U.S. patent number RE46,771 [Application Number 15/164,567] was granted by the patent office on 2018-04-03 for porous substrates filled with nanomaterials.
This patent grant is currently assigned to Lawrence Livermore National Security, LLC. The grantee listed for this patent is Lawrence Livermore National Security, LLC. Invention is credited to Theodore F. Baumann, Joe H. Satcher, Jr., Michael Stadermann, Marcus A. Worsley.
United States Patent |
RE46,771 |
Worsley , et al. |
April 3, 2018 |
Porous substrates filled with nanomaterials
Abstract
A composition comprising: at least one porous carbon monolith,
such as a carbon aerogel, comprising internal pores, and at least
one nanomaterial, such as carbon nanotubes, disposed uniformly
throughout the internal pores. The nanomaterial can be disposed in
the middle of the monolith. In addition, a method for making a
monolithic solid with both high surface area and good bulk
electrical conductivity is provided. A porous substrate having a
thickness of 100 microns or more and comprising macropores
throughout its thickness is prepared. At least one catalyst is
deposited inside the porous substrate. Subsequently, chemical vapor
deposition is used to uniformly deposit a nanomaterial in the
macropores throughout the thickness of the porous substrate.
Applications include electrical energy storage, such as batteries
and capacitors, and hydrogen storage.
Inventors: |
Worsley; Marcus A. (Hayward,
CA), Baumann; Theodore F. (Discovery Bay, CA), Satcher,
Jr.; Joe H. (Patterson, CA), Stadermann; Michael
(Pleasanton, CA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Lawrence Livermore National Security, LLC |
Livermore |
CA |
US |
|
|
Assignee: |
Lawrence Livermore National
Security, LLC (Livermore, CA)
|
Family
ID: |
45527295 |
Appl.
No.: |
15/164,567 |
Filed: |
May 25, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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61369972 |
Aug 2, 2010 |
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61473537 |
Apr 8, 2011 |
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61473654 |
Apr 8, 2011 |
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Reissue of: |
13195752 |
Aug 1, 2011 |
8809230 |
Aug 19, 2014 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01J
21/18 (20130101); B01J 21/18 (20130101); C01B
33/02 (20130101); H01B 1/04 (20130101); B82Y
30/00 (20130101); C01B 32/00 (20170801); C01B
32/162 (20170801); B01J 23/755 (20130101); C01B
33/027 (20130101); B01J 21/185 (20130101); B01J
35/1028 (20130101); B01J 37/0201 (20130101); B82Y
40/00 (20130101); C01B 33/02 (20130101); B01J
23/755 (20130101); B82Y 40/00 (20130101); B01J
21/185 (20130101); C01B 33/027 (20130101); H01B
1/04 (20130101); B82Y 30/00 (20130101); B01J
37/0201 (20130101); B01J 35/1028 (20130101); C01B
32/05 (20170801); C01B 2202/06 (20130101); C01B
2202/06 (20130101) |
Current International
Class: |
H01B
1/18 (20060101); C01B 33/027 (20060101); C01B
33/02 (20060101); B01J 37/02 (20060101); B01J
35/10 (20060101); B01J 23/755 (20060101); B01J
21/18 (20060101); H01B 1/04 (20060101); B82Y
30/00 (20110101); B82Y 40/00 (20110101) |
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|
Primary Examiner: Vincent; Sean E
Attorney, Agent or Firm: Foley & Lardner, LLP
Government Interests
FEDERAL FUNDING STATEMENT
The United States Government has rights in this invention pursuant
to Contract No. DE-AC52-07NA27344 between the United States
Department of Energy and Lawrence Livermore National Security, LLC
for the operation of Lawrence Livermore National Laboratory.
Parent Case Text
RELATED APPLICATIONS
This application .Iadd.is a Reissue Application of U.S. Pat. No.
8,809,230 (previously U.S. application Ser. No. 13/195,752), filed
Aug. 1, 2011, which .Iaddend.claims priority to U.S. provisional
applications U.S. Ser. Nos. 61/369,972 filed Aug. 2, 2010;
61/473,537 filed Apr. 8, 2011; and 61/473,654 filed Apr. 8, 2011,
which are each incorporated herein by reference in their entireties
for all purposes.
Claims
What is claimed is:
1. A composition comprising: at least one porous carbon monolith
comprising internal pores, and at least one nanomaterial disposed
throughout the internal pores, wherein the nanomaterial is a
nanotube or a nanowire, and wherein the porous carbon monolith is
an aerogel, a xerogel, or an open-cell foam.Iadd., and wherein
weight of the nanomaterial is greater than weight of the porous
carbon monolith.Iaddend..
2. The composition of claim 1, wherein the nanomaterial is disposed
uniformly throughout the internal pores.
3. The composition of claim 1, wherein the porous carbon monolith
comprises two external surfaces which define a width and a width
middle for the monolith, and the nanomaterial is disposed uniformly
at the width middle.
4. The composition of claim 1, wherein the nanomaterial increases a
volumetric surface area of the composition relative to a volumetric
surface area of the porous carbon monolith considered independently
of the nanomaterial.
.[.5. The composition of claim 1, wherein the nanomaterial has a
weight, and the porous carbon monolith has a weight, and the weight
of the nanomaterial is greater than the weight of the porous carbon
monolith..].
6. The composition of claim 1, wherein the amount of the porous
carbon monolith is less than about 75% by weight of the
composition.
7. The composition of claim 1, wherein the amount of the porous
carbon monolith is less than about 50% by weight of the
composition.
8. The composition of claim 1, wherein the porous carbon monolith
is an aerogel.
9. The composition of claim 1, wherein the porous carbon monolith
is an activated carbon aerogel.
10. The composition of claim 1, wherein the internal pores comprise
a bimodal pore size distribution.
11. The composition of claim 1, wherein the internal pores comprise
macropores which have an average diameter of 100 nm or more.
12. The composition of claim 1, wherein the internal pores comprise
one set of pores which have an average diameter of 1 micron or more
and another set of pores which have an average diameter of 10 nm or
less.
13. A composition comprising: at least one porous carbon monolith
comprising internal pores, and at least one nanomaterial disposed
throughout the internal pores, wherein the porous carbon monolith
has a BET surface area of at least 2,000 m.sup.2/g, independently
of the nanomaterial disposed in the internal pores.Iadd., and
wherein weight of the nanomaterial is greater than weight of the
porous carbon monolith.Iaddend..
14. The composition of claim 13, wherein the nanomaterial is a
carbon nanotube.
15. The composition of claim 13, wherein the nanomaterial is a
multi-walled carbon nanotube.
16. The composition of claim 13, the composition further comprising
catalyst adapted for nanomaterial growth.
17. The composition of claim 1, wherein the composition comprising
the porous carbon monolith and the nanomaterial has a BET surface
area of at least 1,000 m.sup.2/g.
18. The composition of claim 1, wherein said composition has a bulk
electric conductivity of at least 1 S/cm.
19. A composition comprising: at least one carbon aerogel
comprising internal pores and at least one dimension which is at
least 100 microns, wherein carbon nanotubes are disposed in the
internal pores, wherein the amount of the carbon aerogel is less
than about 75% by weight of the composition.Iadd., wherein the
carbon aerogel is a monolith.Iaddend..
20. The composition of claim 19, wherein the amount of the carbon
aerogel is less than about 50% by weight of the composition.
.[.21. The composition of claim 19, wherein the carbon aerogel is a
monolith..].
22. The composition of claim 19, wherein the carbon nanotubes are
disposed uniformly in the internal pores.
23. The composition of claim 19, wherein the composition further
comprises catalyst for growth of the carbon nanotubes.
24. The composition of claim 19, wherein the carbon nanotubes
increase the volumetric surface area of the composition compared to
the carbon aerogel.
25. The composition of claim 19, wherein the carbon nanotubes
increase the electrical conductivity of the composition compared to
the carbon aerogel.
26. The composition of claim 19, wherein the carbon aerogel
comprise macropores having an average pore diameter of at least 100
nm.
27. The composition of claim 19, wherein the carbon aerogel
comprises a bimodal pore size distribution.
28. The composition of claim 19, wherein the composition comprising
the carbon aerogel and the carbon nanotubes has a BET surface area
of at least 1,000 m.sup.2/g.
29. A method for making the composition of claim 1, comprising:
providing a porous substrate having a thickness of 100 microns or
more, wherein the porous substrate comprises a plurality of
macropores throughout the thickness of the porous substrate;
disposing a catalyst inside the porous substrate; and forming a
nanomaterial in the macropores by vapor deposition, wherein the
catalyst catalyzes the growth of the nanomaterial, and wherein the
nanomaterial is deposited throughout a thickness of porous
substrate.
30. The method of claim 29, the forming step comprises allowing a
precursor to the nanomaterial to fill up the macropores and then
react the precursor in presence of catalyst to form the
nanomaterial in the macropores.
31. The method of claim 29, wherein the substrate is an aerogel, a
xerogel, or an open-cell foam.
