A catalyst for electrocatalytic reduction of nitrate and a method for preparing the same

Abstract

This invention discloses a catalyst for the electrocatalytic reduction of nitrate to ammonia and its preparation method, belonging to the field of industrial wastewater pollution control technology. The catalyst uses basic copper sulfate and cobalt tetroxide as dual active components, and its preparation method includes the following steps: (1) adding cobalt metal precursor, copper metal precursor, urea and ammonium persulfate to ultrapure water, stirring until completely dissolved, heating under high pressure, centrifuging, washing and drying to obtain catalyst material precursor; (2) calcining the catalyst material precursor and then rapidly cooling it to obtain basic copper sulfate material with Co3O4 dispersed on the surface. The catalyst prepared by this invention uses basic copper sulfate and Co3O4 as dual active components, and the two have a heterojunction synergistic effect, which can efficiently convert nitrate into ammonia, with excellent catalytic performance and high activity and selectivity.

Description

Technical Field

[0001] This invention relates to a catalyst for the electrocatalytic reduction of nitrate to ammonia and its preparation method, belonging to the technical field of nitrate wastewater treatment and resource utilization. Background Technology

[0002] With rapid economic development and continuous industrialization, the discharge of industrial wastewater is increasing daily, posing a serious challenge to the ecological environment. Among the pollutants in industrial wastewater, various heavy metal salts are the main pollutants, while nitrates (NO3) are particularly prevalent. - Nitrogen, due to its high content in wastewater and its tendency to be reduced to highly toxic and carcinogenic nitrites, has become a key focus of water environment management. Ammonia is an important chemical raw material and a potential green energy carrier, with broad application prospects in agriculture, industry, and energy. However, the traditional ammonia synthesis process commonly used in industry—the Haber-Bosch process—requires the reaction of nitrogen and hydrogen under high temperature and pressure conditions, which not only consumes enormous amounts of energy but also results in significant greenhouse gas emissions.

[0003] Electrocatalytic reduction of nitrate to ammonia technology (NO3) - Electrocatalytic reduction (ERR) is a green and efficient ammonia synthesis method that utilizes renewable energy to convert nitrate pollutants in water into high-value ammonia under ambient temperature and pressure conditions, offering the dual benefits of pollution control and resource recovery. Significant progress has been made in recent years in exploring the reaction mechanism and designing catalysts. However, most reported high-efficiency catalysts are based on precious metal materials, which are costly and scarce, limiting their large-scale application. In summary, the industry has yet to develop an electrocatalyst for the reduction of nitrates to ammonia that combines low cost, high activity, strong stability, and meets the requirements for industrial-scale application, thus limiting the potential of NO3-containing ammonia production. - The practical application of RR technology in industrial wastewater treatment and green ammonia production. Based on this, developing an electrocatalytic reduction catalyst for nitrate to ammonia production that is adaptable to complex industrial wastewater environments, easy to prepare, cost-controllable, and exhibits excellent catalytic performance has significant practical implications and application value. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a catalyst for the electrocatalytic reduction of nitrates to ammonia and its preparation method. This catalyst can efficiently convert nitrates into ammonia with high activity and selectivity.

[0005] To solve the above-mentioned technical problems, the technical solution provided by the present invention is as follows: A catalyst for the electrocatalytic reduction of nitrate to ammonia, wherein the catalyst has basic copper sulfate (Cu4(OH)6SO4) and cobalt tetroxide (Co3O4) as dual active components.

[0006] Furthermore, the molar ratio of basic copper sulfate to cobalt tetroxide is 3:2.

[0007] A method for preparing a catalyst for the electrocatalytic reduction of nitrate to ammonia includes the following steps: (1) Add cobalt metal precursor, copper metal precursor, urea and ammonium persulfate to ultrapure water, stir until completely dissolved, heat, centrifuge, wash and dry to obtain catalyst material precursor; (2) The catalyst precursor is calcined and then rapidly cooled to obtain a basic copper sulfate material with Co3O4 dispersed on the surface, which is the catalyst for electrocatalytic reduction of nitrate to ammonia.

