Preparation method for in-situ generation of supported catalyst through one-step pyrolysis of metal organic framework and application of supported catalyst

Abstract

The invention relates to a preparation method for in-situ generation of a supported catalyst through one-step pyrolysis of a metal organic framework and application of the supported catalyst. According to the method, an MOFs precursor with regular morphology and uniform particle size distribution is synthesized through a pre-hydrolysis-hydrothermal method, and the supported noble metal catalyst based on the titanium oxide carrier is prepared in situ through dipping and one-step pyrolysis of the MOFs to adsorb the noble metal precursor. Wherein titanium oxide generated by pyrolyzing Ti-based MOFs in situ promotes nucleation and growth of noble metal oxide on a titanium oxide carrier, and a uniform, compact and continuous noble metal oxide covering layer with the thickness of 5-30 nm is formed on the surface of the catalyst. According to the supported catalyst prepared by the method, the noble metal loading amount in a proton exchange membrane electrolyzed water (PEMWE) anode catalyst layer can be remarkably reduced, electron transmission in an electro-catalytic reaction process is ensured, 'electric insulation 'inactivation of an active center caused by overlarge resistance of a catalytic layer surface is avoided, and the anode catalytic performance of the PEMWE is ensured.

Description

Technical Field

[0001] The invention belongs to the field of hydrogen production by electrolysis of water, and in particular relates to a preparation method and application of a supported catalyst generated in situ by one-step pyrolysis of a metal organic framework. Background Art

[0002] The development of water electrolysis hydrogen production technology is conducive to adjusting the energy structure, realizing the large-scale consumption of renewable energy, and promoting energy transformation. Proton exchange membrane water electrolysis (PEMWE) has the advantages of high current density, fast response speed, and small footprint, and has received much attention. However, the slow oxygen evolution reaction (OER) of the PEMWE anode is heavily dependent on the expensive and scarce precious metal Ir (catalytic layer loading ~2 mg Ir cm -2 ), which limits the large-scale development of PEMWE. Therefore, the development of high-performance, low-cost oxygen evolution reaction electrocatalysts is the key to realizing the commercial application of PEMWE.

[0003] The method of using carriers to load precious metal sites can improve the dispersion of precious metal Ir, maximize the density of active centers, and improve the catalytic activity of oxygen evolution. 2 ) is a stable support material that can withstand the strong corrosion environment of PEMWE anodes. Currently, there are TiO-based 2 However, TiO 2 Due to its semiconductor properties, the conductivity is low, and the electron channel in the electrochemical reaction process is completely controlled by the precious metal catalyst (such as Ir or IrO) loaded on the carrier. 2 ) is achieved. Therefore, the precious metal loading on the carrier is usually high to avoid the formation of isolated electrically insulating active centers of precious metal catalysts under low Ir loading, which is not conducive to the construction of the conductive network of the membrane electrode catalyst layer. For example, for imported commercial TiO 2 Load IrO 2 Catalyst (Elyst Ir75, Umicore), Ir loading is as high as 75wt%. Therefore, further reducing the noble metal loading of supported catalysts while ensuring high conductivity of the catalyst layer is very necessary for the development of high-performance low-Ir catalysts. Achieving uniform distribution of noble metal phases on the support surface is an effective means to reduce the noble metal loading of supported catalysts. However, there is currently a lack of effective methods for achieving the noble metal oxide on TiO 2 The preparation process of the carrier surface is uniform, dense and interconnected.

[0004] To solve this problem, the present invention proposes to use Ti-based MOFs as precursors to in-situ prepare TiO by impregnation with noble metal salts and a one-step pyrolysis method. xLoading noble metal electrocatalysts, using TiO generated during MOFs pyrolysis x The redox activity promotes the nucleation and growth of precious metal oxides on titanium oxide, achieving low iridium loading and high iridium content on TiO 2 A uniform, dense, and continuous noble metal oxide coating is formed on the surface, which ensures the conductivity of the catalyst and greatly reduces the amount of noble metal loading in the catalyst. 4+ More active and easily hydrolyzed to form amorphous TiO 2 , which is not conducive to the secondary building blocks of MOFs (Ti 8 O 8 ) is generated, and it is difficult to control its transformation during the crystallization process of MOFs (Progress in Chemistry, 2023, 35(12): 1752-1763). Therefore, the present invention adds different amounts of water to the precursor system before hydrothermal treatment to control the Ti 4+ Compared with the traditional hydrothermal method, the prehydrolysis-hydrothermal method promotes the crystallization of MOFs during the hydrothermal process and ensures the uniform distribution of the particle size of MOFs nanoparticles. Summary of the invention

