U.S. patent application number 14/661764 was filed with the patent office on 2015-12-03 for systems, methods, and materials for producing hydrocarbons from carbon dioxide.
The applicant listed for this patent is INDIAN INSTITUTE OF TECHNOLOGY MADRAS. Invention is credited to Tamilarasan PALANISAMY, Ramaprabhu SUNDARA.
Application Number | 20150345034 14/661764 |
Document ID | / |
Family ID | 54701076 |
Filed Date | 2015-12-03 |
United States Patent
Application |
20150345034 |
Kind Code |
A1 |
SUNDARA; Ramaprabhu ; et
al. |
December 3, 2015 |
SYSTEMS, METHODS, AND MATERIALS FOR PRODUCING HYDROCARBONS FROM
CARBON DIOXIDE
Abstract
Disclosed herein are systems and methods to effectively convert
carbon dioxide to hydrocarbons by electrochemical and/or
photoelectrochemical methods. In one embodiment, a
photoelectro-chemical cell may include an anode, a cathode
comprising a carbon material, wherein the carbon material is
surface functionalized with at least one poly(ionic) liquid, and
wherein at least one metallic nanoparticle is disposed on the
functionalized carbon material surface, and an energy source
configured to irradiate the anode.
Inventors: |
SUNDARA; Ramaprabhu;
(Chennai, IN) ; PALANISAMY; Tamilarasan; (Chennai,
IN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
INDIAN INSTITUTE OF TECHNOLOGY MADRAS |
Chennai |
|
IN |
|
|
Family ID: |
54701076 |
Appl. No.: |
14/661764 |
Filed: |
March 18, 2015 |
Current U.S.
Class: |
205/462 ;
204/242; 204/252; 205/340; 502/167 |
Current CPC
Class: |
Y02P 20/133 20151101;
C25B 11/0489 20130101; C25B 9/10 20130101; Y02P 20/135 20151101;
C25B 3/04 20130101; C25B 11/0405 20130101; C25B 1/003 20130101;
C25B 9/08 20130101; C25B 11/12 20130101 |
International
Class: |
C25B 3/04 20060101
C25B003/04; C25B 11/04 20060101 C25B011/04; C25B 11/12 20060101
C25B011/12; C25B 9/08 20060101 C25B009/08 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 18, 2014 |
IN |
1425/CHE/2014 |
Claims
1. A photoelectrochemical cell comprising: an anode; a cathode
comprising a carbon material, wherein the carbon material is
surface functionalized with at least one poly(ionic) liquid, and
wherein at least one metallic nanoparticle is disposed on the
functionalized carbon material surface; and an energy source
configured to irradiate the anode.
2. (canceled)
3. The photoelectrochemical cell of claim 1, wherein the anode is
in contact with water in a first compartment of the
photoelectrochemical cell.
4. The photoelectrochemical cell of claim 3, wherein the anode is
configured to oxidize water molecules.
5. (canceled)
6. The photoelectrochemical cell of claim 1, wherein the cathode is
in contact with carbon dioxide dissolved in water in a second
compartment of the photoelectrochemical cell.
7. The photoelectrochemical cell of claim 6, wherein the cathode is
configured to reduce carbon dioxide to at least one hydrocarbon
selected from the group consisting of methanol, methane,
isopropanol, formic acid, formaldehyde, glyoxal, ethanol, butanol,
and any combination thereof.
8. (canceled)
9. The photoelectrochemical cell of claim 1, wherein the at least
one metallic nanoparticle comprises Au, Ag, Pd, Co, Cu, Pt, Ni, Fe,
Mn, Cr, V, Ti, Sc, Ce, or any combination thereof.
10. The photoelectrochemical cell of claim 1, wherein the at least
one poly(ionic) liquid comprises 3-ethyl-1-vinylimidazolium
tetrafluoroborate, 1-methyl-3-vinylimidazolium tetrafluoroborate,
1-butyl-3-methylimidazolium tetrafluoroborate,
1-vinyl-3-methylimidazolium tetrafluoroborate,
1-isobutenyl-3-methylimidazolium tetrafluoroborate,
1-allyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide,
1-allyl-3-methylimidazolium bromide,
1,3-bis(cyanomethyl)imidazolium bis(trifluoromethylsulfonyl)imide,
or any combination thereof.
11. The photoelectrochemical cell of claim 1, wherein the carbon
material comprises a carbon nanotube, graphene, graphene oxide, or
any combination thereof.
12-13. (canceled)
14. The photoelectrochemical cell of claim 1, wherein the anode
comprises a metal or a semiconductor.
15-17. (canceled)
18. The photoelectrochemical cell of claim 1, further comprising an
electrolyte in contact with the first compartment and the second
compartment, wherein the electrolyte allows movement of protons
from the first compartment to the second compartment through a
proton exchange membrane.
19. (canceled)
20. The photoelectrochemical cell of claim 1, wherein the energy
source comprises UV light, visible light, sunlight, or any
combination thereof.
21. A method of reducing carbon dioxide to one or more
hydrocarbons, the method comprising: introducing water to a first
compartment of an electrochemical cell, wherein the first
compartment includes an anode; introducing carbon dioxide dissolved
in water to a second compartment of the electrochemical cell,
wherein the second compartment includes a cathode, wherein the
cathode comprises a carbon material that is surface functionalized
with at least one poly(ionic) liquid and at least one metallic
nanoparticle disposed on the functionalized carbon material
surface; and applying an electrical potential between the anode and
the cathode sufficient to reduce carbon dioxide to one or more
hydrocarbons.
22. The method of claim 21, wherein applying the electrical
potential comprises applying the electrical potential by an
external electrical power, irradiation, or any combination
thereof.
23. The method of claim 21, wherein introducing water comprises
introducing water to the first compartment of the electrochemical
cell, wherein the first compartment includes a metal anode or a
semiconductor anode.
24. (canceled)
25. The method of claim 21, wherein introducing carbon dioxide
dissolved in water comprises introducing carbon dioxide dissolved
in water to the second compartment of the electrochemical cell,
wherein the second compartment includes the cathode, wherein the
cathode is a carbon nanotube, graphene, graphene oxide, or any
combination thereof that is surface functionalized with at least
one poly(ionic) liquid and at least one metallic nanoparticle
disposed on the functionalized surface, and wherein the metallic
nanoparticle is selected from Au, Ag, Pd, Co, Cu, Pt, Ni, Fe, Mn,
Cr, V, Ti, Sc, Ce, and any combination thereof.
