A dual-function MOF electrode for proton concentration detection and electrocatalysis, its preparation method, and its application.

Abstract

This invention discloses a dual-function MOF electrode for proton concentration detection and electrocatalysis, its preparation method, and its application. The preparation method of this dual-function MOF electrode includes the following steps: (1) preparing a metal-organic framework (MOF); (2) modifying the MOF using an impregnation method at a temperature of 25℃-180℃ for 2-72 hours to obtain a dual-function MOF' for electrocatalysis and sensing. The impregnation process includes two steps: impregnation with a metal salt solution and impregnation with a functional ligand solution. After the impregnation modification is completed, the dual-function MOF' is washed to obtain the modified MOF'; (3) uniformly dispersing the dual-function MOF' in a Nafion-containing solution, then drop-coating it onto a conductive substrate at a mass ratio of 1:10-1000. After drying to form a film, the dual-function MOF electrode is obtained. The MOF electrode proposed in this invention can achieve both catalysis and in-situ observation of proton concentration on the electrode surface.

Description

Technical Field

[0001] This invention relates to the field of electrocatalysis and in-situ detection technology, and in particular to a dual-function MOF electrode integrating proton concentration detection and electrocatalysis, its preparation method, and its application. Background Technology

[0002] Currently, electrocatalysis technology has been applied in many fields, such as hydrogen production through water electrolysis, electrochemical carbon dioxide reduction, and electrochemical ammonia production. These processes all share a common characteristic: proton-reactant coupling. The proton coupling process is of great significance for both the study of electrocatalysis mechanisms and the control of reaction product selectivity. However, the lack of research tools to monitor the distribution and migration behavior of protons on the electrode surface in situ is a problem that urgently needs to be solved. Summary of the Invention

[0003] This invention solves the above-mentioned problems existing in the prior art. The purpose of this invention is to provide a dual-function MOF electrode for proton concentration detection and electrocatalysis, its preparation method and application. This MOF electrode can realize two functions: catalysis and in-situ observation of proton concentration on the electrode surface.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is: a method for preparing a dual-function MOF electrode integrating proton concentration detection and electrocatalysis, comprising the following steps:

[0005] (1) Preparation of metal-organic framework (MOF) materials;

[0006] (2) Metal-organic framework materials (MOFs) are modified by impregnation. The modification temperature is 25℃-180℃ and the modification time is 2-72h to obtain MOF' with dual electrocatalytic and sensing functions. The impregnation process includes two steps: impregnation with metal salt solution and impregnation with functional ligand solution. The order of the two steps can be interchanged. The MOF' with dual electrocatalytic and sensing functions is washed to obtain the modified MOF'.

[0007] (3) After uniformly dispersing the modified MOF' in a Nafion-containing solution, it is drop-coated onto a conductive substrate. The mass ratio of MOF' to Nafion-containing solution is 1:10 to 1000. After drying to form a film, a bifunctional integrated MOF electrode is obtained.

[0008] Preferably, the metal-organic framework material (MOF) in step (1) is selected from one or more of UiO-66, UiO-67, MOF-808, MIL-101, HKUST-1, and ZIF-8. Step (1) uses a one-pot method to prepare the metal-organic framework material (MOF).

[0009] The synthesis method of metal-organic framework UiO-66 is as follows: using zirconium tetrachloride and terephthalic acid as raw materials, and N,N-dimethylformamide and acetic acid as solvents, the reaction is carried out at 100℃~220℃ for 10-24h, then cooled to room temperature, filtered, washed 4 times each with N,N-dimethylformamide and methanol, and dried to obtain the product UiO-66; wherein, the molar ratio of zirconium tetrachloride, terephthalic acid, N,N-dimethylformamide and acetic acid is 1:1~1.5:1000-1800:200-800.

[0010] The synthesis method of metal-organic framework MOF-808 is as follows: using zirconium oxychloride octahydrate and trimesic acid as raw materials, and N,N-dimethylformamide as solvent, the reaction is carried out at 70℃~150℃ for 10~30h, then cooled to room temperature, filtered, and washed three times with N,N-dimethylformamide to obtain MOF-808; wherein, the molar ratio of zirconium oxychloride octahydrate, trimesic acid, and N,N-dimethylformamide is 1:0.25~1:100~300.

