as the working electrode. The Co3O4@defective ZIF-8 working electrode is activated by pulsed potential in a 1 mol / L potassium hydroxide solution. During the pulsed potential activation process, the cathode potential is -2V for 1 s, and the anode potential is 2V for 1 s. This short cathode potential pulse followed by the anode potential is repeated 150 times for 300 s. This activation process is repeated 5 times, and the total holding time for oxidation and reduction activation is 1500 s. This process is used to activate Zn. 2+ Ions are etched from the organic ligands on 2-methylimidazole, further creating defects in the organic framework, resulting in Co3O4@vacancy type ZIF-8.

[0076] Step 5: Replace with a fresh 1M potassium hydroxide solution and add 100 μmol / L IrCl4·H2O. Perform electrochemical deposition using the same three-electrode system. The cathode potential is -6V for 1 s, and the anode potential is 6V for 1 s. Repeat the short cathode potential pulse immediately following the anode potential 150 times, for a total duration of 300 s. Repeat this deposition process 5 times. The total holding time for oxidation and reduction activation is 1500 s. This deposits Ir ions onto the vacancies of Co3O4@vacancy-type ZIF-8, completing the electrochemical atomic exchange between Zn and Ir in the MOF material, resulting in a Co3O4@Ir deposition-type ZIF-8-3 electrode, i.e., Co3O4@IrO. x catalyst.

[0077] Comparative Example 1

[0078] This comparative example provides a method for preparing Co3O4@defect ZIF-8 materials, and the specific steps are as follows:

[0079] Step 1: Weigh 11.75 mg of cobalt nitrate hexahydrate and 27.5 mg of 2-methylimidazole into two beakers, respectively, according to a molar ratio of 1:8.3. Add 1 ml of methanol to each beaker and sonicate for 10 min to fully dissolve and disperse. Then mix the two solutions and transfer them to a magnetic stirrer at 500 rpm for 3 h. After the reaction time is complete, centrifuge the mixture at 5000 rpm for 10 min to obtain ZIF-67. Sonicate this solution in 3 ml of fresh methanol and label it as the first solution for later use.

[0080] Dissolve 15 mg of cetyltrimethylammonium bromide in 1 ml of methanol and 1135.03 mg of 2-methylimidazole in 17.5 ml. Dissolve each separately by sonication for 10 min and then mix them. Stir magnetically at 500 rpm for 20 min and label the mixture as the second solution for later use.

[0081] Dissolve 72.5 mg of zinc nitrate hexahydrate in 2.5 ml of methanol by sonication for 10 min, and label it as the third solution.

[0082] Step 2: Take the first solution into a 100ml reaction vessel, sonicate for 3 minutes, then pour the second solution into the sonicated first solution, continue sonicating for 5 minutes, pour in the third solution, and continue sonicating for 5 minutes. Then close the reaction vessel and let it stand at room temperature for 24 hours. After the reaction, separate the products by centrifugation at 5000 rpm for 3 minutes. Wash the obtained products with methanol. Sonicate the products for 5 minutes to disperse them in methanol solution, then centrifuge at 5000 rpm for 3 minutes. Repeat this process three times. After the final product is separated, dry it under vacuum at 80℃ for 12 hours. After drying, allow it to cool naturally to room temperature, then remove the dried sample and grind it in an agate grinding mortar for 15 minutes to obtain ZIF-67@ZIF-8 core-shell material.

[0083] Step 3: Weigh 0.3 mg of ZIF-67@ZIF-8 core-shell material and dissolve it in 0.5 ml of ethanol using ultrasonication. Then, drop the solution onto carbon paper that has been ultrasonically cleaned with ethanol. The carbon paper should be 0.5 × 0.5 cm in size. After drying with an infrared lamp, ZIF-67@ZIF-8 electrode sheets are obtained.

