A molybdenum-nickel oxyhydroxide catalyst, a preparation method and application thereof

Abstract

The application discloses a preparation method of a molybdenum-nickel hydroxyl oxide catalyst and application thereof, and the preparation method comprises the following steps: firstly, a precursor MoNi LDH material is obtained through a hydrothermal reaction; and then, the MoNi LDH material is electrochemically oxidized to obtain the molybdenum-nickel hydroxyl oxide material; and the electrochemical oxidation time is 10-60 minutes. The molybdenum-nickel hydroxyl oxide material has excellent urea catalytic activity and stability. When the molybdenum-nickel hydroxyl oxide material is applied as an anode catalyst, urea removal and hydrogen peroxide preparation can be realized, the problem of activity reduction caused by the lack of OH- in a traditional electrocatalytic process is solved, the urea removal rate in water can reach 100%, 28 g / L of hydrogen peroxide is obtained at the same time, the Faraday efficiency of H2O2 generation is maintained at 80%-90%, the device can maintain stable urea removal and H2O2 generation performance in a long running time, the activity of the generated H2O2 is high, and the H2O2 can be used for Fenton treatment of sulfamethoxazole pollutants in water, and the removal rate of sulfamethoxazole is more than 90%.

Description

Technical Field

[0001] This invention relates to the field of new energy, specifically to a molybdenum-nickel hydroxyl oxide catalyst, its preparation method, and its application. Background Technology

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

[0003] Highly electrocatalytically active catalysts are crucial for UOR performance. Non-noble metal catalysts, especially nickel-based materials, have shown 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 as UOR catalysts. However, these catalysts often suffer from insufficient electrocatalytic activity and stability, limiting their practical application. To overcome these limitations, researchers have introduced transition metals (such as cobalt, iron, and molybdenum) into nickel compounds to modulate the electronic structure and lower the activation energy required for UOR, thereby improving catalytic performance. The well-tuned electronic structure and inherent electrochemical activity of these transition metals can be used to improve the performance of Ni-based catalysts. For example, NiMoO4 hydrate electrocatalysts with nanorod structures have shown excellent UOR performance, achieving 10 mA cm⁻¹ at 1.33 V. -2 Despite these advances, the electrocatalytic activity of these catalysts in UOR remains unsatisfactory, and the synthesis of novel transition metal catalysts is crucial for improving UOR.

[0004] Highly efficient cathode reactions, such as the hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR), can be adapted for anode UOR and the collection of valuable byproducts, such as H2 and H2O2. For example, the oxidation of urea on a nickel ferrocyanide (Ni2Fe(CN)6) anode, coupled with the generation of hydrogen peroxide (H2O2) in the cathode chamber, can be achieved at a current density of 26 mA cm⁻¹. -2 At that time, the urea removal rate was 100.2 gm. -2 h-1 The H2O2 formation rate is 155g 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 materials and lower transportation costs. However, research on electrochemical batteries for urea-assisted H2O2 production is still in the exploratory stage.

[0005] Therefore, this study developed a nickel-based bimetallic hydroxyl oxide catalyst (i.e., nickel-molybdenum bimetallic hydroxyl oxide, MoNiOOH) 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 existing UOR catalysts and to provide a method for preparing nickel-based bimetallic hydroxyl oxide catalysts.

[0007] This catalyst, prepared by the electrochemical oxidation of the MoNi LDH precursor, exhibits excellent UOR catalytic activity and stability. Its application as an anode material in a urea removal unit significantly improves catalytic activity and urea removal efficiency, reaching as high as 159.0 ± 17.9 gm. -2 h -1 It achieves a high urea removal rate while maintaining long-term stable operation; in addition, when used in conjunction with hydrogen peroxide generated at the cathode, a high concentration of hydrogen peroxide solution can be obtained.

[0008] A further objective of this invention is to provide a nickel-based bimetallic hydroxyl oxide material.

[0009] A further objective of this invention is to provide an efficient apparatus for removing urea and producing peroxides.

[0010] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for preparing a nickel-based bimetallic hydroxyl oxide material, comprising the following steps:

[0011] A mixed solution of nickel salt, urea and molybdenum salt was subjected to a hydrothermal reaction to obtain the MoNi LDH precursor, which was then electrochemically oxidized to obtain the molybdenum nickel hydroxy oxide.

