Medium-entropy nickel-based metal organic framework nano array electrode and preparation method and application thereof

Abstract

The invention discloses a medium-entropy nickel-based metal organic framework nano-array electrode and a preparation method and application thereof, and relates to the technical field of electrodes, the medium-entropy nickel-based metal organic framework nano-array electrode comprises a conductive net-shaped substrate and a medium-entropy nickel-based metal organic framework nanosheet loaded on the conductive net-shaped substrate, the medium-entropy nickel-based metal organic framework nanosheet is loaded on the conductive net-shaped substrate, and the medium-entropy nickel-based metal organic framework nanosheet is loaded on the medium-entropy nickel-based metal organic framework nano-array electrode. The medium-entropy nickel-based metal organic framework nanosheet is composed of a ligand prepared from nickel potassium cyanide and metal nodes, wherein the metal nodes are prepared from Ni < 2 + > and two or three metal ions selected from Co < 2 + >, Fe < 3 + > and Cr < 3 + >; the preparation method of the electrode is simple and efficient, the used raw materials are metal soluble salt and nickel potassium cyanide, and compared with a noble metal-based catalyst in industrial application, the electrode is low in cost, can be directly used as a self-supporting electrode for electrocatalytic urea oxidation reaction and is excellent in performance.

Description

Technical Field

[0001] The present invention relates to the technical field of electrodes, and particularly relates to a medium-entropy nickel-based metal-organic framework nanoarray electrode and a preparation method and application thereof. Background Art

[0002] The urea oxidation reaction (UOR) is the core reaction of new energy technologies such as direct urea fuel cells (DUFCs) and urea electrolysis. DUFCs can generate electricity using urea in industrial wastewater or domestic sewage, and urea electrolysis can simultaneously achieve energy-saving hydrogen production and purification of urea-rich wastewater. However, the UOR reaction needs to undergo a 6e - transfer process, so the kinetics is slow; and the initial oxidation potential of this reaction is high, and a highly active catalyst is required to promote the reaction rate. These problems greatly limit the development of new energy technologies involving UOR. At present, although the noble metal-based catalysts used have high activity, they have high costs and scarce resources and are difficult to be applied on a large scale. Therefore, it is crucial to develop low-cost and highly active UOR electrocatalysts.

[0003] Research shows that nickel (Ni)-related species are the active sites for electrocatalytic UOR. Nickel metal-organic framework (Ni-MOFs) materials are considered promising UOR catalysts because of their abundant Ni active sites and large specific surface area.

[0004] CN104979104A discloses a preparation method of a Ni-MOF electrode material. An aqueous nickel nitrate solution with a total concentration of 0.0075 - 0.43 mol / l is added to a PTA / DMF solution with a total concentration of 0.005 - 0.03 mol / l at a rate of 2 - 5 ml / min. The volume ratio of the aqueous nickel nitrate solution to the terephthalic acid solution is 1.5 - 3:1. After dissolution and stirring for 1 - 2 h, a precursor solution is obtained. The precursor solution is subjected to a solvothermal reaction in a hydrothermal autoclave at 120 - 200 °C for 12 - 48 h. The obtained green precipitate is centrifugally washed, filtered with DMF and absolute ethanol respectively, and dried at 80 °C to obtain the Ni-MOF electrode material.

[0005] However, most Ni-MOFs powder catalysts still have problems such as poor conductivity and insufficient stability; moreover, the number of active sites of a single Ni-MOFs catalyst is limited, and its electronic structure is difficult to adjust, resulting in limited UOR performance; in addition, the application research of Ni-MOFs in urea-related energy storage devices is still in its infancy, lacking mature technical solutions. In recent years, medium / high-entropy nickel-based nanomaterials (including nickel-based oxides, hydroxides, phosphides, sulfides, alloys, etc.) have received extensive attention in the field of electrocatalysis due to their highly disordered structures, adjustable compositions, and excellent physical and chemical properties. Based on this, the present invention proposes to directly and in-situ grow medium-entropy nickel-based metal-organic framework nanosheets on a conductive substrate to construct a self-supporting medium-entropy nickel-based metal-organic framework nanoarray electrode. Utilizing the synergistic effect between multiple elements and multiple sites, it is expected to further improve the UOR electrocatalytic performance of single Ni-MOFs. Summary of the Invention

