A method for applying a core-shell heterojunction built-in electric field catalyst to nitrate reduction
By preparing a CoO-MoC core-shell heterojunction catalyst, the problem of limited migration during the reduction of low-concentration nitrates was solved, improving reaction efficiency and selectivity, and making it suitable for wastewater treatment and ammonia production.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HUANENG POWER INT INC YINGKOU POWER PLANT
- Filing Date
- 2026-03-17
- Publication Date
- 2026-06-16
AI Technical Summary
In the electrochemical reduction of low-concentration nitrates, nitrate ion migration is restricted, reaction kinetics are sluggish, and there are competing electrochemical reactions, such as hydrogen generation, which affect efficiency.
A core-shell heterojunction catalyst with a built-in electric field was prepared by CoO-MoC. The conductivity of the MoC shell and the built-in electric field promoted the migration of nitrate ions, while the electronic structure of the CoO core was optimized to suppress competitive reactions.
It significantly improves the selectivity and Faraday efficiency of low-concentration nitrate reduction, enhances the stability and durability of the catalyst, and is suitable for wastewater treatment and ammonia production.
Smart Images
Figure CN122214935A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of electrochemical technology, specifically to a method for applying a core-shell heterojunction built-in electric field catalyst to nitrate reduction. Background Technology
[0002] The electrochemical reduction of nitrates has significant applications in wastewater treatment and ammonia production. However, the efficiency of this process becomes a major challenge when dealing with low concentrations of nitrates. This is mainly because the migration of negatively charged nitrate ions near the working electrode is restricted, leading to sluggish reaction kinetics, and the presence of competing electrochemical reactions, such as hydrogen generation.
[0003] The selection and preparation of electrode materials also significantly impact the electrochemical reduction efficiency of nitrates. Metal oxides, with their excellent conductivity and catalytic activity, have garnered widespread attention and recognition as electrode materials. Therefore, further improving the selectivity and stability of catalysts during the reaction process, and optimizing electrode materials, is of great importance for environmental optimization and sustainable energy development. The relatively low conductivity and intrinsic activity of cobalt metal oxides limit their application in the electrochemical nitrate reduction process. Therefore, optimizing both the morphology and electronic structure of cobalt metal can enhance its catalytic performance. Summary of the Invention
[0004] Therefore, this invention provides a method for applying a core-shell heterojunction built-in electric field catalyst to nitrate reduction, in order to solve the problem in the prior art that the migration of negatively charged nitrate ions near the working electrode is restricted, resulting in slow reaction kinetics and competitive electrochemical reactions.
[0005] To achieve the above objectives, the present invention provides the following technical solution:
[0006] A method for applying a core-shell heterojunction built-in electric field catalyst to nitrate reduction includes the following steps:
[0007] Step 1, Preparation of precursor mixed solution: Dissolve cobalt nitrate in a mixed solvent composed of glycerol and isopropanol, and stir vigorously until the solid is completely dissolved to obtain a homogeneous mixed solution;
[0008] Step 2, First hydrothermal reaction: The mixed solution obtained in Step 1 is transferred to a high-pressure reactor lined with polytetrafluoroethylene for hydrothermal reaction. After the reaction is completed, it is naturally cooled to room temperature.
[0009] Step 3, Separation and washing of the precursor: The product obtained after the reaction in Step 2 is subjected to solid-liquid separation, the solid part is collected, and the solid part is washed several times with anhydrous ethanol and deionized water alternately. Then it is dried to obtain the cobalt-based precursor.
[0010] Step 4, Preparation of core-shell structure reaction suspension: The cobalt-based precursor obtained in step 3 is dispersed in anhydrous ethanol, and then molybdenum acetylacetonate and dilute ammonia are added to the dispersion in sequence. The mixture is stirred at high speed until homogeneous to form a reaction suspension.
[0011] Step 5, Second hydrothermal reaction: The reaction suspension prepared in Step 4 is transferred to a high-pressure reactor lined with polytetrafluoroethylene for a second hydrothermal reaction. After the reaction is completed, the mixture is allowed to cool naturally to room temperature.
[0012] Step 6, high-temperature annealing: After solid-liquid separation, washing and drying of the product obtained after the reaction in step 5, it is placed in a tube furnace and subjected to high-temperature annealing under an inert gas protective atmosphere to obtain CoO-MoC catalyst powder with a core-shell heterojunction structure.
