Molecular sieve abstract
A method for manufacturing a carbon molecular sieve with increased
microporosity; a method for manufacturing a carbon molecular sieve
with increased microporosity and improved structural regularity;
a carbon molecular sieve with increased microporosity; a carbon
molecular sieve with increased microporosity and improved structural
regularity; a catalyst for a fuel cell using the carbon molecular
sieve; and a fuel cell using the catalyst are provided.
Molecular sieve claims
35. A carbon molecular sieve having mesopores and micropores, in
which the total volume of pores with a size of 80 nm or less is
1.0 cm.sup.3/g or more and the microporosity is 35% or more.
36. The carbon molecular sieve according to claim 35 wherein the
carbon molecular sieve comprises carbon meso-rods and carbon micro-rods,
the carbon micro-rods providing connections between the carbon meso-rods,
and the carbon meso-rods forming an internal structure while in
a state of being supported by the carbon micro-rods.
37. A catalyst for a fuel cell comprising a porous catalyst carrier
and catalytic metals positioned on pores of the catalyst carrier,
the catalyst carrier being a carbon molecular sieve having mesopores
and micropores, in which the total volume of pores with a size of
80 nm or less is 1.0 cm.sup.3/g or more and the microporosity is
35% or more.
38. The catalyst for a fuel cell according to claim 37 wherein
the carbon molecular sieve comprises carbon meso-rods and carbon
micro-rods, the carbon micro-rods providing connections between
the carbon mesorods, and the carbon meso-rods forming an internal
structure while in a state being supported by the carbon micro-rods.
39. A fuel cell using a catalyst comprising a porous catalyst carrier
and catalytic metals positioned on pores of the catalyst carrier,
the catalyst carrier being a carbon molecular sieve having mesopores
and micropores, in which the total volume of pores with a size of
80 nm or less is 1.0 cm.sup.3/g or more and the microporosity is
35% or more.
40. The fuel cell according to claim 39 wherein the carbon molecular
sieve comprises carbon meso-rods and carbon micro-rods, the carbon
micro-rods providing connections between the carbon mesorods, and
the carbon meso-rods forming an internal structure while in a state
of being supported by the carbon micro-rods.
Molecular sieve description
BACKGROUND OF THE INVENTION
[0001] This application claims the priority of Korean Patent Application
No. 2003-9097 filed on Feb. 13 2003 in the Korean Intellectual
Property Office, the disclosure of which is incorporated herein
in its entirety by reference.
[0002] 1. Field of the Invention
[0003] The present invention relates to a molecular sieve and more
particularly, to a carbon molecular sieve. The present invention
also relates to a fuel cell and more particularly, to a catalyst
and a catalyst support for a fuel cell.
[0004] 2. Description of the Related Art
[0005] Originally, the term "molecular sieve" was the
trade name of a synthetic zeolite commercially manufactured by Linde
Ltd. (USA). A molecular sieve has excellent adsorption capacity
due to its many fine pores with uniform diameter. As derived from
its literal meaning, a molecular sieve is used to selectively sieve
molecules.
[0006] Presently, the term "molecular sieve" is an generic
name in the field of science technology and refers to a porous material
in which uniform-sized pores are arranged in a three dimensional
manner.
[0007] A molecular sieve selectively adsorbs a certain size of
molecules due to its uniform pore size. Therefore, a molecular sieve
can be widely used as a catalyst, a catalyst support, or an adsorbent.
[0008] A carbon molecular sieve is mainly made of a carbon material.
A carbon molecular sieve has many advantages, such as excellent
thermal stability, hydrothermal stability, chemical resistance,
and lipophilicity, when compared to a metal oxide based molecular
sieve such as zeolite. A carbon molecular sieve can also be used
for various purposes, such as a catalyst support, an adsorbent,
a sensor, and an electrode material.
[0009] As one example of a method for synthesis of a carbon molecular
sieve, there is disclosed a pyrolysis process of a natural vegetable
material, such as coconut, or a synthetic polymer. According to
this method, however, pore size and porosity can only be limitedly
increased by pyrolysis temperature adjustment and post-treatment
with oxygen.
[0010] Another example of a method for synthesis of a carbon molecular
sieve is disclosed in Korean Patent Application Laid-Open Publication
Nos. 2001-1127 and 2002-84372. According to these methods, a mesoporous
silica molecular sieve is used as a template. A carbohydrate is
subjected to adsorption into the template, polymerization and pyrolysis.
The template is then removed to thereby produce a carbon molecular
sieve with a structural regularity of uniform-sized pores. However,
a disadvantage exists in that a silica molecular sieve used as a
template must be newly designed to adjust the surface area of the
carbon molecular sieve and the volume ratio of its micropores and
mesopores. In addition, it is difficult to control the volume ratio
between micropores and mesopores.
