Method for improving self-reconstruction degree of electrolyzed water catalyst under assistance of magnetic field, prepared catalyst and application of catalyst

Abstract

The invention belongs to the field of hydrogen production through water electrolysis, and particularly relates to a method for improving the self-reconstruction degree of a water electrolysis catalyst through assistance of a magnetic field, the prepared catalyst and application of the catalyst. The method comprises the following steps: 1) adding a solvent into ferrous salt, cobalt salt, sodium salt, a nitrogen compound and an organic metal compound, and uniformly mixing to obtain a hydrothermal reaction medium; (2) cutting, cleaning and drying a base material, immersing the base material in a hydrothermal reaction medium, carrying out hydrothermal reaction, and cleaning and drying to obtain an electrode plate; 3) assembling the electrode plates into an electrolytic tank, and performing magnetic field-assisted activation to obtain the electrolyzed water catalyst electrode material with high self-reconfiguration degree. According to the catalyst prepared by the invention, high overpotential and polarization intensity in oxygen evolution reaction can be effectively reduced through high self-reconfiguration, and the catalyst has low Tafel slope and high catalytic activity.

Description

Technical Field

[0001] The invention belongs to the field of hydrogen production by water electrolysis, and specifically relates to a method for improving the self-reconstruction degree of a water electrolysis catalyst by utilizing a magnetic field as an aid, the prepared catalyst and the application thereof. Background Art

[0002] In order to achieve large-scale hydrogen production, water electrolysis is usually used in this field. This method is sustainable, green and clean. The process of hydrogen production by water electrolysis includes two half reactions, namely the hydrogen evolution reaction (HER) at the cathode and the oxygen evolution reaction (OER) at the anode. Among them, the OER reaction involves four electron transfer processes, and the slow reaction kinetics limit the rate of the entire water electrolysis reaction. Platinum and iridium with extremely high OER catalytic activity have always been used to promote the breaking of OO bonds, promote rapid electron transfer, and reduce energy consumption, but they have poor durability and high prices. Therefore, there is an urgent need to develop efficient and economical electrocatalysts.

[0003] Transition metal-based materials, especially nickel-based materials, are suitable for combining with oxygen-related intermediates due to their unique electronic structure. As potential alternatives to precious metal catalysts, iron-cobalt-nickel ternary materials and their corresponding sulfides have attracted widespread attention due to their metal-like properties. However, these electrocatalysts are not stable. During the initial activation process of OER, partial oxidation or complete oxidation inevitably occurs. The evolved hydroxyl oxides are proven to be the true OER catalytic active phase. This phenomenon, due to the rapid change of its surface properties, is called surface self-reconstruction. In recent years, magnetic field-assisted electrocatalysis has also been considered to be an effective method to improve the catalytic activity of catalysts. The degree of surface self-reconstruction of electrocatalysts can be effectively improved under the assistance of a magnetic field, which is a key factor in its excellent catalytic performance. Therefore, the present invention purposefully designs and grows nanorod arrays of iron-cobalt-nickel ternary sulfides on nickel foam by a one-step hydrothermal method, and an external magnetic field is added to assist in promoting the catalyst to improve the degree of self-reconstruction. Summary of the invention

[0004] Based on the above content, in order to solve the problems of slow water electrolysis reaction rate and insufficient catalytic performance of nickel-based materials, the present invention proposes a method for improving the self-reconstruction degree of water electrolysis catalyst using a magnetic field to assist.

[0005] The objects of the present invention are: 1. Improve the catalytic performance of nickel-based materials; 2. Improve the degree of self-reconstruction of nickel-based materials; 3. Improve the intrinsic OER kinetics and overall performance of nickel-based materials in hydrogen production by water electrolysis.

[0006] To achieve the above objectives, the present invention adopts the following technical solutions.

[0007] A method for improving the self-reconstruction degree of water electrolysis catalyst using magnetic field assistance, The method comprises: 1) Take ferrous salt, cobalt salt, sodium salt, nitrogen compound, and organic metal compound, add solvent and mix evenly to obtain a hydrothermal reaction medium; 2) Cutting, cleaning and drying the substrate, immersing it in a hydrothermal reaction medium, performing a hydrothermal reaction, and obtaining an electrode sheet after cleaning and drying; 3) The electrode sheets are assembled into an electrolytic cell and subjected to magnetic field-assisted activation to obtain a water electrolysis catalyst electrode material with a high degree of self-reconstruction.

