A strontium-doped low-crystalline nickel oxyhydroxide nanocatalyst for electrolysis of water and a preparation method and application thereof

Abstract

The application discloses a strontium-doped low-crystalline nickel-iron hydroxyl oxide water electrolysis nanocatalyst and a preparation method and application thereof, and belongs to the technical field of electrocatalyst preparation. The catalyst has an ultrathin nanosheet structure and is low-crystalline, and is prepared by in-situ electrooxidation reconstruction of a strontium-doped nickel-iron selenide pre-catalyst. The application weakens the metal-selenium bond strength by strontium (Sr) doping, induces phase change to generate low-crystalline Sr-doped nickel-iron hydroxyl oxide (NiFeOOH) rich in bimetallic active sites, enhances the covalence of metal-oxygen bonds, introduces bimetallic vacancies at the same time, optimizes the adsorption energy of oxygen-containing intermediates, and significantly improves the electrocatalytic activity and stability of an anode oxygen evolution reaction, and has an excellent industrialization application prospect in an anion exchange membrane water electrolysis hydrogen production system.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalyst preparation technology, specifically relating to a strontium (Sr)-doped low-crystallinity nickel-iron hydroxyl oxide electrolytic water nanocatalyst, its preparation method, and its application. Background Technology

[0002] The unsustainability and environmental pollution of traditional fossil fuels are driving green hydrogen to become a key clean energy carrier. However, the inherent intermittency and volatility of renewable energy sources such as wind and solar power significantly constrain the stable operation of power systems, making the energy storage value of green hydrogen increasingly prominent. Among the many green hydrogen production technologies, anion exchange membrane water electrolysis technology has attracted much attention due to its ability to operate under alkaline conditions and its dual advantages of lower material costs and higher system efficiency compared to non-precious metal catalysts. However, the sluggish kinetics of the oxygen evolution reaction at the anode is a key bottleneck restricting overall electrolysis efficiency and equipment economics. Therefore, developing novel anode catalysts with high activity, high stability, and low cost is crucial to overcoming this technological obstacle and promoting its industrialization.

[0003] Currently, nickel-iron hydroxyl oxide (NiFeOOH) has become the most promising non-noble metal catalyst for alkaline oxygen evolution reactions due to its tunable electronic structure and excellent intrinsic activity. Existing technologies typically involve in-situ electrochemical reconstruction to construct crystalline-amorphous heterojunctions and introducing oxygen-containing anions to modify active sites, which can effectively stabilize the active phase structure and enhance intrinsic catalytic activity. For example, according to *Angewandte Chemie*... Angew. Chem. Int. Ed. (2025, 64, e202415132) reported a nitrate-modified NiFe-based precatalyst that undergoes in-situ reconstruction during OER to form a crystalline-amorphous Fe(Ni)OOH heterojunction. The selective adsorption of nitrate enhances the crystallinity of the reconstructed phase and strengthens the stability of Fe-O and Ni-O bonds, thus achieving a synergistic effect of high activity and long lifetime at high current densities. Therefore, optimizing the structure and stability of NiFeOOH through reconstruction becomes an important direction for improving oxygen evolution performance.

[0004] However, existing NiFeOOH catalysts still have significant shortcomings. In the aforementioned systems, the reconstruction process is limited by the pre-catalyst structure, making it difficult to achieve a uniform and stable active phase transformation. Furthermore, under strong oxidation conditions, problems such as active phase instability and metal ion dissolution easily occur, leading to rapid degradation of catalytic performance. Therefore, to date, few studies have achieved stable reconstruction of NiFe-based catalysts and clearly elucidated their structure-activity relationship. This means that the intrinsic catalytic advantages of NiFeOOH cannot be fully utilized in the alkaline oxygen evolution reaction, thus limiting the energy efficiency improvement of anion exchange membrane water electrolysis for hydrogen production. Summary of the Invention

[0005] To address the problems of unstable active phase and easy dissolution of metal ions leading to catalytic performance degradation in existing NiFeOOH catalysts during reconstruction, this application provides a strontium-doped low-crystallinity nickel-iron hydroxyl oxide electrolytic water nanocatalyst, its preparation method, and its application, achieving a synergistic improvement in high catalytic activity and long-term durability.

[0006] To achieve the above objectives, the present invention employs the following technical solution: In a first aspect, the present invention discloses a strontium-doped low-crystallinity nickel-iron hydroxyl oxide electrolytic water catalyst, which has an ultrathin nanosheet structure and is low-crystallinity; the electrocatalyst is prepared by in-situ electro-oxidation reconstruction of a Sr-doped nickel-iron selenide precatalyst.

[0007] As can be seen, the present invention solves the problem of poor stability of the active phase structure by reconstructing the Sr-doped nickel-iron selenide precatalyst through in-situ electro-oxidation, utilizing the Sr element to weaken the metal-selenium bond strength, inducing a phase transition to generate a low-crystallinity Sr-NiFeOOH rich in bimetallic active sites, thereby achieving a synergistic improvement in high catalytic activity and long-term durability.

