A highly hydrophobic molecular catalyst, its preparation method and use

Abstract

The application discloses a kind of high hydrophobicity molecular catalyst and its preparation method and application, belong to electrocatalysis technical field, first hydrophobic agent polytetrafluoroethylene is uniformly mixed with carbon nanotube by equal volume impregnation method, drying, the obtained catalyst carrier is dispersed in N,N-dimethylformamide with molecular catalyst phthalocyanine cobalt, ultrasonic loading, centrifugal, washing, drying phthalocyanine cobalt catalyst are obtained;The polytetrafluoroethylene hydrophobic immobilized phthalocyanine cobalt can be applied in electrocatalysis carbon dioxide preparation carbon monoxide.This application mainly through hydrophobic modification catalyst carrier, for phthalocyanine cobalt constructs microcosmic hydrophobic environment and promotes solid-liquid-gas three-phase contact interface formation, the prepared catalyst shows excellent catalytic carbon dioxide conversion for carbon monoxide performance under large current density.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrocatalysis, and particularly relates to an electrocatalytic carbon dioxide reduction to carbon monoxide catalyst and a preparation method and application thereof. BACKGROUND

[0002] Overconsumption of traditional fossil fuels has led to an increase in atmospheric carbon dioxide (CO2) concentration, resulting in a series of ecological and environmental problems such as the greenhouse effect (Zhu, D. D., Liu, J. L. & Qiao, S. Z. Recent Advances in Inorganic Heterogeneous Electrocatalysts for Reduction of Carbon Dioxide. Adv. Mater. 28, 3423-3452 (2016)). Electrocatalytic CO2 reduction is a key technology for achieving carbon neutrality and closing the carbon cycle (Nam, D.-H. et al. Molecular Enhancement of Heterogeneous CO2 Reduction. Nat. Mater. 19, 266-276 (2020); Bushuyev, O. S. et al. What Should We Make with CO2 and How Can We Make It? Joule 2, 825-832 (2018); De Luna, P. et al. What would it Take for Renewably Powered Electrosynthesis to Displace Petrochemical Processes? Science 364, eaav3506 (An alkaline polymer electrolyte CO2 electrolyzer operated with pure water-04-26)). Cobalt phthalocyanine (CoPc) has been widely used in electrocatalytic CO2 reduction in recent years due to its advantages such as easy regulation of electronic structure, low loading, and low cost (Ren, S. et al. Molecular Electrocatalysts Can Mediate Fast, Selective CO2 Reduction in a Flow Cell. Science 365, 367-369 (2019)). Research on cobalt phthalocyanine catalysis mainly includes homogeneous and heterogeneous catalysis (Wu, Y., Liang, Y. & Wang, H. Heterogeneous Molecular Catalysts of Metal Phthalocyanines for Electrochemical CO2 Reduction Reactions. Acc. Chem. Res. 54, 3149-3159 (2021)).Compared with homogeneous catalysis, in which catalyst molecules shuttle across the electrode surface (Sun, L., Reddu, V., Fisher, A. C. & Wang, X. Electrocatalytic Reduction of Carbon Dioxide: Opportunities with Heterogeneous Molecular Catalysts. Energy Environ. Sci. 13, 374-403 (2020)), heterogeneous catalysis has the advantages of fast electron transfer speed (Zhang, X. et al. Molecular Engineering of Dispersed Nickel Phthalocyanines on Carbon Nanotubes for Selective CO2 Reduction. Nat Energy 5, 684-692 (2020)), high catalyst spatial density (Sathrum, A. J. & Kubiak, C. P. Kinetics and Limiting Current Densities of Homogeneous and Heterogeneous Electrocatalysts. J. Phys. Chem. Lett. 2, 2372-2379 (2011)) and low requirements for electrolyzers (Burdyny, T. & Smith, W. A. CO2 Reduction on Gas-Diffusion Electrodes and Why Catalytic Performance Must be Assessed at Commercially-Relevant Conditions. Energy Environ. Sci. 12, 1442-1453 (2019) and others.Immobilization of cobalt phthalocyanine on carbon support is a common heterogeneous catalysis strategy, which can exhibit near 100% carbon monoxide (CO) selectivity at low current (Marianov, A. N. & Jiang, Y. Mechanism-Driven Design of Heterogeneous Molecular Electrocatalysts for CO2 Reduction. Acc. Mater. Res. 3, 620-633 (2022); Sun, L. et al. Cobalt Quaterpyridine Complexes for Highly Efficient Heterogeneous CO2 Reduction in Aqueous Media. Advanced Energy Materials 12, 2202108 (2022); Zhang, X. et al. Highly Selective and Active CO2 Reduction Electrocatalysts Based on Cobalt Phthalocyanine / Carbon Nanotube Hybrid Structures. Nat Commun 8, 14675 (2017)).