26-28. (canceled)
29. The method of claim 21, wherein applying the electrical
potential comprises applying the electrical potential between the
anode and the cathode sufficient to reduce carbon dioxide to the
one or more hydrocarbons selected from the group consisting of
methanol, isopropanol, formic acid, formaldehyde, glyoxal, ethanol,
butanol, and any combination thereof.
30-31. (canceled)
32. The method of claim 21, further comprising isolating the one or
more hydrocarbons from the second compartment of the
electrochemical cell.
33. A catalyst comprising an exfoliated graphene, wherein the
exfoliated graphene is surface functionalized with at least one
poly(ionic liquid), and wherein at least one metallic nanoparticle
is disposed on the functionalized graphene surface.
34. The catalyst of claim 33, wherein the at least one poly(ionic)
liquid comprises 3-ethyl-1-vinylimidazolium tetrafluoroborate,
1-methyl-3-vinylimidazolium tetrafluoroborate,
1-butyl-3-methylimidazolium tetrafluoroborate,
1-vinyl-3-methylimidazolium tetrafluoroborate,
1-isobutenyl-3-methylimidazolium tetrafluoroborate,
1-allyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide,
1-allyl-3-methylimidazolium bromide,
1,3-bis(cyanomethyl)imidazolium bis(trifluoromethylsulfonyl)imide,
or any combination thereof.
35-36. (canceled)
37. The catalyst of claim 33, wherein the at least one metallic
nanoparticle comprises Au, Ag, Pd, Co, Cu, Pt, Ni, Fe, Mn, Cr, V,
Ti, Sc, Ce, or any combination thereof.
38. (canceled)
39. The catalyst of claim 33, wherein the catalyst is an electrode
in a photoelectrochemical cell, electrochemical cell, or a fuel
cell.
40. A method of preparing a catalyst, the method comprising:
oxidizing graphite to form graphite oxide; exfoliating graphite
oxide to form one or more graphene nanosheets; contacting the one
or more graphene nanosheets with a poly(ionic) liquid to form one
or more coated graphene nanosheets; and contacting a metal compound
with the one or more coated graphene nanosheets.
41. The method of claim 40, wherein oxidizing the graphite
comprises heating a powdered graphite with a mixture of an acid,
sodium nitrate, and an oxidizing agent to a temperature of about
0.degree. C. to about 90.degree. C. for about 30 minutes to about 6
hours.
42-45. (canceled)
46. The method of claim 40, wherein exfoliating the graphite oxide
comprises heating the graphite oxide to a temperature of about
150.degree. C. to about 400.degree. C. in the presence of hydrogen
(H.sub.2).
47. (canceled)
48. The method of claim 40, wherein contacting the one or more
graphene nanosheets with the poly(ionic) liquid comprises refluxing
the one or more graphene nanosheets with the poly(ionic) liquid and
an initiator at a temperature of about 60.degree. C. to about
90.degree. C. for about 10 hours to about 24 hours.
49. The method of claim 48, wherein refluxing comprises refluxing
the one or more graphene nanosheets with the poly(ionic) liquid
selected from the group consisting of 3-ethyl-1-vinylimidazolium
tetrafluoroborate, 1-methyl-3-vinylimidazolium tetrafluoroborate,
1-butyl-3-methylimidazolium tetrafluoroborate,
1-vinyl-3-methylimidazolium tetrafluoroborate,
1-isobutenyl-3-methylimidazolium tetrafluoroborate,
1-allyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide,
1-allyl-3-methylimidazolium bromide,
1,3-bis(cyanomethyl)imidazolium bis(trifluoromethylsulfonyl)imide,
and any combination thereof and the initiator.
50-53. (canceled)
54. The method of claim 40, wherein contacting the metal compound
with the one or more coated graphene nanosheets comprises: mixing
the one or more coated graphene nanosheets with the metal compound
in a solvent to form a solution; and dielectrically heating the
solution.
55. The method of claim 54, wherein mixing comprises mixing the one
or more coated graphene nanosheets with the metal compound selected
from the group consisting of a Au compound, a Ag compound, a Pd
compound, a Co compound, a Cu compound, a Pt compound, a Ni
compound, a Fe compound, a Mn compound, a Cr compound, a V
compound, a Ti compound, a Sc compound, a Ce compound, and any
combination thereof.
56-57. (canceled)
58. The method of claim 54, wherein the dielectrically heating the
solution comprises heating by a radio frequency energy having a
frequency of about 300 MHz to about 300 GHz for about 10 seconds to
about 60 minutes.
59-60. (canceled)
Description
RELATED APPLICATION
[0001] This application claims priority benefit under Title 35
.sctn.119(a) of Indian Patent Application No. 1425/CHE/2014, filed
Mar. 18, 2014, entitled, "SYSTEMS, METHODS, AND MATERIALS FOR
PRODUCING HYDROCARBONS FROM CARBON DIOXIDE," the contents of which
are herein incorporated by reference.
BACKGROUND
[0002] Photoelectrochemical conversion of carbon dioxide (CO.sub.2)
into hydrocarbons is one way of reducing the emission of carbon
dioxide into the environment. This not only helps to reduce carbon
dioxide levels, but also converts renewable energy, such as
sunlight, into a chemical form that can be stored for later use.
The electrochemical techniques and systems used in carbon dioxide
reduction have many limitations, including the stability,
efficiency and cost of materials used in such systems, the ability
to control the processes effectively, and the rate at which carbon
dioxide is converted. Thus, it is desirable to develop economical
and efficient methods and systems to convert carbon dioxide to
hydrocarbons.
SUMMARY
[0003] Disclosed herein are systems and methods to convert carbon
dioxide to one or more hydrocarbons by electrochemical and/or
photoelectrochemical methods. In one embodiment, a
photoelectrochemical cell may include an anode, a cathode
comprising a carbon material, wherein the carbon material is
surface functionalized with at least one poly(ionic) liquid, and
wherein at least one metallic nanoparticle is disposed on the
functionalized carbon material surface, and an energy source
configured to irradiate the anode.
