CN114824318B - Coaxial carbon nano tube/polyoxometallate/conductive polymer electrocatalyst and preparation method thereof - Google Patents

Abstract

The invention belongs to the field of electrocatalyst preparation, and relates to a preparation method of coaxial carbon nanotube/polyoxometalate/conductive polymer electrocatalyst, which includes: using soluble metal salt as the metal source and bisphosphate derivative as the ligand , carry out hydrothermal or solvothermal reaction, wash, centrifuge, and dry to obtain polymetallic salt POM; treat the inner carbon nanotube carrier with surfactant to obtain a modified inner carbon nanotube carrier; The inner carbon nanotube carrier is immersed in the polyoxometallate POM solution, washed, centrifuged, and dried to obtain carbon nanotubes@POMs nanotubes; the carbon nanotubes@POMs nanotubes are added to the conductive polymer precursor The reaction takes place in a solid solution in the presence of a strong oxidizing agent. The coaxial nanocable structure composite material constructed by the present invention sandwich POMs between two layers of conductive carbon materials. This structure will greatly improve the mass transfer performance of the material while ensuring the stability of the POMs and exposing sufficient reactive sites.

Description

A coaxial carbon nanotube/polyoxometalate/conductive polymer electrocatalyst and its preparation Preparation method

Technical field

The invention belongs to the field of electrocatalyst preparation, and specifically relates to a coaxial carbon nanotube/polyoxometalate/conductive polymer electrocatalyst and a preparation method.

Background technique

The information in this Background section is disclosed solely for the purpose of increasing understanding of the general background of the invention and is not necessarily considered to be an admission or in any way implying that the information constitutes prior art that is already known to a person of ordinary skill in the art.

With the depletion of traditional energy, the research and development of new energy and new materials has already received widespread attention and in-depth research. New energy vehicles started late and their prices remain high. Among them, the catalyst and proton membrane in the stack are the main reasons for the high cost. The kinetic process of Oxygen Reduction Reaction (ORR) at the cathode in the battery reaction is slow, which leads to higher requirements for catalysts and a larger amount of catalyst (accounting for 80% of the total catalyst amount). Therefore, the study of ORR catalysts is one of the most important directions in the field of fuel cell research. Traditional cathode catalysts are mainly precious metal platinum (Pt) and its alloy materials, but they are expensive and have poor durability, which greatly limits the application of fuel cells. Therefore, people still need to conduct more in-depth exploration in this field and study cheaper, efficient, and stable ORR catalyst materials. In the early days, researchers mainly reduced the amount of precious metals used by improving the atomic utilization of platinum in the catalyst. Although these methods have proven to be effective, with the rapid development of the automobile industry, platinum demand will still bring huge pressure. Therefore, in order to further reduce costs, more and more researchers are turning their attention to another method: developing non-precious metal catalysts with high catalytic effects.

Among many non-metallic catalysts, polyoxometalates (POM) have been widely used in catalysis and materials science due to their rich and diverse compositions and structures and unique physical and chemical properties (redox, electroactivity, photoactivity, etc.) field. While POMs show great potential in improving catalyst performance, they also show corresponding shortcomings. Its stability is poor, and most POMs are easily soluble in polar solvents; its specific surface area is small and its conductivity is poor, which greatly limits its application.

Contents of the invention

Based on the problems of poor coating mass transfer, insufficient exposure of active sites, and easy dissolution of polyacid in traditional polyacid-based materials, the purpose of the present invention is to provide a coaxial carbon nanotube/polyoxometalate-based material. Preparation method of polyoxometalate/conductive polymer nanocable material. The material prepared by this method has the following advantages: (1) The structure is stronger. The inner and outer carbon layers provide double physical barriers for POMs, fully ensuring the stability of the polyacid; (2) Enhanced conductivity. The inner and outer double conductive carbon layers facilitate the rapid transfer of electrons from the reaction interface to the electrode surface; (3) Large specific surface area and high mass transfer efficiency. The internal hollow structure and multiphase interfaces of nanocables increase the surface area for catalytic reactions while providing more diffusion channels for electrolytes, gases, and reactants.

