Preparation method of Ni / Ni (OH) 2 heterojunction nano electrocatalyst and application of Ni / Ni (OH) 2 heterojunction nano electrocatalyst in hydrogen production

Abstract

The invention discloses a preparation method of a Ni / Ni (OH) 2 heterojunction nano electrocatalyst and application of the Ni / Ni (OH) 2 heterojunction nano electrocatalyst in hydrogen production. The method comprises the following steps: preparing a eutectic solvent; then adding nickel salt, heating and stirring to fully dissolve the nickel salt without crystal precipitation; adding an imidazole additive, and uniformly stirring to obtain an electrolyte; the electrolyte is added into an electrolytic bath for electro-deposition, and a uniform and compact Ni / Ni (OH) 2 heterojunction layer is gradually deposited on the surface of a cathode; and cleaning, drying and activating the cathode electrode to obtain the catalyst. According to the preparation method, imidazole is introduced into a choline chloride-ethylene glycol eutectic solvent system, and an electro-deposition technology is adopted, so that synchronous deposition and interface bonding of nickel and nickel hydroxide are realized at one time, the Ni / Ni (OH) 2 heterojunction is obtained, and a tedious multi-step process in a traditional method is avoided; in addition, the high efficiency and long-term stability of the catalyst for catalyzing the hydrogen evolution reaction are improved, and good repeatability and industrialization potential are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of electrocatalysts, and particularly relates to a preparation method of a Ni / Ni(OH) 2 heterojunction nanoelectrocatalyst and its application in hydrogen production. Background Art

[0002] As a clean and efficient energy production technology, water electrolysis for hydrogen production has important applications in the storage and utilization of renewable energy. Especially in the HER reaction carried out in an alkaline medium, due to its environmental friendliness, low cost and other characteristics, it has gradually become a key research direction. The key to water electrolysis for hydrogen production lies in the development of efficient 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 regarded as ideal substitutes for platinum-based catalysts because of their rich resource reserves, low cost and good catalytic activity, especially showing good activity in the alkaline hydrogen evolution reaction. However, traditional nickel-based catalysts still face some bottlenecks in the application process, 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 catalyst may gradually become inactivated, resulting in a decrease in the hydrogen evolution efficiency. Therefore, how to improve the stability of the nickel-based catalyst, enhance its surface activity and anti-inactivation ability in the long-term reaction has become the key challenge to improve its hydrogen evolution performance.