[0006] In order to solve the deficiencies of the existing technology, the purpose of the present invention is to provide a medium-entropy nickel-based metal-organic framework nanoarray electrode and its preparation method and application. The preparation method of this electrode is simple and efficient, and the raw materials used are metal soluble salts and potassium nickel cyanide. Compared with the noble metal-based catalysts used in industrial applications, the cost is low, and it can be directly used as a self-supporting electrode for electrocatalytic urea oxidation reaction, and the performance is excellent.

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

[0008] A medium-entropy nickel-based metal-organic framework nanoarray electrode, comprising a conductive mesh substrate and medium-entropy nickel-based metal-organic framework nanosheets loaded on the conductive mesh substrate. The medium-entropy nickel-based metal-organic framework nanosheets are composed of a ligand made of potassium nickel cyanide and metal nodes. The metal nodes are made of two or three metal ions selected from Ni 2+ and Co 2+ , Fe 3+ , Cr 3+ .

[0009] Preferably, the medium-entropy nickel-based metal-organic framework nanosheets are composed of a ligand made of potassium nickel cyanide and metal nodes made of four metal ions selected from Ni 2 + , Co 2+ , Fe 3+ , Cr 3+ .

[0010] Preferably, the medium-entropy nickel-based metal-organic framework nanosheets are composed of a ligand made of potassium nickel cyanide, and Ni 2+ and Co 2+ , Fe 3+ , Cr 3+It is composed of metal nodes made of two metal ions selected from among them.

[0011] Preferably, the medium-entropy nickel-based metal-organic framework nanosheet is a ligand made of potassium nickel cyanide and metal nodes made of three metal ions selected from Ni 2 + , Co 2+ , Fe 3+ It is composed of three metal ions.

[0012] Preferably, the medium-entropy nickel-based metal-organic framework nanosheet is a ligand made of potassium nickel cyanide and metal nodes made of three metal ions selected from Ni 2 + , Co 2+ , Cr 3+ It is composed of three metal ions.

[0013] Preferably, the medium-entropy nickel-based metal-organic framework nanosheet is a ligand made of potassium nickel cyanide and metal nodes made of three metal ions selected from Ni 2 + , Fe 3+ , Cr 3+ It is composed of three metal ions.

[0014] Preferably, the conductive mesh substrate is one or more of nickel foam, carbon cloth, titanium mesh, and stainless steel mesh.

[0015] Preferably, the thickness of the medium-entropy nickel-based metal-organic framework nanosheet is 8 to 12 nanometers, and the lateral dimension is several hundred nanometers.

[0016] Preferably, the raw materials of the metal nodes are soluble salts of Ni 2+ , Co 2+ , Fe 3+ , Cr 3+ .

[0017] The present invention also claims to protect a method for preparing the medium-entropy nickel-based metal-organic framework nanoarray electrode, including the following steps:

[0018] (1) Pretreat the conductive mesh substrate;

[0019] (2) Prepare a precursor solution: Dissolve potassium nickel cyanide in deionized water to obtain a ligand solution; Dissolve soluble salts of three or four metal ions selected from Ni 2+ , Co 2+ , Fe 3 + , Cr 3+ in deionized water to obtain a metal ion solution; Mix the ligand solution and the metal ion solution evenly to obtain a precursor solution;

[0020] (3) Preparation of the medium-entropy nickel-based metal-organic framework nanoarray electrode: Immerse the pretreated conductive network substrate in step (1) into the precursor solution prepared in step (2) for hydrothermal reaction. After the reaction, wash and dry the conductive network substrate with medium-entropy nickel-based metal-organic framework nanosheets grown on its surface to obtain the medium-entropy nickel-based metal-organic framework nanoarray electrode.

