Iron oxyhydroxide-copper-clad carbon nanotube coaxial core-shell material and preparation method and application thereof
Technical Field
The invention belongs to the field of preparation of electrochemical energy storage electrode materials, and particularly relates to a ferric hydroxide-copper-coated carbon nanotube coaxial core-shell material as well as a preparation method and application thereof.
Background
With the advent of numerous flexible electronic devices, the design and manufacture of flexible power supplies has become possible. At present, the society has urgent needs for a flexible energy storage system which is efficient, cheap and environment-friendly. As an application technology that has grown up rapidly and is becoming popular, supercapacitors can accomplish charging and discharging at an ultra-fast speed and with extremely high efficiency. The super capacitor overcomes the defect that the traditional physical capacitor and the secondary battery cannot be compatible in power density and energy density. Supercapacitors are now widely used by thousands of different applications, while still being considered for a number of future applications. Supercapacitors are capable of providing rapid pulses of power that cannot be provided by a primary power source, such as an internal combustion engine, fuel cell or ordinary battery, and of rapidly storing excess electrical energy that may be lost for energy recovery, and are therefore promising and have been considered as an important energy source option. One of the great challenges faced by the flexible supercapacitor is how to increase the energy density and reduce the cost of the electrode material while ensuring the flexible characteristics of the electrode material.
Electrode materials of supercapacitors are generally divided into three categories, carbon materials, metal oxides and conductive polymers. Among various metal oxide electrode materials, iron-based oxides have high theoretical capacity values, convenient synthesis methods, low cost and environmental friendliness; the iron oxide material has a wide working window under negative potential, so that the iron oxide material can be used as a novel negative electrode material; the special tunnel structure of the iron oxide material is favorable for the rapid transmission of ions, and is considered as a promising low-cost electrode material, but the poor electronic conductivity of the iron oxide material becomes a main problem limiting the application of the iron oxide material.
Carbon nanotube materials are receiving attention due to their high specific surface area, excellent electrical conductivity, and environmental friendliness. However, its relatively low specific capacitance as an electrode material is not satisfactory. At present, the compounding of carbon nanotubes and iron oxide is also studied, however, carbon nanotubes are often used as conductive fillers in the compounding process, and the three-dimensional oriented structure of the carbon nanotubes is not well utilized. Therefore, a new electrode material preparation method is explored, nano iron oxide with higher energy density and low cost is hybridized with the three-dimensional vertically-arranged carbon nano tubes, and the performance is expected to be improved in a crossing mode.
Disclosure of Invention
Aiming at the problems existing at present, the invention provides a FeOOH-copper-coated carbon nanotube coaxial core-shell material, a preparation method and application thereof.
The technical scheme of the invention is as follows:
a kind of hydroxy oxidize iron-copper to cover the carbon nanotube coaxial nuclear shell material, including carbon material fibrous basement, carbon nanotube sponge, nanometer copper film, villiform hydroxy oxidize iron film; the carbon nanotube sponge grows on the surface of the carbon fiber substrate and is mutually connected to form an integrated structure; the nano copper film is uniformly coated on the surface of the carbon nano tube sponge; the villous iron oxyhydroxide film is coated on the surface of the nano-copper film.
The iron oxyhydroxide-copper-coated carbon nanotube coaxial core-shell material provided by the invention has the coaxial heterogeneous shell-core structural characteristic and also has the bendable integrated characteristic.
Preferably, the diameter of a single carbon nanotube of the carbon nanotube sponge is 20-50 nm; the length of the carbon fiber substrate is 1-5 mu m, and the carbon fiber substrate grows on the surface of the carbon fiber substrate like a spring. The length and diameter ranges can keep the structural characteristics of three-dimensional porous interconnection of the carbon nanotube sponge, and the specific surface area and the conductivity of the whole material are improved. On the contrary, too sparse cannot exert its effect to the maximum, and too dense is not favorable for the formation of the following special structure of the cladding material.
Preferably, the carbon material fiber substrate may be one of carbon cloth fiber, carbon felt fiber, graphene fiber, carbon nanotube fiber, or activated carbon fiber.
Preferably, the thickness of the nano copper film is 50-200 nm, and the nano copper film is uniformly coated on the surface of the carbon nanotube sponge to form a shell-core nano structure. The copper film is uniformly coated on the surface of the carbon nano tube by the thickness, so that the overall conductivity of the material is improved and the carbon fiber substrate is protected; conversely, an increase in thickness reduces the specific surface area and porosity of the material, affecting the electrochemical performance of the material.
Preferably, the thickness of the villous iron oxyhydroxide film is 30-100 nm, and the villous iron oxyhydroxide film is uniformly coated on the surface of the nano copper film to form a shell-core nano structure. The thickness range can keep the villous structure of the iron oxyhydroxide nano, is beneficial to the rapid embedding/separating of electrolyte ions and exerts the electrochemical performance to the maximum extent; on the contrary, the increase of the thickness can cause the agglomeration and caking of the iron oxyhydroxide, damage the appearance of the iron oxyhydroxide and influence the conductivity and the electricity storage performance of the material; too small a thickness does not sufficiently exert its electrochemical performance, resulting in a low electric storage capacity.