[0004] In another embodiment, a method of reducing carbon dioxide
to one or more hydrocarbons includes introducing water to a first
compartment of an electrochemical cell, wherein the first
compartment includes an anode, introducing carbon dioxide dissolved
in water to a second compartment of the electrochemical cell,
wherein the second compartment includes a cathode, wherein the
cathode comprises a carbon material that is surface functionalized
with at least one poly(ionic) liquid and at least one metallic
nanoparticle disposed on the functionalized carbon material
surface, and applying an electrical potential between the anode and
the cathode sufficient to reduce carbon dioxide to one or more
hydrocarbons.
[0005] In an additional embodiment, a catalyst comprises an
exfoliated graphene, wherein the exfoliated graphene is surface
functionalized with at least one poly(ionic) liquid, and wherein at
least one metallic nanoparticle is disposed on the functionalized
graphene surface.
[0006] In a further embodiment, a method of preparing a catalyst
includes oxidizing graphite to form graphite oxide, exfoliating
graphite oxide to form one or more graphene nanosheets, contacting
the one or more graphene nanosheets with a poly(ionic) liquid to
form one or more coated graphene nanosheets, and contacting a metal
compound with the one or more coated graphene nanosheets.
BRIEF DESCRIPTION OF THE FIGURES
[0007] FIG. 1 depicts a schematic diagram of a photoelectrochemical
cell according to an embodiment.
[0008] FIG. 2 shows high resolution transmission electron
microscopy (HRTEM) images of (a) HEG, (b) HEG-PIL, and (c)
Pt/HEG-PIL according to an embodiment.
[0009] FIG. 3 shows a cyclic voltammogram of carbon dioxide
reduction on Pt/HEG-PIL electrode. Electrolyte used was carbon
dioxide saturated 0.5 M KHCO.sub.3, and reference electrode was
saturated Ag/AgCl electrode, according to an embodiment.
[0010] FIG. 4 shows transient current generated by Pt/MWNTs (Pt
loaded multi-walled nanotubes), Pt/HEG, Pt/MWNTs-PIL and Pt/HEG-PIL
catalysts for carbon dioxide electrocatalytic conversion at -0.6 V
in carbon dioxide saturated 0.5 M KHCO.sub.3 aqueous solution,
according to an embodiment.
[0011] FIG. 5 shows an FTIR spectrum of (a) deionized water, (b)
cathode reservoir solution, and (c) commercial methanol, according
to an embodiment.
[0012] FIG. 6 shows a UV-Vis spectrum of cathode reservoir solution
with Pt/HEG and Pt/HEG-PIL cathode electrocatalyst, according to an
embodiment.
DETAILED DESCRIPTION
[0013] This disclosure is not limited to the particular systems,
devices and methods described, as these may vary. The terminology
used in the description is for the purpose of describing the
particular versions or embodiments only, and is not intended to
limit the scope.
[0014] In the detailed description below, reference is made to the
accompanying drawings, which form a part hereof. In the drawings,
similar symbols typically identify similar components, unless
context dictates otherwise. The illustrative embodiments described
in the detailed description, drawings, and claims are not meant to
be limiting. Other embodiments may be used, and other changes may
be made, without departing from the spirit or scope of the subject
matter presented herein. It will be readily understood that the
aspects of the present disclosure, as generally described herein,
and illustrated in the Figures, can be arranged, substituted,
combined, separated, and designed in a wide variety of different
configurations, all of which are explicitly contemplated
herein.
[0015] Disclosed herein are methods and systems for electrochemical
or photoelectro-chemical reduction of carbon dioxide to one or more
hydrocarbons. FIG. 1 illustrates a system in accordance with some
embodiments of the disclosure for catalyzed electrochemical and/or
photoelectrochemical conversion of carbon dioxide to hydrocarbons.
The reduction of carbon dioxide may suitably be achieved in an
efficient manner in a divided electrochemical or
photoelectrochemical cell 100 defining a first compartment 101 that
includes an anode 104, and defining a second compartment 102 which
includes a cathode 105. The cathode electrode comprises a metal
nanoparticle catalyst disposed on a carbon support. The
compartments are separated by an electrolyte 103 such as a proton
exchange membrane (PEM) or any other ion-conducting bridge. The
first compartment and the second compartment may also contain
outlet valves 106 and 108, and inlet valves 107 and 109. Both the
compartments may contain water. Further, carbon dioxide may
continuously be introduced into the second compartment, to form
carbon dioxide saturated water. The anode 104 and cathode 105 are
further connected via electrically conductive conduits 110, in the
case of a photoelectrocehmical cell, to a current collector (not
shown) or in the case of an electrochemical cell, to an external
power source (not shown). Further, the cell 100 may optionally have
a window 111 to allow a light source to illuminate the anode 104.
The hydrocarbons that may be produced from the systems and methods
described herein include, but not limited to, methanol, methane,
isopropanol, formic acid, formaldehyde, glyoxal, ethanol, butanol,
or any combination thereof.
[0016] Carbon dioxide may be obtained from any source, for example,
an exhaust stream from fossil fuel burning power plants, from
geothermal or natural gas wells, or the atmosphere itself. Most
suitably, the carbon dioxide may be obtained from concentrated
point sources of generation prior to being released into the
atmosphere. For example, high concentration carbon dioxide sources
may be obtained from natural gas, flue gases of fossil fuel burning
power plants, exhausts from cement factories, from fermenters used
for industrial fermentation of ethanol, and from the manufacture of
fertilizers and refined oil products, and other sources.
[0017] In some embodiments, the anode 104 in the electrochemical
and/or the photoelectrochemical cell described herein may be a
metal or a semiconductor, or any combination of metal and
semiconductors. Non-limiting examples of the metal that may be used
includes Au, Ag, Zn, Ga, Hg, In, Cd, Ti, Pd, or any combination
thereof. Further, examples of semiconductors that may be used are
TiO.sub.2, ZnO, SnO.sub.2, Nb.sub.2O.sub.5, NiO, CdSe, CdTe, InP,
GaAs, CuInSe.sub.2, Fe.sub.2O.sub.3, SiC, ZnSe, or any combination
thereof. In some embodiments, the semiconductor materials described
herein may be doped with metals, such as Ag, Au, Ru, Pt, Pd, Cd,
In, Pb, Sn, or Ga. In some embodiments, the anode may be
nanoparticles that are disposed on a carbon support. For example,
the anode may be TiO.sub.2 nanoparticles coated on a carbon
fabric.
