Heterostructure electrocatalyst for nitrate electroreduction, method and application

Abstract

The invention discloses a heterostructure electrocatalyst for nitrate electroreduction and a method and application thereof, and belongs to the technical field of electrochemical catalysis. The catalyst is formed by dispersing metal silver nanoclusters on an iron-silver composite oxide matrix, and a heterostructure is formed. The metal silver nanocluster has an electron buffering effect, can dynamically stabilize ferrous ions in an iron-silver composite oxide matrix, and prevents the ferrous ions from being excessively reduced in the electrocatalytic reduction process, so that the activity, selectivity and stability of the catalyst are improved. The preparation method comprises the following steps: packaging silver salt in an iron-based zeolite imidazole framework material to form a composite precursor, oxidizing in an air atmosphere, and then reducing in a reducing atmosphere. The catalyst can be used for preparing ammonia gas through electro-catalysis nitrate radical reduction, and a solution is provided for sustainable ammonia gas synthesis. By introducing metal silver as an electron storage layer, ferrous ions are prevented from being excessively reduced in the electro-catalysis process, and the method can be used for electro-catalysis reaction needing stable low-valence metal.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrochemical catalysis, and in particular relates to a heterogeneous structure electrocatalyst for nitrate electroreduction, a method and an application thereof. Background Art

[0002] Ammonia (NH 3 ) is an important raw material in the chemical and agricultural fields, and is widely used in synthetic fibers, medicines, and fertilizers. At the same time, ammonia is also considered a promising carbon-free energy carrier. The traditional Haber-Bosch process for synthesizing ammonia requires high temperature and high pressure conditions and produces a large amount of greenhouse gas emissions, which is difficult to meet the development requirements of global carbon neutrality. Electrochemical nitrogen (N 2 ) reduction has attracted widespread attention as a green and sustainable method for producing ammonia. However, due to the low solubility and slow decomposition kinetics of nitrogen at room temperature and pressure, the efficiency of electrochemical nitrogen reduction is significantly affected. In contrast, nitrate (NO 3 ⁻) has low dissociation energy and water solubility, which can significantly promote the generation of ammonia, providing an attractive alternative for ammonia synthesis, while helping to solve environmental problems such as water pollution caused by nitrates. However, the electroreduction reaction of nitrates involves multi-electron transfer and the existence of a competitive hydrogen evolution reaction (HER), which largely limits the efficiency of the electroreduction reaction of nitrates to generate ammonia. Therefore, the development of highly active and highly selective electrocatalysts is crucial to further promote sustainable ammonia synthesis.

[0003] In recent years, metal-based nanomaterials have been widely used in the study of nitrate reduction catalysts. In particular, oxide-derived iron (OD-Fe) has been widely used for its ability to stabilize the mixed-valent iron (especially ferrous Fe) of the key reaction intermediates. 2 ⁺) has attracted much attention. For example, studies have shown that Fe in OD-Fe 2 The ⁺ site can reduce the energy barrier of nitrate reduction to generate ammonia and inhibit the hydrogen evolution reaction. 2 ⁺ Usually it is easily reduced to metallic iron at negative potential, resulting in poor catalyst stability and difficult to explain the reaction mechanism. Therefore, the Fe in OD-Fe is stabilized during the nitrate electroreduction reaction. 2 ⁺ is crucial to improving catalytic performance and durability. Currently, methods for dynamically controlling Fe⁺ include pulse electrocatalysis with periodic application of positive and negative potentials. However, the introduction of additional positive potentials will inevitably reduce energy efficiency and reaction rate. Other methods include the use of gas plasma to treat OD-Fe precursors, grain refinement, surface modification, or direct synthesis of bimetallic iron oxides and ferrous coordination polymers. In particular, Ag in bimetallic oxides 0species have been shown to have a good ability to control the behavior of hydrogen, which is crucial for controlling the hydrogen evolution reaction.

