CN118127550A - Preparation method and application of plasma-treated metal organic framework electrocatalyst - Google Patents

Abstract

The present invention discloses a preparation method and application of a plasma-treated metal organic framework (MOFs) electrocatalyst, belonging to the field of catalytic technology. By using argon plasma treatment, the prepared MOF-based electrocatalyst can be surface-modified to adjust its surface properties, thereby improving electrical conductivity and enhancing catalytic activity. The treated MOF material surface exhibits better interface characteristics, has more exposed active sites, modulated coordination environment and optimized electronic structure, making it more suitable for electrocatalytic reactions such as anode oxygen evolution reaction, and has important practical significance for promoting the development of clean energy conversion devices, such as water electrolyzers, metal air batteries and fuel cells.

Description

Preparation method and application of plasma treated metal organic framework electrocatalysts

Technical Field

The present invention relates to the technical field of catalyst preparation, and in particular to a preparation method of a plasma-treated metal organic framework electrocatalyst and application thereof.

Background technique

Electrochemical water splitting can produce high-purity hydrogen with high energy density and zero carbon emissions, and is hailed as a sustainable strategic technology to address global energy needs and mitigate environmental degradation. Among them, the oxygen evolution reaction (OER) at the anode faces challenges caused by the sluggish kinetics of the multi-step proton-coupled electron transfer process, which seriously hinders the successful realization of efficient and reversible chemical/electrical energy conversion at the solid-liquid-gas catalytic interface. Therefore, there is an urgent need to design advanced OER electrocatalysts that can improve the energy conversion efficiency. To date, the precious metal ruthenium (Ru) and iridium (Ir) based catalysts, which are considered to be the commercial standard for OER, have limited their use in commercial applications due to their high cost, limited resources and insufficient durability.

Transition metals are characterized by their abundant earth resources, economical availability, excellent catalytic activity and strong stability, and have made remarkable progress in the research of OER electrocatalysts. Among them, metal organic frameworks (MOFs) materials with independent active sites, porous structures, flexible adjustability and extremely large specific surface area show excellent OER activity and stability, making them promising candidates to replace precious metal-based catalysts. However, most MOFs have disadvantages such as low conductivity, insufficient intrinsic activity and hindered mass transfer, which constitute a bottleneck for the use of MOFs in electrochemical water splitting. At present, the performance regulation methods of MOFs-based anode OER electrocatalysts are limited to complex morphology regulation, expensive ligand replacement, etc. The use of these methods is accompanied by high-energy high-temperature pyrolysis reactions and complex mechanism exploration processes, which hinder the development of MOF-based electrocatalysts. Therefore, a simple and efficient processing technology is needed to achieve the preparation of high-performance, high-activity and high-OER selectivity MOFs-based electrocatalysts.

Summary of the invention

Based on previous research and existing problems, the present invention proposes a method for preparing a metal-organic framework electrocatalyst treated with argon plasma after further research and analysis. Through argon plasma treatment, chemical modification of the surface of the metal-organic framework material can be achieved, the electrical conductivity can be improved and the catalytic activity can be enhanced. The treated metal-organic framework surface exhibits better interface characteristics, making it more suitable for electrocatalytic reactions such as anodic oxygen evolution reaction.

To achieve the above purpose, the present invention provides the following technical solution: The method steps are as follows:

Step 1, pretreatment of nickel foam: removing oxides and organic matter on the surface of nickel foam, and drying for standby use;

Step 2: preparing Ni-MOF-BA/NF on the treated nickel foam, comprising the following steps:

Step 2.1: Add Ni(NO ₃ ) ₂ ·6H ₂ O to a mixed solution containing N,N-dimethylformamide, ethanol, and deionized water to fully dissolve;

Step 2.2: Add terephthalic acid and benzoic acid to the solution of step 2.1 and mix well;

Step 2.3: The solution obtained in step 2.2 is transferred to a reactor, and the pretreated nickel foam is immersed in the solution for reaction. After the reaction, the product is washed with ethanol and deionized water, and dried to obtain Ni-MOF-BA/NF;

Step 3: Place the Ni-MOF-BA/NF obtained in step 2 in a plasma generator, evacuate the chamber and introduce argon gas, turn on the plasma generator to ionize the argon gas to form plasma, and use high-energy particles to modify the Ni-MOF-BA/NF to obtain Ni-MOF-BA-P/NF.