[0008] As a preference, 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 the ferrous sulfate, cobalt nitrate, sodium sulfide, urea and sodium citrate pentahydrate is controlled to be (0.01-0.1): (0.01-0.1): (0.5-1.5): (0.02-0.2): (0.001-0.01); On this basis, the amount of each component compared to ferrous sulfate is calculated as follows: The amount of cobalt nitrate used is 0.12-12.0 g / g of ferrous salt; The amount of sodium sulfide used is 2.1 to 64.3 g / g of ferrous salt; The dosage of the urea is 0.15-15.4 g / g of ferrous salt; The dosage of the sodium citrate pentahydrate is 0.049-4.9 g / g of ferrous salt.

[0009] More preferably, Step 1) the ferrous salt is ferrous sulfate; The cobalt salt is cobalt nitrate, and the amount thereof is 8.4 to 10.5 g / g of ferrous salt; The sodium salt is sodium sulfide, and its dosage is 14.0-42.1 g / g ferrous salt; The nitrogen compound is urea, and its usage is 0.43-4.3 g / g ferrous salt; The organic metal compound is sodium citrate pentahydrate, and its usage is 0.93-3.72 g / g ferrous salt.

[0010] As a preference, Step 1) The solvent is water, and the amount used is 150-200 mL / g ferrous salt.

[0011] As a preference, Step 2) The substrate is nickel foam, cut into pieces of 8 to 10 cm 2 .

[0012] As a preference, Step 2) The cleaning method is to ultrasonically clean in dilute hydrochloric acid, acetone and anhydrous ethanol for 15 to 20 minutes in sequence.

[0013] As a preference, Step 2) The hydrothermal reaction is carried out at 120-140°C for 10-12 hours.

[0014] As a preference, Step 3) The magnetic field assistance is to complete CV activation at 10-50 mT.

[0015] As a preference, Step 3) The electrolytic cell uses the electrode sheet prepared in step 2) as the working electrode, sets a counter electrode and a reference electrode to construct a three-electrode system, and uses a 0.5-2.0 mol / L alkali metal hydroxide solution as the electrolyte.

[0016] A water electrolysis catalyst.

[0017] Application of a water electrolysis catalyst, The water electrolysis catalyst is used in a water electrolysis system and is directly used as an electrode or as a catalytic material on the surface of an electrode.

[0018] In the technical solution of the present invention, ferrous sulfate is used as an iron source, cobalt nitrate is used as a cobalt source, sodium sulfide is used as a sulfur source, and urea is used as a complexing agent, and they are compounded on nickel foam to prepare a nickel-based catalyst. Among them, the sulfur atom has a large electronegativity and a strong electron-withdrawing effect, which increases the electron cloud density of the delocalized π bond of the sulfur-containing atom ring and has a strong catalytic activity.

[0019] In order to further improve the electrocatalytic activity of the material, iron was introduced into this system. 2+ Occupies the octahedral position first, gradually occupies the Co 2+ Octahedral position, the particle diameter decreases, indicating low-spin Fe 2+ The ionic radius is smaller than that of Co 2+ At the same time, according to the research of those skilled in the art, low-spin Fe 2+ It is easier to replace the Ni element in Ni3S2 with the help of Co element, thereby improving the resistivity of the overall catalytic material. According to the response experiments of chronoamperometry and chronopotentiometry, it can be concluded that it has strong durability. In coordination with urea, the material exposes more active sites, the Tafel slope decreases, and the oxygen evolution reaction activity of the surface material increases. As the iron content in the system increases, Co 2+ The tetrahedral sites are occupied, while the particle diameter increases, indicating that the high-spin Fe2+ The ionic radius is larger than that of Co 2+ This indicates that high-spin Fe 2+ The ionic radius is larger than that of low-spin Fe 2+ However, when the amount of ferrous salt is too much, the purity of the crystal decreases, and Fe 2+ Fully occupying the octahedral position, interacting with the Co atoms in the tetrahedral position, resulting in Co 2+ The peak position shifts. Due to the strong spiral effect of cobalt, Fe 2+ The peak strength is weak or even not obvious, that is, the signal is shielded. 2+ It causes serious rejection to the coordination environment, making it difficult to form Co and Fe to replace the Ni element in Ni3S2. After characterization based on effective substitution, SEM mapping results show that the atomic ratio of each element is Fe:Co:Ni=1:1:10, and XRD test finds that the peak of the hydrothermal product matches the peak height of Ni3S2 without impurity peaks, and the presence of trace Fe and Co causes very little deviation in the position of the product peak, which is almost negligible.

