Nickel-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 nickel-cobalt-based spinel oxide nano material as well as a preparation method and application thereof. The nickel-cobalt-based spinel oxide nano material comprises a conductive substrate and a nickel-cobalt-based spinel oxide grown on the surface of the conductive substrate, the nickel-cobalt-based spinel oxide contains nickel, cobalt, iron and manganese elements; the metal doping does not change the intrinsic structure of the spinel, and the spinel phase is still perfectly maintained. Meanwhile, multiple metal elements are highly and uniformly dispersed in the material, so that active sites are comprehensively regulated and controlled, excellent thermodynamic and chemical stability is shown under severe conditions of high temperature, large current, concentrated alkali and the like, the material is suitable for multiple electrolysis modes, no metal dissolution risk exists in long-term operation, the problems of membrane poisoning and membrane degradation can be effectively avoided, and the service life of the material is prolonged. Wide application prospects are shown.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of inorganic advanced nanomaterials, and particularly relates to a nickel-cobalt-based spinel oxide nanomaterial, a preparation method therefor, and use thereof. BACKGROUND

[0002] In pursuit of carbon-neutral economies, the focus has increasingly shifted towards the deployment of sustainable and renewable energy sources, thereby significantly reducing the dependence on fossil energy. Hydrogen (H2) is one of the most important renewable energy sources, with high energy efficiency and zero carbon emissions. Therefore, to achieve clean energy transformation, water electrolysis for renewable "green hydrogen" generation stands out, providing high product purity and enabling the effective utilization of intermittent renewable energy, among which water electrolysis conducted at high current density is considered as a green hydrogen production technology with industrial scale, which has important value for energy decarbonization and numerous sustainable industrial applications.

[0003] However, this renewable energy hydrogen production technology only accounts for 4% of the current hydrogen production, which is mainly attributed to its higher cost compared to other methods (such as the conversion of natural fossil fuels). For commercial water electrolysis systems, the key problems mainly focus on the use of effective but excessively high iridium, ruthenium or platinum catalysts, or economically practical nickel mesh and unsatisfactory active stainless steel. It is imperative but challenging to explore high-activity and cost-effective catalysts with good durability. Among them, transition metal oxides with AB2O4 spinel structure are considered to be the most promising water oxidation electrocatalysts in alkaline electrolytes due to their low price, easy preparation, adjustable structure / element properties and outstanding stability. In spinel oxides, oxygen anions are shared by four adjacent cations (1 tetrahedral site, 3 octahedral sites), and the charge distribution is closely related to the geometric configuration of transition metals (TM): TM in octahedral sites forms high-covalent redox units with oxygen through strong σ bonds, while TM in tetrahedral sites only has weak π bonds or no direct orbital overlap; the direction of electronic polarization is biased towards octahedron, significantly enhancing the octahedral TM–O interaction. Therefore, regulating the electronic structure of spinel oxides can achieve better electrochemical oxygen evolution activity.

[0004] Despite recent important breakthroughs in the development of efficient first-row transition metal catalysts for the oxygen evolution reaction, there is still a gap between the testing conditions (almost at room temperature) and the industrial conditions (50-80℃). The effect of high temperature on the water electrolysis catalysts shows a significant "double-edged sword" effect: on the one hand, from the thermodynamic point of view, high temperature can reduce the electrical energy demand of the water electrolysis reaction, promoting the forward reaction; at the same time, based on the kinetic mechanism of the Arrhenius equation, the increase of temperature can reduce the activation energy and accelerate the reaction rate, while the increase of temperature in the anion exchange membrane electrolysis can enhance the ion conduction efficiency and reduce the internal resistance; on the other hand, high temperature is easy to cause the deterioration of the catalyst structure (such as the sintering and agglomeration of noble metals, the rapid decay of NiFe-based anodes, etc.), resulting in the decrease of active surface area and the decrease of stability. Therefore, it is crucial to prepare catalysts that can stably operate under harsh operating conditions such as high temperature for further practical application.

[0005] To solve the above problems, the present application is proposed. SUMMARY

[0006] The material of the present application takes an electrically conductive substrate as a carrier, and through a two-step synthesis strategy, an array-structured nickel-cobalt-based spinel oxide nanocatalytic layer is constructed in situ on the surface thereof. Compared with traditional nickel-cobalt spinels, the material of the present application is synergistically doped with iron and manganese elements, so that Fe preferentially occupies the tetrahedral site, Ni 3 and Co 2+ are enriched in the octahedral site, and Mn 2+ occupies the octahedral site, optimizing the key active center for the oxygen evolution reaction (OER). The iron and manganese doping not only adjusts the metal d-band electronic structure, improves the adsorption behavior of the reaction intermediates, and improves the catalytic activity, but also enhances the crystal structure stability and the electrode interface bonding force. Compared with the traditional sol-gel preparation method, the array structure significantly alleviates the bubble shielding effect and improves the mass transfer efficiency at the three-phase interface. Under harsh conditions such as high temperature, large current and concentrated alkali, the material maintains structural integrity and exhibits excellent thermodynamic and chemical stability, and is suitable for various electrolysis modes. Compared with the co-doping system with the introduction of iron and zinc metals, the doping system of the present application has no risk of metal leaching in long-term operation, effectively avoids the problems of membrane poisoning and membrane degradation, and shows a broad application prospect.

[0007] The first aspect of the present application provides a nickel-cobalt-based spinel oxide nanomaterial, which comprises: an electrically conductive substrate, a nickel-cobalt-based spinel oxide grown on the surface of the electrically conductive substrate;

[0008] The nickel-cobalt-based spinel oxide contains nickel, cobalt, iron and manganese elements.

[0009] The crystal structure of the nickel-cobalt-based spinel oxide is a nickel-cobalt spinel phase, and there is no other impurity phase.

[0010] Preferably, the nickel-cobalt-based spinel oxide is uniformly distributed with nickel, cobalt, iron and manganese;

[0011] In the nickel-cobalt-based spinel oxide, the molar ratio of each metal is as follows:

[0012] Nickel: Cobalt: Iron: Manganese = (1-2):(1-2):0.01:0.01-(1-2):(1-2):2:2.

[0013] In other words, the molar fraction of nickel and cobalt in the nickel-cobalt-based spinel oxide is 16.7-50%, and the molar fraction of iron and manganese is 0-34% each, based on the total molar number of metals in the nickel-cobalt-based spinel oxide.

[0014] Preferably, the conductive substrate is selected from the group consisting of: foam metal, nickel mesh, iron mesh, nickel-iron alloy mesh, carbon paper or carbon cloth, etc. The foam metal can be selected from one of foam iron, nickel foam (Nickel Foam, i.e. NF), and nickel-iron alloy foam.

[0015] Preferably, the nickel-cobalt-based spinel oxide has a morphology of nanosheet.

[0016] The second aspect of the present application provides a preparation method of the nickel-cobalt-based spinel oxide nanomaterial of the first aspect. The synthesis method of the nickel-cobalt-based spinel oxide nanomaterial includes a two-step synthesis method, the first step is a hydrothermal reaction method or an electrodeposition method, and the second step is high-temperature annealing.

[0017] The first step of the hydrothermal reaction method includes the following steps: adding metal salts, urea and ammonium fluoride into water to obtain a solution, transferring the solution to a hydrothermal reaction kettle, adding a conductive substrate and performing hydrothermal reaction at a certain temperature, and obtaining a precursor after a certain holding time.

[0018] The first step of the electrodeposition method includes the following steps: adding metal salts into water and dissolving, placing an anode, a cathode and a reference electrode in the solution, using a conductive substrate at the cathode, and performing electrodeposition to obtain a precursor.

[0019] The metal salts are water-soluble nickel salts, water-soluble cobalt salts, water-soluble iron salts and water-soluble manganese salts.

[0020] The concentration of each metal salt is 0.01-0.3 mol / L, and the concentration of urea is 2.5-10 times the sum of the concentrations of the metal salts.

[0021] The molar ratio of each metal is as follows:

[0022] Nickel: Cobalt: Iron: Manganese = (1-2):(1-2):0.01:0.01-(1-2):(1-2):2:2.

[0023] the concentration of the ammonium fluoride is 0-0.8 mol / L;

[0024] the second high-temperature annealing step comprises the following steps: calcining the precursor obtained in the first step in an inert gas or air atmosphere for a certain time.

[0025] Preferably, in the first hydrothermal reaction method, the hydrothermal reaction time is 3-48 h and the temperature is 60-200℃.

[0026] More preferably, in the first hydrothermal reaction method, the reaction temperature is 60-200℃ and the holding time is 3-48 h.

[0027] Preferably, in the first electrodeposition method, the electrodeposition voltage is -1.0 V to -2 V vs. mercury-saturated calomel electrode (SCE) and the time is 100 s-7200 s.

[0028] In the second high-temperature annealing step, the temperature is 250-800℃, the heating rate is 2-10℃ / min, the time is 2-10 h, and the reaction atmosphere is air or an inert gas atmosphere. The inert gas can be nitrogen or argon.

