A preparation method of metal organic framework derivative material and application of electrolytic water

Abstract

A preparation method of a metal-organic framework-derived material and its application in electrolytic water, which belongs to the technical field of electrochemically catalytic energy storage materials. This method involves dissolving nickel chloride hexahydrate and fumaric acid in anhydrous methanol and an aqueous NaOH solution respectively; mixing the obtained metal salt solution and organic ligand solution evenly and transferring them to a high-pressure reaction kettle; vertically placing the treated nickel foam into the reaction kettle, heating for reaction and then naturally cooling; taking out the nickel foam, rinsing it with ethanol and water, and finally drying it under vacuum; subjecting the obtained sample to heat treatment in an N2 atmosphere to obtain the MOFs-derived material. In a three-electrode system, the metal-organic framework-derived material electrocatalyst is directly used as the working electrode and placed in the electrolyte to conduct the electrocatalytic water decomposition oxygen evolution reaction. The prepared electrocatalyst has excellent electrocatalytic oxygen evolution activity and stability.

Description

Technical Field

[0001] The invention discloses a preparation method of an electrocatalyst containing α-Ni(OH)2 phase derivative material by converting a metal organic framework material NiFum MOF into an electrocatalyst by heat treatment, and studies its application in alkaline electrocatalytic water decomposition, belonging to the technical field of electrochemical catalytic energy storage materials. Background Art

[0002] The continuous growth of energy demand and the use of non-renewable fossil fuels have led to increasingly serious problems such as energy reserves, climate change, environmental pollution and greenhouse effect. The search for clean and renewable energy is an inevitable trend in the global energy transformation. Hydrogen (H2) as a clean energy and energy carrier has attracted extensive research by scholars. It has abundant sources, high energy density, and its combustion product is water. Its production can be coupled with renewable energy systems and has very broad application prospects. It is one of the important technical paths for my country to achieve the "dual carbon" goal. The production of hydrogen by water electrolysis is a "zero-carbon" hydrogen production method that can achieve green and clean throughout the process, which is of great significance to the establishment of a future decarbonization energy system. However, the dependence on precious metal catalysts (such as Ir and Ru-based catalysts) and low energy conversion efficiency limit the large-scale application of electrocatalytic water decomposition to produce hydrogen. Therefore, the development of low-cost, high-stability and high-efficiency electrocatalysis has become one of the research hotspots in recent years.

[0003] Among various emerging candidate materials, metal organic frameworks (MOFs) show great promise. MOFs are a series of porous coordination polymers constructed by organic ligands and metal centers through coordination bonds. Due to their pre-designed open porous structure, easily exposed catalytic active sites, and structural functional adjustability, they have received great attention in the past two decades and have been widely used in various fields such as sensing, gas separation, energy storage and conversion. However, most MOFs have disadvantages such as low conductivity and poor stability, which lead to hindered charge transfer, thereby reducing their electrochemical performance and limiting their large-scale application. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing an electrocatalyst of MOFs-derived materials containing α-Ni(OH)2 phase by converting MOFs into MOFs-derived materials by heat treatment. The method uses MOFs as a template or precursor and converts them into MOFs-derived metal compounds by heat treatment, chemical treatment and other means; it combines the advantages of MOFs: high specific surface area and porosity, rich metal active sites, and provides great opportunities for MOFs to be used as electrode catalysts for energy conversion.

[0005] NiFum MOF was grown on a nickel foam substrate (NF) by a solvothermal method and then heat treated in a N2 atmosphere to obtain a MOFs-derived electrocatalyst containing an α-Ni(OH)2 phase, which was then applied to the electrocatalytic water oxidation (OER) reaction.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for preparing a metal organic framework derivative material comprises the following steps:

[0008] (1) Cleaning the nickel foam substrate and storing it in ethanol for use;

[0009] (2) dissolving nickel chloride hexahydrate in anhydrous ethanol to obtain a metal salt solution with a concentration of 0.05-0.1 mol / L; dissolving fumaric acid in an aqueous NaOH solution, wherein the molar ratio of fumaric acid to NaOH is 1:2, to obtain a ligand solution with a fumaric acid concentration of 0.05-0.1 mol / L;

[0010] (3) transferring the metal salt solution and the ligand solution into a Teflon-lined stainless steel autoclave, mixing them evenly, vertically placing the dried nickel foam substrate therein, and maintaining the mixture at 60-100° C. for 10-14 hours;

[0011] (4) After the reactor is cooled naturally to room temperature, the nickel foam is taken out and rinsed alternately with ethanol and water. After the rinsing is completed, the sample is placed in a vacuum dryer overnight;

[0012] (5) The obtained NiFum MOF material is placed in a tubular furnace and heat treated in a N2 atmosphere at a temperature of 200-400°C for 40-80 minutes. After cooling to room temperature, a MOFs-derived material containing an α-Ni(OH)2 phase is obtained.

