Nickel-copper bimetallic catalyst as well as preparation method and application thereof

Abstract

The invention discloses a nickel-copper bimetallic catalyst which is of a composite structure of Ni (OH) 2 and Cu (OH) 2, and the whole nickel-copper bimetallic catalyst is of a nanosheet structure. The invention further discloses a preparation method of the nickel-copper bimetallic catalyst and application of the nickel-copper bimetallic catalyst to an electrode. The nickel-copper bimetallic catalyst disclosed by the invention can efficiently and stably catalyze an ammonia electrocatalytic oxidation reaction with high selectivity for a long time, and also has a relatively good application prospect in low-energy-consumption hydrogen production.

Description

Technical Field

[0001] The present invention belongs to the field of catalysis technology, and specifically relates to a nickel-copper bimetallic self-supporting catalyst, a preparation method thereof, and use of an electrode material for preparing nitrite by electrocatalytic oxidation of ammonia. Background Art

[0002] Excessive discharge of ammonia-containing wastewater can cause eutrophication and deterioration of water quality, seriously endangering the ecological environment and human health. Traditional ammonia nitrogen removal methods such as gas stripping, biological methods, and chemical precipitation are widely used, but they suffer from serious secondary pollution, slow reaction rates, and complex operations. In recent years, ammonia electrocatalytic oxidation technology has become a research focus for ammonia wastewater removal due to its advantages such as low investment, strong controllability, and environmental friendliness. It can not only directly convert ammonia nitrogen pollutants into harmless or useful products, but also replace the oxygen evolution reaction in traditional water electrolysis, thereby significantly reducing the energy consumption of hydrogen production from water electrolysis and improving overall energy utilization efficiency.

[0003] N₂ was previously considered an ideal ammonia oxidation product, effective for removing ammonia nitrogen from wastewater. However, its production typically requires overcoming the high energy barrier of nitrogen dimerization. Nitrate is an overoxidation product, and the oxidation of ammonia to nitrate typically requires high potentials or strong oxidizing conditions. At these reaction potentials, side reactions such as the oxygen evolution reaction (OER) often occur, resulting in low Faradaic efficiencies. Nitrite production was once considered harmful and to be avoided in wastewater treatment until the development of short-range denitrification technology, in which ammonia is oxidized to nitrite and then biologically reduced to N₂. Because short-range denitrification is much more efficient than nitrate denitrification, it has greatly encouraged the termination of the ammonia oxidation reaction at the nitrite step. Nitrite itself is a key intermediate in the nitrogen cycle and offers unique advantages over chemically inert N₂. It plays an important role in various fields, including as a meat preservative, pharmaceutical synthesis, and lubricant. Furthermore, the ammonia oxidation reaction (AOR) is an attractive alternative to the anodic oxygen evolution reaction (OER) in hydrogen production, offering a much lower overpotential and thus significantly reducing hydrogen production costs. Although ammonia oxidation to N2 is favored due to its environmentally friendly properties, the nitrite-generating pathway is a more economically viable option from the perspective of coupled hydrogen production, generating NO2 - Instead of N2, more electrons need to be transferred at the anode, which means that when the anode consumes the same amount of ammonia, the cathode will produce more H2. Therefore, the selective conversion of ammonia into nitrite has become a research direction with important application prospects.

[0004] Currently reported electrocatalysts include precious metals (such as Pt, Ru, etc.) and some non-precious metals (such as Ni, Co, Fe) based materials. Although precious metal catalysts have excellent performance and low reaction potential, they are expensive, scarce resources, and often suffer from the problem of catalyst poisoning during use, making them difficult to apply on a large scale. Non-precious metal catalysts also have shortcomings in terms of activity, selectivity, and stability. At present, the material design and reaction mechanism research for ammonia electrocatalytic oxidation mainly focuses on the N2 product. Therefore, there is an urgent need to develop a new electrocatalyst material with low cost, fast reaction rate, high nitrite selectivity, and good stability.

[0005] The present invention is proposed for this purpose. Summary of the Invention

[0006] To address the problems existing in the prior art, the present invention provides a nickel-copper bimetallic self-supporting catalyst and a preparation method thereof. The catalyst of the present invention is used in the electrocatalytic oxidation of ammonia to produce nitrite. The nickel-copper bimetallic catalyst of the present invention can efficiently and stably carry out the electrocatalytic oxidation of ammonia without the use of precious metals, is low-cost, and has a simple preparation method. It has promising application prospects in the resource recovery treatment of ammonia nitrogen in wastewater and in the synergistic production of hydrogen energy.

[0007] The technical solutions of the present invention are as follows:

[0008] The first aspect of the present invention discloses a nickel-copper bimetallic catalyst, which is a composite structure of Ni(OH)2 and Cu(OH)2 and has a nano-sheet structure as a whole.

[0009] Preferably, the molar ratio of Ni(OH)2 to Cu(OH)2 is (9:1)-(1:9); the thickness of the nanosheet is 1-15 nm, the length is 1-8 μm, and the width is 0.3-5 μm.

[0010] Preferably, the electrochemically active surface area of ​​the nickel-copper bimetallic catalyst is 40-100 cm 2 ; After applying a certain voltage, Ni(OH)2 can be converted into the active phase NiOOH.

[0011] The second aspect of the present invention discloses a method for preparing the nickel-copper bimetallic catalyst, comprising the following steps:

[0012] (1) A certain amount of NiCl2·6H2O, CuCl2·2H2O and terephthalic acid are dissolved in a mixed solution of N,N-dimethylformamide, ethanol and deionized water; nickel foam is immersed in the above solution, subjected to hydrothermal reaction, washed and dried to obtain a precursor catalyst;

[0013] (2) In a three-electrode system, the precursor catalyst is activated in a mixed solution of KOH and NH4Cl by cyclic voltammetry to complete electrochemical reconstruction, thereby obtaining the nickel-copper bimetallic catalyst.

[0014] Preferably, before step (1), the nickel foam is pretreated with acetone, hydrochloric acid and deionized water respectively to remove organic matter and nickel oxide on its surface.

