Preparation and application of self-supporting two-dimensional crystalline / amorphous NiO / Ni (OH) 2 nanosheet array electrode

Abstract

The invention discloses a self-supporting two-dimensional crystalline / amorphous NiO / Ni (OH) 2 nanosheet array electrode as well as a preparation method and application of the self-supporting two-dimensional crystalline / amorphous NiO / Ni (OH) 2 nanosheet array electrode. According to the nano-sheet array electrode, a nano-sheet with a crystalline state / amorphous state composite two-dimensional structure is loaded on a foamed nickel substrate of the nano-sheet array electrode, the nano-sheet in the amorphous state is Ni (OH) 2, and the nano-sheet in the crystalline state is NiO nano-crystal. According to the nanosheet array electrode, efficient bifunctional catalysis is achieved through rich active sites and excellent mass transmission capacity. The microscopic surface and interface of the electrode are in seamless contact, so that full exposure of active sites and rapid transfer of charges are promoted, and the catalytic efficiency of an oxygen evolution reaction and a hydrogen evolution reaction is improved. The design not only enhances the catalytic activity, but also ensures the stability of the electrode in long-term application.

Description

Technical Field

[0001] The present invention relates to a catalyst used for electrolyzing water to produce hydrogen, which uses nickel foam as a carrier and has a two-dimensional crystalline / amorphous dual-phase composite NiO / Ni(OH) 2 Nanosheet arrays have a compact microscopic interface structure and can be used as efficient and stable self-supporting catalytic electrodes for water electrolysis, belonging to the field of electrocatalytic technology. Background Art

[0002] In recent years, the attention paid to clean and renewable energy, such as wind energy, solar energy, hydrogen energy, thermal energy, tidal energy, and hydropower, has been increasing. Among them, hydrogen, as an important source of green energy, is regarded as the preferred alternative to contemporary energy due to its wide range of raw materials, renewability, the only combustion product is water, it is green and environmentally friendly, and it is easy to transmit and store. The method of producing hydrogen by electrolysis of water has the advantages of high purity of hydrogen, high electrolysis efficiency, and no pollution in the reaction process. It is regarded as a crucial step in the conversion of hydrogen energy and is currently a reliable method for industrial hydrogen production. In the production of hydrogen by electrolysis of water, that is, electrocatalytic water decomposition, although the theoretical voltage value is 1.23V, due to the energy barriers of each step that must be overcome in the actual reaction process, the actual voltage value is much higher than the theoretical value. The use of high-performance catalysts can effectively improve the adsorption and desorption energy of each step, thereby reducing the voltage value of water decomposition, which has become the focus of high-efficiency water electrolysis to produce hydrogen.

[0003] At present, the research hotspots of high-efficiency water electrolysis catalysts are mainly focused on precious metals and metal compounds of transition elements. Precious metal catalysts, such as Pt, Ir, Ru, etc., are currently considered to be the best materials for catalysts, but they are expensive, scarce in resources, and do not have large-scale industrial applications. Transition element metals and their compounds are cheap, abundant, and the vacancy state of their 3d electron orbitals is very suitable for electron transfer in the catalytic process, which is beneficial to their electrocatalytic performance. Considering that the actual reaction of water electrolysis occurs at the surface active sites of the catalyst, the improvement of electrocatalytic performance mainly focuses on increasing the number of active sites per unit area and the intrinsic activity of a single active site.