The invention provides a FeOOH-copper-coated carbon nanotube coaxial core-shell material which has a shell-core nanostructure and is used as an electrode material in a flexible super capacitor for electrochemical energy storage.
In the charge-discharge process, the electrolyte ion is constantly inserted and is taken off and inlay, can lead to the graphite microcrystal structure of carbon fiber to receive the destruction of certain degree, thereby lead to carbon fiber mechanical properties to reduce, when they are used for ultrafast charge-discharge to use, because the not enough and interface interference of combined material's conductivity, can produce the problem that the performance descends, therefore adopt metal coating to carry out certain protection to the carbon fiber, both can solve carbonaceous fiber material's structural stability problem, improve electrode material's conductivity simultaneously, be expected to promote its electrochemistry multiplying power performance.
The inventor finds that if the copper film is not coated, the embedding/releasing of electrolyte ions can damage the graphite microcrystalline structure of the carbon fiber substrate, so that the mechanical property of the carbon fiber is reduced, and the service life of the material is influenced; if the positions of the copper film and the iron oxyhydroxide film outside the carbon nano tube layer are reversed, a three-dimensional porous structure morphology cannot be formed, and the electrochemical performance of the material cannot be fully exerted. The structure of the invention is needed to realize all the performances, firstly, the basic conductivity and flexibility of the electrode are ensured by the carbon fiber substrate, the extremely high reaction specific surface area and conductivity are ensured by the carbon nanotube sponge, the mechanical performance of the carbon fiber substrate is not damaged by the nano copper film, the conductivity is further improved, and the villous iron oxyhydroxide ensures to provide the optimized electrochemical capacity.
Specifically, the material provided by the invention is characterized in that the surface of the carbon nanotube sponge is uniformly coated with the nano copper film, and the three-dimensional porous "-shell-core" nanostructure can reduce the damage of the embedding/separating of electrolyte ions to the graphite microcrystal structure of the carbon fiber substrate, improve the stability, enhance the conductivity of the carbon nanotube sponge, and improve the rate capability of the electrode material, especially the charge-discharge performance under high current density; the villous iron oxyhydroxide film is coated on the surface of the nano copper film, and the villous shell-core nano structure can efficiently utilize the high theoretical capacity of the iron oxyhydroxide and enhance the electrochemical stability of the iron oxyhydroxide. Therefore, the hybrid material has the characteristics of high specific capacity, high multiplying power and high stability, can be directly applied to electrodes of flexible super capacitors, and has wide application value in the fields of related electrochemistry, such as secondary batteries. Through electrochemical performance tests, the mass specific capacitance of the material can reach 600F/g, and the specific capacity is still maintained above 95% after 2000 cycles of cycle stability tests; in addition, based on the flexibility of the carbon fiber substrate, the material provided by the invention can be bent, and when the bending angle reaches 120 degrees and electrochemical tests after 500 times of repeated bending show that the capacity is hardly attenuated.
The iron oxyhydroxide-copper-coated carbon nanotube coaxial core-shell material provided by the invention has the coaxial heterogeneous shell-core structural characteristic and the bendable integrated characteristic, can be directly applied to an electrode material of a flexible super capacitor, and has wide practical application value and industrial production prospect.
A preparation method of a hydroxyl ferric oxide-copper-coated carbon nano tube coaxial core-shell material comprises the following steps:
(1) preparing carbon nanotube sponge by an acid treatment and vacuum-assisted vapor deposition reaction method: soaking the carbon fiber substrate in concentrated nitric acid, cleaning and drying; putting the carbon fiber material into a solution containing iron, copper or nickel ions to physically adsorb catalyst seed liquid on the surface of the fiber, drying the fiber, putting the fiber into a vapor deposition furnace, vacuumizing the vapor deposition furnace, introducing inert gas, hydrogen and carbon source gas, and carrying out vacuum vapor deposition reaction at high temperature to obtain a carbon material fiber material coated with carbon nanotube sponge;
(2) preparing a copper-coated carbon nanotube core-shell material by a vacuum evaporation method: applying a carbon material fiber material coated by carbon nanotube sponge on a working disc of a vacuum chamber, putting a high-purity copper film material, vacuumizing, setting corresponding parameters according to the film coating thickness, starting an electron beam to heat the melt material, performing heat preservation film coating, closing an evaporation power supply, discharging gas, stopping the furnace, and obtaining a copper-coated carbon nanotube core-shell material;
(3) preparing a hydroxyl ferric oxide-copper-coated carbon nanotube coaxial core-shell material by a nitrogen protection three-electrode constant current electrochemical deposition reaction method: in a three-electrode electrochemical reaction system, a copper-coated carbon nanotube core-shell material is used as a working electrode, a platinum electrode is used as a counter electrode, a saturated calomel electrode is used as a reference electrode, an aqueous solution of sodium acetate and ammonium ferrous sulfate is used as an electrolyte, and an electrochemical deposition reaction is carried out by adopting a constant current method under the protection of nitrogen atmosphere, so that the iron oxyhydroxide-copper-coated carbon nanotube coaxial core-shell material is obtained.
