Preparation method of ni / nih2 heterojunction nanoelectrocatalyst and application thereof in hydrogen production

Abstract

The application discloses a preparation method of a Ni / Ni(OH)2 heterojunction nanoelectrocatalyst and application of the nanoelectrocatalyst in hydrogen production, and the method is as follows: a eutectic solvent is prepared; then, a nickel salt is added and heated and stirred to make the nickel salt fully dissolved and no crystal precipitates; an imidazole additive is added, and the electrolyte is uniformly stirred to obtain an electrolyte; the electrolyte is added into an electrolytic tank for electrodeposition, and a uniform and compact Ni / Ni(OH)2 heterojunction layer is gradually deposited on the surface of a cathode; and the cathode electrode is cleaned, dried and activated to obtain the catalyst. By introducing the imidazole into the choline chloride-ethylene glycol eutectic solvent system and adopting the electrodeposition technology, the synchronous deposition and interface combination of nickel and nickel hydroxide are realized at one time, the Ni / Ni(OH)2 heterojunction is obtained, the cumbersome multi-step process in the traditional method is avoided, the high efficiency and long-term stability of the catalyst in the hydrogen evolution reaction are improved, and the catalyst has good repeatability and industrialization potential.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrocatalysts, in particular to a preparation method of a Ni / Ni(OH)2 heterojunction nanoelectrocatalyst and application thereof in hydrogen production. BACKGROUND

[0002] Water electrolysis for hydrogen production is a clean and efficient energy production technology, which has important applications in renewable energy storage and utilization. In particular, the HER reaction carried out in alkaline medium has gradually become the focus of research due to its environmental friendliness and low cost. The key to water electrolysis for hydrogen production lies in the development of high-efficiency catalysts, and the performance of the catalyst directly determines the kinetic efficiency of the hydrogen evolution reaction and the overall energy conversion efficiency of water electrolysis.

[0003] Nickel-based catalysts are widely considered as ideal substitutes for platinum-based catalysts due to their abundant resource reserves, low cost and good catalytic activity, especially in alkaline hydrogen evolution reactions. However, traditional nickel-based catalysts still face some bottlenecks in application, such as large grain size, insufficient surface active sites and poor catalytic stability, which limit the improvement of their hydrogen evolution performance. In addition, with the progress of the catalytic reaction, the surface active sites of the nickel-based catalysts may gradually deactivate, leading to a decrease in hydrogen evolution efficiency. Therefore, how to improve the stability of the nickel-based catalysts, enhance their surface activity and long-term reaction resistance to deactivation has become a key challenge to improve their hydrogen evolution performance.

