A Cu2O@NiFe-LDH heterostructure electrocatalyst and its integrated catalytic anion exchange membrane electrode, its preparation method and application

Abstract

The application discloses a Cu2O@NiFe-LDH heterostructure electrocatalyst and an integrated catalytic anion exchange membrane electrode, and a preparation method and application thereof. The preparation of the electrocatalyst comprises the following steps: taking NaOH and CuCl2*H2O as raw materials, adding a formaldehyde solution, and synthesizing Cu2O nanoparticles through a self-heat reaction; taking Ni(NO3)2*6H2O and Fe(NO3)3*6H2O as raw materials, and preparing NiFe-LDH nanosheets through a hydrothermal reaction; then adding Cu2O into a reaction system to in-situ grow Cu2O@NiFe-LDH composite materials. The obtained composite materials are loaded on a W-25T anion exchange membrane through an ultrasonic spraying method to obtain an integrated catalytic membrane electrode. The membrane electrode can be used as an anode and a cathode to assemble a symmetrical electrode for hydrogen production by alkaline electrolysis of water. The application has the advantages of strong p-n heterojunction interface effect, fast charge transfer and good stability.

Description

Technical Field

[0001] This invention relates to the field of electrocatalytic materials and alkaline water electrolysis for hydrogen production, specifically to a Cu2O@NiFe-LDH heterostructure electrocatalyst, an integrated catalytic anion exchange membrane electrode, an alkaline water electrolyzer containing the membrane electrode, and their preparation methods and applications. Background Technology

[0002] Integrated membrane electrodes based on Cu2O@NiFe-LDH catalysts offer a novel approach to efficient hydrogen production in non-noble metal systems due to their pn heterojunction interface effect, abundant bimetallic redox active sites, and excellent bifunctional catalytic activity for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). However, traditional powdered catalysts are often loaded onto conductive substrates using manual or mechanical coating methods, leading to increased interfacial resistance, buried active sites, severe bubble retention, and easy peeling and failure of the catalyst layer, which seriously restricts the energy conversion efficiency and long-term operational stability at high current densities. Furthermore, Cu2O exhibits thermodynamic instability at the OER operating potential (>1.2 V vs. RHE), while the intrinsic conductivity of NiFe-LDH layered materials is extremely poor (approximately 10 V). -6 The reduced efficiency (S / cm) further exacerbates charge transfer obstruction and catalytic activity decay. To address these issues, existing strategies involve constructing pn heterojunctions using Cu2O and NiFe-LDH composites to achieve synergistic enhancement and interfacial structural stability, thereby improving the activity and stability of the catalytic material. Simultaneously, integrated membrane electrodes are fabricated by directly integrating the catalyst onto the conductive membrane surface to meet the comprehensive requirements of high-efficiency electrolyzers for high catalytic activity, rapid charge transport, and long-term stability.

[0003] Cu2O@NiFe-LDH heterostructures, with their pn junction interface effect and bimetallic synergistic catalytic activity, have become important non-precious metal catalyst materials in the field of alkaline water electrolysis. However, limitations in traditional electrode fabrication processes lead to increased interfacial resistance, active site shielding, bubble retention, and catalyst layer peeling, severely restricting energy efficiency and operational stability at high current densities. Existing improvement strategies for the aforementioned materials and composite systems mainly focus on nanostructure control, multi-metal doping, interfacial heterostructure construction, and conductive framework compositing to enhance intrinsic activity, conductivity, and local stability. However, these approaches are largely limited to performance optimization at the powder catalyst level, and still face many bottlenecks in the transition to integrated membrane electrode assemblies with long lifespans and high current operating conditions.