Preferably, in step 1, ultrasonic cleaning is performed with HCl, anhydrous ethanol and deionized water for 15 to 20 minutes each, and the mixture is dried for later use.

Preferably, the molar ratio of Ni(NO ₃ ) ₂ ·6H ₂ O, terephthalic acid and benzoic acid is 1-1.1:0.6-0.7:0.4-0.5.

Preferably, the volume ratio of N,N-dimethylformamide, ethanol and deionized water is 16-20:1:1.

Preferably, the solutions in step 2.1 and step 2.2 are stirred with a magnetic stirrer at 700-800 r/min for 10-15 min.

Preferably, in step 2.3, the solution is sealed in an autoclave and maintained at 120° C. for 12 hours.

Preferably, in step 3, after evacuating for 5 minutes and introducing argon for 5 minutes, the plasma generator is turned on, the power is maintained at 80 W, and irradiation is performed for 5 minutes.

On the other hand, the present invention also provides a metal organic framework electrocatalyst, which is prepared by the above-mentioned preparation method.

Furthermore, the present invention also proposes an application of a metal organic framework electrocatalyst as mentioned above, wherein the prepared MOF catalyst is used as a working electrode, a carbon rod is used as a counter electrode, and Hg/HgO is used as a reference electrode; and electrochemical performance tests are carried out in a standard three-electrode system at normal temperature, pressure and room temperature.

Compared with the existing technology, the present invention provides a preparation method and application of a metal organic framework electrocatalyst treated with argon plasma, which has the following beneficial effects:

(1) Surface modification: Argon plasma can change the surface properties of the catalyst, thereby adjusting the activity and selectivity of the catalyst, which provides the possibility of customizing the catalyst to suit specific reaction conditions.

(2) High controllability: The conditions of argon plasma treatment can achieve a highly controllable preparation process by adjusting parameters such as gas composition and electric field strength, which helps to accurately control the structure and performance of the catalyst. The present invention accurately induces a large number of oxygen vacancies on the surface of the Ni-MOF-BA-P/NF catalyst through plasma treatment, which reduces the electronic valence state of the metal nickel site on the catalyst surface, adjusts the electronic structure of the active site on the catalyst surface, and is beneficial to the adsorption and desorption of OER reaction intermediates, thereby improving the catalytic activity.

(3) The argon plasma treatment used in the present invention is an environmentally friendly and efficient surface modification technology, and this process can be carried out at room temperature without the need for additional chemical reagents. The precatalyst prepared by argon plasma treatment can construct a large number of unsaturated coordinated nickel sites with oxygen vacancies on the catalyst surface, which is beneficial to the adsorption and desorption of OER reaction intermediates, thereby improving the catalytic activity.

(4) The present invention provides a simple, economical and efficient synthesis method for synthesizing Ni metal organic framework catalysts with excellent electrocatalytic OER activity, selectivity and stability through argon plasma treatment. This has important practical significance for promoting the development of clean energy conversion devices such as water electrolyzers, metal air batteries and fuel cells.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a scanning electron microscope image of the catalysts prepared in Examples 1, 2 and 3 of the present invention, wherein FIG1 (a, b) is a scanning electron microscope image of Ni-MOF/NF, FIG1 (c) is a scanning electron microscope image of Ni-MOF-BA/NF, and FIG1 (d) is a scanning electron microscope image of Ni-MOF-BA-P/NF;

FIG2 sequentially records the X-ray diffraction diagram, Raman spectrum diagram, X-ray photoelectron spectrum diagram and electron paramagnetic resonance spectrum diagram of the catalysts prepared in three embodiments of the present invention;

FIG3 sequentially records the linear sweep voltammetry curve (a), electrochemical impedance diagram (b), double layer capacitance diagram (c), and conversion frequency diagram (d) of the catalysts prepared in three embodiments of the present invention;

FIG. 4 is a Faraday efficiency diagram (a) and a stability test diagram (b) of the catalyst in Example 3 of the present invention.

Detailed ways

The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

In order to more clearly and in detail introduce the method for preparing the plasma-treated metal organic framework electrocatalyst provided by the embodiment of the present invention, it will be described below in conjunction with specific embodiments.

