A copper-tin metal oxide composite electrocatalyst for efficient ammonia oxidation and a preparation method thereof

Abstract

The application provides a copper-tin metal oxide composite electrocatalyst for efficient ammonia oxidation and a preparation method thereof, and belongs to the technical field of electrocatalysis. The self-supporting SnO2-Cu2O composite electrocatalyst which is not easy to fall off and has good conductivity is obtained by in-situ growth on a conductive substrate through a two-step hydrothermal method. The application utilizes the synergistic effect between Cu2O and SnO2, exhibits excellent AOR performance, and has low initial potential and long-term running stability. The preparation method is simple, and the cost is low. In the fields of electrocatalytic ammonia-nitrogen wastewater treatment and ammonia electrolysis hydrogen production, the application has excellent industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalysis technology, and particularly relates to a copper-tin metal oxide composite electrocatalyst for efficient ammonia oxidation and its preparation method. Background Technology

[0002] Ammonia (NH3), as a carbon-free, high-energy-density (up to 17.6 wt%) hydrogen carrier and potential direct fuel, plays an increasingly important role in the energy transition. Ammonia's mild liquefaction conditions (approximately 0.9 MPa at room temperature) give it significant advantages in storage and transportation compared to high-pressure gaseous hydrogen or cryogenic liquid hydrogen, and the existing global ammonia production and distribution infrastructure is quite mature. Electrochemical ammonia oxidation (AOR) is a key technological pathway for utilizing ammonia energy. Its applications are mainly in two aspects: as the anode reaction in direct ammonia fuel cells (DAFC) or as the anode half-reaction in ammonia electrolysis for hydrogen production; and for treating high concentrations of ammonia nitrogen pollutants in industrial and municipal wastewater.

[0003] The ideal AOR process involves the complete oxidation of ammonia to nitrogen and water, a complex multi-step reaction involving six electron transfers (2NH3 + 6OH-). - → N2 + 6H2O + 6e - However, this reaction exhibits inherent kinetic lag, facing the following main technical challenges: high overpotential; low selectivity; catalyst poisoning and poor stability. To address these challenges, current technologies mainly focus on developing highly efficient AOR electrocatalysts. Currently reported catalysts include noble metal-based catalysts and non-noble metal-based catalysts. Noble metal catalysts have high activity, but their high cost and susceptibility to poisoning by nitrogen-containing intermediates lead to a decrease in activity. To overcome the limitations of noble metal catalysts, the development of non-noble metal catalysts has become a current research direction. Among them, transition metal oxides have attracted much attention due to their low cost, structural stability, and ease of in-situ generation of high-valence active species in alkaline environments. For example, NiOOH generated in-situ on the surface of Ni-based oxides is considered a key active center for AOR, while Cu-based oxides themselves also exhibit good AOR catalytic ability. Researchers aim to optimize electronic structure by constructing bimetallic or multimetallic composite oxides, utilizing the synergistic effect between different metal sites to improve catalytic performance.

[0004] Despite the significant advantages of non-precious metal catalysts in terms of cost and reserves, existing technologies still have obvious limitations: (i) Activity still needs improvement: The activity of most non-precious metal catalysts is still far behind that of precious metals, requiring higher overpotentials to drive the current density for practical applications. (ii) Selectivity issues remain severe: Especially at high potentials, side reactions (generating NO2) are prevalent. - and NO3 -The proportion of ) often increases, leading to a decrease in N2 selectivity. (III) Insufficient stability: Under long-term operation in high current density and strongly alkaline environments, catalyst materials may experience structural collapse, dissolution of active components, and other problems, resulting in performance degradation. A new design idea is to construct a heterojunction interface by introducing a functional second metal oxide to achieve synergistic regulation of activity, selectivity, and stability. In this context, tin-based oxides show unique potential. On the one hand, SnO2 itself has an extremely high overpotential for the oxygen evolution reaction. Combining it with AOR active materials is expected to fundamentally suppress the occurrence of competitive side reactions. On the other hand, the oxyphilicity of SnO2 can preferentially adsorb OH - This synergistically promotes the adsorption and oxidation of NH3 at adjacent active sites, thereby improving the efficiency of AOR and the N2 selectivity [InorganicChemistry, 2023, 62(9): 3986-3992]. Furthermore, chemically stable SnO2 has also been shown to act as a structural stabilizer, enhancing the durability of composite materials.

