Preparation method and application of nanoflower-shaped nickel-iron bimetallic electrocatalyst

Abstract

The application provides a preparation method and application of a nanoflower-shaped nickel-iron bimetallic electrocatalyst, and belongs to the technical field of water electrolysis. The preparation method comprises the following steps: step one, substrate pretreatment: ultrasonic cleaning is performed on the nickel foam; step two, preparation of a precursor solution: nickel salt and iron salt are added into deionized water and dissolved; then, citric acid and sodium bicarbonate are added into the solution, and stirring and mixing are uniformly performed to obtain the precursor solution; and step three, hydrothermal synthesis: the nickel foam treated in step one is immersed into the precursor solution in step two to perform hydrothermal reaction; after the reaction is completed, washing and drying are performed to obtain the nickel-iron bimetallic electrocatalyst. The nickel-iron bimetallic electrocatalyst prepared in the application has unique nanosheet structure characteristics, can expose rich electrochemical active sites, and simultaneously, the material has excellent charge transport capacity, and can realize high-efficiency oxygen evolution reaction at a lower overpotential.

Description

Technical Field

[0001] This invention relates to the field of water electrolysis technology, and more specifically, to a method for preparing and applying a nano-flower-shaped nickel-iron bimetallic electrocatalyst. Background Technology

[0002] With the continued growth of global energy demand and the increasingly severe environmental pollution and carbon emissions caused by the large-scale consumption of fossil fuels, the development of clean, efficient, and renewable alternative energy sources has become a critical issue that urgently needs to be addressed in the energy sector. Hydrogen energy, due to its high energy density, combustion product being only water (zero carbon emissions), wide availability, and ease of storage and transportation, is considered one of the most promising clean energy carriers for the future. Hydrogen production through water electrolysis, as an important green hydrogen production technology, has advantages such as a clean reaction process, high product purity, and strong system controllability. Furthermore, it can be coupled with fluctuating renewable energy sources such as solar and wind power to achieve green and sustainable hydrogen production, thus attracting widespread attention from academia and industry.

[0003] The water electrolysis process mainly includes two half-reactions: the hydrogen evolution reaction (HER) at the cathode and the oxygen evolution reaction (OER) at the anode. The OER involves a complex four-electron transfer process accompanied by the formation and transformation of multiple oxygen intermediates, resulting in a high energy barrier and extremely slow kinetics. This typically requires a high overpotential to drive the reaction, leading to low energy conversion efficiency and becoming a bottleneck restricting the overall efficiency of hydrogen production from water electrolysis. Therefore, developing OER electrocatalysts with low overpotential, high catalytic activity, excellent stability, and low cost is crucial for reducing electrolysis energy consumption and promoting the commercial application of water electrolysis technology.

[0004] Currently, noble metal-based materials are the most widely used oxygen evolution catalysts in industry. Although they exhibit excellent catalytic activity, they suffer from problems such as resource scarcity, high cost, and insufficient long-term operational stability, which seriously hinder their application in large-scale industrial hydrogen production. To address these issues, developing non-noble metal-based catalysts (such as Fe, Co, and Ni-based compounds) that are abundant, environmentally friendly, and inexpensive has become a key research focus in this field.

[0005] Among numerous non-precious metal catalytic materials, nickel-iron (NiFe)-based bimetallic electrocatalysts have attracted considerable attention due to their excellent catalytic performance and low cost. Numerous studies have shown that the electronic interactions and synergistic effects between nickel and iron can effectively modulate the electronic structure of the catalyst, optimize the adsorption / desorption behavior of reaction intermediates, and thus significantly reduce the energy barrier of the oxygen evolution reaction. Simultaneously, the introduction of iron helps to promote the activity of high-valence nickel species (such as Ni...). 3+ / Ni 4+The formation of hydroxyl radicals increases the concentration of oxygen vacancies on the catalyst surface, thereby enhancing the intrinsic catalytic activity and conductivity of the material. Furthermore, NiFe-based materials readily transform in situ into highly active hydroxyl oxides in alkaline electrolytes, further enhancing their catalytic performance.

[0006] Despite this, existing nickel-iron bimetallic electrocatalysts still face numerous technical challenges in practical applications: 1) Most NiFe-based compounds (such as layered double hydroxides, LDHs) have poor conductivity, limiting the rapid charge transfer at the electrode / electrolyte interface and resulting in high reaction impedance. 2) Traditional preparation methods (such as co-precipitation) often lead to severe material agglomeration and a small specific surface area, resulting in the burial of a large number of potential active sites, which cannot fully participate in the catalytic reaction. 3) During long-term electrolysis at high current densities, the catalyst is prone to agglomeration, shedding, or phase transformation, leading to activity decay. 4) In practical industrial applications, especially when using seawater or chlorinated industrial wastewater to produce hydrogen, high concentrations of chloride ions (Cl... - It is extremely easy to corrode the catalyst surface and even trigger competition for the chlorine evolution reaction (CER), leading to catalyst deactivation or substrate corrosion.