[0011] Fuel cells are clean energy sources capable of reducing
dependence on fossil energy, with a high output density and high
energy conversion efficiency. In addition, fuel cells can be operated
at room temperature and can be miniaturized and packed. Therefore,
fuel cells can be widely used in the fields of zero emission vehicles,
domestic power systems, mobile communication equipment, medical
instruments, military equipment, aerospace equipment, and portable
electronic devices. A polymer electrolyte membrane fuel cell (PEMFC)
and a direct methanol fuel cell (DMFC) are electric power generating
systems that allow electrochemical reaction of hydrogen or methanol,
water, and oxygen to produce direct current electricity. These fuel
cells comprise an anode and a cathode which receive a liquid/gaseous
reactant and a proton conducting membrane interposed between the
two electrodes. At the anode, an anode catalyst dissociates hydrogen
or methanol to generate protons. The generated protons are transported
through the proton conducting membrane to the cathode. At the cathode,
the protons react with oxygen by the cathode catalyst. Therefore,
in such structured fuel cells, the role of a catalyst is very important.
Currently, in a PEMFC, platinum (Pt) particles supported on a carbon
support are used as both anode and cathode catalysts. In DMFCs,
platinum-ruthenium (Pt--Ru) black is used as an anode catalyst and
Pt particles by themselves or Pt particles supported on a carbon
support are used as a cathode catalyst. Because metal black by themselves
provide excellent catalytic activity, a supported metal catalyst
system is rarely used in a DMFC. However, because a large portion
of costs incurred in a DMFC is caused by a catalyst, in considering
cost effectiveness, the amount of a used catalyst needs to be decreased.
Therefore, many efforts have been made to research a carbon support
capable of providing improved catalyst activity and dispersion over
a currently used carbon support with no structural regularity, in
order to reduce the catalyst amount used in an anode and a cathode.
SUMMARY OF THE INVENTION
[0012] The present invention provides a method for manufacturing
a carbon molecular sieve with increased microporosity.
[0013] The present invention also provides a method for manufacturing
a carbon molecular sieve with increased microporosity and improved
structural regularity.
[0014] The present invention also provides a carbon molecular sieve
with increased microporosity.
[0015] The present invention also provides a carbon molecular sieve
with increased microporosity and improved structural regularity.
[0016] The present invention also provides a catalyst for a fuel
cell containing the aforementioned carbon molecular sieve.
[0017] The present invention also provides a fuel cell employing
the aforementioned catalyst.
[0018] According to an aspect of the present invention, there is
provided a method for manufacturing a carbon molecular sieve, comprising
the steps of (a) impregnating pores of a mesoporous silica molecular
sieve, used as a template, with a mixture of a silica oligomer,
a condensable or polymerizable carbon-containing compound, used
as a carbon precursor, and a liquid carrier; (b) polymerizing the
carbon precursor to form a carbon precursor polymer within the pores
of the template; (c) carbonizing the carbon precursor polymer using
pyrolysis; and (d) removing the template and the silica oligomer
using a solution capable of dissolving silica selectively.
[0019] According to another aspect of the present invention, there
is provided a method for manufacturing a carbon molecular sieve,
comprising the steps of (a) impregnating micropores of an ordered
mesoporous silica molecular sieve, used as a template, having the
mesopores and the micropores that are responsible for the connections
between the mesopores, with a first mixture comprising a condensable
or polymerizable carbon-containing compound, used as a carbon precursor,
and a liquid carrier; (b) polymerizing the carbon precursor within
the micropores of the template to form a carbon precursor polymer
within the micropores of the template; (c) impregnating the mesopores
of the template with a second mixture comprising a silica oligomer,
a condensable or polymerizable carbon-containing compound, used
as a carbon precursor, and a liquid carrier; (d) polymerizing the
carbon precursor within the mesopores of the template to form a
carbon precursor polymer within the mesopores of the template; (e)
carbonizing the carbon precursor polymers within the template using
pyrolysis; and (f) removing the template and the silica oligomer
using a solution capable of dissolving silica selectively.
[0020] According to another aspect of the present invention, there
is provided a carbon molecular sieve having mesopores and micropores.
The total volume of pores, with a size of 80 nm or less, is 1.0
cm.sup.3/g or more and microporosity is 35% or more.
[0021] According to another aspect of the present invention, there
is provided a catalyst for a fuel cell comprising a porous catalyst
support and catalytic metals dispersed on the catalyst support,
wherein the catalyst support is the aforementioned carbon molecular
sieve.
