US20110272288A1 - Method for fabricating carbon nanotube aluminum foil electrode - Google Patents

Method for fabricating carbon nanotube aluminum foil electrode Download PDF

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US20110272288A1
US20110272288A1 US12/884,971 US88497110A US2011272288A1 US 20110272288 A1 US20110272288 A1 US 20110272288A1 US 88497110 A US88497110 A US 88497110A US 2011272288 A1 US2011272288 A1 US 2011272288A1
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aluminum foil
aluminum
carbon nanotube
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electrode according
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Chuen-Chang LIN
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National Yunlin University of Science and Technology
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
    • C25D11/02—Anodisation
    • C25D11/04—Anodisation of aluminium or alloys based thereon
    • C25D11/12—Anodising more than once, e.g. in different baths
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
    • C25D11/02—Anodisation
    • C25D11/04—Anodisation of aluminium or alloys based thereon
    • C25D11/16—Pretreatment, e.g. desmutting
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
    • C25D11/02—Anodisation
    • C25D11/04—Anodisation of aluminium or alloys based thereon
    • C25D11/18—After-treatment, e.g. pore-sealing
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
    • C25D11/02—Anodisation
    • C25D11/04—Anodisation of aluminium or alloys based thereon
    • C25D11/18—After-treatment, e.g. pore-sealing
    • C25D11/20—Electrolytic after-treatment
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
    • H01G11/00—Hybrid capacitors, i.e. capacitors having different positive and negative electrodes; Electric double-layer [EDL] capacitors; Processes for the manufacture thereof or of parts thereof
    • H01G11/22—Electrodes
    • H01G11/30—Electrodes characterised by their material
    • H01G11/32—Carbon-based
    • H01G11/36—Nanostructures, e.g. nanofibres, nanotubes or fullerenes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/13—Energy storage using capacitors

Definitions

  • the present invention relates to a method for a capacitor electrode, particularly to a method for fabricating a carbon nanotube aluminum foil electrode.
  • Increasing the capacitance and miniaturizing the aluminum electrolytic capacitor thereof is a critical task in the related field.
  • An aluminum-oxide film is formed under a specified voltage, and the thickness of the aluminum-oxide film is proportionally increased by a ratio of 1.3 nm/V.
  • the electrodes have a given spacing therebetween, and the aluminum-oxide film has a fixed dielectric constant permittivity. Therefore, increasing the surface of electrodes is a practicable method to increase the capacitance of the aluminum electrolytic capacitor.
  • the capacitance of the aluminum electrolytic capacitor can be increased via increasing the surface of the anode aluminum foil or the cathode aluminum foil, wherein the anode aluminum foil is anodized to have a thick and dense aluminum oxide film. Further, the cathode aluminum foil has a capacitance much higher than the anode aluminum foil. Therefore, increasing the capacitance of the anode aluminum foil is the most effective method to increase the capacitance of the aluminum electrolytic capacitor.
  • the surface area of an aluminum foil can be increased with a traditional chemical or electrochemical etching method, wherein an acidic solution that is corrosive to aluminum is used to form rugged pits on the surface.
  • Jinwook Kang, Yunho Shin and Yongsug Tak disclosed a reference “Growth of etch pits formed during sonoelectrochemical etching of aluminum” in Electrochimica Acta, Volume 51, Issue 5, 10 Nov. 2005, Pages 1012-1016.
  • different ultrasonic frequencies are used to improve the etch-inhibiting ability of aluminum chloride in an electrochemical etching process undertaken in an electrochemical etching solution (1 M HCl+3 M H 2 SO 4 ) and at a current density of 0.03 A/cm 2 . Then, the forming is processed in a boric acid solution.
  • the conventional technology can achieve a capacitance of about 2 ⁇ F/cm 2 when the anodizing voltage is 50 V.
  • Du, et al. disclosed a reference “Formation of Al 2 O 3 —BaTiO 3 composite thin film to increase the specific capacitance of aluminum electrolytic capacitor” in Thin Solid Films, Volume 516, Issue 23, 1 Oct. 2008, Pages 8436-8440, wherein BaTiO 3 is fabricated by a sol-gel method and coated on an etched aluminum foil. Next, the aluminum foil with BaTiO 3 is heat-treated at different temperatures. Then, the aluminum foil is anodized with an ammonium adipate solution to increase the capacitance.