Preferably, in the step (1), the carbonaceous fiber substrate is soaked in concentrated nitric acid at the temperature of 80-100 ℃ for 0.5-1 h for treatment; the catalyst seed solution is one of copper nitrate, ferric nitrate and nickel nitrate with the concentration of 0.02-0.1 mol/L, wherein the solvent is ethanol or propanol or acetone; the growth process is firstly vacuumized to 1-3 multiplied by 10 in a tube furnace-2MPa, and the vacuum degree in the growth process is kept less than 3 multiplied by 10-2Introducing inert gas to raise the temperature under MPa, wherein the temperature raising rate is 5 ℃/min, the volume concentration is more than 99.9%, the flow rate is 1000-2000 mL/min, when the temperature is raised to 400-600 ℃, introducing hydrogen reduction catalyst seed liquid, the volume concentration is more than 99.9%, the hydrogen flow rate is 50-500 mL/min, and keeping the temperature for 20-30 min; continuously heating the mixture to 600-70 ℃ at a heating rate of 2 ℃/minIntroducing carbon source gas at the temperature of 0 ℃, wherein the volume concentration is more than 99.9%, the carbon source flow is 50-750 mL/min, and growing the carbon nanotube sponge layer at the temperature of 600-700 ℃; the carbon source gas can be one of methane, acetylene and ethylene, the flow ratio of hydrogen to the carbon source gas is 1: 1-1.5, and the growth time is 10-60 min.
Soaking the carbon fiber substrate in concentrated nitric acid, cleaning and drying; putting the carbon fiber material into a solution containing iron, copper or nickel ions to physically adsorb catalyst seed liquid on the surface of the fiber, drying the fiber, putting the fiber into a vapor deposition furnace, vacuumizing the vapor deposition furnace, introducing inert gas, hydrogen and carbon source gas, and carrying out vacuum vapor deposition reaction at high temperature to obtain a carbon material fiber material coated with carbon nanotube sponge; wherein, the growth process is firstly vacuumized to 1-3 multiplied by 10 in a tube furnace-2MPa, and the vacuum degree in the growth process is kept at 2-3 multiplied by 10-2The MPa is determined by repeated tests of the inventor, the parameter can improve the success rate of preparation, reduce the temperature required by the reaction and reduce the energy consumption.
Preferably, in the step (2), the high-purity copper film material with the purity of more than 99.99 percent is placed into a tungsten crucible, a mechanical pump is started, and the vacuum degree of a vacuum chamber is controlled to be 4-5 multiplied by 10-3And Pa, turning on a heating power supply, controlling the temperature of the vacuum chamber to be 20-150 ℃, preserving the heat for 10-15 minutes, starting electron beam heating, heating to 1200-1300 ℃, controlling the evaporation current to be 0.5-1.5A, controlling the evaporation rate to be 1-5A/S, and controlling the evaporation time to be 100-2000S.
Applying a carbon material fiber material coated by carbon nanotube sponge on a working disc of a vacuum chamber, putting a high-purity copper film material, vacuumizing, setting corresponding parameters according to the film coating thickness, starting an electron beam to heat the melt material, performing heat preservation film coating, closing an evaporation power supply, discharging gas, stopping the furnace, and obtaining a copper-coated carbon nanotube core-shell material; wherein, the evaporation rate is controlled to be 0.5-5A/s, and the parameters mainly control the thickness of the copper film.
Preferably, in the step (3), the preparation conditions of the three-electrode constant current electrochemical deposition reaction method are as follows: setting the initial polarity of the core-shell material of the copper-coated carbon nanotube as an anode, and setting the current density of the anode to be 0.2-1.0 mA/cm2Upper limit potential of 0.9 ℃1.0V, the anode reaction time is 3000-8000 s, the copper-coated carbon nanotube core-shell material is used as a working electrode, an aqueous solution of sodium acetate and ammonium ferrous sulfate is used as an electrolyte, a platinum electrode is used as a counter electrode, a saturated calomel electrode is used as a reference electrode, and electrochemical reaction is carried out under the protection of inert gas; wherein the concentration of sodium acetate is 0.01-0.05 mol/L, and the concentration of ammonium ferrous sulfate is 0.005-0.02 mol/L; the water is de-oxygenated deionized water.
In a three-electrode electrochemical reaction system, a copper-coated carbon nanotube core-shell material is used as a working electrode, a platinum electrode is used as a counter electrode, a saturated calomel electrode is used as a reference electrode, an aqueous solution of sodium acetate and ammonium ferrous sulfate is used as an electrolyte, and an electrochemical deposition reaction is carried out by adopting a constant current method under the protection of nitrogen atmosphere, so that the iron oxyhydroxide-copper-coated carbon nanotube coaxial core-shell material is obtained. Wherein, the electrochemical reaction is carried out under the protection of inert gas, the success rate of preparation can be improved, otherwise, the existence of oxygen can cause failure; the water is de-ionized water after de-oxygenation treatment, so that the success rate of preparation can be improved, and on the contrary, the existence of oxygen can cause failure.
