Method for preparing ferromagnetic NiFeCo / CNFs alkaline OER catalyst based on Joule heat

Abstract

The invention belongs to the field of electrochemical catalytic materials, and particularly relates to a method for preparing a ferromagnetic NiFeCo / CNFs alkaline OER catalyst based on Joule heat, which comprises the following steps: preparing a spinning solution, preparing CNFs precursor fibers by electrostatic spinning, and preparing the catalyst by Joule heat at different temperatures (600 / 800 / 1000 / 1200 / 1400 DEG C). Compared with other temperature samples, the NiFeCo / CNFs prepared by Joule heat at 1200 DEG C has the highest saturation magnetization intensity (13.7 emu / g) and the optimal alkaline OER performance, and the 30h stability retention rate exceeds 95%. The preparation method is simple and controllable, the material has high magnetism and high catalytic activity, a high-quality catalyst can be provided for the field of hydrogen production through water electrolysis, and the application prospect is good.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical catalytic materials, specifically relating to a method for preparing Ni-Fe-Co alloy catalysts (NiFeCo / CNFs) supported on ferromagnetic carbon nanofibers based on electrospinning technology and Joule heating. By controlling the high-temperature calcination temperature, the saturation magnetization and alkaline oxygen evolution reaction (OER) performance of the catalyst are optimized, and it can be applied to energy conversion devices such as water electrolysis for hydrogen production, metal-air batteries, and fuel cells. Background Technology

[0002] The oxygen evolution reaction (OER) is a core half-reaction in technologies such as water electrolysis for hydrogen production and renewable energy storage. However, the reaction involves four electron transfer steps, resulting in slow kinetics and requiring highly efficient catalysts to lower the reaction energy barrier. Currently, commercial OER catalysts mainly rely on precious metal-based materials such as Ir and Ru, which suffer from high cost, resource scarcity, and poor long-term stability, making large-scale application difficult.

[0003] To address this issue, researchers have developed non-precious metal-based catalysts (such as Ni, Fe, and Co-based oxides / alloys). However, these catalysts generally suffer from low electron conduction efficiency, insufficient exposure of active sites, and difficulty in balancing catalytic performance and stability. Recent studies have found that the ferromagnetism of catalysts can influence OER activity by modulating electron spin states and promoting charge transfer efficiency. However, a clear structure-activity relationship between intrinsic magnetism and OER performance has not yet been established in current technologies. Most non-precious metal catalysts have not maximized OER performance through optimizing magnetic parameters, resulting in limited catalytic efficiency. Secondly, most ferromagnetic catalysts optimize the adsorption energy of free radical intermediates by applying an external magnetic field, thereby reducing the overall OER reaction barrier. However, external magnetic fields range from hundreds of mT to several T, and are typically applied by placing large permanent magnets near the test electrodes or helical electromagnetic coils outside the reactor vessel. This raises safety concerns and limits process scalability. Therefore, it is more practically valuable to focus on the intrinsic magnetism of materials without applying an external magnetic field, and to leverage the spin polarization caused by the exchange interaction of the magnetic materials themselves to reduce the OER reaction energy barrier and accelerate the reaction kinetics without an external magnetic field.

[0004] Therefore, developing a non-precious metal catalyst that is simple to prepare, low in cost, and can achieve high OER activity and stability by controlling the intrinsic magnetic properties of the material has become a key requirement for promoting the industrialization of alkaline water electrolysis technology. Summary of the Invention

[0005] To address the problems of high cost, low electron conduction efficiency, and poor synergy between magnetic properties and catalytic performance in existing alkaline OER catalysts, this invention aims to provide a method for preparing ferromagnetic catalysts based on electrospinning. By adjusting the ratio of Ni, Fe, and Co metal components, a NiFeCo / CNFs catalyst with the highest saturation magnetization is prepared, achieving a synergistic effect between high saturation magnetization and OER performance, thus meeting the application requirements of alkaline water electrolysis and other scenarios.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: This invention utilizes a two-step core process of electrospinning and Joule heating to prepare Ni-Fe-Co alloy catalysts supported on ferromagnetic carbon nanofibers (CNFs). The specific steps are as follows: (1) Preparation of spinning solution: Polyvinylpyrrolidone (PVP) and metal salts (Ni salt, Fe salt, Co salt) are dissolved in N,N-dimethylformamide (DMF) and magnetically stirred at 300-500 r / min for 4-6 h at 20-30 °C to form a uniform precursor spinning solution; wherein, the mass concentration of PVP in the spinning solution is 18-20%, and the mass ratio of the total mass of metal salts to the mass of PVP is 0.08-0.12, and the spinning solution is denoted as S.