[0004] A search revealed that patent CN 112391649 A discloses a method for preparing a Cu2O / NiFe-LDH core-shell composite material. This method enhances oxygen evolution catalytic activity by constructing a heterogeneous interface through layer-by-layer self-assembly. However, when fabricating the electrode from powder, it still relies on binder coating, failing to solve the problems of interfacial resistance and bubble desorption. Patent CN 110282666 A reports a cuprous oxide / nickel-iron hydrotalcite heterojunction electrocatalyst, using a hydrothermal in-situ growth method to improve the contact between components. However, the powder morphology limits the feasibility of uniform and robust formation on large-area electrodes. Patent CN 119753744 A proposes a self-supporting NiFe-LDH nanosheet array electrode, directly grown on nickel foam using a hydrothermal method, avoiding the use of binders and reducing interfacial resistance. However, the LDH array alone is prone to structural collapse and dissolution of active species at high potentials, and it does not incorporate Cu2O for synergistic enhancement. Patent CN 110433810 A discloses a method for preparing CuO-doped ultrathin nickel-iron-based hydrotalcite nanosheets / graphene bifunctional water splitting catalyst. CuO is embedded into the LDH interlayer by electrodeposition to improve conductivity. However, this method has strict requirements for substrate pretreatment, a narrow process window, and is difficult to control the uniformity and repeatability of large-area film formation.

[0005] Despite the progress made in improving conductivity and stability, several challenges remain when applying these technologies to industrial water electrolysis membrane electrodes. First, insufficient material-functional coupling and fragmented efficiency enhancement mechanisms exist. Existing technologies often treat improving conductivity, increasing active sites, and enhancing stability as isolated objectives. For example, simply introducing carbon materials to improve conductivity sacrifices the loading of active components; simply controlling morphology fails to address intrinsic corrosion at high potentials, and fails to achieve a unified optimization of the electronic structure and long-range stability of Cu2O and NiFe-LDH at the pn heterojunction interface. Second, there is a disconnect between electrode integration processes and material performance compatibility. Most patented technologies remain focused on the synthesis of milligram-scale powder catalysts and half-cell performance evaluation in three-electrode systems. When these fine nanostructures are fabricated into practical electrodes through binder coating or simple pressing, performance is significantly reduced due to binder encapsulation and pore blockage, resulting in a significant gap between high material-level performance and high device-level efficiency. Finally, balancing scalable and controllable fabrication with cost-effectiveness is difficult. While existing methods (such as hydrothermal / solvothermal methods and electrodeposition methods) can construct specific nanoarray structures, they usually rely on high temperature and pressure, conductive rigid substrates (such as foam metals), and long-term fine control. They face severe challenges in the continuous, low-cost, and highly uniform fabrication of large-area flexible membrane electrodes and are difficult to directly meet the roll-to-roll large-scale assembly requirements of membrane electrode assemblies (MEAs) in industrial electrolytic cells.

[0006] In summary, current patent strategies primarily focus on modifying the active sites or controlling the morphology of the powder catalyst itself, with insufficient attention paid to the multi-dimensional synergistic optimization of electron transport efficiency, porous mass transfer channels, and long-term mechanical / chemical stability in the integrated electrode configuration. To overcome these technical bottlenecks, it is necessary to construct a composite catalyst with both high efficiency and a pn heterojunction interface at the system level, from powder materials to integrated electrode engineering; simultaneously, an integrated and stable membrane electrode structure should be prepared through ultrasonic spraying. Summary of the Invention

[0007] The present invention aims to provide a Cu2O@NiFe-LDH heterostructure electrocatalyst and an integrated catalytic anion exchange membrane electrode, as well as their preparation method and application, to overcome the problems of high interfacial resistance, easy shielding of active sites, easy peeling of catalyst layer and poor stability under high current density in the prior art.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] The first aspect is the preparation method of Cu2O@NiFe-LDH heterostructure electrocatalyst.

[0010] This invention provides a method for preparing a Cu2O@NiFe-LDH heterostructure electrocatalyst, comprising the following steps:

[0011] Step S1: To prepare cubic Cu2O nanoparticles, NaOH and CuCl2·H2O were mixed to form a uniform powder material. Then, 37% formaldehyde solution was slowly added for 10 min. The temperature was rapidly raised to 100℃ using the self-exothermic reaction, and the reaction mixture turned yellowish-brown and showed a metallic luster. After naturally cooling to room temperature, water was added, the solid dissolved, and the reaction mixture turned reddish-brown. The product was collected by centrifugation, washed successively with acetone and deionized water, and dried in a vacuum oven at 60℃ to obtain cubic Cu2O nanoparticles.

