A method for improving self-reconstruction degree of electrolytic water catalyst by using magnetic field assistance, the catalyst prepared and application thereof

Abstract

The application belongs to the field of hydrogen production by electrolysis of water, and particularly relates to a method for improving self-reconstruction degree of a water electrolysis catalyst by using a magnetic field and a catalyst prepared by the method and application thereof. The method comprises the following steps: 1) taking ferrous salt, cobalt salt, sodium salt, nitrogen compound and organic metal compound, adding a solvent to mix them uniformly to obtain a hydrothermal reaction medium; 2) taking a substrate, cutting, cleaning and drying the substrate, immersing the substrate in the hydrothermal reaction medium to perform a hydrothermal reaction, and cleaning and drying the substrate to obtain an electrode sheet; and 3) assembling the electrode sheet into an electrolysis cell, performing magnetic field assisted activation, and obtaining an electrode material of the water electrolysis catalyst with high self-reconstruction degree. The catalyst prepared by the application can effectively reduce high overpotential and polarization intensity in an oxygen evolution reaction through high self-reconstruction, and has a low Tafel slope and high catalytic activity.

Description

Technical Field

[0001] This invention belongs to the field of hydrogen production by water electrolysis, specifically relating to a method for improving the self-reconstruction degree of a water electrolysis catalyst using magnetic field assistance, the resulting catalyst, and its application. Background Technology

[0002] To achieve large-scale hydrogen production, water electrolysis is a common method in the field, offering good sustainability and being environmentally friendly. The water electrolysis process involves two half-reactions: the hydrogen evolution reaction (HER) at the cathode and the oxygen evolution reaction (OER) at the anode. The OER reaction involves four electron transfer processes, and its slow reaction kinetics limit the overall rate of the water electrolysis reaction. Platinum and iridium, with their extremely high OER catalytic activity, have long been used to promote O-O bond breaking, accelerate electron transfer, and reduce energy consumption; however, they suffer from poor durability and high cost. Therefore, there is an urgent need to develop efficient and economical electrocatalysts.

[0003] Transition metal-based materials, particularly nickel-based materials, are well-suited for bonding with oxygen-related intermediates due to their unique electronic structure. Iron-cobalt-nickel ternary materials and their corresponding sulfides have attracted considerable attention as potential alternatives to noble metal catalysts due to their metalloid properties. However, these electrocatalysts are unstable, inevitably undergoing partial or complete oxidation during the initial activation of oxygen-induced oxidation (OER). The resulting hydroxyl oxides have proven to be the truly active phase for OER catalysis; this phenomenon, characterized by a dramatic change in surface properties, is known as surface self-reconstruction. In recent years, magnetic field-assisted electrocatalysis has also been considered an effective method to improve catalyst activity. A key factor in achieving superior catalytic performance is the ability to effectively enhance the surface self-reconstruction degree of the electrocatalyst under magnetic field assistance. Therefore, this invention purposefully designs and grows an array of iron-cobalt-nickel ternary sulfides on nickel foam using a one-step hydrothermal method, and applies an external magnetic field to promote the catalyst's self-reconstruction degree. Summary of the Invention

[0004] Based on the above, in order to solve the problems of slow reaction rate and insufficient catalytic performance of nickel-based materials in water electrolysis, this invention proposes a method to improve the self-reconstruction degree of water electrolysis catalysts using magnetic field assistance.

[0005] The purpose of this invention is:

[0006] I. Improve the catalytic performance of nickel-based materials;

[0007] II. Improve the self-reconfiguration degree of nickel-based materials;

[0008] III. Improve the intrinsic OER kinetics and overall performance of nickel-based materials in water electrolysis for hydrogen production.

[0009] To achieve the above objectives, the present invention adopts the following technical solution.

[0010] A method for improving the self-reconstruction degree of water electrolysis catalysts using magnetic field assistance.

[0011] The method includes:

[0012] 1) Take ferrous salt, cobalt salt, sodium salt, nitrogen compound, and organometallic compound, add solvent and mix evenly to obtain hydrothermal reaction medium;

[0013] 2) Take the substrate, cut it, clean it, and dry it. Immerse it in the hydrothermal reaction medium to carry out the hydrothermal reaction. After cleaning and drying, the electrode sheet is obtained.

[0014] 3) Assemble the electrode sheets into an electrolytic cell and perform magnetic field-assisted activation to obtain an electrolytic water catalyst electrode material with a high degree of self-reconfiguration.

