RE-NiFeLDH bifunctional catalytic material as well as preparation method and application thereof

Abstract

The invention discloses an RE-NiFeLDH bifunctional catalytic material as well as a preparation method and application thereof. The catalyst comprises a nickel-iron hydrotalcite (NiFeLDH) main body and a rare earth element (RE) intercalated between layers of the nickel-iron hydrotalcite main body, and has bifunctional catalytic activity of hydrogen evolution reaction and oxygen evolution reaction. The preparation method comprises the following steps: dissolving a nickel salt, an iron salt, a rare earth salt, urea and ammonium fluoride in water to form a mixed solution, immersing the pretreated base material in the mixed solution, carrying out a hydrothermal reaction at 100-160 DEG C for 6-24 h, and carrying out suction filtration, washing and drying on the product to obtain the catalyst. The interlayer spacing and the electronic structure of NiFeLDH are regulated and controlled through rare earth elements, the specific surface area is increased, more active sites are exposed, and the catalytic activity and the electron transmission efficiency are improved; the preparation method is simple and controllable, the cost is low, and the catalyst shows excellent bifunctional catalytic performance in alkaline electrolyte and simulated seawater and has wide engineering application prospects.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of hydrogen energy and electrocatalytic materials, and particularly relates to a RE-NiFeLDH bifunctional catalytic material and a preparation method and application thereof. BACKGROUND

[0002] Water electrolysis for hydrogen production is one of the most promising green hydrogen production technologies due to its mild reaction conditions and abundant raw materials, but its development is limited by the slow kinetics of anode oxygen evolution reaction (OER) and cathode hydrogen evolution reaction (HER). Therefore, related research proposes to use rare earth elements (RE) with larger atomic radii to fill the interlayer spacing of hydrotalcite (LDH) to increase its specific surface area, in order to achieve efficient hydrogen production.

[0003] Rare earth elements have important research value in the design of layered double hydroxide (LDH) material components in recent years due to their unique 4f electron layer structure and adjustable coordination number. Rare earth components have excellent oxygen storage and release performance, which can significantly enhance the catalytic activity by adjusting the surface oxygen vacancy concentration and improve the structural stability of the material in harsh reaction environments. At the same time, transition metal-based LDH materials have broad application prospects in the field of electrocatalytic water splitting due to their flexible electronic structure and lower cost. However, the oxygen evolution reaction (OER) as a typical four-electron transfer process has problems such as slow kinetics, high overpotential, and high energy consumption, and is still highly dependent on noble metal-based catalysts, limiting its large-scale application. Non-noble metal-based catalysts have lower cost, but their catalytic performance still cannot meet the actual demand. Therefore, constructing a rare earth-transition metal multi-component LDH system can not only retain the economic advantage of non-noble metal materials, but also fully exert the unique role of rare earth components in electronic structure and oxygen vacancy regulation, thereby breaking through the limitations of traditional LDH materials in catalytic activity and stability. SUMMARY

[0004] The purpose of the present application is to provide a RE-NiFeLDH bifunctional catalytic material and a preparation method and application thereof. The catalyst introduces rare earth elements into the interlayer of NiFeLDH through a one-step hydrothermal method, effectively regulates the electronic structure and interlayer spacing of the catalyst, realizes high-efficiency HER and OER bifunctional catalysis, reduces the energy consumption of water electrolysis for hydrogen production, improves the stability of the catalyst, and has a simple and controllable preparation method, low cost, and is suitable for large-scale application.

[0005] To achieve the above purpose, the present application provides the following technical solutions: The application provides a RE-NiFeLDH bifunctional catalyst, which comprises a nickel-iron hydrotalcite (NiFeLDH) main body and rare earth elements (RE) intercalated in the interlayer thereof; the RE is at least one selected from lanthanum (La), cerium (Ce), erbium (Er) and dysprosium (Dy); and the catalyst has bifunctional catalytic activity of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER).

[0006] The doping amount of the rare earth elements (RE) is 0.1-5 times the total molar amount of the nickel salt and the iron salt, and the doping amount range can ensure that the rare earth elements fully play a structure regulating and electronic adjusting role, while avoiding crystal structure disorder caused by excessive doping.

[0007] The catalyst is formed in situ on the surface of a substrate by a one-step hydrothermal method; the substrate is selected from pretreated nickel foam, nickel mesh, carbon paper, iron foam or carbon cloth, and such a substrate has good electrical conductivity and pore structure, which can promote electron transmission and provide stable support for catalyst growth.

