A bimetallic LDH catalyst, its preparation method and application

Abstract

This invention discloses a bimetallic LDH catalyst, its preparation method, and its application, belonging to the field of catalysts. The preparation method includes the following steps: mixing a bimetallic salt, urea, NH4F, and a reaction solvent to prepare a precursor solution; completely immersing pretreated nickel foam into the precursor solution, then placing it in a microwave reaction vessel and reacting at 100°C for 20 minutes; finally, washing and drying to obtain the final product. This invention provides a "one-step microwave-driven, multi-metallic, Cl-resistant..." ‑ The bimetallic LDH catalyst and its preparation method, which are "corrosion resistant and adaptable to high current density", have solved the technical bottleneck of direct seawater electrolysis for hydrogen production.

Description

Technical Field

[0001] This invention belongs to the field of catalysts, specifically relating to a bimetallic LDH catalyst, its preparation method, 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] Currently, hydrogen production through water electrolysis mainly relies on freshwater as a raw material. However, freshwater accounts for only about 2.5% of the world's total water resources, and its distribution is uneven. Coastal areas, islands, and offshore energy platforms are severely lacking in freshwater, which greatly limits the large-scale promotion of green hydrogen. Therefore, directly utilizing seawater, which accounts for about 97.5% of the world's water resources, for hydrogen production through electrolysis has become an important direction for breaking through the raw material bottleneck and promoting the implementation of the green hydrogen industry.

[0004] However, the production of hydrogen through seawater electrolysis faces two key challenges: firstly, seawater contains a high concentration of chloride ions (Cl-). - This can lead to catalyst corrosion, metal ion dissolution, competition with the anode OER reaction, and even safety hazards; secondly, industrial hydrogen production requires "high current density" (≥1A / cm). 2 To increase production capacity, existing catalysts are prone to performance degradation under high current due to mass transfer limitations and bubble adhesion. In addition, traditional commercial OER catalysts rely on precious metals such as ruthenium (Ru) and iridium (Ir), which are scarce and expensive (Ir costs about 950 yuan / gram), seriously hindering the commercial application of water electrolysis for hydrogen production.

[0005] To replace precious metal catalysts, the scientific community has focused on non-precious metal electrocatalysts, among which layered hydrogen hydroxides (LDHs) have become a research hotspot. LDHs are layered structures similar to a "sandwich," consisting of two metal cations (such as nickel (Ni), iron (Fe), and cobalt (Co)) forming the layers, with anions (such as nitrate and carbonate) filling the spaces between the layers. This structure has significant advantages: first, the metal cations can be flexibly combined, allowing for optimization of catalytic activity through composition adjustment; second, the layered structure has a large surface area, exposing more "active sites" (the sites in the catalyst that actually participate in the reaction); and third, the metals constituting LDHs, such as Ni, Fe, and Co, are abundant elements in the Earth's crust, resulting in low cost and suitability for large-scale production. However, existing LDH catalysts and preparation technologies still face several unresolved challenges in seawater electrolysis: low synthesis efficiency, complex processes hindering industrial-scale production; insufficient exposure of active sites, poor conductivity, and insufficient intrinsic activity in the OER reaction; and resistance to Cl-. -The existing LDH catalysts have weak corrosion resistance and poor stability in seawater, making them unsuitable for long-term use. They also struggle to meet the high current density requirements of industrial applications, resulting in insufficient production capacity for practical use. These issues prevent the current LDH catalysts from being truly applied to direct seawater electrolysis for hydrogen production. Therefore, it is necessary to develop a novel LDH catalyst and its preparation method that is "highly efficient in synthesis, has excellent performance, and is suitable for seawater environments." Summary of the Invention

[0006] Current synthesis techniques cannot simultaneously solve the problems of low synthesis efficiency, poor compatibility with multiple metals, and poor tolerance to Cl in seawater for LDH electrocatalysts. - The four core pain points are: insufficient corrosion resistance and instability at high current densities. Specifically, at the synthesis level: long reaction time (12 hours for hydrothermal method), complex process (two-step electrodeposition method), microwave is only used as an auxiliary means (failing to leverage the advantages of rapid synthesis), making industrial-scale production difficult; furthermore, the structural design is not adapted to the seawater environment, and it lacks resistance to Cl. - Weak corrosion resistance; Performance-wise: high current density (≥ 1A / cm²) 2 The stability is insufficient to meet the production capacity requirements of industrial hydrogen production.