[0018] In some embodiments, the cathode 105 present in the second
compartment 102 of the electrochemical and/or the
photoelectrochemical cell may be a carbon material, and the carbon
material may be surface functionalized with at least one
poly(ionic) liquid. Further, at least one metallic nanoparticle may
be disposed on the functionalized carbon material surface. For
example, the carbon material may be a carbon nanotube, graphene,
graphene oxide, or any combination thereof. In some embodiments, a
graphene cathode may be a plurality of exfoliated graphene
nanosheets. In some embodiments, the graphene nanosheet may have a
thickness of about 0.2 nanometer to about 100 nanometers, about 0.2
nanometer to about 50 nanometers, about 0.2 nanometer to about 10
nanometers, or about 0.2 nanometer to about 1 nanometer. Specific
examples include about 0.2 nanometer, about 1 nanometer, about 5
nanometers, about 10 nanometers, about 2 nanometers, about 50
nanometers, about 100 nanometers, and ranges between any two of
these values.
[0019] In some embodiments, the poly(ionic) liquid may be
3-ethyl-1-vinylimidazolium tetrafluoroborate,
1-methyl-3-vinylimidazolium tetrafluoroborate,
1-butyl-3-methylimidazolium tetrafluoroborate,
1-vinyl-3-methylimidazolium tetrafluoroborate,
1-isobutenyl-3-methyl-imidazolium tetrafluoroborate,
1-allyl-3-methylimidazolium bis(trifluoromethylsulfonyl)-imide,
1-allyl-3-methylimidazolium bromide,
1,3-bis(cyanomethyl)imidazolium bis(trifluoromethyl-sulfonyl)imide,
or any combination thereof. Further, any ionic liquid with
back-bones, including imidazolium, ammonium, phosponium and
sulfonium, and with polymerizable side chains, such as vinyl, or
allyl can be used. Further, the metallic nanoparticle that may be
disposed on the poly(ionic) liquid functionalized carbon material
surface may be Au, Ag, Pd, Co, Cu, Pt, Ni, Fe, Mn, Cr, V, Ti, Sc,
Ce, or any combination thereof.
[0020] In some embodiments, an electrolyte 103 may be in contact
with the first compartment 101 and the second compartment 102, and
the electrolyte may allow movement of protons from the first
compartment 101 to the second compartment 102. For example, the
electrolyte 103 may be a proton exchange membrane (PEM), a salt
bridge, a proton exchange polymer, a proton exchange ceramic, or
any combination thereof. For example, the proton exchange membrane
may be a sulfonated tetrafluorethylene copolymer. In some
embodiments, the first and the second compartments may be separated
by a porous glass frit, microporous separator, ion exchange
membrane, ion conducting bridge, and the like.
[0021] Also disclosed herein are methods of reducing carbon dioxide
to one or more hydrocarbons. In some embodiments, the method
involves introducing water to a first compartment of an
electrochemical and/or a photoelectrochemical cell described
herein, wherein the first compartment includes an anode. The method
also includes introducing carbon dioxide dissolved in water to a
second compartment of the electrochemical and/or a
photoelectrochemical cell, wherein the second compartment includes
a cathode. The carbon dioxide may be dissolved in a water stream
prior to being introduced to the second compartment or carbon
dioxide may be introduced into water in the second compartment to
dissolve therein. In some embodiments, a combination may be used
where additional carbon dioxide is introduced into water already
containing dissolved carbon dioxide. Since carbon dioxide dissolves
more freely in cold water, the water and/or the second compartment
may be cooled or refrigerated. The cathode may comprise a carbon
material that is surface functionalized with at least one
poly(ionic liquid) and at least one metallic nanoparticle disposed
on the functionalized carbon material surface.
[0022] In some embodiments, the anode 104 in the first compartment
of a photoelctrochemical cell is in contact with water. Further,
the anode may be configured to oxidize water molecules. For
example, when a semiconductor is photoactivated, this induces
movement of electrons from the valence band to the conduction band.
The reactive electron-hole pairs are created as a result of this
migration and this may oxidize water molecules to produce oxygen
molecules, protons and the electrons. An exemplary reaction at
anode may be represented as follows:
(anode) 6H.sub.2O.fwdarw.12H.sup.++12e.sup.-+3O.sub.2
[0023] The first compartment may also include inlet(s) and
outlet(s) to allow continuous entry of water and exit of oxygen,
during the process.
[0024] In some embodiments, carbon dioxide may be continuously
introduced into the second compartment 102 through an inlet 109 to
form carbon dioxide saturated water or the water in the second
compartment may be pre-saturated with carbon dioxide. For example,
the concentration of carbon dioxide present in the second
compartment may range from about 20 mM to about 200 mM. The cathode
105 may be in contact with water containing dissolved carbon
dioxide and may reduce carbon dioxide to one or more hydrocarbons.
The electrons generated in the anode compartment travel through the
external circuit 110 and protons may travel through the proton
exchange membrane 103. In the second compartment, the cathode
described herein may act as a catalyst and may catalyze reduction
of carbon dioxide to one or more hydrocarbons. An exemplary
reaction taking place at cathode may be represented as follows:
(cathode)
2CO.sub.2+12H.sup.++12e.sup.-.fwdarw.CH.sub.3--CH.sub.2--OH+3H.sub.2O
[0025] The electrochemical and/or the photoelectrochemical cell of
the present disclosure may be used to reduce carbon dioxide to a
variety of hydrocarbons including, but not limited to, methanol,
methane, isopropanol, formic acid, formaldehyde, glyoxal, ethanol,
butanol, or any combination thereof.
[0026] Further, in some embodiments, the method includes applying
an electrical potential between the anode and the cathode
sufficient to reduce carbon dioxide to one or more hydrocarbons.
The electrical potential may applied from an external electrical
power source, irradiation, or any combination thereof. The
electrical energy for the electrochemical reduction of carbon
dioxide can come from a conventional energy source, including
nuclear and alternatives (hydroelectric, wind, solar power,
geothermal, etc.), from a solar cell or other non-fossil fuel
source of electricity.