[0004] Since it is difficult to obtain clear Ag 0 To further explore the electrocatalytic mechanism of FeAgOx as an electrocatalyst for nitrate electroreduction reaction, we need to modify FeAg oxide and elucidate its potential electrocatalytic mechanism. Summary of the invention

[0005] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a heterostructure electrocatalyst, method and application for nitrate electroreduction, so as to solve the technical problems of poor catalytic stability, low activity and selectivity caused by the easy reduction of ferrous ions in the nitrate electroreduction reaction.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: The invention discloses a heterogeneous structure electrocatalyst for nitrate electroreduction, comprising: an iron-silver composite oxide matrix, and metallic silver nanoclusters dispersed in the iron-silver composite oxide matrix; the metallic silver nanoclusters serve as electron storage layers, and are used to stabilize ferrous ions in the iron-silver composite oxide matrix during the electrocatalytic process, so as to prevent excessive reduction of the ferrous ions.

[0007] Preferably, the average particle size of the metallic silver nanoclusters is 1-10 nanometers.

[0008] Preferably, the iron-silver composite oxide matrix comprises a mixture of ferrous ions and ferric ions.

[0009] Preferably, the atomic percentage of silver in the heterostructure electrocatalyst for nitrate electroreduction is 0.5%-10%.

[0010] The present invention also discloses a method for preparing the above-mentioned heterogeneous structure electrocatalyst for nitrate electroreduction, comprising the following steps: The silver salt is encapsulated in an iron-based zeolite imidazole framework material, first subjected to an oxidation treatment in an air atmosphere, and then subjected to a reduction treatment in a reducing atmosphere to obtain a heterogeneous structure electrocatalyst for nitrate electroreduction.

[0011] Preferably, the silver salt is silver nitrate; the reducing atmosphere comprises hydrogen and an inert gas, and the inert gas is argon.

[0012] Preferably, the oxidation treatment is carried out at a temperature of 700-900° C. and for a time of 1-3 hours.

[0013] Preferably, the reduction treatment is carried out at a temperature of 300-500° C. and for a time of 1-3 hours.

[0014] The present invention also discloses the use of the above-mentioned heterogeneous structure electrocatalyst for nitrate electroreduction in the preparation of ammonia by nitrate electroreduction, wherein a nitrate-containing solution is contacted with the heterogeneous structure electrocatalyst for nitrate electroreduction, and a cathode potential is applied to the heterogeneous structure electrocatalyst for nitrate electroreduction.

[0015] Preferably, the cathode potential is -0.2 V to -1.0 V relative to the reversible hydrogen electrode; and the solution containing nitrate is an alkaline electrolyte.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention discloses a heterogeneous structure electrocatalyst for nitrate electroreduction, comprising an iron-silver composite oxide matrix and metallic silver nanoclusters dispersed in the iron-silver composite oxide matrix; the metallic silver nanoclusters serve as electron storage layers to stabilize ferrous ions in the iron-silver composite oxide matrix during the electrocatalytic process to prevent excessive reduction of ferrous ions. The heterogeneous structure electrocatalyst for nitrate electroreduction has the following advantages: dynamic stabilization of Fe 2 ⁺; The present invention dynamically introduces metal Ag clusters into the oxidized FeAgO nanosheets to form a heterostructured Ag 0 -FeAgOx, effectively stabilizes Fe 2 ⁺ Status. Ag 0 As an electron acceptor, it prevents Fe from being 2 ⁺Excessive reduction. High activity; Stable Fe 2 ⁺It is conducive to the adsorption of key intermediates, reduces the reaction energy barrier, and significantly improves the activity of nitrate reduction reaction. Compared with traditional iron-based catalysts, the Ag prepared by the present invention 0 -FeAgOx catalysts exhibit higher onset potential and higher electrocatalytic current density. High selectivity; Ag 0 The FeAgOx catalyst achieved a maximum Faradaic efficiency of 91.5% at a potential of -0.6 V vs. RHE, indicating that the electron-deficient Fe sites can optimize the Ag 0 -FeAgOx selectively converts nitrate into ammonia. Compared with iron nanosheets, Ag 0 -FeAgOx produces less byproduct nitrite. High stability; stable Fe 2 ⁺ Make Ag 0 -FeAgOx has excellent long-term stability and can operate stably for 400 hours in the nitrate reduction reaction, which is better than most advanced iron-based electrocatalysts. After stability testing, the crystal structure, morphology and composition of the catalyst remain unchanged. Clear mechanism of action; Ag 0 Acts as an electron buffer layer to transfer electrons from FeO to Ag 0, thus generating electron-deficient Fe sites, which in turn modulate the d-band center of Fe, making it have more favorable adsorption energy for key intermediates and promoting the formation of ammonia. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) confirmed the formation and transformation path of the adsorbed intermediates during the reaction.