The coaxial core-shell material provided by the invention adopts an acid treatment and vacuum-assisted vapor deposition reaction method to prepare the carbon nanotube sponge, adopts a vacuum evaporation method to prepare the copper-coated carbon nanotube core-shell material, and finally adopts a nitrogen-protected three-electrode constant-current electrochemical deposition reaction method to prepare the iron oxyhydroxide-copper-coated carbon nanotube coaxial core-shell material.
Drawings
FIG. 1 is a process flow diagram of the present invention;
in fig. 2, a is a scanning electron microscope image of the carbon fiber material coated with the carbon nanotube sponge prepared in example 2 of the present invention; b is a scanning electron micrograph of the carbon nanotube sponge prepared in example 2 of the present invention; c is a scanning electron microscope image of the core-shell material of the copper-coated carbon nanotube prepared in example 2 of the present invention; d is a scanning electron microscope image of the iron oxyhydroxide-copper-coated carbon nanotube coaxial core-shell material;
fig. 3 is an X-ray diffraction pattern of the carbon nanotube sponge, the copper-coated carbon nanotube core-shell material, and the iron oxyhydroxide-copper-coated carbon nanotube coaxial core-shell material prepared in example 2 of the present invention;
fig. 4 is a raman spectrum of the carbon nanotube sponge, the copper-coated carbon nanotube core-shell material, and the iron oxyhydroxide-copper-coated carbon nanotube coaxial core-shell material prepared in example 2 of the present invention;
in fig. 5, a is a scanning electron microscope image of a core-shell material of a copper-coated carbon nanotube prepared in example 3 of the present invention; b and c are scanning electron micrographs of the iron oxyhydroxide-copper-coated carbon nanotube coaxial core-shell material prepared in example 4 of the invention; 5d is a curved photograph of the iron oxyhydroxide-copper-coated carbon nanotube coaxial core-shell material integrated electrode prepared in example 5 of the present invention;
FIG. 6 is a cyclic voltammetry test chart of iron oxyhydroxide-copper coated carbon nanotube coaxial core-shell material prepared in example 2 of the present invention at different sweep rates;
FIG. 7 is a charge and discharge test chart of the iron oxyhydroxide-copper-coated carbon nanotube coaxial core-shell material prepared in example 2 of the present invention at different current densities;
FIG. 8 is a graph of the capacity of a coaxial core-shell material of iron oxyhydroxide-copper-coated carbon nanotubes prepared in example 2 of the present invention as a function of current density;
FIG. 9 is a graph showing the charge-discharge capacity retention ratio of the iron oxyhydroxide-copper-coated carbon nanotube coaxial core-shell material prepared in example 2 according to the present invention;
FIG. 10 is a cyclic voltammetry test chart of iron oxyhydroxide-copper coated carbon nanotube coaxial core-shell material prepared in example 2 of the present invention under normal and bending conditions;
in the figure, 1 is a carbon fiber substrate, 2 is a carbon nanotube sponge, 3 is a nano copper film, and 4 is a fluffy iron oxyhydroxide film.
Detailed Description
The present invention will be described in further detail with reference to the following examples, but it should not be construed that the scope of the above subject matter is limited to the following examples. All the technologies realized based on the above contents of the present invention belong to the scope of the present invention, and the following embodiments are all completed by adopting the conventional prior art except for the specific description.
The gas concentrations in the following examples are all greater than 99.9% by volume.
Example 1
As shown in fig. 1, a schematic diagram of a preparation process of the iron oxyhydroxide-copper-coated carbon nanotube coaxial core-shell material of the present invention is shown. Firstly, preparing carbon nanotube sponge on the surface of a carbon fiber substrate 1 based on an acid treatment and vacuum-assisted vapor deposition reaction process A: soaking the carbon fiber substrate 1 in concentrated nitric acid, cleaning and drying; putting the carbon fiber material into a solution containing iron, copper or nickel ions to physically adsorb catalyst seed liquid on the surface of the fiber, drying the fiber, putting the fiber into a vapor deposition furnace, vacuumizing the vapor deposition furnace, introducing inert gas, hydrogen and carbon source gas, and carrying out vapor deposition reaction at high temperature to obtain a carbon material fiber material 2 coated with carbon nanotube sponge; secondly, coating a nano copper film 3 on the surface 2 of the carbon nanotube sponge based on a vacuum evaporation reaction process B: the carbon material fiber with the carbon nanotube sponge 2 growing on the surface is pasted on a working disc of a vacuum chamber, a high-purity copper film material is put in the working disc, the working disc is vacuumized, corresponding parameters are set according to the thickness of a film, an electron beam is started to heat a melt material, the film is coated in a heat preservation way, an evaporation power supply is closed, the carbon material fiber is deflated, and the carbon material fiber is taken out of the furnace after being shut down, so that the copper-clad carbon nanotube core-shell material; and finally, coating a villiform iron oxyhydroxide film 4 on the surface of the copper-coated carbon nanotube core-shell material based on a nitrogen protection three-electrode constant current electrochemical deposition reaction process C, in a three-electrode electrochemical reaction system, taking the copper-coated carbon nanotube core-shell material as a working electrode, a platinum electrode as a counter electrode, a saturated calomel electrode as a reference electrode, an aqueous solution of sodium acetate and ammonium ferrous sulfate as an electrolyte, and water as de-oxidized deionized water, and performing electrochemical deposition reaction by adopting a constant current method under the protection of nitrogen atmosphere to obtain the iron oxyhydroxide-copper-coated carbon nanotube coaxial core-shell material.
