Preparation of Prussian blue derivative and copper metal organic framework composite material and OER application

Abstract

The invention discloses a preparation method of a Prussian blue analogue (CoFe-PBA) and copper metal organic framework (HKUST-1) composite core-shell material and application of the composite core-shell material in oxygen evolution reaction (OER). The material is prepared through a step-by-step synthesis and composite process: firstly, synthesizing copper-based MOF (HKUST-1) and a ferrocobalt Prussian blue analogue (CoFe-PBA), then compounding the copper-based MOF (HKUST-1) and the ferrocobalt Prussian blue analogue (CoFe-PBA) through a solvothermal method to form a core-shell structure (HKUST-1-atCoFe-PBA), and further performing high-temperature oxidation and vulcanization treatment to obtain HKUST-1-atCoFe-O and HKUST-1-atCoFe-S materials. According to the composite material, the electron transmission efficiency and the catalytic activity are remarkably improved by utilizing the synergistic effect of multi-metal active sites of Cu, Co and Fe. No precious metal or strong corrosive reagent is used in the preparation process, the cost is low, and the green synthesis requirement is met. An electrochemical test shows that the OER overpotential of the optimized catalyst at the current density of 10mAcm is only 268mV, and the catalyst shows excellent catalytic performance. The material can be widely applied to the fields of water electrolysis hydrogen production and the like, and has important industrial application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of inorganic synthesis and material preparation, and particularly relates to a preparation method of a composite material of a Prussian blue derivative and a copper metal-organic framework, and its application in the OER of water electrolysis for hydrogen production. Background Art

[0002] In the past, noble metal catalysts such as platinum (Pt), ruthenium (Ru), etc. have been widely used in the oxygen evolution reaction (OER) due to their excellent catalytic performance. However, due to their scarcity and high cost, the widespread application of OER technology has been restricted for a long time. Therefore, researchers have turned to more cost-effective non-noble metal catalysts, which are not only abundant and cheap but also can exhibit quite excellent catalytic activity under certain conditions.

[0003] Prussian blue analogs (PBAs) are a class of metal cyanide compounds with rich structures and chemical diversities. In recent years, the research on PBAs as catalyst materials in the oxygen evolution reaction has gradually increased. The advantages of PBAs lie in their good conductivity, structural stability, and abundant transition metal ions, which can effectively promote electrochemical reactions. As a non-noble metal catalyst, PBAs can provide a relatively cheap alternative and exhibit encouraging catalytic activity in the OER reaction. Metal-organic frameworks (MOFs), as a kind of material with high tunability, have received extensive attention in the application of the oxygen evolution reaction in recent years. MOFs are composed of metal ions or metal clusters and organic ligands through coordination interactions, with rich structural diversities, large specific surface areas, high porosities, and good tunability, making them ideal electrocatalyst materials. Due to their unique structural characteristics, MOFs can provide a large number of active sites for OER, which helps to improve the reaction efficiency, and their conductivity and catalytic performance can be further optimized by the selection of metal centers, the modification of ligands, and the regulation of synthesis conditions. Therefore, the research on MOFs in OER has gradually become a hot spot in the field of electrocatalysis.

[0004] A composite material is composed of two or more different components. Through the interaction between different components, a synergistic effect can be achieved. This effect helps to optimize the electronic structure, improve the conductivity, and increase the active sites, thereby enhancing the overall catalytic activity. And the composite material can be designed into a core-shell structure, etc. Such a microstructure design can increase the specific surface area and improve the contact efficiency of the active sites. Summary of the Invention

[0005] The present invention aims to provide a composite material of a Prussian blue derivative and a copper metal-organic framework and a method for its regulated preparation, so as to solve the problem of low activity of existing non-noble metal catalysts. By optimizing the synthesis conditions and treatment means, the material significantly improves the electrocatalytic activity and stability and is applicable to hydrogen production by electrolyzing water.

[0006] The technical problem to be solved by the present invention is to provide a composite material of a Prussian blue derivative and a copper metal-organic framework, a preparation method thereof, and an application, in view of the deficiencies of the prior art.

