U.S. patent application number 15/971223 was filed with the patent office on 2019-02-21 for methods for the electroreduction of carbon dioxide to value added chemicals.
The applicant listed for this patent is The Board of Trustees of the University of Illinois. Invention is credited to Paul J. A. Kenis, Shawn Lu, Sumit Verma.
Application Number | 20190055656 15/971223 |
Document ID | / |
Family ID | 65359883 |
Filed Date | 2019-02-21 |
United States Patent
Application |
20190055656 |
Kind Code |
A1 |
Kenis; Paul J. A. ; et
al. |
February 21, 2019 |
METHODS FOR THE ELECTROREDUCTION OF CARBON DIOXIDE TO VALUE ADDED
CHEMICALS
Abstract
The present disclosure provides a method of electroreducing
carbon dioxide (CO.sub.2). The method of electroreducing carbon
dioxide may include feeding a first stream comprising carbon
dioxide into a chamber through a chamber inlet, the chamber
containing a gas diffusion cathode and a gas diffusion anode;
feeding a second stream comprising glycerol or glucose into the
chamber, the second stream having a pH of 12 to 14; and applying an
electrical potential between the gas diffusion anode and the gas
diffusion cathode to reduce the carbon dioxide and oxidize the
glycerol or glucose.
Inventors: |
Kenis; Paul J. A.;
(Champaign, IL) ; Verma; Sumit; (Champaign,
IL) ; Lu; Shawn; (Champaign, IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
The Board of Trustees of the University of Illinois |
Urbana |
IL |
US |
|
|
Family ID: |
65359883 |
Appl. No.: |
15/971223 |
Filed: |
May 4, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62546044 |
Aug 16, 2017 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C25B 15/08 20130101;
C25B 3/02 20130101; C25B 9/10 20130101; C25B 3/04 20130101 |
International
Class: |
C25B 3/04 20060101
C25B003/04; C25B 3/02 20060101 C25B003/02; C25B 9/10 20060101
C25B009/10 |
Claims
1. A method of electroreducing carbon dioxide, comprising: feeding
a first stream comprising carbon dioxide into a chamber through a
chamber inlet, the chamber containing a gas diffusion cathode and a
gas diffusion anode; feeding a second stream comprising glycerol or
glucose into the chamber, the second stream having a pH of 12 to
14; and applying an electrical potential between the gas diffusion
anode and the gas diffusion cathode to reduce the carbon dioxide
and oxidize the glycerol or glucose.
2. The method of claim 1, further comprising withdrawing a liquid
product stream from an outlet of the chamber, the liquid product
stream comprising an oxidation product of glycerol or glucose or a
reduction product of carbon dioxide and withdrawing a gaseous
product stream comprising a reduction product of carbon dioxide
selected from carbon monoxide, ethylene, methane, and any
combination thereof.
3. The method of claim 2, further comprising: a) purifying the
liquid product stream to obtain a substantially pure stream of the
oxidation product of glycerol or glucose or the reduction product
of carbon dioxide; or b) purifying the gaseous product stream to
obtain a substantially pure stream of the reduction product of
carbon dioxide.
4. The method of claim 1, wherein the gas diffusion cathode divides
the chamber into a gaseous region and a liquid region.
5. The method of claim 1, wherein the second stream comprises from
0.5 M to 2.5 M of an alkali metal hydroxide.
6. The method of claim 1, wherein the carbon dioxide is reduced to
carbon monoxide, and wherein a partial current density for carbon
monoxide is from 15 mA cm.sup.-2 to 350 mA cm.sup.-2 at a cell
potential of -1.0 V to -2.5 V.
7. The method of claim 1, wherein the carbon dioxide is reduced to
a reduction product of carbon dioxide and an onset cell potential
for formation of the reduction product of carbon dioxide is from
-1.5 V to -0.5 V.
8. The method of claim 1, wherein the chamber is divided into a
cathode compartment and an anode compartment by an ion permeable
membrane.
9. The method of claim 8, wherein the second stream comprises an
anolyte stream and a catholyte stream, wherein the anolyte stream
is fed into the anode compartment and the catholyte stream is fed
into the cathode compartment.
10. The method of claim 9, wherein the anolyte stream comprises an
alkali metal hydroxide or an alkali metal carbonate.
11. The method of claim 1, wherein the gas diffusion cathode
comprises an electrocatalytic cathode coating configured for
reducing carbon dioxide.
12. The method of claim 11, wherein the electrocatalytic cathode
coating comprises a metal selected from silver, gold, zinc,
palladium, tin, lead, mercury, indium, copper, and any combination
thereof.
13. The method of claim 1, wherein the gas diffusion anode
comprises an electrocatalytic anode coating configured for
oxidizing glycerol.
14. The method of claim 13, wherein the electrocatalytic anode
coating comprises a platinum black catalyst.
15. The method of claim 1, wherein the chamber further comprises an
ion permeable membrane in contact with the gas diffusion
cathode.
16. The method of claim 1, further comprising reducing the carbon
dioxide to ethanol, formate, or any combination thereof.
17. The method of claim 1, wherein the chamber is defined inside a
flow electrolyzer.
18. The method of claim 1, wherein the pH of the second stream is
12.5 to 14.
19. A method of electroreducing carbon dioxide, comprising: feeding
a gas stream comprising carbon dioxide into chamber divided into a
cathode compartment and an anode compartment by an ion permeable
membrane, the anode compartment containing a gas diffusion anode
and the cathode compartment containing a gas diffusion cathode, the
gas diffusion cathode dividing the cathode compartment into a
gaseous region and a liquid region, wherein the gas stream is fed
into the gaseous region; feeding a catholyte stream into the liquid
region of the cathode compartment; feeding an anolyte stream
comprising glycerol into the anode compartment to contact the gas
diffusion anode; and applying an electrical potential between the
gas diffusion anode and the gas diffusion cathode to reduce the
carbon dioxide to a reduction product and oxidize the glycerol to
an oxidation product, wherein an onset cell potential for formation
of the reduction product is from -1.5 V to -0.5 V.
