CN113277495A

CN113277495A - Three-dimensional carbon nanotube array composite material and preparation method and application thereof

Info

Publication number: CN113277495A
Application number: CN202110546834.2A
Authority: CN
Inventors: 郑波; 刘光祥; 郎雷鸣; 周钺; 陈文书; 潘兆瑞
Original assignee: Nanjing Xiaozhuang University
Current assignee: Nanjing Xiaozhuang University
Priority date: 2021-05-19
Filing date: 2021-05-19
Publication date: 2021-08-20

Abstract

The invention discloses a three-dimensional carbon nanotube array composite material and a preparation method and application thereof, wherein the preparation method comprises the following steps: s1, preparing a cocatalyst precursor by mixing organic transition metal salt, nitrogen-containing heteroatom compound and PDA surface modified foam nickel; s2 co-catalyst catalyzes the growth of the carbon nano tube to prepare the self-supporting carbon nano tube composite material at different temperatures: and (4) putting the co-catalyst precursor prepared in the step (S2) into a tube furnace, heating at a heating rate of 3-8 ℃/min under the condition of nitrogen until the temperature is raised to 600-800 ℃, and keeping the temperature for 1.5-3 hours for calcination to obtain the catalyst. The preparation method provided by the invention provides a simple, effective, low-cost and strong-universality preparation method for the three-dimensional carbon nanotube array composite material, and is convenient for large-scale production of the three-dimensional carbon nanotube array composite material and manufacture of a super capacitor by using the three-dimensional carbon nanotube array composite material.

Description

Three-dimensional carbon nanotube array composite material and preparation method and application thereof

Technical Field

The invention relates to the technical field of electrochemical energy storage and conversion, in particular to a preparation method of a multifunctional self-supporting high-strength three-dimensional carbon nanotube array composite material, the carbon nanotube array composite material, a super capacitor using the carbon nanotube array composite material, hydrogen production by water electrolysis, a fuel cell and a metal air battery.

Background

With the depletion of fossil energy and the ever-increasing demand for energy from people, the development of alternative energy storage and conversion devices has become of particular importance. Nanoelectrodes with composite structures or multiple functions have been proposed to modulate the surface and interface chemistry of nanomaterials to enhance the charge storage capacity of the electrode materials and have made many important advances. However, nanomaterial-based powder electrodes typically contain binders and additives that may cover the active sites of the nanomaterial, thereby diminishing the advantages of the nanomaterial itself. Designing binderless electrode structures and taking full advantage of the relevant surfaces and interfaces of electrochemical energy storage devices is an effective way to address the above-mentioned problems.

One-dimensional carbon nanotubes, which are one of carbon materials, have an extremely high aspect ratio, are light in weight and small in thickness, so that they have a high specific surface area, and thus exhibit good electrical conductivity, mechanical properties, stability, and the like, and are favored in the scientific research community and the industrial community. The synthesis method of the carbon nano tube has various methods, basically comprises the steps of preparing the carbon nano tube by catalyzing and decomposing specific hydrocarbon, and forming different micro crystal structures by adjusting synthesis condition parameters. Each method involves a complicated chemical process, and thus the yield and quality of carbon nanotubes produced by different methods vary. At present, the mainstream carbon nanotube synthesis methods in scientific research and industry comprise three methods involving gas phase processes, such as arc discharge, Chemical Vapor Deposition (CVD), laser ablation, and the like. However, the simple carbon nanotube can not meet the requirement of excellent performance of the material, and chemical modification of the carbon nanotube or preparation of the carbon nanotube composite material are important ways to improve the application performance. Chemical doping is an effective method for realizing regulation and control of physical and chemical properties of materials. Doping of heterogeneous atoms is widely applied to carbon material modification including carbon nanotube materials, and common heterogeneous heteroatoms include N, S, P, B and the like.

Three-dimensional nanoarrays (3D-NAs) have relatively ordered, continuous and fully exposed active surfaces, significantly promote mass and charge transfer at the electrode-electrolyte interface and inside the electrode, and are a promising electrode structure. However, no method capable of mass production is currently available.

3D-NAs are composed of a number of relatively ordered nanostructures such as Nanowires (NWs), Nanorods (NRs), Nanotubes (NTs), Nanobelts (NBs), Nanosheets (NSs), Nanoflower (NFs), and the like. In the electrochemical energy storage application, the 3D-NA electrode means that a film with a nano structure grows on a current collector in situ, and single nano structures can be independent of each other and can be woven with each other to form a three-dimensional network structure. The direct growth of the nanostructure film can be induced by two methods of prefabricating seeds on a current collector and improving the surface chemistry of a substrate; for the latter, the nanoscale surface roughness and wettability of the substrate are critical to reduce the nucleation energy and promote anisotropic growth of 3D-NAs. Despite the tremendous advances made in advanced electrode design and electrochemical energy storage device applications, challenges still remain. If the practical application of the 3D-NAs electrode is realized, the large-scale preparation must be carried out by depending on mature synthesis technology.

