Ultrathin carbon nanosheet-based nickel-iron diatomic catalyst as well as preparation method and application thereof

Abstract

The invention discloses an ultrathin carbon nanosheet-based nickel-iron diatomic catalyst as well as a preparation method and application thereof. The material is an ultra-thin nitrogen-doped carbon nanosheet-based nickel monatomic loaded highly-dispersed phthalocyanine ferroelectric catalyst (FePc / M-LNi-NC), has an ultra-thin nitrogen-doped carbon nanosheet morphology and atomic dispersed Ni sites and Fe-N4 sites, is used for electrocatalysis of a carbon dioxide reduction reaction (CO2RR), and can be applied to electrocatalysis of a carbon dioxide reduction reaction (CO2RR). The composite material has the characteristics of outstanding electrocatalytic activity, good conductivity, high carbon monoxide (CO) selectivity and relatively low overpotential. CO2 is electrically catalyzed to be reduced in an H electrolytic tank, the highest CO Faraday efficiency reaches 98.8%, and the overpotential when the CO Faraday efficiency reaches 95% is reduced to-0.43 V from-0.31 V of M-LNi-NC.

Description

Technical Field

[0001] The present application relates to an ultra-thin carbon nanosheet-based nickel-iron diatomic catalyst and a preparation method and application thereof, and belongs to the technical field of inorganic catalyst materials and electrochemical reduction of CO2. Background Art

[0002] Excessive emissions of greenhouse gas CO2 have led to serious global climate and ecological environmental problems. Electrocatalytic CO2 reduction driven by renewable energy can produce high value-added fuels and chemicals while reducing CO2 emissions. As an effective way to achieve a sustainable carbon cycle, it has attracted increasing attention. However, the application of electrochemical CO2 conversion technology faces obstacles such as low current density, low selectivity, and high overpotential. CO is a widely used chemical raw material and is considered to be the most economical and feasible product for CO2 electroreduction. Atomically dispersed transition metal nitrogen sites in carbon matrices have become a popular catalyst for electrocatalytic CO2 reduction due to their unique electronic structure, clear coordination environment and maximum atomic utilization. Due to its Fe-NC structure, iron phthalocyanine exhibits over 90% CO selectivity, but iron phthalocyanine is easy to agglomerate and only exhibits catalytic activity in a very narrow potential window. Although Ni single-atom catalysts have high CO selectivity, their high overpotential affects energy efficiency. Introducing a second single-atom metal site on the basis of a single-atom catalyst to establish a diatomic site can break the linear relationship between the single-atom catalytic site and the adsorption free energy of different intermediates, adjust the electronic structure of the catalyst, and improve the catalytic performance of the single-atom catalyst. Summary of the invention

