Preparation Method and Application of Copper Nanoparticle Loaded on Hollow Carbon Nanofiber as an Electrocatalyst

Abstract

The present invention discloses a preparation method and application of a copper nanoparticle-loaded hollow carbon nanofiber electrocatalyst. The method includes: dispersing ZIF-8 powder, copper nitrate trihydrate, and a polymer into N,N-dimethylformamide to obtain an outer spinning solution; the polymer is selected from polyacrylonitrile or polyvinylpyrrolidone; dissolving polymethyl methacrylate in an organic solvent to obtain an inner spinning solution; injecting the outer spinning solution into an outer syringe of an electrospinning device, injecting the inner spinning solution into an inner syringe of the electrospinning device, and performing electrospinning to obtain raw fiber; performing carbonization treatment on the raw fiber in an inert atmosphere to obtain a copper nanoparticle-loaded hollow carbon nanofiber electrocatalyst. The obtained hollow carbon nanofiber, as a non-metal substrate, can stabilize metal nanoparticles and change the electron cloud structure of the metal, thereby improving the catalytic activity and selectivity of the catalyst for CO2RR.

Description

Technical Field

[0001] The present invention relates to the technical field of catalyst preparation, and particularly relates to a preparation method and application of a copper nanoparticle-loaded hollow carbon nanofiber electrocatalyst. Background Art

[0002] CO2 is one of the main gases causing the greenhouse effect and is also a cheap, clean, and abundant carbon resource. Developing a cost-effective electrochemical CO2RR process can achieve the transformation of the chemical industry and the sustainable energy economy. The combined use of electrochemical CO2RR with renewable energy such as wind energy or solar energy is conducive to the storage of renewable energy. It can not only weaken the greenhouse effect of the CO2 concentration in the atmosphere but also convert CO2 into basic materials for the production of chemicals.

[0003] CO2RR is a reaction with slow kinetics and requires highly efficient catalysts. The goal is that suitable catalysts can convert CO2 molecules into the desired products at relatively high current densities and maintain stable catalytic performance. Among current materials, copper is the only recognized catalyst that can produce a large amount of hydrocarbons or alcohols in aqueous solutions. However, copper-based electrocatalysts usually generate a chemical mixture of gas and liquid phases. How to control the catalytic selectivity of CO2RR for the desired products remains a challenge.

[0004] Therefore, the prior art still needs to be improved and developed. Summary of the Invention

[0005] In view of the deficiencies of the above prior art, the purpose of the present invention is to provide a copper nanoparticle-loaded hollow carbon nanofiber electrocatalyst, a preparation method, and an application, aiming to solve the problem of how to control the catalytic selectivity of CO2RR for the desired products.

[0006] The technical solution of the present invention is as follows:

[0007] In the first aspect, a preparation method of a copper nanoparticle-loaded hollow carbon nanofiber electrocatalyst, which includes:

[0008] Disperse ZIF-8 powder, copper nitrate trihydrate, and a polymer into N,N-dimethylformamide to obtain an outer spinning solution; the polymer is selected from polyacrylonitrile or polyvinylpyrrolidone;

[0009] Dissolve polymethyl methacrylate in an organic solvent to obtain an inner spinning solution; the organic solvent is N,N-dimethylformamide or absolute ethanol;

[0010] Inject the outer spinning solution into the outer syringe of an electrospinning device, inject the inner spinning solution into the inner syringe of the electrospinning device, and perform electrospinning to obtain raw fiber;

[0011] The as - prepared raw fiber is carbonized in an inert atmosphere to obtain a hollow carbon nanofiber - supported copper nanoparticle electrocatalyst.

[0012] Optionally, for the method for preparing the hollow carbon nanofiber - supported copper nanoparticle electrocatalyst, before carbonizing the as - prepared raw fiber to obtain the hollow carbon nanofiber - supported copper nanoparticle electrocatalyst, the method further includes the step of pre - oxidizing the as - prepared raw fiber in an air atmosphere.

