Preparation method and application of mesoporous copper-based core-shell structure electrocatalyst for ammonia production by nitrate reduction at low overpotential

Abstract

The application discloses a preparation method and application of a mesoporous copper-based core-shell structure electrocatalyst for ammonia production by nitrate reduction at a low overpotential, and belongs to the technical field of catalysts. The catalyst is prepared by the following method: ① dispersing pre-synthesized Cu2O NCs in deionized water to obtain solution 1; ② dissolving DODAC in the solution 1 and incubating in a set oven for a period of time to obtain solution 2; ③ adding a hydrochloric acid solution to adjust the pH of the solution 2 to obtain solution 3; ④ adding a chloropalladic acid solution to the solution 3 to obtain solution 4; ⑤ after the solution 4 is left to stand, injecting ascorbic acid for a reduction reaction; and ⑥ washing with a mixed solution of anhydrous ethanol and deionized water to obtain the mesoporous copper-based core-shell structure electrocatalyst. The catalyst prepared by the application not only reduces the mass of noble metals, but also realizes utilization of wastewater nitrate and efficient synthesis of ammonia at a low energy consumption; and has the advantages of simple process, energy saving and emission reduction, good product stability and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalysts, in particular to a preparation method and application of a mesoporous copper-based core-shell structure electrocatalyst for reducing nitrate to produce ammonia at low overpotential. BACKGROUND

[0002] Although some commercial technologies have been used to convert wastewater rich in nitrate into clean water, their expensive operating costs and low value-added products do not have significant economic advantages.

[0003] For the denitrification of wastewater, the electrochemical nitrate reduction reaction (eNO3RR) has recently become a promising strategy. Among them, the electrochemical reduction of nitrate to nitrogen is considered to be a mild reaction condition and an environmentally friendly approach, but this process is energy-intensive and lacks value-added benefits. In contrast, ammonia (NH3) as an important chemical raw material, carbon-free fuel and clean energy carrier, distributed and sustainable production of ammonia through electrocatalytic nitrate reduction reaction driven by locally generated clean energy is more in line with the green and sustainable development strategy of waste upgrading and low-carbon energy development, and it is also likely to become an alternative to the energy- and carbon-intensive Haber-Bosch process.

[0004] However, electrocatalytic nitrate reduction to ammonia with practical value is still limited by suboptimal performance in realizing industrial applications. Although the electrocatalytic reduction of nitrate to ammonia is thermodynamically favorable (E NO3- / NH3 = 0.69 V), the large number of kinetic barriers in the eight-electron-nine-proton transfer process results in slow kinetics and a significant increase in overpotential. And the difference in rate and potential determining steps often leads to the formation of by-products including nitrite (NO2 - ), nitrogen oxides (NO and N2O) and N2, etc. At the same time, with the increase of overpotential, the competitive hydrogen evolution reaction (HER, 2H + + 2e - → H2) is thermodynamically and kinetically favorable, which inevitably further reduces the faradic efficiency (FE) and energy efficiency (EE) of NH3.

[0005] In recent years, copper (Cu) based catalysts have been widely studied in eNO3RR due to their good combination of NO3 - and the ability to catalyze NO3 - to NO2 - . At the same time, the active hydrogen (*H) formed by water dissociation also plays a crucial role in eNO3RR in aqueous media, which is NO xintermediates. However, Cu has a lower H generation ability, which hinders the competition of HER to some extent, but also promotes the NO2 - intermediates on Cu surface accumulation poisons the active sites (i.e., insufficient hydrogenation ability), leading to lower catalytic activity and selectivity. Recently, researchers have made a lot of efforts to improve the catalytic performance by alloying Cu with noble metals or other transition metals (such as Ru, Pd and Ni), or forming hybrid with molecular solids or metal oxides (e.g., Cu2O) to adjust the proton and / or electron transfer and the intermediate binding strength. However, limited by the linear scaling relationship (LSR), these progresses require relatively high overpotential to induce water dissociation to balance the NO3 RR rate, resulting in increased energy consumption. Therefore, it is of great significance to develop new functionalized electrocatalysts to enable the NO3 RR to be efficiently and energy-savingly electro-synthesized NH3 at positive potential in kinetics.