20. The method of claim 19, wherein the catholyte stream or the
anolyte stream has a pH from 13 to 14.
Description
RELATED APPLICATIONS
[0001] The present patent document claims the benefit of priority
under 35 U.S.C. .sctn. 119(e) to U.S. Provisional Patent
Application No. 62/546,044, filed on Aug. 16, 2017, which is hereby
incorporated by reference in its entirety.
TECHNICAL FIELD
[0002] The present disclosure is related generally to the
electroreduction of carbon dioxide and more particularly to a
method of electrochemically reducing carbon dioxide and oxidizing
glycerol or glucose.
BACKGROUND
[0003] The global atmospheric carbon dioxide (CO.sub.2)
concentrations have been on a constant rise in the past few
decades, with the daily average value crossing and staying above
the 400-ppm mark in 2016, for the first time in recorded human
history. The rise in CO.sub.2 levels has been correlated to the
increase in mean global temperature anomalies (global warming).
Thus, developing cost effective technologies that can mitigate,
capture, or utilize the excess anthropogenic CO.sub.2 emissions
remains a grand challenge of the 21.sup.st century. To limit excess
anthropogenic carbon dioxide (CO.sub.2) emissions (.about.4GtC
yr.sup.-1), and achieve the 2.degree. C. target set forth in the
Paris climate change agreement, a portfolio of technologies, such
as (i) transitioning from fossil fuels to renewable energy (wind,
solar, biofuels, etc.); (ii) improving the energy efficiency of
vehicles and buildings; and (iii) CO.sub.2 capture and
sequestration, need to be implemented together. However, for a
majority of these solutions, the associated costs and impact on
economic growth is high, resulting in slow global adoption. An
alternative to mitigating CO.sub.2 emissions could be the
utilization of CO.sub.2 as a resource to produce value added
chemicals, such as formate/formic acid (HCOO.sup.-/HCOOH), carbon
monoxide (CO), methane (CH.sub.4), methanol (CH.sub.3OH), ethylene
(C.sub.2H.sub.4), and ethanol (C.sub.2H.sub.5OH) via an
electrochemical (i.e., electroreduction) approach, that are
currently manufactured on the industrial scale using carbon
intensive fossil fuel methods.
[0004] The dominant design for state of the art electrochemical
CO.sub.2 conversion processes consists of a cathodic CO.sub.2
reduction reaction (CO.sub.2RR) coupled to an anodic oxygen
evolution reaction (OER). The electrochemical system is
characterized by a standard cell potential (E.sup.0.sub.cell) that
represents the minimum thermodynamic energy required to drive the
reaction. Thermodynamic analysis of these two reactions shows that
.about.90% of the overall energy (hence, cell potential)
requirements comes from the OER. As a result, there is a need to
think beyond OER and identify other oxidation reactions (with a
lower thermodynamic energy barrier) that can lower
E.sup.0.sub.cell.
[0005] Lowering E.sup.0.sub.cell represents one of the most
important factors in making electrochemical conversion of CO.sub.2
economically viable. Additionally, for a practical implementation
of the process, it would be advantageous to drive the reaction
using grid electricity (comprising mainly of fossil fuel resources)
and remain carbon neutral or negative.
BRIEF SUMMARY
[0006] According to one embodiment, a method of electroreducing
carbon dioxide comprises: feeding a first stream comprising carbon
dioxide into a chamber through a chamber inlet, the chamber
containing a gas diffusion cathode and a gas diffusion anode;
feeding a second stream comprising glycerol or glucose into the
chamber, the second stream having a pH of 12 to 14; and applying an
electrical potential between the gas diffusion anode and the gas
diffusion cathode to reduce the carbon dioxide and oxidize the
glycerol or glucose.
[0007] According to another embodiment, a method of electroreducing
carbon dioxide comprises: feeding a gas stream comprising carbon
dioxide into chamber divided into a cathode compartment and an
anode compartment by an ion permeable membrane, the anode
compartment containing a gas diffusion anode and the cathode
compartment containing a gas diffusion cathode, the gas diffusion
cathode dividing the cathode compartment into a gaseous region and
a liquid region, wherein the gas stream is fed into the gaseous
region; feeding a catholyte stream into the liquid region of the
cathode compartment; feeding an anolyte stream comprising glycerol
into the anode compartment to contact the gas diffusion anode; and
applying an electrical potential between the gas diffusion anode
and the gas diffusion cathode to reduce the carbon dioxide to a
reduction product and oxidize the glycerol to an oxidation product,
wherein an onset cell potential for formation of the reduction
product is from -1.5 V to -0.5 V.
[0008] The foregoing has outlined rather broadly the features and
technical advantages of the present disclosure in order that the
detailed description that follows may be better understood.
