U.S. patent application number 12/385763 was filed with the patent office on 2010-04-01 for fabrication method for porous carbon fibers.
This patent application is currently assigned to KOREA ADVANCED INSTITUE OF SCIENCE AND TECHNOLOGY. Invention is credited to Soon Hyung Hong, Yong Jin Jeong, Kyong Ho Lee, Chan Bin Mo.
Application Number | 20100081351 12/385763 |
Document ID | / |
Family ID | 42057962 |
Filed Date | 2010-04-01 |
United States Patent
Application |
20100081351 |
Kind Code |
A1 |
Hong; Soon Hyung ; et
al. |
April 1, 2010 |
Fabrication method for porous carbon fibers
Abstract
Disclosed is a method for fabrication of porous carbon fibers.
More particularly, the method for fabrication of porous carbon
fibers comprises the steps of: processing starch to prepare a
gelled starch solution; adding organic acid to the gelled starch
solution to prepare a starch solution; dissolving carbon nanotubes
in a solvent and adding fiber formable polymer thereto to prepare a
carbon nanotube/fiber formable polymer solution; mixing the starch
solution with the carbon nanotube/fiber formable polymer solution
obtained from the above steps, in order to prepare a carbon
nanotube/starch/fiber formable polymer solution; electro-spinning
or wet-state spinning the prepared carbon nanotube/starch/fiber
formable polymer solution to produce starch composite fibers;
oxidation heating the starch composite fibers, then, executing
carbonization and vacuum heat treatment of the heated fibers, so as
to fabricate the porous carbon fibers. The fabricated porous carbon
fiber has high specific surface area and high capacitance, thereby
being favorably applicable in manufacturing electrodes for a super
capacitor, fuel cell, etc.
Inventors: |
Hong; Soon Hyung;
(Yuseong-ku, KR) ; Jeong; Yong Jin; (Yuseong-ku,
KR) ; Lee; Kyong Ho; (Yuseong-ku, KR) ; Mo;
Chan Bin; (Yuseong-ku, KR) |
Correspondence
Address: |
THE NATH LAW GROUP
112 South West Street
Alexandria
VA
22314
US
|
Assignee: |
KOREA ADVANCED INSTITUE OF SCIENCE
AND TECHNOLOGY
Yuseong-ku
KR
|
Family ID: |
42057962 |
Appl. No.: |
12/385763 |
Filed: |
April 17, 2009 |
Current U.S.
Class: |
442/320 ;
423/447.2; 423/447.4 |
Current CPC
Class: |
H01G 11/34 20130101;
H01M 4/8807 20130101; D04H 1/4242 20130101; Y02P 70/50 20151101;
Y10T 442/50 20150401; H01M 8/0234 20130101; D04H 1/728 20130101;
Y02E 60/13 20130101; H01M 4/8605 20130101; D04H 1/4382 20130101;
H01G 11/22 20130101; D04H 1/4391 20130101; D01D 5/247 20130101;
H01G 11/36 20130101; D01F 1/10 20130101; Y02E 60/50 20130101; D01F
9/16 20130101 |
Class at
Publication: |
442/320 ;
423/447.4; 423/447.2 |
International
Class: |
D04H 1/08 20060101
D04H001/08; D01F 9/14 20060101 D01F009/14 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 30, 2008 |
KR |
10-2008-0096148 |
Claims
1. A method for fabricating a porous carbon fibers comprising: (a)
processing starch to prepare a gelled starch solution; (b) adding
organic acid to the gelled starch solution to prepare a starch
solution; (c) dissolving carbon nanotubes in a solvent and adding
fiber formable polymer thereto to prepare a carbon nanotube/fiber
formable polymer solution; (d) mixing the starch solution of step
(b) with the carbon nanotube/fiber formable polymer solution of
step (c) to prepare a carbon nanotube/starch/fiber formable polymer
solution; (e) electro-spinning or wet-state spinning the prepared
carbon nanotube/starch/fiber formable polymer solution to produce
starch composite fibers; (f) oxidation heating the starch composite
fibers, then, executing carbonization and vacuum heat treatment of
the heated fibers, so as to fabricate the porous carbon fibers.
