Self-supporting NiCu-MOF catalyst, preparation method and application of self-supporting NiCu-MOF catalyst in ammoxidation electrocatalysis

Abstract

The invention provides a self-supporting NiCu-MOF catalyst, a preparation method and application of the self-supporting NiCu-MOF catalyst in ammoxidation electro-catalysis, and belongs to the technical field of ammoxidation electro-catalysis. A conductive substrate is used as a carrier, in-situ growth is carried out on the conductive substrate, and the NiCu-MOF / S bimetallic MOF catalyst which is not prone to falling off and has good conductivity is obtained. Through the synergistic effect of NiCu bimetals, rapid transfer of interface electrons can be promoted, the conductivity of the material is improved, most importantly, formation of high-valence Ni metal active sites (an active center of electrocatalytic ammoxidation (AOR)) is facilitated, and the catalytic performance of the AOR is improved. The NiCu-MOF / NF catalyst prepared by the preparation method disclosed by the invention shows excellent AOR performance and wastewater ammonia removal capability, and particularly has excellent catalytic activity and stability under high current density; the preparation method is simple and repeatable, is beneficial to amplified production, and has excellent industrial application prospects in the field of electrocatalytic ammoxidation.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrocatalytic materials, and relates to a self-supported NiCu-MOF catalyst for ammonia electrooxidation, a preparation method and an application thereof, especially in the fields of ammonia electrolysis for hydrogen production, ammonia removal from wastewater and ammonia fuel cells. Background Art

[0002] The discharge of ammonia-nitrogen-containing wastewater is one of the main factors leading to water eutrophication and damaging the ecological environment. Although traditional treatment technologies such as biological nitrification / denitrification, breakpoint chlorination and air stripping are widely used, they have problems such as complex operation and easy generation of secondary pollution. In contrast, the electrochemical oxidation technology is simple to operate and environmentally friendly, and has great application potential. In addition, ammonia also has the advantages of convenient storage and transportation, high hydrogen content (17.6 wt.%), large energy density (3000 W h kg - 1), low liquefaction temperature and no carbon, etc., and is an ideal candidate carrier for renewable energy. Electrooxidation of ammonia can generate non-toxic N2 and H2, and theoretically can save energy by ~95% compared with hydrogen production by electrolysis of water. At the same time, it can avoid the risk of hydrogen-oxygen mixed explosion, and has significant advantages in terms of energy consumption, cost and safety. It is one of the most promising ways to store intermittent renewable energy and achieve sustainable energy development. Therefore, ammonia removal from wastewater and hydrogen production can be linked through the ammonia oxidation reaction (AOR). On the one hand, the ammonia in the wastewater is electrooxidized to effectively remove ammonia nitrogen in the wastewater, solve the problem of wastewater pollution, and reduce the damage of water eutrophication to the ecological environment. On the other hand, in the AOR process, the conversion of chemical energy to hydrogen energy can be theoretically achieved with lower energy consumption, providing a clean hydrogen source for the hydrogen energy industry. This method not only utilizes the ammonia resources in the wastewater, but also avoids the environmental pollution and energy depletion problems brought by traditional hydrogen production methods, and has a positive effect in many aspects such as energy conservation, environmental protection and resource utilization. However, the AOR process involves a proton-coupled step of 6 electrons and also faces the challenge of a slow reaction kinetics process. Therefore, the development of efficient and stable electrocatalysts is of great significance in reducing the reaction overpotential and accelerating the reaction rate. At present, platinum-based (Pt) and iridium-based (Ir) noble metal catalysts are the most advanced AOR catalysts, but they have low reserves, high costs, and are easily poisoned by adsorbed nitrogen (N ads ) or other oxygen-containing nitrogen, and cannot be applied on a large scale. Therefore, the development of new and efficient non-noble metal catalysts has become the focus and key challenge of current research.