[0006] Inspired by the natural enzyme catalytic system, the concept of tandem catalysis was proposed and applied to various catalytic reactions. By coupling two types of active sites with complementary catalytic selectivity, the LSR can be bypassed, and the NO3 - to NO2 - and NO2 - to NH3 (hydrogenation process) sub-steps, thus effectively alleviating the kinetic barrier to improve the overall efficiency of electrocatalytic nitrate reduction to NH3. Rational design of hierarchical nanostructures is an efficient strategy to enhance tandem catalysis, which is beneficial to optimize the proximity and spatial separation of multiple functional active phases, making the tandem reaction occur with higher efficiency and required order. Excitingly, the active sites distributed in core-shell heterostructures can perfectly achieve this goal, which not only can further shorten the distance between active phases, produce strong coupling effects between different components to accelerate the interface electron transfer and promote the rapid mass transfer of intermediates / *H, but also can improve the reaction stability (inhibit aggregation, leaching), and is expected to realize the spatial and temporal optimization of the tandem reaction process to improve the reaction efficiency and selectivity. Although some important achievements have been made, the development of such catalysts is currently based on empirical considerations, and lacks a rigorous design process and in-depth understanding of the catalytic mechanism, leading to the complexity of identifying and controlling the active phase.

[0007] In addition, in the efficient tandem catalysis process, reaction intermediates need to be transferred between different active sites. These intermediates may have a short life or be prone to dissociation, so further design of nanostructures is needed to achieve the stability and transfer of intermediates. The engineering of mesoporous (2-50 nm) metals at the mesoscale has been considered as a complementary and effective platform to improve the selectivity of electrocatalytic nitrate reduction to ammonia. Mesoporous metals not only efficiently promote electron and mass transport, greatly enhancing the accessibility of active sites, but also perfectly replicate the folded proteins in enzymes with their concave / convex mesopores, which easily provide a nano-confined microenvironment to optimize the enrichment of reaction intermediates / active hydrogen, thus indicating their great potential in intermediate stability and transfer. At the same time, the introduction of mesopores also improves the situation that the active surface of the core active phase may be blocked by the shell structure.

[0008] If mesoporous metals and core-shell tandem catalysis concepts are combined, a mesoporous copper-based core-shell structure electrocatalyst with efficient tandem catalysis and structural stability is developed, which provides an opportunity to improve the performance and reduce the energy consumption of electrocatalytic nitrate reduction to ammonia at low overpotential. Therefore, the present application is proposed. SUMMARY

[0009] The purpose of the present application is to provide a preparation method and application of a mesoporous copper-based core-shell structure electrocatalyst for nitrate reduction to ammonia at low overpotential, which overcomes the technical problems of high overpotential and low catalytic efficiency of existing electrocatalysts for nitrate reduction to ammonia.

[0010] To achieve the above purpose, the present application provides the following technical solution: a preparation method of a mesoporous copper-based core-shell structure electrocatalyst for nitrate reduction to ammonia at low overpotential, the specific preparation method of the mesoporous copper-based core-shell structure electrocatalyst being as follows:

[0011] S1: Preparation of solution 1: dispersing pre-synthesized Cu2O NCs in deionized water to obtain solution 1;

[0012] S2: Preparation of solution 2: dissolving DODAC in the solution 1 and incubating in a set oven for a period of time to obtain solution 2;

[0013] S3: Preparation of solution 3: adding a hydrochloric acid solution to adjust the pH of the solution 2 to obtain solution 3;

[0014] S4: Preparation of solution 4: adding a chloropalladic acid solution to the solution 3 to obtain solution 4;

[0015] S5: Preparation of a mesoporous copper-based core-shell structure electrocatalyst: after the solution 4 is left to stand, injecting ascorbic acid for a reduction reaction; after the reaction is completed, using a mixed solution of anhydrous ethanol and deionized water to centrifugally wash and remove the surfactant to obtain the mesoporous copper-based core-shell structure electrocatalyst.

[0016] Preferably, step S1 specifically includes:

[0017] H1: The specific steps for preparing the pre-synthesized Cu2O NCs are as follows:

[0018] ① Add 1 mL of 1.2 mol·L⁻¹ -1 CuSO4 solution was rapidly injected into 400 mL of deionized water at 25 °C to obtain a dilute CuSO4 solution.

[0019] ② After stirring the dilute CuSO4 solution for 5 minutes, continue to inject 1 mL of 4.8 mol·L⁻¹. -1 NaOH solution, the clear blue solution immediately turns turbid, forming Cu(OH)2, and obtaining Cu(OH)2 turbid solution;

[0020] ③ After 5 minutes, inject 1 mL of freshly prepared 1.2 mol·L⁻¹ Cu(OH)₂ turbid solution into the solution. -1 With ascorbic acid, after a reduction reaction of 0.5 h, the color of the Cu(OH)2 turbid solution rapidly changed from a turbid blue to a yellowish-brown precipitate of Cu2O NCs;

[0021] ④ The precipitate Cu2O NCs was centrifuged and washed with ultrapure water and anhydrous ethanol, and then vacuum dried at room temperature for 12 h to obtain the pre-synthesized Cu2O NCs;

[0022] H2: Disperse 2 mg of the pre-synthesized Cu2O NCs in 10 mL of deionized water.