[0017] Furthermore, the average particle size of the metallic silver nanoclusters is 1-10 nanometers, which can ensure that the silver clusters are evenly dispersed in the iron-silver composite oxide matrix to avoid agglomeration, while providing sufficient electron storage space, effectively stabilizing Fe²⁺, and improving the catalytic performance and stability of the catalyst.

[0018] Furthermore, the iron-silver composite oxide matrix contains a mixture of ferrous ions and ferric ions. The iron-silver composite oxide matrix contains a mixture of ferrous ions and ferric ions, which can provide abundant electron transfer pathways and active sites, which is beneficial to the transfer of electrons and the adsorption of intermediates during the nitrate electroreduction reaction, thereby improving the catalytic efficiency and selectivity.

[0019] Furthermore, in the heterogeneous structure electrocatalyst for nitrate electroreduction, the atomic percentage of silver is 0.5%-10%. The distribution and number of silver clusters in the catalyst can be optimized to ensure sufficient electron storage and transfer capacity while avoiding excessive silver clusters affecting the overall performance and cost of the catalyst.

[0020] The present invention also discloses a method for preparing the above-mentioned heterogeneous structure electrocatalyst for nitrate electroreduction, comprising the following steps: encapsulating the silver salt in an iron-based zeolite imidazole framework material, first performing an oxidation treatment in an air atmosphere, and then performing a reduction treatment in a reducing atmosphere to obtain a heterogeneous structure electrocatalyst for nitrate electroreduction. The step of encapsulating the silver salt in the iron-based zeolite imidazole framework material utilizes the porosity and adsorption of the zeolite imidazole framework material to ensure that the silver salt is uniformly dispersed in the iron-based material. This uniform dispersion helps to form uniformly distributed silver clusters in subsequent oxidation and reduction treatments, thereby improving the overall performance of the catalyst. Oxidation treatment in an air atmosphere can oxidize the iron-based material into iron oxide, and the silver salt is also oxidized into silver oxide. This step is the key to forming a heterogeneous structure because it provides the necessary oxide precursor for the subsequent reduction treatment. In addition, oxidation treatment also helps to remove impurities in the material and improve the purity of the catalyst. Reduction treatment in a reducing atmosphere is the last step in preparing the heterogeneous structure electrocatalyst. In this step, the silver oxide is reduced to metallic silver clusters, and part of the iron oxide is reduced to ferrous ions. This change not only forms the desired heterostructure, but also stabilizes the Fe²⁺ ions, thereby improving the catalytic activity and stability of the catalyst. In addition, the reduction treatment also helps to adjust the electronic structure of the catalyst, making it more selective for the nitrate electroreduction reaction. Through precise control of the above steps, the present invention successfully prepares a heterostructure electrocatalyst with excellent performance. The catalyst not only has high catalytic activity and stability, but also has high selectivity for the nitrate electroreduction reaction. The improvement of these properties makes the catalyst have broad application prospects in green energy conversion technologies such as nitrate electroreduction to prepare ammonia.

[0021] Furthermore, the silver salt is silver nitrate; the reducing atmosphere contains hydrogen and an inert gas, and the inert gas is argon. Silver nitrate is selected as the silver source, which is easy to operate and control; using hydrogen and argon as the reducing atmosphere can ensure the stability and safety of the reduction process, while avoiding the introduction of other impurities.

