Preparation method and application of ultrathin nickel-iron layered double hydroxide

Abstract

The application belongs to the technical field of catalytic electrolysis of water, and relates to a catalyst for electrolysis of water, in particular to a preparation method and application of ultrathin nickel-iron layered double hydroxide. In the application, the growth process of the catalyst crystal is regulated and controlled through low-temperature nucleation reaction, crystal aging growth and formamide layer peeling, so that the NiFe-LDH catalyst with high purity, good crystallinity and nanoscale sheet shape is obtained. The ultrathin nickel-iron layered double hydroxide is coated on a polytetrafluoroethylene plate, and then an oxygen evolution electrode is formed through a heat pressing transfer method, so that the coating and the substrate are well combined and are not easy to fall off, and the application is suitable for industrial large-area production.

Description

Technical Field

[0001] This invention belongs to the field of catalytic water electrolysis technology, and relates to catalysts for water electrolysis, specifically to a method for preparing an ultrathin nickel-iron layered bimetallic hydroxide and its application. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Hydrogen energy, as an ideal clean energy source, is considered one of the energy sources with broad development prospects in the future. Among hydrogen production technologies, anion exchange membrane (AEM) hydrogen production technology combines the advantages of high current density of proton exchange membrane (PEM) hydrogen production and low cost of alkaline water electrolysis (ALK) hydrogen production technology, and is considered to be the most promising technology for large-scale hydrogen production in the future.

[0004] The core reactions in water electrolysis for hydrogen production involve two spatially independent half-reactions: the oxygen evolution reaction (OER) with four-electron transfer at the anode and the hydrogen evolution reaction (HER) with two-electron transfer at the cathode. The energy barrier and slow electron transfer rate in the four-electron OER process are major obstacles limiting the widespread application of water splitting, and catalysts can effectively alleviate these problems. Currently, iridium (Ir), ruthenium (Ru), and their oxides are considered the most effective catalysts for OER. However, the low natural reserves and high operating costs of precious metals significantly increase the production cost of hydrogen energy, hindering its development. Compared to commonly used precious metal catalysts, transition metals (Fe, Co, and Ni, etc.) and their hydroxides have become a research hotspot in recent years due to their relatively high catalytic activity and low cost, especially the hydrotalcite-structured bimetallic hydroxide NiFe-LDH catalyst.

[0005] Currently, the main methods for preparing NiFe-LDH as an anode material for water electrolysis to produce hydrogen are spraying and self-supporting methods. Spraying involves mixing NiFe-LDH with organic solvents (ethanol, isopropanol, etc.) and anionic polymers in a specific ratio to form a slurry, which is then directly sprayed onto a substrate (nickel felt or nickel foam) to form the anode. Self-supporting methods involve depositing NiFe-LDH onto the substrate surface using hydrothermal, electrodeposition, or chemical plating methods to form the NiFe-LDH anode. Compared to self-supporting methods, spraying is simpler to operate, more suitable for large-area NiFe-LDH anode preparation, and more conducive to commercial application. However, spraying has the following drawbacks: directly spraying the NiFe-LDH-containing slurry onto the substrate results in poor adhesion between the slurry and the substrate, making it prone to detachment. The main reasons for the peeling are as follows: First, the NiFe-LDH particles are not uniform and have a large overall particle size, which makes them easy to peel off during use; second, the slurry is prepared using anionic polymer solution, and some anionic polymer solution may oxidize and fail under long-term oxygen evolution environment, resulting in poor adhesion and coating peeling. Summary of the Invention

[0006] To overcome the above problems, the present invention provides a method for preparing ultrathin nickel-iron layered bimetallic hydroxide (NiFe-LDH) and its application.

[0007] To achieve the above technical objectives, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a method for preparing an ultrathin nickel-iron layered bimetallic hydroxide, wherein the ultrathin nickel-iron layered bimetallic hydroxide has a nanosheet structure with a thickness of 8-12 nm, comprising the following steps:

[0009] (1) Dissolve nickel salt and ferric salt in water and mix well to obtain solution A; dissolve sodium carbonate and sodium hydroxide in water and mix well to obtain solution B;

[0010] (2) Add solution A and solution B to the ethanol aqueous solution simultaneously and stir continuously;

[0011] (3) The stirred reaction solution is aged at a limited temperature, the precipitate is collected and washed;

[0012] (4) Disperse the washed precipitate into formamide solution, sonicate it, collect the precipitate after the reaction, wash and dry it to obtain ultrathin nickel-iron layered bimetallic hydroxide.