[0029] Preferably, the step of adding metal salts, urea and ammonium fluoride in water to obtain a solution comprises the following steps: adding a soluble iron source and a soluble manganese source into a solution containing a soluble nickel source and a soluble cobalt source, mixing and dissolving uniformly to obtain a metal salt solution, adding urea, mixing and dissolving uniformly again, adding ammonium fluoride, mixing and dissolving uniformly to obtain a mixture solution.

[0030] Preferably, in the first hydrothermal reaction method, the metal salt is one or more of a metal chloride, a metal nitrate and a metal sulfate.

[0031] Preferably, the soluble manganese source is manganese chloride, manganese chloride tetrahydrate or manganese nitrate tetrahydrate.

[0032] Preferably, the soluble iron source is one of ferric nitrate nonahydrate, ferric chloride or ferric sulfate.

[0033] Preferably, the soluble nickel source is one of nickel nitrate hexahydrate, nickel chloride or nickel sulfate.

[0034] Preferably, the soluble cobalt source is one of cobalt nitrate hexahydrate, cobalt chloride or cobalt sulfate.

[0035] Preferably, the processing method of the conductive substrate material is as follows: for the metal substrate, first clean with ethanol or acetone in an ultrasonic cleaner for 15 minutes, then dry and clean with dilute hydrochloric acid in an ultrasonic cleaner for 15 minutes, clean with deionized water, and then clean with deionized water in an ultrasonic cleaner for 15 minutes; for the carbon paper substrate, clean with ethanol in an ultrasonic cleaner for 15 minutes; for the carbon cloth substrate, clean with ethanol in an ultrasonic cleaner for more than 20 minutes, then dry and clean with deionized water in an ultrasonic cleaner for more than 20 minutes, and then dry and plasma treat for 10 minutes.

[0036] The third aspect of the present application provides a use of the nickel-cobalt-based spinel oxide nanomaterial of the first aspect as an anode material in an alkaline water electrolysis oxygen evolution reaction.

[0037] Preferably, the alkaline water electrolysis oxygen evolution reaction contains an alkaline substance in the electrolyte; the alkaline substance is selected from one or more of sodium hydroxide, potassium hydroxide, lithium hydroxide, rubidium hydroxide, and cesium hydroxide.

[0038] Preferably, the total concentration of the alkaline substance is 1-14 moles per liter.

[0039] Preferably, the temperature range of the alkaline water electrolysis oxygen evolution reaction is 25-120°C.

[0040] Preferably, the current density range of the alkaline water electrolysis oxygen evolution reaction is 0.1-10 amperes per square centimeter.

[0041] Preferably, the electrolysis mode of the alkaline water electrolysis oxygen evolution reaction is constant current, constant voltage, and frequent start-stop.

[0042] Preferably, the nickel-cobalt-based spinel oxide nanomaterial is used to improve the activity and stability of the material in the water electrolysis reaction.

[0043] Compared with the prior art, the present application has the following beneficial effects:

[0044] 1. The conventional method of doping nickel-cobalt-based spinel oxide (AB2O4 type) nanomaterial is to reduce the proportion of nickel or cobalt elements and increase the doping elements by material selection and doping strategy. The total number of doping elements and nickel elements and the proportion of cobalt elements, or the proportion of nickel elements and the total number of doping elements and cobalt elements, still remain 1:2. The essence of the above doping is still limited by the ratio of nickel to cobalt elements being 1:2. Only the doping elements are used to replace the original nickel elements or cobalt elements, and the octahedral and tetrahedral voids in the nickel-cobalt-based spinel oxide are not utilized.

[0045] The application provides a nickel-cobalt-based spinel oxide nanomaterial, breaks through the conventional idea of traditional catalyst design, utilizes the octahedral and tetrahedral voids in the nickel-cobalt-based spinel oxide, and breaks through the limitation that the nickel-cobalt element ratio is 1:2. The spinel crystal is doped by introducing iron and manganese elements in the application, the iron and manganese can partially replace nickel and cobalt in the tetrahedral and octahedral positions in the crystal, simultaneously regulate the crystal field orbital splitting, and make more proportion of nickel enter the octahedral sites, so that the electronic structure stability of the material is enhanced without destroying the intrinsic structure of the spinel.

[0046] Nickel as a key active metal for an oxygen evolution reaction (OER) helps to further improve the catalytic activity. The doped metal atoms are highly uniformly distributed in the material, and no heterogeneous oxide is generated, so that the site occupation behavior is adjusted by regulating the doping elements, thereby enhancing the activity of the catalytic site. In the alkaline oxygen evolution reaction process, the material not only has excellent catalytic activity, but also has good stability. In addition, the introduction of iron and manganese adjusts the metal d-band electron structure, optimizes the reaction kinetic process, reduces the adsorption energy barrier of the reaction intermediate, and significantly improves the application performance in the alkaline water electrolysis anode material.

[0047] 2. In particular, the application breaks through the limitation that the nickel-cobalt element ratio is 1:2 in the AB2O4 spinel structure. The application limits the nickel-cobalt-iron-manganese element ratio to (1-2):(1-2):0.01:0.01-(1-2):(1-2):2:2. It is found that the nickel-cobalt-based spinel oxide nanomaterial has better activity and stability when the nickel-cobalt ratio is 2:2.

[0048] 3. In the prior art, the spinel oxide is generally synthesized by a sol-gel method, but the method has problems such as uncontrollable morphology of the spinel material, limited mass transfer under high current conditions, and weak combination of the powder catalyst and the conductive substrate.

[0049] In view of the above problems, the application innovatively provides a two-step synthesis method for preparing a nanometer array spinel oxide, constructs a nickel-cobalt-based spinel oxide nanomaterial with uniform structure and array structure, and the preparation process is simple and efficient. The nickel-cobalt-based spinel oxide nanomaterial is in-situ constructed on the surface of a conductive substrate by a hydrothermal self-growth method, and an integrated electrode structure of the conductive substrate and the catalyst is formed. The nanometer array structure not only effectively improves the adhesion of the catalyst on the substrate, but also significantly relieves the bubble shielding effect under high current density working conditions, thereby improving the mass transfer performance at the gas-liquid-solid three-phase interface and improving the overall electrocatalytic efficiency.

[0050] 4、In view of the technical bottleneck that the catalytic performance of the catalyst is seriously attenuated after long-time operation under severe conditions such as high temperature (above 40 DEG C), large current (above 0.4 ampere per square centimeter), and concentrated alkali (above 6 moles per liter), an effective solution is provided.Compared with the two-dimensional layered hydrotalcite structure with weak interlayer force and ionic bond in the layer, the spinel metal oxide has high lattice energy structure formed by strong electrostatic interaction and covalent bond network, and exhibits excellent thermodynamic and structural stability.The applicant accidentally found that the proposed nickel-cobalt-based spinel oxide remains complete and stable crystal structure after doping with iron and manganese elements, wherein the manganese element is chemically stable in the alkaline electrolyte and is an oxygen evolution reaction (OER) inert element, and mainly functions in regulating the electronic structure of the catalyst and stabilizing the crystal framework, and does not directly participate in the catalytic process, thereby further enhancing the stability of the structure.Therefore, the doped nickel-cobalt-based spinel oxide can be stably operated under the conditions of wide temperature range, wide current density range, and electrolyte of different alkalinity, and is suitable for various electrolysis modes.

[0051] The applicant shows through comparative study that the nickel-cobalt-based spinel oxide prepared by co-doping with iron and zinc elements under alkaline conditions has certain stability due to the inherent structure of spinel, but the above elements are seriously dissolved under high temperature, large current and concentrated alkali environment, resulting in obvious degradation of the crystal structure and inability to maintain long-term stable operation.In addition, in the application of membrane electrode system, the dissolved metal ions easily poison the ion transmission channel of the polymer ion exchange membrane, hinder the mass transfer process, limit the catalytic reaction, and induce a serious Fenton reaction, accelerating the degradation of the membrane material, thereby further limiting the actual application performance.The nickel-cobalt-based spinel oxide nanomaterial in the application can be operated for a long time under the membrane electrode system, indicating that the material structure is stable and there is no application limitation caused by metal ion dissolution. BRIEF DESCRIPTION OF DRAWINGS

[0052] Figure 1 X-ray diffraction (XRD) pattern of the precursor synthesized by the hydrothermal method of Example 1.

[0053] Figure 2 Non-in situ Raman spectrum of the nickel-cobalt-iron-manganese hydrotalcite precursor synthesized by the hydrothermal method of Example 1.

[0054] Figure 3 X-ray diffraction (XRD) pattern of the nickel-cobalt-based spinel oxide nanomaterial synthesized by the two-step synthesis method of Example 1.

[0055] Figure 4 Non-in situ Raman spectrum of the nickel-cobalt-based spinel oxide nanomaterial synthesized by the two-step synthesis method of Example 1.

[0056] Figure 5 Scanning electron microscope (SEM) image of nickel cobalt based spinel oxide nanomaterial synthesized using two-step synthesis method for Example 1.