[0003] At present, nickel and its oxide-based materials have been proven to be effective electrocatalysts for AOR. Research has shown that NiOOH is the active substance for catalyzing AOR. However, it should be emphasized that current Ni-based catalysts usually still have problems such as insufficient surface-exposed active sites, low intrinsic activity, and poor conductivity, which prevent their practical application. For this reason, researchers have proposed various different strategies to improve catalytic performance. In recent years, metal-organic framework (MOF) materials have received extensive attention in the field of electrocatalysis due to their flexible and controllable structure, well-dispersed metal sites, nanoscale cavities, open pores, and large specific surface area. The MOF structure constructed by coordinating metal ions with carboxylate ligands usually exhibits the characteristics of a metal-oxygen (M-O6) octahedral structure. Therefore, coordinating nickel ions with carboxylate ligands can obtain a NiO6 octahedral structure. From a catalytic perspective, the connected Ni-O-Ni bonds in the structure tend to evolve into NiOOH species with high oxidation states and high activity under the drive of an electric field. This also means that nickel-based MOF has the potential to catalyze AOR. However, pure MOF materials usually have poor conductivity and low stability, resulting in poor electrochemical performance. The use of a self-supporting metal substrate can avoid these problems. It can also serve as a direct metal source during the preparation process, enhancing the conductivity of traditional MOF and improving metal utilization without a binder. At the same time, introducing a second (third) metal during the preparation process can also modulate the electronic structure of Ni, thereby optimizing the adsorption and activation ability of reactants and promoting AOR performance. It should be noted that the weak binding of Cu to NH3 can promote the formation of N-N bonds between adsorbed substances on its surface. Therefore, introducing Cu can promote the recombination and desorption of N2 species. In addition, the synergistic effect of bimetals can also change the d-band center, Fermi level, and interatomic spacing of Ni, thereby improving the electrocatalytic activity of AOR. Research has proven that nickel-copper bimetals have good synergy. Xu et al. prepared a copper-nickel alloy catalyst with a synergistic effect, which exhibited high ammonia oxidation activity and selectivity [Applied Catalysis B: Environmental, 2018, 237: 1101–1109].

[0004] Therefore, preparing a self-supporting NiCu-MOF structure can simultaneously improve the catalytic activity and conductivity of the catalyst, which is a very promising development direction. However, research reports on MOF catalyzing AOR are very limited. There is still a lack of in-depth understanding of constructing advanced NiCu-MOF catalysts with specific structures and compositions for AOR, and in-depth and systematic research needs to be carried out to obtain highly efficient AOR electrocatalytic materials. Summary of the Invention

[0005] In view of the existing problems in current research, the present invention proposes a preparation method of a self-supporting NiCu-MOF catalyst for catalyzing AOR. Using conductive substrates such as copper foam, nickel foam, and carbon paper as the support (S), by in-situ growing a bimetallic MOF on S, the catalyst can have a large electrochemically active surface area, good electrical conductivity, and mechanical stability. The NiCu-MOF / S catalyst is obtained through a simple one-step hydrothermal reaction. The MOF structure formed by the co-coordination of Ni and other metal ions with the carboxylate ligand structure promotes the rapid transfer of interfacial electrons, improves the electrical conductivity of the material, and promotes the formation of highly active Ni 3+ sites, ensuring the high performance of the catalyst. In addition, the preparation method of the present invention is simple, controllable, easy to scale up, and highly economical, which is conducive to large-scale industrial applications. Based on the above description, the object of the present invention is achieved through the following technical solutions:

[0006] A preparation method of a self-supporting NiCu-MOF catalyst, the preparation method: First, using a conductive substrate as the support, by growing a NiM bimetallic MOF catalyst (NiM-MOF) on the support, the catalyst can have a good pore structure, electrical conductivity, and mechanical stability. Specifically, it includes the following steps:

[0007] Step (1) Clean the conductive substrate S to remove possible inorganic and organic impurities on the surface, and then dry to obtain the pretreated support S;

[0008] Step (2) Dissolve metal salts and a reagent containing a ligand in a dispersant to obtain a solution; then put the solution and the pretreated conductive substrate S in step (1) into a reaction kettle for hydrothermal reaction. After cooling to room temperature, washing, and drying, the S-supported Ni-based MOF catalyst NiCu-MOF / S for ammonia oxidation reaction (AOR) is obtained. In this step, the metal salt and the ligand form a metal-ligand complex. Putting it and the pretreated conductive substrate S into the reaction kettle for hydrothermal reaction, the complex nucleates on its surface and grows along a specific crystal plane to form a NiCu-MOF nanosheet structure, and the mutually stacked nanosheets construct a three-dimensional network structure with open pores.