[0004] In order to increase the number of active sites per unit area, first constructing a three-dimensional interconnected structure can greatly increase the specific surface area and the number of active sites of the electrocatalytic material, and shorten the transmission path between the active sites. Among them, the vertically oriented two-dimensional nanosheet structure array can produce abundant electrochemical active sites due to its inherent large specific surface area and rich edge structure, which has now become a key technical point. For example, in the Chinese patent application with application number 202311329030.2, a self-supporting heterostructure composite nanoarray electrolysis catalyst synthesized with transition metal salts using thiocyanate as a sulfur source and reaction medium is disclosed. This technology prepares the catalyst on the surface of the nickel mesh by high-temperature calcination to form a self-coupling interface with excellent electrochemical stability, which is particularly suitable for water electrolysis applications. In the Chinese invention patent with patent number ZL 202110179290.0, a FeOOH / Ni(OH) obtained by treating nickel foam with a weakly alkaline sulfur source, nickel salt and iron salt is disclosed. 2 Nanoflower arrays are characterized by extremely thin nanoflowers, less than 100nm in thickness. In addition, in the Chinese invention patent with patent number ZL 201910983359.8, it is revealed that in the preparation process of FeNi-LDHs / NF nanoarray composite materials, the use of surfactants can adjust the sheet structure of LDHs to form a three-dimensional flower-shaped structure. In addition, through carbon encapsulation and heterogeneous nucleation growth of MOFs, high-quality and neatly arranged arrays are achieved, improving the electron and proton transport properties of the material. Although these technologies have made progress in the field of water electrolysis catalysts, they generally require additional metal sources and have not yet been able to effectively adjust the phase composition of nanosheet arrays. Summary of the invention

[0005] The primary technical problem to be solved by the present invention is to provide a self-supporting two-dimensional crystalline / amorphous NiO / Ni(OH) 2 Nanosheet array electrode (referred to as nanosheet array electrode for short).

[0006] Another technical problem to be solved by the present invention is to provide a method for preparing the above-mentioned nanosheet array electrode.

[0007] In order to achieve the above technical objectives, the present invention adopts the following technical solutions:

[0008] A self-supporting two-dimensional crystalline / amorphous NiO / Ni(OH) 2 The nanosheet array electrode is a nickel foam substrate with a self-supporting two-dimensional structure on the surface. The two-dimensional structure is a sheet of non-crystalline Ni(OH) 2 The structure of crystalline NiO is formed on the contact surface of the nickel foam surface, and the nickel element and the oxygen element are evenly distributed in the entire nanosheet, and the ratio of nickel to oxygen atoms is between 0.7 and 0.9.

[0009] Preparation of the above self-supporting two-dimensional crystalline / amorphous NiO / Ni(OH) 2 Preparation method of nanosheet array electrode:

[0010] Step 1: Remove the oxide layer from the nickel foam;

[0011] Step 2: After mixing ethanol, water, ethylene glycol and Lewis base, inject them into the polytetrafluoroethylene lining of the reactor;

[0012] The Lewis base is ethylenediaminetetraacetic acid (EDTA), hexamethyleneamine (HMTA), ammonia (NH3·H 2 O), methylamine (CH 3 NH 2 ) and urea (CO(NH 2 ) 2 )

[0013] Step 3: immerse a piece of nickel foam treated and pre-cleaned as in step 1 into the reaction solution of step 2, seal the reactor, heat to above 120° C., and react for more than 1 hour;

[0014] Step 4: After the product is naturally cooled to room temperature, the surface reconstructed nickel foam catalyst is taken out, washed and dried;

[0015] Step 5: In a muffle furnace preheated to 280-330°C, the product prepared in step 4 is rapidly calcined for 3 to 6 minutes to obtain a self-supporting nickel foam loaded with crystalline / amorphous NiO / Ni(OH) 2 Nanosheet array catalysts.

[0016] Furthermore, in the step 1, the nickel foam is ultrasonically treated in 0.1 mmol / L hydrochloric acid, ethanol and pure water for 30 minutes in sequence to remove the surface oxide layer.

[0017] Furthermore, in the step 2, the ratio of nickel foam, ethanol, water, ethylene glycol and Lewis base is: 1 part by mass of nickel foam, 1 part by mass of water, 3 parts by mass of ethanol, 8 to 12 parts by mass of ethylene glycol, 3 to 4 parts by mass of ethylenediaminetetraacetic acid (EDTA), and the molar amount of the N element participating in the reaction in other Lewis bases is consistent with the molar amount of the N element in ethylenediaminetetraacetic acid (EDTA).