[0057] Figure 6 Annular dark field - transmission electron microscope (AC-TEM) image of nickel cobalt based spinel oxide nanomaterial synthesized using two-step synthesis method for Example 1.

[0058] Figure 7 Selected area electron diffraction (SADE) image of nickel cobalt based spinel oxide nanomaterial synthesized using two-step synthesis method for Example 1.

[0059] Figure 8 High resolution spectrometer elemental mapping image of nickel cobalt based spinel oxide nanomaterial synthesized using two-step synthesis method for Example 1.

[0060] Figure 9 Scanning electron microscope (SEM) image of nickel cobalt based spinel oxide nanomaterial synthesized using two-step synthesis method for Example 2.

[0061] Figure 10 High resolution spectrometer elemental mapping image of nickel cobalt based spinel oxide nanomaterial synthesized using two-step synthesis method for Example 2.

[0062] Figure 11 Scanning electron microscope (SEM) image of nickel cobalt based spinel oxide nanomaterial synthesized using two-step synthesis method for Example 3.

[0063] Figure 12 High resolution spectrometer elemental mapping image of nickel cobalt based spinel oxide nanomaterial synthesized using two-step synthesis method for Example 3.

[0064] Figure 13 Linear sweep voltammogram of nickel cobalt based spinel oxide nanomaterial synthesized using two-step synthesis method for Example 1.

[0065] Figure 14 Galvanostatic curve plot of nickel cobalt based spinel oxide nanomaterial synthesized using two-step synthesis method for Example 1 at 25 °C, 1 molar KOH, 400 milliampere per square centimeter current density.

[0066] Figure 15 Galvanostatic curve plot of nickel cobalt based spinel oxide nanomaterial synthesized using two-step synthesis method for Example 1 at 45 °C, 6 molar KOH, 2 ampere per square centimeter current density.

[0067] Figure 16Galvanostatic intermittent titration plot of nickel cobalt based spinel oxide nanomaterial synthesized using two step synthesis method of example 1 at 45 °C, 6 mole KOH, 2 ampere per square centimeter current density.

[0068] Figure 17 Potentiostatic plot of nickel cobalt based spinel oxide nanomaterial synthesized using two step synthesis method of example 1 at 80 °C, 6 mole KOH, 1 ampere per square centimeter current density.

[0069] Figure 18 Galvanostatic intermittent titration plot of nickel cobalt based spinel oxide nanomaterial synthesized using two step synthesis method of example 1 at 80 °C, 6 mole KOH, 10 ampere per square centimeter current density.

[0070] Figure 19 Potentiostatic plot of nickel cobalt based spinel oxide nanomaterial synthesized using two step synthesis method of example 1 at 100 °C, 10 mole KOH, 1 ampere per square centimeter current density.

[0071] Figure 20 Potentiostatic plot of nickel cobalt based spinel oxide nanomaterial synthesized using two step synthesis method of example 1 at 120 °C, 14 mole KOH, 1 ampere per square centimeter current density.

[0072] Figure 21 Linear sweep voltammogram of anion exchange membrane (AEM) electrolyzer with nickel cobalt based spinel oxide nanomaterial synthesized using two step synthesis method of example 1 as anode and nickel molybdenum alloy as cathode.

[0073] Figure 22 Potentiostatic plot of anion exchange membrane (AEM) electrolyzer with nickel cobalt based spinel oxide nanomaterial synthesized using two step synthesis method of example 1 as anode and nickel molybdenum alloy as cathode at 60 °C, 1 mole KOH, 1 ampere per square centimeter current density.

[0074] Figure 23 Linear sweep voltammogram of nickel cobalt based spinel oxide nanomaterial obtained after stability test for 5000 hours at 80 °C, 6 mole KOH, 1 ampere per square centimeter current density of application example 11.

[0075] Figure 24 X-ray diffraction (XRD) of nickel cobalt based spinel oxide nanomaterial synthesized using two step synthesis method of example 1 and undoped, single element doped nickel cobalt based spinel oxide nanomaterial of comparative example 1.

[0076] Figure 25Raman spectra of undoped nickel cobalt-based spinel oxide nanomaterial synthesized using two-step synthesis method for Comparative Example 1.

[0077] Figure 26 Linear sweep voltammograms of nickel cobalt-based spinel oxide nanomaterial synthesized using two-step synthesis method for Example 1 and Comparative Example 1 and undoped, single element doped nickel cobalt-based spinel oxide nanomaterials.

[0078] Figure 27 X-ray diffraction (XRD) pattern of nickel iron hydrotalcite nanomaterial prepared using hydrothermal synthesis method for Comparative Example 2.

[0079] Figure 28 Galvanostatic plots of nickel iron hydrotalcite nanomaterial prepared using hydrothermal synthesis method for Comparative Example 2 and nickel cobalt-based spinel oxide nanomaterial synthesized using two-step synthesis method for Example 1 and nickel foam metal substrate (NF) operated at 80 °C, 6 molar KOH, 1 ampere per square centimeter current density for 150 hours.

[0080] Figure 29 Linear sweep voltammograms of nickel iron hydrotalcite nanomaterial for Comparative Example 2 and Comparative Application Example 2 - nickel iron hydrotalcite nanomaterial obtained after stability test at 80 °C, 6 molar KOH, 1 ampere per square centimeter current density for 150 hours.

[0081] Figure 30 X-ray photoelectron spectroscopy of iron element of nickel iron hydrotalcite nanomaterial for Comparative Example 2 and Comparative Application Example 2 - nickel iron hydrotalcite nanomaterial obtained after stability test at 80 °C, 6 molar KOH, 1 ampere per square centimeter current density for 150 hours.

[0082] Figure 31 Scanning electron microscope (SEM) images of nickel iron hydrotalcite nanomaterial for Comparative Example 2 and Comparative Application Example 2 - nickel iron hydrotalcite nanomaterial obtained after stability test at 80 °C, 6 molar KOH, 1 ampere per square centimeter current density for 150 hours.

[0083] Figure 32 Scanning electron microscope (SEM) images of nickel iron hydrotalcite nanomaterial obtained after stability test at 80 °C, 6 molar KOH, 1 ampere per square centimeter current density for 150 hours for Comparative Application Example 2.

[0084] Figure 33 X-ray diffraction (XRD) pattern of iron and zinc element double doped nickel cobalt-based spinel oxide nanomaterial synthesized for Comparative Example 4.

[0085] Figure 34 Scanning electron microscope (SEM) images of iron and zinc element double doped nickel cobalt-based spinel oxide nanomaterial synthesized for Comparative Example 4.

[0086] Figure 35 The EDS mapping image of the iron and zinc element double-doped nickel cobalt-based spinel oxide nanomaterial synthesized for Comparative Example 4.

[0087] Figure 36 The galvanostatic curve of the anion exchange membrane (AEM) electrolyzer with the nickel molybdenum alloy of the iron and zinc element double-doped nickel cobalt-based spinel oxide nanomaterial synthesized for Comparative Example 4 as the cathode under the condition of 60°C, 1 mol KOH, and 1 A / cm2 current density.

[0088] Figure 37 The damage situation of the membrane and electrolyte conduit in the anion exchange membrane (AEM) electrolyzer after running for 438 hours under the condition of 60°C, 1 mol KOH, and 1 A / cm2 current density in Comparative Application Example 4.

[0089] Figure 38 The linear sweep voltammogram of the iron and manganese doped nickel cobalt-based spinel oxide nanomaterial with a lower proportion of nickel content synthesized for Example 4.

[0090] Figure 39 The scanning electron microscope image of the nickel cobalt-based spinel oxide nanomaterial synthesized by electrodeposition-high temperature annealing for Example 5.

[0091] Figure 40 The linear sweep voltammogram of the nickel cobalt-based spinel oxide nanomaterial synthesized by electrodeposition-high temperature annealing for Example 5. DETAILED DESCRIPTION

[0092] The present application will be described in detail below with reference to specific examples, but the embodiments of the present application are not limited thereto. In the examples, the experimental methods not specified with specific conditions are generally performed according to the conventional conditions and the conditions described in the manual, or using the general equipment, materials, reagents, etc. suggested by the manufacturer, unless otherwise specified. The raw materials required in the following examples and comparative examples are commercially available.

[0093] Example 1 Preparation of nickel cobalt-based spinel oxide nanomaterial by hydrothermal-high temperature annealing two-step method

[0094] In this experimental example, the following method was used to prepare the nickel cobalt-based spinel oxide nanomaterial:

[0095] Step (1): using hydrothermal synthesis method to prepare precursor, specifically: configuration 36 milliliter solution: ammonium fluoride 21.6 millimoles, urea 26.4 millimoles, nickel nitrate 0.66 millimoles, cobalt nitrate 0.66 millimoles, iron nitrate 0.33 millimoles, manganese nitrate 0.33 millimoles, water 36 milliliters, pour the solution into the reaction kettle. (In the solution, the concentration of nickel source is 0.02 moles per liter, the concentration of cobalt source is 0.02 moles per liter, the concentration of iron source and manganese source is 0.01 moles per liter, the concentration of urea is: 0.73 moles per liter, the concentration of ammonium fluoride is 0.6 moles per liter). The treated conductive substrate is immersed in the solution, put into the oven, the reaction temperature is 200 degrees Celsius, the time is 3 hours. The obtained precursor material is washed with water, ethanol for 3 times respectively, vacuum drying at 60 degrees Celsius for 10 hours.