[0013] Step 7, Preparation of working electrode and electrochemical reduction: The CoO-MoC catalyst powder obtained in step 6 is coated on a conductive substrate to prepare a cathode working electrode; an electrochemical reduction system is assembled using an alkaline aqueous solution containing nitrates as the electrolyte, and the nitrate reduction reaction is carried out under the applied potential.
[0014] Preferably, in step one, the amount of cobalt nitrate used is 0.2-0.5 mmol; the volume ratio of glycerol to isopropanol in the mixed solvent is 1:(1-3); and the vigorous stirring time is 30-60 minutes.
[0015] In step two, the temperature of the hydrothermal reaction is 170-190℃; the time of the hydrothermal reaction is 5-7 hours.
[0016] In step three, the solid-liquid separation method is centrifugation or filtration; the drying conditions are drying in a vacuum drying oven at 60-80℃ for 6-12 hours.
[0017] In step four, the amount of anhydrous ethanol used is 15-25 ml; the amount of molybdenum acetylacetone added is such that the molar ratio of molybdenum to cobalt in step one is (0.1:1)-(0.5:1); the concentration of dilute ammonia is 0.5-2 mol / L, and the amount added is 2-10 ml; the high-speed stirring speed is 800-1200 rpm, and the time is 20-40 minutes.
[0018] In step five, the temperature of the second hydrothermal reaction is 150-170℃; the reaction time is 1-6 hours.
[0019] In step six, the inert gas is argon or nitrogen; the heating rate of the high-temperature annealing treatment is 2-5℃ / min, the annealing temperature is 300-400℃, and the holding time is 1-3 hours.
[0020] In step seven, the conductive substrate is carbon paper, carbon cloth, or nickel foam; the alkaline aqueous solution containing nitrate is a mixed aqueous solution of potassium nitrate and potassium hydroxide, wherein the concentration of potassium nitrate is 10-100 mM and the concentration of potassium hydroxide is 0.1-1 M.
[0021] Preferably, the CoO-MoC catalyst obtained in step six has a core-shell heterojunction structure, wherein CoO constitutes the core of the catalyst, and MoC is coated on the outside of the CoO core in the form of a shell, and the MoC shell and the CoO core form a tight interfacial contact and build a built-in electric field.
[0022] Preferably, the specific process for preparing the working electrode in step seven is as follows: CoO-MoC catalyst powder, conductive carbon black and binder are mixed in a mass ratio of (7-8):(1-2):1, and isopropanol solvent is added to grind and form a uniform catalyst slurry. Then, the catalyst slurry is uniformly coated on the surface of the conductive substrate, dried at 60-80°C, and then pressed under pressure to obtain a firm coating.
[0023] Preferably, the electrochemical reduction process in step seven is carried out at room temperature and pressure, and the applied potential is in the range of -0.8 V to -1.5 V relative to the reversible hydrogen electrode.
[0024] Preferably, in step four, the amount of molybdenum acetylacetone added is such that the molar ratio of molybdenum to cobalt is (0.2:1) - (0.4:1).
[0025] Preferably, in step six, the temperature of the high-temperature annealing treatment is 350-400℃.
[0026] Preferably, the conductive substrate in step seven is hydrophobic carbon paper, and the hydrophobic carbon paper is subjected to oxygen plasma treatment before coating with catalyst slurry.
[0027] The present invention has the following advantages:
[0028] This invention successfully constructed a core-shell heterojunction catalyst with CoO as the core and MoC as the shell through a stepwise hydrothermal combined with high-temperature annealing preparation strategy. The outer MoC shell has excellent conductivity and good affinity for nitrate ions, which can effectively promote the migration and enrichment of nitrate ions to the electrode surface, providing a rich source of reactants for the reaction and overcoming the problem of mass transfer limitation at low concentrations.
[0029] The MoC shell exerts a significant electronic modulation effect on the internal CoO core. Due to the difference in work function between the two, a built-in electric field is formed at the heterogeneous interface, pointing from MoC to CoO. This electric field can drive the redistribution of interface charge, optimize the electronic structure of Co active sites, and thus significantly enhance its intrinsic catalytic activity, promoting the breaking of NO bonds and hydrogenation in nitrate.