[0008] Further, in step (1), the molar ratio of the copper metal precursor, the cobalt metal precursor, urea, and ammonium persulfate is 2:1:3:1; the cobalt metal precursor is one of cobalt nitrate hexahydrate, anhydrous cobalt chloride, and cobalt acetate; the copper metal precursor is anhydrous copper sulfate; and the ratio of ultrapure water to the copper metal precursor is 40 mL: (0.30-0.35) g. Using copper sulfate as the copper metal precursor, sulfate ions are directionally introduced. Sulfate ions can be adsorbed on the surface of basic copper sulfate, regulating its electron cloud distribution and enhancing the catalyst's response to the anionic reactant NO3. - The adsorption capacity of the sulfate group reduces the initial energy barrier of the reaction; at the same time, the sulfate group can be embedded in the copper oxide lattice to form a stable layered or specific structure, preventing the catalyst from being over-reduced or the structure from collapsing during the reaction.

[0009] Furthermore, in step (1), the heating temperature is 140-220℃ for 2-8 hours; the drying temperature is 40-80℃ for 8-14 hours; the centrifugation speed is 4000 r / min for 3 minutes; and the washing is performed three times with ultrapure water and anhydrous ethanol respectively. Heating promotes the full reaction of cobalt and copper precursors with urea and ammonium persulfate, forming a catalyst precursor with uniform composition; multiple centrifugation and washing remove impurity ions, ensuring the purity of the precursor.

[0010] Furthermore, in step (2), the calcination temperature is 280-400℃, and the calcination time is 4h; the rapid cooling operation is as follows: the calcined catalyst material precursor is placed in dry air at room temperature and rapidly cooled to room temperature. Calcination causes the precursor to undergo a crystal transformation, generating a composite structure of basic copper sulfate and Co3O4; rapid cooling treatment can inhibit excessive grain growth, maintain the nanoscale size and high specific surface area of ​​the catalyst, and at the same time avoid Co3O4 particle agglomeration, ensuring that the active sites are fully exposed. After the calcination and rapid cooling process, Co3O4 is uniformly dispersed on the surface of basic copper sulfate in the form of nanoparticles. The two form a heterojunction interface, which can play a relay catalytic role, promote electron transfer between the two materials, optimize the reaction path, and reduce the energy barrier of the entire reduction process.

[0011] The principle of this invention is as follows: The catalyst prepared in this invention for the electrocatalytic reduction of nitrate to ammonia uses basic copper sulfate and Co3O4 as dual active components. By constructing a heterostructure, synergistic effects, structural regulation, and interface optimization are achieved, ultimately realizing the efficient reduction of nitrate to ammonia. The heterostructure formed by basic copper sulfate and Co3O4 constructs a directional electron transport channel, enhancing the interaction between the two active components. During the electrocatalytic process, the sulfate ions introduced in situ from the basic copper sulfate can regulate the electron distribution on the catalyst surface, further enhancing the reduction of NO3-. - The adsorption capacity of Cu in its crystal lattice 2+ / Cu + Redox pairs provide core active sites for electrocatalytic reactions, and Cu active centers adsorb NO3. - It also catalyzes the deoxygenation of NO to produce NO2. - Co3O4's Co 3+ / Co 2+ The site exhibits excellent hydrogen evolution regulation capabilities, promoting the generation of hydrogen free radicals (H*), which rapidly diffuse to the Cu active center through the heterojunction interface, accelerating NO3- generation. - The RR process involves the intermediate acquiring H* and converting it into NH3. The heterojunction interface formed by Co3O4 and basic copper sulfate promotes the efficient combination of nitrate ions and hydrogen radicals, thereby significantly increasing the ammonia formation rate and selectivity.