[0007] The core objective of this invention is to address these common shortcomings by providing a "one-step microwave driven, multi-metal universal, Cl-resistant" solution. - A bimetallic LDH catalyst and its preparation method that are "corrosion-resistant and adaptable to high current density" were developed to address the technical bottleneck of direct seawater electrolysis for hydrogen production.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows:

[0009] In a first aspect, the present invention provides a method for preparing a bimetallic LDH catalyst, comprising the following steps: A precursor solution was prepared by mixing a bimetallic salt, urea, NH4F, and a reaction solvent. The pretreated nickel foam is completely immersed in the precursor solution, then placed in a microwave reaction vessel and reacted at 60~180℃ for 10~30 min. After cleaning and drying, it is ready.

[0010] In one or more embodiments, the pretreatment steps for nickel foam include substrate cutting, ultrasonic cleaning, and drying. The ultrasonic cleaning includes ultrasonic treatment in an acid solution, followed by washing with water, then washing with alcohol, and finally washing with water.

[0011] Pickling is used to remove the surface oxide layer and metallic impurities. Alcohol washing is used to remove residual acid and oil, and the final water wash is used to completely remove any alcohol residue. Specific pretreatment steps are not limited to achieve the aforementioned surface cleaning objectives.

[0012] Furthermore, the drying conditions are not specifically limited, as long as drying is achieved. However, high temperatures should be avoided to prevent secondary oxidation. Vacuum drying at room temperature is preferable.

[0013] In one or more embodiments, the microwave reaction vessel is an open, sealable container.

[0014] In one or more embodiments, the metal salt is one or more of nitrates and sulfates. The bimetal is any two of Ni, Fe, Co, and Mn. Specifically: Ni(NO3)2 6H2O, Fe(NO3)3 9H2O, Co(NO3)2 6H2O, MnSO4 H2O.

[0015] In one or more embodiments, the molar ratio of the two metal salts in the bimetallic salt is 0.8~1.2:0.8~1.2, preferably 1:1.

[0016] In one or more embodiments, the amounts of bimetallic salt, urea, NH4F and reaction solvent are 2 mmol:(15~25 mmol):(5~15 mmol):(50~100 ml), preferably 2 mmol:(18~22 mmol):(8~12 mmol):(60~80 ml).

[0017] In one or more embodiments, the reaction solvent includes one or more of water and formamide, preferably water.

[0018] In one or more embodiments, the precursor component is dissolved in a reaction solvent (such as water) and stirred at room temperature (25°C) for 10 to 30 minutes until all reagents are completely dissolved, forming a uniform, transparent, light yellow-green solution.

[0019] In one or more embodiments, the pretreated nickel foam is completely immersed in the precursor solution for 2 to 10 minutes to avoid any areas not in contact with the reaction solution.

[0020] In one or more embodiments, the power of the microwave reaction is 800~1200W, specifically 800W, 900W, 1000W, 1100W, 1200W, etc.

[0021] In one or more embodiments, the microwave reaction time may be 10 min, 15 min, 20 min, 25 min, 30 min, etc., preferably 15 to 25 min, and most preferably 20 min.

[0022] In one or more embodiments, the temperature of the microwave reaction may specifically be 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, etc., preferably 80~120°C, more preferably 90~110°C, and most preferably 100°C.

[0023] Different microwave reaction times, microwave reaction temperatures, reaction solvents, and precursor concentrations all affect the effectiveness of catalysts.

[0024] In one or more embodiments, the cleaning involves multiple washes with water and alcohol sequentially to remove unreacted precursors and byproducts adsorbed on the surface. The drying is performed under vacuum at 50-70°C for 8-24 hours.

[0025] In a preferred embodiment, the preparation method specifically includes: 1. Pretreatment steps (activation of nickel foam substrate to ensure in-situ growth effect) (1) Substrate cutting: Cut the nickel foam into rectangular pieces of 3cm×4cm, remove the edge burrs, and ensure that the size is compatible with the reaction vessel. (2) Ultrasonic cleaning; (3) Drying treatment.