[0011] The synthesis method of metal-organic framework MIL-101 is as follows: using ferric chloride hexahydrate and terephthalic acid as raw materials, and N,N-dimethylformamide as solvent, the reaction is carried out at 80℃~160℃ for 2~72h, then cooled to room temperature, filtered, and washed three times with N,N-dimethylformamide and ethanol respectively, the product is MIL-101; wherein, the molar ratio of ferric chloride hexahydrate, terephthalic acid and N,N-dimethylformamide is 1:0.25~3:100~1000.

[0012] The synthesis method of metal-organic framework ZIF-8 is as follows: using zinc nitrate tetrahydrate and 2-methylimidazole as raw materials, and N,N-dimethylformamide as solvent, the reaction is carried out at 100℃~180℃ for 18~36h, then cooled to room temperature, filtered, and washed three times with N,N-dimethylformamide to obtain ZIF-8; wherein, the molar ratio of zinc nitrate tetrahydrate to 2-methylimidazole and N,N-dimethylformamide is 1:0.5~1.5:200~400.

[0013] Preferably, the volume of the metal salt solution or functional ligand solution in step (2) is more than twice the geometric volume of the metal-organic framework (MOF) material.

[0014] In step (2), the metal ions in the metal salt solution are selected from one or more of iron, cobalt, nickel, copper, ruthenium, platinum, and rare earth elements. The functional ligand is a coumarin-derived ligand or a rare earth ion-modified pyridine carboxylic acid ligand. The concentration of the metal salt solution or functional ligand solution is 0.001–2.000 mol / L. The coumarin-derived ligand is 7-hydroxycoumarin-3-propionic acid or 7-hydroxycoumarin-2-acetic acid.

[0015] Preferably, the solvent for the metal salt solution or functional ligand solution in step (2) is selected from water, methanol, ethanol, isopropanol, tetrahydrofuran, toluene, DMF (N,N-dimethylformamide), and NMP (N-methylpyrrolidone). The metal salt is CuCl2, Co(CH3COO)2, or other metal salts.

[0016] Preferably, the Nafion-containing solvent in step (3) is selected from one or more of water, methanol, ethanol, isopropanol, DMF and NMP, and the mass fraction of Nafion in the Nafion-containing solution is 0.1% to 40.0%.

[0017] Preferably, the film-forming environment in step (3) is atmospheric atmosphere, the film-forming temperature is 25℃~200℃, and the film-forming time is 0.5~24.0h.

[0018] Preferably, the conductive substrate material in step (3) is selected from one of ITO conductive glass, FTO conductive glass, foamed metal, glassy carbon, conductive carbon cloth and conductive carbon paper.

[0019] This invention also protects the integrated MOF electrode for proton concentration detection and electrocatalysis prepared according to the above preparation method.

[0020] This invention also protects the application of the above-mentioned dual-functional integrated MOF electrode as a cathode material for electrocatalysis, wherein the electrocatalysis includes water electrolysis, carbon dioxide reduction, nitrogen reduction and nitrate reduction.

[0021] Compared with the prior art, the beneficial effects of the present invention are: the bifunctional integrated MOF electrode prepared by the preparation method of the present invention can be used as a cathode material for technologies such as water electrolysis, carbon dioxide reduction, nitrogen reduction, and nitrate reduction, and at the same time realizes the fluorescence response of the proton concentration change on the electrode surface during the above reactions. Attached Figure Description

[0022] Figure 1 These are the XRD diffraction patterns of the UiO-66 and UiO-66' samples obtained in Example 1;

[0023] Figure 2 These are optical photographs of the UiO-66 and UiO-66' samples obtained in Example 1, along with their corresponding fluorescence emission states (excited at 365 nm).