[0012] Compared with the prior art, the beneficial effects of the present invention are: (1) The catalyst prepared by the present invention uses basic copper sulfate and Co3O4 as dual active components. The two have a heterojunction synergistic effect, resulting in excellent catalytic performance and achieving a balance between high activity and high selectivity. Furthermore, anhydrous copper sulfate is used as the copper source, and sulfate ions are introduced in situ, which can regulate the electronic structure of the catalyst surface, greatly improve the catalyst's adsorption and reduction capabilities for nitrates, and further enhance the catalytic efficiency.

[0013] (2) The present invention uses cobalt and copper non-precious metal salts as raw materials, avoiding the use of precious metals. The raw materials are widely available and inexpensive. Compared with precious metal-based catalysts, the production cost is greatly reduced, making it more suitable for industrial applications.

[0014] (3) The present invention adopts a unique process of hydrothermal synthesis, calcination and rapid cooling to achieve high crystallinity, densification and high stability of the catalyst. Its performance does not decay significantly after long period and multiple cycles, and it has excellent industrial stability. Moreover, the preparation process is simple and low cost, and it is suitable for large-scale production. Attached Figure Description

[0015] Figure 1 These are the XRD patterns of the catalysts in Examples 1-2 and Comparative Example 2; Figure 2 The XRD patterns of the catalysts in Comparative Examples 3-4 are shown. Figure 3 These are LSV diagrams of the catalysts in Example 2 and Comparative Examples 1-4, with a magnified view showing the overpotential. Figure 4 These are the LSV diagrams of the catalysts in Example 2 and Comparative Examples 5-6, with a magnified view showing the overpotential. Figure 5 These are the EIS impedance diagrams of the catalysts in Example 2, Comparative Example 2, and Comparative Examples 5-6; Figure 6 This is a graph showing the ammonia yield and Faraday efficiency of the catalyst in Example 2 at different potentials; Figure 7 This is a current density plot showing the stability of the catalyst in Example 2 at -0.3V vs RHE. Detailed Implementation

[0016] Example 1 A method for preparing a catalyst for the electrocatalytic reduction of nitrate to ammonia includes the following steps: (1) Add 0.291g cobalt nitrate hexahydrate, 0.319g anhydrous copper sulfate, 0.180g urea and 0.228g ammonium persulfate to 40mL of ultrapure water, stir until completely dissolved, transfer to a hydrothermal reactor, heat at 180℃ for 4h, centrifuge at 4000r / min for 3min, wash 3 times with ultrapure water and anhydrous ethanol respectively, and dry in an oven at 60℃ for 12h to obtain the catalyst material precursor; (2) The catalyst material precursor is placed in a muffle furnace and calcined at 280°C for 4 hours. Then it is placed in dry air at room temperature and cooled to room temperature to obtain a basic copper sulfate material with Co3O4 dispersed on the surface, which is the catalyst for electrocatalytic reduction of nitrate to ammonia.

[0017] Example 2 A method for preparing a catalyst for the electrocatalytic reduction of nitrate to ammonia includes the following steps: (1) Add 0.291g cobalt nitrate hexahydrate, 0.319g anhydrous copper sulfate, 0.180g urea and 0.228g ammonium persulfate to 40mL of ultrapure water, stir until completely dissolved, transfer to a hydrothermal reactor, heat at 180℃ for 4h, centrifuge at 4000r / min for 3min, wash 3 times with ultrapure water and anhydrous ethanol respectively, and dry in an oven at 60℃ for 12h to obtain the catalyst material precursor; (2) The catalyst material precursor is placed in a muffle furnace and calcined at 350°C for 4 hours. Then it is placed in dry air at room temperature and cooled to room temperature to obtain a basic copper sulfate material with Co3O4 dispersed on the surface, which is the catalyst for electrocatalytic reduction of nitrate to ammonia.

