Cobalt-based spinel oxide nano material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of inorganic nano materials and electro-catalysis, and particularly relates to a cobalt-based spinel oxide nano material as well as a preparation method and application thereof. The cobalt-based spinel oxide nano material comprises a conductive substrate and cobalt-based spinel oxide grown on the surface of the conductive substrate, the molecular formula of the cobalt-based spinel oxide is MxCo1-xO4, and M is transition metal or P-region metal and is selected from one or more of titanium, vanadium, chromium, manganese, iron, nickel, aluminum, cerium and neodymium. Multiple metal elements are doped into a cobaltosic oxide lattice, and the intrinsic structure of spinel is not changed by metal doping. Multiple metal elements are highly uniformly dispersed in the material, so that active sites are comprehensively regulated and controlled, the material shows excellent thermodynamic and chemical stability under harsh conditions of high temperature, large current, concentrated alkali and the like, is suitable for various electrolysis modes, has no metal dissolution risk in long-term operation, can effectively avoid the problems of membrane poisoning and membrane degradation, and has good application prospects. Wide application prospects are shown.

Description

Technical Field

[0001] This invention belongs to the field of advanced inorganic nanomaterials technology, specifically relating to a cobalt-based spinel oxide nanomaterial, its preparation method, and its applications. Background Technology

[0002] Hydrogen (H2) is one of the most important renewable energy sources, boasting high energy efficiency and zero carbon emissions. Therefore, to achieve a clean energy transition, water electrolysis for renewable "green hydrogen" power generation stands out, offering high product purity and efficient utilization of intermittent renewable energy. Water electrolysis, conducted at high current densities, is considered an industrial-scale green hydrogen production technology.

[0003] However, this renewable energy-based hydrogen production technology accounts for only 4% of current hydrogen production, primarily due to its higher cost compared to other methods, such as the conversion of natural fossil fuels. For commercial water electrolysis systems, key issues mainly focus on the use of effective but excessively high-efficiency iridium, ruthenium, or platinum catalysts, or the economical but unsatisfactory activity of nickel mesh and stainless steel. Exploring highly active and cost-effective catalysts with good durability is imperative, but challenging.

[0004] Despite recent breakthroughs in the development of highly efficient first-row transition metal catalysts for the oxygen evolution reaction (OER), a gap remains between testing conditions (near room temperature) and industrial conditions (50–80 °C). High temperatures exhibit a significant double-edged sword effect on water electrolysis catalysts: on the one hand, thermodynamically, high temperatures reduce the energy requirement of the water electrolysis reaction, promoting the forward reaction; simultaneously, based on the Arrhenius equation kinetic mechanism, increased temperature lowers the activation energy, accelerating the reaction rate, and in anion exchange membrane electrolysis, increased temperature enhances ion conduction efficiency and reduces internal resistance. On the other hand, high temperatures easily induce catalyst structural degradation (such as sintering and agglomeration of noble metals, rapid degradation of NiFe-based layered double hydroxide anodes, etc.), leading to a reduction in active surface area and decreased stability. Therefore, the preparation of catalysts that can operate stably under harsh operating conditions such as high temperatures is crucial for further practical applications.

[0005] To address the above problems, this invention is proposed. Summary of the Invention

[0006] This application uses a conductive substrate as a carrier and employs a two-step synthesis strategy to construct an array-structured cobalt-based spinel oxide nanocatalytic layer in situ on its surface. Compared to traditional cobalt tetroxide spinel, the cobalt-based spinel oxide described in this application has the molecular formula M. x Co 1-xO4, by introducing one or more of titanium, vanadium, chromium, manganese, iron, nickel, aluminum, cerium, and neodymium into co-doped cobalt tetroxide spinel oxide, modulates the electronic structure of spinel oxidation and optimizes key active centers for the oxygen evolution reaction (OER). The introduction of multiple metal dopants into the interatomic spaces of spinel oxygen atoms not only modulates the d-band electronic structure of the metals, improves the adsorption behavior of reaction intermediates, and enhances catalytic activity, but also strengthens crystal structure stability and electrode interface bonding. Compared to the traditional sol-gel method, the array structure prepared by this method significantly alleviates the bubble shielding effect and improves the mass transfer efficiency at the three-phase interface. Under harsh conditions such as high temperature, high current, and concentrated alkali, the material maintains structural integrity, exhibiting excellent thermodynamic and chemical stability, and is suitable for various electrolysis modes. The cobalt-based spinel doped system of this invention has no risk of metal leaching during long-term operation, effectively avoiding membrane poisoning and degradation problems, and showing broad application prospects.

[0007] This application provides a cobalt-based spinel oxide nanomaterial, comprising: a conductive substrate and a cobalt-based spinel oxide grown on the surface of the conductive substrate, wherein the cobalt-based spinel oxide has the molecular formula M. x Co 1-x O4; where M is a transition metal or a p-block metal, and M is selected from one or more elements selected from titanium, vanadium, chromium, manganese, iron, nickel, aluminum, cerium, and neodymium;

[0008] x ranges from 0.01 to 0.667. In other words, the metal doping level is 1% to 66.7%, based on the total molar number of all metals in the cobalt-based spinel oxide.

[0009] Preferably, in the cobalt-based spinel oxide nanomaterial, the doped metal M is uniformly dispersed inside the cobalt-based spinel, and the doped metal M replaces part of the cobalt positions in the crystal lattice. The crystal structure of the cobalt-based spinel oxide is a spinel phase and there are no other impurity phases.

[0010] Preferably, the conductive substrate is selected from: foamed metal, nickel mesh, iron mesh, nickel-iron alloy mesh, carbon paper, or carbon cloth, etc. The foamed metal can be selected from one of foamed iron, foamed nickel (NF), or foamed nickel-iron alloy.

[0011] The second aspect of this application provides a method for preparing the cobalt-based spinel oxide nanomaterial described in the first aspect. The method for synthesizing the cobalt-based spinel oxide nanomaterial includes a two-step synthesis method, the first step being a hydrothermal reaction method or an electrodeposition method, and the second step being a high-temperature annealing method.

[0012] The first step of the hydrothermal reaction method includes the following steps: adding metal salt, water-soluble cobalt salt, urea, and ammonium fluoride to water to obtain a solution, transferring the solution to a hydrothermal reactor, adding a conductive substrate, carrying out a hydrothermal reaction at a certain temperature, and holding the temperature for a certain time to obtain a precursor;

[0013] The first step of the electrodeposition method includes the following steps: adding metal salt and water-soluble cobalt salt to water and dissolving them; placing the anode, cathode and reference electrode in the solution; using a conductive substrate on the cathode; and performing electrodeposition to obtain the precursor.

[0014] The metal salt is a water-soluble metal salt, and the metal is selected from one or more of the following: titanium, vanadium, chromium, manganese, iron, nickel, aluminum, cerium, and neodymium.

[0015] The concentration of each metal salt is 0.001 to 1 mol per liter, the concentration of cobalt salt is 0.01 to 1 mol per liter, and the concentration of urea is 2.5 to 20 times the sum of the concentrations of each metal salt and cobalt salt.

[0016] The second step, high-temperature annealing, includes the following steps: calcining the precursor obtained in the first step under an inert gas or air atmosphere for a certain period of time.

[0017] Preferably, in the first step of the hydrothermal reaction method, the hydrothermal reaction time is 3h to 48h, and the temperature is 60℃ to 200℃.

[0018] Preferably, in the first step of the electrodeposition method, the electrodeposition voltage is -1.0V to -2V vs calomel SCE, and the time is 100s to 7200s.

[0019] The second step, high-temperature annealing, involves a temperature range of 250-800℃, a heating rate of 2-10℃ / min, and a reaction time of 2-10 hours. The inert gas can be nitrogen or argon.

[0020] Preferably, the steps of adding metal salt, urea, and ammonium fluoride to water to obtain a solution are as follows: the soluble metal salt is added to a solution containing a soluble cobalt source, mixed and dissolved evenly to obtain a metal salt solution; urea is added, and the mixture is mixed and dissolved evenly again; then ammonium fluoride is added, and the mixture is mixed and dissolved evenly to obtain a mixed solution.

[0021] Preferably, the metal salt in the first step of the hydrothermal reaction method is one or more of the following: metal chloride, metal nitrate, and metal sulfate.

[0022] Preferably, the pretreatment method for the conductive substrate material is as follows: For metal substrates, the method involves first cleaning with ethanol or acetone in an ultrasonic cleaner for 15 minutes, then drying, cleaning with dilute hydrochloric acid in an ultrasonic cleaner for 15 minutes, rinsing with deionized water, and then cleaning with deionized water in an ultrasonic cleaner for 15 minutes. For carbon paper substrates, the method involves cleaning with ethanol in an ultrasonic cleaner for 15 minutes.

[0023] The pretreatment method for the carbon cloth substrate is as follows: it is cleaned with ethanol in an ultrasonic cleaner for more than 20 minutes, then dried and ultrasonically cleaned with deionized water for more than 20 minutes, then dried and treated with plasma for 10 minutes.

[0024] The third aspect of this application provides the use of the cobalt-based spinel oxide nanomaterial described in the first aspect as an anode material in the oxygen evolution reaction of alkaline water electrolysis.

[0025] Preferably, the electrolyte in the alkaline water electrolysis oxygen evolution reaction contains an alkaline substance; the alkaline substance is selected from one or more of sodium hydroxide, potassium hydroxide, lithium hydroxide, rubidium hydroxide, and cesium hydroxide.

[0026] Preferably, the total concentration of alkaline substances is 1 to 14 moles per liter.

[0027] Preferably, the temperature range for the alkaline water electrolysis oxygen evolution reaction is 25–120°C.

[0028] Preferably, the current density range of the alkaline water electrolysis oxygen evolution reaction is 0.1 to 10 amperes per square centimeter.

[0029] Preferably, the electrolysis mode of the alkaline water electrolysis oxygen evolution reaction is: constant current, constant voltage, or frequent start-stop.

[0030] Preferably, the cobalt-based spinel oxide nanomaterial is used to improve the activity and stability of the material's water electrolysis reaction.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] 1. This invention, a first-time report of cobalt-based spinel nanomaterials doped with multi-metal oxides, replaces some of the cobalt positions in the crystal lattice with doped transition metals or p-block metals. The multi-metal doping does not disrupt the intrinsic structure of spinel, perfectly preserving the crystal structure of the spinel phase cobalt tetroxide. Simultaneously, the doped metals are highly uniformly dispersed within the material, preventing the formation of impurity metal oxides, thus allowing for excellent regulation of active sites. During the alkaline oxygen evolution reaction (OER), this material exhibits not only excellent catalytic activity but also good stability. The introduction of transition metals or p-block metals modulates the d-band electronic structure of the metals, optimizes the reaction kinetics, lowers the adsorption energy barrier of reaction intermediates, and significantly improves its application performance in alkaline water electrolysis anode materials.