[0004] To overcome the performance bottleneck of nickel-based catalysts in hydrogen evolution reaction, strategies have been proposed in recent years to enhance the catalytic performance by constructing heterojunction structures. Conventional methods for preparing heterojunction materials include mechanical exfoliation, hydrothermal method, chemical vapor deposition (CVD), and physical vapor deposition (PVD), etc. Among them, mechanical exfoliation is mainly used to prepare van der Waals heterojunctions of two-dimensional materials, which forms a heterostructure by physically stacking different two-dimensional materials. For example, Ruijie Li, Zhixin Yao, Lei Liu, et al. (Mechanical exfoliation of non-layered metal oxides into ultrathin flakes. Nat. Synth. 2025, 4, 106-115.) used a combination of thermal decomposition of metal salts and water-assisted foaming technology to obtain large aspect ratio sheet structures, and successfully prepared independent and self-supporting two-dimensional flakes by tape stripping these sheets. However, this method relies on the layered structure of the material itself and is only suitable for materials with weak van der Waals interactions, and is not suitable for most bulk metals and non-layered compounds. In addition, the thickness and uniformity of the exfoliated layers are difficult to control accurately, and the yield is low, which is difficult to meet the demand of large-scale preparation. The hydrothermal method is widely used in the construction of heterostructures of metal oxides and composite materials, such as Chen Kansong, Li Yang, Tian Han, Gu Haoshuang (Synthesis and Photocatalytic Performance of Heterostructured Nano-Composite Bi4Ti3O 12 / TiO2[J]. Materials Research Journal, 2014, 28(7): 503-508.) successfully synthesized Bi4Ti3O 12 / TiO2 heterojunction photocatalyst. Although this method can effectively regulate the microstructure of materials under high temperature and high pressure conditions, the preparation period is longer, and there may be problems of insufficient stability in large-scale production. Chemical vapor deposition (CVD) is widely used to prepare high-quality heterojunction films. Zheng Lian, Ting Wu, Xining Zhang, Shuangfei Cai, Youlin Xiong, Rong Yang, Synergistic degradation of tetracycline from Mo2C / MoOx films mediated peroxymonosulfate activation and visible-light triggered photocatalysis, Chemical Engineering Journal, 2023, 469, 143774. Mo-based nano-heterostructure (Mo2C / MoOx) was prepared in situ by CVD on carbon cloth, and a new photocatalytic / PMS oxidation coupling system was constructed. CVD and PVD methods can precisely control the structure and composition of the catalyst, but the equipment cost is high, and the deposition process needs to strictly control the reaction environment, which limits its application in large-scale industrial production. These traditional preparation methods usually require multi-step chemical modification or complex interface assembly, resulting in complex preparation process, high production cost, and may reduce the stability and repeatability of the material. In recent years, the low eutectic solvent, a new type of green organic solvent, has been widely used in electrodeposition of nickel-based catalysts due to its relatively low cost, wide electrochemical window and good conductivity. Researchers have used techniques such as element doping, compounding and adding additives to modify the electronic structure, surface morphology, specific surface area and crystal orientation of nickel. For example, Wang Jian, Liu Jie, Zhao He, et al. ChCl-Urea low eutectic solvent Zn-Ni alloy electrodeposition behavior research [J]. Journal of Shenyang University of Technology, 2023, 42(05): 56-61. Electrodeposited Zn-Ni alloy coating was prepared using choline chloride-urea as the solvent.Andrew P. Abbott (Abbott AP, Ballantyne A, Harris R C, et al. Bright metal coatings from sustainable electrolytes: the effect of molecular additives on electrodeposition of nickel from a deep eutectic solvent [J]. Physical Chemistry Chemical Physics, 2017, 19(4): 3219-3231.) et al. studied the effects of nicotinic acid, methyl nicotinate, 5,5-dimethylhydantoin and boric acid on the electrodeposition of nickel from choline chloride-glycol deep eutectic solvent system, and obtained single-metal nickel-based catalysts. EAMernissi Cherigui (Mernissi Cherigui EA, Sentosun K, Bouckenooge P, et al. A Comprehensive Study of the Electrodeposition of Nickel Nanostructures from Deep Eutectic Solvents: Self-Limiting Growth by Electrolysis of Residual Water [J]. Journal of Physical Chemistry C, 2017) et al. studied the effects of nickel chloride crystal water on the nickel-based catalysts from choline chloride-urea deep eutectic solvent system, and believed that limited residual water might promote the formation of nickel hydroxide. However, in their article, the authors did not mention the application field of the obtained product, nor did they have the performance test results and analysis. In addition, the nickel hydroxide obtained by this method may have the problems of unstable amount and unstable structure, thereby affecting its performance stability. Although the deep eutectic solvent system may generate single-metal catalysts or hydroxide catalysts, stable nickel / nickel hydroxide heterojunction catalysts have not been obtained.Gao (GAO MY, SUN C B, LEIH, et al. Nitrate-induced and in situ electrochemical activation synthesis of oxygen deficiencies-rich nickel / nickel(oxy)hydroxide hybrid films for enhanced electrocatalytic water splitting[J]. Nanoscale, 2018, 10(37): 17546-17551.) et al. prepared nickel / nickel (hydroxide) hetero thin film in choline chloride-glycol eutectic solvent, and introduced oxygen vacancies by using nitrate ions to form a porous and defect-rich structure, in order to improve the electrocatalytic performance of the catalyst in HER and oxygen evolution reaction (OER). However, it should be pointed out that the composition of the eutectic solvent is usually a hydrogen bond acceptor (HBA) and a hydrogen bond donor (HBD) respectively, which can self-associate to form a new eutectic phase with a melting point lower than each individual component. The acceptor and the donor form a spatial network structure through hydrogen bonds. The strength and distribution of this three-dimensional hydrogen bond network determine the tightness of the network, affecting the physical and chemical properties of the solvent (such as melting point, viscosity and solubility) and the mobility and stability of ions. The hydrogen bond network composed of this organic matter can effectively dissolve many polar substances, and relatively speaking, the solubility of non-polar substances or inorganic salt ions in it is relatively low. Therefore, the solubility of nitrate ions in the eutectic solvent will be affected, which in turn affects the uneven distribution of charges in the electric field of the solvent system, causing the migration of nickel ions to be blocked, resulting in poor uniformity of nickel deposition, large nickel particle size, and reducing the specific surface area and catalytic performance of nickel particles.

[0005] In summary, the structural stability of the Ni / Ni(OH)2 heterojunction in the prior art needs to be improved. SUMMARY

[0006] The first object of the present application is to provide a preparation method of Ni / Ni(OH)2 heterojunction nanoelectrocatalyst which improves the stability of the heterojunction by controlling the grain growth and interface environment optimization, thereby improving the catalytic efficiency and long-term stability. The second object of the present application is to provide the application of the Ni / Ni(OH)2 heterojunction nanoelectrocatalyst prepared by the above method in the electrolytic water hydrogen production.

