U.S. patent application number 13/630631 was filed with the patent office on 2013-03-28 for on demand carbon monoxide generator for therapeutic and other applications.
This patent application is currently assigned to DIOXIDE MATERIALS, INC. The applicant listed for this patent is Dioxide Materials, Inc. Invention is credited to Richard I Masel, Brian A Rosen.
Application Number | 20130075273 13/630631 |
Document ID | / |
Family ID | 47910057 |
Filed Date | 2013-03-28 |
United States Patent
Application |
20130075273 |
Kind Code |
A1 |
Masel; Richard I ; et
al. |
March 28, 2013 |
On Demand Carbon Monoxide Generator For Therapeutic and Other
Applications
Abstract
A device that can produce carbon monoxide for therapeutic and
laboratory applications is disclosed. The device includes and
electrochemical cell that converts carbon dioxide or a carbon
dioxide containing molecule such as a carbonate or bicarbonate or
bicarbonate into carbon monoxide and oxygen. The cell contains
additives so pure carbon monoxide is obtained.
Inventors: |
Masel; Richard I;
(Champaign, IL) ; Rosen; Brian A; (Champaign,
IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Dioxide Materials, Inc; |
Champaign |
IL |
US |
|
|
Assignee: |
DIOXIDE MATERIALS, INC
Champaign
IL
|
Family ID: |
47910057 |
Appl. No.: |
13/630631 |
Filed: |
September 28, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61540044 |
Sep 28, 2011 |
|
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|
Current U.S.
Class: |
205/555 ;
204/277 |
Current CPC
Class: |
C25B 9/00 20130101; C25B
1/00 20130101 |
Class at
Publication: |
205/555 ;
204/277 |
International
Class: |
C25B 9/00 20060101
C25B009/00 |
Goverment Interests
STATEMENT OF GOVERNMENT INTEREST
[0002] This invention was made, at least in part, with U.S.
government support under Department of Energy Grant DE-SC0004453.
The U.S. government has certain rights in the invention.
Claims
1. An carbon monoxide generator for chemical laboratory or
therapeutic uses, comprising a. A Carbon Dioxide Source, and b. A
means to convert carbon dioxide to carbon monoxide, wherein the
output of the carbon monoxide generator contains at least 20 times
as much CO as H.sub.2 on a molar basis.
2. The carbon monoxide generator in claim 1 with a Carbon Dioxide
Source comprising at least one of solid CO.sub.2, liquid CO.sub.2,
gaseous CO.sub.2, a carbonate or a bicarbonate.
3. The carbon monoxide generator in claim 1 comprising an
electrochemical cell
4. The carbon monoxide generator in any of the preceding claims,
comprising at least one of a) a Helper Catalyst b) A Directing
Molecule or c) a Hydrogen Suppressor.
5. The Carbon Dioxide Source in claim 1 comprising at least one of
a) a Helper Catalyst b) A Directing Molecule or c) a Hydrogen
Suppressor.
6. The device in claim 4 or 5, with at least one of a) the Helper
Catalyst, b) The Directing Molecule or c) the Hydrogen Supressor
comprising at least one cation and/or at least one anion.
7. The device in any of claim 4, 5, or 6 wherein at least one of a)
the Helper Catalyst, b) The Directing Molecule or c) the Hydrogen
Supressor has a concentration of between about 0.000006 2% and
99.999% by weight.
8. The device of any of claims 4-7, wherein at least one of a) the
Helper Catalyst, b) The Directing Molecule or c) the Hydrogen
Supressor comprises at least one of the following: phosphines,
imidazoliums, pyridiniums, pyrrolidiniums, phosphoniums,
sulfoniums, prolinates, methioninates, or alkali ions.
9. The device of any of claims 4-8, wherein at least one of a) the
Helper Catalyst, b) The Directing Molecule or c) the Hydrogen
Supressor comprises cholines or a choline salt.
10. The device of any one of claims 4 through 9 wherein at least
one of a) the Helper Catalyst, b) The Directing Molecule or c) the
Hydrogen Supressor comprises 1-ethyl-3-methylimidazolium
cations.
11. The device of any of claims 4 through 10 wherein at least one
of a) the Helper Catalyst, b) The Directing Molecule or c) the
Hydrogen Supressor comprises tetrafluoroborate anions.
12. The device of any of claims 4 through 11, wherein at least one
of a) the Helper Catalyst, b) The Directing Molecule or c) the
Hydrogen Supressor comprises potassium or cesium cations.
13. The device of any of claims 4 through 12, wherein at least one
of a) the Helper Catalyst, b) The Directing Molecule or c) the
Hydrogen Supressor comprises tetrafluoroborate anions, and is a
solvent, electrolyte or additive.
14. The device of any of claims 4 through 13 above, wherein the
Director Molecule comprises:a positively charges species further
comprising at least one polar group selected from --OR, --COR,
--COOR, --NR.sub.2, --PR.sub.2, --SR, or halides, where the R
groups can independently be hydrogen or ligands containing
carbon.
15. The device of any of claims 4 through 14 above, wherein the
Hydrogen Suppressor comprises: a choline derivative of the form
R.sub.1R.sub.2R.sub.3N.sup.+ (CH.sub.2).sub.nOH or
R.sub.1R.sub.2R.sub.3N.sup.+ (CH.sub.2).sub.nCl, wherein n=1-4, and
R.sub.1, R.sub.2, and R.sub.3 are independently selected from the
group consisting of aliphatic C.sub.1-C.sub.4 groups, --CH.sub.2OH,
--CH.sub.2CH.sub.2OH, --CH.sub.2CH.sub.2CH.sub.2OH,
--CH.sub.2CHOHCH.sub.3, --CH.sub.2COH, --CH.sub.2CH.sub.2COH, and
--CH.sub.2COCH.sub.3 and molecules where one or more chlorine or
fluorine is substituted for hydrogen in aliphatic C.sub.1-C.sub.4
groups, --CH.sub.2OH, --CH.sub.2CH.sub.2OH,
--CH.sub.2CH.sub.2CH.sub.2OH, --CH.sub.2CHOHCH.sub.3,
--CH.sub.2COH, --CH.sub.2CH.sub.2COH, or --CH.sub.2COCH.sub.3. 16 A
portable carbon monoxide generator for chemical laboratory or
therapeutic use, comprising the device of any of the above
claims.
16. The device of any of claims 2 through 14 above wherein the
device comprises a cartridge that fits in the line between an
oxygen source and a patient.
17. A method of producing carbon monoxide for chemical laboratory
or therapeutic uses, comprising the steps of: providing the device
of any of the above claims; providing carbon dioxide, a carbonate,
or a bicarbonate from the Carbon Dioxide Source to the device;
providing any additional water, solvent, or electrolyte as may be
needed; applying a source of energy, such as an electric current,
to the device; and directing the carbon monoxide thus produced to
the intended point of use.
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] This application claims priority to and the benefit under 35
U.S.C. .sctn.119(e) to U.S. Provisional Application 61/540,044,
entitled "On Demand Carbon Monoxide Generator for Therapeutic and
Other Applications," filed Sep.28, 2011. This application is
related to U.S. Non-Provisional Patent Application US 2011/0237830
filed Jul. 4, 2010, entitled "Novel Catalyst Mixtures," which
claims the benefit of U.S. Provisional Patent Application Ser. No.
61/317,955 filed Mar. 26, 2010, entitled "Novel Catalyst Mixtures,"
and the application is also related to international application WO
2011/120021, entitled "Novel Catalyst Mixtures," filed Mar. 25,
2011, which claims the benefit of both of the above applications.
This application is also related to international patent
application WO201206240, "Novel Catalyst Mixtures," filed Jul. 1,
2011, which claims the benefit of above applications US
2011/0237830 and WO 2011/120021, and which also claims the benefit
of U.S. Provisional Patent Application 61/484,072, "Novel Catalyst
Mixtures," filed May 9, 2011, and U.S. Non-Provisional patent
application Ser. No. 13/174,365, "Novel Catalyst Mixtures," filed
Jun. 30, 2011. The present application is also related to U.S.
Provisional Application 61/499,225, entitled "Low Cost Carbon
Dioxide Sensors," filed Jun. 29, 2011, and U.S. Provisional
Application 61/540,044, entitled "On Demand Carbon Monoxide
Generator for Therapeutic and Other Applications," filed Sep. 28,
2011. The present application is also related to U.S. patent
application Ser. No. 13/530,058 entitled "Sensors for Carbon
Dioxide and Other End Uses," filed Jun. 21, 2012, which claims
benefit from each of the aforementioned patent applications and
provisional patents. The present application is also related to
continuation-in-part application U.S. Ser. No. 13/445,887,
"Electrocatalysts for Carbon Dioxide Conversion," filed Apr. 12,
2012, which is based on the above U.S. Non-Provisional Patent
Application US 2011-0237830 filed Jul. 4, 2010. In addition, the
present application is related to international patent application
PCT/US12/43651, "Low Cost Carbon Dioxide Sensors," filed Jun. 21,
2012, which claims the benefit of the above U.S. Provisional Patent
Application 61/499,255, entitled "Low Cost Carbon Dioxide Sensors,"
filed Jun. 29, 2011. Each of the above applications is hereby
incorporated herein by reference in its entirety.
