Molybdenum-nickel oxyhydroxide catalyst, preparation method and application thereof

Abstract

The invention discloses a preparation method and application of a molybdenum-nickel oxyhydroxide catalyst, and the preparation method comprises the following steps: firstly carrying out hydrothermal reaction to obtain a precursor MoNi LDH material, and then carrying out electrochemical oxidation on the MoNi LDH material to obtain a molybdenum-nickel oxyhydroxide material, the electrochemical oxidation time is 10 to 60 minutes. The molybdenum-nickel oxyhydroxide material has excellent urea catalytic activity and stability. When the molybdenum-nickel oxyhydroxide material is used as an anode catalyst, urea removal and hydrogen peroxide preparation can be realized, the problem of activity reduction caused by insufficient OH <-> in the traditional electro-catalysis process is solved, the removal rate of urea in water can reach 100%, meanwhile, 28g / L hydrogen peroxide is obtained, the Faraday efficiency of H2O2 generation is maintained at 80%-90%, and the hydrogen peroxide can be recycled. The device can keep stable urea removal and H2O2 generation performance within a long operation time, the generated H2O2 has high activity, the device can be used for Fenton treatment of sulfametronidazole pollutants in water, and the removal rate of sulfametronidazole reaches 90% or above.

Description

Technical Field

[0001] The present invention relates to the field of new energy, and in particular to a molybdenum nickel hydroxide catalyst, a preparation method and application thereof. Background Art

[0002] Urea is a widely used chemical with an annual global production of 226 million tons, which has the potential to provide sustainable energy for fuel cells. Urea is also an important component of human metabolism, accounting for 1.5-2.5wt% of urine. Due to the widespread use of urea and the fact that nitrogen in urine accounts for 75-80% of the nitrogen content of domestic sewage, a large amount of urea-containing wastewater is generated. This not only causes harm to humans by irritating the skin, triggering allergies, increasing the risk of eye diseases, and inducing asthma, but also damages the ecological environment, such as increasing the reproduction of algae and other aquatic plants, and accelerating the occurrence of acid rain. The effective decomposition of urea can be used to collect chemical energy and reduce the environmental risks of nitrogen pollution. Electrochemical urea oxidation (UOR) may provide a promising method for the utilization and removal of urea due to its environmental sustainability and high efficiency.

[0003] Catalysts with high electrocatalytic activity are key to the performance of UOR. Non-precious metal catalysts, especially nickel-based materials, show great potential in UOR due to their high activity and cost-effectiveness in urea catalysis. Various nickel compounds, such as nickel hydroxide (Ni(OH)2), sulfides (Ni3S2) and phosphides (Ni2P), have been synthesized and used for UOR catalysts. However, these catalysts often suffer from insufficient electrocatalytic activity and stability, which limits their practical applications. To overcome these limitations, researchers have introduced transition metals (such as cobalt, iron and molybdenum) into nickel compounds to adjust the electronic structure and reduce the activation energy required for UOR, thereby improving the catalytic performance. The well-regulated electronic structure and intrinsic electrochemical activity of these transition metals can be used to improve the performance of Ni-based catalysts. For example, NiMoO4 hydrate electrocatalysts with nanorod structure have shown excellent UOR performance, achieving 10 mA cm at 1.33 V. -2 Despite these advances, the electrocatalytic activities of these catalysts in UOR are still unsatisfactory, and the synthesis of new transition metal catalysts is crucial to improve UOR.

[0004] Efficient cathode reactions, such as hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR), can be adapted to the anode UOR and collect valuable byproducts, such as H2 and H2O2. For example, urea oxidation on the nickel ferrocyanide (Ni2Fe(CN)6) anode coupled with the generation of hydrogen peroxide (H2O2) in the cathode compartment was demonstrated at a current density of 26 mA cm -2 When the urea removal rate is 100.2gm -2 h-1 The H2O2 generation rate is 155 g m -2 h -1 (Nat. Energy, 2021, 6, 904-912). In situ electrochemical synthesis of H2O2 may be safer, more energy-efficient, and more economical to store and transport than H2 production due to the absence of hazardous products and low transportation costs. However, research on electrochemical cells for urea-assisted H2O2 production is still in the exploratory stage.