Additional features and advantages of the disclosure will be
described hereinafter that form the subject of the claims of this
application. It should be appreciated by those skilled in the art
that the conception and the specific embodiments disclosed may be
readily utilized as a basis for modifying or designing other
embodiments for carrying out the same purposes of the present
disclosure. It should also be realized by those skilled in the art
that such equivalent embodiments do not depart from the spirit and
scope of the disclosure as set forth in the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] A detailed description of the invention is hereafter
described with specific reference being made to the drawings in
which:
[0010] FIG. 1 is a block diagram of a system according to an
embodiment of the present disclosure;
[0011] FIG. 2 is a block diagram of a system according to an
embodiment of the present disclosure;
[0012] FIG. 3 is a block diagram of a system according to an
embodiment of the present disclosure;
[0013] FIG. 4A shows partial current density for CO (j.sub.CO) as a
function of the cell potential for the electroreduction of CO.sub.2
to CO coupled to O.sub.2 evolution, glycerol electrooxidation, or
glucose electrooxidation at the anode;
[0014] FIG. 4B shows individual electrode potential as a function
of the total current density (j.sub.Total) for the electroreduction
of CO.sub.2 to CO coupled to O.sub.2 evolution, glycerol
electrooxidation, or glucose electrooxidation at the anode;
[0015] FIG. 5 shows variation in the cell potential and Faradaic
efficiency for CO production as a function of time; and
[0016] FIGS. 6A-6C show partial current density for 6A, HCOO.sup.-
(j.sub.HCOO--) 6B, C.sub.2H.sub.4 (j.sub.C.sub.2.sub.H.sub.4) and
6C, C.sub.2H.sub.5OH (j.sub.C.sub.2.sub.H.sub.5.sub.OH) as a
function of the cell potential for the electroreduction of
CO.sub.2.
DETAILED DESCRIPTION
[0017] Various embodiments are described below. The relationship
and functioning of the various elements of the embodiments may
better be understood by reference to the following detailed
description. The embodiments, however, are not limited to those
illustrated below. In certain instances details may have been
omitted that are not necessary for an understanding of embodiments
disclosed herein.
[0018] The present disclosure provides a method of
electrochemically converting CO.sub.2, glycerol, and glucose to
value added carbon chemical feedstocks. A feature of this method
entails the use of glycerol or glucose electrooxidation as the
anodic reaction instead of the traditionally used OER for CO.sub.2
electroreduction systems. According to the method disclosed herein,
the required cell potentials can be lowered, thereby reducing the
electrical energy requirements by up to 53%. Some benefits may
include (i) the process lowers electrical energy requirement in
comparison to the state of the art CO.sub.2 electroreduction
systems leading to lower operating cost; (ii) the process is close
to economic viability; (iii) the process could potentially be
carbon neutral/negative even when using grid electricity to drive
the process; and (iv) the process produces value added carbon
chemical feedstocks.
[0019] The methods disclosed herein can be performed in
electrochemical cells having different configurations. For example,
FIGS. 1-3 depict embodiments of an electrochemical cell having
different positions of the ion permeable membrane.
[0020] Referring to FIG. 1, a method of electroreducing carbon
dioxide is provided. The method can include feeding a first stream
112 comprising carbon dioxide into a chamber 102 through a chamber
inlet. The chamber 102 contains a gas diffusion cathode 103 and a
gas diffusion anode 104. The method includes feeding a second
stream 113 into the chamber 102. The second stream 113 comprises
glycerol or glucose and has a pH of 12 to 14. The method includes
applying an electrical potential between the gas diffusion anode
104 and the gas diffusion cathode 103 to reduce the carbon dioxide
and oxidize the glycerol or glucose. The gas diffusion cathode 103
may divide the chamber 102 into a gaseous region 106 and a liquid
region 107.
[0021] The electrochemical cell 100 can include a CO.sub.2 source
101 from which the first stream 112 is fed into a chamber 102. A
glycerol or glucose source 110 can be fed into the chamber 102. An
electricity source 109 is connected to the gas diffusion cathode
103 and the gas diffusion anode 104 for applying an electrical
potential between the electrodes to reduce the carbon dioxide and
oxidize the glycerol or glucose.
[0022] Gaseous reduction products 110 can be withdrawn from an
outlet of the compartment in a gaseous product stream 114 to be
purifed. Liquid phase reduction products and oxidation products 111
can be withdrawn from the chamber 102 in a liquid product stream
115 to be purified.
[0023] The liquid phase products 111 include certain reduction
products of CO.sub.2 such as, for example, ethanol or formate and
oxidation products of glycerol or glucose. Without an ion permeable
membrane the liquid products of the reactions at the cathode and
anode mix and are withdrawn together for purification.
[0024] The method is not limited to the cell configuration shown in
FIG. 1. Referring to FIG. 2, an electrochemical cell 200 may
include a chamber 102 divided into a cathode compartment 202 and an
anode compartment 206 by an ion permeable membrane 201. The ion
permeable membrane 201 allows the passage of electrons from one
compartment to the other while preventing transport of certain
molecules.
[0025] Gaseous reduction products 110, liquid phase reduction
products 2033, and oxidation products 204 can be withdrawn from the
chamber 102 and purified. Liquid reduction products 203 can be
withdrawn from the liquid region 107 in a liquid reduction product
stream 205.
[0026] In another embodiment, a method of electroreducing carbon
dioxide is provided. The method can include feeding a gas stream
comprising carbon dioxide into chamber divided into a cathode
compartment and an anode compartment by an ion permeable membrane.
The anode compartment contains a gas diffusion anode and the
cathode compartment contains a gas diffusion cathode. The gas
diffusion cathode divides the cathode compartment into a gaseous
region and a liquid region, where the gas stream is fed into the
gaseous region. The method includes feeding a catholyte stream into
the liquid region of the cathode compartment; feeding an anolyte
stream comprising glycerol into the anode compartment to contact
the gas diffusion anode; and applying an electrical potential
between the gas diffusion anode and the gas diffusion cathode to
reduce the carbon dioxide to a reduction product and oxidize the
glycerol to an oxidation product. The onset cell potential for
formation of the reduction product can be from -1.5 V to -0.5
V.