[0033] 2. Existing technologies commonly employ the sol-gel method to synthesize spinel oxides, but this method suffers from drawbacks such as uncontrollable spinel material morphology, limited mass transfer under high current conditions, and weak adhesion between the powdered catalyst and the conductive substrate. To address these shortcomings, this invention innovatively proposes a two-step synthesis method for preparing an integrated nanoarray spinel oxide alkaline oxygen evolution anode catalyst. This method constructs a cobalt-based spinel oxide nanomaterial with a uniform, array-structured composition, and the preparation process is simple and efficient. The cobalt-based spinel oxide nanomaterial described in this invention is in-situ constructed on the surface of a conductive substrate via hydrothermal self-growth or electrodeposition self-growth methods, forming an integrated electrode structure that integrates the conductive substrate and the catalyst. This nanoarray structure not only effectively improves the adhesion of the catalyst to the substrate but also significantly alleviates the bubble shielding effect under high current density operating conditions, thereby improving the mass transfer performance at the gas-liquid-solid three-phase interface and enhancing the overall electrocatalytic efficiency.

[0034] 3. Addressing the technical bottleneck of severe performance degradation of catalysts under harsh conditions such as high temperature (above 40°C), high current (above 0.4 amperes per square centimeter), and concentrated alkali (above 6 moles per liter) after prolonged operation, this invention proposes an effective solution. Compared to the two-dimensional layered hydrotalcite structure with weak interlayer forces and intralayer ionic bonds, spinel metal oxides exhibit excellent thermodynamic and structural stability due to their high lattice energy structure formed by strong electrostatic interactions and covalent bond networks. Specifically, the applicant discovered that the proposed cobalt-based spinel oxide maintains a complete and stable crystal structure after doping with titanium, vanadium, chromium, manganese, iron, nickel, aluminum, cerium, and neodymium. Octahedral sites are the active centers of spinel. The ionic radii and chemical valence states of the aforementioned elements match the spatial size and charge balance requirements of the spinel octahedral sites, allowing for the adjustment of the electronic state of the octahedral active center metals through doping with these metals.

[0035] Furthermore, this application breaks through the traditional design concept of spinel catalysts. Since the molecule of spinel metal oxide is AB₂O₄, where A occupies tetrahedral sites and B occupies octahedral sites, existing technologies for doping cobalt tetroxide spinel with other metals (M) typically only use a single metal, selectively replacing some tetrahedral or octahedral cobalt sites. The M:Co ratio is usually 1:2, and a large number of vacancies and other defects are introduced to improve activity. However, research on stability is limited, making it unsuitable for industrial production.

[0036] This application utilizes multi-metal simultaneous doping, introducing OER active metal nickel and other high-valence, stable metal elements to optimize and break the traditional 1:2 ratio limitation of OER active metal in tetrahedra and octahedrons of single-metal doped cobalt tetroxide spinel. The molecular formula of this application is M. x Co 1-x O4, with x ranging from 0.01 to 0.667. Therefore, this application successfully introduced metal elements with different properties to simultaneously regulate both the performance and stability of spinel oxide, thereby improving the electrochemical performance of alkaline oxygen evolution catalysts.

[0037] Therefore, this doped cobalt-based spinel oxide can operate stably over a wide temperature range, a wide current density range, and electrolyte conditions with different alkalinities, and is suitable for various electrolysis modes, meeting the requirements of industrial production.

[0038] 4. Comparative studies conducted by the applicant show that, under high temperature, high current, and concentrated alkaline conditions, the hydrotalcite catalyst prepared using the same hydrothermal synthesis method suffers from severe dissolution, leading to significant degradation of the crystal structure and an inability to maintain long-term stable operation. Furthermore, in membrane electrode systems, the dissolved metal ions easily poison the ion transport channels of the polymer ion exchange membrane, hindering mass transfer, limiting catalytic reactions, and inducing severe Fenton reactions, accelerating membrane material degradation, thereby further limiting its practical application performance. The cobalt-based spinel oxide nanomaterials of this invention can operate for extended periods in membrane electrode systems, indicating that the material structure is stable and does not suffer from application limitations caused by metal ion dissolution. Attached Figure Description

[0039] Figure 1 The image shows the X-ray diffraction (XRD) pattern of the nickel-doped cobalt-based spinel synthesized in Example 1.

[0040] Figure 2 This is a scanning electron microscope (SEM) image of the nickel-doped cobalt-based spinel synthesized in Example 1.

[0041] Figure 3 This is an EDS-Mapping diagram of the nickel-doped cobalt-based spinel oxide nanomaterial synthesized in Example 1.

[0042] Figure 4 The image shows the X-ray diffraction (XRD) pattern of the iron-doped cobalt-based spinel synthesized in Example 2.

[0043] Figure 5 This is a scanning electron microscope (SEM) image of the iron-doped cobalt-based spinel synthesized in Example 2.

[0044] Figure 6 This is an EDS-Mapping diagram of the iron-doped cobalt-based spinel oxide nanomaterial synthesized in Example 2.

[0045] Figure 7 The image shows the X-ray diffraction (XRD) pattern of the nickel-vanadium-doped cobalt-based spinel synthesized in Example 3.

[0046] Figure 8 The images show scanning electron microscope (SEM) and EDS-Mapping images of the nickel-vanadium-doped cobalt-based spinel synthesized in Example 3.

[0047] Figure 9 The X-ray diffraction (XRD) pattern of the nickel-chromium-doped cobalt-based spinel synthesized in Example 4 is shown.

[0048] Figure 10 This is a scanning electron microscope (SEM) image of the nickel-chromium-doped cobalt-based spinel synthesized in Example 4.

[0049] Figure 11 This is an EDS-Mapping diagram of the nickel-chromium-doped cobalt-based spinel oxide nanomaterials synthesized in Example 4.

[0050] Figure 12 The X-ray diffraction (XRD) pattern of the nickel-manganese-doped cobalt-based spinel synthesized in Example 5 is shown.

[0051] Figure 13 This is a scanning electron microscope (SEM) image of the nickel-manganese-doped cobalt-based spinel synthesized in Example 5.

[0052] Figure 14 This is an EDS-Mapping diagram of the nickel-manganese-doped cobalt-based spinel oxide nanomaterial synthesized in Example 5.

[0053] Figure 15 The X-ray diffraction (XRD) pattern of the nickel-iron-doped cobalt-based spinel synthesized in Example 6 is shown.

[0054] Figure 16 This is a scanning electron microscope (SEM) image of the nickel-iron-doped cobalt-based spinel synthesized in Example 6.

[0055] Figure 17This is an EDS-Mapping diagram of the nickel-iron doped cobalt-based spinel oxide nanomaterial synthesized in Example 6.

[0056] Figure 18 The X-ray diffraction (XRD) pattern of the nickel-iron-titanium-doped cobalt-based spinel synthesized in Example 7 is shown.

[0057] Figure 19 This is a scanning electron microscope (SEM) image of the nickel-iron-titanium-doped cobalt-based spinel synthesized in Example 7.

[0058] Figure 20 This is an EDS-Mapping diagram of the nickel-iron-titanium doped cobalt-based spinel oxide nanomaterials synthesized in Example 7.

[0059] Figure 21 The X-ray diffraction (XRD) pattern of the nickel-iron-vanadium-doped cobalt-based spinel synthesized in Example 8 is shown.

[0060] Figure 22 This is a scanning electron microscope (SEM) image of the nickel-iron-vanadium-doped cobalt-based spinel synthesized in Example 8.

[0061] Figure 23 This is an EDS-Mapping diagram of the nickel-iron-vanadium doped cobalt-based spinel oxide nanomaterials synthesized in Example 8.

[0062] Figure 24 The X-ray diffraction (XRD) pattern of the nickel-iron-chromium-doped cobalt-based spinel synthesized in Example 9 is shown.

[0063] Figure 25 This is a scanning electron microscope (SEM) image of the nickel-iron-chromium-doped cobalt-based spinel synthesized in Example 9.

[0064] Figure 26 This is an EDS-Mapping diagram of the nickel-iron-chromium-doped cobalt-based spinel oxide nanomaterials synthesized in Example 9.

[0065] Figure 27 The X-ray diffraction (XRD) pattern of the nickel-iron-aluminum doped cobalt-based spinel synthesized in Example 10 is shown.

[0066] Figure 28 The images show scanning electron microscope (SEM) and EDS-Mapping images of the nickel-iron-aluminum doped cobalt-based spinel synthesized in Example 10.

[0067] Figure 29 The X-ray diffraction (XRD) pattern of the nickel-iron-manganese-doped cobalt-based spinel synthesized in Example 11 is shown.

[0068] Figure 30This is a scanning electron microscope (SEM) image of the nickel-iron-manganese-doped cobalt-based spinel synthesized in Example 11.

[0069] Figure 31 This is an EDS-Mapping diagram of the nickel-iron-manganese-doped cobalt-based spinel oxide nanomaterial synthesized in Example 11.

[0070] Figure 32 This is a high-resolution transmission electron microscope image with spherical aberration correction of the nickel-iron-manganese-doped cobalt-based spinel oxide nanomaterial synthesized in Example 11.

[0071] Figure 33 The X-ray diffraction (XRD) pattern of the nickel-cerium-doped cobalt-based spinel synthesized in Example 12 is shown.

[0072] Figure 34 This is a scanning electron microscope (SEM) image of the nickel-cerium-doped cobalt-based spinel synthesized in Example 12.

[0073] Figure 35 This is an EDS-Mapping diagram of the nickel-cerium-doped cobalt-based spinel oxide nanomaterial synthesized in Example 12.

[0074] Figure 36 The X-ray diffraction (XRD) pattern of the nickel-neodymium-doped cobalt-based spinel synthesized in Example 13 is shown.

[0075] Figure 37 This is a scanning electron microscope (SEM) image of the nickel-neodymium-doped cobalt-based spinel synthesized in Example 13.

[0076] Figure 38 This is an EDS-Mapping diagram of the nickel-neodymium-doped cobalt-based spinel oxide nanomaterial synthesized in Example 13.

[0077] Figure 39 The image shows the X-ray diffraction (XRD) pattern of the cobalt tetroxide spinel oxide nanomaterial synthesized in Example 14.

[0078] Figure 40 Scanning electron microscope (SEM) image of the cobalt tetroxide spinel oxide nanomaterials synthesized in Example 14.

[0079] Figure 41 This is the EDS-Mapping diagram of the cobalt tetroxide spinel oxide nanomaterial synthesized in Example 14.

[0080] Figure 42 The polarization curves obtained in the three-electrode system in Application Example 1 are shown.

[0081] Figure 43The polarization curves obtained in the three-electrode system in Application Example 2 are shown.

[0082] Figure 44 The polarization curves obtained in the three-electrode system in Application Example 3 are shown.

[0083] Figure 45 The current-suspension curve of the cobalt-based spinel oxide nanomaterial synthesized by the two-step synthesis method in Example 1 is shown under the conditions of 25°C, 1 mole of KOH, and a current density of 100 mA per square centimeter.

[0084] Figure 46 The current-suspension curve of the cobalt-based spinel oxide nanomaterial synthesized by the two-step synthesis method in Example 7 is shown at 45°C, 6 moles of KOH, and a current density of 2 amps per square centimeter.