[0021] Preferably, in step (1), the pretreatment includes ultrasonic washing of the conductive network substrate in 3M hydrochloric acid, ethanol, and deionized water for 10 - 30 min, and drying at 60 - 80 °C.

[0022] Preferably, in step (2), the molar ratio of each metal ion in the soluble salts of the three or four metal ions to potassium nickel cyanide is 0.1 - 2:1.

[0023] Preferably, in step (2), the dosage ratio of potassium nickel cyanide to deionized water is 1 mmol: 20 - 50 mL; the dosage ratio of the soluble salts of the three or four metal ions to deionized water is 1 mmol: 20 - 50 mL; the volume ratio of the ligand solution to the metal ion solution is 1 - 2:1 - 2.

[0024] Preferably, in step (3), the temperature of the hydrothermal reaction is 60 - 150 °C, and the reaction time is 4 - 12 h.

[0025] The present invention also claims the application of the medium-entropy nickel-based metal-organic framework nanoarray electrode described above in the electrocatalytic urea oxidation reaction.

[0026] Preferably, the electrocatalytic urea oxidation reaction is carried out in an alkaline medium, and the medium-entropy nickel-based metal-organic framework nanoarray electrode is directly used as a self-supporting working electrode for urea fuel cells or urea / water co-electrolysis for hydrogen production.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. The medium-entropy nickel-based metal-organic framework nanoarray electrode of the present invention adopts a unique three-dimensional nanoarray structure design, which consists of a three-dimensional conductive substrate and two-dimensional medium-entropy nickel-based metal-organic framework nanosheets supported by it, endowing the electrode with characteristics such as abundant and highly exposed active sites, a large specific surface area, and an adjustable electronic structure. This carefully designed three-dimensional nanoarray structure also endows the electrode with fast charge transfer ability, and together with the highly exposed active sites, significantly improves the UOR electrocatalytic performance of the electrode, providing an ideal microscopic structural basis for efficient electrocatalytic reactions.

[0029] 2. The present invention significantly enhances the catalytic performance of the electrode through a multi-element synergistic strategy. Both the ternary system (NiCoFe-HCP / NF) and the quaternary system (NiCoFeCr-HCP / NF) exhibit remarkable performance advantages. By introducing multiple metal elements to construct a medium-entropy alloy structure, the problems of limited active site quantity and difficult-to-adjust electronic structure in single Ni-MOFs catalysts are successfully solved. Experimental results show that the quaternary system electrode is the most prominent in the electrocatalytic urea oxidation reaction, and its onset potential and the potential required to reach a specific current density are significantly lower than those of the ternary system, binary system, single system, and commercial noble metal catalysts; the ternary system also shows better catalytic performance than the binary and single systems, indicating that as the number of constituent elements increases, the synergistic effect between multiple elements gradually enhances, the electronic structure of the material is optimized, which not only provides more abundant and highly exposed active sites, but also forms a three-dimensional nanosheet array structure that is more conducive to charge transfer.

[0030] 3. The present invention uses a simple hydrothermal method to prepare a medium-entropy nickel-based metal-organic framework nanoarray electrode. The entire preparation process does not require complex equipment and processes, facilitating large-scale production and application. Compared with traditional preparation methods, the present invention does not need to use strong acids and strong alkalis to etch templates, nor does it produce harmful gases such as PH3, which conforms to the concept of modern green chemistry. More importantly, the raw materials used in the present invention are common nickel, iron, chromium, and cobalt salts, and the cost is significantly reduced compared with noble metal-based catalysts (such as RuO2) in industrial applications, providing economic feasibility for large-scale applications.