[0096] Step (2): put the precursor obtained in step (1) into a muffle furnace (in other embodiments, inert gas or no gas can be passed in a tube furnace), heat to 250℃ at a rate of 2℃ / min, keep for 10 hours, take out after natural cooling, obtain the material grown on the conductive substrate material, namely the nickel-cobalt-based spinel oxide nanomaterial. Characterize the nickel-cobalt-based spinel oxide nanomaterial: the molar fraction of nickel and cobalt elements is 33.4%, the molar fraction of iron and manganese elements is 16.6%, taking the total molar amount of metals in the nickel-cobalt-based spinel oxide nanomaterial as the reference. That is, the proportion of nickel, cobalt, iron and manganese elements in the nickel-cobalt-based spinel oxide is 2:2:1:1.

[0097] In other embodiments, other conditions remain unchanged, the conductive substrate in the above steps is replaced. Namely, the nickel-cobalt-based spinel oxide nanomaterial loaded on different conductive substrates can be respectively prepared. The conductive substrate material is selected from: foam metal, carbon paper or carbon cloth, etc. The foam metal can be selected from foam iron, foam nickel, etc. In this embodiment, the conductive substrate is foam nickel metal (Nickel Foam, namely NF).

[0098] The precursor of the nickel-cobalt-based spinel oxide nanomaterial obtained in the above step (1) is subjected to X-ray diffraction (XRD), and the diffraction pattern is shown in Figure 1 , which is consistent with the standard card of nickel-iron hydrotalcite intercalated with carbonate, indicating that the synthesized precursor is pure hydrotalcite phase, with good crystallinity and no phase separation. Then the precursor is subjected to Raman spectrum test, as shown in Figure 2 , the precursor of the nickel-cobalt-based spinel oxide nanomaterial has obvious vibration signals of Ni-OH, Ni-O, CO3 2- , which again indicates that the precursor is a hydrotalcite structure intercalated with carbonate.

[0099] The nickel-cobalt-based spinel oxide nanomaterial obtained in the above step (2) is subjected to X-ray diffraction (XRD), and the diffraction pattern is shown inFigure 3 The results show that the nickel-cobalt-based spinel oxide nanomaterial synthesized by the two-step method has a nickel-cobalt spinel structure, good crystallinity and no phase separation, consistent with the nickel-cobalt spinel oxide standard card. Then, the spinel oxide nanomaterial is subjected to Raman spectrum testing, as shown in Figure 4 , A 1g is the vibration mode of the octahedral cation in the spinel structure, E g is the vibration mode of the tetrahedron and octahedron, and F 2g is the vibration mode of the tetrahedron. This shows that the iron and manganese elements in the nickel-cobalt-based spinel oxide nanomaterial synthesized by the two-step method replace part of the nickel and cobalt elements and occupy part of the tetrahedral and octahedral positions. The material is subjected to scanning electron microscope (SEM) testing, as shown in Figure 5 , which shows that the nickel-cobalt-based spinel oxide nanomaterial synthesized by the two-step method has a clear flaky morphology.

[0100] The nickel-cobalt-based spinel oxide nanomaterial obtained in the above step (2) is subjected to spherical aberration-corrected transmission electron microscopy (AC-TEM) and high-resolution spectrometer-element distribution testing, as shown in Figure 6 . Figure 6 The results show that the iron and manganese-doped nickel-cobalt-based spinel oxide nanomaterial synthesized by the two-step method maintains a good crystal structure, and the corresponding interplanar spacing parameters meet the characteristics of the nickel-cobalt spinel: the interplanar spacing of 0.462 nm corresponds to the (111) crystal plane of the nickel-cobalt spinel, and the interplanar spacing of 0.246 nm corresponds to the (311) crystal plane of the nickel-cobalt spinel. Then, the sample area is subjected to selected area electron diffraction (SADE), as shown in Figure 7 , a typical single-crystal diffraction pattern further shows that the nickel-cobalt-based spinel oxide nanomaterial synthesized by the two-step method has a single nickel-cobalt spinel phase, good crystallinity and no phase separation. At the same time, the high-resolution spectrometer of the spherical aberration-corrected transmission electron microscope is used to detect the element distribution, as shown in Figure 8 , the proportions of nickel, cobalt, iron and manganese elements at the atomic level resolution are close to the feeding proportions, and the distributions of the elements are uniform.

[0101] Example 2: Preparation of nickel-cobalt-based spinel oxide nanomaterial by hydrothermal-high-temperature two-step method

[0102] A precursor is prepared by a hydrothermal synthesis method, specifically, 36 milliliters of a solution is prepared: 108 millimoles of urea, 10.8 millimoles of nickel nitrate, 10.8 millimoles of cobalt nitrate, 10.8 millimoles of iron nitrate, 10.8 millimoles of manganese nitrate, and 36 milliliters of water, and the solution is poured into a reaction kettle. (In the solution, the concentration of the nickel source is 0.3 moles per liter, the concentration of the cobalt source is 0.3 moles per liter, the concentration of the iron source and the manganese source is 0.3 moles per liter, the concentration of urea is 3 moles per liter, and the concentration of ammonium fluoride is 0 moles per liter.) The treated conductive substrate, foam nickel, is immersed in the solution, and placed in an oven, the reaction temperature is 60 degrees Celsius, and the time is 48 hours. The obtained precursor material is washed with water and ethanol three times, respectively, and vacuum dried at 60 degrees Celsius for 10 hours.

[0103] Step (2): The precursor obtained in step (1) is placed in a muffle furnace (or in a tube furnace with or without inert gas), and heated to 800 degrees Celsius at a heating rate of 10 degrees Celsius per minute, and then kept for 2 hours, and then taken out after natural cooling, to obtain a material grown on a conductive substrate material, that is, a nickel-cobalt-based spinel oxide nanomaterial. The nickel-cobalt-based spinel oxide nanomaterial has a ratio of nickel, cobalt, iron and manganese elements of 2:2:2:2, and the molar fraction of nickel and cobalt elements is 25%, and the molar fraction of iron and manganese elements is 25%, based on the total molar amount of metals in the nickel-cobalt-based spinel oxide nanomaterial.

[0104] The above nickel-cobalt-based spinel oxide nanomaterial is tested by scanning electron microscopy (SEM), as shown in FIG. 1, the results show that the nickel-cobalt-based spinel oxide nanomaterial synthesized by the hydrothermal method has a clear flaky morphology. Meanwhile, the element distribution is detected by high-resolution energy dispersive spectrometer of spherical aberration-corrected transmission electron microscopy, as shown in FIG. 2, under atomic resolution, the ratio of nickel, cobalt, iron and manganese elements is close to the feeding ratio, and the distribution of each element is uniform. Figure 9 Figure 10 The above nickel-cobalt-based spinel oxide nanomaterial is tested by scanning electron microscopy (SEM), as shown in FIG. 1, the results show that the nickel-cobalt-based spinel oxide nanomaterial synthesized by the hydrothermal method has a clear flaky morphology. Meanwhile, the element distribution is detected by high-resolution energy dispersive spectrometer of spherical aberration-corrected transmission electron microscopy, as shown in FIG. 2, under atomic resolution, the ratio of nickel, cobalt, iron and manganese elements is close to the feeding ratio, and the distribution of each element is uniform.

[0105] Example 3: Preparation of a nickel-cobalt-based spinel oxide nanomaterial by electrodeposition-high temperature annealing synthesis

[0106] Step (1): A precursor is prepared by an electrodeposition method, specifically, 120 milliliters of a solution is prepared: 2 millimoles of nickel nitrate, 2 millimoles of cobalt nitrate, 0.01 millimoles of iron nitrate, 0.01 millimoles of manganese nitrate, and 120 milliliters of water. (In the solution, the concentration of the nickel source is 0.017 moles per liter, the concentration of the cobalt source is 0.017 moles per liter, and the concentration of the iron source and the manganese source is 0.00008 moles per liter.) A washed foam nickel is used as a working electrode, a carbon rod electrode is used as a counter electrode, a mercury-mercury electrode is used as a reference electrode, a constant potential of -2V vs SCE is applied, and the time is 100 seconds. The obtained material is washed with water and ethanol three times, respectively, and vacuum dried at 60 degrees Celsius for 10 hours. A nickel-cobalt-based spinel oxide nanomaterial precursor loaded on the foam nickel is obtained.​

[0107] In other embodiments, with other conditions unchanged, increasing the molar amounts of ferric nitrate and manganese nitrate in the above steps can prepare precursors of nickel-cobalt-based spinel oxide nanomaterials with different iron-manganese doping ratios.