[0022] Furthermore, the temperature of the oxidation treatment is 700-900°C and the time is 1-3 hours. Controlling the temperature and time of the oxidation treatment can ensure that the iron-based material is fully oxidized into iron oxides while avoiding damage to the material structure caused by excessively high temperature and excessively long time.

[0023] Furthermore, the temperature of the reduction treatment is 300-500° C. and the time is 1-3 hours. Controlling the temperature and time of the reduction treatment can ensure that the silver oxide is fully reduced to metallic silver clusters while avoiding the degradation of the catalyst performance due to excessively high temperature and excessively long time.

[0024] The present invention also discloses the application of the above-mentioned heterogeneous structure electrocatalyst for nitrate electroreduction in the preparation of ammonia by nitrate electroreduction, wherein a solution containing nitrate is contacted with the heterogeneous structure electrocatalyst for nitrate electroreduction, and a cathode potential is applied to the heterogeneous structure electrocatalyst for nitrate electroreduction. The solution containing nitrate is directly contacted with the heterogeneous structure electrocatalyst to ensure that nitrate ions can effectively contact and react with the catalyst surface. This close contact is conducive to the rapid transfer and conversion of reactants and improves the reaction efficiency. Applying a cathode potential to the heterogeneous structure electrocatalyst is the key to driving the nitrate electroreduction reaction. The application of the cathode potential allows electrons to flow to the catalyst surface, undergo a reduction reaction with nitrate ions, and generate ammonia. This step is the core of achieving ammonia preparation.

[0025] Furthermore, the cathode potential is -0.2V to -1.0V relative to the reversible hydrogen electrode; the solution containing nitrate is an alkaline electrolyte. Too high a potential may lead to side reactions, while too low a potential may make the reaction rate too slow. The selection of this potential range helps to achieve efficient and selective ammonia preparation. Selecting an alkaline electrolyte as a reaction medium is conducive to the occurrence of nitrate electroreduction reaction. The alkaline environment can stabilize the active sites on the catalyst surface to prevent them from being oxidized or deactivated. At the same time, the alkaline electrolyte also helps to increase the solubility and mass transfer rate of the reactants, thereby further improving the reaction efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The present invention is a schematic diagram of the preparation process of the heterogeneous structure electrocatalyst for nitrate electroreduction disclosed in the present invention. DETAILED DESCRIPTION

[0027] The technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] In the present invention, unless otherwise specified, all the embodiments and preferred implementation methods mentioned herein can be combined with each other to form a new technical solution.

[0029] In the present invention, unless otherwise specified, all technical features and preferred features mentioned herein can be combined with each other to form a new technical solution.

[0030] In the present invention, unless otherwise specified, percentage (%) or part refers to the weight percentage or weight part relative to the composition.

[0031] In the present invention, unless otherwise specified, the components or preferred components involved can be combined with each other to form a new technical solution.

[0032] In the present invention, unless otherwise specified, the numerical range "a~b" represents an abbreviation of any real number combination between a and b, where a and b are real numbers. For example, the numerical range "6~22" means that all real numbers between "6~22" have been listed in this document, and "6~22" is just an abbreviation of these numerical combinations.

[0033] The “range” disclosed in the present invention is in the form of a lower limit and an upper limit, which can be one or more lower limits, and one or more upper limits, respectively.

[0034] In the present invention, the term "and / or" used herein refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0035] In the present invention, unless otherwise specified, each reaction or operation step can be carried out sequentially or in accordance with the sequence. Preferably, the reaction method herein is carried out sequentially.

[0036] Unless otherwise specified, the professional and scientific terms used herein have the same meanings as those familiar to those skilled in the art. In addition, any method or material similar or equivalent to the described content may also be applied to the present invention.

[0037] The present invention provides a method for preparing a heterogeneous structure electrocatalyst for nitrate electroreduction, comprising the following steps: Preparation of Fe / Ag-ZIF precursor: Preparation of iron-based zeolite imidazole framework material (Fe-ZIF). A certain amount of silver nitrate solution is added to the Fe-ZIF suspension and stirred for a certain period of time to allow the silver ions to be in situ encapsulated in the Fe-ZIF to obtain a Fe / Ag-ZIF precursor.

