U.S. patent application number 13/787481 was filed with the patent office on 2013-07-18 for reducing carbon dioxide to products.
This patent application is currently assigned to LIQUID LIGHT, INC.. The applicant listed for this patent is Liquid Light, Inc.. Invention is credited to Emily Barton Cole, Kunttal Keyshar, Rishi Parajuli, Narayanappa Sivasankar.
Application Number | 20130180865 13/787481 |
Document ID | / |
Family ID | 48779228 |
Filed Date | 2013-07-18 |
United States Patent
Application |
20130180865 |
Kind Code |
A1 |
Cole; Emily Barton ; et
al. |
July 18, 2013 |
Reducing Carbon Dioxide to Products
Abstract
A method reducing carbon dioxide to one or more organic products
may include steps (A) to (C). Step (A) may introduce an anolyte to
a first compartment of an electrochemical cell, said first
compartment including an anode. Step (B) may introduce a catholyte
and carbon dioxide to a second compartment of said electrochemical
cell. The second compartment may include a tin cathode and a
catalyst. The catalyst may include at least one of pyridine,
2-picoline or 2,6-lutidine. Step (C) may apply an electrical
potential between said anode and said cathode sufficient for said
cathode to reduce said carbon dioxide to at least one of formate or
formic acid.
Inventors: |
Cole; Emily Barton;
(Houston, TX) ; Sivasankar; Narayanappa;
(Plainsboro, NJ) ; Parajuli; Rishi; (Kendell Park,
NJ) ; Keyshar; Kunttal; (Houston, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Liquid Light, Inc.; |
Monmouth Junction |
NJ |
US |
|
|
Assignee: |
LIQUID LIGHT, INC.
Monmouth Junction
NJ
|
Family ID: |
48779228 |
Appl. No.: |
13/787481 |
Filed: |
March 6, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12846221 |
Jul 29, 2010 |
|
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13787481 |
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61607240 |
Mar 6, 2012 |
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61609088 |
Mar 9, 2012 |
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Current U.S.
Class: |
205/441 ;
204/252; 205/440 |
Current CPC
Class: |
C25B 15/00 20130101;
C25B 3/04 20130101; C25B 9/08 20130101; C25B 11/04 20130101 |
Class at
Publication: |
205/441 ;
204/252; 205/440 |
International
Class: |
C25B 3/04 20060101
C25B003/04; C25B 9/08 20060101 C25B009/08 |
Claims
1. A system for electrochemical reduction of carbon dioxide,
comprising: an electrochemical cell including: a first cell
compartment; an anode positioned within said first cell
compartment; a second cell compartment; a separator interposed
between said first cell compartment and said second cell
compartment, said second cell compartment containing an
electrolyte; a cathode and a homogenous catalyst positioned within
said second cell compartment, said cathode comprising tin (Sn),
said catalyst including at least one of pyridine, 2-picoline or
2,6-lutidine; and an energy source operably coupled with said anode
and said cathode, said energy source configured to apply a voltage
between said anode and said cathode to reduce carbon dioxide at
said cathode to at least one of formate or formic acid.
2. The system of claim 1, wherein said catalyst is present in said
second cell compartment in a concentration of between about 1 mM
and 100 mM.
3. The system of claim 2, wherein said catalyst is present in said
second cell compartment in a concentration of about 30 mM.
4. The system of claim 1, wherein said second cell compartment
further includes an acidic solution.
5. The system of claim 4, wherein said second cell compartment
further includes a phosphate buffer.
6. The system of claim 5, wherein said phosphate buffer is a 0.2M
phosphate buffer.
7. The system of claim 4, wherein said second cell compartment has
a pH range of between about 1 and 7.
8. The system of claim 7, wherein said second cell compartment has
a pH range of between about 3 and 6.
9. The system of claim 1, wherein said second cell compartment
further includes a mixture of cations, said mixture of cations
including at least one of a mixture of potassium ions and cesium
ions, a mixture of lithium and potassium ions, a mixture of lithium
and cesium ions, a mixture of sodium and cesium ions, or a mixture
of lithium and sodium ions.
10. The system of claim 9, wherein said at least one of a mixture
of potassium ions and cesium ions, a mixture of lithium and
potassium ions, a mixture of lithium and cesium ions, a mixture of
sodium and cesium ions, or a mixture of lithium and sodium ions
includes a molar ratio of between about 1:1000 and 1000:1.
11. A method for reducing carbon dioxide to one or more organic
products, comprising: (A) introducing an anolyte to a first
compartment of an electrochemical cell, said first compartment
including an anode; (B) introducing a catholyte and carbon dioxide
to a second compartment of said electrochemical cell, said second
compartment including a tin cathode and a catalyst, said catalyst
including at least one of pyridine, 2-picoline or 2,6-lutidine; and
(C) applying an electrical potential between said anode and said
cathode sufficient for said cathode to reduce said carbon dioxide
to at least one of formate or formic acid.
12. The method of claim 11, wherein said catalyst is present in
said second cell compartment in a concentration of between about 1
mM and 100 mM.
13. The system of claim 12, wherein said catalyst is present in
said second cell compartment in a concentration of about 30 mM.
14. The method of claim 1, further comprising: introducing an
acidic solution to said second cell compartment.
15. The method of claim 14, further comprising: introducing a
phosphate buffer to said second cell compartment.
16. The method of claim 15, wherein said phosphate buffer is a 0.2M
phosphate buffer.
17. The method of claim 14, further comprising: maintaining said
second cell compartment at a pH range of between about 1 and 7.
18. The method of claim 17, wherein maintaining said second cell
compartment at a pH range of between about 1 and 7 includes:
maintaining said second cell compartment at a pH range of between
about 3 and 6.
19. The method of claim 11, further comprising: introducing a
mixture of cations to said second cell compartment, said mixture of
cations including at least one of a mixture of potassium ions and
cesium ions, a mixture of lithium and potassium ions, a mixture of
lithium and cesium ions, a mixture of sodium and cesium ions, or a
mixture of lithium and sodium ions.
20. The method of claim 19, wherein said at least one of a mixture
of potassium ions and cesium ions, a mixture of lithium and
potassium ions, a mixture of lithium and cesium ions, a mixture of
sodium and cesium ions, or a mixture of lithium and sodium ions
includes a molar ratio of between about 1:1000 and 1000:1.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional
Application Ser. No. 61/609,088, filed Mar. 9, 2012, to U.S.
Provisional Application Ser. No. 61/607,240, filed Mar. 6, 2012,
and to U.S. application Ser. No. 12/846,221, filed Jul. 29, 2010,
which are hereby incorporated by reference in their entireties.
[0002] The present application incorporates by reference co-pending
U.S. Patent Application Attorney Docket 0016A, entitled REDUCING
CARBON DIOXIDE TO PRODUCTS, in its entirety.
FIELD
[0003] The present invention relates to chemical reduction
generally and, more particularly, to a method and/or apparatus for
implementing reducing carbon dioxide to products.
BACKGROUND
[0004] The combustion of fossil fuels in activities such as the
electricity generation, transportation, and manufacturing produces
billions of tons of carbon dioxide annually. Research since the
1970s indicates increasing concentrations of carbon dioxide in the
atmosphere may be responsible for altering the Earth's climate,
changing the pH of the ocean and other potentially damaging
effects. Countries around the world, including the United States,
are seeking ways to mitigate emissions of carbon dioxide.
[0005] A mechanism for mitigating emissions is to convert carbon
dioxide into economically valuable materials such as fuels and
industrial chemicals. If the carbon dioxide is converted using
energy from renewable sources, both mitigation of carbon dioxide
emissions and conversion of renewable energy into a chemical form
that can be stored for later use will be possible. Electrochemical
and photochemical pathways are means for the carbon dioxide
conversion.
SUMMARY OF THE PREFERRED EMBODIMENTS
[0006] The present disclosure concerns a system for electrochemical
reduction of carbon dioxide. The system may include an
electrochemical cell, which may include a first cell compartment,
an anode positioned within said first cell compartment, a second
cell compartment, a separator interposed between said first cell
compartment and said second cell compartment. The second cell
compartment may contain an electrolyte. The electrochemical cell
may include a cathode and a homogenous catalyst positioned within
said second cell compartment. The cathode may comprise tin (Sn).