[0005] Although some composite catalysts have been developed for electrocatalytic ammonia oxidation, there are no reports on the preparation of copper-tin metal oxides into composite materials. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention proposes a copper-tin metal oxide composite electrocatalyst for efficient ammonia oxidation and its preparation method. The copper-tin metal oxide composite electrocatalyst uses Cu2O as the main catalytic active component and SnO2 as a synergistic catalytic and stabilizing component. The two form a tight composite structure at the nanoscale, which better promotes charge transport.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] This invention proposes a method for preparing a copper-tin metal oxide composite electrocatalyst (SnO2-Cu2O / NF), comprising the following steps:

[0009] (1) Tin dioxide nanostructures were grown in situ on a conductive substrate by a first-step hydrothermal reaction to obtain an intermediate;

[0010] (2) The copper-tin metal oxide composite electrocatalyst is obtained by in-situ growth of cuprous oxide nanostructures on the intermediate through a second hydrothermal reaction.

[0011] Further, in step (1), the temperature of the first hydrothermal reaction is 150-200℃, preferably 170-180℃, and more preferably 180℃.

[0012] Furthermore, in step (1), the first hydrothermal reaction time is 10-12 hours, preferably 11-12 hours, and more preferably 12 hours.

[0013] Further, in step (1), the reaction solution of the first hydrothermal reaction contains a tin source and sodium citrate; the tin source is a soluble tin salt; and the molar ratio of the tin source to sodium citrate is 1:3.

[0014] Furthermore, the soluble tin salt is tin tetrachloride hydrate.

[0015] Furthermore, in step (2), the temperature of the second hydrothermal reaction is 100-120℃, preferably 120℃.

[0016] Furthermore, in step (2), the second step of hydrothermal time is 4-8 hours, preferably 5.5-6 hours, and more preferably 6 hours.

[0017] Further, in step (2), the reaction solution of the second hydrothermal reaction contains a copper source, a reducing agent, urea and ammonium fluoride; the copper source is a soluble copper salt and the reducing agent is ascorbic acid.

[0018] Furthermore, the soluble copper salt is one or more of copper acetate, copper sulfate, or copper nitrate; the molar concentration of the copper source in the reaction solution is 0.02-0.05 mol / L, and the molar ratio of the copper source to the reducing agent in the reaction solution is 10:1.

[0019] Furthermore, the molar ratio of the tin source in the reaction solution of the first hydrothermal reaction to the copper source in the reaction solution of the second hydrothermal reaction is 1:(1-3).

[0020] Further, in step (1), the conductive substrate is nickel foam, nickel mesh, carbon paper, or carbon cloth. Before use, the conductive substrate needs to be cleaned to remove any impurities that may be present on its surface, and then vacuum dried.

[0021] Furthermore, the cleaning process involves ultrasonic cleaning sequentially with acetone, ethanol, and dilute acid; the dilute acid is preferably hydrochloric acid with a concentration of 1-3 mol / L. This invention does not limit the drying method; any method that achieves the desired drying effect is acceptable. For example, the drying method can be vacuum drying or inert gas drying.

[0022] This invention also proposes a copper-tin metal oxide composite electrocatalyst, which is prepared according to the above preparation method.

[0023] This invention also proposes an application of the above-mentioned copper-tin metal oxide composite electrocatalyst in electrochemical ammonia oxidation reactions, such as in ammonia nitrogen wastewater treatment or ammonia electrolysis for hydrogen production, with N2 as the main product and nitrate and nitrite as byproducts.

[0024] Compared with the prior art, the present invention has the following advantages and technical effects:

[0025] (1) This invention provides an electrocatalyst SnO2-Cu2O / NF for electrocatalytic ammonia oxidation, which combines Cu2O with high intrinsic AOR activity and SnO2 with oxygen affinity at the nanoscale, and can synergistically promote OH oxidation. - Adsorption on the catalyst surface releases more active sites for NH3 adsorption. This clear functional division and synergistic catalytic mechanism greatly reduces the overpotential of the ammonia oxidation reaction.