[0018] Example 3 A method for preparing a catalyst for the electrocatalytic reduction of nitrate to ammonia includes the following steps: (1) Add 0.291g cobalt nitrate hexahydrate, 0.319g anhydrous copper sulfate, 0.180g urea and 0.228g ammonium persulfate to 40mL of ultrapure water, stir until completely dissolved, transfer to a hydrothermal reactor, heat at 140℃ for 8h, centrifuge at 4000r / min for 3min, wash 3 times with ultrapure water and anhydrous ethanol respectively, and dry in an oven at 40℃ for 14h to obtain the catalyst material precursor; (2) The catalyst material precursor is placed in a muffle furnace and calcined at 400°C for 4 hours. Then it is placed in dry air at room temperature and cooled to room temperature to obtain a basic copper sulfate material with Co3O4 dispersed on the surface, which is the catalyst for electrocatalytic reduction of nitrate to ammonia.

[0019] Example 4 A method for preparing a catalyst for the electrocatalytic reduction of nitrate to ammonia includes the following steps: (1) Add 0.291g cobalt nitrate hexahydrate, 0.319g anhydrous copper sulfate, 0.180g urea and 0.228g ammonium persulfate to 40mL of ultrapure water, stir until completely dissolved, transfer to a hydrothermal reactor, heat at 220℃ for 2h, centrifuge at 4000r / min for 3min, wash three times with ultrapure water and anhydrous ethanol respectively, and dry in an 80℃ oven for 8h to obtain the catalyst material precursor; (2) The catalyst material precursor is placed in a muffle furnace and calcined at 350°C for 4 hours. Then it is placed in dry air at room temperature and cooled to room temperature to obtain a basic copper sulfate material with Co3O4 dispersed on the surface, which is the catalyst for electrocatalytic reduction of nitrate to ammonia.

[0020] Comparative Example 1 A method for preparing an electrocatalytic reduction catalyst for ammonia production from nitrates includes the following steps: (1) Add 0.582g cobalt nitrate hexahydrate, 0.1595g anhydrous copper sulfate, 0.180g urea and 0.228g ammonium persulfate to 40mL of ultrapure water, stir until completely dissolved, transfer to a hydrothermal reactor, heat at 180℃ for 4h, centrifuge at 4000r / min for 3min, wash three times with ultrapure water and anhydrous ethanol respectively, and dry in a 60℃ oven for 12h to obtain the catalyst.

[0021] Comparative Example 2 A method for preparing an electrocatalytic reduction catalyst for ammonia production from nitrates includes the following steps: (1) Add 0.291g cobalt nitrate hexahydrate, 0.319g anhydrous copper sulfate, 0.180g urea and 0.228g ammonium persulfate to 40 mL of ultrapure water, stir until completely dissolved, transfer to a hydrothermal reactor, heat at 180℃ for 4h, centrifuge at 4000r / min for 3min, wash three times with ultrapure water and anhydrous ethanol respectively, and dry in a 60℃ oven for 12h to obtain the catalyst.

[0022] Comparative Example 3 A method for preparing an electrocatalytic reduction catalyst for ammonia production from nitrates includes the following steps: (1) Add 0.291g cobalt nitrate hexahydrate, 0.180g urea and 0.228g ammonium persulfate to 40mL of ultrapure water, stir until completely dissolved, transfer to a hydrothermal reactor, heat at 180℃ for 4h, centrifuge at 4000r / min for 3min, wash three times with ultrapure water and anhydrous ethanol respectively, and dry in a 60℃ oven for 12h to obtain the catalyst.

[0023] Comparative Example 4 A method for preparing an electrocatalytic reduction catalyst for ammonia production from nitrates includes the following steps: (1) Add 0.319g anhydrous copper sulfate, 0.180g urea and 0.228g ammonium persulfate to 40mL of ultrapure water, stir until completely dissolved, transfer to a hydrothermal reactor, heat at 180℃ for 4h, centrifuge at 4000r / min for 3min, wash three times with ultrapure water and anhydrous ethanol respectively, and dry in a 60℃ oven for 12h to obtain the catalyst.