[0007] Furthermore, the Ni salt is one or more of nickel nitrate hexahydrate (Ni(NO3)2・6H2O), nickel acetate tetrahydrate (Ni(CH3COO)2·4H2O), and nickel chloride (NiCl2); the Fe salt is one or more of ferric nitrate nonahydrate (Fe(NO3)3・9H2O), ferric acetate (C4H7FeO5), and ferric chloride (FeCl3); the Co salt can be one or more of cobalt nitrate hexahydrate (Co(NO3)2・6H2O), cobalt carbonate (CoCO3), and cobalt chloride hexahydrate (CoCl2·6H2O); the molar ratio of the three selected metal salts is strictly controlled to be 1:1:1.

[0008] (2) Preparation of electrospun fiber membrane: The spinning solution S was injected into the syringe of the electrospinning equipment. The spinning parameters were set as follows: voltage 15~20 kV, feed rate 0.5~0.7 mL / h, receiving distance 15~20 cm, ambient temperature 20~25 ℃, relative humidity 30%~50%. The equipment was started to perform electrospinning. The white fiber membrane was collected, which is the precursor carbon nanofiber membrane, denoted as P-CNFs. The P-CNFs were placed in a tube furnace and pretreated at 200 ℃ at a heating rate of 4~6 ℃ / min in air atmosphere.

[0009] (3) Joule heating to prepare NiFeCo / CNFs: The pretreated P-CNFs were placed in the Joule furnace cavity and evacuated. The temperature was rapidly increased to 600~1400 ℃ at a rate of 200~500 ℃ / s, held for 10~20 s, and then naturally cooled to room temperature to obtain a metal-loaded carbon nanofiber film. The calcined film was ground and ultrasonically dispersed in a mixed solution of ethanol and Nafion. 200 μL of the electrode dispersion was slowly dropped onto a nickel foam substrate with an area of ​​1 × 1 square centimeter to obtain the target sample NiFeCo / carbon nanofiber, denoted as NiFeCo / CNFs.

[0010] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The invention employs a combination of electrospinning and rapid Joule heating, achieving synergistic optimization of the intrinsic magnetism of the catalyst and its OER catalytic activity by controlling the Joule heating temperature. The NiFeCo / CNFs-1200 catalyst prepared at 1200 ℃ exhibits the highest saturation magnetization and the best OER performance (10 mA / cm). 2 The overpotential is only 140 mV. This invention regulates catalytic performance by enhancing the intrinsic magnetism of the catalyst, without the need for an external magnetic field, making it more practically valuable.

[0011] (2) Compared with the traditional slow heating method of tube furnace, the Joule heat treatment of the present invention has a fast heating rate, which can suppress alloy grain growth, lock in highly active crystalline phases, and may introduce a large number of defect sites. The optimized NiFeCo / CNFs catalyst not only has high OER activity, but also excellent stability. Attached Figure Description

[0012] The invention will be further described below with reference to the accompanying drawings.