[0026] (3) The catalyst prepared by the present invention is grown in situ on a conductive substrate. The catalyst is tightly bonded to the substrate, avoiding the use of conductive agents and binders in traditional powder catalysts, ensuring excellent electronic conductivity, and facilitating the stable operation of the catalyst under high current density.

[0027] (2) This invention employs a two-step hydrothermal method for in-situ growth on a conductive substrate, resulting in a strong physical bond and tight interfacial contact between SnO2 and Cu2O, effectively inhibiting the dissolution of Cu species. The catalyst of this invention operates at high current densities (approximately 100 mA / cm²). 2 It can operate stably for at least 50 hours under continuous conditions, demonstrating excellent potential for industrial applications. At the same time, it significantly improves the selectivity of the target product N2 and effectively reduces the formation of harmful byproducts such as nitrates and nitrites. Attached Figure Description

[0028] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0029] Figure 1 The X-ray diffraction (XRD) spectra of the catalysts prepared according to Example 1, Comparative Example 1, and Comparative Example 2 are shown.

[0030] Figure 2 Here is a scanning electron microscope (SEM) image of the catalyst prepared according to Example 1;

[0031] Figure 3 The graph shows a comparison of the performance of the catalyst prepared according to Example 1 in the oxygen evolution reaction (OER) and ammonia oxidation reaction (AOR) tested in 1M KOH and 1M KOH + 0.5M NH3·H2O electrolytes, respectively.

[0032] Figure 4 The AOR performance graphs are shown for the catalysts prepared according to Example 1, Comparative Examples 1-2, and the pretreated nickel foam used in Comparative Example 1.

[0033] Figure 5 The AOR performance graphs are shown for the catalysts prepared according to Examples 1 and 2-3.

[0034] Figure 6 The AOR performance graphs are shown for the catalysts prepared according to Examples 1 and 4-6.

[0035] Figure 7 The stability graph shows the catalyst prepared according to Example 1.

[0036] Figure 8 The graph shows the ammonia removal performance and by-product concentration variation of the catalyst prepared according to Example 1. Detailed Implementation

[0037] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0038] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0039] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0040] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0041] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0042] This invention provides a method for preparing a copper-tin metal oxide composite electrocatalyst (SnO2-Cu2O / NF), comprising the following steps:

[0043] (1) Tin dioxide nanostructures were grown in situ on a conductive substrate by a first-step hydrothermal reaction to obtain an intermediate;

[0044] (2) A copper-tin metal oxide composite electrocatalyst was obtained by in-situ growth of cuprous oxide nanostructures on the intermediate through a second-step hydrothermal reaction.

[0045] In step (1) of the preferred embodiment of the present invention, the temperature of the first hydrothermal reaction is 150-200°C and the reaction time is 10-12 hours. Preferably, the temperature of the first hydrothermal reaction is 180°C and the reaction time is 12 hours.

[0046] In step (1) of the preferred embodiment of the present invention, the reaction solution of the first step hydrothermal reaction contains a tin source and sodium citrate; the tin source is a soluble tin salt; the molar ratio of the tin source and sodium citrate is 1:3.

[0047] In a preferred embodiment of the present invention, the soluble tin salt is tin tetrachloride hydrate.

[0048] In step (2) of the preferred embodiment of the present invention, the temperature of the second hydrothermal reaction is 100-120°C and the reaction time is 4-8 hours. Preferably, the temperature of the second hydrothermal reaction is 120°C and the reaction time is 6 hours.

[0049] In step (2) of the preferred embodiment of the present invention, the reaction solution of the second hydrothermal reaction contains a copper source, a reducing agent, urea and ammonium fluoride; the copper source is a soluble copper salt and the reducing agent is ascorbic acid; the soluble copper salt is one or more of copper acetate, copper sulfate or copper nitrate; the molar concentration of the copper source in the reaction solution is 0.02-0.05 mol / L and the molar ratio of the copper source to the reducing agent in the reaction solution is 10:1.