  • the conventional technology can achieve the capacitance of about 95.66 ⁇ F/cm 2 when the heat treatment is undertaken at a temperature of 600° C.
  • Nogami, et al. disclosed another reference “The effects of Hyperbranched poly(siloxysilane)s on Conductive Polymer Aluminum Solid Electrolytic Capacitors” in Journal of Power Sources, Volume 166, Issue 2, 15 Apr. 2007, Pages 584-589, wherein hyperbranched poly(siloxysilane)s that contains a lot of vinyl groups is used to improve the interface character between aluminum oxide and the corresponding [poly-(3,4-ethylenedioxythiophene)] electrode.
  • the conventional technology can achieve a capacitance of about 215.79 ⁇ F/cm 2 .
  • Taiwan patent publication No. 200828368 disclosed an “Electrolytic Capacitor Electrode”, wherein metal oxide is formed on the surface of an aluminum substrate via chemical bonding, and the metal oxide is heat-treated at a temperature of 100-500° C.
  • the capacitance of the metal oxide-coated aluminum substrate can be effectively increased.
  • the metal oxide is generated by the chemical reaction between the precursor thereof and the functional groups on the surface of the aluminum substrate. Therefore, the metal oxide is hard to peel off.
  • the conventional technology can only achieve an electrostatic capacity of about 252-263 ⁇ F/cm 2 .
  • the primary object of the present invention is to increase the surface area of an aluminum foil electrode, whereby the capacitance of an aluminum electrolytic capacitor can be effectively increased.
  • the present invention proposes a method for fabricating a carbon nanotube aluminum foil electrode, which comprises steps:
  • Step S 1 pre-processing an aluminum foil to remove the grease and oxide layer on the surface thereof;
  • Step S 2 electroplating a catalyst, wherein a catalytic material is electroplated on the aluminum foil;
  • Step S 3 growing carbon nanotubes, wherein the carbon nanotubes are grown on the catalyst-coated aluminum foil;
  • Step S 4 sputtering aluminum on the carbon nanotube aluminum foil, wherein an aluminum target and a radio frequency power source are used to sputter aluminum on the aluminum foil where the carbon nanotubes have been grown, and wherein the sputtering is undertaken with a power of 50-95 W for 2-4 hours; and
  • Step S 5 forming an aluminum oxide layer on the carbon nanotube aluminum foil after sputtering aluminum, the forming step is in an anodizing solution, and wherein the forming is undertaken at a temperature of 83-90° C. for 10 minutes, whereby is completed the carbon nanotube aluminum foil electrode of the present invention.
  • the present invention is used to increase the surface area of electrodes via growing carbon nanotubes on the aluminum foil, whereby the capacitance of the aluminum electrolytic capacitor is greatly increased. From experiments, it is known that the aluminum electrolytic capacitor fabricated according to the present invention has a capacitance of as high as 3425.78 ⁇ F/cm 2 and an operation voltage of as high as 38.44 V, which are much higher than the conventional technology. Therefore, the present invention can effectively promote the capacitance of the aluminum electrolytic capacitor.
  • FIG. 1 is a flowchart of a method for fabricating a carbon nanotube aluminum foil electrode according to one embodiment of the present invention
  • FIG. 2A is a schematic view of the surface of the pre-processed aluminum foil according to one embodiment of the present invention.
  • FIG. 2B is a schematic view of the surface of the catalyst-electroplated aluminum foil according to one embodiment of the present invention.
  • FIG. 1 a flowchart of a method for fabricating a carbon nanotube aluminum foil electrode according to one embodiment of the present invention.
  • the method of the present invention comprises the following steps:
  • Step S 1 pre-processing an aluminum foil: An aluminum foil is pre-processed to remove the grease and oxide layer on the surface of the aluminum foil.
  • the aluminum foil is soaked in acetone to remove the grease on the surface.
  • the aluminum foil is soaked in a 1 M solution of sodium hydroxide for two minutes to remove the oxide layer on the surface.
  • the aluminum foil is flushed with deionized water.