Example 2
The preparation method of the iron oxyhydroxide-copper-clad carbon nanotube coaxial core-shell material comprises the following specific steps:
(1) preparing carbon nanotube sponge by an acid treatment and vacuum-assisted vapor deposition reaction method: soaking the carbon cloth fiber substrate in concentrated nitric acid at 90 ℃ for 1.0h, and soaking the carbon cloth fiber substrate in the concentrated nitric acid; cleaning with acetone, ethanol and deionized water in sequence; putting the dried carbon fiber cloth into an acetone solution containing 0.1mol/L ferric nitrate, fully soaking under stirring, taking out and drying, putting into a tubular furnace, vacuumizing to 1 multiplied by 10-2MPa, and the vacuum degree in the growth process is kept less than 3 multiplied by 10-2Introducing argon gas to raise the temperature under MPa, wherein the temperature raising rate is 5 ℃/min, the argon gas flow is 1000mL/min, raising the temperature to 400 ℃, introducing a reducing gas hydrogen reduction catalyst, the hydrogen flow is 50mL/min, keeping the temperature for 20min, continuing to raise the temperature to 600 ℃, the temperature raising rate is 2 ℃/min, then introducing methane gas, the methane flow is 50mL/min, keeping the temperature at 600 ℃ for 60min, and growing a carbon nanotube sponge layer to obtain a scanning electron microscope image of the prepared carbon nanotube sponge, which is shown in figures 2a and 2 b; the length of the carbon nano tube is 1-5 mu m, the diameter of a single carbon nano tube is 20-50 nm, different carbon nano tubes are separated at intervals, grow on the surface of the carbon fiber substrate like a spring and are in a sponge shape as a whole, and the prepared carbon nano tube sponge shows an X-ray diffraction pattern, as shown in figure 3, and shows good graphite-like crystal characteristic diffraction peaks at 2 theta (26 degrees) and 43 degrees; the obtained carbon nanotube sponge has Raman spectrum (shown in FIG. 4) of 1338cm-1And 1589cm-1Shows good characteristic peak of graphite-like crystal.
(2) Preparing a copper-coated carbon nanotube core-shell material by a vacuum evaporation method: applying carbon fiber material coated with carbon nanotube sponge on the working disc of a vacuum chamber, placing copper particles with purity of more than 99.99% in a tungsten crucible, starting a mechanical pump, and controlling the vacuum degree of the vacuum chamber at 5 × 10-3Pa, turning on a heating power supply, controlling the temperature of the vacuum chamber at 150 ℃, and keeping the temperature for 15 min. Starting electron beam heating, heating to 1300 deg.C, controlling the evaporation current at 1.5A, controlling the evaporation rate at 5A/s, and controlling the evaporation time at 400 s. And obtaining the core-shell material of the copper-coated carbon nanotube. The scanning electron microscope picture of the prepared copper-coated carbon nanotube core-shell material is shown in figure 2c, and the thickness of the nano copper film is about200 nm. The X-ray diffraction pattern of the prepared copper-coated carbon nanotube core-shell material is shown in fig. 3, and the prepared carbon nanotube sponge shows good characteristic diffraction peaks of metal copper at 2 theta (50 degrees) and 74 degrees. The Raman spectrum of the prepared copper-coated carbon nanotube core-shell material is shown in FIG. 4, and the prepared copper-coated carbon nanotube core-shell material is 284cm-1And 623cm-1The low wave number band shows very good characteristic peaks of metallic copper.