[0009] Furthermore, the conductive substrate S in step (1) can be carriers such as copper foam, nickel foam, nickel foil, nickel plate, copper mesh, nickel mesh, carbon paper, and nickel-iron foam. The cleaning process can be acetone, hydrochloric acid, ethanol, water, etc. that can dissolve organic substances or inorganic substances of transition metals. Some operation steps can also be deleted according to the cleanliness of the support; the concentration of the hydrochloric acid can be 0.01-5 mol / L, and the drying method can be natural air drying, air oven drying, vacuum drying, hair dryer drying, freeze drying, etc.

[0010] Further, in the step (2), the molar ratio of the metal salt to the ligand reagent is 0.1-10, the total concentration of the metal salt in the solution is not greater than 5 mol / L, and the concentration of the ligand reagent in the solution is not greater than 5 mol / L.

[0011] Further, in the step (2), the temperature of the hydrothermal reaction is preferably 30-180 °C, and the reaction time is 1-48 h.

[0012] Further, in the step (2), the metal salt is a nickel salt, a copper salt, or other metal salts, and the other metal salts include one or more of an iron salt, a cobalt salt, a manganese salt, a zinc salt, and an aluminum salt.

[0013] Further, in the step (2), the metal salt is one or more of a nitrate, a sulfate, and a chloride.

[0014] Further, in the step (2), the reagent containing a ligand includes a reagent containing a phthalate group or a reagent containing a carboxylate group; the reagent containing a phthalate group includes one or more of terephthalic acid, nitroterephthalic acid, aminoterephthalic acid, and hydroxyterephthalic acid, and the reagent containing a carboxylate group includes one or more of benzene-1,3,5-tricarboxylic acid, naphthalene-1,4-dicarboxylic acid, etc. Further, in the step (2), the dispersant is water, or a mixed solvent of water and one or more of an ethanol solution, a methanol solution, an N,N-dimethylformamide solution, or other organic solvents.

[0015] A self-supporting NiCu-MOF catalyst is prepared by the above preparation method. The catalyst in-situ grows a nanosheet structure on the surface of the support, and the nanosheet is composed of a NiCu-MOF crystal phase, where the support is a conductive substrate.

[0016] An application of the self-supporting NiCu-MOF catalyst is to use it for catalyzing the AOR process and removing ammonia nitrogen in wastewater. When catalyzing the AOR process, the potentials at current densities of 10 and 100 mA cm -2 are only 1.348 and 1.421 V, respectively, and it can stably operate at a current density of 100 mA cm -2 for 100 h; in addition, in the ammonia nitrogen removal experiment for simulating ammonia removal from wastewater, the catalyst has excellent NH4 + -N removal performance and a high N2 selectivity, both of which can reach more than 90% at 1.5 V.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] (1) The NiCu-MOF / S catalyst prepared by the present invention forms an open structure in the MOF grown on the substrate, which facilitates the penetration of the electrolyte and the rapid diffusion of ions, is conducive to exposing a large number of active sites and meeting the mass transfer requirements of the electrocatalytic process, and enables the rapid removal of the generated gas products.

[0019] (2) The NiCu-MOF / S catalyst prepared by the present invention is tightly combined with the conductive substrate through in-situ growth on the conductive substrate, is evenly distributed, is not easy to fall off, avoids the use of binders, and has good conductivity and stability.

[0020] (3) The MOF structure formed by the co-coordination of Ni and other metal ions with the MOF structure, the introduction of Cu regulates the electronic structure of Ni, which is conducive to the formation of high-valent Ni 3+ metal active sites, promoting electrocatalysis; in addition, the synergistic effect between the bimetals may also optimize * the adsorption of OH and accelerate the reaction kinetics.

[0021] (4) The NiCu-MOF / S catalyst prepared by the method described in the present invention exhibits excellent electrocatalytic AOR performance and also has excellent ammonia nitrogen removal performance, and has good prospects for the application of the catalyst in electrolytic ammonia, ammonia removal from wastewater, and ammonia fuel cells.