[0005] First, in order to solve the problems of difficult control of crystallization process and uneven particle size distribution in the traditional Ti-based MOFs hydrothermal synthesis process in the prior art, the present invention provides a pre-hydrolysis-hydrothermal synthesis method, which uses the pre-hydrolysis-hydrothermal synthesis method to control the crystallization process of MOFs and promote the uniform distribution of MOFs nanoparticles. In addition, in view of the problems such as discontinuity of the conductive noble metal oxide covering layer in the supported catalyst in PEMWE technology, the present invention provides a method for in-situ generation of titanium oxide-supported noble metal electrocatalysts by using a Ti-based MOFs precursor as a template through precursor impregnation and a one-step pyrolysis method, and utilizing the TiO generated during the pyrolysis of Ti-based MOFs to generate a titanium oxide-supported noble metal electrocatalyst. x The redox activity of the precious metal oxides promoted the nucleation and growth of the TiO 2 At low iridium loading on TiO 2 A uniform, dense, and continuous noble metal oxide coating is formed on the surface, ensuring the conductivity of the catalyst. The in-situ generated supported catalyst with a continuous, uniform, and dense noble metal coating proposed by the present invention can significantly reduce the noble metal load in the anode catalyst layer and ensure the electrical connection between the catalysts, avoiding the "electrical insulation" deactivation of the active center caused by excessive resistance of the catalyst layer. In addition, the tight interface formed in situ can significantly improve the catalyst / carrier interface interaction, thereby improving the intrinsic activity and utilization rate of the noble metals in PEMWE, achieving the purpose of reducing the cost and increasing the efficiency of PEMWE membrane electrodes.

[0006] In order to achieve the purpose of the invention, the present invention adopts the following technical scheme: a preparation method for in-situ generation of supported catalyst by one-step pyrolysis of metal organic framework, synthesizing MOFs precursor with uniform particle size distribution by pre-hydrolysis-hydrothermal method, and in-situ generation of supported catalyst by impregnation method and one-step pyrolysis of metal organic framework (MOFs) method. Precious metal oxide nanoparticles can be highly dispersed on the surface of amorphous titanium oxide carrier, forming a uniform, dense, continuous 5-30nm precious metal oxide covering layer on the catalyst surface, providing an electron path for the electrocatalyst.

[0007] In a preferred embodiment of the present invention, the MOFs precursor is a Ti-based MOFs (NH 2 -MIL-125). More preferably, the pre-hydrolysis-hydrothermal method comprises the following steps:

[0008] (1) N,N-dimethylformamide (DMF) and anhydrous methanol are stirred and dispersed uniformly in a certain volume ratio;

[0009] (2) slowly adding 2-aminoterephthalic acid to the solution prepared in step (1), and stirring until the solution is evenly dispersed;

[0010] (3) adding deionized water to the homogeneous solution obtained in step (2), stirring and dispersing the mixture evenly;

[0011] (4) rapidly adding titanium alkoxide dropwise to the solution system obtained in the above (3) and stirring to perform a pre-hydrolysis step;

[0012] (5) The solution system obtained in (4) above was transferred to a reactor and subjected to hydrothermal reaction at a specific temperature for a period of time. After cooling to room temperature, the solution was washed with DMF and methanol three times each to obtain a MOFs precursor.

[0013] In a preferred embodiment of the present invention, in step (1), the ratio of N,N-dimethylformamide (DMF) to anhydrous methanol is 1:9, and the stirring time is 0.5-10 min.

[0014] In a preferred embodiment of the present invention, in step (3), the volume ratio of the added amount of deionized water to DMF is 0.05-2 v / v%, preferably 0.25 v / v%; and the stirring time is 3-8 min.