[0085] Figure 47 The graph shows the frequent start-stop current curves of the cobalt-based spinel oxide nanomaterial synthesized in Example 8 using a two-step synthesis method, under conditions of 45°C, 6 moles of KOH, and a current density of 2 amps per square centimeter.

[0086] Figure 48 The current-suspension curve of the cobalt-based spinel oxide nanomaterial synthesized by the two-step synthesis method in Example 11 is shown under the conditions of 80°C, 6 moles of KOH, and a current density of 1 amp per square centimeter.

[0087] Figure 49 The graph shows the frequent start-stop current curves of the cobalt-based spinel oxide nanomaterial synthesized in Example 11 using a two-step synthesis method, under conditions of 80°C, 6 moles of KOH, and a current density of 10 amps per square centimeter.

[0088] Figure 50 The current-suspension curve of the cobalt-based spinel oxide nanomaterial synthesized by the two-step synthesis method in Example 10 is shown under the conditions of 100°C, 10 moles of KOH, and a current density of 1 amp per square centimeter.

[0089] Figure 51 The current-suspension curve of the cobalt-based spinel oxide nanomaterial synthesized in Example 12 using a two-step synthesis method is shown at 120°C, 14 moles of KOH, and a current density of 1 amp per square centimeter.

[0090] Figure 52 Linear scan voltammetry of an anion exchange membrane (AEM) electrolyzer used in Example 11, which uses cobalt-based spinel oxide nanomaterials synthesized by a two-step synthesis method as the anode and nickel-molybdenum alloy as the cathode.

[0091] Figure 53The constant current curve of the anion exchange membrane (AEM) electrolyzer used in Example 11, which uses cobalt-based spinel oxide nanomaterials synthesized by a two-step synthesis method as the anode and nickel-molybdenum alloy as the cathode, is shown at 60°C, 1 mole of KOH, and a current density of 1 amp per square centimeter.

[0092] Figure 54 X-ray diffraction (XRD) pattern of nickel-iron hydrotalcite nanomaterials prepared by hydrothermal synthesis for Comparative Example 1.

[0093] Figure 55 The constant current curve of nickel-iron hydrotalcite nanomaterials prepared by hydrothermal synthesis in Comparative Example 1 was obtained after 130 hours of operation at 80℃, 6 moles of KOH, and a current density of 1 amp per square centimeter.

[0094] Figure 56 For Comparative Example 1, the linear sweep voltammetry diagram of nickel-iron hydrotalcite nanomaterials prepared by hydrothermal synthesis was obtained before and after 130 hours of stability testing under the conditions of 80℃, 6 moles of KOH, and 1 A / cm² current density.

[0095] Figure 57 For Comparative Example 1, the nickel-iron hydrotalcite nanomaterials prepared by hydrothermal synthesis were compared with those of Comparative Application Example 1. After a stability test of 130 hours at 80°C, 6 moles of KOH, and a current density of 1 amp per square centimeter, the X-ray photoelectron spectrum of the iron element in the nickel-iron hydrotalcite nanomaterials was obtained.

[0096] Figure 58 For Comparative Example 1, the preparation of nickel-iron hydrotalcite nanomaterials using a hydrothermal synthesis method and the scanning electron microscope (SEM) images of the nickel-iron hydrotalcite nanomaterials are shown.

[0097] Figure 59 To compare the stability test results of nickel-iron hydrotalcite nanomaterials obtained after 130 hours of testing at 80°C, 6 moles of KOH, and a current density of 1 amp per square centimeter in Application Example 1, a scanning electron microscope (SEM) image was obtained.

[0098] Figure 60 The X-ray diffraction (XRD) pattern is shown for the iron and zinc cobalt-doped nickel-cobalt spinel oxide nanomaterial synthesized in Comparative Example 2.

[0099] Figure 61 This is a scanning electron microscope (SEM) image of the iron and zinc co-doped nickel-cobalt spinel oxide nanomaterial synthesized in Comparative Example 4.

[0100] Figure 62This is an energy-dispersive electron microscope (EDS) image of the iron and zinc co-doped nickel-cobalt spinel oxide nanomaterial synthesized in Comparative Example 2.

[0101] Figure 63 The constant current curve of the anion exchange membrane (AEM) electrolyzer with nickel-molybdenum alloy as cathode, synthesized with iron and zinc doped nickel-cobalt spinel oxide nanomaterials as synthesized in Comparative Example 2, under the conditions of 60℃, 1 mole of KOH, and 1 amp per square centimeter current density.

[0102] Figure 64 The image shows the damage to the membrane and electrolyte conduit in the anion exchange membrane (AEM) electrolyzer after 438 hours of operation at 60°C, 1 mole of KOH, and 1 amp per square centimeter, as shown in Application Example 3. Detailed Implementation

[0103] The present invention will be described below with reference to specific embodiments, but the implementation of the present invention is not limited thereto. Experimental methods not specifically described in the embodiments generally use conventional conditions and conditions described in the manual, or conditions recommended by the manufacturer. The general equipment, materials, reagents, etc., used are all commercially available unless otherwise specified. The raw materials used in the following embodiments and comparative examples are all commercially available.

[0104] Example 1: Preparation of Nickel-Doped Cobalt-Based Spinel Oxide Nanomaterials by a Two-Step Hydrothermal-High-Temperature Annealing Method

[0105] Step (1): The precursor was prepared using a hydrothermal synthesis method, specifically as follows: 36 mL of solution was prepared containing 2.2 mmol of ammonium fluoride, 26.4 mmol of urea, 0.66 mmol of nickel nitrate, 0.66 mmol of cobalt nitrate, and 36 mL of water. The solution was poured into a reaction vessel. In this solution, the concentration of nickel salt was 0.018 mol / L, the concentration of cobalt salt was 0.018 mol / L, and the concentration of urea was 20 times the sum of the concentrations of nickel salt and cobalt salt. The treated conductive substrate nickel foam was immersed in the solution and placed in an oven. The reaction temperature was 120°C, and the reaction time was 10 hours. The obtained precursor material was washed three times with water and ethanol, and then vacuum dried at 60°C for 10 hours.

[0106] Step (2): Place the precursor obtained in step (1) into a muffle furnace (in other embodiments, an inert gas can be introduced into a tube furnace or no gas can be introduced), heat it to 250°C at a heating rate of 2°C / min, hold it at that temperature for 10 hours, and remove it after natural cooling to obtain the material grown on the conductive substrate material, which is the cobalt-based spinel oxide nanomaterial. The nickel doping amount in the nickel-doped cobalt-based spinel nanomaterial is 50%. The formula for calculating the nickel doping amount is: Nnickel / (Nnickel+Ncobalt)=33 / 66=50%.

[0107] The cobalt-based spinel oxide nanomaterials obtained above were subjected to X-ray diffraction (XRD). The diffraction pattern is shown in [reference needed]. Figure 1 Consistent with the standard card for cobalt spinel oxide, the results indicate that the cobalt-based spinel oxide nanomaterials synthesized by the two-step synthesis method possess a nickel-cobalt spinel structure, exhibit good crystallinity, and are free from phase separation. The obtained cobalt-based spinel oxide nanomaterials were subjected to scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy-elemental mapping (EDS-Mapping), as shown... Figure 2 As shown, the results indicate that the cobalt-based spinel oxide nanomaterials synthesized by the two-step synthesis method have a distinct lamellar morphology, and as... Figure 3 The uniform distribution of elements shown demonstrates successful nickel ion doping.

[0108] Example 2: Preparation of Iron-Doped Cobalt-Based Spinel Oxide Nanomaterials by a Two-Step Hydrothermal-High-Temperature Annealing Method

[0109] Step (1): The precursor was prepared using a hydrothermal synthesis method. Specifically, a 36 mL solution was prepared containing 21.6 mmol of ammonium fluoride, 9.9 mmol of urea, 0.33 mmol of ferric nitrate, 0.66 mmol of cobalt nitrate, and 36 mL of water. The solution was poured into a reaction vessel. In this solution, the concentration of ferric salt was 0.01 mol / L, the concentration of cobalt salt was 0.018 mol / L, and the concentration of urea was 20 times the sum of the concentrations of ferric salt and cobalt salt. The treated conductive substrate nickel foam was immersed in the solution and placed in an oven. The reaction temperature was 200°C, and the reaction time was 3 hours. The obtained precursor material was washed three times with water and ethanol, and then vacuum dried at 60°C for 10 hours.

[0110] Step (2): Place the precursor obtained in step (1) into a muffle furnace (or in a tube furnace with or without inert gas), heat it to 800℃ at a heating rate of 10℃ / min, hold it at that temperature for 2 hours, and remove it after natural cooling to obtain the material grown on a conductive substrate, which is the cobalt-based spinel oxide nanomaterial. The ratio of cobalt to iron in the cobalt-based spinel oxide nanomaterial is 2:1. The iron doping amount in the iron-doped cobalt-based spinel nanomaterial is 33.3%. The formula for calculating the iron doping amount is: Niron / (Niron+Ncobalt)=33 / 99=33.3%.

[0111] The cobalt-based spinel oxide nanomaterials obtained above were subjected to X-ray diffraction (XRD). The diffraction pattern is shown in [reference needed]. Figure 4Consistent with the standard card for nickel-cobalt spinel oxide, the results indicate that the cobalt-based spinel oxide nanomaterials synthesized by the two-step synthesis method possess a nickel-cobalt spinel structure, exhibit good crystallinity, and are free from phase separation. The obtained cobalt-based spinel oxide nanomaterials were subjected to scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy-elemental mapping (EDS-Mapping), as shown... Figure 5 As shown, the results indicate that the cobalt-based spinel oxide nanomaterials synthesized by the two-step synthesis method have a distinct lamellar morphology, and as... Figure 6 The uniform distribution of elements shown demonstrates successful iron ion doping.

[0112] Example 3: Preparation of Nickel-Vanadium Doped Cobalt-Based Spinel Oxide Nanomaterials by a Two-Step Hydrothermal-High-Temperature Annealing Method

[0113] Step (1): The precursor was prepared using a hydrothermal synthesis method. Specifically, a 36 mL solution was prepared containing 21.6 mmol of ammonium fluoride, 26.4 mmol of urea, 0.66 mmol of nickel nitrate, 0.33 mmol of vanadium tetrachloride, 0.66 mmol of cobalt nitrate, and 36 mL of water. The solution was poured into a reaction vessel. In this solution, the concentration of cobalt salt was 0.018 mol / L, the concentration of nickel salt was 0.018 mol / L, and the concentration of vanadium salt was 0.01 mol / L. The concentration of urea was 16 times the sum of the concentrations of nickel, vanadium, and cobalt salts. The treated conductive carbon paper substrate was immersed in the solution and placed in an oven at 60°C for 48 hours. The obtained precursor material was washed three times with water and ethanol, and then vacuum dried at 60°C for 10 hours.