32. The method of claim 29, wherein the catalyst comprises at least
one metal.
33. The method of claim 29, wherein the average diameter of the
macropores is 100 nm or more.
34. The method of claim 29, wherein the nanomaterial is a carbon
nanotube.
35. The method of claim 29, wherein the deposition of the
nanomaterial increases the bulk electric conductivity of the porous
substrate by 50% or more.
36. The method of claim 29, wherein the deposition of the
nanomaterial increases the mass of the porous substrate by 50% or
more.
37. The method of claim 29, wherein the deposition of the
nanomaterial increases the volumetric surface area of the porous
substrate by 10% or more.
38. The method of claim 29, further comprising the step of removing
the porous substrate from the nanomaterial.
39. A method for making the composition of claim 19, comprising:
providing a carbon aerogel having a thickness of 100 microns or
more, wherein the carbon aerogel comprises a plurality of
macropores throughout the thickness of the carbon aerogel;
disposing a catalyst inside the carbon aerogel; and growing carbon
nanotubes in the macropores by vapor deposition, wherein the
catalyst catalyzes the growth of the carbon nanotubes, and wherein
the carbon nanotubes are deposited throughout the thickness of
carbon aerogel.
40. The method of claim 39, wherein the carbon nanotubes are formed
from a carbon-containing precursor gas, and the carbon aerogel is
first filled with the carbon-containing precursor gas before
heating to grow the carbon nanotubes.
41. The method of claim 39, wherein the carbon aerogel comprises a
bimodal pore size distribution.
42. The method of claim 39, wherein the carbon nanotubes are
multi-walled carbon nanotubes.
43. An article comprising the composition of claim 1, wherein the
article is a capacitor, a battery, an electrode, sensor, a
membrane, a catalyst support, or hydrogen storage device.
44. The composition of claim 1, wherein the nanomaterial is a
carbon nanotube.
45. The composition of claim 1, wherein the nanomaterial is a
silicon nanowire.
46. The composition of claim 19, wherein the carbon aerogel is an
activated carbon aerogel.
.Iadd.47. A device comprising the composition of claim 1 for
desalination, catalysis or electrocatalysis..Iaddend.
.Iadd.48. A device comprising the composition of claim 13 for
desalination, catalysis or electrocatalysis..Iaddend.
.Iadd.49. A device comprising the composition of claim 19 for
desalination, catalysis or electrocatalysis..Iaddend.
.Iadd.50. The composition of claim 1, further comprising metal
oxide or metal nanoparticles coating the internal pores of the
porous carbon monolith..Iaddend.
.Iadd.51. The composition of claim 13, further comprising metal
oxide or metal nanoparticles coating the internal pores of the
porous carbon monolith..Iaddend.
.Iadd.52. The composition of claim 19, further comprising metal
oxide or metal nanoparticles coating the internal pores of the
carbon aerogel..Iaddend.
Description
BACKGROUND
A need exists to prepare better composite materials including
nanostructured composite materials. For example, many energy
applications such as capacitors and batteries require better
performance of materials. Nanostructured materials provide the
ability to engineer important properties such as surface area and
electrical charge transport.
An important class of material is highly porous material which
provides high surface area. For example, carbon aerogels (CAs) are
a unique class of porous materials that are being commercialized
and hold technological promise for a variety of applications,
including catalysis, adsorption and energy storage..sup.[1] The
utility of these materials is derived, at least in part, from their
high surface areas, electrically conductive frameworks, and tunable
porosities. To expand the applications for these materials, efforts
have focused on the incorporation of modifiers, such as carbon
nanotubes (CNTs) or metal nanoparticles, into the carbon framework
that can potentially enhance the thermal, electrical, mechanical,
or catalytic properties of the aerogel..sup.[2] For example, a new
class of ultra low-density CNT-CA composites was recently reported
that exhibit both high electrical conductivity and robust
mechanical properties..sup.[3] These CA composites are believed to
be among the stiffest low-density solids reported and exhibit
elastic behavior to compressive strains as large as about 80%. In
these materials, however, the CNTs are embedded within the skeletal
network of the CA and, as a result, the accessible surface area
associated with the nanotubes is minimal. While this structural
motif does serve to enhance the bulk electrical and mechanical
properties of these low-density materials, a need exists for many
applications to design CA composites that provide functional access
to the surfaces of the CNTs. Other types of composite materials
comprising nanomaterials such as nanowires and nanotubes are
needed, particularly materials having macroscopic dimensions but
nanostructured elements.
SUMMARY
At least some embodiments described herein provide a
straightforward method for the fabrication of novel monolithic
composites, including composites carbon nanotubes and carbon
aerogel. These and other embodiments are described herein.
Embodiments provided herein include compositions, devices, and
articles, as well as methods of making and methods of using the
compositions, devices, and articles.
For example, one aspect provides a composition comprising: at least
one porous carbon monolith comprising internal pores, and at least
one nanomaterial disposed throughout the internal pores.
In one embodiment, the nanomaterial is disposed uniformly
throughout the internal pores.
In one embodiment, the porous carbon monolith comprises two
external surfaces which define a width and a width middle for the
monolith, and the nanomaterial is disposed uniformly at the width
middle.
In one embodiment, the nanomaterial increases a volumetric surface
area of the composition relative to a volumetric surface area of
the porous carbon monolith considered independently of the
nanomaterial.
In one embodiment, the nanomaterial has a weight, and the porous
carbon monolith has a weight, and the weight of the nanomaterial is
greater than the weight of the porous carbon monolith.
In one embodiment, the amount of the porous carbon monolith is less
than about 75% by weight of the composition.
In one embodiment, the amount of the porous carbon monolith is less
than about 50% by weight of the composition.
In one embodiment, the porous carbon monolith is an aerogel, a
xerogel, or an open-cell foam.
In one embodiment, the porous carbon monolith is an aerogel.
In one embodiment, the porous carbon monolith is an activated
carbon aerogel.
In one embodiment, the internal pores comprise a bimodal pore size
distribution.
In one embodiment, the internal pores comprise pores which have an
average diameter of 100 nm or more.
In one embodiment, the internal pores comprise one set of pores
which have an average diameter of 1 micron or more and another set
of pores which have an average diameter of 10 nm or less.
In one embodiment, the porous carbon monolith has a BET surface
area of at least 2,000 m.sup.2/g, independently of the nanomaterial
disposed in the internal pores.
In one embodiment, the nanomaterial is a nanotube or a
nanowire.
In one embodiment, the nanomaterial is a carbon nanotube.
In one embodiment, the nanomaterial is a multi-walled carbon
nanotube.
In one embodiment, the composition further comprises catalyst
adapted for nanomaterial growth.
In one embodiment, the composition comprising the porous carbon
monolith and the nanomaterial has a BET surface area of at least
1,000 m.sup.2/g.
In one embodiment, the composition has a bulk electric conductivity
of at least 1 S/cm.
Another aspect comprises a composition comprising: at least one
carbon aerogel comprising internal pores and at least one dimension
which is at least 100 microns, wherein carbon nanotubes are
disposed in the internal pores, wherein the amount of the carbon
aerogel is less than about 75% by weight of the composition.
In one embodiment, the amount of the carbon aerogel is less than
about 50% by weight of the composition.
In one embodiment, the carbon aerogel is a monolith.
In one embodiment, the carbon nanotubes are disposed uniformly in
the internal pores.
In one embodiment, the composition further comprises catalyst for
growth of the carbon nanotubes.
In one embodiment, the carbon nanotubes increase the volumetric
surface area of the composition compared to the carbon aerogel.
In one embodiment, the carbon nanotubes increase the electrical
conductivity of the composition compared to the carbon aerogel.
In one embodiment, the carbon aerogel comprise pores having an
average pore diameter of at least 100 nm.
In one embodiment, the carbon aerogel comprises a bimodal pore size
distribution.
In one embodiment, the composition comprising the carbon aerogel
and the carbon nanotubes has a BET surface area of at least 1,000
m.sup.2/g.
Another aspect provides a method comprising: providing a porous
substrate having a thickness of 100 microns or more, wherein the
porous substrate comprises a plurality of macropores throughout the
thickness of the porous substrate; disposing a catalyst inside the
porous substrate; and forming a nanomaterial in the macropores by
vapor deposition, wherein the catalyst catalyzes the growth of the
nanomaterial, and wherein the nanomaterial is deposited throughout
a thickness of porous substrate.
In one embodiment, the forming step comprises allowing a precursor
to the nanomaterial to fill up the macropores and then react the
precursor in presence of catalyst to form the nanomaterial in the
macropores.
In one embodiment, the substrate is an aerogel, a xerogel, or an
open-cell foam.
In one embodiment, the catalyst comprises at least one metal.
In one embodiment, the average diameter of the macropores is 100 nm
or more.
In one embodiment, the nanomaterial is a carbon nanotube.
In one embodiment, the deposition of the nanomaterial increases the
bulk electric conductivity of the porous substrate by 50% or
more.
In one embodiment, the deposition of the nanomaterial increases the
mass of the porous substrate by 50% or more.
