A binderless nitrate electrochemical reduction ammonia membrane electrode device

Abstract

The application relates to the technical field of electrochemical water treatment and energy conversion, and discloses a binder-free nitrate electrochemical reduction ammonia production membrane electrode device. The in-situ construction method of the membrane electrode provided by the application integrates the synthesis, loading and activation of the catalyst with the assembly of the membrane electrode, in-situ growth and reconstruction of the cathode and anode catalytic layers are completed in the device, the cumbersome catalyst pre-synthesis, coating, drying and hot pressing steps in the traditional process are abandoned, the process flow is simplified, the cost is reduced, and the device has a scale application potential. Through accurate electrochemical regulation, metal copper nanosheets rich in high-density crystal boundaries are reconstructed in-situ at the cathode side, and high-activity nickel-iron oxyhydroxide is formed at the anode side, rich active sites are exposed, the coverage of the binder on the active sites is avoided, and therefore the catalyst utilization rate is greatly improved. The membrane electrode realizes high ammonia yield, high Faraday efficiency and excellent stability in the nitrate reduction ammonia production reaction.

Description

Technical Field

[0001] This invention relates to the field of electrochemical water treatment and energy conversion technology, and in particular to a binder-free membrane electrode device for the electrochemical reduction of nitrates to ammonia. Background Technology

[0002] Nitrate is a common pollutant in industrial wastewater, widely originating from industries such as machinery manufacturing, electroplating, photovoltaics, and fertilizer production. High concentrations of nitrate emissions not only lead to eutrophication of water bodies but also pose health risks through drinking water. In recent years, electrocatalytic nitrate reduction to ammonia technology has become a research hotspot due to its ability to convert nitrate ions in wastewater into high-value-added ammonia at ambient temperature and pressure, offering the dual advantages of wastewater treatment and resource recovery. Ammonia, as an important chemical raw material and clean energy carrier, offers a new approach to achieving a green and low-carbon nitrogen cycle through its electrochemical synthesis.

[0003] Membrane electrode assembly (MEA) is a core component of the electrochemical nitrate reduction reaction, and its structure and performance directly affect the reaction efficiency and stability. Currently, MEAs are mainly prepared using the catalyst-coated substrate (CCS) method or the catalyst-coated membrane (CCM) method. These two methods typically require first synthesizing catalyst materials through hydrothermal, co-precipitation, or solvothermal methods, then mixing the catalyst with a binder and coating it onto a gas diffusion layer or ion exchange membrane, and finally assembling it into an electrolytic cell device through hot pressing or other methods.

[0004] The aforementioned multi-step preparation methods face numerous technical bottlenecks. First, the process is cumbersome, involving multiple steps such as catalyst synthesis, separation, drying, coating, and hot pressing, resulting in long cycles, high energy consumption, and high costs, hindering large-scale production and widespread adoption. Second, due to the use of binders and physical pressing, it is difficult to form tight contact between the catalyst layer and the substrate, and between the catalyst layer and the ion exchange membrane, resulting in significant interfacial gaps. This leads to increased resistance to electron and ion transport, especially under low-concentration electrolyte conditions, causing severe ohmic polarization loss and limiting reaction rate and energy efficiency. Third, binders may cover active sites on the catalyst surface, reducing catalyst utilization; the physically stacked structure also hinders rapid mass transport, further weakening reaction performance. Finally, traditional methods typically prepare cathode and anode catalysts separately and then assemble them together, making it difficult to achieve synergistic optimization and integrated design of the anode and cathode catalyst layers, affecting the overall device's compatibility and stability.

[0005] Therefore, existing membrane electrode preparation technologies have significant shortcomings in terms of process complexity, interfacial resistance, catalyst utilization, and anode-cathode matching. There is an urgent need to develop a novel membrane electrode construction method that is simple in process, has tight interfacial bonding, and excellent performance, so as to promote the practical application of electrocatalytic nitrate reduction to ammonia production technology. Summary of the Invention

[0006] The present invention aims to at least solve one of the aforementioned technical problems existing in the prior art. Therefore, one objective of the present invention is to provide a method for in-situ construction of a membrane electrode.

[0007] The second objective of this invention is to provide a membrane electrode device.

[0008] The third objective of this invention is to provide applications for this membrane electrode device.

[0009] The fourth objective of this invention is to provide a method for treating nitrate wastewater.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A first aspect of the present invention provides a method for in-situ construction of a membrane electrode, comprising the following steps: S1. The cathode plate, cathode substrate, anion exchange membrane, anode substrate and anode plate are sequentially stacked and assembled to form an electrolytic cell device; S2. Electrolyte I is introduced into the cathode side and electrolyte II is introduced into the anode side. A first voltage is applied to perform the first step of electrochemical treatment, forming a first precursor layer on the cathode substrate surface and a second precursor layer on the anode substrate surface and the anode-side anion exchange membrane. S3. After draining the electrolyte from the cathode and anode sides, electrolyte III is introduced into the cathode side and electrolyte IV is introduced into the anode side. A second voltage opposite to the direction of the first voltage is applied to perform the second electrochemical treatment, so that the first precursor layer is reconstructed in situ into a nitrate reduction catalyst layer and the second precursor layer is reconstructed in situ into an oxygen evolution catalyst layer, thus obtaining a membrane electrode.

[0011] In some embodiments of the present invention, the in-situ construction method of the membrane electrode does not use adhesives.

[0012] In some embodiments of the present invention, in step S1, the cathode plate and the anode plate are selected from nickel plates, stainless steel plates or titanium plates.

[0013] In some preferred embodiments of the present invention, in step S1, the cathode plate and anode plate are selected from pure nickel plates or nickel alloy plates. Nickel plates have good electrical conductivity and resistance to corrosion by alkaline electrolytes, making them suitable for alkaline electrolysis environments.

[0014] In some embodiments of the present invention, in step S1, the thickness of the cathode substrate is 0.1-2.0 mm; and the area is 0.25-100 cm². 2 Porosity is 90%-98%; pore size is 50-500μm.

[0015] In some embodiments of the present invention, in step S1, the cathode substrate is selected from copper foam, copper mesh, or copper felt.

[0016] In some embodiments of the present invention, in step S1, the thickness of the anode substrate is 0.1-2.0 mm; the area matches that of the cathode substrate; and the porosity is 90%-98%.

[0017] In some embodiments of the present invention, in step S1, the anode substrate is selected from nickel foam, nickel mesh, stainless steel felt or titanium mesh.