[0015] In a preferred embodiment of the present invention, in step (4), the titanium alkoxide is selected from one of ethyl titanate, isopropyl titanate, and n-butyl titanate, the dropping method is rapid dropping, and the pre-hydrolysis time is 3-8 min.

[0016] In a preferred embodiment of the present invention, in step (5), the reaction temperature is 120-180°C, preferably 150°C; and the reaction time is 16-48h.

[0017] In a preferred embodiment of the present invention, the one-step pyrolysis of metal organic frameworks (MOFs) to generate a supported catalyst in situ comprises the following steps:

[0018] (1) dispersing the noble metal precursor in a dispersing solvent, stirring with ultrasonic for a certain period of time, and mixing evenly for later use;

[0019] (2) Weighing a certain amount of MOFs precursor, adding it to the noble metal precursor dispersion obtained in step (2), and stirring at room temperature for a certain period of time to allow MOFs to fully adsorb the noble metal precursor;

[0020] (3) filtering the mixed solution obtained in (2) above, repeatedly washing, and drying to obtain a precursor;

[0021] (4) The precursor obtained in (3) is heat treated in air at 200-550° C. for 0.5-12 h, and then cooled to obtain the supported catalyst.

[0022] In a preferred embodiment of the present invention, in step (1), the dispersing solvent is selected from one of DMF, methanol, tetrahydrofuran, ethanol, deionized water, and isopropanol, and the noble metal precursor is selected from one of the noble metal elements iridium, ruthenium, platinum, palladium, rhodium, silver, gold chlorate, chlorate, acetate or acetylacetone complexes or a combination thereof.

[0023] In a preferred embodiment of the present invention, in step (2), the mass ratio of MOFs precursor to noble metal precursor is 0.2-2.

[0024] The present invention also protects the supported catalyst prepared by the above preparation method, which is a heterojunction catalyst. The two parts of the heterojunction are respectively composed of titanium oxide obtained by pyrolysis of titanium-based MOFs and precious metal oxides formed in situ on titanium oxide by precious metal precursors, and the precious metal oxide loading is 5 to 50 wt%.

[0025] The present invention also protects the use of the supported catalyst in PEMWE membrane electrode.

[0026] Compared with the existing technology, 4+Uncontrollable hydrolysis in the air, the present invention firstly improves the traditional hydrothermal method by pre-hydrolysis-hydrothermal method to synthesize Ti-based MOFs nanoparticles with uniform particle size, so as to overcome the problems of poor crystallinity and uneven particle size distribution of the traditional hydrothermal method; then the Ti-based MOFs adsorb the precious metal precursor and obtain the supported electrocatalyst by one-step pyrolysis, and the precious metal oxide nanoparticles are highly dispersed on the titanium oxide surface produced by the pyrolysis of MOFs, forming a uniform and dense precious metal oxide enrichment layer of about 5 to 30nm, while reducing the iridium load of the membrane electrode anode catalyst layer, while maintaining the high conductivity of the catalyst layer. The catalyst prepared by the present invention can be applied to PEMWE membrane electrode, which can greatly reduce the amount of precious metals in the membrane electrode catalyst layer and ensure the conductivity of the catalyst layer at the same time, reduce the cost of PEMWE and increase its service life, which is conducive to the large-scale development of PEMWE.

[0027] The pre-hydrolysis hydrothermal synthesis of Ti-based MOFs provided by the present invention has a simple preparation process and low raw material cost, which is conducive to improving the problems of poor repeatability and poor crystallinity in the traditional hydrothermal synthesis of Ti-based MOFs, and expands the preparation method of Ti-based MOFs.

[0028] The method for preparing a supported electrocatalyst by in-situ pyrolysis using MOFs as a template provided by the present invention has a simple preparation process, low raw material cost, and broad application prospects.

[0029] The supported catalyst prepared by the present invention has strong electrochemical corrosion resistance and strong catalyst-carrier interface interaction, which is beneficial to improving the electrocatalytic intrinsic activity and stability of the noble metal oxide catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The following is a further description with reference to the accompanying drawings.

[0031] Figure 1 is a scanning electron microscope (SEM) image of the Ti-based MOFs synthesized in Example 1.

[0032] Figure 2 These are the transmission electron microscope (TEM) photograph (a), element line distribution (b) and surface distribution (c) of the titanium oxide-supported iridium oxide catalyst in Example 2.

