Three-dimensional carbon nanotube jungle and preparation method and application thereof
阅读说明：本技术 三维碳纳米管丛林及其制备方法与应用 (Three-dimensional carbon nanotube jungle and preparation method and application thereof ) 是由 杨瑞枝 郑祥俊 于 2020-11-23 设计创作，主要内容包括：本发明属于电催化技术领域,具体公开了一种三维碳纳米管丛林及其制备方法与应用,可作为氧气还原反应(ORR)和氧气析出反应(OER)电催化剂在锌-空气电池(ZAB)中应用。将氮前驱体、铁前驱体、镍前驱体与水混合后冷冻,得到前驱体混合物粉末；再将前驱体混合物粉末置入小烧结容器内,然后将小烧结容器倒扣在大烧结容器上,并在大烧结容器上、小烧结容器外侧放置棉布,再于氮气中煅烧,得到三维碳纳米管丛林。本发明为通过一步热解气相法制备高效、可控的三维CNT提供了一条新途径。(The invention belongs to the technical field of electrocatalysis, and particularly discloses a three-dimensional carbon nanotube jungle, and a preparation method and application thereof, wherein the jungle can be used as an Oxygen Reduction Reaction (ORR) and Oxygen Evolution Reaction (OER) electrocatalyst to be applied to a zinc-air battery (ZAB). Mixing a nitrogen precursor, an iron precursor and a nickel precursor with water, and freezing to obtain precursor mixture powder; and putting the precursor mixture powder into a small sintering container, then reversely buckling the small sintering container on the large sintering container, placing cotton cloth on the large sintering container and the outer side of the small sintering container, and calcining in nitrogen to obtain the three-dimensional carbon nanotube jungle. The invention provides a new way for preparing the efficient and controllable three-dimensional CNT by a one-step pyrolysis gas phase method.)
1. The three-dimensional carbon nanotube jungle is characterized in that the preparation method of the three-dimensional carbon nanotube jungle comprises the steps of mixing a nitrogen precursor, an iron precursor and a nickel precursor with water and then freezing to obtain precursor mixture powder; and putting the precursor mixture powder into a small sintering container, then reversely buckling the small sintering container on the large sintering container, placing cotton cloth on the large sintering container and the outer side of the small sintering container, and calcining in nitrogen to obtain the three-dimensional carbon nanotube jungle.
2. The three-dimensional carbon nanotube forest according to claim 1, wherein the nitrogen precursor, the iron precursor, and the nickel precursor are all water-soluble compounds.
3. The three-dimensional carbon nanotube forest according to claim 2, wherein the nitrogen precursor is urea, the iron precursor is ferric nitrate nonahydrate, and the nickel precursor is nickel nitrate hexahydrate.
4. The three-dimensional carbon nanotube forest according to claim 1, wherein the freezing is at-18 ℃ for 12 hours, followed by freeze-drying at-50 ℃ for 24 hours.
5. The three-dimensional carbon nanotube forest according to claim 1, wherein the sintering vessel is a corundum boat.
6. The three-dimensional carbon nanotube forest according to claim 1, wherein the calcination is performed at 800 ℃ for 1 hour, and then the forest is naturally cooled to room temperature.
7. The three-dimensional carbon nanotube forest according to claim 1, wherein the temperature increase rate of the calcination is 10 ℃/min.
8. The method of claim 1, comprising the steps of mixing a nitrogen precursor, an iron precursor, a nickel precursor with water and freezing to obtain a precursor mixture powder; and putting the precursor mixture powder into a small sintering container, then reversely buckling the small sintering container on the large sintering container, placing cotton cloth on the large sintering container and the outer side of the small sintering container, and calcining in nitrogen to obtain the three-dimensional carbon nanotube jungle.
9. Use of the three-dimensional carbon nanotube forest of claim 1 as a battery electrocatalyst.
10. Use of the three-dimensional carbon nanotube forest according to claim 1 for the preparation of a battery.
Technical Field
The invention relates to a novel preparation method of a three-dimensional carbon nanotube jungle and application thereof in the technical field of electrocatalysis, and the jungle can be used as an electrocatalyst of a zinc-air battery.