[0024] Comparative Example 5 A method for preparing an electrocatalytic reduction catalyst for ammonia production from nitrates includes the following steps: The catalyst prepared in Comparative Example 3 was placed in a muffle furnace and calcined at 350°C for 4 hours, and then rapidly cooled to room temperature in dry air at room temperature to obtain the catalyst.

[0025] Comparative Example 6 A method for preparing an electrocatalytic reduction catalyst for ammonia production from nitrates includes the following steps: The catalyst prepared in Comparative Example 4 was placed in a muffle furnace and calcined at 350°C for 4 hours, and then rapidly cooled to room temperature in dry air at room temperature to obtain the catalyst.

[0026] Comparison of catalyst performance in Experiment Example 1 (1) The catalysts of Examples 1-2 were designated as Cu:Co=2:1-280℃ and Cu:Co=2:1-350℃, respectively, and the catalyst of Comparative Example 2 was designated as Cu:Co=2:1. XRD tests were performed on them, and the test results are attached. Figure 1 As shown.

[0027] from Figure 1 It can be seen that the catalyst in Comparative Example 2 has the weakest peak intensity, the widest peak shape, the lowest crystallinity, the smallest grain size, and a relatively loose structure. The catalyst in Example 1 has a significantly improved peak intensity, a sharper peak shape, a markedly increased crystallinity, and more complete grains. The catalyst in Example 2 has the highest peak intensity, the narrowest peak shape, the best crystallinity, and the densest structure, indicating that high-temperature calcination promotes crystal growth and structural ordering. It is evident that high-temperature calcination not only did not destroy the bimetallic basic copper sulfate structure, but also strengthened the synergistic effect of Cu and Co by increasing crystallinity and densifying the structure.

[0028] (2) The catalysts of Comparative Examples 3-4 were labeled as Co and Cu, respectively, and XRD tests were performed on them. The test results are shown in the appendix. Figure 2 As shown.

[0029] from Figure 2 It can be seen that the characteristic peaks of the catalyst in Comparative Example 3 are consistent with the characteristic peaks of the Co3O4 standard card, indicating that the Co3O4 crystal phase can be prepared by using only cobalt nitrate hexahydrate in Comparative Example 3; the characteristic peaks of the catalyst in Comparative Example 4 are completely matched with the characteristic peaks of the standard card, indicating that basic copper sulfate can be prepared by using only anhydrous copper sulfate in Comparative Example 4, but neither of them can prepare the catalyst of the present invention.

[0030] Furthermore, by comparison, the peak positions of the catalysts in Examples 1-2 shifted relative to those of pure Cu / Co, indicating electronic interactions or lattice doping between Cu and Co, which is precisely the reason for their improved electrocatalytic performance. In summary, this invention can successfully prepare structurally stable, dense, and bimetallic synergistic catalysts, laying the foundation for subsequent improvements in electrocatalytic performance.

[0031] Experiment Example 2 The electrocatalytic reduction performance of the catalyst for ammonia production from nitrate was tested in an H-type electrolytic cell using a three-electrode system. The catalyst in Example 2 was designated Cu:Co = 2:1 (-350℃), and the catalysts in Comparative Examples 1-4 were designated Cu:Co = 1:2, Cu:Co = 2:1, Co, and Cu, respectively. Carbon cloth loaded with the catalyst was used as the working electrode, a saturated calomel electrode as the reference electrode, and a platinum sheet electrode as the counter electrode. Performance tests were conducted using an electrochemical workstation to assess the catalytic reduction effect on nitrate. The test results are attached. Figure 3 As shown.