[0018] Furthermore, in the step three, a piece of nickel foam pre-cleaned as in the step one is immersed in the reaction solution of the step two, and the reactor is sealed and heated to 120-150° C. for reaction for 1-18 hours.

[0019] Furthermore, in the step 4, the product obtained in the step 3 is naturally cooled to room temperature to obtain a surface-reconstructed nickel foam catalyst, which is washed several times with water and ethanol and dried in a vacuum oven.

[0020] Furthermore, in the step 5, the temperature of the muffle furnace is 280-330° C., and the product prepared in the step 4 is rapidly calcined for 3-6 minutes.

[0021] The above self-supported two-dimensional crystalline / amorphous NiO / Ni(OH) 2 A nanosheet array electrode, or an application of the nanosheet array electrode obtained by the preparation method in electrocatalytic materials for hydrogen and oxygen evolution.

[0022] Beneficial effects:

[0023] Single component NiO or Ni(OH) 2 The catalytic performance of NiO / Ni(OH) is poor, which is mainly due to its poor electronic conductivity and limited active centers. To overcome these limitations, the present invention provides a self-supporting two-dimensional crystalline / amorphous NiO / Ni(OH) 2 The method for preparing nanosheet array electrodes uses nickel foam as a substrate, and forms a two-dimensional structure with a large number of reaction sites and active centers through a hydrothermal reaction and a rapid calcination process, thereby significantly improving electronic conductivity and catalytic activity.

[0024] Furthermore, the present invention adopts an "interface engineering" strategy to promote electron transfer and improve adsorption performance by adjusting the electronic structure of the electrocatalyst / substrate interface and the internal interface of the electrocatalyst. This regulation reduces the energy barriers of the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), and alleviates the deactivation process of the catalyst. In particular, the interface between the nanosheet array generated by the nickel foam after the hydrothermal reaction and the nickel foam substrate, as well as the crystalline NiO and amorphous Ni(OH) in the nanosheet formed during rapid calcination, 2 The strong coupling interface between them plays a key role.

[0025] Compared with the commonly used powdered catalysts, the self-supporting electrode in the present invention can be grown directly on the conductive substrate without a binder, which simplifies the preparation process, reduces the interface connection resistance, and improves the working stability. In addition, the nanosheet array of the self-supporting structure is conducive to giving full play to the large specific surface area advantage of the nickel foam, and its open structure is conducive to the rapid release of bubbles, further improving the catalytic efficiency.

[0026] Finally, nickel foam, as a typical current collector, has an interconnected three-dimensional macroporous skeleton, providing a large surface area, high porosity and strong mechanical stability. Using nickel foam as a substrate, the self-supporting electrode constructed by the in-situ growth strategy not only increases the accessible active sites, but also the contact surface between the formed seamless interfaces can enrich the exposed active sites and realize rapid charge transfer, thus making it possible to realize a highly active and stable OER and HER catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the SEM image of EDTA-NF-1h.

[0028] Figure 2 This is the SEM image of EDTA-NF-12h.

[0029] Figure 3 This is the SEM image of EDTA-NF-6h.

[0030] Figure 4 This is the SEM image of EDTA-NF-6h.

[0031] Figure 5 This is the SEM image of EDTA-NF-18h.

[0032] Figure 6 This is the SEM image of EDTA-NF-18h.

[0033] Figure 7 This is the HAADF-STEM image of EDTA-NF-12h.

[0034] Figure 8 This is the HAADF-STEM image of EDTA-NF-12h.

[0035] Fig. 9 This is the HAADF-STEM image of EDTA-NF-12h.

[0036] Fig.10 This is the HAADF-STEM image of EDTA-NF-12h.