[0013] Optionally, for the method for preparing the hollow carbon nanofiber - supported copper nanoparticle electrocatalyst, the mass ratio of the ZIF - 8 powder, the polymer, and copper nitrate trihydrate is 10:10:1.

[0014] Optionally, for the method for preparing the hollow carbon nanofiber - supported copper nanoparticle electrocatalyst, the pre - oxidizing the as - prepared raw fiber in an air atmosphere specifically includes:

[0015] Placing the as - prepared raw fiber in a tubular carbonization furnace, heating it in an air atmosphere in a programmed - temperature - rising manner, with a heating rate of 3 - 5 °C·min -1 , and keeping the temperature at 270 °C for 1 - 2 hours.

[0016] Optionally, for the method for preparing the hollow carbon nanofiber - supported copper nanoparticle electrocatalyst, the carbonizing the as - prepared raw fiber in an inert atmosphere to obtain the hollow carbon nanofiber - supported copper nanoparticle electrocatalyst specifically includes: calcining the pre - oxidized as - prepared raw fiber in an inert atmosphere at a calcination temperature of 1000 °C for 1 - 2 hours.

[0017] Optionally, for the method for preparing the hollow carbon nanofiber - supported copper nanoparticle electrocatalyst, the calcination temperature is increased in a programmed - temperature - rising manner, with a heating rate of 3 - 5 °C·min -1 , and keeping the temperature at 1000 °C for 1 - 2 hours.

[0018] Optionally, for the method for preparing the hollow carbon nanofiber - supported copper nanoparticle electrocatalyst, the method for preparing the ZIF - 8 powder includes:

[0019] Adding an aqueous solution of zinc nitrate hexahydrate to an aqueous solution of dimethylimidazole, and reacting under stirring conditions to obtain a white precipitate;

[0020] Centrifuging the white precipitate, washing and drying the separated solid material to obtain the ZIF - 8 powder.

[0021] Optionally, for the preparation method of the hollow carbon nanofiber supported copper nanoparticle electrocatalyst, the mass concentration ratio of zinc nitrate hexahydrate in the zinc nitrate hexahydrate aqueous solution to dimethylimidazole in the dimethylimidazole aqueous solution is 1.5 - 2:1.

[0022] In a second aspect, a hollow carbon nanofiber supported copper nanoparticle electrocatalyst, wherein the hollow carbon nanofiber supported copper nanoparticle electrocatalyst is prepared by using the above-mentioned preparation method.

[0023] In a third aspect, an above-mentioned hollow carbon nanofiber supported copper nanoparticle electrocatalyst is used for electrocatalytic reduction of carbon dioxide.

[0024] Beneficial effects: The present invention provides a preparation method of a hollow carbon nanofiber supported copper nanoparticle electrocatalyst. The raw materials used in this preparation method are all conventional raw materials. The preparation method is simple, and the reaction conditions are easy to achieve and control; for the hollow carbon nanofibers doped with copper nanoparticles, the fiber diameter distribution is uniform, and the diameter size is 300 - 500 nm; the copper particles in the hollow carbon nanofiber catalyst supporting copper nanoparticles serve as the active sites for electrocatalytic reduction of carbon dioxide, and the supported copper particles have a good catalytic effect on the electroreduction of carbon dioxide. The prepared carbon nanofiber electrocatalyst doped with copper particles contains a hollow structure inside, increasing the specific surface area of the catalyst; the prepared carbon nanofiber electrocatalyst doped with copper particles has a wide application prospect in the field of carbon dioxide electroreduction catalysts. Description of the Drawings

[0025] Figure 1 It is the linear sweep voltammetry (LSV) diagram of the electrocatalytic carbon dioxide reduction catalyst implemented in the present invention in 1M KOH;

[0026] Figure 2 It is the Faraday efficiency diagram of the electrocatalytic carbon dioxide reduction catalyst implemented in the present invention for electrolytic production of C2H4, CO, and H2 at different potentials in 1M KOH;

[0027] Figure 3 It is the TEM diagram of the electrocatalytic carbon dioxide reduction catalyst implemented in the present invention;