[0015] Preferably, in step (1), the amount of NiCl2·6H2O and CuCl2·2H2O added is such that the molar ratio of NiCl2·6H2O to CuCl2·2H2O is (9:1)-(1:9); the molar amount of terephthalic acid added is the same as the total molar amount of NiCl2·6H2O and CuCl2·2H2O added, and the concentration is 10-50 mmol L -1 ; The addition ratio of N,N-dimethylformamide, ethanol and water is 15:1:1.

[0016] Preferably, in step (1), the temperature of the hydrothermal reaction is 140-160° C., and the time of the hydrothermal reaction is 10-30 h.

[0017] Preferably, in step (2), cyclic voltammetry activation is performed in a mixed solution of 1 M KOH and 0.1 M NH4Cl in a potential range of 0 V to 0.7 V vs. Ag / AgCl, with a scan rate of 50 mV / s and the number of activation cycles being 15-30.

[0018] The third aspect of the present invention discloses the use of the nickel-copper bimetallic catalyst for preparing a nitrite electrode by electrocatalytic oxidation of ammonia.

[0019] Alternatively, the nickel-copper bimetallic catalyst is used for application in AOR-HER (ammonia oxidation reaction-hydrogen evolution reaction) electrodes.

[0020] The nickel-copper bimetallic catalyst of the present invention is a composite structure of Ni(OH)2 and Cu(OH)2 in a molar ratio of (9:1)-(1:9); the overall structure is a nanosheet structure, the thickness of the nanosheet is 1-15nm, the length is 1-8μm, and the width is 0.3-5μm; the electrochemical active surface area is 40-100cm 2 ; The surface of the nanosheet is relatively rough, which is beneficial for providing a larger specific surface area for subsequent catalytic reactions and exposing abundant active sites.

[0021] The nickel-copper bimetallic catalyst of the present invention is used as a catalyst for the electrocatalytic oxidation reaction of ammonia, and has excellent stability. The active component thereof is a composite structure of nickel hydroxide and copper hydroxide, and no precious metals are required, which can solve the problems of high cost and low reserves of precious metal catalysts. The mechanism of the nickel-copper bimetallic catalyst of the present invention catalyzing the electrocatalytic oxidation reaction of ammonia is as follows: first, during the cyclic voltammetry (CV) activation process, the Ni-BDC MOF structure decomposes and evolves into Ni(OH)2, and then during the electrochemical oxidation reaction, Ni(OH)2 can undergo an in-situ oxidation reaction to generate NiOOH, which is an active site that promotes the electrocatalytic oxidation reaction of ammonia; and the presence of Cu(OH)2 can attract the electrons of Ni in NiOOH, maintain the high valence state of Ni, increase the active sites in the catalyst, and improve the catalytic activity of the material, thereby promoting the electrocatalytic oxidation process of ammonia.

[0022] The nickel-copper bimetallic catalyst of the present invention can be used for the electrocatalytic oxidation of ammonia to produce nitrite in alkaline solutions, and can also be used for coupled electrolytic hydrogen production. It has excellent ammonia electrocatalytic oxidation performance and nitrite selectivity, and has the advantages of high efficiency, low energy consumption, and stability. When a solution of 1M KOH and 0.1M NH4Cl is used as the electrolyte, the catalyst can reach 50mA cm at 1.436V vs. RHE. -2 The current density is 135.7 mV dec. -1 , has excellent reaction kinetics, small charge transfer resistance and large electrochemical active surface area; and, the catalyst of the present invention is used in constant current test, which can operate stably for a long time at 50 mA cm -2 It can operate stably for more than 200 hours at a current density of 1.835V. In addition, the catalyst is used to build a coupled hydrogen electrolyzer, and the overall water decomposition requires 1.835V to reach 50mA cm -2 The current density of AOR-HER (hydrogen evolution reaction) system only needs 1.606V to reach the same current density, which is reduced by 229mV.

[0023] In a solution containing 0.1 M NH4Cl, when the applied potential was 1.55 V, the nickel-copper bimetallic catalyst R-Ni7Cu3 / NF of the present invention showed a kinetic energy of 225.7 mg L -1 h -1 The NH3-N removal rate and 215 mg L -1 h -1 NO2 - -N production rate, NO2 - -N selectivity is as high as 95.25%, and it can maintain a high ammonia oxidation rate and NO2 --N Faraday efficiency is better than most reported catalysts. At the same time, the catalyst shows excellent cyclic stability. In ten cycles, the removal rate of NH3-N and NO2 - -N's Faradaic efficiency always remains above 90%.

[0024] The preparation method of the nickel-copper bimetallic catalyst of the present invention uses a metal organic framework (MOF) as a precursor and obtains an active phase with ammonia electrocatalytic oxidation activity through an electrochemical reconstruction strategy. The present invention uses nickel foam as a carrier, terephthalic acid (BDC) as an organic ligand, NiCl2·6H2O and CuCl2·2H2O as metal precursors, and uses a simple hydrothermal synthesis method to obtain Ni 2+ Ni-MOF is in situ grown on the surface of nickel foam through coordination with BDC, and some Cu 2+ Under the action of nickel foam and ethanol, it is reduced to copper element and loaded on Ni-MOF, forming a precursor catalyst on the surface of the nickel foam; it is then activated in a reaction solution to complete the electrochemical reconstruction of the material surface. In this process, under the dual effects of alkaline environment and cyclic voltage, the MOF structure gradually decomposes and evolves into a true active substance, obtaining the final catalyst. The preparation method of the present invention can effectively regulate the morphology of the nanomaterial by changing the ratio of nickel to copper precursors. The obtained material is used as an electrode material for the preparation of nitrite by the electrocatalytic oxidation reaction of ammonia, which can promote the kinetics of the ammonia oxidation reaction, reduce the charge transfer resistance, optimize the adsorption energy of the intermediate, and achieve efficient and highly selective ammonia oxidation reaction.