[0013] Figure 1 XRD of NiFeCo / CNFs prepared at different temperatures; Figure 2 Figure 1 shows (a) a TEM image of NiFeCo / CNFs-1400; (b) a TEM image of NiFeCo / CNFs-1200; (c) a TEM image of NiFeCo / CNFs-1000; (d) a TEM image of NiFeCo / CNFs-800; and (e) a TEM image of NiFeCo / CNFs-600. Figure 3 These are the hysteresis loops of NiFeCo / CNFs prepared at different temperatures; Figure 4 (a) shows the OER performance curves of NiFeCo / CNFs prepared at different temperatures, and (b) shows the OER performance curves at 10 mA / cm².-2 Overpotential and saturation magnetization (M) s Trend chart; Figure 5 (a) is a comparison of the VSM of G-NiFeCo / CNFs prepared by heating to 1200℃ in a tube furnace under an argon (Ar) atmosphere and NiFeCo / CNFs-1200 prepared by Joule heating; Figure (b) shows the OER performance curves of G-NiFeCo / CNFs-1200 and NiFeCo / CNFs-1200. Figure 6 This is a stability test chart for NiFeCo / CNFs-1200. Detailed Implementation

[0014] The present invention will now be further described with reference to specific embodiments. The following embodiments are intended to illustrate the present invention and not to further limit the present invention. Example 1

[0015] (1) Preparation of spinning solution: 2 g of polymer matrix polyvinylpyrrolidone (PVP, relative molecular weight of 1,300,000) and metal salts (0.08 g of nickel nitrate hexahydrate, 0.12 g of ferric nitrate nonahydrate, and 0.08 g of cobalt nitrate hexahydrate) were dissolved in 10 g of N,N-dimethylformamide (DMF) and magnetically stirred at 300 r / min for 6 h at 20~30℃ to form a uniform precursor spinning solution; wherein, the mass concentration of PVP in the spinning solution was 20%, and the ratio of the total mass of metal salts to the mass of PVP was 0.1, and the spinning solution was denoted as S.

[0016] (2) Preparation of electrospun fiber membrane: The spinning solution S was injected into the syringe of the electrospinning equipment. The spinning parameters were set as follows: voltage 20kV, feed rate 0.5mL / h, receiving distance 15cm, ambient temperature 20~25℃, relative humidity 30%~50%. The equipment was started to perform electrospinning. The white fiber membrane was collected, which is the precursor carbon nanofiber membrane, denoted as P-CNFs. The P-CNFs were placed in a tube furnace and heated to 200℃ at a heating rate of 5℃ / min in an air atmosphere. The temperature was maintained for 2 h for pretreatment.

[0017] (3) Joule heating to prepare NiFeCo / CNFs: The P-CNFs obtained above were placed in the Joule furnace cavity, and after vacuuming, the temperature was rapidly increased to 1400℃ at a rate of 300℃ / s, held for 15s, and then naturally cooled to room temperature to obtain a carbon nanofiber film loaded with metal. The calcined film was ground and ultrasonically dispersed in a mixed solution of ethanol and Nafion. 200μL of the ultrasonically dispersed solution was slowly dropped onto a nickel foam substrate with an area of ​​1×1 square centimeter. After drying, the target sample NiFeCo / carbon nanofiber was obtained, which was denoted as NiFeCo / CNFs-1400.

[0018] Example 2 (1) Preparation of spinning solution: 2 g of polymer matrix polyvinylpyrrolidone (PVP, relative molecular weight 1,300,000) and metal salts (0.08 g of nickel nitrate hexahydrate, 0.12 g of ferric nitrate nonahydrate, and 0.08 g of cobalt nitrate hexahydrate) were dissolved in 10 g of N,N-dimethylformamide (DMF) and magnetically stirred at 300 r / min for 6 h at 20~30℃ to form a uniform precursor spinning solution; wherein, the mass concentration of PVP in the spinning solution was 20%, and the ratio of the total mass of metal salts to the mass of PVP was 0.1, and the spinning solution was denoted as S.

[0019] (2) Preparation of electrospun fiber membrane: The spinning solution S was injected into the syringe of the electrospinning equipment. The spinning parameters were set as follows: voltage 20kV, feed rate 0.5mL / h, receiving distance 15cm, ambient temperature 20~25℃, relative humidity 30%~50%. The equipment was started to perform electrospinning. The white fiber membrane was collected, which is the precursor carbon nanofiber membrane, denoted as P-CNFs. The P-CNFs were placed in a tube furnace and heated to 200℃ at a heating rate of 5℃ / min in an air atmosphere. The temperature was maintained for 2 h for pretreatment.