[0007] While existing technologies have made some improvements through doping and composite conductive substrates, they still fall short in constructing stable structures with abundant exposed active sites, highly conductive pathways, and strong corrosion resistance. For example, simple physical mixing is insufficient to achieve uniform bimetallic distribution at the atomic level, while complex multi-step synthesis processes increase cost and control difficulty.

[0008] Therefore, based on the aforementioned deficiencies in the existing technology, there is an urgent need to develop a method for preparing a nano-flower-shaped nickel-iron bimetallic electrocatalyst that is simple in preparation process, structurally stable, has excellent conductivity, high oxygen evolution catalytic activity, and strong corrosion resistance, so as to meet the actual needs of water electrolysis hydrogen production technology for efficient and long-life operation. Summary of the Invention

[0009] The purpose of this invention is to provide a method for preparing and applying a nano-flower-shaped nickel-iron bimetallic electrocatalyst, aiming to solve the problems of limited conductivity, low utilization of active sites, and insufficient structural stability in the above-mentioned background technology, thereby improving the catalytic activity and stability of the oxygen evolution reaction and increasing the efficiency of hydrogen production by water electrolysis.

[0010] This invention is achieved through a method for preparing a nano-flower-like nickel-iron bimetallic electrocatalyst, comprising the following steps: Step 1, Substrate Pretreatment: Ultrasonic cleaning is performed on the nickel foam to remove oil and oxides from the surface of the nickel foam; Step 2, Preparation of precursor solution: Dissolve nickel salt and iron salt in deionized water. Stir with a magnetic stirrer at room temperature for 5 minutes to dissolve them. Then add citric acid and sodium bicarbonate to the solution and stir to mix evenly to obtain the precursor solution. Step 3, hydrothermal synthesis: The foamed nickel treated in Step 1 is immersed in the precursor solution from Step 2 for hydrothermal reaction, specifically in a high-pressure reactor; after the reaction is completed, the product is washed and dried to obtain the nickel-iron bimetallic electrocatalyst. The washing refers to washing the product multiple times with deionized water.

[0011] Optionally, in step one, the ultrasonic cleaning specifically involves ultrasonically cleaning the nickel foam sequentially with dilute hydrochloric acid, deionized water, and anhydrous ethanol for 10–25 minutes.

[0012] Optionally, in step two, the molar ratio of the nickel salt to the iron salt is 1:(1-5); preferably, the nickel salt is nickel chloride hexahydrate and the iron salt is ferric chloride.

[0013] Optionally, in step two, the amount of citric acid used is 3 mmol relative to 60 mL of deionized water, and the amount of sodium bicarbonate used is 12 mmol.

[0014] Optionally, in step three, the temperature of the hydrothermal reaction is 120–180°C, and the isothermal treatment time is 4–10 hours.

[0015] Optionally, in step three, the drying is performed under vacuum at 60°C.

[0016] Another object of the present invention is to provide a nano-flower-like nickel-iron bimetallic electrocatalyst prepared by the preparation method, wherein the electrocatalyst is grown in situ on a nickel foam substrate and has a flower-like structure assembled from nanosheets.

[0017] Another objective of this invention is to provide the application of the aforementioned nano-flower-shaped nickel-iron bimetallic electrocatalyst in the oxygen evolution reaction of water electrolysis, wherein the electrocatalyst is used as the anode in an alkaline electrolyte to carry out the oxygen evolution reaction. The specific operating steps are as follows: Step a: Use a certain area of ​​nano-flower-shaped nickel-iron bimetallic electrocatalyst as the working electrode, a platinum sheet as the counter electrode, and an Hg / HgO electrode as the reference electrode to construct a three-electrode electrochemical testing system. Place the above electrode system in an alkaline electrolyte of a certain concentration. Step b: Perform linear sweep voltammetry using an electrochemical workstation, record the relationship curve between current density and potential, and calculate the overpotential and Tafel slope to evaluate the catalytic activity of the catalyst in the oxygen evolution reaction. Step c: Electrochemical impedance spectroscopy is used to test the interfacial charge transfer impedance of the catalyst to evaluate its charge transport capability; Step d: Cyclic voltammetry is used to test cyclic voltammetry curves at different scan rates in the non-Radida interval. The electrochemical active surface area of ​​the catalyst is further estimated by calculating the double layer capacitance in order to evaluate the degree of exposure of the active sites of the catalyst. Step e: The catalyst is subjected to long-term stability testing using a constant current method or a constant potential method, and the relationship between potential or current and time is recorded to evaluate the oxygen evolution reaction stability and durability of the catalyst.

