A high-efficiency electrocatalyst for reducing nitrate, a preparation method and applications thereof

Abstract

The application belongs to the technical field of environmental engineering and electrocatalyst, and discloses a high-efficiency electrocatalyst for reducing nitrate, a preparation method and application of the high-efficiency electrocatalyst x ·CeO y , and a large specific surface area of FeS x and CeO y heterojunction on the surface of the compound. The preparation method is a two-step hydrothermal synthesis method, the ratio of elements such as cerium, iron and sulfur and the process are controlled, the obtained compound has a unique microstructure of a catalyst, has excellent activity of electro-reducing nitrate to ammonia, has the best catalytic selectivity for ammonia, can greatly increase electron transfer, regulation and surface adsorption, effectively improves the efficiency and yield of conversion of nitrate to ammonia, and can be widely applied to environmental engineering.

Description

Technical Field

[0001] This invention relates to the fields of environmental engineering and electrocatalyst technology, specifically to a highly efficient electrocatalyst for reducing nitrates, its preparation method, and its application. Background Technology

[0002] Nitrates mainly originate from industrial wastewater and nitrogen oxides from vehicle exhaust that combine with water to form nitrate pollutants. Large amounts of nitrate pollutants entering rivers can be absorbed by the human body, impacting health. Collecting nitrates from wastewater and directly reducing them to ammonia and other high-value compounds using electricity and light energy as catalysts has pointed scientists in the right direction. In particular, electrocatalytic reduction of nitrates to ammonia, compared to the traditional high-temperature, high-pressure Habor-Bosch method, utilizes other clean power generation methods such as wind and tidal energy to form a series circuit, enhancing energy storage efficiency. This method offers milder and more controllable conditions, reduces carbon emissions, achieves a sustainable nitrogen cycle, and turns waste into treasure. Transition metals like copper and cobalt, due to their unique d-block electronic structure, are considered promising catalysts for the electrocatalytic reduction of nitrates to ammonia. However, these catalysts still suffer from low catalytic efficiency, poor activity, poor stability, and a lack of variety. Researchers are continuously modifying them, such as forming bimetallic, oxide, metal-organic framework, and single-atom catalysts, to achieve efficient nitrogen cycling and turn waste into treasure.

[0003] Composite catalysts refer to catalysts composed of two or more substances. Due to their unique heterostructures, they can modulate the physicochemical or structural properties of their interfaces (surface reconstruction, crystal strain, electronic structure modulation, electron transfer capacity, etc.) and thus exhibit better catalytic activity. In contrast, heterojunction catalysts have been less frequently reported as electrocatalysts for the electrocatalytic reduction of nitrate to ammonia to produce nitrogen. For example, Cheng et al. [1] A CuO / Mn2O3 heterojunction catalyst was synthesized. This catalyst has a large specific surface area, and the interface can accelerate electron transfer, thereby accelerating the adsorption of nitrate and the desorption of ammonia. (Li's research group) [2] A two-dimensional CuO / Fe3O4 heterojunction nanoarray was reported. The heterojunction interface improved electron transfer and enhanced the adsorption of nitrate and protons, exhibiting excellent electrocatalytic reduction of nitrate to ammonia. These results indicate that heterojunction catalysts significantly alter reactant adsorption, reactant activation, intermediate transformation, interfacial electron transfer, and product desorption at the interface, thereby affecting the kinetics, reaction pathway, and related reaction mechanisms of the nitrate electrocatalytic reduction reaction. However, such catalysts suffer from several drawbacks, including complex operation, difficulty in industrial scale-up, high catalytic cost, and poor conductivity. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of the prior art by providing a highly efficient electrocatalyst for reducing nitrates, its preparation method, and its application. By simultaneously improving the raw material components, ratios, and preparation process, the product is controlled to possess a unique FexSy / CeO2 heterogeneous interface and microstructure. Based on this heterogeneous interface effect and microstructure, electron transfer, regulation, and surface adsorption are significantly increased, effectively improving the efficiency and yield of nitrate conversion to ammonia, thereby solving the aforementioned technical problems.

[0005] To achieve the above objectives, the technical solution provided by this invention is as follows:

[0006] A highly efficient electrocatalyst for reducing nitrates is characterized by being a sheet-like compound FeSx·CeOy synthesized from cerium oxide and ferric sulfide. The surface of this compound exhibits numerous nanoscale micro-wrinkles and porous, large specific surface area FeSx and CeOy heterogeneous interfaces, where x and y represent non-stoichiometric and mesophase structures. The average size of the sheet-like compound FeSx·CeOy is 100-200 nm, and Fe, S, Ce, and O elements are uniformly distributed on the surface of the compound, forming numerous active sites.