[0013] In one or more embodiments, in step (1), the nickel salt is one or more of nickel chloride, nickel nitrate, nickel sulfate and nickel acetate.

[0014] In one or more embodiments, in step (1), the ferric salt is one or more of ferric chloride, ferric nitrate and ferric sulfate.

[0015] In one or more embodiments, in step (1), the molar ratio of nickel salt to ferric salt is (1~6):(0.2~1.5), preferably 5:1. Under this ratio limitation, the catalytic performance of the ultrathin nickel-iron layered bimetallic hydroxide is optimal.

[0016] In one or more embodiments, in step (1), the concentration of the nickel salt is 0.3~0.5 mM, preferably 0.375 mM.

[0017] In one or more embodiments, in step (1), the molar ratio of sodium carbonate to sodium hydroxide is (0.2~0.6):1, preferably 0.4:1.

[0018] In one or more embodiments, in step (1), the concentration of sodium carbonate is 0.3~0.5 mM, preferably 0.4 mM.

[0019] In one or more embodiments, in step (2), the volume ratio of liquid A to liquid B is (0.8~1.2):1, preferably 1:1.

[0020] In one or more embodiments, in step (2), the volume fraction of ethanol in the aqueous ethanol solution is 5-30%, preferably 25%.

[0021] In one or more embodiments, in step (2), the volume ratio of liquid A to the aqueous ethanol solution is (0.4~0.6):1, preferably 0.5:1.

[0022] In one or more embodiments, in step (2), the stirring speed is 1000~3000 r / min, and the stirring time is 2~6 h. High-speed stirring can make the reaction process more uniform and inhibit the growth and agglomeration of crystal nuclei.

[0023] In one or more embodiments, in step (2), the temperature of the reaction system is controlled at 5~10 °C during the addition of liquid A and liquid B and during stirring. Nucleation at low temperature can further suppress the growth rate of crystals.

[0024] In one or more embodiments, in step (2), the pH of the reaction system is controlled to be 9-11, preferably 10, during the addition of solutions A and B and during stirring. This pH limitation allows Ni to... 2+ and Fe 3+ Complete precipitation can avoid the formation of unnecessary impurities, while a suitable pH can suppress the Wald ripening effect and keep the catalyst at a limited size.

[0025] In one or more embodiments, in step (3), the aging temperature is 60~90 ℃ and the aging time is 12~24 h. Under these limited conditions, crystal aging growth can improve the crystallinity of NiFe-LDH.

[0026] In one or more embodiments, in step (4), the formamide solution contains 25-55% by volume, preferably 50%. Formamide can exfoliate layered NiFe-LDH into nanosheet NiFe LDH.

[0027] In one or more embodiments, in step (4), during the ultrasonic reaction, the ultrasonic power is 400~500 W, preferably 450 W; the ultrasonic reaction time is 15~45 min, preferably 30 min.

[0028] In one or more embodiments, in step (3), the washing method is to wash with water 3 to 5 times.

[0029] In one or more embodiments, in step (4), the washing method is to wash with water and ethanol 3 to 5 times in sequence.

[0030] In a second aspect, the present invention provides the application of the ultrathin nickel-iron layered bimetallic hydroxide prepared by the preparation method described in the first aspect in the catalytic electrolysis of water to produce hydrogen.

[0031] A third aspect of the present invention provides an oxygen evolution electrode, which is based on a nickel felt and coated with a catalyst coating.

[0032] The catalyst in the catalyst coating includes an ultrathin nickel-iron layered bimetallic hydroxide prepared by the preparation method described in the first aspect.

[0033] A fourth aspect of the present invention provides a method for preparing the oxygen evolution electrode described in the third aspect, comprising the following steps:

[0034] The ultrathin nickel-iron layered bimetallic hydroxide prepared by the preparation method described in the first aspect is mixed evenly with isopropanol, water and polymerization liquid to obtain a catalyst slurry.