[0005] Therefore, in this study, a nickel-based bimetallic oxyhydroxide catalyst (i.e., nickel-molybdenum bimetallic oxyhydroxide, MoNiOOH) was developed for urea oxidation and H2O2 generation in a bipolar membrane electrolyzer (BPMEC). Summary of the invention

[0006] The technical problem to be solved by the present invention is to overcome the problem of unsatisfactory electrocatalytic activity of the above-mentioned existing UOR catalysts and to provide a method for preparing a nickel-based bimetallic oxyhydroxide catalyst.

[0007] The catalyst was prepared by electrochemical oxidation of MoNi LDH precursor and showed excellent UOR catalytic activity and stability. It was used as an anode material in a urea removal device, which significantly improved the catalytic activity and urea removal efficiency to as high as 159.0±17.9gm -2 h -1 The urea removal rate can be reduced by 20%. At the same time, long-term stable operation can be achieved. In addition, when used in conjunction with the hydrogen peroxide generated at the cathode, a high-concentration hydrogen peroxide solution can be obtained.

[0008] A further object of the present invention is to provide a nickel-based bimetallic oxyhydroxide material.

[0009] A further object of the present invention is to provide a highly efficient urea removal and peroxide production device.

[0010] In order to solve the above technical problems, the present invention provides a technical solution: a method for preparing a nickel-based bimetallic oxyhydroxide material, comprising the following steps:

[0011] A mixed solution of nickel salt, urea and molybdenum salt is subjected to hydrothermal reaction to obtain a MoNi LDH precursor, and then the molybdenum nickel hydroxide is obtained by electrochemical oxidation;

[0012] The preparation method of the present invention can adjust the molar ratio of nickel salt to molybdenum salt and the time of electrochemical oxidation, so that the morphology of the nanoarray can be adjusted, and the porous nanoarray (diameter of about 200nm) can be uniformly and vertically grown on the surface of nickel foam, and the metal-O and O OHThe ratio of urea to urea was increased, thereby improving the catalytic activity and stability of the catalyst. The nickel-based bimetallic oxyhydroxide material was used as the anode material in the device for efficiently removing urea and producing peroxide, successfully solving the problems of low catalytic activity, slow urea removal rate and unstable pH value of the electrolyte, achieving rapid removal of urea from the solution, and simultaneously electrosynthesizing hydrogen peroxide at the cathode to obtain a high-concentration hydrogen peroxide solution.

[0013] In addition, the nickel-based bimetallic oxyhydroxide material of the present invention does not use precious metals (such as Pt) and does not require high-temperature calcination, and the preparation process is simple, fast, and low-cost.

[0014] The molar ratio of the nickel salt to the molybdenum salt is 1:(0.25-0.75).

[0015] Preferably, the specific process of immersing the nickel foam in a mixed solution containing nickel salt, urea and molybdenum salt is: dissolving 1.0mmol Ni(NO3)2·6H2O, 0.50mmol Na2MoO4 and 6.0mmol CO(NH2)2 in 35mL deionized water and stirring for 15 to 30min.

[0016] Preferably, the hydrothermal reaction is carried out at a temperature of 100 to 140° C. for 6 to 8 hours in a sealed reaction vessel.

[0017] Preferably, the hydrothermal reaction further includes cooling, washing and drying steps.

[0018] More preferably, the washing is performed 3 to 5 times and the drying temperature is 60 to 80°C.

[0019] Preferably, the electrochemical oxidation is performed with an applied current of 10 mA and a time of 10 to 60 minutes.

[0020] Within the electrochemical oxidation time range, the catalytic activity of the prepared molybdenum nickel hydroxide oxide is better.

[0021] More preferably, the electrochemical oxidation time is 30 minutes.

[0022] A molybdenum-nickel hydroxide material is prepared by the above-mentioned preparation method.

[0023] The use of the above molybdenum nickel hydroxide material as an anode in an electrolytic cell device for removing urea and producing peroxide is also within the protection scope of the present invention.

[0024] A highly efficient urea removal and hydrogen peroxide production device comprises an anode chamber, a cathode chamber, an anode, a cathode, an anode liquid, a cathode liquid and a bipolar membrane, wherein the bipolar membrane is used to isolate the anode chamber and the cathode chamber; the anode is the above-mentioned MoNiOOH material; the cathode material is carbon black; the anode liquid is a 0.33M urea+1M KOH solution; and the cathode liquid is a 0.1M Na2SO4 solution.