Background
Zinc-air batteries (ZABs) are considered to be a promising next-generation energy storage power source due to their high theoretical energy density, environmental friendliness, high safety, and low cost. Among them, the Oxygen Reduction Reaction (ORR) involved in the discharge process and the Oxygen Evolution Reaction (OER) in the charging process are two key electrochemical processes of rechargeable ZAB. Since both ORR and OER involve slow multiple electron transfer reaction kinetics, there is an urgent need to develop stable and efficient bifunctional oxygen catalysts and use them in rechargeable ZABs. Although platinum-based materials are currently commercially used as ORR catalysts and iridium/ruthenium-based materials as OER catalysts, these noble metal catalysts exhibit only a single catalytic activity, and their high cost and poor stability greatly limit their application in rechargeable ZABs. Therefore, the search for a reversible bifunctional oxygen electrocatalyst with high efficiency and low cost is urgently needed.
In recent years, a number of studies have reported that transition metal alloy nanoparticles (TMA-NPs) encapsulated in nitrogen-doped carbon nanotubes (N-CNTs) are effective in improving the active sites of electrocatalysts. The strong combination between TMA-NP and N-CNT can effectively improve the electronic structure of carbon skeleton, thereby reducing the adsorption energy barrier of oxygen and its intermediate on the catalyst and being beneficial to the bonding between them. For such composites of N-CNT material embedded with TMA-NPs, a simple direct pyrolysis process like Chemical Vapor Deposition (CVD) has attracted considerable attention involving direct heating of metal salts (e.g. nitrates, chlorides and acetates, etc.) and N/C precursors (e.g. dicyandiamide, melamine, glutamic acid, etc.) in a tube furnace. However, the core/shell structured TMA-NP/N-CNT composite synthesized by this method has some non-negligible problems: direct decomposition of the precursor mixture can lead to agglomeration and non-uniform dispersion of the metal particles, resulting in varying tube diameter sizes of the grown CNTs. Therefore, there is a need to develop a new method for preparing a reversible bifunctional oxygen electrocatalyst suitable for zinc-air batteries.
Disclosure of Invention
The invention discloses a FeNi alloy-inlaid three-dimensional carbon nanotube jungle (FeNi @ NCNT-CP) electrocatalyst which is low in preparation cost, uniform in the diameter and the thickness of a grown CNT and suitable for zinc-air battery electrode catalysis.
The invention adopts the following technical scheme:
the preparation method of the three-dimensional carbon nanotube jungle comprises the steps of mixing a nitrogen precursor, an iron precursor and a nickel precursor with water and then freezing to obtain precursor mixture powder; and putting the precursor mixture powder into a small sintering container, then reversely buckling the small sintering container on the large sintering container, placing cotton cloth on the large sintering container and the outer side of the small sintering container, and calcining in nitrogen to obtain the three-dimensional carbon nanotube jungle.
The creativity of the invention lies in changing the calcination method of the existing metal hybrid carbon nano tube, and exceeding the imagination of obtaining FeNi @ NCNT-CP electrocatalyst, the three-dimensional jungle-shaped network structure which is formed by CNT with small and uniform pipe diameter and is formed by cluster dispersion is uniform, and the relatively strong carbon peak and the relatively weak metal peak are displayed, and the hierarchical three-dimensional porous network structure provides rich three-phase reaction interface and material transmission channel for the electrochemical process, which is beneficial to the adsorption and reaction of oxygen.