[0007] A method for preparing a highly efficient electrocatalyst for reducing nitrates, characterized by a two-step synthesis, wherein cerium salt and iron salt are dissolved separately in a solvent, and fed in a cerium to iron molar ratio of (0.2-5):1. The composition, ratio, and microstructure of the resulting compound are controlled by a predetermined order of addition, reaction time, reaction temperature, and post-catalyst drying conditions, ultimately yielding the plate-like compound FeSx·CeOy. The method includes the following steps:

[0008] S1: Synthesis of cerium oxide

[0009] Cerium salt is dissolved in water to form solution A, and alkali is dissolved in solvent to form solution B. Solution B is slowly added dropwise to solution A under continuous magnetic stirring until it is completely added, and then stirring is continued to obtain a mixture. The mixture is then transferred to a hydrothermal reactor and reacted at 50~150℃. After cooling, the solid and liquid are separated. The solid reactants are washed by centrifugation multiple times with common solvents and then freeze-dried to obtain cerium oxide CeOy powder.

[0010] S2: Preparation of iron and sulfur source solutions

[0011] The iron source was first dissolved in an organic solvent to obtain iron source solution C; the sulfur source was then dissolved in the same organic solvent to obtain sulfur source solution D.

[0012] S3: Synthesis catalyst

[0013] According to the volume ratio of (0.2-5):1, liquid C and liquid D were added to the reaction vessel, stirred, and the temperature was controlled for continuous reaction for 24 h. After cooling, the resulting suspension was transferred to a hydrothermal reactor. Then, cerium oxide CeOy powder prepared in step S1 was added according to the molar ratio of cerium oxide and ferric sulfide (0.2-5):1. The reaction was carried out under solvothermal reaction conditions of 50~150℃ for 24 h. After cooling, solid-liquid separation was performed. The particles were washed by centrifugation multiple times with organic and inorganic solvents. After vacuum drying, the catalyst FeSx·CeOy was obtained.

[0014] The application of a highly efficient electrocatalyst for reducing nitrate in the electrocatalytic reduction of nitrate to ammonia.

[0015] Compared with the prior art, the present invention has at least the following beneficial effects:

[0016] 1. The highly efficient electrocatalyst for reducing nitrate, its preparation method, and its application provided by this invention, through simultaneous improvement of raw material components, ratios, and preparation processes, controls the product to possess a unique FeSx / CeOy heterojunction interface and microstructure. Furthermore, based on this heterojunction interface effect and microstructure, electron transfer, regulation, and surface adsorption are significantly increased. This novel heterojunction catalyst, due to its formation, enhances electron transfer, regulation, and surface adsorption through interface effects, thereby efficiently promoting the activity and selectivity of the electroreduction of nitrate to ammonia, effectively improving the efficiency and yield of nitrate conversion to ammonia, thus solving many problems existing in current technologies.

[0017] 2. The high-efficiency electrocatalyst preparation method provided by this invention employs a controlled two-step method to synthesize a catalyst with a heterojunction interface. First, cerium oxide is synthesized, followed by the reduction of iron salts to form FeSx using a suitable ratio of sulfur source. Then, by adjusting the iron-cerium ratio, a high-efficiency heterojunction catalyst is formed in a hydrothermal reactor. The process is simple, easy to control, and uses inexpensive and readily available raw materials. The prepared catalyst exhibits excellent activity and selectivity, which is of great significance for the effective utilization of nitrate to ammonia conversion. Furthermore, the preparation process is simple, easy to synthesize, and uses inexpensive and readily available raw materials, making it easy to promote and apply industrially.

[0018] 3. When the high-efficiency electrocatalyst provided by this invention is applied to the electrochemical reduction of nitrate, actual tests show that it has the best catalytic selectivity for ammonia, with a selectivity of 91% at -0.5 V and a maximum ammonia yield of 753 μg·h-1·mg-1, which is much higher than that of single-component catalysts. Its performance is also leading among current catalysts, and it has good application prospects. Attached Figure Description

[0019] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0020] Figure 1 This is a schematic diagram of the process for preparing the FeSx·CeOy catalyst according to an embodiment of the present invention;

[0021] Figure 2 Scanning electron microscope image and elemental distribution diagram of the FeSx·CeOy catalyst with heterogeneous interface prepared in Example 1 of this invention;

[0022] Figure 3 This is a schematic diagram of the transmission electron microscopy analysis of the FeSx·CeOy catalyst prepared in Example 1 of the present invention, wherein (a) is a high-resolution transmission electron microscopy image, (b) is a selected area electron diffraction image, and (c) is a high-angle annular dark-field scanning transmission electron microscopy image and the corresponding energy-dispersive X-ray (EDS) elemental mapping image.