[0025] The urea removal and hydrogen peroxide production electrolytic cell device (BPMEC) of the present invention uses molybdenum nickel hydroxide material as the anode. The MoNiOOH catalyst is prepared by a hydrothermal method combined with an electrochemical oxidation method and exhibits excellent electrocatalytic activity for urea oxidation reaction. In the BPMEC, 0.33M urea is heated to 40 mA cm –2 At the current density, urea was almost completely removed after 3.0 hours, and the urea removal rate reached 159.0±17.9gm -2 h -1 Meanwhile, the highest H2O2 concentration (28.7 g L –1 ), with a Faradaic efficiency of 90.6%. The high efficiency of urea removal and H2O2 production is attributed to the superior performance and BPM of the MoNiOOH anode.

[0026] Preferably, the strong alkaline solution is a potassium hydroxide solution or a sodium hydroxide solution, and the concentration can be selected to be 0.1 to 1 mol / L;

[0027] Preferably, the cathode liquid is a sodium sulfate solution, and the concentration of the cathode liquid is 0.05-0.2 mol / L.

[0028] Preferably, the distance between the anode and the cathode is 5 to 10 mm.

[0029] Preferably, the current density of the applied current of the urea removal and hydrogen peroxide production device is 10-100 mA / cm 2 .

[0030] By regulating the current density of the applied current within this range, urea from a low concentration of 0.033 M to a high concentration of 0.33 M can be stably removed, and the removal rate is much higher than that of the urea oxidation device in the prior art.

[0031] More preferably, the external current is provided by a DC power supply.

[0032] A method for urea removal and hydrogen peroxide production is based on the above-mentioned urea removal and hydrogen peroxide production electrolytic cell device.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) The molybdenum nickel hydroxide material of the present invention is prepared by a hydrothermal method and an electrochemical oxidation method, and the obtained material exhibits excellent urea electrocatalytic activity and long-term stability. The molybdenum nickel hydroxide material is used as an anode material in a BPMEC device, which solves the problem of decreased activity due to insufficient OH- in the traditional electrocatalytic process, thereby achieving a high urea removal rate, achieving a 100% urea removal effect, and a urea removal rate of 159.0±17.9gm -2 h -1 In addition, the nickel-based bimetallic hydroxide material of the present invention does not use precious metals (such as Pt) and does not require high-temperature calcination. The preparation process is simple, fast and low-cost.

[0035] (2) The urea removal and hydrogen peroxide production electrolytic cell device of the present invention can maintain the pH stability of the cathode and anode electrolytes during the electrolysis process, which ensures that the Faraday efficiency during the H2O2 generation process is maintained between 80% and 90%, which is conducive to the stable generation of hydrogen peroxide. The device can efficiently and stably produce more than 2.5wt.% hydrogen peroxide under neutral solution conditions (pH 6.0-9.0), significantly improving the production capacity of H2O2. More importantly, the device can maintain stable urea removal and H2O2 generation performance during an operation time of up to 900 minutes, showing its good operational stability and practical application potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a schematic diagram of the structure of the urea removal and hydrogen peroxide production electrolytic cell device (BPMEC) of Example 2.

[0037] Figure 2 X-ray diffraction (XRD) patterns and Raman spectra (Raman) of the molybdenum nickel hydroxide material at different electrochemical oxidation times in Example 1.

[0038] Figure 3 These are scanning electron microscope (SEM) images of molybdenum-nickel oxyhydroxide materials with different molybdenum-nickel molar ratios of Example 1.

[0039] Figure 4 This is an X-ray photoelectron spectroscopy (XPS) graph of molybdenum-nickel hydroxide materials with different molar ratios of molybdenum and nickel in Example 1.

[0040] Figure 5 It is a urea oxidation reaction curve of the molybdenum nickel hydroxide material with different electrochemical oxidation times in Example 1 in 0.33M urea + 1M KOH solution.

[0041] Figure 6This is a urea oxidation reaction curve of the molybdenum-nickel hydroxide material with different molar ratios of molybdenum and nickel in Example 1 in 0.33M urea + 1M KOH solution.