[0032] The test method is as follows: 1.28 mL of isopropanol, 5 μL of 20% Nafion solution, and 715 μL of ultrapure water are mixed, 20 mg of catalyst is added, and the mixture is sonicated to obtain a homogeneous catalyst ink. 20 μL of the catalyst ink is then pipetted into a 1×1 cm⁻¹ volume. 2The catalyst-loaded carbon cloth was vacuum dried on the carbon cloth and then dried at 60°C before testing. Before each measurement, the catalyst-loaded carbon cloth was placed in a blank electrolyte of 1M KOH and 0.1M KCl for 20 cycles of CV activation at a scan rate of 100mV / s and a potential range of -1.1316V vs RHE to -0.4684V vs RHE. When testing LSV, the anolyte was 1M KOH and the catholyte was 1M KOH + 0.1M KNO3. The parameters were set to a scan rate of 50 mV / s, and the potential range was -1.1316 V vs RHE to -0.4684 V vs RHE. During the constant potential electrolysis test, the single electrolysis time was 0.5 h. An appropriate amount of the electrolyte in the cathode chamber after electrolysis was diluted to 5 mL with ultrapure water, and then 0.1 mL of potassium sodium tartrate solution and 0.1 mL of Nessler's reagent were added. After standing for 20 min, the ammonium ions in the final product were determined using a UV spectrophotometer.

[0033] All potentials are converted to reversible hydrogen potentials using the following formula: E(RHE) = E(saturated calomel electrode) + 0.0591pH + 0.241.

[0034] from Figure 3 It can be seen that, compared with the catalysts of Comparative Examples 3-4, the reduction currents of the catalysts of Comparative Examples 1-2 are significantly increased, proving that the composite of Co and Cu components produces a synergistic catalytic effect, which greatly enhances the activity of nitrate reduction to ammonia. The catalyst of Example 2 has the largest absolute value of current density and also exhibits a large current density in the critical reaction range, indicating that it has the fastest catalytic reaction rate and the highest activity under strong reduction potential. This demonstrates that calcination in this invention can improve the crystallinity of the catalyst, optimize the interfacial contact state of the Cu-Co heterojunction, and effectively improve the catalyst's reactivity.

[0035] Experimental Example 3 The electrocatalytic reduction performance of the catalysts for nitrate to ammonia was tested in an H-type electrolytic cell using a three-electrode system. The catalyst in Example 2 was designated Cu:Co = 2:1 - 350℃, and the catalysts in Comparative Examples 5 and 6 were designated Co - 350℃ and Cu - 350℃, respectively. Performance tests were conducted using an electrochemical workstation to assess the catalytic reduction effect on nitrate, following the same testing method as in Example 2. The test results are attached. Figure 4 As shown.

[0036] from Figure 4It can be seen that the catalyst of Comparative Example 5 has the lowest reduction current density, indicating that its adsorption capacity for nitrates is weak, and its activation and hydrogenation capacity for nitrates is insufficient, making it unable to achieve efficient nitrate reduction on its own. The reduction current density of the catalyst of Comparative Example 6 is higher than that of the catalyst of Comparative Example 5, indicating that it forms highly crystalline basic copper sulfate after heat treatment at 350℃, providing a large number of core active sites for nitrate reduction, but it is still much lower than that of the catalyst of Example 2. Compared with the catalysts of Comparative Examples 5 and 6, the onset potential of the catalyst of Example 2 is significantly shifted to a positive potential, and the reduction current density is significantly increased, indicating that there is an electronic synergistic effect between Cu and Co composites, and the Cu active center is conducive to NO3- reduction. - Deoxygenation forms NO2 - The Co component promotes the formation of H* (hydrogen radicals), thereby accelerating NO3 formation. - During the RR process, the intermediate obtains H and is converted into NH3, which significantly improves the activity. It can be seen that under calcination at 350℃, the Cu and Co composite produces a strong synergistic effect, and the activity is far greater than that of the single component.

[0037] Experiment Example 4 The catalyst in Example 2 was designated as Cu:Co = 2:1 - 350℃, the catalyst in Comparative Example 2 as Cu:Co = 2:1, and the catalysts in Comparative Examples 5 and 6 as Co - 350℃ and Cu - 350℃, respectively. Performance tests were conducted using an electrochemical workstation to assess the catalytic reduction effect on nitrates, following the same testing method as in Example 2. The test results are attached. Figure 5 As shown.