[0031] 4. The medium-entropy nickel-based metal-organic framework nanoarray electrode of the present invention can be directly applied as a self-supporting electrode in new energy technology fields such as urea fuel cells (DUFC) and urea / water co-electrolysis for hydrogen production, without the need for additional adhesives or conductive agents, simplifying the equipment structure and production process. In practical applications, the electrode can simultaneously achieve the dual environmental protection goals of energy-saving hydrogen production and purification of urea-rich wastewater. In particular, it can utilize urea in industrial wastewater or domestic sewage to generate electricity, providing a new way for wastewater treatment, showing great environmental benefits and social value, and is expected to become an important technical means to solve energy and environmental problems. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show schematic diagrams of some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0033] Figure 1 It is a scanning electron microscope image of the electrode material obtained in Example 1.

[0034] Figure 2 It is the scanning electron microscope image of the electrode material obtained in Example 2.

[0035] Figure 3 It is the scanning electron microscope image of the electrode material obtained in Comparative Example 1.

[0036] Figure 4 It is the scanning electron microscope image of the electrode material obtained in Comparative Example 2.

[0037] Figure 5 It is the X-ray photoelectron spectroscopy image of the materials obtained in Example 1, Example 2, Comparative Example 1 and Comparative Example 2.

[0038] Figure 6 It is the X-ray diffraction pattern of the materials obtained in Example 1, Example 2, Comparative Example 1 and Comparative Example 2.

[0039] Figure 7 It is the UOR polarization curve of the electrodes obtained in Example 1, Example 2, Comparative Example 1 and Comparative Example 2.

[0040] Figure 8 It is the comparison of UOR potentials of the electrodes obtained in Example 1, Example 2, Comparative Example 1 and Comparative Example 2 at different current densities. Detailed implementation manners

[0041] In order to make the objectives, technical solutions and advantages of the present invention clearer, the following further describes the present invention in detail with reference to examples. Of course, the specific examples described herein are only used to explain the present invention and are not used to limit the present invention.

[0042] Unless otherwise specified, the chemical reagents and materials in the present invention are purchased through the market or synthesized from raw materials purchased through the market.

[0043] A preparation method of a medium-entropy nickel-based metal-organic framework nanoarray electrode includes the following steps:

[0044] (1) Pretreat the conductive network substrate: ultrasonically wash the conductive network substrate in 3M hydrochloric acid, ethanol and deionized water for 10 - 30 min in sequence, and dry it at 60 - 80 °C;

[0045] (2) Prepare the precursor solution: dissolve 1 mmol of potassium nickel cyanide in 20 - 50 mL of deionized water to obtain a ligand solution; dissolve Ni 2+ , Co 2+ , Fe 3+ , Cr 3+The soluble salts of three or four metal ions selected from the group are dissolved in deionized water to obtain a metal ion solution, and the dosage ratio of the soluble salts of the three or four metal ions to deionized water is 1 mmol: 20 - 50 mL; the ligand solution and the metal ion solution are mixed evenly to obtain a precursor solution, and the volume ratio of the ligand solution to the metal ion solution is 1 - 2: 1 - 2;

[0046] (3) Preparation of the medium-entropy nickel-based metal-organic framework nanoarray electrode: Immerse the pretreated conductive mesh substrate in step (1) into the precursor solution prepared in step (2), and carry out hydrothermal reaction at 60 - 150 °C for 4 - 12 h. After the reaction, wash and dry the conductive mesh substrate with medium-entropy nickel-based metal-organic framework nanosheets grown on its surface to obtain the medium-entropy nickel-based metal-organic framework nanoarray electrode.

[0047] The following is a further description of the present invention through specific examples.

[0048] Example 1

[0049] A medium-entropy nickel-based metal-organic framework nanoarray electrode (NiCoFeCr-HCP / NF), and its preparation method includes the following steps:

[0050] (1) Pretreatment of nickel foam: Cut the nickel foam into pieces of 1 cm × 4 cm, and ultrasonically treat them in 3 M hydrochloric acid, ethanol, and deionized water for 15 min in sequence, and then dry for standby;

[0051] (2) Preparation of the precursor solution: Dissolve 0.4 mmol of Ni(NO3)2·6H2O, 0.4 mmol of Co(NO3)2·6H2O, 0.4 mmol of Fe(NO3)3·9H2O, and 0.3 mmol of Cr(NO3)3·9H2O in 30 mL of deionized water to obtain a metal ion solution; dissolve 1.5 mmol of potassium nickel cyanide in 30 mL of deionized water to obtain a ligand solution; mix the metal ion solution and the ligand solution evenly to obtain the precursor solution.