(3) Preparing a hydroxyl ferric oxide-copper-coated carbon nanotube coaxial core-shell material by a nitrogen protection three-electrode constant current electrochemical deposition reaction method: in a three-electrode electrochemical reaction system, a copper-coated carbon nanotube core-shell material is taken as a working electrode, an aqueous solution of sodium acetate and ammonium ferrous sulfate is taken as an electrolyte, and water is deionized water subjected to deoxidation treatment. And (3) carrying out electrochemical reaction under the protection of argon by taking a platinum electrode as a counter electrode and a saturated calomel electrode as a reference electrode. Setting the initial polarity of the core-shell material of the copper-coated carbon nanotube as the anode and the current density of the anode as 1.0mA/cm2The upper limit potential is 1.0V, the anode reaction time is 8000s, wherein the concentration of sodium acetate is 0.05mol/L, and the concentration of ammonium ferrous sulfate is 0.02 mol/L. And obtaining the iron oxyhydroxide-copper-coated carbon nanotube coaxial core-shell material. The scanning electron microscope picture of the prepared iron oxyhydroxide-copper-coated carbon nanotube coaxial core-shell material is shown in figure 2d, the thickness of the villiform iron oxyhydroxide film is 100nm, and the iron oxyhydroxide film is uniformly coated on the surface of the copper-coated carbon nanotube to form a shell-core structure. The X-ray diffraction pattern of the prepared iron oxyhydroxide-copper-coated carbon nanotube coaxial core-shell material is shown in fig. 3, and the prepared iron oxyhydroxide-copper-coated carbon nanotube coaxial core-shell material shows characteristic diffraction peaks of iron oxyhydroxide at 2 theta (37 degrees) and 64 degrees. The Raman spectrum of the obtained iron oxyhydroxide-copper-coated carbon nanotube coaxial core-shell material is shown in FIG. 4, wherein 213cm is-1,275cm-1,394cm-1And 587cm-1The characteristic peak of the iron oxyhydroxide is shown.
Example 3
The preparation method of the iron oxyhydroxide-copper-clad carbon nanotube coaxial core-shell material comprises the following specific steps:
(1) acid treatmentAnd preparing the carbon nano tube sponge by a vacuum-assisted vapor deposition reaction method: soaking the carbon felt fiber substrate in concentrated nitric acid at 100 ℃ for 0.5h, and soaking the carbon felt fiber substrate in the concentrated nitric acid; and then sequentially cleaning the substrate by using acetone, ethanol and deionized water. Putting the dried carbon fiber cloth into an acetone solution containing 0.02mol/L nickel nitrate, taking out, drying, putting into a tube furnace, vacuumizing to 3 multiplied by 10-2MPa, and the vacuum degree in the growth process is kept less than 3 multiplied by 10-2And (2) introducing argon to heat up under the MPa, wherein the heating rate is 5 ℃/min, the argon flow is 2000mL/min, heating up to 600 ℃, introducing a reducing gas hydrogen reduction catalyst, the hydrogen flow is 500mL/min, keeping the temperature for 30min, continuing heating up to 700 ℃, the heating rate is 2 ℃/min, then introducing acetylene gas, the acetylene flow is 750mL/min, keeping the temperature for 10min at 700 ℃, thus preparing the carbon nanotube sponge on the surface of the carbon fiber substrate, the prepared carbon nanotube has the length of 1-4 mu m, the diameter of a single carbon nanotube is 20-40 nm, different carbon nanotubes are separated at intervals, grow on the surface of the carbon fiber substrate like a spring, and the whole carbon nanotube sponge is in a sponge shape.
(2) Preparing a copper-coated carbon nanotube core-shell material by a vacuum evaporation method: applying carbon fiber material coated with carbon nanotube sponge on the working disc of a vacuum chamber, placing copper particles with purity of more than 99.99% in a tungsten crucible, starting a mechanical pump, and controlling the vacuum degree of the vacuum chamber at 4 × 10-3Pa, turning on a heating power supply, controlling the temperature of the vacuum chamber at 20 ℃, and preserving the heat for 10 min. Starting electron beam heating, heating to 1200 ℃, controlling the evaporation current to be 0.5A, controlling the evaporation rate to be 1A/s, and controlling the evaporation time to be 500 s. And obtaining the core-shell material of the copper-coated carbon nanotube. The scanning electron microscope image of the prepared copper-coated carbon nanotube core-shell material is shown in fig. 5a, and the thickness of the nano copper film is about 50nm and is uniformly coated on the surface of the carbon nanotube sponge.
(3) Preparing a hydroxyl ferric oxide-copper-coated carbon nanotube coaxial core-shell material by a nitrogen protection three-electrode constant current electrochemical deposition reaction method: in a three-electrode electrochemical reaction system, a copper-coated carbon nanotube core-shell material is taken as a working electrode, an aqueous solution of sodium acetate and ammonium ferrous sulfate is taken as an electrolyte, and water is deionized water subjected to deoxidation treatment. And (3) carrying out electrochemical reaction under the protection of nitrogen by taking a platinum electrode as a counter electrode and a saturated calomel electrode as a reference electrode. Setting the initial polarity of the core-shell material of the copper-coated carbon nanotube as the anode and the current density of the anode as 0.5mA/cm2The upper limit potential is 0.9V, the anode reaction time is 6000s, wherein the concentration of sodium acetate is 0.02mol/L, and the concentration of ammonium ferrous sulfate is 0.01 mol/L. The iron oxyhydroxide-copper-coated carbon nanotube coaxial core-shell material is obtained, the thickness of the prepared villiform iron oxyhydroxide film is 50nm, and the iron oxyhydroxide film is uniformly coated on the surface of the copper-coated carbon nanotube to form a shell-core structure.