The catalyst may include at least one of pyridine, 2-picoline or
2,6-lutidine. The system may also include an energy source operably
coupled with said anode and said cathode. The energy source may be
configured to apply a voltage between said anode and said cathode
to reduce carbon dioxide at said cathode to at least one of formate
or formic acid.
[0007] The present disclosure concerns a method for reducing carbon
dioxide to one or more organic products may include steps (A) to
(C). Step (A) may introduce an anolyte to a first compartment of an
electrochemical cell, said first compartment including an anode.
Step (B) may introduce a catholyte and carbon dioxide to a second
compartment of said electrochemical cell. The second compartment
may include a tin cathode and a catalyst. The catalyst may include
at least one of pyridine, 2-picoline or 2,6-lutidine. Step (C) may
apply an electrical potential between said anode and said cathode
sufficient for said cathode to reduce said carbon dioxide to at
least one of formate or formic acid.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] These and other objects, features and advantages of the
present invention will be apparent from the following detailed
description and the appended claims and drawings in which:
[0009] FIG. 1 is a block diagram of a system in accordance with a
preferred embodiment of the present invention;
[0010] FIGS. 2A-2C are tables illustrating relative product yields
for different cathode material, catalyst, electrolyte and pH level
combinations;
[0011] FIG. 3 is a formula of an aromatic heterocyclic amine
catalyst;
[0012] FIGS. 4-6 are formulae of substituted or unsubstituted
aromatic 5-member heterocyclic amines or 6-member heterocyclic
amines;
[0013] FIG. 7 is a flow diagram of an example method used in
electrochemical examples; and
[0014] FIG. 8 is a flow diagram of an example method used in
photochemical examples.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] In accordance with some embodiments of the present
invention, an electro-catalytic system is provided that generally
allows carbon dioxide to be converted at modest overpotentials to
highly reduced species in an aqueous solution. Some embodiments
generally relate to simple, efficient and economical conversion of
carbon dioxide to reduced organic products, such as methanol,
formic acid and formaldehyde. Inorganic products such as polymers
may also be formed. Carbon-carbon bonds and/or carbon-hydrogen
bonds may be formed in the aqueous solution under mild conditions
utilizing a minimum of energy. In some embodiments, the energy used
by the system may be generated from an alternative energy source or
directly using visible light, depending on how the system is
implemented.
[0016] The reduction of carbon dioxide may be suitably catalyzed by
aromatic heterocyclic amines (e.g., pyridine, imidazole and
substituted derivatives). Simple organic compounds have been found
to be effective and stable homogenous electrocatalysts and
photoelectrocatalysts for the aqueous multiple electron, multiple
proton reduction of carbon dioxide to organic products, such as
formic acid, formaldehyde and methanol. For production of methanol,
the reduction of carbon dioxide may proceed along a electron (e-)
transfer pathway. High faradaic yields for the reduced products
have generally been found in both electrochemical and
photoelectrochemical systems at low reaction overpotentials.
[0017] Metal-derived multi-electron transfer was previously thought
to achieve highly reduced products such as methanol. Currently,
simple aromatic heterocyclic amine molecules may be capable of
producing many different chemical species on route to methanol
through multiple electron transfers, instead of metal-based
multi-electron transfers.
[0018] Some embodiments of the present invention thus relate to
environmentally beneficial methods for reducing carbon dioxide. The
methods generally include electrochemically and/or
photoelectrochemically reducing the carbon dioxide in an aqueous,
electrolyte-supported divided electrochemical cell that includes an
anode (e.g., an inert conductive counter electrode) in a cell
compartment and a conductive or p-type semiconductor working
cathode electrode in another cell compartment. A catalyst may be
included to produce a reduced product. Carbon dioxide may be
continuously bubbled through the cathode electrolyte solution to
saturate the solution.
[0019] For electrochemical reductions, the electrode may be a
suitable conductive electrode, such as Al, Au, Ag, Bi, C, Cd, Co,
Cr, Cu, Cu alloys (e.g., brass and bronze), Ga, Hg, In, Mo, Nb, Ni,
NiCo.sub.2O.sub.4, Ni alloys (e.g., Ni 625, NiHX), Ni--Fe alloys,
Pb, Pd alloys (e.g., PdAg), Pt, Pt alloys (e.g., PtRh), Rh, Sn, Sn
alloys (e.g., SnAg, SnPb, SnSb), Ti, V, W, Zn, stainless steel (SS)
(e.g., SS 2205, SS 304, SS 316, SS 321), austenitic steel, ferritic
steel, duplex steel, martensitic steel, Nichrome (e.g., NiCr 60:16
(with Fe)), elgiloy (e.g., Co--Ni--Cr), degenerately doped p-Si,
degenerately doped p-Si:As, degenerately doped p-Si:B, degenerately
doped n-Si, degenerately doped n-Si:As, and degenerately doped
n-Si:B. Other conductive electrodes may be implemented to meet the
criteria of a particular application. For photoelectrochemical
reductions, the electrode may be a p-type semiconductor, such as
p-GaAs, p-GaP, p-InN, p-InP, p-CdTe, p-GalnP.sub.2 and p-Si, or an
n-type semiconductor, such as n-GaAs, n-GaP, n-InN, n-InP, n-CdTe,
n-GalnP.sub.2 and n-Si. Other semiconductor electrodes may be
implemented to meet the criteria of a particular application
including, but not limited to, CoS, MoS.sub.2, TiB, WS.sub.2, SnS,
Ag.sub.2S, CoP.sub.2, Fe.sub.3P, Mn.sub.3P.sub.2, MoP, Ni.sub.2Si,
MoSi.sub.2, WSi.sub.2, CoSi.sub.2, TiO.sub.7, SnO.sub.2, GaAs,
GaSb, Ge, and CdSe.
[0020] The catalyst for conversion of carbon dioxide
electrochemically or photoelectrochemically may be a substituted or
unsubstituted aromatic heterocyclic amine. Suitable amines are
generally heterocycles which may include, but are not limited to,
heterocyclic compounds that are 5-member or 6-member rings with at
least one ring nitrogen. For example, pyridines, imidazoles and
related species with at least one five-member ring, bipyridines
(e.g., two connected pyridines) and substituted derivatives were
generally found suitable as catalysts for the electrochemical
reduction and/or the photoelectrochemical reduction. Amines that
have sulfur or oxygen in the rings may also be suitable for the
reductions. Amines with sulfur or oxygen may include thiazoles or
oxazoles. Other aromatic amines (e.g., quinolines, adenine, azoles,
indoles, benzimidazole and 1,10-phenanthroline) may also be
effective electrocatalysts.
[0021] Carbon dioxide may be photochemically or electrochemically
reduced to formic acid with formaldehyde and methanol being formed
in smaller amounts. Catalytic hydrogenation of carbon dioxide using
heterogeneous catalysts generally provides methanol together with
water as well as formic acid and formaldehyde. The reduction of
carbon dioxide to methanol with complex metal hydrides, such as
lithium aluminum hydrides, may be costly and therefore problematic
for bulk production of methanol. Current reduction processes are
generally highly energy-consuming and thus are not efficient ways
for a high yield, economical conversion of carbon dioxide to
various products.
[0022] On the other hand, the use of processes for converting
carbon dioxide to reduced organic and/or inorganic products in
accordance with some embodiments of the invention generally has the
potential to lead to a significant reduction of carbon dioxide, a
major greenhouse gas, in the atmosphere and thus to the mitigation
of global warming. Moreover, some embodiments may advantageously
produce methanol and related products without adding extra
reactants, such as a hydrogen source. The resultant product mixture
may use little in the way of further treatment. For example, a
resultant 1 molar (M) methanol solution may be used directly in a
fuel cell. For other uses, simple removal of the electrolyte salt
and water may be readily accomplished.
[0023] Before any embodiments of the invention are explained in
detail, it is to be understood that the embodiments may not be
limited in application per the details of the structure or the
function as set forth in the following descriptions or illustrated
in the figures of the drawing. Different embodiments may be capable
of being practiced or carried out in various ways. Also, it is to
be understood that the phraseology and terminology used herein is
for the purpose of description and should not be regarded as
limiting. The use of terms such as "including," "comprising," or
"having" and variations thereof herein are generally meant to
encompass the item listed thereafter and equivalents thereof as
well as additional items.
[0024] Further, unless otherwise noted, technical terms may be used
according to conventional usage.