FIELD OF THE INVENTION
[0003] This patent relates to a system for the production of carbon
monoxide on demand. The devices of this invention are applicable,
for example, for production of carbon monoxide in chemical
laboratories or therapeutic settings.
BACKGROUND
[0004] Carbon monoxide (CO) is widely used as an industrial
chemical, in chemical laboratories. Clinical applications of CO are
just starting to appear. There are many chemical processes to
generate carbon monoxide on an industrial scale such as those
disclosed in U.S. Pat. Nos. 2,218,262, 2,665,972, 3,046,093, and
4,564,513. However, clinical and laboratory applications still rely
on gas cylinders to supply carbon monoxide. Carbon monoxide is
poisonous and if a cylinder leaks it could lead to hazardous
conditions. Further, cylinders are not a convenient delivery mode
in a clinical application.
[0005] At present there is a need for a carbon monoxide delivery
system that does not rely on gas cylinders, and instead creates
carbon monoxide on demand.
[0006] A few previous carbon monoxide generators have been
disclosed. For example, U.S. Pat. Nos. 6,948,352, 7,951,273, and
patent application 2005/0100478 disclose devices that are able to
generate nanograms/hr of carbon monoxide for calibration purposes,
but the devices cannot produce the mg/min of carbon monoxide needed
for some clinical applications. Also, the reactions in the devices
produce toxic byproducts when they are run at the mg/min scale.
[0007] Patent application US 2011/0217226 provides a method to
convert formic acid to carbon monoxide, but formic acid is
corrosive to mucus membranes. Traces of formic acid can be released
from the device when cartridges are changed or during a device
failure, which would not be preferred for inhalation therapy.
[0008] There are also a number of electrochemical processes that
convert CO.sub.2 or other compounds into a variety of products
including carbon monoxide, as outlined in U.S. Pat. Nos. 3,959,094,
4,240,882, 4,523,981, 4,545,872, 4,595,465, 4,608,132, 4,608,133,
4,609,440, 4,609,441, 4,609,451, 4,620,906, 4,668,349, 4,673,473,
4,711,708, 4,756,807, 4,818,353, 5,064,733, 5,284,563, 5,382,332,
5,457,079, 5,709,789, 5,928,806, 5,952,540, 6,024,855, 6,660,680,
6,987,134, 7,157,404, 7,378,561, 7,479,570, and the papers reviewed
by Hori (Modern Aspects of Electrochemistry, 42, 89-189, 2008)
("the Hori Review"), Gattrell, et al. (Journal of Electroanalytical
Chemistry, 594, 1-19, 2006) ("the Gattrell review"), DuBois
(Encyclopedia of Electrochemistry, 7a, 202-225, 2006) ("the DuBois
review"). None of the previously disclosed electrochemical methods
produce carbon monoxide at purities suitable for clinical
applications. In particular, most of the previous processes produce
acid or organic byproducts. Further, the Hori review indicates that
all of the electrochemical systems developed so far produce streams
that are less than 90% CO. For example, the Hori review shows that
under the best conditions a gold or silver working electrode
produces a CO stream that contains over 10% hydrogen, and about 1%
of acetic acid. The acetic acid would preclude the use of the
device in inhalation therapy, and the high hydrogen concentration
would create an explosion hazard when the stream is mixed with
oxygen for inhalation therapy.
SUMMARY OF THE INVENTION
[0009] The invention provides a new carbon dioxide generator design
that can produce carbon monoxide on demand at the mg/min rate
needed for clinical applications, at the purities needed for these
applications, and does not use any corrosive or toxic starting
materials. The general approach is to start with carbon dioxide or
a related carbonate or bicarbonate, and use a device to convert
that material into carbon monoxide (CO) on demand. The advantage is
that one does not use any toxic or corrosive starting materials, so
the process is safe even if there is a small leak.
[0010] The device may include an electrochemical cell with a
working electrode, a counter electrode, and an electrolyte in
between, wherein the electrochemical cell is active for CO.sub.2
reduction to carbon monoxide and oxygen. One supplies either
CO.sub.2 or a CO.sub.2 containing compound such as a carbonate or
bicarbonate to the working electrode, and applies a voltage between
the working electrode and the counter electrode to produce carbon
monoxide at a controlled rate.
[0011] The system may also include a means to control the rate of
production of carbon monoxide. Electrochemical devices are
particularly preferred since one can precisely control the rate of
carbon monoxide production by controlling either the voltage or
current to the electrochemical cell.
[0012] Examples of reactions that may occur on the working
electrode of an electrochemical device include:
CO.sub.2+2e-.fwdarw.CO+1/2O.sub.2.sup.2-
CO.sub.2+2H.sup.++2e-.fwdarw.CO+H.sub.2O
CO.sub.2+H.sub.2O+2e-.fwdarw.CO+2OH.sup.-
HCO.sub.3.sup.-+H.sub.2O+e-.fwdarw.CO+2OH.sup.-
HCO.sub.3.sup.-+3H.sup.++2e-.fwdarw.CO+2H.sub.2O
[0013] where e- is an electron. The examples given above are merely
illustrative and are not meant to be an exhaustive list of all
possible reactions on the working electrode.
[0014] Key to the invention is the discovery of a catalyst mixture
for the working electrode that produces at least 20 times more CO
than hydrogen, and does not produce significant quantities of other
impurities. The catalyst mixture may include components that
enhance the rate of CO formation and/or decrease the rate of
hydrogen formation. The catalyst mixture may include at least one
Catalytically Active Element, and at least one Helper Catalyst
and/or Hydrogen Suppressor. The Helper Catalyst can include, for
example salts of choline, or choline derivatives or EMIM and its
derivatives. When the Catalytically Active Element and the Helper
Catalyst are combined, the rate and/or selectivity of a chemical
reaction to produce CO can be enhanced over the rate seen in the
absence of the Helper Catalyst. For example, the overpotential for
electrochemical conversion of carbon dioxide to CO can be
substantially reduced, and the current efficiency (namely,
selectivity) for CO.sub.2 conversion can be substantially
increased.
[0015] In one aspect, the present invention includes an
electrochemical cell with a fluid phase, the cell including a
hydrogen evolution suppressor material. It is preferred that the
hydrogen suppressor has a vapor pressure of less than 10.sup.-2 ton
so as to not substantially contaminate the product stream. The
hydrogen evolution suppressor may include at least one positively
charged nitrogen or phosphorus atom in its structure. The nitrogen
could be, for example, part of a quaternary amine group or an
imidizolium. The hydrogen suppressor molecules can also have at
least one polar group selected from the group consisting of --OR,
--COR, --COOR, --NR.sub.2, --PR.sub.2, --SR and X, where each R
independently can be H or a linear, branched, or cyclic
C.sub.1-C.sub.4 aliphatic group, and X is a halide, such as
chlorine or fluorine. In particular, the polar group or groups can
include at least one hydroxyl group and/or at least one halide
atoms, but these molecules would preferably not contain a
carboxylic acid group or be ionic salts of a carboxylic acid, since
these can lead to acid byproducts. An example of such a hydrogen
evolution suppressor molecule would be a salt including the choline
cation, or a choline derivative of the form
R.sub.1R.sub.2R.sub.3N.sup.+(CH.sub.2).sub.nOH or
R.sub.1R.sub.2R.sub.3N.sup.+(CH.sub.2).sub.nCl, wherein n=1-4, and
R.sub.1, R.sub.2, and R.sub.3 are independently selected from the
group consisting of aliphatic C.sub.1-C.sub.4 groups, --CH.sub.2OH,
--CH.sub.2CH.sub.2OH, --CH.sub.2CH.sub.2CH.sub.2OH,
--CH.sub.2CHOHCH.sub.3, --CH.sub.2COH, --CH.sub.2CH.sub.2COH, and
--CH.sub.2COCH.sub.3 and molecules where one or more chlorine or
fluorine is substituted for hydrogen in aliphatic C.sub.1-C.sub.4
groups, --CH.sub.2OH, --CH.sub.2CH.sub.2OH,
--CH.sub.2CH.sub.2CH.sub.2OH, --CH.sub.2CHOHCH.sub.3,
--CH.sub.2COH, --CH.sub.2CH.sub.2COH, or --CH.sub.2COCH.sub.3. The
electrochemical cell can also include a Catalytically Active
Element, which could be at least one of the following chemical
elements: V, Cr, Mn, Fe, Co, Ni, Cu, Sn, Zr, Nb, Mo, Ru, Rh, Pd,
Ag, Cd, Hf, Ta, W, Re, Ir, Pt, Au, Hg, Al, Si, C, In, Sn, Tl, Pb,
Bi, Sb, Te, U, Sm, Tb, La, Ce, Nd.