  • the aluminum foil is soaked in alcohol and ultrasonically oscillated for 15 minutes. Refer to FIG. 2A for a microscopic photograph of the surface of the pre-processed aluminum foil.
  • Step S 2 electroplating a catalyst: A catalytic material is deposited on the surface of the aluminum foil via electroplating. The catalytic material may be cobalt. The electroplating is undertaken in an electroplating solution containing 5 wt. % CoSO 4 .7H 2 O and 2 wt. % H 3 BO 3 , at an alternating voltage of 13.6 V and a frequency of 60 Hz, for 40 seconds. Refer to FIG. 2B for a microscopic photograph of the surface of the catalyst-electroplated aluminum foil.
  • Step S 3 growing carbon nanotubes: Carbon nanotubes are grown on the surface of the catalyst-deposited aluminum foil with a CVD (Chemical Vapor Deposition) and via the catalytic reaction of the catalyst, wherein argon is the carrier gas and acetylene is the carbon source. The growth is undertaken at a temperature of 575-610° C. for 15-90 minutes, and the flow rate of argon is 100 sccm, and the flow rate of acetylene is 50 sccm. Sccm is a unit of flow rate, meaning the number of cubic centers of the gas flowing through a point at the standard state (at a temperature of 273 K and a pressure of 760 Torr) per minute.
  • CVD Chemical Vapor Deposition
  • Step S 4 sputtering aluminum on the aluminum foil where the carbon nanotubes have been grown: An aluminum target and a radio frequency power source are used to sputter aluminum on the carbon nanotube aluminum foil at an argon flow rate of 25 sccm, a sputtering pressure of 20 mTorr and a sputtering power of 50-95 W for 2-4 hours.
  • Step S 5 forming an aluminum oxide layer on the carbon nanotube aluminum foil after sputtering aluminum:
  • the aluminum foil is placed in an anodizing solution to form an aluminum oxide layer.
  • the forming is undertaken at a temperature of 83-90° C. for 10 minutes.
  • the anodizing solution is formed via mixing 150 g of ammonium adipate with 1 liter of deionized water.
  • anodic aluminum oxide layer may be formed after Step S 1 via the following steps:
  • Step S 1 A electropolishing the aluminum foil: The aluminum foil is placed in an electropolishing solution and electropolished at a voltage of 30 V and a temperature of 25° C. for 15 minutes.
  • the electropolishing solution contains sulfuric acid, phosphoric acid and deionized water by a ratio of 2:2:3.
  • Step S 1 B performing a first anodizing process on the electropolished aluminum foil:
  • the electropolished aluminum foil is placed in a 0.3 M solution of oxalic acid and anodized at a voltage of 30-40 V and a temperature of 5-15° C. for 12 minutes to form an AAO (Anodic Aluminum Oxide) layer.
  • AAO Anadic Aluminum Oxide
  • Step S 1 C performing a second anodizing process on the aluminum foil:
  • an oxide-removing solution is used initially to remove the anodic aluminum oxide formed in the first anodizing process, wherein the oxide-removing solution contains 1.8 wt. % chromic acid and 6 wt. % phosphoric acid.
  • the second anodizing process Refer to FIG. 3A .
  • the aluminum foil is placed in the oxalic acid solution and anodized to form a new AAO layer 10 on the imprint left by the first anodizing process.
  • the new AAO layer 10 has a plurality of pores 11 .
  • the second anodizing process is undertaken in a 0.3 M solution of oxalic acid, at a voltage of 30-40 V and a temperature of 5-15° C. for 12 minutes.
  • Step S 1 D removing a barrier layer: Refer to FIG. 3B a sectional view of the AAO layer according to one embodiment of the present invention.
  • the aluminum foil is soaked in a phosphoric acid solution containing 5 wt. % phosphoric acid at a temperature of 30° C. for 40 minutes to remove a barrier layer on the bottoms of the pores 11 to make the pores 11 interconnect the aluminum foil, whereby the catalytic material 20 can be electroplated on the bottoms of the pores 11 to contact the aluminum foil in abovementioned Step S 2 .
  • Step S 3 the carbon nanotubes are grown along the pores 11 with the catalytic material 20 .