[0012] Step S2: Prepare sheet-like NiFe-LDH. Dissolve Ni(NO3)2·6H2O and Fe(NO3)3·6H2O in deionized water and stir for 30 min to form solution A. Dissolve NH4F and urea in another portion of deionized water to obtain solution B. Pour solution B into solution A and stir at room temperature for 30 min. Transfer to a Teflon-lined reactor and heat at 120℃ for 12 h. After natural cooling, collect the yellow product by vacuum filtration, wash with ethanol, and dry under vacuum at room temperature to obtain sheet-like NiFe-LDH.

[0013] Step S3: Prepare sheet-like Cu2O@NiFe-LDH composite material. Under continuous stirring, the cubic Cu2O nanoparticles obtained in step S1 are rapidly added to solution A described in step S2 to form a homogeneous mixture. Then, the mixture is mixed with solution B and magnetically stirred for 15 min. The mixture is reacted at 120°C for 12 h. The precipitate is collected by filtration, washed with ethanol, and dried in a vacuum drying oven for 12 h to obtain the sheet-like Cu2O@NiFe-LDH composite material.

[0014] In addition to solvothermal reactions, Cu2O nanoparticles can also be synthesized using hydrothermal methods, electrodeposition methods (potential control), hydrothermal reduction methods, thermal decomposition methods (heating to decompose precursors such as copper acetate), or spray pyrolysis methods.

[0015] Besides hydrothermal methods, NiFe-LDH can also be synthesized using co-precipitation, electrodeposition (direct growth on a conductive substrate), anion exchange, sol-gel, microwave-assisted synthesis, or exfoliation. Cu2O@NiFe-LDH composites can be constructed using physical mixing (mechanical mixing or ultrasonic dispersion), electrodeposition / co-deposition (one-step co-deposition onto a substrate), layer-by-layer self-assembly (alternating adsorption of charged nanosheets), chemical vapor deposition, or post-synthetic modification methods, in addition to in-situ hydrothermal composite methods.

[0016] Secondly, a Cu2O@NiFe-LDH heterostructure electrocatalyst is prepared by the same method used for preparing Cu2O@NiFe-LDH heterostructure electrocatalysts.

[0017] Thirdly, a method for preparing an integrated catalytic anion exchange membrane electrode, based on the aforementioned Cu2O@NiFe-LDH heterostructure electrocatalyst, includes the following steps:

[0018] Commercially available diaphragm W-25T was used as the substrate material, with a thickness of 25 μm.

[0019] 5.0 mg of the Cu2O@NiFe-LDH composite material was dissolved in a 20 mL mixed solution consisting of 0.8 mL Nafion (5 wt%), 8 mL ethanol and 11.2 mL deionized water, and the solution was mechanically and ultrasonically stirred for 30 min to obtain a catalyst slurry.

[0020] The catalyst slurry was transferred to a spraying injector and uniformly loaded onto the surface of the W-25T membrane using ultrasonic spraying. The process parameters were: ultrasonic frequency 100 kHz, spraying flow rate 0.5 mL / min, and spraying speed 10 mm / s.

[0021] The distance between the nozzle and the base film is 50 mm, the temperature of the spraying platform is 60℃, and after drying, Cu2O@NiFe-LDH / W-25T composite anion membrane electrode is obtained.

[0022] For the fabrication process of membrane electrodes, a thin layer can also be prepared by using small droplets at a high frequency (60-120 kHz); a reasonable spraying distance of 30-60 mm and a speed of 5-20 mm / s can be used to ensure uniform droplet placement; and a reasonable substrate temperature (40-60℃) can be used to make the coating dry quickly and prevent swelling and flow.