[0037] Fig.11 Linear scan diagram and overpotential diagram of the half-reaction of oxygen evolution reaction (OER) of EDTA-nickel foam (NF)-*h catalyst prepared with different hydrothermal reaction times.

[0038] Fig.12 Linear scans and overpotential diagrams of the half-reaction of oxygen evolution reaction (OER) of Lewis base-NF catalysts prepared with different Lewis bases.

[0039] Fig.13Linear scan diagram and overpotential diagram of the half-reaction of hydrogen evolution reaction (HER) over EDTA-nickel foam (NF)-*h catalysts prepared with different hydrothermal reaction times.

[0040] Fig.14 Trend diagram of the half-reaction of hydrogen evolution reaction (HER) over Lewis base-nickel foam (NF) catalysts prepared with different Lewis bases.

[0041] Fig.15 Schematic diagram of the catalyst preparation process. DETAILED DESCRIPTION

[0042] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings and embodiments. Obviously, the described embodiments are only used to illustrate the technical solution of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are still within the protection scope of the present invention.

[0043] Example 1: EDTA-nickel foam-12h

[0044] like Fig.15 As shown, nickel foam is used as the matrix and also as the nickel source.

[0045] Step 1: Place the nickel foam (2×3cm 2 , about 1.08 g) was ultrasonically treated in 0.1 mmol / L hydrochloric acid, ethanol and pure water for 30 minutes in sequence to remove the surface oxide layer.

[0046] Step 2: 12 g of ethanol, 4 g of water, 30 ml of ethylene glycol (33.39 g) and 4.24 mmol of ethylenediaminetetraacetic acid (EDTA: 12.39 g) were stirred and mixed for 30 minutes, and then injected into a reaction kettle lined with polytetrafluoroethylene.

[0047] Step 3: Immerse a piece of nickel foam that has been pre-cleaned as in step 1 into the reaction solution of step 2, seal the reactor, heat to 120° C., and react for 12 hours.

[0048] Step 4: After the product is naturally cooled to room temperature, the surface-reconstructed nickel foam catalyst is taken out, washed with water and ethanol several times, and dried in a vacuum oven.

[0049] Step 5: Then, the nickel foam was rapidly calcined at 300°C for 5 minutes to successfully prepare a self-supporting crystalline / amorphous NiO / Ni(OH) 2 The catalyst is used, and the heating reaction time in step 3 is 12 hours. The product is: EDTA-foam nickel-12h catalyst.

[0050] Example 2: EDTA-nickel foam-12h (low solubility)

[0051] Nickel foam is used as the matrix and also as the nickel source.

[0052] Step 1: Place the nickel foam (2×3cm 2 ) were ultrasonically treated in 0.1 mmol / L hydrochloric acid, ethanol and pure water for 30 min in sequence to remove the surface oxide layer.

[0053] Step 2: Stir and mix 12 g of ethanol, 4 g of water, 30 ml of ethylene glycol (33.39 g), and 1.0 mmol and 2.2 mmol of ethylenediaminetetraacetic acid (2.93 g and 6.43 g of EDTA), respectively, for 30 minutes, and then inject into a polytetrafluoroethylene-lined reactor.

[0054] Step 3: Immerse a piece of nickel foam that has been pre-cleaned as in step 1 into the reaction solution of step 2, seal the reactor, heat to 120° C., and react for 12 hours.

[0055] Step 4: After the product is naturally cooled to room temperature, the surface-reconstructed nickel foam catalyst is taken out, washed with water and ethanol several times, and dried in a vacuum oven.

[0056] Step 5: Then, the nickel foam was rapidly calcined at 300°C for 5 minutes to successfully prepare a self-supporting crystalline / amorphous NiO / Ni(OH) 2 The catalyst, the heating reaction time in step 3 is 12 hours, and the product is: EDTA-foam nickel-12h (low solubility) catalyst.