  • the AAO layer 10 limits the area where the catalytic material 20 is deposited. However, the pores 11 make the carbon nanotubes hard to peel off from the aluminum foil. Therefore, the carbon nanotube AAO-containing aluminum foil electrode has a higher operation voltage.
  • the carbon nanotubes are preferably grown at a temperature of 600° C. for 60 minutes for both the carbon nanotube aluminum foil electrode and the carbon nanotube AAO-containing aluminum foil electrode.
  • a higher temperature favors the growth of carbon nanotubes.
  • the melting point of aluminum is about 620° C.
  • the growth of the carbon nanotubes becomes unstable when the temperature approaches 620° C.
  • the carbon nanotubes have the maximum average surface area density with a higher capacitance after they have been grown for 60 minutes. Therefore, the time of growing the carbon nanotubes are preferred to be 60 minutes.
  • the thickness of the sputter-deposited aluminum is increased with the sputtering time and the sputtering power.
  • the thicker the sputter-deposited aluminum the thicker the aluminum oxide obtained in the forming step. According to the equation of capacity, the thicker the aluminum oxide has a lower capacitance. However, the thicker the aluminum oxide has a higher operation voltage. Considering the abovementioned factors, the sputtering power and the sputtering time are respectively preferred to be 65 W and 4 hours.
  • the carbon nanotube AAO-containing aluminum foil electrode fabricated according to the abovementioned conditions has a capacitance of 2158.8 ⁇ F/cm 2 and an operation voltage of 55.10 V. But the carbon nanotube aluminum foil electrode fabricated according to the abovementioned conditions has a capacitance of 3425.78 ⁇ F/cm 2 and an operation voltage of 38.44 V.
  • the AAO layer 10 decreases the area where the catalytic material can be electroplated, so that the carbon nanotube AAO-containing aluminum foil electrode has a smaller capacitance and a greater operation voltage.
  • Both the carbon nanotube aluminum foil electrode and the carbon nanotube AAO-containing aluminum foil electrode have a capacitance much greater than the conventional technology. Therefore, the present invention is proved to meet the conditions of a patent. Thus, the Inventor files the application for a patent. It is appreciated if the patent is approved fast.

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Abstract

A method for fabricating a carbon nanotube aluminum foil electrode is used to increase the surface area of the electrode by growing the high-electric conductivity carbon nanotubes on an aluminum foil or an AAO (Anodic Aluminum Oxide)-containing aluminum template, whereby is greatly increased the capacitance of the aluminum electrolytic capacitor. The electrode fabricated via forming the carbon nanotubes on the AAO-containing aluminum template has a capacitance of 2158.6 μF/cm2 and an operation voltage of 55.10 V. The electrode fabricated via directly forming the carbon nanotubes on the aluminum foil has a capacitance of 3425.78 μF/cm2 and an operation voltage of 38.44 V. Therefore, the capacitance of the aluminum electrolytic capacitor is effectively increased. Further, the carbon nanotube aluminum foil electrode fabricated in different ways can meet the different requirements of operation voltages and capacitances.

Description

    FIELD OF THE INVENTION
  • The present invention relates to a method for a capacitor electrode, particularly to a method for fabricating a carbon nanotube aluminum foil electrode.
    • BACKGROUND OF THE INVENTION
  • Increasing the capacitance and miniaturizing the aluminum electrolytic capacitor thereof is a critical task in the related field. There are three ways to increase the capacitance of an aluminum electrolytic capacitor: (1) decreasing the spacing between the electrodes, (2) using a high dielectric constant material as the insulating material between the electrodes, and (3) increasing the surface of electrodes. An aluminum-oxide film is formed under a specified voltage, and the thickness of the aluminum-oxide film is proportionally increased by a ratio of 1.3 nm/V. Further, the electrodes have a given spacing therebetween, and the aluminum-oxide film has a fixed dielectric constant permittivity. Therefore, increasing the surface of electrodes is a practicable method to increase the capacitance of the aluminum electrolytic capacitor. The capacitance of the aluminum electrolytic capacitor can be increased via increasing the surface of the anode aluminum foil or the cathode aluminum foil, wherein the anode aluminum foil is anodized to have a thick and dense aluminum oxide film. Further, the cathode aluminum foil has a capacitance much higher than the anode aluminum foil. Therefore, increasing the capacitance of the anode aluminum foil is the most effective method to increase the capacitance of the aluminum electrolytic capacitor.