[0012] The preparation method of this invention, by adjusting the molar ratio of nickel salt to molybdenum salt and the electrochemical oxidation time, can not only control the morphology of the nanoarray, enabling the porous nanoarray (approximately 200 nm in diameter) to grow uniformly and vertically on the surface of nickel foam, but also increase the metal-O and O... OHThe ratio of nickel-based bimetallic hydroxyl oxide materials was increased, thereby improving the catalytic activity and stability of the catalyst. The application of nickel-based bimetallic hydroxyl oxide materials as anode materials in a high-efficiency urea removal and peroxide production unit successfully solved the problems of low catalytic activity, slow urea removal rate, and unstable electrolyte pH. This achieved rapid removal of urea from the solution, while simultaneously electrolyzing hydrogen peroxide at the cathode, yielding a high-concentration hydrogen peroxide solution in [time].

[0013] Furthermore, the nickel-based bimetallic hydroxyl oxide material of the present invention does not use precious metals (such as Pt) and does not require high-temperature calcination, making the preparation process simple, fast, and inexpensive.

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

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

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

[0017] Preferably, the hydrothermal reaction is followed by 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 a current of 10 mA for a time of 10–60 min.

[0020] Within the electrochemical oxidation time range, the prepared molybdenum nickel hydroxy oxide exhibits better catalytic activity.

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

[0022] A molybdenum-nickel hydroxyl oxide material is prepared by the above-described preparation method.

[0023] The application of the aforementioned molybdenum-nickel hydroxyl oxide material as an anode for urea removal and in peroxide electrolysis cell equipment is also within the scope of protection of this invention.

[0024] A high-efficiency urea removal and hydrogen peroxide production device includes an anode chamber, a cathode chamber, an anode, a cathode, an anolyte, a catholyte, and a bipolar membrane, wherein the bipolar membrane is used to isolate the anode chamber and the cathode chamber; the anode is the aforementioned MoNiOOH material; the cathode is made of carbon black; the anolyte is a 0.33M urea + 1M KOH solution; and the catholyte is a 0.1M Na2SO4 solution.

[0025] The urea removal and hydrogen peroxide production electrolytic cell (BPMEC) of this invention uses molybdenum-nickel hydroxyl oxide (MoNiOOH) as the anode. This MoNiOOH catalyst is prepared via a hydrothermal method combined with electrochemical oxidation and exhibits excellent electrocatalytic activity for urea oxidation. In the BPMEC, 0.33M urea is reacted at 40 mA cm⁻¹. –2 At the specified current density, urea was almost completely removed after 3.0 hours, with a removal rate of 159.0 ± 17.9 gm. -2 h -1 Simultaneously, the highest H2O2 concentration (28.7 g / L) was obtained in the cathode chamber. –1 The Faraday efficiency is 90.6%. The high efficiency of urea removal and H2O2 production is attributed to the superior performance of the MoNiOOH anode and the BPM.

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

[0027] Preferably, the catholyte is a sodium sulfate solution, and the concentration of the catholyte 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 in the urea removal and hydrogen peroxide production unit is 10–100 mA / cm². 2 .

[0030] By adjusting the applied current density within this range, it is possible to stably remove urea from low concentration (0.033M) to high concentration (0.33M), with a removal rate far exceeding that of existing urea oxidation devices.

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

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

[0033] Compared with the prior art, the beneficial effects of the present invention are:

[0034] (1) The molybdenum-nickel hydroxyl oxide material of this invention is prepared by hydrothermal and electrochemical oxidation methods. The resulting material exhibits excellent urea electrocatalytic activity and long-term stability. Using the molybdenum-nickel hydroxyl oxide material as an anode material in a BPMEC device solves the problem of activity decline caused by insufficient OH- in traditional electrocatalysis, thereby achieving a highly efficient urea removal rate of 100%, reaching 159.0 ± 17.9 gm. -2 h -1 Furthermore, the nickel-based bimetallic hydroxyl oxide material of the present invention does not use precious metals (such as Pt) and does not require high-temperature calcination, making the preparation process simple, fast, and inexpensive.