[0027] In some embodiments, the carbon dioxide may be reduced by
photoelectrochemical reduction. In these embodiments, the anode is
a semiconductor, and is suitably illuminated with an
electromagnetic radiation of energy equal to or greater than the
band gap of the semiconductor. A window may be provided in the
photoelectrochemical cell to allow the electromagnetic radiation to
illuminate the anode. For example, electromagnetic radiation may be
provided by any suitable source, such as sunlight, and/or an
artificial light source, such as visible light, UV, or any
combination thereof. In an exemplary embodiment, the
electromagnetic radiation is provided by sunlight. In some
embodiments, light may be provided by sunlight at certain times of
operation of a system (for example, during daytime, on sunny days,
etc.) and artificial light may be used at other times of operation
of the system (for example, during night time, on cloudy days, and
the like.). Non-limiting examples of artificial light sources
include a lamp (mercury-arc lamp, a xenon-arc lamp, a quartz
tungsten filament lamp, and the like.), a laser (for example, argon
ion), and/or a solar simulator. In some embodiments, optical fibers
may be used to guide the electromagnetic radiation to illuminate
the anode.
[0028] During photoelectrochemical reduction of carbon dioxide, the
photoelectrochemical cell may produce electrical current due to the
difference in voltage potential between the anode and the cathode.
For example, the electrical current that may be produced may in the
range of about 50 .mu.A/cm.sup.2 to about 500 milliampere/cm.sup.2,
about 50 .mu.A/cm.sup.2 to about 50 milliampere/cm.sup.2, about 50
.mu.A/cm.sup.2 to about 5 milliampere/cm.sup.2, or about 50
.mu.A/cm.sup.2 to about 500 .mu.A/cm.sup.2. This electrical current
may be collected or stored by a current collector. These methods
help to convert renewable energy, such as sunlight, into a chemical
form that can be stored for later use.
[0029] In some embodiments, the methods described herein may be
carried out at temperatures of about 5.degree. C. to about
40.degree. C., and pressures of about 1 to about 6 atmospheres.
[0030] The hydrocarbons produced by the reactions described herein
may be isolated from the second compartment of the electrochemical
cell. In some embodiments, these hydrocarbons may further be used
as reactants. For example, the hydrocarbons may be used as a
feedstock for the production of plastics or for production of
higher carbon-content hydrocarbons. It is further possible to
convert the hydrocarbons to synthetic petrochemicals. The
hydrocarbons may also be used as fuels or stored in a fuel
container. It is possible to use the hydrocarbons produced in an
internal or external combustion engine. The hydrocarbons may be
oxidized, burned, or combusted in an engine or a fuel cell
installed in any suitable vehicle, such as an automobile, aircraft,
or military vehicle. Additionally, the devices/reactors described
herein may also be installed into any such combustion engine, and
the hydrocarbons produced by the reactor may be oxidized to power
the engine.
[0031] Also described herein are methods to make a catalyst. In
some embodiments, the catalyst may be an exfoliated graphene,
wherein the graphene is surface functionalized with at least one
poly(ionic liquid), and wherein at least one metallic nanoparticle
is disposed on the functionalized graphene surface. The catalyst
may be used as an electrode in a photoelectrochemical cell,
electrochemical cell, or a fuel cell. In some embodiments, the
exfoliated graphene catalyst may be a plurality of exfoliated
graphene nanosheets. In some embodiments, the graphene nanosheet
may have a thickness of about 0.2 nanometer to about 100
nanometers, about 0.2 nanometer to about 50 nanometers, about 0.2
nanometer to about 10 nanometers, or about 0.2 nanometer to about 1
nanometer, and ranges between any two of these values. In some
embodiments, the poly(ionic) liquid may be
3-ethyl-1-vinylimidazolium tetrafluoroborate,
1-methyl-3-vinylimidazolium tetrafluoroborate,
1-butyl-3-methylimidazolium tetrafluoroborate,
1-vinyl-3-methylimidazolium tetrafluoroborate,
1-isobutenyl-3-methyl-imidazolium tetrafluoroborate,
1-allyl-3-methylimidazolium bis(trifluoromethylsulfonyl)-imide,
1-allyl-3-methylimidazolium bromide,
1,3-bis(cyanomethyl)imidazolium bis(trifluoromethyl-sulfonyl)imide,
or any combination thereof. Further, any ionic liquid with
back-bones, including imidazolium, ammonium, phosponium and
sulfonium, and with polymerizable side chains, such as vinyl, or
allyl can be used. Further, the metallic nanoparticle that may be
disposed on the poly(ionic) liquid functionalized carbon material
surface may be Au, Ag, Pd, Co, Cu, Pt, Ni, Fe, Mn, Cr, V, Ti, Sc,
Ce, or any combination thereof. For example, the catalyst may be an
exfoliated graphene surface functionalized with
1-vinyl-3-methylimidazolium tetrafluoroborate, and platinum
nanoparticles disposed on the functionalized surface.
[0032] In some embodiments, a method of preparing a catalyst may
include oxidizing graphite to form graphite oxide, exfoliating
graphite oxide to form one or more graphene nanosheets, contacting
the one or more graphene nanosheets with a poly(ionic) liquid to
form one or more coated graphene nanosheets, and contacting a metal
compound with the one or more coated graphene nanosheets.
[0033] In some embodiments, the graphite may be oxidized by Hummers
method as described in the art. For example, the powdered graphite
may be contacted with a mixture of an acid, sodium nitrate, and an
oxidizing agent. In some embodiments, the oxidizing agent may be a
permanganate compound, a persulfate compound, a nitrate compound,
or any combination thereof. The acid may be sulfuric acid or nitric
acid. In some embodiments, the powdered graphite and the mixture
are heated to a temperature of about 0.degree. C. to about
90.degree. C., about 0.degree. C. to about 70.degree. C., about
0.degree. C. to about 50.degree. C., or about 0.degree. C. to about
30.degree. C. Specific examples include about 0.degree. C., about
10.degree. C., about 20.degree. C., about 40.degree. C., about
60.degree. C., about 90.degree. C., and ranges between any two of
these values. The heating may be carried out for about 30 minutes
to about 6 hours, about 30 minutes to about 4 hours, about 30
minutes to about 3 hours, or about 30 minutes to about 2 hours.
Specific examples include about 30 minutes, about 1 hour, about 2
hours, about 3 hours, about 4 hours, about 6 hours, and ranges
between any two of these values. In some embodiments, the reaction
may be performed in step-wise process, the first step comprising
heating the reactants at temperatures below 10.degree. C. for 30
minutes, and the second step comprising heating at temperatures
between 60.degree. C. and 90.degree. C. for 1 hour.