  • The surface area of an aluminum foil can be increased with a traditional chemical or electrochemical etching method, wherein an acidic solution that is corrosive to aluminum is used to form rugged pits on the surface. Jinwook Kang, Yunho Shin and Yongsug Tak disclosed a reference “Growth of etch pits formed during sonoelectrochemical etching of aluminum” in Electrochimica Acta, Volume 51, Issue 5, 10 Nov. 2005, Pages 1012-1016. In the conventional technology, different ultrasonic frequencies are used to improve the etch-inhibiting ability of aluminum chloride in an electrochemical etching process undertaken in an electrochemical etching solution (1 M HCl+3 M H2SO4) and at a current density of 0.03 A/cm2. Then, the forming is processed in a boric acid solution.
  • The conventional technology can achieve a capacitance of about 2 μF/cm2 when the anodizing voltage is 50 V.
  • Du, et al. disclosed a reference “Formation of Al2O3—BaTiO3 composite thin film to increase the specific capacitance of aluminum electrolytic capacitor” in Thin Solid Films, Volume 516, Issue 23, 1 Oct. 2008, Pages 8436-8440, wherein BaTiO3 is fabricated by a sol-gel method and coated on an etched aluminum foil. Next, the aluminum foil with BaTiO3 is heat-treated at different temperatures. Then, the aluminum foil is anodized with an ammonium adipate solution to increase the capacitance. The conventional technology can achieve the capacitance of about 95.66 μF/cm2 when the heat treatment is undertaken at a temperature of 600° C.
  • Nogami, et al. disclosed another reference “The effects of Hyperbranched poly(siloxysilane)s on Conductive Polymer Aluminum Solid Electrolytic Capacitors” in Journal of Power Sources, Volume 166, Issue 2, 15 Apr. 2007, Pages 584-589, wherein hyperbranched poly(siloxysilane)s that contains a lot of vinyl groups is used to improve the interface character between aluminum oxide and the corresponding [poly-(3,4-ethylenedioxythiophene)] electrode. The conventional technology can achieve a capacitance of about 215.79 μF/cm2.
  • A Taiwan patent publication No. 200828368 disclosed an “Electrolytic Capacitor Electrode”, wherein metal oxide is formed on the surface of an aluminum substrate via chemical bonding, and the metal oxide is heat-treated at a temperature of 100-500° C. The capacitance of the metal oxide-coated aluminum substrate can be effectively increased. The metal oxide is generated by the chemical reaction between the precursor thereof and the functional groups on the surface of the aluminum substrate. Therefore, the metal oxide is hard to peel off. However, the conventional technology can only achieve an electrostatic capacity of about 252-263 μF/cm2.
    • SUMMARY OF THE INVENTION
  • The primary object of the present invention is to increase the surface area of an aluminum foil electrode, whereby the capacitance of an aluminum electrolytic capacitor can be effectively increased.
  • To achieve the abovementioned object, the present invention proposes a method for fabricating a carbon nanotube aluminum foil electrode, which comprises steps:
  • Step S1: pre-processing an aluminum foil to remove the grease and oxide layer on the surface thereof;
  • Step S2: electroplating a catalyst, wherein a catalytic material is electroplated on the aluminum foil;
  • Step S3: growing carbon nanotubes, wherein the carbon nanotubes are grown on the catalyst-coated aluminum foil;
  • Step S4: sputtering aluminum on the carbon nanotube aluminum foil, wherein an aluminum target and a radio frequency power source are used to sputter aluminum on the aluminum foil where the carbon nanotubes have been grown, and wherein the sputtering is undertaken with a power of 50-95 W for 2-4 hours; and
  • Step S5: forming an aluminum oxide layer on the carbon nanotube aluminum foil after sputtering aluminum, the forming step is in an anodizing solution, and wherein the forming is undertaken at a temperature of 83-90° C. for 10 minutes, whereby is completed the carbon nanotube aluminum foil electrode of the present invention.