[0038] The diameter of the semicircle directly corresponds to the charge transfer resistance (Rct). The smaller the semicircle, the lower the Rct, the smoother the transfer of electrons at the catalyst / electrolyte interface, and the faster the electrocatalytic reaction kinetics. Figure 5 As can be seen, compared with the catalysts of Comparative Examples 5-6, the impedance of the catalyst of Comparative Example 2 is significantly reduced, proving that the synergistic effect of Cu and Co optimizes the interfacial electronic structure, lowers the charge transfer energy barrier, and improves electrocatalytic kinetics. Compared with the catalyst of Comparative Example 2, the impedance curve of the catalyst of Example 2 is smaller and more compact, indicating that calcination at 350℃ significantly reduces the charge transfer resistance and interfacial impedance. It is evident that the present invention forms a composite crystalline phase of basic copper sulfate and Co3O4 by calcination at 350℃. The two synergistically optimize the interfacial electronic structure, significantly reducing the charge transfer energy barrier; furthermore, calcination improves the crystallinity and densifies the structure of the catalyst, reducing interfacial defects, thereby optimizing the electron transport path, ultimately achieving lower charge transfer resistance and higher electrocatalytic performance.

[0039] Experimental Example 5 Referring to the test method in Experiment 2, the ammonia yield and Faraday efficiency of the catalyst in Example 2 at different low potentials and the stability current density at -0.3V vs RHE were determined. The test results are as follows: Figure 6-7 As shown.

[0040] from Figure 6 It can be seen that as the potential shifts negatively, the Faraday efficiency first increases and then decreases, reaching a maximum at a potential of -0.3V. Meanwhile, the ammonia yield continuously increases with the negative potential shift, indicating that this catalyst can simultaneously achieve higher electron utilization efficiency and product formation rate at low potentials, exhibiting good selectivity. Figure 7 It can be seen that the current density changes in the first to fourth cycles are highly consistent, with no significant decrease in initial current density, decay trend, or steady-state current. This indicates that the active sites of the catalyst remain stable and the structure is not damaged during repeated use, demonstrating excellent cycle stability. In the fifth cycle, a 10-hour long-term test, the current density rapidly decreased to a steady state within 0-2 hours, and then showed no significant decay trend from 2-10 hours. This indicates that the catalyst can maintain stable catalytic activity under long-term continuous operation conditions, exhibiting excellent long-term operational stability. This demonstrates that the catalyst of this invention exhibits minimal current density decay during multiple electrocatalytic cycles, extremely strong structural and activity stability, and excellent long-term operational reliability and cycle life.

[0041] In summary, the electrocatalyst for the reduction of nitrate to ammonia of the present invention has both high activity and high electronic efficiency, as well as good stability and selectivity, and its overall performance is excellent.

[0042] Experimental Example 6 The catalysts of Examples 1-2 and Comparative Examples 5-6 were subjected to performance tests. Following the test method in Experiment 2, carbon cloth loaded with the catalyst was prepared, and electrochemical tests were performed using an H-type electrolytic cell with a three-electrode system. The cathode and anode chambers were separated by a proton-only Nafion 117 membrane, and the saturated calomel electrode was filled with a saturated KCl solution. The cathode electrolyte was 1M KOH and 0.1M KNO3, and the anode electrolyte was 1M KOH. For impedance testing, the cathode electrolyte was 1M KOH and 0.1M KNO3, and the anode electrolyte was 1M KOH. When testing the Faradaic efficiency and ammonia yield using ITT, the single electrolysis time was 0.5 h. After electrolysis, the products were detected using a UV spectrophotometer. The ammonia yield, Faradaic efficiency, and overpotential at -0.45 V vs RHE potential were measured, and the test results are shown in Table 1.

[0043] The overpotential is the potential (V vs RHE) corresponding to the catalyst reaching a current density of -10 mA / cm in the electrocatalytic reduction of nitrate to ammonia.