[0038] Oxidation treatment: The Fe / Ag-ZIF precursor is placed in a tube furnace and calcined at a certain temperature for a certain number of hours in an air atmosphere to obtain an iron-silver composite oxide (FeAgOx).

[0039] Reduction treatment: Place FeAgOx in a tube furnace and introduce 5% H 2 / Ar mixed gas, reduced at a certain temperature for a certain time, to obtain heterogeneous structure Ag 0 -FeAgOx catalyst.

[0040] Electrode preparation: Prepared Ag 0-FeAgOx catalyst was dispersed in ethanol solution, and then drop-coated on carbon paper after ultrasonic treatment to prepare the working electrode. Platinum sheet was used as the counter electrode, and saturated calomel electrode (SCE) was used as the reference electrode.

[0041] Electrochemical test: In the presence of 0.01MKNO 3 Linear sweep voltammetry (LSV) and chronoamperometry (CA) were performed in 0.1M KOH and 0.1M KOH electrolytes. All potentials were corrected relative to the reversible hydrogen electrode (RHE).

[0042] The present invention discloses a method for preparing the heterogeneous structure electrocatalyst for nitrate electroreduction, which specifically comprises the following steps: (1) Preparation of iron-silver composite oxide precursor: in situ encapsulation of silver salt into an iron-based zeolite imidazole framework material to form a composite precursor; (2) Oxidation treatment: The composite precursor is completely oxidized in an air atmosphere to obtain an iron-silver composite oxide (FeAgOx); (3) Reduction treatment: In a mixed atmosphere of hydrogen and inert gas, the iron-silver composite oxide is reduced at low temperature to obtain a heterogeneous structure Ag. 0 -FeAgOx catalyst.

[0043] Furthermore, the silver salt is silver nitrate.

[0044] The inert gas is argon.

[0045] The low temperature is 300-500°C, preferably 400°C.

[0046] The temperature of the oxidation treatment is 700-900°C, preferably 800°C.

[0047] The time for the oxidation treatment and the reduction treatment is 1-3 hours, preferably 2 hours.

[0048] The present invention discloses a heterogeneous structure electrocatalyst for nitrate electroreduction, wherein the heterogeneous structure electrocatalyst for nitrate electroreduction is composed of metallic silver (Ag 0 ) nanoclusters are dispersed on the iron-silver composite oxide (FeAgOx) matrix to form a heterogeneous structure.

[0049] The particle size of the metallic silver nanoclusters is 1-10 nm, preferably 2-5 nm.

[0050] The iron-silver composite oxide matrix mainly contains Fe 2 ⁺ and Fe 3 ⁺Two valence states of iron ions.

[0051] In the heterostructure electrocatalyst for nitrate electroreduction, the atomic percentage of silver is 0.5%-10%, preferably 1%-5%.

[0052] The heterogeneous structure electrocatalyst for nitrate electroreduction is used in the preparation of ammonia by nitrate electroreduction, and is used as an electrocatalyst for nitrate electroreduction reaction.

[0053] Furthermore, the nitrate electroreduction reaction is carried out in an alkaline electrolyte, preferably a potassium hydroxide solution.

[0054] The heterogeneous structure electrocatalyst for nitrate electroreduction disclosed in the present invention is composed of metallic silver (Ag 0 ) nanoclusters are dispersed on the iron-silver composite oxide (FeAgOx) matrix to form a heterogeneous structure. 0 The nanoclusters have an electronic buffering effect and can dynamically stabilize the ferrous ions (Fe 2+ ), preventing it from being over-reduced during the electrocatalytic reduction process, thereby improving the activity, selectivity and stability of the catalyst. The preparation method includes: encapsulating the silver salt in the iron-based zeolite imidazole framework material to form a composite precursor, oxidizing it in an air atmosphere to obtain FeAgOx, and then reducing it at low temperature in a mixed atmosphere of hydrogen and inert gas to obtain Ag 0 -FeAgOx. The catalyst can be used for electrocatalytic reduction of nitrate to produce ammonia, providing a promising solution for sustainable ammonia synthesis. The present invention also discloses a dynamically stable ferrous ion (Fe 2+ ) method, which introduces metallic silver (Ag 0 ) acts as an electron storage layer to prevent ferrous ions (Fe 2+ ) is over-reduced during the electrocatalytic process and can be used for other electrocatalytic reactions that require stable low-valent metals.