[0033] Figure 3 The left side is the Raman spectrum of titanium oxide loaded iridium oxide in Example 2, and the right side is the electrochemical performance of the titanium oxide loaded iridium oxide catalyst in Example 2.

[0034] Figure 4 On the left is the X-ray diffraction (XRD) spectrum of the titanium oxide-supported ruthenium oxide catalyst in Example 3, and on the right is the electrochemical performance of the titanium oxide-supported ruthenium oxide catalyst in Example 3. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solutions and beneficial effects of the present invention more clear, the present invention is described with the following specific embodiments, but the present invention is by no means limited to these examples.

[0036] Embodiment 1:

[0037] N, N-dimethylformamide (DMF) and anhydrous methanol in a volume ratio of 9:1 were stirred and dispersed uniformly. After stirring for 5 minutes, 2-aminoterephthalic acid was slowly added to the above solution and stirred for 5 minutes until it was uniformly dispersed. Subsequently, a certain amount of deionized water was added to the above solution and stirred for 5 minutes. A certain amount of titanium alkoxide was quickly dropped into the above solution system and stirred for 5 minutes for pre-hydrolysis. Subsequently, the solution system was transferred to a reactor with a Teflon lining and reacted at 150°C for 24 hours. After cooling at room temperature, the Ti-MOFs precursor was washed three times with DMF and methanol respectively, and a series of samples were obtained by controlling the volume ratio of water addition to DMF to 0 v / v%, 0.25 v / v%, 0.5 v / v%, 0.75 v / v%, 1 v / v%, and 2 v / v%. The samples were characterized by SEM. It can be clearly seen from the SEM image that when the water addition amount is 0.25 v / v%, the MOFs nanoparticles are most evenly distributed, and no unreacted bulk reactants are seen in the field of view ( Figure 1 ).

[0038] Embodiment 2:

[0039] 240 mg of IrCl 3 ·3H 2 O was dissolved in 10 ml of methanol. 150 mg of NH 2 -MIL-125, stirred for 10 h, IrCl 3 ·3H 2 After O is fully adsorbed, the mixture is filtered and washed three times with methanol. Dry at 80°C for 12 h. 3 / NH 2 -MIL-125 was placed in a tube furnace at 350℃, 375℃, 400℃, 450℃ or 550℃ and heated in air for 4h (heating rate: 5℃min -1 ), IrO x / TiO x Supported catalysts;

[0040] The physicochemical characterization of the titanium oxide supported iridium oxide catalyst was carried out. Figure 2 a, 2b, and 2c are TEM images, element line distribution, and surface distribution of the titanium oxide supported iridium oxide catalyst, respectively. From the element line distribution and surface distribution, it can be seen that the iridium element is evenly distributed on the catalyst surface, forming a continuous and uniformly distributed IrO with a certain thickness.x layer. Figure 3 a is the Raman spectrum of titanium oxide loaded with iridium oxide in Example 2. Figure 3 b is the linear voltammetric scanning curve of the supported oxygen evolution catalyst and the unsupported iridium oxide catalyst prepared in Example 2. It can be seen that the overpotential of the electrode catalytic reaction is different at different current densities. When the current density is 10 mA cm -2 When the overpotential of the titanium oxide supported iridium oxide catalyst prepared in Example 2 is 233 mV, which is lower than that of the catalyst without IrO 2 (300mV). Compared with commercial IrO 2 , the mass activity of the titanium oxide-supported iridium oxide catalyst at 1.53 V increased by about 8.5 times.

[0041] Example 3

[0042] The operating conditions are the same as those in Example 1, except that the noble metal precursor is ruthenium chloride trihydrate. The XRD spectrum of the obtained catalyst is as follows: Figure 4 The overpotential of the titanium oxide supported ruthenium oxide catalyst prepared in Example 3 is lower than that of the commercial IrO 2 ( Figure 4 b).

[0043] The above is an exemplary description of the present invention. It is obvious that the implementation of the present invention is not limited to the above-mentioned method. Any equivalent implementation scheme or changes that do not deviate from the method concept and technical solution of the present invention, such as the combination, division or repetition of features, or the direct application of the concept and technical solution of the present invention to other occasions without improvement, are all within the protection scope of the present invention.