[0008] As a preferred embodiment, the electrocatalyst is rich in bimetallic vacancies and exhibits enhanced metal-oxygen bond covalentity. By introducing bimetallic vacancies and enhancing metal-oxygen bond covalentity, the adsorption energy of oxygen-containing intermediates is optimized, further improving the electrocatalytic performance of the anodic oxygen evolution reaction.

[0009] As a preferred embodiment, the Sr-doped nickel-iron selenide precatalyst is Sr-NiFeSe2.

[0010] As a preferred solution, at 100mA / cm 2 At a current density of 232 mV, the overpotential of the electrocatalyst is 232 mV; at 500 mA / cm², the overpotential is 232 mV. 2 At a current density of 0.7 mV / h, the electrocatalyst operated stably for 123 hours in an anion exchange membrane water electrolysis hydrogen production system.

[0011] A second aspect of the present invention also provides a method for preparing a strontium-doped low-crystallinity nickel-iron hydroxide electrolytic water catalyst, comprising the following steps: preparing a Sr-doped NiFe LDH precursor; subjecting the Sr-doped NiFe LDH precursor to a solvothermal reaction with a selenium source to obtain Sr-doped nickel-iron selenide ultrathin nanosheets; and subjecting the Sr-doped nickel-iron selenide ultrathin nanosheets to in-situ electrooxidation reconstruction under an alkaline oxygen evolution reaction environment to obtain the Sr-doped low-crystallinity NiFeOOH ultrathin nanosheet electrocatalyst.

[0012] The preparation method of the present invention combines a simple solvothermal method with in-situ electro-oxidation reconstruction. The process is simple, the raw materials are inexpensive and readily available, and the reproducibility is high, which can quickly obtain high-performance reconstructed electrocatalysts.

[0013] As a preferred embodiment, the step of preparing the Sr-doped NiFe LDH precursor includes: dispersing strontium salt, nickel salt, iron salt, ammonium fluoride, and urea in water and carrying out a solvothermal reaction. LDH is short for Layered Double Hydroxide, referring to layered double metal hydroxides; NiFe LDH is a nickel-iron layered double metal hydroxide.

[0014] The above scheme provides specific raw materials and basic methods for precursor preparation, ensuring the successful introduction of Sr element.

[0015] As a preferred embodiment, the solvothermal reaction is carried out at a temperature of 100℃~150℃ for 15~20 hours. This method optimizes the parameters of the solvothermal reaction, which is beneficial for forming a precursor with uniform morphology.

[0016] As a preferred embodiment, the step of solvothermal reaction of the Sr-doped NiFe LDH precursor with a selenium source includes: dispersing the selenium source and sodium borohydride in water, adding the Sr-doped NiFe LDH precursor, and carrying out the solvothermal reaction at 170℃~200℃. This step clarifies the detailed process conditions for selenization treatment, ensuring the successful synthesis of nickel-iron selenide ultrathin nanosheets.

[0017] As a preferred embodiment, the in-situ electro-oxidation reconstruction is carried out in an alkaline electrolyte with a voltage scan range of (0-1.15) V to (1.6-2.0) V vs. RHE. This clarifies the specific electrochemical conditions for the in-situ electro-oxidation reconstruction, ensuring the formation of the low-crystallinity Sr-NiFeOOH active phase.

[0018] As a preferred embodiment, the strontium salt is selected from at least one of strontium nitrate, strontium acetate, or strontium chloride; the nickel salt is selected from at least one of nickel nitrate, nickel chloride, nickel sulfate, or nickel acetylacetonate; the iron salt is selected from at least one of ferric nitrate, ferric chloride, ferric sulfate, or ferric acetylacetonate; and the selenium source is selected from at least one of selenium powder or sodium selenite. The total molar amount of strontium salts, nickel salts, and iron salts was 1:(0.1-1) to the molar amount of selenium source; the molar ratio of strontium salts to nickel salts and iron salts was (0.01-1):(4-9):1.

[0019] A third aspect of the present invention also provides the application of strontium-doped low-crystallinity nickel-iron hydroxyl oxide electrolytic water nanocatalyst as described above in the oxygen evolution reaction at the anode of an anion exchange membrane water electrolysis hydrogen production system.

[0020] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a strontium-doped low-crystalline NiFeOOH nanocatalyst for water electrolysis, which is prepared by a simple solvothermal method using Sr-doped low-crystalline NiFeOOH, followed by in-situ electrocatalytic oxidation and reconstruction. The process is simple, and the raw materials are inexpensive and readily available. Compared with traditional alkaline oxygen evolution reaction electrocatalysts, the low-crystalline Sr-doped NiFeOOH species, rich in bimetallic active sites, induces the formation of unsaturated active metal sites while simultaneously enhancing the metal-oxygen bonding strength.

[0021] The preparation process of this invention is simple, the raw materials are economical and readily available, and the reproducibility is high. With the help of the dynamic regulation strategy of strontium, a high-performance reconstructed electrocatalyst can be rapidly obtained under electro-oxidation reaction conditions.