In the prior art, chinese patent CN109817468B, entitled a method for preparing a flexible nickel disulfide graphene composite electrode material, discloses that a composite electrode material with good flexibility can be prepared by coating a modified foam nickel substrate with polydopamine, and a master paper published by the university of tokyo post and telecommunications: the preparation and performance of a supercapacitor electrode based on a carbon nanotube-graphene-nickel foam three-dimensional composite structure disclose that the electrode of the supercapacitor is prepared by using a metal oxide catalyst, the energy density and the functional density of the supercapacitor can be improved, but the supercapacitor is difficult to popularize and use in batches. Chinese patent CN102161481B, entitled a method for preparing carbon nanotubes in large quantities at low cost, discloses that carbon nanotubes can be produced at low cost using iron-containing catalyst. But the toughness and mechanical property of the prepared carbon nano tube are not enough, and the service performance is not good.

In summary, the existing carbon nanotube composite material is difficult to realize large-scale mass production and application, the overall production cost is relatively high, the mechanical strength and toughness of the obtained carbon nanotube composite material are relatively poor, and the carbon nanotube composite material is difficult to achieve the preset technical requirements and technical function effects when being used in hydrogen production by water electrolysis, fuel cells, metal air batteries and super capacitors.

Disclosure of Invention

To overcome the above-described deficiencies of the prior art, the present invention provides foamed nickel as a catalyst and support substrate; coating and modifying foam nickel by polydopamine to promote the carbon nano tube to firmly grow on the substrate; the PDA surface modified foam nickel and organic transition metal salt are used as a cocatalyst, and an adequate carbon source is provided; the preparation method for preparing the multifunctional self-supporting high-mechanical-strength three-dimensional carbon nanotube array composite material by using the nitrogen-containing heteroatom compound to simultaneously provide a carbon source and a nitrogen source and performing one-step high-temperature heat treatment has the advantages of simplicity, effectiveness, low cost and strong universality, and can be used for preparing the multifunctional self-supporting high-mechanical-strength three-dimensional carbon nanotube array composite material in large-scale production, and a super capacitor, an electrolytic water hydrogen production fuel cell and a metal air cell which use the carbon nanotube array composite material.

The technical scheme adopted by the invention is as follows: the preparation method of the three-dimensional carbon nanotube array composite material comprises the following steps:

s1, preparing a co-catalyst precursor by mixing organic transition metal salt, nitrogen-containing heteroatom compound and PDA surface modified foam nickel PDA @ NF;

s2, catalyzing the growth of the carbon nano tube by the cocatalyst to prepare the self-supporting carbon nano tube composite material at different temperatures:

and (4) putting the co-catalyst precursor prepared in the step (S2) into a tube furnace, and heating at a heating rate of 3-8 ℃/min under the condition of nitrogen until the temperature is raised to 600-800 ℃, and keeping the temperature for 1.5-3 hours for calcination to obtain the catalyst.

Preferably, the PDA surface modified foam nickel is prepared by carrying out polydopamine coating modification treatment on a foam nickel substrate.

Preferably, the PDA surface modified nickel foam PDA @ NF is prepared by adjusting the dopamine concentration and polymerization time to control the thickness of the polymeric layer.

Preferably, the nitrogen-atom-containing compound comprises one or any combination of melamine, polyacrylonitrile, amino acid, dicyandiamide, melamine resin and polyacrylamide, so long as a sufficient nitrogen source is provided.

Preferably, the organic transition metal salt is an iron salt or a cobalt salt, including but not limited to any one of iron acetylacetonate, iron acetate, ferrocene, etc., cobalt acetylacetonate, and cobalt acetate.

Preferably, the co-catalyst precursor, when prepared,

1) firstly, dispersing organic transition metal salt and a nitrogen-containing heteroatom compound in ethanol, and uniformly stirring to obtain a dispersion liquid;

2) then placing PDA @ NF in the dispersion liquid, and stirring for 10-14h, wherein the specific stirring time can be 10, 11, 12, 13 or 14 h;

3) drying the mixture at 60-90 ℃, preferably 80 ℃ to prepare a cocatalyst precursor for catalyzing the growth of the carbon nano tube by the cocatalyst.

The multifunctional self-supporting high-strength three-dimensional carbon nanotube array composite material is prepared by the preparation method, and products obtained at different calcination temperatures of 800 ℃, 700 ℃ and 600 ℃ can be respectively marked as FMPN-800, FMPN-700 and FMPN-600.

A super capacitor is prepared by adopting the multifunctional self-supporting high-strength three-dimensional carbon nanotube array composite material, and in the specific implementation process, the prepared nanotube composite material is clamped by a glassy carbon electrode clamp and directly used as a working electrode. It should be noted that GMPN-800 is relatively brittle and is carefully gripped during fabrication of the working electrode. The carbon nanotube composite material grown by the co-catalyst has very good mechanical strength and can meet the requirement of long-time work.