[0004] To overcome the performance bottleneck of nickel-based catalysts in the hydrogen evolution reaction, strategies to enhance catalytic performance by constructing heterojunction structures have been proposed in recent years. Conventional methods for preparing heterojunction materials include mechanical exfoliation, hydrothermal method, chemical vapor deposition (CVD), physical vapor deposition (PVD), etc. Among them, the mechanical exfoliation method is mainly used to prepare van der Waals heterojunctions of two-dimensional materials by physically stacking different two-dimensional materials to form a heterostructure. 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 metal salt thermal decomposition combined with a water-assisted foaming technique to obtain a large aspect ratio lamellar structure, and these lamellae were successfully prepared into independent and self-supporting two-dimensional flakes by tape peeling. However, this method relies on the layered structure of the material itself and is only applicable to materials with weak van der Waals interactions, not applicable to most bulk metals and non-layered compounds. In addition, it is difficult to precisely control the thickness and uniformity of the exfoliated layer, and the yield is low, making it difficult to meet the requirements of large-scale preparation. The hydrothermal method is widely used in the construction of heterostructures of metal oxides and composite materials. For example, Kansong Chen, Yang Li, Han Tian, Haoshuang Gu (Synthesis and Photocatalytic Performance of Heterostructured Nano-Composite Bi 4 Ti 3 O 12 / TiO 2 [J]. Acta Materiae Compositae Sinica, 2014, 28(7): 503-508.) et al. successfully synthesized Bi 4 Ti 3 O 12 / TiO 2Heterojunction photocatalyst. Although this method can effectively regulate the microstructure of materials under high-temperature and high-pressure conditions, the preparation cycle is long, and problems such as insufficient stability may be faced during large-scale production. Chemical vapor deposition method has been widely used in the preparation of high-quality heterojunction thin films. For example, Rong Yang (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.) in-situ prepared molybdenum-based nanoheterostructures (Mo2C / MoOx) on carbon cloth by CVD method and constructed a new photocatalysis / PMS oxidation coupling system using it. CVD and PVD methods can accurately control the structure and composition of the catalyst, but the equipment cost is expensive, and the reaction environment needs to be strictly controlled during the deposition process, which limits their application in large-scale industrial production. These traditional preparation methods usually require multiple chemical modifications or complex interfacial assemblies, resulting in complex preparation processes, high production costs, and may reduce the stability and repeatability of the materials. In recent years, deep eutectic solvents, a new type of green organic solvent, have been widely used in the electrodeposition preparation of nickel-based catalysts due to their relatively low cost, wide electrochemical window, and good conductivity. Researchers have used techniques such as element doping, compounding, and adding additives to modulate the electronic structure, surface morphology, specific surface area, and crystal orientation of nickel. For example, Jian Wang (Jian Wang, Jie Liu, He Zhao, etc. Study on the electrodeposition behavior of Zn-Ni alloy in choline chloride-urea deep eutectic solvent [J]. Journal of Shenyang Ligong University, 2023, 42(05): 56-61.) et al. prepared Zn-Ni alloy coatings by electrodeposition 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 nickel electrodeposition in the choline chloride-ethylene glycol deep eutectic solvent system and obtained a single-metal nickel-based catalyst. E. A. Mernissi 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 effect of nickel chloride crystal water on the nickel-based catalyst in the choline chloride-urea deep eutectic solvent system and believed that limited residual water might promote the formation of nickel hydroxide. However, in their articles, the authors did not describe the application fields of the obtained products, let alone the relevant performance test results and analysis. In addition, the nickel hydroxide obtained in this way may have problems of unstable quantity and unstable structure, thus 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 CB, 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) heterogeneous films in choline chloride-ethylene glycol low eutectic solvents, and used nitrate ions to introduce oxygen vacancies 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 components of the low eutectic solvent usually act as hydrogen bond acceptors (HBAs) and hydrogen bond donors (HBDs), respectively, which can self-associate to form a new eutectic phase with a melting point lower than that of 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 compactness of the network, affecting the physicochemical properties of the solvent (such as melting point, viscosity and solubility) as well as the mobility and stability of the ions. This hydrogen bond network composed of organic matter can effectively dissolve many polar substances. Relatively speaking, the solubility of non-polar substances or inorganic salt ions in it is relatively low. Therefore, the solubility of nitrate ions in low eutectic solvents is bound to be affected, which in turn affects the uneven charge distribution in the electric field of the solvent system, resulting in the obstruction of the migration of nickel ions, resulting in poor uniformity of nickel deposition, larger nickel particle size, and reduced specific surface area and catalytic performance of nickel particles.

[0005] In summary, the Ni / Ni(OH) 2 The structural stability of the heterojunction needs to be improved. Summary of the invention

[0006] Objective of the invention: The first objective of the present invention is to provide a Ni / Ni(OH) catalyst which improves the stability of the heterojunction by controlling the grain growth and optimizing the interface environment, thereby improving the catalytic efficiency and long-term stability. 2 A method for preparing a heterojunction nano-electrocatalyst; The second object of the present invention is to provide a Ni / Ni(OH) prepared by the above method 2 Application of heterojunction nanoelectrocatalysts in hydrogen production by water electrolysis.

[0007] Technical solution: The Ni / Ni(OH) 2 The preparation method of heterojunction nano electrocatalyst comprises the following steps:

[0008] S1. Prepare a deep eutectic solvent;

[0009] S2. Slowly add a soluble nickel salt to the above deep eutectic solvent, heat and stir to fully dissolve the nickel salt without crystal precipitation; subsequently, add an imidazole additive, continue to stir and cool to room temperature to obtain a stable imidazole-containing deep eutectic solvent electrolyte;

[0010] S3. Add the above electrolyte to an electrolytic cell for electrodeposition, and a uniform and dense Ni / Ni(OH) 2 heterojunction layer is gradually deposited on the cathode surface;

[0011] S4. After the electrodeposition process ends, take out the cathode electrode, wash and dry it to obtain a preliminarily stable Ni / Ni(OH) 2 heterojunction catalyst;

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

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

[0014] Preferably, the choline chloride and the polyol are stirred at 60 °C to 80 °C for 3 to 5 hours to obtain a clear and uniform deep eutectic solvent. Preferably, the rotational speed of the magnetic stirrer is 300 to 700 rpm. During the stirring process, choline chloride and the polyol are fully combined.