[0027] Referring to FIG. 3, an electrochemical cell 300 may include
a chamber 102 where an ion permeable membrane 301 may be in contact
with the gas diffusion cathode 103. The ion permeable membrane 301
is positioned adjacent to and in contact with the gas diffusion
cathode 103. Gaseous reduction products 110 and liquid phase
products 302 can be withdrawn from the chamber 102 and
purified.
[0028] The electrochemical cell of the present disclosure can be
flow electrolyzer that is a modified version of the electrochemical
cell disclosed in U.S. Pat. No. 7,635,530, which is incorporated by
reference in its entirety. In some embodiments, the chamber is
defined inside a flow electrolyzer.
[0029] The methods disclosed herein can include withdrawing a
liquid product stream from an outlet of the chamber. The liquid
product stream can include oxidation products of glycerol or
glucose or reduction products of carbon dioxide. The method can
include withdrawing a gaseous product stream that includes a
reduction products of carbon dioxide. Gaseous reduction products of
carbon dioxide can be selected from carbon monoxide, ethylene,
methane, and any combination thereof. Table 1 shows major products
of the reduction of CO.sub.2 associated with metal catalysts.
TABLE-US-00001 TABLE 1 Cathode Reaction Catalyst Major Product
CO.sub.2 electroreduction Au, Ag, Zn, Pd Carbon monoxide (gas) Sn,
Pb, Hg, In Formate (liquid) Cu Carbon monoxide (gas), ethylene
(gas), ethanol (liquid)
[0030] In some embodiments, the carbon dioxide is reduced to carbon
monoxide. The partial current density for carbon monoxide can be
anywhere from 15 mA cm.sup.-2 to 350 mA cm.sup.-2 at a cell
potential of -1.0 V to -2.5 V. In some embodiments, the partial
current density for carbon monoxide can be anywhere from 15 mA
cm.sup.-2 to 100 mA cm.sup.-2 at a cell potential of -1.0 V to -1.5
V.
[0031] In some embodiments, the carbon dioxide is reduced to
ethanol, formate, or any combination thereof.
[0032] In some embodiments, the carbon dioxide is reduced to a
reduction product of carbon dioxide and an onset cell potential for
formation of the reduction product of carbon dioxide is from -1.5 V
to -0.5 V.
[0033] Table 2 shows major products of the oxidation of glycerol
and glucose.
TABLE-US-00002 TABLE 2 Anode Reaction Catalyst Major Product
Glycerol Pt black Glyceraldehyde (liquid), electrooxidation formate
(liquid), lactate (liquid) Glucose Pt black Gluconate (liquid)
electrooxidation
[0034] In one embodiment, the method can include additional
purification steps to produce substantially pure streams of the
reduction and oxidation products. The method can include purifying
the liquid product stream to obtain a substantially pure stream of
the oxidation product of glycerol or glucose or the reduction
product of carbon dioxide. The method can also include purifying
the gaseous product stream to obtain a substantially pure stream of
the reduction product of carbon dioxide.
[0035] The oxidation and reduction products can be purified using
known techniques. For example, carbon monoxide and other gaseous
products can be separated from the gaseous product stream using
pressure swing adsorption. Ethanol can be separated from the liquid
product stream using distillation.
[0036] The second stream, according to the disclosure, can be an
electrolyte that contacts both the anode and the cathode when an
ion permeable membrane is not present. When an ion permeable
membrane is present that divides the chamber into an anode
compartment and a cathode compartment, the second stream can
include an anolyte stream and a catholyte stream. The anolyte
stream is fed into the anode compartment and the catholyte stream
is fed into the cathode compartment.
[0037] The second stream can include an alkali metal hydroxide or
carbonate salts of Na.sup.+, K.sup.+, Rb.sup.+, or Cs.sup.+. The
concentration of the alkali metal hydroxide or carbonate salt in
the second stream can be from 0.5 M to 2.5 M. In some embodiments,
the concentration of the alkali metal hydroxide or carbonate salt
in the second stream is 2.0 M. Preferably, the second stream
contains 2.0 M of potassium hydroxide.
[0038] The pH of the second stream can range from 12 to 14. For
example, the pH can be from 12.5 to 14, 13 to 14, or greater than
12. In some embodiments, the pH of the catholyte and the anolyte
can be from 12 to 14, 12.5 to 14, 13 to 14, or greater than 12.
[0039] Operating the electrochemical reactions at a pH above 12
enables greater selectivity and selectivity while also lowering
overpotential for CO.sub.2 reduction. The overpotential is the
difference between the theoretical cell potential and the observed
cell potential. In some embodiments, the overpotential for CO.sub.2
reduction can be from -0.1 V to -1.0 V.
[0040] In some embodiments, the catholyte can include an alkali
metal hydroxide salt of Na.sup.+, K.sup.+, Rb.sup.+, or Cs.sup.+.
The catholyte can include 0.5 to 2.5 M of an alkali metal hydroxide
salt. Preferably, the concentration of the alkali metal hydroxide
salt in the catholyte is 2.0 M.
[0041] In some embodiments, the anolyte can include an alkali metal
hydroxide or carbonate salt of Na.sup.+, K.sup.+, Rb.sup.+, or
Cs.sup.+. The anolyte can include 0.5 to 2.5 M of an alkali metal
hydroxide or carbonate salt. Preferably, the concentration of the
alkali metal hydroxide salt in the anolyte is 2.0 M.
[0042] The second stream or anolyte stream can contain from 0.5 M
to 3.0 M of glycerol or glucose. In some embodiments, the
concentration of glycerol or glucose is 2.0 M.
[0043] The gas diffusion cathode, according to the present
disclosure, can include an electrocatalytic cathode coating
configured for reducing carbon dioxide. The electrocatalytic
cathode coating can include a metal selected from silver, gold,
zinc, palladium, tin, lead, mercury, indium, copper, and any
combination thereof.