The multifunctional self-supporting high-strength three-dimensional carbon nanotube array composite material is used as a catalyst for hydrogen production by a cathode of electrolyzed water.

A fuel cell adopts the multifunctional self-supporting high-strength three-dimensional carbon nanotube array composite material as a catalyst for electrocatalytic cathode oxygen reduction.

A metal-air battery adopts the multifunctional self-supporting high-strength three-dimensional carbon nanotube array composite material as a catalyst for electrocatalytic cathode oxygen reduction.

Compared with the prior art, the invention has the beneficial effects that:

(1) two metals are used as a co-catalyst for the growth of the carbon nano tube, the physical and chemical properties of the material can be adjusted, and the multifunctional self-supporting three-dimensional carbon nano tube array composite material with high mechanical strength can be obtained and can be directly used as a working electrode without adding a conductive agent and a binder.

(2) The carbon nanotube array composite material grown on the foam nickel modified by the polydopamine is not easy to fall off, and is beneficial to constructing devices which operate for a long time.

(3) The preparation method of the material is simple and easy to control. The prepared carbon nano tube array composite material has excellent electrochemical performance, shows good electrocatalytic oxygen reduction and hydrogen precipitation performance, and can be well applied to fuel cell metal-air batteries and water electrolysis technologies. In addition, the prepared three-dimensional carbon nanotube array composite material has high charge-discharge capacity and good rate discharge performance, and also has high application value in the field of super capacitors.

The prepared multifunctional self-supporting high-strength three-dimensional carbon nanotube array composite material has the advantages that the conductivity of the doped carbon nanotube material can be changed, meanwhile, due to the fact that certain atoms are doped at the boundary of a carbon-membered ring, a large number of oxygen-containing and hydrogen-containing functional groups are introduced, the surface area of the material is increased, meanwhile, due to the addition of the hydrophilic groups, the hydrophilicity of the material can be improved, and the application of the material in a liquid phase process is facilitated. The introduction of the organic transition metal can grow metal nanoclusters on the carbon nanotubes and form a metal-Nx/C coordination structure, so that the possibility is provided for multifunctional application of the carbon nanotubes.

In summary, the three-dimensional carbon nanotube array composite material, the preparation method and the application thereof provide a simple, effective, low-cost and strong-universality preparation method for the preparation of the three-dimensional carbon nanotube array composite material, are convenient for the large-scale preparation of the three-dimensional carbon nanotube array composite material, and are applied to the catalysis of hydrogen production of a super capacitor and an electrolytic water cathode, the catalysis of a fuel cell and the catalysis of a metal air battery.

Drawings

FIG. 1 is an SEM image of an FMPN-700 sample, wherein: part a is an SEM picture of an FMPN-700 sample, part b is an enlarged SEM picture of the FMPN-700 sample, and part c is an SEM picture of the FMPN-700 sample after a foam nickel substrate is removed through acid dissolution;

fig. 2 is an XRD contrast and a high power SEM contrast of a sample, wherein: part a is the XRD pattern of the nickel foam (pristine Ni foam), GMPN-800, FMPN-700 and FMPN-600 samples, and part b is a low angle magnified view of the nickel foam (pristine Ni foam), GMPN-800, FMPN-700 and FMPN-600 samples; part c is a high power SEM image of the surface of GMPN-800, FMPN-700 and FMPN-600 samples;

FIG. 3 is a Roman spectrum of GMPN-800, FMPN-700, and FMPN-600 samples;

FIG. 4 is a comparison of XPS spectra of GMPN-800 (acid soluble), FMPN-800, FMPN-700 and FMPN-600 samples, wherein the fractions a, b, C, d are high resolution XPS spectra of C1s, N1s, Ni2p and Fe2 p;

FIG. 5 shows GMPN-800, FMPN-700, FMPN-600 samples and Pt/C in N₂And O₂CV curve comparison plots obtained at a scan rate of 20 mV/s in a saturated 0.1MKOH solution;

FIG. 6 shows GMPN-800, FMPN-700, FMPN-600 samples and Pt/C in N₂And O₂Comparison of LSV curves and Tafel curves (f) obtained at a 5 mV/s scan rate in a saturated 0.1MKOH solution, where the a, b, C, d, and e portions are GMPN-800, FMPN-700, FMPN-600 samples and Pt/C at N, respectively₂And O₂LSV curves obtained at a scan rate of 5 mV/s in a saturated 0.1MKOH solution, and taffy curves for GMPN-800, FMPN-700, FMPN-600 samples and Pt/C in part f;

FIG. 7 is a graph of the electrochemical impedance of GMPN-800, FMPN-700, and FMPN-600 samples performed in a 0.1M KOH solution environment;