[0018] In step a, the working electrode size is 1cm × 0.5cm; the electrolyte temperature is 20–30℃. In step b, the scan rate of the linear sweep voltammetry test is 1–10mV / s, preferably 5mV / s; the test potential range is 1.2–1.8V (vs. RHE). In step c, the frequency range of the electrochemical impedance spectroscopy test is 0.01Hz–100kHz. In step d, cyclic voltammetry is used within the non-Radida potential range, with a scan rate of 20–100mV / s. The double-layer capacitance is calculated based on the difference in current density at different scan rates, and the electrochemical active surface area of ​​the catalyst is further estimated. In step e, the long-term stability test uses a constant current test, and the test time is 10–100h.

[0019] Optionally, the alkaline electrolyte is selected from the following components: 1.0 mol / L KOH solution, or a mixed electrolyte composed of 1.0 mol / L KOH and 0.5 to 2.0 mol / L NaCl.

[0020] Optionally, the electrocatalyst is used as an anode catalyst in a two-electrode complete water electrolysis system (with long-term stability testing using the constant current method) or an anion exchange membrane water electrolysis device (with long-term stability testing to evaluate its operational stability and durability in the AEM water electrolysis process).

[0021] The present invention provides a method for preparing and applying a nano-flower-like nickel-iron bimetallic electrocatalyst, which has the following beneficial effects: This invention utilizes a simple one-step hydrothermal method to prepare a nickel-iron bimetallic electrocatalyst with a three-dimensional nanoflower-like structure. This structure not only significantly enhances the activity and kinetics of the oxygen evolution reaction through the bimetallic synergistic effect and abundant active sites, but also possesses excellent conductivity, structural stability, and resistance to chloride ion corrosion. Thus, it exhibits extremely high catalytic efficiency, environmental adaptability, and large-scale application potential in the field of alkaline water electrolysis for hydrogen production.

[0022] Other features and advantages of the invention will become clear from the following detailed description of exemplary embodiments of the invention with reference to the accompanying drawings. Attached Figure Description

[0023] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments of the invention and, together with their description, serve to explain the principles of the invention.

[0024] Figure 1 This is a scanning electron microscope (SEM) image of the nickel-iron bimetallic electrocatalyst prepared in Example 1 of the present invention; Figure 2 Linear sweep voltammetry (LSV) curves of the test examples of Example 2 and Comparative Examples 1, 2 and 3 of the present invention after iR compensation in 1.0 mol / L KOH electrolyte; Figure 3 Tafel slope diagrams for test examples of Embodiment 2 and Comparative Examples 1, 2, and 3 of the present invention; Figure 4 The electrochemical impedance spectroscopy (EIS) spectra of the test examples of Example 2 and Comparative Examples 1, 2 and 3 of this invention are shown. Figure 5 This is a comparison chart of the electrochemical active surface area (ECSA) of test examples from Example 2 and Comparative Examples 1, 2, and 3 of the present invention. Figure 6 This is a comparison of linear sweep voltammetry (LSV) curves in alkaline electrolytes (1M KOH + xM NaCl) with different concentrations of sodium chloride (NaCl) added, as shown in Example 1 of the present invention. Figure 7 The graphs show the long-term stability test results of Example 1 of the present invention in 1.0 mol / L KOH electrolyte and 1.0 mol / L KOH + 1.0 mol / L NaCl mixed electrolyte. Figure 8 This is a long-term stability test diagram of Example 1 of the present invention as an anode catalyst applied to a two-electrode total water splitting system; Figure 9 This is a schematic diagram of the physical connection of the water electrolysis device applied to the anion exchange membrane (AEM) in Embodiment 1 of the present invention. Detailed Implementation

[0025] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0026] Example 1 This embodiment provides a method for preparing a nano-flower-like nickel-iron bimetallic electrocatalyst, which is prepared by in-situ growth using a hydrothermal method, and specifically includes the following steps: Step 1: Substrate pretreatment: Take an appropriate amount of nickel foam and use sufficient dilute hydrochloric acid, deionized water and anhydrous ethanol in sequence for ultrasonic cleaning to thoroughly remove oil and oxides from the surface of the nickel foam, and then take it out for later use. Step 2, Preparation of precursor solution: Accurately weigh 0.713g nickel chloride hexahydrate and 0.487g ferric chloride, add them to a beaker containing 60mL deionized water, and stir magnetically at room temperature until completely dissolved; Step 3, Introduction of complexing and precipitating agents: Under continuous stirring, add 0.576g of citric acid and 1.008g of sodium bicarbonate to the solution obtained in Step 2 in sequence, and continue to stir magnetically for 5min to mix them evenly to obtain the precursor solution. Step 4, hydrothermal reaction: The pretreated nickel foam from Step 1 is immersed in the precursor solution obtained in Step 3, and then transferred to a hydrothermal reactor. The reaction is carried out at a constant temperature of 160°C for 6 hours. After the reaction is completed, the substrate is naturally cooled to room temperature to obtain a substrate with brown product attached to the surface. Step 5, Washing and Drying: Take out the substrate obtained in Step 4, wash it repeatedly with deionized water several times to remove residual free ions on the surface, and then place it in a vacuum drying oven and dry it at 60°C for 12 hours to obtain the nickel-iron bimetallic electrocatalyst.