[0026] 2. Core synthesis steps (microwave-driven one-step in-situ growth) (1) Preparation of precursor solution: Mix the components in proportion at room temperature. (2) Substrate soaking: Immerse the pretreated nickel foam completely in the above precursor solution, ensuring that the nickel foam is fully wetted by the solution. (3) Microwave reaction: Transfer the beaker containing the precursor solution and nickel foam to the microwave reaction vessel, the opening of which can be sealed. Set the microwave reactor parameters.

[0027] 3. Post-processing steps: Cleaning: After the reaction is complete, turn off the microwave reactor and allow the container to cool naturally to room temperature. Remove the nickel foam (the surface of which has formed a brownish-red NiFe-LDH nanosheet array) and clean it multiple times (first rinse with deionized water 5 times, then rinse with anhydrous ethanol 3 times) to remove unreacted precursors and byproducts adsorbed on the surface.

[0028] Vacuum drying: The cleaned nickel foam is placed in a vacuum drying oven (vacuum dried overnight at 50~70℃) to obtain the final product "microwave synthesis NiFe-LDH / NF catalyst".

[0029] Secondly, this invention provides a bimetallic LDH catalyst prepared by the above-described method. The bimetallic LDH catalyst is denoted as AB-LDH / NF, where AB is selected from any two of Ni, Fe, Co, and Mn, and NF refers to nickel foam. NiFe-LDH is supported on nickel foam.

[0030] The bimetallic LDHs include NiFe-LDH / NF, CoFe-LDH / NF, CoNi-LDH / NF, and CoMn-LDH / NF.

[0031] Thirdly, the present invention provides the application of the above-mentioned bimetallic LDH catalyst or the bimetallic LDH prepared by the above-mentioned preparation method in hydrogen production by water electrolysis, preferably in hydrogen production by seawater electrolysis.

[0032] Fourthly, the present invention provides a method for producing hydrogen by seawater electrolysis, comprising: using the above-mentioned bimetallic LDH catalyst as the working electrode to perform an electrocatalytic oxygen evolution reaction. A three-electrode system is adopted, with an Hg / HgO electrode as the reference electrode and a carbon rod as the counter electrode. The electrolyte includes fresh water, seawater, alkaline fresh water, and alkaline seawater.

[0033] The concentration of alkali in the alkaline seawater is 0.5~10M, preferably 0.5~2M.

[0034] Fifthly, the present invention provides an electrolytic cell comprising an anode, a cathode, and an electrolyte, wherein the anode material comprises the aforementioned bimetallic LDH catalyst, and the electrolyte comprises fresh water, seawater, alkaline fresh water, and alkaline seawater.

[0035] One or more of the above technical solutions have the following advantages or beneficial effects: A microwave-driven one-step in-situ synthesis strategy (1000 W, 100 °C, 20 min) was employed to directly grow LDH nanosheet arrays on a nickel foam substrate, eliminating the need for subsequent processing and significantly improving synthesis efficiency and enhancing the bond between the catalyst and the substrate. Partially crystalline structures and nanosheet morphologies were obtained through controlled manipulation, and Ni was enriched. 3+ / Fe 3+ Highly active valence states and surface M-OH (M=Ni, Fe, Co, Mn) groups endow the material with superhydrophilicity (contact angle 0°).

[0036] Catalyst adapted to high concentrations of Cl - In a seawater system, 1 A / cm³ of natural seawater with 1M KOH added... 2 Stable operation for over 100 hours at current density, resistant to Cl - Corrosion resistant, resistant to metal ion leaching, and compatible with 1 A / cm 2 Industrial-grade high current density.

[0037] The synthesis method is versatile across multiple metals. By replacing the metal precursor, bimetallic systems such as CoFe-LDH / NF, CoNi-LDH / NF, and CoMn-LDH / NF can be flexibly prepared, making it suitable for various electrocatalytic scenarios.

[0038] Compared to hydrothermal reactions, the microwave-driven one-step in-situ synthesis strategy provided by this invention produces a catalyst with superior performance in seawater electrolysis for hydrogen production. Furthermore, compared to non-in-situ synthesis, such as drop-coating the precursor solution obtained through microwave synthesis onto nickel foam, the material prepared through in-situ synthesis provided by this invention, as a catalyst, exhibits superior performance in seawater electrolysis for hydrogen production. Attached Figure Description

[0039] 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.