[0023] Figure 4 X-ray diffraction patterns of the FeSx·CeOy catalyst and FeSx or CeOy catalyst prepared in the embodiments of the present invention;

[0024] Figure 5 The excellent catalytic activity of the FeSx·CeOy catalyst prepared in Example 1 of this invention was demonstrated by linear sweep voltammetry.

[0025] Figure 6 This is a schematic diagram comparing the selectivity and ammonia production rate of the FeSx·CeOy catalyst prepared in Example 1 of this invention with those of single CeOy and FeSx catalysts, wherein (a) is the FeSx catalyst. x CeO y Catalyst, (b) is CeO y Catalyst, (c) is FeS x catalyst;

[0026] Figure 7 These are FeS prepared in different proportions according to embodiments of the present invention. x CeO y A schematic diagram comparing ammonia selectivity and ammonia yield at a Fe:Ce atomic ratio of -0.5V in the catalyst. Detailed Implementation

[0027] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments, so that those skilled in the art can implement it based on the description.

[0028] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0029] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0030] Basic Implementation

[0031] See appendix Figures 1 to 7 The highly efficient electrocatalyst for reducing nitrates provided in this embodiment is characterized by being a plate-like compound FeS synthesized from cerium oxide and iron sulfide. x CeO y The surface of this compound exhibits numerous nanoscale micro-wrinkles and porous FeS with a large specific surface area. x and CeO y Heterogeneous interface, where x and y represent non-stoichiometric and intermediate phase structures, and their values ​​are not integers (but can be approximated as integers), specifically determined by the components, concentrations, and reaction process conditions of the feed. For example, x can take values ​​between 1 and 5, and y can take values ​​between 1.5 and 2; the plate-like compound FeS x CeO y The average size is 100-200 nm, and Fe, S, Ce and O elements are uniformly distributed on the surface of the compound, forming a large number of active sites.

[0032] A method for preparing the aforementioned highly efficient electrocatalyst for reducing nitrates involves a two-step synthesis. Cerium and iron salts are dissolved separately in a solvent, and then added at a cerium to iron molar ratio of (0.2-5):1. By controlling the order of addition, reaction time, reaction temperature, and post-catalyst drying conditions, the composition, proportion, and microstructure of the resulting compound are determined, ultimately yielding the plate-like compound FeS. x CeO y It includes the following steps:

[0033] S1: Synthesis of cerium oxide

[0034] Cerium salt was dissolved in water to form solution A, and alkali was dissolved in a solvent to form solution B. Solution B was slowly added dropwise to solution A under continuous magnetic stirring until all the solution was added, followed by continued stirring to obtain a mixture. The mixture was then transferred to a hydrothermal reactor and reacted at 50–150°C. After cooling, the solid and liquid phases were separated. The solid reactants were washed repeatedly by centrifugation using a common solvent and then freeze-dried to obtain cerium oxide (CeO). y Particles; specifically:

[0035] S1-1 dissolves cerium salt in water to form solution A with a concentration of 0.05 M-1.15 M;

[0036] The cerium salt mentioned is one of cerium chloride, cerium sulfate, and cerium nitrate;

[0037] S1-2 Dissolve sodium hydroxide in water to form solution B with a concentration of 1 M-20 M;

[0038] S1-3 Under continuous magnetic stirring at 1600 rpm, solution B is slowly added dropwise to solution A until it is completely added, and then stirring is continued for 20-40 min to obtain a mixture.

[0039] S1-4 The mixture is transferred to a hydrothermal reactor and reacted at 50~150℃ for 10~24 h, then cooled to room temperature to separate the solid and liquid.

[0040] The solid reactants separated from S1-5 were centrifuged, washed, and freeze-dried using conventional solvents to obtain cerium oxide CeOy powder with a porous needle-like structure and a size of 20-50 nm.

[0041] The conventional solvents mentioned include inorganic solvents and organic solvents; inorganic solvents include water, and organic solvents include acetone, ethanol, methanol, etc.

[0042] S2: Preparation of iron and sulfur source solutions

[0043] The iron source was fed into an organic solvent at a molar ratio of Fe:Ce = (0.2-5):1, resulting in solution C. Separately, the sulfur source was dissolved in the same organic solvent to obtain solution D. Specifically:

[0044] S2-1 dissolves the iron source in an organic solvent to obtain an iron source solution C with a concentration of 0.05 M-2.5 M;

[0045] S2-2 Sulfur source solution D with a concentration of 0.03 M-13.31 M was obtained by dissolving the sulfur source in the same organic solvent;

[0046] The iron source is one of ferric sulfate, ferric nitrate, and ferric chloride.

[0047] The organic solvent is one of dimethyl sulfoxide, cyclohexane, ethylene glycol, and dimethylformamide;

[0048] The sulfur source is one of thioacetamide, thiourea, sodium sulfide, or sodium thiosulfate.