[0018] In some embodiments of the present invention, in step S2, the electrolyte I is an alkaline solution; the concentration of alkali in the electrolyte I is 1-6 mol / L.

[0019] In some preferred embodiments of the present invention, in step S2, the solute of electrolyte I is selected from KOH or NaOH.

[0020] In some embodiments of the present invention, in step S2, the flow rate of electrolyte I is 0.1-15 mL / min.

[0021] In some embodiments of the present invention, in step S2, the electrolyte II is a Ni-containing electrolyte. 2+ and / or Fe 2+ / Fe 3+ The solution contains a total concentration of metal ions of 0.01-1 mol / L.

[0022] In some embodiments of the present invention, in step S2, the solute of the electrolyte II is selected from nitrates, sulfates or chlorides of nickel and / or iron / ferrous iron.

[0023] In some embodiments of the present invention, in step S2, the electrolyte II further includes a complexing agent; the concentration of the complexing agent is 0.01-0.3 mol / L (the molar ratio of the complexing agent to the total metal ions is (0.5-3):1).

[0024] In some embodiments of the present invention, in step S2, the complexing agent is selected from at least one of citrate, ethylenediaminetetraacetic acid, and tartrate. The complexing agent is used to complex Ni. 2+ and Fe 3+ This prevents hydrolysis and precipitation, while simultaneously regulating the electrodeposition rate to obtain a uniform deposition layer.

[0025] In some embodiments of the present invention, in step S2, the flow rate of electrolyte II is 1-5 mL / min.

[0026] In some embodiments of the present invention, in step S2, the first voltage includes being applied using a chronopotential method with a current density of 10-100 mA / cm². 2 The electrochemical treatment in the first step takes 10-60 minutes.

[0027] In some preferred embodiments of the present invention, in step S2, the first voltage is applied using a chronopotential method with a current density of 40-60 mA / cm². 2 The electrochemical treatment in the first step takes 10-30 minutes.

[0028] In some embodiments of the present invention, in step S2, the temperature of the cathode plate is 20-80°C.

[0029] In some embodiments of the present invention, in step S2, the first precursor layer is composed of a copper-based precursor; the copper-based precursor includes copper-based oxides / hydroxides.

[0030] In some embodiments of the present invention, in step S2, the morphology of the first precursor layer is selected from at least one of one-dimensional nanowires, two-dimensional nanosheets, and nanoparticle aggregates.

[0031] In some embodiments of the present invention, in step S2, the second precursor layer comprises a nickel / iron-based precursor; the nickel / iron-based precursor comprises nickel-iron layered double hydroxide (NiFe-LDH).

[0032] In some embodiments of the present invention, in step S3, the electrolyte III is an alkaline solution containing nitrate; the concentration of alkali in the electrolyte III is 1-6 mol / L, and the concentration of nitrate is 0.01-1 mol / L.

[0033] In some preferred embodiments of the present invention, in step S3, the electrolyte III is selected from KOH or NaOH solutions containing nitrates.

[0034] In some embodiments of the present invention, in step S3, the flow rate of electrolyte III is 30-50 mL / min.

[0035] In some embodiments of the present invention, in step S3, the electrolyte IV is an alkaline solution; the concentration of alkali in the electrolyte IV is 1-6 mol / L.

[0036] In some preferred embodiments of the present invention, in step S3, the solute of the electrolyte IV is selected from KOH or NaOH.

[0037] In some embodiments of the present invention, in step S3, the flow rate of the electrolyte IV is 30-50 mL / min.

[0038] In some embodiments of the present invention, in step S3, the method of applying the second voltage is selected from linear voltammetry, constant voltage or constant current or cyclic voltammetry; the scanning range is 1-3V, the scanning speed is 0.1-100mV / s; and the time of the second electrochemical treatment is 10-120min.

[0039] In some preferred embodiments of the present invention, in step S3, the second voltage is applied using a linear voltammetric scan method, with a scan range of 1.2-2V and a scan rate of 4-6mV / s; the electrochemical treatment time in the second step is 10-20min.

[0040] In some embodiments of the present invention, in step S3, the nitrate reduction catalyst layer comprises a Cu / Cu2O heterojunction.

[0041] In some preferred embodiments of the present invention, in step S3, the nitrate reduction catalyst layer is composed of a Cu / Cu2O heterostructure.

[0042] In some embodiments of the present invention, in step S3, the oxygen evolution catalyst layer comprises nickel iron hydroxyl oxide (NiFeOOH).

[0043] In some preferred embodiments of the present invention, in step S3, the oxygen evolution catalyst layer is composed of nickel iron hydroxyl oxide (NiFeOOH).

[0044] Specifically, the basic principles of this invention are explained as follows: This invention first assembles an electrolytic cell device comprising a cathode substrate, an anion exchange membrane, and an anode substrate. Under the influence of an electric field, a copper-based precursor is reduced and deposited at the cathode, and a Ni / Fe-based precursor is co-deposited at the anode. A uniform, binder-free coating layer is formed on the surfaces of the cathode substrate, the anode substrate, and the anion exchange membrane on the anode side. Subsequently, by changing the electrolyte and applying a reverse voltage, the copper-based precursor is electrochemically reduced to grain boundary-rich metallic copper nanosheets (CuNS). The grain boundaries and defect structures provide a large number of active sites for nitrate reduction to ammonia production, significantly improving electron transfer efficiency. The Ni / Fe precursor is simultaneously oxidized and reconstructed into nickel-iron hydroxyl oxide (NiFeOOH), a highly efficient catalyst for the oxygen evolution reaction, ensuring that the anode can rapidly and efficiently oxidize water to produce oxygen. By employing a two-step in-situ reconstruction technique to directly construct a high-performance catalytic layer on the membrane electrode assembly, the contact resistance and mass transfer resistance caused by traditional binders are eliminated, greatly reducing ohmic losses and exhibiting low impedance characteristics.

[0045] A second aspect of the present invention provides a membrane electrode device, comprising a membrane electrode fabricated using the in-situ construction method of the membrane electrode described in the first aspect of the present invention.

[0046] In some embodiments of the present invention, the membrane electrode device does not contain an adhesive.

[0047] The third aspect of the present invention provides the application of the membrane electrode device described in the second aspect of the present invention in the electrocatalytic reduction of nitrate to ammonia.

