A method for preparing a nickel ferrite catalyst

Abstract

The application provides a preparation method of a nickel ferrite catalyst, and comprises the following steps: a) dissolving Ni(NO3)2 . 6H2O, Fe(NO3)3 . 9H2O in a mixed solvent to obtain a mixed metal salt solution; the mixed solvent is a mixed solvent of water and an alcohol solvent; b) adding a basic solution dropwise into the mixed metal salt solution to obtain a mixed solution; c) performing heat treatment on the mixed solution, and then performing solid-liquid separation to obtain an initial nickel ferrite powder; and d) performing annealing treatment on the initial nickel ferrite powder in a reducing atmosphere to obtain the nickel ferrite catalyst. The preparation method is simple and efficient, and can effectively solve the problems of low oxygen vacancy density of the nickel ferrite, unstable vacancy structure and high preparation cost, improve the OER performance of water electrolysis hydrogen production, and can be successfully used in the field of industrial water electrolysis under high current density.

Description

Technical Field

[0001] This invention relates to the field of hydrogen energy materials, and in particular to a method for preparing a nickel ferrite catalyst. Background Technology

[0002] With the rapid development of the world economy, energy shortages and environmental pollution have become serious problems facing countries worldwide. Therefore, the development of clean and pollution-free renewable energy is imperative. Hydrogen energy has advantages such as zero pollution, high calorific value, and wide storage and application. Water electrolysis technology can produce hydrogen using renewable energy and fluctuating surplus electricity, and is considered the most ideal and environmentally friendly method of hydrogen production. Therefore, developing renewable energy-based water electrolysis for hydrogen production is of great significance for energy security and CO2 emission reduction.

[0003] Anion exchange membrane electrolysis for hydrogen production has attracted much attention due to its advantages such as low cost, long lifespan, abundant material sources, and suitability for large-scale hydrogen production. However, in large-scale hydrogen production applications, it is still necessary to further improve the current density and energy efficiency of alkaline water electrolysis technology to reduce equipment and power consumption costs. Electrode catalyst materials, as key components, play an indispensable role in this process. The electrode is the site of the electrocatalytic reaction and the core component of the electrolyzer. Its performance directly affects the overpotential of water electrolysis and is one of the key factors restricting the operation of alkaline water electrolysis for hydrogen production at high current densities. The oxygen evolution reaction (OER) at the anolyte, as the rate-determining step of the electrolysis reaction, makes the oxygen evolution activity of the electrode particularly important for the entire electrolysis reaction. OER is the process of converting water into oxygen molecules. The electron transfer of four electrons and the formation of O-O bonds involved are unfavorable to reaction kinetics, thus requiring a large overpotential to drive the reaction. Although noble metals such as RuO2 and IrO2 can effectively catalyze OER, they are expensive, have limited global reserves, and poor stability, making them difficult to meet commercial needs. Developing inexpensive, efficient, and stable electrocatalysts to replace precious metal catalysts has long been a goal for many researchers. Transition metal compounds, due to their low cost, wide availability, and good performance, have been extensively studied and explored as OER electrocatalysts. Among them, iron and nickel-based metal oxides have attracted considerable attention due to their unique physicochemical properties.

[0004] The design of OER electrocatalysts is based on an understanding of the OER catalytic mechanism and the origin of the reaction overpotential. Currently, the most common OER catalytic mechanism is the traditional adsorbent evolution mechanism (AEM). Taking metal-active site catalysis of OER in an alkaline electrolyte environment as an example, AEM can be described as follows: first, OH... - Adsorbed at active sites to form HO * Then, HO * With another OH - The reaction deprotonates to form O * Next, O* With another OH - The reaction forms HOO * Finally, HOO* deprotonates to form O2 and is released. Typically, the adsorption energies of OER reaction intermediates such as HO*, HOO*, and O* involved in AEM are linearly correlated. The elementary reaction steps of OER can be described as follows:

[0005] (1)OH - +*→HO * +e -

[0006] (2)HO * →O * +e - +H +

[0007] (3)O * +OH - →HOO * +e -

[0008] (4) HOO * →*+O2+e - +H +

[0009] Elementary reactions (2) or (3) are usually the rate-determining steps in the catalytic OER process. Ideally, the catalyst's adsorption capacity for reaction intermediates should be neither too strong nor too weak. According to the Nernst equation, the theoretical thermodynamic equilibrium potential for water electrolysis under standard conditions is 1.23V. However, in the entire electrolyzer reaction system, there are electrode overpotentials and ohmic potential drops caused by concentration polarization, electrolyte internal resistance, and other factors. Therefore, the actual voltage required for water electrolysis is much greater than 1.23V. Thus, selecting a suitable OER catalyst can reduce the overpotential and improve the energy conversion efficiency. Furthermore, the electronic structure of the electrocatalyst can be controlled by introducing oxygen vacancies.

[0010] Bao J et al. published a report in Angew. Chem. Int. Ed., 2015, 54:7399 on the synthesis of oxygen-vacancy-rich NiCo2O4 ultrathin nanosheets using local chemical transformation. The presence of oxygen vacancies can reduce Co 3+The inhibition of H2O adsorption at specific sites can improve the efficiency of the OER reaction in water electrolysis. Gan Y et al. published a report on the preparation of nickel ferrite nanosheets rich in active sites by metal heteroatom doping in Nano.Res, 2022, 15:3940-3945. The aim was also to improve the OER reaction activity of water electrolysis by exposing more active sites and abundant oxygen vacancies through vertically grown nanosheets. However, the reported processes for synthesizing nickel ferrite oxides to date are relatively cumbersome, resulting in unstable oxygen vacancy structures, and they cannot be prepared in large quantities or applied efficiently and stably to water electrolysis reactions at industrial current densities.