[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 anolyte electrolytes during electrolysis, which ensures that the Faraday efficiency in the H2O2 generation process is maintained between 80% and 90%, which is beneficial to the stable generation of hydrogen peroxide. This device can efficiently and stably generate more than 2.5 wt.% hydrogen peroxide under neutral solution conditions (pH 6.0–9.0), significantly improving the H2O2 production capacity. More importantly, this device can maintain stable urea removal and H2O2 generation performance for up to 900 minutes of operation, demonstrating its good operational stability and practical application potential. Attached Figure Description

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

[0037] Figure 2 The images show the X-ray diffraction (XRD) patterns and Raman spectra of the molybdenum-nickel hydroxyl oxide materials with different electrochemical oxidation times in Example 1.

[0038] Figure 3 The image shows scanning electron microscope (SEM) images of molybdenum-nickel hydroxyl oxide materials with different molar ratios of molybdenum and nickel in Example 1.

[0039] Figure 4 The image shows the X-ray photoelectron spectroscopy (XPS) spectra of molybdenum-nickel hydroxyoxide materials with different molar ratios of molybdenum and nickel in Example 1.

[0040] Figure 5 The graph shows the urea oxidation reaction curves of molybdenum nickel hydroxy oxide materials with different electrochemical oxidation times in 0.33M urea + 1M KOH solution, as shown in Example 1.

[0041] Figure 6The graph shows the urea oxidation reaction curves of molybdenum-nickel hydroxyoxide materials with different molar ratios in Example 1 in a 0.33M urea + 1M KOH solution.

[0042] Figure 7 The graph shows the urea oxidation reaction curves of molybdenum-nickel hydroxyl oxide materials at different hydrothermal temperatures in 0.33M urea + 1M KOH solution, as shown in Example 1.

[0043] Figure 8 The urea removal at a urea concentration of 0.033M is shown in Examples 2-6 and Comparative Examples 1 and 2.

[0044] Figure 9 The concentration curves for urea removal and hydrogen peroxide production in Example 7 are shown.

[0045] Figure 10 The results are the stability test results of the urea removal and hydrogen peroxide production device in Example 8. Detailed Implementation

[0046] To more clearly and completely describe the technical solution of the present invention, the present invention will be further described in detail below through specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention. Various changes can be made within the scope of the claims of the present invention.

[0047] Example 1

[0048] This embodiment provides a method for preparing a molybdenum-nickel hydroxyl oxide material, the method comprising the following steps:

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

[0050] Example 2

[0051] This embodiment provides a urea removal and hydrogen peroxide production apparatus (BPMEC), which includes an anode chamber, a cathode chamber, an anode disposed in the anode chamber, and a cathode disposed in the cathode chamber; it also includes an anolyte, a catholyte, a bipolar membrane, and a DC power supply.

[0052] like Figure 1 As shown, the anode and cathode chambers are separated by a bipolar membrane (BPM), with the cation exchange layer of the BPM facing the cathode and the anion exchange layer facing the anode. The main body of both the anode and cathode chambers is made of silicone gaskets; the anode is the molybdenum-nickel hydroxyl oxide material (MoNiOOH) from 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 anolyte was a 0.033M urea + 1M KOH solution, and the initial catholyte was a 0.1M sodium sulfate solution.

[0053] The volume of both the anode and cathode chambers is approximately 3.5 mL; the effective area of ​​the anode is 6.257 cm². 2 The effective area of ​​the cathode is 7 cm². 2The distance between the two is 1 cm. The volumes of both the catholyte and anolyte are 15 mL. The catholyte storage bottle is connected to the cathode chamber, and the anolyte storage bottle is connected to the anode chamber. A peristaltic pump circulates the catholyte between the catholyte storage bottle and the cathode chamber, and a peristaltic pump circulates the catholyte between the anolyte storage bottle and the anode chamber. All circulation is performed under ice-water bath conditions, with the peristaltic pump flow rate set to 8.0 mL / min. -1 The DC power supply current is set to 0.0625A, and the current density on the electrodes is 10mA / cm². -2 .

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

[0055] Example 3

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

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

[0058] Example 4

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

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

[0061] Example 5

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

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

[0064] Example 6

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

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

[0067] Example 7

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

[0069] The BPMEC device based on this embodiment 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 in Embodiment 7, except that the anolyte and catholyte are replaced after each running cycle. Each cycle lasts for 180 minutes, and 5 cycles are run for a total of 900 minutes.

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

[0073] Comparative Example 1

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

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

[0076] Comparative Example 2

[0077] This comparative example provides a urea removal and hydrogen peroxide production apparatus (SEC), which is basically the same as the apparatus in Example 2, except that the apparatus does not have a single chamber membrane material.