[0049] S3: Synthesis catalyst

[0050] Liquid C and liquid D were added to the reaction vessel at a volume ratio of (0.2-5):1, stirred, and reacted at a controlled temperature for 24 hours. After cooling, the resulting suspension was transferred to a hydrothermal reactor. Then, cerium oxide (CeOy) particles prepared in step S1 were added at a molar ratio of cerium oxide to ferric sulfide (0.2-5):1. The reaction was carried out under solvothermal conditions at 50-150℃ for 24 hours. After cooling, solid-liquid separation was performed. The particles were washed multiple times by centrifugation with organic and inorganic solvents. After vacuum drying, the catalyst FeSx·CeOy was obtained, specifically:

[0051] S3-1: Add liquid C and liquid D to a glass container at a volume ratio of (0.2-5):1, stir and mix continuously for 5 min, add an appropriate amount of organic solvent, stir for another 5 min, and then transfer the reaction solution to an oil bath.

[0052] S3-2: The reaction was carried out for 24 hours with continuous stirring within a temperature range of 70-120 ℃, and then cooled to room temperature to obtain a suspension.

[0053] S3-3: Transfer all the obtained suspension to a hydrothermal reactor, and add the cerium oxide CeOy particles prepared in step S1 according to the molar ratio of cerium oxide and ferric sulfide (0.25-5):1. React under solvothermal reaction conditions of 50~150℃ for 24 h, and then perform solid-liquid separation after cooling to room temperature.

[0054] S3-4: The solid reactants were washed repeatedly by centrifugation with organic and inorganic solvents, and then thoroughly dried in a vacuum drying oven to obtain the catalyst FeSx·CeOy.

[0055] Application of a highly efficient electrocatalyst for reducing nitrates in the electrocatalytic reduction of nitrates to ammonia.

[0056] The following is in conjunction with the appendix Figure 1-7 The present invention will be further described in detail with reference to several specific embodiments.

[0057] Example 1

[0058] The present invention provides a highly efficient electrocatalyst for reducing nitrates, its preparation method, and its application, which is a concretization of the aforementioned basic embodiment. The provided highly efficient catalyst is FeSx·CeOy, where x and y are determined by the sum of the contributions of each compound. In this embodiment, the Fe:Ce molar ratio is 3:1. Fe loss and Ce residue are controlled during the reaction. The final solid sample of the catalyst is subjected to ICP analysis for composition and acid solubility. The results show that the final product has a Fe:Ce molar ratio of approximately 2.5:1, including four specific compound forms: FeS2, FeS, CeO2, and Ce2O3. FeSx / CeOy composite heterojunctions are formed between these four compounds. The molar ratio of the four compounds is approximately FeS2:FeS = 2:1, CeO2:Ce2O3 = 1:1, and their equivalent molecular formula is approximately 2FeS2·FeS·CeO2·Ce2O3. The charge balance is achieved through Fe²⁺ and Ce²⁺. 4 The synergistic effect of FeS2 / Ce³⁺ and S²⁻ / O²⁻ is achieved. In the final catalyst product, the overall molar ratio of the four compounds is approximately FeS2:FeS:CeO2:Ce2O3 = 4 : 2 : 2 : 2.

[0059] See appendix Figure 1 The components, formulation, and preparation method for the catalyst of this invention are as follows:

[0060] Step 1: Dissolve 0.88g of cerium nitrate hexahydrate in 20ml of deionized water (to obtain solution A), and dissolve 8.44g of NaOH in 15ml of deionized water (to obtain solution B). Add solution B to solution A and slowly add solution B dropwise under continuous magnetic stirring until it is completely added. Stir for another 30 minutes to obtain a mixture. Then transfer the entire mixture to a hydrothermal reactor and react at 100℃ for 24 hours. After cooling, wash the mixture multiple times with deionized water and anhydrous ethanol by centrifugation, and freeze-dry for 12 hours to obtain CeO2.

[0061] See appendix Figure 6 The synthesized CeO2 was a white powder with a size of about 20-50 nm, and SEM showed that it had a porous needle-like microstructure.

[0062] Step 2: Dissolve 1.1g of ferric nitrate nonahydrate in 5ml of DMF, and 2.04g of thioacetamide in 10ml of DMF. Mix 3.2ml of the prepared ferric nitrate solution and 8ml of the thioacetamide solution in a 50ml beaker, then add 30ml of DMF and stir for 10min. Transfer the mixture to an oil bath at 90℃ and react for 24h with continuous stirring. After cooling to room temperature, transfer the resulting suspension to a hydrothermal reactor and add 100mg of CeO2. React at 180℃ for 24h. After cooling, wash the mixture multiple times with deionized water and anhydrous ethanol by centrifugation, and then vacuum dry at 60℃ for 12h in a vacuum drying oven to obtain the FeSx·CeOy catalyst with an equivalent molecular formula of approximately 2FeS2·FeS·CeO2·Ce2O3.