[0011] The presence of oxygen vacancies can promote the adsorption of H2O, increase the activity of reaction sites, and improve OER performance. However, the performance and structural stability of the catalyst are also important indicators for evaluating whether an electrocatalyst is suitable for commercial operation. Currently, the vacancy structures obtained by methods for preparing oxygen vacancies are easily lost under the strong oxidizing conditions of OER catalysis. Therefore, adopting appropriate strategies to stabilize oxygen vacancies in the catalyst under OER testing conditions is also an important research objective. Summary of the Invention

[0012] In view of this, the present invention provides a method for preparing a nickel ferrite catalyst. The preparation method provided by the present invention is simple and efficient, and can effectively solve the problems of low oxygen vacancy density, unstable vacancy structure and high preparation cost of nickel ferrite, thereby improving the OER performance of hydrogen production by water electrolysis, and can be successfully applied in the field of industrial-grade water electrolysis under high current density.

[0013] This invention provides a method for preparing a nickel ferrite catalyst, comprising the following steps:

[0014] a) Put Ni(NO3)2 . 6H2O, Fe(NO3)3 . 9H2O is dissolved in a mixed solvent to obtain a mixed metal salt solution;

[0015] The mixed solvent is a mixture of water and alcohol solvent;

[0016] b) Add an alkaline solution dropwise to the mixed metal salt solution to obtain a mixed solution;

[0017] c) The mixture is heat-treated, and then the solid and liquid are separated to obtain the initial nickel ferrite powder;

[0018] d) The initial nickel ferrite powder is annealed in a reducing atmosphere to obtain a nickel ferrite catalyst.

[0019] Preferably, in step a), the Ni(NO3)2 . 6H2O and Fe(NO3)3 .The molar ratio of 9H2O is 1:(2-4).

[0020] Preferably, in step d), the annealing treatment is performed at a temperature of 300–500°C for 1–3 hours.

[0021] Preferably, in step b), the alkaline solution is a solution obtained by dissolving an alkaline substance in a solvent;

[0022] The alkaline substance is at least one of KOH and NaOH;

[0023] The alkaline substances in the alkaline solution react with Ni(NO3)2 in step a). . The molar ratio of 6H2O is (4-6):1.

[0024] Preferably, in step c), the heat treatment temperature is 180–200°C and the time is 20–32 h.

[0025] Preferably, in step d), the reducing gas providing the reducing atmosphere is CO, NH3, or H2.

[0026] Preferably, in step a), the alcohol solvent is at least one of ethanol, isopropanol, and ethylene glycol.

[0027] Preferably, in step a), the volume ratio of water to alcohol solvent in the mixed solvent is 1:(0.25-4).

[0028] Preferably, the solvent in the alkaline solution is a mixture of water and alcohol.

[0029] The alcohol solvent is at least one of ethanol, isopropanol, and ethylene glycol;

[0030] In the alkaline solution, the volume ratio of water to alcohol solvent is 1:(0.25-4);

[0031] In the alkaline solution, the ratio of alkaline substance to solvent is (4-8) mmol: 60 mL.

[0032] Preferred,

[0033] In step a):

[0034] Ni(NO3)2 . 6H2O, Fe(NO3)3 . The mixing method for dissolving 9H2O in the mixed solvent is stirring; the stirring rate is 600-800 rpm and the time is 20-30 min.

[0035] The Ni(NO3)2 . 6H2O and Fe(NO3)3 .The ratio of the total molar amount of 9H2O to the volume of the mixed solvent is (3-6) mmol: 40 mL;

[0036] In step b):

[0037] After the alkaline solution is added dropwise, the reaction is stirred continuously; the stirring rate is 1000-1200 rpm and the time is 30-60 min.

[0038] In step c):

[0039] The solid-liquid separation method is centrifugal filtration;

[0040] After the solid-liquid separation, the following processes are also performed: washing, drying, and grinding.

[0041] The preparation method provided by this invention is as described in steps a) to d) above. First, in steps a)-b), an alkaline solution is introduced into the mixed metal salt solution, and a precipitate gradually forms in the system, causing the solution to change from transparent to turbid. Then, through high-temperature hydrothermal treatment in step c), the precipitate in the system degrades and interacts with each other to generate nickel ferrite nanoparticles through a dehydration reaction. The alcohol solution in the system adsorbs the precipitate through hydrogen bonding, reducing the size of the nanoparticles. At the same time, the hydrogen bonds can attack the OH groups of the precipitate particles. - The process accelerates the dehydration reaction of Fe(OH)3 and Ni(OH)3 precipitates in solution, thereby generating a small number of initial oxygen vacancy structures in nickel ferrite nanoparticles. Finally, the nickel ferrite nanoparticles with these initial oxygen vacancy structures are treated with a reducing gas at high temperature. The strong reducing effect induces defects in the metal oxides, and by controlling the reduction temperature and time, a high concentration and high stability of vacancy structures are generated. The resulting nickel ferrite catalyst effectively improves the OER (Optical Erector Reactor) activity in water electrolysis for hydrogen production and can be used in industrial water electrolysis at high current densities, exhibiting excellent stability.

[0042] Experimental results show that the series of nickel ferrite catalysts prepared in this invention can effectively perform the OER reaction of water electrolysis (current density of 10 mA / cm²). 2 The overpotential of the catalyst is below 315 mV, which is much lower than the overpotential of commercial nickel ferrite catalysts (350 mV), indicating a significant improvement in the catalytic activity of the water electrolysis OER reaction. Furthermore, the nickel ferrite catalyst prepared in this invention exhibits good performance at an industrial-grade current density of 1 A / cm². 2The initial voltage was below 1.74V, significantly lower than that of commercial nickel ferrite catalysts (1.84V), demonstrating that the reaction performance of the nickel ferrite catalyst obtained in this invention is significantly improved compared to commercial nickel ferrite catalysts under industrial-grade high current densities. After continuous operation for 100 hours, the termination voltage of the nickel ferrite catalyst obtained in this invention was below 1.85V, significantly lower than that of commercial nickel ferrite catalysts (1.96V), proving that the nickel ferrite catalyst prepared by the method of this invention has a stable oxygen vacancy structure and exhibits excellent stability under industrial-grade high current densities. Attached Figure Description

[0043] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0044] Figure 1 The image shows a TEM image of the nickel ferrite powder NiFe2O4-R1 obtained in Example 1; wherein, Figure 1 (a) and 1(b) are TEM images at different magnifications;

[0045] Figure 2 The image shows the XRD pattern of the nickel ferrite powder NiFe2O4-R1 obtained in Example 1.