[0025] The preparation method of the nickel-copper bimetallic catalyst of the present invention comprises the following steps: (1) dissolving a certain amount of NiCl2·6H2O, CuCl2·2H2O and BDC in a mixed solution of N,N-dimethylformamide, ethanol and deionized water and stirring; immersing the foamed nickel in the solution and placing it in a blast drying oven for hydrothermal reaction, reacting at 150°C for 20 hours, washing 3-4 times, and drying to obtain a precursor catalyst; (2) in a three-electrode system, activating the precursor catalyst prepared in step (1) by cyclic voltammetry (CV) in 1M KOH and 0.1M NH4Cl solution and completing electrochemical reconstruction, the potential range is 0V to 0.7V vs. Ag / AgCl, the scan rate is 50mV / s, the number of CV activation cycles is 15-30 cycles, washing 3-4 times, and drying to obtain a final catalyst.

[0026] Wherein, the addition amount of NiCl2·6H2O and CuCl2·2H2O in step (1) is that the molar ratio of NiCl2·6H2O to CuCl2·2H2O is (9:1)-(1:9); when the hydrothermal reaction solution contains both NiCl2·6H2O and CuCl2·2H2O, the XRD spectrum of the precatalyst simultaneously presents characteristic diffraction peaks of Ni-BDC MOF and Cu, indicating the simultaneous presence of the two substances, and the intensity of the Cu diffraction peak increases with the increase of the Cu content in the sample; the SEM image shows that when the Cu loading amount is small, the surface of the precursor catalyst presents a relatively complete nano-sheet structure; when the Cu content increases, the surface sheet structure gradually disappears and gradually presents an agglomerated nano-granular morphology, and the morphological changes caused by the change in the nickel-copper ratio are basically consistent with the XRD spectrum results.

[0027] Among them, the number of CV activation cycles in step (2) is 15-30 cycles; during the CV activation process, the surface structure of the catalyst gradually changes. Although the original flaky structure is retained, its initial Ni-BDC MOF structure decomposes and forms a new active phase Ni(OH)2 / Cu(OH)2. When the number of CV activation cycles is small, the catalyst surface is not completely reconstructed and is insufficient to fully activate and form an active phase; therefore, the number of CV activation cycles in the present invention is preferably 15-30 cycles. Within this range of activation cycles, complete reconstruction of the catalyst can be achieved, achieving higher catalytic activity.

[0028] Beneficial effects of the present invention:

[0029] 1. The nickel-copper bimetallic catalyst of the present invention has a simple composition and structure, and can catalyze the electrocatalytic oxidation reaction of ammonia stably for a long time at low cost, high efficiency, and low energy consumption. It has good application prospects in the treatment of ammonia nitrogen wastewater and low-energy hydrogen production, and can achieve pollutant upgrading of ammonia-containing wastewater in a more sustainable and economical way.

[0030] 2. The preparation method of the nickel-copper bimetallic catalyst of the present invention is simple and does not require the use of precious metals; by controlling the ratio of metal precursors and electrochemical reconstruction conditions, the obtained catalyst can have excellent catalytic activity and stability.

[0031] 3. The electrochemically active surface area of ​​the nickel-copper bimetallic catalyst of the present invention is 40-100 cm 2 , which is beneficial to provide a larger specific surface area for the ammonia electrocatalytic oxidation reaction and is conducive to exposing abundant active sites. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 1-3 and Comparative Examples 1-2 show the XRD patterns of Ni / NF, Ni7Cu3 / NF, Ni5Cu5 / NF, Ni3Cu7 / NF and Cu / NF obtained.

[0033] Figure 2 These are SEM images of Ni / NF(a), Ni7Cu3 / NF(b), Ni5Cu5 / NF(c), Ni3Cu7 / NF(d) and Cu / NF(e) obtained in Examples 1-3 and Comparative Examples 1-2.

[0034] Figure 3 1 is the XRD pattern of Ni7Cu3 / NF and R-Ni7Cu3 / NF obtained in Example 1.

[0035] Figure 4 This is the SEM image of R-Ni7Cu3 / NF obtained in Example 1.

[0036] Figure 5 These are TEM images of Ni7Cu3 / NF (a and b) and R-Ni7Cu3 / NF (c and d) obtained in Example 1.

[0037] Figure 6 These are the XPS graphs of Ni 2p (a) and Cu 2p (b) of Ni7Cu3 / NF and R-Ni7Cu3 / NF obtained in Example 1.

[0038] Figure 7 This is the Raman spectrum of Ni7Cu3 / NF obtained in Example 1 after different CV activation cycles.

[0039] Figure 8 The Ni7Cu3 / NF obtained in Example 1 was subjected to a 1M KOH and 0.1M NH4Cl solution at 1-1.7V vs RHE at 50mV s -1 CV curves obtained after 20 CV cycles at a scan rate of 1.

[0040] Figure 9 (a) CV curves, (b) Tafel plots, (c) Nyquist plots and (d) electrochemically active surface areas of R-Ni / NF, R-Ni7Cu3 / NF, R-Ni5Cu5 / NF, R-Ni3Cu7 / NF and R-Cu / NF obtained in 1 M KOH and 0.1 M NH4Cl solutions in Examples 1-3 and Comparative Examples 1-2.

[0041] Figure 10 The R-Ni7Cu3 / NF obtained in Example 1 was subjected to 1.0M KOH+0.1M NH4 in the presence of (a) different anions, (b) different cations, and (c) different organic compounds. + CV curves in solution.

[0042] Figure 11The R-Ni7Cu3 / NF obtained in Example 1 was subjected to a current density of 50 mA cm in 1 M KOH, 0.1 M NH4Cl and 1 M KOH solutions. -2 Chronopotentiometry curves.

[0043] Figure 12 The removal efficiency of (a) ammonia nitrogen, (b) NH3-N, (c) NO2 in 1M KOH and 0.1M NH4Cl solution at 1.55V vs RHE for R-Ni7Cu3 / NF, R-Ni / NF and R-Cu / NF obtained in Example 1, Comparative Example 1 and Comparative Example 2, - -N and (d)NO3 - -N concentration changes over time.