  • The present invention is used to increase the surface area of electrodes via growing carbon nanotubes on the aluminum foil, whereby the capacitance of the aluminum electrolytic capacitor is greatly increased. From experiments, it is known that the aluminum electrolytic capacitor fabricated according to the present invention has a capacitance of as high as 3425.78 μF/cm2 and an operation voltage of as high as 38.44 V, which are much higher than the conventional technology. Therefore, the present invention can effectively promote the capacitance of the aluminum electrolytic capacitor.
    • BRIEF DESCRIPTION OF THE DRAWINGS
  • FIG. 1 is a flowchart of a method for fabricating a carbon nanotube aluminum foil electrode according to one embodiment of the present invention;
  • FIG. 2A is a schematic view of the surface of the pre-processed aluminum foil according to one embodiment of the present invention;
  • FIG. 2B is a schematic view of the surface of the catalyst-electroplated aluminum foil according to one embodiment of the present invention;
  • FIG. 3A is a schematic view of the surface of the AAO layer on the aluminum foil according to one embodiment of the present invention; and
  • FIG. 3B is a schematic view of the section of the AAO layer on the aluminum foil according to one embodiment of the present invention.
    •  DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
  • Refer to FIG. 1 a flowchart of a method for fabricating a carbon nanotube aluminum foil electrode according to one embodiment of the present invention. The method of the present invention comprises the following steps:
  • Step S1: pre-processing an aluminum foil: An aluminum foil is pre-processed to remove the grease and oxide layer on the surface of the aluminum foil. In one embodiment, the aluminum foil is soaked in acetone to remove the grease on the surface. Next, the aluminum foil is soaked in a 1 M solution of sodium hydroxide for two minutes to remove the oxide layer on the surface. Next, the aluminum foil is flushed with deionized water. Then, the aluminum foil is soaked in alcohol and ultrasonically oscillated for 15 minutes. Refer to FIG. 2A for a microscopic photograph of the surface of the pre-processed aluminum foil.
  • Step S2: electroplating a catalyst: A catalytic material is deposited on the surface of the aluminum foil via electroplating. The catalytic material may be cobalt. The electroplating is undertaken in an electroplating solution containing 5 wt. % CoSO4.7H2O and 2 wt. % H3BO3, at an alternating voltage of 13.6 V and a frequency of 60 Hz, for 40 seconds. Refer to FIG. 2B for a microscopic photograph of the surface of the catalyst-electroplated aluminum foil.
  • Step S3: growing carbon nanotubes: Carbon nanotubes are grown on the surface of the catalyst-deposited aluminum foil with a CVD (Chemical Vapor Deposition) and via the catalytic reaction of the catalyst, wherein argon is the carrier gas and acetylene is the carbon source. The growth is undertaken at a temperature of 575-610° C. for 15-90 minutes, and the flow rate of argon is 100 sccm, and the flow rate of acetylene is 50 sccm. Sccm is a unit of flow rate, meaning the number of cubic centers of the gas flowing through a point at the standard state (at a temperature of 273 K and a pressure of 760 Torr) per minute.
  • Step S4: sputtering aluminum on the aluminum foil where the carbon nanotubes have been grown: An aluminum target and a radio frequency power source are used to sputter aluminum on the carbon nanotube aluminum foil at an argon flow rate of 25 sccm, a sputtering pressure of 20 mTorr and a sputtering power of 50-95 W for 2-4 hours.
  • Step S5: forming an aluminum oxide layer on the carbon nanotube aluminum foil after sputtering aluminum: The aluminum foil is placed in an anodizing solution to form an aluminum oxide layer. The forming is undertaken at a temperature of 83-90° C. for 10 minutes. In one embodiment, the anodizing solution is formed via mixing 150 g of ammonium adipate with 1 liter of deionized water.
  • The present invention uses the abovementioned steps to form a carbon nanotube aluminum foil electrode. Further, an anodic aluminum oxide layer may be formed after Step S1 via the following steps:
  • Step S1A: electropolishing the aluminum foil: The aluminum foil is placed in an electropolishing solution and electropolished at a voltage of 30 V and a temperature of 25° C. for 15 minutes. The electropolishing solution contains sulfuric acid, phosphoric acid and deionized water by a ratio of 2:2:3.