[0052] (3) Preparation of the NiCoFeCr-HCP / NF electrode: Transfer the precursor solution obtained in step (2) and the nickel foam treated in step (1) to a reaction kettle, and react in a blast drying oven at 120 °C for 10 h. After the reaction, take out the discolored nickel foam, wash it with water, and dry it in a vacuum oven at 60 °C to obtain the NiCoFeCr medium-entropy metal-organic framework nanoarray (NiCoFeCr-HCP / NF) electrode supported on nickel foam.

[0053] The scanning electron microscope image of the prepared NiCoFeCr-HCP / NF electrode is as shown in the appendix Figure 1As shown, it can be seen that two-dimensional medium-entropy nickel cobalt iron chromium metal-organic framework (NiCoFeCr-HCP) nanosheets grow uniformly on the surface of the three-dimensional nickel foam substrate, and the thickness and lateral size of the nanosheets are 10 nanometers and several hundred nanometers respectively.

[0054] The X-ray photoelectron spectrum of the obtained NiCoFeCr-HCP powder is as shown in the appendix Figure 5 As shown, characteristic peaks corresponding to Cr, Fe, Co, and Ni elements can be detected in the spectrum, thus confirming the simultaneous presence of Cr, Fe, Co, and Ni elements in NiCoFeCr-HCP.

[0055] The X-ray diffraction pattern of the obtained NiCoFeCr-HCP powder is shown in the appendix Figure 6 . The pattern shows that the diffraction characteristic peaks of NiCoFeCr-HCP are in good agreement with the simulated pattern of a single nickel metal-organic framework material (Ni(H2O)2Ni(CN)4·H2O), thus confirming the successful preparation of the medium-entropy nickel-based metal-organic framework nanoarray electrode (NiCoFeCr-HCP / NF).

[0056] Example 2

[0057] A medium-entropy nickel-based metal-organic framework nanoarray electrode (NiCoFe-HCP / NF), the preparation method thereof includes the following steps:

[0058] (1) Pretreatment of nickel foam: Cut the nickel foam into pieces of 1 cm × 4 cm, and place them in 3M hydrochloric acid, ethanol, and deionized water in sequence for ultrasonic treatment for 15 minutes each, and then dry for later use;

[0059] (2) Preparation of the precursor solution: Dissolve 0.5 mmol of Ni(NO3)2·6H2O, 0.5 mmol of Co(NO3)2·6H2O, and 0.5 mmol of Fe(NO3)3·9H2O in 30 mL of deionized water to obtain a metal ion solution; dissolve 1.5 mmol of potassium nickel cyanide in 30 mL of deionized water to obtain a ligand solution; uniformly mix the metal ion solution and the ligand solution to obtain the precursor solution.

[0060] (3) Preparation of the NiCoFe-HCP / NF electrode: Transfer the precursor solution obtained in step (2) and the nickel foam treated in step (1) to a reaction kettle, react in a forced-air drying oven at 120 °C for 10 hours. After the reaction is completed, take out the discolored nickel foam, wash it with water, and dry it in a vacuum oven at 60 °C. After drying, the nickel foam-supported NiCoFe medium-entropy metal-organic framework nanoarray (NiCoFe-HCP / NF) electrode is obtained.

[0061] The scanning electron microscope image of the obtained NiCoFe-HCP powder is as shown in the appendixFigure 2 As shown, on the surface of the three-dimensional nickel foam substrate, two-dimensional medium-entropy nickel cobalt iron metal-organic framework (NiCoFe-HCP) nanosheets grow. The nanosheets grow in a staggered manner horizontally and vertically, but there is a little stacking of the vertically grown sheets.