[0028] Figure 4 It is the XRD diagram of the electrocatalytic carbon dioxide reduction catalyst implemented in the present invention. Detailed Embodiments

[0029] The present invention provides a copper nanoparticle-loaded electrocatalyst on hollow carbon nanofibers, a preparation method, and an application thereof. To make the objectives, technical solutions, and effects of the present invention clearer and more definite, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0030] Those skilled in the art of the present technology can understand that, unless otherwise defined, all terms (including technical terms and scientific terms) used herein have the same meaning as the general understanding of those of ordinary skill in the technical field to which the present invention belongs. It should also be understood that terms defined in general dictionaries should be understood to have a meaning consistent with the meaning in the context of the prior art, and will not be interpreted in an idealized or overly formal sense unless specifically defined as herein.

[0031] Through research by the inventor, it is found that the reason for the poor catalytic selectivity of the existing CO2RR for the desired product is the various lattice planes, defects or vacancies of polycrystalline and oxidized Cu, which results in poor CO2RR catalytic activity. It is also found that the Cu(100) surface tends to generate ethylene at a relatively low potential, while the Cu(211) surface can produce a large amount of methane and a small amount of ethylene. The adsorption of CO2 molecules and the desorption of the corresponding products on the catalyst surface are the key steps determining the catalyst efficiency. The catalytic activity of the CO2RR electrocatalyst is mainly determined by the surface active sites, and the contribution of the internal atoms is very limited. Therefore, completely exposing and unifying the state of the Cu element is a method to improve the selectivity and efficiency of electrochemical CO2RR.

[0032] Based on the above findings, the inventor proposes the following technical solution: a preparation method of a copper nanoparticle-loaded electrocatalyst on hollow carbon nanofibers, which includes the following steps:

[0033] S10. Disperse ZIF-8 powder, copper nitrate trihydrate, and polyacrylonitrile or polyvinylpyrrolidone into N,N-dimethylformamide to obtain an outer layer spinning solution.

[0034] Specifically, polyacrylonitrile (PAN) can be dissolved in N,N-dimethylformamide to obtain a first solution. The first solution is magnetically stirred for 2 hours under water bath conditions to dissolve it. Then, ZIF-8 powder and copper nitrate trihydrate are added to the first solution, and it is magnetically stirred for another 2 hours under water bath conditions. Finally, the above solution is magnetically stirred at room temperature for 12 - 24 hours to obtain an outer layer spinning solution. Among them, the role of ZIF-8 powder is that after the catalytic material is sintered, the ZIF-8 powder will leave holes on the surface of the carbon fiber, thereby further increasing the active specific surface area of the catalyst and improving the catalytic performance; the role of polyacrylonitrile is to provide the substrate of the carbon fiber, and the role of copper nitrate trihydrate is to provide copper ions. The mass ratio of the ZIF-8 powder, polyacrylonitrile, and copper nitrate trihydrate is 10:10:1.

[0035] In this embodiment, the ZIF-8 powder can be prepared by the following preparation method:

[0036] Step 1: Dissolve dimethylimidazole in deionized water and stir at room temperature for 5 - 10 minutes to obtain a second solution; subsequently, dissolve zinc nitrate hexahydrate in deionized water and stir at room temperature for 5 - 10 minutes to form a third solution; Exemplarily, the mass of dimethylimidazole is 45.4 g, and the mass of zinc nitrate hexahydrate is 2.34 g; the deionized water added to dimethylimidazole is 160 ml, and the deionized water added to zinc nitrate hexahydrate is 16 ml.

[0037] Step 2: Rapidly add the third solution to the second solution and stir at room temperature for 10 - 15 minutes to obtain a white precipitate;

[0038] Step 3: Centrifuge the obtained white precipitate at a centrifugation rate of 7000 - 10000 rpm, wash it with deionized water, and dry the white solid in a vacuum drying oven to obtain white solid powder ZIF-8, where the drying temperature is 60 °C and the time is 12 - 24 hours.