[0063] See appendix Figure 2 , Figure 3 The catalyst with the equivalent molecular formula approximately 2FeS2·FeS·CeO2·Ce2O3 consists of nanosheets with a size of 100-200 nm. The surface of this compound exhibits numerous nanoscale micro-wrinkles and porous, large specific surface area FeSx and CeOy heterogeneous interfaces. The average size of the sheet-like compound 2FeS2·FeS·CeO2·Ce2O3 is 100-200 nm, with Fe, S, Ce, and O elements uniformly distributed on the surface, forming a large number of active sites. This microstructured iron sulfide increases its specific surface area. EDS scanning shows that the distribution of Fe, S, Ce, and O elements on the catalyst is relatively uniform, indicating good interaction and a large number of active sites, which is beneficial for improving catalytic efficiency.

[0064] have Figure 3 (a) High-resolution transmission electron microscopy (HRTEM) images show that adjacent lattice spacings of 0.311 nm and 0.289 nm correspond to the (111) crystal plane of FeSx and the (200) crystal plane of CeOy, respectively, indicating abundant interfaces between FeSx and CeOy. The synthesized FeSx·CeOy electrocatalyst exhibits large-area contact between FeSx and CeOy heterojunctions, which can serve as key active sites for eNO3RR, promoting the reaction. Figure 3 (b) Selected area electron diffraction (SED) of the FeSx·CeOy sample revealed the polycrystalline characteristics of the FeSx·CeOy catalyst, with reflections at 3.03 and 3.33 nm⁻¹ from the (111) and (200) spectral densities of FeSx and CeOy, respectively, consistent with the X-ray diffraction pattern and high-resolution transmission electron microscopy (HRTEM) image. High-angle annular dark-field (HADDF) images and corresponding elemental analyses (… Figure 3 c) Prove that Fe and Ce elements are uniformly distributed in the sample.

[0065] The preparation method provided in this invention is simple to operate, and the catalyst prepared can efficiently improve the selectivity of electroreduction of nitrate to ammonia.

[0066] During the preparation of each solution, the alkaline solution used for the synthesis of cerium oxide and the organic solution of the sulfur source must be freshly prepared and used immediately. Aqueous solutions of cerium salts and organic solutions of iron salts, etc., can be prepared in advance.

[0067] Electrode preparation: Using carbon paper as a carrier, weigh 2-10 mg of the FeSx·CeOy catalyst prepared by the above two-step method into a centrifuge tube, add 100-500 μL of organic solvent and 20-100 μL of Nafion solution, and then perform ultrasonic dispersion; take 50-100 μL of the uniformly dispersed catalyst solution, drop it evenly onto the carbon paper, and then dry it under an infrared lamp for later use.

[0068] Electrochemical reduction of nitrate to ammonia performance was assessed using an electrochemical workstation with a three-electrode system. A graphite rod was used as the counter electrode, and Ag / AgCl was used as the reference electrode. Linear sweep voltammetry and a 1.5-h current-time electrolysis test were performed in 0.1M KOH + 0.1M KNO3 electrolyte. The ammonia product was detected using the indophenol blue method, allowing for the quantitative determination of the Faradaic efficiency and ammonia yield.

[0069] In this embodiment, the indophenol blue method was used to detect the Faraday efficiency of ammonium ions, and the results were comparable to those of other reported ammonia detection methods. The specific steps are as follows:

[0070] 1) Determination of ammonium ion standard curve: Prepare a 10 μg·mL-1 ammonium ion standard solution, dissolve 0.3146g of ammonium chloride in a 100 mL volumetric flask, and then dilute it 100 times to obtain the target standard solution.

[0071] 2) Preparation of a series of gradient standard solutions: Take samples from the standard solution in increments of 20 μL, from 20 μL to 200 μL, add them to a 15 mL sample tube, and dilute with the corresponding electrolyte to 2 mL, to a standard solution of 0.1, 0.2, and 1 µg·mL⁻¹ ammonium ions.

[0072] 3) Preparation of the colorimetric reagent: The colorimetric reagent for the indophenol blue method requires the use of solutions A1, B1, and C1 together.

[0073] Solution A1: Dissolve 5g of salicylic acid, 5g of trisodium citrate trihydrate, and 4g of sodium hydroxide in deionized water, and dilute to 100mL in a volumetric flask.

[0074] Solution B1: Transfer 8.9 mL from a 4% available chlorine sodium hypochlorite solution and dilute to a 100 mL volumetric flask with deionized water.