[0030] The electron density of the CoO core is enhanced under the influence of the built-in electric field, which is beneficial to the adsorption and activation of nitrate ions, but at the same time it relatively inhibits the excessive adsorption and reduction of protons (H+), thereby effectively suppressing the competitive hydrogen evolution reaction and greatly improving the selectivity and Faraday efficiency of the reduction process for the target product ammonia.
[0031] The MoC shell can prevent the internal CoO core from dissolving, agglomerating, or deactivating during long-term electrolysis, greatly enhancing the structural stability and durability of the catalyst under harsh electrochemical conditions, and providing possibilities for practical wastewater treatment or continuous ammonia synthesis. Attached Figure Description
[0032] To more intuitively illustrate the prior art and this application, exemplary drawings are provided below. It should be understood that the specific shapes and structures shown in the drawings should not generally be regarded as limiting conditions for implementing this application; for example, based on the technical concept disclosed in this application and the exemplary drawings, those skilled in the art are able to easily make conventional adjustments or further optimizations to the addition / reduction / classification, specific shapes, positional relationships, connection methods, size ratios, etc. of certain units (components).
[0033] Figure 1 A process diagram of a method for applying a core-shell heterojunction built-in electric field catalyst to nitrate reduction, provided for an embodiment of this application;
[0034] Figure 2 Scanning electron microscope (SEM) images of a Co precursor used in a method for nitrate reduction with a core-shell heterojunction built-in electric field catalyst, provided in this application embodiment;
[0035] Figure 3 Scanning electron microscope (SEM) images of the calcination synthesis of CoO-MoC catalysts using a core-shell heterojunction built-in electric field catalyst for nitrate reduction, as provided in this application embodiment. Detailed Implementation
[0036] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. It should be understood that these embodiments are merely for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Technical engineers in the field can make some non-essential improvements and adjustments to the present invention based on the above-described content. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0037] Please see Figure 1-3 A method for applying a core-shell heterojunction built-in electric field catalyst to nitrate reduction includes the following steps:
[0038] Step 1, Preparation of precursor mixed solution: Dissolve cobalt nitrate in a mixed solvent composed of glycerol and isopropanol, and stir vigorously until the solid is completely dissolved to obtain a homogeneous mixed solution;
[0039] Step 2, First hydrothermal reaction: The mixed solution obtained in Step 1 is transferred to a high-pressure reactor lined with polytetrafluoroethylene for hydrothermal reaction. After the reaction is completed, it is naturally cooled to room temperature.
[0040] Step 3, Separation and washing of the precursor: The product obtained after the reaction in Step 2 is subjected to solid-liquid separation, the solid part is collected, and the solid part is washed several times with anhydrous ethanol and deionized water alternately, and then dried to obtain the cobalt-based precursor.
[0041] Step 4, Preparation of core-shell structure reaction suspension: The cobalt-based precursor obtained in step 3 is dispersed in anhydrous ethanol, and then molybdenum acetylacetonate and dilute ammonia are added to the dispersion in sequence. The mixture is stirred at high speed until homogeneous to form a reaction suspension.
[0042] Step 5, Second hydrothermal reaction: The reaction suspension prepared in Step 4 is transferred to a high-pressure reactor lined with polytetrafluoroethylene for a second hydrothermal reaction. After the reaction is completed, the mixture is allowed to cool naturally to room temperature.
[0043] Step 6, high-temperature annealing: After solid-liquid separation, washing and drying of the product obtained after the reaction in step 5, it is placed in a tube furnace and subjected to high-temperature annealing under an inert gas protective atmosphere to obtain CoO-MoC catalyst powder with a core-shell heterojunction structure.
[0044] Step 7, Preparation of working electrode and electrochemical reduction: The CoO-MoC catalyst powder obtained in step 6 is coated on a conductive substrate to prepare a cathode working electrode; an electrochemical reduction system is assembled using an alkaline aqueous solution containing nitrates as the electrolyte, and the nitrate reduction reaction is carried out under the applied potential.
[0045] In step one, the amount of cobalt nitrate used is 0.2-0.5 mmol; the volume ratio of glycerol to isopropanol in the mixed solvent is 1:(1-3); and the vigorous stirring time is 30-60 minutes.