[0022] From a practical application perspective, the strontium-doped low-crystallinity nickel-iron hydroxyl oxide nanocatalyst for water electrolysis obtained in this invention, through the introduction of Sr, not only optimizes the electronic structure of the active metal and accelerates the reconstruction process, but also induces the generation of metal vacancies and enhances the metal-oxygen bonding strength. In anion exchange membrane water electrolysis hydrogen production systems, it exhibits excellent catalytic activity and long-term operational stability. At 100 mA / cm²... 2 At a current density of only 232 mV, the overpotential of Sr-doped low-crystalline NiFeOOH ultrathin nanosheets is significantly better than that of commercial ruthenium oxide catalysts. At this overpotential, the current density of this catalyst is 53.8 times that of commercial ruthenium oxide catalysts, demonstrating excellent alkaline oxygen evolution reaction activity. Furthermore, in the industrial application of anion exchange membrane water electrolysis, at a voltage of 2 V, the current density of Sr-doped low-crystalline nickel-iron hydroxyl oxide electrolysis nanocatalyst reaches as high as 2.75 A / cm². 2 It is 4.4 times more potent than commercially available ruthenium oxide catalysts. This catalyst operates at 500 mA / cm². 2 In an anion exchange membrane water electrolysis hydrogen production system at a specific current density, the catalyst can operate stably for 123 hours with a decay rate of only 0.7 mV / h. Therefore, the prepared strontium-doped low-crystallinity nickel-iron hydroxyl oxide water electrolysis nanocatalyst achieves both high catalytic activity and excellent structural stability in the field of anion exchange membrane water electrolysis hydrogen production, possessing significant advantages and broad prospects for industrial applications. Attached Figure Description

[0023] Figure 1 Transmission electron microscopy images of the Sr-doped nickel-iron selenide ultrathin nanosheet precatalysts and nickel-iron selenide ultrathin nanosheet precatalysts prepared in Examples 1 and 2; wherein, a is Sr-doped nickel-iron selenide ultrathin nanosheet; b is nickel-iron selenide ultrathin nanosheet.

[0024] Figure 2 Transmission electron microscope images of Sr-doped low-crystalline NiFeOOH ultrathin nanosheets and low-crystalline NiFeOOH ultrathin nanosheets prepared in Examples 1 and 2; wherein, a is Sr-doped low-crystalline NiFeOOH ultrathin nanosheet; b is low-crystalline NiFeOOH ultrathin nanosheet.

[0025] Figure 3 The image shows a scanning transmission electron microscope-elemental analysis of the Sr-doped low-crystalline NiFeOOH ultrathin nanosheets prepared in Example 1; wherein, Figure 3 In the image, 'a' represents a high-angle annular dark field image. Figure 3 In this context, 'b' represents the distribution analysis of Fe element. Figure 3 In this context, 'c' represents the distribution analysis of Ni elements. Figure 3 In this context, d represents the distribution analysis of O elements; Figure 3 In this context, 'e' represents the distribution analysis of Sr elements.

[0026] Figure 4 Comparison of X-ray diffraction (XRD) spectra of Sr-doped low-crystalline NiFeOOH ultrathin nanosheets and their corresponding selenide substrates prepared in Examples 1 and 2. Specifically, a is a comparison of the XRD spectra of Sr-doped low-crystalline NiFeOOH ultrathin nanosheets and their corresponding selenide substrates; b is a comparison of the corresponding selenide precatalysts.

[0027] Figure 5 Comparison of X-ray photoelectron spectra of Sr-doped low-crystalline NiFeOOH ultrathin nanosheets prepared in Examples 1 and 2. Where a represents Ni₂. p X-ray photoelectron spectrum; b is Fe2+. p X-ray photoelectron spectrum; c represents O 1 s The X-ray photoelectron spectrum. d represents O 1. s A comparison of O content in X-ray electron spectroscopy.

[0028] Figure 6 Extended X-ray absorption fine structure (EXPS) spectra of Sr-doped low-crystalline NiFeOOH ultrathin nanosheets and their corresponding selenide substrates prepared in Examples 1 and 2, along with a comparison of the coordination numbers of the Sr-doped and pure low-crystalline NiFeOOH ultrathin nanosheets. Specifically, a and b represent the EXPS spectra and corresponding coordination number diagrams for Ni; c and d represent the EXPS spectra and corresponding coordination number diagrams for Fe.

[0029] Figure 7Polarization curves of Sr-doped low-crystalline NiFeOOH ultrathin nanosheets and low-crystalline NiFeOOH ultrathin nanosheets prepared in Examples 1 and 2, as well as commercial ruthenium oxide catalyst, in the alkaline oxygen evolution reaction.

[0030] Figure 8 The curves show a performance comparison between the Sr-doped low-crystallinity NiFeOOH ultrathin nanosheets prepared in Example 1 and a commercial ruthenium oxide catalyst in an anion exchange membrane water electrolysis hydrogen production system.

[0031] Figure 9 The stability test curve of the Sr-doped low-crystallinity NiFeOOH ultrathin nanosheets prepared in Example 1 in the anion exchange membrane water electrolysis hydrogen production system is shown. Detailed Implementation

[0032] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0033] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0034] The present invention will now be described in further detail with reference to the accompanying drawings: This invention provides a method for preparing Sr-doped low-crystallinity NiFeOOH ultrathin nanosheet electrocatalysts, the method comprising the following steps: Step S1: Prepare Sr-doped NiFe LDH precursor.