[0007] TECHNICAL SOLUTION The preparation method of the Ni / Ni(OH)2 heterojunction nanoelectrocatalyst according to the present application comprises the following steps:

[0008] S1, preparing a eutectic solvent;

[0009] S2, slowly add soluble nickel salt into the above eutectic solvent, heat and stir to make the nickel salt fully dissolved and no crystal precipitates; then, add imidazole additive, continue to stir and cool to room temperature to obtain a stable imidazole-containing eutectic solvent electrolyte;

[0010] S3, add the above electrolyte into an electrolytic cell to perform electrodeposition, and gradually form a uniform and compact Ni / Ni(OH)2heterojunction layer on the surface of the cathode;

[0011] S4, after the electrodeposition process is completed, take out the cathode electrode, clean and dry to obtain a preliminarily stable Ni / Ni(OH)2heterojunction catalyst;

[0012] S5, transfer the dried cathode electrode to an alkaline electrolyte system to perform activation to obtain a stable Ni / Ni(OH)2heterojunction catalyst.

[0013] Preferably, in step S1, the hydrogen bond acceptor of the eutectic solvent is choline chloride, and the hydrogen bond donor is a polyhydric alcohol. Preferably, the polyhydric alcohol is ethylene glycol. The molar ratio of choline chloride to ethylene glycol is 1:2.

[0014] Preferably, the choline chloride and the polyhydric alcohol are stirred at 60-80°C for 3-5 hours to obtain a clear and uniform eutectic solvent. Preferably, the magnetic stirrer rotates at 300-700 rpm. During the stirring process, the choline chloride and the polyhydric alcohol are fully combined.

[0015] Preferably, in step S2, the amount of imidazole additive added is 0.002-0.02 mol / L (0.002-0.02 mol of imidazole is contained in 1 L of eutectic solvent). An appropriate amount of imidazole can form a strong and stable chemical bond with the surface of the catalyst, enhancing the oxidation resistance and durability of the catalyst. Too much imidazole may cause surface blockage, reducing the effective active sites and thus reducing the catalytic performance.

[0016] Preferably, in step S2, the concentration of the nickel salt is in the range of 0.05-0.5 mol / L (0.05-0.5 mol of nickel salt is contained in 1 L of eutectic solvent).

[0017] Preferably, in step S2, the nickel salt is nickel sulfate, nickel chloride or nickel nitrate hydrate.

[0018] Preferably, in step S2, the temperature of the heating and stirring is 60-80°C, the stirring time is maintained for 4-6 hours, and the magnetic stirrer rotates at 300-700 rpm.

[0019] Preferably, in step S3, the conditions for electrodeposition are: the area of the electrodeposition cathode is 0.5-2 cm 2 , and the area of the anode is 1-3 cm2 The electrode spacing is 10-50mm, the electrodeposition temperature is 50-70℃, and the electrodeposition constant current density is -0.5 to -0.8mA / cm 2 .

[0020] Preferably, in step S3, a high-purity metal sheet copper sheet or stainless steel sheet is used as the cathode, a nickel sheet is used as the anode, and a silver / silver trifluoromethanesulfonate electrode is used as the reference electrode.

[0021] Preferably, in step S4, the cleaning is: first cleaning with acetone to remove surface residues, and then secondary cleaning with ethanol to ensure the cleanliness of the electrode surface.

[0022] Preferably, in step S4, the drying is: vacuum drying at 25-80℃ for 3-8 hours.

[0023] Preferably, in step S5, the activation condition is: cyclic voltammetry is performed 50-80 times in the potential range of 0 to -0.5V (vs. RHE), and the alkaline electrolyte is NaOH or KOH. During the activation process, under the electrochemical reaction condition, the surface of the nickel-based catalyst will be restructured to form a more porous and defect-rich structure. This structural change can increase the specific surface area of the catalyst, provide more active sites, and further improve the catalytic performance.

[0024] The application of the Ni / Ni(OH)2heterojunction nanoelectrocatalyst prepared by the method to electrolytic water hydrogen evolution.

[0025] Invention mechanism:

[0026] Choline chloride and ethylene glycol in the eutectic solvent provide a stable chemical environment through a hydrogen bond network, effectively regulating the nucleation and growth behavior of nickel. Imidazole molecules, as an organic additive containing a benzene ring, first, imidazole will interfere with the hydrogen bond network, affecting the electric field distribution in the electrolyte and the migration of nickel ions. Furthermore, imidazole molecules can form complexes with nickel ions, affecting the state of nickel ions in the solution, and thus affecting the reduction process. The nucleation mode of nickel gradually changes from three-dimensional instantaneous nucleation to three-dimensional continuous nucleation. Third, imidazole will also adsorb on the substrate, interfering with the nucleation and growth of nickel, making the grain size more refined, which means that the activity of nickel nanocrystals is significantly improved. Finally, Ni(OH)2is generated in situ on the surface of nickel, forming a stable heterojunction structure.