[0046] In step two, the temperature of the hydrothermal reaction is 170-190℃, preferably 180℃; the time of the hydrothermal reaction is 5-7 hours, preferably 6 hours.
[0047] In step three, the solid-liquid separation method is centrifugation or filtration; the drying conditions are drying in a vacuum drying oven at 60-80℃ for 6-12 hours.
[0048] In step four, the amount of anhydrous ethanol used is 15-25 ml; the amount of molybdenum acetylacetone added is such that the molar ratio of molybdenum to cobalt in step one is (0.1:1)-(0.5:1); the concentration of dilute ammonia is 0.5-2 mol / L, and the amount added is 2-10 ml; the high-speed stirring speed is 800-1200 rpm, and the time is 20-40 minutes.
[0049] In step five, the temperature of the second hydrothermal reaction is 150-170℃, preferably 160℃; the reaction time is 1-6 hours.
[0050] In step six, the inert gas is argon or nitrogen; the heating rate of the high-temperature annealing treatment is 2-5℃ / min, the annealing temperature is 300-400℃, and the holding time is 1-3 hours, preferably 2 hours;
[0051] In step seven, the conductive substrate is carbon paper, carbon cloth, or nickel foam; the alkaline aqueous solution containing nitrate is a mixed aqueous solution of potassium nitrate and potassium hydroxide, wherein the concentration of potassium nitrate is 10-100 mM and the concentration of potassium hydroxide is 0.1-1 M.
[0052] The CoO-MoC catalyst prepared in step six has a well-defined core-shell heterojunction structure, in which CoO constitutes the core of the catalyst, and MoC is coated on the outside of the CoO core in the form of a shell. The MoC shell and the CoO core form a tight interfacial contact and build a built-in electric field.
[0053] The specific process for preparing the working electrode in step seven is as follows: CoO-MoC catalyst powder, conductive carbon black and binder are mixed in a mass ratio of (7-8):(1-2):1, and isopropanol solvent is added to grind and form a uniform catalyst slurry. Then the catalyst slurry is uniformly coated on the surface of the conductive substrate, dried at 60-80℃, and then pressed under pressure to obtain a firm coating.
[0054] The electrochemical reduction process in step seven is carried out at room temperature and pressure, and the applied potential is in the range of -0.8 V to -1.5 V relative to the reversible hydrogen electrode.
[0055] In step four, the amount of molybdenum acetylacetone added is such that the molar ratio of molybdenum to cobalt is (0.2:1) - (0.4:1).
[0056] In step six, the high-temperature annealing treatment is performed at a temperature of 350-400°C.
[0057] The conductive substrate in step seven is hydrophobic carbon paper, and before coating the catalyst slurry, the hydrophobic carbon paper is subjected to oxygen plasma treatment to improve its hydrophilicity.
[0058] Example 1
[0059] Step 1: Weigh 0.291 g (1.0 mmol) of cobalt nitrate hexahydrate and dissolve it in a mixed solvent consisting of 10 ml glycerol and 20 ml isopropanol. Stir magnetically for 45 minutes until completely dissolved.
[0060] Step 2: Transfer the above solution into a 50 ml polytetrafluoroethylene-lined reactor, place it in an oven, and react at 180°C for 6 hours. Allow it to cool naturally.
[0061] Step 3: Centrifuge the reaction product, wash it three times each with anhydrous ethanol and deionized water, and dry the solid in a vacuum drying oven at 70°C for 10 hours to obtain a pink precursor.
[0062] Step 4: Take half of the dried precursor (approximately 0.5 mmol Co) and disperse it in 20 ml of anhydrous ethanol. Add 0.105 g (0.3 mmol) of molybdenum acetylacetonate (Mo:Co molar ratio = 0.3:1) and 5 ml of 1 mol / L dilute ammonia solution, and stir at 1000 rpm for 30 minutes.
[0063] Step 5: Transfer the mixed suspension to a reaction vessel and react at 160°C for 3 hours. After natural cooling, centrifuge to collect the precipitate, wash with deionized water, and dry.
[0064] Step 6: Place the dried powder in a quartz boat, put it into a tube furnace, heat it to 350℃ at 3℃ / min under an argon atmosphere, hold it at that temperature for 2 hours, and then cool it naturally to obtain black CoO-MoC catalyst powder.