[0046] Figure 3 The image shows the XRD pattern of the nickel ferrite powder NiFe2O4-R2 obtained in Example 2.

[0047] Figure 4 The image shows the XRD pattern of the nickel ferrite powder NiFe2O4-R3 obtained in Example 3.

[0048] Figure 5 XPS images of the nickel ferrite powder NiFe2O4-R3 obtained in Example 3 and the commercial nickel ferrite NiFe2O4-COM;

[0049] Figure 6 The graphs show the reaction activity test results of the nickel ferrite catalysts obtained in Examples 1-3 and commercial nickel ferrite catalysts in the water electrolysis reaction.

[0050] Figure 7 The graphs show the reaction performance and stability of the nickel ferrite catalyst obtained in Example 3 and the commercial nickel ferrite catalyst at industrial-grade current densities. Detailed Implementation

[0051] This invention provides a method for preparing a nickel ferrite catalyst, comprising the following steps:

[0052] a) Put Ni(NO3)2 . 6H2O, Fe(NO3)3 . 9H2O is dissolved in a mixed solvent to obtain a mixed metal salt solution;

[0053] The mixed solvent is a mixture of water and alcohol solvent;

[0054] b) Add an alkaline solution dropwise to the mixed metal salt solution to obtain a mixed solution;

[0055] c) The mixture is heat-treated, and then the solid and liquid are separated to obtain the initial nickel ferrite powder;

[0056] d) The initial nickel ferrite powder is annealed in a reducing atmosphere to obtain a nickel ferrite catalyst.

[0057] The preparation method provided by this invention first involves introducing an alkaline solution into a mixed metal salt solution via steps a)-b), causing a precipitate to gradually form in the system, and the solution to change from transparent to turbid. Then, through high-temperature hydrothermal treatment in step c), the precipitate in the system degrades and interacts with each other to generate nickel ferrite nanoparticles via a dehydration reaction. During this hydrothermal reaction, alcohol molecules in the solution accelerate the dehydration reaction of the metal salt precipitates Fe(OH)3 and Ni(OH)3 through bonding, resulting in a small amount of initial oxygen vacancy structures in the nickel ferrite nanoparticles. Then, a reduction strategy involving the introduction of a reducing gas is used to induce defects in the metal oxide, and the reduction temperature and time are controlled to effectively generate high-concentration and highly stable oxygen vacancy structures. This invention, through the above stepwise / stepwise method, prepares high-content and stable oxygen vacancy structures, fundamentally solving the problems of unstable and low-content oxygen vacancy structures. It can effectively improve the reactivity of the OER in water electrolysis for hydrogen production and can be used for industrial water electrolysis at high current densities, exhibiting excellent stability.

[0058] Regarding step a) :

[0059] a) Put Ni(NO3)2 . 6H2O, Fe(NO3)3 . 9H2O is dissolved in a mixed solvent to obtain a mixed metal salt solution.

[0060] In this invention, the Ni(NO3)2 . 6H2O (nickel nitrate), Fe(NO3)3 . There are no special restrictions on the source of 9H2O (i.e., ferric nitrate); any commercially available product is acceptable. Commonly available nickel nitrate is Ni(NO3)2. . 6H2O, commercially available ferric nitrate is Fe(NO3)3. .9H2O. In this invention, the Ni(NO3)2 . 6H2O and Fe(NO3)3 . The preferred molar ratio of 9H2O is 1:(2-4), specifically 1:2, 1:3, 1:4, and more preferably 1:2.

[0061] In this invention, the mixed solvent is a mixture of water and an alcohol solvent. Preferably, the water is ultrapure water. The alcohol solvent is an alcohol-based solvent (or alcohol-based solvent), specifically a monomeric alcohol (rather than a polymeric alcohol) solvent, preferably at least one of ethanol, isopropanol, and ethylene glycol. This invention uses a mixture of water and alcohol as the solvent, which is beneficial for the formation of a stable vacancy structure in the product. The alcohol solvent acts as both a solvent and a reducing agent, adsorbing onto the precipitate surface via hydrogen bonding, leading to anisotropic growth. The adsorbed alcohol molecules and surface charges stabilize the solvent metal ions and reduce particle size. If only water is used, the resulting nanoparticles lack an initial vacancy structure, which is detrimental to subsequent reduction processing. If only an alcohol solvent is used, the resulting initial powder is viscous and difficult to dry, making subsequent processing difficult and the product structure hard to control. In this invention, the volume ratio of water to alcohol solvent in the mixed solvent is preferably 1:(0.25-4), specifically 1:0.25, 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, or 1:4.

[0062] In this invention, the Ni(NO3)2 . 6H2O and Fe(NO3)3 . The ratio of the total molar amount of 9H2O to the volume of the mixed solvent is preferably (3-6) mmol:40 mL, specifically 3 mmol:40 mL, 4 mmol:40 mL, 5 mmol:40 mL, or 6 mmol:40 mL.

[0063] In this invention, Ni(NO3)2 . 6H2O, Fe(NO3)3 . The preferred method for dissolving 9H₂O in the mixed solvent is stirring. The stirring rate is preferably 600–800 rpm, specifically 600 rpm, 650 rpm, 700 rpm, 750 rpm, or 800 rpm. The stirring time is preferably 20–30 min, specifically 20 min, 25 min, or 30 min. Through the above stirring and mixing, the nitrate is fully dissolved in the solvent, resulting in a clear mixed metal salt solution.