[0062] The X-ray photoelectron spectrum of the obtained NiCoFe-HCP powder is as attached Figure 5 As shown, characteristic peaks corresponding to Fe, Co, and Ni elements can be detected in the spectrum, thus confirming the simultaneous presence of Fe, Co, and Ni elements in NiCoFeCr-HCP.

[0063] The X-ray diffraction pattern of the obtained NiCoFe-HCP powder is as attached Figure 6 As shown. The diffraction characteristic peaks of NiCoFe-HCP are similar to the simulated pattern of a single nickel metal-organic framework material (Ni(H2O)2Ni(CN)4·H2O), thus confirming the successful preparation of the medium-entropy nickel-based metal-organic framework nanoarray electrode (NiCoFe-HCP / NF).

[0064] Comparative Example 1

[0065] A nickel iron bimetallic metal-organic framework nanoarray electrode (NiFe-HCP / NF), the preparation method thereof includes the following steps:

[0066] (1) Pretreatment of nickel foam: Cut the nickel foam into pieces of 1 cm × 4 cm, and place them in 3M hydrochloric acid, ethanol, and deionized water in sequence for ultrasonic treatment for 15 min each, and then dry for later use;

[0067] (2) Preparation of the precursor solution: Dissolve 1.5 mmol of Ni(NO3)2·6H2O and 0.75 mmol of Fe(NO3)3·9H2O in 30 mL of deionized water to form a uniform solution, and then drop it into a uniform solution containing 1.5 mmol of potassium nickel cyanide and 30 mL of deionized water while stirring to obtain the required solution.

[0068] (3) Preparation of the NiFe-HCP / NF electrode: Transfer the solution obtained in step (2) and the nickel foam treated in step (1) to a hydrothermal synthesis reaction kettle, and carry out hydrothermal reaction for 10 h in a blast drying oven at 120 °C. After the reaction is completed, take out the discolored nickel foam, wash it with water, and dry it in a vacuum oven at 60 °C. Collect the bottom solution in the inner liner into a centrifuge tube for centrifugation, centrifuge 3 times, wash it with water, and dry it under a vacuum drying oven. After drying, the nickel iron bimetallic metal-organic framework nanoarray electrode supported by nickel foam (NiFe-HCP / NF) is obtained.

[0069] The scanning electron microscope image of the obtained NiFe-HCP powder is as attached Figure 3As shown, it can be seen that two-dimensional nickel-iron bimetallic organic framework (NiFe-HCP) nanosheets grow on the surface of the three-dimensional nickel foam substrate. The nanosheets show interlaced growth in the horizontal and vertical directions, and there are some wrinkles on the surface of the nanosheets.

[0070] The X-ray photoelectron spectrum of the obtained NiFe-HCP powder is as attached Figure 5 As shown. Characteristic peaks corresponding to Fe and Ni elements can be detected in the spectrum, thus confirming the simultaneous presence of Fe and Ni elements in NiFe-HCP.

[0071] The X-ray diffraction pattern of the obtained NiFe-HCP powder is as attached Figure 6 As shown. The diffraction characteristic peaks of NiFe-HCP are similar to the simulated pattern of the single nickel metal organic framework material (Ni(H2O)2Ni(CN)4·H2O), thus confirming the successful preparation of the nickel-iron bimetallic organic framework nanoarray electrode (NiFe-HCP / NF).

[0072] Comparative Example 2

[0073] A nickel metal organic framework nanoarray electrode (Ni-HCP / NF), the preparation method thereof includes the following steps:

[0074] (1) Pretreatment of nickel foam: Cut the nickel foam into pieces of 1 cm × 4 cm, and place them in 3M hydrochloric acid, ethanol, and deionized water in turn for ultrasonic treatment for 15 min each, and then dry for later use;

[0075] (2) Preparation of precursor solution: Dissolve 1.5 mmol of Ni(NO3)2·6H2O in 30 mL of deionized water to form a homogeneous solution, and then drop it into a homogeneous solution containing 1.5 mmol of potassium nickel cyanide and 30 mL of deionized water while stirring to obtain the required solution;