[0020] Compared with commercially available materials, the materials prepared by the present invention have higher electrocatalytic activity. For example, Pt is compounded onto C in the same hydrothermal manner to prepare a Pt / C electrode (i.e., a Pt / C catalyst for electrolysis of water) for comparison. The open circuit voltage of the catalyst (i.e., electrode) prepared by the present invention is slightly higher than that of the catalyst prepared by Pt / C (referred to as Pt / C electrocatalyst or Pt / C electrode). Since sulfides are easily converted into hydroxyls during the OER process, experiments based on this point can clearly show that the performance of the Pt / C catalyst degrades rapidly. According to the charge and discharge polarization curves of the catalyst, it can be found that the catalyst of the present invention has a smaller voltage gap and exhibits excellent reversible oxygen redox ability. At the same charging current density, the catalyst of the present invention requires a lower redox voltage than the Pt / C catalyst. And in the cycle test, the catalyst of the present invention exhibits good cycle stability.

[0021] The magnetic field assistance of the present invention can improve the conversion rate of Ni3S2 on the electrode sheet and the degree of self-reconstruction of Ni3S2 converted into nickel oxyhydroxide during activation. When applied, magnets in the N and S pole directions are placed in the order of passing through the counter electrode and the working electrode in the direction of the magnetic flux lines (i.e., the S pole of the magnet is close to the working electrode). The high energy field generated by the electromagnetic field causes the magnetic field to interact with the active particles, avoiding particle clusters, and the presence of Co and Fe can promote the occurrence of self-reconstruction and increase the active sites, and the replacement of Ni elements in Ni3S2 by Co and Fe enables it to expose more active sites. However, when the magnetic field intensity is low, too little energy cannot promote the uniform dispersion of catalytic active components, and the catalytic active components deposited in the pores will migrate outward with the solution, further exacerbating the uneven distribution of components, thereby causing the activity of the electrode sheet to decrease. With the increase of the magnetic field intensity, the specific pore volume of the product decreases and the pore size increases, which is conducive to improving the catalytic activity of the product, making the particles refined and well dispersed, and increasing the specific surface area of ​​the active components of the electrode sheet. In addition, characterization has found that under excessively large magnetic field strengths, the dispersion of active components on the electrode sheet deteriorates, affecting the distribution of active components in the pores, causing the specific surface area of ​​active components on the electrode sheet to decrease and the active centers to significantly reduce, thereby reducing the catalytic activity of the electrode sheet.

[0022] The beneficial effects of the present invention are as follows: (1) The method provided by the present invention is simple, highly reproducible, and the reaction is controllable; (2) The present invention can effectively improve the self-reconstruction degree of the catalyst, thereby significantly improving the catalytic performance; (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. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the magnetic field-assisted self-reconstruction process of the electrode sheet in Example 1; Figure 2 This is a scanning electron microscope (SEM) image of the electrode sheet of Example 1 after magnetic field-assisted self-reconstruction; Figure 3 This is a transmission electron microscope (TEM) image of the electrode sheet of Example 1 after magnetic field-assisted self-reconstruction; Figure 4 Schematic diagram of the electrode sheet of comparative example 1 under the activation process without magnetic field; Figure 5 is a scanning electron microscope (SEM) image of the electrode sheet of Comparative Example 1 before activation; Figure 6 is a scanning electron microscope (SEM) image of the electrode sheet of comparative example 1 after self-reconstruction without magnetic field assistance; Figure 7This is a transmission electron microscope (TEM) image of the electrode sheet of comparative example 1 after self-reconstruction without magnetic field assistance; Figure 8 A comparison diagram of linear sweep voltammetry (LSV) curves of the electrode sheets of Example 1 and Comparative Example 1 measured with and without magnetic field-assisted self-reconstruction; Fig. 9 It is a comparison diagram of Tafel curves of the electrode sheets of Example 1 and Comparative Example 1 measured with and without magnetic field-assisted self-reconstruction. DETAILED DESCRIPTION

[0024] The present invention is further described in detail below in conjunction with specific embodiments and the accompanying drawings. A person of ordinary skill in the art will be able to implement the present invention based on these descriptions. In addition, the embodiments of the present invention involved in the following description are generally only embodiments of a part of the present invention, rather than all embodiments. Therefore, based on the embodiments of the present invention, all other embodiments obtained by a person of ordinary skill in the art without making creative work should fall within the scope of protection of the present invention.

