Copper electrode based on uiO-66-nh2 metal organic framework thin film modification, preparation method and application thereof

Abstract

The application provides a copper electrode based on a UiO-66-NH2 metal organic framework film, and a preparation method and application thereof, and relates to the fields of electrocatalysis and new energy materials. The electrode is composed of a rough metal copper substrate (rCu) and a continuous and uniform dense film of UiO-66-NH2 on the surface, the rCu is prepared by chemical oxidation of a commercial copper foil to generate CuO nanosheets and then electrochemical reduction, and the film is grown by cathodic electrodeposition for 20 minutes. The electrode is applied to the electrocatalytic reduction of nitrate to synthesize ammonia in a neutral medium, the enrichment of hydrated potassium ions in the film, the reconstruction of the interface water to build a rich-proton limited microenvironment, and the reduction of the activation energy of the rate-determining step. In a continuous flow system, the electrode can be stably operated at a current density of 800 mA cm ‑2 for more than 40 hours, and high-purity ammonium chloride can be recovered, so that the problems of insufficient proton supply, low selectivity and low activity in the prior art are solved.

Description

Technical Field

[0001] This invention relates to the fields of electrocatalysis and new energy materials, and more specifically, to a copper electrode based on a UiO-66-NH2 metal-organic framework thin film modified with copper electrode, its preparation method and application. Background Technology

[0002] Ammonia (NH3) is an important chemical raw material widely used in the production of fertilizers, explosives, and various industrial chemicals. Furthermore, ammonia has attracted increasing attention in recent years as a carbon-free hydrogen carrier in sustainable energy systems. However, the traditional Haber-Bosch ammonia synthesis process operates under harsh conditions of high temperature and pressure, generating significant CO2 emissions, resulting in high energy consumption and poor environmental sustainability.

[0003] Electrochemical nitrate reduction reaction (eNO3RR) has emerged as a promising green alternative for ammonia synthesis. This method not only enables decentralized green ammonia synthesis under environmental conditions but also addresses the environmental crisis caused by nitrate-contaminated wastewater, effectively converting pollutants into resources. However, achieving highly selective and reactive NH3 production remains extremely challenging due to the complex proton-coupled multi-electron transfer steps, competing side reactions (such as the hydrogen evolution reaction), and the lack of effective control over the interfacial reaction microenvironment. Particularly in neutral media, which are preferred in practical applications, the efficiency of eNO3RR is severely limited by the slow proton-coupled electron transfer (PCET) kinetics. In neutral electrolytes, free protons are scarce (H+ ≈ 10⁻⁶). -7 (M) Water molecules must act as the primary proton donor, but the slow water dissociation kinetics severely hinder the PCET step, resulting in a high overpotential and poor ammonia production selectivity due to the competitive hydrogen evolution reaction. Therefore, we propose an improvement, including a copper electrode based on a UiO-66-NH2 metal-organic framework thin film, its preparation method, and its application. Summary of the Invention

[0004] The purpose of this invention is to overcome the above-mentioned defects of the prior art and provide a copper electrode based on metal-organic framework thin film modification, which solves the problems of insufficient proton supply, severe hydrogen evolution competition, and low ammonia production selectivity and activity in the electrocatalytic reduction of nitrate in neutral medium.

[0005] To achieve the above-mentioned objectives, this invention provides the following technical solution: To achieve the above objectives, this invention employs a biomimetic interface microenvironment control strategy to construct an amino-functionalized UiO-66 metal-organic framework (UiO-66-NH2) thin film on the surface of a copper electrode. The specific technical solution is as follows: A method for preparing a copper electrode modified with a UiO-66-NH2 thin film includes the following steps: (1) Preparation of a rough metallic copper substrate (rCu): First, commercial copper foil is chemically oxidized to form CuO nanosheets; then, electrochemical reduction is performed to generate a rough metallic copper (rCu) substrate with high-density active sites. (2) Electrochemical deposition of the UiO-66-NH2 thin film: A UiO-66-NH2 thin film is grown on the above-mentioned rCu surface using a cathodic electrodeposition method. The optimized electrodeposition time is 20 minutes to balance microenvironment regulation and mass transfer, forming a continuous and uniform thin film.

[0006] In the electrocatalytic reduction of nitrates, the UiO-66-NH2 film prepared in this invention acts as an interface organizer, reshaping the distribution of hydrated cations near the metal surface. This amino-functionalized framework preferentially enriches hydrated potassium ions (K+) within the electrical double layer. + The H2O group recombines with the interfacial water, creating a proton-rich and spatially confined microenvironment that facilitates the conversion of nitrates to ammonia.