[0022] (5) Using the preparation method described in the present invention, the process is simple, the raw material cost is low, the catalyst has good repeatability, the reaction parameters in the preparation process are easy to control and reproduce, the performance differences of the catalysts prepared in different batches are extremely small, which ensures the stability of the product quality and is conducive to large-scale industrial production.

[0023] (6) In the preparation process of the catalyst described in the present invention, in addition to Ni and Cu, other heteroatoms can be conveniently introduced for doping modification to further regulate the electronic structure and crystal structure of the catalyst, expand the space for performance optimization, and meet the requirements of different application scenarios. Description of the Drawings

[0024] Figure 1 is the scanning electron microscope (SEM) picture of the catalyst prepared according to Example 1;

[0025] Figure 2 is the transmission electron microscope (TEM) picture of the catalyst prepared according to Example 1;

[0026] Figure 3 (a) is the high-resolution transmission electron microscope (HRTEM) picture of the catalyst prepared according to Example 1; Figure 3 (b) is the partial enlarged view; Figure 3 (c) is the inverse fast Fourier transform picture;

[0027] Figure 4 Energy-dispersive X-ray (EDX) spectrum of the catalyst prepared according to Example 1;

[0028] Figure 5 X-ray diffraction (XRD) spectrum of the catalysts prepared according to Example 1 and Comparative Example 1;

[0029] Figure 6 Comparison chart of OER and AOR performance of the catalyst prepared according to Example 1 when tested in 1M KOH and 1M KOH + 0.2M ammonium chloride electrolytes respectively;

[0030] Figure 7 AOR performance diagram of the catalysts prepared according to Example 1 and Comparative Examples 1-2;

[0031] Figure 8 Ammonia nitrogen removal performance diagram of the catalyst prepared according to Example 1;

[0032] Figure 9 Stability diagram of the catalyst prepared according to Example 1.

[0033] Specific implementation cases:

[0034] The present invention will be described in detail below in conjunction with specific examples. The involved examples are only part of them, and the present invention is not limited to these specific examples.

[0035] Example 1:

[0036] (1) The nickel foam was successively placed in acetone, 3 mol / L -1 hydrochloric acid, ethanol, and water and sonicated for 15 min to remove pollutants and oxide layers, and then vacuum dried to obtain pretreated nickel foam;

[0037] (2) 0.67 mmol of Ni(NO3)2·6H2O, 0.33 mmol of Cu(NO3)2·3H2O, and 0.5 mmol of terephthalic acid (H2BDC) were dissolved in 18 mL of a solvent (volume ratio V 水 :V 无水乙醇 :V N,N-二甲基甲酰胺 = 16:1:1) and sonicated to obtain a uniformly mixed solution. Then, the solution and the nickel foam pretreated in step (1) were placed in a reaction kettle and reacted at 150 °C for 16 h. After washing several times with water and ethanol, it was then dried in a vacuum oven at 60 °C for 4 h to obtain a nickel foam-supported NiCu bimetallic MOF catalyst for ammonia oxidation reaction (NiCu-BDC / NF).

[0038] The NiCu-BDC / NF catalyst prepared in Example 1, at 10 and 100 mA cm -2The AOR potentials at [specific conditions] are only 1.348 V and 1.421 V, and it can operate stably for 100 h at a current density of 100 mA cm -2 ².

[0039] Example 2:

[0040] (1) The copper foam was successively placed in acetone, 3 mol / L -1 hydrochloric acid, absolute ethanol, and water and ultrasonically treated for 20 min to remove pollutants and oxide layers, and then vacuum dried to obtain pretreated copper foam;

[0041] (2) 1 mmol of Ni(NO₃)₂·6H₂O and 0.5 mmol of H₂BDC were dissolved in 18 mL of a solvent (volume ratio V 水 :V 无水乙醇 :V N,N-二甲基甲酰胺 = 16:1:1) and ultrasonically treated to obtain a uniformly mixed solution. Then, the solution and the pretreated copper foam from step (1) were placed in a reaction kettle and reacted at 150 °C for 16 h. After washing several times with water and ethanol, it was then dried in a vacuum oven at 60 °C for 4 h to obtain a NiCu bimetallic MOF catalyst (NiCu-BDC / CF) supported on copper foam for ammonia oxidation reaction.