In the invention, a nitrogen precursor, an iron precursor and a nickel precursor are all water-soluble compounds, for example, the nitrogen precursor is urea, the iron precursor is ferric nitrate nonahydrate, and the nickel precursor is nickel nitrate hexahydrate; in the obtained three-dimensional carbon nanotube forest, the top end of the CNT wraps catalyst metal particles necessary for growth of the CNT, the CNT is of a core-shell structure, the outer layer of the CNT is 3-4 layers of highly graphitized layered carbon, the interlayer spacing is 0.35 nm and corresponds to a C (002) crystal face, the inner metal part of the CNT shows lattice stripes with good resolution, and the lattice spacing is 0.209 nm and corresponds to a (111) crystal face of the FeNi alloy.
In the invention, the freezing is carried out for 12 hours at the temperature of-18 ℃, and then the freezing and drying are carried out for 24 hours at the temperature of-50 ℃; compared with other methods for obtaining mixed powder, the mixed powder obtained by freeze drying can well keep the uniform dispersion of all components in aqueous solution, and the iron and the nickel are not easy to oxidize, so that the problem that the precursors of the iron and the nickel are strong reducibility and can not be heated and dried is solved.
In the invention, precursor mixture powder is filled in a small sintering container, and then the small sintering container is reversely buckled on a large sintering container, and a gap is formed between the small sintering container and the large sintering container; the small sintering container and the large sintering container can be a small corundum boat and a large corundum boat relatively, and as a common sense, the small sintering container and the large sintering container can be reversely buckled on the bottom surface of the large sintering container. The place where the cotton cloth is placed is not particularly limited, and it may be outside the small sintering container, and may be in contact therewith.
In the invention, the calcination is carried out for 1 h at 800 ℃, and then the mixture is naturally cooled to room temperature, wherein the heating rate is 10 ℃/min. In the obtained three-dimensional carbon nanotube jungle, at the position of 2 theta approximately equal to 26 degrees, the XRD pattern of FeNi @ NCNT-CP shows a weaker carbon diffraction peak corresponding to a C (002) crystal face; the alloy shows stronger metal diffraction peaks at 2 theta, 43.5 degrees, 50.8 degrees and 74.6 degrees, which respectively correspond to the (111), (200) and (220) crystal planes of the FeNi alloy; this confirms the presence of carbon and the formation of FeNi alloys and the higher degree of graphitization of the outer CNTs compared to FeNi @ NCNT, FeNi @ NCNT-CP, while the inner metal is more finely and uniformly encapsulated inside the CNTs.
The invention discloses an application of the three-dimensional carbon nanotube jungle as a battery electrocatalyst in the preparation of batteries; can be used as an Oxygen Reduction Reaction (ORR) and Oxygen Evolution Reaction (OER) electrocatalyst to be applied to the preparation of a zinc-air battery (ZAB). The electrocatalyst of the invention is prepared by a simple one-step pyrolysis method by separating C, N and metal precursor mixture from a substrate for growing Carbon Nano Tubes (CNT) by designing a mode of an inverted big and small corundum boat and controlling a rapid temperature rise rate so as to rapidly decompose the precursor mixture to form air flow to be sprayed on a porous cotton cloth substrate, and the FeNi alloy-inlaid three-dimensional carbon nano tube jungle (FeNi @ NCNT-CP) composite material is prepared and shows excellent ORR and OER electrocatalytic performance. Compared with the CNT prepared by the common direct pyrolysis method, the CNT-based bifunctional oxygen electrocatalyst disclosed by the invention has the advantages that: the preparation method is unique, the material structure is novel, the precursor material and the growth substrate are separated in a short distance, the growth substrate is porous, the diameter of the CNT and the particle size of the embedded metal particles are fine, uniform and uniformly dispersed, the CNT has a large specific surface area and rich micro/nano-pore channels, and the CNT is favorable for exposing more active sites and transmitting substances, so that the ZAB shows a very small overpotential and excellent stability in the ORR and OER processes, and is successfully applied to ZAB as a positive electrode catalyst to show good cycle stability and small potential polarization.