[0114] Step (2): Place the precursor obtained in step (1) into a muffle furnace (or in a tube furnace with or without inert gas), heat it to 500℃ at a heating rate of 5℃ / min, hold it at that temperature for 3 hours, and remove it after natural cooling to obtain the material grown on a conductive substrate, which is the cobalt-based spinel oxide nanomaterial. The ratio of nickel, cobalt, and vanadium in the cobalt-based spinel oxide nanomaterial is 2:2:1, and the nickel-vanadium doping amount in the nickel-vanadium-doped cobalt-based spinel nanomaterial is 60%. The formula for calculating the nickel-vanadium doping amount is: Nnickel-vanadium / (Nnickel-vanadium+Ncobalt) = 3 / 5 = 60%.

[0115] The cobalt-based spinel oxide nanomaterials obtained above were subjected to X-ray diffraction (XRD). The diffraction pattern is shown in [reference needed]. Figure 7 Consistent with the standard card for cobalt spinel oxide, the results indicate that the cobalt-based spinel oxide nanomaterials synthesized by the two-step synthesis method possess a nickel-cobalt spinel structure, exhibit good crystallinity, and are free from phase separation. The obtained cobalt-based spinel oxide nanomaterials were subjected to scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy-elemental mapping (EDS-Mapping), as shown... Figure 8As shown in the figure, the results indicate that the cobalt-based spinel oxide nanomaterial synthesized by the two-step synthesis method has a distinct lamellar morphology and a uniform elemental distribution, as shown in the figure, proving the successful doping of nickel and vanadium.

[0116] Example 4 - Preparation of Nickel- and Chromium-Doped Cobalt-Based Spinel Oxide Nanomaterials by a Two-Step Electrodeposition-High-Temperature Annealing Method

[0117] Step (1): The precursor was synthesized using electrodeposition. Specifically, a 120 mL solution was prepared containing 120 mmol of nickel nitrate, 120 mmol of cobalt nitrate, 60 mmol of chromium nitrate, and 120 mL of water. (In this solution, the concentrations of the nickel source and cobalt source were 1 mol / L and 0.5 mol / L, respectively.) Using washed nickel foam as the working electrode, a carbon rod electrode as the counter electrode, and a calomel electrode as the reference electrode, a constant potential of -1 V vs SCE was applied for 7200 seconds. The resulting material was washed three times with water and ethanol, and then vacuum-dried at 60 °C for 10 hours. The precursor of cobalt-based spinel oxide nanomaterials loaded on nickel foam was thus obtained.

[0118] Step (2): Place the precursor obtained in step (1) into a muffle furnace (or in a tube furnace with inert gas or without gas), heat it to 400°C at a heating rate of 5°C / min, hold it at that temperature for 5 hours, and take it out after natural cooling to obtain the material grown on nickel foam, which is the cobalt-based spinel oxide nanomaterial.

[0119] The nickel-cobalt-chromium ratio in the cobalt-based spinel oxide nanomaterial is 2:2:1, and the nickel-vanadium doping content in the nickel-chromium-doped cobalt-based spinel nanomaterial is 60%. The formula for calculating the nickel-chromium doping content is: Nnickel-chromium / (Nnickel-chromium+Ncobalt) = 3 / 5 = 60%.

[0120] The cobalt-based spinel oxide nanomaterials obtained above were subjected to X-ray diffraction (XRD). The diffraction pattern is shown in [reference needed]. Figure 9 Consistent with the spinel oxide standard card, the results indicate that the cobalt-based spinel oxide nanomaterials synthesized by the two-step synthesis method possess a nickel-cobalt spinel structure, exhibit good crystallinity, and are free from phase separation. The obtained cobalt-based spinel oxide nanomaterials were subjected to scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy-elemental mapping (EDS-Mapping), as shown... Figure 10 As shown, the results indicate that the cobalt-based spinel oxide nanomaterials synthesized by the two-step synthesis method have a distinct lamellar morphology, and as... Figure 11 The uniform distribution of elements shown demonstrates the successful doping of nickel and chromium.

[0121] Example 5: Preparation of Nickel- and Manganese-Doped Cobalt-Based Spinel Oxide Nanomaterials by a Two-Step Electrodeposition-High-Temperature Annealing Method

[0122] Step (1): The precursor was synthesized using electrodeposition. Specifically, a 120 mL solution was prepared containing 120 mmol of nickel nitrate, 120 mmol of cobalt nitrate, 60 mmol of manganese nitrate, and 120 mL of water. (In this solution, the concentrations of nickel source and cobalt source were 1 mol / L and 0.5 mol / L, respectively.) The washed nickel foam was used as the working electrode, a carbon rod electrode as the counter electrode, and a calomel electrode as the reference electrode. A constant potential of -2V vs SCE was maintained for 100 seconds. The resulting material was washed three times with water and ethanol, and then vacuum-dried at 60°C for 10 hours. The precursor of cobalt-based spinel oxide nanomaterials loaded on nickel foam was thus obtained.

[0123] Step (2): Place the precursor obtained in step (1) into a muffle furnace (or in a tube furnace with or without inert gas), heat it to 400℃ at a heating rate of 5℃ / min, hold it at that temperature for 5 hours, and remove it after natural cooling to obtain the material grown on nickel foam, which is the cobalt-based spinel oxide nanomaterial. The ratio of nickel, cobalt, and manganese in the cobalt-based spinel oxide nanomaterial is 2:2:1, and the nickel and manganese doping amount in the nickel-manganese-doped cobalt-based spinel nanomaterial is 60%. The formula for calculating the nickel and manganese doping amount is: Nnickel-manganese / (Nnickel-manganese+Ncobalt) = 3 / 5 = 60%.

[0124] The cobalt-based spinel oxide nanomaterials obtained above were subjected to X-ray diffraction (XRD). The diffraction pattern is shown in [reference needed]. Figure 12 Consistent with the standard card for nickel-cobalt spinel oxide, the results indicate that the cobalt-based spinel oxide nanomaterials synthesized by the two-step synthesis method possess a nickel-cobalt spinel structure, exhibit good crystallinity, and are free from phase separation. The obtained cobalt-based spinel oxide nanomaterials were subjected to scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy-elemental mapping (EDS-Mapping), as shown... Figure 13 As shown, the results indicate that the cobalt-based spinel oxide nanomaterials synthesized by the two-step synthesis method have a distinct lamellar morphology, and as... Figure 14 The uniform distribution of elements shown demonstrates the successful doping of nickel and manganese.

[0125] Example 6: Preparation of Nickel-Iron-Doped Cobalt-Based Spinel Oxide Nanomaterials by a Two-Step Hydrothermal-High-Temperature Annealing Method

[0126] Step (1): The precursor was prepared using a hydrothermal synthesis method. Specifically, a 36 mL solution was prepared containing 21.6 mmol of ammonium fluoride, 26.4 mmol of urea, 0.66 mmol of nickel nitrate, 0.66 mmol of cobalt nitrate, 0.33 mmol of ferric nitrate, and 36 mL of water. The solution was poured into a reaction vessel. In this solution, the concentrations of cobalt salt, nickel salt, and ferric salt were 0.018 mol / L, and the concentration of urea was 16 times the sum of the concentrations of nickel, iron, and cobalt salts. The treated conductive substrate foamed iron was immersed in the solution and placed in an oven at 120°C for 10 hours. The obtained precursor material was washed three times with water and ethanol, and then vacuum dried at 60°C for 10 hours.

[0127] Step (2): Place the precursor obtained in step (1) into a muffle furnace (in other embodiments, an inert gas or no gas can be introduced into a tube furnace), heat it to 350°C at a heating rate of 5°C / min, hold it at that temperature for 3 hours, and take it out after natural cooling to obtain the material grown on the conductive substrate material, which is the cobalt-based spinel oxide nanomaterial.

[0128] The ratio of nickel, cobalt, and iron in the cobalt-based spinel oxide nanomaterial is 2:2:1, and the nickel-iron doping content in the nickel-iron-doped cobalt-based spinel nanomaterial is 60%. The formula for calculating the nickel-iron doping content is: Nnickel-iron / (Nnickel-iron+Ncobalt) = 3 / 5 = 60%.

[0129] The cobalt-based spinel oxide nanomaterials obtained above were subjected to X-ray diffraction (XRD). The diffraction pattern is shown in [reference needed]. Figure 15 Consistent with the standard card for nickel-cobalt spinel oxide, the results indicate that the cobalt-based spinel oxide nanomaterials synthesized by the two-step synthesis method possess a nickel-cobalt spinel structure, exhibit good crystallinity, and are free from phase separation. The obtained cobalt-based spinel oxide nanomaterials were subjected to scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy-elemental mapping (EDS-Mapping), as shown... Figure 16 As shown, the results indicate that the cobalt-based spinel oxide nanomaterials synthesized by the two-step synthesis method have a distinct lamellar morphology, and as... Figure 17 The uniform distribution of elements shown demonstrates the successful doping of nickel with iron.

[0130] Example 7: Preparation of Nickel, Iron, and Titanium-Doped Cobalt-Based Spinel Oxide Nanomaterials by a Two-Step Hydrothermal-High-Temperature Annealing Method

[0131] Referring to the method in Example 6, the hydrothermal reaction solution was replaced with: 2.2 mmol of ammonium fluoride, 26.4 mmol of urea, 0.66 mmol of nickel nitrate, 0.66 mmol of cobalt nitrate, 0.33 mmol of ferric nitrate, 0.16 mmol of titanium tetrachloride, and 36 mL of water. In this solution, the concentration of cobalt salt was 0.018 mol / L, the concentration of nickel salt was 0.018 mol / L, and the concentration of ferric salt was 0.01 mol / L. The concentration of urea was 16 times the sum of the concentrations of nickel, ferric, and cobalt salts. With all other conditions unchanged, cobalt-based spinel oxide nanomaterials were obtained.

[0132] The ratio of nickel, cobalt, iron, and titanium in the cobalt-based spinel oxide nanomaterial is 2:2:1:0.5, and the doping amount of nickel, iron, and titanium in the nickel-cobalt-iron-titanium-doped cobalt-based spinel nanomaterial is 63.6%. The formula for calculating the nickel-iron-titanium doping amount is: Nnickel-iron-titanium / (Nnickel-iron-titanium+Ncobalt) = 3.5 / 5.5 = 63.6%.

[0133] The cobalt-based spinel oxide nanomaterials obtained above were subjected to X-ray diffraction (XRD). The diffraction pattern is shown in [reference needed]. Figure 18 Consistent with the standard card for nickel-cobalt spinel oxide, the results indicate that the cobalt-based spinel oxide nanomaterials synthesized by the two-step synthesis method possess a nickel-cobalt spinel structure, exhibit good crystallinity, and are free from phase separation. The obtained cobalt-based spinel oxide nanomaterials were subjected to scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy-elemental mapping (EDS-Mapping), as shown... Figure 19 As shown, the results indicate that the cobalt-based spinel oxide nanomaterials synthesized by the two-step synthesis method exhibit a distinct needle-like and lamellar mixed morphology, and as... Figure 20 The uniform distribution of elements shown demonstrates the successful doping of nickel, iron, and titanium.