[0075] Solution C1: Weigh 0.25 g of sodium nitrosoferricyanide dihydrate and dilute to 25 mL in a volumetric flask with deionized water.

[0076] 4) Colorimetric Reaction: Add 4 mL of colorimetric solution A and 2 mL of colorimetric solution C1 to 4 mL of blank electrolyte, then add 400 μL of colorimetric solution C1 to prepare a blank control sample. Add 2 mL of colorimetric solution A, 1 mL of colorimetric solution B1, and 200 μL of colorimetric solution C1 to 2 mL of the standard ammonium ion solution to be tested. Incubate at room temperature in the dark for 1 h, and perform wavelength scanning using a UV-Vis spectrophotometer with a scan width of 800 nm to 500 nm. The maximum absorption wavelength of ammonia is 655 nm. Based on the obtained data, construct a standard concentration curve. Calculate the ammonia content in the test sample solution using the linearly fitted standard curve to obtain the Faraday efficiency and ammonia yield of the reaction.

[0077] Ammonia Faraday efficiency and yield are calculated using the following formula:

[0078]

[0079] Where N is the number of electrons transferred to produce 1 mol of ammonia, F is the Faraday constant, t is the reaction time, n is the amount of ammonia produced, j is the current magnitude, V is the electrolyte volume, A is the electrode area, and is the concentration of ammonia produced.

[0080] See Figures 6-7 This catalyst exhibits excellent electrocatalytic properties. Verification of the synthesized catalyst with the equivalent molecular formula approximately 2FeS2·FeS·CeO2·Ce2O3 showed excellent activity in the electroreduction of nitrate to ammonia. The steps were as follows: In 0.1 M KOH solution, linear sweep voltammetry confirmed that the catalyst possessed good catalytic activity (compared to a single catalyst) (results are shown in...). Figure 4 In the electrocatalytic reduction of potassium nitrate in 0.1 M KOH solution at -0.4 V to -0.8 V (vs. RHE), it exhibits the best catalytic selectivity for ammonia, with a selectivity of 91% at -0.5 V and a maximum ammonia yield of 753 μg·h⁻¹·mg⁻¹, which is far superior to the performance of single-component catalysts and ranks among the top in performance of catalysts reported to date.

[0081] from Figure 4The X-ray diffraction patterns in the samples show that the FeSx sample clearly corresponds well with PDF# 42-1340, with the (110), (111), (200), and (210) crystal planes clearly visible, confirming that it is a FeSx sample. In the CeOy sample, 28.8°, 33.3°, 47.7°, and 56.5° belong to the (111), (200), (220), and (311) crystal planes, respectively, indicating that the CeOy phase is the main component, corresponding to standard card PDF# 34-0394. In addition to the above crystal planes, the XRD patterns of FeSx·CeOy also show the (100) and (102) crystal planes of FeS, which may be due to the formation of other iron-sulfur compounds during crystal growth.

[0082] Example 2

[0083] The efficient electrocatalyst for reducing nitrates, its preparation method, and its application provided by this invention are basically the same as those in the examples. The difference lies in that, based on Example 1, the composition and concentration of solutions A, B, C, and D are changed accordingly. The cerium salt is cerium chloride, the iron source is ferric chloride, and the sulfur source is thiourea. The organic solvent is dimethyl sulfoxide, and the feed is carried out according to a Fe:Ce molar ratio of 1:1. The content distribution of the four compounds in the prepared efficient catalyst FeSx·CeOy is different, and the specific FeSx / CeOy composite heterointerface formed in the end is slightly different.

[0084] In the final product of the catalyst, the overall molar ratio of the four compounds is approximately FeS2:FeS:CeO2:Ce2O3 = 10:5:6:6. If the reaction conditions are adjusted, catalysts with other overall molar ratios can also be obtained (the proportion of each element in the whole will change), but the ratios of FeS2:FeS = 2:1 and CeO2:Ce2O3 = 1:1 in the product will remain unchanged.

[0085] Example 3

[0086] The efficient electrocatalyst for reducing nitrates, its preparation method, and its application provided by this invention are basically the same as those in the examples. The difference lies in that, based on Example 1, the composition and concentration of solutions A, B, C, and D are changed accordingly; the cerium salt is cerium sulfate; the iron source is ferric sulfate; the sulfur source is sodium sulfide; the organic solvent is cyclohexane; and the feed is carried out according to a Fe:Ce molar ratio of 1:3. The content distribution of the four compounds in the prepared efficient catalyst FeSx·CeOy is different, and the specific FeSx / CeOy composite heterointerface formed in the end is slightly different.