[0015] Preferably, in step S2, the addition amount of the imidazole additive is 0.002 to 0.02 mol / L (0.002 to 0.02 mol of imidazole is contained in 1 L of the deep eutectic solvent). An appropriate amount of imidazole can enhance the antioxidant and durability of the catalyst by forming strong and stable chemical bonds with the catalyst surface. Excessive imidazole may cause surface blockage, reduce the effective active sites, and thus reduce the catalytic performance.

[0016] Preferably, in step S2, the concentration range of the nickel salt is 0.05 to 0.5 mol / L (0.05 to 0.5 mol of the nickel salt is contained in 1 L of the deep 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 °C to 80 °C, the stirring time is maintained for 4 to 6 hours, and the rotational speed of the magnetic stirrer is 300 to 700 rpm.

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

[0020] Preferably, in step S3, a metal sheet, a high-purity copper sheet or a 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 as follows: first, clean with acetone to remove surface residues, and then perform secondary cleaning with ethanol to ensure the cleanliness of the electrode surface.

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

[0023] Preferably, in step S5, the activation conditions are as follows: perform cyclic voltammetry for 50 - 80 cycles in the potential range of 0 - -0.5 V (vs. RHE), and the alkaline electrolyte is NaOH or KOH. During the activation process, under the conditions of electrochemical reaction, the surface of the nickel-based catalyst will undergo reconstruction 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] Application of the Ni / Ni(OH) 2 heterojunction nanoelectrocatalyst prepared by the method of the present invention in hydrogen evolution of electrolyzed water.

[0025] Invention mechanism:

[0026] Choline chloride and ethylene glycol in the deep eutectic solvent provide a stable chemical environment through a hydrogen bond network, effectively regulating the nucleation and growth behavior of nickel. As an organic additive containing a benzene ring, imidazole molecules, first of all, will interfere with the hydrogen bond network, affect the electric field distribution in the electrolyte and the migration of nickel ions. Moreover, imidazole molecules can form complexes with nickel ions, affect the state of nickel ions in the solution, and thus affect their reduction process. The nucleation mode of nickel gradually changes from three-dimensional instantaneous nucleation to three-dimensional continuous nucleation. Thirdly, imidazole will also have an adsorption effect 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, and finally Ni(OH) is in-situ generated on the nickel surface 2 , forming a stable heterojunction structure.

[0027] Through the choline chloride-ethylene glycol eutectic solvent system, an electron-rich nitrogen-containing organic compound imidazole is introduced into it. By virtue of its hydrogen bond interaction with the hydrogen bond network of the eutectic solvent and its coordination interaction with nickel ions, a simple electrodeposition technique is used to directly obtain Ni / Ni(OH) 2 heterojunction, realizing the synchronous deposition and interfacial combination of nickel and nickel hydroxide at one time, and avoiding the cumbersome multi-step processes in traditional methods. Further, through an activation technique, its application in alkaline water electrolysis for hydrogen production is realized.

[0028] Ni / Ni(OH) 2 The heterojunction structure has a significant interfacial synergistic effect: nickel provides high conductivity to ensure rapid electron transfer; Ni(OH) 2 enhances the adsorption and dissociation ability of water molecules and optimizes the adsorption and desorption processes 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 improves the contact efficiency between the electrolyte and the active sites. Through the adsorption regulation of imidazole and the optimization of the interfacial environment, the self-assembly of the Ni / Ni(OH) 2 heterojunction is realized, and a porous nanocatalyst with excellent hydrogen evolution performance is constructed.