[0027] The morphology of the nickel-iron bimetallic electrocatalyst prepared in this embodiment was characterized, and its scanning electron microscope (SEM) image is shown below. Figure 1 As shown. By Figure 1 As can be seen, this nickel-iron bimetallic electrocatalyst is grown in situ on a nickel foam substrate and exhibits a three-dimensional flower-like microstructure assembled from interconnected nanosheets. This unique flower-like structure can effectively expose more catalytic active sites and promote electrolyte penetration and gas release.

[0028] Comparative Example 1 This comparative example provides a method for preparing a single-supported iron catalyst, used for comparison with Example 1 to verify the necessity of the synergistic effect of nickel-iron bimetallic catalysts. The preparation steps are as follows: Step 1: Substrate pretreatment: Take an appropriate amount of nickel foam and use sufficient dilute hydrochloric acid, deionized water and anhydrous ethanol in sequence for ultrasonic cleaning to thoroughly remove oil and oxides from the surface of the nickel foam, and then take it out for later use. Step 2, Preparation of precursor solution: Accurately weigh 0.487g of ferric chloride and add it to a beaker containing 60mL of deionized water. Stir magnetically continuously at room temperature until completely dissolved. Step 3, Introduction of complexing and precipitating agents: Under continuous stirring, add 0.576g of citric acid and 1.008g of sodium bicarbonate to the solution obtained in Step 2 in sequence, and continue to stir magnetically for 5min to mix them evenly to obtain the precursor solution. Step 4, hydrothermal reaction: The pretreated nickel foam from Step 1 is immersed in the precursor solution obtained in Step 3, and then transferred to a hydrothermal reactor. The reaction is carried out at a constant temperature of 160°C for 6 hours. After the reaction is completed, the substrate is naturally cooled to room temperature to obtain a substrate with brown product attached to the surface. Step 5, Washing and Drying: Take out the substrate obtained in Step 4, wash it repeatedly with deionized water several times to remove residual free ions on the surface, and then place it in a vacuum drying oven and dry it at 60°C for 12 hours to obtain the single supported iron catalyst.

[0029] The difference between this comparative example and Example 1 is that nickel chloride hexahydrate was not added in step two, meaning the precursor solution did not contain a nickel source. The catalyst prepared by this comparative example can be used to evaluate the catalytic performance of a single iron component under the same preparation conditions, thereby demonstrating in subsequent electrochemical tests the key role of the "nickel-iron bimetallic" combination in Example 1 in enhancing the activity of the oxygen evolution reaction (OER).

[0030] Comparative Example 2 This comparative example provides a method for preparing a single-supported nickel catalyst, used for comparison with Example 1 to further verify the necessity of the synergistic effect of nickel-iron bimetallic catalysts. The preparation steps are as follows: Step 1: Substrate pretreatment: Take an appropriate amount of nickel foam and use sufficient dilute hydrochloric acid, deionized water and anhydrous ethanol in sequence for ultrasonic cleaning to thoroughly remove oil and oxides from the surface of the nickel foam, and then take it out for later use. Step 2, Preparation of precursor solution: Accurately weigh 0.713g of nickel chloride hexahydrate and add it to a beaker containing 60mL of deionized water. Stir magnetically continuously at room temperature until completely dissolved. Step 3, Introduction of complexing and precipitating agents: Under continuous stirring, add 0.576g of citric acid and 1.008g of sodium bicarbonate to the solution obtained in Step 2 in sequence, and continue to stir magnetically for 5min to mix them evenly to obtain the precursor solution. Step 4, hydrothermal reaction: The pretreated nickel foam from Step 1 is immersed in the precursor solution obtained in Step 3, and then transferred to a hydrothermal reactor. The reaction is carried out at a constant temperature of 160°C for 6 hours. After the reaction is completed, the substrate is naturally cooled to room temperature to obtain a substrate with brown product attached to the surface. Step 5, Washing and Drying: Take out the substrate obtained in Step 4, wash it repeatedly with deionized water several times to remove residual free ions on the surface, and then place it in a vacuum drying oven and dry it at 60°C for 12 hours to obtain the single-supported nickel catalyst.