[0015] As a preferred option

[0016] Step 1) The ferrous salt is ferrous sulfate;

[0017] The cobalt salt is cobalt nitrate, the sodium salt is sodium sulfide, the nitrogen compound is urea, and the organometallic compound is sodium citrate pentahydrate;

[0018] The molar ratio of ferrous sulfate, cobalt nitrate, sodium sulfide, urea, and sodium citrate pentahydrate is controlled as (0.01~0.1):(0.01~0.1):(0.5~1.5):(0.02~0.2):(0.001~0.01).

[0019] Based on this, the dosage of each component relative to ferrous sulfate is calculated as follows:

[0020] The amount of cobalt nitrate used is 0.12–12.0 g / g ferrous salt;

[0021] The amount of sodium sulfide used is 2.1–64.3 g / g ferrous salt;

[0022] The dosage of urea is 0.15–15.4 g / g ferrous salt;

[0023] The amount of sodium citrate pentahydrate used is 0.049–4.9 g / g ferrous salt.

[0024] More preferably,

[0025] Step 1) The ferrous salt is ferrous sulfate;

[0026] The cobalt salt is cobalt nitrate, and its dosage is 8.4–10.5 g / g ferrous salt;

[0027] The sodium salt is sodium sulfide, and its dosage is 14.0–42.1 g / g ferrous salt;

[0028] The nitrogen compound is urea, and its dosage is 0.43–4.3 g / g ferrous salt;

[0029] The organometallic compound is sodium citrate pentahydrate, and its dosage is 0.93–3.72 g / g ferrous salt.

[0030] As a preferred option

[0031] The solvent used in step 1) is water, and the amount used is 150-200 mL / g ferrous salt.

[0032] As a preferred option

[0033] Step 2) The substrate is nickel foam, cut to 8-10 cm. 2 .

[0034] As a preferred option

[0035] Step 2) The cleaning method is to ultrasonically clean the product sequentially in dilute hydrochloric acid, acetone and anhydrous ethanol for 15 to 20 minutes.

[0036] As a preferred option

[0037] The hydrothermal reaction described in step 2) is carried out at a constant temperature of 120–140 °C for 10–12 h.

[0038] As a preferred option

[0039] Step 3) The magnetic field assistance is used to complete CV activation at 10~50 mT.

[0040] As a preferred option

[0041] In step 3), the electrolytic cell uses the electrode sheet prepared in step 2) as the working electrode, sets up a counter electrode and a reference electrode to construct a three-electrode system, and uses an alkali metal hydroxide solution of 0.5 to 2.0 mol / L as the electrolyte.

[0042] A catalyst for water electrolysis.

[0043] Application of a water electrolysis catalyst

[0044] The water electrolysis catalyst is used in water electrolysis systems, either directly as an electrode or as a catalytic material on the electrode surface.

[0045] In this invention, a nickel-based catalyst is prepared by composite bonding of ferrous sulfate as the iron source, cobalt nitrate as the cobalt source, sodium sulfide as the sulfur source, and urea as the complexing agent onto nickel foam. Sulfur atoms have high electronegativity and a strong electron-withdrawing effect, which increases the electron cloud density of the delocalized π-bonds in the sulfur-containing rings, resulting in strong catalytic activity.

[0046] To further enhance the electrocatalytic activity of the material, iron was introduced into this system. 2+ It first occupied the octahedral position, and gradually occupied the Co position. 2+ The octahedral position and the decrease in particle diameter indicate low-spin Fe. 2+ The ionic radius is smaller than that of Co. 2+ Meanwhile, according to research by those skilled in the art, low-spin Fe 2+ It is easier to achieve the substitution of Ni element in Ni3S2 with the cooperation of Co element, thereby improving the overall resistivity of the catalytic material. Based on its response experiments using chronoamperometry and chronopotentialography, its high durability can be concluded. Synergistic effect with urea exposes more active sites in the material, reduces the Tafel slope, and increases the oxygen evolution reaction activity of the surface material. With the increase of iron content in the system, Co... 2+ The tetrahedral positions are occupied, while the particle diameter increases, indicating high-spin Fe... 2+ The ionic radius is greater than that of Co. 2+ This indicates that high-spin Fe 2+ The ionic radius is greater than that of low-spin Fe. 2+ However, when too much ferrous salt is used, the crystal purity decreases, and Fe... 2+ It occupies all octahedral positions and interacts with Co atoms in tetrahedral positions, resulting in Co... 2+ Peak shift. Due to the strong helical effect of cobalt, Fe... 2+ The peak intensity is weak or even indistinct, indicating that the signal is being shielded. Excess high-spin Fe 2+ The substitution effect creates a severe repulsion in the coordination environment, making it difficult for Co and Fe to replace Ni in Ni3S2. Characterization based on effective substitution revealed that the atomic ratio of Fe:Co:Ni was 1:1:10 according to SEM mapping results. XRD analysis showed that the peaks of the hydrothermal products highly matched the Ni3S2 peaks with no impurities. The trace amounts of Fe and Co had a negligible impact on the peak positions.