[0020] (3) Joule heating to prepare NiFeCo / CNFs: The P-CNFs obtained above were placed in the Joule furnace cavity, and after vacuuming, the temperature was rapidly increased to 1200℃ at a rate of 300℃ / s, held for 15s, and then naturally cooled to room temperature to obtain a carbon nanofiber film loaded with metal. The calcined film was ground and ultrasonically dispersed in a mixed solution of ethanol and Nafion. 200μL of the ultrasonically dispersed solution was slowly dropped onto a nickel foam substrate with an area of ​​1×1 square centimeter. After drying, the target sample NiFeCo / carbon nanofiber was obtained, which was denoted as NiFeCo / CNFs-1200. Example 3

[0021] (1) Preparation of spinning solution: 2 g of polymer matrix polyvinylpyrrolidone (PVP, relative molecular weight 1,300,000) and metal salts (0.08 g of nickel nitrate hexahydrate, 0.12 g of ferric nitrate nonahydrate, and 0.08 g of cobalt nitrate hexahydrate) were dissolved in 10 g of N,N-dimethylformamide (DMF) and magnetically stirred at 300 r / min for 6 h at 20~30℃ to form a uniform precursor spinning solution; wherein, the mass concentration of PVP in the spinning solution was 20%, and the ratio of the total mass of metal salts to the mass of PVP was 0.1, and the spinning solution was denoted as S.

[0022] (2) Preparation of electrospun fiber membrane: The spinning solution S was injected into the syringe of the electrospinning equipment. The spinning parameters were set as follows: voltage 20kV, feed rate 0.5mL / h, receiving distance 15cm, ambient temperature 20~25℃, relative humidity 30%~50%. The equipment was started to perform electrospinning. The white fiber membrane was collected, which is the precursor carbon nanofiber membrane, denoted as P-CNFs. The P-CNFs were placed in a tube furnace and heated to 200℃ at a heating rate of 5℃ / min in an air atmosphere. The temperature was maintained for 2 h for pretreatment.

[0023] (3) Joule heating to prepare NiFeCo / CNFs: The P-CNFs obtained above were placed in the Joule furnace cavity, and after vacuuming, the temperature was rapidly increased to 1000℃ at a rate of 300℃ / s, held for 15s, and then naturally cooled to room temperature to obtain a carbon nanofiber film loaded with metal. The calcined film was ground and ultrasonically dispersed in a mixed solution of ethanol and Nafion. 200μL of the ultrasonically dispersed solution was slowly dropped onto a nickel foam substrate with an area of ​​1×1 square centimeter. After drying, the target sample NiFeCo / carbon nanofiber was obtained, which was denoted as NiFeCo / CNFs-1000.

[0024] Example 4 (1) Preparation of spinning solution: 2 g of polymer matrix polyvinylpyrrolidone (PVP, relative molecular weight 1,300,000) and metal salts (0.08 g of nickel nitrate hexahydrate, 0.12 g of ferric nitrate nonahydrate, and 0.08 g of cobalt nitrate hexahydrate) were dissolved in 10 g of N,N-dimethylformamide (DMF) and magnetically stirred at 300 r / min for 6 h at 20~30 °C to form a uniform precursor spinning solution; wherein, the mass concentration of PVP in the spinning solution was 20%, and the ratio of the total mass of metal salts to the mass of PVP was 0.1, and the spinning solution was denoted as S.

[0025] (2) Preparation of electrospun fiber membrane: The spinning solution S was injected into the syringe of the electrospinning equipment. The spinning parameters were set as follows: voltage 20 kV, feed rate 0.5 mL / h, receiving distance 15 cm, ambient temperature 20~25 ℃, relative humidity 30%~50%. The equipment was started to perform electrospinning. The white fiber membrane was collected, which is the precursor carbon nanofiber membrane, denoted as P-CNFs. The P-CNFs were placed in a tube furnace and heated to 200 ℃ at a heating rate of 5 ℃ / min in an air atmosphere. The temperature was maintained for 2 hours for pretreatment.

