U.S. patent application number 13/957021 was filed with the patent office on 2014-01-23 for system and process for making formic acid.
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, Narayanappa Sivasankar, Ian Sullivan, Kyle Teamey.
Application Number | 20140021059 13/957021 |
Document ID | / |
Family ID | 46794543 |
Filed Date | 2014-01-23 |
United States Patent
Application |
20140021059 |
Kind Code |
A1 |
Sivasankar; Narayanappa ; et
al. |
January 23, 2014 |
System and Process for Making Formic Acid
Abstract
Methods and systems for electrochemical production of formic
acid are disclosed. A method may include, but is not limited to,
steps (A) to (D). Step (A) may introduce water to a first
compartment of an electrochemical cell. The first compartment may
include an anode. Step (B) may introduce carbon dioxide to a second
compartment of the electrochemical cell. The second compartment may
include a solution of an electrolyte and a cathode. The cathode is
selected from the group consisting of indium, lead, tin, cadmium,
and bismuth. The second compartment may include a pH of between
approximately 4 and 7. Step (C) may apply an electrical potential
between the anode and the cathode in the electrochemical cell
sufficient to reduce the carbon dioxide to formic acid. Step (D)
may maintain a concentration of formic acid in the second
compartment at or below approximately 500 ppm.
Inventors: |
Sivasankar; Narayanappa;
(Plainsboro, NJ) ; Sullivan; Ian; (Point Pleasant,
NJ) ; Cole; Emily Barton; (Houston, TX) ;
Teamey; Kyle; (Washington, DC) ; 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: |
46794543 |
Appl. No.: |
13/957021 |
Filed: |
August 1, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13416896 |
Mar 9, 2012 |
8562811 |
|
|
13957021 |
|
|
|
|
61450704 |
Mar 9, 2011 |
|
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|
Current U.S.
Class: |
205/440 ;
204/233; 204/242 |
Current CPC
Class: |
C25B 3/04 20130101; C25B
1/003 20130101; Y02P 20/133 20151101; C25B 3/00 20130101; C25B 9/08
20130101 |
Class at
Publication: |
205/440 ;
204/242; 204/233 |
International
Class: |
C25B 3/00 20060101
C25B003/00 |
Claims
1.-10. (canceled)
11. A system for electrochemical production of at least formic
acid, comprising: an electrochemical cell including: a cathode; and
a catholyte, the pH of the catholyte being maintained from 4.3 to
5.5, the catholyte including formic acid maintained at a
concentration of no greater than about 500 ppm.
12. The system of claim 11, wherein the electrolyte includes at
least one of potassium sulfate, potassium chloride, sodium
chloride, sodium sulfate, lithium sulfate, sodium perchlorate, or
lithium chloride.
13. The system of claim 11, wherein the second cell compartment
includes a heterocyclic aromatic amine selected from the group
consisting of 4-hydroxy pyridine, adenine, a heterocyclic amine
containing sulfur, a heterocyclic amine containing oxygen, an
azole, benzimidazole, a bipyridine, furan, an imidazole, an
imidazole related species with at least one five-member ring, an
indole, methylimidazole, an oxazole, phenanthroline, pterin,
pteridine, a pyridine, a pyridine related species with at least one
six-member ring, pyrrole, quinoline, or a thiazole, and mixtures
thereof.
14. The system of claim 13, wherein the heterocyclic aromatic amine
is 4-hydroxy pyridine.
15. The system of claim 13, wherein a multi-carbon containing
product is produced in the cell.
16. The system of claim 11, wherein the cathode is selected from
the group consisting of indium, lead, tin, cadmium, and
bismuth.
17. The system of claim 16, wherein the cathode comprises
indium.
18. The system of claim 11, further including: an extractor
configured for extraction of formic acid from the second cell
compartment to maintain the concentration of formic acid to no
greater than about 500 ppm.
19. A method for electrochemical production of at least formic
acid, comprising: (A) introducing a liquid to a first compartment
of an electrochemical cell, the first compartment including an
anode; (B) introducing carbon dioxide to a second compartment of
the electrochemical cell, the second compartment including a
solution of an electrolyte and a cathode, the electrolyte in the
second compartment having a pH which provides a concentration of
hydrogen ions, carbon dioxide, and water at a surface of the
cathode to favor reduction of carbon dioxide at the cathode; (C)
applying an electrical potential between the anode and the cathode
in the electrochemical cell sufficient for the cathode to reduce
the carbon dioxide to at least formic acid; and (D) maintaining a
concentration of formic acid in the second compartment at or below
approximately 500 ppm.