[0027] The application introduces an electron-rich nitrogen-containing organic substance imidazole into a choline chloride-ethylene glycol eutectic solvent system, and directly obtains a Ni / Ni(OH)2 heterojunction by means of hydrogen bonding of the hydrogen bonding network of the eutectic solvent and the coordination of nickel ions, by means of simple electrodeposition technology, realizes the synchronous deposition and interface combination of nickel and nickel hydroxide at one time, and avoids the cumbersome multi-step process in the traditional method. Further through the activation technology, the application in the alkaline water decomposition for hydrogen production is realized.

[0028] The heterojunction structure of Ni / Ni(OH)2 has a significant interface synergistic effect: nickel provides high electrical conductivity to ensure fast electron transfer; Ni(OH)2 enhances the adsorption and dissociation ability of water molecules, and optimizes the adsorption and desorption process of intermediates (such as H*). This synergistic effect effectively reduces the activation energy of the hydrogen evolution reaction and significantly improves the catalytic performance.

[0029] In addition, the Ni / Ni(OH)2 heterojunction has a porous hierarchical structure, which significantly increases the specific surface area and increases the contact efficiency of the electrolyte and the active sites. Through the adsorption regulation of imidazole and the optimization of the interface environment, the spontaneous assembly of the Ni / Ni(OH)2 heterojunction is realized, and a porous nano-catalyst with excellent hydrogen evolution performance is constructed.

[0030] Advantages: Compared with the prior art, the application has the following significant advantages: (1) By introducing imidazole molecules, the application inhibits the excessive aggregation of nickel grains, realizes grain refinement, changes the charge distribution of the electrolyte, promotes the in-situ generation of Ni(OH)2, and then directly constructs a Ni / Ni(OH)2 heterojunction nano-catalyst. Through the control of grain growth and the optimization of the interface environment, the high efficiency and long-term stability of the catalyst are ensured, and the catalyst has good repeatability and industrialization potential; (2) Compared with the traditional method, the application simplifies the preparation process, and the process is simple, mild and easy to realize; the experimental materials are easy to obtain, the production cost is reduced, and the application is suitable for large-scale industrial production; (3) The Ni / Ni(OH)2 heterojunction structure prepared by the method of the application has a significant interface synergistic effect, effectively reduces the activation energy of the hydrogen evolution reaction, significantly improves the catalytic performance, and the Ni / Ni(OH)2 heterojunction has a porous structure, increases the specific surface area, improves the contact efficiency of the electrolyte and the active sites, and further enhances the catalytic reaction performance. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 SEM image of the catalyst prepared by electrodeposition in step S4 in Example 1;

[0032] Figure 2 XRD image of the catalyst prepared by electrodeposition in step S4 in Example 2;

[0033] Figure 3XPS chart of catalyst prepared by electrodeposition of step S4 in embodiment 3, wherein a is XPS total spectrum; b is N1s photoelectron spectrum; c is Ni 2p photoelectron spectrum;

[0034] Figure 4 Comparison chart of hydrogen evolution catalytic efficiency of catalysts prepared in embodiments 1-3 and comparative examples 1-2;

[0035] Figure 5 Comparison chart of hydrogen evolution catalytic efficiency of catalysts prepared in comparative example 1 and embodiment 2;

[0036] Figure 6 Long-term catalytic stability test of catalyst prepared in embodiment 4;

[0037] Figure 7 Long-term catalytic stability test of catalyst prepared in comparative example 2. DETAILED DESCRIPTION

[0038] The technical solutions of the present application are further described below in combination with embodiments.

[0039] Embodiment 1

[0040] The preparation method of the Ni / Ni(OH)2heterojunction nanoelectrocatalyst described in the present application comprises the following steps:

[0041] S1, mix choline chloride and ethylene glycol at a molar ratio of 1:2, stir at a constant temperature of 60°C for 5 hours, and the stirring speed is 700 rpm, until a clear and uniform eutectic solvent is formed. After stirring, 50 mL is measured for standby.

[0042] S2, slowly add 10 mmol of NiCl2·6H2O (concentration: 0.2 mol of nickel salt per 1 L of eutectic solvent) to 50 mL of eutectic solvent in step S1, and stir at a constant temperature of 60°C for 6 hours, the stirring speed is 700 rpm, so that the nickel salt is fully dissolved and no crystals are precipitated. Then, add 1 mmol of imidazole (concentration: 0.02 mol of imidazole per 1 L of eutectic solvent) to the solution and continue to stir to room temperature, to obtain a transparent and stable imidazole-containing eutectic solvent electrolyte.