[0040] Figure 1 This is a process flow diagram in an embodiment of the present invention; Figure 2 This is a SEM image of the NiFe-LDH / NF prepared in Example 1 of the present invention; Figure 3 This is a TEM image of NiFe-LDH prepared in Example 1 of the present invention; Figure 4 The XRD patterns of NiFe-LDH and NiFeLDH / NF prepared in Example 1 of this invention are shown below. Figure 5 SEM images of CoFe-LDH / NF, CoNi-LDH / NF, and CoMn-LDH / NF materials, and linear sweep voltammetry (LSV) curves of oxygen evolution reaction (OER) for different catalysts are shown. Among them, (a) CoFe-LDH / NF synthesized by microwave method, (b) CoNi-LDH / NF synthesized by microwave method, (c) CoMn-LDH / NF synthesized by microwave method; (d) comparison of the OER LSV curves of CoFe-LDH / NF, CoNi-LDH / NF, CoMn-LDH / NF materials with NiFe-LDH / NF. Figure 6 The images show the physical images of the samples and the current density diagrams at the same potential; where a is a physical image of the samples (where 1 is the NiFe-LDH / NF grown in situ on a nickel foam substrate in Example 1 by a one-step method; 2 is the material prepared in Comparative Example 3; and 3 is the ink in Comparative Example 3 before it was dipped), and b is the current density diagrams of the catalysts prepared in Example 1 and Comparative Example 3 at the same potential. Figure 7 The effect of NH4F addition on morphology is shown; where a is the morphology of the material synthesized without NH4F, b is the morphology of the material synthesized with NH4F, and c is the linear sweep voltammetry (LSV) curve of the oxygen evolution reaction (OER) for both the material synthesized without NH4F and the material synthesized with NH4F. Figure 8 The effects of microwave synthesis temperature, reaction time, and precursor concentration are shown; where (a) is the LSV curve current density of materials synthesized at different microwave synthesis temperatures, (b) is the LSV curve current density of materials synthesized at different reaction times, and (c) is the LSV curve current density of materials synthesized at different precursor concentrations. Figure 9 Electrochemical linear sweep voltammetry (LSV) curves for different catalysts; Figure 10 The graph shows the electrochemical stability test results for different catalysts. Detailed Implementation

[0041] In this invention, unless otherwise specified, all other experimental materials and instruments are conventional experimental materials in the field and can be purchased through commercial channels.

[0042] 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.

[0043] Example 1 1. Pretreatment steps (activation of nickel foam substrate to ensure in-situ growth effect) Substrate cutting: Cut the nickel foam into 3cm×4cm rectangular pieces, remove edge burrs, and ensure that the size is compatible with the reaction vessel.

[0044] Ultrasonic cleaning: Step 1: Place the cut nickel foam into a 3M HCl solution and sonicate for 30 minutes (100W power, 40kHz frequency) to remove the surface oxide layer and metal impurities.

[0045] Step 2: Remove the nickel foam, rinse it three times with deionized water, and then ultrasonically clean it in ethanol for 30 minutes to remove residual HCl and oil.

[0046] Step 3: Finally, immerse in deionized water and ultrasonically clean for 30 minutes to completely remove any ethanol residue.

[0047] Drying treatment: Place the cleaned nickel foam into a vacuum drying oven and vacuum dry at room temperature for 2 hours for later use (avoid secondary oxidation caused by high temperature).

[0048] 2. Core synthesis steps (microwave-driven one-step in-situ growth) Precursor solution preparation: Weigh 1 mmol of Ni(NO3)2 by weight. 6H2O, 1 mmol Fe(NO3)3 Add 9H₂O, 20 mmol urea, and 10 mmol NH₄F sequentially to a 100 mL beaker. Add 70 mL of deionized water, place the beaker on a magnetic stirrer, and stir at room temperature (25°C) for 20 minutes until all reagents are completely dissolved, forming a uniform, transparent, light yellow-green solution.

[0049] Substrate immersion: Immerse the pretreated nickel foam completely in the above precursor solution to ensure that the nickel foam is fully wetted by the solution (immersion time is 5 minutes to avoid local areas not in contact with the reaction solution).

[0050] Microwave reaction: Transfer the beaker containing the precursor solution and nickel foam to a custom-made microwave reaction vessel (high borosilicate material, 500mL volume), with a sealable opening. Set the microwave reactor parameters: power 1000 W, reaction temperature 100℃, holding time 20 minutes (microwaves are the core driving force, directly dominating catalyst nucleation and crystal growth, without auxiliary heating).