[0008] The application provides a preparation method of the above-mentioned RE-NiFeLDH bifunctional catalyst, which comprises the following steps: (1) dissolving a nickel salt, an iron salt, a rare earth salt, urea (CO(NH2)2) and ammonium fluoride (NH4F) in water to form a mixed solution; wherein the nickel salt is nickel nitrate hexahydrate, the iron salt is ferric chloride nonahydrate, and the rare earth salt is one or more of cerium nitrate nonahydrate, lanthanum nitrate nonahydrate, erbium nitrate nonahydrate or dysprosium nitrate nonahydrate; (2) immersing a pretreated substrate in the mixed solution and performing hydrothermal reaction at 100-160 DEG C for 6-24 hours; the hydrothermal reaction temperature and time can control the crystal structure, morphology and growth thickness of the catalyst, and within the range, a catalyst material with appropriate crystallinity and regular morphology can be obtained; The pretreatment comprises sequentially performing organic solvent cleaning, acid pickling and water washing, and then performing drying; the organic solvent is preferably acetone, which is used for removing oil stains and organic impurities on the surface of the substrate; the acid pickling adopts 1M HCl solution, which is used for removing the oxide layer and metal impurities on the surface of the substrate; each cleaning step is ultrasonic cleaning for 10 minutes.

[0009] (3) the reaction product is subjected to suction filtration, washing and drying at 50-70 DEG C for 6-24 hours to obtain the RE-NiFeLDH bifunctional catalyst.

[0010] The molar ratio of the nickel salt, the iron salt, the rare earth salt, the urea, and the ammonium fluoride is (0.01-0.25):(0.01-0.25):(0.01-0.5):(0.05-10):(1-8); preferably 0.05:0.05:0.35:10:4, the optimal molar ratio can realize the synergistic effect of each component, realize the effective intercalation of the rare earth element, and maximize the catalytic activity and stability of the catalyst.

[0011] The application provides application of the above-mentioned RE-NiFeLDH bifunctional catalyst in water electrolysis hydrogen production, and the catalyst is used for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in an alkaline electrolyte.

[0012] The alkaline electrolyte is a 1-3M KOH solution or a KOH / NaCl mixed solution; in the KOH / NaCl mixed solution, the molar ratio of KOH to NaCl is 1:0.5-1:1.5.

[0013] Compared with the prior art, the technical scheme of the application has the following beneficial effects: (1) excellent bifunctional catalytic performance: the structure and electronic properties of the NiFeLDH are regulated by intercalation of the rare earth element, so that the catalyst has high HER and OER bifunctional catalytic activity, effectively reduces the energy consumption of the four-electron transfer process of the anode OER and the thermodynamic potential barrier of the cathode HER, significantly improves the water electrolysis hydrogen production efficiency, and avoids the limitations of the single function of the traditional catalyst.

[0014] (2) optimized structure and electronic properties: the large atomic radius of the rare earth element can effectively expand the interlayer spacing of the NiFeLDH, increase the specific surface area and expose more active sites; at the same time, the high valence state of the rare earth element can adjust the electronic structure of Ni and Fe, improve the oxidation state, and thus enhance the catalytic activity and improve the electronic transmission efficiency.

[0015] (3) good stability: the introduction of the rare earth element can improve the structural stability of the material in harsh reaction environments, avoid serious damage to the material structure during the catalytic process, prolong the service life of the catalyst, and still exhibit excellent catalytic performance in a simulated seawater system (KOH / NaCl mixed solution), so the application scenarios are wide.

[0016] (4) significant advantages of the preparation method: prepared by one-step hydrothermal method in situ, the process is simple and controllable, the conditions are mild, the cost is low, complex equipment and expensive raw materials are not needed, it is suitable for large-scale production, and has extremely high industrial application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is the XRD pattern of the Ce-NiFeLDH prepared in Example 1 and the NiFeLDH prepared in Comparative Example 1. Figure 2 SEM images of Ce-NiFe LDH prepared in Example 1 and NiFe LDH prepared in Comparative Example 1; Figure 3 Raman spectra of Ce-NiFe LDH prepared in Example 1 and NiFe LDH prepared in Comparative Example 1; Figure 4 XPS spectra of Ce-NiFe LDH prepared in Example 1 and NiFe LDH prepared in Comparative Example 1; Figure 5 Linear sweep voltammetry curves of Example 1 and Comparative Example 1 in 1M KOH electrolyte; Figure 6 Linear sweep voltammetry curves of Example 1 and Comparative Example 1 in simulated seawater for hydrogen evolution. DETAILED DESCRIPTION

[0018] The application will be further explained in conjunction with specific embodiments.