[0003] It is not difficult to find that although the corresponding research has explored the ligand, carrier and catalytic path of the material, there is no detailed research on the microenvironment regulation to inhibit the occurrence of hydrogen evolution reaction at high current density. The cobalt phthalocyanine catalyst cannot maintain high selectivity at high current, which is still a key technical problem to be solved. SUMMARY

[0004] The present application aims to solve the technical problems of micro-hydrophobic environment regulation and interface CO2 concentration control of molecular catalyst cobalt phthalocyanine, and provides a high-hydrophobic molecular catalyst preparation method and application. The hydrophobicity of the immobilized cobalt phthalocyanine catalyst is improved by introducing a hydrophobic agent, polytetrafluoroethylene (PTFE), to construct a micro-hydrophobic environment, inhibit proton transfer during the reaction and promote the formation of solid-liquid-gas three-phase contact interface, increase the CO2 concentration at the catalytic interface, inhibit the hydrogen evolution reaction and improve the CO Faraday efficiency, which can be well applied in the field of electrocatalytic CO2 reduction.

[0005] The technical purpose of the present application is achieved by the following technical scheme.

[0006] A high-hydrophobic molecular catalyst, which is an immobilized cobalt phthalocyanine catalyst with particulate polytetrafluoroethylene, is prepared according to the following steps:

[0007] The carbon nanotubes hydrophobized by granular polytetrafluoroethylene and cobalt phthalocyanine are mixed in a mass ratio of 15:(1-3), and N,N-dimethylformamide is added for acute ultrasonic dispersion, the addition amount of N,N-dimethylformamide is (20-30) milliliters per milligram of cobalt phthalocyanine, centrifugation and removal of supernatant, after washing and drying, a high hydrophobic molecular catalyst is obtained, wherein:

[0008] After mixing polytetrafluoroethylene and carbon nanotubes, deionized water is added for dispersion to obtain a slurry material, and after drying at room temperature, the carbon nanotubes hydrophobized by granular polytetrafluoroethylene are obtained; after mixing polytetrafluoroethylene and carbon nanotubes, the mass percentage of polytetrafluoroethylene is 10-30wt%.

[0009] Further, after mixing polytetrafluoroethylene and carbon nanotubes, the mass percentage of polytetrafluoroethylene is 20wt%.

[0010] Further, the mass ratio of the carbon nanotubes hydrophobized by granular polytetrafluoroethylene to cobalt phthalocyanine is 15:1.

[0011] Further, the addition amount of N,N-dimethylformamide is (20-25) milliliters per milligram of cobalt phthalocyanine.

[0012] The application of the high hydrophobic molecular catalyst in the electrocatalytic reduction of carbon dioxide to carbon monoxide.

[0013] In use, the high hydrophobic molecular catalyst (i.e. the supported cobalt phthalocyanine catalyst of the application), FAA solution and DMF are mixed into a homogeneous solution, which is sprayed on a gas diffusion electrode as a working electrode (i.e. a catalytic electrode), and the loading is 1-3 mg / cm 2 The foam nickel loaded with iridium oxide is used as a counter electrode, and the electrocatalytic reaction is carried out under electricity; an alkaline solution such as 1 mol / L KOH aqueous solution is used as an electrolyte.

[0014] Compared with the prior art, the application has the following specific beneficial effects:

[0015] (1) The PTFE-CoPc / CNT (i.e. the supported cobalt phthalocyanine catalyst hydrophobized by granular polytetrafluoroethylene) of the application constructs a micro-hydrophobic environment for the catalyst cobalt phthalocyanine, can inhibit proton mass transfer at a large current density, promote the increase of CO2 concentration at the active site, and inhibit the hydrogen evolution reaction. In addition, the micron flake structure constructed has the function of trapping CO2, promotes the formation of gas-liquid-solid three-phase interface at the reaction interface, improves the selectivity of CO, and achieves a CO faradic efficiency of 93%.