[0065] Step 7: Mix 5 mg of catalyst, 1 mg of conductive carbon black (Vulcan XC-72), and 0.7 mg of Nafion solution (5 wt%), add 1 ml of isopropanol, and sonicate to form a homogeneous slurry. Take 50 μl of the slurry and drop it onto a 1 × 1 cm² sheet of oxygen plasma-treated carbon paper. After air-drying at room temperature, press it under 5 MPa pressure for 10 seconds to obtain the working electrode. Using 0.1 M KOH + 50 mM KNO3 solution as the electrolyte, in an H-type electrolytic cell, with the above electrode as the working electrode, a Pt sheet as the counter electrode, and Ag / AgCl as the reference electrode, electrolyze for 2 hours at -1.2 V (vs. RHE). After the reaction, detect the ammonia concentration in the electrolyte and calculate the Faraday efficiency.
[0066] Comparative Example 1
[0067] Except for step four, where molybdenum acetylacetonate and dilute ammonia are not added, the precursor is directly subjected to the annealing treatment in step six to obtain the CoO catalyst. The remaining steps are the same as in Example 1.
[0068] Comparative Example 2
[0069] Except for step four, where molybdenum acetylacetonate is not added, only dilute ammonia is added to obtain the Co-based catalyst. The remaining steps are the same as in Example 1.
[0070] Comparative Example 3
[0071] A Pt / C catalyst (20 wt% Pt) was used as the working electrode catalyst, with the same coating amount and electrolysis conditions as in Example 1.
[0072] Effect test
[0073] Electrochemical reduction tests of nitrate were conducted using electrodes prepared in Example 1 and Comparative Examples 1-3 (under the same conditions as step seven of Example 1). The ammonia production was determined using indophenol blue spectrophotometry, and the corresponding Faradaic efficiency (FE) was calculated. Simultaneously, the catalyst stability was tested using chronoamperometry. The results are shown in the table below:
[0074]
[0075] As shown in the table above, the core-shell CoO-MoC catalyst prepared in Example 1 of this invention exhibits the highest ammonia yield and Faradaic efficiency in the reduction of nitrate to ammonia, along with excellent stability and minimal current density decay. The pure CoO catalyst in Comparative Example 1 shows lower activity and selectivity, and poor stability. Comparative Example 2 demonstrates that while the performance of the Co-based catalyst without MoC shell modification is improved, it is far inferior to that of the core-shell structure. The commercial Pt / C catalyst in Comparative Example 3 primarily tends to reduce nitrate to nitrogen, exhibiting extremely low selectivity for ammonia. This fully demonstrates the synergistic advantages of the core-shell heterojunction structure and its built-in electric field designed in this invention in improving the activity, selectivity, and stability of the reduction of nitrate to ammonia.
[0076] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A method for applying a core-shell heterojunction built-in electric field catalyst to nitrate reduction, characterized in that, Includes the following steps: Step 1, Preparation of precursor mixed solution: Dissolve cobalt nitrate in a mixed solvent composed of glycerol and isopropanol, and stir vigorously until the solid is completely dissolved to obtain a homogeneous mixed solution; Step 2, First hydrothermal reaction: The mixed solution obtained in Step 1 is transferred to a high-pressure reactor lined with polytetrafluoroethylene for hydrothermal reaction. After the reaction is completed, it is naturally cooled to room temperature. Step 3, Separation and washing of the precursor: The product obtained after the reaction in Step 2 is subjected to solid-liquid separation, the solid part is collected, and the solid part is washed several times with anhydrous ethanol and deionized water alternately. Then it is dried to obtain the cobalt-based precursor. Step 4, Preparation of core-shell structure reaction suspension: The cobalt-based precursor obtained in step 3 is dispersed in anhydrous ethanol, and then molybdenum acetylacetonate and dilute ammonia are added to the dispersion in sequence. The mixture is stirred at high speed until homogeneous to form a reaction suspension. Step 5, Second hydrothermal reaction: The reaction suspension prepared in Step 4 is transferred to a high-pressure reactor lined with polytetrafluoroethylene for a second hydrothermal reaction. After the reaction is completed, the mixture is allowed to cool naturally to room temperature. Step 6, high-temperature annealing: After solid-liquid separation, washing and drying of the product obtained after the reaction in step 5, it is placed in a tube furnace and subjected to high-temperature annealing under an inert gas protective atmosphere to obtain CoO-MoC catalyst powder with a core-shell heterojunction structure. Step 7, Preparation of working electrode and electrochemical reduction: The CoO-MoC catalyst powder obtained in step 6 is coated on a conductive substrate to prepare a cathode working electrode; an electrochemical reduction system is assembled using an alkaline aqueous solution containing nitrates as the electrolyte, and the nitrate reduction reaction is carried out under the applied potential.