[0035] The catalyst slurry is sprayed onto the upper surface of the first polytetrafluoroethylene plate to form a catalyst coating.

[0036] Pretreated nickel felt and a second polytetrafluoroethylene plate are stacked sequentially on the upper surface of the catalyst coating;

[0037] The first polytetrafluoroethylene plate, catalyst coating, nickel felt, and second polytetrafluoroethylene plate after being stacked are hot-pressed to obtain an oxygen evolution electrode.

[0038] In one or more embodiments, the polymerization liquid is a polytetrafluoroethylene emulsion, wherein the mass fraction of polytetrafluoroethylene (PTFE) in the polytetrafluoroethylene emulsion is 55-65%.

[0039] Preferably, the mass of polytetrafluoroethylene in the polymerization solution is 10% to 20% of the mass of the catalyst.

[0040] In one or more embodiments, the pretreatment method for nickel felt includes:

[0041] The nickel felt was soaked in sodium hydroxide solution, washed, then soaked in hydrochloric acid, washed with water, and dried.

[0042] Preferably, the mass fraction of the sodium hydroxide solution is 10-30%; the soaking time in the sodium hydroxide solution is 60-120 min.

[0043] Preferably, the hydrochloric acid concentration is 0.5~1.5 mol / L; and the immersion time in hydrochloric acid is 5~10 min.

[0044] In one or more embodiments, the porosity of the nickel felt is 60-80%.

[0045] In one or more embodiments, the hot pressing conditions are: pressure of 5~10 MPa, temperature of 80~150 ℃, and time of 300~600 s.

[0046] The beneficial effects of this invention are as follows:

[0047] (1) In this invention, the growth process of the catalyst crystal is controlled by low-temperature nucleation reaction, crystal aging growth, and formamide layered exfoliation to obtain a high-purity, highly crystallized, nanoscale sheet-like NiFe-LDH catalyst. Specifically, during the nucleation process, the reaction temperature, pH value, and stirring speed of the solution are controlled to enable NiFe-LDH to nucleate rapidly at low temperature, high concentration, and high speed, thereby inhibiting the growth rate of NiFe-LDH crystal nuclei. At the same time, limiting the temperature and time of crystal aging growth allows the crystal nuclei to grow slowly, ultimately obtaining a NiFe LDH catalyst with good crystallinity. Then, the layered NiFe-LDH is exfoliated with formamide to further separate the NiFe LDH plate structure and obtain a nanoscale sheet-like structure. The low-temperature nucleation reaction, crystal aging growth, and formamide layered exfoliation work together to obtain nanoscale sheet-like NiFe-LDH.

[0048] (2) The present invention coats an ultrathin nickel-iron layered bimetallic hydroxide onto a polytetrafluoroethylene plate, and then further forms an oxygen evolution electrode by hot pressing transfer method. The coating has good adhesion to the substrate and is not easy to fall off, making it suitable for large-scale industrial production. Attached Figure Description

[0049] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0050] Figure 1 This is an electron microscope image of the ultrathin nickel-iron layered bimetallic hydroxide obtained in Example 1;

[0051] Figure 2 The image shows the XRD pattern of the ultrathin nickel-iron layered bimetallic hydroxide powder obtained in Example 1.

[0052] Figure 3 Electron micrographs of nickel-iron layered bimetallic hydroxides obtained in Comparative Examples 1-5 are shown, where a, b, c, d and e correspond to Comparative Examples 1, 2, 3, 4 and 5, respectively.

[0053] Figure 4 This is a schematic diagram of the hot pressing process of the oxygen evolution electrode;

[0054] Figure 5 This is a photograph of the actual oxygen evolution electrode.

[0055] Figure 6 Linear sweep voltammetry (LSV) curves of oxygen evolution electrodes prepared from the ultrathin nickel-iron layered bimetallic hydroxide obtained in Example 1 and the nickel-iron layered bimetallic hydroxides obtained in Comparative Examples 1-5. Detailed Implementation

[0056] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0057] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0058] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0059] The polytetrafluoroethylene emulsion is Daikin Japan D-210C PTFE emulsion.