In one embodiment, the deposition of the nanomaterial increases the
volumetric surface area of the porous substrate by 10% or more.
In one embodiment, the method further comprises the step of
removing the porous substrate from the nanomaterial.
Another aspect provides a method comprising: providing a carbon
aerogel having a thickness of 100 microns or more, wherein the
carbon aerogel comprises a plurality of macropores throughout the
thickness of the carbon aerogel; disposing a catalyst inside the
carbon aerogel; and growing carbon nanotubes in the macropores by
vapor deposition, wherein the catalyst catalyzes the growth of the
carbon nanotubes, and wherein the carbon nanotubes are deposited
throughout the thickness of porous substrate.
In one embodiment, the carbon nanotubes are formed from a
carbon-containing precursor gas, and the carbon aerogel is first
filled with the carbon-containing precursor gas before heating to
grow the carbon nanotubes.
In one embodiment, the carbon aerogel comprises a bimodal pore size
distribution.
In one embodiment, the carbon nanotubes are multi-walled carbon
nanotubes.
Another aspect comprises making a carbon-nanotube-filled activated
carbon aerogel, comprising the steps of: preparing an activated
carbon aerogel substrate, and carbonizing the activated carbon
aerogel substrate to produce the carbon nanotube-filled activated
carbon aerogel.
Another aspect are articles comprising the composition described
herein. For example, an article can comprise the compositions as
described herein, wherein the article is a capacitor, a battery, an
electrode, sensor, a membrane, a catalyst support, or hydrogen
storage device.
In at least some embodiments, the approach involves the catalyzed
CVD growth of multi-walled CNTs on the inner surfaces of activated
CA substrates. In these embodiments, the bimodal pore structure of
the substrate allows for efficient diffusion of the CVD gases
through the aerogel during the growth process and provides
substantial surface area for the growth of CNTs. Microstructural
analysis of the composites indicates substantially uniform CNT
yield throughout the free internal pore volume of CA monoliths with
macroscopic dimensions. The resulting composite structures exhibit
large surface areas and high electrical conductivity and, as such,
provide a robust platform for the design of materials for a variety
of applications, including, for example, battery electrodes,
capacitors, membranes and/or catalyst supports. In addition, the
flexibility associated with this approach provides ability to adapt
material properties for specific applications. For example, the use
of alternative graphitization catalysts can be used either to
change characteristics (i.e. diameter, number of walls) of the CNTs
or to grow other types of carbon nanostructures, such carbon
nanobelts or nanocoils, within the activated CA substrate.
BRIEF SUMMARY OF THE FIGURES
FIG. 1 shows an SEM image of an activated carbon aerogel (ACA)
substrate prior to CVD treatment. The inset show the size of the
ACA monolith used for the CVD experiments.
FIG. 2 shows an SEM image of the multi-walled CNT network grown
within the Ni-loaded ACA substrate.
FIG. 3 shows an SEM images of a fracture surface of the ACA-CNT
composite showing uniform CNT yield from (a) the surface to (b) the
center (about 365 .mu.m from surface) of the monolith.
FIG. 4 shows a TEM image of multi-walled CNTs grown within the
Ni-loaded ACA substrate.
DETAILED DESCRIPTION
Introduction
References cited herein can be used to practice and better
understand the claimed inventions and are incorporated by reference
herein in their entireties for all purposes.
Priority US provisional applications U.S. Ser. Nos. 61/369,972
filed Aug. 2, 2010; 61/473,537 filed Apr. 8, 2011; and 61/473,654
filed Apr. 8, 2011 are each incorporated herein by reference in
their entireties for all purposes.
The article, "High Surface Area Carbon Aerogels as Porous
Substrates for Direct Growth of Carbon Nanotubes," Worsley et al,
Chem. Commun., 2010, 46, 9253-9255 (DOI: 10.1039/c0cc03457f) is
hereby incorporated by reference in its entirety.
The article, "Advanced Carbon Aerogels for Energy Applications,"
Biener et al., Energy & Environmental Science, 2011, 4,
656-667, is hereby incorporated by reference in its entirety.
US Patent Publication 2011/0024698 to Worsely et al., "Mechanically
Stiff, Electrically Conductive Composites of Polymers and Carbon
Nanotubes" is hereby incorporated by reference in its entirety.
US Patent Publication 2010/0190639 to Worsley et al., "HIGH SURFACE
AREA, ELECTRICALLY CONDUCTIVE NANOCARBON-SUPPORTED METAL OXIDE" is
hereby incorporated by reference in its entirety.
US Patent Publication 2010/0187484 to Worsley et al., "MECHANICALLY
ROBUST, ELECTRICALLY CONDUCTIVE ULTRALOW-DENSITY CARBON
NANOTUBE-BASED AEROGELS" is hereby incorporated by reference in its
entirety.
US Patent Publication 2010/0139823 to Gash et al., "PYROPHORIC
METAL-CARBON FOAM COMPOSITES AND METHODS OF MAKING THE SAME" is
hereby incorporated by reference in its entirety.
Various terms used in this patent application are described further
hereinbelow.
CA=carbon aerogel
ACA=activated carbon aerogel
CNT=carbon nanotubes
CNT-CA=carbon nanotube and carbon aerogel composite
SWNT=single-walled carbon nanotubes
DWNT=double-walled carbon nanotubes
PVA=polyvinyl alcohol
CVD=chemical vapor deposition
TEM=transmission electron microscopy
SEM=scanning electron microscopy
RF=resorcinol and formaldehyde solids
BET=Brunauer-Emmett-Teller
"Mechanically Robust"=can withstand strains greater than 10% before
fracture
"Electrically Conductive"=Exhibits an electrical conductivity of 10
S/m or greater.
"Carbon Nanotube-Based Aerogel"=porous carbon material comprising
5% to 95% carbon nanotubes by weight. In another embodiment, the
porous carbon material can comprise 5% to 99% carbon nanotubes by
weight.
Also, as used in the specification and claims, the singular form
"a", "an" and "the" include plural references unless the context
clearly dictates otherwise. For example, the term "a nanotube"
includes a plurality of nanotubes.
As used herein, the term "comprising" is intended to mean that, for
example, the compositions and methods include the recited elements,
but do not exclude others. "Consisting essentially of" when used to
define, for example, compositions and methods, shall mean excluding
other elements of any essential significance to the combination for
the intended use. "Consisting of" shall mean excluding more than
trace elements of other ingredients and substantial method steps
for administering the compositions of this invention. Embodiments
defined by each of these transition terms are within the scope of
this invention.
Embodiments are described herein for disposing of nanomaterials
within porous substrates. For example, in some of the embodiments
described herein, the fabrication of novel CNT-CA composites
through the catalytic growth of CNTs by chemical vapor deposition
(CVD) directly on the internal surface area of CA substrates is
described. This approach, for at least some embodiments, offers a
straightforward route to the design of monolithic carbon composite
structures that exhibit both large surface areas and high
electrical conductivity. While the CVD growth of carbon
nanostructures on porous carbon substrates has been previously
reported,.sup.[4] carbon deposition in those systems occurred
primarily on the surfaces of powders or granular samples. By
contrast, for at least some embodiments described herein, the
embodiments represent the first example of uniform CNT growth
throughout the internal pore volume of a monolithic porous carbon.
High CNT yield within CA monoliths with macroscopic dimensions is
shown. It is also shown that growth of the CNTs within these
substrates can enhance the bulk electrical conductivity of the
material. These CNT-CA composites are also mechanically robust and,
as such, can be readily formed into different shapes for use as,
for example, novel catalyst supports, electrodes for
electrochemical devices, or membranes for adsorption or
separation.
For example, one embodiment provides a composition comprising: at
least one porous carbon monolith comprising internal pores, and at
least one nanomaterial disposed throughout the internal pores.
Porous Carbon Monolith and Porous Substrate
Porous substrates and porous carbon monoliths are known in the art.
A porous substrate can be used for depositing nanomaterial, through
which the porous substrate is functionalized. The porous substrate
can be an aerogel, a xerogel, or an open cell-foam. In a preferred
embodiment, the porous substrate is a carbon aerogel or an
activated carbon aerogel. In a more preferred embodiment, the
porous substrate is an activated carbon aerogel prepared from, for
example, resorcinol and formaldehyde. Description of carbon aerogel
and activated carbon aerogel, as well as the preparation thereof,
can be found in US 2011/0024698, US 2010/0190639, US 2010/0187484,
US 2010/0139823, and Baumann et al., J. Non-Cryst. Solids, 354:3513
(2008), all of which are incorporated herein by reference in their
entireties.
Monoliths and methods of making monoliths are described in, for
example, U.S. Pat. Nos. 5,207,814; 5,885,953; 5,879,744; 7,378,188;
7,410,718; and 7,811,711.
The porous substrate can be, for example, at least 80% by weight
carbon, or at least 85% by weight carbon, or at least 90% by weight
carbon, or at least 95% by weight carbon, or at least 98% by weight
carbon. The porous substrate can be substantially free of
non-carbon materials such as silicates or binders including
polymeric binders.