FIG. 8 is a graph of a current-time (i-t) curve and a timed current response, wherein: parts a and b are FMPN-700 and Pt/C at O₂Current-time (i-t) curve in saturated 0.1M KOH solution; part C and part d are FMPN-700 and Pt/C at O₂A curve of timed current response after 3.0M methanol was added to a saturated 0.1M KOH solution;

FIG. 9 is a LSV curve (5 mV/s) for GMPN-800, FMPN-700 samples in Ar saturated 1M KOH solution;

fig. 10 is a CV diagram of FMPN-800, a constant current charge and discharge curve, and an ac impedance diagram, wherein: the part a and the part b are CV diagrams under different scanning speeds in 1M KOH solution, the part c is a constant current charging and discharging curve under different current densities, and the part d is an AC impedance diagram under different current densities;

FIG. 11 is a CV diagram of FMPN-700 with a constant current charge and discharge curve and an AC impedance diagram, where parts a and b are CV diagrams at different sweep rates in 1M KOH solution, part c is a constant current charge and discharge curve at different current densities, and part d is an AC impedance diagram at different current densities;

FIG. 12 is a CV curve and an LSV curve of CMPN-700 and a constant current charge and discharge curve, wherein: part a is at N₂And O₂CV curves obtained at a scan rate of 20 mV/s in a saturated 0.1M KOH solution (ORR Performance test); part b is the LSV curve (HER Performance test, 5 mV/s) in Ar saturated 1M KOH solution; the part c is a constant current charge-discharge curve under different current densities in 1M KOH solution;

FIG. 13 is a schematic diagram of a method for preparing a three-dimensional carbon nanotube array composite.

Detailed Description

For the purpose of enhancing the understanding of the present invention, the present invention will be further explained with reference to the accompanying drawings and examples, which are only for the purpose of explaining the present invention and do not limit the scope of the present invention.

As shown in fig. 13, the flow chart of the method for preparing the three-dimensional carbon nanotube array composite material includes the following steps:

1) coating and modifying foam nickel by polydopamine;

2) mixing organic transition metal salt, nitrogen-containing heteroatom compound and polydopamine-coated modified foam nickel;

3) high temperature catalysis of carbon nanotube growth.

In a specific embodiment, the preparation and material preparation engineering is as follows, the preparation method of the self-supporting three-dimensional carbon nanotube array composite material comprises the following steps:

1) polydopamine-coated modified foam nickel substrate

Clean nickel foam was placed in a clean 200 mL beaker, 80 mg dopamine hydrochloride was added and polymerization was performed with magnetic stirring in 50 mL Tris-HCl buffer solution (pH = 8.5). The surface of the foam nickel presents black attachments, which are marked as PDA @ NF, and the surface of the PDA is modified foam nickel.

2) Preparation of organic transition metal compound salt, nitrogen-containing heteroatom compound and PDA @ NF mixed precursor

Taking out PDA surface modified foam nickel (PDA @ NF), respectively washing with purified water and ethanol for three times, weighing organic transition metal compound salt (such as ferric acetylacetonate) and nitrogen-containing heteroatom compound (such as melamine) powder, adding ethanol with a certain volume, magnetically stirring the mixture overnight, and oven drying in an oven at 80 deg.C (60 deg.C, 70 deg.C, 90 deg.C) for use.

3) Co-catalyst catalyzed growth of carbon nanotube

And (3) putting the prepared precursor into a tube furnace, heating at a heating rate of 3-8 ℃/min under the condition of nitrogen until the temperature is raised to 600-800 ℃, keeping for 1.5-3 hours, and calcining to finally obtain the self-supporting carbon nanotube composite material at different temperatures. The products obtained at different calcination temperatures are designated FMPN-800, FMPN-700 and FMPN-600.

4) Single nickel substrate catalyzed carbon nanotube growth

For comparison, a single nickel substrate was prepared to catalytically grow carbon nanotubes. Mixing the PDA surface modified foam nickel (PDA @ NF) with melamine and glucose (the mass ratio is 40: 1), placing the mixture in a porcelain boat, calcining the mixture in a tubular furnace under the nitrogen atmosphere, heating to 800 ℃, and maintaining for 2 hours. The product was labeled GMPN-800.

5) Working electrode preparation

The prepared nanotube composite material is clamped by a glassy carbon electrode clamp and directly used as a working electrode. It should be noted that GMPN-800 is relatively brittle and is carefully gripped during fabrication of the working electrode. The carbon nanotube composite material grown by the co-catalyst has very good mechanical strength and can meet the requirement of long-time work.

Example 1: FMPN-800 preparation

(1) Foam nickel pretreatment

Cutting the foamed nickel into round pieces by a button cell punching machine, sequentially soaking the round pieces in 1 mol/L hydrochloric acid, absolute ethyl alcohol and deionized water, respectively carrying out ultrasonic treatment for 20 min, and finally drying the round pieces in a 60 ℃ drying oven.