2. The method according to claim 1, wherein the processing in step
(a) includes heating starch at 100 to 150.degree. C. and then
cooling the same to room temperature.
3. The method according to claim 1, wherein the organic acid in
step (b) is at least one selected from a group consisting of
p-toluene sulfonic acid, methane sulfonic acid, trifluoromethane
sulfonic acid, alkylbenzene sulfonic acid and p-aminobenzene
sulfonic acid.
4. The method according to claim 1, wherein the solvent in step (c)
is at least one selected from a group consisting of water, ethanol,
methanol, dichloromethanol, isopropanol, acetone and
hexafluoroisopropanol (HFIP).
5. The method according to claim 1, wherein the fiber formable
polymer in step (c) is at least one selected from a group
consisting of polyvinyl alcohol, polyethylene oxide, polycarboate,
polylactic acid, polyvinylcarbazole, polymethacrylate, cellulose
acetate, collagen, polycaprolactone and poly(2-hydroxyethyl
methacrylate).
6. The method according to claim 1, wherein the fiber formable
polymer is added to the starch, in a ratio of percent (%) by weight
of 5:5 to 8:2 for starch: fiber formable polymer.
7. The method according to claim 1, wherein the oxidation heating
in step (f) is executed at 150 to 300.degree. C.
8. The method according to claim 1, wherein the carbonization in
step (f) is executed at 500 to 1,400.degree. C. under vacuum or an
inert gas atmosphere.
9. The method according to claim 1, wherein the vacuum heat
treatment in step (f) is executed at 1,400 to 2,200.degree. C.
10. The method according to claim 1, wherein the porous carbon
fiber has a great amount of mesopores with an average diameter
ranging from 5 to 10 nm.
11. A porous carbon fiber fabricated by the method as set forth in
claim 1.
12. A felt including the porous carbon fiber as set forth in claim
11.
13. Use of the porous carbon fiber as set forth in claim 11 in
manufacturing an electrode for a super capacitor having high
capacitance.
14. Use of the porous carbon fiber as set forth in claim 11 in
manufacturing an electrode for a fuel cell.
Description
[0001] This application claims priority to Korean Patent
Application No. 10-2008-96148, filed on Sep. 30, 2008, in the
Korean Intellectual Property Office, the entire contents of which
are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a method for fabrication of
porous carbon fibers, and more particularly, to a method for
fabrication of porous carbon fibers, comprising: preparing starch
composite fibers using eco-friendly and economically advantageous
natural polymers such as starch; oxidation heating the prepared
starch composite fibers; and executing carbonization and vacuum
heat treatment of the treated fibers. Such fabricated porous carbon
fibers contain a great amount of mesopores as a porous structure
readily penetrable by electrolyte. Accordingly, the porous carbon
fibers of the present invention are suitable for manufacturing
electrodes with high electric capacity.
[0004] 2. Description of the Related Art
[0005] A great deal of studies and investigation into electrode
materials for super capacitors are underway and such super
capacitors using activated carbon have been commercially available
in Japan since early 1980s. However, such studies substantially
presently face technical limitations, while research and
development for oxide electrodes are being continued centering
around the United States and Japan.
[0006] Researches for carbon nanotube composite materials for
electrode materials useful for super capacitors are being actively
executed by advanced countries including the United States and
Japan. These are mostly directed to use of carbon nanotube itself
as an electrode material and/or preparation of carbon nanotube
composite materials. Such a carbon nanotube composite material is
prepared by mixing carbon nanotubes with activated carbon, which is
widely used as an electrode material for a super capacitor, and/or
depositing carbon nanotubes with metal oxides such as RuO.sub.2 or
IrO.sub.2 or conductive polymer such as polyaniline.
[0007] There are presently active efforts to manufacture electrode
materials for an electric double layer type super capacitor using
activated carbon with less cost burden. However, capacitance per
unit weight of an electrode made of carbon nanotube composite
material is still considerably lower than those of existing metal
oxides (700 F/g) and conductive polymer (500 F/g). Accordingly,
there is a strong requirement for development of a novel carbon
nanotube composite material based electrode using activated carbon
with improved capacitance per unit weight thereof.