Sol-gel methods can be used to form an aerogel. The type of aerogel
can include, for example, resorcinol-formaldehyde,
resorcinol-furfural, phloroglucinol-formaldehyde,
phenol-formaldehyde, cresol-formaldehyde, and phenol-furfuryl
alcohol. Sol gel catalysts include, for example, acids and bases
such as, for example, nitric acid, acetic acid, ascorbic acid,
hydrochloric acid, sulfuric acid, sodium carbonate, sodium
hydroxide, ammonium hydroxide, and calcium sulfate. Sol gel
catalyst concentrations can be expressed in reactant-to-catalyst
ratio (R/C) which can range from, for example, ratios of 10 to
5,000, or 10 to 2,000, or 10 to 1,000.
In one embodiment, an activated carbon aerogel can be formed
according to the following exemplary steps: (1) creating a reaction
mixture comprising, for example, resorcinol and formaldehyde, and
also, for example, acetic acid as reaction catalyst; (2) curing the
reaction mixture to form a wet gel; (3) washing the wet gel with,
for example, acetone to remove water; (4) drying the wet gel using,
for example, supercritical CO.sub.2 to form a dry gel; (5)
pyrolyzing the dry gel at, for example, 1050.degree. C. under inert
atmosphere (e.g., N.sub.2) to form a carbon aerogel; and (6)
thermally activate the carbon aerogel at, for example, 950.degree.
C. using, for example, CO.sub.2 to form an activated carbon
aerogel.
In some embodiments, the porous substrate can be characterized by a
length, width, and height. Thickness can be also measured. The
substrate can have two opposing surfaces which define a width and a
width middle. At least one of the surfaces can be subjected to a
vapor deposition process, and one can examine the extent to which
the deposition occurs in the interior of the material. The
thickness of the porous substrate can be 100 microns or more, or
300 microns or more, or 500 microns or more, or 700 microns or
more. The porous substrate can be a monolithic solid. Examples
include substantially slab shaped materials with a length, width,
and height, wherein the length, width, and height are each at least
100 microns, or each at least 250 microns, or each at least 500
microns, or each at least 750 microns, or each at least one mm.
The porous substrate can be characterized by a surface area before
the nanomaterial is disposed in the porous substrate to form a
composite. For example, the surface area of the porous substrate
can be 500 m.sup.2/g or more, or 1,000 m.sup.2/g or more, or 1,500
m.sup.2/g or more, or 2,000 m.sup.2/g or more, or 3,000 m.sup.2/g
or more.
The electrical conductivity of the porous substrate can be, for
example, 5 S/cm or less, or 4 S/cm or less, or 3 S/cm or less.
The porous substrate can exclude powders, particles, and/or
granular samples of material. Rather, a monolith can be used. For
example, a particle based approach, in contrast, is described in Su
et al., Angew. Chem., Int. Ed., 2005, 44, 5488. In one embodiment,
the porous substrate does not comprise an aggregate of activated
carbon particles.
Moreover, the porous substrate can be mechanically robust. One can
determine the appropriate balance of mechanical robustness and
surface area. The porous substrate can be formed into different
shapes for different applications.
Pores
The porous substrate can provide pores which are adapted to have a
nanomaterial disposed therein including throughout the porous
substrate, including the interior of the porous substrate. The
pores can be evaluated with an average pore size and a pore size
distribution. The pores can provide a continuous network to allow
material for the nanomaterial to be disposed throughout the porous
substrate.
In embodiment described herein, pores can include macropores,
micropores, and mesopores, as well as combinations thereof.
Macropores can be generally defined as pores of a diameter or width
of more than 50 nm. Micropores can be generally defined as pores of
a diameter or width of less than 2 nm. Mesopores can be generally
defined as pores of a diameter or width of 2-50 nm. See, for
example, Pure & Appl. Chem. Vol. 66, No. 8, pp. 1739-1758
(1994).
The porous substrate can comprise a plurality of macropores
throughout its thickness. In one embodiment, the average diameter
of the macropores inside the porous substrate is 100 nm or more, or
200 nm or more, or 500 nm or more, or 1 micron or more. In a
further embodiment, the macropores form a continuous network inside
the porous substrate, allowing the precursor gas of a nanomaterial
to be able to diffuse uniformly throughout the thickness of the
porous substrate.
In addition to macropores, the porous substrate may also comprise
micropores and/or mesopores throughout its thickness. In one
embodiment, the average diameter of the combined micropores and/or
mesopores (or pores) is 10 nm or less, or 5 nm or less, or 2 nm or
less. The number of micropores and the mesopores can be increased
by activating, including thermally activating, a carbon
aerogel.
In one embodiment, a porous substrate with bimodal pore size
distribution is used. For example, the porous substrate can have a
first set of pores of an average diameter of 1 micron or more and a
second set of pores of an average diameter of 10 nm or less. Larger
pores can provide access to the whole material and help avoid
"clogging" of the external surfaces. Smaller pores can increase the
internal surface area.
In one embodiment, the porous substrate is not dominated by
mesopores. Rather, micropores and macropores can be the predominant
pore structure.
Nanomaterials/Carbon Nanotubes
Any nanomaterial that can be deposited, grown, or otherwise
disposed in a porous substrate via, for example, vapor deposition,
including chemical vapor deposition, can be used. In one
embodiment, the nanomaterial can be nanotubes, nanowires, nanorods,
nanofibers, nanocoils, nanoribbons, or nanoparticles.
The nanomaterial can be a carbon nanomaterial and a
carbon-containing nanomaterial.
In a preferred embodiment, the nanomaterial can be silicon
nanowires or carbon nanotubes, including single-walled carbon
nanotubes, double-walled carbon nanotubes, or multi-walled carbon
nanotubes. The average diameter of the silicon nanowire deposited
inside the porous substrate can be, for example, 10 nm to 500 nm,
or 10 nm to 100 nm. The average diameter of carbon nanotubes
deposited inside the porous substrate can be, for example, 1 nm to
50 nm. The average diameter of the multi-walled carbon nanotubes
deposited inside the porous substrate can be, for example, 10 nm to
50 nm.
In one embodiment, carbon nanotubes are the predominant
nanomaterial disposed inside the pores. Graphitic nanostructures
can be only minimally present or substantially excluded in favor of
the carbon nanotubes. Graphitic nanostructures can include, for
example, ribbons, coils, or fibers.
Carbon nanotubes are described in Marc J. Madou's Fundamentals of
Microfabrication, The Science of Miniaturization, 2nd Ed., pages
454 455, including carbon nanotube preparation by CVD from
patterned catalysts. Carbon nanotubes are also described in the
text, Carbon Nanotubes, by Dresselhaus et al., Springer-Verlag,
2000. See also, Special-Section, "Carbon Nanotubes" Physics World,
vol. 13, pp. 29 53, 2000. Carbon nanotubes can be single-walled
carbon nanotubes (SWNTs), multi-walled carbon nanotubes (MWNTs),
nanohorns, nanofibers, or nanotubes. They can be conducting or
semiconducting depending on the form of the nanotube. They can be
open, closed, and have different kinds of spiral structure. They
can be in zigzag and armchair form and have varying steepness which
alters the chiral form.
Documents which are incorporated by reference, and which relate to
nanotube technology, including CVD fabrication and catalysis,
applications of carbon nanotubes in devices, purification of
nanotubes once formed, and which can be used to in practicing the
present invention include: (1) Hannes Kind et al. Advanced
Materials, 1999, 11, 1285. (2) Y. Y. Wei et al. J. Vac. Sci.
Technol. B, 2000, 18(6), 3586 (3) H. Wang et al. Applied Surface
Science, 2001, 181, 248 254. (4) Chin Li Cheung, PNAS, 2000, 97(8),
3809 3813. (5) J. H. Hafner, J. Am. Chem. Soc., 1999, 21, 9750
9751. (6) Cao et al. Applied Surface Science, 2001, 181, 234 238.
(7) Dai et al., "Growth and Characterization of Carbon Nanotubes,"
book chapter in "Topics in Applied Physics", Vol. 80, Ed. M.
Dresselhaus, Springer Verlag (2000). (8) Dai et al. Appl. Phys.
Lett., 75, 3566 3568 (1999). (9) Dai et al. J. Am. Chem. Soc., 121
7975 7976 (1999). (10) Dai et al. Phys. Chem., 103, 6484 6492
(1999). (11) Dai et al. Appl. Phys. Lett., 627 629, 75 (1999). (12)
Dai et al. Science, 283, 512 (1999). (13) Dai et al. Nature, 395,
878, (1998). (14) M. S. Dresselhaus et al., Science of Fullerenes
and Carbon Nanotubes, Academic Press, San Diego, 1996. (15) Li et
al, Chem. Mater., 13, 1008 1014, (2001). (16) U.S. Patent
Publication, 2003/0148577 ("Controlled Alignment of Catalytically
Grown Nanostructures in a Large Scale Synthesis Process") by
Merkulov et al., published Aug. 7, 2003. (17) U.S. Patent
Publication 2002/0127336, published Aug. 1, 2002 to Richard Smalley
et al. (18) U.S. Patent Publication 2002/0113714, published Aug. 1,
2002 to Richard Smalley et al. (19) U.S. Patent Publication
2002/0102203, published Aug. 1, 2002 to Richard Smalley et al. (20)
U.S. Pat. No. 6,183,714 ("Method of Making Ropes of Single-Wall
Carbon Nanotubes") to Richard Smalley et al., issued Feb. 6, 2001.