[0057] In this example, the catalysts prepared with 1.0 mmol EDTA and 2.2 mmol EDTA have certain effects, but are not as effective as the catalyst prepared with 4.24 mmol EDTA selected in Example 1.

[0058] Example 3: EDTA-nickel foam-*h

[0059] Different EDTA-nickel foam-*h catalysts were prepared with the other steps being the same. The difference was that in step 3, the heating reaction time was *h=1, 6, 12 and 18 hours respectively. The last steps 4 and 5 were also the same.

[0060] The products are catalysts of EDTA-foam nickel-1h, EDTA-foam nickel-6h, EDTA-foam nickel-12h and EDTA-foam nickel-18h respectively.

[0061] Figure 1 to Figure 6SEM images of the catalysts of EDTA-nickel foam-1h, EDTA-nickel foam-6h, EDTA-nickel foam-12h and EDTA-nickel foam-18h respectively.

[0062] Without adding any additional metal element sources, with the assistance of the common Lewis base ethylenediaminetetraacetic acid (EDTA), a simple hydrothermal treatment was performed at 120 °C according to the dissolution-deposition mechanism: first, Ni(OH) 2 Nanosheet array. Metal foam nickel mainly undergoes oxidative dissolution, and releases EDTA-Ni after dissolution. 2+ The complex is used as a Ni source. As the hydrothermal reaction time increases, the deposition process gradually becomes dominant. Subsequently, it is rapidly calcined in air at about 300°C for about 5 minutes to convert Ni(OH) 2 The precursor is transformed into crystalline / amorphous NiO / Ni(OH) with a large number of crystalline / amorphous heterointerfaces 2 Nanosheet arrays are formed, thereby obtaining a catalyst product with a large number of active sites.

[0063] Similarly, by replacing EDTA with other Lewis bases, the steps and process for preparing X-nickel foam-12h catalyst are similar to the preparation method of EDTA-nickel foam-12h, and the obtained catalyst product also has a comparable effect.

[0064] The EDTA-nickel foam-xh catalysts were prepared by changing the hydrothermal reaction time. Their surface morphology was shown by high / low magnification SEM images. Figure 1 to Figure 6 Many etching pits with a size of tens of nanometers can be observed in the microstructure of EDTA-nickel foam-1h, indicating that metal Ni is partially oxidized and dissolved from nickel foam to Ni under hydrothermal conditions. 2+ . With OH - After the reaction, Ni(OH) is directly deposited 2 In the presence of EDTA, EDTA-Ni 2+ The complex then follows the reaction:

[0065] EDTA-Ni 2+ +2H 2 O=Ni(OH) 2 +EDTA+2H + Deposition of Ni(OH) 2

[0066] Its specific morphology is also controlled by the Lewis base EDTA.

[0067] As the reaction time changes, during the entire hydrothermal process, it can be observed that 2D flake structures preferentially grow from the pits on the rough nickel foam surface; then nanosheets are gradually deposited and the pits are gradually filled. After 3 hours of hydrothermal reaction, the SEM image shows that the density of the electrocatalyst-substrate interface begins to increase, which is the turning point of 3 hours. At the same time, nanosheets continue to deposit on the nickel foam surface. After 12 hours of hydrothermal reaction, a dense, uniform, and continuous nanosheet array is formed on the nickel foam. As the hydrothermal time is further extended, Ni(OH) 2 The excessive deposition of N resulted in the partial collapse of the nanosheet arrays, which could be observed in the SEM of EDTA-Ni foam-18h.

[0068] Example 4: Hexamethyleneamine (HMTA; hexamethylenetetramine)-nickel foam

[0069] Step 1: Place the nickel foam (2×3cm 2 ) were ultrasonically treated in 0.1 mmol / L hydrochloric acid, ethanol and pure water for 30 min in sequence to remove the surface oxide layer.