[0035] This step aims to construct a layered bimetallic hydroxide and introduce Sr element during the early stages of layered structure formation. Strontium, nickel, and iron salts are grown in a hydrothermal environment with the assistance of ammonium fluoride and urea to form an Sr-doped NiFe LDH precursor. This Sr-doped NiFe LDH precursor not only provides a metal ion source for the subsequent selenization reaction, but more importantly, the pre-doping of Sr in the LDH layer ensures its uniform distribution in the subsequent conversion products.

[0036] Step S2 involves reacting the Sr-doped NiFe LDH precursor with a selenium source via a solvothermal reaction to obtain a Sr-doped nickel-iron selenide precatalyst.

[0037] Specifically, the Sr-doped NiFe LDH precursor obtained in step S1 is placed in an aqueous solution containing a selenium source and a reducing agent (such as sodium borohydride) and subjected to solvothermal treatment again. During this process, Se atoms gradually replace oxygen atoms or hydroxide ions in the LDH layer, ultimately generating Sr-doped nickel-iron selenide precatalyst. In this process, the doping of Sr further weakens the metal-selenium bond, making the precursor more susceptible to structural dissociation and reconstruction under subsequent electrochemical conditions.

[0038] Step S3: The Sr-doped nickel-iron selenide precatalyst is reconstructed in situ by electro-oxidation under an alkaline oxygen evolution reaction environment to obtain the Sr-doped low-crystallinity NiFeOOH ultrathin nanosheet electrocatalyst.

[0039] Specifically, the Sr-doped nickel-iron selenide precatalyst obtained in step S2 is placed as the working electrode in an alkaline electrolyte, and an oxidation potential is applied for scanning. Under the action of a strong oxidation potential, the metal-selenium bond breaks, and Se element dissolves in the form of selenate, etc., while external O atoms or OH atoms are released. - The Se vacancies are rapidly filled, and the NiFeOOH active phase is reconstructed. Since Sr doping is accompanied by lattice distortion and vacancy formation during the electro-oxidation process, Sr-NiFeOOH ultrathin nanosheets with low crystallinity and rich in bimetallic vacancies are finally obtained.

[0040] Preferably, in step S1, the specific method for preparing the Sr-doped NiFe LDH precursor is as follows: Strontium salt, nickel salt, iron salt, ammonium fluoride and urea are dispersed in water and subjected to a solvothermal reaction.

[0041] Specifically, this step includes the following operations: 1) Disperse strontium salt, nickel salt, iron salt, ammonium fluoride and urea in deionized water according to a preset ratio, and stir magnetically to form a homogeneous mixed solution; 2) Transfer the above mixed solution to a reaction vessel for a solvothermal reaction. The temperature of the solvothermal reaction is 100℃-150℃, and the time is 15-20 hours.

[0042] The solvothermal reaction temperature is a key factor determining the crystallinity and morphology of the LDH precursor. If the reaction temperature is too low (e.g., below 100℃), the urea hydrolysis rate is slow, making it difficult to form a well-crystallized LDH layered structure, and the product may contain a large number of amorphous impurities, affecting the uniformity of the subsequent selenization reaction. If the reaction temperature is too high (e.g., above 150℃), although the reaction rate is accelerated, it may lead to excessive growth and aggregation of the LDH layered structure, or even trigger side reactions, destroying the morphology of the ultrathin nanosheets of the precursor and hindering ion exchange and structural transformation in the subsequent selenization process. Therefore, controlling the reaction temperature within the range of 100℃-150℃ can balance crystal nucleation and growth rates, obtaining a Sr-doped NiFe LDH precursor with uniform morphology and a clear layered structure.

[0043] The choice of reaction time also significantly affects the product structure. If the reaction time is too short (e.g., less than 15 hours), urea hydrolysis will be incomplete, and metal ions will not react sufficiently, resulting in low product yield and poor crystallinity, failing to form a continuous and complete layered structure. If the reaction time is too long (e.g., more than 20 hours), although it ensures a complete reaction, the excessively long reaction time may cause the nanosheets to agglomerate, reducing the specific surface area of ​​the product. Therefore, controlling the reaction time to 15-20 hours ensures complete precursor reaction and good crystallinity while maintaining the morphological characteristics of the ultrathin nanosheets, providing high-quality precursor materials for subsequent steps.

[0044] By optimizing the process parameters described above, a uniformly Sr-doped NiFeLDH precursor with a consistent morphology was successfully prepared in this step. This precursor possesses a regular layered structure, providing an ideal reaction template for subsequent selenization treatment and forming a crucial structural basis for obtaining a high-performance Sr-doped, low-crystallinity NiFeOOH ultrathin nanosheet electrocatalyst.

[0045] Preferably, in step S2, the step of performing a solvothermal reaction between the Sr-doped NiFe LDH precursor and the selenium source includes: dispersing the selenium source and sodium borohydride in water, adding the Sr-doped NiFe LDH precursor, and performing a solvothermal reaction at 170°C to 200°C.