[0044] Figure 13 The R-Ni7Cu3 / NF obtained in Example 1 was subjected to different potentials in 1M KOH and 0.1M NH4Cl solutions (a) NH3-N, (b) NO2 - -N and (c)NO3 - -N concentration changes over time.

[0045] Figure 14 The R-Ni7Cu3 / NF obtained in Example 1 was subjected to 1.0M KOH+0.1M NH4 in the presence of (a) different anions, (b) different cations, and (c) different organic compounds. + Degradation performance in solution.

[0046] Figure 15 The R-Ni7Cu3 / NF obtained in Example 1 was tested in a continuous cycle of NO2 - Faradaic efficiency and NH3-N removal rate.

[0047] Figure 16 The R-Ni7Cu3 / NF obtained in Example 1 has a high Ni 2+ and Cu 2+ leaching concentration.

[0048] Figure 17 This is the IT curve of the continuous cycle stability test of R-Ni7Cu3 / NF obtained in Example 1 at 1.55V vs. RHE.

[0049] Figure 18 This is the in situ Raman spectrum of Ni7Cu3 / NF obtained in Example 1 at different potentials in 1M KOH and 0.1M NH4Cl.

[0050] Figure 19(a) LSV curves and (b) potential comparisons at different current densities of the OER-HER and AOR-HER systems with R-Ni7Cu3 / NF obtained in Example 1 as the anode and Pt / C as the cathode. DETAILED DESCRIPTION

[0051] It should be noted that the following examples are only used to illustrate and explain the present invention in detail, and the scope of application of the present invention is not limited by the conditions in the examples.

[0052] Example 1: Preparation of R-Ni7Cu3 / NF.

[0053] Step 1: Nickel foam (NF) was ultrasonically pretreated with acetone, hydrochloric acid, and deionized water for 15 minutes to remove surface organic matter and oxides, and then the nickel foam was dried in a vacuum drying oven at 60°C.

[0054] Step 2: Dissolve 1.4 mmol of NiCl2·6H2O, 0.6 mmol of CuCl2·2H2O, and 2 mmol of terephthalic acid in a mixture of 60 mL of N,N-dimethylformamide, 4 mL of ethanol, and 4 mL of deionized water, and stir. Immerse the nickel foam in the solution and place it in a forced-air drying oven for a hydrothermal reaction at 150°C for 20 hours. Wash the foam 3-4 times and vacuum dry it at 60°C overnight to obtain the precursor catalyst, named Ni7Cu3 / NF.

[0055] The XRD spectrum of Ni7Cu3 / NF is as follows: Figure 1 As shown in the SEM images Figure 2 shown.

[0056] Step 3: The prepared precursor catalyst Ni7Cu3 / NF was activated and electrochemically reconstructed by simple cyclic voltammetry (CV) in 1M KOH and 0.1M NH4Cl solution. The potential range was 0V to 0.7V vs. Ag / AgCl, the scan rate was 50mV / s, and it was cycled 20 times in a three-electrode system. The reconstructed catalyst was washed three times with deionized water to obtain the final catalyst, named R-Ni7Cu3 / NF.

[0057] Example 2: Preparation of R-Ni5Cu5 / NF.

[0058] The steps are the same as in Example 1;

[0059] Step 2: Dissolve 1 mmol of NiCl2·6H2O, 1 mmol of CuCl2·2H2O, and 2 mmol of terephthalic acid in a mixture of 60 mL of N,N-dimethylformamide, 4 mL of ethanol, and 4 mL of deionized water, and stir. Immerse the nickel foam in this solution and place it in a forced-air drying oven for a hydrothermal reaction at 150°C for 20 hours. Wash 3-4 times and vacuum dry overnight at 60°C to obtain the precursor catalyst, designated Ni5Cu5 / NF.

[0060] The XRD spectrum of Ni5Cu5 / NF is as follows: Figure 1 As shown in the SEM images Figure 2 shown.

[0061] Step 3: The prepared precatalyst Ni5Cu5 / NF was activated and electrochemically reconstructed by simple cyclic voltammetry (CV) in 1 M KOH and 0.1 M NH4Cl solution in the potential range of 0 V to 0.7 V vs. Ag / AgCl, with a scan rate of 50 mV / s, and cycled 20 times in a three-electrode system. The reconstructed catalyst was washed three times with deionized water to obtain the final catalyst, named R-Ni5Cu5 / NF.

[0062] Example 3: Preparation of R-Ni3Cu7 / NF.

[0063] The steps are the same as in Example 1;

[0064] Step 2: Dissolve 0.6 mmol NiCl2·6H2O, 1.4 mmol CuCl2·2H2O, and 2 mmol terephthalic acid in a mixture of 60 mL N,N-dimethylformamide, 4 mL ethanol, and 4 mL deionized water, and stir. Immerse the nickel foam in the solution and place it in a forced-air drying oven for a hydrothermal reaction at 150°C for 20 hours. Wash 3-4 times and vacuum dry overnight at 60°C to obtain the precursor catalyst, designated Ni3Cu7 / NF.

[0065] The XRD spectrum of Ni3Cu7 / NF is shown in Figure 2. Figure 1 As shown in the SEM images Figure 2 shown.

[0066] Step 3: The prepared precatalyst Ni3Cu7 / NF was activated and electrochemically reconstructed by simple cyclic voltammetry (CV) in 1 M KOH and 0.1 M NH4Cl solution in the potential range of 0 V to 0.7 V vs. Ag / AgCl, with a scan rate of 50 mV / s, and cycled 20 times in a three-electrode system. The reconstructed catalyst was washed three times with deionized water to obtain the final catalyst, named R-Ni3Cu7 / NF.

[0067] Comparative Example 1: Preparation of R-Ni / NF.

[0068] The steps are the same as in Example 1;

[0069] Step 2: Dissolve 2 mmol of NiCl₂·6H₂O and 2 mmol of terephthalic acid in a mixture of 60 mL of N,N-dimethylformamide, 4 mL of ethanol, and 4 mL of deionized water, and stir. Immerse the nickel foam in this solution and place it in a forced-air drying oven for a hydrothermal reaction at 150°C for 20 hours. Wash 3-4 times and vacuum dry overnight at 60°C to obtain the precursor catalyst, designated Ni / NF.