[0070] Step 2: 12 g of ethanol, 4 g of water, 30 ml of ethylene glycol and 2.12 mmol of urotropine were stirred and mixed for 20 minutes, and then injected into a reaction kettle lined with polytetrafluoroethylene.

[0071] In this embodiment, the reaction materials are the same as those in Example 1, and the molar number of nitrogen element participating in the reaction in the hexamethylenetetramine is the same as the amount of EDTA used in Example 1. Step 3: Immerse a piece of nickel foam pre-cleaned as in Step 1 into the reaction solution of Step 2, and seal the reactor, heat to 130° C., and react for 10 hours.

[0072] Step 4: After the product obtained in step 3 is naturally cooled to room temperature, the surface-reconstructed nickel foam catalyst is taken out, washed with water and ethanol several times, and dried in a vacuum oven.

[0073] Step 5: Then, the nickel foam was rapidly calcined at 285°C for 6 minutes to successfully prepare a self-supporting crystalline / amorphous NiO / Ni(OH) 2 The product is: HMTA-nickel foam catalyst.

[0074] Example 5: Ammonia (NH 3 ·H 2 O)-Nickel Foam

[0075] Step 1: Place the nickel foam (2×3cm 2 ) were ultrasonically treated in 0.1 mmol / L hydrochloric acid, ethanol and pure water for 30 min in sequence to remove the surface oxide layer.

[0076] Step 2: Mix 12 g ethanol, 4 g water, 30 ml ethylene glycol and 8.48 mmol ammonia (NH 3 ·H 2 O), stirred and mixed for 10 minutes, and then injected into a reactor lined with polytetrafluoroethylene.

[0077] Step 3: Immerse a piece of nickel foam that has been pre-cleaned as in step 1 into the reaction solution of step 2, seal the reactor, heat to 115° C., and react for 12 hours.

[0078] Step 4: After the product is naturally cooled to room temperature, the surface-reconstructed nickel foam catalyst is taken out, washed with water and ethanol several times, and dried in a vacuum oven.

[0079] Step 5: Then, the nickel foam was rapidly calcined at 280°C for 5 minutes to successfully prepare a self-supporting crystalline / amorphous NiO / Ni(OH) 2 The product is: ammonia (NH 3 ·H 2 O)-nickel foam catalyst.

[0080] Example 6: Methylamine (CH 3 NH 2 )-Nickel Foam

[0081] Step 1: Place the nickel foam (2×3cm 2 ) were ultrasonically treated in 0.1 mmol / L hydrochloric acid, ethanol and pure water for 30 min in sequence to remove the surface oxide layer.

[0082] Step 2: Mix 12 g ethanol, 4 g water, 30 ml ethylene glycol and 8.48 mmol methylamine (CH 3 NH 2 ), stirred and mixed for 30 minutes, and then injected into a reactor lined with polytetrafluoroethylene.

[0083] Step 3: Immerse a piece of nickel foam that has been pre-cleaned as in step 1 into the reaction solution of step 2, seal the reactor, heat it to 140° C., and react for 8 hours.

[0084] Step 4: After the product is naturally cooled to room temperature, the surface-reconstructed nickel foam catalyst is taken out, washed with water and ethanol several times, and dried in a vacuum oven.

[0085] Step 5: Then, the nickel foam was rapidly calcined at 310°C for 4 minutes to successfully prepare a self-supporting crystalline / amorphous NiO / Ni(OH) 2 The product is: methylamine (CH 3 NH 2 )-nickel foam catalyst.

[0086] Example 7: Urea (CO (NH 2 ) 2 )-Nickel Foam

[0087] Step 1: Place the nickel foam (2×3cm 2 ) were ultrasonically treated in 0.1 mmol / L hydrochloric acid, ethanol and pure water for 30 min in sequence to remove the surface oxide layer.