The invention improves the existing pyrolysis method, and separates and places a precursor mixture (urea, ferric nitrate hexahydrate and nickel nitrate hexahydrate) and a growth substrate (cotton cloth) of CNT by an inverted big corundum boat and a small corundum boat, provides a novel preparation method, controllably synthesizes a FeNi alloy-inlaid uniform carbon nanotube jungle (FeNi @ NCNT-CP) composite material with a three-dimensional network structure, shows high-efficiency catalytic performance and excellent stability in ORR and OER, and can be successfully applied to rechargeable ZAB as an anode catalyst. The preparation process is novel and simple, the raw materials are rich in source and low in cost, and the wide application prospect is shown.
Drawings
FIGS. 1a-c are SEM images at different magnifications of FeNi @ NCNT-CP, (d) TEM and HRTEM images;
FIGS. 2a and b are SEM images of FeNi @ NCNT at different magnifications;
FIG. 3 (a) X-ray diffraction patterns of FeNi @ NCNT-CP and FeNi @ NCNT and Fe0.64Ni0.36(ii) PDF card of (b) FeNi @ NCNT-CP and N of FeNi @ NCNT2Adsorption and desorption isotherms, (c) and the corresponding pore size distribution;
FIG. 4(a) ORR electrochemical performances of FeNi @ NCNT-CP, FeNi @ NCNT and commercial Pt/C; (b) FeNi @ NCNT-CP, FeNi @ NCNT and commercial IrO2OER electrochemical performance of (a); ORR (c) and OER (d) electrochemical stability of FeNi @ NCNT-CP;
FIG. 5 is a graph of the discharge polarization curve of ZAB based on FeNi @ NCNT-CP and commercial Pt/C and its power density (a) and rate capability for constant current discharge (b); (c) based on FeNi @ NCNT-CP and commercial Pt/C-IrO2The charge-discharge cycle curve of the chargeable ZAB of (a);
FIG. 6 is a combination view of a reversed big and small corundum boat with cotton cloth according to the present invention;
FIG. 7 is a combination diagram of inverted big and small corundum boats of comparative example, wherein a is a combination state after calcination, and b is a separation state after calcination;
in FIG. 8, a and b are SEM images of different magnifications of the product obtained by mixing and calcining the precursor mixture and cotton cloth, respectively;
in FIG. 9, a and b are FeNi @ NCNT-CP at 2.5 ℃ for min-1SEM images at different magnifications;
in FIG. 10, a and b are ORR and OER electrochemical performances of FeNi @ NCNT-CP at different calcination temperatures, respectively.
Detailed Description
The raw materials involved in the invention are all conventional products sold on the market, and the cotton cloth is pure cotton fabric and provides a source; the specific operation method and the test method adopted by the invention are conventional methods in the field, and if no special description is given, the related experimental operation is carried out under the conventional environment.
Mixing a nitrogen precursor, an iron precursor and a nickel precursor with water, and freezing to obtain precursor mixture powder; and putting the precursor mixture powder into a small sintering container, then reversely buckling the small sintering container on the large sintering container, placing cotton cloth on the large sintering container and the outer side of the small sintering container, and calcining in nitrogen to obtain the three-dimensional carbon nanotube jungle.
The invention does not need other reagents and additional preparation steps, and the obtained product FeNi @ NCNT-CP has excellent ORR and OER performances, and the ZAB based on the product has the cutoff current density of 300 mA cm-2The peak power density of the time is 200 mW cm-2Achieves ZAB (130 mW cm) based on commercial Pt/C-2) 154% of the total amount of the catalyst, and the cycle life of the catalyst is far more than that of the catalyst based on commercial Pt/C + IrO2ZAB of (1).
Electrochemical performance was tested on a three-electrode system rotating disk (glassy carbon disk: area 0.196 cm 2) and an electrochemical workstation from Pine, usa. Wherein the three-electrode system mainly uses a glassy carbon rod as a counter electrode, an Ag/AgCl-saturated KCl electrode as a reference electrode (all voltages are calibrated to be relative to a standard hydrogen electrode), and a glassy carbon electrode in which a catalyst is dripped as a working electrode (the loading amount of the catalyst is 0.4 mg cm)-2). Can be tested by linear scanning on an electrochemical workstationAnd obtaining ORR and OER polarization curves of the material, wherein the test voltage interval of the ORR is 0.1-1.1V, and the test voltage interval of the OER is 1-2V. The stability of the material can be obtained through accelerated aging test, and polarization curves obtained before and after long-time multi-turn linear scanning test are respectively compared.