[0013] The MOFs-derived material is used as a water electrolysis catalyst and is directly used for the electrocatalytic water decomposition reaction. Further, the pretreated nickel foam (NF) is dried;

[0014] 0.5 mmol NiCl2·6H2O was dissolved in methanol solution and ultrasonicated for 30 seconds to obtain a metal salt solution; 0.5 mmol fumaric acid was dissolved in NaOH aqueous solution and ultrasonicated for 1 minute to obtain a colorless and transparent ligand solution;

[0015] The metal salt solution and the ligand solution were mixed evenly and transferred to a 15 mL stainless steel autoclave lined with Teflon, and the treated NF foam nickel substrate was placed vertically and kept at 80 °C for 12 h;

[0016] After the autoclave was cooled naturally to room temperature, the NF was rinsed with ethanol and water, and the obtained sample was dried in a vacuum drying oven at 60°C to obtain NiFum MOF.

[0017] The obtained NiFum MOF material was placed in a tubular furnace and heat treated in a N2 atmosphere at a temperature of 200-400°C for 60 minutes. After cooling to room temperature, a MOFs-derived material containing an α-Ni(OH)2 phase was obtained.

[0018] Furthermore, the size of the nickel foam substrate is 2×2.5 cm -2 The samples were ultrasonically cleaned with 1M HCl, acetone, ethanol, and deionized water for 15 to 30 minutes.

[0019] Further, NiCl2·6H2O was dissolved in 6 mL of anhydrous methanol solution, and fumaric acid was dissolved in 6 mL of NaOH aqueous solution (0.167 M), and ultrasound was used to promote dissolution.

[0020] Furthermore, under solvothermal conditions, the temperature was slowly increased and maintained at 80° C. for 12 h.

[0021] Furthermore, the autoclave was naturally cooled to below 40° C. in an oven, and the foamed nickel sample was taken out with tweezers and rinsed three times with ethanol and water alternately to remove unreacted metal salts, ligands, impurities, etc.

[0022] Furthermore, the cleaned NiFum MOF sample was placed in a 60°C vacuum drying oven for overnight drying.

[0023] Furthermore, the obtained NiFum MOF material was placed in a tubular furnace and heat treated in a N2 atmosphere with a gas flow rate of 15 mL / h. It was heated to 200-400°C at a heating rate of 2°C / min and maintained for 60 minutes. After the reaction was completed, it was naturally cooled to room temperature to obtain a MOFs derivative material containing an α-Ni(OH)2 phase.

[0024] Furthermore, the above materials were directly used for electrocatalytic water-oxygen resorption reaction (OER) using a standard three-electrode system (Hg / HgO as reference electrode, platinum wire as counter electrode and working electrode), and the electrolyte was 1M KOH solution.

[0025] Compared with the prior art, the technical advantages of the present invention are:

[0026] 1) NiFum MOF was in situ grown on a nickel foam substrate with good conductivity by a one-step solvothermal method, which can be directly used in electrolysis reactions, facilitating efficient mass and charge transfer, and avoiding the defects of powdered MOFs that require polymer binders, resulting in partial coverage of active sites and obstructed mass transfer at the catalyst-electrolyte interface.

[0027] 2) Using MOFs as precursors, a MOFs-derived material with an α-Ni(OH)2 phase was obtained through a simple heat treatment. The increase in heat treatment temperature resulted in the removal of interlayer water, resulting in an α-Ni(OH)2 phase MOFs-derived material with a lattice contraction phenomenon.

[0028] 3) Electrochemical performance tests show that the derivative material obtained by heat treatment at 300°C has the smallest overpotential, the fastest reaction kinetics, the smallest charge transfer resistance and the largest electrochemically active surface area as well as long-term electrochemical stability at the same current density compared with other comparison samples, and has excellent OER performance.