[0134] Example 8: Preparation of Nickel, Iron, and Vanadium-Doped Cobalt-Based Spinel Oxide Nanomaterials by a Two-Step Hydrothermal-High-Temperature Annealing Method

[0135] Referring to the method in Example 6, the hydrothermal reaction solution was replaced with: 21.6 mmol of ammonium fluoride, 26.4 mmol of urea, 0.66 mmol of nickel nitrate, 0.66 mmol of cobalt nitrate, 0.33 mmol of ferric nitrate, 0.16 mmol of vanadium tetrachloride, and 36 mL of water. In this solution, the concentrations of cobalt salt, nickel salt, ferric salt, and vanadium salt were 0.018 mol / L, 0.01 mol / L, and 0.004 mol / L, respectively. The concentration of urea was 14.6 times the sum of the concentrations of nickel, ferric, vanadium, and cobalt salts. With all other conditions unchanged, cobalt-based spinel oxide nanomaterials were obtained.

[0136] The ratio of nickel, cobalt, iron, and vanadium in the cobalt-based spinel oxide nanomaterial is 2:2:1:0.5, and the doping amount of nickel, iron, and vanadium in the nickel-iron-vanadium-doped cobalt-based spinel nanomaterial is 63.6%. The formula for calculating the nickel-iron-vanadium doping amount is: Nnickel-iron-vanadium / (Nnickel-iron-vanadium+Ncobalt) = 3.5 / 5.5 = 63.6%.

[0137] The cobalt-based spinel oxide nanomaterials obtained above were subjected to X-ray diffraction (XRD). The diffraction pattern is shown in [reference needed]. Figure 21 Consistent with the standard card for nickel-cobalt spinel oxide, the results indicate that the cobalt-based spinel oxide nanomaterials synthesized by the two-step synthesis method possess a nickel-cobalt spinel structure, exhibit good crystallinity, and are free from phase separation. The obtained cobalt-based spinel oxide nanomaterials were subjected to scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy-elemental mapping (EDS-Mapping), as shown... Figure 22 As shown, the results indicate that the cobalt-based spinel oxide nanomaterials synthesized by the two-step synthesis method have a distinct lamellar morphology, and as... Figure 23 The uniform distribution of elements shown demonstrates the successful doping of nickel, iron, and vanadium.

[0138] Example 9: Preparation of Nickel, Iron, and Chromium-Doped Cobalt-Based Spinel Oxide Nanomaterials by a Two-Step Hydrothermal-High-Temperature Annealing Method

[0139] Referring to the method in Example 6, the hydrothermal reaction solution was replaced with: 2.2 mmol of ammonium fluoride, 26.4 mmol of urea, 0.66 mmol of nickel nitrate, 0.66 mmol of cobalt nitrate, 0.33 mmol of ferric nitrate, 0.33 mmol of chromium nitrate, and 36 mL of water. In this solution, the concentrations of cobalt salt, nickel salt, ferric salt, and chromium salt were 0.01 mol / L, and the concentration of urea was 13 times the sum of the concentrations of nickel, ferric, chromium, and cobalt salts. With all other conditions unchanged, cobalt-based spinel oxide nanomaterials were obtained.

[0140] The nickel-cobalt-iron-chromium ratio in the cobalt-based spinel oxide nanomaterial is 2:2:1:1, and the nickel-iron-chromium doping content in the cobalt-iron-chromium-doped cobalt-based spinel nanomaterial is 63.6%. The formula for calculating the nickel-iron-chromium doping content is: Nnickel-iron-chromium / (Nnickel-iron-chromium + Ncobalt) = 4 / 6 = 66.7%.

[0141] The cobalt-based spinel oxide nanomaterials obtained above were subjected to X-ray diffraction (XRD). The diffraction pattern is shown in [reference needed]. Figure 24Consistent with the standard card for nickel-cobalt spinel oxide, the results indicate that the cobalt-based spinel oxide nanomaterials synthesized by the two-step synthesis method possess a nickel-cobalt spinel structure, exhibit good crystallinity, and are free from phase separation. The obtained cobalt-based spinel oxide nanomaterials were subjected to scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy-elemental mapping (EDS-Mapping), as shown... Figure 25 As shown, the results indicate that the cobalt-based spinel oxide nanomaterials synthesized by the two-step synthesis method have a distinct lamellar morphology, and as... Figure 26 The uniform distribution of elements shown demonstrates the successful doping of nickel, iron, and chromium.

[0142] Example 10: Preparation of Nickel, Iron, and Aluminum-Doped Cobalt-Based Spinel Oxide Nanomaterials by a Two-Step Hydrothermal-High-Temperature Annealing Method

[0143] Referring to the method in Example 6, the hydrothermal reaction solution was replaced with: 2.2 mmol of ammonium fluoride, 26.4 mmol of urea, 0.66 mmol of nickel nitrate, 0.66 mmol of cobalt nitrate, 0.165 mmol of ferric nitrate, 0.165 mmol of aluminum nitrate, and 36 mL of water. In this solution, the concentration of cobalt salt was 0.018 mol / L, the concentration of nickel salt was 0.018 mol / L, and the concentrations of iron salt and aluminum salt were 0.004 mol / L each. The concentration of urea was 16 times the sum of the concentrations of nickel, iron, aluminum, and cobalt salts. With all other conditions unchanged, cobalt-based spinel oxide nanomaterials were obtained.

[0144] The ratio of nickel, cobalt, iron, and aluminum in the cobalt-based spinel oxide nanomaterial is 2:2:0.5:0.5, and the doping amount of nickel, iron, and chromium in the cobalt-iron-aluminum doped cobalt-based spinel nanomaterial is 60%. The formula for calculating the cobalt-iron-aluminum doping amount is: Nnickel-iron-aluminum / (Nnickel-iron-aluminum + Ncobalt) = 3 / 5 = 60%.

[0145] The cobalt-based spinel oxide nanomaterials obtained above were subjected to X-ray diffraction (XRD). The diffraction pattern is shown in [reference needed]. Figure 27 Consistent with the standard card for nickel-cobalt spinel oxide, the results indicate that the cobalt-based spinel oxide nanomaterials synthesized by the two-step synthesis method possess a nickel-cobalt spinel structure, exhibit good crystallinity, and are free from phase separation. The obtained cobalt-based spinel oxide nanomaterials were subjected to scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy-elemental mapping (EDS-Mapping), as shown... Figure 28 As shown in the figure, the results indicate that the cobalt-based spinel oxide nanomaterial synthesized by the two-step synthesis method has a distinct needle-like morphology and a uniform elemental distribution, as shown in the figure, proving the successful doping of nickel, iron, and aluminum.

[0146] Example 11: Preparation of Nickel, Iron, and Manganese-Doped Cobalt-Based Spinel Oxide Nanomaterials by a Two-Step Hydrothermal-High-Temperature Annealing Method

[0147] Referring to the method in Example 6, the hydrothermal reaction solution was replaced with: 2.2 mmol of ammonium fluoride, 26.4 mmol of urea, 0.66 mmol of nickel nitrate, 0.66 mmol of cobalt nitrate, 0.33 mmol of ferric nitrate, 0.165 mmol of manganese nitrate, and 36 mL of water. In this solution, the concentrations of cobalt salt, nickel salt, iron salt, and manganese salt were 0.018 mol / L, 0.01 mol / L, and 0.004 mol / L, and the concentration of urea was 14.5 times the sum of the concentrations of nickel, iron, manganese, and cobalt salts. With all other conditions unchanged, cobalt-based spinel oxide nanomaterials were obtained.

[0148] The ratio of cobalt, nickel, iron, and manganese in the cobalt-based spinel oxide nanomaterial is 2:2:1:0.5, and the doping amount of nickel, iron, and manganese in the nickel-iron-manganese-doped cobalt-based spinel nanomaterial is 63.6%. The formula for calculating the nickel-iron-manganese doping amount is: Nnickel-iron-manganese / (Nnickel-iron-manganese+Ncobalt) = 3.5 / 5.5 = 63.6%.

[0149] The cobalt-based spinel oxide nanomaterials obtained above were subjected to X-ray diffraction (XRD). The diffraction pattern is shown in [reference needed]. Figure 29 Consistent with the standard card for nickel-cobalt spinel oxide, the results indicate that the cobalt-based spinel oxide nanomaterials synthesized by the two-step synthesis method possess a nickel-cobalt spinel structure, exhibit good crystallinity, and are free from phase separation. The obtained cobalt-based spinel oxide nanomaterials were subjected to scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy-elemental mapping (EDS-Mapping), as shown... Figure 30 As shown, the results indicate that the cobalt-based spinel oxide nanomaterials synthesized by the two-step synthesis method have a distinct lamellar morphology, and as... Figure 31 The uniform elemental distribution shown demonstrates successful nickel-iron-manganese doping. Subsequent aberration-corrected transmission microscopy characterization was then performed, as shown... Figure 32 In the figure, 0.462nm and 0.246nm correspond to the 111 and 311 crystal planes of nickel-cobalt spinel. It can be seen that due to the doping of nickel-iron-manganese, the crystal structure is complete and the lattice size is expanded.

[0150] Example 12: Preparation of Nickel-Cerium-Doped Cobalt-Based Spinel Oxide Nanomaterials by a Two-Step Hydrothermal-High-Temperature Annealing Method

[0151] Referring to the method in Example 6, the hydrothermal reaction solution was replaced with: 2.2 mmol of ammonium fluoride, 26.4 mmol of urea, 0.66 mmol of nickel nitrate, 0.66 mmol of cobalt nitrate, 0.33 mmol of cerium nitrate, and 36 mL of water. In this solution, the concentrations of cobalt salt, nickel salt, and cerium salt were 0.01 mol / L, and the concentration of urea was 16 times the sum of the concentrations of nickel, cerium, and cobalt salts. The muffle furnace calcination conditions were: a heating rate of 5 °C / min, a holding temperature of 400 °C, and a holding time of 3 hours. This yielded cobalt-based spinel oxide nanomaterials.

[0152] The nickel-cobalt-cerium ratio in the cobalt-based spinel oxide nanomaterial is 2:2:1, and the nickel-cerium doping content in the nickel-neodymium-doped cobalt-based spinel nanomaterial is 60%. The formula for calculating the nickel-cerium doping content is: Nnickel-cerium / (Nnickel-cerium+Ncobalt) = 3 / 5 = 60%.

[0153] The cobalt-based spinel oxide nanomaterials obtained above were subjected to X-ray diffraction (XRD). The diffraction pattern is shown in [reference needed]. Figure 33 Consistent with the standard card for nickel-cobalt spinel oxide, the results indicate that the cobalt-based spinel oxide nanomaterials synthesized by the two-step synthesis method possess a nickel-cobalt spinel structure, exhibit good crystallinity, and are free from phase separation. The obtained cobalt-based spinel oxide nanomaterials were subjected to scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy-elemental mapping (EDS-Mapping), as shown... Figure 34 As shown, the results indicate that the cobalt-based spinel oxide nanomaterials synthesized by the two-step synthesis method exhibit a distinct nanoflower-like morphology, and as shown... Figure 35 The uniform distribution of elements shown demonstrates the successful doping of nickel and cerium.