[0042] Figure 7 It is a urea oxidation reaction curve of the molybdenum nickel hydroxide material of Example 1 at different hydrothermal temperatures in 0.33M urea + 1M KOH solution.

[0043] Figure 8 This is the urea removal situation at 0.033M urea concentration in Examples 2 to 6 and Comparative Examples 1 and 2.

[0044] Fig. 9 This is the concentration curve of urea removal and hydrogen peroxide production in Example 7.

[0045] Fig.10 These are the stability test results of the urea removal and hydrogen peroxide production device of Example 8. DETAILED DESCRIPTION

[0046] In order to more clearly and completely describe the technical solution of the present invention, the present invention is further described in detail through specific embodiments below. It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention. Various changes can be made within the scope of the rights of the present invention.

[0047] Example 1

[0048] This embodiment provides a method for preparing a molybdenum nickel oxyhydroxide material, and the preparation method comprises the following steps:

[0049] 1.0mmol Ni(NO3)2·6H2O, 0.50mmol Na2MoO4 and 6.0mmol CO(NH2)2 were dissolved in 35mL deionized water. The pretreated nickel foam (NF) was placed in the above solution and sealed in a 50mL autoclave. The effect of temperature on the catalyst was explored at different temperatures (i.e., 100℃, 120℃ and 140℃). After heating for 8 hours, the products (i.e., different MoNi layered double hydroxides, MoNi LDH) were taken out, washed with deionized water and dried. Finally, the MoNi-LDH products were electrochemically oxidized by a three-electrode system on an electrochemical workstation (DH7001, Jiangsu Donghua Analytical Instrument Co., Ltd., China). The working electrode (i.e., MoNi-LDH product) was treated in 1.0M KOH solution at a constant current of 10mA for different operation times (i.e., 10 minutes, 30 minutes and 60 minutes). Hg / HgO electrode was used as reference electrode and graphite rod (length × diameter = 60 × 6 mm) was used as counter electrode. The final catalysts were named MoNiOOH-10, MoNiOOH-30 and MoNiOOH-60, representing 10 min, 30 min and 60 min treatment, respectively. In addition, the effect of different Mo to Ni molar ratios (i.e., 0.25, 0.50 and 0.75) on the urea oxidation reaction (UOR) of MoNiOOH catalyst was studied by changing the mass of the above-mentioned Na2MoO4.

[0050] Example 2

[0051] The present embodiment provides a urea removal and hydrogen peroxide production device (BPMEC), which includes an anode chamber, a cathode chamber, an anode arranged in the anode chamber, and a cathode arranged in the cathode chamber; it also includes an anode liquid, a cathode liquid, a bipolar membrane and a DC power supply.

[0052] like Figure 1 As shown, the anode chamber and the cathode chamber are separated by a bipolar membrane (BPM), the cation exchange layer of the bipolar membrane faces the cathode, and the anion exchange layer faces the anode. The material of the anode chamber and the cathode chamber body is a silica gel gasket; the anode is the molybdenum nickel hydroxide material (MoNiOOH) of Example 1, and the cathode is a gas diffusion cathode (GDC); titanium wire is used to connect the anode, cathode and DC power supply. The initial anode liquid is 0.033M urea + 1M KOH solution, and the initial cathode liquid is 0.1M sodium sulfate solution.

[0053] The volume of the anode chamber and cathode chamber is about 3.5mL; the effective area of ​​the anode is 6.257cm 2 The effective area of ​​the cathode is 7cm 2The distance between them is 1 cm. The volume of the cathode liquid and the anode liquid is 15 mL. The cathode liquid storage bottle is connected to the cathode chamber, and the anode liquid storage bottle is connected to the anode chamber. Then the cathode liquid is circulated between the cathode liquid storage bottle and the cathode chamber by a peristaltic pump, and the cathode liquid is circulated between the anode liquid storage bottle and the anode chamber by a peristaltic pump. The circulation is carried out under ice water bath conditions, and the flow rate of the peristaltic pump is set to 8.0 mL min -1 The current of the DC power supply was set to 0.0625 A, and the current density on the electrode was 10 mA cm -2 .

[0054] The BPMEC device based on this example removes urea and produces hydrogen peroxide solution.