[0022] According to yet another aspect of the present invention,
there is provided a fuel cell using the aforementioned catalyst.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The above and other features and advantages of the present
invention will become more apparent by describing in detail exemplary
embodiments thereof with reference to the attached drawings in which:
[0024] FIG. 1A is an X-ray diffraction (XRD) pattern of a carbon
molecular sieve according to an embodiment of the present invention;
[0025] FIG. 1B is a nitrogen adsorption-desorption curve of a carbon
molecular sieve according to an embodiment of the present invention;
[0026] FIG. 2A is an XRD pattern of a carbon molecular sieve according
to another embodiment of the present invention; and
[0027] FIG. 2B is a nitrogen adsorption-desorption curve of a carbon
molecular sieve according to another embodiment of the present invention;
DETAILED DESCRIPTION OF THE INVENTION
[0028] A method for manufacturing a carbon molecular sieve according
to a first aspect of the present invention comprises the steps of
(a) impregnating pores of a mesoporous silica molecular sieve, used
as a template, with a mixture of a silica oligomer, a condensable
or polymerizable carbon-containing compound, used as a carbon precursor,
and a liquid carrier; (b) polymerizing the carbon precursor to form
a carbon precursor polymer within the pores of the template; (c)
carbonizing the carbon precursor polymer using pyrolysis; and (d)
removing the template and the silica oligomer using a solution capable
of dissolving silica selectively.
[0029] In this method, when the mixture containing the silica oligomer
and the carbon precursor undergoes polymerization and pyrolysis,
the mesopores of the template are filled with solid carbon that
includes the silica oligomer. In step (d), the template and the
silica oligomer are removed altogether. Removing the silica oligomer
creates micropores. In addition to the micropores created by removing
the silica oligomer, many other micropores are present in the solid.
The microporosity and micropore size of a carbon molecular sieve
can be adjusted by controlling the particle size and content of
the silica oligomer.
[0030] As used herein, the term "mesopore" refers to
a pore with a size of about 1 to about 80 nm and the term "micropore"
refers to a pore with a size of about 1 nm or less.
[0031] Hereinafter, the method for manufacturing a carbon molecular
sieve according to a first aspect of the present invention will
be described in more detail.
[0032] Examples of the mesoporous silica molecular sieve used as
a template include a cubic MCM-48 (Ia3d), another cubic SBA-1 (Pn3m),
SBA-16 (Im3m), KIT-1 or MSU-1 having a three-dimensional disordered
pore network, and SBA-15 of which one-dimensional mesopores are
interconnected through micropores.
[0033] MCM-48 may be prepared using a method introduced by Kim
et al. [Chem. Commun., 1998 259]. SBA-1 may be prepared using a
method introduced by Kim and Ryoo [Chem. Mater., 1999 11 487].
SBA-15 and SBA-16 may be prepared using a method introduced by Kim
and Stucky [Chem. Commun., 2000 1159].
[0034] The silica oligomer may be obtained by hydrolysis of tetraalkylorthosilicate.
More particulary, the silica oligomer may be prepared by reacting
tetraethylorthosilicate (TEOS) with an aqueous solution of hydrochloric
acid. There are no particular limitations to an average particle
size of the silica oligomer. The silica oligomer can have different
average particle sizes depending on the degree of polymerization.
After the removal of the silica oligomer, micropores with the same
size as the average particle size of the silica oligomer are formed
on the carbon molecular sieve. For example, a silica oligomer with
an average particle size of about 0.5 to about 5 nm may be used.
In this case, a carbon molecular sieve having the increased porosity
of pores with a size of about 0.5 to 5 nm can be obtained. In order
to increase the porosity of micropores with a size of about 1 nm
or less on a carbon molecular sieve, it is preferable to limit the
average particle size of the silica oligomer to about 1 nm or less.
[0035] The carbon precursor is a condensable or polymerizable carbon-containing
compound. Examples of the carbon precursor include a carbohydrate
and a monomer.
[0036] A carbohydrate is classified into monosaccharide, oligosaccharide,
and polysaccharide. Preferably, monosaccharide, oligosaccharide,
or a mixture thereof is used. Representative examples of monosaccharide
include glucose, fructose, mannose, galactose, ribose, and xylose.
They may be used alone or in combination. Oligosaccharide contains
two or more monosaccharide units joined by a glycoside bond. The
term, "oligosaccharide" is a general name that can describe
disaccharide through decasaccharide. Oligosaccharide may be classified
into a simple oligosaccharide containing the same monosaccharides
and a complex oligosaccharide containing two or more different monosaccharides.
Oligosaccharides which exist in the free state in nature are mainly
disaccharides. Exemplary disaccharides are sucrose, which is contained
in sugar canes; maltose, which is a product obtained by amylase
hydrolysis of starch and is a raw material of wheat-gluten; and
lactose, which is found in mammal's milk.
[0037] A reducing group and a hydroxyl group on a carbohydrate
or a hydroxyl group on a compound except for a carbohydrate may
undergo a dehydrocondensation process.
[0038] A representative example of the monomer used as the carbon
precursor is furfuryl alcohol.