[0154] Example 13: Preparation of Nickel- and Neodymium-Doped Cobalt-Based Spinel Oxide Nanomaterials by a Two-Step Hydrothermal-High-Temperature Annealing Method

[0155] Referring to the method in Example 6, the hydrothermal reaction solution was replaced with: 2.2 mmol of ammonium fluoride, 26.4 mmol of urea, 0.05 mmol of nickel nitrate, 9.9 mmol of cobalt nitrate, 0.05 mmol of neodymium nitrate, and 36 mL of water. In this solution, the cobalt salt concentration was 0.275 mol / L, and the nickel and neodymium salt concentrations were 0.001 mol / L respectively. The urea concentration was 2.64 times the sum of the nickel, neodymium, and cobalt salt concentrations. The muffle furnace calcination conditions were: a heating rate of 5 °C / min, a holding temperature of 400 °C, and a holding time of 3 hours. This yielded cobalt-based spinel oxide nanomaterials.

[0156] The nickel-neodymium doping amount in the cobalt-based spinel oxide nanomaterial is 1%. The formula for calculating the nickel-neodymium doping amount is: Nnickel-neodymium / (Nnickel-neodymium+Ncobalt) = 1 / 100 = 1%.

[0157] The cobalt-based spinel oxide nanomaterials obtained above were subjected to X-ray diffraction (XRD). The diffraction pattern is shown in [reference needed]. Figure 36 Consistent with the standard card for nickel-cobalt spinel oxide, the results indicate that the cobalt-based spinel oxide nanomaterials synthesized by the two-step synthesis method possess a nickel-cobalt spinel structure, exhibit good crystallinity, and are free from phase separation. The obtained cobalt-based spinel oxide nanomaterials were subjected to scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy-elemental mapping (EDS-Mapping), as shown... Figure 37 As shown, the results indicate that the cobalt-based spinel oxide nanomaterials synthesized by the two-step synthesis method exhibit a distinct nanoflower-like morphology, and as shown... Figure 38 The uniform distribution of elements shown demonstrates the successful doping of nickel and neodymium.

[0158] Example 14: Preparation of Cobalt Tetraoxide Spinel Oxide Nanomaterials by a Two-Step Hydrothermal-High-Temperature Annealing Method

[0159] Referring to the method in Example 6, the hydrothermal reaction solution was replaced with: 2.2 mmol of ammonium fluoride, 26.4 mmol of urea, 0.99 mmol of cobalt nitrate, and 36 mL of water. The muffle furnace calcination conditions were: a heating rate of 10 °C / min, a holding temperature of 400 °C, and a holding time of 5 hours. This yielded cobalt-based spinel oxide nanomaterials. The doping content in the cobalt-based spinel oxide nanomaterials was 0%.

[0160] The cobalt-based spinel oxide nanomaterials obtained above were subjected to X-ray diffraction (XRD). The diffraction pattern is shown in [reference needed]. Figure 39 Consistent with the standard card for cobalt spinel oxide, the results indicate that the spinel phase cobalt tetroxide synthesized by the two-step synthesis method exhibits good crystallinity and no phase separation. The obtained cobalt-based spinel oxide nanomaterials were subjected to scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy-elemental mapping (EDS-Mapping), as shown... Figure 40 As shown, the results indicate that the cobalt-based spinel oxide nanomaterials synthesized by the two-step synthesis method exhibit a distinct nanoflower-like morphology, and as shown... Figure 41 The elements shown are evenly distributed.

[0161] Application Example 1

[0162] The electrolytic oxygen evolution performance of the cobalt-based spinel oxide nanomaterials obtained in Examples 1 (NiCo Spinel), 2 (CoFe Spinel), 12 (NiCoCeSpinel), 13 (NiCoNd Spinel), and 14 (Co3O4) was tested using a three-electrode system: a mercury oxide electrode was used as the reference electrode, a platinum sheet electrode as the counter electrode, and the working electrodes were the cobalt-based spinel oxide nanomaterials of Examples 1, 2, 12, 13, and 14 with an effective area of ​​1*1 cm². A 1 mol / L potassium hydroxide solution was used as the electrolyte, and the electrolyte temperature was 25°C. Cyclic voltammetry was first performed in the range of 0–1 V vs RHE until the electrode reached a stable state. Then, a fresh electrolyte was used, and a linear scan was performed at 5 mV / s in the range of 0–1 V vs RHE. The resulting linear scan voltammetry is shown below. Figure 42 As shown in the figure, the multi-metal-doped cobalt-based spinel nanomaterials obtained in Examples 1, 2, 12, and 13 exhibit better oxygen evolution performance in water electrolysis, significantly superior to the cobalt tetroxide material obtained in Example 14. The overpotentials of the materials in Examples 1, 2, 12, 13, and 14 at a current density of 10 mA / cm² are, respectively, 310, 275, 250, 301, and 360 mV.

[0163] Application Example 2

[0164] The electrolytic oxygen evolution performance of the cobalt-based spinel oxide nanomaterials obtained in Examples 3 (NiCoV Spinel), 4 (NiCoCr Spinel), 5 (NiCoMnSpinel), 6 (NiCoFe Spinel), and 14 (Co3O4) was tested using a three-electrode system: a mercury oxide electrode as the reference electrode, a platinum sheet electrode as the counter electrode, and the cobalt-based spinel oxide nanomaterials of Examples 3, 4, 5, 6, and 14 with an effective area of ​​1*1 cm² as the working electrode. A 1 mol / L potassium hydroxide solution was used as the electrolyte at a temperature of 25°C. Cyclic voltammetry was first performed in the range of 0–1 V vs RHE until the electrode reached a stable state. Then, a fresh electrolyte was added, and a linear scan was performed at 5 mV / s in the range of 0–1 V vs RHE. The resulting linear scan voltammetry plots are shown below. Figure 43 As shown in the figure, the multi-metal-doped cobalt-based spinel nanomaterials obtained in Examples 3, 4, 5, and 6 exhibit better oxygen evolution performance in water electrolysis, significantly superior to the cobalt tetroxide material obtained in Example 14. The overpotentials of the materials in Examples 3, 4, 5, 6, and 14 at a current density of 10 mA / cm² are 313, 298, 298, 252, and 360 mV, respectively.

[0165] Application Example 3

[0166] The electrolytic oxygen evolution performance of the cobalt-based spinel oxide nanomaterials obtained in Examples 7 (NiCoFeTi Spinel), 8 (NiCoFeV Spinel), 9 (NiCoFeCrSpinel), 10 (NiCoFeAl Spinel), 11 (NiCoFeMn Spinel), and 14 (Co3O4) was tested using a three-electrode system: a mercury oxide electrode as the reference electrode, a platinum sheet electrode as the counter electrode, and the cobalt-based spinel oxide nanomaterials of Examples 7, 8, 9, 10, 11, and 14 with an effective area of ​​1*1 cm² as the working electrode. A 1 mol / L potassium hydroxide solution was used as the electrolyte at a temperature of 25°C. Cyclic voltammetry was first performed in the range of 0–1 V vs RHE until the electrode reached a stable state. Then, a fresh electrolyte was used, and a linear scan was performed at 5 mV / s in the range of 0–1 V vs RHE. The resulting linear scan voltammetry plots are shown below. Figure 44 As shown in the figure, the multi-metal-doped cobalt-based spinel nanomaterials obtained in Examples 7, 8, 9, 10, and 11 exhibit better oxygen evolution performance in water electrolysis, significantly superior to the cobalt tetroxide material obtained in Example 14. The overpotentials of the materials in Examples 7, 8, 9, 10, 11, and 14 at a current density of 10 mA / cm² are, respectively, 260, 252, 233, 234, 234, and 360 mV.

[0167] Application Example 4: Stability Test of Oxygen Evolution Reaction of Cobalt-Based Spinel Oxide Nanomaterials under Constant Current Condition at 25℃

[0168] The oxygen evolution stability of the cobalt-based spinel oxide nanomaterial obtained in Example 1 under alkaline water electrolysis was tested using a two-electrode system: the cobalt-based spinel oxide nanomaterial was used as the anode of the electrolyzer, and a platinum sheet electrode was used as the cathode electrode. The stability was tested in alkaline water electrolysis. The anode was the cobalt-based spinel oxide nanomaterial of Example 1 with an effective area of ​​1*1 square centimeters, and the cathode was a platinum sheet electrode with an effective area of ​​1*1 square centimeters. A constant current test was conducted at 100 mA per square centimeter in 1 mol / L potassium hydroxide solution.

[0169] At an electrolyte temperature of 25°C, using 1 mol / L potassium hydroxide as the electrolyte, a constant current test was performed at a current of 100 mA / cm², and the resulting constant current curve is shown below. Figure 45 As shown, the nickel-doped cobalt-based spinel oxide nanomaterials obtained in Example 1 can operate stably under these conditions and can operate for at least 1000 hours.

[0170] Application Example 5: Stability Test of Oxygen Evolution Reaction of Cobalt-Based Spinel Oxide Nanomaterials under Constant Current Condition at 45℃

[0171] The oxygen evolution stability of the cobalt-based spinel oxide nanomaterial obtained in Example 7 under alkaline water electrolysis was tested using a two-electrode system: the cobalt-based spinel oxide nanomaterial was used as the anode of the electrolyzer, and a platinum sheet electrode was used as the cathode electrode. The stability test was conducted in alkaline water electrolysis. The anode was the cobalt-based spinel oxide nanomaterial of Example 7 with an effective area of ​​1*1 square centimeters, and the cathode was a platinum sheet electrode with an effective area of ​​1*1 square centimeters.

[0172] At an electrolyte temperature of 45℃, using 6 mol / L potassium hydroxide as the electrolyte, a constant current test was performed at a current of 2 amps per square centimeter. The resulting constant current curve is shown below. Figure 46 As shown, the cobalt-based spinel oxide nanomaterial described in Example 7 can operate stably under these conditions and can operate for at least 4300 hours.

[0173] Application Example 6: Stability Test of Oxygen Evolution Reaction of Cobalt-based Spinel Oxide Nanomaterials under Intermittent Start-Stop Conditions at 45°C

[0174] The oxygen evolution stability of the cobalt-based spinel oxide nanomaterial obtained in Example 8 under alkaline water electrolysis was tested using a two-electrode system: the cobalt-based spinel oxide nanomaterial was used as the anode of the electrolyzer, and a nickel foam metal electrode was used as the cathode electrode. The stability was tested in alkaline water electrolysis. The anode was the cobalt-based spinel oxide nanomaterial of Example 8 with an effective area of ​​1*1 square centimeters, and the cathode was a nickel foam metal electrode with an effective area of ​​1*1 square centimeters.

[0175] At an electrolyte temperature of 45°C, using 6 mol / L potassium hydroxide as the electrolyte, a simulated intermittent electrolysis stability test was conducted with 12-hour start-up and shutdown cycles at a current of 2 amps per square centimeter. The obtained voltage-time curves are shown below. Figure 47 As shown, the cobalt-based spinel oxide nanomaterials obtained in Example 8 can operate stably under these conditions and can operate for at least 3500 hours.