[0048] The membrane electrode device of this invention, when used for nitrate reduction to ammonia, utilizes the CuNS‖NiFeOOH electrode pairing. Through the functional complementarity of the cathode and anode, efficient operation of the electrolytic cell is achieved: the grain boundary-rich metallic Cu on the cathode provides highly active nitrate reduction sites for ammonia production, NO3 - Electrons are gradually gained and protonated on the cathode surface, leading to the formation of NH3 through multi-stage reduction. In this process, compared to room temperature, the higher temperature not only reduces charge transfer resistance but also promotes the hydrogenation conversion of intermediates, thereby simultaneously improving Faraday efficiency and ammonia yield. The NiFeOOH catalyst on the anode efficiently catalyzes the rapid oxidation of water to produce oxygen, maintaining charge balance, and its migration also helps maintain the pH gradient across the membrane, optimizing the cathode reaction environment.

[0049] A fourth aspect of the present invention provides a method for treating nitrate wastewater, comprising the following steps: The membrane electrode device described in the second aspect of the present invention contains an electrolyte on its cathode side; Replace the electrolyte on the cathode side with nitrate wastewater; A voltage is applied to the membrane electrode device to reduce nitrate on the cathode side to ammonia.

[0050] In some embodiments of the present invention, the concentration of nitrate in the nitrate wastewater is 0.001-10 mol / L.

[0051] In some preferred embodiments of the present invention, the concentration of nitrate in the nitrate wastewater is 0.01-5 mol / L.

[0052] In some more preferred embodiments of the present invention, the concentration of nitrate in the nitrate wastewater is 0.1-0.5 mol / L.

[0053] In some embodiments of the present invention, the nitrate wastewater undergoes alkalization and dilution pretreatment.

[0054] Compared with the prior art, the beneficial effects of the present invention are: 1) The in-situ construction method of membrane electrode provided by the present invention integrates the synthesis-loading-activation of catalyst with the assembly of membrane electrode, and completes the in-situ growth and reconstruction of the anode and cathode catalyst layers inside the device. It eliminates the cumbersome steps of catalyst pre-synthesis, coating, drying and hot pressing in the traditional process, greatly simplifies the process flow, reduces manufacturing costs, and has significant potential for large-scale application. 2) The in-situ construction method of membrane electrode provided by the present invention allows the catalyst to grow in situ on the surface of a three-dimensional porous substrate and anion exchange membrane, forming a binder-free three-dimensional interpenetrating network structure. This achieves close contact between the catalyst layer and the substrate and ion exchange membrane, fundamentally eliminating the physical interface and high impedance layer present in the traditional coating method, significantly reducing the resistance to electron and ion transport, and improving the mass transfer efficiency under low-concentration electrolyte. 3) The in-situ construction method of the membrane electrode provided by the present invention, through precise electrochemical control, reconstructs copper nanosheets rich in high-density grain boundaries in situ on the cathode side and forms highly active nickel-iron hydroxyl oxide on the anode side, exposing abundant active sites and avoiding the covering of active sites by binders, thereby greatly improving the catalyst utilization rate. The experimental results show that the membrane electrode achieves high ammonia yield, high Faradaic efficiency and excellent operating stability in the nitrate reduction ammonia production reaction. 4) The membrane electrode device provided by this invention exhibits an exponential increase in current density with temperature. High temperatures enhance the ionic conductivity of the electrolyte, reducing solution resistance and simultaneously decreasing interfacial charge transfer resistance, thus suppressing hydrogen evolution side reactions and allowing more electrons to be used for nitrate reduction. This is particularly relevant in large-area (25cm²) applications. 2 The device can still maintain high current density and high stability, and has the potential for industrial application; 5) The nitrate wastewater treatment method provided by the present invention uses a binder-free membrane electrode device, which maintains the core ammonia production performance. The ammonia production performance is not significantly reduced due to the complexity of the wastewater composition, providing an efficient, reliable and easily scalable technical solution for the resource-based treatment of nitrate wastewater. Attached Figure Description

[0055] Figure 1 This is a schematic diagram of the process for in-situ construction of the membrane electrode according to the present invention; Figure 2 This is a SEM image of the first precursor layer on the surface of the cathode substrate in Example 1; Figure 3 This is a SEM image of the first precursor layer on the cathode substrate surface in Example 2; Figure 4 This is a SEM image of the first precursor layer on the cathode substrate surface in Example 3; Figure 5 This is a SEM image of the first precursor layer on the cathode substrate surface in Example 4; Figure 6 This is a SEM image of the first precursor layer on the cathode substrate surface in Example 5; Figure 7 SEM images of the cathode catalyst layer (a) and the anode catalyst layer (b) in the membrane electrode device of Example 1; Figure 8The images show STEM (a), TEM (b), energy dispersive spectroscopy (EDS) analysis of Cu elemental distribution (c), and O elemental distribution (d) of the cathode catalyst layer in the membrane electrode device of Example 1. Figure 9 The images shown are HRTEM (a) and SAED (b) images of the cathode catalyst layer in the membrane electrode device of Example 1. Figure 10 The images show the Raman spectra of the second precursor layer and the anode catalyst layer in the membrane electrode device of Example 1. Figure 11 Here is a photograph of the electrode catalytic material of the membrane electrode device in Example 6; Figure 12 The linear sweep voltammetry curve (a) and electrochemical impedance spectroscopy (b) from Application Example 1 are shown. Figure 13 To apply the Faraday efficiency and ammonia yield from Example 1; Figure 14 The linear sweep voltammetry curve in Application Example 2; Figure 15 To apply the Faraday efficiency (a) and ammonia yield (b) from Example 2; Figure 16 The results of the nitrate reduction ammonia production cycle stability test in Application Example 2; Figure 17 The linear sweep voltammetric curve in Example 3 is used; Figure 18 Apply the Faraday efficiency and ammonia yield from Example 3; Figure 19 This is a statistical chart of the continuous electrolysis ammonia production output in Application Example 3. Detailed Implementation

[0056] The present invention will be further described in detail below through specific embodiments. Unless otherwise specified, the raw materials, reagents, or apparatus used in the embodiments can be obtained from conventional commercial sources or by existing technical methods. Unless otherwise specified, the experimental or testing methods are conventional methods in the art.