[0055] Example 3

[0056] This embodiment provides a urea removal and hydrogen peroxide production device (BPMEC), which is basically the same as that of Example 2, except that the current of the DC power supply is set to 20 mA cm -2 .

[0057] The BPMEC device based on this example removes urea and produces hydrogen peroxide solution.

[0058] Example 4

[0059] This embodiment provides a urea removal and hydrogen peroxide production device (BPMEC), which is basically the same as that of Example 2, except that the current of the DC power supply is set to 40 mA cm -2 .

[0060] The BPMEC device based on this example removes urea and produces hydrogen peroxide solution.

[0061] Example 5

[0062] This embodiment provides a urea removal and hydrogen peroxide production device (BPMEC), which is basically the same as that of Example 2, except that the current of the DC power supply is set to 60 mA cm -2 .

[0063] The BPMEC device based on this example removes urea and produces hydrogen peroxide solution.

[0064] Example 6

[0065] This embodiment provides a urea removal and hydrogen peroxide production device (BPMEC), which is basically the same as that of Example 2, except that the current of the DC power supply is set to 100 mA cm -2 .

[0066] The BPMEC device based on this example removes urea and produces hydrogen peroxide solution.

[0067] Example 7

[0068] This embodiment provides a urea removal and hydrogen peroxide production device (BPMEC), which is basically the same as that of Example 4, except that the initial anolyte is 0.33M urea+1M KOH solution.

[0069] The BPMEC device based on this example removes urea and produces hydrogen peroxide solution.

[0070] Example 8

[0071] This embodiment provides a urea removal and hydrogen peroxide production device (BPMEC), which is basically the same as that of Example 7, except that new anolyte and cathode liquid are replaced after each operation cycle, the operation time of each cycle is 180 minutes, and 5 cycles are run for a total of 900 minutes.

[0072] The BPMEC device based on this example removes urea and produces hydrogen peroxide solution.

[0073] Comparative Example 1

[0074] This comparative example provides a urea removal and hydrogen peroxide production device (PEMEC), which is basically the same as the device in Example 2, except that the compartment membrane material is a proton exchange membrane (PEM).

[0075] The PEMEC device based on this example removes urea and produces hydrogen peroxide solution.

[0076] Comparative Example 2

[0077] This comparative example provides a urea removal and hydrogen peroxide production device (SEC), which is basically the same as the device in Example 2, except that the device has no compartment membrane material (Single chamber).

[0078] The SEC device based on this example removes urea and produces a hydrogen peroxide solution.

[0079] Performance Testing

[0080] 1. Characterization of morphology and material composition

[0081] In Example 1, molybdenum nickel hydroxide materials (including MoNiOOH-10, MoNiOOH-30 and MoNiOOH-60) and precursors (MoNi LDH) were subjected to X-ray diffraction (XRD) tests to analyze changes in their crystal structures. The test results show that two diffraction peaks are observed at 34.0° and 59.9°, corresponding to MoNi LDH ( Figure 2 A). As MoNi LDH undergoes electrochemical oxidation treatment for different time periods, the diffraction peaks at 38.9°, 44.5°, and 51.8° can be attributed to hexagonal Ni(OH)2·NiOOH (JCPDS 06-0044), indicating that the precursor MoNi LDH has been successfully converted into MoNiOOH. This conversion is accompanied by structural reorganization and phase change, further confirming the effect of electrochemical oxidation treatment on the material structure. Raman spectroscopy further reveals the chemical bond changes of the MoNiOOH material. The precursor MoNi LDH does not show obvious characteristic peaks in the Raman spectrum ( Figure 2 B), which indicates that its chemical bond characteristics are weak or no obvious active sites are formed. However, the MoNiOOH catalyst after electrochemical treatment has the highest peaks at 330, 470 and 870 cm -1 Three peaks were observed at , which corresponded to Mo=O bonds, NiOOH species and Mo-O-Ni bonds, respectively. With the increase of time, electrochemical oxidation did not significantly affect the NiOOH peak intensity of the MoNiOOH catalyst, which was consistent with previous reports (Electrochim. Acta, 2013, 108, 660-665).