[0050] In a preferred embodiment of the present invention, the molar ratio of tin source in the reaction solution of the first hydrothermal reaction to copper source in the reaction solution of the second hydrothermal reaction is 1:(1-3).

[0051] In step (1) of the preferred embodiment of the present invention, the conductive substrate is nickel foam, nickel mesh, carbon paper, or carbon cloth. Before use, the conductive substrate needs to be cleaned to remove any impurities that may be present on its surface, and then vacuum dried. The cleaning process involves ultrasonic cleaning with acetone, ethanol, and dilute acid in sequence; the dilute acid is preferably hydrochloric acid with a concentration of 1-3 mol / L; the drying method can be vacuum drying or inert gas drying.

[0052] This invention also proposes a copper-tin metal oxide composite electrocatalyst, which is prepared according to the above preparation method.

[0053] This invention also proposes an application of the above-mentioned copper-tin metal oxide composite electrocatalyst in electrochemical ammonia oxidation reactions, such as in ammonia nitrogen wastewater treatment or ammonia electrolysis for hydrogen production, with N2 as the main product and nitrate and nitrite as byproducts.

[0054] In the embodiments of the present invention, the conductive substrate used is nickel foam. Before use, the nickel foam needs to be placed in acetone, 3 mol / L hydrochloric acid solution, anhydrous ethanol and deionized water and sonicated for 15 minutes to remove impurities and surface oxide layer. Then, it is vacuum dried to obtain pretreated nickel foam.

[0055] All raw materials used in the embodiments of this invention were purchased commercially.

[0056] The technical solution of the present invention will be further illustrated by the following embodiments.

[0057] Example 1

[0058] A method for preparing a copper-tin metal oxide composite electrocatalyst (SnO2-Cu2O / NF) includes the following steps:

[0059] (1) Dissolve 1 mmol of tin tetrachloride pentahydrate (SnCl4·5H2O) and 3 mmol of sodium citrate in 40 mL of pure water, mix and stir to obtain a homogeneous solution, then put the solution and pretreated nickel foam into a 50 mL reactor and react at 180 °C for 12 h. After cooling and drying, take out the nickel foam and wash it several times with pure water and anhydrous ethanol. Then dry it in a vacuum oven at 60 °C for 6 h to obtain an intermediate loaded with SnO2 (SnO2 / NF).

[0060] (2) Dissolve 1 mmol copper nitrate trihydrate (Cu(NO3)2·3H2O), 0.1 mmol ascorbic acid, 1 mmol urea and 0.5 mmol ammonium fluoride in 60 mL of deionized water and stir to obtain a uniformly mixed solution. Then put the solution and the SnO2 / NF intermediate obtained in step (1) into a 100 mL reaction vessel and react at 120 °C for 6 h. After taking it out, wash it several times with pure water and anhydrous ethanol, and then put it into a vacuum oven at 60 °C to dry for 6 h to obtain a copper-tin metal oxide composite electrocatalyst (SnO2-Cu2O / NF) supported on nickel foam for ammonia oxidation reaction (denoted as SnO2-Cu2O / NF-1:1 or SnO2-Cu2O / NF-1:1-180).

[0061] Example 2

[0062] A method for preparing a copper-tin metal oxide composite electrocatalyst (SnO2-Cu2O / NF) includes the following steps:

[0063] (1) Dissolve 0.5 mmol of tin tetrachloride pentahydrate (SnCl4·5H2O) and 1.5 mmol of sodium citrate in 40 mL of pure water, mix and stir to obtain a homogeneous solution, then put the solution and pretreated nickel foam into a 50 mL reaction vessel and react at 180 °C for 12 h. After cooling and drying, take out the nickel foam and wash it several times with pure water and anhydrous ethanol. Then dry it in a vacuum oven at 60 °C for 6 h to obtain an intermediate loaded with SnO2 (SnO2 / NF).

