Preparation method and application of high-efficiency electrocatalytic synthesis ammonia CoFe2O4 / FeOOH@IF self-supporting electrode

Abstract

A method for preparing and applying a highly efficient CoFe₂O₄ / FeOOH@IF self-supporting electrode for electrocatalytic ammonia synthesis. This invention relates to a method for preparing and applying a CoFe₂O₄ / FeOOH@IF self-supporting electrode with high ammonia yield and Faradaic efficiency in the field of nanomaterials. The purpose of this invention is to solve the problem of low yield and Faradaic efficiency in the electrochemical reduction of nitrate to synthesize ammonia. Preparation method: Using iron foam (IF), cobalt nitrate hexahydrate, ferric chloride hexahydrate, urea, and ammonium fluoride as raw materials, a CoFeOOH@IF precursor material is prepared through a one-step hydrothermal reaction. Then, the CoFe₂O₄ / FeOOH@IF self-supporting electrode with high ammonia yield and Faradaic efficiency is successfully prepared by calcination in a tube furnace. The CoFe₂O₄ / FeOOH@IF self-supporting electrode can be directly used as the working electrode for the electrocatalytic reduction of nitrate to synthesize ammonia.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of nitrate reduction synthesis of ammonia, and in particular to a preparation method and application of a high-efficiency electrocatalytic synthesis of ammonia self-supporting electrode. BACKGROUND

[0002] The widespread use of artificial nitrogen fertilizer, combined with the combustion of nitrogen-containing fossil fuels, has led to a serious imbalance in the global nitrogen cycle. Nitrogen oxides emitted by industrial wastewater and vehicles have also caused the accumulation of nitrogen oxides in the biosphere. Among them, nitrate is considered one of the primary pollutants of drinking water. Among various methods to address nitrate pollution, catalytic conversion of nitrate into valuable chemical products such as NH3 (a fertilizer and emerging fuel) is one of the most practical options. Currently, photocatalytic reduction of nitrate to synthesize ammonia has failed to achieve high ammonia yield and selectivity, and there is still a distance from large-scale industrial application. Biological catalysis has high requirements for conditions and a long cycle. In contrast, electrocatalytic reduction of nitrate (NO3 – RR) to synthesize ammonia can achieve a relatively efficient ammonia synthesis process at room temperature and pressure. However, due to the involvement of eight-electron redox and slow kinetics, accompanied by competition with hydrogen evolution reaction (HER), the efficiency of electrocatalytic reduction of nitrate to synthesize ammonia still needs to be improved. Therefore, the preparation of high-performance catalysts is one of the key technologies.

[0003] Non-noble transition metals are abundant in reserves and low in price, which can meet the mass production of industrialization, and are ideal raw materials for electrocatalysts. At the same time, there are unoccupied d orbitals in transition metals. They can accept lone pair electrons in NO3 - , weaken the N=O double bond, and reduce the energy barrier of the catalytic reaction. Spinel CoFe2O4 is a metal oxide with good electrocatalytic performance. It has good electrical conductivity and can effectively transfer electrons. In electrocatalytic reactions, the rapid transfer of electrons is the key to improving catalytic efficiency, and the good electrical conductivity of CoFe2O4 makes it have good catalytic potential in the electrocatalytic reduction of nitrate. At the same time, CoFe2O4 shows good stability under alkaline conditions and is not easily oxidized or decomposed, which enables it to maintain high catalytic activity and cycle stability during long-term electrocatalytic processes. The iron element in β-FeOOH material has good catalytic activity and can adsorb and activate nitrate ions. Compared with many other electrocatalytic materials, β-FeOOH has high stability, especially under alkaline conditions, and can maintain high catalytic activity in long-term catalytic reactions.