[0176] Application Example 7: Stability Test of Oxygen Evolution Reaction of Cobalt-Based Spinel Oxide Nanomaterials under Constant Current Condition at 80℃

[0177] The oxygen evolution stability of the cobalt-based spinel oxide nanomaterial obtained in Example 11 under alkaline water electrolysis was tested using a two-electrode system: the cobalt-based spinel oxide nanomaterial was used as the anode of the electrolyzer, and a platinum sheet electrode was used as the cathode electrode. The stability test was conducted in alkaline water electrolysis. The anode was the cobalt-based spinel oxide nanomaterial of Example 11 with an effective area of ​​1*1 square centimeters, and the cathode was a platinum sheet electrode with an effective area of ​​1*1 square centimeters.

[0178] At an electrolyte temperature of 80℃, using 6 mol / L potassium hydroxide as the electrolyte, a constant current test, i.e., chronopotentiometry (CP), was performed at a current of 1 amp / cm². The resulting constant current curve is shown below. Figure 48 As shown, the cobalt-based spinel oxide nanomaterial described in Example 11 can operate stably under these conditions and can operate for at least 5000 hours.

[0179] Application Example 8: Stability Test of Oxygen Evolution Reaction of Cobalt-based Spinel Oxide Nanomaterials under Intermittent Start-Stop Conditions at 80℃

[0180] The oxygen evolution stability of the cobalt-based spinel oxide nanomaterial obtained in Example 11 under alkaline water electrolysis was tested using a two-electrode system: the cobalt-based spinel oxide nanomaterial was used as the anode of the electrolyzer, and a nickel foam metal electrode was used as the cathode electrode. The stability was tested in alkaline water electrolysis. The anode was the cobalt-based spinel oxide nanomaterial of Example 11 with an effective area of ​​1*1 square centimeters, and the cathode was a nickel foam metal electrode with an effective area of ​​1*1 square centimeters.

[0181] At an electrolyte temperature of 80℃, using 8 mol / L potassium hydroxide as the electrolyte, a constant current test was performed at a current of 10 amps per square centimeter. The resulting constant current curve is shown below. Figure 49 As shown, the cobalt-based spinel oxide nanomaterial described in Example 11 can operate stably under these conditions and can operate for at least 200 hours.

[0182] Application Example 9: Stability Test of Cobalt-Based Spinel Oxide Nanomaterials under Constant Current Condition at 100℃ for Oxygen Evolution Reaction

[0183] The oxygen evolution stability of the cobalt-based spinel oxide nanomaterial obtained in Example 10 under alkaline water electrolysis was tested using a two-electrode system: the cobalt-based spinel oxide nanomaterial was used as the anode of the electrolyzer, and a platinum sheet electrode was used as the cathode electrode. The stability test was conducted in alkaline water electrolysis. The anode was the cobalt-based spinel oxide nanomaterial of Example 10 with an effective area of ​​1*1 square centimeters, and the cathode was a platinum sheet electrode with an effective area of ​​1*1 square centimeters.

[0184] At an electrolyte temperature of 100℃, using 8 mol / L potassium hydroxide as the electrolyte, a constant current test was performed at a current of 1 amp / cm², and the resulting constant current curve is shown below. Figure 50 As shown, the cobalt-based spinel oxide nanomaterial described in Example 10 can operate stably under these conditions and can operate for at least 4000 hours.

[0185] Application Example 10: Stability Test of Oxygen Evolution Reaction of Cobalt-Based Spinel Oxide Nanomaterials under Constant Current Condition at 120℃

[0186] The oxygen evolution stability of the cobalt-based spinel oxide nanomaterial obtained in Example 12 under alkaline water electrolysis was tested using a two-electrode system: the cobalt-based spinel oxide nanomaterial was used as the anode of the electrolyzer, and a platinum sheet electrode was used as the cathode electrode. The stability test was conducted in alkaline water electrolysis. The anode was the cobalt-based spinel oxide nanomaterial of Example 12 with an effective area of ​​1*1 square centimeters, and the cathode was a platinum sheet electrode with an effective area of ​​1*1 square centimeters.

[0187] At an electrolyte temperature of 120℃, using 14 mol / L potassium hydroxide as the electrolyte, a constant current test was performed at a current of 1 amp / cm², and the resulting constant current curve is shown below. Figure 51 As shown, the cobalt-based spinel oxide nanomaterial described in Example 12 can operate stably under these conditions and can operate for at least 2000 hours.

[0188] Application Example 11: Oxygen Evolution Reaction Activity Test of Cobalt-Based Spinel Oxide Nanomaterials in an Anion Exchange Membrane (AEM) Electrolyzer at 60°C

[0189] The electrocatalytic oxygen evolution performance of the cobalt-based spinel oxide nanomaterial obtained in Example 11 as the anode of the AEM electrolyzer was tested in an anion exchange membrane (AEM) electrolyzer: the cobalt-based spinel oxide nanomaterial of Example 11 was used as the anode of the electrolyzer, and a nickel-molybdenum alloy electrode was used as the cathode electrode of the electrolyzer. The activity was tested in alkaline electrolyzed water. The anode was the cobalt-based spinel oxide nanomaterial of Example 11 with an effective area of ​​2*2 square centimeters, and the cathode was a nickel-molybdenum alloy electrode with an effective area of ​​2*2 square centimeters.

[0190] At an electrolyte temperature of 60℃, using 1 mol / L potassium hydroxide as the electrolyte, the electrolytic cell performance was tested using linear sweep voltammetry, and the obtained current-potential curves are shown below. Figure 52 As shown, when the cobalt-based spinel oxide nanomaterial of Example 11 is used as the anode of the electrolyzer and the nickel-molybdenum alloy electrode is used as the cathode electrode, the anion exchange membrane electrolyzer exhibits good performance: the voltage of the anion exchange membrane can be only 1.71 volts when the current density is 1 amp per square centimeter; and the voltage of the anion exchange membrane is 1.8 volts when the current density is 2 amps per square centimeter.

[0191] Application Example 12: Stability test of cobalt-based spinel oxide nanomaterials in oxygen evolution reaction under constant current conditions at 60°C in an anion exchange membrane (AEM) electrolyzer.

[0192] The electrocatalytic oxygen evolution performance of the cobalt-based spinel oxide nanomaterial obtained in Example 11 as the anode of the AEM electrolyzer was tested in an anion exchange membrane (AEM) electrolyzer: the cobalt-based spinel oxide nanomaterial of Example 11 was used as the anode of the electrolyzer, and a nickel-molybdenum alloy electrode was used as the cathode electrode of the electrolyzer. The activity was tested in alkaline electrolyzed water. The anode was the cobalt-based spinel oxide nanomaterial of Example 11 with an effective area of ​​2*2 square centimeters, and the cathode was a nickel-molybdenum alloy electrode with an effective area of ​​2*2 square centimeters.

[0193] At an electrolyte temperature of 60℃, using 1 mol / L potassium hydroxide as the electrolyte, a constant current test was performed at a current of 1 ampere per square centimeter. The resulting constant current curve is shown below. Figure 53 As shown, the anion exchange membrane electrolyzer using the cobalt-based spinel oxide nanomaterial of Example 11 as the anode and the nickel-molybdenum alloy electrode as the cathode electrode can operate stably under these conditions and can operate for at least 1750 hours.

[0194] Comparative Example 1 - Synthesis of Nickel-Iron Hydrotalcite Nanomaterials

[0195] Nickel-iron hydrotalcite nanomaterials were prepared using a hydrothermal synthesis method. Specifically, a 36 mL solution was prepared containing 21.6 mmol of ammonium fluoride, 26.4 mmol of urea, 0.66 mmol of nickel nitrate, 0.33 mmol of ferric nitrate, and 36 mL of water. The solution was then poured into a reaction vessel. The concentrations of the nickel source in this solution were 0.02 mol / L, the iron source concentration was 0.01 mol / L, the urea concentration was 0.73 mol / L, and the ammonium fluoride concentration was 0.6 mol / L. The treated conductive substrate was immersed in the solution and placed in an oven at 120°C for 10 hours. The resulting material was washed three times with water and ethanol, and then vacuum-dried at 60°C for 10 hours.

[0196] The precursor of the above nickel-iron hydrotalcite nanomaterial was subjected to X-ray diffraction (XRD). The diffraction pattern is shown in [reference needed]. Figure 54 The results are consistent with the standard card for nickel-iron hydrotalcite with carbonate intercalation, indicating that the synthesized nickel-iron hydrotalcite nanomaterial is a pure hydrotalcite phase with good crystallinity and no phase separation.

[0197] Comparative Application Example 1 - Stability Test of Oxygen Evolution Reaction of Nickel-Iron Hydrotalcite Nanomaterials under Constant Current Condition at 80℃

[0198] The oxygen evolution stability of the nickel-iron layered double hydroxide nanomaterial obtained in Comparative Example 1 under alkaline water electrolysis was tested using a two-electrode system: the nickel-iron layered double hydroxide nanomaterial was used as the anode of the electrolytic cell, and a platinum sheet electrode was used as the cathode electrode. The stability test was conducted in alkaline water electrolysis. The anode was the nickel-iron layered double hydroxide nanomaterial obtained in Comparative Example 1 with an effective area of ​​1*1 square centimeters, and the cathode was a platinum sheet electrode with an effective area of ​​1*1 square centimeters.

[0199] At an electrolyte temperature of 80℃, using 6 mol / L potassium hydroxide as the electrolyte, a constant current test was performed at a current of 1 amp / cm², and the resulting constant current curve is shown below. Figure 55 As shown, the nickel-iron hydrotalcite nanomaterial obtained in Comparative Example 1 exhibits severe voltage decay under these conditions. After 150 hours of operation, the electrolytic cell voltage decayed from an initial 2.08 volts to 2.42 volts after 130 hours, a decay rate of 2.6 millivolts per hour. Compared to the oxygen evolution reaction stability test of the cobalt-based spinel oxide nanomaterial in Application Example 7 under constant current conditions at 80°C, the cobalt-based spinel oxide nanomaterial in Example 11 of Application Example 7 operates at a voltage of 2.2 volts, and exhibits zero decay rate from the initial voltage after 5000 hours of operation. If simultaneously applied to industrial applications, the cobalt-based spinel oxide nanomaterial in Example 11 can significantly save on electrical resources.

[0200] Comparative Application Example 2 - Oxygen Evolution Reaction and Analysis of Nickel-Iron Hydrotalcite Nanomaterials under Constant Current Condition at 80℃

[0201] The electrolytic oxygen evolution performance of the nickel-iron layered double hydroxide nanomaterial obtained in Comparative Example 1 was tested using a three-electrode system: a mercury oxide electrode was used as the reference electrode, a platinum sheet electrode as the counter electrode, and the nickel-iron layered double hydroxide nanomaterial obtained in Comparative Example 1 with an effective area of ​​1*1 square centimeters was used as the working electrode. A 1 mol / L potassium hydroxide solution was used as the electrolyte. Cyclic voltammetry was first performed in the range of 0–1 V vs RHE until the electrode reached a stable state. Then, a fresh electrolyte was used, and a linear scan was performed at 5 mV / s in the range of 0–1 V vs RHE. The obtained linear scan voltammetry is shown below. Figure 56 As shown, the overpotential of the nickel-iron hydrotalcite in Comparative Example 1 before the reaction was 215 mV at 10 mA.