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

[0079] Performance testing

[0080] 1. Characterization of morphology and material composition

[0081] In Example 1, X-ray diffraction (XRD) tests were performed on molybdenum nickel hydroxyl oxide materials (including MoNiOOH-10, MoNiOOH-30, and MoNiOOH-60) and the precursor (MoNi LDH) to analyze changes in their crystal structure. The test results showed two diffraction peaks at 34.0° and 59.9°, corresponding to MoNi LDH (…). Figure 2 A). After electrochemical oxidation treatment of MoNi LDH 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 to MoNiOOH. This conversion is accompanied by structural reorganization and phase transition, further confirming the influence of electrochemical oxidation treatment on the material structure. Raman spectroscopy further reveals the chemical bond changes in the MoNiOOH material; the precursor MoNi LDH does not show obvious characteristic peaks in the Raman spectrum. Figure 2 B) This indicates that its chemical bonding characteristics are relatively weak or that no obvious active sites are formed. However, the MoNiOOH catalyst after electrochemical treatment showed good performance at 330, 470 and 870 cm⁻¹. -1 Three peaks were observed, corresponding to Mo=O bonds, NiOOH species, and Mo-O-Ni bonds, respectively. Electrochemical oxidation did not significantly affect the NiOOH peak intensity of the MoNiOOH catalyst with increasing time, which is consistent with previous reports (Electrochim. Acta, 2013, 108, 660-665).

[0082] To better understand the effect of the molar ratio of nickel salt to molybdenum salt on the morphology and performance of molybdenum nickel hydroxyl oxide catalysts, scanning electron microscopy (SEM) was performed on the molybdenum nickel hydroxyl oxide 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 in the SEM images, different Mo and Ni molar ratios significantly affect the nanostructure and porosity of the MoNiOOH catalyst. When the Mo salt content is low (MoNiOOH: 0.25-30), the nanoarray arrangement is relatively loose and uneven. With the increase of Mo salt content, especially in MoNiOOH: 0.50-30 and MoNiOOH: 0.75-30, a more dense and uniformly distributed nanoarray (approximately 200 nm in diameter) is formed. These nanoarrays grow uniformly and vertically on the surface of the nickel foam, exhibiting a highly ordered porous structure. This structure facilitates sufficient contact between reactants such as urea and the active sites of the catalyst, thereby improving the efficiency of the electrocatalytic reaction. X-ray photoelectron spectroscopy (XPS) was used to analyze the elemental electronic morphology of the surface of the molybdenum-nickel hydroxyl oxide material in Example 2 in detail, and the chemical states of Mo, Ni, and O were studied. Figure 4 In the Mo 3d spectrum, the two distinct peaks at 232.1 eV and 235.3 eV are attributed to Mo, respectively. 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, respectively. 3 / 2 and NiOOH 2p 1 / 2 ( Figure 4 C). In the O1s spectrum, one peak at 530.5 eV belongs to metallic O, and another peak at 531.4 eV corresponds to hydroxide (O). OH ()( Figure 4 D). As the ratio of Mo to Ni (i.e., 0.25, 0.50, and 0.75) increases, the metallic -O reacts with O. OH The proportion increased from 0.26 to 1.43. Mo plays a key role in regulating the electronic structure within the MoNiOOH lattice, thereby affecting the exposure of active sites and electron transport capabilities of the catalyst. The introduction of Mo not only helps to form a stable nanoarray structure but may also enhance the catalytic activity of NiOOH through electronic effects.