[0004] The application prepares CoFeOOH@IF precursor loaded on foam iron (abbreviated as IF) by one-step hydrothermal method, and further generates CoFe2O4 / FeOOH@IF self-supporting electrode material by tube furnace calcination. The method combines CoFe2O4 and β-FeOOH closely, and in-situ growth on foam iron with larger specific surface and excellent conductivity. Through the synergistic effect of CoFe2O4, β-FeOOH and IF, the CoFe2O4 / FeOOH@IF self-supporting electrode exhibits excellent performance in electrocatalytic reduction of nitrate, and provides an important way for the preparation of high-efficiency electrocatalytic nitrate reduction ammonia synthesis catalyst. SUMMARY

[0005] The purpose of the application is to obtain a high-efficiency electrocatalytic ammonia synthesis CoFe2O4 / FeOOH@IF self-supporting electrode, solve the problems of low yield and Faraday efficiency of electrochemical nitrate reduction synthesis ammonia, and provide a CoFe2O4 / FeOOH@IF material preparation method and application.

[0006] A preparation method of a high-efficiency electrocatalytic ammonia synthesis CoFe2O4 / FeOOH@IF self-supporting electrode, comprising the following steps:

[0007] I. Dissolve cobalt nitrate hexahydrate, ferric chloride hexahydrate, urea and ammonium fluoride into distilled water at the same time, then stir for a period of time until the solution is transparent, to obtain a pink solution.

[0008] The molar ratio of cobalt nitrate to ferric chloride described in step one is 2:(1.0-2.0);

[0009] The molar ratio of cobalt nitrate to ammonium fluoride described in step one is 1:(15.0-20.0);

[0010] The molar ratio of cobalt nitrate to urea described in step one is 1:(3.0-5.0);

[0011] The amount of substance of cobalt nitrate described in step one to the volume of distilled water is 1.0 mmol:(20-30) mL.

[0012] II. Cut the foam iron to a size of 2*3 cm, and clean it with acetone, 1 mol·L -1 Sulfuric acid and deionized water for 5-10 min, respectively.

[0013] 3. Add the pink reaction solution to a polytetrafluoroethylene (PTFE) reactor, then add the cleaned foamed iron. React in the PTFE reactor at 120℃ for 6 hours, then allow the PTFE reactor to cool naturally to room temperature. Remove the foamed iron and wash it several times with distilled water and anhydrous ethanol. Finally, place the resulting brown foamed iron in a vacuum drying oven at 60℃ and dry it overnight. Place the dried foamed iron in a tube furnace and heat it at 350℃ for 2 hours under a N2 atmosphere. The resulting black foamed iron is the CoFe2O4 / FeOOH@IF self-supporting electrode.

[0014] The CoFe2O4 / FeOOH@IF self-supporting electrode is used as an electrocatalyst to electrocatalyze the reduction of nitrate to ammonia.

[0015] Compared with the prior art, this embodiment has the following characteristics:

[0016] I. This invention employs a simple hydrothermal synthesis technique, utilizing ferric nitrate hexahydrate, ferric chloride hexahydrate, urea, and ammonium fluoride dissolved in distilled water to obtain a precursor for a uniformly loaded CoFeOOH@IF self-supporting electrode on foamed iron via a one-step hydrothermal method. Then, through tube furnace calcination, the CoFe2O4 / FeOOH@IF self-supporting electrode was successfully prepared. The preparation process requires only a short time to obtain high-performance self-assembled nanomaterials without the need for complex equipment.

[0017] II. The CoFe2O4 / FeOOH@IF material prepared in this invention is an in-situ grown self-supporting electrode. This in-situ growth strategy overcomes the drawback of traditional powder catalysts requiring binders for coating, preserving the original microstructure of the catalyst, increasing the contact area between the active and reactant substances, and simultaneously increasing the electron conduction rate, thus promoting the electrocatalytic reduction of nitrate. At pH 13, 0.1 mol·L⁻¹ –1 In a KOH and KNO3 electrolyte, the ammonia yield is 15.1 mg / h. -1 cm -2 The Faraday efficiency reaches 97.67%. Therefore, the CoFe2O4 / FeOOH@IF material has excellent application value in the field of electrocatalytic nitrate reduction.