[0064] Regarding step b) :

[0065] b) Add an alkaline solution dropwise to the mixed metal salt solution to obtain a mixed solution.

[0066] In this invention, the alkaline solution is a solution obtained by dissolving an alkaline substance in a solvent.

[0067] in:

[0068] The alkaline substance is preferably at least one of KOH and NaOH, and more preferably KOH.

[0069] The solvent is preferably a mixture of water and an alcohol solvent. The water is preferably ultrapure water. The alcohol solvent is an alcohol-based solvent (or alcohol-based solvent), specifically a monomeric alcohol (not a polymeric alcohol) solvent, preferably at least one of ethanol, isopropanol, and ethylene glycol. Using a mixture of water and alcohol as the solvent for the alkaline substance in this invention also helps to form a stable vacancy structure in the product. In this invention, the volume ratio of water to alcohol solvent in the mixed solvent is preferably 1:(0.25-4), specifically 1:0.25, 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, or 1:4.

[0070] The preferred ratio of alkaline substance to solvent is (4-8) mmol:60 mL, specifically 4 mmol:60 mL, 5 mmol:60 mL, 6 mmol:60 mL, 7 mmol:60 mL, or 8 mmol:60 mL.

[0071] The preferred method for dissolving alkaline substances in a solvent is ultrasonic dispersion, that is, to fully dissolve the alkaline substances in the solvent through ultrasonic dispersion. The ultrasonic dispersion power is preferably 80–100 W, specifically 80 W, 85 W, 90 W, 95 W, or 100 W; the ultrasonic dispersion time is preferably 10–20 min, specifically 10 min, 15 min, or 20 min. Through the above ultrasonic dispersion treatment, the alkaline substances are completely dispersed and dissolved in the solvent until the solution becomes clear, thereby obtaining an alkaline solution.

[0072] In this invention, when an alkaline solution is added dropwise to the mixed metal salt solution obtained in step a), the alkaline substance in the alkaline solution reacts with Ni(NO3)2 in step a). . The preferred molar ratio of 6H2O is (4-6):1, specifically 4:1, 5:1, or 6:1, and more preferably 4:1. In this invention, there are no special restrictions on the temperature conditions for the above-mentioned dropwise addition operation; it can be carried out at room temperature.

[0073] In this invention, after adding the alkaline solution, it is preferable to continue stirring the reaction. The stirring is vigorous, preferably at a speed of 1000–1200 rpm, specifically 1000 rpm, 1100 rpm, or 1200 rpm. The stirring time is preferably 30–60 minutes, specifically 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes, or 60 minutes. In this invention, there are no special restrictions on the temperature conditions for the continued stirring reaction; it can be carried out at room temperature. This invention introduces an alkaline solution, in which the alkaline substances act as both a precipitant and create an alkaline environment, adjusting the pH value of the system and combining with metal ions to produce precipitates (Fe(OH)3 and Ni(OH)2). After the above stirring reaction is complete, a mixed solution is obtained.

[0074] Regarding step c) :

[0075] c) The mixture is heat-treated, and then the solid and liquid are separated to obtain the initial nickel ferrite powder.

[0076] In this invention, the preferred temperature for heat treatment is 180–200°C, specifically 180°C, 185°C, 190°C, 195°C, or 200°C. The preferred heat treatment time is 20–32 hours, specifically 20 hours, 22 hours, 24 hours, 26 hours, 28 hours, 30 hours, or 32 hours. The preferred heat treatment method is hydrothermal treatment; specifically, the mixture obtained in step b) is placed in a hydrothermal reactor for heat treatment. Through the above high-temperature hydrothermal treatment reaction, the precipitate in the mixture degrades and interacts with each other to generate nickel ferrite nanoparticles through a dehydration reaction. The alcohol solution in the solution adsorbs the precipitate through hydrogen bonding, reducing the size of the nanoparticles. Simultaneously, the hydrogen bonds can attack the OH groups of the precipitate particles. - This allows nickel ferrite nanoparticles to develop an initial oxygen vacancy structure.

[0077] In this invention, solid-liquid separation is performed after the aforementioned heat treatment. Preferably, cooling is performed before solid-liquid separation, i.e., cooling the reaction solution obtained after heat treatment. The cooling is preferably natural cooling, more preferably natural cooling to room temperature. The solid-liquid separation is preferably performed by centrifugal filtration. The centrifugal filtration speed is preferably 5000–8000 rpm, specifically 5000 rpm, 6000 rpm, 7000 rpm, or 8000 rpm. A solid product is obtained through the aforementioned solid-liquid separation.

[0078] In this invention, after the above solid-liquid separation, the following steps are preferably performed: washing, drying, and grinding. The washing is preferably performed sequentially with deionized water and ethanol. The drying temperature is preferably 60–80°C, specifically 60°C, 65°C, 70°C, 75°C, or 80°C; the drying time is preferably 10–15 hours, specifically 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, or 15 hours. The grinding time is preferably 20–30 minutes, specifically 20 minutes, 25 minutes, or 30 minutes. After the above post-processing, initial nickel ferrite powder is obtained. The initial nickel ferrite powder is nickel ferrite powder with an initial oxygen vacancy structure.

[0079] Regarding step d) :

[0080] d) The initial nickel ferrite powder is annealed in a reducing atmosphere to obtain a nickel ferrite catalyst.

[0081] In this invention, the reducing gas providing the reducing atmosphere is preferably CO, NH3, or H2. The flow rate of the reducing gas is preferably 100–250 sccm.