[0034] In some embodiments, the graphite oxide prepared by the
method described herein may be exfoliated by a thermal process. For
example, the graphite oxide may be heated to a temperature of about
150.degree. C. to about 400.degree. C., about 150.degree. C. to
about 300.degree. C., or about 150.degree. C. to about 200.degree.
C. in the presence of hydrogen (H.sub.2). Other exfoliation
techniques that may be used are solar exfoliation, vacuum
exfoliation, microwave exfoliation, electrochemical exfoliation,
ultrasonic exfoliation, and the like.
[0035] In some embodiments, contacting the graphene nanosheets with
a poly(ionic) liquid involves refluxing the graphene nanosheets
with a poly(ionic) liquid and an initiator. Non-limiting examples
of the poly(ionic) liquid include 3-ethyl-1-vinylimidazolium
tetrafluoroborate, 1-methyl-3-vinylimidazolium tetrafluoroborate,
1-butyl-3-methylimidazolium tetrafluoroborate, 1-tetrafluoroborate,
1-allyl-3-methylimidazolium bis(trifluoro-methylsulfonyl)imide,
1-allyl-3-methylimidazolium bromide,
1,3-bis(cyanomethyl)-imidazolium
bis(trifluoromethyl-sulfonyl)imide, or any combination thereof. In
some embodiments, the initiator may be an azo compound, a peroxide,
or any combination thereof.
[0036] In some embodiments, refluxing the graphene nanosheets with
a poly(ionic) liquid and an initiator may be performed at an
elevated temperature, such as a temperature of about 60.degree. C.
to about 90.degree. C., about 60.degree. C. to about 80.degree. C.,
about 60.degree. C. to about 70.degree. C., or about 60.degree. C.
to about 65.degree. C. Specific examples include about 60.degree.
C., about 65.degree. C., about 70.degree. C., about 80.degree. C.,
about 90.degree. C., and ranges between any two of these values. In
some embodiments, the refluxing may be performed for a variety of
times, such as for about 10 hours to about 24 hours, about 10 hours
to about 24 hours, about 10 hours to about 24 hours, or about 10
hours to about 24 hours. Specific examples include about 10 hours,
about 12 hours, about 15 hours, about 18 hours, about 24 hours, and
ranges between any two of these values. The method may further
include the steps of filtering, washing, and drying the graphene
nanosheets coated with poly(ionic) liquid.
[0037] In some embodiments, the poly(ionic) liquid coated graphene
nanosheets may be contacted with a metal compound by mixing them in
a solvent to form a solution, and dielectrically heating the
solution. Non-limiting examples of the metal compound that may be
used are compounds or salts of Au, Ag, Pd, Co, Cu, Pt, Ni, Fe, Mn,
Cr, V, Ti, Sc, Ce, or any combination thereof. Suitable solvent
that may be used include ethylene glycol, propylene glycol,
dimethylformamide, or any combination thereof. When mixed, the
solution may have a pH of about 7 to about 10, about 7 to about 9,
or about 7 to about 8. Specific examples include about pH 7, about
pH 8, about pH 9, about pH 10, and ranges between any two of these
values.
[0038] In some embodiments, the method further includes
dielectrically heating the solution by a radio frequency energy
having a frequency of about 300 MHz to about 300 GHz. For example,
the dielectrically heating step may involve heating by a microwave
energy having a frequency of about 300 MHz to about 300 GHz, about
600 MHz to about 300 GHz, about 1 GHz to about 300 GHz, about 30
GHz to about 300 GHz, or about 100 GHz to about 300 GHz. Specific
examples include, but are not limited to, about 300 MHz, about 5
GHz, about 100 GHz, about 200 GHz, about 300 GHz, and ranges
between any two of these values (including their endpoints). The
dielectric heating may be performed by any device known in the art,
such as an oven.
[0039] In some embodiments, the dielectrically heating step may be
performed for generally any duration of time, for example, for
about 10 seconds to about 60 minutes, about 1 minute to about 60
minutes, about 10 minutes to about 60 minutes, or about 30 minutes
to about 60 minutes. Specific examples include, but are not limited
to, about 10 seconds, about 1 minute, about 5 minutes, about 10
minutes, about 30 minutes, about 60 minutes, and ranges between any
two of these values (including their endpoints). In some
embodiments, the method may further include washing the coated
graphene nanosheets disposed with metal nanoparticles, and
filtering the coated graphene nanosheets disposed with metal
nanoparticles.
EXAMPLES
Example 1
Preparation of PT/Graphene Catalyst
[0040] Graphitic oxide was prepared by Hummers method. Briefly,
about 100 grams of powdered flake graphite and 50 grams of sodium
nitrate were mixed with 2.3 liters of sulfuric acid. The
ingredients were mixed in a 15-liter battery jar that had been
cooled to 0.degree. C. in an ice-bath. While maintaining vigorous
agitation, about 300 grams of potassium permanganate was added to
the suspension. The rate of addition was controlled carefully to
prevent the temperature of the suspension from exceeding 20.degree.
C. The ice-bath was then removed and the temperature of the
suspension was brought to 35.degree. C., where it was maintained
for 30 minutes. About 4.6 liters of water was slowly stirred into
the paste, causing violent effervescence and an increase in
temperature to 98.degree. C. The diluted suspension, brown in
color, was maintained at this temperature for 15 minutes. The
suspension was then further diluted to approximately 14 liters with
warm water and treated with 37% hydrogen peroxide to reduce the
residual permanganate and manganese dioxide. Upon treatment with
the peroxide, the suspension turned bright yellow. The suspension
was filtered resulting in a yellow-brown filter cake. After washing
the yellowish-brown filter cake three times with a total of 14
liters of warm water, the graphite oxide residue was dispersed in
32 liters of water. The remaining salt impurities were removed by
treating with resinous anion and cation exchangers. The dry form of
graphite oxide was obtained by centrifugation followed by
dehydration at 40.degree. C. over phosphorus pentoxide under
vacuum.
[0041] The above obtained graphite oxide was thermally exfoliated
at 200.degree. C. under hydrogen (H.sub.2) atmosphere in a tubular
furnace. The graphene obtained by hydrogen exfoliation technique
had wrinkled structure due to the rapid removal of oxygen
containing functional groups.
[0042] The hydrogen exfoliated graphene (HEG) obtained above was
surface functionalized with a poly(ionic) liquid. Graphene (HEG)
(100 milligrams) was dispersed in methanol (25 mL) by
ultrasonication, followed by the addition of 200 milligrams of
1-vinyl-3-methylimidazolium tetrafluoroborate [(VMIM)BF.sub.4] and
7 milligrams of 2,2'-azobisiso-butyronitrile (AIBN) under stirring.