[0018] This invention can obtain a CoFe2O4 / FeOOH@IF self-supporting electrode. Attached Figure Description

[0019] Figure 1 A scanning electron microscope (SEM) schematic diagram of the CoFe2O4 / FeOOH@IF self-supporting electrode prepared in Example 1;

[0020] Figure 2 A scanning electron microscope (SEM) schematic diagram of the CoFe2O4 / FeOOH@IF self-supporting electrode prepared in Example 1;

[0021] Figure 3 A schematic diagram of powder X-ray diffraction of the CoFe2O4 / FeOOH@IF self-supporting electrode prepared in Example 1;

[0022] Figure 4 The CoFe2O4 / FeOOH@IF self-supporting electrode prepared in Example 1 was subjected to 0.1 mol·L⁻¹ –1 KNO3 and KOH solution and 0.1 mol·L –1 Linear sweep voltammetry curves performed in KOH solution;

[0023] Figure 5 The CoFe2O4 / FeOOH@IF self-supporting electrode prepared in Example 1 was subjected to 0.1 mol·L⁻¹ –1 Electrocatalytic synthesis of ammonia was carried out in KNO3 and KOH solutions, and the UV-Vis absorption spectra of ammonia were detected at different voltages.

[0024] Figure 6 The ammonia yield and Faraday efficiency of the CoFe2O4 / FeOOH@IF self-supporting electrode prepared in Example 1 are shown under different voltages. Detailed Implementation

[0025] The technical solutions of this invention are not limited to the specific embodiments listed below. These specific embodiments are merely illustrative and not intended to limit the technical solutions described in the embodiments of this invention. Those skilled in the art should understand that modifications or equivalent substitutions can still be made to this invention to achieve the same technical effects. Any modifications or substitutions that meet the usage requirements are within the protection scope of this invention.

[0026] Specific Implementation Method 1: Preparation method of CoFe2O4 / FeOOH@IF self-supporting electrode, including the following steps:

[0027] 1. Dissolve cobalt nitrate hexahydrate, ferric chloride hexahydrate, urea, and ammonium fluoride simultaneously in distilled water at room temperature, and then stir for a period of time until the solution becomes transparent, resulting in a pink solution.

[0028] The molar ratio of cobalt nitrate to ferric chloride described in step one is 2:(1.0~2.0);

[0029] The molar ratio of cobalt nitrate to ammonium fluoride described in step one is 1:(15.0~20.0);

[0030] The molar ratio of cobalt nitrate to urea described in step one is 1:(3.0-5.0);

[0031] The amount of cobalt nitrate described in step one is in the volume ratio of 1.0 mmol to (20-30) mL of distilled water.

[0032] 2. Cut the foam iron to a size of 2×3cm, and then use acetone and 1 mol·L⁻¹ to... -1 Rinse with sulfuric acid and deionized water for 5-10 minutes each.

[0033] 3. Add the pink reaction solution to the polytetrafluoroethylene (PTFE) reactor, then add the cleaned foamed iron. React in the PTFE reactor at 120℃ for 6 hours. Then allow the PTFE reactor to cool naturally to room temperature. Remove the foamed iron and wash it several times with distilled water and anhydrous ethanol. Finally, place the obtained brown foamed iron in a vacuum drying oven at 60℃ and dry it overnight. Place the dried foamed iron in a tube furnace and heat it at 350℃ for 2 hours under N2 atmosphere. The resulting black foamed iron is the CoFe2O4 / FeOOH@IF self-supporting electrode.

[0034] Compared with the prior art, this embodiment has the following characteristics:

[0035] I. This invention employs a simple hydrothermal synthesis technique, utilizing cobalt nitrate hexahydrate, ferric chloride hexahydrate, urea, and ammonium fluoride dissolved in distilled water to successfully prepare a CoFe₂O₄ / FeOOH@IF self-supporting electrode. This is a one-step hydrothermal method to obtain a uniformly loaded FeOOH and CoFe₂O₄ bicomponent self-supporting electrode precursor on foamed iron. Further calcination in a tube furnace successfully prepares the CoFe₂O₄ / FeOOH@IF self-supporting electrode. The preparation process requires only a short time to obtain high-performance self-assembled nanomaterials without the need for complex equipment.