[0023] Preferably, step S2 is as follows: 30 mg of DODAC is dissolved in solution 1 and incubated in a set oven for a certain period of time to obtain solution 2;

[0024] Preferably, the temperature of the oven is set to 80°C; and the time is set to 30 minutes.

[0025] Preferably, step S3 specifically involves adding 0.05 mL of 0.2 mol·L⁻¹ solution at 80°C. -1 The pH of solution 2 was adjusted with hydrochloric acid solution to obtain solution 3.

[0026] Preferably, step S4 specifically involves: adding 0.6 mL of 0.01 mol·L⁻¹ solution. -1 Chloropalladic acid solution was added to solution 3 to obtain solution 4.

[0027] Preferably, step S5 is as follows: after solution 4 has been allowed to stand at 80°C for 20 minutes, ascorbic acid is injected to carry out a reduction reaction; after the reaction is completed, the surfactant is removed by centrifugation and washing with a mixed solution of anhydrous ethanol and deionized water to obtain a mesoporous copper-based core-shell electrocatalyst.

[0028] Preferably, in the S5, the ascorbic acid is specifically 1 mL of 0.3 mol·L -1 The ascorbic acid is reduced, and the reduction reaction time is 25 min.

[0029] Preferably, in the S5, the volume ratio of the anhydrous ethanol to the deionized water is 3:1.

[0030] The mesoporous copper-based core-shell structure electrocatalyst is applied in the electrochemical reduction of nitrate to synthesize ammonia.

[0031] Compared with the prior art, the application has the beneficial effects that:

[0032] (1) The catalyst prepared by the application has unique functional characteristics, and is applied in the electrochemical reduction of nitrate to synthesize ammonia. The Cu2O / Cu@mesoPdCu NCs catalyst has the structure of Cu2O / Cu heterojunction (core) and mesoporous PdCu alloy (shell), and can realize the structural synergistic effect of promoting the NO3 - to NH3 series electrocatalysis. The use of the catalyst can realize the relatively optimal activity, selectivity and stability of the electro-reduction of nitrate to synthesize ammonia at a low overpotential.

[0033] (2) The catalyst prepared by the application greatly reduces the mass of noble metals, greatly reduces the raw material cost, and has the advantages of simple process, easy operation, mild reaction condition, good product stability, and can be mass produced, and is suitable for large-scale industrial production.

[0034] (3) The catalyst prepared by the application can accelerate the hydrogenation deoxidation step of the electro-synthesis of ammonia, and realize the high-rate electro-synthesis of ammonia at a positive potential. The catalyst realizes “double win” in the degradation of nitrate wastewater and low-energy consumption value-added. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 is the X-ray diffraction pattern (XRD) of the mesoporous core-shell type Cu2O / Cu@mesoPdCu NCs catalyst prepared in Example 1 of the application and comparative catalysts (physical mixture of mesoporous Pd NCs and Cu2O NCs (mesoPd / Cu2O NCs), mesoporous PdCu NCs (mesoPdCu NCs), Cu2O NCs);

[0036] Figure 2 is the transmission electron microscope (TEM) image of the Cu2O / Cu@mesoPdCu NCs catalyst prepared in Example 1 of the application;

[0037] Figure 3is a linear scan analysis graph of the Cu2O / Cu@mesoPdCu NCs catalyst prepared in Example 1 of the present application;

[0038] Figure 4 is a linear scan voltammetry (LSV) curve of the Cu2O / Cu@mesoPdCu NCs catalyst prepared in Example 1 of the present application (with and without KNO3);

[0039] Figure 5 is a LSV curve of the Cu2O / Cu@mesoPdCu NCs catalyst prepared in Example 1 of the present application and comparative catalysts (mesoPd / Cu2O NCs, mesoPdCu NCs, Cu2O NCs);

[0040] Figure 6 is a performance graph of the electro-reduction of nitrate to synthesize ammonia of the Cu2O / Cu@mesoPdCu NCs catalyst prepared in Example 1 of the present application and comparative catalysts (mesoPd / Cu2O NCs, mesoPdCu NCs, Cu2O NCs) (electrolysis for 1 hour at different voltages, electrolyte is 1.0 mol·L -1 KOH+0.1 mol·L -1 KNO3).