[0023] Fourthly, an integrated catalytic anion exchange membrane electrode is prepared by the above-mentioned method for preparing an integrated catalytic anion exchange membrane electrode.

[0024] Fifthly, an alkaline water electrolyzer includes the integrated catalytic anion exchange membrane electrode, wherein the membrane electrode serves as both an anode and a cathode, and is assembled into a symmetrical electrode.

[0025] The sixth aspect concerns the application of the integrated catalytic anion exchange membrane electrode in alkaline water electrolysis for hydrogen production.

[0026] The beneficial effects of this invention are:

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] (1) Excellent catalytic activity and charge transfer capability: In this invention, Cu2O is synthesized through a solvothermal reaction and combined with NiFe-LDH nanosheets to construct a tight Cu2O@NiFe-LDH heterostructure. The interface effect enhances the charge transfer capability and simultaneously improves the bifunctional catalytic activity of the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The resulting integrated membrane electrode enhances catalytic activity and conductivity through the pn heterojunction.

[0029] (2) High interface stability and low resistance: In-situ hydrothermal growth technology is adopted to enable NiFe-LDH to grow directly on the Cu2O surface, forming a strong chemical bond interface, avoiding the problems of easy detachment and high interface resistance in traditional physical mixing methods. Combined with the integrated film electrode configuration, the resistance is effectively reduced and the core-shell structure improves stability.

[0030] (3) Mild process conditions, simple operation, and green environmental protection: Cu2O is synthesized instantaneously by self-exothermic reaction at room temperature and pressure. The hydrothermal temperature of NiFe-LDH and composite materials is only 120℃, and no high-temperature calcination is required throughout the process. No harmful substances are generated during the synthesis process, and the use of highly toxic organic solvents and strong acids is avoided throughout the process, which is in line with the concepts of green chemistry and sustainable development.

[0031] (4) Excellent practical performance: The Cu2O@NiFe-LDH / W-25T integrated catalytic membrane electrode prepared exhibits high catalytic activity, fast charge transport capability and long-term operational stability in alkaline water electrolysis devices. It is especially suitable for high current density conditions and has low synthesis cost. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of this application, 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 some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 SEM image of Cu2O nanoparticles synthesized in Example 1.

[0034] Figure 2 SEM image of NiFe-LDH nanosheets synthesized in Example 2.

[0035] Figure 3 SEM image of the Cu2O@NiFe-LDH composite material synthesized in Example 3.

[0036] Figure 4 In Example 4, (a) a commercial W-25T anion exchange membrane substrate; and (b) a composite membrane electrode Cu2O@NiFe-LDH / W-25T with catalyst material sprayed on both sides.

[0037] Figure 5 Example 4: A schematic diagram of the structure assembled into an electrolytic water tank.

[0038] Figure 6 In Example 5, the electrochemical water splitting performance was tested. (a) LSV curves of hydrogen evolution performance of W-25T and Cu2O@NiFe-LDH / W-25T composite membrane electrodes, and (b) long-term current-time curves of Cu2O@NiFe-LDH / W-25T at different reaction temperatures. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention.

[0040] Example 1: Synthesis of cubic Cu₂O nanoparticles

[0041] Sodium hydroxide (0.5 mmol) and copper chloride (1.5 mmol) were weighed and mixed, then 5 mL of formaldehyde solution (37%) was added. The reaction released a large amount of heat instantaneously, and the mixture turned a metallic yellowish-brown. Deionized water was then added to the system; the solid dissolved rapidly, and the solution turned reddish-brown. The product was collected by centrifugation, washed successively with acetone and deionized water, and dried in a vacuum oven at 60 °C to obtain cubic Cu₂O nanoparticles. Their SEM morphology is shown below. Figure 1 As shown.