SUMMARY OF THE INVENTION
[0008] Accordingly, the present invention has been proposed to
solve conventional problems described above and an object of the
present invention is to provide a method for fabrication of porous
carbon fibers, having a great amount of mesopores as a porous
structure readily penetrable by electrolyte.
[0009] Another object of the present invention is to provide use of
the porous carbon fiber fabricated according to the present
invention in manufacturing an electrochemical electrode.
[0010] In order to achieve the above objects of the present
invention, there is provided a method for fabrication of porous
carbon fibers comprising : (a) processing starch to prepare a
gelled starch solution; (b) adding organic acid to the gelled
starch solution to prepare a starch solution; (c) dissolving carbon
nanotubes in a solvent and adding fiber formable polymer thereto to
prepare a carbon nanotube/fiber formable polymer solution; (d)
mixing the starch solution of step (b) with the carbon
nanotube/fiber formable polymer solution of step (c) to prepare a
carbon nanotube/starch/fiber formable polymer solution; (e)
electro-spinning or wet-state spinning the prepared carbon
nanotube/starch/fiber formable polymer solution to produce starch
composite fibers; and (f) oxidation heating the starch composite
fibers, then, executing carbonization and vacuum heat treatment of
the heated fibers, so as to fabricate the porous carbon fibers.
[0011] According the present invention, such fabricated porous
carbon fiber exhibits high specific surface area and excellent
electrochemical properties such as high capacitance. The porous
carbon fiber also contains a great amount of mesopores having an
average diameter ranging from 5 to 10 nm, through which electrolyte
is easily penetrated, thereby being favorably used as an electrode
material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] These and other objects, features, aspects, and advantages
of the present invention will be more fully described in the
following detailed description of preferred embodiments and
examples, taken in conjunction with the accompanying drawings. In
the drawings:
[0013] FIG. 1 is schematic view illustrating an essential concept
for a mesoporous carbon fiber according to the present
invention;
[0014] FIG. 2A is a scanning electron microscopic (SEM) photograph
of starch composite fibers according to the present invention;
[0015] FIG. 2B is an enlarged SEM photograph of one of the starch
composite fibers shown in FIG. 2A;
[0016] FIG. 3 is a SEM photograph of porous carbon fibers having
mesopores with a size of 10 nm;
[0017] FIG. 4 is a graph illustrating discharge current density
depending on applied voltage for a porous carbon fiber having
mesopores with a size of 10 nm;
[0018] FIG. 5A is a SEM photograph of porous carbon fibers coated
with platinum (Pt) nanoparticles; and
[0019] FIG. 5B a graph illustrating EDAX analysis results of the
porous carbon fibers coated with Pt nanoparticles shown in FIG.
5A.
DETAILED DESCRIPTION OF THE INVENTION
[0020] The present invention provides a method for fabricating
porous carbon fibers, which comprises: (a) processing starch to
prepare a gelled starch solution; (b) adding organic acid to the
gelled starch solution to prepare a starch solution; (c) dissolving
carbon nanotubes in a solvent and adding fiber formable polymer
thereto to prepare a carbon nanotube/fiber formable polymer
solution; (d) mixing the starch solution of step (b) with the
carbon nanotube/fiber formable polymer solution of step (c) to
prepare a carbon nanotube/starch/fiber formable polymer solution;
(e) electro-spinning or wet-state spinning the prepared carbon
nanotube/starch/fiber formable polymer solution to produce starch
composite fibers; and (f) oxidation heating the starch composite
fibers, then, executing carbonization and vacuum heat treatment of
the heated fibers, so as to fabricate the porous carbon fibers.
[0021] The porous carbon fiber fabricated as described above is
shown in FIG. 1 which is an essential concept diagram illustrating
the mesoporous carbon fiber of the present invention.
[0022] The processing in step (a) may include heating starch at 100
to 150.degree. C. and then cooling the same to room temperature. It
is known that starch has crystalline and amorphous nanosized
structures alternately laminated to one another.