[0025] In the following description of methods, process steps may
be carried out over a range of temperatures (e.g., approximately
10.degree. C. (Celsius) to 50.degree. C.) and a range of pressures
(e.g., approximately 1 to 10 atmospheres) unless otherwise
specified. Numerical ranges recited herein generally include all
values from the lower value to the upper value (e.g., all possible
combinations of numerical values between the lowest value and the
highest value enumerated are considered expressly stated). For
example, if a concentration range or beneficial effect range is
stated as 1% to 50%, it is intended that values such as 2% to 40%,
10% to 30%, or 1% to 3%, etc., are expressly enumerated. The above
may be simple examples of what is specifically intended.
[0026] A use of electrochemical or photoelectrochemical reduction
of carbon dioxide, tailored with certain electrocatalysts, may
produce methanol and related products in a high yield of about 60%
to about 100%, based on the amount of carbon dioxide, suitably
about 75% to 90%, and more suitably about 85% to 95%. At an
electric potential of about -0.50 to -2 volts (V) with respect to a
saturated calomel electrode (SCE), methanol may be produced with
good faradaic efficiency at the cathode.
[0027] An example of an overall reaction for the reduction of
carbon dioxide may be represented as follows:
CO.sub.2+2H.sub.2O.fwdarw.CH.sub.3OH+3/2O.sub.2
For a 6 e- reduction, the reactions at the cathode and anode may be
represented as follows:
CO.sub.2+6H.sup.++6e-.fwdarw.CH.sub.3OH+H.sub.2O (cathode)
3H.sub.2O.fwdarw.3/2O.sub.2+6H.sup.++6e- (anode)
[0028] The reduction of the carbon dioxide may be suitably achieved
efficiently in a divided electrochemical or photoelectrochemical
cell in which (i) a compartment contains an anode that is an inert
counter electrode and (ii) another compartment contains a working
cathode electrode and a catalyst. The compartments may be separated
by a porous glass frit or other ion conducting bridge. Both
compartments generally contain an aqueous solution of an
electrolyte. Carbon dioxide gas may be continuously bubbled through
the cathodic electrolyte solution to saturate the solution.
[0029] In the working electrode compartment, carbon dioxide may be
continuously bubbled through the solution. In some embodiments, if
the working electrode is a conductor, an external bias may be
impressed across the cell such that the potential of the working
electrode is held constant. In other embodiments, if the working
electrode is a p-type semiconductor, the electrode may be suitably
illuminated with light. An energy of the light may be matching or
greater than a bandgap of the semiconductor during the
electrolysis. Furthermore, either no external source of electrical
energy may be used or a modest bias (e.g., about 500 millivolts)
may be applied. The working electrode potential is generally held
constant relative to the SCE. The electrical energy for the
electrochemical reduction of carbon dioxide may come from a normal
energy source, including nuclear and alternatives (e.g.,
hydroelectric, wind, solar power, geothermal, etc.), from a solar
cell or other nonfossil fuel source of electricity, provided that
the electrical source supply at least 1.6 volts across the cell.
Other voltage values may be adjusted depending on the internal
resistance of the cell employed.
[0030] Advantageously, the carbon dioxide may be obtained from any
sources (e.g., an exhaust stream from fossil-fuel burning power or
industrial 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 frequently accompany natural gas in
amounts of 5% to 50%, exist in flue gases of fossil fuel (e.g.,
coal, natural gas, oil, etc.) burning power plants and nearly pure
carbon dioxide may be exhausted from cement factories and from
fermenters used for industrial fermentation of ethanol. Certain
geothermal steams may also contain significant amounts of carbon
dioxide. The carbon dioxide emissions from varied industries,
including geothermal wells, may be captured on-site. Separation of
the carbon dioxide from such exhausts is known. Thus, the capture
and use of existing atmospheric carbon dioxide in accordance with
some embodiments of the present invention generally allow the
carbon dioxide to be a renewable and unlimited source of
carbon.
[0031] For electrochemical conversions, the carbon dioxide may be
readily reduced in an aqueous medium with a conductive electrode.
Faradaic efficiencies have been found high, some reaching about
100%. For photoelectrochemical conversions, the carbon dioxide may
be readily reduced with a p-type semiconductor electrode, such as
p-GaP, p-GaAs, p-InP, p-InN, p-WSe.sub.2, p-CdTe, p-GalnP.sub.2 and
p-Si.
[0032] The electrochemical/photoelectrochemical reduction of the
carbon dioxide generally utilizes one or more catalysts in the
aqueous solution. Aromatic heterocyclic amines may include, but are
not limited to, unsubstituted and substituted pyridines and
imidazoles. Substituted pyridines and imidazoles may include, but
are not limited to mono and disubstituted pyridines and imidazoles.
For example, suitable catalysts may include straight chain or
branched chain lower alkyl (e.g., C1-C10) mono and disubstituted
compounds such as 2-methylpyridine, 4-tertbutyl pyridine,
2,6-dimethylpyridine (2,6-lutidine); bipyridines, such as
4,4'-bipyridine; amino-substituted pyridines, such as
4-dimethylamino pyridine; and hydroxyl-substituted pyridines (e.g.,
4-hydroxy-pyridine) and substituted or unsubstituted quinoline or
isoquinolines. The catalysts may also suitably include substituted
or unsubstituted dinitrogen heterocyclic amines, such as pyrazine,
pyridazine and pyrimidine. Other catalysts generally include
azoles, imidazoles, indoles, oxazoles, thiazoles, substituted
species and complex multi-ring amines such as adenine, pterin,
pteridine, benzimidazole, phenonthroline and the like.
[0033] Referring to FIG. 1, a block diagram of a system 100 is
shown in accordance with a preferred embodiment of the present
invention. The system (or apparatus) 100 generally comprises a cell
(or container) 102, a liquid source 104, a power source 106, a gas
source 108, an extractor 110 and an extractor 112. A product may be
presented from the extractor 110. An output gas may be presented
from the extractor 112. Another output gas may be presented from
the cell 102.
[0034] The cell 102 may be implemented as a divided cell. The
divided cell may be a divided electrochemical cell and/or a divided
photochemical cell. The cell 102 is generally operational to reduce
carbon dioxide (CO.sub.2) and protons into one or more organic
products and/or inorganic products. The reduction generally takes
place by bubbling carbon dioxide into an aqueous solution of an
electrolyte in the cell 102. A cathode in the cell 102 may reduce
the carbon dioxide into one or more compounds.
[0035] The cell 102 generally comprises two or more compartments
(or chambers) 114a-114b, a separator (or membrane) 116, an anode
118 and a cathode 120. The anode 118 may be disposed in a given
compartment (e.g., 114a). The cathode 120 may be disposed in
another compartment (e.g., 114b) on a side of the separator 116
opposite the anode 118. An aqueous solution 122 may fill both
compartments 114a-114b. A catalyst 124 may be added to the
compartment 114b containing the cathode 120.
[0036] The liquid source 104 may implement a water source. The
liquid source 104 may be operational to provide pure water to the
cell 102.
[0037] The power source 106 may implement a variable voltage
source. The source 106 may be operational to generate an electrical
potential between the anode 118 and the cathode 120. The electrical
potential may be a DC voltage.
[0038] The gas source 108 may implement a carbon dioxide source.
The source 108 is generally operational to provide carbon dioxide
to the cell 102. In some embodiments, the carbon dioxide is bubbled
directly into the compartment 114b containing the cathode 120 and
the electrolyte 122. In a preferred embodiment, a carbon
dioxide-saturated electrolyte is introduced to the cell 102. The
electrolyte 122 may include one or more of Na.sub.2SO.sub.4, KCl,
NaNO.sub.3, NaCl, NaF, NaClO.sub.4, KClO.sub.4, K.sub.2SiO.sub.3,
CaCl.sub.2, a guanidinium cation, a H.sup.+ ion, an alkali metal
cation, an ammonium cation, an alkylammonium cation, a halide ion,
an alkyl amine, a borate, a carbonate, a guanidinium derivative, a
nitrite, a nitrate, a phosphate, a polyphosphate, a perchlorate, a
silicate, a sulfate, and a tetraalkyl ammonium salt.
[0039] The extractor 110 may implement an organic product and/or
inorganic product extractor. The extractor 110 is generally
operational to extract (separate) products (e.g., formic acid,
acetone, glyoxal, isopropanol, formaldehyde, methanol, polymers and
the like) from the electrolyte 122. The extracted products may be
presented through a port 126 of the system 100 for subsequent
storage and/or consumption by other devices and/or processes.