[0016] In another aspect, the present invention includes a method
of suppressing hydrogen gas evolution from water that might be
present in a system to create carbon monoxide on demand, the method
including the steps of: (i) providing an electrochemical cell
having a fluid phase and a negative electrode, (ii) providing in
the fluid phase a hydrogen evolution suppressor as described above
that includes a cation containing at least one positively charged
nitrogen or phosphorus group and at least one polar group selected
from the group consisting of --OR, --COR, --COOR, --NR.sub.2,
--PR.sub.2, --SR and X, where each R independently can be H or a
linear, branched, or cyclic C.sub.1-C.sub.4 aliphatic group, and X
is a halide, and (iii) operating the electrochemical cell with the
negative electrode at a potential that would cause hydrogen gas
evolution from water that might be present in an electrochemical
cell if the hydrogen evolution suppressor were not present. The
electrochemical cell could be as described in the previous
paragraph.
[0017] In yet another aspect, the present invention includes a
carbon monoxide generator that includes an Active Element, Helper
Catalyst Mixture, in which the addition of the Helper Catalyst
improves the rate or yield of CO production, while simultaneously
decreasing the rate or yield of the undesired side reactions. The
undesired reaction may be the evolution of hydrogen gas or the
creation of some poisonous impurity. The Helper Catalyst can
include a cation containing at least one positively charged
nitrogen or phosphorus group and at least one polar group selected
from the group consisting of --OR, --COR, --COOR, --NR.sub.2,
--PR.sub.2, --SR and X, where each R independently can be H or a
linear, branched, or cyclic C.sub.1-C.sub.4 aliphatic group, --COOR
is not a carboxylic acid, and X is a halide. For example, the
cation could contain at least one quaternary amine group and at
least one halide or hydroxyl group, but no carboxylic acid group or
carboxylic acid salt. The quaternary amine cation can be, for
example, choline cations, or choline cation derivatives of the form
R.sub.1R.sub.2R.sub.3N.sup.+(CH.sub.2).sub.nOH or
R.sub.1R.sub.2R.sub.3N.sup.+(CH.sub.2).sub.nCl, where n=1-4, and
R.sub.1, R.sub.2, and R.sub.3 are independently selected from the
group that includes aliphatic C.sub.1-C.sub.4 groups, --CH.sub.2OH,
--CH.sub.2CH.sub.2OH, --CH.sub.2CH.sub.2CH.sub.2OH
--CH.sub.2CHOHCH.sub.3 , --CH.sub.2COH, --CH.sub.2CH.sub.2COH, and
--CH.sub.2COCH.sub.3 and molecules where one or more chlorine or
fluorine is substituted for hydrogen in aliphatic C.sub.1-C.sub.4
groups, --CH.sub.2OH, --CH.sub.2CH.sub.2OH,
--CH.sub.2CH.sub.2CH.sub.2OH, --CH.sub.2CHOHCH.sub.3,
--CH.sub.2COH, --CH.sub.2CH.sub.2COH, and --CH.sub.2COCH.sub.3
[0018] In still another aspect of the present invention, this
application discloses a catalyst mixture having a Catalytically
Active Element and a Helper Catalyst in which the Helper Catalyst
also functions as a director molecule. The Helper Catalyst/director
molecule would be a molecule containing at least one positively
charged group and at least one group for surface attachment. The
positively charged group can be, for example, a phosphonium group,
or an amine group, such as a quaternary amine. The group for
surface attachment can be, for example, a polar group selected from
the group consisting of --OR, --COR, --COOR, --NR.sub.2,
--PR.sub.2, --SR and X, where each R independently can be H or a
linear, branched, or cyclic C.sub.1-C.sub.4 aliphatic group, --COOR
is not a carboxylic acid, and X is a halide.
[0019] In still another aspect of the invention, this application
discloses a carbon monoxide generator that includes a removable
cartridge containing CO.sub.2 or a chemical compound containing
CO.sub.2 such as a carbonate or bicarbonate, and a means to convert
CO.sub.2 to CO with hydrogen concentrations below 5% of the CO
concentration, and less than 5 ppm of acetic acid or other
impurities.
[0020] Finally the invention is not limited to the production of
CO. A similar design with other reactants may be used as a
generator for other therapeutic gases such as nitric oxide.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a diagram of a typical electrochemical cell.
[0022] FIG. 2 is a schematic diagram of how the potential of the
system changes as it proceeds along the reaction coordinate in the
absence of the ionic liquid if the system goes through a
(CO.sub.2).sup.- intermediate. The reaction coordinate indicates
the fraction of the reaction that has been completed. A high
potential for (CO.sub.2).sup.- formation can create a high
overpotential for the reaction, which leads to enhanced hydrogen
production.
[0023] FIG. 3 illustrates how the potential could change when a
Helper Catalyst is used. In this case the reaction could go through
a CO.sub.2 complex rather than a (CO.sub.2).sup.- intermediate,
substantially lowering the overpotential for the reaction.
[0024] FIGS. 4a, 4b and 4c illustrate some of the cations that can
be used to form a complex with (CO.sub.2).sup.-.
[0025] FIGS. 5a and 5b illustrate some of the anions that can help
to stabilize the (CO.sub.2).sup.- anion.
[0026] FIG. 6 illustrates some of the neutral molecules that can be
used to form a complex with (CO.sub.2).sup.-.
[0027] FIG. 7 shows a schematic diagram of a cell used for the
experiments in testing Catalytically Active Element, Helper
Catalyst Mixtures, and in Specific Examples 1 and 4 to 7.
[0028] FIG. 8 represents a comparison of the cyclic voltammetry for
(i) a blank scan where the catalyst was synthesized as in the
described testing procedure for Catalytically Active Element,
Helper Catalyst Mixtures, where the EMIM-BF4 was sparged with
argon, and (ii) a scan where the EMIM-BF4 was sparged with
CO.sub.2. Notice the large negative peak associated with CO.sub.2
complex formation.
[0029] FIG. 9 represents a series of Broad Band Sum Frequency
Generation (BB-SFG) spectra taken sequentially as the potential in
the cell was scanned from +0.0 V to -1.2 V with respect to the
standard hydrogen electrode (SHE).
[0030] FIG. 10 shows a CO stripping experiment done by holding the
potential at -0.6 V for 10 or 30 minutes and then measuring the
size of the CO stripping peak between 1.2 and 1.5 V with respect to
the reversible hydrogen electrode (RHE).
[0031] FIG. 11 Is a plot of the Faradaic efficiency of the process
of forming the desired CO and the undesired hydrogen, and the
turnover rate as a function of the applied cell potential for the
cell in Specific Example 3.
[0032] FIG. 12 shows a comparison of the cyclic voltammetry for (i)
a blank scan where the catalyst was synthesized as in Specific
Example 4 where the water-choline chloride mixture was sparged with
argon and (ii) a scan where the water-choline chloride mixture was
sparged with CO.sub.2.
[0033] FIG. 13 represents a comparison of the cyclic voltammetry
for (i) a blank scan where the catalyst was synthesized as in
Example 5 where the water-choline iodide mixture was sparged with
argon and (ii) a scan where the water-choline iodide mixture was
sparged with CO.sub.2.
[0034] FIG. 14 shows a comparison of the cyclic voltammetry for (i)
a blank scan where the catalyst was synthesized as in Example 6
where the water-choline chloride mixture was sparged with argon and
(ii) a scan where the water-choline chloride mixture was sparged
with CO.sub.2.
[0035] FIGS. 15a and 15b each show a plot of cyclic voltammetry of
palladium in the presence of different hydrogen suppressors. In
each case the potential is reported versus the measured value of
RHE.
[0036] FIGS. 16a and 16b each show a plot of cyclic voltammetry of
platinum in the presence of different hydrogen suppressors. In each
case the potential is reported versus the measured value of
RHE.
[0037] FIGS. 17a and 17b each show a plot of cyclic voltammetry of
platinum/ruthenium in the presence of different hydrogen
suppressors. In each case the potential is reported versus the
measured value of RHE.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT(S)
[0038] It is understood that the invention is not limited to the
particular methodology, protocols, and reagents, etc., described
herein, as these can vary as the skilled artisan will recognize It
is also to be understood that the terminology used herein is used
for the purpose of describing particular embodiments only, and is
not intended to limit the scope of the invention. It also is to be
noted that as used herein and in the appended claims, the singular
forms "a", "an", and "the" include the plural reference unless the
context clearly dictates otherwise. Thus, for example, a reference
to "a linker" is a reference to one or more linkers and equivalents
thereof known to those familiar with the technology involved here.
Also, the term "and/or" is used to indicate one or both stated
cases may occur, for example A and/or B includes (A and B) and (A
or B).
[0039] 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 to which the invention pertains. The
embodiments of the present invention and the various features and
advantageous details thereof are explained more fully with
reference to the non-limiting embodiments and/or illustrated in the
accompanying drawings and detailed in the following description. It
should be noted that the features illustrated in the drawings are
not necessarily drawn to scale, and features of one embodiment can
be employed with other embodiments as the skilled artisan would
recognize, even if not explicitly stated herein.