(21) U.S. Patent Publication 2002/0088938 to Colbert et al.,
published Jul. 11, 2002 ("Methods for forming an array of
single-wall carbon nanotubes and compositions thereof"). (22) U.S.
Patent Publication 2003/0143327, published Jul. 31, 2003 to Rudiger
et al. (23) U.S. Pat. No. 6,146,227 to Mancevski issued Nov. 14,
2000 (Method for manufacturing carbon nanotubes as functional
elements of MEMS devices"). (24) U.S. Pat. No. 6,277,318 to Bower
et al., issued Aug. 21, 2001 ("Method for fabrication of patterned
carbon nanotube films"). (25) U.S. Pat. No. 6,333,016 to Resasco et
al. issued Dec. 25, 2001 ("Method of producing carbon nanotubes").
(26) U.S. Patent Publication 2002/0130353 to Lieber et al.,
published Sep. 19, 2002 (Nanoscopic wire-based devices, arrays, and
methods of their manufacture").
Methods for making Si nanowires via vapor deposition including CVD
are known in the art. For example, Si nanowires may be grown by
metal-catalyzed CVD, which is based on a vapor-liquid solid (VLS)
growth process. During growth, a precursor gas such as SiH.sub.4
can decompose at the nucleating particle catalyst surface, Si can
diffuse in the catalyst, then when supersaturation occurs, the Si
atoms can precipitate out at the catalyst-substrate interface to
form a silicon nanowire of diameter similar to that of the catalyst
nucleating particle. During this vapor-liquid-solid (VLS) growth
process, nano-sized metal catalysts, such as gold nucleating
particles, can be used to catalyze the decomposition of the
precursor gas such as SiH.sub.4. Other catalysts, such as Zn and
Ti, are also known to be suitable for making Si nanowires. In one
embodiment, the precursor gas is heated to a temperature at which
1) the gas dissociates into its free component atoms, and 2) the
nucleating particles (e.g. metal catalyst) melts to a liquid. The
free gas molecules can then diffuse into the metal catalyst to form
a liquid alloy droplet. Methods for making Si nanowire are
disclosed in, for example, Chung et al., Applied Physics Letters,
76(15): 2068-2070 (2000), and US Patent Publication
2011/0156003.
Catalyst and Catalyst Precursors
Nanomaterial can be disposed or deposited in the porous substrate
with use of catalyst or without catalyst.
To deposit nanomaterial in the porous substrate, preferably, a
catalyst can be used to catalyze the growth of nanomaterial in the
macropores. Any catalyst that can catalyze the growth of
nanomaterial can be used. The catalyst can be a metal such as, for
example, Fe, Co, Ni, Au, Cu, Mo, and Re. An oxide like zirconium
oxide can be used. The catalyst can be, for example, a main group
metal such as Sn. The catalyst can be, for example, a semiconductor
like Si, Ge, or SiC. It can be a non-metal. In one embodiment, for
example, the catalyst is Ni. In another embodiment, the catalyst is
Fe or Co. The catalyst can be in the form of nanoparticles.
The catalyst can be deposited inside the porous substrate using
established metal ion impregnation and reduction techniques, as
described in, for example, Li et al., J. Phys. Chem. C, 111:11086
(2007), which is incorporated herein by reference in its entirety.
In one embodiment, for example, Ni catalyst is loaded into the
porous substrate according to the following steps: (1) immersing
the porous substrate in a dilute NiCl.sub.2 solution, (2) removing
the porous substrate from the metal salt solution and drying it
under a stream of N.sub.2, and (3) reducing the Ni.sup.2+ ions
adsorbed within the porous substrate to metal nanoparticles at
elevated temperatures using H.sub.2.
The content of the catalyst relative to the porous substrate can be
measured. It can be, for example, 1 wt. % to 20 wt. %, or 2 wt. %
to 15 wt. %, or 3 wt. % to 10 wt. %.
Vapor Deposition and CVD
Vapor deposition and chemical vapor deposition is known among
skilled artisans. In one embodiment, the catalyst facilitates the
conversion of the precursor gas to the nanomaterial inside the
catalyst-loaded porous substrate at a growth temperature. In a
preferred embodiment, before the growth temperature is applied, the
precursor material (e.g., gas) is diffused into the pores,
including macropores, to reach a uniform precursor gas
concentration throughout the thickness of the porous substrate.
This diffusion is executed before conversion of precursor material
to the nanomaterial. In one embodiment, for example, the step of
depositing the nanomaterial does not comprise heating the porous
substrate before the precursor gas is substantially fully or fully
diffused into the porous substrate, i.e., heating before the
precursor gas reaches substantially the same or the same
concentration inside and outside the porous substrate.
The growth temperature can be, for example, 600.degree. C. to
1,000.degree. C., or 700.degree. C. to 900.degree. C., or about
800.degree. C. The exposure time between the precursor gas and the
porous substrate can be, for example, 2-10 minutes, 3-7 minutes, or
4-6 minutes, or about 5 minutes. The flow rate of the precursor gas
can be, for example, 5-20 sccm, or 8-12 sccm, or about 10 sccm.
In one embodiment, chemical vapor deposition is used to uniformly
deposit carbon nanotubes throughout the thickness of the porous
substrate according to the following steps: (1) exposing the
catalyst-loaded porous substrate to a flow of a precursor gas (e.g.
C.sub.2H.sub.4) to allow uniform diffusion of the precursor gas in
the pores, including macropores, throughout the thickness of the
porous substrate; (2) heating the porous substrate to allow
sufficient carbon nanotube growth; and (3) cooling the porous
substrate filled with carbon nanotubes.
Characterization of Composites
The nanomaterial can be disposed throughout the internal pores. In
particular, the nanomaterial can be disposed uniformly throughout
the internal pores. For example, the porous carbon monolith can
comprises two external surfaces which define a width and a width
middle for the monolith, and the nanomaterial can be disposed
uniformly at the width middle. In a monolith, for example, the
number and length of the nanotubes can be measured at different
parts of the material, and can be relatively uniformly found
throughout the material. Methods known in the art can be used to
characterize the interior of the composite material.
The nanomaterials can be formed at or disposed at a region which is
at least 100 microns, or at least 200 microns, or at least 300
microns, or at least 350 microns, from the nearest surface.
In one embodiment, the deposition of the nanomaterial via CVD
increases the bulk electrical conductivity of the porous substrate
by 20% or more, or 50% or more, or 80% or more. In one embodiment,
after the deposition of the nanomaterial via CVD, the porous
substrate has a bulk electrical conductivity of 4 S/cm or more, or
6 S/cm or more, or 8 S/cm or more, or 10 S/cm or more.
The nanomaterial can increase the volumetric surface area of the
composition relative to the volumetric surface area of the porous
carbon monolith considered independently of the nanomaterial. For
example, in one embodiment, the nanomaterial increases the
volumetric surface area of the porous substrate by 5% or more, or
10% or more, or 20% or more.
In one embodiment, after the deposition of the nanomaterial via,
for example, CVD, the porous substrate can have a surface area of
500 m.sup.2/g or more, or 700 m.sup.2/g or more, or 1,000 m.sup.2/g
or more, or 1,300 m.sup.2/g, or 1,500 m.sup.2/g or more.
In one embodiment, the nanomaterial can increase the mass of the
porous substrate by 20% or more, or 50% or more, or 80% or more.
For example, the amount of the porous carbon monolith can be less
than about 75% by weight, or less than 50% by weight, of the
composition. For example, in a composite material, the nanomaterial
can have a weight, and the porous carbon monolith can have a
weight, and the weight of the nanomaterial can be greater than or
equal to the weight of the porous carbon monolith.
In one embodiment, the deposition of the nanomaterial via CVD
increases the hydrogen storage capacity of the porous substrate by
10% or more, or 20% or more, or 50% or more, or 80% or more.
Devices and, Applications, and Methods of Using
The aerogel deposited with nanomaterial has excellent potential in
a variety of applications and devices. See, for example, Biener et
al., Energy & Environmental Science article cited above.
Applications include, for example, hydrogen storage, electrical
energy storage, capacitors and super-capacitors, batteries
(including lithium and lithium-ion batteries), catalysis,
electrocatalysis, desalination, membranes, sensors, and
actuators.
In one embodiment, the aerogel deposited with nanomaterial can be
used in a capacitor. In another embodiment, the aerogel deposited
with nanomaterial can be used in a hydrogen storage device.