[0040] The extractor 112 may implement an oxygen extractor. The
extractor 112 is generally operational to extract oxygen (e.g.,
O.sub.2) byproducts created by the reduction of the carbon dioxide
and/or the oxidation of water. The extracted oxygen may be
presented through a port 128 of the system 100 for subsequent
storage and/or consumption by other devices and/or processes.
Chlorine and/or oxidatively evolved chemicals may also be
byproducts in some configurations. The organic pollutants may be
rendered harmless by oxidization. Any other excess gases (e.g.,
hydrogen) created during the reduction of the carbon dioxide may be
vented from the cell 102 via a port 130.
[0041] In the process described, water may be oxidized (or split)
to protons and oxygen at the anode 118 while the carbon dioxide is
reduced to organic products at the cathode 120. The electrolyte 122
in the cell 102 may use water as a solvent with any salts that are
water soluble and with a pyridine or pyridine-derived catalyst 124.
The catalysts 124 may include, but are not limited to, nitrogen,
sulfur and oxygen containing heterocycles. Examples of the
heterocyclic compounds may be pyridine, imidazole, pyrrole,
thiazole, furan, thiophene and the substituted heterocycles such as
amino-thiazole and benzimidazole. Cathode materials generally
include any conductor. Any anode material may be used. The overall
process is generally driven by the power source 106. Combinations
of cathodes 120, electrolytes 122, catalysts 124, introduction of
carbon dioxide to the cell 102, introduction of divalent cations
(e.g., Ca.sup.2+, Mg.sup.2+, Zn.sup.2+) to the electrolytes 122, pH
levels and electric potential from the power source 106 may be used
to control the reaction products of the cell 102. For instance, the
pH of electrolyte solution may be maintained between about pH 1 and
pH 8 with a suitable range depending on what product or products
are desired. Organic products and inorganic products resulting from
the reaction may include, but are not limited to, acetaldehyde,
acetate, acetic acid, acetone, 1-butanol, 2-butanol, 2-butanone,
carbon, carbon monoxide, carbonates, ethane, ethanol, ethylene,
formaldehyde, formate, formic acid, glycolate, glycolic acid,
glyoxal, glyoxylate, glyoxylic acid, graphite, isopropanol,
lactate, lactic acid, methane, methanol, oxalate, oxalic acid, a
polymer containing carbon dioxide, 1-propanal, 1-propanol, and
propionic acid.
[0042] In particular implementations, the cell 102 includes a tin
(Sn) cathode for the production of formate. A catalyst is
preferably used, with the catalyst preferably including one or more
of pyridine, 2-picoline and 2,6-lutadine. The preferred catalyst
concentration is between about 1 ppm and 100 mM, and more
preferably between about 0.01 mM and 30 mM. The electrolyte in the
cell 102 may include potassium chloride with a concentration of 0.5
M, however other electrolytes may be utilized, including but not
limited to, another chloride electrolyte (e.g., LiCl, CsCl,
NH.sub.4Cl), a perchlorate electrolyte, a phosphate electrolyte, a
bicarbonate electrolyte, and a sulfate electrolyte. During
operation of the cell, a surface hydroxide may develop on the
surface of the tin cathode. Such surface hydroxide development may
lead to a decrease in current density of the cell, but product
yields may remain stable for an extended period of time. For
example, in one preferred embodiment, stable yields were obtained
in a duration that exceeded 145 hours. To address the surface
hydroxide development, an acidic solution may be introduced to the
cathode compartment, where additional protons may be made available
at the cathode surface to neutralize the hydroxide to water. A pH
buffer may be utilized to maintain a preferred pH range in the
cathode compartment of between about 1 and 7, with a more
preferable pH range of between 3 and 6, and even more preferable pH
range of between 3 and 4.5. In one embodiment, the pH buffer is a
phosphate buffer, which may be a 0.2M phosphate buffer. A cation
mixture may also be introduced to the catholyte compartment which
also may address the formation of the surface hydroxide
development. Preferred cations include mixture of cations such as
K+/Cs+, Li+/K+ and Li+/Cs+ combinations, which may be introduced in
a molar ratio between about 1:1000 and 1000:1. Na+ works equally
good in place of K+.
[0043] In some nonaqueous embodiments, the solvent may include
methanol, acetonitrile, and/or other nonaqueous solvents. The
electrolytes 122 generally include tetraalkyl ammonium salts and a
heterocyclic catalyst. A primary product may be oxalate in a
completely nonaqueous system. In a system containing a nonaqueous
catholyte and an aqueous anolyte, the products generally include
all of the products seen in aqueous systems with higher yields.
[0044] Experiments were conducted in one, two and three-compartment
electrochemical cells 102 with an SCE as the reference electrode.
The experiments were generally conducted at ambient temperature and
pressure. Current densities were observed to increase with
increased temperature, but the experiments were generally operated
at ambient temperature for best efficiency. Carbon dioxide was
bubbled into the cells during the experiments. A potentiostat or DC
power supply 106 provided the electrical energy to drive the
process. Cell potentials ranged from 2 volts to 4 volts, depending
on the cathode material. Half cell potentials at the cathode ranged
from -0.7 volts to -2 volts relative to the SCE, depending on the
cathode material used. Products from the experiments were analyzed
using gas chromatography and a spectrometer.
[0045] The process is generally controlled to get a desired product
by using combinations of specific cathode materials, catalysts,
electrolytes, surface morphology of the electrodes, introduction of
reactants relative to the cathode, introduction of divalent cations
to the electrolyte, adjusting pH levels and/or adjusting electrical
potentials. Faradaic yields for the products generally range from
less than 1% to more than 90% with the remainder being hydrogen,
though methane, carbon monoxide and/or ethylene may also be
produced as gaseous byproducts.
[0046] Referring to FIGS. 2A-2C, tables illustrating relative
product yields for different cathode material, catalyst,
electrolyte, pH level and cathode potential combinations are shown.
The combinations listed in the tables generally are not the only
combinations providing a given product. The combinations
illustrated may demonstrate high yields of the products at the
lowest potential. The cathodes tested generally include all
conductive elements on the periodic table, steels, nickel alloys,
copper alloys such as brass and bronze and elgiloy. Most of the
conductors may be used with heterocyclic catalysts 124 to reduce
the carbon dioxide. The products created may vary based on which
cathode material is used. For instance, a W cathode 120 with
pyridine catalyst 124 may give acetone as a product whereas a Sn
cathode 120 with pyridine may primarily give formic acid and
methanol as products. A product yield may also be changed by the
manner in which the carbon dioxide was bubbled into the cell 102.
For instance, with a stainless steel 2205 cathode 120 in a KCl
electrolyte 122, if the carbon dioxide bubbles directly contact the
cathode 120, the product mix may switch to methanol and
isopropanol, rather than formic acid and acetone when the carbon
dioxide bubbles avoid contact with the cathode 120 (i.e., the
carbon dioxide bubbles circumvent the cathode 120 in the cell
102).
[0047] Cell design and cathode treatment (e.g., surface morphology
or surface texture) may affect both product yields and current
density at the cathode. For instance, a divided cell 102 with a
stainless steel 2205 cathode 120 in a KCl electrolyte 122 generally
has higher yields with a heavily scratched (rough) cathode 120 than
an unscratched (smooth) cathode 120. In some embodiments, the
roughness or smoothness of a cathode surface may be determined by a
comparison between a surface area measurement and the geometric
surface area of the cathode, where the greater the difference
between the surface area measurement and the geometric surface
area, the rougher the cathode. Matte tin generally performs
different than bright tin. Maintaining carbon dioxide bubbling only
on the cathode side of the divided cell 102 (e.g., in compartment
114b) may also increase yields.
[0048] Raising or lowering the cathode potential may also alter the
reduced products. For instance, ethanol is generally evolved at
lower potentials between -0.8 volts and -1 volt using the duplex
steel/pyridine/KCl, while methanol is favored beyond -1 volt.
[0049] Faradaic yields for the products may be improved by
controlling the electrical potential of the reaction. By
maintaining a constant potential at the cathode 120, hydrogen
evolution is generally reduced and faradaic yields of the products
increased. Addition of hydrogen inhibitors, such as acetonitrile,
certain heterocycles, alcohols, and other chemicals may also
increase yields of the products.