[0024] Figure 3 The UiO-66' obtained in Example 1 is for different H + Fluorescence sensing image of concentration solution (365nm excitation);

[0025] Figure 4The polarization curve of UiO-66' obtained in Example 1 for electrocatalytic water splitting to produce hydrogen is shown below.

[0026] Figure 5 The polarization curve of UiO-66' obtained in Example 1 for electrocatalytic reduction of nitrate to synthesize ammonia is shown.

[0027] Figure 6 These are the XRD diffraction patterns of MOF-808 and MOF-808' samples obtained in Example 2;

[0028] Figure 7 These are optical photographs of the MOF-808 and MOF-808' samples obtained in Example 2, along with their corresponding fluorescence emission states (excited at 365 nm).

[0029] Figure 8 The MOF-808' obtained in Example 2 is effective against different H... + Fluorescence sensing of concentration solutions (365nm excitation);

[0030] Figure 9 The image shows the polarization curve of MOF-808' obtained in Example 2 for electrocatalytic urea synthesis. Detailed Implementation

[0031] The following embodiments are further illustrations of the present invention, but not limitations thereof. Unless otherwise specified, the equipment used in the present invention is a commercially available product conventional in this technical field.

[0032] Example 1

[0033] A method for preparing a bifunctional MOF electrode integrating proton concentration detection and electrocatalysis includes the following steps:

[0034] (1) Synthesis of UiO-66 by one-pot method: using zirconium tetrachloride and terephthalic acid as raw materials, N,N-dimethylformamide and acetic acid as solvents, the reaction was carried out at 120℃ for 18h, then cooled to room temperature, filtered, washed 4 times each with N,N-dimethylformamide and methanol, and dried, the product was UiO-66; wherein, the molar ratio of zirconium tetrachloride, terephthalic acid, N,N-dimethylformamide and acetic acid was 1:1.2:1400:500;

[0035] (2) The UiO-66 obtained in step (1) was soaked in a DMF solution of 7-hydroxycoumarin-3-propionic acid and heated at 80°C for 24 hours. The concentration of 7-hydroxycoumarin-3-propionic acid in the DMF solution of 7-hydroxycoumarin-3-propionic acid was 0.2 mol / L.

[0036] (3) After washing the soaked UiO-66, transfer it to CuCl2 aqueous solution and soak it at room temperature for 24 hours. The concentration of CuCl2 aqueous solution is 10 mmol / L to obtain UiO-66'.

[0037] (4) After washing and drying the material obtained in step (3), it is ultrasonically dispersed with a 5% Nafion-ethanol solution to obtain a uniform suspension.

[0038] (5) Drop the suspension onto conductive carbon cloth and air dry it at 25°C. The film formation time is 24h, and a dual-function integrated UiO-66 electrode is obtained.

[0039] XRD analysis was performed on the UiO-66 obtained in step (1) and the modified UiO-66' obtained in step (3), as follows: Figure 1 As shown. From Figure 1 It can be seen that this modification method does not change or destroy the crystal structure of the sample.

[0040] The UiO-66 obtained in step (1) and the modified UiO-66' obtained in step (3) and their corresponding fluorescence emission states when excited at a wavelength of 365 nm are as follows: Figure 2 As shown. From Figure 2 It can be seen that the unmodified UiO-66 has no fluorescence at a wavelength of 365nm, while the modified UiO-66' has significant fluorescence characteristics.

[0041] The UiO-66' sample obtained in step (3) was placed in different H... + In solutions of varying concentrations (pH = 1–14) and excited at a wavelength of 365 nm, the corresponding fluorescence states are as follows: Figure 3 As shown. From Figure 3 It can be seen that the modified UiO-66' affects H + The concentration exhibits a significant fluorescence response behavior; the fluorescence intensity decreases as the hydrogen ion concentration increases.