[0043] S3, use 1 cm 2 High-purity copper sheet as cathode, 2 cm 2 Nickel sheet as anode, and silver / silver trifluoromethanesulfonate as reference electrode. The electrolyte obtained in step S2 is introduced into the electrolysis tank, and electrodeposition is carried out at a constant temperature of 50°C for 1 hour at a constant current density of-0.5 mA / cm 2 The three-electrode interelectrode distance is maintained at 20 mm.

[0044] S4, after the electrodeposition is finished, the cathode electrode is taken out, first washed with acetone to remove the electrolyte and surface residues, and then washed with ethanol for the second time. Subsequently, the cathode electrode is placed in a vacuum environment under a constant temperature condition of 25 DEG C for drying for 8 hours until there is no residual solvent on the electrode surface, and a preliminarily stable Ni / Ni(OH)2heterojunction nanoelectrocatalyst electrode is obtained.

[0045] S5, the dried cathode electrode is placed into a 1 mol / L KOH electrolyte, and cyclic voltammetry scanning is performed in a potential range of 0~0.5V (vs. RHE) for 50 cycles to complete activation.

[0046] Example 2

[0047] On the basis of Example 1, the addition amount of imidazole is changed to 0.1 mmol (the concentration is 0.002 mol of imidazole contained in 1 L of eutectic solvent), and the rest of the conditions remain unchanged.

[0048] Example 3

[0049] On the basis of Example 1, the addition amount of imidazole is changed to 0.75 mmol (the concentration is 0.015 mol of imidazole contained in 1 L of eutectic solvent), and the rest of the conditions remain unchanged.

[0050] Example 4

[0051] The preparation method of the Ni / Ni(OH)2heterojunction nanoelectrocatalyst disclosed in the application comprises the following steps:

[0052] S1, choline chloride and ethylene glycol are mixed according to a molar ratio of 1:2, stirred under a constant temperature condition of 70 DEG C for 4 hours, and the stirring speed is 600 rpm until a clear and uniform eutectic solvent is formed. After the stirring is finished, 50 mL is measured for standby.

[0053] S2, 25 mmol of Ni(NO3)2.6H2O (the concentration is 0.5 mol of nickel salt contained in 1 L of eutectic solvent) is slowly added into 50 mL of the eutectic solvent in step S1, and stirred under a constant temperature condition of 80 DEG C for 4 hours, and the stirring speed is 300 rpm so that the nickel salt is fully dissolved and no crystal is precipitated. Subsequently, 0.1 mmol of imidazole (the concentration is 0.002 mol of imidazole contained in 1 L of eutectic solvent) is added into the solution to continue stirring until the room temperature is reached, and a transparent and stable eutectic solvent electrolyte containing imidazole is obtained.

[0054] S3, the eutectic solvent electrolyte obtained in step S2 is introduced into an electrolytic cell, and the cathode electrode is plated with nickel under a constant temperature condition of 70 DEG C at a current density of-0.6 mA / cm 2 A high-purity stainless steel sheet is used as the cathode, a 3 cm 2 A nickel sheet is used as the anode, and silver / silver trifluoromethanesulfonate is used as the reference electrode. The electrolyte obtained in step S2 is introduced into an electrolytic cell, and the cathode electrode is plated with nickel under a constant temperature condition of 70 DEG C at a current density of-0.6 mA / cm 2The electrodeposition was performed at a constant current density for 1 hour, and the three-electrode interelectrode distance was maintained at 50 mm.

[0055] S4, after the electrodeposition was completed, the cathode electrode was taken out, first cleaned with acetone to remove the electrolyte and surface residues, and then cleaned twice with ethanol. Subsequently, the cathode electrode was placed in a vacuum environment at a constant temperature of 45℃ for drying for 4 hours until there was no residual solvent on the surface of the electrode, and a preliminarily stable Ni / Ni(OH)2heterojunction nanoelectrocatalyst was obtained. The XRD of the obtained catalyst is shown in Figure 2 , and the XPS is shown in Figure 3 .

[0056] S5, the dried cathode electrode was placed in a 1 mol / L KOH electrolyte, and cyclic voltammetry scanning was performed at a potential range of 0 to -0.5 V (vs. RHE) for 50 cycles to complete activation.

[0057] The catalyst obtained in this example has basically the same hydrogen evolution reaction performance as that in Example 2.

[0058] Example 5

[0059] The preparation method of the Ni / Ni(OH)2heterojunction nanoelectrocatalyst according to the present application comprises the following steps:

[0060] S1, choline chloride and ethylene glycol were stirred at a constant temperature of 80℃ for 3 hours at a speed of 300 rpm according to a molar ratio of 1:2 until a clear and uniform eutectic solvent was formed. After the stirring was completed, 50 mL was measured for standby.