[0042] For the NiCu-BDC / CF catalyst prepared in Example 2, the AOR potentials at 10 and 100 mA cm -2 are only 1.378 and 1.467 V, and it can operate stably for 60 h at a current density of 100 mA cm -2 ².

[0043] Example 3:

[0044] (1) The nickel foam was successively placed in acetone, 3 mol / L -1 hydrochloric acid, absolute ethanol, and ultrapure water and ultrasonically treated for 20 min to remove pollutants and oxide layers, and then vacuum dried to obtain pretreated nickel foam;

[0045] (2) 200 mmol of Ni(NO₃)₂·6H₂O, 100 mmol of Cu(NO₃)₂·3H₂O, and 30 mmol of H₂BDC were dissolved in 60 mL of solvent water and ultrasonically treated to obtain a uniformly mixed solution. Then, the solution and the pretreated nickel foam from step (1) were placed in a reaction kettle and reacted at 30 °C for 48 h. After washing several times with water and ethanol, it was then dried in a vacuum oven at 60 °C for 4 h to obtain a NiCu bimetallic MOF catalyst (NiCu-BDC / NF) supported on nickel foam for ammonia oxidation reaction.

[0046] For the NiCu-BDC / NF catalyst prepared in Example 3, at 10 and 100 mA cm-2 The AOR potentials at this time are only 1.351 and 1.442 V, and it can operate stably for 100 h at a current density of 100 mA cm -2 .

[0047] Example 4:

[0048] (1) The carbon cloth was successively placed in acetone, 5 mol / L -1 hydrochloric acid, ethanol, and water and ultrasonically treated for 15 min to remove pollutants and oxide layers, and then vacuum dried to obtain pretreated nickel foam;

[0049] (2) 2 mmol of Ni(NO3)2·6H2O, 1 mmol of Cu(NO3)2·3H2O, and 1.5 mmol of H2BDC were dissolved in 18 mL of a solvent (volume ratio V 水 :V 无水乙醇 :V N,N-二甲基甲酰胺 = 16:1:1) and ultrasonically treated to obtain a uniformly mixed solution. Then, the solution and the pretreated nickel foam in step (1) were placed in a reaction kettle and reacted at 180 °C for 1 h. After washing several times with water and ethanol, it was then dried in a vacuum oven at 60 °C for 4 h to obtain a NiCu bimetallic MOF catalyst (NiCu-BDC / CC) supported on nickel foam for ammonia oxidation reaction.

[0050] For the NiCu-BDC / CC catalyst prepared in Example 4, the AOR potentials at 10 and 100 mA cm -2 are only 1.357 and 1.452 V, and it can operate stably for 100 h at a current density of 100 mA cm -2 .

[0051] Example 5:

[0052] (1) The nickel foam was successively placed in acetone, 0.1 mol / L -1 hydrochloric acid, absolute ethanol, and ultrapure water and ultrasonically treated for 20 min to remove pollutants and oxide layers, and then vacuum dried to obtain pretreated nickel foam;

[0053] (2) 10 mmol of NiCl2·6H2O, 5 mmol of Cu(NO3)2·3H2O, 5 mmol of Fe(NO3)3·9H2O, and 15 mmol of nitroterephthalic acid were dissolved in 100 mL of absolute ethanol solvent and ultrasonically treated to obtain a uniformly mixed solution. Then, the solution and the pretreated nickel foam in step (1) were placed in a reaction kettle and reacted at 90 °C for 48 h. After washing several times with water and ethanol, it was then dried in a vacuum oven at 60 °C for 4 h to obtain a NiCu bimetallic MOF catalyst (NiCu-BDC / NF) supported on nickel foam for ammonia oxidation reaction.

[0054] The NiCu-MOF / NF catalyst prepared in Example 5 has AOR potentials of only 1.364 and 1.448 V at 10 and 100 mA cm -2 , and can stably operate for 100 h at a current density of 100 mA cm -2 .