[0007] The copper electrode based on the UiO-66-NH2 metal-organic framework film modification includes a rough copper substrate (rCu) and a UiO-66-NH2 film layer covering the surface of the rCu. The UiO-66-NH2 film is a continuous, uniform, and dense structure, and the rCu is a nanosheet structure with high-density active sites.

[0008] As a preferred technical solution of the present invention, the UiO-66-NH2 thin film is grown on the rCu surface by cathodic electrodeposition for a time of 20 minutes.

[0009] The method for preparing a copper electrode based on a UiO-66-NH2 metal-organic framework thin film includes the following steps: Step (1) Preparation of rough metallic copper substrate (rCu): Commercial copper foil is chemically oxidized sequentially to form CuO nanosheets, and then electrochemically reduced to obtain rCu with nanosheet structure; Step (2) Electrochemical deposition of UiO-66-NH2 thin film: UiO-66-NH2 thin film is grown on the surface of rCu prepared in step (1) by cathodic electrodeposition method, and the electrodeposition time is controlled to be 20 minutes to form a continuous, uniform and dense thin film layer.

[0010] As a preferred technical solution of the present invention, the purpose of the chemical oxidation treatment in step (1) is to form CuO nanosheets on the surface of commercial copper foil, and the purpose of the electrochemical reduction treatment is to transform the CuO nanosheets into a rough metallic copper substrate with high-density active sites.

[0011] As a preferred technical solution of the present invention, the process parameters of the cathode electrodeposition in step (2) are optimized so that the UiO-66-NH2 microcrystals merge to form a dense structure, and the film thickness balances the microenvironment control effect and mass transfer efficiency.

[0012] The application of copper electrodes modified with UiO-66-NH2 metal-organic framework films in the electrocatalytic reduction of nitrate to ammonia synthesis, wherein the reaction medium is a neutral electrolyte, and the copper electrode participates as a cathode in the electrocatalytic reduction of nitrate (eNO3RR).

[0013] As a preferred technical solution of the present invention, in the electrocatalytic nitrate reduction reaction, the UiO-66-NH2 thin film enriches hydrated potassium ions (K... + (·H2O) and recombine interfacial water to construct a proton-rich confined microenvironment on the electrode surface, reducing NO3. - The rate-determining activation energy for conversion into NHO3.

[0014] As a preferred embodiment of the present invention, the electrocatalytic performance of the application satisfies the following conditions: Faradaic efficiency (FE) ≥ 95%, ammonia yield ≥ 5.02 mmol / cm². -2 h -1 Ammonia partial current density ≥ 1 A cm -2 It should maintain stable operation.

[0015] As a preferred embodiment of the present invention, the operational stability of the application satisfies the following conditions: catalytic activity decay is negligible after 20 consecutive cycles in the batch circulation system; and the catalytic activity remains stable at 800 mA cm⁻¹ in the continuous flow system. -2 Stable operation at current density for ≥40 hours with Faraday efficiency maintained above 95%.

[0016] As a preferred technical solution of the present invention, the application also includes recovering high-purity ammonium chloride (NH4Cl) powder from the electrolyte after the reaction. The recovery process is achieved by integrating a gas stripping system with the electrolysis reaction.

[0017] Compared with the prior art, the beneficial effects of this invention are as follows: This invention significantly improves ammonia production performance: The optimized UiO-66-NH2@Cu electrode exhibits excellent electrocatalytic performance, with a Faradaic efficiency (FE) of 98.6% and an ammonia yield of 5.02 mmol / cm³. -2 h -1 And can exceed 1 A cm -2 It maintains stable operation under the ammonia part current density.

[0018] Excellent operational stability: In batch cyclic systems, the catalytic activity decay is negligible after 20 consecutive cycles; in continuous flow systems, at 800 mA cm⁻¹...-2 Under high current density, the catalyst operates stably for more than 40 hours, and the Faraday efficiency remains above 95%.

[0019] Lowering the activation energy of the rate-determining step: Hydrated cations (K+) enriched in the thin film layer + H₂O has a superior proton-donating function compared to bulk water, significantly reducing the amount of protons drawn from NO₃⁻. - The activation barrier at the rate-determining step of NHO3 significantly accelerates the proton-coupled electron transfer process. Attached image description: Figure 1 This is a schematic diagram of electrode preparation and characterization provided by the present invention; Figure 2 This is a schematic diagram of the electrocatalytic nitrate reduction activity provided by the present invention; Figure 3 This is a schematic diagram of the interface water structure provided by the present invention for in-situ infrared spectral analysis. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are specific implementations of the present invention and are not limited to all embodiments.