[0003] This application introduces a second metal active center to construct a dual-atom site catalyst (DASCs), which can adjust the electronic structure of the metal center and optimize the reaction free energy of reactants and intermediates, thereby breaking the constraints of the linear relationship of single-atom sites, and has broad application prospects in complex multi-step reactions such as electrocatalytic CO2 reduction. Through π-π stacking, the iron phthalocyanine is dispersed at the molecular level on the ultra-thin nitrogen-doped carbon nanosheet-based nickel atom catalyst, which can effectively reduce the energy in the CO2 reduction process and improve the activity, selectivity and energy efficiency of the catalytic reaction. According to one aspect of the present application, an ultrathin carbon nanosheet-based nickel-iron diatomic catalyst is provided, comprising ultrathin nitrogen-doped carbon nanosheet-based nickel single atoms and molecularly dispersed iron phthalocyanine supported by π-π stacking; The nickel atoms are dispersed at the atomic level in the ultra-thin nitrogen-doped carbon nanosheets; The iron phthalocyanine is dispersed at the molecular level in the ultra-thin nitrogen-doped carbon nanosheet; The thickness of the ultra-thin nitrogen-doped carbon nanosheet is 1.78 to 1.98 nm; Optionally, the thickness of the carbon nanosheet is any value among 1.78 nm, 1.88 nm, 1.98 nm, or a range value between any two of them. The length of the ultra-thin nitrogen-doped carbon nanosheet is 3 to 5 μm; Optionally, the length of the carbon nanosheet is any value among 3 μm, 4 μm, 5 μm, or any range between them. The specific surface area of ​​the ultra-thin nitrogen-doped carbon nanosheet is 936.5 to 956.5 m 2 / g; Optionally, the specific surface area of ​​the carbon nanosheet is 936.5 m 2 / g, 946.5m 2 / g, 956.5m 2 / g, or any range of values ​​between them. The pore volume of the ultrathin nitrogen-doped carbon nanosheet is 0.66 to 0.86 cm 3 / g; Optionally, the pore volume of the carbon nanosheet is 0.66 cm 3 / g, 0.76cm 3 / g, 0.86cm 3 / g, or any range of values ​​between them. The pore size of the ultra-thin nitrogen-doped carbon nanosheet is 3.03-3.23 nm; Optionally, the pore diameter of the carbon nanosheet is any value among 3.03 nm, 3.13 nm, 3.23 nm, or a range between any two values. The nickel content of the ultra-thin carbon nanosheet-based nickel-iron diatomic catalyst is 1.04 wt %. The ultra-thin carbon nanosheet-based nickel-iron diatomic catalyst has an iron content of 0.43 to 1.23 wt %; Optionally, the iron content of the ultra-thin carbon nanosheet-based nickel-iron diatomic catalyst is any value among 0.43wt%, 0.63wt%, 0.83wt%, 1.23wt% or any range between the two. According to another aspect of the present application, a method for preparing an ultrathin carbon nanosheet-based nickel-iron diatomic catalyst is provided, comprising the following steps: a) ultrasonically dispersing ultrathin nitrogen-doped carbon nanosheet-based nickel single atoms in N,N-dimethylformamide (DMF) to obtain a suspension A; b) dissolving FePc in solvent DMF to obtain solution B; c) mixing the suspension A and the solution B, subjecting them to ultrasonic treatment, and reacting by stirring at room temperature to obtain the ultrathin carbon nanosheet-based nickel-iron diatomic catalyst. The suspension A, the ratio of ultrathin nitrogen-doped carbon nanosheet-based nickel single atoms to DMF is 1 mg:1 mL, and ultrasonic dispersion is performed for 0.5 h. In the solution B, the concentration of iron phthalocyanine is 1 mg / mL. The mass ratio of the ultra-thin nitrogen-doped carbon nanosheet-based nickel single atom to iron phthalocyanine is 1:0.05 to 1:0.15; Optionally, the mass ratio of ultrathin nitrogen-doped carbon nanosheet-based nickel single atoms to iron phthalocyanine is any value among 1:0.05, 1:0.075, 1:0.1, 1:0.125, 1:0.15, or a range value between any two of them. c) In the reaction system after the suspension A and the solution B are mixed, the ratio of the ultrathin nitrogen-doped carbon nanosheet-based nickel single atom to DMF is 1 mg:1.2 mL. c) sonicating the suspension A and solution B after mixing for 1 hour. c) The suspension A and solution B are mixed and stirred at room temperature for 20 hours. 1. The preparation method according to claim 2, characterized in that: c) The product was post-treated by suction filtration, washing with ethanol three times, and vacuum drying at 80° C. for 10 h. Specifically, the steps include: (1) 15 mg of ultrathin nitrogen-doped carbon nanosheet-based nickel single atoms were ultrasonically dispersed in 15 mL of N,N-dimethylformamide (DMF) for 0.5 h to obtain a suspension A; (2) dissolving 1.5 mg of iron phthalocyanine in 1.5 mL of DMF solvent to obtain solution B; (3) Pour solution B into solution A, add 1.5 mL of DMF solvent, sonicate for 1 h, and then stir at room temperature for 20 h; (4) After the reaction, the solution was filtered, and the solid was washed with ethanol three times and dried in a vacuum at 80°C for 10 h. BRIEF DESCRIPTION OF THE DRAWINGS