[0076] (3) Preparation of Ni-HCP / NF electrode: Transfer the solution obtained in step (2) and the nickel foam treated in step (1) to a hydrothermal synthesis reactor, and carry out hydrothermal reaction at 120 °C in a forced air drying oven for 10 h. After the reaction, take out the discolored nickel foam, wash it with water, and dry it in a vacuum oven at 60 °C. Collect the bottom solution in the inner liner into a centrifuge tube for centrifugation, centrifuge 3 times, wash with water, and dry under vacuum. After drying, the nickel metal organic framework nanoarray electrode supported by nickel foam (Ni-HCP / NF) is obtained.

[0077] The scanning electron microscope image of the obtained Ni-HCP powder is as attached Figure 4As shown, it can be seen that two-dimensional nickel-iron bimetallic organic framework (NiFe-HCP) nanosheets grow vertically and uniformly on the surface of the three-dimensional nickel foam substrate, and the lateral size of the Ni-HCP nanosheets is larger than that of the samples obtained in Example 1, Example 2, and Comparative Example 1.

[0078] The X-ray photoelectron spectrum of the obtained Ni-HCP powder is as shown in the appendix Figure 5 As shown. Characteristic peaks corresponding to C, O, N, and Ni elements can be detected in the spectrum.

[0079] The X-ray diffraction pattern of the obtained Ni-HCP / NF electrode is as shown in the appendix Figure 6 As shown. The pattern shows that the sample obtained in Comparative Example 2 exhibits diffraction peaks similar to those of the samples obtained in Example 1, Example 2, and Comparative Example 1, and is consistent with the simulated pattern of the single nickel metal-organic framework material (Ni(H2O)2Ni(CN)4·H2O), thus confirming the successful preparation of the nickel metal-organic framework nanoarray electrode (Ni-HCP / NF) electrode. At the same time, it is found that with the increase in the number of doped elements, the crystallinity of the obtained samples gradually decreases, indicating that the introduction of metal elements has no obvious effect on the crystal structure of the material.

[0080] Using the electrodes obtained in the above Example 1, Example 2, Comparative Example 1, and Comparative Example 2 as the working electrode, a carbon rod as the counter electrode, and a Hg / HgO electrode as the reference electrode, linear cyclic voltammetry scans were performed under a three-electrode system to evaluate their UOR electrocatalytic performance. The test electrolyte was a mixed solution of 0.5 M urea + 1.0 M potassium hydroxide.

[0081] The commercial RuO2 (99.95 wt.%) catalyst was loaded on the surface of nickel foam at the same loading amount for comparison. Its preparation method was: the calculated commercial RuO2 (99.95 wt.%) catalyst was dispersed in an anhydrous ethanol solution, and then drop-coated on a clean nickel foam to prepare the RuO2 / nickel foam (RuO2 / NF) electrode, and the UOR activity test was carried out in the same manner as above.

[0082] Appendix Figure 7 The appendix gives the UOR polarization curves of the electrodes obtained in Example 1, Example 2, Comparative Example 1, Comparative Example 2, and RuO2 / NF in a mixed solution of 0.5 M urea + 1.0 M potassium hydroxide. It can be seen that the NiCoFeCr-HCP / NF electrode obtained in Example 1 of the present invention requires a UOR potential of only 1.45 V (vs. RHE) to output a high current density of 100 mA cm -2 which is significantly better than the electrodes obtained in Example 2, Comparative Example 1, Comparative Example 2, and the commercial noble metal-based catalyst (RuO2 / NF).

[0083] Appendix Figure 8The UOR current densities of the electrodes obtained in Example 1, Example 2, Comparative Example 1, and Comparative Example 2 at different electrode potentials are given. As can be seen from the figure, (1) under the same electrochemical test conditions, the NiCoFeCr-HCP / NF electrode obtained in Example 1 of the present invention has a higher UOR current density than the electrodes obtained in Example 2, Comparative Example 1, Comparative Example 2, and the commercial noble metal-based catalyst (RuO2 / NF); (2) under the same test conditions, the UOR onset potential of the electrode obtained in Example 1 is the lowest compared to Comparative Example 1, Comparative Example 2, and the commercial RuO2 / NF catalyst.