[0036] II. The CoFe2O4 / FeOOH@IF material prepared in this invention is an in-situ grown self-supporting electrode. This in-situ growth strategy overcomes the drawback of traditional powder catalysts requiring binders for coating, preserving the original microstructure of the catalyst, increasing the contact area between the active and reactant substances, and simultaneously increasing the electron conduction rate, thus promoting the electrocatalytic reduction of nitrate. At pH 13, 0.1 mol·L⁻¹ –1 In a KOH and KNO3 electrolyte, the ammonia yield is 15.1 mg / h. -1 cm -2 The Faraday efficiency reaches 97.67%. Therefore, the CoFe2O4 / FeOOH@IF material has excellent application value in the field of electrocatalytic nitrate reduction.

[0037] This invention can obtain a CoFe2O4 / FeOOH@IF self-supporting electrode.

[0038] Specific Implementation Method Two: The difference between this implementation method and Specific Implementation Method One is that the molar ratio of cobalt nitrate to ferric chloride is 2:1. All other steps are the same as in Specific Implementation Method One.

[0039] Specific Implementation Method Three: The difference between this implementation method and one of Specific Implementation Methods One or Two is that the molar ratio of cobalt nitrate to ammonium fluoride is 1:20. The other steps are the same as in Specific Implementation Method One or Two.

[0040] Specific Implementation Method Four: The difference between this implementation method and one of Specific Implementation Methods One to Three is that the molar ratio of cobalt nitrate to urea is 1:5. The other steps are the same as those in Specific Implementation Methods One, Two, or Three.

[0041] Specific Implementation Method Five: The difference between this implementation method and one of Specific Implementation Methods One to Four is that the amount of cobalt nitrate and the volume ratio of distilled water are 1 mmol: 20 mL. The other steps are the same as in Specific Implementation Methods One to Four.

[0042] Specific Implementation Method Six: In this implementation method, the black foamed iron obtained is CoFe2O4 / FeOOH@IF self-supporting electrode, which is directly used as the working electrode to electrocatalyze the reduction of nitrate to ammonia.

[0043] At pH = 13, 0.1 mol·L⁻¹ –1 In KOH and KNO3 solution, the ammonia yield is 15.1 mg / h. -1 cm -2 The Faraday efficiency reached 97.67%.

[0044] The beneficial effects of the present invention are verified using the following embodiments:

[0045] Example 1: The preparation method of the CoFe2O4 / FeOOH@IF self-supporting electrode is carried out according to the following steps:

[0046] 1. Dissolve cobalt nitrate hexahydrate, ferric chloride hexahydrate, 6.25 mmol urea and 25 mmol ammonium fluoride simultaneously in 25 mL of distilled water, and then stir the solution at room temperature for a period of time until the solution becomes clear.

[0047] 2. Cut the foam iron to a size of 2×3cm, and then use acetone and 1 mol·L⁻¹ to... –1 Rinse with sulfuric acid and deionized water for 5-10 minutes each.

[0048] 3. Add the pink reaction solution to the polytetrafluoroethylene (PTFE) reactor, then add the cleaned foamed iron. React in the PTFE reactor at 120℃ for 6 hours. Then allow the PTFE reactor to cool naturally to room temperature. Remove the foamed iron and wash it several times with distilled water and anhydrous ethanol. Finally, place the obtained brown foamed iron in a vacuum drying oven at 60℃ and dry it overnight. Place the dried foamed iron in a tube furnace and heat it at 350℃ for 2 hours under N2 atmosphere. The resulting black foamed iron is the CoFe2O4 / FeOOH@IF self-supporting electrode.