[0055] Example 6:

[0056] (1) Place nickel foam successively in acetone, 3 molL -1 hydrochloric acid, absolute ethanol, and ultrapure water, and ultrasonicate for 20 min to remove contaminants and oxide layers, then vacuum dry to obtain pretreated nickel foam;

[0057] (2) Dissolve 0.5 mmol of Ni(NO3)2·6H2O, 0.5 mmol of Cu(NO3)2·3H2O, and 10 mmol of trimesic acid in 18 mL of solvent (volume ratio V 水 :V 无水乙醇 :V N,N-二甲基甲酰胺 = 16:1:1), ultrasonicate to obtain a uniformly mixed solution, then put the solution and the pretreated nickel foam from step (1) into a reaction kettle, and react at 150 °C for 16 h. After washing several times with water and ethanol, then dry in a vacuum oven at 60 °C for 4 h to obtain a NiCu bimetallic MOF catalyst (NiCu-BTC / NF) supported on nickel foam for ammonia oxidation reaction.

[0058] The NiCu-BTC / NF catalyst prepared in Example 6 has AOR potentials of only 1.374 and 1.446 V at 10 and 100 mA cm -2 , and can stably operate for 80 h at a current density of 100 mA cm -2 .

[0059] Comparative Example 1 (compared with Example 1):

[0060] (1) Place nickel foam successively in acetone, 3 molL -1 hydrochloric acid, absolute ethanol, and ultrapure water, and ultrasonicate for 20 min to remove contaminants and oxide layers, then vacuum dry to obtain pretreated nickel foam;

[0061] (2) Dissolve 1 mmol of Ni(NO3)2·6H2O and 0.5 mmol of H2BDC in 18 mL of solvent (volume ratio V 水 :V 无水乙醇 :V N,N-二甲基甲酰胺= 16:1:1), an ultrasonically homogeneous solution was obtained, and then the solution and the nickel foam pretreated in step (1) were placed in a reaction kettle and reacted at 150 °C for 16 h. After washing several times with water and ethanol, it was dried in a vacuum oven at 60 °C for 4 h to obtain a NiBDC catalyst supported on nickel foam (NiBDC / NF).

[0062] Comparative Example 2 (compared with Example 1):

[0063] (1) The copper foam was successively sonicated in acetone, 3 mol / L -1 hydrochloric acid, absolute ethanol, and ultrapure water for 20 min to remove pollutants and oxide layers, and then vacuum dried to obtain pretreated copper foam;

[0064] (2) 1 mmol of Cu(NO3)2·3H2O and 0.5 mmol of H2BDC were dissolved in 18 mL of solvent (V 水 : V 无水乙醇 : V N,N-二甲基甲酰胺 = 16:1:1), an ultrasonically homogeneous solution was obtained, and then the solution and the nickel foam pretreated in step (1) were placed in a reaction kettle and reacted at 150 °C for 16 h. After washing several times with water and ethanol, it was dried in a vacuum oven at 60 °C for 4 h to obtain a Cu2O catalyst supported on copper foam (Cu2O / CF).

[0065] Figure 1 is the scanning electron microscope (SEM) photograph of the catalyst prepared according to Example 1. From Figure 1 it can be seen that the catalyst exhibits a morphology of mutually stacked nanosheets, and these nanosheets form a large number of irregular nano-spaces with a highly open three-dimensional network.

[0066] Figure 2 is the transmission electron microscope (TEM) photograph of the catalyst prepared according to Example 1. From Figure 2 it can be seen that the catalyst exhibits a nanosheet morphology, which is consistent with the SEM result.

[0067] Figure 3 (a) is the high-resolution transmission electron microscope (HRTEM) photograph of the catalyst prepared according to Example 1, and (b) is its partial enlarged view, from which the lattice fringes can be clearly seen. Further, (c) was obtained through inverse fast Fourier transform. After measurement, it can be known that the lattice spacing on the surface of the nanosheet is 1.09 nm, corresponding to the (200) crystal plane of the NiCu-BDC structure. And Figure 3 it was observed that elements such as Ni, Cu, C, and O were uniformly distributed on the nanosheets, indicating that the catalytic material formed a double-metal MOF crystal structure of NiCu-BDC. Figure 4