[0084] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, making equivalent substitutions or changes should be covered within the protection scope of the present invention.

Claims

1. A medium-entropy nickel-based metal-organic framework nanoarray electrode, comprising a conductive mesh substrate and medium-entropy nickel-based metal-organic framework nanosheets loaded on the conductive mesh substrate, wherein, The medium-entropy nickel-based metal-organic framework nanosheets are composed of ligands and metal nodes made from potassium nickel cyanide, and the metal nodes are made from two or three metal ions selected from Ni 2 + and Co2+, Fe3+, Cr 3 +.

2. The medium-entropy nickel-based metal-organic framework nanoarray electrode according to claim 1, wherein The conductive network substrate is one or more of nickel foam, carbon cloth, titanium mesh, and stainless steel mesh.

3. The medium-entropy nickel-based metal-organic framework nanoarray electrode according to claim 1, wherein The raw material of the metal node is Ni 2 +, Co2+, Fe3+, Cr 3 + soluble salts.

4. A method for preparing a medium-entropy nickel-based metal-organic framework nanoarray electrode according to any one of claims 1 to 3, characterized in that, It includes the following steps: (1) Pretreat the conductive network substrate; (2) Prepare the precursor solution: Dissolve potassium nickel cyanide in deionized water to obtain a ligand solution; Dissolve soluble salts of three or four metal ions selected from Ni 2 +, Co2+, Fe3+, Cr 3 + in deionized water to obtain a metal ion solution; Mix the ligand solution and the metal ion solution evenly to obtain a precursor solution; (3) Preparation of the medium-entropy nickel-based metal-organic framework nanoarray electrode: Immerse the pretreated conductive network substrate in the precursor solution prepared in step (2) for hydrothermal reaction. After the reaction, wash and dry the conductive network substrate with medium-entropy nickel-based metal-organic framework nanosheets grown on its surface to obtain the medium-entropy nickel-based metal-organic framework nanoarray electrode.

5. The preparation method of the medium-entropy nickel-based metal-organic framework nanoarray electrode according to claim 4, characterized in that, In step (1), the pretreatment includes ultrasonically washing the conductive network substrate in 3M hydrochloric acid, ethanol, and deionized water for 10 - 30 min, and drying it at 60 - 80 °C.

6. The preparation method of the medium-entropy nickel-based metal-organic framework nanoarray electrode according to claim 4, characterized in that, In step (2), the molar ratio of each metal ion in the soluble salts of the three or four metal ions to potassium nickel cyanide is 0.1 - 2:

1.

7. The preparation method of the medium-entropy nickel-based metal-organic framework nanoarray electrode according to claim 4, characterized in that, In step (2), the dosage ratio of potassium nickel cyanide to deionized water is 1 mmol:20 - 50 mL; the dosage ratio of the soluble salts of the three or four metal ions to deionized water is 1 mmol:20 - 50 mL; the volume ratio of the ligand solution to the metal ion solution is 1 - 2:1 - 2.

8. The preparation method of the medium-entropy nickel-based metal-organic framework nanoarray electrode according to claim 4, characterized in that, In step (3), the temperature of the hydrothermal reaction is 60 - 150 °C, and the reaction time is 4 - 12 h.

9. Application of the medium-entropy nickel-based metal-organic framework nanoarray electrode according to any one of claims 1 - 3 in the electrocatalytic urea oxidation reaction.

10. The application according to claim 10, wherein The electrocatalytic urea oxidation reaction is carried out in an alkaline medium, and the medium-entropy nickel-based metal-organic framework nanoarray electrode is used directly as a self-supporting working electrode for urea fuel cells or urea / water co-electrolysis for hydrogen production.

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