[0087] In the final product of the catalyst, the overall molar ratio of the four compounds is approximately FeS2:FeS:CeO2:Ce2O3 = 10:5:6:6.

[0088] Example 4

[0089] The efficient electrocatalyst for reducing nitrates, its preparation method, and its application provided by this invention are basically the same as those in the examples. The difference lies in that, based on Example 1, the composition and concentration of solutions A, B, C, and D are changed accordingly. The feed is carried out according to the Fe:Ce molar ratio of 1:5, the cerium salt is cerium sulfate, the iron source is ferric sulfate, the sulfur source is sodium thiosulfate, and the organic solvent is ethylene glycol. In the final catalyst product, the overall molar ratio of the four compounds is approximately FeS2:FeS:CeO2:Ce2O3 = 10:5:30:30.

[0090] Example 5

[0091] The efficient electrocatalyst for reducing nitrates, its preparation method, and its application provided by this invention are basically the same as those in the examples. The difference lies in that, based on Example 1, the composition and concentration of solutions A, B, C, and D are changed accordingly. The feed is prepared according to a Fe:Ce molar ratio of 5:1, the cerium salt is cerium sulfate, the iron source is ferric sulfate, the sulfur source is sodium thiosulfate, and the organic solvent is ethylene glycol. In the final catalyst product, the overall molar ratio of the four compounds is approximately FeS2:FeS:CeO2:Ce2O3 = 50:25:6:6.

[0092] Example 6

[0093] The efficient electrocatalyst for reducing nitrates, its preparation method, and its application provided by this invention are basically the same as those in the examples. The difference is that, based on Example 1, the composition and concentration of solutions A, B, C, and D are changed accordingly, and the feed is carried out according to the Fe:Ce molar ratio of 2:1. In the final catalyst product, the overall molar ratio of the four compounds is approximately FeS2:FeS:CeO2:Ce2O3 = 4:2:3:3.

[0094] Example 7

[0095] The efficient electrocatalyst for reducing nitrates, its preparation method, and its application provided by this invention are basically the same as those in the examples. The difference is that, based on Example 1, the composition and concentration of solutions A, B, C, and D are changed accordingly, and the feed is carried out according to the Fe:Ce molar ratio of 1:2. In the final catalyst product, the overall molar ratio of the four compounds is approximately FeS2:FeS:CeO2:Ce2O3 = 2:1:2:2.

[0096] The catalysts prepared in the above embodiments of the present invention have uniform powder size distribution and abundant FeSx and CeOy heterointerfaces. By controlling the feeding ratio of iron and sulfur sources, the molar amount of cerium oxide and ferric sulfide, and the selection of cerium salt, iron salt, and organic solvent, combined with technical means such as reaction sequence, reaction time, required temperature, preparation method, hydrothermal time, amount of solution added, reactant ratio, and drying treatment method during catalyst synthesis, the components (compound form), proportions, element distribution, powder size, and microstructure of the final product are controlled. On the surface of the compound, a FeSx and CeOy heterointerface with many nanoscale micro-folds and pores is formed, which has excellent activity for the electroreduction of nitrate to ammonia, has the best catalytic selectivity for ammonia, can significantly increase electron transfer, regulation, and surface adsorption, and ultimately significantly improve its electrocatalytic performance, effectively improving the efficiency and yield of nitrate to ammonia conversion, and can be widely used in environmental engineering.

[0097] It should be particularly noted that other technical solutions obtained by specific selection within the range of components, proportions, and process parameters described in this invention can all achieve the technical effects of this invention, and therefore will not be listed one by one. Furthermore, other catalyst technical solutions obtained by using equivalent components, proportions, preparation methods, and applications as described in this invention are all included within the protection scope of this invention.

[0098] In the description of this invention, the terms "one embodiment," "some embodiments," "specific embodiment," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this invention, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0099] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A highly efficient electrocatalyst for reducing nitrates, characterized in that, It is a plate-like compound FeS synthesized from cerium oxide and ferric sulfide. x CeO y The surface of this compound exhibits numerous nanoscale micro-wrinkles and porous FeS with a large specific surface area. x and CeO y Heterogeneous interface, where x and y represent non-stoichiometric and intermediate phase structures, and their values ​​are not integers, but are determined by the composition, concentration and reaction process conditions of the feed. x takes a value between 1 and 5, and y takes a value between 1.5 and 2. The sheet-like compound FeS x CeO y The average size is 100-200 nm, and Fe, S, Ce and O elements are uniformly distributed on the surface of the compound, forming a large number of active sites. The preparation of the highly efficient electrocatalyst for reducing nitrate involves a two-step synthesis. Cerium and iron salts are dissolved separately in solvents and added at a cerium-to-iron molar ratio of (0.2-5):