[0108] Step (2): Place the precursor obtained in step (1) into a muffle furnace (or in a tube furnace with or without inert gas), heat to 300℃ at a heating rate of 4℃ / min, hold for 3 hours, and remove after natural cooling to obtain the material grown on nickel foam, which is the nickel-cobalt-based spinel oxide nanomaterial. In this nickel-cobalt-based spinel oxide, the molar fraction of nickel and cobalt is 49.75%, and the molar fraction of iron and manganese is 0.25%, based on the total molar amount of metal in the nickel-cobalt-based spinel oxide nanomaterial. The ratio of nickel, cobalt, iron, and manganese in the metal salt solution is 2:2:0.1:0.1.

[0109] In other embodiments, by increasing the molar amounts of ferric nitrate and manganese nitrate in step (1), nickel-cobalt-based spinel oxide nanomaterials with different iron-manganese doping ratios can be prepared. The ratio of nickel, cobalt, iron, and manganese elements in the metal salt solution is (1-2):(1-2):0.01:0.01-(1-2):(1-2):2:2.

[0110] The material was tested using scanning electron microscopy (SEM), such as... Figure 11 The results showed that the nickel-cobalt-based spinel oxide nanomaterials synthesized by electrodeposition exhibited a distinct sheet-like array structure. The above-mentioned nickel-cobalt-based spinel oxide nanomaterials were subjected to aberration-corrected transmission electron microscopy (AC-TEM) and high-resolution energy dispersive spectroscopy (EDS) elemental distribution analysis. Figure 12 Figure 8 As shown. Figure 12 It can be seen that, at atomic-level resolution, the proportions of nickel, cobalt, iron, and manganese are close to the feeding ratio, and the elements are evenly distributed.

[0111] Application Example 1: Oxygen Evolution Reaction Activity Test of Nickel-Cobalt Based Spinel Oxide Nanomaterials at 25℃

[0112] The electrolytic oxygen evolution performance of the nickel-cobalt-based spinel oxide nanomaterial obtained 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 the working electrode being the nickel-cobalt-based spinel oxide nanomaterial of Example 1 with an effective area of ​​1*1 square centimeters. 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 voltammetry chromatogram is shown below.Figure 13 as shown.

[0113] By Figure 13 It can be seen that the overpotential of the nickel-cobalt-based spinel oxide nanomaterial of Example 1 is 225 mV at a current density of 10 mA cm -2 , the overpotential of the nickel-cobalt-based spinel oxide nanomaterial of Example 1 is 240 mV at a current density of 50 mA cm -2 , which is 180 mV lower than the overpotential of the nickel-cobalt-based spinel oxide nanomaterial of Example 1. If applied to industrialization at the same time, the nickel-cobalt-based spinel oxide nanomaterial of Example 1 can save a large amount of power resources. -2

[0114] Application Example 2: Stability test of nickel-cobalt-based spinel oxide nanomaterial in oxygen evolution reaction at 25°C under constant current condition

[0115] The alkaline water electrolysis oxygen evolution stability of the nickel-cobalt-based spinel oxide nanomaterial obtained in Example 1 was tested by a two-electrode system: the nickel-cobalt-based spinel oxide nanomaterial was used as the anode of the electrolytic cell, and a platinum sheet electrode was used as the cathode electrode of the electrolytic cell. The stability test was carried out in alkaline water electrolysis. The anode was the nickel-cobalt-based spinel oxide nanomaterial of Example 1 with an effective area of 1*1 square centimeter, and the cathode was a platinum sheet electrode with an effective area of 1*1 square centimeter. The constant current test was carried out at 1 mole per liter of potassium hydroxide and 100 milliampere per square centimeter.

[0116] The constant current curve obtained by carrying out the constant current test at an electrolyte temperature of 25°C, using 1 mole per liter of potassium hydroxide as the electrolyte, and at a current of 100 milliampere per square centimeter is shown in Figure 14 , indicating that the nickel-cobalt-based spinel oxide nanomaterial of Example 1 can run smoothly under this condition and can run for at least 1000 hours.

[0117] Application Example 3: Stability test of nickel-cobalt-based spinel oxide nanomaterial in oxygen evolution reaction at 45°C under constant current condition

[0118] The alkaline water electrolysis oxygen evolution stability of the nickel-cobalt-based spinel oxide nanomaterial obtained in Example 1 was tested by a two-electrode system: the nickel-cobalt-based spinel oxide nanomaterial was used as the anode of the electrolytic cell, and a platinum sheet electrode was used as the cathode electrode of the electrolytic cell. The stability test was carried out in alkaline water electrolysis. The anode was the nickel-cobalt-based spinel oxide nanomaterial of Example 1 with an effective area of 1*1 square centimeter, and the cathode was a platinum sheet electrode with an effective area of 1*1 square centimeter.

[0119] ​The constant current test was carried out at 45 °C, 6 mol / L KOH electrolyte, 2 A / cm2current, and the constant current curve is shown in Figure 15 FIG. 3, which shows that the nickel-cobalt-based spinel oxide nanomaterial of Example 1 can run stably under this condition and can run for at least 4300 hours.

[0120] Application Example 4: Test of oxygen evolution reaction stability of nickel-cobalt-based spinel oxide nanomaterial under intermittent conditions of frequent start-stop at 45 °C

[0121] The alkaline water electrolysis oxygen evolution stability of the nickel-cobalt-based spinel oxide nanomaterial obtained in Example 1 was tested by using a two-electrode system: the nickel-cobalt-based spinel oxide nanomaterial was used as the anode of the electrolytic cell, and a platinum electrode was used as the cathode of the electrolytic cell. The anode was the nickel-cobalt-based spinel oxide nanomaterial of Example 1 with an effective area of 1*1 cm2, and the cathode was a platinum electrode with an effective area of 1*1 cm2.

[0122] The simulated intermittent electrolysis stability test was carried out at 45 °C, 6 mol / L KOH electrolyte, 2 A / cm2current, and the voltage-time curve is shown in Figure 16 FIG. 4, which shows that the nickel-cobalt-based spinel oxide nanomaterial of Example 1 can run stably under this condition and can run for at least 3500 hours.

[0123] Application Example 5: Test of oxygen evolution reaction stability of nickel-cobalt-based spinel oxide nanomaterial under constant current conditions at 80 °C

[0124] The alkaline water electrolysis oxygen evolution stability of the nickel-cobalt-based spinel oxide nanomaterial obtained in Example 1 was tested by using a two-electrode system: the nickel-cobalt-based spinel oxide nanomaterial was used as the anode of the electrolytic cell, and a platinum electrode was used as the cathode of the electrolytic cell. The anode was the nickel-cobalt-based spinel oxide nanomaterial of Example 1 with an effective area of 1*1 cm2, and the cathode was a platinum electrode with an effective area of 1*1 cm2.

[0125] The constant current test was carried out at 80 °C, 6 mol / L KOH electrolyte, 1 A / cm2current, and the constant current curve is shown in Figure 17 FIG. 6, which shows that the nickel-cobalt-based spinel oxide nanomaterial of Example 1 can run stably under this condition and can run for at least 5000 hours.

[0126] Application Example 6 Stability test of the nickel cobalt-based spinel oxide nanomaterial in the oxygen evolution reaction under the intermittent condition of frequent start-stop at 80℃

[0127] Stability test of the nickel cobalt-based spinel oxide nanomaterial obtained in Example 1 in the alkaline electrolytic water oxygen evolution reaction by using a two-electrode system: the nickel cobalt-based spinel oxide nanomaterial is used as the anode of the electrolytic cell, and a nickel foam metal electrode is used as the cathode electrode of the electrolytic cell. The anode is the nickel cobalt-based spinel oxide nanomaterial with an effective area of 1*1 square centimeter, and the cathode is a nickel foam metal electrode with an effective area of 1*1 square centimeter.

[0128] When the temperature of the electrolyte is 80℃, the electrolyte is 8 moles per liter of potassium hydroxide, and the constant current test is carried out at a current of 10 amperes per square centimeter, the obtained constant current curve is as shown in Figure 18 , which shows that the nickel cobalt-based spinel oxide nanomaterial of Example 1 can run smoothly under this condition and can run for at least 200 hours.

[0129] Application Example 7 Stability test of the nickel cobalt-based spinel oxide nanomaterial in the oxygen evolution reaction under the constant current condition at 100℃

[0130] Stability test of the nickel cobalt-based spinel oxide nanomaterial obtained in Example 1 in the alkaline electrolytic water oxygen evolution reaction by using a two-electrode system: the nickel cobalt-based spinel oxide nanomaterial is used as the anode of the electrolytic cell, and a platinum sheet electrode is used as the cathode electrode of the electrolytic cell. The anode is the nickel cobalt-based spinel oxide nanomaterial with an effective area of 1*1 square centimeter, and the cathode is a platinum sheet electrode with an effective area of 1*1 square centimeter.

[0131] When the temperature of the electrolyte is 100℃, the electrolyte is 8 moles per liter of potassium hydroxide, and the constant current test is carried out at a current of 10 amperes per square centimeter, the obtained constant current curve is as shown in Figure 19 , which shows that the nickel cobalt-based spinel oxide nanomaterial of Example 1 can run smoothly under this condition and can run for at least 400 hours.