[0070] The obtained XRD spectrum of Ni / NF is as follows: Figure 1 As shown in the SEM images Figure 2 shown.

[0071] Step 3: The prepared precatalyst Ni / NF was activated and electrochemically reconstructed by simple cyclic voltammetry (CV) in 1 M KOH and 0.1 M NH4Cl solution. The potential range was 0 V to 0.7 V vs. Ag / AgCl, the scan rate was 50 mV / s, and the three-electrode system was cycled 20 times. The reconstructed catalyst was washed three times with deionized water to obtain the final catalyst, named R-Ni / NF.

[0072] Comparative Example 2: Preparation of R-Cu / NF.

[0073] The steps are the same as in Example 1;

[0074] Step 2: Dissolve 2 mmol of CuCl₂·2H₂O and 2 mmol of terephthalic acid in a mixture of 60 mL of N,N-dimethylformamide, 4 mL of ethanol, and 4 mL of deionized water, and stir. Immerse the nickel foam in this solution and place it in a forced-air drying oven for a hydrothermal reaction at 150°C for 20 hours. Wash 3-4 times and vacuum dry overnight at 60°C to obtain the precursor catalyst, designated Cu / NF.

[0075] The XRD spectrum of Cu / NF is shown in Figure 2. Figure 1 As shown in the SEM images Figure 2 shown.

[0076] Step 3: The prepared precatalyst Cu / NF was activated and electrochemically reconstructed by simple cyclic voltammetry (CV) in 1 M KOH and 0.1 M NH4Cl solution in the potential range of 0 V to 0.7 V vs. Ag / AgCl at a scan rate of 50 mV / s. It was cycled 20 times in a three-electrode system. The reconstructed catalyst was washed three times with deionized water to obtain the final catalyst, named R-Cu / NF.

[0077] Precursor catalyst analysis.

[0078] The composition and morphology of the precursor catalysts Ni / NF, Ni7Cu3 / NF, Ni5Cu5 / NF, Ni3Cu7 / NF and Cu / NF prepared in step 2 of Examples 1-3 and Comparative Examples 1-2 were analyzed as follows:

[0079] (1) The crystal structure of the synthesized catalyst was characterized by X-ray diffractometer (Bruker-Nonius D8 Focus); Figure 1 As shown, Ni / NF and Ni7Cu3 / NF exhibit diffraction peaks at 9.0°, 14.2°, 15.9°, 18.0°, 29.0°, and 31.1°, which are consistent with the diffraction peak positions simulated using Ni-BDC MOF crystal data. This indicates that nickel ions successfully coordinate with terephthalic acid to form a MOF structure and are loaded on the nickel foam surface. Cu / NF exhibits distinct diffraction peaks at 43.3°, 50.4°, and 74.1°, corresponding to the characteristic diffraction peaks of Cu. This indicates that copper ions do not readily coordinate with terephthalic acid and are instead reduced and present as copper particles on the nickel foam surface. The XRD spectra of Ni5Cu5 / NF and Ni3Cu7 / NF exhibit characteristic diffraction peaks for both Ni-BDC MOF and Cu, indicating the coexistence of these two species. Furthermore, the intensity of the Cu diffraction peak increases with increasing Cu content in the samples. (Note: There is no corresponding XRD standard card for Ni-BDC MOF, so the diffraction peak position of this substance was further simulated using the retrieved Ni-BDC MOF crystal data. The target sample and several nickel-containing comparison samples showed diffraction peaks corresponding to Ni-BDC MOF, indicating the presence of this substance in these samples, which also shows that nickel ions are successfully coordinated with terephthalic acid to form a MOF structure.)

[0080] (2) Scanning electron microscopy (Thermo Scientific Apreo S) was used to observe the surface morphology and microstructure of different catalysts; Figure 2 As shown in the figure, the surface morphology of Ni / NF presents a typical nanosheet structure. When the Cu loading is low, the surface morphology of Ni7Cu3 / NF and Ni5Cu5 / NF is similar to that of Ni / NF, showing a relatively complete nanosheet structure. When the Cu content is further increased, the surface sheet structure of Ni3Cu7 / NF changes slightly, while the surface of Cu / NF presents an agglomerated nanoparticle morphology. The change in the nickel-copper ratio leads to the change in the morphology of the catalyst.

[0081] Analysis of precursor catalyst Ni7Cu3 / NF and catalyst R-Ni7Cu3 / NF.

[0082] The precursor catalyst Ni7Cu3 / NF prepared in step 2 of Example 1 and the catalyst R-Ni7Cu3 / NF prepared in step 3 were used as test objects, and the structure and composition analysis were performed as follows:

[0083] (1) Scanning electron microscope (Thermo Scientific Apreo S) was used to observe the surface morphology and microstructure of different catalysts; Figure 4 As shown, compared with Ni7Cu3 / NF, R-Ni7Cu3 / NF retains the basic morphology before reconstruction, presenting a nanosheet structure with a length of 1-8μm, a width of 0.3-5μm, and a thickness of 1-15nm; but the surface of the nanosheet becomes rougher, which is beneficial for providing a larger specific surface area for subsequent catalytic reactions and exposing abundant active sites.

[0084] (2) The crystal structure of the synthesized catalyst was characterized by X-ray diffractometer (Bruker-Nonius D8 Focus); Figure 3 As shown in Figure 3, after reconstruction, the characteristic diffraction peaks of the original Ni7Cu3 / NF completely disappeared, while new peaks appeared at 33.1° and 60.0°, corresponding to the (101) and (110) crystal planes of α-Ni(OH)2, respectively.