[0055] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. The components of the embodiments of the present invention described and shown in the drawings here can usually be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0056] Example 1 A method for preparing a heterogeneous structure electrocatalyst for nitrate electroreduction comprises the following steps: Precursor synthesis: 0.01 mol of silver nitrate was dissolved in 100 mL of water, and then added to 1 g of an iron-based zeolite imidazole framework material suspension (Fe-ZIF precursor) synthesized from iron salt and imidazole ligand, and stirred for 2 hours.

[0057] Oxidation treatment: The Fe / Ag-ZIF precursor was placed in a tube furnace and calcined at 700°C for 1 hour in an air atmosphere to obtain an iron-silver composite oxide (FeAgOx).

[0058] Reduction treatment: Place FeAgOx in a tube furnace and introduce 5% H 2 / Ar mixed gas, reduced at 300°C for 1 hour to obtain heterostructured Ag 0 -FeAgOx catalyst, in which the atomic percentage of silver (Ag) is about 0.5%, and the average particle size of the metallic silver nanoclusters is about 1 nanometer.

[0059] Electrode preparation: 5 mg of prepared Ag 0 -FeAgOx catalyst was dispersed in 1mL ethanol solution, and after ultrasonic treatment for 30 minutes, 10μL was dropped on 1cm² carbon paper to prepare the working electrode. The platinum sheet was used as the counter electrode and the saturated calomel electrode (SCE) was used as the reference electrode.

[0060] Electrochemical test: In the presence of 0.01MKNO 3 Linear sweep voltammetry (LSV) tests were performed in an electrolyte of 50% KOH and 0.1 M KOH at a scan rate of 5 mV / s. Chronoamperometry (CA) tests were performed at a potential of -0.2 V vs. RHE for 1 h.

[0061] Figure 1 The figure is a schematic diagram of the preparation process of the heterogeneous structure electrocatalyst for nitrate electroreduction disclosed in the present invention. As can be seen from the figure, the heterogeneous structure electrocatalyst for nitrate electroreduction disclosed in the present invention is composed of metallic silver (Ag 0 ) nanoclusters are dispersed on the iron-silver composite oxide (FeAgOx) matrix to form a heterogeneous structure. The preparation method includes: encapsulating silver salt in an iron-based zeolite imidazole framework material to form a composite precursor, oxidizing it in an air atmosphere to obtain FeAgOx, and then reducing it at low temperature in a mixed atmosphere of hydrogen and inert gas to obtain Ag 0 -FeAgOx. By introducing metallic silver nanoclusters as electron storage layers, the ferrous ions in the iron-silver composite oxide matrix are effectively stabilized, significantly improving the catalytic stability, activity and selectivity of the nitrate electroreduction reaction.

[0062] Example 2 A method for preparing a heterogeneous structure electrocatalyst for nitrate electroreduction comprises the following steps: Precursor synthesis: 0.1 mol of silver nitrate was dissolved in 100 mL of water, and then added to 1 g of a suspension of an iron-based zeolite imidazole framework material (Fe-ZIF) synthesized from an iron salt and an imidazole ligand, and stirred for 2 hours.

[0063] Oxidation treatment: The Fe / Ag-ZIF precursor was placed in a tube furnace and calcined at 900°C for 3 hours in an air atmosphere to obtain an iron-silver composite oxide (FeAgOx).

[0064] Reduction treatment: Place FeAgOx in a tube furnace and introduce 5% H 2 / Ar mixed gas, reduced at 500°C for 3 hours to obtain heterostructured Ag 0 -FeAgOx catalyst, in which the atomic percentage of silver (Ag) is about 10%, and the average particle size of the metallic silver nanoclusters is about 10 nanometers.