20. The method of claim 19, wherein the cathode includes at least
one of indium, lead, tin, cadmium, bismuth, or indium.
21. The method of claim 20, wherein the cathode comprises
indium.
22. The method of claim 19, wherein the liquid is water.
23. A process for reducing carbon dioxide, the process comprising:
(A) providing an electrochemical cell have a catholyte; (B)
applying a voltage to the cell; and (C) monitoring the pH of the
catholyte and the concentration of formic acid in the catholyte to
generate a faradaic yield of at least 50%.
24. The process of claim 22, wherein the cell includes an indium
cathode.
25. The process of claim 22, wherein the cell includes divalent
ions.
26. The process of claim 22, wherein the faradic yield is at least
60%.
27. The process of claim 22, wherein the faradic yield is at least
70%.
28. The process of claim 22, wherein the faradic yield is at least
80%.
29. The process of claim 22, wherein the pH of the catholyte is
maintained between about 4.3 and about 5.5.
30. The process of claim 26, wherein the applied voltage is about
-1.46 V vs. SCE.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] Noon The present application claims the benefit under 35
U.S.C. .sctn.119(e) of U.S. patent application Ser. No. 61/450,704,
filed Mar. 9, 2011.
[0002] The above-listed application is hereby incorporated by
reference in its entirety.
FIELD
[0003] The present disclosure generally relates to the field of
electrochemical reactions, and more particularly to methods and/or
systems for electrochemical production of formic acid from carbon
dioxide.
BACKGROUND
[0004] The combustion of fossil fuels in activities such as
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.
SUMMARY OF THE PREFERRED EMBODIMENTS
[0006] The present invention is directed to using metal cathodes
and a controlled electrolytic solution to reduce carbon dioxide to
various carbon moieties, preferably including formic acid. The
electrolytic solution is preferably controlled by one or more of
regulating its pH, selectively choosing a buffering system,
regulating its temperature, and regulating the concentration of the
carbon moieties. The present invention includes the process,
system, and various components thereof.
[0007] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory only and are not necessarily restrictive of the
disclosure as claimed. The accompanying drawings, which are
incorporated in and constitute a part of the specification,
illustrate an embodiment of the disclosure and together with the
general description, serve to explain the principles of the
disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The numerous advantages of the present disclosure may be
better understood by those skilled in the art by reference to the
accompanying figures in which:
[0009] FIG. 1 is a block diagram of a preferred system in
accordance with an embodiment of the present disclosure;
[0010] FIG. 2 displays a table including preferred electrolytes
used in electrochemical reactions of carbon dioxide and water to
produce formic acid with an indium cathode;
[0011] FIG. 3 displays a chart of reactivity for hydrogen ions,
carbon dioxide, and water species at the surface of the cathode
from lower to higher pH ranges;
[0012] FIG. 4 displays a table of results of continuous removal of
formic acid from an electrochemical cell according to one
embodiment;
[0013] FIG. 5 displays a table of pH values and formic acid
concentrations for production of formic acid from carbon dioxide
and water with an electrochemical system using an indium
cathode;
[0014] FIG. 6 is a flow diagram of a preferred method of
electrochemical production of formic acid; and
[0015] FIG. 7 is a flow diagram of another preferred method of
electrochemical production of formic acid.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0016] Reference will now be made in detail to the presently
preferred embodiments of the present disclosure, examples of which
are illustrated in the accompanying drawings.
[0017] In accordance with some embodiments of the present
disclosure, an electrochemical system is provided that generally
allows carbon dioxide and water to be converted to formic acid. The
present disclosure provides methods and/or systems for formic acid
production with high efficiency and high stability preferably using
an indium cathode in a system with appropriate electrolytes and pH
range. Further, embodiments disclosed herein may employ a
particular pH range without the use of a catalyst, and another pH
range with use of a heterocyclic catalyst. Use of a heterocyclic
catalyst may facilitate providing products including formic acid
and other higher carbon-containing products.
[0018] The process of the present invention preferably produces
formic acid electrochemically according to the following
formula:
CO.sub.2+H.sub.2O.fwdarw.HCOOH+1/2 O.sub.2
[0019] Embodiments are provided herein which describe use of a
metal cathode, preferably indium, under appropriate process and
cell conditions.
[0020] 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. 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. Further, unless otherwise noted, technical terms may be used
according to conventional usage.