[0023] Accordingly, in order to fabricate a porous carbon fiber
having mesopores in great amount, starch must undergo gelation
thereof.
[0024] The organic acid in step (b) is at least one selected from a
group consisting of p-toluenesulfonic acid, methanesulfonic acid,
trifluoromethanesulfonic acid, alkylbenzenesulfonic acid and
p-aminobenzenesulfonic acid.
[0025] Such organic acid may be used alone or in combination of two
or more thereof.
[0026] The solvent in step (c) is at least one selected from a
group consisting of water, ethanol, methanol, dichloromethanol,
isopropanol, acetone and hexafluoroisopropanol (HFIP). Such solvent
may be used alone or in combination of two or more thereof.
[0027] The fiber formable polymer in step (c) is at least one
selected from a group consisting of polyvinyl alcohol, polyethylene
oxide, polycarboate, polylactic acid, polyvinylcarbazole,
polymethacrylate, cellulose acetate, collagen, polycaprolactone and
poly(2-hydroxyethyl methacrylate). Such fiber formable polymer may
be used alone or in combination of two or more thereof.
[0028] The fiber formable polymer is preferably added to the
starch, in a ratio of percent (%) by weight of 5:5 to 8:2 for
starch:fiber formable polymer.
[0029] Then, the oxidation heating in step (f) is preferably
executed at 150 to 300.degree. C., while the carbonization may be
conducted at 500 to 1,400.degree. C. under vacuum or an inert gas
atmosphere. Also, the vacuum heat treatment in step (f) may be
conducted at 1,400 to 2,200.degree. C.
[0030] The starch composite fiber obtained through addition of the
organic acid in step (b) has desired resistance to oxidation
heating and vacuum heat treatment and exhibits improved carbonizing
rate owing to carbonization.
[0031] The porous carbon fiber may include mesopores having an
average diameter ranging from 5 to 10 nm in large amount.
[0032] The present invention also provides a felt including the
porous carbon fiber fabricated as described above.
[0033] The present invention provides use of the fabricated porous
carbon fiber in manufacturing an electrode for a super capacitor
having high capacitance.
[0034] The present invention further provides use of the fabricated
porous carbon fiber in manufacturing an electrode for a fuel
cell.
[0035] Hereinafter, preferred embodiments of the present invention
will be described in detail in the following examples which are
given for illustrative purposes only and should not be construed as
limiting the spirit and scope of the invention.
EXAMPLE 1
[0036] Preparation of Starch Composite Fiber
[0037] After dissolving 2 g of starch in 30 ml of water, the
solution was heated and boiled at 100 to 150.degree. C. The heated
starch was cooled to room temperature and stored in an incubator at
a low temperature of 5.degree. C. to prepare a gelled starch
solution. Then, 0.2 mmol of p-toluenesulfonic acid as an organic
acid was added to the gelled starch solution to obtain a starch
solution.
[0038] Next, 0.02 g of carbon nanotubes and 0.02 g of NaDDBS as a
dispersant were introduced to 20 ml of water, followed by
ultrasonic treatment to prepare a homogeneous mixture.
[0039] Since starch has fiber formation resistance, a desired
dispersant such as NaDDBS is required to fabricate starch composite
fibers through the electro-spinning process.
[0040] Afterward, 2 g of polyvinyl alcohol (PVA) as the fiber
formable polymer was further added thereto to obtain a carbon
nanotube/PVA solution.
[0041] Subsequently, the gelled starch solution was mixed with the
above carbon nanotube/PVA solution to prepare a carbon
nanotube/starch/PVA solution. This carbon nanotube/starch/PVA
solution was found to have a viscosity in the range of 300 to 1,500
cP.
[0042] Finally, the resulting carbon nanotube/starch/PVA solution
was charged in a syringe. High voltage (10 to 30 kV) was applied to
the syringe, followed by spinning the same through spinning nozzles
to produce starch composite fibers. A distance between the spinning
nozzle and a spinneret ranges from 15 to 20 cm.