[0040] Any numerical value ranges recited herein include all values
from the lower value to the upper value in increments of one unit
provided that there is a separation of at least two units between a
lower value and a higher value. As an example, if it is stated that
the concentration of a component or value of a process variable
such as, for example, size, angle size, pressure, time and the
like, is, for example, from 1 to 90, specifically from 20 to 80,
more specifically from 30 to 70, it is intended that values such as
15 to 85, 22 to 68, 43 to 51, 30 to 32 etc., are expressly
enumerated in this specification. For values which are less than
one, one unit is considered to be 0.0001, 0.001, 0.01 or 0.1 as
appropriate. These are only examples of what is specifically
intended and all possible combinations of numerical values between
the lowest value and the highest value are to be treated in a
similar manner.
[0041] Moreover, provided immediately below is a "Definitions"
section, where certain terms related to the present invention are
defined specifically. Particular methods, devices, and materials
are described, although methods and materials similar or equivalent
to those described herein can be used in the practice or testing of
the present invention. All references referred to herein are
incorporated by reference herein in their entirety.
Definitions
[0042] The term "electrochemical conversion of CO.sub.2" as used
here refers to an electrochemical process where carbon dioxide,
carbonate, or bicarbonate is converted into another chemical
substance in a step of the process.
[0043] The term "CV" as used here refers to a cyclic voltammogram
or cyclic voltammetry.
[0044] The term "Overpotential" as used here refers to the
potential (voltage) difference between a reaction's
thermodynamically determined reduction or oxidation potential and
the potential at which the event is experimentally observed.
[0045] The term "Cathode Overpotential" as used here refers to the
overpotential on the cathode of an electrochemical cell.
[0046] The term "Anode Overpotential" as used here refers to the
overpotential on the anode of an electrochemical cell.
[0047] The term "Electron Conversion Efficiency" refers to
selectivity of an electrochemical reaction. More precisely, it is
defined as the fraction of the current that is supplied to the cell
that goes to the production of a desired product.
[0048] The term "Catalytically Active Element" as used here refers
to a chemical element that can serve as a catalyst for the
electrochemical conversion of CO.sub.2 or another species of
interest in a desired reaction.
[0049] The term "Helper Catalyst" refers to an organic molecule or
mixture of organic molecules that does at least one of the
following: (a) speeds up a chemical reaction, or (b) lowers the
overpotential of the reaction, without being substantially consumed
in the process.
[0050] The term "Active Element, Helper Catalyst Mixture" refers to
a mixture that includes one or more Catalytically Active Element(s)
and at least one Helper Catalyst.
[0051] The term "Ionic Liquid" refers to salts or ionic compounds
that form stable liquids at temperatures below 200 .degree. C.
[0052] The term "Deep Eutectic Solvent" refers to an ionic solvent
that includes a mixture which forms a eutectic with a melting point
lower than that of the individual components.
[0053] The term "Director Molecule" (or "Director Ion") refers to a
molecule or ion that increases the selectivity of a reaction. If a
director molecule (or ion) is added to a reaction mixture, the
selectivity for a desired reaction goes up. This effect may be the
result of suppressing undesired side reactions, even if the desired
reaction is also slowed, as long as the selectivity toward the
desired reaction is increased.
[0054] The term "Hydrogen Suppressor" refers to a molecule that
either: (a) decreases the rate of hydrogen formation, or (b)
increases the overpotential for hydrogen formation, when the
molecule is added to a reaction mixture.
[0055] The term "EMIM" refers to 1-ethyl-3-methylimidazolium.
[0056] The term "Carbon Dioxide Source" refers to a device or
molecule that can provide carbon dioxide to a system. The source
may be in the form of a bottle, packet, cartridge or other form.
The Carbon Dioxide Source may include gaseous, liquid, solid or
supercritical carbon dioxide, and chemical compounds that can be
easily converted to carbon dioxide such as carbonates and
bicarbonates.
[0057] The term "Pure Enough To Be Used In A Clinical Application"
refers to a gas mixture that a) includes carbon monoxide, b) has at
least 10 times as much carbon monoxide as hydrogen on a molar basis
and c) has less than 1 ppm of any corrosive or toxic material other
than carbon monoxide.
Specific Description
[0058] The earlier related applications U.S. Ser. No. 12/830,338,
U.S. Ser. No. 13/174365, PCT/US11/42809, PCT/US11/30098 and
provisional patent application U.S. 61/499,225 by Masel et al.
described Active Element, Helper Catalyst Mixtures where the
mixture does at least one of the following: (1) speeds up a
chemical reaction; or (2) lowers the overpotential of the reaction,
without being substantially consumed in the process.
[0059] For example, such mixtures can lower the overpotential for
CO.sub.2 conversion to a value less than the overpotential seen
when the same Catalytically Active Element is used without the
Helper Catalyst.
[0060] In the course of exploring these Active Element, Helper
Catalyst Mixtures, it was found that certain materials that were
being tested as Helper Catalysts, such as salts of the choline
cation (N,N,N-trimethylethanolammonium cation) and/or
1-ethyl-3-methylimidazolium tetrafluoroborate could also raise the
overpotential for certain undesirable side reactions, including the
evolution of hydrogen gas from electrolysis of water and the
formation of side products such as acetic acid. As part of this
effort, we found that it was possible to produce carbon monoxide
electrochemically with purity to meet the needs for a therapeutic
carbon monoxide generator i.e. 20 times as much carbon monoxide as
hydrogen, and less than 1 ppm of other byproducts. Further, one
could precisely control the CO delivery rate by controlling the
current or voltage applied to the electrochemical cell.
[0061] Without wishing to be bound by theory, the present
disclosure provides data supporting the hypothesis that when a
monolayer of an organic compound is adsorbed on a metal surface,
the presence of the organic compound can change the binding energy
of key intermediates of reactions occurring on (or near) the metal
surface. This can lead to changes in reaction rates. For example,
data herein suggests that the adsorption of a cationic species such
as a quaternary amine on an electrode (typically the negative
electrode) of an electrochemical cell tends to stabilize anionic
intermediates and destabilize cationic intermediates in
electrochemical reactions. If the amine binds too strongly, it will
simply poison the surface, but if the binding strength is modest,
rate enhancement is possible. Aliphatic quaternary amines would
tend to be merely electrostatically attracted to a metal electrode
surface, since the positively charged nitrogen is sterically
shielded by the aliphatic groups and cannot interact directly with
the metal surface. For the same reason, quaternary ammonium cations
tend to be electrochemically stable across a wide window of
electrode potentials. Choline salts in particular are commercially
attractive quaternary amines, because choline chloride is a common
food additive for livestock, and it is also sold as a dietary
supplement for humans. It is inexpensive, is readily available, and
presents minimal hazard. One could reasonably expect that
quaternary amine cations with structures similar to choline (for
example, structures in which one or more of the methyl groups on
the nitrogen is replaced with other small aliphatic groups such as
ethyl or propyl groups) would behave in a fashion similar to the
choline data disclosed in the present application.
[0062] Ionic liquids such as 1-ethyl-3-methylimidazolium
tetrafluoroborate (EMIM-BF4) could also be used. Imidazoliums would
tend to be merely electrostatically attracted to a metal electrode
surface, since the positively charged nitrogen is sterically
shielded by the aliphatic groups and cannot interact directly with
the metal surface. They have very low vapor pressures due to their
ionic nature, so they could be used in systems for inhalation
therapy.
[0063] According to the Hori review, Gattrell, et al. (Journal of
Electroanalytical Chemistry, 594, 1-19, 2006), DuBois (Encyclopedia
of Electrochemistry, 7a, 202-225, 2006) and references therein,
catalysts including one or more of In, Sn, Cd, Zn, Au, Ag, Cu V,
Cr, Mn, Fe, Co, Ni, Cu, Sn, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta,
W, Re, Ir, Pt, Au, Hg, Al, Si, In, Sn, Tl, Pb, Bi, Sb, Te, U, Sm,
Tb, La, Ce, and Nd all show activity for CO.sub.2 conversion. Hori
reports that only Au, Ag, Cu, Zn, Pd, In, Sn and Ga produce
significant amounts of CO, but the data disclosed in the specific
examples in this patent shows that in the presence of an
appropriate helper catalyst, CO is produced on additional metals.
Therefore, V, Cr, Mn, Fe, Co, Ni, Cu, Sn, Zr, Nb, Mo, Ru, Rh, Pd,
Ag, Cd, Hf, Ta, W, Re, Ir, Pt, Au, Hg, Al, Si, In, Sn, Tl, Pb, Bi,
Sb, Te, U, Sm, Tb, La, Ce, and Nd are each examples of
Catalytically Active Elements, but the present invention is not
limited to this list of chemical elements.
[0064] FIGS. 2 and 3 illustrate one possible mechanism by which a
Helper Catalyst can enhance the rate of CO.sub.2 conversion to CO.