The liquid zinc-air battery is composed of carbon paper loaded with electrocatalyst as air electrode, metal Zn sheet as negative electrode, and 6.0M KOH containing 0.2M zinc acetate as electrolyte. The electrocatalyst was applied by dropping onto carbon paper with a loading of 1.0 mg cm-2. The two electrode plates are assembled into a liquid-box type battery by three different acrylic plates and screws. The performance of the zinc-air battery is mainly performed on a blue power LAND CT2001A, a constant current discharge curve can be obtained by testing the relation between voltage and time under constant current density, and a charge-discharge cycle curve can be obtained by repeatedly charging and discharging under fixed capacity. The discharge polarization curve of the battery is tested on a ZAHNER electrochemical workstation, the set voltage is gradually reduced, and the change curve of the current along with the voltage is obtained.
Examples
Preparation of precursor mixture: 3 g of urea (CO (NH)2)2) 0.105 g of iron nitrate nonahydrate (Fe (NO)3)3·9H2O), 0.075 g Nickel nitrate hexahydrate (Ni (NO)3)2·6H2O) and 20 mL of ultrapure water are added into a beaker and are stirred and dissolved at room temperature; then transferring the beaker into a refrigerator to be frozen for 12 h at the temperature of 18 ℃ below zero, and then carrying out freeze drying for 24 h at the temperature of 50 ℃ below zero in a freeze dryer to obtain precursor mixture powder containing C, N, Fe and Ni.
Filling the precursor mixture powder into a small corundum boat, and reversely buckling the small corundum boat in the middle of a large corundum boat; then two clean pieces 2 x 5 cm2The cotton sheets are respectively placed at the vacant parts of the large corundum boats at the two ends and are contacted with the outer sides of the small corundum boats.
And at room temperature, transferring the combination of the inverted big corundum boat and the inverted small corundum boat with the cotton cloth to the middle part of a tube furnace, heating to 800 ℃ at the speed of 10 ℃/min in nitrogen atmosphere, calcining for 1 h, and naturally cooling to room temperature to obtain the three-dimensional carbon nanotube jungle FeNi @ NCNT-CP.
Comparative example 1
Preparation of precursor mixture: 3 g of urea (CO (NH)2)2) 0.105 g of iron nitrate nonahydrate (Fe (NO)3)3·9H2O), 0.075 g Nickel nitrate hexahydrate (Ni (NO)3)2·6H2O) and 20 mL of ultrapure water are added into a beaker and are stirred and dissolved at room temperature; then transferring the beaker into a refrigerator to be frozen for 12 h at the temperature of 18 ℃ below zero, and then carrying out freeze drying for 24 h at the temperature of 50 ℃ below zero in a freeze dryer to obtain precursor mixture powder containing C, N, Fe and Ni.
Filling the precursor mixture powder into a small corundum boat, inversely buckling the small corundum boat in the middle of a large corundum boat, transferring the small corundum boat and the large corundum boat together to the middle part of a tubular furnace, heating to 800 ℃ at a speed of 10 ℃/min in a nitrogen atmosphere, calcining for 1 h, and naturally cooling to room temperature to obtain the carbon nano tube FeNi @ NCNT embedded with the FeNi alloy; the amount of precursor mixture powder used and the size of the corundum boat were the same as in the examples, except that no cotton cloth was placed.