Example 4
The preparation method of the iron oxyhydroxide-copper-clad carbon nanotube coaxial core-shell material comprises the following specific steps:
(1) preparing carbon nanotube sponge by an acid treatment and vacuum-assisted vapor deposition reaction method: soaking the carbon fiber substrate in concentrated nitric acid at 95 ℃ for 0.5h, and soaking the carbon fiber substrate in the concentrated nitric acid; and then sequentially cleaning the substrate by using acetone, ethanol and deionized water. Putting the dried carbon fiber cloth into an acetone solution containing 0.08mol/L copper nitrate, taking out and drying the carbon fiber cloth, putting the carbon fiber cloth into a tube furnace, and vacuumizing the tube furnace to 2 multiplied by 10-2MPa, and the vacuum degree in the growth process is kept less than 3 multiplied by 10-2And (2) introducing nitrogen to heat up under the MPa, wherein the heating rate is 5 ℃/min, the nitrogen flow is 1500mL/min, heating up to 500 ℃, introducing a reducing gas hydrogen reduction catalyst, the hydrogen flow is 200mL/min, keeping the temperature for 30min, continuing heating up to 700 ℃, the heating rate is 2 ℃/min, then introducing ethylene gas, the ethylene flow is 200mL/min, keeping the temperature for 30min at 700 ℃, and thus preparing carbon nanotube sponge on the surface of the carbon fiber substrate, wherein the prepared carbon nanotube has the length of 2-5 mu m, the diameter of a single carbon nanotube is 30-50 nm, different carbon nanotubes are separated at intervals and grow on the surface of the carbon fiber substrate like a spring, and the whole carbon nanotube sponge is in a sponge shape.
(2) Preparing a copper-coated carbon nanotube core-shell material by a vacuum evaporation method: applying carbon fiber material coated with carbon nanotube sponge on the working disc of a vacuum chamber, placing copper particles with purity of more than 99.99% in a tungsten crucible, starting a mechanical pump, and controlling the vacuum degree of the vacuum chamber to 510-3Pa, turning on a heating power supply, controlling the temperature of the vacuum chamber at 60 ℃, and keeping the temperature for 15 minutes. Starting electron beam heating, heating to 1300 ℃, controlling the evaporation current to be 1.0A, controlling the evaporation rate to be 3A/s, and controlling the evaporation time to be 335 s. The core-shell material of the copper-coated carbon nano tube is obtained, and the prepared nano copper film has the thickness of about 100nm and is uniformly coated on the surface of the carbon nano tube sponge.
(3) Preparing a hydroxyl ferric oxide-copper-coated carbon nanotube coaxial core-shell material by a nitrogen protection three-electrode constant current electrochemical deposition reaction method: in a three-electrode electrochemical reaction system, a copper-coated carbon nanotube core-shell material is taken as a working electrode, an aqueous solution of sodium acetate and ammonium ferrous sulfate is taken as an electrolyte, and water is deionized water subjected to deoxidation treatment. And (3) carrying out electrochemical reaction under the protection of nitrogen by taking a platinum electrode as a counter electrode and a saturated calomel electrode as a reference electrode. Setting the initial polarity of the core-shell material of the copper-coated carbon nanotube as the anode and the current density of the anode as 0.2mA/cm2The upper limit potential is 0.9V, the anode reaction time is 3000s, wherein the concentration of sodium acetate is 0.01mol/L, and the concentration of ammonium ferrous sulfate is 0.005 mol/L. And obtaining the iron oxyhydroxide-copper-coated carbon nanotube coaxial core-shell material. The scanning electron microscope pictures of the prepared iron oxyhydroxide-copper-coated carbon nanotube coaxial core-shell material are shown in fig. 5b and 5c, the thickness of the villous iron oxyhydroxide film is 30nm, and the iron oxyhydroxide film is uniformly coated on the surface of the copper-coated carbon nanotube to form a shell-core structure.
Example 5
The preparation method of the iron oxyhydroxide-copper-clad carbon nanotube coaxial core-shell material comprises the following specific steps:
(1) preparing carbon nanotube sponge by an acid treatment and vacuum-assisted vapor deposition reaction method: soaking the carbon fiber cloth substrate in concentrated nitric acid at 80 ℃ for 1.0h, and soaking the carbon fiber cloth substrate in the concentrated nitric acid; and then sequentially cleaning the substrate by using acetone, ethanol and deionized water. Putting the dried carbon fiber cloth into an acetone solution containing 0.08mol/L ferric nitrate, taking out and drying the carbon fiber cloth, putting the carbon fiber cloth into a tube furnace, and vacuumizing the tube furnace to 2 multiplied by 10-2MPa, and the vacuum degree in the growth process is kept less than 3 multiplied by 10-2Introducing argon to raise the temperature under MPa, wherein the temperature raising rate is 5 ℃/min, and the argon flow is1000mL/min, heating to 450 ℃, introducing a reducing gas hydrogen reduction catalyst, keeping the hydrogen flow at 300mL/min, keeping the temperature for 20min, continuing heating to 650 ℃, heating at the rate of 2 ℃/min, introducing acetylene gas, keeping the acetylene flow at 450mL/min, keeping the temperature at 650 ℃ for 20min, and preparing carbon nanotube sponge on the surface of the carbon fiber cloth substrate, wherein the length of the prepared carbon nanotube is 1-4 mu m, the diameter of a single carbon nanotube is 20-40 nm, different carbon nanotubes are separated at intervals and grow on the surface of the carbon fiber substrate like a spring, and the whole carbon nanotube sponge is in a sponge shape.