[0132] Application Example 8 Stability test of the nickel cobalt-based spinel oxide nanomaterial in the oxygen evolution reaction under the constant current condition at 120℃

[0133] Stability test of the nickel cobalt-based spinel oxide nanomaterial obtained in Example 1 in the alkaline electrolytic water oxygen evolution reaction by using a two-electrode system: the nickel cobalt-based spinel oxide nanomaterial is used as the anode of the electrolytic cell, and a platinum sheet electrode is used as the cathode electrode of the electrolytic cell. The anode is the nickel cobalt-based spinel oxide nanomaterial with an effective area of 1*1 square centimeter, and the cathode is a platinum sheet electrode with an effective area of 1*1 square centimeter.

[0134] The constant current curve obtained by performing constant current test at 1 ampere per square centimeter under the condition of electrolyte temperature of 120℃ and 14 moles per liter of potassium hydroxide is shown in FIG. 1, which indicates that the nickel-cobalt-based spinel oxide nanomaterial of Example 1 can be operated stably under this condition and can be operated for at least 2000 hours. Figure 20

[0135] Application Example 9: Oxygen evolution reaction activity test of nickel-cobalt-based spinel oxide nanomaterial in anion exchange membrane (AEM) electrolyzer under the condition of 60℃

[0136] The electrocatalytic oxygen evolution performance of the nickel-cobalt-based spinel oxide nanomaterial obtained in Example 1 as the anode of an AEM electrolyzer was tested in an anion exchange membrane (AEM) electrolyzer: the nickel-cobalt-based spinel oxide nanomaterial of Example 1 was used as the anode of the electrolyzer, and a nickel-molybdenum alloy electrode was used as the cathode electrode of the electrolyzer, and the activity test was performed in alkaline electrolytic water, the anode being the nickel-cobalt-based spinel oxide nanomaterial of Example 1 with an effective area of 2*2 square centimeters, and the cathode being a nickel-molybdenum alloy electrode with an effective area of 2*2 square centimeters.

[0137] The current-potential curve obtained by performing linear sweep voltammetry test on the electrolyzer under the condition of electrolyte temperature of 60℃ and 1 mole per liter of potassium hydroxide is shown in FIG. 2, which indicates that when the nickel-cobalt-based spinel oxide nanomaterial of Example 1 is used as the anode of the electrolyzer and a nickel-molybdenum alloy electrode is used as the cathode electrode of the electrolyzer, the voltage of the anion exchange membrane is 1.71 volts when the current density is 1 ampere per square centimeter, and the voltage of the anion exchange membrane is 1.8 volts when the current density is 2 ampere per square centimeter. Figure 21

[0138] Application Example 10: Stability test of oxygen evolution reaction of nickel-cobalt-based spinel oxide nanomaterial in anion exchange membrane (AEM) electrolyzer under the condition of constant current of 60℃

[0139] The electrocatalytic oxygen evolution performance of the nickel-cobalt-based spinel oxide nanomaterial obtained in Example 1 as the anode of an AEM electrolyzer was tested in an anion exchange membrane (AEM) electrolyzer: the nickel-cobalt-based spinel oxide nanomaterial of Example 1 was used as the anode of the electrolyzer, and a nickel-molybdenum alloy electrode was used as the cathode electrode of the electrolyzer, and the activity test was performed in alkaline electrolytic water, the anode being the nickel-cobalt-based spinel oxide nanomaterial of Example 1 with an effective area of 2*2 square centimeters, and the cathode being a nickel-molybdenum alloy electrode with an effective area of 2*2 square centimeters.

[0140] The constant current curve obtained by performing constant current test at 1 ampere per square centimeter under the condition of electrolyte temperature of 60℃ and 1 mole per liter of potassium hydroxide is shown in FIG. 2.​​Figure 22 As shown, the anion exchange membrane electrolyzer using the nickel-cobalt-based spinel oxide nanomaterial of Example 1 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.

[0141] Application Example 11: Performance Testing of Nickel-Cobalt-Based Spinel Oxide Nanomaterials After Oxygen Evolution Reaction Stability Test at 80℃ and Constant Current Condition

[0142] The electrocatalytic oxygen evolution reaction (OER) performance of the nickel-cobalt-based spinel oxide nanomaterial after the OER stability test in Application Example 5 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 working electrode with an effective area of ​​1*1 cm². 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 voltammetry scan was performed at 5 mV / s in the range of 0–1 V vs RHE. The resulting linear voltammetry chromatogram is shown below. Figure 23 As shown.

[0143] like Figure 23 As shown, the obtained linear sweep voltammetry plot indicates that after 5000 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 nickel-cobalt-based spinel oxide nanomaterial in Application Example 5 has an overpotential of 204 mV at 10 mA / cm². This is an improvement in performance compared to the nickel-cobalt-based spinel oxide nanomaterial before the reaction in Application Example 1. This indicates that the surface of the spinel oxide is fully activated and the structure is stable after long-term operation, thus improving the performance of the oxygen evolution reaction in water electrolysis after long-term constant current electrolysis.

[0144] Comparative Example 1 - Synthesis of undoped and single-element doped nickel-cobalt based spinel oxide nanomaterials

[0145] The methods for preparing undoped and single-element-doped nickel-cobalt-based spinel oxide nanomaterials are the same as in Example 1, except that soluble iron salts and soluble manganese salts are added simultaneously. Specifically, the following nickel-cobalt-based spinel oxide comparative samples were synthesized: nickel-cobalt spinel oxide, nickel-cobalt-iron spinel oxide, and nickel-cobalt-manganese spinel oxide.

[0146] The above nickel-cobalt-based spinel oxide nanomaterials were subjected to X-ray diffraction (XRD). The diffraction pattern is shown in [reference needed]. Figure 24The results show that the nickel cobalt-based spinel oxide nanomaterial synthesized by the two-step synthesis method has a nickel cobalt spinel structure, good crystallinity and no phase separation, consistent with the nickel cobalt spinel oxide standard card. Then, the Raman spectrum of the undoped nickel cobalt-based spinel oxide nanomaterial is tested, as shown in Figure 25 Compared with the iron-manganese-doped nickel cobalt spinel in Example 1, the iron-manganese-doped nickel cobalt spinel has a significantly enhanced A 1g Compared with the E g vibration peak, A 1g is the vibration mode of the octahedral cation in the spinel structure, E g is the vibration mode of the tetrahedron and octahedron. This shows that the iron-manganese-doped nickel cobalt-based spinel in Example 1 increases the octahedral metal occupation due to the incorporation of iron and manganese, thereby improving the catalytic activity.

[0147] The oxygen evolution reaction activity test of the undoped, single-element-doped nickel cobalt-based spinel oxide nanomaterial and the nickel foam metal substrate in Comparative Application Example 1 at 25°C

[0148] The electrolytic alkaline water electrocatalytic oxygen evolution performance of the undoped, single-element-doped nickel cobalt-based spinel oxide and the nickel foam metal substrate obtained in Comparative Example 1 is tested by a three-electrode system: the reference electrode is a mercury oxide electrode, the counter electrode is a platinum sheet electrode, and the working electrode is the undoped, single-element-doped nickel cobalt-based spinel oxide and the nickel foam metal substrate (Nickel Foam, i.e. NF) obtained in Comparative Example 1 with an effective area of 1*1 square centimeter, and the electrolyte is a 1 mole per liter potassium hydroxide solution. The electrolyte temperature is 25°C. First, cyclic voltammetry scanning is performed in the range of 0-1V vs RHE until the electrode reaches a stable state. Then, a new electrolyte is replaced, and linear scanning is performed in the range of 0-1V vs RHE at 5mV / s. The obtained linear scan voltammogram is shown in Figure 26 At a current density of 10 milliamperes per square centimeter, the oxygen evolution reaction overpotential of the undoped, single-element-doped nickel cobalt-based spinel oxide nanomaterial in Comparative Example 1 is specifically: the oxygen evolution reaction overpotential of the nickel cobalt spinel oxide is 328 millivolts, the oxygen evolution reaction overpotential of the nickel cobalt manganese spinel oxide is 298 millivolts, the oxygen evolution reaction overpotential of the nickel cobalt iron spinel oxide is 250 millivolts, and the overpotential of the nickel foam metal substrate is 360 millivolts. It can be seen that the oxygen evolution reaction overpotential of the undoped, single-element-doped nickel cobalt-based spinel oxide nanomaterial in Comparative Example 1 is higher than that of the nickel cobalt-based spinel oxide nanomaterial in Application Example 1 (the oxygen evolution reaction overpotential is 225 millivolts).

[0149] Synthesis of nickel iron hydrotalcite nanomaterial in Comparative Example 2

[0150] 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.

[0151] 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 27 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.