[0041] Figure 7 is an energy efficiency (EE) graph of the electro-reduction of nitrate to synthesize ammonia of the Cu2O / Cu@mesoPdCu NCs catalyst prepared in Example 1 of the present application and comparative catalysts (mesoPd / Cu2O NCs, mesoPdCu NCs, Cu2O NCs).

[0042] Figure 8 is a cycle stability performance graph of the Cu2O / Cu@mesoPdCu NCs catalyst prepared in Example 1 of the present application (electrolyte is 1.0 mol·L -1 KOH+0.1 mol·L -1 KNO3). DETAILED DESCRIPTION

[0043] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application. The experimental methods in the following embodiments are conventional methods, and the reagents and materials are commercially available, unless otherwise specified.

[0044] DODAC refers to dioctadecyldimethylammonium chloride; Cu2O NCs refers to cuprous oxide nanocubes; Cu2O / Cu@mesoPdCu NCs refers to mesoporous copper-based core-shell structure electrocatalyst.

[0045] Example 1

[0046] (1) Preparation of mesoporous copper-based core-shell structure electrocatalyst (Cu2O / Cu@mesoPdCu NCs):

[0047] The preparation of pre-synthesized Cu2O NCs is shown in (2) Preparation of anode precursor material Cu2O NCs.

[0048] 2 mg of pre-synthesized Cu2O NCs were dispersed in 10 mL of deionized water. Then 30 mg of DODAC was dissolved in the above reaction solution and incubated in an oven at 80°C for 30 min; then 0.05 mL of 0.2 mol·L -1 hydrochloric acid solution was added to adjust the pH of the above reaction solution; 0.6 mL of 0.01 mol·L -1 palladic acid solution was added to the reaction solution obtained in the previous step; after the reaction solution was placed at 80°C for 20 min, 1 mL of fresh 0.3 mol·L -1 ascorbic acid was quickly injected for reduction, and the reaction time was 25 min; after the reaction was completed, the surfactant was removed by centrifugal washing with a mixed solution of anhydrous ethanol and deionized water in a volume ratio of 3:1 to obtain mesoporous copper-based core-shell structure electrocatalyst (Cu2O / Cu@mesoPdCu NCs).

[0049] (2) Preparation of anode precursor material Cu2O NCs:

[0050] 1 mL of 1.2 mol·L -1 CuSO4 solution was quickly injected into 400 mL of deionized water at 25°C. After stirring for 5 min, 1 mL of 4.8 mol·L -1 NaOH solution was further injected into the above solution. The clear blue solution immediately turned turbid, indicating the formation of Cu(OH)2. After 5 min, 1 mL of freshly prepared 1.2 mol·L -1 ascorbic acid was injected for reduction for 0.5 h. The color of the solution quickly changed from turbid blue to yellow-brown. The obtained precipitate (Cu2O NCs) was centrifuged, washed with ultrapure water and anhydrous ethanol, and vacuum dried at room temperature for 12 h to obtain the anode precursor material Cu2O NCs.

[0051] (3) Preparation of working electrode

[0052] Cu2O / Cu@mesoPdCu NCs catalyst was prepared, 5 mg of which was mixed with 2.5 mg of Vulcan XC-72 carbon black solution and stirred (for more than 3 h) to physically load for catalysis. 5 mg of Cu2O / Cu@mesoPdCu NCs catalyst after loading carbon black was mixed with 0.4 mL of deionized water, 0.52 mL of anhydrous ethanol and 0.08 mL of naphthol solution, and 5 mg mL -1 of Cu2O / Cu@mesoPdCu NCs catalyst solution was obtained after the above mixed solution was ultrasonically treated for 0.5 h. 0.01 mL of the catalyst solution was uniformly drop-coated on a 1 cm x 2 cm clean carbon paper using a pipette, so that the catalyst loading was 0.1 mg / cm -2 . After drying, it was used as a working electrode with a sandwich electrode. The carbon paper was washed several times with an ethanol / water solution before use to remove possible contaminants.

[0053] (4) Synthesis of ammonia by electrocatalytic reduction of nitrate

[0054] The electrochemical reduction of nitrate to ammonia was carried out using a Chenhua 660e electrochemical workstation. The test used a typical three-electrode system, Cu2O / Cu@mesoPdCu NCs as the working electrode, a saturated Ag / AgCl electrode as the reference electrode, and a 1 cm x 2 cm platinum sheet electrode as the counter electrode. The electrolysis cell used was an H-type electrolysis cell, and the mixed solution of 1.0 mol·L -1 KOH and 0.1 mol·L -1 KNO3 was used as the electrolyte. Argon gas (purity > 99.9%) was bubbled to saturation before and during the entire reduction process. The test temperature was 25°C. In the electrochemical test, the reaction temperature was 25°C, and the applied potential was +0.2 V to -0.7 V vs. RHE.