[0047] Compared to commercially available materials, the material prepared in this invention exhibits higher electrocatalytic activity. For example, Pt is composited onto C using the same hydrothermal method to prepare a Pt / C electrode (i.e., a Pt / C catalyst for water electrolysis) for comparison. The catalyst (i.e., the electrode) prepared in this invention has a slightly higher open-circuit voltage than the catalyst prepared by Pt / C (referred to as Pt / C electrocatalyst or Pt / C electrode). Since sulfides readily convert to hydroxyl groups during OER, experiments based on this point clearly show that the performance of the Pt / C catalyst degrades rapidly. Based on the charge-discharge polarization curves of the catalyst, it can be found that the catalyst of this invention has a smaller voltage gap, exhibiting excellent reversible oxygen redox capability. At the same charging current density, the catalyst of this invention requires a lower redox voltage than the Pt / C catalyst. Furthermore, in cycling tests, the catalyst of this invention exhibits good cycling stability.

[0048] This invention utilizes a magnetic field to improve the conversion rate of Ni3S2 on the electrode sheet and enhance the self-reconstruction degree of Ni3S2 into nickel hydroxide during activation. In application, magnets with their N and S poles aligned sequentially (i.e., the S pole of the magnet is close to the working electrode) are placed in the order of the magnetic field lines passing through the counter electrode and the working electrode. The high-energy field generated by the electromagnetic field causes interaction between the magnetic field and the active particles, preventing particle clustering. The presence of Co and Fe further promotes self-reconstruction and increases the number of active sites. Furthermore, the substitution of Ni in Ni3S2 by Co and Fe exposes more active sites. However, when the magnetic field strength is low, insufficient energy fails to promote uniform dispersion of the catalytically active components. Moreover, the catalytically active components deposited in the pores migrate outwards with the solution, further exacerbating the uneven distribution and leading to a decrease in electrode sheet activity. As the magnetic field strength increases, the specific pore volume of the product decreases and the pore size increases, which is beneficial for improving the catalytic activity of the product, resulting in finer particles, better dispersion, and an increased specific surface area of ​​the active components on the electrode sheet. In addition, characterization revealed that under excessive magnetic field strength, the dispersion of active components on the electrode sheet deteriorated, affecting the distribution of active components in the pores, resulting in a decrease in the specific surface area of ​​active components on the electrode sheet and a significant reduction in active centers, thereby leading to a decrease in the catalytic activity of the electrode sheet.

[0049] The beneficial effects of this invention are as follows:

[0050] (1) The method provided by this invention is simple, highly reproducible, and the reaction is controllable;

[0051] (2) The present invention can effectively improve the self-reconstruction degree of the catalyst, thereby significantly improving the catalytic performance;

[0052] (3) The catalyst prepared by the present invention can effectively reduce the high overpotential and polarization intensity in the oxygen evolution reaction, and has a low Tafel slope and high catalytic activity. Attached Figure Description

[0053] Figure 1 This is a schematic diagram of the electrode sheet in Example 1 undergoing a magnetic field-assisted self-reconfiguration process;

[0054] Figure 2 This is a scanning electron microscope (SEM) image of the electrode sheet in Example 1 after magnetic field-assisted self-reconstruction;

[0055] Figure 3 This is a transmission electron microscope (TEM) image of the electrode sheet in Example 1 after magnetic field-assisted self-reconstruction;

[0056] Figure 4 This is a schematic diagram of the activation process of the electrode sheet in Comparative Example 1 under conditions without a magnetic field.

[0057] Figure 5 The image shows a scanning electron microscope (SEM) image of the electrode sheet in Comparative Example 1 before activation.

[0058] Figure 6 The image shows a scanning electron microscope (SEM) image of the electrode sheet in Comparative Example 1 after self-reconstruction without magnetic field assistance.

[0059] Figure 7 This is a transmission electron microscope (TEM) image of the electrode sheet in Comparative Example 1 after self-reconstruction without magnetic field assistance;

[0060] Figure 8 The graph shows a comparison of the linear sweep voltammetry (LSV) curves of the electrode sheets in Example 1 and Comparative Example 1 under the conditions of self-reconstruction with and without magnetic field assistance.

[0061] Figure 9 This is a comparison chart of Tafel curves measured by the electrode sheets of Example 1 and Comparative Example 1 with and without magnetic field-assisted self-reconstruction. Detailed Implementation

[0062] The present invention will be further described clearly and in detail below with reference to specific embodiments and the accompanying drawings. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0063] Unless otherwise specified, all raw materials used in the embodiments of the present invention are commercially available or obtainable by those skilled in the art; unless otherwise specified, all methods used in the embodiments of the present invention are methods mastered by those skilled in the art.