[0025] Unless otherwise specified, the raw materials used in the examples of the present invention are all commercially available or available to those skilled in the art; unless otherwise specified, the methods used in the examples of the present invention are all methods known to those skilled in the art.

[0026] Unless otherwise specified, when the electrode sheets prepared in the embodiments and / or comparative examples are characterized in the embodiments of the present invention, the electrode sheets referred to are all water electrolysis catalyst products prepared by the complete preparation process of the current embodiments / comparative examples.

[0027] Example 1 A method for improving the self-reconstruction degree of a water electrolysis catalyst by using a magnetic field as an aid, the method comprising: 1) Take 0.2 g of ferrous sulfate, 1.68 g of cobalt nitrate, 2.8 g of sodium sulfide, 0.09 g of urea, and 0.19 g of sodium citrate pentahydrate, add 30 mL of water and mix well to obtain a hydrothermal reaction medium; 2) Cut the nickel foam into a rectangular material of 2 cm × 4 cm, immerse it in dilute hydrochloric acid, acetone and anhydrous ethanol for ultrasonic cleaning in sequence, dry it after 15 min, immerse the nickel foam in a hydrothermal reaction medium, keep it at 120 °C for 12 h, wash it with deionized water and dry it to obtain an electrode sheet; 3) An electrolytic cell was assembled with the electrode sheet as the working electrode, Hg / HgCl (saturated KCl) electrode as the reference electrode, carbon rod as the counter electrode, and 1 mol / L KOH as the electrolyte. Under a magnetic field strength of 10 mT, magnets with N and S poles were placed in the order of the magnetic flux lines passing through the counter electrode and the working electrode (i.e., the S pole of the magnet was close to the working electrode), and 30 cycles of CV activation were completed within 15 min.

[0028] The electrode sheet prepared in this example was characterized. The SEM and TEM electron microscopy results are shown in the attached Figure 2 , 3 .

[0029] At room temperature, an electrochemical workstation (CHI 760D) was used to test the electrochemical performance of the water electrolysis catalyst (as an electrode sheet) prepared in this example. The schematic diagram of the device is attached. Figure 1 Among them, the electrolytic cell is a standard three-electrode system, and the calibration formula of 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 A cycle experiment was carried out under the conditions of 1000 Hz to observe whether cracks appeared on the electrode sheet, whether the current and voltage fluctuated, to characterize the current loss rate within 40 h, and to characterize its voltage gap.

[0030] The results are as follows. Oxygen evolution overpotential (mV) Tafel slope (mV / dec) Current loss rate (%) Stable working time (h) 372 48.9 10.9 106

[0031] The high energy field generated by the electromagnetic field causes the magnetic field to interact with the active particles, reducing the energy required for self-reconstruction and exposing more active sites. According to the SEM and TEM images, it can be seen that there is a certain degree of adhesion / agglomeration at the tip of the nanorod. The material has clear lattice stripes, but a layer of amorphous material is obviously generated on the outside. After characterization, it is judged that these substances are hydroxy metal oxides. The characteristic points of hydroxy metal oxides are dense, that is, the catalytic sites are rich, indicating that the electrode sheet prepared in this example has good catalytic performance. According to the overpotential and Tafel slope of the oxygen evolution reaction, it can be analyzed that the overpotential of the electrolytic cell in this example is low, the reaction is easy to occur, and the rate is fast. There are no cracks in the electrode sheet, and its voltage gap is 1.46 V. After 28 h, the voltage gap decreases significantly, and a large amount of sulfide is converted into hydroxyl until the charging voltage drops to 0.01V. Due to the degradation of the electrolytic cell performance, its voltage gap increases again.

[0032] Furthermore, the magnetic field strength of 10 mT in step 3) was adjusted to 20 mT, 30 mT, and 50 mT, respectively, and the electrochemical performance test was carried out as above, and the results are as follows. Oxygen evolution overpotential (mV) Tafel slope (mV / dec) Current loss rate (%) Stable working time (h) 361 44.3 9.1 112 359 42.8 8.5 120 365 46.5 9.6 108

[0033] As the magnetic field strength increases, the adhesion / agglomeration phenomenon at the tips of the nanorods becomes obvious. This morphological change is due to the application of the magnetic field, which further changes the catalyst surface. As the magnetic field strength increases, the specific pore volume of the product decreases and the pore size increases, which is beneficial to improving the catalytic activity of the product, making the particles finer and more dispersed, and increasing the specific surface area of ​​the active components of the electrode sheet.