[0039] After the step S10, it includes step S20: Dissolve polymethyl methacrylate in N,N-dimethylformamide or absolute ethanol to obtain an inner layer spinning solution.

[0040] Specifically, dissolve polymethyl methacrylate (PMMA) in N,N-dimethylformamide, and magnetically stir the above solution at room temperature for 12 - 24 hours to obtain an inner layer spinning solution, and the stirring rate is 400 - 600 rpm. Among them, the role of polymethyl methacrylate is that after the catalytic material is sintered, the polymethyl methacrylate will volatilize accordingly to form a hollow structure, thereby further increasing the active specific surface area of the catalyst and improving the catalytic performance. In the inner layer spinning solution, the concentration of polymethyl methacrylate is about 10 wt%.

[0041] After the step S20, it includes step S30: injecting the outer layer spinning solution into the outer syringe of the electrospinning device, injecting the inner layer spinning solution into the inner syringe of the electrospinning device, and performing electrospinning to obtain raw fiber.

[0042] Specifically, the outer layer spinning solution and the inner layer spinning solution are respectively injected into the outer syringe and the inner syringe of the electrospinning device for electrospinning. The spinning voltage can be set to 15 kV, the vertical distance from the needle to the receiving screen is 12 cm, and the circular roller (covered with aluminum foil) receives the electrospun nanofibers to collect the raw fiber.

[0043] After the step S30, it includes step S40: carbonizing the raw fiber in an inert atmosphere to obtain a hollow carbon nanofiber supported copper nanoparticle electrocatalyst.

[0044] Specifically, the collected raw fiber can be pre-oxidized before carbonization. Through the pre-oxidation treatment, the unstable carbon on the surface layer of the carbon fiber can be oxidized to improve the mechanical strength of the carbon fiber. Among them, the pre-oxidation treatment specifically includes: placing the raw fiber in a tubular carbonization furnace, heating it in an air atmosphere by a programmed heating method, and the heating rate is 5 °C·min -1 , and keeping it at 270 °C for 2 hours.

[0045] Calcining the pre-oxidized raw fiber in an inert atmosphere means calcining it under nitrogen protection. The calcining temperature is 1000 °C and the time is 1 - 2 hours. Among them, the calcining process is carried out by a programmed heating method, and the heating rate is °C·min -1 , and the gas flow rate is 80 ml·min -1 . Through calcining, the raw fiber can be carbonized to form a hollow structure, making the Cu element fully exposed, providing more active sites, and thus being able to improve the electrochemical CO2RR efficiency.

[0046] In this embodiment, the prepared hollow carbon nanofiber, as a non-metallic substrate, can not only reduce the metal usage amount and improve the metal atom utilization rate, but also stabilize the metal nanoparticles and change the electron cloud structure of the metal, thereby enhancing the CO2RR catalytic activity and selectivity of the catalyst.

[0047] Based on the same inventive concept, the present invention also provides a hollow carbon nanofiber supported copper nanoparticle electrocatalyst, which is prepared by the above preparation method. At the same time, it also provides an application of the hollow carbon nanofiber supported copper nanoparticle electrocatalyst, using it for electrocatalytic carbon dioxide reduction.

[0048] The preparation method of the copper nanoparticle-loaded hollow carbon nanofiber electrocatalyst provided by the present invention will be further explained below through specific preparation examples.

[0049] Preparation of ZIF-8: In a typical synthesis method, 45.4 g of dimethylimidazole was dissolved in 160 ml of deionized water and stirred at room temperature for 10 min; subsequently, 2.34 g of zinc nitrate hexahydrate was dissolved in 16 ml of deionized water and stirred at room temperature for 10 min; the above solutions were mixed and stirred at room temperature for 15 min to obtain a white solid mixture. The white solid was extracted by repeated centrifugation (10000 rpm, 10 minutes) and washed three times with deionized water, and the white solid was dried in a vacuum drying oven at 60 °C for 12 h to obtain ZIF-8.