[0082] In this invention, the annealing temperature is preferably 300–500°C, specifically 300°C, 350°C, 400°C, 450°C, and 500°C. The annealing time is preferably 1–3 hours, specifically 1 hour, 1.5 hours, 2 hours, 2.5 hours, and 3 hours. Under the above high-temperature conditions, treating nickel ferrite nanoparticles with an initial oxygen vacancy structure with a reducing gas induces defects in the metal oxide, thereby generating a stable vacancy structure. Providing a reducing atmosphere and controlling the temperature and time of the reduction reaction are crucial. After the above treatment, a nickel ferrite catalyst is obtained. The final obtained nickel ferrite catalyst is nanoparticles, specifically a mixed structure of polyhedral and irregular sphere particles with a particle size between 20 and 30 nm. It possesses a high concentration and high stability of oxygen vacancy structure, making it an ultra-stable nickel ferrite catalyst for anion exchange membrane water electrolysis.

[0083] The preparation method provided by this invention is as described in steps a) to d) above. First, in steps a)-b), an alkaline solution is introduced into the mixed metal salt solution, and a precipitate gradually forms in the system, causing the solution to change from transparent to turbid. Then, through high-temperature hydrothermal treatment in step c), the precipitate in the system degrades and interacts with each other to generate nickel ferrite nanoparticles through a dehydration reaction. The alcohol solution in the system adsorbs the precipitate through hydrogen bonding, reducing the size of the nanoparticles. At the same time, the hydrogen bonds can attack the OH groups of the precipitate particles. -The process accelerates the dehydration reaction of Fe(OH)3 and Ni(OH)3 precipitates in solution, thereby generating a small number of initial oxygen vacancy structures in nickel ferrite nanoparticles. Finally, the nickel ferrite nanoparticles with these initial oxygen vacancy structures are treated with a reducing gas at high temperature. The strong reducing effect induces defects in the metal oxides, and by controlling the reduction temperature and time, a high concentration and high stability of vacancy structures are generated. The resulting nickel ferrite catalyst effectively improves the OER (Optical Erector Reactor) activity in water electrolysis for hydrogen production and can be used in industrial water electrolysis at high current densities, exhibiting excellent stability.

[0084] This invention also provides a nickel ferrite catalyst prepared by the method described in the above technical solution. The nickel ferrite catalyst prepared by this invention can be used as an anode catalyst for hydrogen production by anion exchange membrane electrolysis of water.

[0085] This invention also provides an application of the above-mentioned nickel ferrite catalyst in anion exchange membrane water electrolysis for hydrogen production. In the above application, the nickel ferrite catalyst is used as an anode catalyst.

[0086] The present invention has the following beneficial effects:

[0087] 1. Traditional methods for preparing oxygen vacancies result in unstable vacancy structures that are easily destroyed under the strong oxidizing conditions of the OER reaction in water electrolysis. This invention utilizes a stepwise method to synthesize high-content and stable oxygen vacancy structures, fundamentally solving the problems of unstable and low-content oxygen vacancy structures. The synthesis method is simple, efficient, green, economical, and inexpensive, and the experimental synthesis equipment is simple, making it easy for large-scale industrial production.

[0088] 2. The synthesized nickel ferrite catalyst material is an undoped pure phase oxide with a simple structure, which helps to improve the content and stability of oxygen vacancies.

[0089] 3. The synthesized nickel ferrite catalyst exhibits high activity and good stability in water electrolysis, achieving an industrial-grade efficiency of 1 A / cm². 2 After working at high current density for 100 hours, there is no significant performance degradation; the OER reaction performance of water electrolysis is 10% higher than that of commercial nickel ferrite catalysts, and the stability is also better than that of commercial nickel ferrite catalysts.

[0090] Experimental results show that the series of nickel ferrite catalysts prepared in this invention can effectively perform the OER reaction of water electrolysis (current density of 10 mA / cm²). 2 The overpotential of the catalyst is below 315 mV, which is much lower than the overpotential of commercial nickel ferrite catalysts (350 mV), indicating a significant improvement in the catalytic activity of the water electrolysis OER reaction. Furthermore, the nickel ferrite catalyst prepared in this invention exhibits good performance at an industrial-grade current density of 1 A / cm². 2The initial voltage was below 1.74V, significantly lower than that of commercial nickel ferrite catalysts (1.84V), demonstrating that the reaction performance of the nickel ferrite catalyst obtained in this invention is significantly improved compared to commercial nickel ferrite catalysts under industrial-grade high current densities. After continuous operation for 100 hours, the termination voltage of the nickel ferrite catalyst obtained in this invention was below 1.85V, significantly lower than that of commercial nickel ferrite catalysts (1.96V), proving that the nickel ferrite catalyst prepared by the method of this invention has a stable oxygen vacancy structure and exhibits excellent stability under industrial-grade high current densities.

[0091] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims of the present invention.

[0092] Unless otherwise specified, the raw materials or reagents used in the following examples are commercially available products. Among them, Ni(NO3)2... . 6H2O, Fe(NO3)3 . 9H₂O (analytical grade), KOH (analytical grade), and commercial nickel ferrite (CAS No. 12168-54-6, referred to as NiFe₂O₄-COM below) were purchased from Aladdin Reagent Network. Ultrapure water was produced in-house using a laboratory ultrapure water system. Equipment and instruments: XRD patterns were obtained using a Bruker X8 X-ray diffractometer (Germany); TEM patterns were obtained using a JEOL Analytical Instruments 1400 transmission electron microscope (Japan); XPS patterns were obtained using a PHI-5000versaprobeIII instrument; the electrolytic water stability test in the application example was performed using a single-channel alkaline water electrolysis system from Xiamen Jiamo Technology Co., Ltd.

[0093] Example 1

[0094] 1. Sample preparation

[0095] a) Add 1 mmol of Ni(NO3)2 . 6H2O and 2 mmol Fe(NO3)3 . Mix 9H2O and dissolve it in a mixed solvent of ultrapure water and ethylene glycol (the volume of the mixed solvent is 40 mL, where the volume ratio of water to glycol is 1:1). Stir at 600 rpm for 30 min to clarify the solution and obtain a mixed metal salt solution.