[0202] The electrolytic oxygen evolution performance of the nickel-iron layered double hydroxide nanomaterial tested in Example 1 was tested using a three-electrode system: a mercury oxide electrode as the reference electrode, a platinum sheet electrode as the counter electrode, and a nickel-iron layered double hydroxide nanomaterial with an effective area of ​​1*1 square centimeters as the working electrode. A 1 mol / L potassium hydroxide solution was used as the electrolyte. Cyclic voltammetry was first performed in the range of 0–1 V vs RHE until the electrode reached a stable state. Then, a fresh electrolyte was used, and a linear scan was performed at 5 mV / s in the range of 0–1 V vs RHE. The resulting linear voltammetry is shown below. Figure 56 As shown.

[0203] like Figure 56 As shown, the obtained linear sweep voltammetry plot indicates that after 150 hours of continuous operation with an electrolyte of 6 mol / L potassium hydroxide, an electrolyte temperature of 80°C, and a current density of 1 A / cm², the overpotential of the nickel-iron hydrotalcite nanomaterial tested in Comparative Application Example 1 was 251 mV at 10 mA / cm², indicating a significant performance degradation compared to the nickel-iron hydrotalcite before the reaction.

[0204] Next, X-ray photoelectron spectroscopy (XPS) was performed on the nickel-iron hydrotalcite nanomaterials tested in Comparative Example 1 and Comparative Application Example 2. The chemical information of the sample surface, including the type, content, chemical state, and electronic structure of elements, was analyzed by measuring the energy distribution of photoelectrons. The results are as follows: Figure 57 As shown.

[0205] The detection limit for X-ray photoelectron spectroscopy (XPS) is typically 0.1% (atomic percentage). Figure 57 As shown, the iron element in the nickel-iron layered double hydroxide nanomaterial of Comparative Example 1 has a +3 valence. In contrast, the iron element on the surface of the nickel-iron layered double hydroxide nanomaterial obtained after a 150-hour constant current stability test in Application Example 1 is below the detection limit. This indicates that in Application Example 1, when the electrolyte temperature is 80°C, the electrolyte is 6 mol / L potassium hydroxide, and a constant current test is performed at 1 amp / cm² for 150 hours, the iron element in the nickel-iron layered double hydroxide is almost completely dissolved.

[0206] The nickel-iron hydrotalcite nanomaterials obtained in Comparative Example 1 were subjected to scanning electron microscopy (SEM) testing, such as... Figure 58 As shown, the nickel-iron hydrotalcite nanomaterial obtained in Comparative Example 1 has a regular sheet-like nanoarray structure. The nickel-iron hydrotalcite nanomaterial obtained in Comparative Application Example 1 was subjected to scanning electron microscopy (SEM) testing, as shown... Figure 59As shown, the nickel-iron hydrotalcite nanomaterial obtained in Comparative Application Example 1 exhibits an irregular morphology due to structural collapse. This indicates that in Comparative Application Example 1, when the electrolyte temperature was 80°C, the electrolyte used was 6 mol / L potassium hydroxide, and a constant current test was conducted at 1 amp / cm² for 150 hours, the geometric structure of the nickel-iron hydrotalcite completely collapsed.

[0207] Therefore, by comparing and analyzing the oxygen evolution activity of alkaline electrolysis water before and after the reaction of nickel-iron hydrotalcite, the iron content in the material, and the surface morphology of the material, it is shown that when the electrolyte temperature is 80℃, the electrolyte is 6 mol / L potassium hydroxide, and a constant current test is performed at a current of 1 amp / cm², the material stability is poor and the structure-property relationship of the material is seriously changed.

[0208] Comparative Example 2 - Synthesis of Nickel-Cobalt-Based Spinel Oxide Nanomaterials Doped with Iron and Zinc

[0209] The method for preparing nickel-cobalt-based spinel oxide nanomaterials doped with iron and zinc is the same as in Example 11, except that soluble iron salt and soluble zinc salt are added during synthesis instead of soluble iron salt and soluble manganese salt.

[0210] The above nickel-cobalt-based spinel oxide nanomaterials were subjected to X-ray diffraction (XRD). The diffraction pattern is shown in [reference needed]. Figure 60 Consistent with the standard card for nickel-cobalt spinel oxide, the results indicate that the nickel-cobalt-based spinel oxide nanomaterials synthesized by the two-step synthesis method possess a nickel-cobalt spinel structure, exhibit good crystallinity, and are free from phase separation. Scanning electron microscopy (SEM) and EDS mapping analyses were performed on the material, as shown... Figure 61 and Figure 62 As shown. Figure 61 This indicates that the nickel-cobalt-based spinel oxide nanomaterials synthesized by the two-step synthesis method have a distinct lamellar morphology. Figure 62 As shown, the metal elements in the iron- and zinc-doped nickel-cobalt-based spinel oxide nanomaterials supported on a nickel foam substrate are uniformly distributed. This indicates the successful synthesis of the iron- and zinc-doped nickel-cobalt-based spinel oxide material.

[0211] Comparative Application Example 3 - Stability Test of Oxygen Evolution Reaction under Constant Current Condition at 60°C in an Anion Exchange Membrane (AEM) Electrolyte with Iron and Zinc Co-doped Nickel-Cobalt-based Spinel Oxide Nanomaterials.

[0212] The electrocatalytic oxygen evolution performance of the iron and zinc doped nickel-cobalt spinel oxide nanomaterial obtained in Comparative Example 2 as the anode of the AEM electrolyzer was tested in an anion exchange membrane (AEM) electrolyzer: The iron and zinc doped nickel-cobalt spinel oxide nanomaterial obtained in Comparative Example 2 was used as the anode of the electrolyzer, and a nickel-molybdenum alloy electrode was used as the cathode electrode. The activity was tested in alkaline electrolyzed water. The anode was the nickel-cobalt spinel oxide nanomaterial of Comparative Example 2 with an effective area of ​​2*2 square centimeters, and the cathode was the nickel-molybdenum alloy electrode with an effective area of ​​2*2 square centimeters.

[0213] At an electrolyte temperature of 60℃, using 1 mol / L potassium hydroxide as the electrolyte, a constant current test was performed at a current of 1 ampere per square centimeter. The resulting constant current curve is shown below. Figure 63 As shown, the iron and zinc co-doped nickel-cobalt spinel oxide nanomaterial obtained in Comparative Example 2, used as the anode of the electrolyzer, resulted in an anion exchange membrane electrolyzer with a nickel-molybdenum alloy electrode as the cathode electrode, which could only operate for 438 hours under these conditions. The AEM electrolyzer voltage rose from an initial 1.80V to a final 1.93V, ultimately terminating due to membrane damage. Figure 64 As shown, in membrane electrode systems, dissolved metal ions easily poison the ion transport channels of the polymer ion exchange membrane, hindering mass transfer, limiting catalytic reactions, and inducing severe Fenton reactions. The originally transparent anion exchange membrane is oxidized to yellow due to the Fenton effect. Simultaneously, the degradation of the anion exchange membrane causes the electrolyte to become contaminated with the polymeric components from the degraded anion exchange membrane, further affecting the reaction. Therefore, these factors ultimately lead to membrane electrode damage, causing an internal short circuit and terminating electrolysis.

[0214] The above explanation shows that not any metal doping into nickel-cobalt-based spinel oxide can improve the stability of oxygen evolution reaction in AEM devices.

Claims

1. A cobalt-based spinel oxide nanomaterial, characterized in that, The cobalt-based spinel oxide nanomaterial includes: a conductive substrate and a cobalt-based spinel oxide grown on the surface of the conductive substrate; The cobalt-based spinel oxide has the molecular formula M. x Co 1-x O4, where M is a transition metal or a p-block metal, and M is selected from one or more of the following: titanium, vanadium, chromium, manganese, iron, nickel, aluminum, cerium, and neodymium. x ranges from 0.01 to 0.

667.

2. The cobalt-based spinel oxide nanomaterial according to claim 1, characterized in that, In the cobalt-based spinel oxide nanomaterial, the doped metal M is uniformly dispersed inside the cobalt-based spinel, and the doped metal M replaces part of the cobalt positions in the crystal lattice. The crystal structure of the cobalt-based spinel oxide is a spinel phase and there are no other impurity phases.

3. A method for preparing the cobalt-based spinel oxide nanomaterial according to claim 1, characterized in that, The preparation method includes a two-step synthesis method, the first step being a hydrothermal reaction method or an electrodeposition method, and the second step being high-temperature annealing; The first step of the hydrothermal reaction method includes the following steps: adding metal salt, water-soluble cobalt salt, urea, and ammonium fluoride to water to obtain a solution, transferring the solution to a hydrothermal reactor, adding a conductive substrate, carrying out a hydrothermal reaction at a certain temperature, and holding the temperature for a certain time to obtain a precursor; The first step of the electrodeposition method includes the following steps: adding metal salt and water-soluble cobalt salt to water and dissolving them; placing the anode, cathode and reference electrode in the solution; using a conductive substrate on the cathode; and performing electrodeposition to obtain the precursor. The metal salt is a water-soluble metal salt, and the metal is selected from one or more of titanium, vanadium, chromium, manganese, iron, nickel, aluminum, cerium, and neodymium. The second step, high-temperature annealing, includes the following steps: calcining the precursor obtained in the first step under an inert gas or air atmosphere for a certain period of time.

4. The preparation method according to claim 3, characterized in that, In the first step of the hydrothermal reaction method, the reaction temperature is 60–200℃ and the holding time is 3–48h. The electrodeposition voltage is -1.0V to -2V vs calomel SCE, and the time is 100s to 7200s.

5. The preparation method according to claim 3, characterized in that, In the solution of the first step, the concentration of each metal salt is 0.001 to 1 mol per liter, the concentration of cobalt salt is 0.01 to 1 mol per liter, and the concentration of urea is 2.5 to 20 times the sum of the concentrations of each metal salt and cobalt salt.

6. The preparation method according to claim 3, characterized in that, The second step, high-temperature annealing, has a temperature of 250–800℃, a heating rate of 2–10℃ / min, and a reaction time of 2–10 hours.

7. The use of the cobalt-based spinel oxide nanomaterial of claim 1 as an anode material in an alkaline water electrolysis oxygen evolution reaction.

8. The use according to claim 7, characterized in that, The electrolyte in the alkaline water electrolysis oxygen evolution reaction contains an alkaline substance, which is selected from one or more of sodium hydroxide, potassium hydroxide, lithium hydroxide, rubidium hydroxide, and cesium hydroxide, and the total concentration of the alkaline substance is 1 to 14 mol per liter. The temperature range for the alkaline water electrolysis oxygen evolution reaction is 25–120°C. The current density range for the alkaline water electrolysis oxygen evolution reaction is 0.1 to 10 amperes per square centimeter.

9. The use according to claim 8, characterized in that, The electrolysis mode of the alkaline water electrolysis oxygen evolution reaction is: constant current, constant voltage, or frequent start-stop.

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