[0030] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages: (1) By introducing imidazole molecules, the present invention inhibits the excessive aggregation of nickel grains, realizes grain refinement, and changes the charge distribution of the electrolyte, promoting the in-situ generation of Ni(OH) 2 , and then directly constructs a Ni / Ni(OH) 2 heterojunction nanocatalyst. By controlling grain growth and optimizing the interfacial environment, the high efficiency and long-term stability of the catalyst are ensured, and it has good repeatability and industrialization potential; (2) Compared with traditional methods, the present invention simplifies the preparation process, has simple technology, mild conditions, and is easy to implement; the experimental materials are easy to obtain, the production cost is reduced, and it is suitable for large-scale industrial production applications; (3) The Ni / Ni(OH) 2 heterojunction structure prepared by the method of the present invention has a significant interfacial 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, which increases the specific surface area and improves the contact efficiency between the electrolyte and the active sites, further enhancing the catalytic reaction performance. Description of the Drawings

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

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

[0033] Figure 3 XPS pattern of the catalyst prepared by electrodeposition in step S4 of Example 3, where a is the total XPS spectrum; b is the N1s photoelectron spectrum; c is the Ni 2p photoelectron spectrum;

[0034] Figure 4 Hydrogen evolution catalytic efficiency comparison chart of Examples 1 - 3 and Comparative Examples 1 - 2;

[0035] Figure 5 Hydrogen evolution reaction catalytic efficiency comparison chart of the catalysts prepared in Comparative Example 1 and Example 2;

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

[0037] Figure 7 Long - term catalytic stability test of the catalyst prepared in Comparative Example 2. Detailed implementation mode

[0038] The technical solution of the present invention will be further described below in conjunction with the examples.

[0039] Example 1

[0040] The preparation method of the Ni / Ni(OH) 2 heterojunction nano - electrocatalyst includes 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 at a rotation speed of 700 rpm until a clear and uniform eutectic solvent is formed. After the stirring ends, measure 50 mL for standby.

[0042] S2. Slowly add 10 mmol of NiCl 2 ·6H 2 O (the concentration is 0.2 mol of nickel salt per 1 L of the eutectic solvent) into the 50 mL of the eutectic solvent in step S1, and stir at a constant temperature of 60 °C for 6 hours at a rotation speed of 700 rpm to fully dissolve the nickel salt without crystal precipitation. Subsequently, add 1 mmol of imidazole (the concentration is 0.02 mol of imidazole per 1 L of the eutectic solvent) to the solution and continue stirring until it cools to room temperature to obtain a transparent and stable imidazole - containing eutectic solvent electrolyte.

[0043] S3. Using a 1 cm 2A high-purity copper sheet is used as the cathode, 2 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 the electrolytic cell, and under the condition of a constant temperature of 50 °C, a constant current density of -0.5 mA / cm 2 is used for electro-deposition for 1 hour, and the three-electrode spacing is maintained at 20 mm.

[0044] S4. After the electro-deposition is completed, the cathode electrode is taken out, first washed with acetone to remove the electrolyte and surface residues, and then washed twice with ethanol. Subsequently, the cathode electrode is placed in a vacuum environment at a constant temperature of 25 °C and dried for 8 hours until there is no residual solvent on the electrode surface, obtaining a preliminarily stable Ni / Ni(OH) 2 heterojunction nanoelectrocatalyst electrode.

[0045] S5. The dried cathode electrode is placed in a 1 mol / L KOH electrolyte, and cyclic voltammetry scanning is performed in the potential range of 0 to -0.5 V (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 per 1 L of the deep eutectic solvent), and the other 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 per 1 L of the deep eutectic solvent), and the other conditions remain unchanged.

[0050] Example 4

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

[0052] S1. Choline chloride and ethylene glycol are mixed according to a molar ratio of 1:2, stirred at a constant temperature of 70 °C for 4 hours at a rotation speed of 600 rpm until a clear and uniform deep eutectic solvent is formed. After the stirring is completed, 50 mL is measured and reserved.

[0053] S2. 25 mmol of Ni(NO 3 ) 2 ·6H 2O (with a concentration of 0.5 mol of nickel salt per 1 L of the deep eutectic solvent) was slowly added to 50 mL of the deep eutectic solvent in step S1, and stirred at a constant temperature of 80 °C for 4 hours at a rotation speed of 300 rpm to fully dissolve the nickel salt without crystal precipitation. Subsequently, 0.1 mmol of imidazole (with a concentration of 0.002 mol of imidazole per 1 L of the deep eutectic solvent) was added to the solution and stirred until it cooled to room temperature to obtain a transparent and stable imidazole-containing deep eutectic solvent electrolyte.