According to Chandrasekaran, et al. (Surface Science, 185, 495-514,
1987) the high overpotentials for CO.sub.2 conversion occur because
the first step in the electroreduction of CO.sub.2 is the formation
of a (CO.sub.2).sup.- intermediate. It takes energy to form the
intermediate as illustrated in FIG. 2. This results in a high
overpotential for the reaction.
[0065] FIG. 3 illustrates what might happen if a solution
containing 1-ethyl-3-methylimidazolium cations (EMIM.sup.+) is
added to the mixture. EMIM.sup.+ might be able to form a complex
with the (CO.sub.2).sup.- intermediate. In that case, the reaction
could proceed via the EMIM.sup.+-(CO.sub.2).sup.- complex instead
of going through a bare (CO.sub.2).sup.- intermediate as
illustrated in FIG. 3. If the energy to form the
EMIM.sup.+-(CO.sub.2).sup.- complex is less than the energy to form
the (CO.sub.2).sup.- intermediate, the overpotential for CO.sub.2
conversion could be substantially reduced. Therefore a substance
that includes EMIM.sup.+ cations could act as a Helper Catalyst for
CO.sub.2 conversion.
[0066] In most cases, solvents only have small effects on the
progress of catalytic reactions. The interaction between a solvent
and an adsorbate is usually much weaker than the interaction with a
Catalytically Active Element, so the solvent only makes a small
perturbation to the chemistry occurring on metal surfaces. However,
the diagram in FIG. 3 shows that such an effect could be large.
[0067] Of course a Helper catalyst, alone, will be insufficient to
convert CO.sub.2 to CO. Instead, one still needs a Catalytically
Active Element that can catalyze reactions of (CO.sub.2).sup.- in
order to get high rates of CO.sub.2 conversion. Catalysts including
at least one of the following Catalytically Active Elements have
been previously reported to be active for electrochemical
conversion of CO.sub.2: V, Cr, Mn, Fe, Co, Ni, Cu, Sn, Zr, Nb, Mo,
Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Ir, Pt, Au, Hg, Al, Si, In, Sn,
Tl, Pb, Bi, Sb, Te, U, Sm, Tb, La, Ce, and Nd.
[0068] Many of these catalysts also show activity for a number of
other reactions. All of the above elements are specifically
included as Catalytically Active Elements for the purposes of the
present invention. This list of elements is meant for illustrative
purposes only, and is not meant to limit the scope of the present
invention.
[0069] Further, those skilled in the technology involved here
should realize that the diagram in FIG. 3 could be drawn for any
molecule that could form a complex with (CO.sub.2).sup.-. Previous
literature indicates that solutions including one or more of: ionic
liquids; deep eutectic solvents; and amines and phosphines,
including specifically imidazoliums (also called imidazoniums),
pyridiniums, pyrrolidiniums, phosphoniums, ammoniums, prolinates,
and methioninates, as well as sulfoniums, can form complexes with
CO.sub.2. Consequently, they can serve as Helper Catalysts. Also
Davis Jr., et al. (in ACS Symposium Series 856: Ionic Liquids as
Green Solvents: Progress and Prospects, 100-107, 2003) list a
number of other salts that show ionic properties. Specific examples
include compounds including one or more of acetylcholines,
alanines, aminoacetonitriles, methylammoniums, arginines, aspartic
acids, threonines, chloroformamidiniums, thiouroniums,
quinoliniums, pyrrolidinols, serinols, benzamidines, sulfamates,
acetates, carbamates, triflates, alkali cations and cyanides. These
salts can act as Helper Catalysts. These examples are meant for
illustrative purposes only, and are not meant to limit the scope of
the present invention.
[0070] Of course, not every substance that forms a complex with
(CO.sub.2).sup.- will act as a Helper Catalyst. Masel (Chemical
Kinetics and Catalysis, Wiley, pages 717-720, 2001,) notes that
when an intermediate binds to a catalyst, the reactivity of the
intermediate decreases. If the intermediate bonds too strongly to
the catalyst, the intermediate will become unreactive, so the
substance will not be effective. This provides a key limitation on
substances that act as Helper Catalysts. The Helper Catalyst cannot
form so strong a bond with the (CO.sub.2).sup.- that the
(CO.sub.2).sup.- is unreactive toward the Catalytically Active
Element or forms an undesired stable reaction product with the
material that was intended to be a Helper Catalyst.
[0071] More specifically, one wishes the substance to form a
complex with the (CO.sub.2).sup.- so that the complex is stable
(that is, has a negative free energy of formation) at potentials
less negative than -1 V with respect to the standard hydrogen
electrode (SHE). However, the complex should not be so stable that
the free energy of the reaction between the complex and the
Catalytically Active Element is more positive than about 3
kcal/mol.
[0072] Those familiar with the technology involved here should
realize that the ability of the Helper Catalyst to stabilize the
(CO.sub.2).sup.- also varies with the anion. For example Zhao, et
al. (The Journal of Supercritical Fluids, 32, 287-291, 2004)
examined CO.sub.2 conversion in 1-n-butyl-3-methylimidazolium
hexafluorophosphate (BMIM-PF6), but FIG. 3 in Zhao, et al., shows
that the BMIM-PF6 did NOT lower the overpotential for the reaction
(that is, the BMIM-PF6 did not act as a Helper Catalyst). This may
be because the BMIM-PF6 formed such a strong bond to the
(CO.sub.2).sup.- that the CO.sub.2 was unreactive with the copper.
Similarly Yuan, et al., Electrochimica Acta 54, pages
2912-2915(2009), examined the reaction between methanol and
CO.sub.2 in 1-butyl-3-methylimidazolium bromide (BMIM-Br). The
BMIM-Br did not act as a Helper Catalyst. This may be because the
complex was too weak or that the bromine poisoned the reaction.
[0073] Solutions that include one or more of the cations in FIGS.
4a, 4b and 4c, the anions in FIGS. 5a and 5b, and/or the neutral
species in FIG. 6, where R.sub.1, R.sub.2 and R.sub.3 (and
R.sub.4-R.sub.17) include H, OH or a ligand containing at least one
carbon atom, are believed to form complexes with CO.sub.2 or
(CO.sub.2).sup.-. Specific examples include: imidazoliums (also
called imidazoniums), pyridiniums, pyrrolidiniums, phosphoniums,
ammoniums, sulfoniums, prolinates, and methioninates. All of these
examples might be able to be used as Helper Catalysts for CO.sub.2
conversion, and are specifically included in the present invention.
These examples are meant for illustrative purposes only, and are
not meant to limit the scope of the present invention.
[0074] In general one can determine whether a given substance S is
a Helper Catalyst for a reaction R catalyzed by an active metal M
as follows:
[0075] (a) Fill a standard 3-electrode electrochemical cell with
the electrolyte commonly used for reaction R. Common electrolytes
such as 0.1 M sulfuric acid or 0.1 M KOH in water can also be
used.
[0076] (b) Mount the active metal into the 3 electrode
electrochemical cell and provide an appropriate counter
electrode.
[0077] (c) Run several CV cycles to clean the active metal.
[0078] (d) Measure the reversible hydrogen electrode (RHE)
potential in the electrolyte.
[0079] (e) Load the reactants for the reaction R into the cell, and
measure a CV of the reaction R, noting the potential of the peak
associated with the reaction R.
[0080] (f) Calculate V1=the difference between the onset potential
of the peak associated with reaction and RHE.
[0081] (g) Calculate V1A=the difference between the maximum
potential of the peak associated with reaction and RHE.
[0082] (h) Add 0.0001 to 99.9999% of the substance S to the
electrolyte.
[0083] (i) Measure RHE in the reaction solution with Helper
Catalyst.
[0084] (j) Measure the CV of reaction R again, noting the potential
of the peak associated with the reaction R.
[0085] (k) Calculate V2=the difference between the onset potential
of the peak associated with reaction and RHE.
[0086] (1) Calculate V2A=the difference between the maximum
potential of the peak associated with reaction and RHE.
[0087] If V2<V1 or V2A<V1A at any concentration of the
substance S between 0.0001 and 99.9999%, the substance S is a
Helper Catalyst for the reaction.
[0088] Further, the Helper Catalyst could be in any one of the
following forms: (i) a solvent for the reaction; (ii) an
electrolyte; (iii) an additive to a component of the system; or
(iv) something that is bound to at least one of the catalysts in a
system. These examples are meant for illustrative purposes only,
and are not meant to limit the scope of the present invention.
[0089] Those familiar with the technology involved here should
recognize that one might only need a tiny amount of the Helper
Catalyst to have a significant effect. Catalytic reactions often
occur on distinct active sites. The active site concentration can
be very low, so in principle a small amount of Helper Catalyst can
have a significant effect on the rate. One can obtain an estimate
of how little of the helper catalyst would be needed to change the
reaction from the Pease, et al., JACS 47, 1235 (1925) study of the
effect of carbon monoxide (CO) on the rate of ethylene
hydrogenation on copper. This paper is incorporated into this
disclosure by reference. Pease, et al., found that 0.05 cc (62
micrograms) of carbon monoxide (CO) was sufficient to almost
completely poison a 100 gram catalyst towards ethylene
hydrogenation. This corresponds to a poison concentration of
0.0000062% by weight of CO in the catalyst. Those familiar with the
technology involved here know that if 0.0000062% by weight of the
poison in a Catalytically Active Element-poison mixture could
effectively suppress a reaction, then as little as 0.0000062% by
weight of Helper Catalyst in an Active Element, Helper Catalyst
Mixture could enhance a reaction. This provides an estimate of a
lower limit to the Helper Catalyst concentration in an Active
Element, Helper Catalyst Mixture.