In order to achieve the above technical objectives, the present invention adopts the following technical solutions:

A first aspect of the invention provides a preparation method of coaxial carbon nanotube/polyoxometalate/conductive polymer electrocatalyst, including:

Using soluble metal salts as metal sources and bisphosphate derivatives as ligands, perform hydrothermal or solvothermal reactions, wash, centrifuge, and dry to obtain polyoxometalate POM;

Treat the inner carbon nanotube carrier with surfactant to obtain a modified inner carbon nanotube carrier;

The modified inner carbon nanotube carrier is immersed in the polyoxometallate POM solution, washed, centrifuged, and dried to obtain carbon nanotubes@POMs nanotubes;

The carbon nanotube@POMs nanotube is added to the solution of the conductive polymer precursor, and the reaction is carried out in the presence of a strong oxidizing agent.

The present invention explores an effective preparation method to achieve effective fixation and protection of polyacid, and constructs a composite material with a coaxial nanocable structure. From this, the present invention sandwiches POMs between two layers of conductive carbon materials. , this structure will greatly improve the mass transfer performance of the material, while ensuring the stability of POMs and exposing sufficient reactive sites.

A second aspect of the present invention provides a coaxial carbon nanotube/polyoxometalate/conductive polymer electrocatalyst prepared by the above method.

The beneficial effects of the present invention are:

The nanocable structure formed by wrapping POMs in the form of nanosheets between two porous conductive carbon layers according to the present invention enables the material to have the following advantages:

(1) The structure is stronger. The inner and outer carbon layers provide double physical barriers for POMs, fully ensuring the stability of the polyacid;

(2) Enhanced electrical conductivity. The inner and outer double conductive carbon layers facilitate the rapid transfer of electrons from the reaction interface to the electrode surface;

(3) Large specific surface area and high mass transfer efficiency. The internal hollow structure and multiphase interfaces of nanocables increase the surface area for catalytic reactions while providing more diffusion channels for electrolytes, gases, and reactants.

(4) The preparation method of the present invention is simple, easy to operate, highly practical, and easy to promote.

Description of the drawings

The description and drawings that constitute a part of the present invention are used to provide a further understanding of the present invention. The illustrative embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention.

Figure 1 is a scanning electron microscope image of the coaxial material of the sample prepared in Example 1.

Figure 2 is a scanning electron microscope image of the coaxial material of the sample prepared in Example 2.

Figure 3 is a scanning electron microscope image of the coaxial material of the sample prepared in Example 3.

Figure 4 is the LSV curve of the electrocatalytic ORR of the samples prepared in Example 1, Example 2, and Example 3.

Detailed ways

It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings commonly understood by one of ordinary skill in the art to which this invention belongs.

A coaxial carbon nanotube/polyoxometalate/conductive polymer electrocatalyst and preparation method, specifically including the following steps:

(1) Preparation of polyoxometalates (POM): Use hydrothermal or solvothermal methods, use soluble metal salts as metal sources, and select bisphosphate derivatives with high and low chelation degrees (connected aminopyridine organic fragments) ) as a ligand, a mixture of deionized water and organic solvent as the reaction solution, use a pH adjuster (such as HCl or NaOH) to adjust the acidity and alkalinity of the mixture and then perform a hydrothermal or solvothermal reaction. The product is centrifuged, washed and dried.

(2) Preparation of carbon nanotube@POMs nanotube array: Select an appropriate inner carbon nanotube carrier, use a certain concentration of polyacid prepared above as the reaction starting material, and use organic solution as the surfactant and coating agent, using self-assembly method to prepare POMs nanosheets and then compounding with carbon nanotubes through electrostatic interaction through dipping method. The product is centrifuged, washed and dried.

(3) Preparation of carbon nanotube@POMs@conductive polymer nanocable: Using in-situ polymerization method, the above-mentioned carbon nanotube@POMs nanotube is used as template, and conductive polymer precursor is used as carbon source to prepare nanocable material. Put the carbon nanotube@POMs nanotube prepared above into a hydrochloric acid solution containing a carbon source, add a strong oxidant, and react at a specific temperature for a period of time. The product is centrifuged, washed and dried.