[0042] Example 2: Preparation of NiFe-LDH Nanosheets

[0043] Nickel nitrate hexahydrate (1.5 mmol) and ferric nitrate nonahydrate (0.5 mmol) were weighed and dissolved in 40 mL of deionized water, and stirred continuously for 30 min to form a homogeneous solution A. NH4F (4.0 mmol) and urea (10.0 mmol) were slowly dissolved in another 40 mL of deionized water to obtain solution B. Solution B was poured into solution A and stirred at room temperature for 30 min. The resulting mixture was transferred to a 100 mL Teflon-lined reactor and heated at 120 °C for 12 h. After naturally cooling to room temperature, the yellow product was collected by vacuum filtration, washed repeatedly with ethanol, and dried under vacuum at room temperature to obtain NiFe-LDH nanosheets. Its SEM morphology is shown below. Figure 2 As shown.

[0044] Example 3: Preparation of Cu2O@NiFe-LDH composite material

[0045] Under continuous stirring, 20 mg of Cu2O nanoparticles prepared in Example 1 were rapidly added to solution A described in Example 2 to form a homogeneous mixture. This mixture was then mixed with solution B and magnetically stirred for 15 min. The resulting mixture was reacted at 120 °C for 12 h. The precipitate was collected by filtration, washed repeatedly with ethanol, and dried in a vacuum drying oven for 12 h to obtain the Cu2O@NiFe-LDH composite material. Its SEM morphology is shown below. Figure 3 As shown, a clear core-shell structure is visible.

[0046] Example 4: Preparation of Cu2O@NiFe-LDH / W-25T composite anion exchange membrane electrode and assembly of water electrolysis tank

[0047] Commercially available anion exchange membranes were cut to 2×2 cm pieces. 2Specifications (W-25T, thickness 25 μm, EVE Energy Co., Ltd.). 5.0 mg of Cu2O@NiFe-LDH composite material prepared in Example 3 was weighed and dissolved in a 20 mL mixed solution consisting of 0.8 mL Nafion (5wt%), 8 mL ethanol, and 11.2 mL deionized water. The solution was mechanically ultrasonically stirred for 30 min to obtain a catalyst slurry. The catalyst slurry was transferred to a spraying syringe and uniformly loaded onto the surface of the W-25T membrane using ultrasonic spraying. The process parameters were: ultrasonic frequency 100 kHz, spraying flow rate 0.5 mL / min, spraying speed 10 mm / s, nozzle-to-base membrane distance 50 mm, and spraying platform temperature 60℃. After drying, the Cu2O@NiFe-LDH / W-25T composite anion exchange membrane electrode was obtained. Its morphology is as follows. Figure 4 As shown, (a) is a commercial W-25T anion exchange membrane substrate, and (b) is a composite membrane electrode after catalyst is sprayed on both sides.

[0048] The alkaline water electrolyzer is self-made with a metal frame, and the effective reaction area of ​​the electrodes is 2 × 2 cm. 2 A water splitting device was assembled using a Cu2O@NiFe-LDH / W-25T composite membrane as a multifunctional membrane electrode. A nickel mesh was used as the current collector. The electrocatalytic activity and stability of the overall water splitting were tested in a 6.0 M KOH electrolyte. A schematic diagram of the assembled water electrolysis tank is shown below. Figure 5 As shown.

[0049] Example 5: Performance Testing of Alkaline Water Electrolysis Device

[0050] The Cu2O@NiFe-LDH / W-25T composite membrane prepared in Example 4 was used as a multifunctional membrane electrode, serving as both the anode and cathode, to assemble a symmetrical electrode alkaline water electrolysis device for water electrolysis performance testing. The overall water splitting LSV curve of the device was tested, and long-term current-time curves at different reaction temperatures were recorded.

[0051] Test results are as follows Figure 6 As shown: Figure 6 (a) The LSV curves of hydrogen evolution performance of W-25T and Cu2O@NiFe-LDH / W-25T composite membrane electrodes show that the composite membrane electrode has significantly improved catalytic activity. Figure 6 (b) shows the long-term current-time curves of Cu2O@NiFe-LDH / W-25T at different reaction temperatures, confirming that it has good long-term operational stability under different temperature conditions.