[0054] S3. Using a 0.5 cm 2 high-purity stainless steel sheet as the cathode, a 3 cm 2 nickel sheet as the anode, and silver / silver trifluoromethanesulfonate as the reference electrode. The electrolyte obtained in step S2 was introduced into the electrolytic cell, and at a constant temperature of 70 °C, electrodeposition was carried out at a constant current density of -0.6 mA / cm 2 for 1 hour, keeping the three-electrode spacing at 50 mm.

[0055] S4. After the electrodeposition was completed, the cathode electrode was taken out, first washed with acetone to remove the electrolyte and surface residues, and then washed twice with ethanol. Subsequently, the cathode electrode was placed in a vacuum environment at a constant temperature of 45 °C and dried for 4 hours until there was no residual solvent on the electrode surface to obtain a preliminarily stable Ni / Ni(OH) 2 heterojunction nanoelectrocatalyst. 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 carried out in the potential range of 0 to -0.5 V (vs. RHE) for 50 cycles to complete activation.

[0057] The hydrogen evolution reaction performance of the catalyst obtained in this example is basically equivalent to that of Example 2.

[0058] Example 5

[0059] The preparation method of the Ni / Ni(OH) 2 heterojunction nanoelectrocatalyst of the present invention includes the following steps:

[0060] S1. Choline chloride and ethylene glycol were stirred at a molar ratio of 1:2 at a constant temperature of 80 °C for 3 hours at a rotation speed of 300 rpm until a clear and uniform deep eutectic solvent was formed. After the stirring was completed, 50 mL was measured and reserved.

[0061] S2. 17.5 mmol of NiSO 4 ·6H 2O was slowly added to 50 mL of the eutectic solvent in step S1, and stirred at a constant temperature of 70 °C for 5 hours at a rotation speed of 650 rpm to fully dissolve the nickel salt without crystal precipitation. Subsequently, 0.75 mmol of imidazole (the concentration was 0.015 mol of imidazole per 1 L of the eutectic solvent) was added to the solution, and stirring was continued until the temperature dropped to room temperature to obtain a transparent and stable electrolyte containing imidazole eutectic solvent.

[0062] S3. Using a 0.5 cm 2 high-purity stainless steel sheet as the cathode, a 1.5 cm 2 nickel sheet as the anode, and silver / silver trifluoromethanesulfonate as the reference electrode. The electrolyte obtained in step S2 was introduced into the electrolytic cell, and at a constant temperature of 65 °C, electro-deposition was carried out at a constant current density of -0.8 mA / cm 2 for 1 hour, and the three-electrode spacing was maintained at 35 mm.

[0063] S4. After the electro-deposition was completed, the cathode electrode was taken out, first washed with acetone to remove the electrolyte and surface residues, and then washed twice with ethanol. Subsequently, the cathode electrode was placed in a vacuum environment at a constant temperature of 85 °C and dried for 3 hours until there was no residual solvent on the electrode surface to obtain a preliminarily stable Ni / Ni(OH) 2 heterojunction nanoelectrocatalyst.

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

[0065] The catalytic hydrogen evolution reaction performance of the catalyst obtained in this example is basically equivalent to that of Example 3.

[0066] Comparative Example 1

[0067] Based on Example 2, imidazole was not added, and the other conditions remained unchanged.

[0068] Comparative Example 2

[0069] Based on Example 3, the activation step of S5 was not carried out, and the other conditions remained unchanged.

[0070] Structural Characterization

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

[0072] Figure 1SEM image of the catalyst prepared by electrodeposition in step S4 of Example 1. As can be seen from the figure, the surface of the catalyst presents a complex porous structure. The particle morphology is irregular, mainly presenting polyhedrons and spheres. The particles are evenly distributed, and the pore sizes are different, forming a network structure. There are obvious voids between the particles, and the pore diameters range from nanometers to hundreds of nanometers. This multi-level pore structure not only provides more active sites but also helps to improve the adsorption, diffusion, and charge transfer efficiency of reactants.