[0085] (3) Transmission electron microscopy (FEI Talos F200X) was used to compare the micromorphology of Ni7Cu3 / NF before and after reconstruction. Figure 5 As shown in the figure, Ni7Cu3 / NF presents a typical sheet-like structure, with uniformly distributed nanoparticles on its surface. The nanoparticles show a lattice spacing of 0.210 nm, corresponding to the (111) crystal plane of Cu. In contrast, the TEM image of R-Ni7Cu3 / NF obtained after electrochemical reconstruction shows a looser nanosheet structure with a thickness of 1-15 nm. Analysis of its lattice fringes shows that the lattice spacing of 0.263 nm and 0.156 nm corresponds to the (101) and (110) planes of α-Ni(OH)2, while the lattice spacing of 0.225 nm corresponds to the (130) plane of Cu(OH)2.

[0086] (4) X-ray photoelectron spectroscopy (Thermo Scientific K-Alpha) was used to analyze the surface chemical composition and valence distribution of the samples. Figure 6 As shown in the figure, the Ni 2p spectrum of Ni7Cu3 / NF shows two characteristic peaks at 855.85eV and 873.57eV, corresponding to Ni 2+ 2p 3 / 2 and Ni 2+ 2p 1 / 2The two peaks at 861.50eV and 879.50eV are Ni 2+ The valence state of Ni in the reconstructed R-Ni7Cu3 / NF is still +2, and its Ni 2+ 2p 3 / 2 and Ni 2+ 2p 1 / 2 The characteristic peaks appear at 855.40eV and 872.98eV respectively. The Cu 2p spectrum of Ni7Cu3 / NF appears at 931.89eV and 951.67eV, which belong to Cu 0 / Cu + The characteristic peaks of Cu appear at 934.43eV and 953.93eV. 2+ characteristic peaks; it is worth noting that Cu 0 / Cu + The peak intensity is much higher than that of Cu 2+ The peak intensity indicates that Cu exists mainly in a low valence state, while the Cu 2p spectrum of R-Ni7Cu3 / NF presents 6 peaks, with the main peaks at 934.06 and 954.70 eV, corresponding to Cu 2+ 2p 3 / 2 and Cu 2+ 2p 1 / 2 , the other four strong satellite peaks are closely related to Cu 2+ This confirms that the catalyst was reconstructed during the electrochemical activation process.

[0087] (5) The Raman spectra of samples after different CV activation cycles were tested. Figure 7 As shown, the Raman spectra of Ni7Cu3 / NF are at 632, 868, 1142, 1442, 1563 and 1614 cm -1 The characteristic peaks are attributed to the vibration modes of the benzene ring, carboxylic acid group and metal ions (Ni 2+ 、Cu 2+ ) and the organic ligand terephthalic acid, confirming the successful formation of the metal organic framework. As the number of CV activation cycles increases, the intensity of these peaks related to the organic ligand decreases significantly, indicating that the organic framework gradually collapses. At the same time, at ~525 cm -1 A new strong peak appears at , and its intensity increases. This peak is usually considered to be the Ni-O oscillation peak of Ni(OH)2.

[0088] (6) In a three-electrode system, 20 CV scans were performed in a 1 M KOH solution containing 0.1 M NH4Cl using CHI760E; Figure 8As shown in the figure, the current response of Ni7Cu3 / NF gradually increases with the number of CV cycles, and the area of ​​the redox peak gradually increases, indicating that the catalyst surface is gradually reconstructed during the electrochemical activation process. After 20 cycles, the current density gradually stabilizes, indicating that the activation process has been completed and a steady-state active surface has been formed.

[0089] The electrochemical performance of the products R-Ni / NF, R-Ni7Cu3 / NF, R-Ni5Cu5 / NF, R-Ni3Cu7 / NF and R-Cu / NF catalysts were tested.

[0090] The electrochemical performance of the R-Ni / NF, R-Ni7Cu3 / NF, R-Ni5Cu5 / NF, R-Ni3Cu7 / NF and R-Cu / NF catalysts prepared in Examples 1-3 and Comparative Examples 1-2 was tested in a three-electrode system using CHI760E. 2 The platinum sheet was used as the counter electrode, the products obtained in Examples 1-3 and Comparative Examples 1-2 were used as working electrodes, and Ag / AgCl was used as the reference electrode to test the electrochemical performance of ammonia oxidation of the products. The CV curves obtained were ( Figure 9 a) Tafel slope ( Figure 9 b) Nyquist curve ( Figure 9 c) and C dl curve( Figure 9 d), such as Figure 9 As shown. Figure 9 As can be seen in a, R-Ni7Cu3 / NF has the highest current response and the lowest onset potential, requiring only 1.436 V vs. RHE to reach 50 mA cm -2 The Tafel slope was further used to evaluate the kinetics of the electrocatalytic reaction. Figure 9 As can be seen in b, the Tafel slope of R-Ni7Cu3 / NF is 135.7mV dec -1 , which is significantly lower than other catalysts, proving that R-Ni7Cu3 / NF has more superior ammonia oxidation reaction (AOR) kinetics. Figure 9 As can be seen in Figure c, the Nyquist curve of R-Ni7Cu3 / NF shows a smaller semicircle diameter, indicating that it has a smaller charge transfer resistance. Its larger electrochemical active surface area (98.25 cm 2 ,See Figure 9 d) It also shows that the catalyst has more active sites.

[0091] The ammonia electrocatalytic oxidation performance of R-Ni7Cu3 / NF, R-Ni / NF, and R-Cu / NF catalysts was tested in 1 M KOH and 0.1 M NH4Cl solutions.