[0042] The electrode obtained in step (5) was used for hydrogen production by water electrolysis under the following conditions: a three-electrode system was used, the electrolyte solution was 0.5M Na2SO4, the UiO-66 electrode (modified UiO-66') was used as the working electrode, the graphite rod was used as the counter electrode, and Ag / AgCl was used as the reference electrode. The resulting electrochemical polarization curve is shown in Figure 1. Figure 4 As shown. From Figure 4 It is known that modified UiO-66' can be used for electrocatalytic water splitting to produce hydrogen. Unmodified UiO-66 is generally considered to have no electrocatalytic activity or extremely poor activity.

[0043] The electrode obtained in step (5) was used for the electrocatalytic reduction of nitric acid to synthesize ammonia under the following conditions: a three-electrode system was used, the electrolyte solution was 1.0M PBS + 1.0M KNO3, the UiO-66 electrode (modified UiO-66') was used as the working electrode, the graphite rod was used as the counter electrode, and Ag / AgCl was used as the reference electrode. The resulting electrochemical polarization curve is shown in Figure 1. Figure 5 As shown. From Figure 5 It is known that modified UiO-66' can be used for the electrocatalytic reduction of nitric acid to synthesize ammonia. Unmodified UiO-66 is generally considered to have no electrocatalytic activity or extremely poor activity.

[0044] Combination Figure 3 , Figure 4 and Figure 5 It can be concluded that the electrode constructed with modified UiO-66' can be used in electrocatalytic processes such as water splitting for hydrogen production and nitrate reduction for ammonia synthesis. Furthermore, combined with fluorescence luminescence detection technology, H2O on the electrode surface can be detected during these electrocatalytic processes. + In-situ detection of concentration.

[0045] Example 2

[0046] A method for preparing a bifunctional MOF electrode integrating proton concentration detection and electrocatalysis includes the following steps:

[0047] (1) MOF-808 was synthesized by one-pot method: zirconium oxychloride octahydrate and trimesic acid were used as raw materials, and N,N-dimethylformamide was used as solvent. The reaction was carried out at 100℃ for 12 h, then cooled to room temperature, filtered, washed 3 times with N,N-dimethylformamide, and dried. The product was MOF-808. The molar ratio of zirconium oxychloride octahydrate, trimesic acid and N,N-dimethylformamide was 1:0.3:120.

[0048] (2) The MOF-808 obtained in step (1) was soaked in a DMF solution of 7-hydroxycoumarin-2-acetic acid and heated at 80°C for 24 hours. The concentration of 7-hydroxycoumarin-2-acetic acid in the DMF solution of 7-hydroxycoumarin-2-acetic acid was 0.05 mol / L.

[0049] (3) After washing the impregnated MOF-808, transfer it to a Co(CH3COO)2 aqueous solution and soak it at room temperature for 24 hours. The concentration of the Co(CH3COO)2 aqueous solution is 50 mmol / L to obtain MOF-808'.

[0050] (4) After washing and drying the material obtained in step (3), it is ultrasonically dispersed with a 5% Nafion-ethanol solution to obtain a uniform suspension.

[0051] (5) Drop the suspension onto conductive carbon cloth and air dry it at 25°C. The film formation time is 24h to obtain the dual-function integrated MOF-808 electrode.

[0052] XRD analysis was performed on the MOF-808 obtained in step (1) and the modified MOF-808' obtained in step (3), as follows: Figure 6 As shown. From Figure 6 It can be seen that this modification method does not change or destroy the crystal structure of the sample.

[0053] The MOF-808 samples obtained in step (1) and the modified MOF-808' samples obtained in step (3), and their corresponding fluorescence emission states when excited at a wavelength of 365 nm, are as follows: Figure 7 As shown. From Figure 7 It can be seen that the unmodified MOF-808 has no fluorescence at a wavelength of 365nm, while the modified MOF-808' has significant fluorescence characteristics.

[0054] The MOF-808' sample obtained in step (3) was placed in different H... + In solutions of varying concentrations (pH = 1–14) and excited at a wavelength of 365 nm, the corresponding fluorescence states are as follows: Figure 8 As shown. From Figure 8 It can be seen that the modified MOF-808' affects H + The concentration exhibits a significant fluorescence response behavior; the fluorescence intensity decreases as the hydrogen ion concentration increases.