[0051] Post-processing steps: After the reaction is complete, turn off the microwave reactor and allow the container to cool naturally to room temperature (about 10 minutes). Remove the nickel foam (the surface of which has formed a brownish-red NiFe-LDH nanosheet array), rinse it 5 times with deionized water, and then rinse it 3 times with anhydrous ethanol to remove unreacted precursors and byproducts adsorbed on the surface.

[0052] Vacuum drying: The cleaned nickel foam was placed in a vacuum drying oven and dried under vacuum at 60°C overnight (12 hours) to obtain the final product "microwave synthesis NiFe-LDH / NF catalyst".

[0053] Figure 1 The process flow diagram of an embodiment of the present invention is shown. NiFe-LDH / NF with a nanosheet array structure can be obtained by microwave reaction at 100°C for 20 minutes.

[0054] Figure 2 The image shows a SEM image of the NiFe-LDH / NF prepared in Example 1 of this invention. The SEM image shows that the NiFe-LDH synthesized by this method has a good nanosheet structure.

[0055] Figure 3 The images show the TEM image and selected area electron diffraction (SAED) pattern of NiFe-LDH prepared in Example 1 of this invention. Together, they demonstrate the successful synthesis of NiFe-LDH and its partially crystalline structure exhibiting short-range order and long-range disorder.

[0056] Figure 4 The image shows the XRD pattern of NiFe-LDH / NF prepared in Example 1 of this invention. Figure 4As shown, the blue curve corresponds to the "NiFe-LDH / NF catalyst synthesized by microwave and loaded onto a nickel foam substrate," and the gray curve corresponds to the "NiFe-LDH powder sample collected directly under the same process." The dashed lines and marked crystal planes (such as (0012), (2010), etc.) in the figure are compared with the characteristic peak positions of the standard diffraction card (PDF#26-1286) of NiFe-LDH. From the peak position matching perspective: whether it is the sample loaded on nickel foam or the powder sample, its main characteristic diffraction peaks (such as the peaks corresponding to the crystal planes (0012), (2010), (220), etc.) are highly coincident with the peak positions of the standard PDF card of NiFe-LDH, confirming that the phase of both samples is a NiFe-LDH layered structure, indicating that the microwave synthesis process successfully prepared the target product. The diffraction peaks of both samples show the characteristics of "weak intensity and broad peak shape," and the sharp, strong diffraction peaks typical of highly crystalline materials do not appear. This peak-shaped characteristic corresponds to a "partially crystalline" structure: that is, the material maintains the order of the layered structure only in the short range, and the long-range order is insufficient (there are lattice defects).

[0057] Example 2 Preparation of CoFe-LDH / NF: Keeping other components and parameters constant, 1 mmol Co(NO3)2 was used. 6H2O replaces Ni(NO2)2 6H2O, the remaining steps are completely consistent with Example 1.

[0058] Example 3 Preparation of CoNi-LDH / NF: Keeping other components and parameters constant, 1 mmol Co(NO3)2 was used. 6H2O replaces Fe(NO3)3 9H2O, the remaining steps are completely consistent with Example 1.

[0059] Example 4 Preparation of CoMn-LDH / NF: Keeping other components and parameters constant, 1 mmol Co(NO3)2 was used. 6H2O replaces Ni(NO3)2 6H2O, with 1 mmol MnSO4 H2O replaces Fe(NO3)3 9H2O, the remaining steps are completely consistent with Example 1.

[0060] Figure 5SEM images of CoFe-LDH / NF, CoNi-LDH / NF, and CoMn-LDH / NF materials, and linear sweep voltammetry (LSV) curves of oxygen evolution reaction (OER) for different catalysts are shown. The electrolyte for the OER reaction is 1M KOH alkaline desalinated water. Figure 5 (a), (b), and (c) are scanning electron microscope (SEM) images (scale bar is 400 nm), corresponding to CoFe-LDH / NF, CoNi-LDH / NF, and CoMn-LDH / NF materials synthesized by microwave method, respectively. All three products exhibit a uniform nanosheet interwoven morphology without obvious agglomeration, demonstrating the controllability of the morphology of different bimetallic LDHs by the microwave synthesis process. Figure 5 (d) shows a comparison of the linear sweep voltammetry (LSV) curves of the oxygen evolution reaction (OER) of the three materials and NiFe-LDH / NF: at the same potential, NiFe-LDH / NF has a higher current density and better OER activity; the other three bimetallic LDHs also have certain catalytic activity, indicating that this microwave synthesis method can be used to prepare a variety of bimetallic LDH electrocatalysts.