[0064] Unless otherwise specified, when characterizing the electrode sheets prepared in the embodiments and / or comparative examples of this invention, the electrode sheets referred to are all water electrolysis catalyst products prepared by the complete preparation process of the current embodiment / comparative example.

[0065] Example 1

[0066] A method for improving the self-reconstruction degree of a water electrolysis catalyst using magnetic field assistance, the method comprising:

[0067] 1) Take 0.2 g ferrous sulfate, 1.68 g cobalt nitrate, 2.8 g sodium sulfide, 0.09 g urea, and 0.19 g sodium citrate pentahydrate, add 30 mL of water and mix well to obtain a hydrothermal reaction medium;

[0068] 2) Take nickel foam and cut it into rectangular pieces of 2 cm × 4 cm. Soak them in dilute hydrochloric acid, acetone and anhydrous ethanol in sequence for ultrasonic cleaning. After 15 min, dry them. Soak the nickel foam in a hydrothermal reaction medium and keep it at 120 ℃ for 12 h. After cleaning with deionized water and drying, the electrode sheet is obtained.

[0069] 3) Using an electrode sheet as the working electrode, an Hg / HgCl (saturated KCl) electrode as the reference electrode, a carbon rod as the counter electrode, and 1 mol / L KOH as the electrolyte, an electrolytic cell was assembled. Under a magnetic field strength of 10 mT, magnets with N and S poles (i.e., the S pole of the magnet is close to the working electrode) were placed in the order of passing through the counter electrode and the working electrode in the direction of the magnetic field lines. 30 cycles of CV activation were completed within 15 min.

[0070] The electrode sheet prepared in this example was characterized, and the SEM and TEM characterization results are shown in the appendix. Figure 2 , 3 .

[0071] The electrochemical performance of the water electrolysis catalyst (used as an electrode) prepared in this example was tested at room temperature using an electrochemical workstation (CHI 760D). A schematic diagram of the apparatus is attached. Figure 1 The electrolytic cell is a standard three-electrode system, and the calibration formula for the reversible hydrogen electrode (RHE) potential is: E vs·RHE =Measured value (vs. Hg / HgCl) + 0.2412 + 0.0591 pH. LSV and Tafel characterization results are attached. Figure 8 , 9 Furthermore, at 100 mA·cm -2 Cyclic experiments were conducted to observe whether cracks appeared on the electrode plates, and whether the current and voltage fluctuated. The current loss rate within 40 hours was characterized, and the voltage gap was also characterized.

[0072] The results are as follows.

[0073] Oxygen evolution overpotential (mV) Tafel slope (mV / dec) Current loss rate (%) Stable working hours (h) 372 48.9 10.9 106

[0074] The high-energy field generated by the electromagnetic field facilitates interaction between the magnetic field and the active particles, reducing the energy required for self-reconstruction and exposing more active sites. SEM and TEM images show some adhesion / agglomeration at the nanorod tips. The material exhibits clear lattice fringes, but a distinct layer of amorphous material forms on the outer surface; characterization identifies this material as hydroxyl metal oxides. The dense concentration of hydroxyl metal oxide characteristic sites indicates abundant catalytic sites, suggesting good catalytic performance of the electrode sheet prepared in this example. Based on the overpotential and Tafel slope of the oxygen evolution reaction, the electrolytic cell in this example exhibits a low overpotential, indicating a rapid and readily occurring reaction. No cracks were observed in the electrode sheet, and the voltage gap was 1.46 V. After 28 h, the voltage gap significantly decreased as a large amount of sulfides were converted to hydroxyl groups until the charging voltage dropped to 0.01 V. Due to the degradation of the electrolytic cell performance, the voltage gap increased again.

[0075] Furthermore, the magnetic field strength of 10 mT in step 3) was adjusted to 20 mT, 30 mT and 50 mT respectively, and the same electrochemical performance test was performed. The results are as follows.

[0076] Oxygen evolution overpotential (mV) Tafel slope (mV / dec) Current loss rate (%) Stable working hours (h) 361 44.3 9.1 112 359 42.8 8.5 120 365 46.5 9.6 108

[0077] As the magnetic field strength increases, the adhesion / agglomeration phenomenon at the tips of the nanorods becomes more pronounced. This morphological change is due to the application of the magnetic field, which further alters the catalyst surface. With increasing magnetic field strength, the specific pore volume of the product decreases while the pore size increases, which is beneficial for improving the catalytic activity of the product, resulting in finer particles, better dispersion, and an increased specific surface area of ​​the active component on the electrode sheet.