[0082] In order to better understand the effect of the molar ratio of nickel salt to molybdenum salt on the morphology and performance of molybdenum nickel hydroxide catalyst, scanning electron microscopy (SEM) tests were performed on molybdenum nickel hydroxide materials with different molar ratios in Example 1 (including MoNiOOH: 0.25-30, MoNiOOH: 0.50-30 and MoNiOOH: 0.75-30). The results are as follows: Figure 3As shown. The SEM image clearly shows that different Mo and Ni molar ratios have a significant effect on the nanostructure and porosity of the MoNiOOH catalyst. When the Mo salt content is low (MoNiOOH: 0.25-30), the arrangement of the nanoarray is relatively loose and uneven. With the increase of the Mo salt content, especially in MoNiOOH: 0.50-30 and MoNiOOH: 0.75-30, a more compact and evenly distributed nanoarray (diameter of about 200nm) is formed, which grows evenly and vertically on the surface of the nickel foam, showing a highly ordered porous structure. This structure is conducive to the full contact of reactants such as urea with the active sites of the catalyst, thereby improving the efficiency of the electrocatalytic reaction. X-ray photoelectron spectroscopy (XPS) conducted a detailed analysis of the elemental electronic morphology of the molybdenum nickel hydroxide material surface of Example 2, and studied the chemical state of the Mo, Ni, and O elements ( Figure 4 In the Mo 3d spectrum, the two different peaks at 232.1eV and 235.3eV are respectively attributed to Mo 6+ 3d 5 / 2 and Mo 6+ 3d 3 / 2 ( Figure 4 B). In the Ni 2p spectrum, the peaks at 855.6 eV and 873.3 eV are attributed to NiOOH 2p 3 / 2 and NiOOH 2p 1 / 2 ( Figure 4 C). In the O1s spectrum, one peak at 530.5 eV is attributed to metal-O, and another peak at 531.4 eV corresponds to hydroxide (O OH )( Figure 4 D). As the ratio of Mo to Ni increases (i.e., 0.25, 0.50, and 0.75), the metal-O and O OH The ratio of Mo increased from 0.26 to 1.43. Mo plays a key role in regulating the electronic structure within the MoNiOOH lattice, which in turn affects the active site exposure and electron transport capacity of the catalyst. The introduction of Mo not only helps to form a stable nanoarray structure, but also may enhance the catalytic activity of NiOOH through electronic effects.

[0083] 2. Electrochemical performance test

[0084] The molybdenum nickel hydroxide materials obtained in Example 1 were tested for electrocatalytic activity. In 0.33 M urea + 1 M KOH solution, different MoNiOOH electrodes showed higher current density than MoNi LDH and nickel foam (NF) electrodes, indicating that MoNiOOH materials have higher electrocatalytic activity in urea oxidation reaction (UOR). Specifically, the oxidation current density of MoNiOOH-30 catalyst (189.7 mA cm-2 ) is a MoNi LDH catalyst (95.4 mA cm -2 ) Figure 5 A). This result indicates that the activity of the catalyst is significantly improved by converting MoNi LDH to MoNiOOH. Further analysis of the onset potential shows that the onset potentials of MoNiOOH-30 and MoNiOOH-60 electrodes are almost the same, both 1.31 V vs. RHE, which is lower than the onset potentials of MoNiOOH-10, MoNi LDH and NF electrodes, which are 1.32 V, 1.36 V and 1.37 V vs. RHE, respectively. Figure 5 B). The lower starting potential indicates that MoNiOOH-30 and MoNiOOH-60 are more easily activated in UOR, allowing the reaction to occur at a lower potential, thereby improving the electrocatalytic efficiency. By comparing MoNiOOH electrodes with different Mo / Ni molar ratios, it was found that the MoNiOOH-30 electrode with a Mo / Ni ratio of 0.50 had the highest UOR activity ( Figure 6 ), which shows that adjusting the Mo / Ni ratio is crucial to optimizing the catalyst performance. Further, the effect of different synthesis temperatures on the performance of MoNiOOH-30 electrode was studied, and 120°C was determined to be the optimal temperature for preparing MoNiOOH-30 electrode ( Figure 7 ). The electrode synthesized at this temperature showed the best electrocatalytic activity and stability. Therefore, in the subsequent electrochemical tests, the MoNiOOH-30 electrode was synthesized at a Mo / Ni ratio of 0.50 and 120°C, which ensured the efficient performance of the catalyst in the urea oxidation reaction. This study provides a clear direction for the further development and optimization of efficient UOR catalysts, especially in terms of the importance of regulating the Mo / Ni ratio and synthesis temperature.