Embodiment 1

This embodiment provides a method for preparing a plasma-treated metal organic framework electrocatalyst, and the detailed steps are as follows:

1. Pretreatment of nickel foam: Cut nickel foam (NF) with a size of 2cm*4cm. In order to remove oxides and organic impurities, use 5M HCl, anhydrous ethanol, and deionized water for ultrasonic treatment for 15 minutes, and then dry for use.

2. Use a high-precision electronic balance to accurately weigh 1mmoL Ni(NO ₃ ) ₂ ·6H ₂ O and place it in a clean beaker with a magnetic rotor. Use a pipette to measure 32mL N,N-dimethylformamide (DMF), 2mL ethanol, and 2mL deionized water and add them to the beaker. Seal the beaker with plastic wrap. Stir the solution with a magnetic stirrer at 700r/min for 10min to fully dissolve it.

3. Use a high-precision electronic balance to weigh 1 mmoL of terephthalic acid (H ₂ BDC) and add it to the solution in step 2. Stir magnetically at a speed of 700 r/min for 10 min to mix the solution evenly.

4. After stirring evenly, transfer the solution obtained in step 3 to the inner liner of a 50 mL reactor, immerse the pretreated NF in the solution, seal the autoclave and keep it at 120°C for 12 hours (heating rate is 1°C/min). Cool to room temperature with the furnace, rinse the product thoroughly with ethanol and deionized water, and then dry it in a vacuum drying oven at 50°C to obtain Ni-MOF/NF.

The Ni-MOF/NF prepared above was used as the working electrode, 1M KOH as the electrolyte, the carbon rod as the counter electrode, and Hg/HgO as the reference electrode; the electrochemical performance test was carried out in a standard three-electrode system at room temperature, pressure and room temperature.

Embodiment 2

This embodiment provides a method for preparing a plasma-treated metal organic framework electrocatalyst, and the detailed steps are as follows:

1. Pretreatment of nickel foam: Cut nickel foam (NF) with a size of 2cm*4cm. In order to remove oxides and organic impurities, use 5M HCl, anhydrous ethanol, and deionized water for ultrasonic treatment for 15 minutes, and then dry for use.

2. Use a high-precision electronic balance to accurately weigh 1mmoL Ni(NO ₃ ) ₂ ·6H ₂ O and place it in a clean beaker with a magnetic rotor. Use a pipette to measure 32mL N,N-dimethylformamide (DMF), 2mL ethanol, and 2mL deionized water and add them to the beaker. Seal the beaker with plastic wrap. Stir the solution with a magnetic stirrer at 700r/min for 10min to fully dissolve it.

3. Use a high-precision electronic balance to weigh 0.6 mmol terephthalic acid (H ₂ BDC) and 0.4 mmol benzoic acid (BA) and add them to the solution in step 2. Stir magnetically at a speed of 700 r/min for 10 min to mix the solution evenly.

4. After stirring evenly, transfer the solution obtained in step 3 to the inner liner of a 50 mL reactor, immerse the pretreated NF in the solution, seal the autoclave and keep it at 120°C for 12 hours (heating rate is 1°C/min). Cool to room temperature with the furnace, rinse the product thoroughly with ethanol and deionized water, and then dry it in a vacuum drying oven at 50°C to obtain Ni-MOF-BA/NF.

The Ni-MOF-BA/NF prepared above was used as the working electrode, 1MKOH as the electrolyte, the carbon rod as the counter electrode, and Hg/HgO as the reference electrode; the electrochemical performance test was carried out in a standard three-electrode system at room temperature, pressure and room temperature.

Embodiment 3

This embodiment provides a method for preparing a plasma-treated metal organic framework electrocatalyst, and the detailed steps are as follows:

1. Pretreatment of nickel foam: Cut nickel foam (NF) with a size of 2cm*4cm. In order to remove oxides and organic impurities, use 5M HCl, anhydrous ethanol, and deionized water for ultrasonic treatment for 15 minutes, and then dry for use.