[0057] Figure 1 This is a schematic diagram of the in-situ construction process of the membrane electrode according to the present invention. Figure 1It can be seen that the in-situ construction method of the membrane electrode provided by the present invention has the following specific steps: (1) Pre-assembly: The cathode plate, cathode substrate (such as copper foam), anion exchange membrane, anode substrate (such as nickel foam) and anode plate are stacked and assembled in sequence to form an electrolytic cell device; (2) Applying a first voltage to perform the first step of electrochemical treatment: Electrolyte I is introduced into the cathode substrate side and electrolyte II is introduced into the anode side. The first voltage is applied to cause the cathode substrate to undergo electro-oxidation, and copper-based precursors are generated in situ on the cathode substrate surface; at the same time, metal ions on the anode substrate side migrate directionally under the action of the electric field, and anion exchange membranes are generated on the anode substrate surface and the anode side. Electrodeposition occurs on the film to form a nickel-iron-based precursor layer; (3) A second voltage is applied for the second step of electrochemical treatment: the electrolyte in the cathode and anode sides is drained, electrolyte III is introduced into the cathode side, electrolyte IV is introduced into the anode side, and a second voltage opposite to the first voltage is applied to cause electrochemical reduction on the cathode substrate surface, which is reconstructed in situ into a metallic copper nanosheet catalytic layer with high grain boundary density, used to catalyze the nitrate reduction reaction. At the same time, the nickel-iron-based hydroxide precursor on the anode substrate surface undergoes oxidative reconstruction to form a highly active nickel-iron hydroxyl oxide or similar catalytic layer, used to catalyze the oxygen evolution reaction. The following will be combined with Figure 1 The fabrication of the membrane electrode devices in Examples 1-6 is described below: Example 1 This embodiment prepares a binder-free membrane electrode device, using the following components / electrolyte: Cathode plate, anode plate: nickel alloy plate; Cathode substrate: copper foam, 0.5 mm thick, 1 cm × 1 cm in size, with a porosity of 90%-98%; Anion exchange membrane: PiperION-A20 anion exchange membrane; Anode substrate: Nickel foam, 0.4 mm thick, 1 cm × 1 cm in size, with a porosity of 90%-98%; Electrolyte I: 3 mol / L KOH solution; Electrolyte II: A mixture of 0.02 mol / L Ni(NO3)2, 0.02 mol / L Fe(NO3)3, 0.1 mol / L KNO3 and 0.06 mol / L C6H5Na3O7, with a total metal ion concentration of 0.04 mol / L and a molar ratio of complexing agent C6H5Na3O7 to metal ions of 1.5:1; Electrolyte III: 1 mol / L KOH solution containing 0.1 mol / L KNO3; Electrolyte IV: 1 mol / L KOH solution.

[0058] The preparation steps are as follows: S11. The nickel alloy plate, copper foam, anion exchange membrane, nickel foam and nickel alloy plate are stacked and assembled in sequence to form an electrolytic cell device. S21. Electrolyte I is introduced into the cathode side at a flow rate of 3 mL / min, and electrolyte II is introduced into the anode side at a flow rate of 1 mL / min. A first voltage is applied using a chronopotential method to perform simultaneous electrochemical oxidation and electrodeposition. The connectors of the working electrode and the sensing electrode are connected to the copper foam side, and the connectors of the reference electrode and the counter electrode are connected to the nickel foam side. The oxidation current density is controlled at 50 mA cm⁻¹. -2 The processing time is 20 minutes. During the processing, the cathode plate is heated and its temperature is controlled at 70°C, thereby forming a first precursor layer on the surface of the cathode substrate and a second precursor layer on the surface of the anode substrate and on the anion exchange membrane on the anode side. S31. Drain the electrolyte from the cathode and anode sides, rinse the flow channel with deionized water, then introduce electrolyte III into the cathode side at a flow rate of 40 mL / min and electrolyte IV into the anode side at a flow rate of 40 mL / min. Reverse the electrodes and apply a reverse voltage using a linear voltammetric scan method. The scan range is 1.2-2 V, the scan rate is 5 mV / s, the processing time is 10 min, and the temperature is 25 °C. Perform electroreduction activation and electrooxidation reconstruction treatments simultaneously on the anode and cathode to reconstruct the first precursor layer in situ into a nitrate reduction catalyst layer and the second precursor layer in situ into an oxygen evolution catalyst layer, thus obtaining the membrane electrode device.

[0059] Example 2 This embodiment prepares a binder-free membrane electrode device. The components / electrolyte used are the same as in Example 1, and the preparation steps are as follows: S11. The nickel alloy plate, copper foam, anion exchange membrane, nickel foam and nickel alloy plate are stacked and assembled in sequence to form an electrolytic cell device. S21. Electrolyte I is introduced into the cathode side at a flow rate of 3 mL / min, and electrolyte II is introduced into the anode side at a flow rate of 1 mL / min. A first voltage is applied using a chronopotential method to perform simultaneous electrochemical oxidation and electrodeposition. The connectors of the working electrode and the sensing electrode are connected to the copper foam side, and the connectors of the reference electrode and the counter electrode are connected to the nickel foam side. The oxidation current density is controlled at 50 mA cm⁻¹. -2 The processing time is 20 minutes. During the processing, the cathode plate is heated and its temperature is controlled at 25°C, thereby forming a first precursor layer on the surface of the cathode substrate and a second precursor layer on the surface of the anode substrate and on the anion exchange membrane on the anode side. S31. Drain the electrolyte from the cathode and anode sides, rinse the flow channel with deionized water, then introduce electrolyte III into the cathode side at a flow rate of 40 mL / min and electrolyte IV into the anode side at a flow rate of 40 mL / min. Reverse the electrodes and apply a reverse voltage using a linear voltammetric scan method. The scan range is 1.2-2 V, the scan rate is 5 mV / s, the processing time is 10 min, and the temperature is 25 °C. Perform electroreduction activation and electrooxidation reconstruction treatments simultaneously on the anode and cathode to reconstruct the first precursor layer in situ into a nitrate reduction catalyst layer and the second precursor layer in situ into an oxygen evolution catalyst layer, thus obtaining the membrane electrode device.

[0060] Example 3 This embodiment prepares a binder-free membrane electrode device. The components / electrolyte used are the same as in Example 1, and the preparation steps are as follows: S11. The nickel alloy plate, copper foam, anion exchange membrane, nickel foam and nickel alloy plate are stacked and assembled in sequence to form an electrolytic cell device. S21. Electrolyte I is introduced into the cathode side at a flow rate of 3 mL / min, and electrolyte II is introduced into the anode side at a flow rate of 1 mL / min. A first voltage is applied using a chronopotential method to perform simultaneous electrochemical oxidation and electrodeposition. The connectors of the working electrode and the sensing electrode are connected to the copper foam side, and the connectors of the reference electrode and the counter electrode are connected to the nickel foam side. The oxidation current density is controlled at 50 mA cm⁻¹. -2 The processing time is 20 minutes. During the processing, the cathode plate is heated and its temperature is controlled at 40°C, thereby forming a first precursor layer on the surface of the cathode substrate and a second precursor layer on the surface of the anode substrate and on the anion exchange membrane on the anode side. S31. Drain the electrolyte from the cathode and anode sides, rinse the flow channel with deionized water, then introduce electrolyte III into the cathode side at a flow rate of 40 mL / min and electrolyte IV into the anode side at a flow rate of 40 mL / min. Reverse the electrodes and apply a reverse voltage using a linear voltammetric scan method. The scan range is 1.2-2 V, the scan rate is 5 mV / s, the processing time is 10 min, and the temperature is 25 °C. Perform electroreduction activation and electrooxidation reconstruction treatments simultaneously on the anode and cathode to reconstruct the first precursor layer in situ into a nitrate reduction catalyst layer and the second precursor layer in situ into an oxygen evolution catalyst layer, thus obtaining the membrane electrode device.