[0060] Example 1

[0061] Preparation of ultrathin nickel-iron layered bimetallic hydroxides:

[0062] (1) Dissolve 3.5653g of nickel chloride hexahydrate and 0.6757g of ferric chloride hexahydrate in 40 mL of water and mix well to obtain solution A; dissolve 1.696g of anhydrous sodium carbonate and 1.6g of sodium hydroxide in 40 mL of water and mix well to obtain solution B;

[0063] (2) Low-temperature nucleation of nickel-iron layered bimetallic hydroxide: 20 mL of ethanol was poured into 60 mL of water to form an ethanol-water solution; solutions A and B were simultaneously added dropwise to the ethanol-water solution at a rate of 0.5 mL / min, with a stirring rate of 1500 r / min during the addition process. After the addition was completed, the stirring was continued at the original speed for 3 h; the temperature of the reaction system was controlled at 5 °C during the addition of solutions A and B and during the subsequent stirring process; the pH of the reaction system was controlled at 10 during the addition of solutions A and B and during the subsequent stirring process.

[0064] (3) After stirring, the stirred reaction solution is transferred to the reaction vessel for aging growth at 60°C for 24 hours. After aging, the precipitate is collected and washed with water 3 to 5 times.

[0065] (4) Disperse the washed precipitate into 100 mL of formamide solution (50 mL of formamide and 50 mL of water), sonicate (450 W) for 30 min, collect the precipitate after the reaction, wash it with water and ethanol 3 to 5 times in sequence, and dry it in a vacuum environment (25 °C) overnight to obtain ultrathin nickel-iron layered bimetallic hydroxide.

[0066] Figure 1 The image shows an electron microscope image of the ultrathin nickel-iron layered bimetallic hydroxide obtained in Example 1. As can be seen from the image, the synthesized nickel-iron layered bimetallic hydroxide has a nanosheet structure with a thickness of about 10 nm.

[0067] Figure 2 The image shows the powder diffraction pattern of the ultrathin nickel-iron layered bimetallic hydroxide obtained in Example 1. As can be seen from the image, the synthesized catalyst has diffraction peaks at 11.3°, 23.01° and 34.33°, which is a typical NiFe LDH structure, indicating that the NiFe LDH catalyst was successfully synthesized.

[0068] Example 2

[0069] Compared with Example 1, the stirring rate during nucleation in step (2) was adjusted to 3000 r / min and the stirring time was 2 h; other conditions were exactly the same as in Example 1.

[0070] The ultrathin nickel-iron layered bimetallic hydroxide obtained in this embodiment has a nanosheet structure with a thickness of about 9 nm.

[0071] Example 3

[0072] Compared with Example 1, the nucleation temperature in step (2) was adjusted to 10 °C; other conditions were exactly the same as in Example 1.

[0073] The ultrathin nickel-iron layered bimetallic hydroxide obtained in this embodiment has a nanosheet structure with a thickness of about 12 nm.

[0074] Example 4

[0075] Compared with Example 1, the pH during nucleation in step (2) was adjusted to 11; other conditions were exactly the same as in Example 1.

[0076] The ultrathin nickel-iron layered bimetallic hydroxide obtained in this embodiment has a nanosheet structure with a thickness of about 8 nm.

[0077] Example 5

[0078] Compared with Example 1, the aging temperature in step (3) was adjusted to 90 °C, while other conditions were exactly the same as in Example 1.

[0079] The ultrathin nickel-iron layered bimetallic hydroxide obtained in this embodiment has a nanosheet structure with a thickness of about 11 nm.

[0080] Comparative Example 1

[0081] Compared to Example 1, the nucleation temperature was adjusted.

[0082] (1) Dissolve 3.5653g of nickel chloride hexahydrate and 0.6757g of ferric chloride hexahydrate in 40 mL of water and mix well to obtain solution A; dissolve 1.696g of anhydrous sodium carbonate and 1.6g of sodium hydroxide in 40 mL of water and mix well to obtain solution B;

[0083] (2) Pour 20 mL of ethanol into 60 mL of water to form an ethanol-water solution; add solution A and solution B dropwise into the ethanol-water solution at a rate of 0.5 mL / min, and stir at 1500 r / min during the dropwise addition. After the dropwise addition is completed, continue stirring at the original speed for 3 h; control the temperature of the reaction system to be 25 °C during the dropwise addition of solution A and solution B and during the subsequent stirring; control the pH of the reaction system to be 10 during the dropwise addition of solution A and solution B and during the subsequent stirring.