  • Step S1B: performing a first anodizing process on the electropolished aluminum foil: The electropolished aluminum foil is placed in a 0.3 M solution of oxalic acid and anodized at a voltage of 30-40 V and a temperature of 5-15° C. for 12 minutes to form an AAO (Anodic Aluminum Oxide) layer.
  • Step S1C: performing a second anodizing process on the aluminum foil: In order to make the AAO layer arranged orderly, an oxide-removing solution is used initially to remove the anodic aluminum oxide formed in the first anodizing process, wherein the oxide-removing solution contains 1.8 wt. % chromic acid and 6 wt. % phosphoric acid. Next it is undertaken the second anodizing process. Refer to FIG. 3A. The aluminum foil is placed in the oxalic acid solution and anodized to form a new AAO layer 10 on the imprint left by the first anodizing process. The new AAO layer 10 has a plurality of pores 11. Similarly to the first anodizing process, the second anodizing process is undertaken in a 0.3 M solution of oxalic acid, at a voltage of 30-40 V and a temperature of 5-15° C. for 12 minutes.
  • Step S1D: removing a barrier layer: Refer to FIG. 3B a sectional view of the AAO layer according to one embodiment of the present invention. After the second anodizing process, the aluminum foil is soaked in a phosphoric acid solution containing 5 wt. % phosphoric acid at a temperature of 30° C. for 40 minutes to remove a barrier layer on the bottoms of the pores 11 to make the pores 11 interconnect the aluminum foil, whereby the catalytic material 20 can be electroplated on the bottoms of the pores 11 to contact the aluminum foil in abovementioned Step S2. Next, following Step S3, the carbon nanotubes are grown along the pores 11 with the catalytic material 20. The AAO layer 10 limits the area where the catalytic material 20 is deposited. However, the pores 11 make the carbon nanotubes hard to peel off from the aluminum foil. Therefore, the carbon nanotube AAO-containing aluminum foil electrode has a higher operation voltage.
  • The carbon nanotubes are preferably grown at a temperature of 600° C. for 60 minutes for both the carbon nanotube aluminum foil electrode and the carbon nanotube AAO-containing aluminum foil electrode. A higher temperature favors the growth of carbon nanotubes. However, the melting point of aluminum is about 620° C. Thus, the growth of the carbon nanotubes becomes unstable when the temperature approaches 620° C. Experiments show that the carbon nanotubes have the maximum average surface area density with a higher capacitance after they have been grown for 60 minutes. Therefore, the time of growing the carbon nanotubes are preferred to be 60 minutes. In Step S4, the thickness of the sputter-deposited aluminum is increased with the sputtering time and the sputtering power. The thicker the sputter-deposited aluminum, the thicker the aluminum oxide obtained in the forming step. According to the equation of capacity, the thicker the aluminum oxide has a lower capacitance. However, the thicker the aluminum oxide has a higher operation voltage. Considering the abovementioned factors, the sputtering power and the sputtering time are respectively preferred to be 65 W and 4 hours.
  • The carbon nanotube AAO-containing aluminum foil electrode fabricated according to the abovementioned conditions has a capacitance of 2158.8 μF/cm2 and an operation voltage of 55.10 V. But the carbon nanotube aluminum foil electrode fabricated according to the abovementioned conditions has a capacitance of 3425.78 μF/cm2 and an operation voltage of 38.44 V. The AAO layer 10 decreases the area where the catalytic material can be electroplated, so that the carbon nanotube AAO-containing aluminum foil electrode has a smaller capacitance and a greater operation voltage. Both the carbon nanotube aluminum foil electrode and the carbon nanotube AAO-containing aluminum foil electrode have a capacitance much greater than the conventional technology. Therefore, the present invention is proved to meet the conditions of a patent. Thus, the Inventor files the application for a patent. It is appreciated if the patent is approved fast.
  • The embodiments described above are only to exemplify the present invention but not to limit the scope of the present invention. Any equivalent modification or variation according to the technical contents or spirit of the present invention is to be also included within the scope of the present invention.