[0046] In this process, sodium borohydride, as a strong reducing agent, can reduce selenium powder or sodium selenite to selenium ions. These selenium ions then combine with metal ions in the precursor to replace the original interlayer anions or hydroxide ions, generating Sr-doped nickel-iron selenide precatalyst.

[0047] More preferably, the choice of reaction temperature has a decisive influence on the crystallinity and morphology of the product during this process. If the reaction temperature is too low (e.g., below 170°C), the reduction reaction rate is slow, the concentration of selenium ions generated is insufficient, leading to incomplete selenization; if the reaction temperature is too high (e.g., above 200°C), the generated selenide nanosheets may undergo excessive growth or aggregation, destroying the ultrathin nanosheet structure of the precatalyst. Therefore, controlling the reaction temperature within the range of 170°C to 200°C ensures both the full progress of the selenization reaction and the maintenance of the morphological characteristics of the ultrathin nanosheets, providing an ideal precatalyst structure for subsequent in-situ electro-oxidation reconstruction.

[0048] Preferably, in step S3, the voltage range during the in-situ electro-oxidation reconstruction process is (0-1.15) V ~ (1.6-2.0) V vs. RHE; specifically, this step is the core step in inducing the formation of a low-crystalline active phase. On the one hand, the alkaline electrolyte (such as potassium hydroxide solution) provides the OH- required for the oxygen evolution reaction. - More importantly, the selection of the voltage scanning range is crucial. The starting potential is set at 0~1.15V vs. RHE, and the ending potential is set at 1.6~2.0V vs. RHE. This potential range covers the redox potential values ​​of NiFe-based materials to ensure deep oxidation reconstruction.

[0049] Therefore, this invention achieves precise control of the reconstruction process by precisely controlling the voltage range. If the termination potential is too low (e.g., below 1.6V vs. RHE), the applied oxidation driving force is insufficient, the metal-selenium bonds in the precursor are difficult to break completely, and the Se element cannot dissolve sufficiently, resulting in incomplete reconstruction and failure to form a defect-rich low-crystalline structure. If the termination potential is too high (e.g., above 2.0V vs. RHE), the excessively high anolyte potential will cause a violent oxygen evolution reaction, generating a large number of bubbles, and the resulting mechanical impact may cause the catalyst layer to peel off from the substrate. Therefore, controlling the termination potential within the range of 1.6~2.0V vs. RHE is a prerequisite for achieving deep reconstruction of the selenide precatalyst.

[0050] The innovative advantages of the method described above in this invention will be illustrated below through specific embodiments and verification experiments.

[0051] Example 1 A method for preparing Sr-doped low-crystalline NiFeOOH ultrathin nanosheets, comprising the following steps: Step 1, Preparation of Sr-doped NiFe LDH precursor: At room temperature, 575.8 mg of nickel nitrate hexahydrate, 200 mg of ferric nitrate nonahydrate, 26.5 mg of strontium nitrate, 370 mg of ammonium fluoride and 1.5 g of urea were dissolved in 40 mL of water. After magnetic stirring for 30 min, the mixture was reacted at 120 °C for 16 h. The resulting solution was centrifuged, washed with water and ethanol and dried under vacuum to obtain the strontium-doped NiFe LDH precursor.

[0052] Step 2, Preparation of Sr-doped NiFeSe2 ultrathin nanosheet precatalyst: 130 mg of sodium borohydride was dissolved in 30 mL of water, and 130 mg of selenium powder was added. After stirring for 1 hour under an argon atmosphere, 40 mg of Sr-doped NiFe LDH precursor was added. The mixture was magnetically stirred for 30 min and reacted at 180 °C for 16 hours. The resulting solution was centrifuged, washed with water and ethanol, and vacuum dried to obtain Sr-doped NiFeSe2 ultrathin nanosheet precatalyst.

[0053] Step 3, Preparation of Sr-doped low-crystalline NiFeOOH ultrathin nanosheets: The selenide precatalyst prepared above was dispersed in an alcohol solution of Nafion to prepare catalyst ink. An appropriate amount of ink was coated on the surface of the working electrode. After drying, the working electrode was placed in a 1 mol / L oxygen-saturated potassium hydroxide electrolyte. In-situ electrocatalytic oxidation was performed in the voltage range of 1.11V~1.7V vs. RHE at a scan rate of 50mV / s to obtain the reconstructed Sr-doped low-crystallinity NiFeOOH ultrathin nanosheet electrocatalyst, namely the strontium-doped low-crystallinity hydroxyl oxide nickel iron electrolysis water nanocatalyst.

[0054] Example 2 A method for preparing a low-crystallinity NiFeOOH ultrathin nanosheet catalyst differs from Example 1 in that Sr salt is not added, and the amounts of Ni salt and Fe salt are different.