[0084] (3) After stirring, the stirred reaction solution is transferred to the reaction vessel for aging growth at 60°C for 24 hours. After aging, the precipitate is collected and washed with water 3 to 5 times.

[0085] (4) Disperse the washed precipitate into 100 mL of formamide solution (50 mL of formamide and 50 mL of water), sonicate (450 W) for 30 min, collect the precipitate after the reaction, wash it with water and ethanol 3 to 5 times in sequence, and dry it in a vacuum environment (25 °C) overnight to obtain nickel-iron layered bimetallic hydroxide.

[0086] Electron micrograph of nickel-iron layered bimetallic hydroxide as shown in the figure. Figure 3 As shown in Figure a, the results show that the nickel-iron layered bimetallic hydroxide obtained in this embodiment has a nanosheet structure with a size of about 50 nm.

[0087] Comparative Example 2

[0088] Compared to Example 1, the pH during nucleation was adjusted.

[0089] (1) Dissolve 3.5653g of nickel chloride hexahydrate and 0.6757g of ferric chloride hexahydrate in 40 mL of water and mix well to obtain solution A; dissolve 1.696g of anhydrous sodium carbonate and 1.6g of sodium hydroxide in 40 mL of water and mix well to obtain solution B;

[0090] (2) Pour 20 mL of ethanol into 60 mL of water to form an ethanol-water solution; add solution A and solution B dropwise into the ethanol-water solution at a rate of 0.5 mL / min, and stir at a rate of 1500 r / min during the dropwise addition. After the dropwise addition is completed, continue stirring at the original speed for 3 h; control the temperature of the reaction system to be 25 °C during the dropwise addition of solution A and solution B and during the subsequent stirring; control the pH of the reaction system to be 14 during the dropwise addition of solution A and solution B and during the subsequent stirring.

[0091] (3) After stirring, the stirred reaction solution is transferred to the reaction vessel for aging growth at 60°C for 24 hours. After aging, the precipitate is collected and washed with water 3 to 5 times.

[0092] (4) Disperse the washed precipitate into 100 mL of formamide solution (50 mL of formamide and 50 mL of water), sonicate (450 W) for 30 min, collect the precipitate after the reaction, wash it with water and ethanol 3 to 5 times in sequence, and dry it in a vacuum environment (25 °C) overnight to obtain nickel-iron layered bimetallic hydroxide.

[0093] Electron micrograph of nickel-iron layered bimetallic hydroxide as shown in the figure. Figure 3As shown in Figure b, the results show that the nickel-iron layered bimetallic hydroxide obtained in this embodiment has a nanosheet structure with a size of about 42 nm.

[0094] Comparative Example 3

[0095] Compared to Example 1, the rotational speed during nucleation was adjusted.

[0096] (1) Dissolve 3.5653g of nickel chloride hexahydrate and 0.6757g of ferric chloride hexahydrate in 40 mL of water and mix well to obtain solution A; dissolve 1.696g of anhydrous sodium carbonate and 1.6g of sodium hydroxide in 40 mL of water and mix well to obtain solution B;

[0097] (2) Pour 20 mL of ethanol into 60 mL of water to form an ethanol-water solution; add solution A and solution B dropwise into the ethanol-water solution at a rate of 0.5 mL / min, and stir at a rate of 500 r / min during the dropwise addition. After the dropwise addition is completed, continue stirring at the original rate for 3 h; control the temperature of the reaction system to be 5 °C during the dropwise addition of solution A and solution B and during the subsequent stirring; control the pH of the reaction system to be 10 during the dropwise addition of solution A and solution B and during the subsequent stirring.

[0098] (3) After stirring, the stirred reaction solution is transferred to the reaction vessel for aging growth at 60°C for 24 hours. After aging, the precipitate is collected and washed with water 3 to 5 times.