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

[0074] Figure 3 XPS pattern of the catalyst prepared by electrodeposition in step S4 of Example 3. Figure 3 b is the N1s XPS photoelectron spectroscopy of the catalyst, indicating the presence of nitrogen doping signals on the catalyst surface. The peak position of N 1s is mainly concentrated at 398.5 eV. Among them, 398.5 eV corresponds to M-N (metal-nitrogen bond), indicating that imidazole participates in the electrodeposition process of nickel and may form a Ni-N structure, which helps to improve the catalytic activity. From Figure 3 c, it can be seen that nickel in the prepared catalyst mainly exists in the metallic state (Ni) and divalent nickel (Ni 2+ ) forms. The binding energy range Ebe = 845 eV to 865 eV corresponds to the characteristic peaks of Ni 2p1 and Ni 2p3. Among them, the Ni 2p3 peak with a binding energy Ebe = 852.7 eV indicates that nickel is mainly 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 surface of the catalyst is a mixed product of nickel and nickel hydroxide. In addition, an appropriate amount of oxygen vacancies can promote the redistribution of electrons on the catalyst surface, thereby balancing the electron transfer ability and optimizing the adsorption and desorption of reaction intermediates. The atomic ratio of Ni 0 to Ni 2+ is 40.49:59.51, indicating that the presence of imidazole significantly affects the valence state distribution of Ni and can effectively adjust the oxygen vacancy level by controlling its concentration, thereby improving the catalytic performance.

[0075] Performance Test

[0076] 1. HER Performance Test

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

[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 a Hg / HgO electrode was used as the reference electrode to form a three-electrode system. Linear voltammetry scans were performed at a scan rate of 2 mV / s in the voltage range of 0 to -0.4 V in a 1 mol / L KOH solution at room temperature to evaluate the hydrogen evolution performance of the catalyst. The test results are as Figure 4 shown

[0079] It can be obtained from Figure 4 that at a current density of 10 mA / cm -2 , the hydrogen evolution overpotential of the catalyst in Example 1 was -271 mV, and the Tafel slope was 68.62 mV·dec -1 ; the hydrogen evolution overpotential of the catalyst in Example 2 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] From the data of Examples 1 - 3, it can be seen that as the concentration of imidazole increases, the hydrogen evolution performance of the catalyst first increases and then decreases. This is because imidazole has a refining effect on the grain formation of the nickel-based catalyst. As the concentration increases, the grain size gradually decreases, and the morphology changes from a mixed structure of flakes and particles to a needle-like and serrated structure. At low concentrations, grain refinement helps to improve catalytic activity; at high concentrations, imidazole complexes with Ni 2+ , reducing the effective concentration of free Ni 2+ in the solution, thus affecting the precipitation of Ni(OH) 2 , resulting in a decrease in the formation of nickel hydroxide, a poor adhesion of the deposition layer, an unstable structure, and a decrease in catalytic activity. At the same time, an appropriate amount of Ni(OH) 2Beneficial to the HER reaction, it can promote water dissociation and enhance electron transport ability, but excessive Ni(OH) 2 may cover the active sites of metallic Ni, increase the electrode resistance, and reduce the activity and stability of the catalyst. Therefore, there is a certain balance in the influence of imidazole concentration on hydrogen evolution performance, and it is necessary to optimize its addition amount to obtain good catalytic effects.

[0081] Compared with Example 2, the catalytic hydrogen evolution reaction performance of Comparative Example 1 decreased because imidazole was not added in Comparative Example 1, lacking the effect of refining the grains and regulating the morphology of the nickel-based catalyst, resulting in larger catalyst grains, fewer surface active sites, and a relatively loose or uneven deposition layer structure, thereby reducing the hydrogen evolution performance of the catalyst.

[0082] Compared with Example 3, the catalytic hydrogen evolution reaction performance of Comparative Example 2 decreased because activation was not carried out in Comparative Example 2, resulting in more oxides or unstable substances on the catalyst surface, affecting the conductivity of the electrode and the exposure of active sites, and further reducing the catalytic efficiency and stability of the water electrolysis hydrogen evolution reaction.