[0090] The upper limit is illustrated in Example 1 below, where the
Active Element, Helper Catalyst Mixture could have approximately
99.999% by weight of Helper Catalyst, and the Helper Catalyst could
be at least an order of magnitude more concentrated. Thus, the
range of Helper Catalyst concentrations for the present invention
can be 0.0000062% to 99.9999% by weight.
[0091] Further, the Helper Catalyst could enhance the rate of a
reaction even if it does not form a complex with a key
intermediate. Examples of possible mechanisms of action include the
Helper Catalyst (i) lowering the energy to form a key intermediate
by any means, (ii) donating or accepting electrons or atoms or
ligands, (iii) weakening bonds or otherwise making them easier to
break, (iv) stabilizing excited states, (v) stabilizing transition
states, (vi) holding the reactants in close proximity or in the
right configuration to react, or (vii) blocking side reactions.
Each of these mechanisms is described on pages 707-742 of Masel,
Chemical Kinetics and Catalysis, Wiley, NY (2001). All of these
modes of action are within the scope of the present invention.
[0092] Also, the invention is not limited to just the catalyst.
Instead it includes a process or device that uses an Active
Element, Helper Catalyst Mixture as a catalyst. Electrolytic cells
and other devices to produce CO that include Helper Catalysts or
Hydrogen Suppressors are specifically included in the present
invention.
[0093] In particular it includes a device that includes an
electrochemical device for the production of CO that includes an
Active Element and either a Helper Catalyst and/or a Hydrogen
Suppressor and a means to deliver the CO to a patient. The device
may include a means to supply CO.sub.2 to the device. It may also
include a CO sensor that allows the CO concentration to be
accurately controlled.
[0094] A specific design is an inline cartridge that would be
mounted between the oxygen source and the patient. The cartridge
would contain a source of CO.sub.2 such as a carbonate or
bicarbonate, an electrochemical cell including an Active Element
and either a Helper Catalyst and/or a Hydrogen Suppressor, and a CO
sensor. It might include a battery and control system.
[0095] Without further elaboration, it is believed that one skilled
in the art using the preceding description can utilize the present
invention to the fullest extent. The following examples are
illustrative only, and not limiting of the disclosure in any way
whatsoever. These are merely illustrative and are not meant to be
an exhaustive list of all possible embodiments, applications or
modifications of the present invention.
SPECIFIC EXAMPLE 1
[0096] The following section describes the testing procedure used
for an Active Element, Helper Catalyst Mixture as previously
disclosed in the related applications cited above. These particular
experiments measured the ability of an Active Element, Helper
Catalyst Mixture consisting of platinum and
1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM-BF4) to lower
the overpotential for electrochemical conversion of CO.sub.2 to CO
and raise the selectivity (current efficiency) of the reaction.
Therefore, the test can determine whether EMIM-BF4 and the
EMIM.sup.+ ion can serve as director molecules and director ions,
respectively, for the desired reaction. The desired reaction in
this test will be the electrochemical reduction of carbon dioxide
(typically to primary products such as CO).
[0097] The experiments used the glass three electrode cell shown in
FIG. 7. The cell consisted of a three neck flask 101, to hold the
anode 108, and the cathode 109. Seal 107 forms a seal around anode
wire 108. Fitting 106 compresses seal 107 around anode wire 108.
Rotary seal 110 facilitates rotation of shaft 111, which in turn
causes gold plug 115 to spin. Seal 119 closes the unused third neck
of flask 101.
[0098] A silver/0.01 molar silver ion reference electrode 103 in
acetonitrile was connected to the cell through a Luggin Capillary
102, which includes a seal 117. The reference electrode 103 was
fitted with a porous Vycor glass frit (available from Corning,
Inc., Corning, N.Y., USA) to prevent the reference electrode
solution from contaminating the ionic liquid in the capillary. The
reference electrode was calibrated against the ferrocene Fc/Fc+
redox couple. A conversion factor of +535 was used to convert our
potential axis to reference the Standard Hydrogen Electrode (SHE).
A 25.times.25 mm platinum gauze 113 (size 52) was connected to the
anode while a 0.33 cm.sup.2 polycrystalline gold plug 115 was
connected to the cathode.
[0099] Prior to the experiments all glass parts were put through a
1% Nochromix bath (2hrs) (available from Godax Laboratories, Inc.,
Cabin John, Md., USA), followed by a 50/50 v/v nitric acid/water
bath (12 hrs), followed by rinsing with Millipore filtered water
(Millipore Corporation, Billerica, Mass., USA). In addition, the
gold plug 115 and platinum gauze 113 were mechanically polished
using procedures known to workers trained in the technology
involved here. The glass parts were then cleaned in a sulfuric acid
bath for 12 hours.
[0100] During the experiment a catalyst ink comprising a
Catalytically Active Element, platinum, was first prepared as
follows: First 0.056 grams of Johnson-Matthey Hispec 1000 platinum
black purchased from Alfa-Aesar was mixed with 1 gram of Millipore
water and sonicated for 10 minutes to produce a solution containing
a 5.6 mg/ml suspension of platinum black in Millipore water. A 25
.mu.l drop of the ink was placed on the gold plug 115 and allowed
to dry under a heat lamp for 20 min, and subsequently allowed to
dry in air for an additional hour. This yielded a catalyst with
0.00014 grams of Catalytically Active Element, platinum, on a gold
plug. The gold plug was mounted into the three neck flask 101. Next
a Helper Catalyst, EMIM-BF4 (EMD Chemicals, Inc., San Diego,
Calif., USA) was heated to 120.degree. C. under a -23 in. Hg vacuum
for 12 hours to remove residual water and oxygen. The concentration
of water in the ionic liquid after this procedure was found to be
approximately 90 mM by conducting a Karl-Fischer titration. (That
is, the ionic liquid contained 99.9999% of Helper Catalyst.) 13
grams of the EMIM-BF4 was added to the vessel, creating an Active
Element, Helper Catalyst Mixture that contained about 99.999% of
the Helper Catalyst. The geometry was such that the gold plug
formed a meniscus with the EMIM-BF4. Next, ultra-high-purity (UHP)
argon was fed through the sparging tube 104 and glass frit 112 for
2 hours at 200 sccm to further remove any moisture picked up by
contact with the air. Connector 105 was used to attach the cell to
a tube leading to the gas source.
[0101] Next, the cathode was connected to the working electrode
connection in an SI 1287 Solartron electrical interface (Solartron
Analytical, Schaumburg, Ill., USA), the anode was connected to the
counter electrode connection and the reference electrode was
connected to the reference electrode connection on the Solartron.
Then the potential on the cathode was swept from -1.5 V versus a
standard hydrogen electrode (SHE) to 1 V vs. SHE, and then back to
-1.5 volts versus SHE thirty times at a scan rate of 50 mV/s. The
current produced during the last scan is labeled as the "argon"
scan in FIG. 8.
[0102] Next carbon dioxide was bubbled through the sparging tube at
200 sccm for 30 minutes, and the same scanning technique was used.
That produced the CO.sub.2 scan in FIG. 8. Notice the peak starting
at -0.2 volts with respect to SHE, and reaching a maximum at -0.4 V
with respect to SHE. That peak is associated with CO.sub.2
conversion.
[0103] The applicants have also used broad-band sum frequency
generation (BB-SFG) spectroscopy to look for products of the
reaction, as shown in FIG. 9. Only the desired product carbon
monoxide was detected in the voltage range shown (namely, the
selectivity is about 100%). Oxalic acid was detected at higher
potentials.
[0104] Table 1 compares these results to results from the previous
literature. The table shows the actual cathode potential. More
negative cathode potentials correspond to higher overpotentials.
More precisely, the overpotential is the difference between the
thermodynamic potential for the reaction (about -0.2 V with respect
to SHE) and the actual cathode potential. The values of the cathode
overpotential are also given in the table. Notice that the addition
of the Helper Catalyst has reduced the cathode overpotential
(namely, lost work) on platinum by a factor of 4.5 and improved the
selectivity from near zero to nearly 100%.