[0099] (4) Disperse the washed precipitate into 100 mL of formamide solution (50 mL of formamide and 50 mL of water), sonicate (450 W) for 30 min, collect the precipitate after the reaction, wash it with water and ethanol 3 to 5 times in sequence, and dry it in a vacuum environment (25 °C) overnight to obtain nickel-iron layered bimetallic hydroxide.

[0100] Electron micrograph of nickel-iron layered bimetallic hydroxide as shown in the figure. Figure 3 As shown in Figure c, the results show that the nickel-iron layered bimetallic hydroxide obtained in this embodiment has a nanosheet structure with a size of about 38 nm.

[0101] Comparative Example 4

[0102] Compared to Example 1, the aging temperature was adjusted.

[0103] (1) Dissolve 3.5653g of nickel chloride hexahydrate and 0.6757g of ferric chloride hexahydrate in 40 mL of water and mix well to obtain solution A; dissolve 1.696g of anhydrous sodium carbonate and 1.6g of sodium hydroxide in 40 mL of water and mix well to obtain solution B;

[0104] (2) Pour 20 mL of ethanol into 60 mL of water to form an ethanol-water solution; add solution A and solution B dropwise into the ethanol-water solution at a rate of 0.5 mL / min, and stir at a rate of 1500 r / min during the dropwise addition. After the dropwise addition is completed, continue stirring at the original rate for 3 h; control the temperature of the reaction system to be 5 °C during the dropwise addition of solution A and solution B and during the subsequent stirring; control the pH of the reaction system to be 10 during the dropwise addition of solution A and solution B and during the subsequent stirring.

[0105] (3) After stirring, the stirred reaction solution is transferred to the reaction vessel for aging growth at 110°C for 24 hours. After aging, the precipitate is collected and washed with water 3 to 5 times.

[0106] (4) Disperse the washed precipitate into 100 mL of formamide solution (50 mL of formamide and 50 mL of water), sonicate (450 W) for 30 min, collect the precipitate after the reaction, wash it with water and ethanol 3 to 5 times in sequence, and dry it in a vacuum environment (25 °C) overnight to obtain nickel-iron layered bimetallic hydroxide.

[0107] Electron micrograph of nickel-iron layered bimetallic hydroxide as shown in the figure. Figure 3 As shown in Figure d, the results show that the nickel-iron layered bimetallic hydroxide obtained in this embodiment has a nanosheet structure with a size of about 35 nm.

[0108] Comparative Example 5

[0109] Compared to Example 1, no formamide lamellar peeling was performed.

[0110] (1) Dissolve 3.5653g of nickel chloride hexahydrate and 0.6757g of ferric chloride hexahydrate in 40 mL of water and mix well to obtain solution A; dissolve 1.696g of anhydrous sodium carbonate and 1.6g of sodium hydroxide in 40 mL of water and mix well to obtain solution B;

[0111] (2) Pour 20 mL of ethanol into 60 mL of water to form an ethanol-water solution; add solution A and solution B dropwise into the ethanol-water solution at a rate of 0.5 mL / min, and stir at a rate of 1500 r / min during the dropwise addition. After the dropwise addition is completed, continue stirring at the original rate for 3 h; control the temperature of the reaction system to be 5 °C during the dropwise addition of solution A and solution B and during the subsequent stirring; control the pH of the reaction system to be 10 during the dropwise addition of solution A and solution B and during the subsequent stirring.

[0112] (3) After stirring, the stirred reaction solution is transferred to the reactor for aging growth at 60°C for 24 hours. After aging, the precipitate is collected and washed with water and ethanol 3-5 times in sequence. It is then dried in a vacuum environment (25°C) overnight to obtain nickel-iron layered bimetallic hydroxide.

[0113] Electron micrograph of nickel-iron layered bimetallic hydroxide as shown in the figure. Figure 3 As shown in Figure e, the results show that the nickel-iron layered bimetallic hydroxide obtained in this embodiment has a nanosheet structure with a size of about 30 nm.