[0064] (2) Dissolve 1 mmol copper nitrate trihydrate (Cu(NO3)2·3H2O), 0.1 mmol ascorbic acid, 1 mmol urea and 0.5 mmol ammonium fluoride in 60 mL of deionized water and stir to obtain a uniformly mixed solution. Then, put the solution and the SnO2 / NF intermediate obtained in step (1) into a 100 mL reactor and react at 120 °C for 6 h. After taking it out, wash it several times with pure water and anhydrous ethanol, and then put it into a vacuum oven at 60 °C to dry for 6 h to obtain a copper-tin metal oxide composite electrocatalyst (SnO2-Cu2O / NF) supported on nickel foam for ammonia oxidation reaction (denoted as SnO2-Cu2O / NF-1:2).

[0065] Example 3

[0066] A method for preparing a copper-tin metal oxide composite electrocatalyst (SnO2-Cu2O / NF) includes the following steps:

[0067] (1) Dissolve 0.6 mmol of tin tetrachloride pentahydrate (SnCl4·5H2O) and 1.8 mmol of sodium citrate in 40 mL of pure water, mix and stir to obtain a homogeneous solution, then put the solution and pretreated nickel foam into a 50 mL reactor and react at 180 °C for 12 h. After cooling and drying, take out the nickel foam and wash it several times with pure water and anhydrous ethanol. Then dry it in a vacuum oven at 60 °C for 6 h to obtain an intermediate loaded with SnO2 (SnO2 / NF).

[0068] (2) Dissolve 1.8 mmol copper nitrate trihydrate (Cu(NO3)2·3H2O), 0.12 mmol ascorbic acid, 1.2 mmol urea and 0.6 mmol ammonium fluoride in 60 mL of deionized water and stir to obtain a homogeneous solution. Then, put the solution and the SnO2 / NF intermediate obtained in step (1) into a 100 mL reactor and react at 120 °C for 6 h. After taking it out, wash it several times with pure water and anhydrous ethanol, and then put it into a vacuum oven at 60 °C to dry for 6 h to obtain a copper-tin metal oxide composite electrocatalyst (SnO2-Cu2O / NF) supported on nickel foam for ammonia oxidation reaction (denoted as SnO2-Cu2O / NF-1:3).

[0069] Example 4

[0070] A method for preparing a copper-tin metal oxide composite electrocatalyst (SnO2-Cu2O / NF) includes the following steps:

[0071] (1) Dissolve 1 mmol of tin tetrachloride pentahydrate (SnCl4·5H2O) and 3 mmol of sodium citrate in 40 mL of pure water, mix and stir to obtain a homogeneous solution, then put the solution and pretreated nickel foam into a 50 mL reaction vessel and react at 150 °C for 12 h. After cooling and drying, take out the nickel foam and wash it several times with pure water and anhydrous ethanol. Then dry it in a vacuum oven at 60 °C for 6 h to obtain an intermediate loaded with SnO2 (SnO2 / NF).

[0072] (2) Dissolve 1 mmol copper nitrate trihydrate (Cu(NO3)2·3H2O), 0.1 mmol ascorbic acid, 1 mmol urea and 0.5 mmol ammonium fluoride in 60 mL of deionized water and stir to obtain a uniformly mixed solution. Then, put the solution and the SnO2 / NF intermediate obtained in step (1) into a 100 mL reactor and react at 120 °C for 6 h. After taking it out, wash it several times with pure water and anhydrous ethanol, and then put it into a vacuum oven at 60 °C to dry for 6 h to obtain a copper-tin metal oxide composite electrocatalyst (SnO2-Cu2O / NF) supported on nickel foam for ammonia oxidation reaction (denoted as SnO2-Cu2O / NF-1:1-150).

[0073] Example 5

[0074] A method for preparing a copper-tin metal oxide composite electrocatalyst (SnO2-Cu2O / NF) includes the following steps:

[0075] (1) Dissolve 1 mmol of tin tetrachloride pentahydrate (SnCl4·5H2O) and 3 mmol of sodium citrate in 40 mL of pure water, mix and stir to obtain a homogeneous solution, then put the solution and pretreated nickel foam into a 50 mL reactor and react at 170 °C for 12 h. After cooling and drying, take out the nickel foam and wash it several times with pure water and anhydrous ethanol. Then dry it in a vacuum oven at 60 °C for 6 h to obtain an intermediate loaded with SnO2 (SnO2 / NF).