[0039] The liquid carrier acts as a dispersing medium for the silica
oligomer, a solvent for dissolving the carbon precursor, and a transport
medium for transporting the carbon precursor and the silica oligomer
into the pores of the template. The liquid carrier may be selected
from water, an organic solvent, and a mixture thereof. Preferably,
the organic solvent is alcohols. More preferably, the alcohol is
ethanol. Furfuryl alcohol may be used as both the carbon precursor
and the liquid carrier. Furfuryl alcohol used as the carbon precursor,
may act as the liquid carrier by itself.
[0040] The mixture may further comprise an acid. The acid catalyzes
the condensation or polymerization of the carbon precursor. The
acid may be selected from sulfuric acid, hydrochloric acid, nitric
acid, sulfonic acid, a derivative thereof, and a mixture thereof.
Representative sulfonic acid is methylsulfonic acid.
[0041] There are no particular limitations to the content of each
component in the mixture, as long as the objects of the present
invention are accomplished. However, it is preferable that the content
of each component in the mixture is as follows.
[0042] If the content of the silica oligomer is too low, microporosity
is slightly increased. On the other hand, if it is too high, the
structure of the resultant carbon molecular sieve may be destroyed.
Therefore, it is preferable that the content of the silica oligomer
is within a range of about 1 to about 40 parts by weight based on
100 parts by weight of the carbon precursor.
[0043] If the content of the liquid carrier is too low, it is difficult
to impregnate the template with the mixture. On the other hand,
if it is too high, the filling density of carbonaceous components
in the template may be significantly reduced. For this reason, disadvantageously,
steps (a) and (b) must be overly repeated. Therefore, it is preferable
that the content of the carrier is within a range of about 300 to
about 1000 parts by weight based on 100 parts by weight of the
carbon precursor.
[0044] If the content of the acid is too low, the facilitation
effect of the condensation or polymerization of the carbon precursor
by the acid addition may be slight. On the other hand, because the
facilitation effect is not continuously increased in proportion
to the added amount of the acid, excess addition of the acid is
also not preferable. Therefore, it is preferable that the content
of the acid is within a range of about 1 to about 30 parts by weight
based on 100 parts by weight of the carbon precursor.
[0045] In step (a), the pores of the template, i.e., the pores
of the mesoporous silica molecular sieve are filled with the mixture
of the silica oligomer, the condensable or polymerizable carbon-containing
compound used as a carbon precursor, and the liquid carrier. Various
impregnation processes may be used. For example, the mixture and
the template can be simply mixed to initiate a contact with each
other. Consequently, through such contact, the template is impregnated
with the mixture.
[0046] In step (b), the carbon precursor, filled in the template,
undergoes polymerization. After the polymerization, the carbon precursor
polymer is formed within the pores of the template. The polymerization
of the carbon precursor may be accomplished by heating. If the heating
temperature is too low, the polymerization is slightly carried out.
While, if it is too high, the uniformity of the obtained carbon
molecular sieve may be decreased. Therefore, it is preferable that
the heating temperature for the polymerization is within a range
of about 50 to about 250.degree. C. The heating may be divided into
two steps, i.e., first heating and second heating. For example,
the first heating may be carried out at a temperature range of about
50 to about 150.degree. C. and the second heating at a temperature
range of about 150 to about 250.degree. C. During the heating, the
carbon precursor undergoes polymerization. At the same time, the
liquid carrier may be dried.
[0047] In step (c), the carbon precursor polymer within the pores
of the template is carbonized by pyrolysis. For this, the template
containing the carbon precursor polymer may be subjected to heating
at about 400 to about 1400.degree. C. under a non-oxidizing atmosphere.
The non-oxidizing atmosphere may be selected from a vacuum atmosphere,
a nitrogen atmosphere, and an inert gas atmosphere. During the carbonizing
process, the liquid carrier and/or acid are removed by evaporation
or decomposition.
[0048] In step (d), the template and the silica oligomer are removed
using a solution capable of dissolving silica. Examples of the solution
include an aqueous fluoric acid solution and an aqueous sodium hydroxide
solution. The silica is converted to soluble silicate by alkaline
melting or carbonate fusion, or the silica reacts with fluoric acid
(HF) to form very erosive SiF.sub.4. According to the type of the
silica molecular sieve used as the template, the template and the
silica oligomer may be treated several times with the silica dissolving
solution, or may be treated with a silica dissolving solution which
further comprises ethanol. When the template is removed, a carbon
molecular sieve is obtained. Furthermore, the silica oligomer contained
in the carbon molecular sieve is also removed, thus the microporosity
of the carbon molecular sieve is increased.
[0049] Before step (c), steps (a) and (b) may be repeated once
or more. Thus, a larger amount of the carbon precursor polymers
may be formed in the pores of the template.
[0050] Hereinafter, the method for manufacturing a carbon molecular
sieve according to a second aspect of the present invention will
be described.