[0026] (3) Joule heating to prepare NiFeCo / CNFs: The P-CNFs obtained above were placed in the Joule furnace cavity, and after vacuuming, the temperature was rapidly increased to 800 ℃ at a rate of 300 ℃ / s, held for 15 s, and then naturally cooled to room temperature to obtain a carbon nanofiber film loaded with metal. The calcined film was ground and ultrasonically dispersed in a mixed solution of ethanol and Nafion. 200 μL of the ultrasonically dispersed solution was slowly dropped onto a nickel foam substrate with an area of ​​1×1 square centimeter. After drying, the target sample NiFeCo / carbon nanofiber was obtained, which was denoted as NiFeCo / CNFs-800. Example 5

[0027] (1) Preparation of spinning solution: 2 g of polymer matrix polyvinylpyrrolidone (PVP, relative molecular weight 1,300,000) and metal salts (0.08 g of nickel nitrate hexahydrate, 0.12 g of ferric nitrate nonahydrate, and 0.08 g of cobalt nitrate hexahydrate) were dissolved in 10 g of N,N-dimethylformamide (DMF) and magnetically stirred at 300 r / min for 6 h at 20~30 °C to form a uniform precursor spinning solution; wherein, the mass concentration of PVP in the spinning solution was 20%, and the ratio of the total mass of metal salts to the mass of PVP was 0.1, and the spinning solution was denoted as S.

[0028] (2) Preparation of electrospun fiber membrane: The spinning solution S was injected into the syringe of the electrospinning equipment. The spinning parameters were set as follows: voltage 20 kV, feed rate 0.5 mL / h, receiving distance 15 cm, ambient temperature 20~25 ℃, relative humidity 30%~50%. The equipment was started to perform electrospinning. The white fiber membrane was collected, which is the precursor carbon nanofiber membrane, denoted as P-CNFs. The P-CNFs were placed in a tube furnace and heated to 200℃ at a heating rate of 5℃ / min in an air atmosphere. The temperature was maintained for 2 h for pretreatment.

[0029] (3) Joule heating to prepare NiFeCo / CNFs: The P-CNFs obtained above were placed in the Joule furnace cavity, and after vacuuming, the temperature was rapidly increased to 600 ℃ at a rate of 300 ℃ / s, held for 15 s, and then naturally cooled to room temperature to obtain a carbon nanofiber film loaded with metal. The calcined film was ground and ultrasonically dispersed in a mixed solution of ethanol and Nafion. 200 μL of the ultrasonically dispersed solution was slowly dropped onto a nickel foam substrate with an area of ​​1 × 1 square centimeter. After drying, the target sample NiFeCo / carbon nanofiber was obtained, which was denoted as NiFeCo / CNFs-600. Example 6

[0030] (1) Preparation of spinning solution: 2 g of polymer matrix polyvinylpyrrolidone (PVP, relative molecular weight 1,300,000) and metal salts (0.08 g of nickel nitrate hexahydrate, 0.12 g of ferric nitrate nonahydrate, and 0.08 g of cobalt nitrate hexahydrate) were dissolved in 10 g of N,N-dimethylformamide (DMF) and magnetically stirred at 300 r / min for 6 h at 20~30 °C to form a uniform precursor spinning solution; wherein, the mass concentration of PVP in the spinning solution was 20%, and the ratio of the total mass of metal salts to the mass of PVP was 0.1, and the spinning solution was denoted as S.

[0031] (2) Preparation of electrospun fiber membrane: The spinning solution S was injected into the syringe of the electrospinning equipment. The spinning parameters were set as follows: voltage 20 kV, feed rate 0.5 mL / h, receiving distance 15 cm, ambient temperature 20~25 ℃, relative humidity 30%~50%. The equipment was started to perform electrospinning. The white fiber membrane was collected, which is the precursor carbon nanofiber membrane, denoted as P-CNFs. The P-CNFs were placed in a tube furnace and heated to 200 ℃ at a heating rate of 5 ℃ / min in an air atmosphere. The temperature was maintained for 2 hours for pretreatment.