Claims (10)

1. A method for fabricating a carbon nanotube aluminum foil electrode comprising steps:
Step S1: pre-processing an aluminum foil to remove the grease and oxide layer on a surface thereof;
Step S2: electroplating a catalytic material on the aluminum foil;
Step S3: growing carbon nanotubes on the catalytic material-coated aluminum foil;
Step S4: sputtering aluminum on the carbon nanotube aluminum foil, wherein an aluminum target and a radio frequency power source are used to sputter aluminum on the aluminum foil where the carbon nanotubes have been grown, and wherein the sputtering is undertaken with a power of 50-95 W for 2-4 hours; and
Step S5: forming an aluminum oxide layer on the carbon nanotube aluminum foil after sputtering aluminum, the forming step is in an anodizing solution, and wherein the forming is undertaken at a temperature of 83-90° C. for 10 minutes, whereby is completed the carbon nanotube aluminum foil electrode.
2. The method for fabricating a carbon nanotube aluminum foil electrode according to claim 1, wherein after the Step S1 comprises a Step S1A: electropolishing the aluminum foil which is placed in an electropolishing solution containing sulfuric acid, phosphoric acid and deionized water by a ratio of 2:2:3.
3. The method for fabricating a carbon nanotube aluminum foil electrode according to claim 2, wherein after the Step S1A comprises a Step S1B: performing a first anodizing process on the aluminum foil, wherein the electropolished aluminum foil is anodized in an oxalic acid solution to form an Anodic Aluminum Oxide layer.
4. The method for fabricating a carbon nanotube aluminum foil electrode according to claim 3, wherein after the Step S1B has a Step S1C: performing a second anodizing process on the aluminum foil, wherein an oxide-removing solution is used to remove the Anodic Aluminum Oxide layer formed in the first anodizing process, and then the aluminum foil is anodized in the oxalic acid solution to form a new Anodic Aluminum Oxide layer on the imprint left by the first anodizing process; the new Anodic Aluminum Oxide layer has a plurality of pores.
5. The method for fabricating a carbon nanotube aluminum foil electrode according to claim 4, wherein the oxide-removing solution contains 1.8 wt. % chromic acid and 6 wt. % phosphoric acid.
6. The method for fabricating a carbon nanotube aluminum foil electrode according to claim 4, wherein the first anodizing process and the second anodizing process are undertaken at a voltage of 30-40 V and a temperature of 5-15° C. for 12 minutes, and wherein the oxalic acid solution has a concentration of 0.3 M.
7. The method for fabricating a carbon nanotube aluminum foil electrode according to claim 4, wherein after the Step S1C has a Step S1D: after the second anodizing process, soaking the aluminum foil in a phosphoric acid solution containing 5 wt. % phosphoric acid at a temperature of 30° C. for 40 minutes to remove a barrier layer that is formed on the bottoms of the pores and contacts the aluminum foil.
8. The method for fabricating a carbon nanotube aluminum foil electrode according to claim 1, wherein the catalytic material is cobalt, and wherein the electroplating is undertaken in an electroplating solution containing 5 wt. % CoSO4.7H2O and 2 wt. % H3BO3, at an alternating voltage of 13.6 V and a frequency of 60 Hz, for 40 seconds.
9. The method for fabricating a carbon nanotube aluminum foil electrode according to claim 1, wherein in Step S3, the carbon nanotubes are grown with a Chemical Vapor Deposition method, and wherein argon is the carrier gas and acetylene is the carbon source, and wherein the growth is undertaken at a temperature of 575-610° C. for 15-90 minutes, and wherein the flow rate of argon is 100 sccm, and the flow rate of acetylene is 50 sccm.
10. The method for fabricating a carbon nanotube aluminum foil electrode according to claim 1, wherein the anodizing solution is formed via mixing ammonium adipate and deionized water.
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WO2016210249A1 (en) * 2015-06-25 2016-12-29 Vladimir Mancevski Apparatus and methods for high volume production of graphene and carbon nanotubes on large-sized thin foils
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WO2016210249A1 (en) * 2015-06-25 2016-12-29 Vladimir Mancevski Apparatus and methods for high volume production of graphene and carbon nanotubes on large-sized thin foils
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US10109410B2 (en) 2017-01-17 2018-10-23 Palo Alto Research Center Incorporated Out of plane structures and methods for making out of plane structures
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