[0021] Therefore, the following detailed description of embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely illustrates some embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0022] It should be noted that, in the absence of conflict, the embodiments and features and technical solutions in the embodiments of the present invention can be combined with each other. It should be noted that similar reference numerals and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0023] Example 1: Preparation of rough metallic copper substrate (rCu) Commercial Cu foil was first chemically oxidized to form CuO nanosheets on its surface, and then placed in an electrolyte for electrochemical reduction treatment to finally generate rough metallic copper (rCu) with a dense nanosheet structure as an electrode substrate. This substrate can provide a high surface area support for the subsequent growth of thin films.

[0024] Example 2: Fabrication of UiO-66-NH2@Cu Modified Electrode. A UiO-66-NH2 thin film was grown on the rCu substrate prepared in Example 1 using cathodic electrodeposition. The optimal electrodeposition time was controlled to be 20 minutes, allowing the MOF microcrystals to coalesce into a dense and uniform thin film layer covering the copper surface. This deposition time provides sufficient interfacial microenvironment control while avoiding mass transfer obstacles caused by excessive film thickness, thereby achieving close contact between the MOF and Cu and maintaining an efficient charge transfer pathway.

[0025] Example 3: Electrocatalytic Nitrate Reduction and Ammonia Production Performance Test The UiO-66-NH2@Cu electrode prepared in Example 2 was applied to test the electrocatalytic nitrate reduction reaction in a neutral medium. Experimental results showed that, at the applied reduction potential, compared to a pure copper electrode (only about 54% Faradaic efficiency), this modified electrode achieved a Faradaic efficiency as high as 98.6% at -1.1 V vs RHE potential, with a record ammonia yield of 5.02 mmol / cm³. -2 h -1 Simultaneously, by integrating this catalytic reaction with a gas stripping system and electrolyzing for 24 hours, high-purity ammonium chloride (NH4Cl) powder was successfully recovered from the electrolyte. Furthermore, at 800 mA cm⁻¹... -2 After running in a high-current continuous flow system for 40 hours, the catalyst exhibited excellent stability, with the Faraday efficiency remaining stable at over 95%, and the morphology, crystal structure, and chemical state of the thin-film modified electrode showed no significant changes after the reaction.

[0026] Example 4: A copper electrode modified with a UiO-66-NH2 metal-organic framework thin film, comprising a rough copper substrate (rCu) and a UiO-66-NH2 thin film layer covering the surface of rCu. The UiO-66-NH2 thin film is a continuous, uniform, and dense structure, and rCu is a nanosheet structure with high-density active sites.

[0027] UiO-66-NH2 thin films were grown on the rCu surface by cathodic electrodeposition for 20 minutes.

[0028] The method for preparing a copper electrode based on a UiO-66-NH2 metal-organic framework thin film includes the following steps: Step (1) Preparation of rough metallic copper substrate (rCu): Commercial copper foil is chemically oxidized sequentially to form CuO nanosheets, and then electrochemically reduced to obtain rCu with nanosheet structure; Step (2) Electrochemical deposition of UiO-66-NH2 thin film: UiO-66-NH2 thin film is grown on the surface of rCu prepared in step (1) by cathodic electrodeposition method, and the electrodeposition time is controlled to be 20 minutes to form a continuous, uniform and dense thin film layer.

[0029] The purpose of chemical oxidation treatment in step (1) is to form CuO nanosheets on the surface of commercial copper foil, and the purpose of electrochemical reduction treatment is to transform CuO nanosheets into a rough metallic copper substrate with high-density active sites.

[0030] In step (2), the process parameters of cathode electrodeposition are optimized so that UiO-66-NH2 microcrystals merge to form a dense structure, and the film thickness balances the microenvironment control effect and mass transfer efficiency.

[0031] The application of copper electrodes modified with UiO-66-NH2 metal-organic framework films in the electrocatalytic reduction of nitrate to ammonia synthesis. The reaction medium used is a neutral electrolyte, and the copper electrode participates in the electrocatalytic reduction of nitrate (eNO3RR) as the cathode.

[0032] In the electrocatalytic nitrate reduction reaction, the UiO-66-NH2 membrane enriches hydrated potassium ions (K... + (·H2O) and recombine interfacial water to construct a proton-rich confined microenvironment on the electrode surface, reducing NO3. - The rate-determining activation energy for conversion into NHO3.

[0033] The electrocatalytic performance of the application meets the following requirements: Faradaic efficiency (FE) ≥ 95%, ammonia yield ≥ 5.02 mmol / cm². -2 h -1 Ammonia partial current density ≥ 1 A cm -2 It should maintain stable operation.

[0034] The application's operational stability meets the following requirements: catalytic activity degradation is negligible after 20 consecutive cycles in a batch circulating system; and in a continuous flow system, catalytic activity remains stable at 800 mA cm⁻¹. -2 Stable operation at current density for ≥40 hours with Faraday efficiency maintained above 95%.