[0061] Example 4 This embodiment prepares a binder-free membrane electrode device. The components / electrolyte used are the same as in Example 1, and the preparation steps are as follows: S11. The nickel alloy plate, copper foam, anion exchange membrane, nickel foam and nickel alloy plate are stacked and assembled in sequence to form an electrolytic cell device. S21. Electrolyte I is introduced into the cathode side at a flow rate of 0.18 mL / min, and electrolyte II is introduced into the anode side at a flow rate of 1 mL / min. A first voltage is applied using a chronopotential method to perform simultaneous electrochemical oxidation and electrodeposition. The connectors of the working electrode and the sensing electrode are connected to the copper foam side, and the connectors of the reference electrode and the counter electrode are connected to the nickel foam side. The oxidation current density is controlled at 50 mA cm⁻¹. -2 The processing time is 20 minutes. During the processing, the cathode plate is heated and its temperature is controlled at 70°C, thereby forming a first precursor layer on the surface of the cathode substrate and a second precursor layer on the surface of the anode substrate and on the anion exchange membrane on the anode side. S31. Drain the electrolyte from the cathode and anode sides, rinse the flow channel with deionized water, then introduce electrolyte III into the cathode side at a flow rate of 40 mL / min and electrolyte IV into the anode side at a flow rate of 40 mL / min. Reverse the electrodes and apply a reverse voltage using a linear voltammetric scan method. The scan range is 1.2-2 V, the scan rate is 5 mV / s, the processing time is 10 min, and the temperature is 25 °C. Perform electroreduction activation and electrooxidation reconstruction treatments simultaneously on the anode and cathode to reconstruct the first precursor layer in situ into a nitrate reduction catalyst layer and the second precursor layer in situ into an oxygen evolution catalyst layer, thus obtaining the membrane electrode device.

[0062] Example 5 This embodiment prepares a binder-free membrane electrode device. The components / electrolyte used are the same as in Example 1, and the preparation steps are as follows: S11. The nickel alloy plate, copper foam, anion exchange membrane, nickel foam and nickel alloy plate are stacked and assembled in sequence to form an electrolytic cell device. S21. Electrolyte I is introduced into the cathode side at a flow rate of 10 mL / min, and electrolyte II is introduced into the anode side at a flow rate of 1 mL / min. A first voltage is applied using a chronopotential method to perform simultaneous electrochemical oxidation and electrodeposition. The connectors of the working electrode and the sensing electrode are connected to the foamed copper side, and the connectors of the reference electrode and the counter electrode are connected to the foamed nickel side. The oxidation current density is controlled at 50 mA cm⁻¹. -2 The processing time is 20 minutes. During the processing, the cathode plate is heated and its temperature is controlled at 70°C, thereby forming a first precursor layer on the surface of the cathode substrate and a second precursor layer on the surface of the anode substrate and on the anion exchange membrane on the anode side. S31. Drain the electrolyte from the cathode and anode sides, rinse the flow channel with deionized water, then introduce electrolyte III into the cathode side at a flow rate of 40 mL / min and electrolyte IV into the anode side at a flow rate of 40 mL / min. Reverse the electrodes and apply a reverse voltage using a linear voltammetric scan method. The scan range is 1.2-2 V, the scan rate is 5 mV / s, the processing time is 10 min, and the temperature is 25 °C. Perform electroreduction activation and electrooxidation reconstruction treatments simultaneously on the anode and cathode to reconstruct the first precursor layer in situ into a nitrate reduction catalyst layer and the second precursor layer in situ into an oxygen evolution catalyst layer, thus obtaining the membrane electrode device.

[0063] Example 6 This embodiment prepares a binder-free membrane electrode device. The cathode substrate is made of copper foam with a size of 5cm × 5cm, and the anode substrate is made of nickel foam with a size of 5cm × 5cm. The remaining components / electrolyte are the same as in Example 1. The preparation steps are as follows: S11. The nickel alloy plate, copper foam, anion exchange membrane, nickel foam and nickel alloy plate are stacked and assembled in sequence to form an electrolytic cell device. S21. Electrolyte I is introduced into the cathode side at a flow rate of 12 mL / min, and electrolyte II is introduced into the anode side at a flow rate of 3 mL / min. A first voltage is applied using a chronopotential method to perform simultaneous electrochemical oxidation and electrodeposition. The connectors of the working electrode and the sensing electrode are connected to the copper foam side, and the connectors of the reference electrode and the counter electrode are connected to the nickel foam side. The oxidation current density is controlled at 50 mA cm⁻¹. -2 The processing time is 20 minutes. During the processing, the cathode plate is heated and its temperature is controlled at 70°C, thereby forming a first precursor layer on the surface of the cathode substrate and a second precursor layer on the surface of the anode substrate and on the anion exchange membrane on the anode side. S31. Drain the electrolyte from the cathode and anode sides, rinse the flow channel with deionized water, then introduce electrolyte III into the cathode side at a flow rate of 40 mL / min and electrolyte IV into the anode side at a flow rate of 40 mL / min. Reverse the electrodes and apply a reverse voltage using a linear voltammetric scan method. The scan range is 1.2-2 V, the scan rate is 5 mV / s, the processing time is 10 min, and the temperature is 25 °C. Perform electroreduction activation and electrooxidation reconstruction treatments simultaneously on the anode and cathode to reconstruct the first precursor layer in situ into a nitrate reduction catalyst layer and the second precursor layer in situ into an oxygen evolution catalyst layer, thus obtaining the membrane electrode device.

[0064] 1. Scanning electron microscopy characterization of the first precursor layer formed on the surface of the cathode substrate in Examples 1-5: Figure 2 This is a SEM image of the first precursor layer on the cathode substrate surface in Example 1. Figure 2It can be seen that during the electrochemical oxidation stage, when the temperature of the cathode plate is 70°C, the morphology of the first precursor layer formed on the cathode substrate surface in Example 1 is a two-dimensional nanosheet.