[0055] As a comparative example of step (4), in order to qualitatively test whether the catalyst has nitrate reduction activity, the process of Example 4 was repeated, except that no nitrate was added to the electrolyte (pure KOH).

[0056] Comparative Example 1

[0057] Preparation of Cu2O NCs

[0058] 1 mL of 1.2 mol·L -1 CuSO4 solution was quickly injected into 400 mL of deionized water at 25°C. After stirring for 5 min, 1 mL of 4.8 mol·L -1 NaOH solution was injected into the above solution. The clear blue solution immediately became turbid, indicating the formation of Cu(OH)2. After 5 min, 1 mL of 1.2 mol·L-1 Ascorbic acid was applied, and the solution was reduced for 0.5 h. The color of the solution rapidly changed from a turbid blue to a yellowish-brown. The obtained Cu₂O NCs were centrifuged and washed with ultrapure water and anhydrous ethanol, and then vacuum dried at room temperature for 12 h.

[0059] Comparative Example 2

[0060] Preparation of mesoPdCu NCs

[0061] At room temperature, 0.325 mg of hexadecyltrimethylammonium chloride (CTAC) was dissolved in 5.0 mL of deionized water, and then 0.24 mL of 0.08 mol·L⁻¹ solution was added sequentially. -1 Potassium chloride solution, 0.25 mL 0.01 mol·L⁻¹ -1 Chloropalladium acid solution and 0.125 mL 0.01 mol·L⁻¹ -1 The copper nitrate solution was incubated at 50°C for 30 min. Finally, 0.50 mL of freshly prepared 0.30 mol·L⁻¹ copper nitrate solution was added. -1 The ascorbic acid solution was rapidly injected into the above reaction solution. After reacting for 1.0 h, mesoPdCu NCs were collected by centrifugation using a mixture of anhydrous ethanol and deionized water in a volume ratio of 3:1.

[0062] Comparative Example 3

[0063] Preparation of mesoPd / Cu2O NCs

[0064] Pre-prepared mesoPd NCs and Cu2O NCs were physically mixed in equal mass.

[0065] Preparation of mesoPd NCs

[0066] At room temperature, 0.325 mg of hexadecyltrimethylammonium chloride (CTAC) was dissolved in 5.0 mL of deionized water, and then 0.10 mL of 0.2 mol·L⁻¹ sodium chloride solution was added. -1 The pH of the reaction solution was adjusted with hydrochloric acid. Then, 0.24 mL of 0.08 mol·L⁻¹ hydrochloric acid was added sequentially. -1 A potassium chloride solution and 0.25 mL of 0.01 mol·L⁻¹ -1 The solution of chloropalladium acid was incubated at 50°C for 30 min. Finally, 0.50 mL of freshly prepared 0.30 mol·L⁻¹ solution was added. -1 The ascorbic acid solution was rapidly injected into the above reaction solution. After reacting for 1.0 h, mesoPd NCs were collected by centrifugation using a mixture of anhydrous ethanol and deionized water in a volume ratio of 3:1.

[0067] In the test of electrocatalytic reduction of nitrate to synthesize ammonia, linear sweep voltammetry (LSV) is used to record the current density (j) in the range of applied voltage, which can be used to characterize the electrochemical behavior in the range of applied voltage, wherein the LSV scan rate is 10 mVs -1 , the scan voltage range is -0.6V~+0.4V vs.RHE relative to the reversible hydrogen electrode; the constant voltage method is used to record the current-time (i-t) curve at the applied potential, and the charge quantity (Q) is recorded to calculate the Faraday efficiency (FE); the applied voltage range of the embodiment of the present application is +0.2V~-0.7V vs.RHE relative to the reversible hydrogen electrode; the classic indigo blue colorimetric method is used to test the ammonia yield rate after the reduction of nitrate, and the ultraviolet spectrophotometry is used for quantitative analysis.

[0068] The calculation method of the Faraday efficiency of ammonia is as follows:

[0069] FE NH3 =(8×F×C NH3 ×V×10 -3 ) / Q×100%

[0070] The calculation method of the ammonia yield rate is as follows:

[0071] Yield rate (NH3) = (C NH3 ×V×17) / (t×m)

[0072] Wherein C NH3 is the measured NH3 concentration (mol·L -1 ); V is the volume of the electrolyte (30mL); m is the mass of the catalyst (0.05mg); t is the electrolysis time (1h); F is the Faraday constant (96485C mol· -1 ); Q(C) is the total charge quantity through the electrode, which is the result of i-t curve integration.