[0078] The results in the table show that the overpotential and Tafel slope of the catalyst material initially decrease and then increase with increasing magnetic field strength, indicating that a higher magnetic field strength is not necessarily more beneficial. The catalyst obtained at a magnetic field strength of 30 mT exhibits superior performance.

[0079] Example 2

[0080] A method for improving the self-reconstruction degree of a water electrolysis catalyst using magnetic field assistance, the method comprising:

[0081] 1) Take 0.2 g ferrous sulfate, 1.68 g cobalt nitrate, 2.8 g sodium sulfide, 0.09 g urea, and 0.19 g sodium citrate pentahydrate, add 30 mL of water and mix well to obtain a hydrothermal reaction medium;

[0082] 2) Take nickel foam and cut it into rectangular pieces of 2 cm × 4 cm. Soak them in dilute hydrochloric acid, acetone and anhydrous ethanol in sequence for ultrasonic cleaning. After 15 min, dry them. Soak the nickel foam in a hydrothermal reaction medium and keep it at 120 ℃ for 12 h. After cleaning with deionized water and drying, the electrode sheet is obtained.

[0083] 3) Using an electrode sheet as the working electrode, an Hg / HgCl (saturated KCl) electrode as the reference electrode, a carbon rod as the counter electrode, and 1 mol / L KOH as the electrolyte, an electrolytic cell was assembled. Under magnetic field strengths of 10 mT, 20 mT, 30 mT, and 50 mT, magnets with the S and N poles (i.e., the N pole of the magnet is close to the working electrode) were placed in the order of passing through the counter electrode and the working electrode in the direction of the magnetic field lines. 30 cycles of CV activation were completed within 15 min.

[0084] Based on Example 1, only the S and N poles of the magnetic field were interchanged to obtain materials with different magnetic field strengths under opposite magnetic field directions. The electrochemical performance of the catalyst in this example was tested in the same way as in Example 1, and the results are as follows.

[0085] Magnetic field strength (mT) Oxygen evolution overpotential (mV) Tafel slope (mV / dec) Current loss rate (%) Stable working hours (h) 10 374 49.7 11.2 104 20 363 45.1 9.8 108 30 362 44.5 9.1 110 50 368 47.2 9.8 106

[0086] According to the results in the table, different magnetic field directions also affect catalyst performance. Compared to Example 1, the material exhibits better catalytic performance when the S pole of the magnetic field is closer to the working electrode. Catalyst performance significantly improves with increasing magnetic field strength.

[0087] Example 3

[0088] A method for improving the self-reconstruction degree of a water electrolysis catalyst using magnetic field assistance, the method comprising:

[0089] 1) Take 0.2 g ferrous sulfate, 2.1 g cobalt nitrate, 2.8 g sodium sulfide, 0.09 g urea, and 0.19 g sodium citrate pentahydrate, add 30 mL of water and mix well to obtain a hydrothermal reaction medium;

[0090] 2) Take nickel foam and cut it into rectangular pieces of 2 cm × 4 cm. Soak them in dilute hydrochloric acid, acetone and anhydrous ethanol in sequence for ultrasonic cleaning. After 15 min, dry them. Soak the nickel foam in a hydrothermal reaction medium and keep it at 120 ℃ for 12 h. After cleaning with deionized water and drying, the electrode sheet is obtained.

[0091] 3) Using an electrode sheet as the working electrode, an Hg / HgCl (saturated KCl) electrode as the reference electrode, a carbon rod as the counter electrode, and 1 mol / L KOH as the electrolyte, an electrolytic cell was assembled. Under a magnetic field strength of 30 mT, magnets with N and S poles (i.e., the S pole of the magnet is close to the working electrode) were placed in the order of passing through the counter electrode and the working electrode in the direction of the magnetic field lines. 30 cycles of CV activation were completed within 15 min.

[0092] The catalyst in this example was subjected to the same electrochemical performance test as in Example 1, and the results are as follows.

[0093] Oxygen evolution overpotential (mV) Tafel slope (mV / dec) Current loss rate (%) Stable working hours (h) 363 46.1 9.6 106

[0094] In this example, Fe and Co can effectively replace Ni in Ni3S2. According to research by those skilled in the art, low-spin Fe... 2+ This can increase the resistivity of nickel hydroxide, and based on response experiments using chronoamperometry and chronopotentialography, a structure enhancing catalyst durability can be derived. In this example, Fe... 2+ Insert Co in a high-spin configuration 2+ Tetrahedral positions result in larger particle diameters. High-spin Fe 2+ It has a certain degree of repulsion to the coordination environment. Due to the strong helical effect of cobalt, the replacement difficulty increases and the energy required for the self-reconfiguration process cannot be effectively reduced, resulting in a decline in catalyst performance.