[0050] With some embodiments, stability may be improved with
cathode materials known to poison rapidly when reducing carbon
dioxide. Copper and copper-alloy electrodes commonly poison in less
than an hour of electrochemically reducing carbon dioxide. However,
when used with a heterocyclic amine catalyst, copper-based alloys
were operated for many hours without any observed degradation in
effectiveness. The effects were particularly enhanced by using
sulfur containing heterocycles. For instance, a system with a
copper cathode and 2-amino thiazole catalyst showed very high
stability for the reduction of carbon dioxide to carbon monoxide
and formic acid.
[0051] Heterocycles other than pyridine may catalytically reduce
carbon dioxide in the electrochemical process using many
aforementioned cathode materials, including tin, steels, nickel
alloys and copper alloys. Nitrogen-containing heterocyclic amines
shown to be effective include azoles, indoles, 4,4'-bipyridines,
picolines (methyl pyridines), lutidines (dimethyl pyridines),
hydroxy pyridines, imidazole, benzimidazole, methyl imidazole,
pyrazine, pyrimidine, pyridazine, pyridazineimidazole, nicotinic
acid, quinoline, adenine and 1,10-phenanthroline. Sulfur containing
heterocycles include thiazole, aminothiazoles, thiophene. Oxygen
containing heterocycles include furan and oxazole. As with
pyridine, the combination of catalyst, cathode material and
electrolyte may be used to control product mix.
[0052] Some process embodiments of the present invention for
making/converting hydrocarbons generally consume a small amount of
water (e.g., approximately 1 to 3 moles of water) per mole of
carbon. Therefore, the processes may be a few thousand times more
water efficient than existing production techniques.
[0053] Referring to FIG. 3, a formula of an aromatic heterocyclic
amine catalyst is shown. The ring structure may be an aromatic
5-member heterocyclic ring or 6-member heterocyclic ring with at
least one ring nitrogen and is optionally substituted at one or
more ring positions other than nitrogen with R. L may be C or N. R1
may be H. R2 may be H if L is N or R2 is R if L is C. R is an
optional substitutent on any ring carbon and may be independently
selected from H, a straight chain or branched chain lower alkyl,
hydroxyl, amino, pyridyl, or two R's taken together with the ring
carbons bonded thereto are a fused six-member aryl ring and n=0 to
4.
[0054] Referring to FIGS. 4-6, formulae of substituted or
unsubstituted aromatic 5-member heterocyclic amines or 6-member
heterocyclic amines are shown. Referring to FIG. 4, R3 may be H.
R4, R5, R7 and R8 are generally independently H, straight chain or
branched chain lower alkyl, hydroxyl, amino, or taken together are
a fused six-member aryl ring. R6 may be H, straight chain or
branched chain lower alkyl, hydroxyl, amino or pyridyl.
[0055] Referring to FIG. 5, one of L1, L2 and L3 may be N, while
the other L's may be C. R9 may be H. If L1 is N, R10 may be H. If
L2 is N, R11 may be H. If L3 is N, R12 may be H. INA, L2 or L3 is
C, then R10, R11, R12, R13 and R14 may be independently selected
from straight chain or branched chain lower alkyl, hydroxyl, amino,
or pyridyl.
[0056] Referring to FIG. 6, R15 and R16 may be H. R17, R18 and R19
are generally independently selected from straight chain or
branched chain lower alkyl, hydroxyl, amino, or pyridyl.
[0057] Suitably, the concentration of aromatic heterocyclic amine
catalysts is about 1 millimolar (mM) to 1 M. The electrolyte may be
suitably a salt, such as KCl, NaNO.sub.3, Na.sub.2SO.sub.4,
NaClO.sub.4, NaF, NaClO.sub.4, KClO.sub.4, K.sub.2SiO.sub.3, or
CaCl.sub.2 at a concentration of about 0.5 M. Other electrolytes
may include, but are not limited to, all group 1 cations (e.g., H,
Li, Na, K, Rb and Cs) except Francium (Fr), Ca, ammonium cations,
alkylammonium cations and alkyl amines. Additional electrolytes may
include, but are not limited to, all group 17 anions (e.g., F, Cl,
Br, I and At), borates, carbonates, nitrates, nitrites,
perchlorates, phosphates, polyphosphates, silicates and sulfates.
Na generally performs as well as K with regard to best practices,
so NaCl may be exchanged with KCl. NaF may perform about as well as
NaCl, so NaF may be exchanged for NaCl or KCl in many cases. Larger
anions tend to change the chemistry and favor different products.
For instance, sulfate may favor polymer or methanol production
while Cl may favor products such as acetone. The pH of the solution
is generally maintained at about pH 3 to 8, suitably about 4.7 to
5.6.
[0058] At conductive electrodes, formic acid and formaldehyde were
found to be intermediate products along the pathway to the 6 e-
reduced product of methanol, with an aromatic amine radical (e.g.,
the pyridinium radical, playing a role in the reduction of both
intermediate products). The intermediate products have generally
been found to also be the final products of the reduction of carbon
dioxide at conductive electrodes or p-type semiconductor
electrodes, depending on the particular catalyst used. Other C--C
couple products may also be possible. For example, reduction of
carbon dioxide may suitably yield formaldehyde, formic acid,
glyoxal, methanol, isopropanol, or ethanol, depending on the
particular aromatic heterocyclic amine used as the catalyst. The
products of the reduction of carbon dioxide are generally
substitution-sensitive. As such, the products may be selectively
produced. For example, use of 4,4'-bipyridine as the catalyst may
produce methanol and/or 2-propanol. Lutidines and amino-substituted
pyridines may produce 2-propanol. Hydroxy-pyridine may produce
formic acid.
[0059] The effective electrochemical/photoelectrochemical reduction
of carbon dioxide disclosed herein may provide new methods of
producing methanol and other related products in an improved,
efficient, and environmentally beneficial way, while mitigating
carbon dioxide-caused climate change (e.g., global warming).
Moreover, the methanol product of reduction of carbon dioxide may
be advantageously used as (1) a convenient energy storage medium,
which allows convenient and safe storage and handling, (2) a
readily transported and dispensed fuel, including for methanol fuel
cells and (3) a feedstock for synthetic hydrocarbons and
corresponding products currently obtained from oil and gas
resources, including polymers, biopolymers and even proteins, that
may be used for animal feed or human consumption. Importantly, the
use of methanol as an energy storage and transportation material
generally eliminates many difficulties of using hydrogen for such
purposes. The safety and versatility of methanol generally makes
the disclosed reduction of carbon dioxide further desirable.
[0060] Some embodiments of the present invention may be further
explained by the following examples, which should not be construed
by way of limiting the scope of the invention.
Example 1
General Electrochemical Methods
[0061] Chemicals and materials. All chemicals used were >98%
purity and used as received from the vendor (e.g., Aldrich),
without further purification. Either deionized or high purity water
(Nanopure, Barnstead) was used to prepare the aqueous electrolyte
solutions.
[0062] Electrochemical system. The electrochemical system was
composed of a standard two-compartment electrolysis cell 102 to
separate the anode 118 and cathode 120 reactions. The compartments
were separated by a porous glass frit or other ion conducting
bridge 116. The electrolytes 122 were used at concentrations of 0.1
M to 1 M, with 0.5 M being a typical concentration. A concentration
of between about 1 mM to 1 M of the catalysts 124 were used. The
particular electrolyte 122 and particular catalyst 124 of each
given test were generally selected based upon what product or
products were being created.
[0063] Referring to FIG. 7, a flow diagram of an example method 140
used in the electrochemical examples is shown. The method (or
process) 140 generally comprises a step (or block) 142, a step (or
block) 144, a step (or block) 146, a step (or block) 148 and a step
(or block) 150. The method 140 may be implemented using the system
100.
[0064] In the step 142, the electrodes 118 and 120 may be activated
where appropriate. Bubbling of the carbon dioxide into the cell 102
may be performed in the step 144. Electrolysis of the carbon
dioxide into organic and/or inorganic products may occur during
step 146. In the step 148, the products may be separated from the
electrolyte. Analysis of the reduction products may be performed in
the step 150.