[0049] The CoFe2O4 / FeOOH@IF self-supporting electrode prepared in Example 1 was subjected to scanning electron microscopy (SEM) testing, and the SEM image of the CoFe2O4 / FeOOH@IF self-supporting electrode prepared in Example 1 was obtained.

[0050] Figure 1 This is a scanning electron microscope (SEM) schematic diagram of the CoFe2O4 / FeOOH@IF self-supporting electrode prepared in Example 1.

[0051] Depend on Figure 1 It can be seen that the CoFe2O4 / FeOOH composite material prepared in Example 1 is uniformly and densely distributed on the foamed iron.

[0052] Figure 2 This is a scanning electron microscope (SEM) schematic diagram of the CoFe2O4 / FeOOH@IF self-supporting electrode prepared in Example 1.

[0053] Depend on Figure 2 It can be seen that the CoFe2O4 / FeOOH@IF material prepared in Example 1 has a polyhedral morphology and uniformly distributed pores.

[0054] X-ray powder diffraction (PXRD) was performed on the CoFe2O4 / FeOOH@IF self-supporting electrode prepared in Example 1, and the X-ray powder diffraction pattern of the CoFe2O4 / FeOOH@IF self-supporting electrode prepared in Example 1 was obtained, as shown below. Figure 3 As shown.

[0055] Figure 3 This is a schematic diagram of powder X-ray diffraction of the CoFe2O4 / FeOOH@IF self-supporting electrode sheet prepared in Example 1.

[0056] Figure 3In the diagram, 1 represents the diffraction peak of the CoFe₂O₄ standard card, corresponding to standard card number 22-1068. The diffraction peaks 2θ = 18.29°, 30.08°, 35.44°, 37.06°, 43.06°, 53.45°, 56.97°, 62.59°, 65.75°, 74.00°, 78.97°, 81.93°, and 86.77° point to the (111), (220), (311), (222), (400), (422), (511), (440), (531), (533), (444), (551), and (642) crystal planes of the CoFe₂O₄ phase. 2 represents the diffraction peak of the FeOOH standard card, corresponding to standard card number 34-1266. The diffraction peaks 2θ = 26.73°, 34.00°, 35.16°, 39.22°, 52.05°, and 55.09° point to the (310), (400), (211), (301), (600), and (620) crystal planes of the FeOOH phase. Peak 3 is the actual diffraction peak of the CoFe2O4 / FeOOH@IF self-supporting electrode, which is consistent with the peak positions of the standard cards of CoFe2O4 and FeOOH. It can be confirmed that the material obtained in the experiment is the CoFe2O4 / FeOOH@IF self-supporting electrode composed of CoFe2O4, FeOOH, and IF, and the material has high purity.

[0057] Linear sweep voltammetry was performed on the CoFe2O4 / FeOOH@IF self-supporting electrode prepared in Example 1, and the linear sweep voltammetry curve of the CoFe2O4 / FeOOH@IF self-supporting electrode prepared in Example 1 was obtained, as shown in the figure. Figure 4 As shown;

[0058] from Figure 4 It can be seen that the CoFe2O4 / FeOOH@IF self-supporting electrode prepared in Example 1 was effective at 0.1 mol·L⁻¹. -1 KNO3 and KOH solution, 0.1 mol·L -1 Linear sweep voltammetry curves of KOH solution showed that, within the same voltage range, the reduction current density of CoFe2O4 / FeOOH@IF in nitrate-containing electrolyte was significantly higher than that in electrolyte without nitrate, indicating that the CoFe2O4 / FeOOH@IF catalyst has good electrocatalytic ability to reduce nitrate to ammonia.

[0059] Figure 5 The image shows a CoFe₂O₄ / FeOOH@IF self-supporting electrode at 0.1 mol·L⁻¹. -1 The ammonia synthesis reaction is carried out in KNO3 and KOH solutions. The UV-Vis absorption spectra at different voltages are shown below. Figure 5As shown, with the increase of voltage, the absorbance of the electrolyte that underwent color development after the catalytic test also gradually increased with the voltage in the absorbance test.