[0016] (2) The PTFE-CoPc / CNT preparation method of the present application is simple, the reaction conditions are mild, the synthesis route is controllable and repeatable, large-scale instrument equipment is not required, it is economically feasible, and the prepared material has superior performance in CO2 to CO, and has great industrialization potential.

[0017] (3) The PTFE-CoPc / CNT of the present application can be used as a high-efficiency electrocatalytic CO2 reduction to CO material, can maintain a high CO Faraday efficiency under a large current density, has a selectivity comparable to noble metal catalysts such as gold and silver, and has a loading of only one thousandth of gold and silver metal catalysts, thereby significantly reducing the cost of catalyst preparation and facilitating commercialization of carbon dioxide to carbon monoxide, providing technical support for the double-carbon policy. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is a synthesis route diagram of the polytetrafluoroethylene hydrophobic immobilized cobalt phthalocyanine obtained in Example 2.

[0019] Figure 2 is a SEM characterization result diagram of the PTFE-CoPc / CNT obtained in Example 2.

[0020] Figure 3 is an EDS characterization result diagram of the PTFE-CoPc / CNT obtained in Example 2.

[0021] Figure 4 is an XRD characterization result diagram of the cobalt phthalocyanine catalyst obtained in Examples 1-2.

[0022] Figure 5 is a cross-sectional SEM characterization result diagram of the cobalt phthalocyanine catalytic electrode obtained in Examples 3-4.

[0023] Figure 6 is a CLSM characterization result diagram of the cobalt phthalocyanine catalytic electrode obtained in Examples 3-4.

[0024] Figure 7 is a contact angle test result diagram of the cobalt phthalocyanine catalytic electrode obtained in Examples 3-4.

[0025] Figure 8 is a Faraday efficiency characterization result diagram of the product CO of the cobalt phthalocyanine catalytic electrode obtained in Examples 3-4.

[0026] Figure 9 is a local current density characterization result diagram of the product CO of the cobalt phthalocyanine catalytic electrode obtained in Examples 3-4. DETAILED DESCRIPTION

[0027] The application will be further described in detail below through specific examples, which can make the professional technical personnel more fully understand the application, but do not limit the application in any way.

[0028] Example 1

[0029] Accurately weigh 15 mg of carbon nanotubes and 1 mg of cobalt phthalocyanine in a beaker, add 20 mL of N,N-dimethylformamide (DMF), ultrasonic treatment for 30 min, remove the supernatant after centrifugation at a speed of 7000 r / min for 3 min, and sequentially wash the obtained solid with DMF, ethanol and deionized water, and dry in an oven at 80℃ for 10 h to obtain the supported cobalt phthalocyanine (CoPc / CNT).

[0030] Example 2

[0031] (1) Accurately weigh 20 mg of carbon nanotubes in a beaker, take 5.6 μL of PTFE emulsion (i.e. PTFE aqueous suspension) with a mass concentration of 0.9 g / mL and dilute to 200 μL with deionized water, and add the diluted emulsion dropwise into the beaker, ultrasonic treatment for 10 min to uniformly mix the emulsion and carbon nanotubes and form a mud-like mixture (the mass fraction of PTFE in the solid is 20 wt%, i.e. the mass of PTFE / the sum of the mass of PTFE and the mass of carbon nanotubes).

[0032] (2) The obtained mud-like mixture is left to stand at room temperature (20-30℃) overnight (8 h), and dried in an oven at 80℃ for 10 h to obtain PTFE-CNT (20 wt%).

[0033] (3) Take 15 mg of PTFE-CNT powder and 1 mg of cobalt phthalocyanine in a beaker, add 20 mL of N,N-dimethylformamide (DMF), ultrasonic treatment for 30 min, remove the supernatant after centrifugation at a speed of 7000 r / min for 3 min, and sequentially wash the obtained solid with DMF, ethanol and deionized water, and dry in an oven at 80℃ for 10 h to obtain PTFE-CoPc / CNT.