[0051] The method for manufacturing a carbon molecular sieve according
to the second aspect of the present invention comprises the steps
of (a) impregnating micropores of an ordered mesoporous silica molecular
sieve, used as a template, having the mesopores and the micropores
that provide the connections between the mesopores, with a first
mixture of a condensable or polymerizable carbon-containing compound,
used as a carbon precursor, and a liquid carrier; (b) polymerizing
the carbon precursor within the micropores of the template to form
a carbon precursor polymer within the micropores of the template;
(c) impregnating the mesopores of the template with a second mixture
of a silica oligomer, a condensable or polymerizable carbon-containing
compound, used as a carbon precursor, and a liquid carrier; (d)
polymerizing the carbon precursor within the mesopores of the template
to form a carbon precursor polymer within the mesopores of the template;
(e) carbonizing the carbon precursor polymers within the template
using pyrolysis; and (f) removing the template and the silica oligomer
using a solution capable of dissolving silica selectively.
[0052] This method is characterized in that an ordered mesoporous
silica molecular sieve having mesopores and micropores in which
the micropores provide connections between the mesopores, is used
as a template and the micropores and mesopores of the template are
filled with different mixtures. That is, the silica oligomer is
contained in the mesopores but not in the micropores of the template.
[0053] A carbon molecular sieve manufactured according to the second
aspect of the present invention comprises carbon meso-rods and carbon
micro-rods. The carbon micro-rods provide connections between the
carbon meso-rods. Each carbon meso-rod has a diameter corresponding
to the size of each mesopore of the template and each carbon micro-rod
has a diameter corresponding to the size of each micropore of the
template. Due to the absence of the silica oligomer, the microporous
carbon rods have strength sufficient to maintain the structural
regularity of the carbon molecular sieve. On the other hand, the
carbon meso-rods have increased microporosity due to the spaces
created by the removal of the silica oligomer.
[0054] According to the second aspect of the present invention,
the ordered mesoporous silica molecular sieve having mesopores and
micropores in which the micropores provide connections between the
mesopores is used as a template. Illustrative examples are SBA-15
and SBA-16.
[0055] An average particle size of the silica oligomer may be about
0.5 to about 5 nm. Accordingly, an obtained carbon molecular sieve
contains mesoporous carbon rods with the increased ratio of pores
with a size of about 0.5 to about 5 nm. In order to increase micropores
with a size of about 1 nm or less in a carbon molecular sieve, it
is preferable that the average particle size of the silica oligomer
is about 1 nm or less.
[0056] The carbon precursors and carriers, as used in the first
and the second mixtures, may be the same as mentioned above.
[0057] The first and the second mixtures may further comprise an
acid. The acid may be selected from sulfuric acid, hydrochloric
acid, nitric acid, sulfonic acid, a derivative thereof, and a mixture
thereof.
[0058] There are no particular limitations to the content of each
component in the first mixture provided that each component can
accomplish the objects of the present invention. However, it is
preferable that the content of each component in the first mixture
is as follows.
[0059] If the content of the liquid carrier in the first mixture
is too low, it is difficult to impregnate the template with the
first mixture. On the other hand, if it is too high, the filling
density of carbonaceous components in the template may be significantly
reduced, and thus disadvantageously, impregnating and polymerizing
must be repeated several times. Therefore, it is preferable that
the content of the carrier in the first mixture is within a range
of about 300 to about 1000 parts by weight based on 100 parts by
weight of the carbon precursor in the first mixture.
[0060] If the content of the acid in the first mixture is too low,
the facilitation effect of the condensation or polymerization of
the carbon precursor by the acid addition may be slight. On the
other hand, because the facilitation effect is not continuously
increased in proportion to the added amount of the acid, excess
addition of the acid is also not preferable. Therefore, it is preferable
that the content of the acid in the first mixture is within a range
of about 1 to about 30 parts by weight based on 100 parts by weight
of the carbon precursor in the first mixture.
[0061] There are no particular limitations to the content of each
component in the second mixture as long as the objects of the present
invention are accomplished. However, it is preferable that the content
of each component in the second mixture is as follows.
[0062] If the content of the silica oligomer in the second mixture
is too low, microporosity is barely increased. On the other hand,
if it is too high, the structure of the obtained carbon molecular
sieve may be destroyed. Therefore, it is preferable that the content
of the silica oligomer in the second mixture is within a range of
about 1 to about 40 parts by weight based on 100 parts by weight
of the carbon precursor in the second mixture.
[0063] If the content of the liquid carrier in the second mixture
is too low, it is difficult to impregnate the template with the
second mixture. On the other hand, if it is too high, the filling
density of carbonaceous components in the template may be significantly
reduced, thus disadvantageously, impregnating and polymerizing must
be repeated several times. Therefore, it is preferable that the
content of the carrier in the second mixture is within a range of
about 300 to about 1000 parts by weight based on 100 parts by weight
of the carbon precursor in the second mixture.