[0031] The difference between this comparative example and Example 1 is that ferric chloride was not added in step two, meaning that the precursor solution did not contain an iron source. The catalyst prepared by this comparative example can be used to evaluate the catalytic performance of a single nickel component under the same preparation conditions, thus forming a complete chain of evidence with Example 1 and Comparative Example 1 in subsequent electrochemical tests, fully demonstrating the key role of the "nickel-iron bimetallic" combination in Example 1 in enhancing the activity of the oxygen evolution reaction (OER).

[0032] Comparative Example 3 This comparative example provides a blank nickel foam substrate for comparison with Example 1, Comparative Example 1, and Comparative Example 2, to verify the necessity of in-situ growth of a nickel-iron bimetallic catalyst on the surface of nickel foam for improving catalytic performance. The preparation steps are as follows: Substrate pretreatment: Take an appropriate amount of nickel foam and ultrasonically clean it in sequence with sufficient dilute hydrochloric acid, deionized water and anhydrous ethanol to thoroughly remove oil and oxides from the surface of the nickel foam. Then take it out for later use to obtain the blank nickel foam substrate.

[0033] The difference between this comparative example and Example 1 is that no precursor solution preparation or hydrothermal reaction steps were performed; only the nickel foam underwent cleaning pretreatment. This comparative example can be used to evaluate the oxygen evolution reaction (OER) activity of the pure nickel foam substrate itself. In subsequent electrochemical tests, it was used as a blank control group, which can intuitively reflect the decisive role of the "nanoflower-like nickel-iron bimetallic structure" in Example 1 in significantly improving catalytic activity and reducing overpotential.

[0034] Example 2 This embodiment provides a method for evaluating the catalytic activity and stability of the nickel-iron bimetallic electrocatalyst prepared in Example 1 for the oxygen evolution reaction (OER). The specific electrochemical testing and characterization steps are as follows: Step 1: Construction of the three-electrode system: A standard three-electrode system was used, with 1.0 mol / L KOH solution as the electrolyte at room temperature, and performance was evaluated using an electrochemical workstation. The catalyst prepared in Example 1 was cut into 1 cm × 0.5 cm pieces to serve as the working electrode, a mercury / mercury oxide (Hg / HgO) electrode as the reference electrode, and a platinum sheet as the counter electrode.

[0035] Step 2: Oxygen Evolution Reaction Activity Test: The polarization curves of the catalyst were tested using linear sweep voltammetry (LSV). The test parameters were set as follows: scan rate of 5 mV / s, potential range of 1.2–1.8 V (vs. RHE), and 95% iR compensation was applied to eliminate the influence of solution resistance. Based on the obtained polarization curves, the overpotential and Tafel slope of the catalyst were calculated to characterize its oxygen evolution reaction kinetics.

[0036] Step 3: Charge transfer impedance test: The charge transfer impedance at the catalyst interface was evaluated using electrochemical impedance spectroscopy (EIS). The test frequency range was set from 0.01 kHz to 100 kHz.

[0037] Step 4: Electrochemical Active Surface Area Assessment: Cyclic voltammetry (CV) was used to test the catalyst at scan rates of 20, 40, 60, 80, and 100 mV / s within the non-Radida potential range. By calculating the linear relationship between the current density difference and the scan rate at different scan rates, the double-layer capacitance (Cdl) was obtained, and the electrochemical active surface area (ECSA) of the catalyst was estimated to evaluate the exposure degree of its effective active sites.

[0038] Step 5, Chloride Ion Interference Resistance Test: To evaluate the catalyst's adaptability to complex water conditions (such as seawater), the catalyst prepared in Example 1 was placed in the following four mixed electrolytes for LSV testing: 1.0 mol / L KOH + 0.5 mol / L NaCl, 1.0 mol / L KOH + 1.0 mol / L NaCl, 1.0 mol / L KOH + 1.5 mol / L NaCl, and 1.0 mol / L KOH + 2.0 mol / L NaCl, to investigate the effect of different salinities on the oxygen evolution reaction performance.

[0039] Step Six: Long-term Stability and Corrosion Resistance Testing: The long-term stability of the catalyst was evaluated using the galvanostatic method (chronopotential method). Potential changes over time were recorded in 1.0 mol / L KOH soda ash solution and a mixed electrolyte of 1.0 mol / L KOH + 1.0 mol / L NaCl to verify the structural stability and corrosion resistance of the catalyst in both conventional alkaline and chlorine-containing alkaline environments.