[0061] S2, 17.5 mmol of NiSO4·6H2O was slowly added to the 50 mL eutectic solvent in step S1, and stirred at a constant temperature of 70℃ for 5 hours at a speed of 650 rpm, so that the nickel salt was fully dissolved and no crystals were precipitated. Subsequently, 0.75 mmol of imidazole (concentration: 0.015 mol of imidazole per 1 L of eutectic solvent) was added to the solution, and the stirring was continued to room temperature, to obtain a transparent and stable imidazole-containing eutectic solvent electrolyte.

[0062] S3, the three-electrode interelectrode distance was maintained at 35 mm, and the electrodeposition was performed at a constant current density for 1 hour. 2 A high-purity stainless steel sheet was used as the cathode, a 1.5 cm 2 nickel sheet was used as the anode, and silver / silver trifluoromethanesulfonate was used as the reference electrode. The electrolyte obtained in step S2 was introduced into the electrolysis tank, and the electrodeposition was performed at a constant current density of -0.8 mA / cm 2 The electrodeposition was performed at a constant current density for 1 hour, and the three-electrode interelectrode distance was maintained at 50 mm.

[0063] S4, after the electrodeposition, the cathode electrode was taken out, first cleaned with acetone to remove the electrolyte and surface residues, and then cleaned with ethanol for the second time. Subsequently, the cathode electrode was placed in a vacuum environment at 85°C constant temperature for drying for 3 hours until there was no residual solvent on the surface of the electrode, and a preliminarily stable Ni / Ni(OH)2heterojunction nanoelectrocatalyst was obtained.

[0064] S5, the dried cathode electrode was subjected to cyclic voltammetry scanning in 1 mol / L NaOH electrolyte at a potential range of 0 to -0.5V (vs. RHE) for 50 cycles to complete the activation. The long-term stability test of the catalyst obtained under the above conditions is shown in Figure 4 .

[0065] The catalyst obtained in the example has basically the same hydrogen evolution reaction performance as that in Example 3.

[0066] Comparative Example 1

[0067] On the basis of Example 2, no imidazole was added, and the other conditions were unchanged.

[0068] Comparative Example 2

[0069] On the basis of Example 3, the activation step S5 was not performed, and the other conditions were unchanged.

[0070] Structural characterization

[0071] The catalysts prepared in Examples 1-3 were characterized, and the results are shown in Figures 1 to 3 .

[0072] Figure 1 The SEM image of the catalyst prepared in step S4 of Example 1 is shown in the figure. As can be seen from the figure, the surface of the catalyst presents a complex porous structure, the particle morphology is irregular, mainly presents polyhedron and sphere, the particles are uniformly distributed, and the pore sizes are different, forming a network structure. There are obvious gaps between the particles, and the pore sizes vary from nanometer to hundreds of nanometers. Such multi-level pore structure not only provides more active sites, but also helps to improve the adsorption, diffusion and charge transfer efficiency of the reactants.

[0073] Figure 2The image shows the XRD pattern of the catalyst prepared by electrodeposition in step S4 of Example 2. As can be seen from the image, except for 43.3°, 50.4°, 74.1°, and 89.9° (attributed to the Cu substrate), the catalyst prepared in Example 2 exhibits obvious diffraction peaks at 44.5°, 51.8°, and 76.4°, corresponding to the (111), (200), and (220) crystal planes of Ni, respectively. Due to the low Ni(OH)₂ content, weak diffraction signals were detected only at 33.1° ((101) crystal plane) and 38.5° ((110) crystal plane). This demonstrates that electrodeposition using a eutectic solvent system can stably prepare Ni / Ni(OH)₂ heterojunction nanocatalysts.

[0074] Figure 3 XPS plot of the catalyst prepared by electrodeposition in step S4 of step 3. Figure 3 b shows the N1s XPS photoelectron spectrum of the catalyst, indicating the presence of nitrogen doping signals on the catalyst surface. The N1s peak is mainly concentrated at 398.5 eV. Here, 398.5 eV corresponds to MN (metal-nitrogen bond), indicating that imidazole participates in the nickel electrodeposition process and may form a Ni-N structure, which helps to improve catalytic activity. Figure 3 c shows that the nickel in the prepared catalyst is mainly in the metallic state (Ni) and divalent nickel (Ni). 2+ The nickel hydroxide exists in the form of nickel hydroxide, with binding energies ranging from 845 eV to 865 eV corresponding to the characteristic peaks of Ni 2p1 and Ni 2p3. The Ni 2p3 peak at Ebe = 852.7 eV indicates that nickel is predominantly in the metallic state (Ni), while the transition at Ebe = 856 eV is related to the chemical characteristics of nickel hydroxide. These results further verify that the catalyst surface is a mixture of nickel and nickel hydroxide. Furthermore, an appropriate amount of oxygen vacancies can promote the redistribution of electrons on the catalyst surface, thereby balancing electron transfer capacity and optimizing the adsorption and desorption of reaction intermediates. 0 with Ni 2+ The atomic ratio of 40.49:59.51 indicates that the presence of imidazole significantly affects the valence state distribution of Ni, and the oxygen vacancy level can be effectively adjusted by regulating its concentration, thereby improving catalytic performance.