Claims

1. A method for preparing a supported catalyst by in-situ pyrolysis of a metal organic framework, characterized in that: MOFs precursors with regular morphology and uniform particle size distribution were synthesized by a prehydrolysis-hydrothermal method, and supported catalysts were generated in situ by impregnation and one-step pyrolysis of MOFs.

2. The preparation method according to claim 1, characterized in that: The MOFs precursor is a Ti-based MOFs (NH2-MIL-125) prepared by a pre-hydrolysis-hydrothermal method; more preferably, the pre-hydrolysis-hydrothermal method comprises the following steps: (1) N,N-dimethylformamide (DMF) and anhydrous methanol are stirred and dispersed uniformly in a certain volume ratio; (2) slowly adding 2-aminoterephthalic acid to the solution prepared in step (1), and stirring until the solution is evenly dispersed; (3) adding deionized water to the homogeneous solution obtained in step (2), stirring and dispersing the mixture evenly; (4) rapidly adding titanium alkoxide dropwise to the solution system obtained in the above (3) and stirring to perform a pre-hydrolysis step; (5) The solution system obtained in (4) above is transferred to a reactor and subjected to hydrothermal reaction at a specific temperature for a period of time. After cooling to room temperature, the solution is washed with N,N-dimethylformamide (DMF) and methanol three times each to obtain a MOFs precursor.

3. The preparation method according to claim 2, characterized in that: In step (1), the ratio of DMF to anhydrous methanol is 1:9, and the stirring time is 0.5-10 min. In step (3), the volume ratio of the added amount of deionized water to DMF is 0.05-2 v / v%, preferably 0.25 v / v%, and the stirring time is 3-8 min.

4. The preparation method according to claim 2, characterized in that: In step (4), the titanium alkoxide is selected from titanium trichloride, titanium tetrachloride, ethyl titanate, isopropyl titanate or n-butyl titanate, and the dropping method is rapid dropping, and the pre-hydrolysis time is 3-8 minutes; in step (5), the reaction temperature is 120-180°C, preferably 150°C; and the reaction time is 16-48 hours.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The one-step pyrolysis method for preparing a supported catalyst in situ by pyrolyzing MOFs comprises the following steps: (1) Dispersing the noble metal precursor in a solvent, stirring with ultrasound for a certain period of time, and mixing evenly for later use; (2) Weighing a certain amount of MOFs precursor, adding it to the noble metal precursor dispersion obtained in step (2), and stirring at room temperature for a certain period of time to allow MOFs to fully adsorb the noble metal precursor; (3) filtering the mixed solution obtained in (2) above, repeatedly washing, and drying to obtain a precursor; (4) The precursor obtained in (3) is heat treated in air at 200-550° C. for 0.5-12 h, and then cooled to obtain the supported catalyst.

6. The preparation method according to claim 5, characterized in that: In step (1), the dispersing solvent is selected from one of DMF, methanol, tetrahydrofuran, ethanol, deionized water, and isopropanol, and the noble metal precursor is selected from one of the noble metal elements iridium, ruthenium, platinum, palladium, rhodium, silver, and gold chlorate, chlorate, acetate, or acetylacetone complexes, or a combination thereof.

7. The preparation method according to claim 5, characterized in that: In step (2), the mass ratio of MOFs precursor to noble metal precursor is 0.2-2.

8. The supported catalyst prepared by the preparation method according to any one of claims 1 to 7, characterized in that: It is a heterojunction catalyst. The two parts of the heterojunction are composed of titanium oxide obtained by pyrolysis of titanium-based MOFs and noble metal oxides formed in situ on titanium oxide by noble metal precursors. The noble metal oxide loading is 5 to 50 wt%.

9. The supported catalyst according to claim 8, characterized in that The noble metal oxide nanoparticles can be highly dispersed on the surface of the amorphous titanium oxide carrier, forming a uniform, dense, continuous 5 to 30 nm noble metal oxide covering layer on the catalyst surface, providing an electron pathway for the electrocatalytic reaction.

10. Use of the supported catalyst according to any one of claims 8 to 9 in a PEMWE membrane electrode.

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