[0044] The gas diffusion anode, according to the present
disclosure, can include an electrocatalytic anode coating
configured for oxidizing glycerol. The electrocatalytic anode
coating comprises a platinum black catalyst.
[0045] The methods electrochemically reducing CO.sub.2 to platform
chemicals such as carbon monoxide, formate, ethylene, and ethanol
on a silver, gold, zinc, palladium, tin, lead, mercury, indium, or
copper catalyst, while simultaneously performing an electrochemical
oxidation of glycerol, glucose to value added products such as
glyceraldehyde, formate, lactate, gluconate on a platinum black
catalyst. The CO.sub.2 electroreduction catalysts may be in a
nanoparticle form. In a related embodiment of the method, the
electroreduction of carbon monoxide to ethylene and ethanol on
copper nanoparticle catalyst can be coupled to the electrochemical
oxidation of glycerol or glucose to glyceraldehyde, formate,
lactate, gluconate on a platinum black catalyst. All the
electrochemical reactions can be carried out in a gas diffusion
electrode based flow electrolyzer.
Rationale for Method
[0046] The electroreduction of CO.sub.2 could become carbon neutral
and/or negative even with grid electricity. The current share of
low carbon renewables in the U.S. electricity grid is low (13%),
and projected not to exceed 30% by 2040. Being able to drive
CO.sub.2 electroreduction using grid electricity instead of pure
renewables and still be carbon neutral and/or negative could be an
ideal scenario, as the process can be integrated into the existing
infrastructure.
[0047] Thus, utilizing anode reactions with energy requirements
lower than OER could be a strategy for radically lowering the
energy requirements for CO.sub.2 electroreduction. The anodic
oxidation of glycerol, a cheap byproduct of industrial biodiesel
and soap production, coupled to the cathodic reduction of CO.sub.2
(i.e., co-electrolysis of CO.sub.2 and glycerol) can lower the
energy requirements compared to OER. Co-electrolysis of CO.sub.2
and glycerol lowers the CO.sub.2 electroreduction cell potential by
about 0.85 V, resulting in a reduction in electricity consumption
by up to 53%.
[0048] Glycerol can be obtained on an industrial scale as a waste
byproduct either from the biodiesel industry or the soap industry.
Due to the increase in the global biodiesel production, glycerol
supply (2.4 MT in 2007) far exceeds demand (1 MT in 2007), and has
resulted in a drop in the glycerol prices to values as low as $0.05
lb.sup.-1. On the other hand, glucose can be obtained in large
amounts as a renewable energy source from waste agricultural
biomass or energy crops such as corn.
[0049] The electrooxidation of high volume building block chemicals
such as glycerol, biomass derived glucose, or even CH.sub.4 (large
natural gas reserves, otherwise flared off-gas at oil fields),
could satisfy the process design rules for suitable anode
reactions. Table 3 shows the calculated .DELTA.G.sup.0.sub.reaction
and |E.sup.0.sub.cell| values for select combinations of CO.sub.2
electroreduction with glycerol, glucose, and CH.sub.4
electrooxidation. The values suggest that a significant lowering of
|E.sup.0.sub.cell| and hence, electricity requirements can be
realized by moving away from the anodic OER.
[0050] In certain cases, the electroreduction of CO.sub.2 to
CH.sub.3OH, C.sub.2H.sub.4, or C.sub.2H.sub.5OH on the cathode with
the electrooxidation of glucose to gluconic acid on the anode the
process becomes spontaneous (.DELTA.G.sup.0.sub.reaction<0),
i.e., behaves like a fuel cell, and can thus in principle, be used
for the simultaneous production of electricity and carbon
chemicals.
[0051] The Gibb's free energy of reaction can be calculated using
the following formula:
.DELTA.G.sup.0.sub.reaction=.SIGMA.v.sub.product*.DELTA.G.sub.f.sub.prod-
uct.sup.0-.SIGMA.v.sub.reactant*.DELTA.G.sub.f.sub.reactant.sup.0
where v=stoichiometric coefficient and .DELTA.G.sup.0.sub.f=Gibb's
free energy of formation. |E.sup.0.sub.cell|=|-.DELTA.G.sup.0/z*F|
where z=number of electrons transferred and F=Faraday's
constant=96485 C mol.sup.-1. All thermodynamic properties are
reported under standard conditions (1 bar and 298 K).
TABLE-US-00003 TABLE 3 .DELTA.G.sup.0.sub.reaction
|E.sup.0.sub.cell| Cathode reaction Possible anode reactions [kJ
mol.sup.-1] [V] Carbon dioxide .fwdarw. Water .fwdarw. Oxygen
257.20 1.33 Carbon monoxide 2OH.sup.- .fwdarw. H.sub.2O +
0.5O.sub.2 + 2e.sup.- CO.sub.2 + H.sub.2O + 2e.sup.- .fwdarw. CO +
Overall: CO.sub.2 .fwdarw. CO + 0.5O.sub.2 2OH.sup.- Glycerol
.fwdarw. Glyceraldehyde 97.48 0.51 C.sub.3H.sub.8O.sub.3 +
2OH.sup.- .fwdarw. C.sub.3H.sub.6O.sub.3 + 2H.sub.2O + 2e.sup.-
CO.sub.2 + C.sub.3H.sub.8O.sub.3 .fwdarw. CO +
C.sub.3H.sub.6O.sub.3 + H.sub.2O Glycerol .fwdarw. Lactic acid
68.08 0.35 C.sub.3H.sub.8O.sub.3 + 2OH.sup.- .fwdarw.