The mixture was transferred to a 50 mL round-bottomed flask
equipped with a condenser and refluxed for 16 hours at 80.degree.
C. under vigorous stirring and N.sub.2 protection. Further, about
100 mL of double-distilled water was added to the mixture and
filtered through a nylon 66 membrane. The filtered material was
repeatedly washed with double-distilled water and acetone several
times in order to remove physically absorbed polymer and unreacted
monomer. The final product was dried in a vacuum oven at 60.degree.
C. and labeled as HEG-PIL (hydrogen exfoliated graphene-poly(ionic)
liquid).
[0043] The decoration of Pt nanoparticles over the surface of HEG
(hydrogen exfoliated graphene) and HEG-PIL was carried out by
microwave assisted reduction method. Briefly, 50 milligrams of HEG
or HEG-PIL was dispersed in 50 mL ethylene glycol followed by the
drop wise addition of 2.77 mL aqueous solution of H.sub.2PtCl.sub.6
(3.6 milligrams Pt in 1 ml solution). The solution was mixed
thoroughly by stirring and pH value of the solution was adjusted to
8-9 with 1.0 M NaOH aqueous solution. The mixture was exposed to
the microwave irradiation (800 W) for 5 minutes and then diluted
with double-distilled water, filtered through a Nylon 66 membrane,
and washed with double-distilled water and acetone several times.
The product with HEG support was labeled as "Pt/HEG", and with
HEG-PIL support was labeled "Pt/HEG-PIL".
Example 2
Characterization of PT/HEG-PIL Catalyst
[0044] The HEG, Pt/HEG, and Pt/HEG-PIL obtained in Example 1 were
subjected to high resolution transmission electron microscopy
(HRTEM). Images of HEG revealed the disorder induced in graphite
structure resulting in the form of sheets by exfoliation (FIG. 2A).
The rapid removal of intercalated oxygen containing functional
groups and other functional groups during exfoliation resulted in a
wrinkled structure of graphene sheets. The HRTEM image showed the
presence of wrinkles in the planar graphene sheets. FIG. 2B shows
morphology of the poly(ionic) liquid functionalized HEG, where the
presence of islands of poly(ionic) liquid were clearly visible. The
HRTEM image of platinum nanoparticle dispersed HEG-PIL (FIG. 2C)
showed the good dispersion of Pt nanoparticles. In HEG-PIL, the PIL
film on the HEG produced an uniform distribution of the imidazole
groups that may serve as functional groups for the immobilization
of Pt through electrostatic interaction and coordination.
Example 3
Electrochemical Analysis of PT/HEG-PIL
[0045] The electrochemical CO.sub.2 conversion behavior of the
prepared electrocatalyst was determined by conventional three
electrode system. The three electrode system consisted of a working
electrode, a counter electrode, and a reference electrode along
with electrolyte solution. Ag/AgCl electrode was used as reference
electrode, Pt wire as used as a counter electrode, and CO.sub.2
saturated 0.5 M KHCO.sub.3 as electrolyte. The catalyst was
dispersed in isopropanol medium by ultrasonication followed by the
addition of 5 wt % Nafion solution as a binder to form a slurry.
Then the glassy carbon electrode was modified with the slurry of
electrocatalyst and used as a working electrode in three electrode
measurement system. The electrocatalytic reduction potential of
Pt/HEG-PIL with carbon dioxide saturated 0.5 M KHCO.sub.3 was
evaluated by half-cell measurement using cyclic voltammetry (FIG.
3). The glassy carbon electrode was modified with the
electrocatalyst and used as a working electrode in three electrode
measurement system. The reduction signals at -0.6 and -0.48 V were
observed with respect to saturated Ag/AgCl electrode, for the
formation of liquid phase methanol and gas phase methane,
respectively.
Example 4
Electrochemical Analysis of PT/HEG-PIL
[0046] Chronoamperometric technique, a useful method for the
evaluation of the electrocatalysts in fuel cells, was employed to
further investigate the electrochemical performance of the prepared
electrocatalysts and compare their activity. In this method, the
change in current at certain voltage was measured with respect to
time, and the results are shown in FIG. 4.
Example 5
Photoelectrochemical Cell
[0047] TiO.sub.2 coated carbon cloth (anode) and Pt/HEG or
Pt/HEG-PIL coated carbon cloth (cathode) were hot pressed on either
sides of Nafion 117 membrane at 130.degree. C. with 2 ton load for
4 minutes. The cathode dimension was maintained at 11.56 cm.sup.2
with 0.5 mg/cm.sup.2 Pt loading. This membrane-electrode assembly
was further equipped with anode and cathode reservoirs to the
respective sides. The electrical connections were given by
stainless steel plates. Anode reservoir was filled with deionized
water, while the cathode reservoir was continuously circulated with
carbon dioxide saturated deionized water (68 mM, 3 grams/liter at 1
atmosphere partial pressure). The anode reservoir was exposed to
light from a 150 W mercury lamp. The oxygen gas produced under
light exposure was removed frequently by anode reservoir outlet.
Prior to the experiment, the cell was activated for 4 cycles of 15
minutes light exposure in a short circuit.
[0048] Visible light was irradiated to the anode side of the cell
to split water into protons and oxygen molecules. The produced
protons migrated to cathode side of the cell through the Nafion
membrane. At the cathode, protons reacted with dissolved carbon
dioxide molecules to produce hydrocarbons methanol and gas phase
methane. The dissolved methanol in deionized water was sampled at
various time periods and analyzed by spectroscopic techniques. The
Fourier transform infrared (FTIR) spectrum of the cathode solution
was similar to that of methanol, and showed the stretching
vibrations of C--H at around 2800-3000 cm.sup.-1 (FIG. 5). This
clearly confirmed the conversion of carbon dioxide into methanol in
the cathode chamber.
[0049] The quantification of methanol produced in the cathode
chamber was carried out by UV-Vis spectroscopy, using commercial
methanol as a reference standard (absorption band at 240 nm, inset
in FIG. 6). With reference to this peak, the analyzer was
calibrated in the range of 0.5 M to 0.00155 M by serial dilutions.