[0044] Table 1 Comparison of Catalyst Performance Table 1 shows that the catalyst in Comparative Example 5 has the most negative overpotential, indicating extremely low activity; the catalyst in Comparative Example 6 has the most positive overpotential and the lowest Faradaic efficiency, indicating high activity but poor selectivity. This demonstrates that single-component catalysts have significant drawbacks due to low activity or poor selectivity, failing to meet the requirements for efficient ammonia production. Compared to catalysts in Comparative Examples 5-6, the catalysts in Examples 1-2 simultaneously exhibit higher overpotential, Faradaic efficiency, and ammonia yield. This indicates that the heterostructure constructed from basic copper sulfate and Co3O4 has a synergistic catalytic effect, effectively lowering the reaction energy barrier for the electrocatalytic reduction of nitrate to ammonia, significantly improving catalytic activity and ammonia selectivity. The catalyst achieves a balance of low overpotential, high ammonia yield, and high Faradaic efficiency, demonstrating catalytic performance far superior to single-component catalysts.

[0045] Experimental Example 7 Following the test method in Experimental Example 6, the performance of the catalyst for the electrocatalytic reduction of nitrate to ammonia of this invention and existing cobalt-doped copper heterostructure catalysts were tested at a potential of -0.45V vs RHE. The test results are listed in Table 2.

[0046] The cobalt-doped copper heterostructure catalyst is a cobalt-doped cuprous oxide / copper heterostructure catalyst prepared by the method of patent CN117070994A; the copper-cobalt alloy catalyst is a CuCo / CoOx catalyst prepared by the method of patent CN121250423A.

[0047] Table 2 Comparison of Catalyst Performance As shown in Table 2, compared with the catalysts disclosed in the prior art, the ammonia yield of the catalyst of the present invention is significantly improved, indicating that the catalyst of the present invention generates ammonia at a faster rate per unit mass of active component and has higher catalytic activity. The high Faradaic efficiency indicates that the catalyst of the present invention has ultra-high ammonia selectivity, excellent selectivity, and superior catalytic activity. This demonstrates that the catalyst of the present invention achieves a significant increase in ammonia yield while maintaining high Faradaic efficiency. It proves that the present invention achieves a synergistic improvement in catalytic activity and selectivity by constructing a heterojunction of basic copper sulfate and Co3O4 as dual active phases and using a unique calcination and rapid cooling process to strengthen the structure and interface. The resulting catalyst exhibits excellent catalytic performance, significantly superior to copper-cobalt based catalysts in the prior art, and is more suitable for industrial applications of electrocatalytic nitrate reduction to ammonia.

Claims

1. A catalyst for the electrocatalytic reduction of nitrates to ammonia, characterized in that: The catalyst uses basic copper sulfate and cobalt tetroxide as dual active components.

2. A method for preparing the catalyst for the electroreduction of nitrate to ammonia as described in claim 1, characterized in that: Includes the following steps: (1) Add cobalt metal precursor, copper metal precursor, urea and ammonium persulfate to ultrapure water, stir until completely dissolved, heat, centrifuge, wash and dry to obtain catalyst material precursor; (2) The catalyst precursor is calcined and then rapidly cooled to obtain a basic copper sulfate material with Co3O4 dispersed on the surface, which is a copper-based catalyst for electrocatalytic reduction of nitrate to ammonia.

3. The method for preparing the catalyst for the electroreduction of nitrate to ammonia according to claim 2, characterized in that: In step (1), the molar ratio of the copper metal precursor, the cobalt metal precursor, urea and ammonium persulfate is 2:1:3:

1.

4. The method for preparing the catalyst for the electroreduction of nitrate to ammonia according to claim 3, characterized in that: In step (1), the heating temperature is 140-220℃ and the heating time is 2-8h; the drying temperature is 40-80℃ and the drying time is 8-14h.

5. The method for preparing the catalyst for the electroreduction of nitrate to ammonia according to claim 4, characterized in that: In step (2), the calcination temperature is 280-400℃ and the calcination time is 4h.

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