C.sub.3H.sub.6O.sub.3 + 2H.sub.2O + 2e.sup.- Overall: CO.sub.2 +
C.sub.3H.sub.8O.sub.3 .fwdarw. CO + C.sub.3H.sub.6O.sub.3 +
H.sub.2O Glycerol .fwdarw. Formic acid 46.53 0.24
C.sub.3H.sub.8O.sub.3 + 8OH.sup.- .fwdarw. 3HCOOH + 5H.sub.2O +
8e.sup.- Overall: CO.sub.2 + 0.25C.sub.3H.sub.8O.sub.3 .fwdarw. CO
+ 0.75HCOOH + 0.25H.sub.2O Glucose .fwdarw. Gluconic acid 6.20 0.03
C.sub.6H.sub.12O.sub.6 + 2OH.sup.- .fwdarw. C.sub.6H.sub.12O.sub.7
+ H.sub.2O + 2e.sup.- CO.sub.2 + C.sub.6H.sub.12O.sub.6 .fwdarw. CO
+ C.sub.6H.sub.12O.sub.7 Methane .fwdarw. Methanol 141.10 0.73
CH.sub.4 + 2OH.sup.- .fwdarw. CH.sub.3OH + H.sub.2O + 2e.sup.-
Overall: CO.sub.2 + CH.sub.4 .fwdarw. CO + CH.sub.3OH Methane
.fwdarw. Carbon monoxide 52.68 0.36 CH.sub.4 + 6OH.sup.- .fwdarw.
5H.sub.2O + CO + 6e.sup.- Overall: 0.75CO.sub.2 + 0.25CH.sub.4
.fwdarw. CO + 0.5H.sub.2O Carbon dioxide .fwdarw. Water .fwdarw.
Oxygen 1331.40 1.15 Ethylene 2OH.sup.- .fwdarw. H.sub.2O +
0.5O.sub.2 + 2e.sup.- 2CO.sub.2 + 8H.sub.2O + 12e.sup.- .fwdarw.
Overall: 2CO.sub.2 + 2H.sub.2O .fwdarw. C.sub.2H.sub.4 + 3O.sub.2
C.sub.2H.sub.4 + 12OH.sup.- Glycerol .fwdarw. Glyceraldehyde 373.08
0.32 C.sub.3H.sub.8O.sub.3 + 2OH.sup.- .fwdarw.
C.sub.3H.sub.6O.sub.3 + 2H.sub.2O + 2e.sup.- Overall: 2CO.sub.2 +
6C.sub.3H.sub.8O.sub.3 .fwdarw. C.sub.2H.sub.4 +
6C.sub.3H.sub.6O.sub.3 + 4H.sub.2O Glycerol .fwdarw. Lactic acid
196.68 0.17 C.sub.3H.sub.8O.sub.3 + 2OH.sup.- .fwdarw.
C.sub.3H.sub.6O.sub.3 + 2H.sub.2O + 2e.sup.- Overall: 2CO.sub.2 +
6C.sub.3H.sub.8O.sub.3 .fwdarw. C.sub.2H.sub.4 +
6C.sub.3H.sub.6O.sub.3 + 4H.sub.2O Glycerol .fwdarw. Formic acid
67.35 0.06 C.sub.3H.sub.8O.sub.3 + 8OH.sup.- .fwdarw. 3HCOOH +
5H.sub.2O + 8e.sup.- Overall: 2CO.sub.2 + 1.5C.sub.3H.sub.8O.sub.3
+ 0.5H.sub.2O .fwdarw. C.sub.2H.sub.4 + 4.5HCOOH Glucose .fwdarw.
Gluconic acid -174.60 0.15 C.sub.6H.sub.12O.sub.6 + 2OH.sup.-
.fwdarw. C.sub.6H.sub.12O.sub.7 + H.sub.2O + 2e.sup.- Overall:
2CO.sub.2 + 6C.sub.6H.sub.12O.sub.6 + 2H.sub.2O .fwdarw.
C.sub.2H.sub.4 + 6C.sub.6H.sub.12O.sub.7 Methane .fwdarw. Methanol
634.80 0.55 CH.sub.4 + 2OH.sup.- .fwdarw. CH.sub.3OH + H.sub.2O +
2e.sup.- Overall: 2CO.sub.2 + 6CH.sub.4 + 2H.sub.2O .fwdarw.
C.sub.2H.sub.4 + 6CH.sub.3OH Methane .fwdarw. Carbon monoxide
209.60 0.18 CH.sub.4 + 6OH.sup.- .fwdarw. 5H.sub.2O + CO + 6e.sup.-
Overall: 2CO.sub.2 + 2CH.sub.4 .fwdarw. C.sub.2H.sub.4 + 2CO +
2H.sub.2O
EXAMPLES
Example 1. Electrochemical Performance for the Electroreduction of
CO.sub.2
[0052] Unless stated otherwise, all experiments were performed
under ambient conditions of 1 atm and 293 K, all commercially
available materials were used as received, and >18.0 MO cm
deionized (DI) water was used when required.
[0053] The electrolytes used herein were prepared by dissolving the
appropriate amount of the salt and/or chemical in DI water. The
salts and chemicals used were: potassium hydroxide (Fisher
Chemical, product number: P250), glycerol (Alfa Aesar, product
number: 38988), D-(+)-glucose (Sigma Life Science, product number:
49139). The pH and conductivity of the different electrolytes were
measured using an Orion 4-star pH conductivity meter.