[0061] Example 5 Unlike Example 1, the microwave synthesis temperature was different. Specifically, the synthesis temperature was 60°C, and the reaction solvent was water.

[0062] Example 6 Unlike Example 1, the microwave synthesis temperature and reaction solvent are different. Specifically, the synthesis temperature is 140°C, and the reaction solvent is formamide (CH3NO).

[0063] Example 7 Unlike Example 1, the microwave synthesis temperature and reaction solvent are different. Specifically, the synthesis temperature is 180°C, and the reaction solvent is formamide (CH3NO).

[0064] Example 8 The only difference from Example 1 is the microwave synthesis time. Specifically, the synthesis times are 10 min and 30 min, respectively.

[0065] Example 9 The difference from Example 1 lies only in the precursor concentration. Specifically, the precursor concentrations are 1.5×NiFe-LDH, 2×NiFe-LDH, and 3×NiFe-LDH. Here, "1.5×" refers to a molar ratio of Ni to Fe of 1.5:1; "2×" refers to a molar ratio of Ni to Fe of 2:1; and "3×" refers to a molar ratio of Ni to Fe of 3:1.

[0066] Comparative Example 1 Unlike Example 1, a hydrothermal method was used for synthesis. The specific hydrothermal process is as follows: The pretreated nickel foam and the dissolved precursor solution were transferred to a high-pressure reactor and hydrothermally reacted at 100°C for 12 hours.

[0067] Comparative Example 2 RuO2 / NF was prepared using commercially available ruthenium dioxide. The specific preparation process is as follows: Purchased commercial ruthenium dioxide powder was made into ink in the same proportion, and then evenly dropped onto the treated nickel foam under a baking lamp (around 80°C). After baking, RuO2 / NF was obtained.

[0068] Comparative Example 3 Unlike Example 1, instead of an in-situ synthesis process, NiFe-LDH powder was first synthesized using microwave technology and then drop-coated onto nickel foam. The specific preparation process is as follows: 1. The pretreatment steps for nickel foam are the same as in Example 1.

[0069] 2. Microwave one-step synthesis: The preparation of the precursor solution is the same as in Example 1.

[0070] Microwave reaction: Transfer the beaker containing the precursor solution to a custom-made microwave reaction vessel (high borosilicate glass, 500mL volume), with a sealable opening. Set the microwave reactor parameters: power 1000 W, reaction temperature 100℃, and holding time 20 minutes.

[0071] Drop coating: After the reaction is complete, the microwave reactor is turned off and the container is allowed to cool naturally to room temperature (about 10 minutes). The synthesized catalyst powder is collected by centrifugation. The ink prepared from the microwave-synthesized NiFe-LDH powder is slowly drop-coated onto the pretreated nickel foam under a baking lamp (about 80°C).

[0072] Post-treatment steps: First rinse 5 times with deionized water, then rinse 3 times with anhydrous ethanol to remove unreacted precursors and byproducts adsorbed on the surface.

[0073] Vacuum drying: Place the cleaned nickel foam into a vacuum drying oven and vacuum dry overnight (12 hours) at 60°C to obtain the final product.

[0074] Figure 6 The figures show physical images of the samples and current density graphs at the same potential. In figure a, we have a physical image of the sample (where 1 is the NiFe-LDH / NF grown in situ on a nickel foam substrate using a one-step microwave method in Example 1; 2 is the material prepared in Comparative Example 3; and 3 is the ink in Comparative Example 3 before coating). Figure b shows the current density graphs of the catalysts prepared in Examples 1 and 3 at the same potential. The electrolyte for the oxygen evolution reaction is 1M KOH alkaline desalinated water.

[0075] Specifically, Figure 6 In the image, 'a' represents the actual sample: the left side is "1" in 'a', which is NiFe-LDH / NF grown in situ on a nickel foam substrate using a one-step microwave method; the right side contains two parts: "3" in 'a' is the ink (in a centrifuge tube) prepared from the microwave-synthesized NiFe-LDH powder in Comparative Example 3, and "2" in 'a' is the sample in Comparative Example 3 where the powder was prepared into ink and then drop-coated onto the nickel foam, visually demonstrating the difference between the two loading methods of "in-situ growth" and "powder drop coating". Figure 6 In the figure, b represents the linear sweep voltammetry (LSV) curves of the oxygen evolution reaction (OER) for both materials: the in-situ grown material prepared in Example 1 (red curve) has a much higher current density at the same potential than the powder drop-coated sample prepared in Comparative Example 3 (blue curve).