[0064] If the content of the acid in the second mixture is too
low, the facilitation effect of the condensation or polymerization
of the carbon precursor by the acid addition may be slight. On the
other hand, because the facilitation effect is not continuously
increased in proportion to the added amount of the acid, excess
addition of the acid is also not preferable. Therefore, it is preferable
that the content of the acid in the second mixture is within a range
of about 1 to about 30 parts by weight based on 100 parts by weight
of the carbon precursor in the second mixture.
[0065] In step (a), the micropores of the template are filled with
the first mixture. Various impregnation processes may be used. For
example, the first mixture and the template can be simply mixed
to initiate a contact with each other. Through a capillary phenomenon
caused by such contact, the template is impregnated with the first
mixture. In order to selectively fill the micropores of the template
with the first mixture, it is preferable to allow the volume of
the first mixture to approximate to that of the micropores of the
template. For example, the content of the carbon precursor in the
first mixture may be about 10 to about 50 parts by weight based
on 100 parts by weight of the carbon precursor in the second mixture.
[0066] In step (b), the first mixture-containing template may be
heated at a temperature range of about 50 to about 250.degree. C.
The heating may comprise (b-1) first heating the first mixture-containing
template at a temperature range of 50 to 150.degree. C. and (b-2)
second heating the previously heated template at a temperature range
of 150 to 250.degree. C.
[0067] In step (d), the second mixture-containing template may
be heated at a temperature range of about 50 to about 250.degree.
C. The heating may comprise (d-1) first heating the second mixture-containing
template at a temperature range of 50 to 150.degree. C. and (d-2)
second heating the previously heated template at a temperature range
of 150 to 250.degree. C.
[0068] In step (e), the template containing the carbon precursor
polymer may be subjected to heating at about 400 to about 1400.degree.
C. under a non-oxidizing atmosphere. The non-oxidizing atmosphere
may be selected from a vacuum atmosphere, a nitrogen atmosphere,
and an inert gas atmosphere.
[0069] The silica dissolving solution in step (f) may be an aqueous
fluoric acid or an aqueous sodium hydroxide solution.
[0070] Before step (e), steps (c) and (d) may be repeated once
or more.
[0071] Other detailed descriptions of the second aspect of the
present invention are as described in the first aspect of the present
invention.
[0072] As used herein, the term "microporosity" refers
to the volume percentage of micropores with a size of 1 nm or less
to the total volume of pores with a size of 80 nm or less. In carbon
molecular sieves which are manufactured according to the embodiments
of the present invention and comprise mesopores and micropores,
the total volume of pores with a size of 80 nm or less is about
1.0 cm.sup.3 /g or more, and the microporosity is about 35% or more.
[0073] The method according to the second aspect of the present
invention provides an ordered carbon molecular sieve containing
carbon meso-rods and carbon micro-rods. The carbon micro-rods provide
connections between the carbon meso-rods. The carbon meso-rods have
a diameter corresponding to the size of the mesopores of the template.
The carbon micro-rods have a diameter corresponding to the size
of the micropores of the template. The carbon meso-rods form the
internal structure of the carbon molecular sieve while in a state
of being supported by the carbon micro-rods. The spaces between
the carbon meso-rods provide substantially uniform sized mesopores.
The carbon meso-rods have increased microporosity due to the removal
of the silica oligomer.
[0074] The carbon molecular sieve of the present invention may
be used for various purposes, including a catalyst carrier, an adsorbent,
a sensor, and an electrode material.
[0075] A carbon molecular sieve of the present invention may be
used in a catalyst for a fuel cell. Generally, a catalyst for a
fuel cell may comprise a porous catalyst support and catalytic metals
positioned on pores of the catalyst carrier. According to the present
invention, a catalyst for a fuel cell uses the aforementioned carbon
molecular sieve as the catalyst support. The catalytic metals may
be titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron
(Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), aluminum
(Al), molybdenum (Mo), selenium (Se), tin (Sn), platinum (Pt), ruthenium
(Ru), palladium (Pd), tungsten (W), iridium (Ir), osmium (Os), rhodium
(Rh), niobium (Nb), tantalum (Ta), lead (Pb), or a mixture thereof.
The catalyst for a fuel cell of the present invention may be prepared,
for example, using a method comprising impregnating a porous catalyst
support with a catalytic metal precursor solution and reducing the
catalytic metal precursor. Such a method is disclosed in various
documents and thus the detailed description thereof is omitted.
[0076] The catalyst of the present invention may be used in, for
example, a phosphoric acid fuel cell, a polymer electrolyte membrane
fuel cell, and a direct methanol fuel cell. There are no particular
limitations to the structures and the preparation methods of these
fuel cells. Illustrative examples are disclosed in various documents
and thus the detailed descriptions thereof are omitted.
[0077] Hereinafter, the present invention will be described in
more detail with reference to examples but is not limited thereto.