(2) Polymerization coating of dopamine on surface of foam nickel

10 pieces of clean nickel foam were placed in a clean 200 mL beaker, 80 mg dopamine hydrochloride was added, and polymerization was performed by magnetic stirring in 50 mL Tris-HCl buffer (pH = 8.5) for 3 days. The surface of the foam nickel showed a black deposit, designated PDA @ NF.

(3) High temperature catalytic carbon nanotube growth

Taking out the PDA surface modified foam nickel (PDA @ NF), respectively washing with purified water and ethanol for three times, adding 0.35 g of ferric acetylacetonate, 0.50 g of melamine and 20 mL of ethanol, magnetically stirring overnight, and drying in an oven at 80 ℃. And placing the dried mixture into a porcelain boat, calcining in a tubular furnace under nitrogen atmosphere at the heating rate of 5 ℃/min for 2h at 800 ℃, and obtaining FMPN-800.

Example 2: FMPN-700 preparation

The preparation procedure was the same as in example 1, except that the calcination temperature was changed to 700 ℃.

Example 3: FMPN-600 preparation

The procedure was the same as in example 1, except that the calcination temperature was changed to 600 ℃.

Example 4: GMPN-800 preparation

0.45g of PDA surface modified foam nickel (PDA @ NF) and 1.37g of melamine and glucose (the mass ratio is 40: 1) are mixed, placed in a porcelain boat, calcined in a tube furnace under the nitrogen atmosphere, heated to 800 ℃ for 400 min and maintained for 2 h. The product was labeled GMPN-800.

Example 5: CMPN-700

Taking out the PDA surface modified foam nickel (PDA @ NF), respectively washing with purified water and ethanol for three times, adding 0.1776g of cobalt acetate, 0.5 g of melamine and 20 mL of ethanol, magnetically stirring overnight, and drying in an oven at 80 ℃. And placing the dried mixture into a porcelain boat, calcining in a tubular furnace under the nitrogen atmosphere, fixing the temperature rise time for 180 min, and maintaining the calcination time for 2 h. The calcination temperature was varied and the product was labeled as CMPN-700.

Electrochemical test method:

all electrochemical measurements were performed on CHI760E electrochemical workstation (shanghai chen hua, china). The standard three-electrode test method was used at room temperature, with the working electrode being the prepared electrode plate, the reference electrode being the KCl saturated Ag/AgCl electrode, and the counter electrode being the graphite rod. For reference, a commercial Pt 20%/C catalyst working electrode fabrication method: 100 mu L of 4mg/mL Pt/C solution is dripped on the foam nickel and dried at 70 ℃.

The electrocatalytic oxygen reduction (ORR) test was performed in 0.1 mol/L KOH solution saturated with nitrogen or oxygen, with a Cyclic Voltammetry (CV) scan rate of 20 mV/s and a Linear Sweep Voltammetry (LSV) scan rate of 5 mV/s. Chronoamperometry (i-t) test potential was 0.6V vs. RHE, and methanol crossover and durability evaluations were performed.

The electrocatalytic Hydrogen Evolution Reaction (HER) was carried out in a 1 mol/L KOH solution saturated with argon, with a Linear Sweep Voltammetry (LSV) sweep rate of 5 mV/s. Cyclic Voltammetry (CV) was tested using different scan rates.

The capacitance performance was tested in 1 mol/L KOH solution using cyclic voltammetry and constant current charging and discharging (chronopotentiometry).

Electrochemical Impedance Spectroscopy (EIS) was tested at an AC amplitude of 5 mV in the frequency range of 0.1Hz-100KHz at open circuit potential.

Various properties of the example samples are described in detail below with reference to the accompanying drawings 1 to 13 of the specification:

FIG. 1 is an SEM image of part a low power and part b high power of FMPN-700 sample. As can be seen from the figure, a large number of three-dimensional porous network structures formed by disordered stacking of multi-wall carbon nanotubes grow on the foamed nickel substrate. Part c of fig. 1 is an SEM image of FMPN-700 sample after acid dissolution to remove the foamed nickel substrate, which shows that the carbon nanotubes still maintain a relatively intact array structure after the substrate is removed.

Part a of FIG. 2 is the XRD pattern of samples of nickel foam (pristine Ni foam), GMPN-800, FMPN-700 and FMPN-600. The three sharp diffraction peaks correspond to characteristic peaks of the metallic nickel substrate. The portion b in fig. 2 is a low-angle enlarged view for comparing the crystalline phase structures of the carbon materials on the surfaces of the substrates of different samples. The GMPN-800 corresponds to a carbon (002) diffraction peak at 26 ℃, but the FMPN-800, FMPN-700 and FMPN-600 samples have no significant carbon (002) diffraction peak, probably because the amount of carbon material is too small compared to the foamed nickel substrate, and the diffraction peak is weakly masked. The SEM image of the sample surface is shown in part c of fig. 2, which shows that the carbon nanotube array material was produced.