[0084] The ZIF-67@ZIF-8 electrode sheets were placed inside a quartz boat, which was then placed in a tube furnace for pyrolysis in air. The pyrolysis temperature was 350℃, and the heating rate was 5℃·min. -1 The electrode was kept at 350℃ for 0.5 hours and then allowed to cool naturally to obtain a Co3O4@defect type ZIF-8 electrode sheet.

[0085] A standard three-electrode system was used, with a carbon rod as the counter electrode, an Hg / HgO electrode as the reference electrode, and the Co3O4@defect-type ZIF-8 electrode sheet prepared above as the working electrode. The performance of water electrolysis was tested in 1M potassium hydroxide solution.

[0086] Figure 1 The image shown is a field emission scanning electron microscope image of ZIF-67@ZIF-8 synthesized in Example 1 of this invention. It can be seen that the material has a regular dodecahedral structure with an average particle size of 350 nm.

[0087] Figure 2 The image shown is a field emission scanning electron microscope image of ZIF-67@ZIF-8 synthesized in Example 2 of this invention. It can be seen that the material has a regular dodecahedral structure. Due to the reduction in the ratio of cobalt nitrate hexahydrate to dimethylimidazole, the particle size of the product is also reduced to an average particle size of 170 nm.

[0088] Figure 3 The image shown is a field emission scanning electron microscope image of ZIF-67@ZIF-8 synthesized in Example 3 of this invention. It can be seen that the material has a regular dodecahedral structure. Due to the shortened reaction time, the particle size of the product is also reduced to an average particle size of 150 nm.

[0089] Figure 4 This is a real-energy filtered transmission electron microscope image of ZIF-67@ZIF-8 synthesized in Example 1 of this invention. It can be seen that the Zn element coats the Co element, indicating that the core-shell structure of ZIF-67@ZIF-8 was successfully constructed.

[0090] Figure 5 The image shows a field emission scanning electron microscope (FESEM) image of the ZIF-67@ZIF-8 synthesized in Example 1 of this invention after calcination at 350°C in air. It can be seen that the polyhedral morphology of the MOF is still maintained, the particle size is slightly reduced to 320 nm, and it has become a hollow structure, i.e., a Co3O4@defective ZIF-8. Compared to the original ZIF-67@ZIF-8, the Co3O4@defective ZIF-8 introduces a large number of uncoordinated N and C sites as active sites due to defects introduced on the shell side and collapse on the core side, which is beneficial for the subsequent anchoring of Ir atoms.

[0091] Figure 6 The images show the ZIF-67@ZIF-8 raw material synthesized in Example 1 of this invention and its powder X-ray diffraction patterns after electrochemical etching and electrochemical deposition, respectively. PDF#36-1451 and PDF#43-1003 correspond to the standard PDF cards of cubic cobalt oxide Co3O4 and metallic cobalt, respectively. It can be seen that the characteristic peaks of ZIF-67@ZIF-8 after calcination are consistent with those of Co3O4, indicating that ZIF-67 collapses into Co3O4.