[0021] In certain preferred embodiments, the reduction of the
carbon dioxide to produce formic acid may be suitably achieved
efficiently in a divided electrochemical or photoelectrochemical
cell in which (i) a compartment contains an anode suitable to
oxidize water, and (ii) another compartment contains a working
cathode electrode, and in some embodiments, a catalyst. The
compartments may be separated by a porous glass frit, microporous
separator, ion exchange membrane, 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 or the
solution may be pre-saturated with carbon dioxide.
[0022] Referring to FIG. 1, a block diagram of a system 100 is
shown in accordance with an embodiment of the present invention.
System 100 may be utilized for electrochemical production of formic
acid from carbon dioxide and water. The system (or apparatus) 100
generally comprises a cell (or container) 102, a liquid source 104
(preferably a water source), an energy source 106, a gas
treatment/pressurization unit 108, a product extractor 110 and an
oxygen extractor 112. A product or product mixture may be output
from the product extractor 110 after extraction. An output gas
containing oxygen may be output from the oxygen extractor 112 after
extraction.
[0023] 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) into formic acid. The reduction generally
takes place by introducing (e.g., bubbling) carbon dioxide into an
aqueous solution of an electrolyte in the cell 102. A cathode 120
in the cell 102 may reduce the carbon dioxide into a formic acid
(and potentially other products). For instance, other products may
include hydrogen, carbon monoxide, methanol and multi-carbon
products such as acetone and isopropanol.
[0024] 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 an opposite side of the
separator 116 as the anode 118. In a preferred implementation, the
cathode 120 is an indium cathode, although other cathode materials
may be suitable, including, without limitation, lead, bismuth, tin,
and cadmium, provided the material facilitates the reduction of
carbon dioxide to formic acid. An aqueous or preferably protic
solution 122 (e.g., anolyte or catholyte 122) may fill both
compartments 114a-114b. The aqueous solution 122 preferably
includes water as a solvent and water soluble salts for providing
various cations and anions in solution. Such anions may include,
for example, sulfate (SO.sub.4.sup.2-), perchlorate
(ClO.sub.4.sup.-), and chloride (Cl.sup.-). The catholyte 122 may
include potassium sulfate, potassium chloride, sodium chloride,
sodium sulfate, lithium sulfate, sodium perchlorate, and/or lithium
chloride. A table 200 of exemplary electrolytes 202 used in
electrochemical reactions of carbon dioxide and water to produce
formic acid with an indium cathode is shown in FIG. 2. The table
200 also includes an indication of a pH 204, a potential (in volts
vs. SCE (saturated calomel electrode)) 206, a FY (faradaic yield)
208, and a range of faradaic yields 210 for each electrolyte 202.
Faradaic yield refers to the efficiency of electron transfer (as a
percentage of total electrons transferred) for generation of a
product, preferably formic acid in the present invention. Faradaic
yield may be determined based on the formula: moles of
product=Q/nF, where Q is the charge, n is the number of moles of
electrons, and F is the Faraday constant (approximately 96485
C/mole).
[0025] In particular embodiments, a heterocyclic catalyst 124 may
be added to the compartment 114b containing the cathode 120,
although in other embodiments, no heterocyclic catalyst 124 may be
present. The heterocyclic catalyst 124 may include, for example,
4-hydroxy pyridine. The heterocyclic catalyst 124 may include one
or more of adenine, a heterocyclic amine containing sulfur, a
heterocyclic amine containing oxygen, an azole, benzimidazole, a
bipyridine, furan, an imidazole, an imidazole related species with
at least one five-member ring, an indole, methylimidazole, an
oxazole, phenanthroline, pterin, pteridine, a pyridine, a pyridine
related species with at least one six-member ring, pyrrole,
quinoline, or a thiazole. When no heterocyclic catalyst 124 is
utilized, formic acid is primarily produced by the cell 102. Use of
the heterocyclic catalyst may enable the formation of products
other than formic acid. It is believed that when a heterocyclic
catalyst is used, the only products produced in significant amounts
are formic acid, methanol, acetone, and isopropanol.