[0065] Electrode preparation: Same as Example 1.

[0066] Electrochemical test: Same as Example 1.

[0067] Example 3 A method for preparing a heterogeneous structure electrocatalyst for nitrate electroreduction comprises the following steps: Precursor synthesis: Same as Example 1.

[0068] Oxidation treatment: Same as Example 1.

[0069] Reduction treatment: FeAgOx was placed in a tube furnace and 5% H 2 / Ar mixed gas, reduced at 300°C and 500°C for 2 hours to obtain Ag 0 -FeAgOx-300 and Ag 0 -FeAgOx-500 catalyst.

[0070] Electrode preparation: Same as Example 1.

[0071] Electrochemical test: Same as Example 1.

[0072] Performance Comparison: Comparing Ag 0 -FeAgOx-300 and Ag 0 -Nitrate reduction performance (Faraday efficiency, ammonia production rate) of FeAgOx-500 at different cathode potentials.

[0073] Example 4 A method for preparing a heterogeneous structure electrocatalyst for nitrate electroreduction comprises the following steps: Catalyst preparation: Same as Example 1.

[0074] Nitrate electroreduction performance test: Electrode preparation: Same as Example 1.

[0075] Electrochemical test: In the presence of 0.01MKNO 3 Linear sweep voltammetry (LSV) tests were performed in 0.1M KOH and 0.1M KOH electrolytes. Chronoamperometry (CA) tests were performed at potentials of -0.2 V, -0.6 V, and -1.0 V vs. RHE for 1 hour.

[0076] Example 5 A method for preparing a heterogeneous structure electrocatalyst for nitrate electroreduction comprises the following steps: Catalyst preparation: Same as Example 1.

[0077] Nitrate electroreduction performance test: Electrode preparation: Same as Example 1.

[0078] Electrochemical test: in the presence of 0.01MKNO 3 Linear sweep voltammetry (LSV) tests were performed in an electrolyte solution of 0.01 M LiOH, 0.01 M NaOH, and 0.01 M KOH. Chronoamperometry (CA) tests were performed at a potential of -0.6 V vs. RHE for 1 hour.

[0079] Example 6 A method for preparing a heterogeneous structure electrocatalyst for nitrate electroreduction comprises the following steps: Precursor synthesis: 0.1 mol of silver nitrate was dissolved in 100 mL of water, and then added to 1 g of a suspension of an iron-based zeolite imidazole framework material (Fe-ZIF) synthesized from an iron salt and an imidazole ligand, and stirred for 2 hours.

[0080] Oxidation treatment: The Fe / Ag-ZIF precursor was placed in a tube furnace and calcined at 800°C for 2 hours in an air atmosphere to obtain an iron-silver composite oxide (FeAgOx).

[0081] Reduction treatment: Place FeAgOx in a tube furnace and introduce 5% H 2 / Ar mixed gas, reduced at 400°C for 2 hours to obtain heterostructured Ag 0 -FeAgOx catalyst, in which the atomic percentage of silver (Ag) is about 5%, and the average particle size of the metallic silver nanoclusters is about 5 nanometers.

[0082] Electrode preparation: Same as Example 1.

[0083] Electrochemical test: Same as Example 1.