[0052] This invention provides a Cu2O@NiFe-LDH heterostructure electrocatalyst and an integrated catalytic anion exchange membrane electrode, along with their preparation method and applications. The preparation process is mild, low-cost, and environmentally friendly. The prepared membrane electrode exhibits excellent catalytic activity and stability in alkaline water electrolysis for hydrogen production. This technology can meet the demand for efficient, long-life, and low-cost non-precious metal electrode materials for large-scale renewable energy hydrogen production, and has clear industrial application prospects, especially suitable for the large-scale preparation of membrane electrode assemblies for alkaline water electrolyzers.

[0053] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A method for preparing a Cu2O@NiFe-LDH heterostructure electrocatalyst, characterized in that, Includes the following steps: Step S1: To prepare cubic Cu2O nanoparticles, NaOH and CuCl2·H2O were mixed to form a uniform powder material. Then, 37% formaldehyde solution was slowly added for 10 min. The temperature was rapidly raised to 100℃ using the self-exothermic reaction, and the reaction mixture turned yellowish-brown and showed a metallic luster. After naturally cooling to room temperature, water was added, the solid dissolved, and the reaction mixture turned reddish-brown. The product was collected by centrifugation, washed successively with acetone and deionized water, and dried in a vacuum oven at 60℃ to obtain cubic Cu2O nanoparticles. Step S2: Prepare sheet-like NiFe-LDH. Dissolve Ni(NO3)2·6H2O and Fe(NO3)3·6H2O in deionized water and stir for 30 min to form solution A. Dissolve NH4F and urea in another portion of deionized water to obtain solution B. Pour solution B into solution A and stir at room temperature for 30 min. Transfer to a Teflon-lined reactor and heat at 120℃ for 12 h. After natural cooling, collect the yellow product by vacuum filtration, wash with ethanol, and dry under vacuum at room temperature to obtain sheet-like NiFe-LDH. Step S3: Prepare sheet-like Cu2O@NiFe-LDH composite material. Under continuous stirring, the cubic Cu2O nanoparticles obtained in step S1 are rapidly added to solution A described in step S2 to form a homogeneous mixture. Then, the mixture is mixed with solution B and magnetically stirred for 15 min. The mixture is reacted at 120°C for 12 h. The precipitate is collected by filtration, washed with ethanol, and dried in a vacuum drying oven for 12 h to obtain the sheet-like Cu2O@NiFe-LDH composite material.

2. A Cu2O@NiFe-LDH heterostructure electrocatalyst, characterized in that, It is prepared by the method described in claim 1.

3. A method for preparing an integrated catalytic anion exchange membrane electrode, characterized in that, The Cu2O@NiFe-LDH heterostructure electrocatalyst based on claim 2 includes the following steps: Commercially available diaphragm W-25T was used as the substrate material, with a thickness of 25 μm. 5.0 mg of the Cu2O@NiFe-LDH composite material was dissolved in a 20 mL mixed solution consisting of 0.8 mL Nafion (5 wt%), 8 mL ethanol and 11.2 mL deionized water, and the solution was mechanically and ultrasonically stirred for 30 min to obtain a catalyst slurry. The catalyst slurry was transferred to a spraying injector and uniformly loaded onto the surface of the W-25T membrane using ultrasonic spraying. The process parameters were: ultrasonic frequency 100 kHz, spraying flow rate 0.5 mL / min, and spraying speed 10 mm / s. The distance between the nozzle and the base film is 50 mm, the temperature of the spraying platform is 60℃, and after drying, Cu2O@NiFe-LDH / W-25T composite anion membrane electrode is obtained.

4. An integrated catalytic anion exchange membrane electrode, characterized in that, It is prepared by the method described in claim 3.

5. An alkaline water electrolysis cell, characterized in that, The integrated catalytic anion exchange membrane electrode as described in claim 4 is assembled into a symmetrical electrode, wherein the membrane electrode serves as both an anode and a cathode.

6. The application of the integrated catalytic anion exchange membrane electrode according to claim 5 in alkaline water electrolysis for hydrogen production.

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