[0040] Step 7: Application test of actual water electrolysis device: Using the catalyst prepared in Example 1 as the anode catalyst, an anion exchange membrane (AEM) water electrolysis device was assembled, and long-term operational stability test was conducted to evaluate the application potential and operational reliability of the catalyst in the actual industrial-grade water electrolysis hydrogen production process.

[0041] Combination Figures 2 to 5 The electrochemical test results show that the catalyst prepared in Example 1 exhibits excellent oxygen evolution reaction activity, low reaction impedance, and abundant electrochemical active sites. Figure 6 LSV tests at different NaCl concentrations showed that the catalyst maintained excellent corrosion resistance and long-term stability in chlorine-containing electrolytes. Figure 7 Stability tests further confirmed its anti-interference ability in the NaCl system; Figure 8 and Figure 9This visually demonstrates the excellent performance of the catalyst in the total water splitting system and the AEM water electrolysis device, proving that it has extremely high practical application value.

[0042] Test case of Comparative Example 1 This test example aims to evaluate the oxygen evolution reaction (OER) catalytic activity of the single supported iron catalyst prepared in Comparative Example 1, and compare it with the test results of Example 1 to verify the synergistic effect of nickel-iron bimetallic catalyst on improving catalytic performance. The specific electrochemical test procedures are as follows: Step 1: Construction of the three-electrode system: A standard three-electrode system was used, with 1.0 mol / L KOH solution as the electrolyte at room temperature, and performance was evaluated using an electrochemical workstation. The catalyst prepared in Comparative Example 1 was cut into 1 cm × 0.5 cm pieces to serve as the working electrode, a mercury / mercury oxide (Hg / HgO) electrode as the reference electrode, and a platinum sheet as the counter electrode.

[0043] Step 2: Oxygen Evolution Reaction Activity Test: The polarization curve of the catalyst was tested using linear sweep voltammetry (LSV). The test parameters were set as follows: scan rate of 5 mV / s, potential range of 1.2–1.8 V (vs. RHE), and 95% iR compensation was applied to eliminate the influence of solution resistance. Based on the obtained polarization curves, the overpotential and Tafel slope of the single supported iron catalyst were calculated.

[0044] Step 3: Charge transfer impedance test: The charge transfer impedance at the catalyst interface was evaluated using electrochemical impedance spectroscopy (EIS). The test frequency range was set from 0.01 kHz to 100 kHz.

[0045] Step 4: Electrochemical Active Surface Area Assessment: Cyclic voltammetry (CV) was used to test the catalyst at scan rates of 20, 40, 60, 80, and 100 mV / s within the non-Radida potential range. By calculating the linear relationship between the current density difference and the scan rate at different scan rates, the double-layer capacitance (Cdl) was obtained, and the electrochemical active surface area (ECSA) of the catalyst was estimated.

[0046] The test conditions described above are completely consistent with steps one through four in Example 2, with the only variable being the working electrode material (i.e., this test example uses the pure iron catalyst of Comparative Example 1, while Example 2 uses a nickel-iron bimetallic catalyst). By comparing the two sets of test data (such as LSV curves, Tafel slopes, EIS impedance, and ECSA), it can be intuitively and quantitatively demonstrated that, under the same preparation process, introducing nickel to form a bimetallic structure can significantly reduce the overpotential of the oxygen evolution reaction, accelerate the reaction kinetics, and expose more effective active sites.

[0047] Test case of Comparative Example 2 This test example aims to evaluate the oxygen evolution reaction (OER) catalytic activity of the single-supported nickel catalyst prepared in Comparative Example 2, and compare it with the test results of Example 1 to further verify the synergistic effect of nickel-iron bimetallic catalyst on improving catalytic performance. The specific electrochemical test procedures are as follows: Step 1: Construction of the three-electrode system: A standard three-electrode system was used, with 1.0 mol / L KOH solution as the electrolyte at room temperature, and performance was evaluated using an electrochemical workstation. The catalyst prepared in Comparative Example 2 was cut into 1 cm × 0.5 cm pieces to serve as the working electrode, a mercury / mercury oxide (Hg / HgO) electrode as the reference electrode, and a platinum sheet as the counter electrode.

[0048] Step 2: Oxygen Evolution Reaction Activity Test: The polarization curve of the catalyst was tested using linear sweep voltammetry (LSV). The test parameters were set as follows: scan rate of 5 mV / s, potential range of 1.2–1.8 V (vs. RHE), and 95% iR compensation was applied to eliminate the influence of solution resistance. Based on the obtained polarization curves, the overpotential and Tafel slope of the single-supported nickel catalyst were calculated.

[0049] Step 3: Charge transfer impedance test: The charge transfer impedance at the catalyst interface was evaluated using electrochemical impedance spectroscopy (EIS). The test frequency range was set from 0.01 kHz to 100 kHz.