[0055] Step 1, Preparation of NiFe LDH precursor: At room temperature, 604.8 mg of nickel nitrate hexahydrate, 210.1 mg of ferric nitrate nonahydrate, 370 mg of ammonium fluoride and 1.5 g of urea were dissolved in 40 mL of water. After magnetic stirring for 30 min, the mixture was reacted at 120 °C for 16 h. The resulting solution was centrifuged, washed with water and ethanol, and dried under vacuum to obtain the NiFe LDH precursor.

[0056] Step 2, Preparation of pure NiFeSe2 ultrathin nanosheet precatalyst: 130 mg sodium borohydride was dissolved in 30 mL of water, and 130 mg selenium powder was added. After stirring for 1 hour under an argon atmosphere, 40 mg NiFe LDH precursor was added, and the mixture was magnetically stirred for 30 min. The reaction was carried out at 180 °C for 16 hours. The resulting solution was centrifuged, washed with water and ethanol, and vacuum dried to obtain pure NiFeSe2 ultrathin nanosheet precatalyst.

[0057] Step 3, Preparation of low-crystallinity NiFeOOH ultrathin nanosheets: The above-prepared nickel-iron selenide ultrathin nanosheet precursor was dispersed in an alcohol solution of Nafion to prepare catalyst ink. An appropriate amount of ink was coated on the surface of the working electrode. After drying, the working electrode was placed in a 1 mol / L oxygen-saturated potassium hydroxide electrolyte. In-situ electrocatalytic oxidation was performed in the voltage range of 1.11V~1.70V vs. RHE at a scan rate of 50mV / s to obtain the reconstructed low-crystallinity NiFeOOH ultrathin nanosheet electrocatalyst.

[0058] The structure of the Sr-doped low-crystalline NiFeOOH ultrathin nanosheets prepared in the above embodiments was tested.

[0059] Test 1: Transmission electron microscopy and elemental analysis.

[0060] like Figure 1 Figures a and b, transmission electron microscopy images of strontium-doped nickel-iron selenide and pure nickel-iron selenide prepared in Examples 1 and 2, show that the obtained samples are all two-dimensional ultrathin nanosheet structures. Figure 2 Figures a and b, transmission electron microscopy images of the Sr-doped low-crystalline NiFeOOH ultrathin nanosheets and low-crystalline NiFeOOH prepared in Examples 1 and 2, show that this ultrathin nanosheet morphology can significantly increase the specific surface area of ​​the electrocatalyst, expose more active sites, and shorten the charge transport path and diffusion distance of reaction intermediates, thereby improving the kinetics of the electrocatalytic reaction. It is worth noting that... Figure 1 The Sr-doped nickel-iron selenide precatalyst shown also possesses an ultrathin nanosheet structure, while Figure 2 The product shown after in-situ electro-oxidation reconstruction retains this ultrathin nanosheet morphology. The reconstructed sample retains a two-dimensional ultrathin nanosheet structure, indicating that reconstruction does not change the nanosheet structure of the substrate selenide.

[0061] like Figure 3 As shown, the scanning transmission electron microscope-elemental analysis diagram of the Sr-doped low-crystalline NiFeOOH ultrathin nanosheets prepared in Example 1 shows that, Figure 3 In the image, 'a' represents a high-angle annular dark field image. Figure 3 In this context, 'b' represents the distribution analysis of Fe element. Figure 3 In this context, 'c' represents the distribution analysis of Ni elements. Figure 3 In this context, d represents the distribution analysis of O elements; Figure 3 In this context, 'e' represents the distribution analysis of Sr elements. Figure 3 It can be seen that Fe, Ni, O and Sr elements are uniformly distributed in the ultrathin nanosheets, and no obvious element agglomeration phenomenon is observed. This indicates that Sr element has been successfully doped into NiFeOOH ultrathin nanosheets.

[0062] Test 2: X-ray diffraction pattern analysis.

[0063] like Figure 4 The image shows a comparison of the X-ray diffraction spectra of the Sr-doped low-crystalline NiFeOOH ultrathin nanosheets and their corresponding selenide substrates prepared in Examples 1 and 2. Figure 4 It can be seen that the obtained Sr-doped low-crystalline NiFeOOH ultrathin nanosheets have the same phase structure as the original low-crystalline NiFeOOH ultrathin nanosheets, and both undergo a phase transition from high-crystalline to low-crystalline. Furthermore, Sr doping does not change the peak positions, indicating that Sr exists on the surface of the NiFeOOH ultrathin nanosheets in atomic form. The XRD pattern shows obvious broadened diffraction peaks, which contrasts sharply with the sharp diffraction peaks of the pre-catalyst. This peak broadening phenomenon indicates that the electrocatalyst prepared in this invention has low-crystalline characteristics, i.e., its long-range ordered structure is weak, containing a large number of lattice defects and amorphous regions. This low-crystalline structure typically has abundant defect sites, which can effectively regulate the electronic structure and coordination environment of the catalyst, optimize the adsorption energy barrier of reaction intermediates, and thus improve the catalytic reaction kinetics.