2. Use a high-precision electronic balance to accurately weigh 1mmoL Ni(NO ₃ ) ₂ ·6H ₂ O and place it in a clean beaker with a magnetic rotor. Use a pipette to measure 32mL N,N-dimethylformamide (DMF), 2mL ethanol, and 2mL deionized water and add them to the beaker. Seal the beaker with plastic wrap. Stir the solution with a magnetic stirrer at 700r/min for 10min to fully dissolve it.

3. Use a high-precision electronic balance to weigh 0.6 mmol terephthalic acid (H ₂ BDC) and 0.4 mmol benzoic acid (BA) and add them to the solution in step 2. Stir magnetically at a speed of 700 r/min for 10 min to mix the solution evenly.

4. After stirring evenly, transfer the solution obtained in step 3 to the inner liner of a 50 mL reactor, immerse the pretreated NF in the solution, seal the autoclave and keep it at 120°C for 12 hours (heating rate is 1°C/min). Cool to room temperature with the furnace, rinse the product thoroughly with ethanol and deionized water, and then dry it in a vacuum drying oven at 50°C to obtain Ni-MOF-BA/NF.

5. Place the Ni-MOF-BA/NF obtained in step 4 in a plasma generator, evacuate for 5 minutes and introduce argon for 5 minutes, then turn on the plasma generator, maintain the power at 80 W, and irradiate for 5 minutes to obtain Ni-MOF-BA-P/NF.

The Ni-MOF-BA-P/NF prepared above was used as the working electrode, 1MKOH as the electrolyte, the carbon rod as the counter electrode, and Hg/HgO as the reference electrode; the electrochemical performance test was carried out in a standard three-electrode system at room temperature, pressure and room temperature.

The scanning electron microscope (SEM) in Figure 1 shows that Ni-MOF/NF exhibits an ultrathin nanosheet morphology, and after argon plasma treatment, Ni-MOF-BA-P/NF exhibits a rough and porous morphology.

The X-ray diffraction diagram in Figure 2 shows that after plasma treatment, the position of the diffraction peak moves to the left, that is, lattice expansion occurs. Lattice expansion causes changes in the electronic structure of the adsorption site on the catalyst surface, thereby affecting the adsorption capacity of the intermediates in the reaction and improving the reaction rate and selectivity. At the same time, lattice expansion may also change the pore structure inside the catalyst and affect the mass transfer properties of reactants and products. The Raman spectrum shows that the intensity of the diffraction peak decreases after plasma treatment. This may be due to the generation of a large number of oxygen vacancies on the catalyst surface after plasma treatment, resulting in a decrease in the crystallization performance of the crystal. The X-ray photoelectron energy spectrum shows that after plasma treatment, the peak of divalent nickel moves to a low binding energy and the electronic structure changes. This is because after plasma treatment, a large number of oxygen vacancies are generated on the catalyst surface, which promotes the transfer of electrons from oxygen to nickel and reduces the valence state of nickel. This electron transfer affects the electronic structure of the catalyst, thereby promoting the formation of reaction intermediates and regulating the activity of the catalyst. The electron paramagnetic resonance spectrum shows that after plasma treatment, a stronger oxygen vacancy peak is generated.

As shown in Figure 3, (a) in 1.0M KOH alkaline solution, the Ni-MOF-BA-P/NF catalyst modified electrode has the best oxygen evolution catalytic activity. At a current density of 100mA cm ^-2 , the overpotential is 300mV, which is better than the catalytic activity of commercial _RuO2 catalyst. This shows that the OER activity of the catalyst can be effectively improved after plasma treatment.

(b) The Ni-MOF-BA-P/NF catalyst obtained by the test has the lowest charge transfer resistance, indicating that Ni-MOF-BA-P/NF has better conductivity. This shows that after plasma treatment, its charge transfer ability is significantly improved. At the same time, the reduction in charge transfer resistance means that electrons are more easily transferred between catalyst surfaces, which can reduce the loss of electrons on the catalyst surface, and more electrons can effectively participate in the catalytic reaction, which makes the active center of the catalyst more fully participate in the reaction and improves the catalytic activity.

(c) Ni-MOF-BA-P/NF with the highest electrochemical active area (ECSA) can expose more catalytic active sites. This indicates that after plasma treatment, Ni-MOF-BA-P/NF has more active sites to participate in the catalytic reaction, and more surface area provides more reaction centers, which helps to adsorb and activate reactants, thus increasing the reaction rate.