In some embodiments, the soluble metal salt described in step one can be cobalt, iron, or nickel salt.

In some embodiments, the organic solvent described in step one can be ethanol or diethyl ether.

In some embodiments, the pH described in step one is generally between 5 and 8.

In some embodiments, the inner carbon nanotube carrier described in step 2 may be a polypyrrole tube, a one-dimensional MOF tube or a carbon nanotube.

In some embodiments, the surfactant described in step 2 can be tetrabutylammonium bromide, cetyl ammonium bromide, myristyltrimethylamine, PDDA (polydiallyldimethyl ammonium chloride).

In some embodiments, the conductive polymer precursor described in step three can be one of aniline, dopamine, and pyrrole.

In some embodiments, the strong oxidizing agent in step three may be one of potassium permanganate, potassium dichromate, and hydrogen peroxide.

In some embodiments, the reaction time in acid and strong oxidizing agent described in step three is 5-10 h.

The present invention will be further described in detail below with reference to specific embodiments. It should be pointed out that the specific embodiments are for explanation rather than limitation of the present invention.

In the following examples, Na ₂ H ₂ AlePy: is a material pre-synthesized according to the literature (reference: A. Saad, G. Rousseau, H. El Moll, O. Oms, P. Mialane, J. Marrot, L. Parent ,I.- M.Mbomekall¦, R. Dessapt, A. Dolbecq, J. Cluster Sci. 2014, 25, 795)

Na ₉ [A-PW ₉ O ₃₄ ]·7H ₂ O: also a pre-synthesized material (Reference: Inorganic Syntheses, Vol. 27 (Ed.: AP Ginsberg), Wiley, New York, 1990.)

Example 1

Step 1: Preparation of polyacids. Na ₂ H ₂ AlePy (0.612 g, 1.40 mmol) and Na ₉ [APW ₉ O ₃₄ ]·7H ₂ O (2400 g, 0.937 mmol) were added to the aqueous solution of CoCl ₂ ·6H ₂ O (0.6 g, 2.52 mmol). (60 mL), adjust the pH of the solution to neutral with 4 M NaOH, and stir at 80 °C for 40 min. Cool to room temperature, centrifuge the precipitate in the solution, and add KCl (0.9 g, 12.08 mmol) to the clear filtrate. After standing at room temperature for 3 days, purple crystals of the product can be obtained at the bottom of the cup.

Step 2: Preparation of binary coaxial objects. Add 100 mg CNT to 100 ml PDDA (4%), stir for 1 hour, and centrifuge to remove the supernatant. CNT-PDDA was put into a 10 mg/ml polyacid solution and stirred for 12 hours. The CNT/Co-POM was centrifuged in a centrifuge. After washing with water and ethanol, it was placed in a vacuum drying oven and dried at 60 degrees. CNT/Co-POM was obtained.

Step 3: Preparation of ternary coaxial objects. Dissolve 0.1g of CNT/POM and 0.25ml of aniline in 50ml of 1M HCl. After ultrasonic for 30 minutes, add 0.25g of K ₂ Cr ₂ O ₇ and stir for 6h. The CNT/Co-POM/PANI was centrifuged in a centrifuge, washed with water and ethanol, and then placed in a vacuum drying oven to dry at 60 degrees. Get CNT/Co-POM/PANI.

Figure 1 is a scanning electron microscope image of the coaxial material of the sample prepared in Example 1. It can be seen from Figure 1 that after compounding, the polyacid and conductive polymer are coated on the surface of the carbon nanotubes, and rough particle coatings can be seen on the surface of the carbon nanotubes.

From the LSV of electrocatalytic ORR in Example 1 in Figure 4, it can be seen that the composite material exhibits certain catalytic activity, with an initial potential of catalytic oxygen reduction of 0.76V and a current density of 3.2mA cm ^-2 .

Example 2:

The difference between this embodiment and Example 1 is that the concentration of the polyacid salt described in step (2) is 20 mg/ml.