[0029] In summary, the present invention obtains a MOFs-derived material having an α-Ni(OH)2 phase by in-situ growth of NiFum MOF on a nickel foam substrate and then performing a simple heat treatment. The preparation method is simple and easy to implement. The prepared catalyst has a small overpotential and excellent durability in OER process applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below.

[0031] Figure 1 This is the X-ray diffraction spectrum of the metal-organic framework material NiFum MOF prepared by the solvothermal method.

[0032] Figure 2 This is the X-ray diffraction spectrum of the MOFs-derived material NiFum MOF-T-1 obtained after heat treatment.

[0033] Figure 3 This is a scanning electron microscope image of the MOFs-derived material NiFum MOF-300-1 obtained after heat treatment.

[0034] Figure 4 This is the EDS spectrum of the MOFs derived material NiFum MOF-300-1 obtained after heat treatment.

[0035] Figure 5(a) is the LSV curve of the MOFs-derived material NiFumMOF-300-1 obtained after heat treatment and its comparison sample; (b) is the Tafel slope of the MOFs-derived material NiFumMOF-300-1 obtained after heat treatment and its comparison sample; (c) is the impedance diagram of the MOFs-derived material NiFumMOF-300-1 obtained after heat treatment and its comparison sample; (d) is the active surface area of ​​the MOFs-derived material NiFumMOF-300-1 obtained after heat treatment and its comparison sample.

[0036] Figure 6 IT test of MOFs derived material NiFum MOF-300-1 obtained after heat treatment.

[0037] Figure 7 LSV curves of NiFum MOF-300-1 before and after it testing.

[0038] Figure 8 X-ray diffraction spectra of NiFum MOF-300-1 before and after it testing.

[0039] Fig. 9 This is the in-situ electrochemical infrared spectrum test spectrum of NiFum MOF-300-1. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention is further described below in conjunction with specific embodiments, but the present invention is not limited to the following embodiments.

[0041] Example 1 Preparation of MOFs-derived electrocatalytic materials

[0042] Cut the nickel foam base into 2×2.5cm -2 The size of the samples was ultrasonically cleaned with 1M HCl, acetone, ethanol, and deionized water for 15 to 30 min, respectively. After cleaning, they were stored in anhydrous ethanol for future use.

[0043] The pretreated nickel foam (NF) was placed in a vacuum drying oven at 60°C for 30 min for drying;

[0044] Dissolve 0.5mmol NiCl2·6H2O in 6mL anhydrous methanol solution and sonicate for 30s to obtain a metal salt solution; dissolve 0.5mmol fumaric acid in 6mL NaOH aqueous solution (0.167M) and sonicate for 1min to obtain a colorless and transparent ligand solution;

[0045] The metal salt solution and the ligand solution were mixed evenly and transferred to a 15 mL stainless steel autoclave lined with Teflon, the treated NF foam nickel substrate was placed vertically, and the temperature was slowly increased to 80°C at a heating rate of 2°C / min and maintained at 80°C for 12 hours;

[0046] After the reactor is cooled to room temperature naturally, the nickel foam sample is taken out with tweezers and rinsed three times with ethanol and water alternately to remove unreacted metal salts, ligands, impurities, etc.;

[0047] The cleaned NiFum MOF sample was placed in a vacuum drying oven for overnight drying;

[0048] The obtained NiFum MOF material was placed in a tubular furnace and heat treated in a N2 atmosphere with a gas flow rate of 15 mL / h. It was heated to 200°C, 300°C, and 400°C at a heating rate of 2°C / min and maintained for 60 min. After the reaction was completed, it was naturally cooled to room temperature to obtain MOFs derivative materials containing α-Ni(OH)2 phase, NiFum MOF-200-1, NiFum MOF-300-1, and NiFum MOF-400-1, respectively.

[0049] Example 2 Application of MOFs-derived electrocatalytic materials in OER processes

[0050] The prepared NiFum MOF-300-1 was cut into 1×2 cm 2 Directly used for working electrode, the area immersed in the electrolyte solution is 1×1cm 2 The electrochemical performance of the catalyst was evaluated using a standard three-electrode system (Hg / HgO as reference electrode, platinum wire as counter electrode and working electrode), and the electrolyte was 1M KOH solution. The electrochemical workstation model was Shanghai Chenhua CHI 760.