[0026] The pH of the compartment 114b is preferably maintained
between approximately 4 and 7 when no heterocyclic catalyst 124 is
present. This pH range may be suitable to provide long-term
stability of the cathode. In even more preferred implementations,
the pH range is maintained between approximately 4.3 and 5.5 to
provide concentrations of hydrogen ions (H.sup.+), carbon dioxide,
and water at the surface of the cathode 120 that favor kinetics of
carbon dioxide reduction at the cathode 120. The surface
concentration of hydrogen ions, carbon dioxide, and water at the
cathode 120 may play a role in the reduction of carbon dioxide or
in another reaction, depending on the pH. FIG. 3 displays a chart
of an approximated reactivity for hydrogen ions, carbon dioxide,
and water species at the surface of the cathode 120 from lower to
higher pH ranges. At low pH (e.g., less than about 4), the kinetics
at the surface of the cathode 120 favor the reduction of hydrogen
ions to hydrogen (H.sub.2), whereas at a higher pH (e.g., greater
than about 7), the kinetics favor the reduction of water to
hydroxide species, which may cause the surface of the cathode 120
to become basic, thereby decreasing the kinetics of carbon dioxide
reduction. At a moderate pH range (e.g., between about 4 and 7, and
in particular, between about 4.3 and 5.5), the surface of the
cathode 120 may favor the reduction of carbon dioxide, since a
favorable distribution of hydrogen ions, water, and carbon dioxide
species are present at the surface. In a preferred embodiment, the
ratio of carbon dioxide to hydrogen ions and water at the surface
of the cathode 120 generally includes about 5% to 60% carbon
dioxide with about 40% to 95% hydrogen ions and water, and more
preferably the ratio is 1:2 (e.g., about 33.3% carbon dioxide and
about 66.6% hydrogen ions and water). When the heterocyclic
catalyst 124 is present and an indium cathode is used, the pH of
the cathode compartment 114b is preferably below 5.5.
[0027] The liquid source 104 preferably includes a water source,
such that the liquid source 104 may be operational to provide pure
water to the cell 102.
[0028] The energy source 106 may include a variable voltage source.
The energy 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. In preferred embodiments, the
applied electrical potential is generally at or about -1.46 V vs.
SCE, preferably from about -1.42 V vs. SCE to about -1.60 V vs.
SCE, and more preferably from about -1.42 V vs. SCE to about -1.46
V vs. SCE.
[0029] The gas treatment/pressurization unit 108 preferably
includes a carbon dioxide source, such that the gas
treatment/pressurization unit 108 may be 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. For instance, the compartment 114b may include a
carbon dioxide input, such as a port 126a configured to be coupled
between the carbon dioxide source and the cathode 120.
[0030] Advantageously, the carbon dioxide may be obtained from any
source (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 high purity
carbon dioxide may be exhausted from cement factories, from
fermenters used for industrial fermentation of ethanol, and from
the manufacture of fertilizers and refined oil products. 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. 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] The product extractor 110 may include an organic product
and/or inorganic product extractor. The product extractor 110 is
generally operational to extract (separate) one or more products
(e.g., formic acid) from the electrolyte 122. The extracted
products may be presented through a port 126b of the system 100 for
subsequent storage and/or consumption by other devices and/or
processes. For instance, in particular implementations, formic acid
is continuously removed from the cell 102, where cell 102 operates
on a continuous basis, such as through a continuous flow-single
pass reactor where fresh catholyte and carbon dioxide is fed
continuously as the input, and where the output from the reactor is
continuously removed. In other preferred implementations, the
formic acid is continuously removed from the catholyte 122 via one
or more of adsorbing the formic acid to a solid sorbent,
liquid-liquid extraction, electrodialysis, and feeding the formic
acid to bacteria that convert it to a secondary product. Removal of
the product on a continuous basis may serve to prevent decreases in
stability of an indium cathode, which may experience decreased
stability at particular organic product concentrations. In a
preferred implementation, the concentration of formic acid within
the compartment 114b is maintained at or below approximately 500
ppm, particularly when the applied voltage is -1.46 V vs SCE. In
another preferred implementation, the concentration of formic acid
within the compartment 114b is maintained at or below approximately
300 ppm, particularly when the applied voltage is -1.46 V vs SCE.
The concentration of formic acid may be detected via any suitable
method, such as, for example, using ion chromatography (IC) to
detect anionic species present in the aqueous solution and/or using
Nuclear Magnetic Resonance (NMR) spectroscopy with a water
suppression technique. Samples of the product of the cell 102 may
be taken via an automated system for detection of the concentration
of formic acid.
[0032] An example of results of continuous removal of formic acid
from the cell 102 as the product is produced can be seen in table
400 of FIG. 4. Table 400 presents faradaic yields 404 over time (in
hours) 402 of formic acid observed in electrochemical reactions of
carbon dioxide and water with an indium cathode and a 0.5 M
potassium sulfate (K.sub.2SO.sub.4) electrolyte with a potential of
-1.46 V vs SCE. Formic acid concentrations were maintained between
approximately 8 and 15 ppm for about 28 hours by continuously
removing formic acid product from the compartment 114b.