[0032] (3) Preparation of NiFeCo / CNFs by heating in a tube furnace: The P-CNFs obtained above were placed in the tube furnace cavity and slowly heated to 1200 ℃ in an Ar atmosphere at a heating rate of 5 ℃ / s. The temperature was held for 2 h and then naturally cooled to room temperature to obtain a carbon nanofiber film loaded with metal. The calcined film was ground and ultrasonically dispersed in a mixed solution of ethanol and Nafion. 200 μL of the ultrasonically dispersed solution was slowly dropped onto a nickel foam substrate with an area of ​​1×1 square centimeter. After drying, the target sample NiFeCo / carbon nanofiber was obtained, which was denoted as G-NiFeCo / CNFs-1200.

[0033] The performance of the electrocatalyst was evaluated using a three-electrode system (working electrode: catalyst supported on a nickel foam matrix, reference electrode: Hg / HgO electrode, counter electrode: graphite rod) with 1 MkOH solution (pH = 14) as the electrolyte. The electrocatalyst was tested using linear sweep voltammetry (LSV, scan rate 5 mV / s) on a Chenhua CHI760E electrochemical workstation in the voltage range of 0.9–1.9 V vs. RHE.

[0034] Table 1: Performance comparison of NiFeCo / CNFs catalysts prepared at different Joule heating temperatures

[0035] Table 2: Comparison of catalyst performance between Joule heating and tubular furnace methods (Examples 2 and 6)

[0036] Figure 1 The XRD patterns of the catalysts prepared in Examples 1-5 are obtained by X-ray diffraction analysis. The peaks at 44°, 51.4°, and 75.2° correspond to the face-centered cubic (PDF#04-006-6387) structure of Ni, respectively, and the peaks at (111), (200), and (220) planes. Notably, all diffraction peaks exhibited a redshift after Fe / Co doping. This phenomenon is directly attributed to the larger atomic radii of Fe (0.126 nm) and Co (0.125 nm) compared to Ni (0.124 nm), and the increased interplanar spacing, quantitatively verified by Bragg's law. Furthermore, the redshift of the XRD diffraction peaks of NiFeCo / CNFs-1000 is slightly greater than that of the diffraction peak at 1200 °C, indicating that the Ni lattice expansion caused by Fe and Co doping is more severe. Secondly, as the annealing temperature increased, the intensity of the diffraction peaks in the sample decreased when the temperature reached 1400 ℃. This is attributed to the increased thermal motion of metal atoms under high-temperature conditions, leading to a higher probability of atoms deviating from their equilibrium lattice positions. This deviation disrupts the strict periodicity of the atomic arrangement, causing a phase difference between the scattered waves of different atoms, resulting in a decrease in the signal intensity of the diffraction peaks, thus affecting the synergistic effect between ferromagnetic metals. The catalyst sample prepared at 1200 ℃ exhibited the highest XRD diffraction peak intensity, indicating that the sample prepared at 1200 ℃ has better crystallinity. This is beneficial for the synergistic optimization of the intrinsic magnetism of the catalyst by ferromagnetic metals. Furthermore, the spin polarization induced by exchange interactions in the intrinsic magnetism of the material can regulate the electronic spin state, atomic coordination environment, and electronic structure, thereby affecting the catalyst's adsorption / activation capacity for reactants and its electrocatalytic kinetics.

[0037] Figure 2 The images are TEM images of the catalysts prepared in Examples 1-5. Figure 2(a) is a TEM image of NiFeCo / CNFs-1400; Figure 2 (b) is a TEM image of NiFeCo / CNFs-1200; Figure 2 (c) TEM image of NiFeCo / CNFs-1000; Figure 2 (d) Transmission electron microscopy (TEM) image of NiFeCo / CNFs-800; Figure 2 (e) is a TEM image of NiFeCo / CNFs-600; as shown in the figure, the NiFeCo alloy particles are all loaded on carbon nanofibers, proving that the NiFeCo / CNFs catalyst prepared by the Joule heating method was successfully prepared.