[0064] It is particularly important to note that the electrocatalyst prepared in this embodiment was obtained by in-situ electro-oxidation reconstruction of a Sr-doped nickel-iron selenide precatalyst. Specifically, the Sr-doped nickel-iron selenide precatalyst (such as...) Figure 4 As shown in Figure b), under alkaline oxygen evolution reaction conditions, the metal-selenium bond breaks and transforms into a metal-oxygen bond during in-situ electro-oxidation. Due to the large ionic radius of Sr, it can effectively weaken the binding strength of the metal-selenium bond in the crystal lattice, reduce the reconstruction energy barrier, and thus induce the formation of a defect-rich, low-crystallinity Sr-doped NiFeOOH active phase.

[0065] Test 3: X-ray electron spectroscopy analysis.

[0066] like Figure 5 , Figure 5 Comparison of X-ray photoelectron spectroscopy (XPS) spectra of Sr-doped low-crystalline NiFeOOH ultrathin nanosheets prepared in Examples 1 and 2. Figure 5 a and Figure 5As shown in section b, compared to NiFeOOH ultrathin nanosheets, the binding energies of the active metal elements Ni and Fe in Sr-doped low-crystalline NiFeOOH ultrathin nanosheets both shift positively, indicating a decrease in valence electron cloud density. From... Figure 5 c and Figure 5 As shown in Figure d, the position of the oxygen binding energy peak remains unchanged, but the number of metal-oxygen bonds increases significantly, indicating enhanced metal-oxygen covalentity. Furthermore, the increased adsorbed O content indicates enhanced affinity of oxygen-containing species in the Sr-doped low-crystalline NiFeOOH ultrathin nanosheets.

[0067] Test 4: Fine-grained structural analysis.

[0068] like Figure 6 The figures show extended X-ray absorption fine structure spectra and corresponding coordination number diagrams of the Sr-doped low-crystalline NiFeOOH ultrathin nanosheets and their corresponding selenide precatalysts prepared in Examples 1 and 2. Figure 6 It is evident that, compared to low-crystalline NiFeOOH ultrathin nanosheets, the coordination numbers of Ni-Ni and Fe-Fe in Sr-doped low-crystalline NiFeOOH ultrathin nanosheets are significantly lower, confirming that Sr-doped low-crystalline NiFeOOH ultrathin nanosheets are rich in bimetallic vacancies. This invention, through the introduction of Sr, induces lattice rearrangement during in-situ electro-oxidation reconstruction, thereby forming a unique structure rich in bimetallic vacancies. The presence of these bimetallic vacancies can effectively modulate the electronic structure of surrounding atoms, enhance the affinity between the metal atoms surrounding the vacancies and oxygen species, thereby improving the activity of the electrocatalytic oxygen evolution reaction. Simultaneously, Figure 6 The fitting results show that the metal-oxygen bond length of Sr-doped low-crystallinity NiFeOOH ultrathin nanosheets is shortened, which further illustrates that the enhanced metal-oxygen covalentity is beneficial to activating lattice oxygen, changing the reaction pathway, and thus reducing the theoretical overpotential.

[0069] Test 5: Performance testing and comparison of Sr-doped low-crystalline NiFeOOH ultrathin nanosheets and commercial ruthenium oxide catalysts in alkaline oxygen evolution reaction.

[0070] The Sr-doped low-crystalline NiFeOOH ultrathin nanosheets and low-crystalline NiFeOOH ultrathin nanosheets prepared in Examples 1 and 2, along with a commercial ruthenium oxide catalyst, were used as working electrodes, and their catalytic activity in the alkaline oxygen evolution reaction was determined in 1 mol / L oxygen-saturated potassium hydroxide solution. The polarization curves obtained at a rotation speed of 1600 rpm and a scan rate of 5 mV / s are shown below. Figure 7 As shown. At a current density of 100 mA / cm². 2At this time, the overpotential of the Sr-doped low-crystallinity NiFeOOH ultrathin nanosheet electrocatalyst is only 232 mV, which is significantly better than that of commercial ruthenium oxide catalysts. Simultaneously, at an overpotential of 232 mV, the current density of this catalyst is 53.8 times that of commercial ruthenium oxide catalysts, demonstrating its excellent catalytic activity in the alkaline water electrolysis anodic oxygen evolution reaction.

[0071] Test 6: Performance testing and comparison of Sr-doped low-crystallinity NiFeOOH ultrathin nanosheets in anion exchange membrane water electrolysis hydrogen production system.

[0072] The Sr-doped low-crystallinity NiFeOOH ultrathin nanosheet catalyst prepared in Example 1 was used as the working electrode, and its performance in an anion exchange membrane water electrolysis hydrogen production system was tested in 1 mol / L potassium hydroxide solution. The obtained linear sweep curve is shown below. Figure 8 As shown, at a tank voltage of 2V, the current density reaches as high as 2.75A / cm². 2 It is 4.4 times that of commercial ruthenium oxide catalysts. Furthermore, such as... Figure 9 As shown, at 500mA / cm 2 At a given current density, after 123 hours of stability testing, the decay rate was only 0.7 mV / h, demonstrating the excellent catalytic stability of this catalyst in anion exchange membrane water electrolysis hydrogen production systems. Therefore, the prepared Sr-doped low-crystallinity NiFeOOH ultrathin nanosheet electrocatalyst achieves both high catalytic activity and excellent structural stability in the field of anion exchange membrane water electrolysis hydrogen production, possessing significant advantages and broad prospects for industrial applications.