[0068] Figure 5 ​XRD patterns of the catalysts prepared according to Example 1 and Comparative Example 1. The results are as follows Figure 1 shown. The diffraction peaks in the XRD patterns of the catalysts prepared in Example 1 and Comparative Example 1 correspond to the simulated NiBDC structure and Ni (PDF#04-0850). The metallic Ni should originate from the nickel foam substrate, indicating the formation of Ni-based MOF crystals. It is worth noting that compared with NiBDC / NF prepared in Comparative Example 1, the diffraction angle of the (200) crystal plane of NiCu-BDC / NF prepared in Example 1 shifts towards a smaller angle, indicating a lattice expansion phenomenon in the structure of the material. This phenomenon should be attributed to the doped Cu 2+ ions with a larger ionic radius (r(Cu 2+ ) = 73 pm, r(Ni 2+ ) = 69 pm), which further confirms the successful synthesis of the NiCu-BDC structure of the present invention.

[0069] Figure 6 OER and AOR performance comparison diagrams of the catalysts prepared according to Example 1 tested in 1 M KOH and 1 M KOH + 0.2 M ammonium chloride electrolytes respectively. The test method is as follows: The NiCu-BDC / NF electrode prepared in Example 1 is fixed on the electrode clamp as the working electrode, a carbon rod as the counter electrode, and silver / silver chloride as the reference electrode, with a scan rate of 5 mV s -1 . The results are as follows Figure 6 shown. The potential required for the NiCu-BDC / NF catalyst prepared in Example 1 to reach a current density of 100 mA cm -2 in AOR is 1.421 V, which is 265 mV lower than that in OER, indicating that the electrolysis of ammonia has lower energy consumption than the electrolysis of water for hydrogen production. This is because the prepared NiCu-MOF catalyst has a large number of AOR active sites, and the dual-metal synergistic effect of Ni and Cu can optimize the adsorption of intermediates, enabling the AOR process to occur at a lower voltage for the catalyst.

[0070] Figure 7 AOR performance diagrams of the catalysts prepared according to Example 1 and Comparative Examples 1-2. The test method is as follows: The NiCu-BDC / NF electrode prepared in Example 1 is fixed on the electrode clamp as the working electrode, a carbon rod as the counter electrode, and silver / silver chloride as the reference electrode, with an electrolyte of 1 M KOH + 0.2 M ammonium chloride and a scan rate of 5 mV s -1 . The NiBDC / NF electrode prepared in Comparative Example 1 and the Cu2O / CF electrode prepared in Comparative Example 2 are used as the working electrodes respectively for AOR performance comparison. As can be seen from Figure 7 the NiCu-BDC / NF catalyst prepared in Example 1 has current densities of 10 and 100 mA cm -2The potentials at that time were only 1.348 and 1.421 V, much lower than those of the NiBDC / NF electrode prepared in Comparative Example 1 (1.381 and 1.632 V) and the Cu2O / CF electrode prepared in Comparative Example 2 (1.392 and 1.693 V). It can be seen that NiCu-BDC / NF exhibits more excellent AOR activity than the samples of pure nickel and pure copper. This is because the bimetallic synergistic effect of Ni and Cu regulates the electronic structure of Ni, effectively improves the charge transfer ability, and accelerates the reaction kinetics of AOR.

[0071] Figure 8 It is the ammonia nitrogen removal performance diagram of the catalyst prepared according to Example 1. The test method is as follows: The NiCu-BDC / NF electrode prepared in Example 1 is fixed on the electrode clamp as the working electrode, the carbon rod is used as the counter electrode, and silver / silver chloride is used as the reference electrode. The simulated ammonia-containing wastewater solution is electrolyzed for 5 h at different voltages (1.4, 1.45, 1.5, 1.55, 1.6 V). Figure 9 It can be seen that as the voltage increases, the ammonia nitrogen removal efficiency of the NiCu-BDC / NF catalyst prepared in Example 1 also increases. When the voltage exceeds 1.55 V, the ammonia nitrogen removal efficiency can reach 100%. And it tends to show a relatively high total nitrogen efficiency of 95.4% at 1.50 V, which means that the N2 selectivity also exceeds 90% at this time.