[0054] The electrochemical characterization of the different
combinations of CO.sub.2 electroreduction at the cathode with the
O.sub.2 evolution reaction and glycerol, glucose, or CH.sub.4
electrooxidation at the anode was performed in a gas diffusion
electrode based dual electrolyte channel flow electrolyzer with a
precisely machined active geometric area of 1 cm.sup.2, as
described previously. The catholyte and the anolyte chamber was
separated by a Fumapem FAA-3-PK-75 anion exchange membrane to
prevent crossover of the liquid products from the cathode to the
anode and vice versa. The catholyte for all experiments was 2.0 M
KOH. The anolyte for studying the OER and CH.sub.4 electrooxidation
was 2.0 M KOH whereas the anolyte for studying the electrooxidation
of glycerol and glucose was 2.0 M KOH+2.0 M glycerol and 2.0 M
KOH+2.0 M glucose, respectively. Electrochemical experiments were
performed by maintaining a constant cell potential using a
potentiostat (Autolab PGSTAT-30, EcoChemie). The individual cathode
and anode potentials were measured with a multimeter (AMPROBE
15XP-B) connected between the appropriate electrode and an Ag/AgCl
reference electrode (3 mol kg.sup.-1, RE-5B BASi). The individual
electrode potentials (vs. Ag/AgCl) were then converted to the RHE
scale using the Nernst equation:
E.sub.RHE=E.sub.Ag/AgCl+0.210+0.058.times.pH. All cell, cathode,
and anode potentials are reported as measured without any iR
corrections. The CO.sub.2 (Airgas) feed for the reaction was
provided as a continuous stream over the teflonized side of the
cathode gas diffusion layer (GDL) using a flow controller (Smart
Trak 2, Sierra Instruments). A CO.sub.2 flow rate of 17 sccm was
maintained for cell potentials at which the total current density
(j.sub.Total) was >5 mA cm.sup.-2 and lowered to 5 sccm for cell
potentials at which j.sub.Total was <5 mA cm.sup.-2, to enable a
gas product analysis with high sensitivity. A pressure controller
(Cole Parmer, 00268TC) was used in the electrolyzer downstream to
maintain a low pressure of 14.20 psi and thus facilitate an easy
transfer of the gas products from the cathode GDL to the effluent
gas stream. A low downstream pressure also minimized the
dissolution of the reacting CO.sub.2 and the gas products into the
electrolyte stream. Both the catholyte and the anolyte stream was
circulated through the electrolyte channels of the electrolyzer
using a syringe pump (PHD 2000, Harvard Apparatus) at flow rate of
0.5 mL min.sup.-1 for cell potentials at which j.sub.Total was
>5 mA cm.sup.-2 and lowered to 0.2 mL min.sup.-1 for cell
potentials at which j.sub.Total was <5 mA cm.sup.-2, to enable a
liquid product analysis with high sensitivity. For all
electrochemical experiments, after a particular cell potential was
switched on, the resulting current was allowed to stabilize for at
least 180 seconds before the product analysis was initiated.
[0055] For a particular cell potential, the gas products of
CO.sub.2 electroreduction were analyzed for a total time period of
180 seconds by diverting 1 mL of the effluent gas stream, thrice,
at regular intervals of 90 seconds to an on-line gas chromatograph
(Thermo Finnigan Trace GC with a Carboxen 1000 column from
Supelco). The GC was equipped with both the thermal conductivity
detector (TCD) and the flame ionization detector (FID). Helium with
a flow rate of 20 sccm was used as the carrier gas. The
concentration of the gas products was quantified by averaging the
peak areas over the three sample injections and using the
appropriate calibration curves. Meanwhile, the liquid products were
analyzed for the same 180 second time period by collecting both the
catholyte and the anolyte streams followed by ex situ .sup.1H NMR
(UI500NB, Varian) analysis (16 scans with solvent suppression). The
liquid samples for the .sup.1H NMR analysis were prepared by mixing
100 .mu.L of the collected electrolyte with 400 .mu.L of D.sub.2O
(Aldrich, product number: 151882) and 100 .mu.L of an internal
standard comprising of 1.25 mM DMSO in D.sub.2O. The concentration
of the liquid products was quantified using the appropriate
calibration curves. The total current density (=the total current
as the electrolyzer area is 1 cm.sup.2) was quantified by averaging
the data obtained during the same 180 second time period when the
CO.sub.2 electroreduction products were being analyzed. The
Faradaic efficiency for the different CO.sub.2 electroreduction
products was calculated per the following equation:
FE ( % ) = znF Q .times. 100 ##EQU00001##
where z is the number of electrons exchanged to form a particular
CO.sub.2 electroreduction product, n is the number of moles of the
product formed, F is the Faraday's constant (96485 C mol.sup.-1),
and Q is the amount of charge passed. The partial current density
for a particular product was calculated by multiplying j.sub.Total
with the Faradaic efficiency for that product. The onset cell
potential for a specific CO.sub.2 electroreduction product defined
in this work refers to the lowest (least negative) cell potential
at which the product is first observed in the GC (for gas products)
or .sup.1H NMR analysis (for liquid products).
[0056] The cathode was a 1.+-.0.1 mg cm.sup.-2 Ag nanoparticle
coated gas diffusion layer (GDL) electrode. The anode was a
1.+-.0.1 mg cm.sup.-2 IrO.sup.2 coated GDL electrode for O.sub.2
evolution, and a 1.+-.0.1 mg cm.sup.-2 Pt black coated GDL
electrode for glycerol and glucose electrooxidation. All data
collected under ambient conditions of 1 atm and 293 K.
[0057] As indicated by the Gibb's free energy analysis, many
different anode reactions other than OER can be utilized to lower
|E.sup.0.sub.cell|, and hence the overall electricity requirements
for CO.sub.2 electroreduction. To assess the practicality of such
processes, we performed an experimental electroanalytical
evaluation of the different combinations proposed in Table 3, using
a gas diffusion layer (GDL) electrode based dual electrolyte
channel flow electrolyzer under ambient conditions. The catholyte
was chosen as 2.0 M KOH, previously demonstrated by us to lower
overpotentials and improve activity for CO.sub.2 electroreduction.