[0051] Example 3

[0052] (1) Physical characterization of catalytic materials

[0053] Figure 1 The XRD results show that the experimentally synthesized NiFum MOF is in good agreement with the simulation results, indicating the successful preparation of NiFumMOF. The XRD results of heat treatment at 200, 300, and 400 °C are shown in Figure 2. Figure 2As shown in the figure, it can be seen that after heat treatment at 200 and 300℃, the original MOFs were transformed into α-Ni(OH)2 and basic nickel carbonate. After heat treatment at 300℃, the (0 0 6) crystal plane of α-Ni(OH)2 shifted to a high angle. It is speculated that the increase in heat treatment temperature led to a decrease in intercalated water, which led to lattice contraction. The scanning electron microscopy results of NiFum MOF-300-1 are shown in the figure. Figure 3 As shown, it can be seen that the nickel foam base is covered by irregular blocky particles. Figure 4 The EDS results show that C, O and Ni elements are evenly distributed in NiFum-300-1.

[0054] (2) Evaluation of OER electrochemical performance of catalysts

[0055] Figure 5 The LSV results in (a) show that NiFum-300-1 has the smallest overpotential at the same current density. -2 and 100mA·cm -2 The overpotentials are 205 and 370 mV respectively. Figure 5 In (b), NiFum-300-1 also has the smallest Tafel slope of 67.15 mV·dec -1 , indicating that it has the fastest reaction kinetics. Figure 5 (c) In the impedance test results, NiFum MOF-300-1 exhibits the smallest arc and has the smallest charge transfer resistance. Figure 5 (d) The electrochemically active surface area of ​​the materials was evaluated by double-layer capacitance. NiFum MOF-300-1 had the largest slope, indicating that it had the largest electrochemically active surface area and could provide abundant active sites for the reaction. Figure 6 The stability test results show that NiFumMOF-300-1 material can withstand 10 mA cm -2 The current density is stable for 118h. Figure 7 Before and after the stability test, the overpotential of NiFum MOF-300-1 increased by only 25mV, indicating that the material has excellent stability. The electrochemical performance test results show that the MOFs material after heat treatment exhibits excellent OER performance and has potential application value.

[0056] (3) Characterization of NiFum MOF-300-1 after stability test

[0057] Figure 8 The crystalline structure of NiFum MOF-300-1 completely disappeared after 118 h of stability test, presumably transforming into an amorphous hydroxide or oxyhydroxide.

[0058] (4) NiFum MOF-300-1 in situ electrochemical test

[0059] In order to explore the active species of NiFum MOF-300-1 in the OER process, in situ electrochemical infrared spectroscopy tests were carried out at different potentials. Fig. 9 When the voltage is applied to 1.4V, at 1043cm -1 An obvious infrared characteristic peak appeared at the position and intensified with the increase of applied voltage, which can be attributed to the generation of key *OOH species.

[0060] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a metal organic framework derivative material, characterized in that: Using metal organic framework materials as precursors, MOFs-derived materials containing α-Ni(OH)2 phase were prepared by heat treatment as water electrolysis catalysts. The specific steps include: (1) Cleaning the nickel foam substrate and storing it in ethanol for use; (2) dissolving nickel chloride hexahydrate in anhydrous methanol to obtain a metal salt solution with a concentration of 0.05-0.1 mol / L; dissolving fumaric acid in an aqueous NaOH solution, wherein the molar ratio of fumaric acid to NaOH is 1:2, to obtain a ligand solution with a concentration of 0.05-0.1 mol / L; (3) transferring the metal salt solution and the ligand solution into a Teflon-lined stainless steel autoclave, mixing them evenly, vertically placing the dried nickel foam substrate therein, and maintaining the mixture at 60-100° C. for 10-14 hours; (4) After the reactor is cooled naturally to room temperature, the nickel foam is taken out and rinsed alternately with ethanol and water. After the rinsing is completed, the sample is placed in a vacuum dryer overnight; (5) The obtained NiFum MOF material is placed in a tubular furnace and heat treated in a N2 atmosphere at a heat treatment temperature t, 200≤t<400°C, maintained for 40-80 min, and cooled to room temperature to obtain a MOFs derivative material containing an α-Ni(OH)2 phase.

2. The use of the MOFs derivative material obtained by the preparation method according to claim 1, characterized in that: The MOFs-derived material is used as a water electrolysis catalyst and is directly used in an electrocatalytic water decomposition reaction.

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