[0034] The results in the table show that as the magnetic field strength increases, the overpotential and Tafel slope of the catalyst material first decrease and then increase, indicating that the greater the magnetic field strength, the more favorable it is. At a magnetic field strength of 30 mT, the obtained catalyst exhibits better performance.

[0035] Example 2 A method for improving the self-reconstruction degree of a water electrolysis catalyst by using a magnetic field as an aid, the method comprising: 1) Take 0.2 g of ferrous sulfate, 1.68 g of cobalt nitrate, 2.8 g of sodium sulfide, 0.09 g of urea, and 0.19 g of sodium citrate pentahydrate, add 30 mL of water and mix well to obtain a hydrothermal reaction medium; 2) Cut the nickel foam into a rectangular material of 2 cm × 4 cm, immerse it in dilute hydrochloric acid, acetone and anhydrous ethanol for ultrasonic cleaning in sequence, dry it after 15 min, immerse the nickel foam in a hydrothermal reaction medium, keep it at 120 °C for 12 h, wash it with deionized water and dry it to obtain an electrode sheet; 3) An electrolytic cell was assembled with the electrode sheet as the working electrode, the Hg / HgCl (saturated KCl) electrode as the reference electrode, the carbon rod as the counter electrode, and 1 mol / L KOH as the electrolyte. Under magnetic field intensities of 10 mT, 20 mT, 30 mT, and 50 mT, magnets with S and N poles were placed in the order of the magnetic flux lines passing through the counter electrode and the working electrode (i.e., the N pole of the magnet was close to the working electrode), and 30 cycles of CV activation were completed within 15 min.

[0036] On the basis of Example 1, only the S and N poles of the magnetic field are swapped to obtain a material with different magnetic field strengths in the opposite magnetic field direction. The electrochemical performance test of the catalyst in this example is carried out in the same manner as in Example 1, and the results are as follows. Magnetic field strength (mT) Oxygen evolution overpotential (mV) Tafel slope (mV / dec) Current loss rate (%) Stable working time (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

[0037] According to the results in the table, different magnetic field directions also have an impact on the catalyst performance. Compared with Example 1, the catalytic performance of the material is better when the S pole of the magnetic field is closer to the working electrode. As the magnetic field strength increases, the catalyst performance is significantly enhanced.

[0038] Example 3 A method for improving the self-reconstruction degree of a water electrolysis catalyst by using a magnetic field as an aid, the method comprising: 1) Take 0.2 g of ferrous sulfate, 2.1 g of cobalt nitrate, 2.8 g of sodium sulfide, 0.09 g of urea, and 0.19 g of sodium citrate pentahydrate, add 30 mL of water and mix well to obtain a hydrothermal reaction medium; 2) Cut the nickel foam into a rectangular material of 2 cm × 4 cm, immerse it in dilute hydrochloric acid, acetone and anhydrous ethanol for ultrasonic cleaning in sequence, dry it after 15 min, immerse the nickel foam in a hydrothermal reaction medium, keep it at 120 °C for 12 h, wash it with deionized water and dry it to obtain an electrode sheet; 3) An electrolytic cell was assembled with the electrode sheet as the working electrode, the Hg / HgCl (saturated KCl) electrode as the reference electrode, the carbon rod as the counter electrode, and 1 mol / L KOH as the electrolyte. Under a magnetic field strength of 30 mT, magnets with N and S poles were placed in the order of the magnetic flux lines passing through the counter electrode and the working electrode (i.e., the S pole of the magnet was close to the working electrode), and 30 cycles of CV activation were completed within 15 min.

[0039] The electrochemical performance test of the catalyst in this example was carried out in the same manner as in Example 1, and the results are as follows. Oxygen evolution overpotential (mV) Tafel slope (mV / dec) Current loss rate (%) Stable working time (h) 363 46.1 9.6 106

[0040] In this example, Fe and Co can effectively replace the Ni element in Ni3S2. 2+ It can improve the resistivity of nickel hydroxide, and according to the response experiments of chronoamperometry and chronopotentiometry, it can be concluded that the catalyst durability is enhanced. 2+ Insertion of Co in high spin form 2+ Tetrahedral position, the resulting particle diameter is large. High spin Fe 2+ There is a certain repulsion to the coordination environment. Due to the influence of the strong spiral effect of cobalt, the difficulty of replacement increases and the energy required for the self-reconstruction process cannot be effectively reduced, resulting in a decrease in catalyst performance.