TABLE-US-00001 TABLE 1 (Comparison of data in this test to results
reported in previous literature) Cathode Selectivity to
Catalytically potential Cathode Carbon Reference Active Element
versus SHE overpotential Monoxide Data from Platinum -0.4 V 0.2 V
~100% this test (+EMIM-BF.sub.4) Hori review Platinum -1.07 V 0.87
V 0.1% Table 3 (+water)
TABLE-US-00002 TABLE 2 (Cathode potentials where CO.sub.2
conversion starts on a number of Catalytically Active Elements as
reported in the Hori review). Cathode Cathode Cathode potential
potential potential Metal (SHE) Metal (SHE) Metal (SHE) Pb -1.63 Hg
-1.51 Tl -1.60 In -1.55 Sn -1.48 Cd -1.63 Bi -1.56 Au -1.14 Ag
-1.37 Zn -1.54 Pd -1.20 Ga -1.24 Cu -1.44 Ni -1.48 Fe -0.91 Pt
-1.07 Ti -1.60
[0105] Table 2 indicates the cathode potential needed to convert
CO.sub.2. Notice that all of the values are more negative than -0.9
V. By comparison, FIG. 8 shows that CO.sub.2 conversion starts at
-0.2 V with respect to the reversible hydrogen electrode (RHE),
when the Active Element, Helper Catalyst Mixture is used as a
catalyst. More negative cathode potentials correspond to higher
overpotentials. This is further confirmation that Active Element,
Helper Catalyst Mixtures are advantageous for CO.sub.2
conversion.
[0106] FIG. 9 shows a series of broad band sum-frequency generation
(BB-SFG) spectra taken during the reaction. Notice the peak at 2350
cm.sup.-1. This peak corresponded to the formation of a stable
complex between the Helper Catalyst and (CO.sub.2).sup.-. It is
significant that the peak starts at -0.1 V with respect to SHE.
According to the Hori review, (CO.sub.2).sup.- is thermodynamically
unstable unless the potential is more negative than -1.2 V with
respect to SHE on platinum. Yet FIG. 9 shows that the complex
between EMIM-BF4 and (CO.sub.2).sup.- is stable at -0.1 V with
respect to SHE.
[0107] Those familiar with the technology involved here should
recognize that this result is very significant. According to the
Hori review, the Dubois review and references therein, the
formation of (CO.sub.2).sup.- is the rate determining step in
CO.sub.2 conversion to products on V, Cr, Mn, Fe, Co, Ni, Cu, Sn,
Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Ir, Pt, Au, Hg, Al,
Si, In, Sn, Tl, Pb, Bi, Sb, Te, U, Sm, Tb, La, Ce, and Nd. The
(CO.sub.2).sup.- is thermodynamically unstable at low potentials,
which leads to a high overpotential for the reaction as indicated
in FIG. 2. The data in FIG. 9 shows that one can form the
EMIM-BF4-(CO.sub.2).sup.- complex at low potentials. Thus, the
reaction can follow a low energy pathway for CO.sub.2 conversion to
CO as indicated in FIG. 3.
The Effect of Dilution on the Electrochemical Conversion of
CO.sub.2
[0108] This experiment shows that water additions speed the
formation of CO in the previous reaction. The experiment used the
cell and procedures described above, with the following exception:
a solution containing 98.55% EMIM-BF4 and 0.45% water was
substituted for the 99.9999% EMIM-BF4 used in the experiment above,
the potential was held for 10 or 30 minutes at -0.6 V with respect
to RHE, and then the potential was ramped positively at 50 mV/sec.
FIG. 10 shows the result. Notice the peak between 1.2 and 1.5 V.
This is the peak associated with CO formation and is much larger
than in the first experiment above. Thus the addition of water has
accelerated the formation of CO. Notice also that there is no
hydrogen peak in the spectrum. This result shows that EMIM-BF4 can
be used as a Hydrogen Suppressor.
SPECIFIC EXAMPLE 2
Steady State Production of Carbon Monoxide
[0109] This experiment used the flow cell described in Devin T.
Whipple, E. C. Finke, and P. J. A. Kenis, Electrochem. &
Solid-State Lett., 2010, 13 (9), B109-B111 ("the Whipple paper").
First, catalyst inks were prepared as follows:
[0110] For the cathode: 10 mg of silver nanoparticles (Sigma
Aldrich) was sonicated into a solution containing 100 .mu.L of
water, 100 .mu.L of isopropyl alcohol and 5.6 .mu.L of 5%
perfluorosulfonic acid solution (available under the trade
designation Nafion, from Ion Power, Inc., New Castle, Del., USA).
The resultant catalyst ink was painted on a 1.times.1.5 cm section
of a 2.times.3 cm piece of carbon paper (Ion Power, Inc.) and dried
with a heat lamp.
[0111] The preparation was identical for anode except 4 mg of
HiSpec 1000 platinum black (Sigma Adrich) was substituted for the
silver.
[0112] Both catalysts were mounted in the flow cell described in
the Whipple Paper. Five sccm of CO.sub.2 was fed to the anode, and
a solution containing 18 mole percent of EMIM-BF4 in water was fed
into the gap between the anode and the cathode. At any one time the
cell contained approximately 10 mg of silver nanoparticles and
approximately 40 mg of EMIM-BF4 Helper Catalyst. A potential was
applied to the cell, and the data in Table 3 were measured with a
gas chromatograph. Notice that at higher potentials one is able to
produce about 0.5 mg/min of CO, without significant hydrogen or
other by products. Further, notice that one can precisely control
the CO production rate by carefully adjusting the voltage (or
applied current). This has the key advantage.
[0113] These results demonstrate that steady state production of
useful products can be obtained with Catalytically Active
Element-Helper Catalyst Mixtures. It is believed that choline salts
or other Helper Catalysts that suppress hydrogen evolution could be
readily substituted for the Helper Catalyst EMIM-BF4.
TABLE-US-00003 TABLE 3 (Products produced at various conditions)
Hydrogen Carbon monoxide Cathode potential production rate,
production rate, Volts vs. RHE .mu.g/min .mu.g/min CO/H.sub.2 ratio
-0.358 0 0 -0.862 1.1 2.6 2.4 -1.098 1.4 50 35 -1.434 1.1 250 230
-1.788 0 560 >1000
SPECIFIC EXAMPLE 3
High Quality Carbon Monoxide Production Over a Wide Range of
Rates
[0114] Example 2 showed that CO could be produced at high rates and
selectivities, but when the voltage was decreased, so the rate
decreased, the CO.sub.2 to hydrogen ratio was less than 20. This
could create a problem in clinical systems where there is a need to
produce carbon monoxide over a wide range of rates. This example
describes a modified design that allows one to produce pure carbon
monoxide over a wider range of conditions.
[0115] The apparatus and procedures were the same as in Specific
Example 2, except that a Nafion 117 membrane (available from Ion
Power, Inc.) was inserted between the cathode and the anode to
create separate anode and cathode compartments. The anode
compartment contained 100 mM aqueous sulfuric acid flowing at 0.5
ml/min. The cathode compartment contained 18 mol % EMIM-BF.sub.4 in
water at 0.5 ml/min. A potential was applied to the cell, and the
data in FIG. 11 were measured with a gas chromatograph.
Experimentally, only hydrogen, CO and CO.sub.2 were detected at the
cathode and only O.sub.2 was detected at the anode. In all cases
there was more than 20 times as much CO as H.sub.2 and no other
reaction products were detected with the gas chromatograph. This
result shows that it is possible to create carbon monoxide
electrochemically with enough purity to be used in clinical
applications.
SPECIFIC EXAMPLE 4
Use of an Active Element, Helper Catalyst Mixture That Includes
Nickel and Choline Chloride to Lower the Overpotential for
Electrochemical Conversion of CO.sub.2 to CO and Suppress Hydrogen
Formation
[0116] This example is to demonstrate that the present invention
can be practiced using a second metal, namely, nickel and a second
helper catalyst, choline chloride.
[0117] The experiment used the cell and procedures described in
Specific Example 1 above, with the following exceptions: i) a 10.3%
by weight of a Helper Catalyst, choline iodide, in water solution
was substituted for the 1-ethyl-3-methylimidazolium
tetrafluoroborate and ii) a 0.25 cm.sup.2 Ni foil purchased from
Alfa Aesar of Ward Hill, Mass., USA, was substituted for the gold
plug and platinum black on the cathode, and a silver/silver
chloride reference was used.
[0118] The cell contained 52 mg of nickel and 103 mg of helper
catalyst, so the overall catalyst mixture contained 66% of helper
catalyst.
[0119] FIG. 12 shows a comparison of the cyclic voltammetry for i)
a blank scan where the water-choline chloride mixture was sparged
with argon and ii) a scan where the water-choline chloride mixture
was sparged with CO.sub.2. Notice the negative going peaks starting
at about -0.6. This shows that CO.sub.2 is being reduced at -0.6 V.
By comparison, the data in Table 2 indicates that a voltage more
negative than -1.48 V is needed to convert CO.sub.2 on nickel in
the absence of the Helper Catalyst. Thus, the Helper Catalyst has
lowered the overpotential for CO.sub.2 conversion.
[0120] Another important point is that there is no strong peak for
hydrogen formation. A bare nickel catalyst would produce a large
hydrogen peak at about --0.4 V at a pH of 7, while the hydrogen
peak moves to -1.2 V in the presence of the Helper Catalyst. The
Hori review reports that nickel is not an effective catalyst for
CO.sub.2 reduction because the side reaction producing hydrogen is
too large. The data in FIG. 12 show that the Helper Catalysts are
effective in suppressing hydrogen formation.