[0083] To evaluate the catalytic performance of the catalyst at high current densities in an industrial environment, the hydrogen evolution reaction (HER) performance of the catalysts prepared in Example 2 and Comparative Example 1 was tested at current densities of 10 mA / cm 2 and 100 mA / cm 2 respectively. The test results are as Figure 5 shown.

[0084] From Figure 5 it can be obtained that at a current density of 10 mA / cm 2 the overpotential of Comparative Example 1 without added imidazole was -312.4 mV, about 1.3 times higher than that of Example 2 with added imidazole. At high current densities, Example 2 with added imidazole performed more excellently, only increasing by 54.72 mV, and was more suitable for industrial scenario applications.

[0085] 2. Long-term stability test of the catalyst

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

[0087] The test method was the same as the HER performance test. The stability test was a chronopotentiometry test carried out at a current density of 0 mA·cm -2 for 24 h. The test results are as Figure 6 and 7 shown.

[0088] The catalyst of Example 4 at 10 mA·cm -2When used as the cathode for HER at a current density of, the initial overpotential was -292 mV and decreased to -340 mV after 5.8 h. As the measurement continued, the overpotential remained almost unchanged and stabilized at approximately 340 mV even after 15 h, indicating that the catalyst had good electrochemical stability during long-term operation, could maintain a low overpotential for a long time, and reduce voltage loss. In addition, this also showed that the active sites of the catalyst did not undergo obvious inactivation or loss, exhibiting high durability and reliability, and was suitable for long-term electrolytic water hydrogen evolution applications.

[0089] The long-term stability test of the catalyst obtained from Comparative Example 2 without activation is shown in Figure 7 , in the first 12 hours, the overpotential showed a relatively slow growth trend, but by the 15th hour, the overpotential showed obvious fluctuations, and the fluctuations became more obvious after 20 hours, 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: The following steps are involved: S1. preparing a deep eutectic solvent; S2, adding a soluble nickel salt to the above-mentioned low eutectic solvent, heating and stirring to fully dissolve the nickel salt without crystal precipitation; then, adding an imidazole additive, continuing to stir and cooling to room temperature, to obtain a stable imidazole-containing low eutectic solvent electrolyte; S3, adding the above electrolyte into the electrolytic cell for electrodeposition, and gradually depositing on the cathode surface to form a uniform and compact Ni / Ni(OH)2 heterojunction layer; S4. After the electrodeposition process is completed, the cathode electrode is taken out, cleaned and dried; S5. Transfer the dried cathode electrode to an alkaline electrolyte system for activation to obtain a stable Ni / Ni(OH)2 heterojunction catalyst.

2. The method for preparing the Ni / Ni(OH)2 heterojunction nano-electrocatalyst according to claim 1, characterized in that: In step S2, the amount of the imidazole additive added is 0.002-0.02 mol / L.

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

4. The method for preparing the Ni / Ni(OH)2 heterojunction nano-electrocatalyst according to claim 1, characterized in that: In step S5, the activation condition is: performing cyclic voltammetry for 50 to 80 cycles in a potential range of 0 to -0.5 V, and the alkaline electrolyte is a NaOH or KOH solution.

5. The method for preparing the Ni / Ni(OH)2 heterojunction nano-electrocatalyst according to claim 1, characterized in that: In step S2, the nickel salt concentration ranges from 0.05 to 0.5 mol / L.

6. The method for preparing the 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.

7. The method for preparing the Ni / Ni(OH)2 heterojunction nano-electrocatalyst according to claim 1, characterized in that: In step S1, the hydrogen bond acceptor of the deep eutectic solvent is choline chloride, and the hydrogen bond donor is a polyol.

8. The method for preparing the Ni / Ni(OH)2 heterojunction nano-electrocatalyst according to claim 7, characterized in that: The choline chloride and the polyol are stirred at 60° C. to 80° C. for 3 to 5 hours to obtain a clear and uniform low eutectic solvent.

9. The method for preparing the Ni / Ni(OH)2 heterojunction nano-electrocatalyst according to claim 1, characterized in that: In step S4, the cleaning is: first cleaning with acetone to remove surface residues, and then cleaning again with ethanol.

10. Use of a Ni / Ni(OH)2 heterojunction nano-electrocatalyst prepared by the method according to any one of claims 1 to 9 in hydrogen evolution by electrolysis of water.

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