[0073] The calculation method of the energy efficiency (EE) of ammonia is as follows:

[0074] EE (NH3) = (1.23-E NH3 0 )×FE (NH3) / (1.23-E)×100%

[0075] E NH3 0 is the equilibrium potential (0.70V) of the electroreduction of nitrate to synthesize ammonia in alkaline medium: FE NH3 is the Faraday efficiency of NH3: 1.23V is the water oxidation equilibrium potential (i.e. the water oxidation overpotential is assumed to be zero); E is the applied potential for synthesizing NH3 (relative to the reversible hydrogen electrode).

[0076] Results analysis of catalyst performance test obtained from examples and comparative examples:

[0077] Figure 1 is the X-ray diffraction pattern (XRD) of mesoporous core-shell Cu2O / Cu@mesoPdCu NCs catalyst prepared in Example 1 of the present application compared with comparative catalysts (Cu2O NCs, mesoPdCu NCs, mesoPd / Cu2O NCs) of Comparative Examples 1-3. In the figure, the characteristic peaks of Cu2O / Cu@mesoPdCu NCs are attributed to Pd (PDF#46-1043), Cu2O (PDF#05-0667) and Cu (PDF#04-0836), indicating the coexistence of heterogeneous structure. In addition, no other alloy phase was found except for the PdCu alloy shell (Pd diffraction peak shift), which confirmed the spatial separation of PdCu alloy and Cu2O / Cu phase.

[0078] Figure 2 is the transmission electron microscopy image (TEM) of Cu2O / Cu@mesoPdCu NCs catalyst prepared in Example 1 of the present application. In the figure, the catalyst has monodisperse and clear core-shell cubic morphology, with a solid core of Cu2O / Cu and a mesoporous shell of PdCu alloy. Figure 2 a) Single Cu2O / Cu@mesoPdCu NCs clearly shows the obvious radial distribution and cylindrical open mesoporous channels in the shell region, with a shell thickness of about 16 nm, a mesoporous size of 3.3 nm, and a wall thickness of 4.7 nm Figure 2 b) In addition, high-resolution TEM images and the corresponding fast Fourier transform (FFT) patterns further reveal the crystal structure at the atomic scale Figure 2 c) The (111) crystal plane of PdCu and Cu2O (200) / Cu (111) phase exist in the shell region and core region, respectively, further confirming the successful preparation of mesoporous core-shell Cu2O / Cu@mesoPdCu NCs catalyst.

[0079] Figure 3 is the line scanning analysis image of Cu2O / Cu@mesoPdCu NCs catalyst prepared in Example 1 of the present application. In the figure, the phase-separated core-shell heterostructure of Cu2O / Cu@mesoPdCu NCs catalyst is further revealed.

[0080] Figure 4 is the LSV curve of Cu2O / Cu@mesoPdCu NCs catalyst prepared in Example 1 of the present application in the electrochemical nitrate reduction test. In the figure, compared with the electrolyte without nitrate (1.0 mol·L -1 KOH), the Cu2O / Cu@mesoPdCu NCs catalyst has 1.0 mol·L -1 potassium hydroxide and 0.1 mol·L-1 The nitrate reduction current density of the potassium nitrate mixed solution as electrolyte is obviously increased, indicating that the Cu2O / Cu@mesoPdCu NCs catalyst has electrocatalytic nitrate reduction activity.

[0081] Figure 5 is the LSV curve of the Cu2O / Cu@mesoPdCu NCs catalyst prepared in Example 1 of the present application and comparative catalysts (Cu2O NCs, mesoPdCu NCs, mesoPd / Cu2O NCs) of Comparative Examples 1-3. As shown in the figure, the nitrate reduction current density of the Cu2O / Cu@mesoPdCu NCs catalyst is the largest, indicating that the mesoporous Pd 63 Cu 37 The nano-catalyst has the best electrocatalytic nitrate reduction activity.

[0082] Figure 6 is the ammonia production and Faraday efficiency performance diagram of the electro-reduction of nitrate to synthesize ammonia of the Cu2O / Cu@mesoPdCu NCs catalyst prepared in Example 1 of the present application and comparative catalysts (Cu2O NCs, mesoPdCu NCs, mesoPd / Cu2O NCs) of Comparative Examples 1-3. As shown in the figure, the Cu2O / Cu@mesoPdCu NCs catalyst achieves the best Faraday efficiency of 96.2% at +0.1V vs. RHE, and the corresponding ammonia production is 13.3 mg h -1 mg cat -1 The performance is better than that of the comparative catalysts Cu2O NCs (69.8%), mesoPdCu NCs (64.8%) and mesoPd / Cu2O NCs (79.8%) under the optimal conditions.