[0038] Figure 3 The graphs show the hysteresis loops of the catalysts prepared in Examples 1-5. Analysis of the graphs reveals that NiFeCo / CNFs-1200 exhibits the strongest intrinsic magnetism, followed by NiFeCo / CNFs-1000, NiFeCo / CNFs-800, NiFeCo / CNFs-600, and NiFeCo / CNFs-1400. The strength of the intrinsic magnetism is attributed to enhanced magnetic atom coordination at higher annealing temperatures, which favors the increase of the Fe / Co oxidized state and Ni reduced state, thereby amplifying the spin-polarized electronic states near the Fermi level. These electronic states can modulate the adsorption / desorption energy of intermediates, and are related to M... s The trend is consistent.

[0039] Figure 4 (a) OER performance diagram of NiFeCo / CNFs, in which NiFeCo / CNFs-1200 is significantly better than NiFeCo / CNFs-1400, NiFeCo / CNF-1000, NiFeCo / CNFs-800 and NiFeCo / CNFs-600; Figure 4 (b) The NiFeCo / CNFs prepared at different temperatures were statistically analyzed at 10 mA / cm². -2 Overpotential and M s The numerical values ​​revealed that the NiFeCo / CNF electrocatalyst prepared by annealing at 1200 ℃ possessed higher OER activity than catalysts prepared by other annealing temperatures. Its performance was consistent with the M values ​​obtained from VSM testing. s The values ​​are positively correlated because choosing too low or too high an annealing temperature weakens the synergistic effect of magnetic elements. Specifically, if the temperature is too low, the synergistic effect between ferromagnetic metals cannot reach the expected level, while if the temperature is too high, it will exceed the Curie temperature of ferromagnetic metals, directly leading to a weakening of magnetism. As a result, the valence state of metal ions does not change, which weakens the spin state of the material near the Fermi level and thus affects the catalytic activity.

[0040] Figure 5(a) is the hysteresis loop diagram of the catalysts prepared in Examples 2 and 6. Analysis of the diagram shows that the magnetic properties produced by different heating methods vary. The M of NiFeCo / CNFs-1200 is... s The value is significantly stronger than that of G-NiFeCo / CNFs-1200; Figure 5 (b) shows the LSV performance comparison curves of NiFeCo / CNFs and G-NiFeCo / CNFs. Analysis of the figure clearly shows that the catalyst prepared using Joule heating exhibits significantly better performance than the catalyst prepared using a tube furnace. Due to the different heating rates, there are differences in molecular thermal motion and crystallinity, suggesting that rapid heating and cooling are beneficial to the magnetic synergistic effect between Fe and Co. The XRD patterns of samples prepared by both methods are predominantly face-centered cubic, but the actual contributor to the magnetic moment is the body-centered cubic phase of Fe. Furthermore, although the introduction of Co and Ni inhibits the nucleation and growth of the body-centered cubic phase, Co forms a strong exchange interaction with Fe, promoting an increase in the magnetic moment of Fe, thus contributing the majority of the magnetic moment. Samples prepared using a tube furnace exhibit relatively stable nucleation and crystallization due to the slow heating rate, resulting in slower grain growth and grain sizes ranging from 20 to 200 nm. Furthermore, both Co and Ni inhibit the body-centered cubic phase of Fe, thereby weakening the magnetic moment. In contrast, Joule heating inhibits grain growth (grain size <20 nm) due to rapid heating and cooling, while locking the body-centered cubic phase. Consequently, the inhibitory effects of Co and Ni on Fe are not significant, and the nucleation and growth of the body-centered cubic phase are not excessively suppressed. This promotes the exchange interaction between Fe and Co. Additionally, rapid quenching may generate numerous defects (point defects, lattice distortion), which can also positively impact the catalytic effect.

[0041] Figure 6 This is a stability test graph of the NiFeCo / CNFs-1200 catalyst at 60 mA / cm². -2 After 30 hours of continuous exposure, the material exhibited robust durability with an activity decay of <5%, indicating that the prepared NiFeCo / CNFs material possesses excellent stability. These test results confirm that the NiFeCo / CNFs prepared in this invention, due to its highest saturation magnetization, demonstrates optimal alkaline OER activity and stability, and can be used as a highly efficient non-precious metal catalyst in fields such as water electrolysis for hydrogen production.