Based on this calibration curve, the concentration of methanol in
the cathode solution was determined. The cathode reservoir showed a
methanol concentration of 12.63 mM for Pt/HEG-PIL cathode, while it
was 3.08 mM for Pt/HEG cathode, after 250 minutes of reaction (FIG.
6).
[0050] Further, the electricity generated was measured by open
circuit potential (OCP) and current at low load. Pt/HEG-PIL and
Pt/HEG showed an OCP of 510 mV and 450 mV, respectively. Further,
Pt/HEG-PIL cathode generated a current density of of 238
.mu.A/cm.sup.2 at 45 mV potential, while Pt/HEG generated a current
density of 174 .mu.A/cm.sup.2 at 28 mV. These values clearly
indicate the better performance of Pt/HEG-PIL over Pt/HEG in carbon
dioxide conversion and electricity production.
[0051] The present disclosure is not to be limited in terms of the
particular embodiments described in this application, which are
intended as illustrations of various aspects. Many modifications
and variations can be made without departing from its spirit and
scope, as will be apparent to those skilled in the art.
Functionally equivalent methods and apparatuses within the scope of
the disclosure, in addition to those enumerated herein, will be
apparent to those skilled in the art from the foregoing
descriptions. Such modifications and variations are intended to
fall within the scope of the appended claims. The present
disclosure is to be limited only by the terms of the appended
claims, along with the full scope of equivalents to which such
claims are entitled. It is to be understood that this disclosure is
not limited to particular methods, reagents, compounds,
compositions or biological systems, which can, of course, vary. It
is also to be understood that the terminology used herein is for
the purpose of describing particular embodiments only, and is not
intended to be limiting.
[0052] As used in this document, the singular forms "a," "an," and
"the" include plural references unless the context clearly dictates
otherwise. Unless defined otherwise, all technical and scientific
terms used herein have the same meanings as commonly understood by
one of ordinary skill in the art. Nothing in this disclosure is to
be construed as an admission that the embodiments described in this
disclosure are not entitled to antedate such disclosure by virtue
of prior invention. As used in this document, the term "comprising"
means "including, but not limited to."
[0053] While various compositions, methods, and devices are
described in terms of "comprising" various components or steps
(interpreted as meaning "including, but not limited to"), the
compositions, methods, and devices can also "consist essentially
of" or "consist of" the various components and steps, and such
terminology should be interpreted as defining essentially
closed-member groups.
[0054] With respect to the use of substantially any plural and/or
singular terms herein, those having skill in the art can translate
from the plural to the singular and/or from the singular to the
plural as is appropriate to the context and/or application. The
various singular/plural permutations may be expressly set forth
herein for sake of clarity.
[0055] It will be understood by those within the art that, in
general, terms used herein, and especially in the appended claims
(for example, bodies of the appended claims) are generally intended
as "open" terms (for example, the term "including" should be
interpreted as "including but not limited to," the term "having"
should be interpreted as "having at least," the term "includes"
should be interpreted as "includes but is not limited to," etc.).
It will be further understood by those within the art that if a
specific number of an introduced claim recitation is intended, such
an intent will be explicitly recited in the claim, and in the
absence of such recitation no such intent is present. For example,
as an aid to understanding, the following appended claims may
contain usage of the introductory phrases "at least one" and "one
or more" to introduce claim recitations. However, the use of such
phrases should not be construed to imply that the introduction of a
claim recitation by the indefinite articles "a" or "an" limits any
particular claim containing such introduced claim recitation to
embodiments containing only one such recitation, even when the same
claim includes the introductory phrases "one or more" or "at least
one" and indefinite articles such as "a" or "an" (for example, "a"
and/or "an" should be interpreted to mean "at least one" or "one or
more"); the same holds true for the use of definite articles used
to introduce claim recitations. In addition, even if a specific
number of an introduced claim recitation is explicitly recited,
those skilled in the art will recognize that such recitation should
be interpreted to mean at least the recited number (for example,
the bare recitation of "two recitations," without other modifiers,
means at least two recitations, or two or more recitations).
Furthermore, in those instances where a convention analogous to "at
least one of A, B, and C, etc." is used, in general such a
construction is intended in the sense one having skill in the art
would understand the convention (for example, "a system having at
least one of A, B, and C" would include but not be limited to
systems that have A alone, B alone, C alone, A and B together, A
and C together, B and C together, and/or A, B, and C together,
etc.). In those instances where a convention analogous to "at least
one of A, B, or C, etc." is used, in general such a construction is
intended in the sense one having skill in the art would understand
the convention (for example, "a system having at least one of A, B,
or C" would include but not be limited to systems that have A
alone, B alone, C alone, A and B together, A and C together, B and
C together, and/or A, B, and C together, etc.). It will be further
understood by those within the art that virtually any disjunctive
word and/or phrase presenting two or more alternative terms,
whether in the description, claims, or drawings, should be
understood to contemplate the possibilities of including one of the
terms, either of the terms, or both terms. For example, the phrase
"A or B" will be understood to include the possibilities of "A" or
"B" or "A and B."
[0056] In addition, where features or aspects of the disclosure are
described in terms of Markush groups, those skilled in the art will
recognize that the disclosure is also thereby described in terms of
any individual member or subgroup of members of the Markush
group.
[0057] As will be understood by one skilled in the art, for any and
all purposes, such as in terms of providing a written description,
all ranges disclosed herein also encompass any and all possible
subranges and combinations of subranges thereof. Any listed range
can be easily recognized as sufficiently describing and enabling
the same range being broken down into at least equal halves,
thirds, quarters, fifths, tenths, etc. As a non-limiting example,
each range discussed herein can be readily broken down into a lower
third, middle third and upper third, etc. As will also be
understood by one skilled in the art all language such as "up to,"
"at least," and the like include the number recited and refer to
ranges which can be subsequently broken down into subranges as
discussed above. Finally, as will be understood by one skilled in
the art, a range includes each individual member. Thus, for
example, a group having 1-3 cells refers to groups having 1, 2, or
3 cells. Similarly, a group having 1-5 cells refers to groups
having 1, 2, 3, 4, or 5 cells, and so forth.
[0058] Various of the above-disclosed and other features and
functions, or alternatives thereof, may be combined into many other
different systems or applications. Various presently unforeseen or
unanticipated alternatives, modifications, variations or
improvements therein may be subsequently made by those skilled in
the art, each of which is also intended to be encompassed by the
disclosed embodiments.
* * * * *