[0088] Step 2: Mix 12 g ethanol, 4 g water, 30 ml ethylene glycol and 4.24 mmol urea (CO(NH 2 ) 2 ), stirred and mixed for 30 minutes, and then injected into a reactor lined with polytetrafluoroethylene.

[0089] Step 3: Immerse a piece of nickel foam that has been pre-cleaned as in step 1 into the reaction solution of step 2, seal the reactor, heat to 130° C., and react for 10 hours.

[0090] Step 4: After the product is naturally cooled to room temperature, the surface-reconstructed nickel foam catalyst is taken out, washed with water and ethanol several times, and dried in a vacuum oven.

[0091] Step 5: Then, the nickel foam was rapidly calcined at 310°C for 4 minutes to successfully prepare a self-supporting crystalline / amorphous NiO / Ni(OH) 2 The product is: urea (CO (NH 2 ) 2 )-nickel foam catalyst.

[0092] Example 8: Analysis

[0093] like Figure 7 to Figure 10 As shown in the figure, high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) shows that Ni and O elements are uniformly distributed throughout the nanosheet. The calculated ratio of Ni to O atoms is 0.84, which is between 0.5 and 1, confirming that NiO and Ni(OH) 2 coexistence in the nanosheets. Under the conditions of hydrothermal reaction, Ni(OH) 2 The nanosheets are deposited on the chemically etched nickel foam surface through EDTA ligands (or other Lewis bases), and the EDTA-Ni 2+ It is the only metal source. Ni(OH) 2 The epitaxial growth of the nanosheets is energetically more favorable to occur on the etched pits, forming a strong interface bond and stably anchoring the nanosheet array on the nickel foam surface. Then, during the rapid calcination at 280-330°C for 3-6 minutes, the nanoarray / nickel foam interface induces the formation of crystalline / amorphous NiO / Ni(OH)2 The formation of nano-interfaces can effectively adjust the electronic structure, reduce the overpotential of electrocatalytic water decomposition, and make the hydrogen evolution reaction more effective.

[0094] like Figure 11 to Figure 14 The trend diagrams of the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) half-reactions are shown for catalysts prepared with different hydrothermal times and catalysts obtained by hydrothermal reactions with different Lewis bases. These results show that the performance of OER and HER continues to improve with the increase of the Lewis basicity of the Lewis base used, and the promotion of HER is more significant than that of OER. The promotion of OER and HER may be due to the increased oxidative dissolution of the nickel foam substrate during the hydrothermal treatment step, which promotes the Ni(OH) 2 During the subsequent calcination at 300 °C, the electrocatalyst nickel foam interface can promote the deposition of a large amount of crystalline / amorphous NiO / Ni(OH) 2 Interface formation. Self-supported NiO / Ni(OH) 2 Both interfacial sites in nickel foam are active sites for OER and HER, which enhance the adsorption of reaction intermediates and accelerate mass and electron transfer, thereby improving electrocatalytic OER and HER activities. This dual-interface engineering strategy has a more significant promoting effect on HER.

[0095] Compared with the existing technology, the nanosheet array electrode cleverly combines multiple key technical elements, making it an efficient bifunctional catalyst, especially suitable for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The electrode has a rich number of active sites, which provides more conversion opportunities for reactant molecules. At the same time, the rapid mass transfer capability of the electrode ensures that the reactants can quickly reach the active sites and the products can be removed in time to avoid site blockage, thereby maintaining the continuity and efficiency of the catalytic reaction. The microscopic surface interface of the electrode forms a seamless contact, which not only promotes the full exposure of the active sites, but also accelerates the charge transfer rate, which is crucial for the kinetics of the electrocatalytic reaction. This structural design enables the electrode to exhibit high activity during the catalytic process, and due to its stability, it can maintain performance in long-term operation and is not easy to deactivate or degrade. Therefore, the nanosheet array electrode not only performs well in catalytic activity, but also has significant advantages in stability, making it an ideal bifunctional electrode catalyst in the electrolysis of water.