[0083] 2. Electrochemical performance testing

[0084] The electrocatalytic activity of the molybdenum-nickel hydroxyl oxide materials obtained in Example 1 was tested. In a 0.33 M urea + 1 M KOH solution, different MoNiOOH electrodes exhibited higher current densities than the MoNi LDH and nickel foam (NF) electrodes, indicating that the MoNiOOH material has high electrocatalytic activity in the urea oxidation reaction (UOR). Specifically, the oxidation current density of the MoNiOOH-30 catalyst was 189.7 mA cm⁻¹.-2 ) is a MoNi LDH catalyst (95.4 mA cm⁻¹) -2 2 times () Figure 5 A). This result indicates that converting MoNi LDH to MoNiOOH significantly improves the catalyst activity. Further analysis of the onset potential revealed that the onset potentials of the MoNiOOH-30 and MoNiOOH-60 electrodes were almost identical, both at 1.31V vs. RHE, lower than the onset potentials of the MoNiOOH-10, MoNi LDH, and NF electrodes, which were 1.32V, 1.36V, and 1.37V vs. RHE, respectively. Figure 5 B). The lower onset potential indicates that MoNiOOH-30 and MoNiOOH-60 are more easily activated in UOR, allowing the reaction to occur at lower potentials and thus improving electrocatalytic efficiency. Comparison of MoNiOOH electrodes with different Mo / Ni molar ratios revealed that the MoNiOOH-30 electrode with a Mo / Ni ratio of 0.50 exhibited the highest UOR activity. Figure 6 This indicates that adjusting the Mo / Ni ratio is crucial for optimizing catalyst performance. Furthermore, the effect of different synthesis temperatures on the performance of the MoNiOOH-30 electrode was investigated, and 120℃ was determined to be the optimal temperature for preparing the MoNiOOH-30 electrode. Figure 7 The electrode synthesized at this temperature exhibited optimal electrocatalytic activity and stability. Therefore, in subsequent electrochemical tests, a MoNiOOH-30 electrode was synthesized using a Mo / Ni ratio of 0.50 and a temperature of 120 °C, ensuring the catalyst's high efficiency in the urea oxidation reaction. This study provides a clear direction for the further development and optimization of high-efficiency UOR catalysts, particularly validating the importance of controlling the Mo / Ni ratio and synthesis temperature.

[0085] Under the conditions of Example 2, the urea removal performance of different molybdenum nickel hydroxyl oxide materials (including MoNiOOH-10, MoNiOOH-30, and MoNiOOH-60) and the precursor MoNi LDH material from Example 1 was tested. Since urine is typically diluted tenfold when flushing the toilet (i.e., the urea concentration decreases from 0.33M to 0.033M), we first investigated the urea removal effect in the electrochemical cell at an initial urea concentration of 0.033M after dilution. The urea removal was carried out at a current density of 10 mA cm⁻¹. -2 Under the specified conditions, an electrochemical cell using MoNiOOH-30 as the anode successfully achieved efficient urea removal within 75 minutes. Figure 8 A) This indicates that the MoNiOOH-30 anode still exhibits good electrocatalytic activity under low urea concentration conditions. The urea removal rate-time graphs under the conditions of Examples 2-6 are shown below. Figure 8 As shown in B, further increasing the current density has a significant impact on the urea removal rate. When using the same MoNiOOH-30 anode, the current density increases to 100 mA cm⁻¹. -2 At this time, the urea removal rate is significantly accelerated. Under these conditions, a urea removal rate of over 95% can be achieved in just 21 minutes, demonstrating the excellent performance of the MoNiOOH-30 anode at high current densities. This accelerated urea removal process illustrates that by adjusting the current density, a highly efficient urea removal target can be achieved in a short time.

[0086] Under the conditions of Example 4 and Comparative Examples 1 and 2, urea removal tests were conducted on different membrane electrochemical cells, and the results are as follows: Figure 8 As shown in Figure C. With an initial urea concentration of 0.033 M and a current density of 40 mA / cm². -2 Under the specified conditions, the bipolar membrane electrochemical cell (BPMEC) using a MoNiOOH-30 anode exhibited significant advantages over the conventional 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 result. Figure 8 C), indicating that BPMEC can achieve complete urea removal in a relatively short 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 show that the kinetic constant for urea removal in BPMEC is 0.85 times and 2.32 times (0.143 min) that of PEMEC and SEC, respectively. -1 Comparison 0.077min -1 and 0.043min -1 This further demonstrates the rapid response capability and superior performance of BPMEC in urea removal. Figure 8 D). These results show that the MoNiOOH-30 anode, in BPMEC configuration, can achieve efficient and rapid urea removal, with significant application potential, especially suitable for the treatment of low-concentration urea wastewater.