In a further embodiment, the aerogel deposited with nanomaterial
can be used as an electrode in a Li-ion battery, wherein the Li-ion
battery can have a capacity of 300 Ah/kg or more, or 450 Ah/kg or
more, or 600 Ah/kg or more, or 800 Ah/kg or more.
In one embodiment, the processes used herein can be used for the
fabrication of the nanomaterial without the substrate. For example,
the porous substrate can be removed to yield the nanomaterial,
e.g., carbon nanotubes. One can obtain more nanomaterial via a
three dimensional growth process compared to a two dimensional
growth process.
In another embodiment, the composite monolith can be ground up into
smaller units of the material.
Working Examples
Additional embodiments are also provided in the following
non-limiting working examples. For example, ACA-CNT composites were
prepared and characterized.
1. Porous Substrate
Activated CAs (ACAs) with large surface areas (over 2000 m.sup.2/g)
and bimodal porosity (macro- and micropores) were utilized as CVD
substrates. Relative to mesoporous CAs, these macroporous
substrates provided enhanced diffusion efficiency of the CVD
synthesis gas throughout the aerogel structure and substantially
more surface area for deposition of catalyst particles and growth
of CNTs. The ACAs were prepared through carbonization and thermal
activation of organic aerogels derived from resorcinol and
formaldehyde, as previously described..sup.[5] The skeletal
structure of the ACA substrate comprises interconnected
micron-sized carbon ligaments that define the continuous
macroporous network (FIG. 1). The ligaments were porous as well, as
the activation process creates micropores and small mesopores in
the walls of the carbon framework. Monolithic ACA parts
(20.times.5.times.1 mm, see inset of FIG. 1) with BET surface areas
about 2400 m.sup.2 g.sup.-1 were used.
More particularly, the ACA substrates were prepared through the
sol-gel polymerization of resorcinol (R) and formaldehyde (F) using
acetic acid as the reaction catalyst, as previously
reported..sup.[5] The organic RF aerogels were then carbonized at
1050.degree. C. under N.sub.2 and subsequently activated at
950.degree. C. using carbon dioxide. An electric cutting tool was
used to slice thin slab of the ACA with approximate dimensions of
20.times.5.times.1 mm.
2. Catalyst
The ACA substrates were loaded with CNT catalysts using metal ion
impregnation and reduction techniques..sup.[6] Nickel was selected
as catalyst because nickel nanoparticles are known to efficiently
catalyze the growth of carbon nanotubes. .sup.[7] In this process,
the monolithic slabs were immersed in dilute NiCl.sub.2 solutions
to allow for complete infiltration of the aerogel porosity. After
drying the parts under a stream of nitrogen, the Ni.sup.2+ ions
adsorbed within the ACA were reduced to metal nanoparticles at
elevated temperatures using H.sub.2, yielding uniform dispersions
of accessible and catalytically active nickel nanoparticles within
the substrate.
More particularly, for the catalyst loading, these parts were
immersed in a 0.1 M acetone solution of NiCl.sub.2.6H.sub.2O for
about 24 h, then removed from the metal salt solution and dried
under a stream of N.sub.2. The slabs of the Ni-loaded CA were
placed in a 2.5-cm long segment of 1-cm diameter quartz tubing and
inserted into the middle of a 2.7-cm inner diameter quartz process
tube. The tube was flushed with He at a rate of 60 sccm for 10-20
minutes and then placed into a clamshell furnace. The sample was
then heated to 400.degree. C. under a stream of He (60 sccm) and
H.sub.2 (40 sccm) and held at that temperature for 10 min to reduce
the impregnated nickel ions to metal nanoparticles.
3. Carbon Nanotube Growth
The CVD growth of CNTs was performed by exposing thin slabs of the
Ni-loaded ACA to a flow of H.sub.2 and C.sub.2H.sub.4 for a period
of five minutes at 800.degree. C. While a variety of CVD conditions
(growth temperature, exposure times, precursor flow rates) were
tested in the course of this work, the conditions described above
provided the best yield of CNTs within the aerogel substrates.
More particularly, after catalytic nickel nanoparticle formation,
ethylene (10 sccm) was introduced to the He/H.sub.2 stream and the
temperature was held at 400.degree. C. for 5 min to facilitate
diffusion of ethylene into the sample. Finally, the sample was
heated to 800.degree. C. at a rate of 40.degree. C./min and held at
that temperature for 5 min to allow for CNT growth. The tube was
subsequently removed from the furnace and cooled to room
temperature under a flow of He (60 sccm).
4. Characterization of Composite
The Ni-loaded ACA materials exhibited significant increases in mass
following CVD treatment, indicating carbon deposition had occurred
on the aerogel substrate. For the growth conditions used in this
work, the mass of the Ni.sup.2+-loaded aerogel parts approximately
doubled following the metal reduction and CVD treatment steps.
Examination of these materials by scanning electron microscopy
(SEM) shows entangled networks of CNTs throughout the ACA
architecture (FIG. 2). The CNTs appear to grow from the surfaces of
the Ni-loaded carbon substrate into the free pore volume of the
aerogel.
To determine the uniformity of CNT yield throughout the ACA slab,
we examined cross-sectional areas of fracture surfaces of these
monolithic substrates following CVD treatment. As shown in FIG. 3,
CNT yield is indeed uniform across the full thickness of the
aerogel slab (about 0.75 mm), indicating that the pore structure of
the ACA does allow for efficient diffusion of CVD gases during the
growth process. Closer examination of the CNTs by transmission
electron microscopy (TEM) shows that the tubes appear to be
multi-walled with diameters between 10 and 30 nm (FIG. 4). The
range of nanotube diameters is likely a consequence of the size
distribution of nickel catalyst particles formed during the
reduction step. Interestingly, the formation of other graphitic
nanostructures, such as ribbons, coils or fibers, was not observed
in these substrates after CVD treatment.
The BET surface areas of the ACA-CNT composites (about 1200 m.sup.2
g.sup.-1) were lower than that of the untreated ACA substrate. This
decrease in surface area can be attributed to plugging of the
micropores and small mesopores in the ACA substrate that occurs
during both catalyst incorporation and CVD treatment, as evidenced
by the reduced micropore volume observed in the ACA-CNT composites
(about 0.45 cm.sup.3 g.sup.-1) relative to that of the parent ACA
substrate (0.89 cm.sup.3 g.sup.-1). Despite these changes in
textural properties, the approach presented here allows for the
high-yield growth of accessible CNT networks within the substrate,
while retaining relatively large surface areas in the composite
structure.
On a volumetric basis, the surface area in the ACA-CNT monoliths
(about 580 m.sup.2/cm.sup.3) was actually greater than that of the
untreated ACA (480 m.sup.2/cm.sup.3). A large percentage of this
surface area can be attributed to the microporosity of the aerogel
substrate, as evidenced by the micropore volume (0.45 cm.sup.3/g)
measured for the composite material. Nevertheless, the presence of
the CNTs within the ACA architecture increased the volumetric
surface area of these monolithic composites. Volumetric surface
areas were calculated from the gravimetric surface areas and the
bulk densities of the ACA substrates before (0.2 g/cm.sup.3) and
after (0.49 g/cm.sup.3) CVD treatment.
The influence of the CNTs on the bulk electrical properties of
these monolithic carbon structures was also examined. Electrical
conductivity in CAs typically scales with density, as electron
transport through the material is dependent on the
interconnectivity of the carbon framework..sup.[8] It was recently
demonstrated that dispersions of double-walled and single-walled
CNTs within the carbon network, even at low loading levels, enhance
the bulk electrical conductivity of CAs..sup.[2d,9] For the
examples described here, however, the CNTs populate the surfaces of
the aerogel substrate and are not embedded directly in the carbon
skeleton. Yet the ACA-CNT composites exhibited significant
increases in electrical conductivity following the CVD treatment.
For example, the electrical conductivity of an ACA-CNT slab with a
bulk density of 0.49 g cm.sup.-1 was measured at 6.6 S cm.sup.-1,
nearly a twofold enhancement relative to that of the untreated ACA
(3.6 S cm.sup.-1). While the primary conduction pathway in these
composites is likely still the skeletal network of the ACA, these
results indicate that the CNTs are involved in electron transport
through the monolith.
Additional measurement information is provided. The bulk densities
of the composites were determined by measuring the dimensions and
mass of the monolithic samples. Scanning electron microscopy (SEM)
was performed on a JEOL 7401-F. Imaging was done at 5-10 keV (20
.mu.A) in SEI mode with a working distance of 2-8 mm. Transmission
electron microscopy (TEM) was performed on a Phillips CM300FEG
operating at 300 keV. Surface area and pore volume were determined
using Brunauer-Emmett-Teller (BET) and Dubinin-Ashtakov (DA)
methods using as ASAP 2010 Surface Area Analyzer
(Micromeritics)..sup.[10] Composite samples were heated to
300.degree. C. under vacuum (10.sup.-5 Torr) for 24 hours to remove
all adsorbed species prior to analysis. Electrical conductivity was
measured using the four-probe method similar to previous
studies..sup.[8] Metal electrodes were attached to the ends of the
CNT-ACA slabs. The amount of current transmitted through the sample
during measurement was 100 mA and the voltage drop along the sample
was measured over distances of 3 to 6 mm with seven or more
measurements taken on each sample.