2. The method for applying a core-shell heterojunction built-in electric field catalyst to nitrate reduction according to claim 1, characterized in that, In step one, the amount of cobalt nitrate used is 0.2-0.5 mmol; the volume ratio of glycerol to isopropanol in the mixed solvent is 1:(1-3); and the vigorous stirring time is 30-60 minutes. In step two, the temperature of the hydrothermal reaction is 170-190℃; the time of the hydrothermal reaction is 5-7 hours. In step three, the solid-liquid separation method is centrifugation or filtration; the drying conditions are drying in a vacuum drying oven at 60-80℃ for 6-12 hours. In step four, the amount of anhydrous ethanol used is 15-25 ml; the amount of molybdenum acetylacetone added is such that the molar ratio of molybdenum to cobalt in step one is (0.1:1)-(0.5:1); the concentration of dilute ammonia is 0.5-2 mol / L, and the amount added is 2-10 ml; the high-speed stirring speed is 800-1200 rpm, and the time is 20-40 minutes. In step five, the temperature of the second hydrothermal reaction is 150-170℃; the reaction time is 1-6 hours. In step six, the inert gas is argon or nitrogen; the heating rate of the high-temperature annealing treatment is 2-5 ℃ / min, the annealing temperature is 300-400℃, and the holding time is 1-3 hours. In step seven, the conductive substrate is carbon paper, carbon cloth, or nickel foam; the alkaline aqueous solution containing nitrate is a mixed aqueous solution of potassium nitrate and potassium hydroxide, wherein the concentration of potassium nitrate is 10-100 mM and the concentration of potassium hydroxide is 0.1-1 M.
3. The method for applying a core-shell heterojunction built-in electric field catalyst to nitrate reduction according to claim 1, characterized in that, The CoO-MoC catalyst prepared in step six has a core-shell heterojunction structure, wherein CoO constitutes the core of the catalyst, and MoC is coated on the outside of the CoO core in the form of a shell. The MoC shell and the CoO core form a tight interfacial contact and build a built-in electric field.
4. The method for applying a core-shell heterojunction built-in electric field catalyst to nitrate reduction according to claim 1, characterized in that, The specific process for preparing the working electrode in step seven is as follows: CoO-MoC catalyst powder, conductive carbon black and binder are mixed in a mass ratio of (7-8):(1-2):1, and isopropanol solvent is added to grind and form a uniform catalyst slurry. Then the catalyst slurry is uniformly coated on the surface of the conductive substrate, dried at 60-80℃, and then pressed under pressure to obtain a firm coating.
5. The method for applying a core-shell heterojunction built-in electric field catalyst to nitrate reduction according to claim 1, characterized in that, The electrochemical reduction process in step seven is carried out at room temperature and pressure, and the applied potential is in the range of -0.8 V to -1.5 V relative to the reversible hydrogen electrode.
6. The method for applying a core-shell heterojunction built-in electric field catalyst to nitrate reduction according to claim 2, characterized in that, In step four, the amount of molybdenum acetylacetone added is such that the molar ratio of molybdenum to cobalt is (0.2:1) - (0.4:1).
7. The method for applying a core-shell heterojunction built-in electric field catalyst to nitrate reduction according to claim 2, characterized in that, In step six, the high-temperature annealing treatment is performed at a temperature of 350-400°C.
8. The method for applying a core-shell heterojunction built-in electric field catalyst to nitrate reduction according to claim 4, characterized in that, The conductive substrate in step seven is hydrophobic carbon paper, and the hydrophobic carbon paper is subjected to oxygen plasma treatment before coating with catalyst slurry.