[0033] Other methods for ameliorating stability issues with
cathodes at relatively high product concentrations include: adding
more electrolyte to the compartment 114b, adding divalent cations
(preferably magnesium ions (Mg.sup.2+), barium ions (Bar),
strontium ions (Sr2.sup.+), and/or calcium ions (Ca2.sup.+)) to the
compartment 114b (generally between about 0.001 mM to about 100 mM,
preferably between about 1 mM to about 30 mM, and in a preferred
embodiment the concentration of the divalent cations is about 2.65
mM (about 100 ppm)), increasing the temperature of the electrolyte
122, and/or increasing the pH of the compartment 114b. An example
of results of increasing the pH can be seen in table 500 of FIG. 5,
where formic acid was produced from carbon dioxide and water with
electrochemical system is using an indium cathode. Table 500
presents faradaic yields 508 over varying pH levels 504, various
electrolyte compositions 502, and potentials (in volts vs. SCE)
506, where some electrolyte compositions 502 include 500 ppm of
formic acid. As can be seen from table 500, while the observed
faradaic yield 508 at a given pH level 504 decreased for every
instance of including 500 ppm of formic acid as compared to when
the 500 ppm of formic acid was not present, the decrease was less
substantial at higher pH levels 504 (e.g., at pH of 6.6--with a
decrease of approximately 17% with the 500 ppm of formic acid as
compared to no added formic acid) than at lower pH levels 504
(e.g., at pH of 4.8--with a decrease of approximately 50% with the
500 ppm of formic acid as compared to no added formic acid).
[0034] The oxygen 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. In preferred
embodiments, the oxygen extractor 112 is a disengager/flash tank.
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, such as in
an embodiment of processes other than oxygen evolution occurring at
the anode 118. Such processes may include chlorine evolution,
oxidation of organics to other saleable products, waste water
cleanup, and corrosion of a sacrificial anode. Any other excess
gases (e.g., hydrogen) created by the reduction of the carbon
dioxide and water may be vented from the cell 102 via a port
130.
[0035] Referring to FIG. 6, a flow diagram of a preferred method
600 for electrochemical production of at least formic acid from
carbon dioxide and water in is shown. The method (or process) 600
generally comprises a step (or block) 602, a step (or block) 604, a
step (or block) 606, and a step (or block) 608. The method 600 may
be implemented using the system 100.
[0036] In the step 602, water may be introduced to a first
compartment of an electrochemical cell. The first compartment may
include an anode. Introducing carbon dioxide to a second
compartment of the electrochemical cell may be performed in the
step 604. The second compartment may include a solution of an
electrolyte, a cathode selected from the group consisting of
indium, lead, tin, cadmium, and bismuth, and a pH of between
approximately 4 and 7. In the step 606, an electric potential may
be applied between the anode and the cathode in the electrochemical
cell sufficient to reduce the carbon dioxide to formic acid.
Maintaining a concentration of formic acid in the second
compartment below approximately 500 ppm may be performed in the
step 608.
[0037] Referring to FIG. 7, a flow diagram of another preferred
method 700 for electrochemical production of at least formic acid
from carbon dioxide and water in is shown. The method (or process)
700 generally comprises a step (or block) 702, a step (or block)
704, a step (or block) 706, and a step (or block) 708. The method
700 may be implemented using the system 100.
[0038] In the step 702, a liquid may be introduced to a first
compartment of an electrochemical cell. The first compartment may
include an anode. Introducing carbon dioxide to a second
compartment of the electrochemical cell may be performed in the
step 704. The second compartment may include a solution of an
electrolyte and a cathode. The electrolyte in the second
compartment may have a pH which provides a concentration of
hydrogen ions, carbon dioxide, and water at a surface of the
cathode to favor reduction of carbon dioxide at the cathode. In the
step 706, an electric potential may be applied between the anode
and the cathode in the electrochemical cell sufficient to reduce
the carbon dioxide to at least formic acid. Maintaining a
concentration of formic acid in the second compartment below
approximately 500 ppm may be performed in the step 708.
[0039] It is believed that the present disclosure and many of its
attendant advantages will be understood by the foregoing
description, and it will be apparent that various changes may be
made in the form, construction and arrangement of the components
thereof without departing from the scope and spirit of the
disclosure or without sacrificing all of its material advantages.
The form herein before described being merely an explanatory
embodiment thereof, it is the intention of the following claims to
encompass and include such changes.
* * * * *