[0092] Figures 7-9 The images shown are, in order, the X-ray photoelectron spectra of cobalt, zinc, and iridium in the three types of ZIF-8 synthesized in Example 1 of this invention: Co3O4@defective ZIF-8, Co3O4@vacancy ZIF-8, and Co3O4@Ir deposition ZIF-8. Figure 7 The presence of Co in the Co3O4@defective ZIF-8 indicates that after calcination, the shell-side ZIF-8 formed defective pores or channels, exposing the core-side Co. Furthermore, it can be observed that Co in the Co3O4@defective ZIF-8 possesses the 2p orbital electrons characteristic of transition metals. 3 / 2 and 2p 3 / 2 Two characteristic peaks, in X-ray photoelectron spectroscopy analysis, for Co²⁺ at 2p⁻. 3 / 2 The peak is located around 780.5 eV, 2p 1 / 2 The peak is located around 796.5 eV; while Co 3+ 2p 3 / 2 The peak appears around 779.0 eV, 2p 1 / 2The peak is located near 794.0 eV, indicating that ZIF-67@ZIF-8 is transformed into Co3O4 after calcination. Figure 8 In Co3O4@defective ZIF-8, Zn can be detected, particularly Zn2p. 3 / 2 The binding energy ranges from 1020 eV to 1025 eV for Zn2p. 1 / 2 The binding energy ranges from 1045 eV to 1050 eV. The Co3O4@vacancy type ZIF-8 surface no longer contains Co or Zn elements, indicating that Zn has been etched off the surface. Figure 9 In the Co3O4@Ir depositional ZIF-8, Ir contains Ir4f. 7 / 2 The binding energy ranges from 61.5 eV to 63.5 eV, Ir4f 5 / 2 Ir with a binding energy in the range of 64.5–66.5 eV 4+ and Ir4f 7 / 2 The binding energy ranges from 63.5 to 65.0 eV, Ir4f 5 / 2 Ir with a binding energy in the range of 66.5 eV to 68.0 eV 3+ Collectively referred to as IrO x This indicates successful Ir deposition.

[0093] Figure 10 Inductively coupled plasma (ICP) analysis was performed on three electrodes: the etching solution for Co3O4@defective ZIF-8 electrode, the deposition solution for Co3O4@Ir-deposited ZIF-8 electrode, and the electrode itself. In the original ZIF-67@ZIF-8 preparation, the masses of zinc nitrate hexahydrate and cobalt nitrate hexahydrate were 72.5 mg and 11.75 mg, respectively, and the molar ratio of Zn to Co was 6:1. Only Zn detached from the etching electrolyte and the Ir deposition electrolyte. However, the Co3O4@Ir-deposited ZIF-8 electrode had a smaller amount of Ir and Zn compared to Co, indicating that the etching of Zn and the deposition of Ir achieved successful atomic exchange.

[0094] Figure 11 This is a TEM image of the core-shell surface of the Co3O4@Ir deposition type ZIF-8 synthesized in Example 1 of this invention at 0 nm defocus. It can be seen that the Ir atomic clusters of the product are distributed on the surface.

[0095] Figure 12 This is a TEM image of the core-shell interior of the Co3O4@Ir deposition type ZIF-8 synthesized in Example 1 of this invention at 58 nm defocus, showing that the Ir atoms in the product were successfully deposited.

[0096] Figure 13This is an electrochemical active surface area diagram of Co3O4@defective ZIF-8, Co3O4@vacancy-type ZIF-8, Co3O4@Ir-deposited ZIF-8 synthesized in Example 1, Co3O4@Ir-deposited ZIF-8-2 synthesized in Example 2, and Co3O4@Ir-deposited ZIF-8-3 synthesized in Example 3. It can be seen that the electrochemical active surface area of ​​Co3O4@defective ZIF-8 increases from 1.28 mF·cm⁻¹ after pulse-induced vacancy creation and after Ir deposition. -2 Up to 8.41 mF·cm -2 49.27mF·cm -2 The gradual increase indicates that during the electrochemical atomic exchange process, i.e., after electrochemical etching and deposition, the number of active sites exposed on the catalyst surface increases, leading to an increase in the number of active sites participating in the oxygen evolution reaction. This allows the catalyst to withstand a higher current density, which is beneficial for improving catalytic performance. However, the electrochemical active surface areas of Co3O4@Ir deposited ZIF-8-2 and Co3O4@Ir deposited ZIF-8-3 obtained in Examples 2 and 3 are not as large as those of Co3O4@Ir deposited ZIF-8 in Example 1. This suggests that the improvement in electrochemical performance is greatly related to the reaction time of the reactants, the calcination temperature, and the degree of Ir deposition. The parameters used in Example 1 are the best.