[0007] The preparation method of the above composite material includes the following steps:

[0008] (1) Weigh copper nitrate trihydrate, 1,3,5-benzenetricarboxylic acid (H3BTC), and polyvinylpyrrolidone (PVP), add them to deionized water and absolute ethanol respectively, mix the two solutions after stirring at room temperature, and obtain a homogeneous solution by ultrasonic treatment. Transfer the mixed system to a reaction kettle for heating, naturally cool to room temperature, collect the blue particles, wash them several times with ethanol / water, and dry the precipitate in an oven overnight to obtain the blue copper metal-organic framework material, copper 1,3,5-benzenetricarboxylate (HKUST-1) product, whose molecular formula is C 18 H 12 Cu3O 15 .

[0009] (2) Dissolve cobalt nitrate hexahydrate and sodium citrate in deionized water to form solution A. At the same time, disperse potassium ferricyanide in deionized water to obtain solution B. Then, under magnetic stirring, slowly add solution B to solution A until the two solutions are evenly mixed, let it stand at room temperature, centrifuge to collect the precipitate, wash it with water and ethanol, and dry it in an oven overnight to obtain the cobalt-iron Prussian blue (CoFe-PBA) product.

[0010] (3) Uniformly disperse HKUST-1 and CoFe-PBA powders in methanol, stir at room temperature, then transfer the mixed solution to a reaction kettle for heating. Wash the obtained precipitate three times with water and dry it in an oven overnight to obtain the composite material of the copper metal-organic framework and the Prussian blue analog, denoted as HKUST-1@CoFe-PBA.

[0011] (4) Heat HKUST-1@CoFe-PBA in a muffle furnace to obtain a black product after oxidation, denoted as HKUST-1@CoFe-O.

[0012] (5) Place the obtained HKUST-1@CoFe-O and thiourea at both ends of a tubular furnace respectively, heat in an argon atmosphere, and cool to room temperature with the furnace after the reaction is completed to obtain the composite material of the Prussian blue derivative and the copper metal-organic framework, denoted as HKUST-1@CoFe-S.

[0013] Compared with the prior art, the advantages of the present invention are as follows:

[0014] The present invention discloses the composite of copper metal-organic framework (HKUST-1) and cobalt-iron Prussian blue analogue (CoFe-PBA), and through subsequent sulfidation operation, the synergistic effect of multi-metal (Cu, Co, Fe) active sites is formed to improve the electron transfer efficiency and catalytic activity. The use of non-precious metals such as Cu, Co, Fe avoids the high cost of precious metals such as platinum (Pt) and iridium (Ir), and strong corrosive reagents (such as HF) are not involved in the process, which conforms to the trend of green synthesis.

[0015] Experimental tests show that in a 1M KOH electrolyte, the overpotential of oxygen evolution reaction (OER) of this material is only 268 mV at a current density of 10 mA / cm², providing a low-cost and high-stability technical solution for large-scale production of green hydrogen energy. Brief Description of the Drawings

[0016] Figure 1 X-ray powder diffraction pattern for preparing HKUST-1@CoFe-PBA composite material;

[0017] Figure 2 Electron microscope image of HKUST-1@CoFe-PBA composite material;

[0018] Figure 3 Electron microscope section and eds image of HKUST-1@CoFe-PBA;

[0019] Figure 4 Electron microscope image of HKUST-1@CoFe-S composite material;

[0020] Figure 5 OER curves and overpotential data graphs obtained from individual tests of different materials;

[0021] Figure 6 OER curves and overpotential data graphs of HKUST-1@CoFe-O obtained at different oxidation temperatures;

[0022] Figure 7 OER curves and overpotential data graphs of HKUST-1@CoFe-S obtained at different sulfidation temperatures;

[0023] Figure 8 OER curves and overpotential data graphs of HKUST-1@CoFe-S obtained by different sulfidation methods. Detailed Embodiments

[0024] The present invention will be further described in detail below in conjunction with the embodiments and the drawings.