[0019] Example 1: Preparation of Ce-NiFe LDH catalyst (1) Pretreatment of substrate: Cut the nickel foam with a thickness of 0.5 mm into a standard rectangle of 1 cm*1.5 cm, and sequentially ultrasonically clean with acetone, 1M HCl, and deionized water for 10 minutes each, and dry for standby use.

[0020] (2) Solution preparation: Dissolve 0.05 mmol of nickel nitrate hexahydrate (Ni(NO3)2·6H2O), 0.05 mmol of ferric chloride nonahydrate (FeCl3·9H2O), 0.35 mmol of cerium nitrate hexahydrate (Ce(NO3)3·6H2O), 10 mmol of urea (CO(NH2)2), and 4 mmol of ammonium fluoride (NH4F) in 30 mL of deionized water, and ultrasonically disperse for 1 hour at room temperature to form a uniform mixed solution. (3) Hydrothermal reaction: Immerse the pretreated nickel foam into the above mixed solution, and place it in a 100 mL Teflon-lined stainless steel autoclave, and react at 140°C for 12 hours.

[0021] (4) Post-treatment: After cooling to room temperature, take out the sample, repeatedly wash with deionized water and ethanol, and then dry in a 60°C vacuum drying oven for 6 hours to obtain the Ce-NiFe LDH catalyst grown on the nickel foam.

[0022] Example 2: The difference between this example and Example 1 is that Ce(NO3)3·6H2O is replaced by an equal molar amount of La(NO3)3·6H2O, and the remaining preparation steps and parameters are completely consistent with those of Example 1, and finally a La-NiFe LDH bifunctional catalyst is obtained.

[0023] Comparative Example 1: The difference between this comparative example and Example 1 is that no rare earth salt (Ce(NO3)3·6H2O) was added to the mixed solution. The rest of the preparation steps and parameters were completely consistent with Example 1, and NiFeLDH catalyst without rare earth elements was finally obtained.

[0024] Example 3 Characterization of catalyst structure and morphology The crystal structure and morphology of the catalysts prepared in Example 1 and Comparative Example 1 were observed using powder X-ray diffraction, scanning transmission electron microscopy, and Raman spectroscopy, respectively.

[0025] like Figure 1 The XRD patterns of the Ce-NiFeLDH catalyst prepared in Example 1 and the NiFeLDH catalyst prepared in Comparative Example 1 are shown. It can be seen that the diffraction peaks correspond to the characteristic peaks of NiFeLDH (PDF#40-0215), confirming that the catalysts synthesized in Comparative Example 1 and Example 1 have a nickel-iron layered double hydroxide crystal structure. It was also found that after introducing the high-valence rare earth metal element Ce, the diffraction peak intensity decreased, the crystallinity decreased, and the diffraction peaks shifted slightly to the left, indicating that the interlayer spacing increased.

[0026] like Figure 2 The image shows the SEM images of the Ce-NiFeLDH catalyst prepared in Example 1 and the NiFeLDH catalyst prepared in Comparative Example 1. It can be seen that the catalysts synthesized in Comparative Example 1 and Example 1 have a flower-like structure composed of nanosheets.

[0027] like Figure 3 The image shows the Raman spectra of the Ce-NiFeLDH catalyst prepared in Example 1 and the NiFeLDH catalyst prepared in Comparative Example 1. It can be seen that at 453 and 531 cm⁻¹... -1 The characteristic peak at that location corresponds to This confirms that after Ce doping, Ni is oxidized to a higher valence state of trivalent nickel.

[0028] The electronic structures of Example 1 and Comparative Example 1 were observed using X-ray photoelectron spectroscopy (XPS), and the oxygen bonding states of Example 1 and Comparative Example 1 were observed respectively. Figure 4 Figure 1 shows the XPS spectra of the Ce-NiFeLDH catalyst prepared in Example 1 and the NiFeLDH catalyst prepared in Comparative Example 1. Figure (a) shows the XPS spectra of Ni2+. p The spectrum, Figure (b) shows Fe2 p The spectra show that the introduction of high-valence rare earth metal element Ce affects the electronic structure of Ni and Fe, causing the characteristic peaks of Ni and Fe to shift to the right and increasing their oxidation state, which can effectively improve their catalytic activity.