[0076] This result confirms that the microwave one-step in-situ growth process can enhance the interfacial bonding between the catalyst and the substrate, optimize charge transport efficiency, and ultimately enable the material to exhibit superior electrocatalytic performance, highlighting the technical advantages of this in-situ synthesis method.

[0077] Figure 9 The figures show the electrochemical linear sweep voltammetry results for different catalysts. As can be seen from the figures, the microwave-synthesized NiFe-LDH / NF exhibits superior performance compared to the hydrothermally synthesized NiFe-LDH / NF. The electrolyte used in the tests was 1M KOH alkaline fresh water. At high current densities, the microwave-synthesized NiFe-LDH / NF significantly outperforms commercially available ruthenium dioxide (RuO2 / NF).

[0078] Comparative Example 4 Unlike Example 1, NH4F was not added.

[0079] Figure 7 The effect of NH4F addition on morphology is shown in Figure 1. Figure 1 shows the morphology of the material synthesized without NH4F, Figure 2 shows the morphology of the material synthesized with NH4F, and Figure 3 shows the linear sweep voltammetry (LSV) curves of the oxygen evolution reaction (OER) for both the material synthesized without NH4F and the material synthesized with NH4F. The electrolyte for the OER reaction was 1M KOH alkaline desalinated water.

[0080] Figure 7 In the figure, 'a' corresponds to the material synthesized without the addition of NH4F, which has the morphology of randomly aggregated bulk material with blurred nanosheet structure and severe stacking. Figure 7 In Example 1, b corresponds to the material synthesized under NH4F regulation. A uniformly dispersed nanosheet array structure can be clearly observed, with regular morphology and no obvious agglomeration, which intuitively demonstrates the inducing and regulating effect of NH4F on the nanosheet structure. Figure 7c represents the linear sweep voltammetry (LSV) curves of the oxygen evolution reaction (OER) for both materials: the material prepared in Example 1 with added NH4F (orange curve) has a significantly higher current density at the same potential than the sample prepared in Comparative Example 4 without added NH4F (blue curve).

[0081] This result indicates that NH4F can induce the formation of clearer nanosheet structures and improve the exposure of active sites through morphology optimization, ultimately achieving a significant improvement in electrocatalytic performance.

[0082] Figure 8 The effects of microwave synthesis temperature, reaction time, and precursor concentration are shown; where (a) represents the LSV curve current density of materials synthesized at different microwave synthesis temperatures, (b) represents the LSV curve current density of materials synthesized at different reaction times, and (c) represents the LSV curve current density of materials synthesized at different precursor concentrations.

[0083] Test background: In an electrolyte of 1 M KOH alkaline fresh water, at a voltage of 2 mV... s -1 The scanning rate was tested. Under the above testing conditions, the microwave synthesis temperature, reaction time, and precursor concentration were screened and optimized. Specifically: Figure 8 In the figure, 'a' represents the optimization of the microwave synthesis temperature. Variable parameters: microwave synthesis temperature (60, 100, 140, 180℃). The current density of the LSV curves corresponding to NiFe-LDH synthesized at different temperatures varies. The temperature corresponding to the curve with the higher current density is the microwave temperature more conducive to improving the catalytic activity of the material. Based on this, the optimal synthesis temperature can be selected as 100℃, with water as the reaction solvent.

[0084] Figure 8 In the figure, 'b' represents the optimization of the microwave reaction time. Variable parameters: microwave reaction time (10, 20, 30 min). The reaction time affects the nucleation and growth process of NiFe-LDH (e.g., morphology, crystallinity). The difference in current density in the LSV curves visually reflects the influence of different reaction times on catalytic activity. The optimal reaction time can be determined to be 20 min through comparison.

[0085] Figure 8 In the figure, 'c' represents the optimization of the precursor concentration. Variable parameters: Precursor concentration (labeled as 1×, 2×, 3×). The precursor concentration alters the concentration level of metal ions in the reaction system, thereby regulating the nucleation and growth process of the material, and consequently affecting its morphology and structure. By comparing the current density of the LSV curves, the optimal precursor concentration for preparing highly active NiFe-LDH / NF was determined to be 1×NiFe-LDH.