[0025] The preparation method of the Prussian blue analogue and copper metal-organic framework composite material of the embodiment includes the following steps:

[0026] (1) Weigh 0.535 g of copper nitrate trihydrate, 0.234 g of BTC, and 0.1 g of PVP respectively, add them into 10 ml of deionized water and 10 ml of absolute ethanol respectively. After stirring at room temperature for 15 min, mix the two solutions and ultrasonicate for 10 min to obtain a homogeneous solution. Transfer the mixed system to a 50 ml autoclave, heat it at 100 °C for 12 h, naturally cool it to room temperature, collect the blue particles, wash them several times with ethanol / water (volume ratio 1:1), and dry the precipitate in an oven at 60 °C overnight to obtain a blue HKUST-1 product with the molecular formula C 18 H 12 Cu3O 15 .

[0027] (2) Dissolve 0.58 g of cobalt nitrate hexahydrate and 0.66 g of sodium citrate in 50 ml of deionized water to form solution A. At the same time, disperse 0.33 g of potassium ferricyanide in 50 ml of deionized water to obtain solution B. Then, under magnetic stirring, slowly add solution B to solution A until the two solutions are evenly mixed. Let it stand at room temperature for 24 h, centrifuge to collect the precipitate, wash it three times with water and ethanol, and dry it overnight at 60 °C to obtain the CoFe-PBA product.

[0028] (3) Disperse 20 mg of HKUST-1 and 40 mg of CoFe-PBA powder in 20 ml of methanol, stir at room temperature for 6 h, then transfer the mixed solution to an autoclave, heat it at 60 °C for 8 h, wash the obtained precipitate three times with water, and dry it overnight in an oven at 60 °C to obtain the HKUST-1@CoFe-PBA composite material.

[0029] (4) Place HKUST-1@CoFe-PBA in a muffle furnace and heat it to 350 °C at a rate of 2 °C / min to obtain a black product denoted as HKUST-1@CoFe-O. For comparison, calcine the raw materials at 300 °C and 400 °C respectively, and the obtained results are as Figure 6 shown. Place the obtained HKUST-1@CoFe-O product and thiourea at a mass ratio of 1:20 at both ends of a tubular furnace, heat it to 400 °C at a heating rate of 2 °C / min in an argon atmosphere, and cool it to room temperature with the furnace after the reaction is completed to obtain the HKUST-1@CoFe-S material. For comparison, calcine the raw materials at 300 °C and 500 °C respectively, and the obtained results are as Figure 7 shown.

[0030] To form a contrast with the prepared materials, different sulfidation methods were used for comparison, namely directly sulfiding the original materials without oxidation, hydrothermally sulfiding the oxidized materials, and changing the sulfur source (changing the used thiourea to sulfur powder) and then sulfiding in a tube furnace at 400 °C. The obtained results are as Figure 8 shown.

[0031] The following is the basic characterization of the HKUST-1@CoFe-S material prepared by the preparation method in the embodiments of the present invention.

[0032] Figure 1 is the XRD pattern of the prepared HKUST-1@CoFe-PBA, Figure 2 is the scanning electron microscope image of HKUST-1@CoFe-PBA, Figure 3 is the scanning electron microscope image of HKUST-1@CoFe-S. SEM and XRD tests prove that the material was successfully synthesized. As Figure 1 shown, the diffraction peaks of the HKUST-1@CoFe-PBA material match well with the diffraction peaks of the simulated synthesized HKUST-1 and CoFe-PBA standard cards (PDF: 46-0907). Figure 2 is the SEM image of the HKUST-1@CoFe-PBA material. It can be seen that a layer of CoFe-PBA nanoparticles is wrapped around the periphery of the standard octahedral morphology of HKUST-1, thus forming a core-shell structure. Figure 3 is the electron microscope section and EDS image of the material. It can be seen that the elements Fe, Co, and Cu are all distributed in the material, which proves that the composite material was successfully synthesized. HKUST-1 is a typical metal-organic framework material with a very high specific surface area, which means that the composite material provides a large number of active sites, which is conducive to improving the efficiency of catalytic reactions. And Co and Fe elements have high electrocatalytic activity. Such a microstructure design can increase the specific surface area and improve the contact efficiency between the electrolyte and the active sites. Figure 4 is the SEM image of HKUST-1@CoFe-S. It can be seen that after a series of high-temperature treatments, the material gradually loses its standard octahedral structure, but the CoFe-PBA nanoparticles still adhere to its surface and do not fall off due to excessive temperature. This shows that the composite material has high stability, thus extending the service life of the catalyst.