[0004] Figure 1 It is the scanning electron microscope image of FePc / M-LNi-NC; Figure 2 This is the atomic force microscope electron microscope image of FePc / M-LNi-NC; Figure 3 This is the spherical aberration electron microscope image of FePc / M-LNi-NC; Figure 4 Fourier transform EXAFS spectra of FePc / M-LNi-NC and M-LNi-NC; Figure 5 The low temperature nitrogen adsorption desorption diagram of FePc / M-LNi-NC and M-LNi-NC; Figure 6 LSV diagram of FePc / M-LNi-NC electrocatalytic carbon dioxide reduction; Figure 7 This is the Faraday efficiency diagram of FePc / M-LNi-NC electrocatalytic carbon dioxide reduction; Figure 8 Energy efficiency diagram of FePc / M-LNi-NC electrocatalytic carbon dioxide reduction. DETAILED DESCRIPTION

[0005] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments. Unless otherwise specified, the raw materials and reagents in the examples of the present application were purchased through commercial channels, and the carbon cloth was purchased from Carbon Energy Technology Co., Ltd. Example 1 Preparation of Ultrathin Carbon Nanosheet-Based Nickel-Iron Diatomic Catalyst (FePc / M-LNi-NC) Sample (1) 15 mg of ultrathin nitrogen-doped carbon nanosheet-based nickel single atoms were ultrasonically dispersed in 15 mL of N,N-dimethylformamide (DMF) for 0.5 h to obtain a suspension A; (2) dissolving 1.5 mg of iron phthalocyanine in 1.5 mL of DMF solvent to obtain solution B; (3) Pour solution B into solution A, add 1.5 mL of DMF solvent, sonicate for 1 h, and then stir at room temperature for 20 h; (4) After the reaction, the solution was filtered, and the solid was washed with ethanol three times and dried in a vacuum at 80°C for 10 h. Example 2 Characterization of Ultrathin Carbon Nanosheet-Based Nickel-Iron Diatomic Catalyst (FePc / M-LNi-NC) Sample The morphology of the ultrathin carbon nanosheet-based nickel-iron diatomic catalyst obtained in Example 1 was characterized in detail using a scanning electron microscope. Figure 1 As shown, it can be clearly observed that the prepared samples have the shape of ultrathin nanosheets; Atomic force electron microscopy was used to characterize the materials, such as Figure 2 As shown, the thickness of FePc / M-LNi-NC is about 1.88 nm; Spherical aberration electron microscopy is used to characterize the materials, such as Figure 3 As shown, diatomic sites can be observed; The materials were characterized using synchrotron radiation. Figure 4 It is the Fourier transform EXAFS spectrum of the material, which shows that nickel atoms are distributed in a single atom state and iron atoms are near nickel atoms; Figure 5The low temperature nitrogen adsorption desorption diagram of FePc / M-LNi-NC shows that the BET specific surface area of ​​FePc / M-LNi-NC is 946.5 m 2 / g; Example 3 Performance test of ultrathin carbon nanosheet-based nickel-iron diatomic catalyst (FePc / M-LNi-NC) in a conventional H-type electrolytic cell (1) Take 10 mg of dried catalyst, add 1 mL of anhydrous ethanol and 30 μL of 5 wt% Nafion solution, and ultrasonicate for 30 min to form a uniform slurry. Apply 2×50 μL of the catalyst dispersion droplets on a carbon cloth (1 cm×1 cm) and dry. The catalyst loading on each piece of carbon cloth is 1 mg / cm 2 ; (2) In a conventional H-type electrolytic cell, 25 mL of a 0.5 M potassium bicarbonate solution saturated with carbon dioxide was added to the cathode and anode electrolytic cells respectively; (3) Using Ag|AgCl electrode as reference electrode and carbon rod as counter electrode, CV test was performed in the range of -1.2 to 0 V to activate the electrode; (4) Perform a linear scan curve (LSV) test at a scan rate of 5 mV / s; (5) Perform constant point test to obtain the IT curve at different points, take samples when the charge is -5C, and calculate the Faraday efficiency; Figure 6 It is the current curve of the electrocatalytic CO2 reduction of the material in the H electrolytic cell. It can be seen that when the potential is between -0.4 and -0.8 V, the current density of FePc / M-LNi-NC is significantly higher than that of M-LNi-NC, and the starting potential of FePc / M-LNi-NC (-0.39 V) is also lower than that of M-LNi-NC (-0.47 V). Figure 7 This is the Faraday efficiency diagram of the electrocatalytic CO2 reduction of the material. It can be seen from the figure that the CO Faraday efficiency of FePc / M-LNi-NC is as high as 98.8%; Figure 8 This is the energy efficiency diagram of the material's electrocatalytic CO2 reduction. At -0.6 V, the energy efficiency of FePc / M-LNi-NC reaches 71.2%, which is higher than 60.8% of M-LNi-NC. The above are only a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Any technician familiar with the profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. An ultra-thin carbon nanosheet-based nickel-iron diatomic catalyst, characterized in that: It includes ultrathin nitrogen-doped carbon nanosheet-based nickel single atoms and molecularly dispersed iron phthalocyanine supported by π-π stacking; The thickness of the ultra-thin carbon nanosheet-based nickel-iron diatomic catalyst is 1.78-1.98 nm; the length of the nanosheet is 3-5 μm, and the specific surface area is 936.5-956.5 m 2 / g, pore volume is 0.66~0.86cm 3 / g, pore size of 3.03-3.23nm, nickel content of 1.04wt%, iron content of 0.43-1.23wt%; The nickel atoms are dispersed at the atomic level in the ultra-thin nitrogen-doped carbon nanosheets; The iron phthalocyanine supported by the carbon nanosheet is in a molecular-level dispersed state.