[0083] Figure 7 is the energy efficiency (EE) diagram of the electro-reduction of nitrate to synthesize ammonia of the Cu2O / Cu@mesoPdCu NCs catalyst prepared in Example 1 of the present application and comparative catalysts (Cu2O NCs, mesoPdCu NCs, mesoPd / Cu2O NCs) of Comparative Examples 1-3. As shown in the figure, the EE of the Cu2O / Cu@mesoPdCu NCs catalyst is 46.0% at +0.1V vs. RHE, which is much better than that of the comparative catalysts.

[0084] Figure 8 is the cycle stability diagram of the electro-reduction of nitrate to synthesize ammonia of the Cu2O / Cu@mesoPdCu NCs catalyst prepared in Example 1 of the present application. As shown in the figure, the performance of the Cu2O / Cu@mesoPdCu NCs catalyst has almost no attenuation after 20 cycles.

[0085] This invention marks the first synthesis of a mesoporous copper-based core-shell electrocatalyst with unique functional characteristics, and its application in the electrochemical reduction of nitrate to ammonia. The Cu2O / Cu@mesoPdCu NCs catalyst, possessing a Cu2O / Cu heterojunction (core) and a mesoporous PdCu alloy (shell), perfectly promotes NO3- synthesis. - The structure exhibits a synergistic effect in the tandem electrocatalysis of NH3. On one hand, Cu2O / Cu@mesoPdCu exhibits good matching with the tandem active sites. The Cu2O / Cu heterojunction (core) is accompanied by numerous oxygen vacancy sites and a heterogeneous interface, significantly reducing the oxygen emission from NO3. - The high barrier to *NO2 (NO3) - (NO2 → NO3). Simultaneously, the Pd sites in the shell facilitate hydrolysis to generate *H radicals, thereby promoting the subsequent hydrodeoxygenation reaction of *NO2 to electrosynthesize NH3. On the other hand, the core-shell heterogeneous interface kinetics formed by Cu2O / Cu and PdCu accelerates the transport of the active intermediate / *H, promoting the rapid overflow of *H enriched at Pd sites within the mesoporous shell into Cu2O / Cu. Correspondingly, the potential-determining step of *NO2 → *NO → *NOH is significantly promoted, thus accelerating the hydrodeoxygenation step in the electrosynthesis of NH3. The results indicate that the continuous NO3 in adjacent two phases... - and NO2 - The tandem reduction successfully achieved high-rate electrosynthesis of NH3 at a positive potential. Simultaneously, the mesoporous shell provided an ideal "semi-closed" nanoconfinement environment, optimizing the formation and stabilization of *H radicals, and further facilitating their reaction with intermediates in the Cu2O / Cu core. Furthermore, in addition to the intrinsic ability of the mesoporous and core-shell structures to suppress physical Ostwald ripening, the electrochemical reduction process occurring on Cu2O / Cu (Cu2O + 2e⁻)… - +H₂O→2Cu+2OH - ) and spontaneous redox reaction (2Cu + NO3) - →Cu₂O + NO₂ - The coexistence of these substances stabilizes the active Cu(I) / Cu(O) compounds and inhibits their dissolution, thereby significantly improving electrocatalytic stability. Therefore, the use of this catalyst can simultaneously achieve superior activity, selectivity, and stability in the electroreduction of nitrate to ammonia at low overpotentials.

[0086] The catalyst prepared by the application can accelerate the hydrogenation deoxidation step of the electric synthesis of ammonia due to the optimized electronic structure, heterojunction kinetics and efficient series catalytic mechanism, and realizes the high rate electric synthesis of ammonia at a positive potential. Therefore, the application realizes "double win" in the degradation of nitrate wastewater and the low energy consumption value-added. More importantly, the structure / component advantage of the catalyst prepared by the application can greatly reduce the mass of noble metal, greatly reduce the raw material cost, and the process is simple, easy to operate, the reaction condition is mild, the product stability is good, and a large amount of preparation is suitable for large-scale industrial production.

[0087] Finally, it should be noted that: the above only for the preferred embodiments of the application, and not for limiting the application, although the application has been described in detail with reference to the foregoing embodiments, for those skilled in the art, it still can be modified to the technical scheme recorded in the foregoing embodiments, or equivalent replacement of some technical features. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the application shall be included in the protection scope of the application.