[0041] Comparative Example 1 A method for improving the self-reconstruction degree of a water electrolysis catalyst by using a magnetic field as an aid, the method comprising: 1) Take 0.2 g of ferrous sulfate, 1.68 g of cobalt nitrate, 2.8 g of sodium sulfide, 0.09 g of urea, and 0.19 g of sodium citrate pentahydrate, add 30 mL of water and mix well to obtain a hydrothermal reaction medium; 2) Cut the nickel foam into a rectangular material of 2 cm × 4 cm, immerse it in dilute hydrochloric acid, acetone and anhydrous ethanol for ultrasonic cleaning in sequence, dry it after 15 min, immerse the nickel foam in a hydrothermal reaction medium, keep it at 120 °C for 12 h, wash it with deionized water and dry it to obtain an electrode sheet; 3) Use the electrode sheet as the working electrode, Hg / HgCl (saturated KCl) electrode as the reference electrode, carbon rod as the counter electrode, and 1 mol / L KOH as the electrolyte. Figure 4 The assembly shown is an electrolytic cell that completed 30 cycles of CV activation in 15 min.

[0042] The electrode sheet prepared in step 2) before activation was characterized by SEM. 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 electron microscopy characterization results are shown in the attached Figure 6 , 7 , LSV, Tafel characterization results are attached Figure 8 , 9 .

[0043] The electrochemical performance test of the catalyst in this example was carried out in the same manner as in Example 1, and the results are as follows. Oxygen evolution overpotential (mV) Tafel slope (mV / dec) Current loss rate (%) Stable working time (h) 465 64.3 15.9 92

[0044] In this case, there is no magnetic field assisted activation. The surface morphology of the electrode sheet before activation is nano-pine needle-like. After activation, its surface morphology is nano-pine needle-like. The amorphous material in this case is significantly reduced, which can be judged that the magnetic field assisted activation process can effectively improve the degree of self-reconstruction of the catalyst. At 100 mA cm -2 Under 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 the charge transfer capability.

[0045] Furthermore, after 20, 30 and 50 cycles of CV activation, the overpotential of the catalyst at different activation times without magnetic field assistance was measured. A 10 mT magnetic field was applied and the above operation was repeated, and the results are as follows. Activation time (cycles) (Without magnetic field) Oxygen evolution overpotential (mV) (Magnetic field applied) Oxygen evolution overpotential (mV) 10 465 457 20 404 394 30 395 371 50 450 431

[0046] Without magnetic field assistance, the oxygen evolution overpotential is 465 mV at an activation time of 10 CV cycles. After applying an external magnetic field, the overpotential at the same activation time is reduced to 457 mV. With the increase of activation time, the overpotential of the material shows a trend of first decreasing and then increasing, but the overpotential of the material is lower in the case of an external magnetic field than in the case of no magnetic field, indicating that the external magnetic field can effectively enhance the electrocatalytic performance of the catalyst.

[0047] Combined with the above conclusions, it is shown that the magnetic field-assisted electrocatalyst activation process can effectively improve the self-reconstruction degree of the electrocatalyst, thereby affecting the OER performance of the electrocatalyst. This method can effectively reduce the difficulty of hydrogen production by water electrolysis and has great development potential in the field of hydrogen production by water electrolysis.

[0048] Comparative Example 2 A method for improving the self-reconstruction degree of a water electrolysis catalyst by using a magnetic field as an aid, the method comprising: 1) Take 0.2 g of ferrous sulfate, 2.2 g of cobalt nitrate, 2.8 g of sodium sulfide, 0.09 g of urea, and 0.19 g of sodium citrate pentahydrate, add 30 mL of water and mix well to obtain a hydrothermal reaction medium; 2) Cut the nickel foam into a rectangular material of 2 cm × 4 cm, immerse it in dilute hydrochloric acid, acetone and anhydrous ethanol for ultrasonic cleaning in sequence, dry it after 15 min, immerse the nickel foam in a hydrothermal reaction medium, keep it at 120 °C for 12 h, wash it with deionized water and dry it to obtain an electrode sheet; 3) An electrolytic cell was assembled with the electrode sheet as the working electrode, the Hg / HgCl (saturated KCl) electrode as the reference electrode, the carbon rod as the counter electrode, and 1 mol / L KOH as the electrolyte. Under a magnetic field strength of 30 mT, magnets with N and S poles were placed in the order of the magnetic flux lines passing through the counter electrode and the working electrode (i.e., the S pole of the magnet was close to the working electrode), and 30 cycles of CV activation were completed within 15 min.