[0085] Under the conditions of Example 2, the urea removal performance of different molybdenum nickel hydroxide materials (including MoNiOOH-10, MoNiOOH-30 and MoNiOOH-60) and the precursor MoNi LDH material in Example 1 was tested. Since urine is usually diluted ten times when flushing the toilet (i.e., the urea concentration is reduced from 0.33M to 0.033M), we first studied the urea removal effect in the electrochemical cell at the diluted initial urea concentration of 0.033M. At a current density of 10mA cm -2 Under the conditions of 1.5 wt % urea, the electrochemical cell using MoNiOOH-30 as the anode successfully achieved efficient urea removal within 75 min ( Figure 8 A), which shows that the MoNiOOH-30 anode still has good electrocatalytic activity under low urea concentration conditions. Under the conditions of Examples 2 to 6, the urea removal rate-time graph is as follows Figure 8 As shown in B, further increasing the current density has a significant effect on the urea removal rate. When the current density increases to 100 mA cm -2 The urea removal rate was significantly accelerated when the current density was adjusted. Under this condition, more than 95% urea removal rate was achieved in just 21 minutes, demonstrating the excellent performance of the MoNiOOH-30 anode at high current density. This accelerated urea removal process shows that by adjusting the current density, efficient urea removal can be achieved in a short time.

[0086] Under the conditions of Example 4 and Comparative Examples 1 and 2, urea removal tests were performed on different membrane electrochemical cells. The results are as follows: Figure 8 C. When the initial urea concentration was 0.033 M and the current density was 40 mA cm -2 Under the conditions of 2.5 mol / L, the bipolar membrane electrochemical cell (BPMEC) using MoNiOOH-30 anode showed significant advantages over the traditional single chamber electrolyzer (SEC) and proton exchange membrane electrolyzer (PEMEC). Specifically, BPMEC achieved 100% urea removal in just 27 minutes, while SEC and PEMEC required 90 minutes and 45 minutes, respectively, to achieve the same effect ( Figure 8 C), which indicates that BPMEC can achieve complete urea removal in a shorter time. To further quantify the kinetics of the urea removal process, we calculated the urea removal rate using a pseudo-first-order kinetic model. The results showed that the kinetic constants for urea removal in BPMEC were 0.85 and 2.32 times those of PEMEC and SEC (0.143 min -1 Compare 0.077min -1 and 0.043min -1 ), which further proves the rapid response ability and superior performance of BPMEC in urea removal ( Figure 8 D). These results show that the MoNiOOH-30 anode can achieve efficient and rapid urea removal in the BPMEC configuration and has significant application potential, especially for the treatment of low-concentration urea wastewater.

[0087] In Example 7, the overall performance of urea removal and H2O2 generation was tested in BPMEC using MoNiOOH-30 anode and gas diffusion cathode (GDC) ( Fig. 9 ). In 0.33 M urea + 1 M KOH solution and 40 mA cm -2 Under the operating conditions, BPMEC can effectively remove urea, and the urea removal rate in the anolyte is as high as 159.0±17.9gm -2 h -1 , achieving almost 100% removal effect ( Fig. 9 A). This efficient urea removal performance indicates the excellent catalytic activity of MoNiOOH-30 anode in BPMEC. During the urea removal process, a high level of nitrite (NO2 - ) accumulation, reaching 9.67±0.3 g L -1 , which is consistent with previous literature reports (Adv. Funct. Mater. 2023, 33, 202300687). In the cathode electrolyte, the generation of H2O2 also showed excellent performance. During the 180-min operation, the concentration of H2O2 reached 28.7 g L -1 ( Fig. 9 B). Although the Faradaic efficiency based on H2O2 generation decreased slightly with the extension of the operation time, it still remained at a high level of 90.6% at the end of the cycle (i.e., 180 minutes). This shows that BPMEC can not only efficiently remove urea, but also stably generate high concentrations of H2O2, and its energy utilization efficiency is high.