[0084] In summary, the heterogeneous structure electrocatalyst for nitrate reduction of the present invention constructs a unique electron transfer and storage system by ingeniously embedding metallic silver nanoclusters in the iron-silver composite oxide (FeAgO) matrix. These highly dispersed silver clusters act as efficient electron acceptors and storage layers. During the electrocatalytic nitrate reduction reaction, they can dynamically capture and store electrons released from the iron oxide part, thereby effectively inhibiting the conversion of ferrous ions (Fe²⁺) to metallic iron (Fe 0 ) over-reduction, significantly enhancing the structural stability and catalytic activity of the catalyst. This stabilization effect not only enables the catalyst to maintain excellent catalytic performance in a continuous reaction of up to 400 hours, but also its crystal structure, surface morphology and chemical composition all show a high degree of stability, which is difficult to match with traditional iron-based catalysts. At the same time, the stable Fe²⁺ state provides more favorable conditions for the adsorption of key reaction intermediates, reduces the energy barrier of the reaction, and thus greatly improves the rate and efficiency of the nitrate electroreduction reaction. In addition, the catalyst achieved a Faradaic efficiency of up to 91.5% at a potential of -0.6V vs. RHE, which indicates that it has a very high preference for the selective conversion of nitrate to ammonia, while effectively inhibiting the formation of by-products such as nitrite. This high selectivity not only improves the utilization efficiency of resources, but also reduces the risk of environmental pollution. In terms of mechanism research, advanced techniques such as in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) were used to reveal the Ag 0 How to adjust the d-band center of Fe as an electron buffer layer, thereby optimizing its adsorption energy for key intermediates and promoting the efficient generation of ammonia. This discovery not only deepens the understanding of electron transfer and surface chemistry in the electrocatalytic process, but also provides valuable scientific guidance and theoretical basis for the design of more efficient and environmentally friendly electrocatalysts in the future. This heterostructure electrocatalyst has shown outstanding performance advantages in the field of nitrate electroreduction. Its design ideas, stable catalytic performance, efficient reaction rate and in-depth research on the mechanism of action have all made important contributions to the development of green energy conversion technology.

[0085] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A heterogeneous structure electrocatalyst for nitrate electroreduction, characterized in that: include: An iron-silver composite oxide matrix and metallic silver nanoclusters dispersed in the iron-silver composite oxide matrix; the metallic silver nanoclusters serve as electron storage layers for stabilizing ferrous ions in the iron-silver composite oxide matrix during electrocatalysis to prevent excessive reduction of ferrous ions.

2. The heterogeneous structure electrocatalyst for nitrate electroreduction according to claim 1, characterized in that: The average particle size of the metallic silver nanoclusters is 1-10 nanometers.

3. The heterogeneous structure electrocatalyst for nitrate electroreduction according to claim 1, characterized in that: The iron-silver composite oxide matrix comprises a mixture of ferrous ions and ferric ions.

4. The heterogeneous structure electrocatalyst for nitrate electroreduction according to claim 1, characterized in that: In the heterogeneous structure electrocatalyst for nitrate electroreduction, the atomic percentage of silver is 0.5%-10%.

5. The method for preparing a heterogeneous structure electrocatalyst for nitrate electroreduction according to any one of claims 1 to 4, characterized in that: The following steps are involved: The silver salt is encapsulated in an iron-based zeolite imidazole framework material, first subjected to an oxidation treatment in an air atmosphere, and then subjected to a reduction treatment in a reducing atmosphere to obtain a heterogeneous structure electrocatalyst for nitrate electroreduction.

6. The method for preparing a heterogeneous structure electrocatalyst for nitrate electroreduction according to claim 5, characterized in that: The silver salt is silver nitrate; the reducing atmosphere comprises hydrogen and an inert gas, and the inert gas is argon.

7. The method for preparing a heterogeneous structure electrocatalyst for nitrate electroreduction according to claim 5, characterized in that: The oxidation treatment is carried out at a temperature of 700-900° C. and for a time of 1-3 hours.

8. The method for preparing a heterogeneous structure electrocatalyst for nitrate electroreduction according to claim 5, characterized in that: The reduction treatment is carried out at a temperature of 300-500° C. and for a time of 1-3 hours.

9. Use of the heterogeneous structure electrocatalyst for nitrate electroreduction according to any one of claims 1 to 4 in preparing ammonia by nitrate electroreduction, characterized in that: A nitrate-containing solution is contacted with a heterostructure electrocatalyst for nitrate electroreduction, and a cathode potential is applied to the heterostructure electrocatalyst for nitrate electroreduction.

10. Use of the heterogeneous structure electrocatalyst for nitrate electroreduction according to claim 9 in preparing ammonia by nitrate electroreduction, characterized in that: The cathode potential is -0.2V to -1.0V relative to the reversible hydrogen electrode; and the nitrate-containing solution is an alkaline electrolyte.

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