[0049] The electrochemical performance test of the catalyst in this example was carried out in the same manner as in Example 1, and the results are as follows. Oxygen evolution overpotential (mV) Tafel slope (mV / dec) Current loss rate (%) Stable working time (h) 403 67.5 12.2 84

[0050] When the amount of ferrous salt is too much, the microstructure of the FeCoNi ternary metal chalcogenide (FCND) nanorod array will change, presenting an uneven nanosheet morphology, which induces the evolution of nanosheets, causes the nanorod array to change, reduces the active specific surface area, and leads to a decrease in catalytic performance.

[0051] Comparative Example 3 A method for improving the self-reconstruction degree of a water electrolysis catalyst by using a magnetic field as an aid, the method comprising: 1) Take 4.96 g of chloroplatinic acid and 30 mL of water and mix them evenly to obtain a hydrothermal reaction medium. Take another carbon cloth and cut it into a rectangular material of 2 cm×4 cm. Immerse it in dilute hydrochloric acid, acetone and anhydrous ethanol for ultrasonic cleaning in sequence. Dry it after 15 min. Immerse the carbon cloth in the hydrothermal reaction medium and keep it at 120 °C for 12 h. After washing with deionized water and drying, obtain an electrode sheet. 2) An electrolytic cell was assembled with the electrode sheet as the working electrode, the Hg / HgCl (saturated KCl) electrode as the reference electrode, the carbon rod as the counter electrode, and 1 mol / L KOH as the electrolyte. Under a magnetic field strength of 30 mT, magnets with N and S poles were placed in the order of the magnetic flux lines passing through the counter electrode and the working electrode (i.e., the S pole of the magnet was close to the working electrode), and 30 cycles of CV activation were completed within 15 min.

[0052] The electrochemical performance test of the catalyst in this example was carried out in the same manner as in Example 1, and the results are as follows. Oxygen evolution overpotential (mV) Tafel slope (mV / dec) Current loss rate (%) Stable working time (h) 442 81.4 15.8 73

[0053] The performance of the Pt / C catalyst (electrode, the same below) prepared in this example degrades rapidly. According to the charge and discharge polarization curve of the catalyst, it can be found that the catalyst in this example has a large voltage gap and poor reversible oxygen redox ability. At the same charging current density, the Pt / C catalyst requires a higher charging voltage. In the cycle test, the long-term charge and discharge stability of the catalyst is poor. It can be seen that the performance of the catalyst of the present invention is significantly improved.

[0054] Comparative Example 4 A method for improving the self-reconstruction degree of a water electrolysis catalyst by using a magnetic field as an aid, the method comprising: 1) Take 0.2 g of ferrous sulfate, 1.68 g of cobalt nitrate, 2.8 g of sodium sulfide, 0.09 g of urea, and 0.19 g of sodium citrate pentahydrate, add 30 mL of water and mix well to obtain a hydrothermal reaction medium; 2) Cut the nickel foam into a rectangular material of 2 cm × 4 cm, immerse it in dilute hydrochloric acid, acetone and anhydrous ethanol for ultrasonic cleaning in sequence, dry it after 15 min, immerse the nickel foam in a hydrothermal reaction medium, keep it at 120 °C for 12 h, wash it with deionized water and dry it to obtain an electrode sheet; 3) An electrolytic cell was assembled with the electrode sheet as the working electrode, Hg / HgCl (saturated KCl) electrode as the reference electrode, carbon rod as the counter electrode, and 1 mol / L KOH as the electrolyte. Under a magnetic field strength of 5 mT, magnets with N and S poles were placed in the order of the magnetic flux lines passing through the counter electrode and the working electrode (i.e., the S pole of the magnet was close to the working electrode), and 30 cycles of CV activation were completed within 15 min.

[0055] The electrochemical performance test of the catalyst in this example was carried out in the same manner as in Example 1, and the results are as follows. Oxygen evolution overpotential (mV) Tafel slope (mV / dec) Current loss rate (%) Stable working time (h) 396 50.6 10.7 100

[0056] When the magnetic field intensity is low, the energy is too small to cause the catalytically active components to disperse evenly. Moreover, the catalytically active components deposited in the pores will migrate outward with the solution, resulting in a decrease in the degree of self-reconstruction, thereby causing a decrease in the activity of the electrode sheet.