[0065] Figure 3 This is a SEM image of the first precursor layer on the cathode substrate surface in Example 2. Figure 3 It can be seen that during the electrochemical oxidation stage, when the temperature of the cathode plate is 25°C, the morphology of the first precursor layer formed on the cathode substrate surface in Example 2 is a one-dimensional nanowire.

[0066] Figure 4 This is a SEM image of the first precursor layer on the cathode substrate surface in Example 3. Figure 4 It can be seen that during the electrochemical oxidation stage, when the temperature of the cathode plate is 40°C, the first precursor layer formed on the cathode substrate surface in Example 3 has a mixed morphology of one-dimensional nanowires and two-dimensional nanosheets.

[0067] Figure 5 This is a SEM image of the first precursor layer on the cathode substrate surface in Example 4. Figure 5 It can be seen that during the electrochemical oxidation stage, when the temperature of the cathode plate is 70°C and the flow rate of electrolyte I is reduced from 3 mL / min to 0.18 mL / min, the first precursor layer formed on the cathode substrate surface in Example 4 has a two-dimensional nanosheet morphology that is different from that in Example 1.

[0068] Figure 6 This is a SEM image of the first precursor layer on the cathode substrate surface in Example 5. Figure 6 It can be seen that during the electrochemical oxidation stage, when the temperature of the cathode plate is 70°C and the flow rate of electrolyte I is increased from 3 mL / min to 10 mL / min, the morphology of the first precursor layer formed on the cathode substrate surface in Example 5 is a dense aggregate of nanoparticles.

[0069] Depend on Figures 2-6 It can be seen that by changing the flow rate of electrolyte I and the temperature of the cathode plate during the electrochemical oxidation stage, the morphology of the first precursor layer formed on the cathode substrate surface can be controlled.

[0070] 2. Characterization of the catalyst layers formed on the cathode and anode substrates in the membrane electrode device of Example 1: Figure 7 These are SEM images of the cathode catalytic layer (a) and anode catalytic layer (b) in the membrane electrode device of Example 1. Figure 7 It can be seen that the catalyst layer formed on the copper foam retains the nanosheet array characteristics of the precursor and forms metallic copper nanosheets after reduction; the catalyst layer formed on the nickel foam is a rough, porous, discontinuous covering layer formed by nickel iron hydroxyl oxide, and the porous structure is conducive to electrolyte mass transfer and oxygen evolution reaction.

[0071] Figure 8 The images shown are STEM images (a), TEM images (b), energy dispersive spectroscopy (EDS) analysis of the Cu elemental distribution (c), and O elemental distribution (d) of the cathode catalyst layer in the membrane electrode device of Example 1. Figure 8 It can be seen that the cathode catalyst layer exhibits a particle agglomeration, and the particles have light and dark regions inside, indicating that it has a polycrystalline or phase-separated structure. The distribution of Cu elements is highly consistent with the particle morphology, indicating that Cu elements are uniformly present in the catalyst material. The distribution of O elements is consistent with the particle region, indicating that O elements coexist with Cu elements. This means that the electroreduction process forms a hierarchical structure with metallic copper as the main phase and Cu / Cu2O heterostructure on the surface of the copper matrix.

[0072] Figure 9 The images shown are HRTEM (a) and SAED (b) images of the cathode catalyst layer in the membrane electrode device of Example 1. Figure 9 HRTEM images show that the electro-reduced copper grains exhibit a face-centered cubic structure. Measurements of the lattice spacing indicate the presence of two main characteristic spacings: 0.220 nm and 0.182 nm, corresponding to the (111) and (200) crystal planes of Cu, respectively (PDF# 04-0836). In some regions, lattice fringes of 0.246 nm and 0.240 nm are observed, which correspond to the spacing of the (111) crystal plane of Cu2O (PDF# 05-0667), indicating that there is incomplete reduction during the electro-reduction process and that cuprous oxide phase exists in local areas. At the edge of the copper grains, lattice fringes of the (111) crystal plane of Cu2O and the (111) crystal plane of Cu, with an alternating arrangement, show a lattice orientation difference of approximately 12° at the interface between the two phases. The d values ​​corresponding to the main diffraction rings in SAED are 2.08 Å (Cu(111)), 1.81 Å (Cu(200)) and 1.28 Å (Cu(220)), which are consistent with the standard copper diffraction data. Weak diffraction spots of 2.46 Å (Cu2O(111)) and 2.13 Å (Cu2O(200)) were also detected in the diffraction pattern, corresponding to the residual Cu2O grains.

[0073] Figure 10 The images shown are Raman spectra of the second precursor layer and the anode catalyst layer in the membrane electrode device of Example 1. Figure 10 It can be seen that the characteristic peak of the second precursor corresponds to Ni 2+ -O, Ni 2+ -OH, Fe-O and other bonded structures, after reconstruction, Ni appears in the product. 3+Characteristic peaks such as -OH and NiO indicate that Ni undergoes oxidation from +2 to +3 oxidation states, transforming from nickel-iron hydroxide (NiFe LDH) into highly active nickel-iron hydroxyl oxide (NiFeOOH). The characteristic peaks of the Fe-O bond are retained, ensuring the structural stability of the catalyst layer.

[0074] Figure 11 This is a photograph of the electrode catalytic material of the membrane electrode device in Example 6. Figure 6 It shows 5cm×5cm (25cm) 2 The macroscopic physical form of the large-area film electrode proves that the process of the present invention is scalable and has the potential for large-scale production.

[0075] Application Example 1 This application example uses the binder-free membrane electrode device prepared in Example 1 for electrocatalytic nitrate reduction to ammonia, and the steps are as follows: The electrolytes on the cathode and anode sides of the membrane electrode device in Example 1 were drained, and the flow channels were rinsed with deionized water. Two peristaltic pumps were used to control the circulation of the electrolytes on the cathode and anode sides, respectively. Electrolyte III (1 mol / L KOH solution containing 0.1 mol / L KNO3) was stored in the cathode side reservoir, and electrolyte IV (1 mol / L KOH solution) was stored in the anode side reservoir. The electrolytes in the reservoirs were pumped into the corresponding flow channels of the membrane electrode device through the peristaltic pumps. The outlet pipe of the device was connected to the reservoir to form a closed loop. The flow rates of the electrolytes at both the anode and cathode were controlled at 40 mL / min. The cathode and anode plates of the membrane electrode device were electrically connected to the electrochemical workstation through tabs.