[0050] Preparation of CuP-HCNFs: Copper particle hollow carbon nanofibers were synthesized by electrospinning. First, 1.5 g of polyacrylonitrile (Mw = 130000) was mixed with 20 ml of N,N-dimethylformamide and magnetically stirred in a water bath at 60 °C for 2 h. Immediately afterwards, 1.0 g of ZIF-8 and 100 mg of copper nitrate trihydrate prepared were added to the above solution and magnetically stirred in a water bath at 60 °C for 2 h. Finally, the above solution was magnetically stirred at room temperature for 12 h to obtain a spinning solution. The spinning solution was injected into a 20 ml syringe for electrospinning. The experimental parameters were as follows: a stainless steel metal needle with an inner needle diameter of 1.12 mm and an outer needle diameter of 1.99 mm was used as the nozzle, the spinning voltage was 15 kV, the vertical distance from the needle to the receiving screen was 12 cm, the inner feeding rate was 0.6 ml / h, and the outer feeding rate was 0.9 ml / h. The electrospun nanofibers were collected on a circular roller (covered with aluminum foil) to obtain the as-spun fibers.

[0051] The as-spun fibers were placed in a muffle furnace and pre-oxidized at a heating rate of 1 °C / min to 270 °C and held for 1 h in an air atmosphere; then the pre-oxidized sample was placed in a high-temperature tubular carbonization furnace and carbonized at a heating rate of 5 °C / min to 1000 °C and held for 1 h under a nitrogen atmosphere protection, and cooled to room temperature to obtain a highly graphitized carbon nanofiber composite CuP-HCNFs.

[0052] Electrochemical reduction of CO2 to C2H4 using the single CuP-HCNFs catalyst material produced by the implementation example: First, grind the prepared CuP-HCNFs for standby. Subsequently, uniformly mix ethanol and 5 wt.% Nafion membrane solution in a volume ratio of 920:80 to make a Nafion dilution solution. Then, add 4.5 mg of CuP-HCNFs powder into 1000 μl of the Nafion dilution solution and disperse it evenly by ultrasonic treatment. Then, spray the dispersion evenly on a carbon paper (divided into two parts after spraying) that has been washed with hydrochloric acid, deionized water, and ethanol, with dimensions of 1.5×3 cm 2 After baking and drying with an infrared lamp, a working electrode is obtained. Using a carbon paper with dimensions of 1.0×1.0 cm 2 containing 1 mg of the catalyst as the working electrode, an Ag / AgCl electrode (containing saturated KCl solution) as the reference electrode, and a 1.0×1.0 cm 2 foam nickel as the counter electrode, using a flow cell separated by a Nafion-117 proton exchange membrane for the anode and cathode chambers as the reaction vessel, and using 1.0 M KOH solution as the electrolyte, the test is carried out at room temperature and atmospheric pressure. Before the catalyst performance test, first perform cyclic voltammetry (CV) scanning test at a scanning rate of 50 mV / s between -0.4 V and -2.0 V (relative to the saturated Ag / AgCl electrode) for 10 cycles. The results are as Figure 1 、 Figure 2 shown. As can be seen from Figure 1 、 2 , at a potential of -1.8 V, the Faraday efficiency of C2H4 is 51%.

[0053] Among them, attached Figure 1 is the LSV diagram of the electrocatalytic carbon dioxide reduction catalyst in the implementation example of the present invention in an aqueous solution containing 1.0 M KOH. The electrochemical test is carried out on an electrochemical test system (CHI 760E, CH Instrument Inc). The test device is a flow cell. The gas diffusion electrode (hydrophobic carbon paper) loaded with the catalyst is used as the working electrode, the foam nickel electrode is used as the auxiliary electrode, and Ag / AgCl is used as the reference electrode.

[0054] As Figure 2 shown, in the potential range of -0.4 to -2.0 V vs RHE of the catalyst in the implementation example, the Faraday efficiency of generating C2H4 is 51%. Attached Figure 3 are the SEM and TEM diagrams of the electrocatalytic carbon dioxide reduction catalyst in the implementation example of the present invention. As Figure 3 shown, there is an obvious hollow structure. Attached Figure 4 is the XRD diagram of the electrocatalytic carbon dioxide reduction catalyst in the implementation example of the present invention. As Figure 4 shown, the diffraction peaks of the copper crystal plane are very obvious.