[0050] Step 4: Electrochemical Active Surface Area Assessment: Cyclic voltammetry (CV) was used to test the catalyst at scan rates of 20, 40, 60, 80, and 100 mV / s within the non-Radida potential range. By calculating the linear relationship between the current density difference and the scan rate at different scan rates, the double-layer capacitance (Cdl) was obtained, and the electrochemical active surface area (ECSA) of the catalyst was estimated.

[0051] The test conditions described above are completely consistent with steps one through four in Example 2, with the only variable being the working electrode material (i.e., this test example uses the pure nickel catalyst of Comparative Example 2, while Example 2 uses a nickel-iron bimetallic catalyst). By comparing the two sets of test data, it can be intuitively and quantitatively demonstrated that, under the same preparation process, introducing iron to form a bimetallic structure can significantly reduce the overpotential of the oxygen evolution reaction, accelerate the reaction kinetics, and expose more effective active sites. Combined with the test results of Comparative Example 1 (pure iron), this test example and Comparative Example 1 together constitute a complete chain of evidence for "controlled variables," fully demonstrating the key role of the "nickel-iron bimetallic" combination in Example 1 in enhancing the activity of the oxygen evolution reaction (OER).

[0052] Comparative Example 3 This test example aims to evaluate the oxygen evolution reaction (OER) catalytic activity of the blank nickel foam substrate in Comparative Example 3 and compare it with the test results of Example 1 to verify the decisive role of in-situ growth of a nickel-iron bimetallic catalyst on the nickel foam surface in improving catalytic performance. The specific electrochemical test procedures are as follows: Step 1: Construction of the three-electrode system: A standard three-electrode system was used, with 1.0 mol / L KOH solution as the electrolyte at room temperature, and performance was evaluated using an electrochemical workstation. Specifically, the blank nickel foam prepared in Comparative Example 3 was cut into 1 cm × 0.5 cm pieces to serve as the working electrode, a mercury / mercury oxide (Hg / HgO) electrode as the reference electrode, and a platinum sheet as the counter electrode.

[0053] Step 2: Oxygen Evolution Reaction Activity Test: The polarization curve of blank nickel foam was tested using linear sweep voltammetry (LSV). The test parameters were set as follows: scan rate of 5 mV / s, potential range of 1.2–1.8 V (vs. RHE), and 95% iR compensation was applied to eliminate the influence of solution resistance. Based on the obtained polarization curves, the overpotential and Tafel slope of the blank nickel foam were calculated.

[0054] Step 3: Charge transfer impedance test: The charge transfer impedance of the blank nickel foam interface was evaluated using electrochemical impedance spectroscopy (EIS). The test frequency range was set from 0.01 kHz to 100 kHz.

[0055] Step 4: Electrochemical Active Surface Area Assessment: Cyclic voltammetry (CV) was used to perform tests at scan rates of 20, 40, 60, 80, and 100 mV / s within the non-Radida potential range. By calculating the linear relationship between the current density difference and the scan rate at different scan rates, the double-layer capacitance (Cdl) was obtained, and the electrochemical active surface area (ECSA) of the blank nickel foam was estimated.

[0056] The test conditions described above are completely consistent with steps one through four in Example 2, with the only variable being the working electrode material (i.e., blank nickel foam without any catalyst modification used in this test example). In subsequent electrochemical tests, this comparative example was used as a blank control group, which can directly eliminate the interference of the activity of the nickel foam substrate itself, thus strongly demonstrating the decisive role of the "nanoflower-like nickel-iron bimetallic structure" in Example 1 in significantly improving the catalytic activity of the oxygen evolution reaction (OER) and reducing the overpotential.

[0057] Test Result Analysis Combination Figure 2-8 The oxygen evolution reaction (OER) catalytic activity test results show that the nickel-iron bimetallic electrocatalyst prepared in Example 1 is significantly superior to the comparative examples in catalytic performance. Specifically, the catalyst in Example 1 achieves an OER catalytic activity of 10 mA·cm⁻¹. -2At the specified current density, the catalyst not only requires a lower overpotential but also exhibits a smaller Tafel slope and lower charge transfer impedance. Simultaneously, it displays a larger double-layer capacitance (Cdl) and a more abundant electrochemically active surface area (ECSA). These data clearly demonstrate that the nickel-iron bimetallic structure effectively exposes more electrocatalytic active sites, endowing the material with superior interfacial charge transport capabilities and faster oxygen evolution reaction kinetics. Furthermore, combined with the aforementioned tests, the catalyst demonstrates excellent long-term stability and operational performance in both chlorine-containing alkaline electrolytes and complete water electrolysis systems, proving its broad prospects for practical industrial water electrolysis applications.