[0065] The working electrode was of a known area. All potentials
were measured with respect to a saturated calomel reference
electrode (Accumet). Before and during all electrolysis, carbon
dioxide (Airgas) was continuously bubbled through the electrolyte
to saturate the solution. The resulting pH of the solution was
maintained at about pH 3 to pH 8 with a suitable range depending on
what product or products were being made. For example, under
constant carbon dioxide bubbling, the pH levels of 10 mM solutions
of 4-hydroxy pyridine, pyridine and 4-tertbutyl pyridine were 4.7,
5.28 and 5.55, respectively. For Nuclear Magnetic Resonance (NMR)
experiments, isotopically enriched NaH.sup.13CO.sub.3 (99%) was
obtained from Cambridge Isotope Laboratories, Inc.
Example 2
General Photoelectrochemical Methods
[0066] Chemicals and materials. All chemicals used were analytical
grade or higher. Either deionized or high purity water (Nanopure,
Barnstead) was used to prepare the aqueous electrolyte
solutions.
[0067] Photoelectrochemical system. The photoelectrochemical system
was composed of a Pyrex three-necked flask containing 0.5 M KCl as
supporting electrolyte and a 1 mM to 1 M catalyst (e.g., 10 mM
pyridine or pyridine derivative). The photocathode was a single
crystal p-type semiconductor etched for approximately 1 to 2
minutes in a bath of concentrated HNO.sub.3:HCl, 2:1 v/v prior to
use. An ohmic contact was made to the back of the freshly etched
crystal using an indium/zinc (2 wt. % Zn) solder. The contact was
connected to an external lead with conducting silver epoxy (Epoxy
Technology H31) covered in glass tubing and insulated using an
epoxy cement (Loctite 0151 Hysol) to expose only the front face of
the semiconductor to solution. All potentials were referenced
against a saturated calomel electrode (Accumet). The three
electrode assembly was completed with a carbon rod counter
electrode to minimize the reoxidation of reduced carbon dioxide
products. During all electrolysis, carbon dioxide gas (Airgas) was
continuously bubbled through the electrolyte to saturate the
solution. The resulting pH of the solution was maintained at about
pH 3 to 8 (e.g., pH 5.2).
[0068] Referring to FIG. 8, a flow diagram of an example method 160
used in the photochemical examples is shown. The method (or
process) 160 generally comprises a step (or block) 162, a step (or
block) 164, a step (or block) 166, a step (or block) 168 and a step
(or block) 170. The method 160 may be implemented using the system
100.
[0069] In the step 162, the photoelectrode may be activated.
Bubbling of the carbon dioxide into the cell 102 may be performed
in the step 164. Electrolysis of the carbon dioxide into the
products may occur during step 166. In the step 168, the products
may be separated from the electrolyte. Analysis of the reduction
products may be performed in the step 170.
[0070] Light sources. Four different light sources were used for
the illumination of the p-type semiconductor electrode. For initial
electrolysis experiments, a Hg--Xe arc lamp (USHIO UXM 200H) was
used in a lamp housing (PTI Model A-1010) and powered by a PTI
LTS-200 power supply. Similarly, a Xe arc lamp (USHIO UXL 151H) was
used in the same housing in conjunction with a PTI monochromator to
illuminate the electrode at various specific wavelengths.
[0071] A fiber optic spectrometer (Ocean Optics 52000) or a silicon
photodetector (Newport 818-SL silicon detector) was used to measure
the relative resulting power emitted through the monochromator. The
flatband potential was obtained by measurements of the open circuit
photovoltage during various irradiation intensities using the 200
watt (W) Hg--Xe lamp (3 W/cm.sup.2-23 W/cm.sup.2). The photovoltage
was observed to saturate at intensities above approximately 6
W/cm.sup.2.
[0072] For quantum yield determinations, electrolysis was performed
under illumination by two different light-emitting diodes (LEDs). A
blue LED (Luxeon V Dental Blue, Future Electronics) with a luminous
output of 500 milliwatt (mW)+/-50 mW at 465 nanometers (nm) and a
20 nm full width at half maximum (FWHM) was driven at to a maximum
rated current of 700 mA using a Xitanium Driver (Advance
Transformer Company). A Fraen collimating lens (Future Electronics)
was used to direct the output light. The resultant power density
that reached the window of the photoelectrochemical cell was
determined to be 42 mW/cm.sup.2, measured using a Scientech 364
thermopile power meter and silicon photodetector. The measured
power density was assumed to be greater than the actual power
density observed at the semiconductor face due to luminous
intensity loss through the solution layer between the wall of the
photoelectrochemical cell and the electrode.
Example 3
Analysis of Products of Electrolysis
[0073] Electrochemical experiments were generally performed using a
CH Instruments potentiostat or a DC power supply with current
logger to run bulk electrolysis experiments.
[0074] Gas Chromatography. The electrolysis samples were analyzed
using a gas chromatograph (HP 5890 GC) equipped with a FID
detector.
[0075] Ion Chromatography. The presence of formaldehyde and formic
acid was also determined by the chromotropic acid assay.
[0076] Mass spectrometry. Mass spectral data was also collected to
identify all organic compounds.
[0077] Nuclear Magnetic Resonance. NMR spectra of electrolyte
volumes after bulk electrolysis were also obtained using an
automated Bruker Ultrashield.TM. 500 Plus spectrometer.
[0078] The following Table may provide other examples of
embodiments of the present invention.
TABLE-US-00001 TABLE 1 Cathode Catalyst Electrolyte Results Pt 10
mM 0.5M KCl pyr Cu 10 mM 0.5M KCl pyr SS2205 10 mM 0.5M KCl IC:
0.44% acetate + 0.14% formate (E = -0.9 V) pyr (-0.9 V), ~2%
acetate (-0.4 mA/cm2) NMR: acetate Ni625 10 mM 0.5M KCl IC:
acetate(0.04%). (E = -0.8 V) pyr GC: Trace 1-Pyr--Al (0.002%) NMR:
Me--OH PdAg (-1.13 V) 10 mM 0.1M CaCl.sub.2 IC: 2.3% acetate pyr
PdAg (-1 V) 10 mM 0.1M CaCl.sub.2 IC: 69% acetate pyr GC: trace
1-Bu--OH(~0.1%) NMR: acetate NiCr 10 mM 0.5M KCl IC:
Acetate(<0.01%) (-1 V) pyr GC: 0.44% IPA + 0.4% 1-Pyr--Al NMR:
Et--OH CoNiCr 10 mM 0.5M KCl NMR: Me--OH (-0.9 V) pyr ss 316 10 mM