[0060] Figure 6 The image shows a CoFe₂O₄ / FeOOH@IF self-supporting electrode at 0.1 mol·L⁻¹. -1 The ammonia synthesis reaction is carried out in KNO3 and KOH solutions, and the ammonia yield and Faraday efficiency are plotted under different voltages. Figure 6 As shown, at a potential of -0.74V vs. RHE, the best Faraday efficiency of 97.67% is achieved, corresponding to an ammonia production of 15.1 mg h⁻¹. –1 cm –2 The CoFe2O4 / FeOOH@IF self-supporting electrode exhibits excellent performance in the electrocatalytic reduction of nitrate. Therefore, it can serve as a highly efficient electrocatalytic catalyst for the reduction of nitrate to ammonia.

[0061] In summary, the CoFe2O4 / FeOOH@IF electrocatalytic self-supporting material prepared in Example 1 has a strong ability to reduce nitrate under alkaline conditions, making it a high-performance electrocatalyst with excellent application potential for catalytic reduction of nitrate to ammonia.

Claims

1. A method for the preparation of a high-efficiency electrocatalytic synthesis of ammonia CoFe2O4 / FeOOH@IF self-supporting electrode, characterized by The method comprises the following steps: I. Dissolve cobalt nitrate hexahydrate, ferric chloride hexahydrate, urea and ammonium fluoride into distilled water at room temperature, and then stir until the solution is transparent to obtain a pink solution; The molar ratio of cobalt nitrate to ferric chloride in step I is 2: (1.0-2.0); The molar ratio of cobalt nitrate to ammonium fluoride in step I is 1: (15.0-20.0); The molar ratio of cobalt nitrate to urea in step I is 1: (3.0-5.0); The volume ratio of the amount of substance of cobalt nitrate to distilled water in step I is 1.0 mmol: (20-30) mL; II. The foamed iron was cut into 2 x 3 cm size, and sequentially cleaned with acetone, 1 mol / L HCl, 1 mol / L NaOH, and deionized water for 5-10 min each. -1 sulfuric acid and deionized water for 5-10 min each. III. Add the pink solution into a polytetrafluoroethylene reaction kettle, then add the cleaned foamed iron, react in the polytetrafluoroethylene reaction kettle at a temperature of 120 ℃ for 6 h, then naturally cool the polytetrafluoroethylene reaction kettle to room temperature, take out the foamed iron, and wash with distilled water and anhydrous ethanol for multiple times, finally dry the obtained brown foamed iron in a 60 ℃ vacuum drying oven overnight; place the dried foamed iron in a tube furnace, heat at 350 ℃ under N2 atmosphere for 2 h, and the obtained black foamed iron is a CoFe2O4 / FeOOH@IF self-supporting electrode.

2. The preparation method of the high-efficiency electrocatalytic synthesis ammonia CoFe2O4 / FeOOH@IF self-supporting electrode according to claim 1, characterized in that The molar ratio of cobalt nitrate to ferric chloride in step I is 2:

1.

3. The method for preparing a high-efficiency electrocatalytic synthesis ammonia CoFe2O4 / FeOOH@IF self-supporting electrode according to claim 1, characterized in that The molar ratio of cobalt nitrate to ammonium fluoride in step I is 1:

20.

4. The method for preparing a high-efficiency electrocatalytic synthesis ammonia CoFe2O4 / FeOOH@IF self-supporting electrode according to claim 1, characterized in that The molar ratio of cobalt nitrate to urea in step I is 1:

5.

5. The method according to claim 1, wherein the method is characterized by The volume ratio of the amount of substance of cobalt nitrate to distilled water in step I is 1 mmol: 20 mL.

6. Use of the CoFe204 / FeOOH@IF self-supporting electrode according to claim 1, characterized in that The catalyst CoFe2O4 / FeOOH@IF directly acts as a working electrode to electrocatalytically reduce nitrate to ammonia.

Images