Raman spectroscopy is a sensitive surface testing technique, and further uses Raman to characterize the surface structure of a sample. FIG. 3 is a Roman spectrum of GMPN-800, FMPN-700, and FMPN-600 samples. Obvious characteristic carbon D peak (-1338 cm) can be observed in all samples in the graph^-1) And peak G (. about.1586 cm)^-1) The carbon material is illustrated as growing on the surface of the substrate. G peak ascribed to ordered sp²In-plane vibrational mode E associated with bonded carbon atoms_2g。I_D/I_GThe scale is typically used to assess structural defects. I of GMPN-800, FMPN-700 and FMPN-600_D/I_G1.14, 1.06, 1.02 and 1.06, respectively. Greater I_D/I_GThe ratio indicates that nitrogen atom doping causes a number of defects that may provide more active sites for electrocatalytic small molecule reactions. Meanwhile, the doping of nitrogen is beneficial to improving the hydrophilic performance of the material and promoting the improvement of the electrochemical performance. Compared with GMPN-800, the defects of the carbon material in the FMPN-800, FMPN-700 and FMPN-600 compounds are reduced, which shows that the addition of iron enhances the graphitization degree of the carbon material and reduces the defects in the material.

X-ray photoelectron spectroscopy (XPS) is a highly sensitive surface analysis technique that provides information about the elemental composition, content, and morphology of a sample surface. XPS test is carried out after collecting carbon material on the surfaces of FMPN-800, FMPN-700 and FMPN-600 by scraping with a knife. The GMPN-800 sample is brittle and cannot scrape off carbon materials, and the sample is collected by an acid-soluble nickel substrate method and is subjected to XPS test.

Table 1 shows the analysis of the carbon, nitrogen, oxygen, nickel and iron content in GMPN-800 (acid wash), FMPN-800, FMPN-700 and FMPN-600 samples. Comparing FMPN-800, FMPN-700, and FMPN-600 samples, nitrogen content decreased as the calcination temperature increased. In addition, the atomic ratios of Ni to Fe in the three samples were 1.63, 1.23 and 0.44, respectively. FIG. 4 is a high resolution XPS spectrum of samples C1s, N1s, Ni2p and Fe2 p.

TABLE 1GMPN-800-acid (acid wash), FMPN-800, FMPN-700 and FMPN-600 samples for carbon, nitrogen, oxygen, nickel and iron content analysis (XPS)

Sample	C (at%)	N(at%)	O(at%)	Ni(at%)	Fe(at%)
						GMPN-800-acid	88.49	4.39	5.81	1.31
FMPN-800	78.67	3.90	12.25	3.21	1.97
						FMPN-700	80.78	4.12	10.33	2.64	2.14
FMPN-600	84.00	6.12	7.90	0.60	1.37

FIG. 5 shows GMPN-800, FMPN-700, FMPN-600 samples and Pt/C in N₂And O₂CV curve obtained at a scan rate of 20 mV/s in a saturated 0.1M KOH solution. In N₂No redox peak was observed in saturated KOH solutions, but in O₂A significant reduction peak was present in saturated 0.1M KOH solution. Among them, FMPN-700 has the most positive reduction peak potential, almost equivalent to commercial Pt/C, indicating that it has very good catalytic activity on ORR.

FIGS. 6a, b, C, d, e parts GMPN-800, FMPN-700, FMPN-600 samples and Pt/C at N₂And O₂LSV curve obtained at a scan rate of 5 mV/s in a saturated 0.1M KOH solution. The initial potential of ORR of FMPN-700 sample is as high as 1.048V vs. RHE, and the half-wave potential and the reduction peak potential are 0.872 and 0.811V vs. RHE respectively, which are superior to the activity of commercial Pt/C catalyst. The ORR catalytic performance of the prepared four samples is sequentially shown as FMPN-700> FMPN-800> FMPN-600> GMPN-800。

And (5) obtaining kinetic information of the reaction process by Tafel analysis. As shown in FIG. 6e, FMPN-700 and Pt/C have similar Tafel slopes, indicating that they have similar ORR kinetics, i.e., 4e reduction.

FIG. 7 is an electrochemical impedance plot (EIS) of GMPN-800, FMPN-700, and FMPN-600 samples. The Nyquist impedance diagram shows an incomplete semicircle in the high frequency region. The diameter of the semicircle corresponds to the charge transfer resistance (Rct) at the interface between the electrode and the electrolyte. A smaller diameter of the semicircle means a faster kinetic reaction. The linear portion of the low frequency region is defined as the Warburg resistance (W), reflecting the diffusion/transport of ions. The GMPN-800 has the largest charge transfer resistance and the smallest slope of the low frequency line, indicating that the ions are diffused in the electrode structure the slowest. The FMPN-700, FMPN-800, and FMPN-600 samples all exhibited small charge transfer resistances, indicating a rapid kinetic reaction process.