[0097] Figure 14 The linear sweep voltammetry curves of Co3O4@defect type ZIF-8, Co3O4@vacancy type ZIF-8, and Co3O4@Ir deposit type ZIF-8 synthesized in Example 1, Co3O4@Ir deposit type ZIF-8-2 synthesized in Example 2, and Co3O4@Ir deposit type ZIF-8-3 synthesized in Example 3 show that after electrochemical etching and deposition, the overpotential of the catalyst at η=210mV decreased from 1.65V to about 1.45V, indicating that the driving energy required for the oxygen evolution reaction of the material is reduced, and the reaction is more likely to occur. However, the kinetic performance of Co3O4@Ir deposit type ZIF-8-2 synthesized in Example 2 and Co3O4@Ir deposit type ZIF-8-3 synthesized in Example 3 is not as good as that of Co3O4@Ir deposit type ZIF-8 in Example 1, requiring a larger overpotential. Figure 12 This echoes the conclusion.

[0098] Figure 15The Tafel slope diagrams of Co3O4@defect type ZIF-8, Co3O4@vacancy type ZIF-8, and Co3O4@Ir deposition type ZIF-8 synthesized in Example 1, Co3O4@Ir deposition type ZIF-8-2 synthesized in Example 2, and Co3O4@Ir deposition type ZIF-8-3 synthesized in Example 3 show that the Tafel slope gradually decreases during the electrochemical atom exchange process, i.e., after electrochemical etching and deposition, from 88.8 mV·dec -1 Reduced to 65.6 mV·dec -1 That is, the faster the current density increases with the increase of overpotential, the more favorable the reaction kinetics are, which also means that the catalyst’s ability to accelerate the oxygen evolution reaction rate is enhanced after electrochemical atom exchange.

[0099] Figure 16 The constant potential long-cycle test of the Co3O4@Ir deposited ZIF-8 synthesized in Example 1 of this invention shows that the Co3O4@Ir deposited ZIF-8 catalyst can maintain good performance by operating stably for 1500h in long cycles. It is more likely to be applied in practical electrocatalytic devices and has high industrial application value.

[0100] In the prior art, Liang et al. prepared Ir-doped ZIF-67@CoFe PBA hollow nanomaterials in "Ir-Doped Bilayer Heterojunction Hollow Nanoboxes for Electrocatalytic Oxygen Evolution" published in Inorganic Chemistry, Volume 62, Issue 49, 2023. The Ir-ZIF-67@CoFe PBA material has an overpotential of 269 mV at 10 mA·cm, which is higher than the overpotential of 210 mV of Co3O4@Ir deposited ZIF-8 in this invention.

[0101] In their paper "Fluorination of ZIF-67 framework templated Prussian blue analogue nano-box for efficient electrochemical oxygen evolution reaction" published in Volume 403 of the Chemical Engineering Journal in 2021, Gu et al. prepared ZIF-67 framework templated Prussian blue analogue hollow nanomaterials. After calcination at 250 °C, ZIF-67@CoFe-PBA-F-250 was obtained. The ZIF-67@CoFe-PBA-F-250 material has an overpotential of 243 mV at 10 mA·cm. Although this is lower than that of commercially available IrO2 catalysts, it is still higher than the overpotential of 210 mV of the Co3O4@Ir deposited ZIF-8 in this invention. It can be seen that the Co3O4@Ir deposited ZIF-8 in this invention has better catalytic performance for oxygen absorption reaction.

[0102] Compared with existing technologies, this invention improves the atomic exchange method for Co3O4@defective ZIF-8. Unlike traditional atomic exchange methods such as solution impregnation, gas-phase permeation, and high-temperature solid-phase methods, which require high temperatures and long reaction times, this invention employs an electrochemical method to sequentially exchange Zn... 2+ The etching of ions and deposition of Ir are simple, precise, and controllable methods. This approach can effectively control the degree of defect etching and Ir deposition in ZIF-8 materials, providing abundant active sites, which facilitates electron transfer and improves the energy storage performance of ZIF-67@ZIF-8 as an oxygen evolution electrocatalyst. Furthermore, the material synthesis and etching methods are simple to operate, convenient to implement, and suitable for large-scale production, offering significant green and economic benefits, and can be widely applied in the field of electrocatalysis.