1. By controlling the order of addition, reaction time, reaction temperature, and post-catalyst drying conditions, the composition, proportion, and microstructure of the resulting compound are determined, ultimately yielding the plate-like compound FeS. x CeO y This includes the following steps: S1: Synthesis of cerium oxide Cerium salt was dissolved in water to form solution A, and alkali was dissolved in a solvent to form solution B. Solution B was slowly added dropwise to solution A under continuous magnetic stirring until all the solution was added, followed by continued stirring to obtain a mixture. The mixture was then transferred to a hydrothermal reactor and reacted at 50–150°C. After cooling, the solid and liquid phases were separated. The solid reactants were washed repeatedly by centrifugation using a common solvent and then freeze-dried to obtain cerium oxide (CeO). y Powder; S2: Preparation of iron and sulfur source solutions The iron source was first dissolved in an organic solvent to obtain iron source solution C; the sulfur source was then dissolved in the same organic solvent to obtain sulfur source solution D. S3: Synthesis catalyst Add solutions C and D to the reaction vessel at a volume ratio of (0.2-5):1, stir, and continue the reaction at a controlled temperature for 24 hours. After cooling, transfer the resulting suspension to a hydrothermal reactor, and then add cerium oxide (CeO) prepared in step S1 at a molar ratio of cerium oxide to ferric sulfide (0.25-5):

1. y The powder was reacted under solvothermal conditions of 50-150℃ for 24 hours. After cooling, solid-liquid separation was performed. The particulate matter was washed repeatedly by centrifugation with organic and inorganic solvents. After vacuum drying, the catalyst FeS was obtained. x CeO y .

2. The highly efficient electrocatalyst for reducing nitrate according to claim 1, characterized in that, Step S1 specifically includes the following steps: S1-1 dissolves cerium salt in water to form solution A with a concentration of 0.05 M-1.15 M; The cerium salt mentioned is one of cerium chloride, cerium sulfate, and cerium nitrate; S1-2 Dissolve sodium hydroxide in water to form solution B with a concentration of 1 M-20 M; S1-3 at 1600 rpm -1 Under continuous magnetic stirring, slowly add liquid B dropwise to liquid A until it is completely added, and then continue stirring for 20-40 minutes to obtain a mixture. S1-4 The mixture is transferred to a hydrothermal reactor and reacted at 50~150℃ for 10~24 h, then cooled to room temperature to separate the solid and liquid. The solid reactants separated from S1-5 were centrifuged, washed, and freeze-dried using conventional solvents to obtain cerium oxide (CeO) with a porous needle-like structure and a size of 20-50 nm. y .

3. The highly efficient electrocatalyst for reducing nitrate according to claim 1, characterized in that, Step S2 involves preparing an iron source and a sulfur source solution, with the materials added in a molar ratio of Fe:Ce = (0.2-5):

1. The specific steps include the following: S2-1 dissolves the iron source in an organic solvent to obtain an iron source solution C with a concentration of 0.05 M-2.5 M; S2-2 Sulfur source solution D with a concentration of 0.03 M-13.31 M was obtained by dissolving the sulfur source in the same organic solvent.

4. The method for preparing the highly efficient electrocatalyst for reducing nitrate according to claim 3, characterized in that, The iron source is one of ferric sulfate, ferric nitrate, or ferric chloride; The organic solvent is one of dimethyl sulfoxide, cyclohexane, ethylene glycol, and dimethylformamide; The sulfur source is one of thioacetamide, thiourea, sodium sulfide, or sodium thiosulfate.

5. The highly efficient electrocatalyst for reducing nitrate according to claim 1, characterized in that, Step S3 specifically includes the following steps: S3-1: Add liquid C and liquid D to a glass container at a volume ratio of (0.2-5):1, stir and mix continuously for 5 minutes, add an appropriate amount of organic solvent, stir for another 5 minutes, and then transfer the reaction solution to an oil bath. S3-2: The reaction was carried out for 24 hours with continuous stirring within a temperature range of 70-120 ℃, and then cooled to room temperature to obtain a suspension. S3-3: Transfer the obtained suspension entirely into a hydrothermal reactor, and then add the cerium oxide (CeO) prepared in step S1 at a molar ratio of cerium oxide to ferric sulfide (0.2-5):

1. y The powder was reacted under solvothermal reaction conditions of 50~150℃ for 24 hours, and then separated into solid and liquid components after cooling to room temperature. S3-4: The solid reactants were washed repeatedly by centrifugation with organic and inorganic solvents, and then thoroughly dried in a vacuum drying oven to obtain the catalyst FeS. x CeO y .

6. The application of the highly efficient electrocatalyst for reducing nitrate as described in claim 1 in the electrocatalytic reduction of nitrate to ammonia.

Images