[0096] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A self-supporting two-dimensional crystalline / amorphous NiO / Ni(OH)2 nanosheet array electrode, characterized in that: The nanosheet array electrode is a nickel foam substrate, and its surface is loaded with a self-supporting two-dimensional structure, which is a sheet of non-crystalline Ni(OH)2 and a crystalline NiO structure formed on the structure in contact with the nickel foam surface. In addition, nickel and oxygen elements are evenly distributed in the entire nanosheet, and the ratio of nickel and oxygen atoms is between 0.7 and 0.

9.

2. A method for preparing a self-supporting two-dimensional crystalline / amorphous NiO / Ni(OH)2 nanosheet array electrode, characterized in that The steps include: Step 1: Remove the oxide layer from the nickel foam; Step 2: After mixing ethanol, water, ethylene glycol and Lewis base, inject them into the polytetrafluoroethylene lining of the reactor; The Lewis base is one of ethylenediaminetetraacetic acid, hexamethyleneamine, ammonia, methylamine and urea; Step 3: immerse a piece of nickel foam treated and pre-cleaned as in step 1 into the reaction solution of step 2, seal the reactor, heat to above 120° C., and react for more than 1 hour; Step 4: After the product is naturally cooled to room temperature, the surface reconstructed nickel foam catalyst is taken out, washed and dried; Step 5: In a muffle furnace preheated to above 280-330°C, the product prepared in step 4 is rapidly calcined for 3 to 6 minutes to obtain a catalyst of crystalline / amorphous NiO / Ni(OH)2 nanosheet arrays loaded on a self-supporting nickel foam.

3. The method for preparing the self-supporting two-dimensional crystalline / amorphous NiO / Ni(OH)2 nanosheet array electrode according to claim 2, characterized in that: In the step 1, the nickel foam is ultrasonically treated in 0.1 mmol / L hydrochloric acid, ethanol and pure water for 30 minutes in sequence to remove the surface oxide layer.

4. The method for preparing the self-supporting two-dimensional crystalline / amorphous NiO / Ni(OH)2 nanosheet array electrode according to claim 2, characterized in that: In the step 2, the ratio of nickel foam, ethanol, water, ethylene glycol and Lewis base is: 1 part by mass of nickel foam, 1 part by mass of water, 3 parts by mass of ethanol, 8 to 12 parts by mass of ethylene glycol, 3 to 4 parts by mass of ethylenediaminetetraacetic acid, and the molar amount of the N element participating in the reaction in other Lewis bases is consistent with the molar amount of the N element in ethylenediaminetetraacetic acid.

5. The method for preparing the self-supporting two-dimensional crystalline / amorphous NiO / Ni(OH)2 nanosheet array electrode according to claim 2, characterized in that: In the step three, a piece of nickel foam pre-cleaned as in the step one is immersed in the reaction solution of the step two, and the reactor is sealed and heated to 120-150° C. for reaction for 1-18 hours.

6. The method for preparing the self-supporting two-dimensional crystalline / amorphous NiO / Ni(OH)2 nanosheet array electrode according to claim 2, characterized in that: In the step 4, the product obtained in the step 3 is naturally cooled to room temperature to obtain a surface-reconstructed nickel foam catalyst, which is washed with water and ethanol several times and dried in a vacuum oven.

7. The method for preparing the self-supporting two-dimensional crystalline / amorphous NiO / Ni(OH)2 nanosheet array electrode according to claim 2, characterized in that: In the step 5, the temperature of the muffle furnace is 280-330° C., and the product prepared in the step 4 is rapidly calcined for 3-6 minutes.

8. Use of the self-supporting two-dimensional crystalline / amorphous NiO / Ni(OH)2 nanosheet array electrode as claimed in claim 1, or the nanosheet array electrode obtained by the preparation method as claimed in claims 2 to 7 in electrocatalytic materials for hydrogen and oxygen evolution.

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