(d) Ni-MOF-BA-P/NF with higher turnover frequency (TOF) has higher intrinsic catalytic activity. This indicates that after plasma treatment, Ni-MOF-BA-P/NF reflects more efficient catalyst active sites, which means that the catalyst can more effectively convert reactants and improve catalytic activity.

As shown in Figure 4, the Ni-MOF-BA-P/NF prepared in Example 3 has an OER Faraday efficiency of 99.2%, indicating that it has high OER selectivity. And the Ni-MOF-BA-P/NF catalyst was tested for stability for 250 hours at a current density of 100mA cm ^-2 , and the catalytic activity did not significantly decline, indicating that the Ni-MOF-BA-P/NF catalyst prepared by us has very excellent electrochemical stability. Stable catalysts can maintain their catalytic activity for a long time and are not prone to deactivation, which is particularly critical for long-term catalytic reactions, especially in industrial production.

Therefore, the Ni-MOF-BA-P/NF catalyst prepared by plasma treatment has excellent OER activity, stability and selectivity, which provides new ideas and insights for the design and development of new efficient, stable and low-cost catalysts.

The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for a person skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to replace some of the technical features therein with equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions claimed to be protected by the present invention.

Claims (9)

1. The preparation method of the plasma-treated metal organic framework electrocatalyst is characterized by comprising the following steps:

step 1, foam nickel pretreatment: removing oxides and organic matters on the surface of the foam nickel, and drying for later use;

step 2, preparing Ni-MOF-BA/NF on the treated foam nickel, which comprises the following steps:

Step 2.1: adding Ni (NO ₃)₂·6H₂ O into a mixed solution containing N, N-dimethylformamide, ethanol and deionized water, and fully dissolving;

step 2.2: adding terephthalic acid and benzoic acid into the solution obtained in the step 2.1, and uniformly mixing;

Step 2.3: transferring the solution obtained in the step 2.2 into a reaction kettle, immersing the pretreated foam nickel into the solution for reaction, washing the product after the reaction is finished by ethanol and deionized water, and drying to obtain Ni-MOF-BA/NF;

And 3, placing the Ni-MOF-BA/NF obtained in the step two in a plasma generator, vacuumizing, introducing argon, starting the ion generator to ionize the argon into plasma, and modifying the Ni-MOF-BA/NF by using high-energy particles to obtain the Ni-MOF-BA-P/NF.

2. The method for preparing the plasma-treated metal-organic framework electrocatalyst according to claim 1, wherein in step 1, HCl, absolute ethyl alcohol and deionized water are sequentially used for ultrasonic cleaning for 15-20 min, and the metal-organic framework electrocatalyst is dried for standby.

3. The method for preparing a plasma-treated metal-organic framework electrocatalyst according to claim 1, wherein the molar ratio of Ni (NO ₃)₂·6H₂ O, terephthalic acid, and benzoic acid) is 1 to 1.1:0.6 to 0.7:0.4 to 0.5.

4. A method of preparing a plasma treated metal organic framework electrocatalyst according to claim 2 or 3, wherein the volume ratio of N, N-dimethylformamide, ethanol and deionized water is from 16 to 20:1:1.

5. The method for preparing a plasma-treated metal-organic framework electrocatalyst according to claim 4, wherein the solutions in step 2.1 and step 2.2 are each stirred with a magnetic stirrer at 700-800r/min for 10-15 min.

6. The method for preparing a plasma-treated metal-organic framework electrocatalyst according to claim 4, wherein in step 2.3, the solution is sealed in an autoclave at 120 ℃ for 12 hours.

7. The method for preparing a plasma-treated metal-organic framework electrocatalyst according to claim 1, wherein in step 3, after vacuumizing for 5min and introducing argon for 5min, the plasma generator is turned on, and the power is maintained at 80W and irradiated for 5min.

8. A metal organic framework electrocatalyst prepared by the method of any one of claims 1 to 7.

9. Use of a metal organic framework electrocatalyst according to claim 8 wherein the MOF catalyst prepared is used as a working electrode, a carbon rod is used as a counter electrode and Hg/HgO is used as a reference electrode; electrochemical performance testing was performed in a standard three-electrode system at room temperature, normal pressure and room temperature.