[0152] Comparative Application Example 2 - Stability Test of Oxygen Evolution Reaction of Nickel-Iron Hydrotalcite Nanomaterials under Constant Current Condition at 80℃

[0153] The oxygen evolution stability of the nickel-iron layered double hydroxide nanomaterial obtained in Comparative Example 2 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 was tested in alkaline water electrolysis. The anode was the nickel-iron layered double hydroxide nanomaterial obtained in Comparative Example 3 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.

[0154] 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 28 As shown, the nickel-iron hydrotalcite nanomaterial obtained in Comparative Example 3 exhibits severe voltage decay under these conditions. After 150 hours of operation, the electrolytic cell voltage decayed from the initial 2.08 volts to 2.38 volts, a decay rate of 2 millivolts per hour. Compared to the oxygen evolution reaction stability test of the nickel-cobalt-based spinel oxide nanomaterial in Application Example 5 under constant current conditions at 80°C, the nickel-cobalt-based spinel oxide nanomaterial in Example 1 of Application Example 5 operates at a voltage of 2.2 volts, and exhibits a decay rate of 0% compared to the initial voltage after 5000 hours of operation. If simultaneously applied to industrial applications, the nickel-cobalt-based spinel oxide nanomaterial in Example 1 can significantly save on electricity resources.

[0155] Comparative Application Example 3 - Failure Analysis of Oxygen Evolution Reaction in Nickel-Iron Hydrotalcite Nanomaterials under Constant Current Condition at 80℃

[0156] The electrolytic alkaline water electrocatalytic oxygen evolution performance of the nickel-iron hydrotalcite nanomaterial obtained in Comparative Example 2 was tested by using a three-electrode system: the reference electrode was a mercury oxide electrode, the counter electrode was a platinum plate electrode, the working electrode was the nickel-iron hydrotalcite nanomaterial obtained in Comparative Example 2 with an effective area of 1*1 cm2, and the electrolyte was a 1 mol / L potassium hydroxide solution. First, cyclic voltammetry scanning was performed in the range of 0-1 V vs RHE until the electrode reached a stable state. Then, new electrolyte was replaced, and linear scanning was performed in the range of 0-1 V vs RHE at a rate of 5 mV / s. The obtained linear scanning voltammogram is shown in Figure 29 . Figure 29 The results show that the overpotential of the nickel-iron hydrotalcite in Comparative Example 2 before the reaction was 215 mV at a current density of 10 mA / cm2.

[0157] The electrolytic alkaline water electrocatalytic oxygen evolution performance of the nickel-iron hydrotalcite nanomaterial after testing in Comparative Application Example 2 was tested by using a three-electrode system: the reference electrode was a mercury oxide electrode, the counter electrode was a platinum plate electrode, the working electrode was the nickel-iron hydrotalcite nanomaterial after testing in Comparative Application Example 2 with an effective area of 1*1 cm2, and the electrolyte was a 1 mol / L potassium hydroxide solution. First, cyclic voltammetry scanning was performed in the range of 0-1 V vs RHE until the electrode reached a stable state. Then, new electrolyte was replaced, and linear scanning was performed in the range of 0-1 V vs RHE at a rate of 5 mV / s. The obtained linear scanning voltammogram is shown in Figure 29 .

[0158] As shown in Figure 29 , the obtained linear scanning voltammogram shows that the overpotential of the nickel-iron hydrotalcite nanomaterial after testing in Comparative Application Example 2 was 251 mV at a current density of 10 mA / cm2 after continuous operation for 150 hours at a current density of 1 A / cm2 in an electrolyte with a potassium hydroxide concentration of 6 mol / L and an electrolyte temperature of 80°C, which indicates that the performance of the nickel-iron hydrotalcite nanomaterial after testing in Comparative Application Example 2 deteriorated severely compared to the performance before the reaction.

[0159] Next, the nickel-iron hydrotalcite nanomaterials after testing in Comparative Example 2 and Comparative Application Example 2 were subjected to X-ray photoelectron spectroscopy testing to analyze the chemical information on the surface of the samples, including the types, contents, chemical states, and electronic structures of the elements, by measuring the energy distribution of photoelectrons. The results are shown in Figure 30 .

[0160] The detection limit of X-ray photoelectron spectroscopy (XPS) is generally 0.1% (atomic percentage). From Figure 30As shown, the iron element in the nickel-iron hydrotalcite nanomaterial of Comparative Example 2 is +3 valence; the surface iron element of the nickel-iron hydrotalcite nanomaterial obtained after 150 hours of constant current stability test in Comparative Application Example 2 is below the detection limit. This indicates that after 150 hours of constant current test at a current of 1 ampere per square centimeter under the electrolyte temperature of 80°C and with 6 moles per liter of potassium hydroxide in the electrolyte in Comparative Application Example 2, the iron element in the nickel-iron hydrotalcite is almost completely dissolved out.

[0161] Subsequently, the obtained nickel-iron hydrotalcite nanomaterial is subjected to scanning electron microscope test (SEM), as shown in FIG. 4. Figure 31 As shown, the nickel-iron hydrotalcite nanomaterial obtained in Comparative Example 2 has regular flaky nanometer array structure. The nickel-iron hydrotalcite nanomaterial obtained in Comparative Application Example 2 is subjected to scanning electron microscope test (SEM), as shown in FIG. 5. Figure 32 As shown, the nickel-iron hydrotalcite nanomaterial obtained in Comparative Application Example 2 has structure collapse into irregular morphology. This indicates that after 150 hours of constant current test at a current of 1 ampere per square centimeter under the electrolyte temperature of 80°C and with 6 moles per liter of potassium hydroxide in the electrolyte in Comparative Application Example 2, the geometry of the nickel-iron hydrotalcite is completely collapsed.

[0162] Therefore, in combination with the oxygen evolution activity of alkaline electrolytic water before and after the reaction of nickel-iron hydrotalcite, the iron element content in the material, and the morphology of the material, it is shown that when the electrolyte temperature is 80°C, the electrolyte uses 6 moles per liter of potassium hydroxide, and the constant current test is performed at a current of 1 ampere per square centimeter, the material stability is poor, and the material structure-activity relationship changes seriously.

[0163] Synthesis of nickel-cobalt-based spinel oxide nanomaterial doped with iron and zinc elements

[0164] The method for preparing the nickel-cobalt-based spinel oxide nanomaterial doped with iron and zinc elements is the same as that in Example 1, except that soluble iron salt and soluble zinc salt are added instead of soluble iron salt and soluble manganese salt during synthesis.

[0165] The above nickel-cobalt-based spinel oxide nanomaterial is subjected to X-ray diffraction (XRD), and the diffraction pattern is shown in FIG. 8. Figure 33 , which is consistent with the nickel-cobalt spinel oxide standard card, and the results show that the nickel-cobalt-based spinel oxide nanomaterial synthesized by the two-step synthesis method has nickel-cobalt spinel structure, good crystallinity, and no phase separation. The material is subjected to scanning electron microscope test (SEM) and EDS mapping analysis, as shown in FIG. 9 and FIG. 10. Figure 34 and 35 . Figure 34 This indicates that the nickel-cobalt-based spinel oxide nanomaterial synthesized by the two-step synthesis method has obvious flaky morphology. Figure 35As shown, the metal elements are uniformly distributed in the iron and zinc element double-doped nickel cobalt-based spinel oxide nanomaterial loaded on the foam nickel metal substrate. This indicates the successful synthesis of the iron and zinc element double-doped nickel cobalt-based spinel oxide material.

[0166] Example 4 - Stability test of oxygen evolution reaction of iron and zinc element double-doped nickel cobalt-based spinel oxide nanomaterial in anion exchange membrane (AEM) electrolyzer

[0167] The iron and zinc element double-doped nickel cobalt-based spinel oxide nanomaterial obtained in Comparative Example 4 was tested as an anode of an AEM electrolyzer for electrocatalytic oxygen evolution performance in an anion exchange membrane (AEM) electrolyzer: the iron and zinc element double-doped nickel cobalt-based spinel oxide nanomaterial obtained in Comparative Example 4 was used as the anode of the electrolyzer, and a nickel molybdenum alloy electrode was used as the cathode of the electrolyzer. The active test was carried out in alkaline electrolytic water, with the anode being the nickel cobalt-based spinel oxide nanomaterial of Example 1 having an effective area of 2*2 square centimeters, and the cathode being a nickel molybdenum alloy electrode having an effective area of 2*2 square centimeters.

[0168] The constant current test was carried out at a temperature of 60°C of the electrolyte, with 1 mole per liter of potassium hydroxide as the electrolyte, at a current of 1 ampere per square centimeter. The constant current curve obtained is shown in Figure 36 As shown, the anion exchange membrane electrolyzer with the iron and zinc element double-doped nickel cobalt-based spinel oxide nanomaterial obtained in Comparative Example 4 as the anode and a nickel molybdenum alloy electrode as the cathode of the electrolyzer was only able to run for 438 hours under this condition, with the voltage of the AEM electrolyzer rising from the initial 1.80V to the final 1.93V, and the reaction eventually terminated due to membrane damage. As shown in Figure 37 As shown, in the membrane electrode system application, the dissolved metal ions easily poison the ion transport channels of the polymer ion exchange membrane, hinder the mass transfer process, limit the catalytic reaction, and induce a serious Fenton reaction. The originally transparent anion exchange membrane is oxidized to yellow due to the Fenton effect, and the electrolyte is contaminated with the high molecular components of the degraded anion exchange membrane, further affecting the reaction. Therefore, the above reasons ultimately lead to membrane electrode damage causing internal short circuit, and electrolysis termination.