[0076] The electrochemical performance of the membrane electrode device was tested using an electrochemical workstation (Zahner XC, Germany). The scanning method was linear voltammetry, with a scan range of 1.2–2 V and a scan rate of 5 mV / s. The reaction temperatures were set at 25 °C, 60 °C, and 80 °C. The temperature was controlled by heating the cathode plate, and the linear voltammetric curves at different temperatures were recorded. Figure 12 To apply the linear sweep voltammetry curve (a) and electrochemical impedance spectroscopy (b) from Example 1, from Figure 12 It can be seen that at the same potential, the current density increases significantly with increasing temperature, and the interfacial charge transfer resistance decreases effectively with increasing temperature. This indicates that heating can significantly accelerate electrode reaction kinetics, reduce cell voltage, improve energy utilization efficiency, or obtain a higher reaction rate at the same cell voltage. This is attributed to the fact that heating reduces electrolyte viscosity and accelerates ion migration rate and interfacial charge transfer kinetics.

[0077] The ammonia production performance of the membrane electrode device was tested in constant potential mode. The applied voltage was set to 2V, and the reaction temperatures were set to 25℃, 60℃, and 80℃, respectively. The temperature was controlled by heating the cathode plate. Ammonia concentration was measured by periodically sampling from the cathode-side storage tank, and the Faraday efficiency and ammonia yield were calculated. Figure 13 To apply the Faraday efficiency and ammonia yield from Example 1, from Figure 13 It can be seen that as the temperature increases, the Faraday efficiency of the membrane electrode device in Example 1 shows an upward trend, indicating that heating can improve the electron selectivity of ammonia generation, suppress side reactions such as hydrogen evolution, and allow more electrons to be used for nitrate reduction to produce ammonia. The increase in ammonia yield is much greater than that of Faraday efficiency, indicating that heating mainly increases the ammonia generation rate by accelerating reaction kinetics and mass transfer rate.

[0078] Application Example 2 This application example uses the binder-free membrane electrode device prepared in Example 6 for electrocatalytic nitrate reduction to ammonia production, and the steps are as follows: The electrolytes on the cathode and anode sides of the membrane electrode device in Example 6 were drained, and the flow channels were rinsed with deionized water. Two peristaltic pumps were used to control the electrolyte circulation on the cathode and anode sides, respectively. Electrolyte III (1 mol / L KOH solution containing 0.1 mol / L KNO3) was stored in the cathode side reservoir, and electrolyte IV (1 mol / L KOH solution) was stored in the anode side reservoir. The electrolytes in the reservoirs were pumped into the corresponding flow channels of the membrane electrode device through the peristaltic pumps. The device outlet pipe was connected to the reservoir to form a closed loop. The flow rates of the anode and cathode electrolytes were both controlled at 40 mL / min. The cathode and anode plates of the membrane electrode device were electrically connected to the electrochemical workstation through tabs.

[0079] The electrochemical performance of the membrane electrode device was tested using an electrochemical workstation (Zahner XC, Germany). The scanning method was linear voltammetry, with a scan range of 1.2–2 V and a scan rate of 5 mV / s. The reaction temperatures were set at 25 °C and 80 °C, respectively. The temperature was controlled by heating the cathode plate, and the linear voltammetric curves at different temperatures were recorded. Figure 14 To apply the linear sweep voltammetric curve in Example 2, from Figure 14 It can be seen that, at the same potential, as the temperature increases, the current density of the membrane electrode device in Example 6 gradually increases, which is the same as that of the membrane electrode device in Example 1. This indicates that the temperature regulation law on the reaction rate still holds after the process is scaled up, and the electrochemical performance of the large-area membrane electrode is not reduced due to the size increase.

[0080] The ammonia production performance of the membrane electrode device was tested in constant potential mode. The applied voltages were set to 1.8V, 1.9V, 2.0V, 2.1V, and 2.2V, and the reaction temperatures were set to 25℃ and 80℃, respectively. The temperature was controlled by heating the cathode plate. Ammonia concentration was measured by periodically sampling from the cathode-side storage tank, and the Faraday efficiency and ammonia yield were calculated. Figure 15 To apply the Faraday efficiency (a) and ammonia yield (b) from Example 2, from Figure 15 It can be seen that within the voltage range of 1.8-2.2V, the Faraday efficiency of the membrane electrode device in Example 6 is stable at around 80%, and the ammonia yield is as high as 2-3 mmol / h. -1 cm -2 Furthermore, at the same potential, both the Faraday efficiency and ammonia yield increase with increasing temperature, indicating that large-area membrane electrodes can achieve high-yield ammonia production.

[0081] To test the cyclic stability of the membrane electrode device used for nitrate reduction to ammonia production, the electrolytes on the cathode and anode sides of the membrane electrode device from Example 6 were drained, and the flow channels were rinsed with deionized water. Then, electrolyte III (1 mol / L KOH solution containing 0.1 mol / L KNO3) was introduced into the cathode side at a flow rate of 40 mL / min, and electrolyte IV (1 mol / L KOH solution) was introduced into the anode side at a flow rate of 40 mL / min. A constant potential mode was applied with a voltage of 2 V and a temperature of 80 °C for a certain period of time. The current density and Faraday efficiency were recorded. After the operation, the electrolytes on the cathode and anode sides were drained, and fresh electrolytes III and IV were replaced. This process was repeated 10 times. Figure 16 Based on the cyclic stability test results of nitrate reduction to ammonia production in Example 2, from Figure 16 It can be seen that the linear scanning voltammetric curves measured after each cycle almost overlap, indicating that the electrochemical activity of the electrode has not decayed and the corresponding Faraday efficiency value remains stable without significant decrease. This means that the catalyst layer does not detach or deactivate significantly during high-speed liquid flow scouring and repeated electrochemical cycles, and the in-situ constructed membrane electrode structure has excellent mechanical and chemical stability.

[0082] Application Example 3 This application example uses the binder-free membrane electrode device prepared in Example 6 for the treatment of nitrate wastewater. The nitrate wastewater is electroplating wastewater taken from the Jinmaoyuan Huizhou Surface Treatment Circular Economy Industrial Park. After alkalization and dilution treatment, NO3 in the wastewater is reduced. - The concentration is 0.5 mol / L, and the treatment steps are as follows: The electrolytes on the cathode and anode sides of the membrane electrode device in Example 6 were drained, and the flow channels were cleaned with deionized water. Two peristaltic pumps were used to control the electrolyte circulation on the cathode and anode sides, respectively. Nitrate wastewater was stored in the cathode side storage tank, and electrolyte IV (1 mol / L KOH solution) was stored in the anode side storage tank. The electrolyte in the storage tank was pumped into the corresponding flow channel of the membrane electrode device through the peristaltic pump. The device outlet pipe was connected to the storage tank to form a closed loop. The flow rate of the anode and cathode electrolytes was controlled at 40 mL / min. The cathode and anode plates of the membrane electrode device were electrically connected to the electrochemical workstation through tabs.