[0076] (2) Dissolve 1 mmol copper nitrate trihydrate (Cu(NO3)2·3H2O), 0.1 mmol ascorbic acid, 1 mmol urea and 0.5 mmol ammonium fluoride in 60 mL of deionized water and stir to obtain a uniformly mixed solution. Then, put the solution and the SnO2 / NF intermediate obtained in step (1) into a 100 mL reactor and react at 120 °C for 6 h. After taking it out, wash it several times with pure water and anhydrous ethanol, and then put it into a vacuum oven at 60 °C to dry for 6 h to obtain a copper-tin metal oxide composite electrocatalyst (SnO2-Cu2O / NF) supported on nickel foam for ammonia oxidation reaction (denoted as SnO2-Cu2O / NF-1:1-170).

[0077] Example 6

[0078] A method for preparing a copper-tin metal oxide composite electrocatalyst (SnO2-Cu2O / NF) includes the following steps:

[0079] (1) Dissolve 1 mmol of tin tetrachloride pentahydrate (SnCl4·5H2O) and 3 mmol of sodium citrate in 40 mL of pure water, mix and stir to obtain a uniform solution, then put the solution and pretreated nickel foam into a 50 mL reactor and react at 200 °C for 12 h. After cooling and drying, take out the nickel foam and wash it several times with pure water and anhydrous ethanol. Then dry it in a vacuum oven at 60 °C for 6 h to obtain an intermediate loaded with SnO2 (SnO2 / NF).

[0080] (2) Dissolve 1 mmol copper nitrate trihydrate (Cu(NO3)2·3H2O), 0.1 mmol ascorbic acid, 1 mmol urea and 0.5 mmol ammonium fluoride in 60 mL of deionized water and stir to obtain a homogeneous solution. Then, put the solution and the SnO2 / NF intermediate obtained in step (1) into a 100 mL reactor and react at 120 °C for 6 h. After taking it out, wash it several times with pure water and anhydrous ethanol, and then dry it in a vacuum oven at 60 °C for 6 h to obtain a copper-tin metal oxide composite electrocatalyst (SnO2-Cu2O / NF) supported on nickel foam for ammonia oxidation reaction (denoted as SnO2-Cu2O / NF-1:1-200).

[0081] Comparative Example 1

[0082] Nickel foam was sequentially placed in acetone, 3 mol / L hydrochloric acid solution, anhydrous ethanol, and deionized water and sonicated for 15 minutes to remove impurities and surface oxide layer, and then vacuum dried to obtain pretreated nickel foam (NF).

[0083] 1 mmol of tin tetrachloride pentahydrate (SnCl4·5H2O) and 3 mmol of sodium citrate were dissolved in 40 mL of pure water and mixed and stirred to obtain a homogeneous solution. The solution and pretreated nickel foam were then placed in a 50 mL reactor and reacted at 180 °C for 12 h. After cooling and drying, the nickel foam was removed and washed several times with pure water and anhydrous ethanol. Subsequently, it was dried in a vacuum oven at 60 °C for 6 h to obtain the electrocatalyst SnO2 / NF.

[0084] Comparative Example 2

[0085] The nickel foam was sequentially placed in acetone, 3 mol / L hydrochloric acid solution, anhydrous ethanol, and deionized water and sonicated for 15 minutes to remove impurities and surface oxide layer, and then vacuum dried to obtain pretreated nickel foam.

[0086] 1 mmol copper nitrate trihydrate (Cu(NO3)2·3H2O), 0.1 mmol ascorbic acid, 1 mmol urea and 0.5 mmol ammonium fluoride were dissolved in 60 mL of deionized water and stirred to obtain a homogeneous solution. The solution and pretreated nickel foam were then placed in a 100 mL reactor and reacted at 120 °C for 6 h. After being removed, the mixture was washed several times with pure water and anhydrous ethanol and then dried in a vacuum oven at 60 °C for 6 h to obtain the electrocatalyst Cu2O / NF.