[0095] Comparative Example 1

[0096] A method for improving the self-reconstruction degree of a water electrolysis catalyst using magnetic field assistance, the method comprising:

[0097] 1) Take 0.2 g ferrous sulfate, 1.68 g cobalt nitrate, 2.8 g sodium sulfide, 0.09 g urea, and 0.19 g sodium citrate pentahydrate, add 30 mL of water and mix well to obtain a hydrothermal reaction medium;

[0098] 2) Take nickel foam and cut it into rectangular pieces of 2 cm × 4 cm. Soak them in dilute hydrochloric acid, acetone and anhydrous ethanol in sequence for ultrasonic cleaning. After 15 min, dry them. Soak the nickel foam in a hydrothermal reaction medium and keep it at 120 ℃ for 12 h. After cleaning with deionized water and drying, the electrode sheet is obtained.

[0099] 3) Using an electrode sheet as the working electrode, an Hg / HgCl (saturated KCl) electrode as the reference electrode, a carbon rod as the counter electrode, and 1 mol / L KOH as the electrolyte, such as... Figure 4 The assembly shown is an electrolytic cell, which completes 30 cycles of CV activation within 15 minutes.

[0100] The electrode sheet obtained in step 2) before activation was characterized by SEM, and the results are as follows: Figure 5 As shown, the electrode sheet prepared after activation in step 3) of this example was characterized. The SEM and TEM characterization results are shown in the appendix. Figure 6 , 7 The LSV and Tafel characterization results are attached. Figure 8 , 9 .

[0101] The catalyst in this example was subjected to the same electrochemical performance test as in Example 1, and the results are as follows.

[0102] Oxygen evolution overpotential (mV) Tafel slope (mV / dec) Current loss rate (%) Stable working hours (h) 465 64.3 15.9 92

[0103] In this example, without magnetic field-assisted activation, the surface morphology of the electrode sheet before activation resembled nano-pine needles; after activation, the surface morphology remained nano-pine needle-like. The amorphous material in this example was significantly reduced, indicating that magnetic field-assisted activation can effectively improve the self-reconstruction degree of the catalyst. (At 100 mA cm⁻¹) -2 At the current density, the Tafel slope of the material in this example increases significantly. Combined with the results in the table of Example 1, it can be analyzed that magnetic field-assisted activation can enhance charge transfer capability.

[0104] Furthermore, after 20, 30, and 50 cycles of CV activation, the overpotential of the catalyst under different activation times without magnetic field assistance was measured. The above operation was repeated with an external 10 mT magnetic field applied, and the results are as follows.

[0105] Activation time (cycle) Oxygen evolution overpotential (mV) without magnetic field Oxygen evolution overpotential (mV) when a magnetic field is applied 10 465 457 20 404 394 30 395 371 50 450 431

[0106] Without magnetic field assistance, the oxygen evolution overpotential was 465 mV at an activation time of 10 cycles CV. After applying an external magnetic field, the overpotential decreased to 457 mV at the same activation time. With increasing activation time, the overpotential of the material showed a trend of first decreasing and then increasing. However, the overpotential of the material was lower with and without a magnetic field, indicating that the external magnetic field can effectively enhance the electrocatalytic performance of the catalyst.

[0107] Based on the above conclusions, it is evident that the magnetic field-assisted activation process of electrocatalysts can effectively improve the degree of self-reconstruction of the electrocatalyst, thereby affecting its OER performance. This method can effectively reduce the difficulty of hydrogen production through water electrolysis and has great development potential in the field of hydrogen production through water electrolysis.

[0108] Comparative Example 2

[0109] A method for improving the self-reconstruction degree of a water electrolysis catalyst using magnetic field assistance, the method comprising:

[0110] 1) Take 0.2 g ferrous sulfate, 2.2 g cobalt nitrate, 2.8 g sodium sulfide, 0.09 g urea, and 0.19 g sodium citrate pentahydrate, add 30 mL of water and mix well to obtain a hydrothermal reaction medium;

[0111] 2) Take nickel foam and cut it into rectangular pieces of 2 cm × 4 cm. Soak them in dilute hydrochloric acid, acetone and anhydrous ethanol in sequence for ultrasonic cleaning. After 15 min, dry them. Soak the nickel foam in a hydrothermal reaction medium and keep it at 120 ℃ for 12 h. After cleaning with deionized water and drying, the electrode sheet is obtained.

[0112] 3) Using an electrode sheet as the working electrode, an Hg / HgCl (saturated KCl) electrode as the reference electrode, a carbon rod as the counter electrode, and 1 mol / L KOH as the electrolyte, an electrolytic cell was assembled. Under a magnetic field strength of 30 mT, magnets with N and S poles (i.e., the S pole of the magnet is close to the working electrode) were placed in the order of passing through the counter electrode and the working electrode in the direction of the magnetic field lines. 30 cycles of CV activation were completed within 15 min.