[0121] Also the Helper Catalyst is very effective in improving the
selectivity of the reaction. The Hori review reports that hydrogen
is the major product during carbon dioxide reduction on nickel in
aqueous solutions. The reported hydrolysis data shows 1.4%
selectivity to formic acid, and no selectivity to carbon monoxide.
By comparison, analysis of the reaction products in this example by
CV indicated that carbon monoxide was the major product during
CO.sub.2 conversion on nickel in the presence of the Helper
Catalyst. There may have been some formate formation. However, no
hydrogen was detected. This example shows that the Helper Catalyst
had tremendously enhanced the selectivity of the reaction toward
CO.
[0122] This example also demonstrates that the present invention
can be practiced with a second metal, nickel, and a second helper
catalyst, choline chloride. Further, those familiar with the
technology involved here will note that there is nothing special
about the Active Element, Helper Catalyst pair of nickel and
choline chloride.
[0123] Those familiar with the technology involved here should
realize that since choline chloride and choline iodide (in Specific
Example 5 below) are active, other choline salts such as choline
bromide, choline fluoride and choline acetate should be active as
well.
PREDICTIVE EXAMPLES OF DIRECTOR MOLECULES AND DIRECTOR IONS
[0124] The applicants believe that to serve as a director molecule
(or ion) for purposes such as suppressing hydrogen evolution in an
electrochemical cell, the chemical species should have at least one
positively charged group and at least one group for surface
attachment (for example, for attachment to the negative electrode).
In other words, what is needed is a positively charged species with
something to hold the positive charge near the surface, but not to
bind so strongly that the surface is poisoned. A number of
alcohols, aldehydes, ketones, and carboxylic acids should work,
although some carboxylic acids might bind too tightly to the
electrode surface, and may thus poison the desired reaction.
Similarly, other polar groups in addition to --OR, --COR, and
--COOR, such as --NR.sub.2, --PR.sub.2, --SR and halides, where the
R groups can independently be hydrogen or ligands containing
carbon, (with the possible exception of carboxylic acid groups and
their salts,) could serve as satisfactory surface attachment
groups. For the positively charged group, a variety of amines and
phosphoniums should be satisfactory. The key is to add an attached
group to bind them to the surface, and the positive group(s) should
not be so large as to be hydrophobic. Methyl, ethyl and propyl
quaternary amines should perform well. Imidazoliums (sometimes also
called imidazoniums) should also be satisfactory, provided they
contain an attachment group. Potassium and cesium cations could
also work, since potassium and cesium can attach to the surface
under certain conditions. A significant aspect of the present
invention is the identification of molecules or ions that can serve
as both Helper Catalysts (accelerating or lowering the
overpotential for desired reactions) and director molecules
(increasing the selectivity toward the desired reaction, for
example, by poisoning undesired reactions more than the desired
reaction).
COMPARATIVE EXAMPLE 1
Use of an Active Element, Helper Catalyst Mixture Including
Palladium and Choline Iodide to Lower the Overpotential for
Electrochemical Conversion of CO.sub.2 in Water and Suppress
Hydrogen Formation
[0125] This example is to demonstrate that hydrogen can be
suppressed using palladium as an active element and choline iodide
as a Helper Catalyst, but formic acid formation occurs.
[0126] The experiment used the cell and procedures described in
Specific Example 1, with the following exceptions: i) a 10.3% by
weight of a Helper Catalyst, choline iodide, in water solution was
substituted for the 1-ethyl-3-methylimidazolium tetrafluoroborate
and ii) a 0.25 cm.sup.2 Pd foil purchased from Alfa Aesar of Ward
Hill, Mass., USA, was substituted for the gold plug and platinum
black on the cathode, and a silver/silver chloride reference was
used.
[0127] The cell contained 52 mg of palladium and 103 mg of helper
catalyst, so the overall catalyst mixture contained 66% of helper
catalyst.
[0128] FIG. 13 shows a CV taken under these conditions. There is a
large negative peak near zero volts with respect to SHE associated
with iodine transformations and a negative going peak at about -0.8
V associated with conversion of CO.sub.2. By comparison the data in
Table 2 indicates that one needs to use a voltage more negative
than -1.2 V to convert CO.sub.2 on palladium in the absence of the
Helper Catalyst. Thus, the Helper Catalyst has lowered the
overpotential for CO.sub.2 formation by about 0.5 V.
[0129] Unfortunately, analysis of the products of the reaction
showed that a significant amount of formic acid was formed.
Therefore, this catalyst system would not be preferred for
generation of carbon monoxide.
COMPARATIVE EXAMPLE 2
Use of an Active Element, Helper Catalyst Mixture That Includes
Palladium and Choline Chloride to Suppress Hydrogen Formation
[0130] This example is to demonstrate that hydrogen can be
suppressed using palladium as an active element and choline
chloride as a Helper Catalyst, but formic acid formation
occurs.
[0131] The experiment used the cell and procedures in Counter
Example 1, with the following exception: a 6.5% by weight choline
chloride in water solution was substituted for the choline iodide
solution.
[0132] The cell contained 52 mg of palladium and 65 mg of Helper
Catalyst, so the overall catalyst mixture contained 56% of Helper
Catalyst. FIG. 14 shows a comparison of the cyclic voltammetry for
(i) a blank scan where the water-choline chloride mixture was
sparged with argon and (ii) a scan where the water-choline chloride
mixture was sparged with CO.sub.2. Notice the negative going peaks
starting at about -0.6. This shows that CO.sub.2 is being reduced
at -0.6 V. By comparison the data in Table 2 indicates that a
voltage more negative than -1.2 V is needed to convert CO.sub.2 on
palladium in the absence of the Helper Catalyst. Thus, the
overpotential for CO.sub.2 conversion has been lowered by 0.6 V by
the Helper Catalyst.
[0133] Another important point is that there is no strong peak for
hydrogen formation. A bare palladium catalyst would produce a large
hydrogen peak at about -0.4 V at a pH of 7, while the hydrogen peak
moves to -1.2 V in the presence of the Helper Catalyst. The Hori
review reports that palladium is not an effective catalyst for
CO.sub.2 reduction because the side reaction producing hydrogen is
too large. The data in FIG. 12 show that the Helper Catalysts are
effective in suppressing hydrogen formation. The same effect can be
observed in FIG. 13 for the choline iodide solution on palladium in
Comparative Example 1
[0134] Cyclic voltammetry was also used to analyze the reaction
products. Formic acid was the only product detected. By comparison,
the Hori review reports that the reaction is only 2.8% selective to
formic acid in water. Thus the Helper Catalyst has substantially
improved the selectivity of the reaction to formic acid.
Unfortunately, formic acid is not preferred for therapeutic
applications.
SPECIFIC EXAMPLE 5
(Demonstration of Hydrogen Suppression With Other Choline
Derivatives)
[0135] The experiments were the same as in Specific Example 4,
except that one of (a) choline acetate, (b) choline BF4, (c)
(3-chloro-2-hydroxypropyl)trimethyl ammonium chloride, (d)
butyrylcholine chloride, and (e) (2-chloroethyl)trimethylammonium
chloride were used instead of choline chloride (which is also shown
here for comparison.) FIGS. 15a, 15b, 16a, 16b, 17a and 17b show
CVs taken as described in Specific Example 1 on platinum, palladium
and platinum/ruthenium catalysts. Note that these CVs are plotted
vs. RHE, rather than vs. SHE as in FIGS. 8, 10, and 12-14. In all
cases hydrogen evolution is expected at 0V with respect to RHE, but
negligible hydrogens observed. This result shows that (a) choline
acetate, (b) choline BF4, (c) (3-chloro-2-hydroxypropyl)trimethyl
ammonium chloride, (d) butyrylcholine chloride, and (e)
(2-chloroethyl)trimethylammonium chloride are all hydrogen
suppressors.
[0136] The examples given above are merely illustrative and are not
meant to be an exhaustive list of all possible embodiments,
applications or modifications of the invention. Thus, various
modifications and variations of the described methods and systems
of the invention will be apparent to those skilled in the art
without departing from the scope and spirit of the invention.
Although the invention has been described in connection with
specific embodiments, it should be understood that the invention as
claimed should not be unduly limited to such specific embodiments.
Indeed, various modifications of the described modes for carrying
out the invention which are obvious to those skilled in the
chemical arts or in the relevant fields are intended to be within
the scope of the appended claims.
[0137] The disclosures of all references and publications cited
above are expressly incorporated by reference in their entireties
to the same extent as if each were incorporated by reference
individually.
[0138] While particular elements, embodiments and applications of
the present invention have been shown and described, it will be
understood that the invention is not limited thereto, since
modifications can be made by those skilled in the art without
departing from the scope of the present disclosure, particularly in
light of the foregoing teachings.
* * * * *