FIG. 8 shows FMPN-700 and commercial Pt/C in O₂Current-time (i-t) curves in saturated 0.1M KOH solution and chronoamperometric response after addition of 3.0M methanol. The durability of the FMPN-700 catalyst was investigated by current-time chronoamperometry (see fig. 8a section). The current retention rate is 92.3 percent after the test of 22000 s, and the good stability is shown. And the Pt/C catalyst has poor stability for long-time operation (see part b of figure 8), and the current retention rate is reduced to 38.2%. For ORR catalysts, the tolerance of cross effects in practical fuel cells must be considered. In the case of O injected with 3.0M methanol as in FIG. 8c₂In saturated KOH solution, FMPN-700 cathodic current creates a transient disturbance, which then recovers rapidly, representing the excellent ability of the catalyst to avoid methanol cross-poisoning. As shown in FIG. 8d, the Pt/C catalyst produced a distinct oxidation current peak after addition of methanol, reflecting that its catalytic site has been poisoned, and is less resistant to methanol poisoning. The result shows that FMPN-700 has better stability and methanol cross-poisoning resistance.

FIG. 9 is an LSV curve (sweep rate 5 mV/s) of GMPN-800, FMPN-800, and FMPN-700 samples catalyzing HER in Ar saturated 1M KOH solution. As can be seen from the figure, at 10 mA/cm²The overpotentials at current densities were 265, 250 and 206 mvvs. RHE, respectively, indicating that FMPN-700 has the best catalytic hydrogen evolution effect.

Fig. 10 and 11 are CV graphs (see corresponding parts a and b) of FMPN-800 and FMPN-700 at different sweep rates in 1M KOH solution, constant current charge and discharge curves (see corresponding part c in the figure) and ac impedance graphs (part d in the figure) at different current densities, respectively. CV diagrams of FMPN-800 and FMPN-700 are basically rectangular under high scanning speed and low scanning speed, constant current charging and discharging curves under different current densities are approximate to isosceles triangles, and the fact that the storage performance mechanism of the prepared capacitor is a typical double-layer capacitor is shown, and the capacitor has good multiplying power performance. The capacitance values for FMPN-800 and FMPN-700 are given in tables 2 and 3 for different current densities.

TABLE 2 capacitance values of FMPN-800 at different current densities

Current Density (mA/cm)²)	0.44	0.88	1.77	4.42	8.85
						Cs ( mF/cm²)	48.27	44.62	42.96	37.13	37.08

TABLE 3 capacitance values of FMPN-700 at different current densities

Current Density (mA/cm)²)	0.44	0.88	1.77	4.42	8.85
						Cs( mF/cm²)	70.64	67.45	63.33	51.28	48.33

In general, FMPN-700 exhibits better supercapacitor performance. The AC impedance plots show that FMPN-800 and FMPN-700 have very low charge transfer resistances (Rct), 0.22 and 0.17 ohms, respectively, indicating their very good conductivity.

Part a in FIG. 12 is CMPN-700 at N₂And O₂CV curve obtained at a scan rate of 20 mV/s in a saturated 0.1M KOH solution. Compared with N₂In, O₂An obvious reduction peak appears in the saturated solution, and the peak potential is 0.772 Vvs. RHE, which shows that the CMPN-700 has good ORR catalytic performance. FIG. 12b part is a test of HER performance in Ar saturated 1M KOH solution at 10 mA/cm²The current density has a lower overpotential, whose value is 178 mvvs. FIG. 12c is a graph showing the constant current charge and discharge curves of CMPN-700 at different current densities in 1M KOH solution. At 0.44, 0.88, 1.77, 4.42 and 8.85mA/cm²The surface capacitance under the current density is respectively 118, 109.4, 102.4, 91.6 and 84.0 mF/cm²Super good in performanceThe capacitance performance.

Fig. 13 is a schematic view of a method for preparing a three-dimensional carbon nanotube array composite. Foamed nickel as a catalyst and support substrate; coating and modifying foam nickel by polydopamine to promote the carbon nano tube to firmly grow on the substrate; organic transition metal salts as co-catalysts and provide an adequate carbon source; and (3) providing a carbon source and a nitrogen source by the nitrogen-containing heteroatom compound, and preparing the self-supporting carbon nanotube composite material by one-step high-temperature heat treatment.

The preparation method of the self-supporting three-dimensional carbon nanotube array composite material adopts foamed nickel and introduced other organic transition metal salts as co-catalysts for forming the carbon nanotubes, anions in the organic transition metal salts are used as carbon sources, nitrogen-containing heteroatom compounds simultaneously provide the carbon sources and the nitrogen sources, and the formation of the three-dimensional network of the carbon nanotubes is catalyzed on the foamed nickel with high specific surface area and porous structure. The introduction of other organic transition metal salts can reduce the consumption of a nickel substrate in the process of generating the carbon nano tube, is beneficial to obtaining a composite material with better mechanical strength, can be directly used as an electrode material for the research in the field of electrochemical energy storage and conversion, and shows good ORR, HER and super-capacitor performances.