[0029] Example 4: Electrochemical performance test The catalysts prepared in Example 1 and Comparative Example 1 were subjected to electrochemical performance test using a three-electrode system, with the catalyst as the working electrode, a graphite sheet as the counter electrode, and Hg / HgO as the reference electrode. Linear sweep voltammetry (LSV) was performed in 1M KOH solution (alkaline electrolyte) and 1M KOH + 0.5M NaCl solution (simulated seawater electrolyte), respectively, with a scanning potential range of 0.2-1V and a scanning rate of 10mV / s. The test results are as follows: (1) Performance in alkaline electrolyte: As shown in Figure 5 compared with the NiFeLDH of Comparative Example 1, the Ce-ion doped Example 1 has a more efficient water electrolysis hydrogen production capacity, effectively improving the catalytic performance while avoiding the serious destruction of the NiFeLDH structure. The Ce-NiFeLDH of Example 1 has a lower overpotential of 199mV and 153mV for OER and HER, respectively, at a current density of 10mA cm -2 , indicating that the introduction of Ce element significantly improves the HER and OER bifunctional catalytic activity of the catalyst, reducing the energy consumption of water electrolysis.

[0030] (2) Performance in simulated seawater electrolyte: As shown in Figure 6 , the Ce-NiFeLDH of Example 1 still exhibits excellent catalytic performance in simulated seawater, with a lower overpotential of 330mV and 183mV for OER and HER, respectively, at a current density of 10mA cm -2 , which is significantly higher than the 390mV and 241mV of Comparative Example 1, indicating that the doping of rare earth elements not only enhances the catalytic activity, but also improves the stability of the catalyst in complex systems, laying a foundation for its application in seawater electrolysis hydrogen production.

[0031] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A RE-NiFeLDH bifunctional catalyst, characterized in that, The catalyst comprises a NiFeLDH substrate and rare earth elements intercalated between its layers, wherein the rare earth elements are selected from at least one of lanthanum, cerium, erbium, and dysprosium; the catalyst simultaneously possesses dual catalytic activity for hydrogen evolution reaction and oxygen evolution reaction.

2. The catalyst according to claim 1, characterized in that: The amount of rare earth element doping is 0.1-5 times the total molar amount of nickel salt and iron salt.

3. The catalyst according to claim 1, characterized in that: The catalyst is formed in situ on the surface of a substrate by a one-step hydrothermal method; the substrate is selected from pretreated nickel foam, nickel mesh, carbon paper, iron foam or carbon cloth.

4. A method for preparing the RE-NiFeLDH bifunctional catalyst according to any one of claims 1 to 3, characterized in that, Includes the following steps: (1) Dissolve nickel salt, iron salt, rare earth salt, urea and ammonium fluoride in water to form a mixed solution; (2) Immerse the pretreated substrate in the mixed solution and perform a hydrothermal reaction at 100~160℃ for 6~24 hours; (3) The reaction product is filtered, washed, and dried at 50-70℃ for 6-24 hours to obtain the catalyst.

5. The preparation method according to claim 4, characterized in that: The molar ratio of the nickel salt, iron salt, rare earth salt, urea, and ammonium fluoride is (0.01~0.25):(0.01~0.25):(0.01~0.5):(0.05~10):(1~8).

6. The preparation method according to claim 5, characterized in that: The molar ratio of the nickel salt, iron salt, rare earth salt, urea and ammonium fluoride is 0.05:0.05:0.35:10:

4.

7. The preparation method according to claim 4, characterized in that: The nickel salt is nickel nitrate hexahydrate, the iron salt is ferric chloride nonahydrate, and the rare earth salt is one or more of cerium nitrate nonahydrate, lanthanum nitrate nonahydrate, erbium nitrate nonahydrate, or dysprosium nitrate nonahydrate.

8. The preparation method according to claim 4, characterized in that: The pretreatment includes sequential organic solvent cleaning, acid washing, and water washing, followed by drying.

9. The application of the RE-NiFeLDH bifunctional catalyst according to any one of claims 1 to 3 in water electrolysis for hydrogen production, characterized in that: Used for hydrogen evolution and oxygen evolution reactions in alkaline electrolytes.

10. The application according to claim 9, characterized in that, The alkaline electrolyte is a 1-3M KOH solution or a KOH / NaCl mixed solution; in the potassium hydroxide / sodium chloride mixed solution, the molar ratio of potassium hydroxide to sodium chloride is 1:0.5 to 1:1.5.

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