2. A method for preparing the ultrathin carbon nanosheet-based nickel-iron diatomic catalyst according to claim 1, characterized in that: The steps include: a) ultrasonically dispersing ultrathin nitrogen-doped carbon nanosheet-based nickel single atoms in N,N-dimethylformamide (DMF) to obtain a suspension A; b) dissolving iron phthalocyanine in solvent DMF to obtain solution B; c) mixing the suspension A and the solution B, subjecting them to ultrasonic treatment, and reacting by stirring at room temperature to obtain the ultrathin carbon nanosheet-based nickel-iron diatomic catalyst.

3. The preparation method according to claim 2, characterized in that: The suspension A, the ratio of ultrathin nitrogen-doped carbon nanosheet-based nickel single atoms to DMF is 1 mg:1 mL, and ultrasonic dispersion is performed for 0.5 h; In the solution B, the concentration of iron phthalocyanine is 1 mg / mL.

4. The preparation method according to claim 2, characterized in that: The mass ratio of the ultra-thin nitrogen-doped carbon nanosheet-based nickel single atom to iron phthalocyanine is 1:0.05 to 1:0.15; c) In the reaction system after the suspension A and the solution B are mixed, the ratio of the ultrathin nitrogen-doped carbon nanosheet-based nickel single atom to DMF is 1 mg:1.2 mL.

5. The preparation method according to claim 2, characterized in that: c) ultrasonically mixing the suspension A and the solution B for 1 h; c) The suspension A and solution B are mixed and stirred at room temperature for 20 hours.

6. The preparation method according to claim 2, characterized in that: c) The product was post-treated by suction filtration, washing with ethanol three times, and vacuum drying at 80° C. for 10 h.

Images