(2) Preparing a copper-coated carbon nanotube core-shell material by a vacuum evaporation method: applying carbon fiber material cloth coated with carbon nanotube sponge on a working disc of a vacuum chamber, placing copper particles with purity of more than 99.99% in a tungsten crucible, starting a mechanical pump, and controlling the vacuum degree of the vacuum chamber at 4 × 10-3Pa, turning on a heating power supply, controlling the temperature of the vacuum chamber at 80 ℃, and preserving the heat for 10 minutes. Starting electron beam heating, heating to 1200 ℃, controlling the evaporation current to be 1.2A, controlling the evaporation rate to be 3A/s, and controlling the evaporation time to be 400 s. The core-shell material of the copper-coated carbon nano tube is obtained, and the prepared nano copper film has the thickness of about 120nm and is uniformly coated on the surface of the carbon nano tube sponge.
(3) Preparing a hydroxyl ferric oxide-copper-coated carbon nanotube coaxial core-shell material by a nitrogen protection three-electrode constant current electrochemical deposition reaction method: in a three-electrode electrochemical reaction system, a copper-coated carbon nanotube core-shell material is taken as a working electrode, an aqueous solution of sodium acetate and ammonium ferrous sulfate is taken as an electrolyte, and water is deionized water subjected to deoxidation treatment. And (3) carrying out electrochemical reaction under the protection of nitrogen by taking a platinum electrode as a counter electrode and a saturated calomel electrode as a reference electrode. Setting the initial polarity of the core-shell material of the copper-coated carbon nanotube as the anode and the current density of the anode as 0.6mA/cm2The upper limit potential is 1.0V, the anode reaction time is 7000s, wherein the concentration of sodium acetate is 0.04mol/L, and the concentration of ammonium ferrous sulfate is 0.02 mol/L. And obtaining the iron oxyhydroxide-copper-coated carbon nanotube coaxial core-shell material. The thickness of the prepared villous iron oxyhydroxide film is 80nm, and the iron oxyhydroxide film is uniformly coated on the surface of the copper-coated carbon nano tube to form a shell-core structure. The obtained hydroxyl radicalA bending photograph of the iron oxide-copper-coated carbon nanotube-based coaxial core-shell material is shown in fig. 5 d. The material has the bendable integrated characteristic and can be directly used as an electrode of a flexible supercapacitor.
Testing
The iron oxyhydroxide-copper-coated carbon nanotube coaxial core-shell material prepared by the invention is applied to an electrode material of a flexible super capacitor.
The test method is as follows: in a three-electrode system, 1.0mol/L sodium sulfate solution is used as a working electrolyte, the iron oxyhydroxide-copper-coated carbon nanotube coaxial core-shell material prepared in example 2 is used as a working electrode, a platinum sheet is used as an auxiliary electrode, a saturated calomel electrode is used as a reference electrode, an electrochemical workstation (CHI660E) is used for cyclic voltammetry, an initial potential of 0.0V, a high potential of 0.0V, a low potential of-0.8V, a scanning speed of 5-60 mV/s is set, and a scanning period is 1 cycle, and the result is shown in FIG. 6.
In a three-electrode system, 1.0mol/L sodium sulfate solution is used as working electrolyte, the iron oxyhydroxide-copper-coated carbon nanotube coaxial core-shell material prepared in example 2 is used as a working electrode, a platinum sheet is used as an auxiliary electrode, a saturated calomel electrode is used as a reference electrode, an electrochemical workstation is adopted for constant current charge and discharge test, a high potential of 0.0V, a low potential of-0.8V and a current density of 0.5-2.5 mA/cm are set2And scanning for 1 cycle, wherein the result is shown in figure 7, the calculated mass specific capacitance can reach 600F/g, the total mass of the active substances is 2.5mg, and the result is shown in figure 8.
In a three-electrode system, 1.0mol/L sodium sulfate solution is used as working electrolyte, the iron oxyhydroxide-copper-coated carbon nanotube coaxial core-shell material prepared in example 2 is used as a working electrode, a platinum sheet is used as an auxiliary electrode, a saturated calomel electrode is used as a reference electrode, an electrochemical workstation is adopted for constant current test, a high potential of 0.0V, a low potential of-0.8V and a current density of 5A/g are set, and a scanning period is 2000 cycles. The specific capacity retention rate is still maintained above 95% after 2000 cycles of the cycling stability test, and good cycling stability is shown, and the result is shown in figure 9; the electrochemical test at the time when the electrode was bent at 120 ° and after 500 times of repeated bending showed almost no capacity fade, and the results are shown in fig. 10.