[0034] Figure 1 is the synthesis route of the polytetrafluoroethylene hydrophobic supported cobalt phthalocyanine obtained in Example 2. Figure 2 is the scanning electron microscope image of PTFE-CoPc / CNT obtained in Example 2, in which PTFE presents a granular morphology. Figure 3 is the energy spectrum of PTFE-CoPc / CNT obtained in Example 2, and it can be seen that the F element is gathered and distributed, i.e. PTFE is polymerized with each other. The X-ray diffraction characterization results of the cobalt phthalocyanine catalysts obtained in Examples 1-2 are shown in Figure 4 , and Example 2 has a clear diffraction peak at 2θ = 18°, indicating that PTFE is successfully modified on CNT.

[0035] Example 3

[0036] Take 10 mg of CoPc / CNT catalyst prepared in Example 1, 80 μL of FAA solution (purchased from Fuel Cell Store company, mass percentage is 25 wt%), 10 mL of DMF in a beaker, ultrasonic treatment for 30 min to form a uniform mixed solution. With nitrogen as the carrier gas, the mixed solution is sprayed onto a 2x2 cm 2 gas diffusion electrode at an operating condition of 75°C to obtain a catalytic electrode. The mass of the gas diffusion electrode is weighed before and after spraying using an analytical balance to control the solid loading of the electrode to be 1.5 mg / cm 2 .

[0037] Example 4

[0038] Take 10 mg of PTFE-CoPc / CNT catalyst prepared in Example 2, 80 μL of FAA solution (purchased from Fuel Cell Store company, mass percentage is 25 wt%), 10 mL of DMF in a beaker, ultrasonic treatment for 30 min to form a uniform mixed solution. With nitrogen as the carrier gas, the mixed solution is sprayed onto a 2x2 cm 2 gas diffusion electrode at an operating condition of 75°C to obtain a catalytic electrode. The mass of the gas diffusion electrode is weighed before and after spraying using an analytical balance to control the solid loading of the electrode to be 1.5 mg / cm 2 .

[0039] Figure 5 The cross-sectional SEM characterization results of the catalytic electrodes prepared in Examples 3-4 can obtain the thickness and structure of the catalytic electrode, and the thickness of Example 4 is greater than that of Example 3. Figure 6 The laser confocal scanning electron microscope characterization graph of the catalytic electrode prepared in Examples 3-4 can be seen that the fluorescence intensity of Example 4 attenuates slowly, indicating that the formation degree of gas-liquid-solid three-phase interface is higher, reference literature Shi, R. et al. Efficient Wettability-Controlled Electroreduction of CO2 to CO at Au / C Interfaces. Nat Commun 11, 3028 (2020). The contact angle test results of the catalytic electrodes obtained in Examples 3-4 are shown in Figure 7 , and the contact angles of Examples 3-4 increase in turn, indicating that the modification of PTFE significantly improves the hydrophobicity of the catalyst.

[0040] Example 5

[0041] The performance of the catalytic electrode was tested using a membrane electrode reactor, which was referenced from Zhang, G. et al. Efficient CO2 Electroreduction on Facet-Selective Copper Films with High Conversion Rate. Nat Commun 12, 5745 (2021). The test electrolyte was 1 mol / L KOH aqueous solution, and the electrode area was 4 cm 2 The product was detected by gas chromatography.

[0042] The CO Faraday efficiency values of the catalytic electrode prepared in Example 3-4 under different test current densities are shown in Table 2 Figure 8 It can be seen that the performance of PTFE-CoPc / CNT is significantly better than that of CoPc / CNT, that is, the improvement of hydrophobicity inhibits proton transport, improves the CO2 concentration at the reaction interface, and still maintains high reaction selectivity under high current density. The CO local current density of the catalytic electrode prepared in Example 3-4 under different test current densities is shown in Table 3 Figure 9 It can be seen that the law is similar to Table 2, and the local current density of PTFE-CoPc / CNT is significantly higher than that of CoPc / CNT. Figure 8

[0043] Although the preferred embodiments of the present application are described above with reference to the accompanying drawings, the present application is not limited to the specific embodiments described above, and the specific embodiments described above are only illustrative and not limiting. Those skilled in the art can make many forms of specific changes under the inspiration of the present application without departing from the purpose of the present application and the scope protected by the claims, and these all belong to the protection scope of the present application.​