[0073] In summary, this invention prepares a Sr-doped nickel-iron selenide precatalyst via a solvothermal method, and then reconstructs it into Sr-NiFeOOH through in-situ electrooxidation in an alkaline water electrolysis oxygen evolution environment. Sr doping weakens the metal-selenium bond strength in the precatalyst, inducing a phase transition to generate a low-crystallinity Sr-NiFeOOH rich in bimetallic active sites. Simultaneously, it introduces bimetallic vacancies, enhances the covalent nature of the metal-oxygen bond, promotes the participation of lattice oxygen in the reaction, and reduces the theoretical overpotential. When used in the anodic reaction of anion exchange membrane water electrolysis for hydrogen production, this catalyst exhibits both excellent catalytic activity and stability, providing a new strategy for the industrialization of this technology.

[0074] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A strontium-doped low-crystallinity nickel-iron hydroxyl oxide electrolytic water-splitting nanocatalyst, characterized in that, The electrocatalyst was prepared by in-situ electrochemical reconstruction from Sr-doped nickel-iron selenide precatalyst. The electrocatalyst has an ultrathin nanosheet structure and is in a low-crystallinity state.

2. The strontium-doped low-crystallinity nickel-iron hydroxyl oxide electrolytic water nanocatalyst according to claim 1, characterized in that, The Sr-doped nickel-iron selenide precatalyst is Sr-NiFeSe2.

3. The strontium-doped low-crystallinity nickel-iron hydroxyl oxide electrolytic water nanocatalyst according to claim 1, characterized in that, This electrocatalyst operates at 100 mA / cm². 2 At current density, the overpotential is 232mV, and at 500mA / cm 2 At a current density of 0.7 mV / h, the system operated stably for 123 hours in an anion exchange membrane water electrolysis hydrogen production system.

4. A method for preparing a strontium-doped low-crystallinity nickel-iron hydroxyl oxide electrolytic water nanocatalyst, characterized in that, include: Preparation of Sr-doped NiFe LDH precursor; The Sr-doped NiFe LDH precursor was subjected to a solvothermal reaction with a selenium source to obtain an Sr-doped nickel-iron selenide precatalyst. Sr-doped nickel-iron selenide precatalyst was reconstructed in situ by electro-oxidation under an alkaline oxygen evolution reaction environment to obtain strontium-doped low-crystallinity nickel-iron hydroxyl oxide electrolytic water nanocatalyst.

5. The preparation method of the strontium-doped low-crystallinity nickel-iron hydroxyl oxide electrolytic water nanocatalyst according to claim 4, characterized in that, The preparation of the Sr-doped NiFe LDH precursor includes: Sr-doped NiFe LDH precursor was prepared by dispersing strontium salt, nickel salt, iron salt, ammonium fluoride and urea in water and carrying out a solvothermal reaction at 100-150℃ for 15-20 hours.

6. The preparation method of the strontium-doped low-crystallinity nickel-iron hydroxyl oxide electrolytic water nanocatalyst according to claim 5, characterized in that, The strontium salt is selected from at least one of strontium nitrate, strontium acetate, and strontium chloride; the nickel salt is selected from at least one of nickel nitrate, nickel chloride, nickel sulfate, and nickel acetylacetonate; the iron salt is selected from at least one of ferric nitrate, ferric chloride, ferric sulfate, and ferric acetylacetonate; and the selenium source is selected from selenium powder or sodium selenite. The ratio of the total molar amount of strontium salts, nickel salts, and iron salts to the molar amount of selenium source is 1:(0.1-1); the molar ratio of strontium salts to nickel salts and iron salts is (0.01-1):(4-9):

1.

7. The preparation method of the strontium-doped low-crystallinity nickel-iron hydroxyl oxide electrolytic water nanocatalyst according to claim 4, characterized in that, The process of solvothermal reaction between Sr-doped NiFe LDH precursor and selenium source includes: The selenium source and sodium borohydride were dispersed in water, and the Sr-doped NiFe LDH precursor was added. The reaction was carried out at 170℃~200℃ for 15~20 hours.

8. The method for preparing the strontium-doped low-crystallinity nickel-iron hydroxyl oxide electrolytic water nanocatalyst according to claim 4, characterized in that, In-situ electro-oxidative reconstruction is carried out in an alkaline electrolyte, potassium hydroxide or sodium hydroxide.

9. The method for preparing the strontium-doped low-crystallinity nickel-iron hydroxyl oxide electrolytic water nanocatalyst according to claim 4, characterized in that, The in-situ electro-oxidation reconstruction conditions are as follows: voltage range of (0-1.15)V~(1.6-2.0)V vs. RHE, and scan rate of 1mV / s~500mV / s.

10. The application of the strontium-doped low-crystallinity nickel-iron hydroxyl oxide electrolytic water nanocatalyst according to any one of claims 1-3 in the oxygen evolution reaction at the anode of an anion exchange membrane water electrolysis hydrogen production system.

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