Figure 2 is a scanning electron microscope image of the coaxial material of the sample prepared in Example 2. It can be seen from Figure 2 that after compounding, more polyacids and conductive polymers are coated on the surface of carbon nanotubes, and the carbon nanotubes become nanorod structures.

From the LSV of electrocatalytic ORR in Example 2 of Figure 4, it can be seen that the starting potential of the composite material for catalyzing oxygen reduction is 0.8V, and the current density is 4.3mA cm ^-2 . Its performance is significantly improved compared to that of Example 1.

Example 3:

The difference between this embodiment and Example 1 is that the concentration of the polyacid salt described in step (2) is 50 mg/ml.

Figure 3 is a scanning electron microscope image of the coaxial material of the sample prepared in Example 3. It can be seen from Figure 3 that the carbon nanotube structure is wrapped into a cluster structure after composite. It can be seen that as the polyacid concentration increases, the polyacid content on the surface of the carbon nanotube increases, and subsequently the surface conductive polymer content increases.

From the LSV of the electrocatalytic ORR in Example 3 in Figure 4, it can be seen that the starting potential of the composite material for catalyzing oxygen reduction is 0.85V, and the current density is 4.3mA cm ^-2 . Its performance is significantly improved compared to that in Examples 1 and 2. It can be seen that the polyacid salt serves as a catalytically active center, and as its content increases, the performance of the composite material increases.

Although the specific embodiments of the present invention have been described above, they do not limit the scope of the present invention. Those skilled in the art should understand that based on the technical solution of the present invention, those skilled in the art can do it without any creative work. Various modifications or variations are still within the protection scope of the present invention.

Claims (9)

1. A method for preparing a coaxial carbon nanotube/polyoxometallate/conductive polymer electrocatalyst, comprising:

taking soluble metal salt as a metal source, taking a bisphosphate derivative as a ligand, performing hydrothermal or solvothermal reaction, washing, centrifuging and drying to obtain polyoxometallate POM;

treating the inner-layer carbon nano tube carrier by a surfactant to obtain a modified inner-layer carbon nano tube carrier;

immersing the modified inner-layer carbon nanotube carrier in the polyoxometallate POM solution, washing, centrifuging and drying to obtain a carbon nanotube@POMs nanotube;

and adding the carbon nano tube @ POMs nano tube into the solution of the conductive polymer precursor, and reacting in the presence of a strong oxidant to obtain the conductive polymer.

2. The method for preparing the coaxial carbon nanotube/polyoxometallate/conductive polymer electrocatalyst according to claim 1, wherein the soluble metal salt is at least one of cobalt, iron, and nickel salts.

3. The method for preparing the coaxial carbon nanotube/polyoxometallate/conductive polymer electrocatalyst according to claim 1, wherein the solvent for the solvothermal reaction is ethanol or diethyl ether.

4. The method for preparing the coaxial carbon nanotube/polyoxometallate/conductive polymer electrocatalyst according to claim 1, wherein the surfactant is at least one of tetrabutylammonium bromide, cetylammonium bromide, tetradecyltrimethylamine, PDDA.

5. The method for preparing the coaxial carbon nanotube/polyoxometallate/conductive polymer electrocatalyst according to claim 1, wherein the conductive polymer precursor is at least one of aniline, dopamine, and pyrrole.

6. The method for preparing the coaxial carbon nanotube/polyoxometallate/conductive polymer electrocatalyst according to claim 1, wherein the strong oxidant is at least one of potassium permanganate, potassium dichromate, and hydrogen peroxide.

7. The method for preparing the coaxial carbon nanotube/polyoxometallate/conductive polymer electrocatalyst according to claim 1, wherein the reaction is performed for 5 to 10 hours in the presence of a strong oxidant.

8. A coaxial carbon nanotube/polyoxometalate/conductive polymer electrocatalyst prepared by the method of any one of claims 1 to 7.

9. The coaxial carbon nanotube/polyoxometallate/conductive polymer electrocatalyst of claim 8, used to make a fuel cell.