Performance analysis
The SEM images of FIGS. 1a and b show that the prepared FeNi @ NCNT-CP electrocatalyst is a three-dimensional, uniformly dispersed, network structure of clusters of CNTs of small and uniform tube diameter. FIG. 1c is a further enlarged SEM image of FeNi @ NCNT-CP where the CNTs are intertwined to form a network structure, and the CNTs are bamboo-like structures with a diameter of about 20 nm and a wall thickness of about 5 nm. It can be seen from the TEM and HRTEM images shown in fig. 1d that the CNT tips encapsulate the catalyst metal particles necessary for its growth, and are a core-shell structure. The outer layer is 3-4 layers of highly graphitized layered carbon, and the interlayer spacing is 0.35 nm and corresponds to a C (002) crystal face. While the inner metal part showed lattice fringes with good resolution, and the lattice spacing of 0.209 nm corresponded to the FeNi (111) crystal plane.
Figures 2a and b show that the CNTs obtained without direct calcination of cotton cloth are in a disordered powder form, the diameter of the CNTs exceeding 50 nm. And the agglomeration of metal particles is very serious and has different sizes, and part of metal particles are even agglomerated into large particles with the diameter exceeding 100 nm. In addition, the precursor powder is directly put into an open big corundum boat or a small corundum boat for direct calcination, and almost no catalyst product is obtained.
FIG. 3a is an X-ray diffraction (XRD) pattern of FeNi @ NCNT-CP and FeNi @ NCNT, both of which show weaker carbon diffraction peaks at 2 theta ≈ 26 DEG, corresponding to the C (002) crystal plane. The diffraction peaks of the metal are stronger at 2 theta ≈ 43.5 degrees, 50.8 degrees and 74.6 degrees, and correspond to the (111), (200) and (220) crystal planes of the FeNi alloy. This confirms the presence of carbon and the formation of the FeNi alloy and is consistent with the results of fig. 1 and 2. Compared with FeNi @ NCNT, the FeNi @ NCNT-CP has the advantages that the outer-layer CNT is more graphitized, and the metal of the inner layer is more finely and uniformly wrapped in the CNT, so that the XRD pattern of the FeNi @ NCNT-CP shows a relatively strong carbon peak and a weak metal peak.
FIGS. 3b and c show N as FeNi @ NCNT-CP and FeNi @ NCNT samples, respectively2Adsorption and desorption curves and pore size distribution. The surface area of the FeNi @ NCNT is only 34 m due to the large metal particles and the existence of uneven carbon clusters2 g-1. In contrast, the FeNi @ NCNT-CP with the three-dimensional network structure shows higher specific surface area (275 m)2 g-1) And simultaneously has obvious micropores and mesopores. The hierarchical three-dimensional porous network structure provides rich three-phase reaction interfaces and substance transmission channels for the electrochemical process, and is favorable for the adsorption and reaction of oxygen.
FIG. 4a shows that FeNi @ NCNT-CP has more excellent ORR electrochemical performance and shows higher ORR half-wave potential (E)1/2= 0.851V), not only much higher than that of FeNi @ NCNT (E)1/2= 0.71V) and can be compared with the ORR performance of commercial Pt/C1/2= 0.851V). In addition, FIG. 4b shows that the OER electrochemical performance of FeNi @ NCNT-CP is also very excellent at 10 mA cm-2The potential at (E) is 1.596V, which is much lower than the OER potential (E) of FeNi @ NCNTj=10= 1.683V) or even beyond the commercial IrO2OER Performance (E)j=10= 1.598V). FIG. 4c shows cycling up to 10000 cyclesThe ORR potential of FeNi @ NCNT-CP then produced only a negligible 4 mV decay. And figure 4d also shows that there is no significant decay in the OER potential of the FeNi @ NCNT-CP after consecutive 20000 cycles. The above results indicate that the FeNi @ NCNT-CP jungle is a bifunctional oxygen electrocatalyst with excellent ORR and OER catalytic performance and stability.