[0087] In Example 7, the overall performance of urea removal and H2O2 generation was tested in a BPMEC using a MoNiOOH-30 anode and a gas diffusion cathode (GDC). Figure 9 In 0.33M urea + 1M KOH solution and 40mA cm -2 Under the specified operating conditions, BPMEC can effectively remove urea, achieving a urea removal rate of up to 159.0 ± 17.9 gm in the anolyte. -2 h -1 It achieved almost 100% removal effect. Figure 9 A). This highly efficient urea removal performance demonstrates the excellent catalytic activity of the MoNiOOH-30 anode in BPMEC. High levels of nitrite (NO2) were also detected during the urea removal process. - The accumulated amount reached 9.67 ± 0.3 g L. -1 This is consistent with previous literature reports (Adv. Funct. Mater. 2023, 33, 202300687). In the cathode electrolyte, H2O2 generation also exhibited excellent performance, with the H2O2 concentration reaching 28.7 g L⁻¹ during 180 minutes of operation. -1 ( Figure 9 (B) Although the Faraday efficiency based on H2O2 generation decreased slightly with prolonged operation, it remained at a high level of 90.6% at the end of the cycle (i.e., 180 minutes). This indicates that BPMEC can not only efficiently remove urea but also stably generate high concentrations of H2O2 with high energy utilization efficiency.

[0088] Under the conditions of Example 8, the performance stability of BPMEC during long-term operation was further evaluated. We measured the performance at 40 mA cm⁻¹. -2 Urea removal and H2O2 generation tests were conducted for up to 900 minutes at a current density. Figure 10 (A and B). The results showed that BPMEC was able to achieve almost 100% urea removal throughout the entire operation, while maintaining a high H2O2 concentration. Specifically, the average H2O2 concentration was 26.2 g / L over 900 minutes. -1 The average Faraday efficiency is 82.6% ( Figure 10 B). These results demonstrate that BPMEC has excellent long-term operating capability, maintaining efficient urea removal and H2O2 generation over extended periods.

[0089] In summary, the molybdenum-nickel hydroxyl oxide material of the present invention can be applied to urea removal and H2O2 generation in BPMEC.

[0090] The present invention and its embodiments have been described above. This description is not restrictive, and the accompanying drawings are only one embodiment of the present invention; the actual structure is not limited thereto. In conclusion, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the invention, such designs should fall within the protection scope of the present invention.

Claims

1. A method for preparing a molybdenum nickel oxyhydroxide, characterized in that: The method comprises the following steps: soaking a mixed solution containing a nickel salt, urea and a molybdenum salt in foamed nickel to perform a hydrothermal reaction to obtain a MoNi LDH precursor; and performing electrochemical oxidation on the precursor to obtain the molybdenum-nickel oxyhydroxide.

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

75.

3. The method for preparing a molybdenum nickel oxyhydroxide according to claim 1 or 2, characterized in that: The mixed solution is prepared by dissolving 1.0 mmol of nickel nitrate, 0.50 mmol of sodium molybdate and 6.0 mmol of urea in 35 mL of deionized water and stirring for 15-30 min. The hydrothermal reaction is performed at a temperature of 100-140°C for 6-8 hours in a sealed reaction container, and the MoNi LDH precursor is obtained after the hydrothermal reaction, and then the MoNi LDH precursor is cooled, washed and dried. The washing is performed for 3-5 times, and the drying is performed at a temperature of 60-80°C.

4. The method for preparing a molybdenum nickel oxyhydroxide according to claim 3, characterized in that: In the electrochemical oxidation reaction, the working electrode is foamed nickel, the counter electrode is a carbon rod, and the reference electrode is a Hg / HgO electrode. In the electrochemical oxidation, a current of 10 mA is applied for 10-60 min.

5. A molybdenum nickel oxyhydroxide material characterized by: The molybdenum-nickel oxyhydroxide is prepared by the method of any one of claims 1-4.

6. The molybdenum-nickel oxyhydroxide of claim 5 is applied in an apparatus for anodic degradation of urea and cathodic electrosynthesis of hydrogen peroxide.

7. An apparatus for anodic degradation of urea and cathodic electrosynthesis of hydrogen peroxide, characterized in that: The apparatus comprises an anode chamber, a cathode chamber, an anode, a cathode, an anode solution, a cathode solution and a bipolar membrane. The bipolar membrane separates the anode chamber and the cathode chamber, the anode is the molybdenum-nickel oxyhydroxide of claim 5, and the cathode is made of a carbon-based material. The anode solution is a strong alkali solution, and the cathode solution is a neutral electrolyte solution, and urea is removed by an external current.

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

9. The device for anodic degradation of urea, cathodic electrosynthesis of hydrogen peroxide solution 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 of anodically degrading urea, characterized by: The apparatus for anodic degradation of urea and cathodic electrosynthesis of hydrogen peroxide is based on any one of claims 7-9.

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