[0087] Performance testing

[0088] Figure 1 The X-ray diffraction (XRD) patterns of the SnO2-Cu2O / NF composite electrocatalyst prepared in Example 1 of the present invention, the SnO2 / NF catalyst prepared in Comparative Example 1, and the Cu2O / NF catalyst prepared in Comparative Example 2 are shown. Figure 1 The medium-intensity diffraction peaks are attributed to the substrate nickel foam (Ni, PDF#04-0850). In the spectrum of Comparative Example 1 (SnO2 / NF), except for the peaks of nickel foam, the remaining diffraction peaks correspond to the standard card of tetragonal rutile SnO2 (PDF#41-1445), proving the successful preparation of SnO2. In the spectrum of Comparative Example 2 (Cu2O / NF), except for the peaks of nickel foam, the remaining diffraction peaks correspond to the standard card of cubic Cu2O (PDF#05-0667), proving the successful preparation of Cu2O. In the spectrum of Example 1 (SnO2-Cu2O / NF), characteristic diffraction peaks belonging to both SnO2 and Cu2O are clearly observed simultaneously, and no diffraction peaks of other impurity phases appear. This result strongly demonstrates that a composite material composed of two phases, SnO2 and Cu2O, was successfully prepared by the preparation method described in this invention.

[0089] Figure 2 The scanning electron microscope (SEM) image of the catalyst prepared according to Example 1 shows that the catalyst exhibits a nanosheet morphology, and the nanosheets aggregate to form a nanosphere structure.

[0090] Figure 3 The graph shows a comparison of the OER and AOR performance of the catalyst prepared according to Example 1 in 1M KOH and 1M KOH + 0.5M NH3·H2O electrolytes. It can be seen that the catalyst exhibits excellent AOR reactivity in the ammonia-containing electrolyte. Its initial potential is approximately 1.35 V, and the current density increases rapidly with increasing potential, reaching 10 mA / cm² at 1.39 V. 2 The catalyst exhibits a lower reaction overpotential. In an ammonia-free electrolyte, the oxygen evolution reaction (OER) activity of the catalyst is significantly suppressed. Throughout the entire potential range where AOR occurs, the current density of OER is much lower than that of AOR. The comparison of the two curves strongly demonstrates the high selectivity of the catalyst of this invention for the ammonia oxidation reaction. The introduction of SnO2 effectively suppresses the competing OER side reaction, allowing the charge to be used more efficiently for the target reaction of ammonia oxidation, which is consistent with the technical concept of this invention and is key to achieving high selectivity and high Faraday efficiency.

[0091] Figure 4The AOR performance graphs for the catalysts prepared according to Example 1, Comparative Examples 1-2, and the pretreated nickel foam used in Comparative Example 1 are used to evaluate the AOR performance of different materials. Under the same test conditions, the pretreated nickel foam and Comparative Example 1 exhibited poor AOR activity, with high onset potentials and slow current density increases. Comparative Example 2 showed some AOR activity, but its onset potential was low. The SnO2-Cu2O / NF composite electrocatalyst prepared in Example 1 exhibited the best overall catalytic performance. Compared with the comparative examples containing only a single component, it not only had a lower onset potential, but also its current density was significantly higher than SnO2 / NF and NF after the potential increased, and superior to Cu2O / NF. This performance comparison strongly demonstrates the significant synergistic catalytic effect between SnO2 and Cu2O, accelerating the AOR reaction kinetics.

[0092] Figure 5 Linear sweep voltammetry (LSV) curves of the electrocatalysts (SnO2-Cu2O / NF) prepared according to Examples 1, 2, and 3 in 1 M KOH + 0.5 M NH3·H2O were used to evaluate the effect of different Sn / Cu molar ratios on AOR activity. The results show that the technical solution of the present invention can improve its electrocatalytic oxidation performance, and when the Sn to Cu molar ratio is controlled at 1:1, the composite electrode material with the best synergistic catalytic effect can be obtained.

[0093] Figure 6 The LSV curves of the electrocatalyst (SnO2-Cu2O / NF) composite materials prepared at different synthesis temperatures according to Examples 1 and 4-6 are shown to illustrate the effect of synthesis temperature on electrocatalytic performance. The results indicate that 180℃ is the preferred synthesis temperature for preparing the SnO2-Cu2O / NF composite material in this invention.