[0055] The electrode obtained in step (5) was used for electrocatalytic urea synthesis under the following conditions: a three-electrode system was used, the electrolyte solution was 1.0 M CO2-KHCO3 + 1.0 M KNO3, the MOF-808 electrode (modified MOF-808') was used as the working electrode, the graphite rod was used as the counter electrode, and Ag / AgCl was used as the reference electrode. The resulting electrochemical polarization curve is shown in Figure 1. Figure 9 As shown. From Figure 9 It is known that modified MOF-808' can be used for electrocatalytic urea synthesis. Unmodified MOF-808 is generally considered to have no electrocatalytic activity or extremely poor activity.

[0056] Combination Figure 8 and Figure 9 It can be concluded that the electrode constructed from modified MOF-808 can be used in electrocatalytic processes such as urea synthesis, and combined with fluorescence luminescence detection technology, H2O on the electrode surface can be detected during electrocatalytic processes. + In-situ detection of concentration.

[0057] The above are merely preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be considered as limitations on the present invention, and the scope of protection of the present invention should be determined by the scope defined in the claims. For those skilled in the art, several improvements and modifications can be made without departing from the spirit and scope of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a proton concentration detection and electrocatalysis bifunctional integrated MOF electrode, characterized in that, It comprises the following steps: (1) preparing a metal organic framework material MOF; (2) modifying the metal organic framework material MOF using an immersion method, the modification temperature is 25-180℃, the modification time is 2-72 h, obtaining an MOF' with dual functions of electrocatalysis and sensing, the immersion process comprises two steps of metal salt solution immersion and functional ligand solution immersion, washing the MOF' with dual functions of electrocatalysis and sensing to obtain the modified MOF', the metal ions in the metal salt solution are selected from one or more of iron, cobalt, nickel, copper, ruthenium, platinum and rare earth elements, and the functional ligand is a coumarin-derived carboxylic acid ligand or a rare earth ion-modified pyridine carboxylic acid ligand; (3) after the modified MOF' is uniformly dispersed in a Nafion-containing solution, it is drop-coated on a conductive substrate, the mass ratio of the MOF' to the Nafion-containing solution is 1:10-1000, and after drying into a film, a dual-function integrated MOF electrode is obtained.

2. The production method according to claim 1, characterized by, The metal organic framework material MOF in step (1) is selected from one or more of UiO-66, UiO-67, MOF-808, MIL-101, HKUST-1 and ZIF-8.

3. The production method according to claim 1, characterized by, The volume of the metal salt solution or the functional ligand solution in step (2) is more than 2 times the geometric volume of the metal organic framework material MOF.

4. The production method according to claim 1 or 3, characterized by, The concentration of the metal salt solution or the functional ligand solution in step (2) is 0.001-2.000 mol / L.

5. The preparation method according to claim 4, characterized in that, The solvent of the metal salt solution or the functional ligand solution in step (2) is selected from one of water, methanol, ethanol, isopropanol, tetrahydrofuran, toluene, DMF and NMP.

6. The method of claim 1, wherein, The solvent of the Nafion-containing solution in step (3) is selected from one or more of water, methanol, ethanol, isopropanol, DMF and NMP, and the mass fraction of Nafion in the Nafion-containing solution is 0.1%-40.0%.

7. The preparation method according to claim 1, characterized in that, The film-forming environment in step (3) is an atmospheric atmosphere, the film-forming temperature is 25-200℃, and the film-forming time is 0.5-24.0 h.

8. The method of claim 1, wherein, The conductive substrate material in step (3) is selected from one of ITO conductive glass, FTO conductive glass, foamed metal, glassy carbon, conductive carbon cloth and conductive carbon paper.

9. The dual-function integrated MOF electrode with proton concentration detection and electrocatalysis prepared by the preparation method of claim 1.

10. Use of the bifunctional integrated MOF electrode according to claim 9 as a cathode material in electrocatalysis, characterized in that, The electrocatalysis includes electrolysis of water, carbon dioxide reduction, nitrogen reduction and nitrate reduction.

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