[0113] The catalyst in this example was subjected to the same electrochemical performance test as in Example 1, and the results are as follows.

[0114] Oxygen evolution overpotential (mV) Tafel slope (mV / dec) Current loss rate (%) Stable working hours (h) 403 67.5 12.2 84

[0115] Excessive use of ferrous salts can alter the microstructure of FeCoNi ternary metal chalcogenide (FCND) nanorod arrays, resulting in an uneven nanosheet morphology. This induces the evolution of the nanosheets, altering the nanorod array, reducing the active specific surface area, and leading to a decrease in catalytic performance.

[0116] Comparative Example 3

[0117] A method for improving the self-reconstruction degree of a water electrolysis catalyst using magnetic field assistance, the method comprising:

[0118] 1) Take 4.96 g of chloroplatinic acid and 30 mL of water and mix them evenly to obtain a hydrothermal reaction medium. Take carbon cloth and cut it into rectangular materials of 2 cm × 4 cm. Soak it in dilute hydrochloric acid, acetone and anhydrous ethanol in sequence for ultrasonic cleaning. After 15 min, dry it. Immerse the carbon cloth in the hydrothermal reaction medium and keep it at 120 ℃ for 12 h. After cleaning with deionized water and drying, obtain the electrode sheet.

[0119] 2) Using an electrode sheet as the working electrode, an Hg / HgCl (saturated KCl) electrode as the reference electrode, a carbon rod as the counter electrode, and 1 mol / L KOH as the electrolyte, an electrolytic cell was assembled. Under a magnetic field strength of 30 mT, magnets with N and S poles (i.e., the S pole of the magnet is close to the working electrode) were placed in the order of passing through the counter electrode and the working electrode in the direction of the magnetic field lines. 30 cycles of CV activation were completed within 15 min.

[0120] The catalyst in this example was subjected to the same electrochemical performance test as in Example 1, and the results are as follows.

[0121] Oxygen evolution overpotential (mV) Tafel slope (mV / dec) Current loss rate (%) Stable working hours (h) 442 81.4 15.8 73

[0122] The Pt / C catalyst (electrode, hereinafter the same) prepared in this example exhibits rapid performance degradation. Based on the charge-discharge polarization curves of the catalyst, it can be observed that this catalyst has a large voltage gap and poor reversible oxygen redox capability. At the same charging current density, the Pt / C catalyst requires a higher charging voltage. In cycle tests, the catalyst shows poor long-term charge-discharge stability. Therefore, it is evident that the catalyst of this invention significantly improves performance.

[0123] Comparative Example 4

[0124] A method for improving the self-reconstruction degree of a water electrolysis catalyst using magnetic field assistance, the method comprising:

[0125] 1) Take 0.2 g ferrous sulfate, 1.68 g cobalt nitrate, 2.8 g sodium sulfide, 0.09 g urea, and 0.19 g sodium citrate pentahydrate, add 30 mL of water and mix well to obtain a hydrothermal reaction medium;

[0126] 2) Take nickel foam and cut it into rectangular pieces of 2 cm × 4 cm. Soak them in dilute hydrochloric acid, acetone and anhydrous ethanol in sequence for ultrasonic cleaning. After 15 min, dry them. Soak the nickel foam in a hydrothermal reaction medium and keep it at 120 ℃ for 12 h. After cleaning with deionized water and drying, the electrode sheet is obtained.

[0127] 3) Using an electrode sheet as the working electrode, an Hg / HgCl (saturated KCl) electrode as the reference electrode, a carbon rod as the counter electrode, and 1 mol / L KOH as the electrolyte, an electrolytic cell was assembled. Under a magnetic field strength of 5 mT, magnets with N and S poles (i.e., the S pole of the magnet is close to the working electrode) were placed in the order of passing through the counter electrode and the working electrode in the direction of the magnetic field lines. 30 cycles of CV activation were completed within 15 min.

[0128] The catalyst in this example was subjected to the same electrochemical performance test as in Example 1, and the results are as follows.

[0129] Oxygen evolution overpotential (mV) Tafel slope (mV / dec) Current loss rate (%) Stable working hours (h) 396 50.6 10.7 100

[0130] When the magnetic field strength is low, the energy is too small to promote the uniform dispersion of the catalytic active components. Moreover, the catalytic active components deposited in the pores will migrate outward with the solution, resulting in a decrease in the degree of self-reconstruction, which in turn leads to a decrease in the activity of the electrode sheet.