EXAMPLE 1
First Aspect of the Present Invention
[0078] 0.94 g of sucrose, 3.75 g of distilled water, and 0.11 g
of a 97% by weight aqueous solution of sulfuric acid were mixed
to prepare a solution A. 0.63 g of TEOS, 0.63 g of ethanol, and
0.21 g of a 10.sup.-3 M aqueous solution of hydrochloric acid were
mixed and stirred at 40.degree. C. for one hour to prepare a solution
B containing a silica oligomer.
[0079] 1.0 g of calcined SBA-15A was impregnated with a mixture
of the solution A and the solution B.
[0080] The SBA-15 so impregnated was dried at 100.degree. C. for
6 hours and again heated at 160.degree. C. for 6 hours. The heated
SBA-15 was once again subjected to the above processes except that
the amount of each of the solution A and the solution B was reduced
to 60%.
[0081] The obtained SBA-15 was heated at 900.degree. C. under a
nitrogen atmosphere for two hours.
[0082] Then, the SBA-15 was added into a mixed HF-H.sub.2O-EtOH
solution (10% by weight of HF, 10% by weight of H.sub.2O, 80% by
weight of EtOH) and stirred at room temperature for two hours. The
resultant was filtered and washed with deionized secondary distilled
water five times. The stirring, filtering, and washing were repeated
twice. The carbon molecular sieve that was finally obtained, was
dried at 100.degree. C. for 12 hours.
[0083] An X-ray diffraction (XRD) pattern and a nitrogen adsorption-desorption
curve of the carbon molecular sieve of Example 1 are shown in FIG.
1A and FIG. 1B, respectively. In addition, the porosity of the carbon
molecular sieve of Example 1 was measured and the result is presented
in Table 1.
1TABLE 1 Total pore Mesopore Micropore Surface volume volume volume
area (<80 nm) (1-80 nm) (<1 nm) Micro- Sample (m.sup.2/g)
(cm.sup.3/g) (cm.sup.3/g) (cm.sup.3/g) porosity CMK-3 1480 1.44
0.99 0.45 0.31 Example 1 1950 1.67 1.05 0.62 0.37 Increased effect
32% 16% 6% 38% 20%
[0084] The result of porosity of CMK-3 a carbon molecular sieve
of Korean Patent Application Laid-Open Publication No. 2002-84372
is also presented in Table 1. CMK-3 is a carbon molecular sieve
using sucrose as a carbon precursor and SBA-15 as a template. A
silica oligomer was not used in CMK-3 manufacturing as disclosed
in the cited reference.
[0085] A surface area, a total volume of pores with a size of 80
nm or less, a volume of mesopores with a size of 1 to 80 nm , a
volume of micropores with a size of 1 nm or less, and a microporosity,
i.e., the ratio of the micropore volume to the total pore volume,
of each carbon molecular sieve are listed in Table 1.
[0086] In the carbon molecular sieve of Example 1 a surface area
was increased by about 32%, a total pore volume by about 16%, a
mesopore volume by about 6%, a micropore volume by about 38%, and
microporsosity by about 20%, when compared to CMK-3.
[0087] It can be seen from the results that the use of a silica
oligomer can increase the porosity or microporosity of the carbon
molecular sieve, and the microporosity of the carbon molecular sieve
can be adjusted by controlling the amount or size of a silica oligomer.
EXAMPLE 2
Second Embodiment of the Present Invention
[0088] 1.0 g of calcined SBA-15 was impregnated with a first mixture
of 0.125 g of sucrose, 0.014 g of a 97% by weight aqueous solution
of sulfuric acid, and 0.5 g of distilled water.
[0089] The impregnated SBA-15 was dried at 100.degree. C. for 6
hours and then again heated at 160.degree. C. for 6 hours.
[0090] 1.25 g of sucrose, 0.14 g of a 97% by weight aqueous solution
of sulfuric acid, and 5.0 g of distilled water were mixed to prepare
a solution A. 0.75 g of TEOS, 0.25 g of a 10.sup.-3 M aqueous solution
of HCl, and 0.75 g of ethanol were mixed and stirred at 40.degree.
C. for one hour to prepare a solution B containing a silica oligomer.
[0091] The solution A and the solution B were mixed to prepare
a second mixture. The heated SBA-15 was impregnated with the second
mixture.
[0092] Then, the SBA-15 was dried at 100.degree. C. for 6 hours
and again heated at 160.degree. C. for 6 hours. The heated SBA-15
was again impregnated with the second mixture and again underwent
drying and heating.
[0093] The resultant SBA-15 was heated at 900.degree. C. under
a nitrogen atmosphere for two hours.
[0094] Thus treated SBA-15 was added into a mixed HF-H.sub.2O-EtOH
solution (10% by weight of HF, 10% by weight of H.sub.2O, 80% by
weight of EtOH) and stirred at room temperature for two hours. The
resultant was filtered and washed with secondary distilled water
three to five times. The stirring, filtering, and washing were repeated
twice. The finally obtained carbon molecular sieve was dried at
100.degree. C. for 12 hours.