0.1M TMAC GC: 3% 1-pyr--OH, 0.2%Me--OH + (-1 V) pyr 0.47%Bu--OH Mo
10 mM 0.1M TMAC IC: 0.25% Acetate (-0.85 V) pyr GC: 0.15% 2-Bu--OH
Pb 10 mM 40 wt % IC: 17% Formate and 0.2% glycolate (-1.57 V) pyr
TEAC GC: 0.3%Et--OH NMR: Et--OH C 10 mM 40 wt % IC: Trace Formate:
0.2% (-1.6 V) pyr TEAC GC: 0.2% 1pyr--Al NMR: Et--OH Bi 10 mM 40 wt
% IC: Trace Formate: 0.4% (-1.33 V) pyr TEAC GC: 1.5%Me--OH + 0.08%
Acetone NMR: Me--OH SnPb 10 mM 40 wt % IC: 7% Formate (-1.46 V) pyr
TEAC GC: 1.4%Et--OH + <1% acetone NMR: Et--OH Pb 30 mM 0.5M KCl
4- high pH aminopyr C 30 mM 0.5M KCl IC: trace formate (-1.6 V) 4-
high pH NMR: acetate aminopyr Bi 30 mM 0.5M KCl IC: trace formate
(-1.2 V) 4- high pH aminopyr SnPb 30 mM 0.5M KCl IC: 0.88% acetate
+ 1.64% formate (-1.46 V) 4- high pH NMR: Acetate aminopyr Pb --
0.1M IC: 0.26% glycolate -1.744 V TMAC-High pH Pb -- 0.1M IC: 4%
formate + 0.1% glyolate -1.944 V TMAC-High pH NMR: Me--OH C -- 0.1M
IC: Trace Formate + 24% acetate -0.945 V TMAC/TMAOH Pb -- 0.1M IC:
Trace formate -1.745 V TMAC/MeOH C 10 mM 0.5M KCl IC: Acetate (FY
1%) (-1.6 V) pyr GC: 1-Pyr--Al (0.0056%) NMR: acetate and Me--OH Pb
10 mM 0.5M KCl IC: formate(20%) + lactate (~0.58% FY) (-1.57 V) pyr
GC: MeOH (0.4%) + 1-Pyr--Al (0.08%) Au 10 mM 0.5M KCl IC: Trace
formate (-1.07 V) pyr Zn 10 mM 0.5M KCl IC: 5% formate (-1.5 V) pyr
GC: 0.026% 2-Bu--OH Bi 10 mM 0.5M KCl IC: 16% formate (-1.33 V) pyr
In 10 mM 0.5M KCl IC: 8% formate (-1.32 V) pyr Sn 10 mM 0.5M KCl
IC: 25% formate (-1.33 V) pyr SnAg 10 mM 0.5M KCl IC: 11% formate
(-1.33 V) pyr GC: 4.45% acetone + 2.77% 1pyr--Al + 0.15% Et--OH
NMR: acetone SnSb 10 mM 0.5M KCl IC: 9% formate (-1.41 V) pyr GC:
2.76% Me--OH NMR: acetate and MeOH SnPb 10 mM 0.5M KCl IC: 5%
formate (-1.46 V) pyr GC: 23% acetone NMR: acetone Ni625 10 mM 0.5M
KCl IC: Trace Formate (-1.13 V) pyr Mo 10 mM 0.5M KCl IC: Trace
formate(< 0.1%) (-1 V) pyr PdAg 10 mM 0.5M KCl GC: 0.04% Acetone
+ 0.06% 2-Bu--OH (-0.87 V) pyr NMR: acetate NiFe 10 mM 0.5M KCl IC:
Trace formate <0.1% (-1.1 V) pyr ss316 10 mM 0.5M KCl NMR:
Me--OH (-0.94 V) pyr ss304 10 mM 0.5M KCl IC: Trace oxlate, formate
(~0.01% each), (-0.97 V) pyr 3.97% acetate NMR: Me--OH and acetate
ss321 10 mM 0.5M KCl IC: 0.11% Oxlate, 0.17% acetate + trace (-1 V)
pyr Formate NMR: acetate and Me--OH NiHX 10 mM 0.5M KCl GC: 0.22%
Me--OH + 0.01% 2-Bu--OH (-1 V) pyr NMR: acetate Rh 10 mM 0.5M KCl
GC: 0.57% Me--OH + 0.05% Acetone + (-0.85 V) pyr 0.06% 2-Bu--OH
NMR: acetate and Me--OH Co 10 mM 0.5M KCl IC: Trace formate + 0.19%
acetate (-1.08 V) pyr NMR: acetate PtRh 10 mM 0.5M KCl 10% CE
acetic acid with trace formic pyr acid and methanol ss304 10 mM
0.5M KCl 2.2% acetate, 3.65% Me--OH (-0.7 V) pyr Rh 10 mM 0.5M KCl
0.8%-12.6% acetate, .06%-7.7% (-0.65 V) pyr glycolate, 0.02-0.07%
IPA, 0.005-1.09% Bu--OH, 0-0.41% acetone NiCr 60:16 10 mM 0.5M KCl
IC: Trace fomate, 0.7% acetate (with Fe) pyr (-0.7 V) PdAg 10 mM
0.5M KCl IC: Trace formate, 4% acetate (-0.55 V) pyr CoS 10 mM 0.5M
KCl IC: 0.3% FA, trace oxalate, 1.4% (-1.2 V) pyr Acetate GC: Trace
IPA, EtOH, acetone, prAL, 1- BuOH NMR: 1-BuOH, piperidine MoS.sub.2
10 mM 0.5M KCl IC: 1.1% FA, 0.02% Oxalate (-1.4 V) pyr NMR: MeOH,
(EtOH or BuOH) TiB 10 mM 0.5M KCl IC: 0.1% FA, 0.08% Oxalate,
0.005% (-1.0 V) pyr glycolate WS.sub.2 10 mM 0.5M KCl IC: 0.2% FA,
1.6% acetate (-1.0 V) pyr SnS 10 mM 0.5M KCl IC: 0.64% FA, 14% FY
acetate (-1.2 V) pyr GC: 0.77% acetone, 0.8% 1-BuOH NMR: MeOH,
1-BuOH, Propylene glycol Ag.sub.2S 10 mM 0.5M KCl IC: 0.04% FA,
2.8% acetate (-1.2 V) pyr CoP.sub.2 10 mM 0.5M KCl IC: 0.2% FA,
0.005% oxalate, 4% (-1.2 V) pyr acetate GC: trace 1-BuOH, acetone
NMR: 2-BuOH, propylene glycol. Fe.sub.3P 10 mM 0.5M KCl IC: 0.27%
FA, 1.5% Acetate (-1.1 V or 5 mA) pyr GC: trace amounts of EtOH,
acetone, PrAl NMR: EtOH, MeOH, acetone Mn.sub.3P.sub.2 10 mM 0.5M
KCl IC: 3% FY glycolate, 30% FY acetate, (-1.0 V) pyr 0.6% FA GC:
trace acetone PrAl MoP 10 mM 0.5M KCl IC: 0.32% FA, 35% acetate,
0.8% (-0.8 V) pyr Oxalate GC: trace Acetone, MeOH NMR: MeOH, 1-BuOH
Ni.sub.2Si 10 mM 0.5M KCl IC: 0.08% FA, 0.4% acetic (-1.0 V) pyr
MoSi.sub.2 10 mM 0.5M KCl 0.14% acetone,0.3% 1-propanal, 0.2% (-1.0
V) pyr IPA, 0.1% butanone WSi.sub.2 10 mM 0.5M KCl IC: 0.6% FA,
0.2% Glycolate, 4.5% (-1.0 V) pyr Acetate CoSi.sub.2 10 mM 0.5M KCl
IC: 1.02% FA, 15.8% Acetate (-1.1 V) pyr Ebonex (TiO7) 10 mM 0.5M
KCl IC: 4.3% FA, 99% acetate (-1.0 V or 500 uA) pyr GC: 2.1% MeOH,
0.33% acetone, 1.2% 1-BuOH, 0.2% Butanone NMR: 1-butanol, propylene
glycol, MeOH SnO2 10 mM 0.5M KCl IC: 1.75% FA, 0.09% oxalate, 65%
(-1.0 V or 500 pyr acetate uA) GC: 0.5% Et--OH, 0.4% acetone, 0.3%
IPA NMR: IPA, 1-BuOH, MeOH, propylene glycol GaAs 10 mM 0.5M KCl
IC: 12-23% CE acetic acid, 0.3-2% CE (130 uA/cm{circumflex over (
)}2) pyr formic p-GaAs 10 mM 0.5M KCl IC: 7.3% FA, 37.5% acetate
(130 uA/cm{circumflex over ( )}2) pyr GC: 0.8% Et--OH, 0.19%
acetone, 0.2% prAl, 1.32 IPA, 1.2 1-BuOH p-GaAs epoxy 10 mM 0.5M
KCl 4 ppm MeOH, 1 ppm IPA, 0.2 ppm Et--OH, control pyr 0.15 ppm
2-BuOH GaSb 10 mM 0.5M KCl 5% CE acetic acid, 0.6-4.5% formic acid
(-1.4 V) pyr Ge 10 mM 0.5M KCl IC: 4-19% CE acetic acid, 0.6-1.2%
CE (130 uA/cm{circumflex over ( )}2) pyr formic GC: 0.4% IPA, 0.1
1-buOH NMR: propylene glycol, acetone CdSe 10 mM 0.5M KCl IC: 7% FA
(-1.6 V) pyr
[0079] The following tables provide additional examples of
embodiments of the present invention. In particular, Table 2 shows
faradaic efficiencies for formate (HCOO.sup.-) production, with a
system employing a controlled potential electrolysis at -1.37V vs.
SCE in CO.sub.2 saturated water with a 0.5M KCl electrolyte. The
catalyst concentration in the cathode compartment was 30 mM. The
anode compartment contained water with 0.17M K.sub.2SO.sub.4. The
electrolysis was carried out in a three chambered glass cell with
separated cathode and anode chambers. Carbon dioxide was
continuously bubbled on the cathode chamber. In Table 2,
j(mA/cm.sup.2) represents average current density, and FY(%)
represents Faradaic Yield, which was calculated from the ppm of the
formate measured by IC analysis on the catholyte solution collected
after the electrolysis, and the total charge passed during the
electrolysis.