[0103] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0104] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A Co3O4@IrO x A method for preparing a catalyst, characterized in that, Includes the following steps: Using ZIF-67 as the core, quaternary ammonium salt surfactants and imidazole organic ligands were added to coordinate with a zinc source to prepare ZIF-67@ZIF-8 core-shell materials. ZIF-67@ZIF-8 electrode sheets were prepared by coating ZIF-67@ZIF-8 core-shell material onto carbon paper; In an air atmosphere, ZIF-67@ZIF-8 electrode sheets are pyrolyzed at 300℃~400℃. During the pyrolysis process, ZIF-67 collapses into Co3O4, resulting in Co3O4@defect type ZIF-8 electrode sheets. A standard three-electrode system was used, with a carbon rod as the counter electrode, an Hg / HgO electrode as the reference electrode, and a Co3O4@defective ZIF-8 electrode sheet as the working electrode. The Co3O4@defective ZIF-8 electrode sheet was subjected to pulsed potential etching in potassium hydroxide solution. During the pulsed potential etching process, zinc ions on the surface of the defective ZIF-8 were etched away, resulting in a Co3O4@vacancy-type ZIF-8 electrode sheet. A standard three-electrode system was used, with a carbon rod as the counter electrode, an Hg / HgO electrode as the reference electrode, and a Co3O4@defect-type ZIF-8 electrode as the working electrode. Iridium was deposited onto the zinc ion vacancies of the Co3O4@vacancy-type ZIF-8 electrode through electrochemical deposition in an iridium-containing potassium hydroxide solution, yielding Co3O4@IrO. x catalyst.

2. The Co3O4@IrO according to claim 1 x A method for preparing a catalyst, characterized in that, During the pulsed potential etching process, short pulses of cathode potential and short pulses of anode potential are repeated. The cathode potential is -2V and the duration is 1s~2s; the anode potential is 2V and the duration is 1s~2s. This process is repeated 150 times to form one activation cycle. The activation cycle is 3 to 4 times.

3. A Co3O4@IrO according to claim 1 x A method for preparing a catalyst, characterized in that, During the electrochemical deposition process, short pulses of cathode potential and short pulses of anode potential are repeated. The cathode potential is -6V and the duration is 1s~2s; the anode potential is 6V and the duration is 1s~2s. This process is repeated 500 times to form one activation cycle. The activation cycle is 5 to 10 times.

4. A Co3O4@IrO according to claim 1 x A method for preparing a catalyst, characterized in that, In the potassium hydroxide solution containing iridium, the concentration of iridium is 100 μmol / L.

5. A Co3O4@IrO according to claim 1 x A method for preparing a catalyst, characterized in that, The pyrolysis time is 0.5 h.

6. A Co3O4@IrO according to claim 1 x A method for preparing a catalyst, characterized in that, The mass ratio of quaternary ammonium salt surfactant to imidazole organic ligand is 15:1135~1136; The mass ratio of quaternary ammonium salt surfactant to zinc source is 15:72~73.

7. A Co3O4@IrO according to claim 1 x A method for preparing a catalyst, characterized in that, The ratio of ZIF-67 to quaternary ammonium salt surfactant is 6.9~7.4:

15.

8. A Co3O4@IrO according to claim 1 x A method for preparing a catalyst, characterized in that, The quaternary ammonium salt surfactant is hexadecyltrimethylammonium bromide, and the imidazole organic ligand is 2-methylimidazole.

9. A Co3O4@IrO prepared by the preparation method according to any one of claims 1 to 8 x catalyst.

10. A Co3O4@IrO as described in claim 9 x Application of catalysts in oxygen evolution electrocatalysis.

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