FIG. 5a shows that, due to the excellent ORR performance of FeNi @ NCNT-CP, ZAB based thereon has a cut-off current density of 300 mA cm-2The peak power density of the time is 200 mW cm-2Achieves ZAB (130 mW cm) based on commercial Pt/C-2) 154% of the total. In addition, as shown in fig. 5b, the open circuit voltage was measured as high as 1.551V, and also showed good rate capability. Whether at 10 mA cm-2Is still at a current density of 20 mA cm-2The discharge voltage is not reduced obviously for a long time under the high current density. Based on its excellent ORR activity and stability, FIG. 5C shows that when FeNi @ NCNT-CP is used as a rechargeable ZAB positive electrode catalyst, even with commercial Pt/C-IrO2Compared to the blends of (a), rechargeable ZAB based on FeNi @ NCNT-CP has a smaller charge-discharge potential difference. And at 10 mA cm-2After 250 h of continuous cycling at the current density of (a), only 0.12V of potential was reduced, showing good battery life.
The invention fills the precursor mixture powder into the small corundum boat, and the small corundum boat is reversely buckled in the middle of the large corundum boat, so that a gap is formed; then two clean pieces 2 x 5 cm2The cotton pieces are respectively placed on the vacant parts of the big corundum boat at the two ends and are contacted with the outer side of the small corundum boat, and the figure 6 shows. By contrast, using a similar synthesis method, the precursor mixture was placed in a small corundum boat and inverted in a large corundum boat for calcination, and disordered carbon nanotube (FeNi @ NCNT) electrocatalysts inlaid with FeNi alloy were obtained in the gap portions of the small and large corundum boats, with no catalyst product remaining inside the small corundum boat (see fig. 7).
Comparative example No. two
3 g of urea (CO (NH)2)2) 0.105 g of iron nitrate nonahydrate (Fe (NO)3)3·9H2O), 0.075 g Nickel nitrate hexahydrate (Ni (NO)3)2·6H2O) and 20 mL of ultrapure water are added into a beaker and are stirred and dissolved at room temperature; the cotton cloth in the first embodiment is soaked in the beaker, the solution is completely absorbed, the cotton cloth is frozen for 12 hours at the temperature of 18 ℃ below zero in a refrigerator, then the cotton cloth is frozen and dried for 24 hours at the temperature of 50 ℃ below zero in a freeze dryer, the cotton cloth is placed in a corundum boat and transferred to the middle of a tube furnace, the temperature is increased to 800 ℃ in nitrogen atmosphere at the temperature of 10 ℃/min, the cotton cloth is calcined for 1 hour, then the cotton cloth is naturally cooled to the room temperature, and the calcined product cannot form the shape of a carbon nano tube jungle. As shown in FIG. 8, it can be clearly seen that no significant carbon nanotubes are formed on the cotton fiber, but a lot of large metal particles are embedded therein, which is not suitable for use as a catalyst.
Further, on the basis of the first embodiment, the cotton cloth is replaced by the carbon cloth with the same size, and the rest is unchanged, so that the surface of the carbon cloth is smooth after calcination, and no metal particles or carbon nano tubes are generated.
Example two
Preparation of precursor mixture: 3 g of urea (CO (NH)2)2) 0.105 g of iron nitrate nonahydrate (Fe (NO)3)3·9H2O), 0.075 g Nickel nitrate hexahydrate (Ni (NO)3)2·6H2O) and 20 mL of ultrapure water are added into a beaker and are stirred and dissolved at room temperature; then transferring the beaker into a refrigerator to be frozen for 12 h at the temperature of 18 ℃ below zero, and then carrying out freeze drying for 24 h at the temperature of 50 ℃ below zero in a freeze dryer to obtain precursor mixture powder containing C, N, Fe and Ni.
Filling the precursor mixture powder into a small corundum boat, and reversely buckling the small corundum boat in the middle of a large corundum boat; then two clean pieces 2 x 5 cm2The cotton sheets are respectively placed at the vacant parts of the large corundum boats at the two ends and are contacted with the outer sides of the small corundum boats.