[0096] b) Add KOH solution dropwise to the mixed metal salt solution. After the addition is complete, stir at 1000 rpm for 30 min to obtain the mixed solution.

[0097] The KOH solution was prepared by mixing 4 mmol of KOH with 60 mL of solvent (a mixture of water and ethylene glycol, wherein the volume ratio of water to glycol is 1:1) and sonicating for 20 min to obtain the KOH solution.

[0098] c) Place the mixture in a high-pressure hydrothermal reactor and react at 180°C for 24 hours. Then cool naturally to room temperature, centrifuge and filter. Wash the obtained solid three times with deionized water and twice with anhydrous ethanol. Dry in an oven at 80°C for 12 hours and then grind for 30 minutes to obtain the initial nickel ferrite powder.

[0099] d) The initial nickel ferrite powder was loaded into a corundum boat and calcined at 400°C for 1 h in a reducing atmosphere of H2 to obtain a nickel ferrite powder catalyst, denoted as NiFe2O4-R1.

[0100] 2. Sample Characterization

[0101] (1) TEM characterization

[0102] The microstructure of the nickel ferrite powder NiFe2O4-R1 obtained in Example 1 was characterized using scanning electron microscopy, and the results are as follows: Figure 1 As shown, Figure 1 This is a TEM image of the nickel ferrite powder NiFe2O4-R1 obtained in Example 1, wherein... Figure 1 (a) and (b) are TEM images at different magnifications. It can be seen that the obtained nickel ferrite powder is nanoparticle, specifically a mixture of polyhedral and irregular sphere structure particles, with a particle size between 20 and 30 nm.

[0103] (2) XRD characterization

[0104] X-ray diffraction tests were performed on the nickel ferrite powder NiFe2O4-R1 obtained in Example 1, and the results are as follows: Figure 2 As shown, Figure 2 The XRD pattern of the nickel ferrite powder NiFe2O4-R1 obtained in Example 1 shows obvious diffraction peaks (111), (220), (311), (222), (400), (422), (511), and (440).

[0105] Example 2

[0106] 1. Sample preparation

[0107] a) Add 1 mmol of Ni(NO3)2 . 6H2O and 2 mmol Fe(NO3)3 .Mix 9H2O and dissolve it in a mixed solvent of ultrapure water and ethylene glycol (the volume of the mixed solvent is 40 mL, where the volume ratio of water to glycol is 1:1). Stir at 600 rpm for 30 min to clarify the solution and obtain a mixed metal salt solution.

[0108] b) Add KOH solution dropwise to the mixed metal salt solution. After the addition is complete, stir at 1000 rpm for 30 min to obtain the mixed solution.

[0109] The KOH solution was prepared by mixing 4 mmol of KOH with 60 mL of solvent (a mixture of water and ethylene glycol, wherein the volume ratio of water to glycol is 1:1) and sonicating for 20 min to obtain the KOH solution.

[0110] c) The mixture was placed in a high-pressure hydrothermal reactor and reacted at 180°C for 24 hours. Then it was allowed to cool naturally to room temperature, centrifuged and filtered. The resulting solid was washed three times with deionized water and twice with anhydrous ethanol. It was then dried in an oven at 80°C for 12 hours and then ground for 30 minutes to obtain the initial nickel ferrite powder.

[0111] d) The initial nickel ferrite powder was loaded into a corundum boat and calcined at 400°C for 2 hours in a reducing atmosphere of H2 to obtain a nickel ferrite powder catalyst, denoted as NiFe2O4-R2.

[0112] 2. Sample Characterization

[0113] XRD characterization

[0114] X-ray diffraction tests were performed on the nickel ferrite powder NiFe2O4-R2 obtained in Example 2, and the results are as follows: Figure 3 As shown, Figure 3 The XRD pattern of the nickel ferrite powder NiFe2O4-R2 obtained in Example 2 shows obvious diffraction peaks (111), (220), (311), (222), (400), (422), (511), and (440).

[0115] Example 3

[0116] 1. Sample preparation

[0117] a) Add 1 mmol of Ni(NO3)2 . 6H2O and 2 mmol Fe(NO3)3 . Mix 9H2O and dissolve it in a mixed solvent of ultrapure water and ethylene glycol (the volume of the mixed solvent is 40 mL, where the volume ratio of water to glycol is 1:1). Stir at 600 rpm for 30 min to clarify the solution and obtain a mixed metal salt solution.

[0118] b) Add KOH solution dropwise to the mixed metal salt solution. After the addition is complete, stir at 1000 rpm for 30 min to obtain the mixed solution.

[0119] The KOH solution was prepared by mixing 4 mmol of KOH with 60 mL of solvent (a mixture of water and ethylene glycol, wherein the volume ratio of water to glycol is 1:1) and sonicating for 20 min to obtain the KOH solution.

[0120] c) Place the mixture in a high-pressure hydrothermal reactor and react at 180°C for 24 hours. Then cool naturally to room temperature, centrifuge and filter. Wash the obtained solid three times with deionized water and twice with anhydrous ethanol. Dry in an oven at 80°C for 12 hours and then grind for 30 minutes to obtain the initial nickel ferrite powder.

[0121] d) The initial nickel ferrite powder was loaded into a corundum boat and calcined at 400°C for 3 hours in a reducing atmosphere of H2 to obtain a nickel ferrite powder catalyst, denoted as NiFe2O4-R3.