Comparative Example
For at least some of these embodiments, an important aspect was the
design of a CA substrate with requisite porosity to allow for
efficient diffusion of the CVD gases through the monolith during
the growth process. Previous efforts in this area showed that the
short mean free path of diffusion intrinsic to traditional
mesoporous CAs (materials with pore diameters primarily between
about 2 and about 50 nm) limited the growth of CNTs within these
substrates..sup.[4a,d] For example, CVD growth of CNTs within
Fe-loaded CAs did not occur beyond a depth of about 1 .mu.m from
the surface of the monolithic CA substrate. For another comparative
example, see FIG. 9 in reference 4a.
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Additional Embodiment
A for Silicon Nanowires
Additional embodiments are described here as "Embodiments A". See,
for example, U.S. Provisional Application Ser. No. 61/473,537 filed
Apr. 8, 2011 which is hereby incorporated by reference in its
entirety for all purposes ("SILICON NANOWIRES ON CARBON AEROGEL
SCAFFOLD").
One form of nanomaterial is the nanowire, including silicon
nanowires. By way of additional background, silicon is a promising
anode material for Li-ion batteries. The theoretical capacity of a
silicon anode is 4200 Ah/kg. The lithium alloys with the silicon to
form Li 4.4 Si. During the intercalation process, the volume of the
electrode can increase to as much as 400% of the original volume.
These volume changes may cause the Si to lose contact with the
current collector, reducing capacity and shortening battery
lifetime.
One way of overcoming these limitations has been to coat silicon
onto a current collector as a thin film, but these coatings
typically have too little active material to make a viable battery.
Alternatively, silicon in the form of nanowires have been
demonstrated as viable electrodes. The nanowires are deposited via
chemical vapor deposition onto a metal foil, which acts as the
current collector. These devices showed capacities of 2100 Ah/kg at
high discharge rates, based on the mass of the silicon. However, if
the total mass of the electrode is used as basis for calculating
the capacity, the capacity drops significantly: the silicon
nanowires have a density of 2.33 g/cm.sup.3, a height of -10 um,
and a volume occupancy of less than 100%. The electrode, on the
other hand, has a density of 8 g/cm.sup.3 and a thickness of 20
.mu.m. Thus, the capacity calculated by total mass drops to less
than 120 Ah/kg, which is not substantially better than that of
conventional Li-ion anodes.
This disclosure provides an efficient and cost effective system to
overcome this limitation.
Additional embodiments are summarized. In one aspect, this
disclosure provides a silicon nanowire-based anode with a
substantially higher loading rate of silicon nanowires. A
conductive porous conductor, can be used as a substrate. The pore
size of the conductor can be in the 10-50 .mu.m range. The
conductor may have a secondary pore size in the nanometer range.
The surface area of the scaffold can range from 50-220
cm.sup.2/cm.sup.3.
The silicon nanowires are synthesized directly onto this scaffold.
Catalyst may be deposited by immersing the scaffold in an aqueous
solution of the salt of the catalyst and subsequent precipitation
of the catalyst onto the scaffold, or by patterning the catalyst
onto the scaffold using a polymeric template. The synthesis of the
nanowires is preformed using chemical vapor deposition.
The thickness of the active material is no longer limited by the
wire length and can be chosen in thicknesses equal to that of a
conventional Li-ion anode (150-200 .mu.m). For an identical volume
occupancy of nanowires, the amount of silicon increases by a factor
of 40. Factoring in the reduced density of the scaffold material
(2.2 g/cm.sup.3 for carbon, at 24% volume occupancy), the
achievable capacity of the monolithic electrode should lie around
650 Ah/kg, more than five times the capacity currently achieved on
a flat electrode.
For easier integration of the scaffold material, the scaffold can
be milled into particles and deposited onto a metal electrode like
a conventional battery material. When this process is used, the
capacity drops to 350 Ah/kg, still almost three times as high as
the capacity of the flat electrode.
The cost of this type of anode per Ah of capacity is expected to be
lower than that of an anode made on a flat substrate, since a
greater amount of nanowires can be produced at identical use of
reactants and furnace time:
Additional detailed description is provided.
Provided herein is a novel anode structure for Li-ion batteries
based on silicon nanowires. The nanowires are synthesized in a
conductive porous structure. In this manner, the volumetric density
of the silicon nanowires can be drastically increased, and the mass
of non-functional material in the anode structure is decreased. The
anode structure can be used as monolithic block. In one embodiment
for silicon nanowires, it can be milled into 50 .mu.m-sized
particles and utilized in a conventional fabrication method.
Thus, in one aspect, provided is an article comprising, or
alternatively consisting essentially of, or yet further consisting
of, at least one lithium-ion battery comprising, or alternatively
consisting essentially of, or yet further consisting of, at least
one anode, wherein the anode comprises, or alternatively consists
essentially of, or yet further consist of, at least one porous
conductor comprising external and internal surfaces, wherein the
porous conductor further comprises silicon nanowires. Non-limiting
examples of porous conductors include, an aerogel, such as a carbon
aerogel, a xerogel, or an open-cell foam.
Thus, in one aspect, the conductive scaffold is an article
comprising: or alternatively consisting essentially of, or yet
further consisting of, at least one porous conductor comprising
external and internal surfaces, wherein the porous conductor
internal surfaces are functionalized directly with at least one
material which is an active material for energy storage. In one
aspect, the porous conductor has pores for which the aspect ratio
and pore shape are adapted to enhance a mass transport rate and
reduce internal resistance and concentration polarization through
the pores for use in energy storage.
In another aspect, the porous conductor is one or more of an
aerogel, such as a carbon aerogel.
In a further aspect, the material conformally coats the internal
surfaces of the porous conductor. In a yet further aspect, the
porous conductor comprises a bimodal pore structure. Alternatively,
the porous conductor comprises a bimodal pore structure comprising
(i) micropores or mesopores, and (ii) macropores. Non-limiting
examples of such include a bimodal pore structure comprising (i)
micropores or mesopores, and (ii) macropores, wherein the
micropores have an average pore diameter of less than 2 nm, or
alternatively less than 1.5 nm, or alternatively less than 1.0 nm,
or alternatively less than 0.5 nm, and wherein micropores or
mesopores are interconnected by a continuous network of the
macropores which have an average pore diameter of 100 nm to 10
microns, and variations there between.
This conductor can have pores, e.g., column-shaped pores. The
material can comprise a metal or metal oxide, non-limiting examples
of such include titanium dioxide, manganese dioxide, cobalt
dioxide, and/or ruthenium.
Various dimensions are contemplated. A non-limiting example is a
porous conductor having a surface area of about 50 to about 220
cm.sup.2/cm.sup.3.
In one aspect, the porous conductor has pores with a bimodal pore
size distribution. Yet further, the porous conductor has pores with
a bimodal pore size distribution, wherein one set of pores has an
average diameter of at least one micron, and a second set of pores
has an average diameter of less than 10 nm.
Various methods known to the skilled artisan can be used to grow
the nanowires, non-limiting examples of which include by chemical
vapor deposition. In a further aspect, the silicon nanowires are
made by chemical vapor deposition and the porous conductor
comprises catalyst for formation of the silicon nanowires.
The thickness of the conductor can vary, e.g., the porous conductor
can have a thickness of about 150 to about 200 microns.
In addition, the silicon nanowires can have an average diameter of
about 10 nm to about 500 nm, or about 10 nm to about 100 nm.
Also provided is a method of making the material, the method
comprising, or alternatively consisting essentially of, or yet
further consisting of, grinding into a powder or having a powder
comprising a material comprising at least one porous conductor
comprising external and internal surfaces, wherein the porous
conductor further comprises silicon nanowires. In one aspect, the
powder is deposited onto an electrode. Electrodes containing the
powder are further provided herein.
An alternative method comprises, or alternatively consists
essentially of, or yet further consists of, providing a material
containing at least one porous conductor having external and
internal surfaces, providing a catalyst in the pores of the
material, and depositing by chemical vapor deposition silicon
nanowires in the porous conductor.
Materials produced by these methods are further provided herein and
devices containing them, e.g., batteries, battery-powered devices
or hybrid electric devices, are also provided.
Additional description for aerogels and composite materials can be
found in, for example, U.S. Patent Publication Nos. 2009/0042101;
2010/0139823; 2010/0187484; 2010/0190639; and 2011/0024698.
One embodiment provides an article comprising: at least one
lithium-ion battery comprising at least one anode, wherein the
anode comprises: at least one porous conductor comprising external
and internal surfaces, wherein the porous conductor further
comprises silicon nanowires.