[0075] Performance testing

[0076] 1. HER performance testing

[0077] The catalysts prepared in Examples 1-3 and Comparative Examples 1-2 were subjected to a current of 10 mA / cm². -2 or 100mA / cm -2 HER performance was tested at current density.

[0078] Test Method: The catalyst was fixed on the cathode side of an H-type electrolytic cell with a Luggin capillary. An anion exchange membrane FAB-PK-130 was used to separate the anode and cathode chambers. A graphite rod was used as the anode, and an Hg / HgO electrode was used as the reference electrode, forming a three-electrode system. The hydrogen evolution performance of the catalyst was evaluated by linear voltammetry at a scan rate of 2 mV / s within a voltage range of 0 to -0.4 V in a 1 mol / L KOH solution at room temperature. The test results are as follows: Figure 4 As shown.

[0079] Depend on Figure 4 It can be seen that at 10mA / cm -2 At the given current density, the hydrogen evolution overpotential of the catalyst in Example 1 was -271 mV, and the Tafel slope was 68.62 mV·dec. -1 In Example 2, the hydrogen evolution overpotential of the catalyst was -240.18 mV, and the Tafel slope was 55.22 mV·dec. -1 The hydrogen evolution overpotential of the catalyst in Example 3 was -225 mV, and the Tafel slope was 51.98 mV·dec. -1 The hydrogen evolution overpotential of the catalyst in Comparative Example 1 was -312.4 mV, and the Tafel slope was 85.43 mV·dec. -1 The hydrogen evolution overpotential of the catalyst in Comparative Example 2 was -287 mV, and the Tafel slope was 68.15 mV·dec. -1 .

[0080] Data from Examples 1-3 show that the hydrogen evolution performance of the catalyst first increases and then decreases with increasing imidazole concentration. This is because imidazole has a grain-refining effect on the nickel-based catalyst; as the concentration increases, the grain size gradually decreases, and the morphology changes from a mixed structure of lamellar and particulate to a needle-like and serrated structure. At low concentrations, grain refinement helps to improve catalytic activity; at high concentrations, imidazole and Ni... 2+ Complexation occurs, reducing the amount of free Ni in the solution. 2+ The effective concentration of imidazole affects the precipitation of Ni(OH)2, reducing the formation of nickel hydroxide, leading to poor adhesion and structural instability of the deposited layer, and consequently decreasing catalytic activity. Simultaneously, an appropriate amount of Ni(OH)2 is beneficial to the HER reaction, promoting water dissociation and enhancing electron transport capacity; however, excessive Ni(OH)2 may cover the active sites of metallic Ni, increasing electrode resistance and reducing catalyst activity and stability. Therefore, the effect of imidazole concentration on hydrogen evolution performance is a matter of balance, requiring optimization of its addition amount to achieve optimal catalytic performance.

[0081] Compared to Example 2, Comparative Example 1 showed a decrease in catalytic hydrogen evolution reaction performance. This is because Comparative Example 1 did not contain imidazole, which lacked the effect of refining the grain size and regulating the morphology of the nickel-based catalyst. As a result, the catalyst grain size was larger, the surface active sites were reduced, and the deposition layer structure was more loose or uneven, thereby reducing the hydrogen evolution performance of the catalyst.

[0082] Compared to Example 3, Comparative Example 2 showed a decrease in the performance of the hydrogen evolution reaction. This is because Comparative Example 2 was not activated, resulting in more oxides or unstable substances on the catalyst surface, which affected the conductivity of the electrode and the exposure of active sites, thereby reducing the catalytic efficiency and stability of the water desorption hydrogen reaction.

[0083] To evaluate the catalytic performance of the catalyst under high current density in an industrial environment, at 10 mA / cm², the catalyst was subjected to various current densities. 2 and 100mA / cm 2 The hydrogen evolution reaction (HER) performance of the catalysts prepared in Example 2 and Comparative Example 1 was tested at a current density of [value missing]. The test results are as follows: Figure 5 As shown.

[0084] Depend on Figure 5 It can be seen that at 10mA / cm 2 At a current density of -312.4mV, the overpotential of Comparative Example 1 without imidazole was -312.4mV, which was about 1.3 times higher than that of Example 2 with imidazole. However, at a high current density, Example 2 with imidazole performed better, with an increase of only 54.72mV, making it more suitable for industrial applications.