[0033] The electrocatalytic OER performance of the material HKUST-1@CoFe-S is as Figure 5 shown. The sulfidation treatment greatly improves its OER performance. Specifically, in the OER test, the sulfided HKUST-1@CoFe-S after sulfidation treatment has a current density of 10 mA cm -2The overpotential at this point decreased from the original 335 mV to 268 mV, a decrease of 67 mV. This performance improvement is mainly due to the fact that sulfidation treatment regulates the electronic structures of Fe, Co, and Cu, reducing the OER energy barrier. Different choices of oxidation temperature, sulfidation temperature, and sulfidation method will have different effects. For example, Figure 6 , 7 , as shown in Figure 8. After experiments, the optimal oxidation temperature was finally obtained as 350 °C, and the optimal sulfidation temperature was 400 °C with tube furnace sulfidation.

[0034] The electrochemical performance of the material HKUST-1@CoFe-S was evaluated by testing and analyzing with a Chenhua electrochemical workstation. The specific steps are as follows:

[0035] (1) Treatment of NF: The nickel foam (NF) was ultrasonically treated in 3M HCl solution, ethanol, and deionized water for 15 minutes respectively, and then dried in an oven at 60 °C for 3 h.

[0036] (2) Weigh 5 mg of the prepared sample and grind it in a mortar for 30 min. Add the obtained powder into a mixed solution of 50 μL of 5% Nafion solution and 450 μL of absolute ethanol, and ultrasonically treat it for 30 min to obtain a uniform catalyst ink. Take 50 μL of this catalyst ink and evenly drop it on the already treated nickel foam (1*1 cm -2 ) three times repeatedly. After drying, it is used as the working electrode.

[0037] (3) Prepare a KOH electrolyte with a concentration of 1M. Take 30 ml and add it into the electrolytic cell. A graphite rod and Hg / HgO are used as the counter electrode and reference electrode respectively for cyclic voltammetry testing to activate the sample. The voltage range for cyclic voltammetry testing is 0~1.8 V (relative to the Hg / HgO electrode), the scanning rate is 0.05 V / s, and the number of cycles is 80. Then, by using linear sweep voltammetry (LSV), the voltage range is 1.0~1.8 V (relative to the Hg / HgO electrode), and the OER polarization curve without iR compensation is obtained at a rate of 10 mV s -1 . According to the reversible hydrogen electrode (RHE) standard, all measured potentials are calibrated using the equation E RHE = E Hg / HgO + 0.059pH + 0.098.

Claims

1. A composite material of a Prussian blue derivative and a copper metal-organic framework, and its morphological characteristics are as follows: A layer of Prussian blue analogue nanoparticles adheres to the outside of the HKUST-1 standard octahedron to form a core-shell structure. After high-temperature heat treatment, its octahedral characteristics gradually disappear, but the surrounding Prussian blue nanoparticles do not fall off and still maintain the core-shell structure.

2. A preparation method of a composite material of a Prussian blue derivative and a copper metal-organic framework, characterized in that It includes the following steps: (1) Disperse 20 mg of HKUST-1 and 40 mg of CoFe-PBA powder into methanol, stir at room temperature, then transfer the mixed solution to a reaction kettle for heating. The obtained precipitate is washed three times with water and ethanol, and dried overnight in an oven to obtain the HKUST-1@CoFe-PBA composite material. (2) Place HKUST-1@CoFe-PBA in a muffle furnace and heat it to obtain a black product denoted as HKUST-1@CoFe-O. The obtained HKUST-1@CoFe-O product and thiourea are respectively placed at both ends of a tubular furnace according to a mass ratio of 1:20, and heated in an argon atmosphere. After the reaction is completed, it is cooled to room temperature with the furnace to obtain the HKUST-1@CoFe-S material.

3. The preparation method according to claim 2, wherein: In the step 3), the heating temperature of the muffle furnace is 300-400 °C In the step 3), the heating rate in the tubular furnace is 2 °C per minute, and the heating temperature is 300-400 °C.

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