[0131] Comparative Example 5

[0132] A method for improving the self-reconstruction degree of a water electrolysis catalyst using magnetic field assistance, the method comprising:

[0133] 1) Take 0.2 g ferrous sulfate, 1.68 g cobalt nitrate, 2.8 g sodium sulfide, 0.09 g urea, and 0.19 g sodium citrate pentahydrate, add 30 mL of water and mix well to obtain a hydrothermal reaction medium;

[0134] 2) Take nickel foam and cut it into rectangular pieces of 2 cm × 4 cm. Soak them in dilute hydrochloric acid, acetone and anhydrous ethanol in sequence for ultrasonic cleaning. After 15 min, dry them. Soak the nickel foam in a hydrothermal reaction medium and keep it at 120 ℃ for 12 h. After cleaning with deionized water and drying, the electrode sheet is obtained.

[0135] 3) Using an electrode sheet as the working electrode, an Hg / HgCl (saturated KCl) electrode as the reference electrode, a carbon rod as the counter electrode, and 1 mol / L KOH as the electrolyte, an electrolytic cell was assembled. Under a magnetic field strength of 60 mT, magnets with N and S poles (i.e., the S pole of the magnet is close to the working electrode) were placed in the order of passing through the counter electrode and the working electrode in the direction of the magnetic field lines. 30 cycles of CV activation were completed within 15 min.

[0136] The catalyst in this example was subjected to the same electrochemical performance test as in Example 1, and the results are as follows.

[0137] Oxygen evolution overpotential (mV) Tafel slope (mV / dec) Current loss rate (%) Stable working hours (h) 389 49.6 10.5 102

[0138] Under excessive magnetic field strength, the dispersion of active components on the electrode sheet deteriorates, affecting the distribution of active components in the pores. This results in a decrease in the specific surface area of ​​active components on the electrode sheet and a significant reduction in active centers, thereby reducing the degree of self-reconstruction of nickel-based nanorods and consequently reducing the catalytic activity of the electrode sheet.

Claims

1. A method for improving the self-reconstruction degree of a water electrolysis catalyst using magnetic field assistance, characterized in that, The method includes: 1) Take ferrous salt, cobalt salt, sodium salt, nitrogen compound, and organometallic compound, add solvent and mix evenly to obtain hydrothermal reaction medium; 2) Take the substrate, cut it, clean it, and dry it. Immerse it in the hydrothermal reaction medium to carry out the hydrothermal reaction. After cleaning and drying, the electrode sheet is obtained. 3) Assemble the electrode sheets into an electrolytic cell and perform magnetic field-assisted activation to obtain an electrolytic water catalyst electrode material with a high degree of self-reconfiguration; Step 1) The ferrous salt is ferrous sulfate, the cobalt salt is cobalt nitrate, the sodium salt is sodium sulfide, the nitrogen compound is urea, and the organometallic compound is sodium citrate pentahydrate; The molar ratio of ferrous sulfate, cobalt nitrate, sodium sulfide, urea, and sodium citrate pentahydrate is controlled as (0.01~0.1):(0.01~0.1):(0.5~1.5):(0.02~0.2):(0.001~0.01). Step 3) The magnetic field assistance is used to complete CV activation at 10~50 mT.

2. The method for improving the self-reconstruction degree of a water electrolysis catalyst using magnetic field assistance according to claim 1, characterized in that, The solvent used in step 1) is water, and the amount used is 150-200 mL / g ferrous salt.

3. The method for improving the self-reconstruction degree of a water electrolysis catalyst using magnetic field assistance according to claim 1, characterized in that, Step 2) The substrate is nickel foam, cut to 8-10 cm. 2 .

4. A method for improving the self-reconstruction degree of a water electrolysis catalyst using magnetic field assistance according to claim 1 or 3, characterized in that, Step 2) The cleaning method is to ultrasonically clean the product sequentially in dilute hydrochloric acid, acetone and anhydrous ethanol for 15 to 20 minutes.

5. A method for improving the self-reconstruction degree of a water electrolysis catalyst using magnetic field assistance according to claim 1 or 3, characterized in that, The hydrothermal reaction described in step 2) is carried out at a constant temperature of 120–140 °C for 10–12 h.

6. The method for improving the self-reconstruction degree of a water electrolysis catalyst using magnetic field assistance according to claim 1, characterized in that, In step 3), the electrolytic cell uses the electrode sheet prepared in step 2) as the working electrode, sets up a counter electrode and a reference electrode to construct a three-electrode system, and uses an alkali metal hydroxide solution of 0.5 to 2.0 mol / L as the electrolyte.

7. A water electrolysis catalyst prepared by any one of claims 1 to 6.

8. The application of the water electrolysis catalyst as described in claim 7, characterized in that, The water electrolysis catalyst is used in water electrolysis systems, either directly as an electrode or as a catalytic material on the electrode surface.

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