[0085] 2. Catalyst long-term stability test

[0086] The long-term stability of the catalysts in Example 4 and Comparative Example 2 was tested.

[0087] The testing method is the same as the HER performance test; the stability test is conducted at 0 mA·cm. -2 A 24-hour chronopotential method test was performed at a current density of [value missing]. The test results are as follows: Figure 6 and 7 As shown.

[0088] The catalyst in Example 4 at 10 mA·cm -2The initial overpotential was -292 mV when used as a cathode for HER at a current density of 10 mA cm-2, and decreased to -340 mV after 5.8 h. As the measurement proceeded further, the overpotential remained almost unchanged, stabilizing at about 340 mV even after 15 h, indicating that the catalyst has good electrochemical stability during long-term operation, can maintain a lower overpotential for a long time, and reduce voltage loss. In addition, this also indicates that the active sites of the catalyst do not undergo significant deactivation or loss, showing high durability and reliability, and is suitable for long-term water electrolysis hydrogen evolution applications.

[0089] The long-term stability test of the catalyst obtained from Comparative Example 2 without activation is shown in Figure 6. In the first 12 hours, the overpotential showed a slower growth trend, but by the 15th hour, the overpotential fluctuated significantly, and after 20 hours, the fluctuation was more obvious, indicating that the stability of the catalyst surface structure gradually decreased. Figure 7 The long-term stability test of the catalyst obtained from Comparative Example 2 without activation is shown in Figure 6. In the first 12 hours, the overpotential showed a slower growth trend, but by the 15th hour, the overpotential fluctuated significantly, and after 20 hours, the fluctuation was more obvious, indicating that the stability of the catalyst surface structure gradually decreased.

Claims

1. A method for preparing a Ni / Ni(OH)₂ heterojunction nano-electrocatalyst, characterized in that, Includes the following steps: S1. Preparation of eutectic solvent; S2. Add the soluble nickel salt to the above eutectic solvent, heat and stir to fully dissolve the nickel salt and prevent crystal precipitation; then add the imidazole additive, continue stirring and cool to room temperature to obtain a stable imidazole-containing eutectic solvent electrolyte. S3. Add the above electrolyte to the electrolytic cell and perform electrodeposition. A uniform and dense Ni / Ni(OH)2 heterojunction layer is gradually deposited on the cathode surface. S4. After the electrodeposition process is completed, remove the cathode electrode, clean and dry it; S5. The dried cathode electrode is transferred to an alkaline electrolyte system for activation to obtain a stable Ni / Ni(OH)2 heterojunction catalyst. In step S1, the hydrogen bond acceptor of the eutectic solvent is choline chloride, and the hydrogen bond donor is a polyol. In step S2, the amount of imidazole additive added is 0.002~0.02 mol / L, specifically meaning that 1L of eutectic solvent contains 0.002~0.02 mol of imidazole; In step S5, the activation conditions are: 50 to 80 cycles of cyclic voltammetry in a potential range of 0 to -0.5 V, and the alkaline electrolyte is NaOH or KOH solution.

2. The method for preparing Ni / Ni(OH)₂ heterojunction nano-electrocatalyst according to claim 1, characterized in that, In step S3, the electrodeposition conditions are as follows: the electrodeposition cathode area is 0.5~2 cm². 2 The anode area is 1~3 cm². 2 The electrode spacing is 10~50 mm, the electrodeposition temperature is 50℃~70℃, and the electrodeposition constant current density is -0.5~-0.8 mA / cm².

3. The method for preparing Ni / Ni(OH)₂ heterojunction nano-electrocatalyst according to claim 1, characterized in that, In step S2, the concentration of the nickel salt is in the range of 0.05~0.5 mol / L, specifically meaning that 1L of eutectic solvent contains 0.05~0.5 mol of nickel salt.

4. The method for preparing Ni / Ni(OH)₂ heterojunction nano-electrocatalyst according to claim 1, characterized in that, In step S2, the nickel salt is nickel sulfate, nickel chloride, or nickel nitrate hydrate.

5. The method for preparing Ni / Ni(OH)₂ heterojunction nano-electrocatalyst according to claim 1, characterized in that, The choline chloride and polyol are stirred at 60℃~80℃ for 3~5 hours to obtain a clear and uniform eutectic solvent.

6. The method for preparing Ni / Ni(OH)₂ heterojunction nano-electrocatalyst according to claim 1, characterized in that, In step S4, the cleaning process involves first cleaning with acetone to remove surface residues, and then performing a second cleaning with ethanol.

7. The application of the Ni / Ni(OH)2 heterojunction nano-electrocatalyst prepared by the method according to any one of claims 1 to 6 in the electrolysis of water to produce hydrogen.

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