Claims

1. A method for preparing a mesoporous copper-based core-shell electrocatalyst for ammonia production from nitrate reduction at low overpotential, characterized in that: The specific preparation method of the mesoporous copper-based core-shell structured electrocatalyst is as follows: S1: Solution 1 preparation: The pre-synthesized Cu2O NCs are dispersed in deionized water to obtain solution 1; the specific steps of S1 are as follows: H1: The specific steps for preparing the pre-synthesized Cu2O NCs are as follows: ① Add 1 mL of 1.2 mol•L -1 CuSO4 solution was rapidly injected into 400 mL of deionized water at 25°C to obtain a dilute CuSO4 solution. ② After stirring the dilute CuSO4 solution for 5 min, add 1 mL of 4.8 mol•L⁻¹. -1 NaOH solution, the clear blue solution immediately turns turbid, forming Cu(OH)2, and obtaining Cu(OH)2 turbid solution; ③ After 5 min, inject 1 mL of freshly prepared 1.2 mol•L into the Cu(OH)2 turbid solution. -1 Ascorbic acid, reduction reaction for 0.5 h, the color of the Cu(OH)2 turbid liquid rapidly changed from turbid blue to yellowish-brown precipitate Cu2O NCs; ④ The precipitate Cu2O NCs was centrifuged and washed with ultrapure water and anhydrous ethanol, and then vacuum dried at room temperature for 12 h to obtain the pre-synthesized Cu2O NCs; H2: Disperse 2 mg of the pre-synthesized Cu2O NCs in 10 mL of deionized water; S2: Solution 2 preparation: Dissolve DODAC in the solution 1 and incubate in a set oven for a certain period of time to obtain solution 2; S3: Solution 3 preparation: Add hydrochloric acid solution to adjust the pH of solution 2 to obtain solution 3; S4: Solution 4 preparation: Add chloropalladium acid solution to solution 3 to obtain solution 4; S5: Preparation of mesoporous copper-based core-shell electrocatalyst: After solution 4 is allowed to stand, ascorbic acid is injected to carry out a reduction reaction; after the reaction is completed, the surfactant is removed by centrifugation and washing with a mixed solution of anhydrous ethanol and deionized water to obtain the mesoporous copper-based core-shell electrocatalyst.

2. The method for preparing a mesoporous copper-based core-shell electrocatalyst for ammonia production from nitrate reduction at low overpotential according to claim 1, characterized in that: The specific step of S2 is as follows: Dissolve 30 mg of DODAC in the solution 1, incubate in a set oven for a certain period of time to obtain solution 2.

3. A method for preparing a mesoporous copper-based core-shell electrocatalyst for ammonia production from nitrate reduction at low overpotential, as described in claim 1 or 2, characterized in that: The oven temperature is set to 80°C; the time is set to 30 minutes.

4. The method for preparing a mesoporous copper-based core-shell electrocatalyst for ammonia production from nitrate reduction at low overpotential according to claim 1, characterized in that: The specific step S3 is as follows: at 80°C, add 0.05 mL of 0.2 mol•L... -1 The pH of solution 2 was adjusted with hydrochloric acid solution to obtain solution 3.

5. The method for preparing a mesoporous copper-based core-shell electrocatalyst for ammonia production from nitrate reduction at low overpotential according to claim 1, characterized in that: The specific step S4 is as follows: Add 0.6 mL of 0.01 mol•L... -1 Chloropalladic acid solution was added to solution 3 to obtain solution 4.

6. The method for preparing a mesoporous copper-based core-shell electrocatalyst for ammonia production from nitrate reduction at low overpotential according to claim 1, characterized in that: The specific steps of S5 are as follows: after solution 4 has been allowed to stand at 80°C for 20 min, ascorbic acid is injected to carry out a reduction reaction; after the reaction is completed, the surfactant is removed by centrifugation and washing with a mixed solution of anhydrous ethanol and deionized water to obtain a mesoporous copper-based core-shell electrocatalyst.

7. A method for preparing a mesoporous copper-based core-shell electrocatalyst for ammonia production from nitrate reduction at low overpotential, as described in claim 1 or 6, characterized in that: In step S5, the ascorbic acid is specifically administered by rapidly injecting 1 mL of fresh 0.3 mol•L... -1 Ascorbic acid is reduced, and the reduction reaction takes 25 minutes.

8. A method for preparing a mesoporous copper-based core-shell electrocatalyst for ammonia production from nitrate reduction at low overpotential, as described in claim 1 or 6, characterized in that: In S5, the anhydrous ethanol and the deionized water are mixed solutions with a volume ratio of 3:

1.

9. The application of the mesoporous copper-based core-shell electrocatalyst for ammonia production from nitrate reduction at low overpotential as described in claim 1, characterized in that: The mesoporous copper-based core-shell electrocatalyst is used in the electrochemical reduction of nitrate to synthesize ammonia.

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