[0083] The electrochemical performance of the membrane electrode device was tested using an electrochemical workstation (Zahner XC, Germany). The scanning method was linear voltammetry, with a scan range of 1.2–2 V and a scan rate of 5 mV / s. The reaction temperature was set to 80 °C, and the temperature was controlled by heating the cathode plate. The linear voltammetric curves were recorded. Figure 17 To apply the linear sweep voltammetric curve in Example 3, from Figure 17 As can be seen, when the membrane electrode device in Example 6 is used to treat real wastewater, the current density is close to that of the simulated electrolyte, indicating that the impurities in the wastewater do not significantly inhibit the electrochemical reaction, and the device still maintains its core ammonia production performance, showing the potential to move from the laboratory to industrial applications.

[0084] The ammonia production performance of the membrane electrode device was tested in constant potential mode. The applied voltages were set to 1.8V, 1.9V, 2.0V, 2.1V, and 2.2V, and the reaction temperature was set to 80℃. The temperature was controlled by heating the cathode plate. Ammonia concentration was measured by periodically sampling from the cathode-side storage tank, and the Faraday efficiency and ammonia yield were calculated. Figure 18 Applying the Faraday efficiency and ammonia yield from Example 3, by Figure 18 It can be seen that when the membrane electrode device in Example 6 is used to treat real wastewater, the Faraday efficiency is stable at 65%-80%, and the ammonia yield remains at 1.5-3 mmol / h. -1 cm -2 The performance was similar to that of the simulated electrolyte, and the ammonia production performance did not decrease significantly due to the complex composition of the wastewater.

[0085] The electrolytes on the cathode and anode sides of the membrane electrode device in Example 6 were drained, and the flow channels were rinsed with deionized water. Then, 0.1 L of alkalized and diluted electroplating wastewater was introduced to the cathode side at a flow rate of 40 mL / min, and electrolyte IV (1 mol / L KOH solution) was introduced to the anode side at a flow rate of 40 mL / min. A constant potential electrolysis experiment was conducted using a voltage of 2 V and a reaction temperature of 80 °C to verify the continuous working capability of the in-situ constructed membrane electrode device in a real wastewater environment. Figure 19 To illustrate the production statistics of continuous electrolytic ammonia production in Application Example 3, from... Figure 19 As can be seen, when the membrane electrode device in Example 6 is used to treat real wastewater, the ammonia production increases linearly with electrolysis time without a plateau period, indicating that nitrate can be continuously reduced without mass transfer limitations. A total of 22 mmol of ammonia is generated within 2 hours, proving that the membrane electrode has a high-efficiency and stable continuous ammonia production capacity in the real wastewater system, indicating that the membrane electrode can be adapted to the continuous treatment conditions of industrial wastewater.

Claims

1. A method for in-situ construction of a membrane electrode, characterized in that, Includes the following steps: S1. The cathode plate, cathode substrate, anion exchange membrane, anode substrate and anode plate are sequentially stacked and assembled to form an electrolytic cell device; S2. Electrolyte I is introduced into the cathode side and electrolyte II is introduced into the anode side. A first voltage is applied to perform the first step of electrochemical treatment, forming a first precursor layer on the cathode substrate surface and a second precursor layer on the anode substrate surface and the anode-side anion exchange membrane. S3. After draining the electrolyte from the cathode and anode sides, electrolyte III is introduced into the cathode side and electrolyte IV is introduced into the anode side. A second voltage opposite to the direction of the first voltage is applied to perform the second electrochemical treatment, so that the first precursor layer is reconstructed in situ into a nitrate reduction catalyst layer and the second precursor layer is reconstructed in situ into an oxygen evolution catalyst layer, thus obtaining a membrane electrode.

2. The in-situ construction method of the membrane electrode according to claim 1, characterized in that, In step S1, the cathode substrate is selected from copper foam, copper mesh, or copper felt; And / or, the anode substrate is selected from nickel foam, nickel mesh, stainless steel felt, or titanium mesh.

3. The in-situ construction method of the membrane electrode according to claim 1, characterized in that, In step S2, the electrolyte I is an alkaline solution; the concentration of alkali in the electrolyte I is 1-6 mol / L. And / or, the electrolyte II is Ni-containing 2+ and / or Fe 2+ / Fe 3+ The solution contains a total concentration of metal ions of 0.01-1 mol / L.

4. The in-situ construction method of the membrane electrode according to claim 3, characterized in that, In step S2, the first voltage is applied using a chronopotential method with a current density of 10-100 mA / cm². 2 The electrochemical treatment in the first step takes 10-60 minutes.

5. The in-situ construction method of the membrane electrode according to claim 1, characterized in that, In step S3, the electrolyte III is an alkaline solution containing nitrates; the concentration of alkali in the electrolyte III is 1-6 mol / L, and the concentration of nitrates is 0.01-1 mol / L. And / or, the electrolyte IV is an alkaline solution; the concentration of alkali in the electrolyte IV is 1-6 mol / L.

6. The in-situ construction method of the membrane electrode according to claim 5, characterized in that, In step S3, the method for applying the second voltage is selected from linear voltammetry, constant voltage or constant current or cyclic voltammetry; the scan range is 1-3V, the scan rate is 0.1-100mV / s; the time for the second electrochemical treatment is 10-120min.

7. A membrane electrode device, characterized in that, This includes preparation using the in-situ construction method of the membrane electrode according to any one of claims 1-6.

8. The application of the membrane electrode device according to claim 7 in the electrocatalytic reduction of nitrate to ammonia.

9. A method for treating nitrate wastewater, characterized in that, Includes the following steps: The membrane electrode device according to claim 7 is used, wherein the cathode side of the membrane electrode device contains an electrolyte; Replace the electrolyte on the cathode side with nitrate wastewater; A voltage is applied to the membrane electrode device to reduce nitrate on the cathode side to ammonia.

10. The method for treating nitrate wastewater according to claim 9, characterized in that, The concentration of nitrate in the nitrate wastewater is 0.001-10 mol / L.

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