And at room temperature, transferring the combination of the inverted big corundum boat and the inverted small corundum boat with the cotton cloth to the middle part of a tube furnace, heating to 800 ℃ at the speed of 2.5 ℃/min in the nitrogen atmosphere, calcining for 1 h, and naturally cooling to room temperature to obtain the three-dimensional carbon nanotube jungle FeNi @ NCNT-CP.
When the temperature rising rate of the calcination is reduced to 2.5 ℃ for min-1When the temperature is 10 ℃ min, it can be observed by SEM image of the product, compared with FeNi @ NCNT-CP-1The morphology of the product of (1) at 2.5 ℃ for min-1The product obtained at a low temperature rise rate has a significantly poorer morphology. FIG. 9a shows the morphology where a full clump of carbon nanotubes is not formed, and a dense portion of the carbon nanotubes are not formed. And it can be seen from the enlarged SEM image (fig. 9 b) that the carbon nanotubes are relatively distributed more sparsely and the tube diameter is relatively large, which indicates that the temperature-rising rate has a large influence on the material, and the temperature-rising rate defined by the present invention is beneficial to the growth of the carbon nanotube forest.
EXAMPLE III
Preparation of precursor mixture: 3 g of urea (CO (NH)2)2) 0.105 g of iron nitrate nonahydrate (Fe (NO)3)3·9H2O), 0.075 g Nickel nitrate hexahydrate (Ni (NO)3)2·6H2O) and 20 mL of ultrapure water are added into a beaker and are stirred and dissolved at room temperature; then transferring the beaker into a refrigerator to be frozen for 12 h at the temperature of 18 ℃ below zero, and then carrying out freeze drying for 24 h at the temperature of 50 ℃ below zero in a freeze dryer to obtain precursor mixture powder containing C, N, Fe and Ni.
Filling the precursor mixture powder into a small corundum boat, and reversely buckling the small corundum boat in the middle of a large corundum boat; then two clean pieces 2 x 5 cm2The cotton sheets are respectively placed at the vacant parts of the large corundum boats at the two ends and are contacted with the outer sides of the small corundum boats.
Transferring the combination of the inverted large and small corundum boats with cotton cloth to the middle part of a tubular furnace at room temperature, heating to the design temperature at 10 ℃/min in a nitrogen atmosphere, calcining for 1 h, and naturally cooling to room temperature to obtain a three-dimensional carbon nanotube jungle FeNi @ NCNT-CP; wherein the design temperature is 600 deg.C, 700 deg.C, 900 deg.C, 1000 deg.C respectively.
As shown in FIG. 10, when the calcination temperatures were controlled to 600 deg.C, 700 deg.C, 800 deg.C, 900 deg.C, and 1000 deg.C, respectively, a relatively large change in both ORR and OER properties of the material was observed. When the temperature of calcination is from 600 ℃ to 800 ℃, the appearance is goodThe half-wave potential of the ORR polarization curve of FeNi @ NCNT-CP was observed to be gradually shifted in the positive direction, and the OER polarization curve was observed to be 10 mA cm-2The potential at the current density is gradually shifted negative. While the change in the ORR and OER polarization curves show the opposite trend as the calcination temperature is increased from 800 ℃ to 1000 ℃. This indicates that the calcination temperature has a large impact on the material's performance, and that FeNi @ NCNT-CP has the best ORR and OER electrochemical performance at the calcination temperature of 800 ℃.
In conclusion, the invention reports a low-cost and simple method for synthesizing CNT, which adopts porous cotton cloth as a growth substrate and forms a self-injection gas phase method through a special corundum boat combination, so that a FeNi alloy-embedded three-dimensional carbon nanotube bush (FeNi @ NCNT-CP) electrocatalyst is synthesized in a large scale, and the electrocatalyst has potential commercial value in oxygen reduction and precipitation reactions and chargeable ZAB. Further provides a simple and novel method for preparing the CNT-based electrocatalyst with low price, uniform appearance and high efficiency, and simultaneously proves the wide application prospect of the CNT-based electrocatalyst in an energy storage and conversion system.
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