[0092] The R-Ni7Cu3 / NF, R-Ni / NF, and R-Cu / NF catalysts prepared in Example 1 and Comparative Examples 1-2 were tested for ammonia electrocatalytic oxidation performance in a three-electrode system using a CHI760E. 2 The catalyst's electrocatalytic oxidation performance for ammonia was tested using a platinum sheet as the counter electrode, the sample to be tested as the working electrode, and Ag / AgCl as the reference electrode. The reaction was carried out in a 1M KOH and 0.1M NH4Cl solution at 1.55V vs RHE. The reaction solution was collected regularly and diluted to the measurement range. The concentrations of reactants and products were determined using a UV-visible intelligent multi-parameter water quality meter. Ammonia nitrogen (NH3-N) concentration was determined using Nessler's reagent spectrophotometry according to the National Environmental Protection Standard HJ 535-2009, with absorbance measured at 420nm. Nitrite nitrogen (NO2 - -N) concentration was determined by the spectrophotometric method using naphthylethylenediamine hydrochloride according to the national standard GB 7493-87, measuring NO2 at 540 nm. - -N absorption peak; nitrate nitrogen (NO3 — N) concentration was determined by the thymol method according to the national standard GB / T 5750.5, and the absorbance was measured at 220 nm. Figure 12 As shown in Figure 2, the NH3-N concentration in the R-Ni7Cu3 / NF reaction system decreased steadily from 1395.2 ppm to 40.9 ppm during the reaction at a voltage of 1.55 V vs. RHE, indicating that the NH3-N conversion efficiency was 97.07% and the removal rate reached 225.7 mg L -1 h -1 , about 3.74 times that of R-Ni / NF and 2.43 times that of R-Cu / NF; at the same time, NO2 - -N concentration gradually increased to 1290ppm, the selectivity reached 95.25%, NO2 - -N yield reached 215 mg L -1 h -1 .

[0093] Ammonia electrocatalytic oxidation performance test of R-Ni7Cu3 / NF catalyst at different reaction voltages.

[0094] The R-Ni7Cu3 / NF catalyst prepared in Example 1 was tested for its ammonia electrocatalytic oxidation performance in a three-electrode system using a CHI760E. 2 The platinum sheet was used as the counter electrode, the sample to be tested was the working electrode, and Ag / AgCl was used as the reference electrode to test the ammonia electrocatalytic oxidation performance of the catalyst at different reaction voltages; Figure 13As shown in the figure, at relatively low potential (1.45V~1.55V), the current response and NH3-N degradation rate increase with increasing potential. Within 6 hours of degradation, the NH3-N removal rate increased from 59.07% at 1.45V to 97.07% at 1.55V. As the voltage continued to increase, the ammonia oxidation rate continued to increase but not significantly. - -N generation rate shows a similar pattern. - The selectivity of -N gradually increases with the increase of potential, which is mainly due to the - -N is more easily over-oxidized at higher potentials.

[0095] Ammonia electrocatalytic oxidation performance test of R-Ni7Cu3 / NF catalyst under complex reaction environment.

[0096] The R-Ni7Cu3 / NF catalyst prepared in Example 1 was tested for its ammonia electrocatalytic oxidation performance in a three-electrode system using a CHI760E. 2 The platinum sheet was used as the counter electrode, the sample to be tested was the working electrode, and Ag / AgCl was used as the reference electrode to test the ammonia electrocatalytic oxidation performance of the catalyst in a complex reaction environment. - ,NO3 - ,SO4 2- ,CO3 2- and CH3COO - ), cations (Na + ,Mg 2+ ,Ca 2+ ,Fe 3+ and Co 2+ ) and organic matter (phenol, humic acid, urea and glucose) in the electrolyte and carried out CV test and degradation performance test; Figure 10 and Figure 14 As shown in the figure, the catalyst maintained excellent electrochemical performance under all test conditions, indicating that it has strong anti-interference ability in complex water environment. 2- and Ca 2+ Except for the solution systems in which the degradation efficiencies were only 85.93% and 80.34% respectively, the R-Ni7Cu3 / NF catalyst could maintain a degradation efficiency of more than 90% in other different reaction systems, indicating that it has strong adaptability in complex environments.

[0097] The stability of ammonia electrocatalytic oxidation performance of R-Ni7Cu3 / NF catalyst was tested.

[0098] The R-Ni7Cu3 / NF catalyst prepared in Example 1 was tested for its ammonia electrocatalytic oxidation performance in a three-electrode system using a CHI760E. 2 The platinum sheet was used as the counter electrode, the sample to be tested was the working electrode, and Ag / AgCl was used as the reference electrode to test the electrochemical performance stability of the catalyst for ammonia electrocatalytic oxidation. The chronopotentiometry test was carried out in a 1M KOH solution containing or not containing 0.1M NH4Cl. At the same time, in order to avoid errors caused by the decrease in electrolyte ammonia concentration during the reaction, a circulating flow device was used for the test. Figure 11 As shown in the figure, the test results show that, whether in KOH solution with or without ammonia, at a constant current density of 50 mA cm -2 The catalyst can basically maintain good stability within 200 hours.

[0099] The stability and reusability of the ammonia electrocatalytic oxidation performance of R-Ni7Cu3 / NF catalyst were tested.

[0100] The R-Ni7Cu3 / NF catalyst prepared in Example 1 was tested for its ammonia electrocatalytic oxidation performance in a three-electrode system using a CHI760E. 2 The platinum sheet was used as the counter electrode, the sample to be tested was the working electrode, and Ag / AgCl was used as the reference electrode to test the stability of the catalyst in the cyclic application of ammonia electrocatalytic oxidation and analyze its cyclic stability and reusability. 1M KOH + 0.1M NH4Cl solution was used as the electrolyte, and a voltage of 1.55V vs. RHE was applied to the working electrode. The current density change was recorded. The electrolyte solution was replaced every 6 hours and repeated 10 times to detect NH3-N and NO2 - -N concentration changes, calculate NH3-N removal rate and NO2 - The change of -N Faradaic efficiency was measured by atomic absorption spectrophotometer (Beijing TAS-900) to detect the metal ion leaching concentration and record the change of current during the cycle. The Faradaic efficiency (FE) was calculated using the following formula: Where m is the molar amount of the product, n is the number of electron transfers to generate the corresponding product (for NO2 — N is 6), F is the Faraday constant (96485C mol -1 ), Q 实际 is the total transferred charge (integral of current density over time). Figure 15 As shown in Figure 2, the removal rates of NH3-N and NO2 in 16 cycles were --N's Faradaic efficiency always remained above 90%. This excellent reproducibility indicates that the R-Ni7Cu3 / NF catalyst has excellent durability and can effectively catalyze AOR for up to 96 hours. The concentration of leached metal ions in the solution after each cycle was detected, such as Figure 16 As shown, leached Ni 2+ The concentration is always below 0.3ppm, and the leached Cu 2 + The concentration is always below 2ppm. In the cyclic chronoamperometric test, Figure 17 As shown in the figure, the current density of the R-Ni7Cu3 / NF catalyst in each reaction cycle decreases rapidly with the extension of the reaction time; however, when the electrolyte is replaced with a fresh ammonia solution, the electrochemical signal recovers again; this indicates that the decrease in current density is caused by the consumption of ammonia in the solution rather than the deactivation of the catalyst itself, which further confirms that R-Ni7Cu3 / NF has excellent electrochemical stability.