[0088] Under the conditions of Example 8, we further evaluated the performance stability of BPMEC in long-term operation at 40 mA cm -2 Urea removal and H2O2 generation tests were conducted for up to 900 min at a current density of Fig.10 A and B). The results show that BPMEC was able to achieve almost 100% urea removal throughout the operation, and the H2O2 concentration was maintained at a high level. Specifically, the average H2O2 concentration was 26.2 g L-1 over 900 min. -1 , the average Faraday efficiency is 82.6% ( Fig.10 B) These results indicate that BPMEC has excellent long-term operation capability and is able to maintain efficient urea removal and H2O2 generation over a long period of time.

[0089] In conclusion, the molybdenum nickel hydroxide material of the present invention can be applied to BPMEC urea removal and H2O2 generation.

[0090] The present invention and its embodiments are described above, and such description is not restrictive. The drawings show only one embodiment of the present invention, and the actual structure is not limited thereto. In short, if ordinary technicians in the field are inspired by it, without departing from the purpose of the invention, they can design a structure and embodiment similar to the technical solution without creativity, which should belong to the protection scope of the present invention.

Claims

1. A method for preparing molybdenum nickel oxyhydroxide, characterized in that: The method comprises the following steps: soaking nickel foam in a mixed solution containing nickel salt, urea and molybdenum salt to perform hydrothermal reaction to obtain a precursor; and electrochemically oxidizing the precursor to obtain the molybdenum nickel hydroxide.

2. The method for preparing molybdenum nickel oxyhydroxide according to claim 1, characterized in that: The nickel source is nickel nitrate, the molybdenum source is sodium molybdate, and the molar ratio of the nickel salt to the molybdenum salt is 1:0.25-0.

75.

3. A method for preparing a molybdenum nickel oxyhydroxide according to claim 1 or 2, characterized in that: The preparation of the mixed solution is specifically as follows: 1.0 mmol nickel nitrate, 0.50 mmol sodium molybdate and 6.0 mmol urea are dissolved in 35 mL deionized water and stirred for 15 to 30 minutes; The temperature of the hydrothermal reaction is 100 to 140° C., the time is 6 to 8 hours, and the reaction is carried out in a sealed reaction container. After the hydrothermal reaction, a MoNi LDH precursor is obtained, and the MoNi LDH precursor is cooled, washed and dried; The washing times are 3 to 5 times, and the drying temperature is 60 to 80°C.

4. The method for preparing a molybdenum nickel oxyhydroxide according to claim 1 or 3, characterized in that: In the electrochemical oxidation reaction, the working electrode is nickel foam, the counter electrode is a carbon rod, and the reference electrode is a Hg / HgO electrode; The electrochemical oxidation applies a current of 10 mA for a time of 10 to 60 minutes.

5. A molybdenum nickel oxyhydroxide material, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 4.

6. Use of the molybdenum nickel hydroxide according to claim 5 in a device for degrading urea as an anode and simultaneously electrosynthesizing hydrogen peroxide as a cathode.

7. A device for degrading urea at the anode and electrosynthesizing hydrogen peroxide at the cathode, characterized in that: It includes an anode chamber, a cathode chamber, an anode, a cathode, an anolyte, a cathode solution and a bipolar membrane; The bipolar membrane separates the anode chamber and the cathode chamber, the anode is the molybdenum nickel hydroxide described in claim 6, and the cathode material is a carbon-based material; The anolyte is a strong alkaline solution; the catholyte is a neutral electrolyte solution, and urea is removed by applying an external current.

8. The device for urea degradation at the anode and electrosynthesis of hydrogen peroxide solution at the cathode according to claim 7, characterized in that: The cathode liquid is a sodium sulfate solution, and the anode liquid is a mixed solution of urea and potassium hydroxide or sodium hydroxide.

9. The device for urea degradation at the anode and electrosynthesis of hydrogen peroxide solution at the cathode according to claim 8, characterized in that: The concentration of potassium hydroxide or sodium hydroxide is 0.1-1 mol / L, the concentration of sodium sulfate solution is 0.05-0.2 mol / L, the distance between the anode and the cathode is 5-10 mm, and the current density of the applied current is 10-100 mA / cm 2 .

10. A method for anodic degradation of urea, characterized in that: The method is carried out based on the device for anode urea degradation and cathode electrosynthesis of hydrogen peroxide as described in any one of claims 7 to 9.

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