[0095] An XRD pattern and a nitrogen adsorption-desorption curve
of the carbon molecular sieve of Example 2 are shown in FIG. 2A
and FIG. 2B, respectively. In addition, the porosity of the carbon
molecular sieve of Example 2 was measured and the result is presented
in Table 2.
2TABLE 2 Total pore Mesopore Micropore Surface volume volume volume
area (<80 nm) (1-80 nm) (<1 nm) Micro- Sample (m.sup.2/g)
(cm.sup.3/g) (cm.sup.3/g) (cm.sup.3/g) porosity CMK-3 1480 1.44
0.99 0.45 0.31 Example 2 1513 1.56 1.00 0.56 0.36 Increased effect
2% 8% 1% 24% 20%
[0096] As shown in Table 2 in the carbon molecular sieve of Example
2 a surface area was increased by about 2%, a total pore volume
by about 8%, a mesopore volume by about 1%, a micropore-volume by
about 24%, and microporsosity by about 20%, when compared to CMK-3.
These results again demonstrate that use of a silica oligomer can
increase the porosity or microporosity of the carbon molecular sieve.
[0097] Referring to FIG. 2A, a peak was observed at about 2 degrees.
This indicates that carbon meso-rods for the carbon molecular sieve
of Example 2 are regularly arranged.
[0098] Accordingly, the carbon molecular sieve, manufactured according
to the second aspect of the present invention, has increased microporosity
and maintains the strength of carbon micro-rods sufficient to provide
connection between carbon meso-rods.
EXAMPLE 3
Catalyst for Fuel Cell
[0099] 1 g of the carbon molecular sieve of Example 2 was put into
a plastic envelope. Then, a solution of 1.099 g of H.sub.2PtCl.sub.6
in 1 ml of acetone was added to the plastic envelope and mixed for
5 to 10 minutes. The resultant mixture was dried in the air for
four hours. The dried carbon carrier was transferred to a crucible
and again dried at 60.degree. C. The crucible was placed in an electric
furnace and a nitrogen gas was fed into the furnace for 10 minutes.
The nitrogen gas was then replaced with a hydrogen gas and then
catalyst reduction was carried out at 200.degree. C. After the hydrogen
gas was again replaced with a nitrogen gas, the temperature of the
furnace was raised to 250.degree. C. for 10 minutes, maintained
at that temperature for two hours, and cooled to room temperature.
[0100] A slurry containing the Pt/C catalyst thus prepared, a commercially
available ionomer, and isopropyl alcohol (IPA) was coated on a carbon
paper using a spray method so that the loading of Pt reached 3 mg/cm.sup.2
and then heated to prepare a cathode. As for an anode, a commercially
available Pt--Ru alloy catalyst was used and an amount of a supported
catalyst was 8 mg/cm.sup.2. Nafion 115 (Dupont) was used as an electrolyte
membrane. A 2 M solution of aqueous methanol and air were fed into
the unit cell so prepared and the performance of the cell was measured.
[0101] COMPARATIVE EXAMPLE 1
Use of Carbon Black
[0102] A unit cell was prepared in the same manner as in Example
3 except that for preparation of a cathode, a Pt/C catalyst (E-TEK)
containing activated carbon powder as a catalyst carrier, instead
of a carbon molecular sieve, was used and the loading of platinum
supported catalyst was 3 mg/cm.sup.2. The performance of the unit
cell was measured in the same manner as in Example 3.
[0103] A current density of each fuel cell of Example 3 and Comparative
example 1 was measured at a cell voltage of 0.3 V. According to
the results, a fuel cell of Example 3 exhibited a current density
of 112 mA/cm.sup.2 whereas a fuel cell of Comparative example 1
exhibited a current density of 85 mA/cm.sup.2. It can be seen from
the results that a carbon molecular sieve of the present invention
has improved catalytic activity, when compared to a conventional
activated carbon powder.
[0104] As apparent from the above description, a carbon molecular
sieve manufactured according to the first aspect of the present
invention has increased surface area and/or microporosity.
[0105] A carbon molecular sieve manufactured according to the second
aspect of the present invention has increased surface area and/or
microporosity, while simultaneously maintaining the structural regularity.
[0106] The carbon molecular sieve of the present invention can
be more effectively used as a catalyst carrier that supports catalytic
metals because of the increased surface area and/or microporosity.
[0107] A catalyst using the carbon molecular sieve of the present
invention as a catalyst carrier and a fuel cell using the catalyst
exhibit enhanced catalytic activity and efficiency, when compared
to using a conventional activated carbon powder as a catalyst carrier.
[0108] While the present invention has been particularly shown
and described with reference to exemplary embodiments thereof, it
will be understood by those of ordinary skill in the art that various
changes in form and details may be made therein without departing
from the spirit and scope of the present invention as defined by
the following claims. |