[0055] It should be understood that the application of the present invention is not limited to the above examples. For those of ordinary skill in the art, improvements or modifications can be made according to the above description, and all such improvements and modifications shall fall within the protection scope of the appended claims of the present invention.

Claims

1. A preparation method of a copper nanoparticle-loaded hollow carbon nanofiber electrocatalyst, characterized in that, Comprising: Disperse ZIF-8 powder, copper nitrate trihydrate and a polymer into N,N-dimethylformamide to obtain an outer layer spinning solution; the polymer is selected from polyacrylonitrile or polyvinylpyrrolidone; Dissolve polymethyl methacrylate in an organic solvent to obtain an inner layer spinning solution; the organic solvent is N,N-dimethylformamide or absolute ethanol; Inject the outer layer spinning solution into the outer syringe of an electrospinning device, and inject the inner layer spinning solution into the inner syringe of the electrospinning device, and perform electrospinning to obtain raw fiber; Carry out carbonization treatment on the raw fiber in an inert atmosphere to obtain a hollow carbon nanofiber supported copper nanoparticle electrocatalyst; the copper nanoparticles are completely exposed; Before carrying out the carbonization treatment on the raw fiber to obtain a hollow carbon nanofiber supported copper nanoparticle electrocatalyst, the following step is further included: carry out pre-oxidation treatment on the raw fiber in an air atmosphere; The mass ratio of the ZIF-8 powder, the polymer and the copper nitrate trihydrate is 10:10:

1.

2. The preparation method of the copper nanoparticle-loaded hollow carbon nanofiber electrocatalyst according to claim 1, characterized in that, The step of carrying out pre-oxidation treatment on the raw fiber in an air atmosphere specifically includes: Place the raw fiber in a tubular carbonization furnace and heat it in an air atmosphere using a programmed heating method with a heating rate of 3-5 °C·min -1 , and keep the temperature at 270 °C for 1-2 hours.

3. The preparation method of the copper nanoparticle-loaded hollow carbon nanofiber electrocatalyst according to claim 2, characterized in that, The step of carrying out carbonization treatment on the raw fiber in an inert atmosphere to obtain a hollow carbon nanofiber supported copper nanoparticle electrocatalyst specifically includes: under an inert atmosphere, calcine the pre-oxidized raw fiber, the calcination temperature is 1000 °C, and the calcination time is 1-2 hours.

4. The preparation method of the copper nanoparticle-loaded hollow carbon nanofiber electrocatalyst according to claim 3, characterized in that, The calcination temperature is increased by a programmed heating method, and the heating rate is 3-5 °C·min -1 , and it is held at 1000 °C for 1-2 hours.

5. The preparation method of the copper nanoparticle-loaded hollow carbon nanofiber electrocatalyst according to claim 1, characterized in that, The preparation method of the ZIF-8 powder includes: Add an aqueous solution of zinc nitrate hexahydrate to an aqueous solution of dimethylimidazole, and react under stirring conditions to obtain a white precipitate; Centrifuge the white precipitate, wash and dry the separated solid matter to obtain ZIF-8 powder.

6. The preparation method of the copper nanoparticle-loaded hollow carbon nanofiber electrocatalyst according to claim 5, characterized in that, The mass concentration ratio of zinc nitrate hexahydrate in the aqueous solution of zinc nitrate hexahydrate to dimethylimidazole in the aqueous solution of dimethylimidazole is 1.5-2:

1.

7. A copper nanoparticle-loaded hollow carbon nanofiber electrocatalyst, characterized in that, The hollow carbon nanofiber supported copper nanoparticle electrocatalyst is prepared by using the preparation method according to any one of claims 1-6.

8. A copper nanoparticle-loaded hollow carbon nanofiber electrocatalyst according to claim 7, which is used for electrocatalytic reduction of carbon dioxide.

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