Example 6

The conventional supercapacitor electrode material is generally prepared by mixing an active substance, conductive carbon black and a polytetrafluoroethylene adhesive in a mass ratio of 8: 1 in N-methyl pyrrolidone, coating the mixture on a foam nickel sheet with the area of 1cm multiplied by 1cm, and drying the foam nickel sheet in vacuum at 100 ℃ for 12 hours.

The multifunctional self-supporting high-strength three-dimensional carbon nanotube array composite material prepared in the embodiments 1 to 5 can be directly used as an electrode of a supercapacitor to replace a complicated traditional electrode preparation process, and can realize higher charge and discharge capacity and better rate discharge performance.

Example 7

The existing electrocatalytic cathode oxygen reduction (ORR) proton exchange membrane fuel cell is driving into a motorway as an important direction of a new energy automobile strategy. However, the electrode reaction of the fuel cell, especially the cathode oxygen reduction, which is currently the mainstream, mostly adopts a noble metal platinum catalyst, and the problems of high cost, insufficient resources and durability of the noble metal platinum catalyst are increasingly prominent. Therefore, at present, there is an urgent need to research a cheap non-noble metal catalyst, reduce the use cost, and improve the stability, so that the catalyst can replace a noble metal platinum catalyst, which has a great propulsion effect on the development and popularization of fuel cells.

Electrocatalytic Hydrogen Evolution Reaction (HER): with the over-development and utilization of fossil fuels, all mankind is currently facing a series of severe environmental problems and energy crisis. Each country is also increasing support for development and utilization of new energy. Hydrogen is a clean energy with combustion products only containing water, is one of the key directions for developing new energy, is also considered as the most promising technology for producing clean and renewable hydrogen fuel, and is expected to effectively alleviate the energy crisis in the future. Therefore, the development of a non-noble metal Hydrogen Evolution Reaction (HER) electrocatalyst with high catalytic activity and low cost in an alkaline medium is of great significance for the development of an anion exchange membrane electrolysis hydrogen production technology. However, the alkaline HER activity of platinum (Pt) -based materials is 2-3 orders of magnitude lower than that of acidic media, placing higher demands on the metal mass load of practical alkaline electrolyzers. Among these, weakly basic HER kinetics are mainly influenced by slow water adsorption and desorption steps (Volmer step). The high conductivity of carbonaceous materials is a very significant advantage and is therefore widely used in electrocatalyst supports. However, they do not have a function of decomposing water and cannot be used as a catalyst promoter for basic HER. Therefore, how to impart excellent performance to the carbonaceous material, thereby accelerating the development of the carbonaceous material to a high-efficiency heterostructure alkaline HER electrocatalyst, will become a hot point of research.

The embodiments of the present invention are disclosed as the preferred embodiments, but not limited thereto, and those skilled in the art can easily understand the spirit of the present invention and make various extensions and changes without departing from the spirit of the present invention.

Claims

1. The preparation method of the three-dimensional carbon nanotube array composite material is characterized by comprising the following steps: the preparation method comprises the following steps:

s1, mixing organic transition metal salt, nitrogen-containing heteroatom compound and PDA surface modified foam nickel to prepare a cocatalyst precursor;

2. The method of claim 1, wherein:

the PDA surface modified foam nickel is prepared by carrying out polydopamine coating modification treatment on a foam nickel substrate.

3. The method of claim 2, wherein:

the PDA surface modified foam nickel is prepared by adjusting the concentration of dopamine and the polymerization time to control the thickness of a polymerization layer.

4. The method of claim 1, wherein:

the nitrogen-containing heteroatom compound comprises one or any combination of melamine, polyacrylonitrile, amino acid, dicyandiamide, melamine resin and polyacrylamide.

5. The production method according to any one of claims 1 to 4, characterized in that:

the organic transition metal salt is iron salt or cobalt salt, including but not limited to any one of iron acetylacetonate, iron acetate, ferrocene, cobalt acetylacetonate, and cobalt acetate.

6. The method of claim 5, wherein:

during the preparation of the co-catalyst precursor,

2) then placing the PDA @ NF in the dispersion liquid, and stirring for 10-14 h;

3) drying the mixture.

7. The multifunctional self-supporting high-strength three-dimensional carbon nanotube array composite material is characterized in that:

prepared by the preparation method of any one of claims 1 to 6.

8. A supercapacitor, characterized by:

the multifunctional self-supporting high-strength three-dimensional carbon nanotube array composite material of claim 7 is used as an electrode material for preparing a supercapacitor.