TABLE-US-00002 TABLE 2 Catalysts Time (hrs) j(mA/cm.sup.2) FY (%)
pyridine 6 0.78 20.4-21.6 4-picoline 6 1.96 19.3-39.1 Imidazole 6
0.26 1.7-4.8 2-picoline 6 1.02 36.4-42.2 2,6-Lutadine 6 0.73 .sup.
30-43.8 Benzamidazole 6 0.32 0.4-1.0 2,2'-bipyridine 6 0.07 1.7-3.1
Nicotinic acid 6 0.21 13.2-13.3
[0080] Table 3 illustrates faradaic efficiencies for formate
production using tin cathodes with 30 mM 2-picoline catalyst in the
cathode compartment, with various electrolytes. The electrolytes
were saturated with carbon dioxide and present in 0.5M
concentrations.
TABLE-US-00003 TABLE 3 Electrolytes pH HCOO.sup.- FY (%) KCl 6.0
40.0 LiCl 5.9 30.1 CsCl 5.8 40.1 NH.sub.4Cl 5.9 34.8
Na.sub.2B.sub.4O.sub.7.cndot.10H.sub.2O 6.0 0.7 NaH.sub.2PO.sub.4
6.0 26.4 NaClO.sub.4 5.74 34.5
[0081] Table 4 illustrates faradaic efficiencies for formate
production using tin cathodes obtained from electrolysis in a
divided H-Cell, with a controlled potential at -1.37V vs. SCE, in
SCE in CO.sub.2 saturated water with a 0.5M KCl electrolyte. The
cathode compartment included a catalyst of 30 mM 2-picoline, with
the anode compartment including water with 0.17M K.sub.2SO.sub.4.
The cathode compartment and anode compartment were separated by a
proton exchange membrane (Selemion HSF). The pH was monitored
continuously in situ by a glass electrode immersed in the cathode
compartment.
TABLE-US-00004 TABLE 4 Time (hr) pH.sup.b j/(mA/cm.sup.2) FY (%) 3
6.0 0.80 42.0 22 5.88 0.31 40.7 30 5.94 0.26 41.3 47 -- 0.17 38.4
53 -- 0.13 39.4 77 5.93 0.11 38.5 145 5.97 0.08 43.0
[0082] Table 5 illustrates the effects of 2-picoline concentrations
on faradaic efficiencies for formate production using tin
electrodes. Without use of 2-picoline as a catalyst, the average
faradaic yield may be about 25% for the electrolysis in the
CO.sub.2 saturated KCl solution.
TABLE-US-00005 TABLE 5 [2- picoline] Electrolyte FY (%) 1 mM 0.5M
KCl 37.7 5 mM 0.5M KCl 40.5 30 mM 0.5M KCl 40.0 100 mM 0.5M KCl
28.6
[0083] Table 6 illustrates the effects of pH for formate production
using tin cathodes. The pH was adjusted using HCl or KOH solution
after saturating with CO.sub.2.
TABLE-US-00006 TABLE 6 Electrolytes pH FY (%) 0.5M KCl 3 27 0.5M
KCl 4 30 0.5M KCl 5 28 0.5M KCl 6 40
[0084] Table 7 illustrates faradaic efficiencies for formate
production using tin cathodes buffered at 4.5 pH. The system
employed a controlled potential electrolysis (-1.37V vs. SCE) in
CO.sub.2 saturated 0.5M KCl prepared in 0.2M phosphate buffer pH
4.5 (Alfa Aesar). The catalyst in the cathode compartment was 1 mM
2-picoline, with 0.17M K.sub.2SO.sub.4 in the anode compartment.
The cathode compartment and anode compartment were separated by a
proton exchange membrane.
TABLE-US-00007 TABLE 7 pH j (mA/cm.sup.2) FY (%) Time With 2-
Without 2- With 2- Without 2- With 2- Without 2- (hr) picoline
picoline picoline picoline picoline picoline 3 4.69 4.86 1.16 3.94
37.1 5.8 6.5 4.71 5.10 1.08 3.01 30.0 2.4 23 4.55 5.17 0.97 2.90
28.5 3.0 28 4.57 -- 1.01 -- 33.5 --
[0085] Table 8 illustrates faradaic efficiencies for formate
production using tin cathodes in water with an electrolyte
including 0.25M KCl and 0.25M CsCl. The cathode compartment
included 30 mM 2-picoline as a homogenous catalyst. The system
employed a controlled potential electrolysis (-1.37V vs. SCE) in
CO.sub.2 saturated 0.5M KCl. The anode compartment included 0.17M
K.sub.2SO.sub.4. The cathode compartment and anode compartment were
separated by a proton exchange membrane. Without use of 2-picoline
as a catalyst, the average faradaic yield may be about 17.2% for
the electrolysis in the CO.sub.2 saturated KCl and CsCl
solution.
TABLE-US-00008 TABLE 8 Time (hrs) pH (mA/cm.sup.2) FY (%) 24 5.98
0.26 44.9 30 5.98 0.25 63.8 96 6.1 0.14 45.2
[0086] Carbon dioxide may be efficiently converted to value-added
products, using either a minimum of electricity (that may be
generated from an alternate energy source) or directly using
visible light. Some processes described above may generate high
energy density fuels that are not fossil-based as well as being
chemical feedstock that are not fossil or biologically based.
Moreover, the catalysts for the processes may be
substituents-sensitive and provide for selectivity of the
value-added products.
[0087] By way of example, a fixed cathode (e.g., stainless steel
2205) may be used in an electrochemical system where the
electrolyte and/or catalyst are altered to change the product mix.
In a modular electrochemical system, the cathodes may be swapped
out with different materials to change the product mix. In a hybrid
photoelectrochemical system, the anode may use different
photovoltaic materials to change the product mix.
[0088] Some embodiments of the present invention generally provide
for new cathode materials, new electrolyte materials and new sulfur
and oxygen-containing heterocyclic catalysts. Specific combinations
of cathode materials, electrolytes, catalysts, pH levels and/or
electrical potentials may be used to get a desired product. The
organic products may include, but are not limited to, acetaldehyde,
acetone, carbon, carbon monoxide, carbonates, ethanol, ethylene,
formaldehyde, formic acid, glyoxal, glyoxylic acid, graphite,
isopropanol, methane, methanol, oxalate, oxalic acid. Inorganic
products may include, but are not limited to, polymers containing
carbon dioxide. Specific process conditions may be established that
maximize the carbon dioxide conversion to specific chemicals beyond
methanol.
[0089] Cell parameters may be selected to minimize unproductive
side reactions like H.sub.2 evolution from water electrolysis.
Choice of specific configurations of heterocyclic amine pyridine
catalysts with engineered functional groups may be utilized in the
system 100 to achieve high faradaic rates. Process conditions
described above may facilitate long life (e.g., improved
stability), electrode and cell cycling and product recovery. The
organic products created may include methanol, formaldehyde, formic
acid, glyoxal, acetone, and isopropanol using the same pyridine
catalyst with different combinations of electrolytes, cathode
materials, bubbling techniques and cell potentials. Heterocyclic
amines related to pyridine may be used to improve reaction rates,
product yields, cell voltages and/or other aspects of the reaction.
Heterocyclic catalysts that contain sulfur or oxygen may also be
utilized in the carbon dioxide reduction.
[0090] Some embodiments of the present invention may provide
cathode and electrolyte combinations for reducing carbon dioxide to
products in commercial quantities. Catalytic reduction of carbon
dioxide may be achieved using steel or other low cost cathodes.
High faradaic yields (e.g., >20%) of organic products with steel
and nickel alloy cathodes at ambient temperature and pressure may
also be achieved. Copper-based alloys used at the electrodes may
remain stabile for long-term reduction of carbon dioxide. The
relative low cost and abundance of the combinations described above
generally opens the possibility of commercialization of
electrochemical carbon dioxide reduction.
[0091] Various process conditions disclosed above, including
cathode materials, cathode surface morphology, electrolyte choice,
catalyst choice, cell voltage, pH level and manner in which the
carbon dioxide is bubbled, generally improve control of the
reaction so that different products or product mixes may be made.
Greater control over the reaction generally opens the possibility
for commercial systems that are modular and adaptable to make
different products. The new materials and process conditions
combinations generally have high faradaic efficiency and relatively
low cell potentials, which allows an energy efficient cell to be
constructed.
[0092] While the invention has been particularly shown and
described with reference to the preferred embodiments thereof, it
will be understood by those skilled in the art that various changes
in form and details may be made without departing from the scope of
the invention.
* * * * *