[0094] Figure 7 The SnO2-Cu2O / NF composite electrocatalyst prepared in Example 1 was subjected to long-term AOR (autocorrelation) chronoamperometry (CA) testing using a three-electrode method at a constant potential of 1.52 V. The results show that the catalyst can rapidly reach and maintain an AOR of approximately 100 mA / cm² in the initial stage of the test. 2 The high current density was observed. During a continuous electrolysis process lasting up to 50 hours, the current density showed only a slight decrease. These results demonstrate that the composite electrocatalyst prepared in this invention not only possesses high catalytic activity but, more importantly, exhibits excellent long-term operational stability and durability, confirming its great potential in practical applications such as continuous hydrogen production through ammonia oxidation or wastewater treatment.

[0095] Figure 8This is a graph showing the changes in the concentrations of ammonia, nitrate, and nitrite in the electrolyte over time during a long-term (24-hour) constant potential AOR test of the SnO2-Cu2O / NF composite electrocatalyst prepared according to Example 1 of the present invention. It can be seen that as the electrolysis reaction proceeds, the ammonia concentration in the electrolyte decreases almost linearly, from an initial 0.5 mol / L to approximately 0.13 mol / L after 24 hours, indicating that the catalyst can continuously and efficiently catalyze the oxidative degradation of ammonia. During the entire 24-hour reaction process, the concentrations of the byproducts nitrate and nitrite slightly increased. At the end of the reaction, NO3... - and NO2 - The total concentration was only about 0.15 mol / L, with only a very small portion being over-oxidized into nitrogen-containing oxides.

[0096] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. The application of a copper-tin metal oxide composite electrocatalyst in the electrochemical ammonia oxidation reaction, characterized in that, The preparation method of the copper-tin metal oxide composite electrocatalyst includes the following steps: (1) Tin dioxide nanostructures were grown in situ on a conductive substrate by a first-step hydrothermal reaction to obtain an intermediate; (2) The copper-tin metal oxide composite electrocatalyst is obtained by in-situ growth of cuprous oxide nanostructures on the intermediate through a second hydrothermal reaction. In step (1), the reaction solution of the first hydrothermal reaction contains a tin source and sodium citrate; the conductive substrate is nickel foam, nickel mesh, carbon paper or carbon cloth; In step (2), the reaction solution of the second hydrothermal reaction contains a copper source, a reducing agent, urea and ammonium fluoride.

2. The application of the copper-tin metal oxide composite electrocatalyst according to claim 1 in the electrochemical ammonia oxidation reaction, characterized in that, In step (1), the temperature of the first hydrothermal reaction is 150-200℃ and the reaction time is 10-12 hours.

3. The application of the copper-tin metal oxide composite electrocatalyst according to claim 1 in the electrochemical ammonia oxidation reaction, characterized in that, The tin source is a soluble tin salt.

4. The application of the copper-tin metal oxide composite electrocatalyst according to claim 1 in the electrochemical ammonia oxidation reaction, characterized in that, The molar ratio of the tin source to sodium citrate is 1:

3.

5. The application of the copper-tin metal oxide composite electrocatalyst according to claim 1 in the electrochemical ammonia oxidation reaction, characterized in that, In step (2), the temperature of the second hydrothermal reaction is 100-120℃ and the time is 4-8 hours.

6. The application of the copper-tin metal oxide composite electrocatalyst according to claim 1 in the electrochemical ammonia oxidation reaction, characterized in that, The copper source is a soluble copper salt, and the reducing agent is ascorbic acid.

7. The application of the copper-tin metal oxide composite electrocatalyst according to claim 6 in the electrochemical ammonia oxidation reaction, characterized in that, The soluble copper salt is one or more of copper acetate, copper sulfate, or copper nitrate; the molar concentration of the copper source in the reaction solution of the second hydrothermal reaction is 0.02-0.05 mol / L, and the molar ratio of the copper source to the reducing agent in the reaction solution is 10:

1.

8. The application of the copper-tin metal oxide composite electrocatalyst according to claim 1 in the electrochemical ammonia oxidation reaction, characterized in that, The molar ratio of tin source in the reaction solution of the first hydrothermal reaction to copper source in the reaction solution of the second hydrothermal reaction is 1:(1-3).

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