[0114] Example 6

[0115] The nickel-iron layered bimetallic hydroxides prepared in Example 1 and Comparative Examples 1-5 were respectively prepared according to... Figure 4 The schematic diagram of the hot-pressing process shown is used to fabricate an oxygen evolution electrode for AEM. Fabrication of the oxygen evolution electrode:

[0116] 0.3 g of catalyst was mixed with 8 mL of ethanol, 2 mL of water and 0.6 mL of polymerization solution in a cold bath for 60 min at a temperature of 5 °C. After thorough mixing, a catalyst slurry was obtained.

[0117] The catalyst slurry was uniformly sprayed onto the upper surface of the first polytetrafluoroethylene plate using a spraying machine (spraying speed 0.5 mL / min) to form a catalyst coating, wherein the area of ​​the catalyst coating was 50 cm². 2 The thickness is 0.1 mm, and then it is air-dried;

[0118] Nickel felt with a diameter of 9.5 cm and a porosity of 70% was immersed in a 20% NaOH solution for 60 min to remove oil. After washing with water, it was immersed in 1 mol / L dilute hydrochloric acid for 10 min to remove the oxide layer on the surface of the nickel felt. After washing with water, it was dried for later use.

[0119] Pretreated nickel felt and a second polytetrafluoroethylene plate are stacked sequentially on the upper surface of the catalyst coating;

[0120] The stacked first polytetrafluoroethylene plate, catalyst coating, nickel felt, and second polytetrafluoroethylene plate are fastened together and then placed in a hot press for hot pressing treatment. The hot pressing pressure is 6 MPa, the hot pressing temperature is 100 ℃, and the hot pressing time is 300 s. Afterward, the first polytetrafluoroethylene plate and the second polytetrafluoroethylene plate are removed to obtain the oxygen evolution electrode.

[0121] Comparative Example 6

[0122] 0.3 g of the ultrathin nickel-iron layered bimetallic hydroxide prepared in Example 1 was mixed with 14 mL of isopropanol, 6 mL of water and 0.06 mL of polymerization liquid in a cold bath for 60 min at a cold bath temperature of 5 °C. After mixing evenly, a catalyst slurry was obtained.

[0123] The catalyst slurry was evenly sprayed onto the pretreated nickel felt using a sprayer (spraying speed 0.5 mL / min), without hot pressing, to obtain... Figure 5 The oxygen evolution electrode is shown.

[0124] Example 7

[0125] The electrode prepared in Example 6 was cut into pieces measuring 1 cm × 1.5 cm (actual reaction area 1 cm × 1 cm). Linear sweep voltammetry (LSV) curves of the oxygen evolution electrodes prepared with the catalysts in Examples 1 and 1-5 were tested on an electrochemical workbench (Shanghai Chenhua CHI760E). The test conditions were as follows:

[0126] The three-electrode system uses a platinum electrode as the auxiliary electrode, an Hg / HgO electrode as the reference electrode (with a 1 mol / L KOH solution as the reference solution), and a 1 mol / L KOH solution as the electrolyte. Figure 6 It can be seen that the polarization potential of Example 1 is the lowest under the same current density, indicating that the catalyst synthesized in Example 1 has high active sites in the ultrathin nanosheets and good electrocatalytic performance.

[0127] Example 8

[0128] The oxygen evolution electrodes prepared in Example 6 and Comparative Example 6 were subjected to long-term stability tests. The test conditions were: room temperature and pressure, electrolyte was 5% KOH solution, and current density was 1 A / cm². 2 The runtime was 1500 hours. The results are shown in Table 1.

[0129] Table 1 Stability Test Results

[0130]

[0131] The results showed that, using the ultrathin nickel-iron layered bimetallic hydroxide prepared in Example 1 as the catalyst, the oxygen evolution electrode formed by hot pressing had a tank pressure of approximately 1.9V after 1500 hours of operation, and no precipitation was found in the alkali tank. However, using the nickel-iron layered bimetallic hydroxide prepared in Comparative Examples 1-5 as the catalyst, the oxygen evolution electrodes formed by hot pressing and the oxygen evolution electrode not formed by hot pressing in Comparative Example 6 all showed varying degrees of tank pressure increase after 1500 hours of operation, and precipitation was found in the alkali tank in both cases. This indicates that large catalyst particles can easily detach. Furthermore, Comparative Example 6 showed the largest amount of precipitation and the largest increase in tank pressure, indicating that the direct spraying process resulted in poor adhesion between the catalyst and the substrate surface, leading to easy catalyst detachment and unstable performance. The oxygen evolution electrode formed by hot pressing transfer printing showed good adhesion between the coating and the substrate, was less prone to detachment, and was suitable for large-scale industrial production.