[0072] Figure 9 It is the stability diagram of the catalyst prepared according to Example 1. The test method is as follows: The NiCu-BDC / NF electrode prepared in Example 1 is fixed on the electrode clamp as the working electrode, the carbon rod is used as the counter electrode, and silver / silver chloride is used as the reference electrode. The electrolyte is 1 M KOH + 0.2 M ammonium chloride, and the stability is measured by the voltage-time curve under a constant current density. The NiCu-BDC / NF catalyst prepared in Example 1 shows almost no attenuation after continuous electrolysis for 100 h at a current density of 100 mA cm -2 and has extremely excellent stability, indicating that this catalyst has great industrial application prospects in efficient ammonia oxidation and treatment of ammonia-rich wastewater.

[0073] The above embodiments only represent the implementation modes of the present invention, but should not be construed as limiting the scope of the present invention patent. It should be noted that for those skilled in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. A preparation method of a self-supporting NiCu-MOF catalyst, characterized in that, The described preparation method includes the following steps: Step (1): Clean and dry the conductive substrate S to obtain the pretreated carrier S; Step (2): Dissolve the metal salt and the ligand-containing reagent in a dispersant to obtain a solution; then put the solution and the conductive substrate S pretreated in step (1) into a reaction kettle for hydrothermal reaction. The hydrothermal reaction temperature is 30 - 180 °C, and the reaction time is 1 - 48 h; after the reaction, cool it to room temperature to obtain the S-supported Ni-based MOF catalyst NiCu-MOF / S for the ammonia oxidation reaction AOR.

2. The preparation method of a self-supporting NiCu-MOF catalyst according to claim 1, characterized in that, In step (1), the conductive substrate S is copper foam, nickel foam, nickel foil, nickel plate, copper mesh, nickel mesh, carbon paper, or nickel-iron foam.

3. The preparation method of a self-supporting NiCu-MOF catalyst according to claim 1, characterized in that, In step (2), the molar ratio of the metal salt to the ligand reagent is 0.5 - 10, the total concentration of the metal salt in the solution is not greater than 5 mol / L, and the concentration of the ligand reagent in the solution is not greater than 5 mol / L.

4. The preparation method of a self-supporting NiCu-MOF catalyst according to claim 1, characterized in that, In step (2), the metal salt is one or more of nitrates, sulfates, and chlorides, including nickel salts, copper salts, and other metal salts. The other metal salts include one or more of iron salts, cobalt salts, manganese salts, zinc salts, and aluminum salts.

5. The preparation method of a self-supporting NiCu-MOF catalyst according to claim 1, characterized in that, In step (2), the ligand-containing reagent includes a phthalate root-containing reagent or a carboxylate root-containing reagent.

6. The preparation method of a self-supporting NiCu-MOF catalyst according to claim 5, characterized in that, In step (2), the phthalate root-containing reagent includes one or more of terephthalic acid, nitroterephthalic acid, aminoterephthalic acid, and hydroxyterephthalic acid, and the carboxylate root-containing reagent includes one or more of trimesic acid and 1,4-naphthalenedicarboxylic acid.

7. The preparation method of a self-supporting NiCu-MOF catalyst according to claim 1, characterized in that, In step (2), the dispersant is water, or a mixed solvent of water and one or more of ethanol solution, methanol solution, N,N-dimethylformamide solution, or other organic solvents.

8. A self-supported NiCu-MOF catalyst, characterized in that, The self-supporting NiCu-MOF catalyst is prepared by the preparation method described in any one of claims 1 - 7. The self-supporting NiCu-MOF catalyst in-situ grows a nanosheet structure on the surface of the conductive substrate, and the nanosheet is composed of the NiCu-BDC crystal phase.

9. Use of the self-supporting NiCu-MOF catalyst according to claim 8, characterized in that, The self-supporting NiCu-MOF catalyst is used for catalyzing the AOR process to remove ammonia nitrogen in wastewater.

10. Use of a self-supported NiCu-MOF catalyst according to claim 9, characterized in that, During the AOR process catalyzed by the self-supporting NiCu-MOF catalyst, the potentials at current densities of 10 and 100 mA cm -2 are 1.348 and 1.421 V, respectively, and it can operate stably at a current density of 100 mA cm -2 for 100 h; in the removal of ammonia nitrogen from wastewater, the catalyst has excellent NH4 + -N removal performance and high N2 selectivity, both of which can reach over 90% at 1.5 V.

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