[0058] The above embodiments of the present invention provide a method for preparing and applying a nano-flower-like nickel-iron bimetallic electrocatalyst, with the following main advantages: 1) The nickel-iron bimetallic electrocatalyst prepared in this invention possesses a unique three-dimensional nanoflower-like structure composed of interconnected ultrathin nanosheets, which significantly increases the specific surface area of ​​the catalyst, thereby exposing more electrochemical active sites. Electrochemical testing results show that this catalyst exhibits extremely low overpotential and a small Tafel slope in alkaline media, significantly superior to catalysts with single nickel or iron components, demonstrating that the synergistic effect between the nickel-iron bimetallic components can effectively optimize the reaction pathway and accelerate the oxygen evolution reaction kinetics.

[0059] 2) This nanoflower-like structure not only facilitates mass transport but also promotes rapid electron transfer, significantly reducing the charge transfer impedance at the electrode / electrolyte interface. Simultaneously, the in-situ growth of the catalyst on the nickel foam substrate ensures strong interaction and good conductive contact between the catalyst and the substrate, preventing catalyst detachment and thus endowing the material with excellent long-term cycling stability.

[0060] 3) In particular, the catalyst of this invention maintains excellent catalytic activity and structural integrity in mixed electrolytes containing chloride ions (such as NaCl), exhibiting good corrosion resistance and anti-interference ability. This characteristic overcomes the bottleneck of traditional catalysts being easily deactivated in complex water qualities (such as seawater), greatly expanding its application prospects in practical industrial water electrolysis for hydrogen production (especially seawater hydrogen production).

[0061] 4) This invention employs a one-step hydrothermal method for preparation, which features a simple process flow, mild reaction conditions (120–180°C), and eliminates the need for complex post-processing or expensive precious metal raw materials. This method is easy to scale up and control, exhibits good repeatability and controllability, and is suitable for large-scale industrial production, significantly reducing the material cost of hydrogen production via water electrolysis.

[0062] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for preparing a nano-flower-like nickel-iron bimetallic electrocatalyst, characterized in that, Includes the following steps: Step 1, Substrate Pretreatment: Ultrasonic cleaning of the nickel foam; Step 2, Preparation of precursor solution: Dissolve nickel salt and iron salt in deionized water; then add citric acid and sodium bicarbonate to the solution, stir and mix evenly to obtain the precursor solution; Step 3, hydrothermal synthesis: The foamed nickel treated in Step 1 is immersed in the precursor solution from Step 2 for hydrothermal reaction; after the reaction is completed, it is washed and dried to obtain the nickel-iron bimetallic electrocatalyst.

2. The preparation method of the nano-flower-like nickel-iron bimetallic electrocatalyst according to claim 1, characterized in that, In step one, the ultrasonic cleaning specifically involves: The nickel foam was ultrasonically cleaned sequentially with dilute hydrochloric acid, deionized water, and anhydrous ethanol for 10–25 minutes.

3. The preparation method of the nano-flower-like nickel-iron bimetallic electrocatalyst according to claim 1, characterized in that, In step two, the molar ratio of the nickel salt to the iron salt is 1:(1-5); The nickel salt is nickel chloride hexahydrate, and the iron salt is ferric chloride.

4. The preparation method of the nano-flower-like nickel-iron bimetallic electrocatalyst according to claim 3, characterized in that, In step two, the amount of citric acid used is 3 mmol relative to 60 mL of deionized water, and the amount of sodium bicarbonate used is 12 mmol.

5. The method for preparing the nano-flower-like nickel-iron bimetallic electrocatalyst according to claim 1, characterized in that, In step three, the temperature of the hydrothermal reaction is 120–180°C, and the isothermal treatment time is 4–10 hours.

6. The method for preparing the nano-flower-like nickel-iron bimetallic electrocatalyst according to claim 1, characterized in that, In step three, the drying is performed under vacuum at 60°C.

7. A nano-flower-like nickel-iron bimetallic electrocatalyst prepared by the preparation method according to any one of claims 1-6, characterized in that, The electrocatalyst is grown in situ on a nickel foam substrate and has a flower-like structure assembled from nanosheets.

8. The application of the nano-flower-like nickel-iron bimetallic electrocatalyst as described in claim 7 in the oxygen evolution reaction of water electrolysis, characterized in that, The electrocatalyst is used as the anode in an alkaline electrolyte to carry out the oxygen evolution reaction.

9. The application according to claim 8, characterized in that, The alkaline electrolyte is selected from the following components: A 1.0 mol / L KOH solution, or a mixed electrolyte consisting of 1.0 mol / L KOH and 0.5–2.0 mol / L NaCl.

10. The application according to claim 8, characterized in that, The electrocatalyst is used as an anode catalyst in a two-electrode total water electrolysis system or an anion exchange membrane water electrolysis device.

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