[0101] In situ Raman analysis of Ni7Cu3 / NF catalyst was performed.

[0102] The Ni7Cu3 / NF catalyst prepared in step 2 of Example 1 was subjected to in situ Raman testing in a three-electrode system using an InVia reflex Raman spectrometer coupled with an electrochemical workstation CHI760E. Platinum wire was used as the counter electrode, the sample to be tested was used as the working electrode, and Ag / AgCl was used as the reference electrode. In situ Raman spectroscopy was used to monitor the formation and structural evolution of NiOOH during the electrocatalytic process to explore the true active phase. Figure 18 As shown in Figure 2, after applying an external potential, the intensity of the characteristic peak associated with the MOF structure gradually decreases, and eventually disappears completely above 1.6 V as the voltage increases, indicating that the original structure is completely decomposed and reconstructed into a new catalytic phase; when the applied potential exceeds 1.35 V, the peak at 469 cm -1 and 552cm -1 New Raman peaks appeared at δ(Ni 3+ –O) bending vibration mode and ν(Ni 3+ –O) stretching vibration mode, these signals are typical characteristic peaks of NiOOH species; with the further increase of applied potential, the intensity of these NiOOH-related Raman peaks continues to increase, indicating that NiOOH species are gradually generated during the electrocatalytic process and are key intermediates in the electrocatalytic process.

[0103] The performance of R-Ni7Cu3 / NF catalyst in ammonia oxidation reaction coupled with hydrogen evolution reaction was tested.

[0104] The R-Ni7Cu3 / NF catalyst prepared in Example 1 was tested for its ammonia oxidation reaction coupled with hydrogen evolution reaction performance in a two-electrode system using CHI760E. The R-Ni7Cu3 / NF catalyst prepared in Example 1 was used as the anode and a commercial platinum-carbon catalyst was used as the cathode. The LSV curves were measured in an electrolytic cell with an electrolyte of 1M KOH or 1MKOH+0.1M NH4Cl solution and compared. Figure 19 As shown, the overall water splitting requires 1.835 V to reach 50 mA cm -2 The current density of the AOR-HER system of the present invention only requires 1.606V to achieve the same current density, which is 229mV lower. Compared with the overall water splitting, the electrolytic cell potential is much lower and can be used to simultaneously produce NO2 - and H2, which undoubtedly indicates that the utilization rate of the device is improved, the energy conversion efficiency is improved, and the economic benefits are improved.

[0105] The above description is only used to introduce the specific embodiments of the present invention in detail, but the technical solutions proposed by the present invention are not limited to the above methods. Without departing from the basic principles of the present technology, equivalent modifications and variations made by those skilled in the art to the technology proposed by the present invention should be included in the scope of the claims of the present invention.

Claims

1. A nickel-copper bimetallic catalyst, characterized in that It is a composite structure of Ni(OH)2 and Cu(OH)2, and the overall structure is a nanosheet.

2. The nickel-copper bimetallic catalyst according to claim 1, characterized in that The molar ratio of Ni(OH)2 to Cu(OH)2 is (9:1)-(1:9); the thickness of the nanosheets is 1-15 nm, the length is 1-8 μm, and the width is 0.3-5 μm.

3. The nickel-copper bimetallic catalyst according to claim 1, characterized in that The electrochemically active surface area of ​​the nickel-copper bimetallic catalyst is 40-100 cm 2 ; After applying a certain voltage, Ni(OH)2 can be converted into the active phase NiOOH.

4. The method for preparing the nickel-copper bimetallic catalyst according to any one of claims 1 to 3, characterized in that: The following steps are involved: (1) A certain amount of NiCl2·6H2O, CuCl2·2H2O and terephthalic acid are dissolved in a mixed solution of N,N-dimethylformamide, ethanol and deionized water; nickel foam is immersed in the above solution, subjected to hydrothermal reaction, washed and dried to obtain a precursor catalyst; (2) In a three-electrode system, the precursor catalyst is activated in a mixed solution of KOH and NH4Cl by cyclic voltammetry to complete electrochemical reconstruction, thereby obtaining the nickel-copper bimetallic catalyst.

5. The preparation method according to claim 4, characterized in that Before step (1), the nickel foam is pretreated with acetone, hydrochloric acid and deionized water respectively to remove organic matter and nickel oxide on its surface.

6. The preparation method according to claim 4, characterized in that In step (1), the amount of NiCl2·6H2O and CuCl2·2H2O added is such that the molar ratio of NiCl2·6H2O to CuCl2·2H2O is (9:1)-(1:9); the molar amount of terephthalic acid added is the same as the total molar amount of NiCl2·6H2O and CuCl2·2H2O added, and the concentration is 10-50 mmol L -1 ; The addition ratio of N,N-dimethylformamide, ethanol and water is 15:1:

1.

7. The preparation method according to claim 4, characterized in that In step (1), the temperature of the hydrothermal reaction is 140-160° C., and the time of the hydrothermal reaction is 10-30 h.

8. The preparation method according to claim 4, characterized in that In step (2), cyclic voltammetry activation is performed in a mixed solution of 1 M KOH and 0.1 M NH 4 Cl in a potential range of 0 V to 0.7 V vs. Ag / AgCl, with a scan rate of 50 mV / s and 15-30 activation cycles.

9. Use of the nickel-copper bimetallic catalyst according to any one of claims 1 to 3 for preparing a nitrite electrode by electrocatalytic oxidation of ammonia.

10. Use of the nickel-copper bimetallic catalyst according to any one of claims 1 to 3 in an AOR-HER electrode.

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