[0122] 2. Sample Characterization

[0123] (1) XRD characterization

[0124] X-ray diffraction tests were performed on the nickel ferrite powder NiFe2O4-R3 obtained in Example 3, and the results are as follows: Figure 4 As shown, Figure 4 The XRD pattern of the nickel ferrite powder NiFe2O4-R3 obtained in Example 3 shows obvious diffraction peaks at (111), (220), (311), (222), (400), (422), (511), and (440). Meanwhile, Figure 2-4 The XRD spectrum of commercial nickel ferrite NiFe2O4-COM is also shown. By comparing it with the sample of the example, it can be seen that the nickel ferrite powder obtained in the example has stronger diffraction peaks and smaller grains than commercial nickel ferrite, and the lattice has obvious shift. The comparison of Example 3 is more obvious, indicating that a stable oxygen vacancy structure has been generated.

[0125] (2) XPS characterization

[0126] XPS characterization was performed on the nickel ferrite powder NiFe2O4-R3 obtained in Example 3 and the commercial nickel ferrite NiFe2O4-COM. The results are as follows: Figure 5 As shown, Figure 5XPS plots of the nickel ferrite powder NiFe2O4-R3 obtained in Example 3 and the commercial nickel ferrite NiFe2O4-COM are shown. It can be seen that at a binding energy of 531 eV on the horizontal axis, the oxygen vacancy content of the nickel ferrite powder NiFe2O4-R3 prepared in Example 3 is significantly higher than that of the commercial nickel ferrite NiFe2O4-COM, meaning that NiFe2O4-R3 contains a higher number of oxygen vacancies. The principle is that during the hydrothermal synthesis process, alcohol molecules in the mixed solution accelerate the dehydration reaction of the metal salt precipitates Fe(OH)3 and Ni(OH)3 in the solution through bonding, generating an initial small number of oxygen vacancies. Based on the initial oxygen vacancy obtained using a reducing solvent, a further reduction strategy involving the introduction of a reducing gas induces defects in the metal oxide. By controlling the reduction time and temperature, oxygen vacancies with high concentration and high stability can be effectively produced.

[0127] Application Example 1: Application Performance Testing

[0128] Electrolysis performance and stability tests were conducted on the nickel ferrite powder obtained in Examples 1-3 and commercial nickel ferrite.

[0129] Electrolysis of water (OER) reaction performance test: The catalyst sample (1cm × 1cm) was sprayed onto a nickel foam substrate as the working electrode, a graphite rod as the counter electrode, mercuric oxide as the reference electrode, and an aqueous solution of KOH (1M concentration) as the electrolyte. A three-electrode test was conducted. Results are as follows: Figure 6 As shown, Figure 6 The graphs show the reaction activity tests of the nickel ferrite catalysts obtained in Examples 1-3 and commercial nickel ferrite catalysts in the water electrolysis reaction.

[0130] Stability test: The cathode catalyst used was a platinum-carbon catalyst Pt / C (loading 1 mg / cm³). 2 The anode catalyst is nickel ferrite powder (loading 1.5 mg / cm³). 2 The anion exchange membrane used is a polydiphenylene oxide (PBPA) ion exchange membrane independently developed by Xiamen Jiamo Technology Co., Ltd., with a current density of 1 A / cm². 2 A constant current charging test was performed under the specified conditions. The results are as follows: Figure 7 As shown, Figure 7 The graphs show the reaction performance and stability of the nickel ferrite catalyst obtained in Example 3 and the commercial nickel ferrite catalyst at industrial-grade current densities.

[0131] Depend on Figure 6 It can be seen that the catalytic performance of the nickel ferrite powders obtained in Examples 1-3 is significantly improved compared with that of commercial nickel ferrite catalysts. As shown in the figure, the current density is 10 mA / cm². 2In this study, the overpotentials of the nickel ferrite catalysts obtained in Examples 1-3 for the water electrolysis OER reaction were all lower than those of commercial nickel ferrite catalysts. Specifically, the overpotentials of the nickel ferrite catalysts NiFe2O4-R1, NiFe2O4-R2, and NiFe2O4-R3 obtained in Examples 1-3 were only 310mV, 300mV, and 285mV, respectively, while the overpotential of the commercial nickel ferrite catalyst NiFe2O4-COM for the OER reaction was as high as 350mV. It can be seen that the nickel ferrite catalysts obtained in this invention significantly improve the catalytic activity of the water electrolysis OER reaction.

[0132] Depend on Figure 7 It can be seen that at an industrial-grade current density of 1 A / cm² 2 In Example 3, the onset voltage of the nickel ferrite catalyst NiFe2O4-R3 was only 1.68V, while the onset voltage of the commercial nickel ferrite catalyst NiFe2O4-COM was 1.84V, significantly higher than that of the present invention. This demonstrates that, under industrial-grade high current densities, the reaction performance of the nickel ferrite catalyst obtained in this invention is also significantly improved compared to the commercial nickel ferrite catalyst, with an improvement rate of up to 10%. Meanwhile, after 100 hours of continuous operation, the voltages of both the nickel ferrite catalyst NiFe2O4-R3 obtained in Example 3 and the commercial nickel ferrite catalyst NiFe2O4-COM tended to stabilize, without significant increases. However, the termination voltage (1.76V) of the nickel ferrite catalyst NiFe2O4-R3 obtained in Example 3 was much lower than that of the commercial nickel ferrite catalyst NiFe2O4-COM (1.97V), proving that the nickel ferrite catalyst prepared by the method of this invention has a stable oxygen vacancy structure and exhibits excellent stability under industrial-grade high current density. Moreover, the termination voltage (1.76V) of the nickel ferrite catalyst NiFe2O4-R3 obtained in Example 3 was even lower than the starting voltage (1.84V) of the commercial nickel ferrite catalyst NiFe2O4-COM, indicating that the reaction performance of the nickel ferrite catalyst of this invention is significantly better than that of commercial nickel ferrite. Therefore, from Figure 7 It can be seen that the reaction performance and stability of the nickel ferrite catalyst obtained by the present invention are superior to those of commercial nickel ferrite.

[0133] Example 4

[0134] The experiment was carried out in accordance with Example 3, except that the reaction temperature of the hydrothermal reactor in step c) was 190°C and the calcination temperature in step d) was 300°C.