Claims

1. A highly hydrophobic molecular catalyst, characterized in that, The highly hydrophobic molecular catalyst is a supported cobalt phthalocyanine catalyst hydrophobically treated with particulate polytetrafluoroethylene, and is prepared according to the following steps: Carbon nanotubes treated with hydrophobic granular polytetrafluoroethylene (PTFE) were mixed with cobalt phthalocyanine at a mass ratio of 15:(1-3). N,N-dimethylformamide was added and ultrasonically dispersed. The amount of N,N-dimethylformamide added was (20-30) mL per milligram of cobalt phthalocyanine. After centrifugation and removal of the supernatant, the mixture was washed and dried to obtain a highly hydrophobic molecular catalyst. The carbon nanotubes treated with hydrophobic granular PTFE were prepared as follows: PTFE and carbon nanotubes were mixed, with PTFE having a mass percentage of 10-30 wt%. The mass percentage of PTFE was calculated as the sum of the mass of PTFE and the mass of carbon nanotubes. Deionized water was then added for dispersion to obtain a slurry-like material. After standing and drying at room temperature, carbon nanotubes treated with hydrophobic granular PTFE were obtained.

2. The highly hydrophobic molecular catalyst of claim 1, wherein, After mixing polytetrafluoroethylene (PTFE) and carbon nanotubes, the mass percentage of PTFE is 20 wt%.

3. The highly hydrophobic molecular catalyst according to claim 1, characterized in that, The mass ratio of hydrophobic carbon nanotubes made of particulate polytetrafluoroethylene to cobalt phthalocyanine is 15:

1.

4. The highly hydrophobic molecular catalyst according to claim 1, characterized in that, The amount of N,N-dimethylformamide added is (20-25) ml per milligram of cobalt phthalocyanine.

5. A method for preparing a highly hydrophobic molecular catalyst as described in claim 1, characterized in that, The highly hydrophobic molecular catalyst is a hydrophobic supported cobalt phthalocyanine catalyst with particulate polytetrafluoroethylene, and is prepared according to the following steps: Carbon nanotubes treated with hydrophobic granular polytetrafluoroethylene (PTFE) were mixed with cobalt phthalocyanine at a mass ratio of 15:(1-3). N,N-dimethylformamide was added and ultrasonically dispersed. The amount of N,N-dimethylformamide added was (20-30) mL per milligram of cobalt phthalocyanine. After centrifugation and removal of the supernatant, the mixture was washed and dried to obtain a highly hydrophobic molecular catalyst. The carbon nanotubes treated with hydrophobic granular PTFE were prepared as follows: PTFE and carbon nanotubes were mixed, with PTFE having a mass percentage of 10-30 wt%. The mass percentage of PTFE was calculated as the sum of the mass of PTFE and the mass of carbon nanotubes. Deionized water was then added for dispersion to obtain a slurry-like material. After standing and drying at room temperature, carbon nanotubes treated with hydrophobic granular PTFE were obtained.

6. The method for preparing a highly hydrophobic molecular catalyst according to claim 5, characterized in that, After mixing polytetrafluoroethylene (PTFE) and carbon nanotubes, the mass percentage of PTFE is 20 wt%.

7. The method for preparing a highly hydrophobic molecular catalyst according to claim 5, characterized in that, The mass ratio of hydrophobic carbon nanotubes made of particulate polytetrafluoroethylene to cobalt phthalocyanine is 15:

1.

8. The method for preparing a highly hydrophobic molecular catalyst according to claim 5, characterized in that, The amount of N,N-dimethylformamide added is (20-25) ml per milligram of cobalt phthalocyanine.

9. The application of a highly hydrophobic molecular catalyst as described in any one of claims 1-4 in the electrocatalytic reduction of carbon dioxide to carbon monoxide.

10. The application of the highly hydrophobic molecular catalyst according to claim 9 in the electrocatalytic reduction of carbon dioxide to carbon monoxide, characterized in that, In use, the highly hydrophobic molecular catalyst, FAA solution and DMF are mixed into a homogeneous solution, which is sprayed on a gas diffusion electrode as a working electrode, with a loading of 1-3 mg / cm 2 The electrolyte is an alkali solution, and the counter electrode is a foam nickel loaded with iridium oxide.

11. The application of the highly hydrophobic molecular catalyst according to claim 10 in the electrocatalytic reduction of carbon dioxide to carbon monoxide, characterized in that, The alkaline solution is a 1 mol / L KOH aqueous solution.

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