[0086] Applications in seawater electrolysis: Electrolysis tests were conducted using a three-electrode system: the NiFe-LDH / NF synthesized using microwave in Example 1 was used as the working electrode (anode), the Hg / HgO electrode as the reference electrode, and the carbon rod as the counter electrode; the electrodes were placed in an alkaline seawater electrolyte at a concentration of 1 A cm⁻¹. -2 Constant current electrolysis was performed at a current density, and the test results showed that the system could operate stably for more than 100 hours.

[0087] Figure 10 The "1 M KOH + seawater" electrolyte is prepared by using filtered natural seawater instead of traditional deionized water as the solvent to prepare an alkaline seawater electrolyte with a KOH concentration of 1 mol / L. (That is, KOH solid is directly dissolved in filtered seawater to achieve a KOH molar concentration of 1 mol / L, rather than adding additional KOH to the seawater.) Figure 10 This is a potentiostatic graph showing the electrochemical stability of different catalysts. In the seawater electrolysis system, it can achieve a potential stability of 1 A cm⁻¹. -2 The current density of the synthesized material remained stable for 100 hours with almost no performance degradation, while the NiFe-LDH / NF synthesized by the traditional hydrothermal method could only operate stably for about 10 hours.

[0088] 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 bimetallic LDH catalyst, characterized in that, Includes the following steps: A precursor solution was prepared by mixing a bimetallic salt, urea, NH4F, and a reaction solvent. The pretreated nickel foam is completely immersed in the precursor solution, then placed in a microwave reaction vessel and reacted at 60~180℃ for 10~30 min. After cleaning and drying, it is ready.

2. The preparation method according to claim 1, characterized in that, The metal salt is one or more of nitrates and sulfates; Preferably, the bimetal is any two of Ni, Fe, Co, and Mn.

3. The preparation method according to claim 1, characterized in that, In the bimetallic salt, the molar ratio of the two metal salts is 0.8~1.2:0.8~1.2, preferably 1:1; Preferably, the amounts of bimetallic salt, urea, NH4F and reaction solvent are 2 mmol:(15~25 mmol):(5~15 mmol):(50~100 ml), and more preferably 2 mmol:(18~22 mmol):(8~12 mmol):(60~80 ml); Preferably, the reaction solvent includes one or more of water and formamide, with water being the most preferred.

4. The preparation method according to claim 1, characterized in that, The pretreated nickel foam is completely immersed in the precursor solution for 2 to 10 minutes.

5. The preparation method according to claim 1, characterized in that, The power of the microwave reaction is 800~1200W; Preferably, the microwave reaction time is 15-25 minutes, and more preferably 20 minutes; Preferably, the temperature of the microwave reaction is 80~120℃, and more preferably 90~110℃.

6. A bimetallic LDH catalyst, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 5.

7. The multi-metal LDH catalyst according to claim 6, characterized in that, The bimetallic LDH catalyst is denoted as AB-LDH / NF, where AB is selected from any two of Ni, Fe, Co, and Mn; Preferably, the bimetallic LDH catalyst includes NiFe-LDH / NF, CoFe-LDH / NF, CoNi-LDH / NF, and CoMn-LDH / NF.

8. The application of a bimetallic LDH catalyst prepared by any one of claims 1 to 5 or the bimetallic LDH catalyst of claim 6 or 7 in hydrogen production by water electrolysis, preferably in hydrogen production by seawater electrolysis.

9. A method for producing hydrogen by electrolysis of water, characterized in that, include: Using the bimetallic LDH catalyst prepared by any one of claims 1 to 5, or the bimetallic LDH catalyst of claim 6 or 7 as the working electrode, an electrocatalytic oxygen evolution reaction is carried out. Preferably, the electrolyte includes fresh water, seawater, alkaline fresh water, and alkaline seawater.

10. An electrolytic cell, characterized in that, It includes an anode, a cathode, and an electrolyte. The anode material includes a bimetallic LDH catalyst prepared by the preparation method according to any one of claims 1 to 5 or a bimetallic LDH catalyst according to claim 6 or 7. The electrolyte includes fresh water, seawater, alkaline fresh water, and alkaline seawater.

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