[0043] FIG. 2 shows SEM photographs of starch composite fibers
fabricated as described above, especially, FIG. 2A is a SEM
photograph of the fabricated starch composite fibers while FIG. 2B
is an enlarged SEM photograph of one of the starch composite fibers
shown in FIG. 2A.
EXAMPLE 2
[0044] Fabrication of Porous Carbon Fiber
[0045] The starch composite fibers fabricated in Example 1 were
stabilized by an oxidation heating process at 150 to 300.degree. C.
Then, the treated fibers were carbonized at 500 to 1,400.degree. C.
under vacuum or an inert gas atmosphere to produce porous carbon
fibers.
[0046] Next, the prepared porous carbon fibers were subjected to
vacuum heat treatment at 1,400 to 2,200.degree. C., finally
resulting in porous carbon fibers with an average pore size of 10
nm. The porous carbon fiber product obtained in the above
temperature range was found to have a specific surface area ranging
from 320 to 480 m.sup.2/g.
[0047] FIG. 3 is a SEM photograph of porous carbon fibers having
mesopores with a size of 10 nm.
EXAMPLE 3
[0048] The porous carbon fiber fabricated in Example 2 was cut in a
dimension of 1 cm.times.1 cm and subjected to measurement of
specific capacitance of an electric double layer type super
capacitor. In this regard, the porous carbon fiber itself was an
electrode of the super capacitor and 1 mol of sulfuric acid
solution was used as electrolyte. Charge/discharge voltage ranged
from 0.0 to 0.5V and, as a result of calculating the specific
capacitance by an equation of C=I (.DELTA.V)/(.DELTA.t), the
specific capacitance of the above super capacitor was 170 F/g.
[0049] FIG. 4 is a graph illustrating discharge current density
depending on applied voltage for the porous carbon fiber used
above. It can be seen that the graph has substantially an ideal
rectangular shape.
EXAMPLE 4
[0050] Fabrication of Porous Carbon Fiber Coated with Pt
Nanoparticles
[0051] A felt made of the porous carbon fibers fabricated in
Example 2 was cut in a dimension of 1 cm.times.1 cm and subjected
to sputtering of Pt nanoparticles. As a result, porous carbon
fibers coated with Pt nanoparticles were obtained.
[0052] FIG. 5A is a SEM photograph of porous carbon fibers coated
with Pt nanoparticles, which were fabricated in Example 4, and FIG.
5B illustrates EDAX analysis results of the same. From the EDAX
results shown in FIG. 5B, it can be seen that the surface of the
carbon fiber is coated with Pt nanoparticles.
[0053] Although an electro-spinning process was used in the above
example, it is of course possible to adopt a wet-state spinning
process in place of the electro-spinning process.
[0054] While the present invention has been described with
reference to preferred embodiments, it will be understood by those
skilled in the art that various modifications and variations may be
made therein without departing from the scope of the present
invention as defined by the appended claims.
[0055] As is apparent from the above disclosure, the present
invention provides porous carbon fibers fabricated using fiber
formation resistant starch. Comparing to a conventional technique,
which uses fiber formable polymer such as PAN or pitch based
polymer in fabricating carbon fibers, the porous carbon fibers of
the present invention exhibit excellent electro-chemical properties
including high capacitance, as well as high specific surface
area.
[0056] Briefly, the present invention provides a method for
fabrication of carbon fibers from starch through electro-spinning
or wet-state spinning wherein the starch is an eco-friendly and
economically advantageous natural polymer having fiber formation
resistance. The inventive method may produce porous carbon fibers
containing a great amount of mesopores having an average diameter
of 10 nm by controlling carbonization. Consequently, the porous
carbon fibers fabricated by the present invention may overcome
conventional limitations of existing activated carbon fibers having
micropores of less than 1 nm in large amount, which seldom allow
penetration of electrolyte.
[0057] In addition, the porous carbon fibers of the present
invention may be used in a wide range of applications including,
for example, fuel cell electrodes as well as electrodes for super
capacitors requiring high specific surface area and high electric
conductivity, thereby exhibiting considerably improved industrial
applicability.
* * * * *