[0057] Comparative Example 5 A method for improving the self-reconstruction degree of a water electrolysis catalyst by using a magnetic field as an aid, the method comprising: 1) Take 0.2 g of ferrous sulfate, 1.68 g of cobalt nitrate, 2.8 g of sodium sulfide, 0.09 g of urea, and 0.19 g of sodium citrate pentahydrate, add 30 mL of water and mix well to obtain a hydrothermal reaction medium; 2) Cut the nickel foam into a rectangular material of 2 cm × 4 cm, immerse it in dilute hydrochloric acid, acetone and anhydrous ethanol for ultrasonic cleaning in sequence, dry it after 15 min, immerse the nickel foam in a hydrothermal reaction medium, keep it at 120 °C for 12 h, wash it with deionized water and dry it to obtain an electrode sheet; 3) An electrolytic cell was assembled using the electrode sheet as the working electrode, the Hg / HgCl (saturated KCl) electrode as the reference electrode, the carbon rod as the counter electrode, and 1 mol / L KOH as the electrolyte. Under a magnetic field strength of 60 mT, magnets with N and S poles were placed in the order that the magnetic flux lines pass through the counter electrode and the working electrode (i.e., the S pole of the magnet is close to the working electrode), and 30 cycles of CV activation were completed within 15 min.

[0058] The electrochemical performance test of the catalyst in this example was carried out in the same manner as in Example 1, and the results are as follows. Oxygen evolution overpotential (mV) Tafel slope (mV / dec) Current loss rate (%) Stable working time (h) 389 49.6 10.5 102

[0059] Under excessively high magnetic field intensity, the dispersion of active components on the electrode sheet deteriorates, affecting the distribution of active components in the pores, resulting in a decrease in the specific surface area of ​​active components in the electrode sheet and a significant reduction in active centers, thereby reducing the degree of self-reconstruction of nickel-based nanorods, and further leading to a decrease in the catalytic activity of the electrode sheet.

Claims

1. A method for improving the self-reconstruction degree of water electrolysis catalyst using magnetic field assistance, characterized in that: The method comprises: 1) Take ferrous salt, cobalt salt, sodium salt, nitrogen compound, and organic metal compound, add solvent and mix evenly to obtain a hydrothermal reaction medium; 2) Cutting, cleaning and drying the substrate, immersing it in a hydrothermal reaction medium, performing a hydrothermal reaction, cleaning and drying, and obtaining an electrode sheet; 3) The electrode sheets are assembled into an electrolytic cell and subjected to magnetic field-assisted activation to obtain a water electrolysis catalyst electrode material with a high degree of self-reconstruction.

2. The method of claim 1, wherein the method comprises: 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 the ferrous sulfate, cobalt nitrate, sodium sulfide, urea and sodium citrate pentahydrate is controlled to be (0.01-0.1): (0.01-0.1): (0.5-1.5): (0.02-0.2): (0.001-0.01).

3. The method of claim 1, wherein the method comprises: Step 1) The solvent is water, and the amount used is 150-200 mL / g ferrous salt.

4. The method of claim 1, wherein the method comprises: Step 2) The substrate is nickel foam, cut into pieces of 8 to 10 cm 2 .

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

6. A method for improving the self-reconstruction degree of water electrolysis catalyst using magnetic field assistance according to claim 1 or 4, characterized in that: Step 2) The hydrothermal reaction is carried out at 120-140°C for 10-12 hours.

7. The method of claim 1, wherein the method comprises: Step 3) The magnetic field assistance is to complete CV activation at 10-50 mT.

8. A method for improving the self-reconstruction degree of water electrolysis catalyst using magnetic field assistance according to claim 1 or 7, characterized in that: Step 3) The electrolytic cell uses the electrode sheet prepared in step 2) as the working electrode, sets a counter electrode and a reference electrode to construct a three-electrode system, and uses a 0.5-2.0 mol / L alkali metal hydroxide solution as the electrolyte.

9. A water electrolysis catalyst prepared by the method of claims 1 to 8.

10. A use of the water electrolysis catalyst as claimed in claim 9, characterized in that: The water electrolysis catalyst is used in a water electrolysis system and is directly used as an electrode or as a catalytic material on the surface of an electrode.

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