[0042] The embodiments of the present invention are given for illustrative and descriptive purposes only, and are not intended to be exhaustive or to limit the invention to the forms disclosed. Many modifications and variations will be apparent to those skilled in the art. The embodiments were chosen and described in order to better illustrate the principles and practical application of the invention, and to enable those skilled in the art to understand the invention and to design various embodiments with various modifications suitable for a particular purpose.

Claims

1. A method for preparing ferromagnetic NiFeCo / CNFs alkaline OER catalyst based on Joule heating, characterized by: It comprises the following steps: (1) Dissolve polyvinylpyrrolidone polymer matrix, Ni salt, Fe salt and Co salt in an organic solvent, and stir to form a uniform precursor spinning solution; (2) Using electrospinning technology, the precursor spinning solution is spun into a precursor carbon nanofiber film, denoted as P-CNFs; (3) After pretreatment, the P-CNFs are placed in a joule furnace and subjected to rapid joule heat treatment under vacuum conditions, after rapid heating and short holding, and then naturally cooled to obtain a metal-loaded carbon nanofiber film; the calcined film is ground and ultrasonically dispersed in a solution, and the ultrasonically dispersed solution is dropped onto a nickel foam substrate to obtain a ferromagnetic NiFeCo / CNFs, denoted as ferromagnetic NiFeCo / CNFs alkaline OER catalyst; Wherein, the heating temperature of joule heat treatment is 600-1400 ℃, the heating rate is 200-500 ℃ / s, and the holding time is 10-20 s.

2. The method for preparing ferromagnetic NiFeCo / CNFs alkaline OER catalyst based on Joule heat according to claim 1, characterized in that: The Ni salt is one or more of nickel nitrate, nickel acetate and nickel chloride; the Fe salt is one or more of iron nitrate, iron acetate and iron chloride; the Co salt is one or more of cobalt nitrate, cobalt carbonate and cobalt chloride; and the organic solvent is N, N-dimethylformamide.

3. The method for preparing ferromagnetic NiFeCo / CNFs alkaline OER catalyst by Joule heating according to claim 1, characterized in that: The molar ratio of the three metal salts of Ni salt, Fe salt and Co salt is 1:1:

1.

4. The method for preparing ferromagnetic NiFeCo / CNFs alkaline OER catalyst by Joule heating according to claim 1, characterized in that: The mass concentration of the polymer matrix in the spinning solution is 18-20%, and the mass ratio of the total mass of the metal salt to the mass of PVP is 0.08-0.

12.

5. The method of claim 1, wherein the method of joule-heating preparation of a NiFeCo / CNFs ferromagnetic basic OER catalyst is characterized by: The process parameters of electrospinning in step (2) are as follows: spinning voltage 15-20 kV, spinning solution propelling rate 0.5-0.7 mL / h, and receiving distance 15-20 cm.

6. The method of claim 1, wherein the method of joule-heating preparation of a NiFeCo / CNFs ferromagnetic basic OER catalyst is characterized by: The pretreatment in step (3) is as follows: the obtained precursor carbon nanofiber film (P-CNFs) needs to be put into a tubular furnace and pretreated at an air atmosphere with a heating rate of 4-6 ℃ / min to 200 ℃.

7. The method of claim 1, wherein the method of joule heating preparation of NiFeCo / CNFs ferromagnetic basic OER catalyst is characterized by: The solution in step (3) is a mixed solution of Nafion with a concentration of 20% and ethanol with a concentration of 95%; the ultrasonic treatment time is 25-35 min, and the concentration of the P-CNFs dispersion liquid is 1.5 mg / mL.

8. A ferromagnetic NiFeCo / CNFs alkaline OER catalyst prepared by the method of any one of claims 1-7.

9. The ferromagnetic NiFeCo / CNFs alkaline OER catalyst of claim 8 is used in the electrolysis of water to produce hydrogen, metal-air batteries or fuel cells.

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