[0035] Applications also include the recovery of high-purity ammonium chloride (NH4Cl) powder from the electrolyte after the reaction, with the recovery process being integrated with the electrolysis reaction via a gas stripping system.

[0036] The above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described herein. Although the present invention has been described in detail with reference to the above embodiments, the present invention is not limited to the specific embodiments described above. Therefore, any modifications or equivalent substitutions to the present invention, as well as all technical solutions and improvements that do not depart from the spirit and scope of the invention, are covered within the scope of the claims of the present invention.

Claims

1. A copper electrode modified with a UiO-66-NH2 metal-organic framework thin film, characterized in that, It includes a rough metallic copper substrate (rCu) and a UiO-66-NH2 thin film layer covering the surface of the rCu. The UiO-66-NH2 thin film has a continuous, uniform, and dense structure, and the rCu has a nanosheet structure with high-density active sites.

2. The copper electrode based on UiO-66-NH2 metal-organic framework thin film modification according to claim 1, characterized in that, The UiO-66-NH2 thin film was grown on the rCu surface by cathodic electrodeposition for 20 minutes.

3. A method for preparing a copper electrode based on a UiO-66-NH2 metal-organic framework thin film modified as described in claim 1, characterized in that, Includes the following steps: Step (1) Preparation of rough metallic copper substrate (rCu): Commercial copper foil is chemically oxidized sequentially to form CuO nanosheets, and then electrochemically reduced to obtain rCu with nanosheet structure; Step (2) Electrochemical deposition of UiO-66-NH2 thin film: UiO-66-NH2 thin film is grown on the surface of rCu prepared in step (1) by cathodic electrodeposition method, and the electrodeposition time is controlled to be 20 minutes to form a continuous, uniform and dense thin film layer.

4. The method for preparing a copper electrode based on a UiO-66-NH2 metal-organic framework thin film modified according to claim 3, characterized in that, The purpose of the chemical oxidation treatment in step (1) is to form CuO nanosheets on the surface of commercial copper foil, and the purpose of the electrochemical reduction treatment is to transform the CuO nanosheets into a rough metallic copper substrate with high-density active sites.

5. The method for preparing a copper electrode based on a UiO-66-NH2 metal-organic framework thin film modified according to claim 3, characterized in that, The process parameters of the cathode electrodeposition in step (2) are optimized so that the UiO-66-NH2 microcrystals merge to form a dense structure, and the film thickness balances the microenvironment control effect and mass transfer efficiency.

6. The application of the copper electrode modified with a UiO-66-NH2 metal-organic framework thin film as described in claim 1 in the electrocatalytic reduction of nitrate to ammonia, characterized in that, The reaction medium used in this application is a neutral electrolyte, and the copper electrode serves as the cathode in the electrocatalytic reduction reaction of nitrate (eNO3RR).

7. The application of the copper electrode modified with a UiO-66-NH2 metal-organic framework thin film according to claim 6 in the electrocatalytic reduction of nitrate to ammonia, characterized in that, In the electrocatalytic nitrate reduction reaction, the UiO-66-NH2 membrane enriches hydrated potassium ions (K... + (·H2O) and recombine interfacial water to construct a proton-rich confined microenvironment on the electrode surface, reducing NO3. - The rate-determining activation energy for conversion into NHO3.

8. The application of the copper electrode modified with a UiO-66-NH2 metal-organic framework thin film according to claim 6 in the electrocatalytic reduction of nitrate to ammonia, characterized in that, The electrocatalytic performance of the application meets the following requirements: Faraday efficiency (FE) ≥ 95%, ammonia yield ≥ 5.02 mmol / cm². -2 h -1 Ammonia partial current density ≥ 1 A cm -2 It should maintain stable operation.

9. The application of the copper electrode modified with a UiO-66-NH2 metal-organic framework thin film according to claim 6 in the electrocatalytic reduction of nitrate to ammonia, characterized in that, The operational stability of the application meets the following requirements: catalytic activity decay is negligible after 20 consecutive cycles in the batch cycle system; and in the continuous flow system, the catalytic activity remains stable at 800 mA cm⁻¹. -2 Stable operation at current density for ≥40 hours with Faraday efficiency maintained above 95%.

10. The application of the copper electrode modified with a UiO-66-NH2 metal-organic framework thin film according to claim 6 in the electrocatalytic reduction of nitrate to ammonia, characterized in that, The application also includes the recovery of high-purity ammonium chloride (NH4Cl) powder from the electrolyte after the reaction, with the recovery process being integrated with the electrolysis reaction via a gas stripping system.

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