[0135] Example 5

[0136] The experiment was carried out according to Example 3, except that the reaction temperature of the hydrothermal reactor in step c) was 200°C, and the calcination temperature in step d) was 500°C and the time was 2 hours.

[0137] Comparative Example 1

[0138] The embodiment was carried out according to Example 3, except that the reducing gas obtained in step d) was replaced with air.

[0139] Comparative Example 2

[0140] The method was implemented according to Example 3, except that the calcination time in step d) was adjusted to 0.5 h.

[0141] Comparative Example 3

[0142] The method was implemented according to Example 3, except that the calcination time in step d) was adjusted to 5 hours.

[0143] Application Example 2: Application Performance Testing

[0144] The nickel ferrite catalysts obtained in Examples 4-5 and Comparative Examples 1-3 were subjected to water electrolysis performance and stability tests according to the application performance test method in Application Example 1. The results are shown in Table 1.

[0145] Table 1: Performance test results of samples obtained from each embodiment and comparative example

[0146]

[0147] As can be seen from the test results in Table 1, Examples 1-5 of this invention showed that the OER reaction of water electrolysis (current density of 10 mA / cm²) was satisfactory. 2 The overpotential (at time) is below 315 mV, far lower than the overpotential of commercial nickel ferrite catalysts (350 mV), indicating a significant improvement in the catalytic activity of the water electrolysis OER reaction. Furthermore, in Examples 1-5 of this invention, at an industrial-grade current density of 1 A / cm²... 2 The initial voltage was below 1.74V, significantly lower than that of commercial nickel ferrite catalysts (1.84V), demonstrating that the reaction performance of the nickel ferrite catalyst obtained by this invention is significantly improved compared to commercial nickel ferrite catalysts under industrial-grade high current densities. After continuous operation for 100 hours, the termination voltage of the nickel ferrite catalysts obtained in Examples 1-5 was below 1.85V, significantly lower than that of commercial nickel ferrite catalysts (1.97V), proving that the nickel ferrite catalyst prepared by the method of this invention has a stable oxygen vacancy structure and exhibits excellent stability under industrial-grade high current densities. The overall performance of Comparative Examples 1-3 was worse than that of Example 3, proving that the final step of this invention, carried out under a reducing atmosphere and with controlled reaction time, is necessary to effectively improve the performance of the nickel ferrite catalyst.

[0148] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of these embodiments are merely to aid in understanding the method and core ideas of the present invention, including the best mode, and to enable any person skilled in the art to practice the present invention, including manufacturing and using any device or system, and implementing any combined method. It should be noted that those skilled in the art can make various improvements and modifications to the present invention without departing from its principles, and these improvements and modifications also fall within the scope of protection of the claims. The scope of protection of this patent is defined by the claims and may include other embodiments that can be conceived by those skilled in the art. If these other embodiments have structural elements similar to those expressed in the claims, or if they include equivalent structural elements that are not substantially different from those expressed in the claims, then these other embodiments should also be included within the scope of the claims.

Claims

1. A method for preparing a nickel ferrite catalyst, characterized in that, Includes the following steps: a) Put Ni(NO3)2 . 6H2O, Fe(NO3)3 . 9H2O is dissolved in a mixed solvent to obtain a mixed metal salt solution; The mixed solvent is a mixture of water and alcohol; wherein the volume ratio of water to alcohol is 1:(0.25~4). b) Add an alkaline solution dropwise to the mixed metal salt solution to obtain a mixed solution; c) The mixture is subjected to high-temperature hydrothermal treatment, followed by solid-liquid separation to obtain initial nickel ferrite powder; d) The initial nickel ferrite powder was annealed in a reducing atmosphere to obtain a nickel ferrite catalyst; The annealing process is performed at a temperature of 300-500℃ for 1-3 hours.

2. The preparation method according to claim 1, characterized in that, In step a), the Ni(NO3)2 . 6H2O and Fe(NO3)3 . The molar ratio of 9H2O is 1:(2~4).

3. The preparation method according to claim 1, characterized in that, In step b), the alkaline solution is a solution obtained by dissolving an alkaline substance in a solvent; The alkaline substance is at least one of KOH and NaOH; The alkaline substances in the alkaline solution are similar to Ni(NO3)2 in step a). . The molar ratio of 6H2O is (4~6):

1.

4. The preparation method according to claim 1, characterized in that, In step c), the high-temperature hydrothermal treatment is performed at a temperature of 180~200℃ for a time of 20~32h.

5. The preparation method according to claim 1, characterized in that, In step d), the reducing gas providing the reducing atmosphere is CO, NH3, or H2.

6. The preparation method according to claim 1, characterized in that, In step a), the alcohol solvent is at least one of ethanol, isopropanol, and ethylene glycol.

7. The preparation method according to claim 1 or 3, characterized in that, The solvent in the alkaline solution is a mixture of water and alcohol. The alcohol solvent is at least one of ethanol, isopropanol, and ethylene glycol; In the alkaline solution, the volume ratio of water to alcohol solvent is 1:(0.25~4); In the alkaline solution, the ratio of alkaline substance to solvent is (4~8) mmol: 60 mL.

8. The preparation method according to claim 1, characterized in that, In step a): Ni(NO3)2 . 6H2O, Fe(NO3)3 . The mixing method for dissolving 9H2O in the mixed solvent is stirring; the stirring rate is 600~800 rpm and the time is 20~30 min. The Ni(NO3)2 . 6H2O and Fe(NO3)3 . The ratio of the total molar amount of 9H2O to the volume of the mixed solvent is (3~6) mmol: 40 mL; In step b): After the alkaline solution is added dropwise, the reaction is stirred continuously; the stirring rate is 1000~1200 rpm and the time is 30~60 min. In step c): The solid-liquid separation method is centrifugal filtration; After the solid-liquid separation, the following processes are also performed: washing, drying, and grinding.

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