In one embodiment, the porous conductor is an aerogel. In one
embodiment, wherein the porous conductor is a carbon aerogel. In
one embodiment, the porous conductor has a surface area of about 50
to about 220 cm.sup.2/cm.sup.3. In one embodiment, the porous
conductor has pores with a bimodal pore size distribution. In one
embodiment, the porous conductor has pores with a bimodal pore size
distribution, wherein one set of pores has an average diameter of
at least one micron, and a second set of pores has an average
diameter of less than 10 nm.
In one embodiment, the silicon nanowires are made by chemical vapor
deposition. In one embodiment, the silicon nanowires are made by
chemical vapor deposition and the porous conductor comprises
catalyst for formation of the silicon nanowires.
In one embodiment, the porous conductor has a thickness of about
150 to about 200 microns. In one embodiment, the silicon nanowires
have an average diameter of about 10 nm to about 500 nm, or about
10 nm to about 100 nm.
Another embodiment provides a method comprising: providing a
material comprising at least one porous conductor comprising
external and internal surfaces, wherein the porous conductor
further comprises silicon nanowires; grinding the material into a
powder.
In one embodiment, the method further comprises the step of
depositing the powder onto an electrode.
Another embodiment provides a method comprising: providing a
material comprising at least one porous conductor comprising
external and internal surfaces, providing a catalyst in the pores
of the material, depositing by chemical vapor deposition silicon
nanowires in the porous conductor.
In one aspect, this disclosure provides a silicon nanowire-based
anode with a substantially higher loading rate of silicon
nanowires. A conductive porous conductor can be used as a
substrate. The pore size of the conductor is in the 10-50 .mu.m
range.
Additional Embodiment
B
Additional embodiments are described here as "Embodiments B". See,
for example, U.S. Provisional Application Ser. No. 61/473,654 filed
Apr. 8, 2011 which is hereby incorporated by reference in its
entirety for all purposes ("NANOWIRES AND NANOTUBE SYNTHESIS USING
3-D POROUS SUBSTRATES").
By way of additional background, nanomaterials, such as carbon
nanotubes, silicon nanowires, or nanoparticles, have emerged in the
last decade as advanced materials for applications ranging from
sensing and logic circuits to energy storage and structural
fillers. To date, most of these applications have not been
commercially realized due to difficulties with nanomaterial
synthesis and processing. For example, most synthesis methods for
nanotubes or nanowires require a substrate on which catalytic
growth of the nanomaterial is performed. In almost all cases, the
substrate is flat to minimize the impact of mass transport on the
synthesis. This approach severely limits the volume of nanomaterial
production, increases the cost of the materials and reduces the
flexibility for applications.
This disclosure provides an efficient and cost effective system to
overcome these limitations.
This disclosure provides a strategy to address the limitations of
the current state of the art and by changing the architecture of
the substrate. Utilization of a three-dimensionally porous solid as
a substrate provides significantly more surface area for growth of
nanomaterials relative to a flat substrate, and thus has the
potential to Improve both the rate and cost of nanomaterials
production. Even if a substrate with relatively large pore sizes
(10 to 100 microns in diameter) is chosen, the available surface
area is still enhanced by three to four orders of magnitude over
that of a flat substrate.
In one aspect, provided herein is a novel approach for the
production of carbon nanotubes and inorganic nanowires that
utilizes three-dimensionally porous substrates, such as aerogels,
xerogels or open cell foams. In this approach, the catalytic growth
of the nanomaterials occurs on the inner surfaces of the porous
substrate. Due to the increased surface area available for growth
of the nanowires or nanotubes, these porous substrates allow
production of the nanomaterials at a higher rate and lower cost
than those techniques that utilize flat surfaces as substrates.
The pore structures of the substrates are design to allow efficient
transport of gas- or liquid-phase precursors to the catalysts that
are distributed on the internal surface area. In addition, the pore
structure of the substrate can engineered to control the morphology
of the nanotubes/wires. For example, isolated micropores can be
created on the inner surfaces of the substrate that serve as
nucleation sites for catalyst nanoparticles. These micropores will
define the size and morphology of the catalysts during deposition
and prevent ripening of these particles during the nanowire growth,
thereby providing control over the final nanowire dimensions.
These substrates can be engineered as sacrificial templates that
are removed (either chemically or thermally) from the
nanotube/wires after growth. Alternatively, the properties of the
substrate can be tailored to allow for integration of the
substrate/nanowire composite structure directly into the device of
interest. As an example, silicon nanowires grown on the inner
surfaces of an electrically-conductive porous carbon substrate can
be used as an anode for next generation Li-ion batteries. Finally,
the porous substrate approach enables the fabrication of
well-separated nanotubes/wires without post-processing steps that
can potentially degrade the as-grown material. Applicants have
demonstrated the utility of this approach in the growth of
multi-walled carbon nanotubes on the inner surfaces of carbon
aerogel structures.
Further detailed description is provided.
Provided herein is an article comprising, or alternatively
consisting essentially of, or yet further consisting of, at least
one porous conductor, wherein the porous conductor comprises at
least one nanomaterial in the pores of the porous conductor.
Non-limiting examples of nanomaterials include a nanotube or a
nanowire, e.g., a carbon nanotube, an inorganic nanowire or a
silicon nanowire, including mixtures thereof.
In one aspect, the porous substrate comprises an aerogel, a
xerogel, or an open-cell foam.
The porous substrate can comprise micropores, wherein catalyst
nanoparticles are disposed in the micropores which catalyze growth
of the nanomaterial. In another aspect, the porous substrate can
comprise micropores, wherein catalyst nanoparticles are disposed in
the micropores which catalyze growth of the nanomaterial, wherein a
diameter of the nanomaterial is determined by a diameter of the
micropore.
Devices and materials containing the articles are further provided
herein. Such devices include, for example, an energy storage
device, an electrode for a capacitor, an ultra-capacitor or an
electrode for a battery, e.g., an electrode for a Li-ion
battery.
Also provided herein is a method for producing the articles, the
method comprising, or alternatively consisting essentially of, or
yet further consisting of, growing at least one nanomaterial in at
least one porous conductor, wherein the at least one porous
conductor comprises external and internal surfaces, and in the
presence of a catalyst. In a further aspect, the method comprises,
or alternatively consists essentially of, or yet further consists
of, removing the porous conductor after the nanomaterial is grown.
Various methods are known to the skilled artisan for removing the
porous conductor. Non-limiting examples include thermal removal
after the nanomaterial is grown or chemical removal after the
nanomaterial is grown.
Materials produced by these methods as well as their use are also
provided herein.
It is to be understood that while the invention has been described
in conjunction with the above embodiments, that the foregoing
description and examples are intended to illustrate and not limit
the scope of the invention. Other aspects, advantages and
modifications within the scope of the invention will be apparent to
those skilled in the art to which the invention pertains.
Additional description for aerogels and composite materials can be
found in, for example, U.S. Patent Publication Nos. 2009/0042102;
2010/0139823; 2010/0187484; 2010/0190639; and 2011/0024698.
One embodiment provides an article comprising: at least one porous
conductor, wherein the porous conductor comprises at least one
nanomaterial in the pores of the porous conductor.
Another embodiment provides that the nanomaterial is a nanotube or
a nanowire.
In another embodiment, the nanomaterial is a carbon nanotube. In
another embodiment, the nanomaterial is an inorganic nanowire. In
another embodiment, the nanomaterial is a silicon nanowire.
In another embodiment, the porous substrate comprises an aerogel, a
xerogel, or an open-cell foam.
In another embodiment, the porous substrate comprises micropores,
wherein catalyst nanoparticles are disposed in the micropores which
catalyze growth of the nanomaterial.
In another embodiment, the porous substrate comprises micropores,
wherein catalyst nanoparticles are disposed in the micropores which
catalyze growth of the nanomaterial, wherein a diameter of the
nanomaterial is determined by a diameter of the micropore.
In another embodiment, the article is an energy storage device. In
another embodiment, the article is an electrode for a capacitor or
an ultracapacitor. In another embodiment, the article is an
electrode for a battery. In another embodiment, the article is an
electrode for a Li-ion battery. Another embodiment provides a
method comprising growing in the presence of a catalyst at least
one nanomaterial in at least one porous conductor, the porous
conductor comprising external and internal surfaces.
In another embodiment, the porous conductor is removed after the
nanomaterial is grown. In another embodiment, the porous conductor
is thermally removed after the nanomaterial is grown. In another
embodiment, the porous conductor is chemically removed after the
nanomaterial is grown.
Provided herein is an article containing at least one nanomaterial
in the pores of the porous conductor. Non-limiting examples of
nanomaterials include a nanotube or a nanowire, e.g., a carbon
nanotube, an inorganic nanowire or a silicon nanowire, including
mixtures thereof.
Applicants are providing this description to give a broad
representation of the invention. Various changes and modifications
within the spirit and scope of the invention will become apparent
to those skilled in the art from this description and by practice
of the invention. The scope of the invention is not intended to be
limited to the particular forms disclosed and the invention covers
all modifications, equivalents, and alternatives falling within the
spirit and scope of the invention as defined by the claims.
* * * * *