[0132] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing an ultrathin nickel-iron layered double hydroxide, characterized by, The ultrathin nickel-iron layered double hydroxide is in a nanosheet structure, and the thickness of the nanosheet is 8-12 nm, and the preparation method comprises the following steps: (1) dissolving nickel salt and trivalent iron salt in water, mixing uniformly to obtain A liquid; dissolving sodium carbonate and sodium hydroxide in water, mixing uniformly to obtain B liquid; (2) adding A liquid and B liquid into an aqueous ethanol solution at the same time, continuously stirring; controlling the temperature of the reaction system during the adding process of A liquid and B liquid and the stirring process to be 5-10 ℃; the stirring speed is 1000-3000 r / min, and the stirring time is 2-6 h; controlling the pH of the reaction system during the adding process of A liquid and B liquid and the stirring process to be 10-11; (3) aging the stirred reaction liquid at a limited temperature, collecting the precipitate and washing; the aging temperature is 60-90 ℃; (4) dispersing the washed precipitate into a formamide solution, ultrasonic reaction, collecting the precipitate after reaction, and washing and drying to obtain the ultrathin nickel-iron layered double hydroxide; the volume fraction of formamide is 25-55%; during the ultrasonic reaction, the ultrasonic power is 400-500 W, and the ultrasonic reaction time is 15-45 min.

2. The production method according to claim 1, wherein In step (1), the nickel salt is one or more of nickel chloride, nickel nitrate, nickel sulfate and nickel acetate; In step (1), the trivalent iron salt is one or more of ferric chloride, ferric nitrate and ferric sulfate; In step (1), the molar ratio of nickel salt to trivalent iron salt is (1-6):(0.2-1.5).

3. The production method according to claim 1, wherein In step (1), the concentration of nickel salt is 0.3-0.5 mM; In step (1), the molar ratio of sodium carbonate to sodium hydroxide is (0.2-0.6):1; In step (1), the concentration of sodium carbonate is 0.3-0.5 mM.

4. The production method according to claim 1, wherein In step (2), the volume ratio of A liquid to B liquid is (0.8-1.2):1; In step (2), the volume fraction of ethanol in the aqueous ethanol solution is 5-30%; In step (2), the volume ratio of A liquid to the aqueous ethanol solution is (0.4-0.6):

1.

5. The production method according to claim 1, wherein In step (3), the aging time is 12-24 h.

6. The ultrathin nickel-iron layered double hydroxide prepared by the preparation method of any one of claims 1-5 is applied in catalytic electrolytic water hydrogen production.

7. An oxygen evolving electrode characterized by, It takes nickel felt as a substrate, and is coated with a catalyst coating layer; The catalyst in the catalyst coating layer comprises the ultrathin nickel-iron layered double hydroxide prepared by the preparation method of any one of claims 1-5.

8. The method of making an oxygen evolving electrode of claim 7, wherein, Comprise the following steps: mixing the ultrathin nickel-iron layered double hydroxide prepared by the preparation method of any one of claims 1-5 with ethanol, water and a polymerization solution uniformly to obtain a catalyst slurry; spraying the catalyst slurry on the upper surface of the first polytetrafluoroethylene plate to form a catalyst coating layer; sequentially stacking the pretreated nickel felt and the second polytetrafluoroethylene plate on the upper surface of the catalyst coating layer; hot-pressing the stacked first polytetrafluoroethylene plate, catalyst coating layer, nickel felt and second polytetrafluoroethylene plate to obtain an oxygen evolution electrode.

9. The method of making an oxygen evolving electrode of claim 8, wherein The hot-pressing condition is: pressure 5-10 MPa, temperature 80-150 ℃, time 300-600 s.

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