[0169] The above description does not mean that any metal doped into nickel cobalt-based spinel oxide can improve the stability of the oxygen evolution reaction in AEM devices.

[0170] Example 4 - Synthesis and oxygen evolution reaction activity test of iron and manganese double-doped nickel cobalt-based spinel oxide nanomaterial with lower proportion of nickel content

[0171] The method for preparing nickel-cobalt-based spinel oxide nanomaterials with a lower nickel content is the same as in Example 1, except that the amount of soluble nickel salt added during synthesis is half that in Example 1. That is, the ratio of nickel, cobalt, iron, and manganese elements in the nickel-cobalt-based spinel oxide is 1:2:1:1.

[0172] The electrocatalytic oxygen evolution performance of the iron-manganese dual-doped nickel-cobalt-based spinel oxide nanomaterial with a low nickel content obtained in Example 4 was tested using a three-electrode system: a mercury oxide electrode was used as the reference electrode, a platinum sheet electrode was used as the counter electrode, and the working electrode was the iron-manganese dual-doped nickel-cobalt-based spinel oxide nanomaterial with a low nickel content obtained in Example 4 with an effective area of ​​1*1 square centimeters. 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.

[0173] The obtained linear scan voltammetry is as follows Figure 38 As shown, at a current density of 10 mA / cm², the oxygen evolution reaction overpotential of the iron-manganese co-doped nickel-cobalt-based spinel oxide nanomaterial with a lower nickel content synthesized in Example 4 is 251 mV. This is in contrast to the 225 mV overpotential of the iron-manganese-doped nickel-cobalt-based spinel with a nickel-cobalt ratio of 2:2 in Example 1. The results indicate that, unlike the conventional NiCo₂O₄ spinel with a NiCo ratio of 1:2, the iron-manganese-doped nickel-cobalt-based spinel with a nickel-cobalt ratio of 2:2 in Example 1 breaks through the conventional approach to catalyst design and achieves better catalytic activity.

[0174] Example 5: Preparation of Nickel-Cobalt-Based Spinel Oxide Nanomaterials by Electrodeposition-High Temperature Annealing and Testing of Oxygen Evolution Performance in Water Electrolysis

[0175] 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, 30 mmol of iron nitrate, 30 mmol of manganese nitrate, and 120 mL of water. (In this solution, the concentrations of the nickel source and cobalt source were 1 mol / L, and the concentrations of the iron and manganese sources were 0.25 mol / L.) 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 nickel-cobalt-based spinel oxide nanomaterials loaded on nickel foam was thus obtained.

[0176] In other embodiments, the molar number of the ferric nitrate and the manganese nitrate in the above step is increased, and other conditions remain unchanged, to prepare a precursor of a nickel-cobalt-based spinel oxide nanomaterial with different iron-manganese doping ratios

[0177] Step (2): The precursor obtained in step (1) is placed in a muffle furnace (or in a tube furnace with or without inert gas), and is heated to 300°C at a heating rate of 5°C / min, and is kept at 300°C for 5 hours. After natural cooling, the material grown on the foamed nickel is obtained, that is, the nickel-cobalt-based spinel oxide nanomaterial. In the nickel-cobalt-based spinel oxide, the molar fraction of nickel and cobalt is 40%, and the molar fraction of iron and manganese is 15%, based on the total molar amount of metals in the nickel-cobalt-based spinel oxide nanomaterial. The ratio of nickel, cobalt, iron and manganese in the metal salt solution is 2:2:0.5:0.5.

[0178] In other embodiments, the molar number of the ferric nitrate and the manganese nitrate in step (1) is increased, and other conditions remain unchanged, to prepare a nickel-cobalt-based spinel oxide nanomaterial with different iron-manganese doping ratios. The ratio of nickel, cobalt, iron and manganese in the metal salt solution is (1-2):(1-2):0.01:0.01-(1-2):(1-2):2:2.

[0179] The material is subjected to scanning electron microscope test (SEM), as shown in Figure 39 The results show that the nickel-cobalt-based spinel oxide nanomaterial synthesized by the electrodeposition method has a clear sheet array structure morphology.

[0180] The electrolytic alkaline water electrocatalytic oxygen evolution performance of the nickel-cobalt-based spinel oxide nanomaterial obtained in Example 1 is tested by using a three-electrode system: the reference electrode is a mercury oxide electrode, the counter electrode is a platinum sheet electrode, the working electrode is the nickel-cobalt-based spinel oxide nanomaterial with an effective area of 1*1 square centimeter in Example 1, and the electrolyte is a 1 mol / L potassium hydroxide solution, and the electrolyte temperature is 25°C. First, cyclic voltammetry scanning is performed in the range of 0-1V vs RHE until the electrode reaches a stable state. Then, new electrolyte is replaced, and linear scanning is performed in the range of 0-1V vs RHE at a rate of 5mV / s. The obtained linear scanning voltammogram is as shown in Figure 40 Experiments show that the nickel-cobalt-based spinel oxide nanomaterial synthesized by the method has an overpotential of 229mV at a current density of 10mA cm -2 This shows that the nickel-cobalt-based spinel oxide nanomaterial in the present application has good electrolytic alkaline water electrocatalytic oxygen evolution activity.

Claims

1. A nickel-cobalt-based spinel oxide nanomaterial, characterized in that, The nickel-cobalt-based spinel oxide nanomaterial comprises: a conductive substrate, a nickel-cobalt-based spinel oxide grown on the surface of the conductive substrate. The nickel-cobalt-based spinel oxide contains nickel, cobalt, iron and manganese elements. The crystal structure of the nickel-cobalt-based spinel oxide is nickel-cobalt spinel phase, and there is no other impurity phase.

2. The nickel-cobalt-based spinel oxide nanomaterial of claim 1, wherein, The nickel, cobalt, iron and manganese in the nickel-cobalt-based spinel oxide are uniformly distributed. In the nickel-cobalt-based spinel oxide, the molar ratio of each metal is as follows: Nickel: Cobalt: Iron: Manganese = (1-2):(1-2):0.01:0.01-(1-2):(1-2):2:

2.

3. The method for preparing the nickel-cobalt-based spinel oxide nanomaterial of claim 1, characterized in that, The synthesis method of the nickel-cobalt-based spinel oxide nanomaterial comprises a two-step synthesis method, the first step is a hydrothermal reaction method or an electrodeposition method, and the second step is high-temperature annealing. The first step of the hydrothermal reaction method comprises the following steps: adding metal salts, urea and ammonium fluoride into water to obtain a solution, transferring the solution to a hydrothermal reaction kettle, adding a conductive substrate and performing hydrothermal reaction at a certain temperature, and obtaining a precursor after heat preservation for a certain time. The first step of the electrodeposition method comprises the following steps: adding metal salts into water and dissolving, placing an anode, a cathode and a reference electrode in the solution, using a conductive substrate at the cathode, and performing electrodeposition to obtain a precursor. The metal salts are water-soluble nickel salts, water-soluble cobalt salts, water-soluble iron salts and water-soluble manganese salts. The concentration of each metal salt is 0.00008-1 mol / L, and the concentration of urea is 2.5-10 times the sum of the concentrations of the metal salts. The molar ratio of each metal is as follows: Nickel: Cobalt: Iron: Manganese = (1-2):(1-2):0.01:0.01-(1-2):(1-2):2:

2. The concentration of ammonium fluoride is 0-0.8 mol / L. The second step of high-temperature annealing comprises the following steps: calcining the precursor obtained in the first step in an inert gas or air atmosphere for a certain time.

4. The production method according to claim 3, characterized by, In the first step of the hydrothermal reaction method, the reaction temperature is 60-200°C, and the heat preservation time is 3-48h.

5. The preparation method according to claim 3, characterized in that, The voltage of the electrodeposition is-1.0V to-2V vs. mercury-mercury SCE, and the time is 100s-7200s.

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

7. Use of the nickel-cobalt-based spinel oxide nanomaterial of claim 1 as an anode material for an alkaline electrolytic water oxygen evolution reaction.

8. Use according to claim 7, characterized in that, The alkaline electrolytic water oxygen evolution reaction electrolyte contains an alkaline substance; the alkaline substance is selected from one or more of sodium hydroxide and potassium hydroxide, and the total concentration of the alkaline substance is 1-14 mol / L.

9. Use according to claim 7, characterized in that, The temperature range of the alkaline electrolytic water oxygen evolution reaction is 25-120°C. The current density range of the alkaline electrolytic water oxygen evolution reaction is 0.1-10 A / cm2.

10. Use according to claim 7, characterized in that, The electrolysis mode of the alkaline electrolytic water oxygen evolution reaction is constant current, constant voltage or frequent start-stop.

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