The anolyte was chosen as a mixture of 2.0 M KOH and 2.0 M
glycerol, a mixture of 2.0 M KOH and 2.0 M glucose, and 2.0 M KOH
for the electrooxidation of glycerol, glucose, and CH.sub.4
respectively.
[0058] The electrooxidation of glycerol or glucose on a Pt black
coated GDL anode coupled to the electroreduction of CO.sub.2 on a
Ag coated GDL cathode resulted in a significant lowering (i.e.,
less negative value) of the onset cell potential for CO formation,
with a value of -0.75 and -0.95 V being observed, respectively, in
comparison to the state of the art value of -1.6 V with OER at the
anode (FIG. 4A). However, the activity (partial current density for
CO, j.sub.CO) with glucose electrooxidation (j.sub.CO=12.47 mA
cm.sup.-2 or production rate=0.065 kg.sub.CO m.sup.-2 h.sup.-1 at a
cell potential of -1.5 V) was much lower than with glycerol
electrooxidation (j.sub.CO=88.44 mA cm.sup.-2 or production
rate=0.462 kg.sub.CO m.sup.-2 h.sup.-1 at a cell potential of -1.5
V) at the anode. These results indicate that the electroreduction
of CO.sub.2 to CO could indeed become carbon neutral and/or
negative even when using the present-day grid electricity mix to
drive the process. Depending on the j.sub.CO value, the
electrooxidation of glycerol at the anode instead of OER results in
a 37 to 53% reduction in electricity requirements, thus improving
the process economics. Single electrode plot suggests the major
improvement to be at the anode with the cathodic CO.sub.2
electroreduction remaining unaffected (FIG. 4B). The anodic
glycerol electrooxidation results in the formation of value-added
chemicals such as formate and lactate that further improves the
economics of the overall process. Further, we also evaluated the
durability of CO.sub.2-glycerol co-electrolysis with respect to CO
production (FIG. 5). The results indicate the cell potential and
FE.sub.CO to be fairly stable over a 1.5 h time period. However,
flooding of the electrolyte through the cathode GDL was observed at
-1.5 h (similar to earlier observations in the literature)
indicating the need to develop more durable GDLs to improve the
prospects of this process.
[0059] A similar lowering in onset cell potentials for the
electroreduction of CO.sub.2 to HCOO.sup.-, C.sub.2H.sub.4, and
C.sub.2H.sub.5OH was observed when utilizing the electrooxidation
of glycerol at the anode instead of OER (FIG. 6A). For example, the
onset cell potential for the electroreduction of CO.sub.2 to
HCOO.sup.- on a Sn coated GDL cathode and C.sub.2H.sub.4,
C.sub.2H.sub.5OH on a Cu coated GDL cathode was -0.9, -0.95, and
-1.3 V, respectively, with the anodic electrooxidation of glycerol,
in comparison to -1.75, -1.8, and -2.1 V with the anodic OER (FIG.
6B and FIG. 6C). Preliminary experiments with the electrooxidation
of CH.sub.4 on a Pt black, Cu, Pd, IrO.sub.2, and Pt--Ru black
coated GDL anode coupled to the electroreduction of CO.sub.2 on a
Ag coated GDL cathode did not result in a change in the onset cell
potentials for CO production, in comparison to OER at the anode.
This is of course expected due to the high dissociation enthalpy of
the C--H bond in CH.sub.4 (435 kJ mol.sup.-1). For these
experiments, the anode was a 1.+-.0.1 mg cm.sup.-2 IrO.sub.2 coated
GDL electrode for 02 evolution and 1.+-.0.1 mg cm.sup.-2 Pt black
coated GDL electrode for glycerol electrooxidation. The catholyte
included 2.0 M KOH. The anolyte included 2.0 M KOH for 02
evolution, and 2.0 M KOH+2.0 M glycerol for glycerol
electrooxidation. All data collected under ambient conditions of 1
atm and 293 K.
[0060] In summary, we have shown that the prospects of CO.sub.2
electroreduction, in terms of both cradle-to-gate CO.sub.2
emissions and economics can be drastically improved by looking
beyond the conventionally used OER at the anode, which essentially
acts as an energy sink. The indicate that several different anodic
reactions are available to replace the OER, thereby yielding
superior thermodynamic processes with a lower |E.sup.0.sub.cell|.
Of the alternatives, the electrooxidation of glycerol (a cheap
industrial waste) seems particularly promising with the resulting
process (co-electrolysis of CO.sub.2 and glycerol) lowering the
electricity requirements for conventional CO.sub.2 electroreduction
approaches by up to 53%. The new process offers avenues for
integrating two different CO.sub.2 mitigation approaches i.e.,
CO.sub.2 electroreduction and biodiesel production as well.
Furthermore, with the future development of more active and
selective catalysts (particularly for glycerol electrooxidation),
co-electrolysis of CO.sub.2 and glycerol can be improved even
further, resulting in low energy pathways for the production of
carbon chemicals from waste CO.sub.2.
[0061] All of the methods disclosed and claimed herein can be made
and executed without undue experimentation in light of the present
disclosure. While this invention may be embodied in many different
forms, there are described in detail herein specific preferred
embodiments of the invention. The present disclosure is an
exemplification of the principles of the invention and is not
intended to limit the invention to the particular embodiments
illustrated. In addition, unless expressly stated to the contrary,
use of the term "a" is intended to include "at least one" or "one
or more." For example, "a device" is intended to include "at least
one device" or "one or more devices."
[0062] Any ranges given either in absolute terms or in approximate
terms are intended to encompass both, and any definitions used
herein are intended to be clarifying and not limiting.
Notwithstanding that the numerical ranges and parameters setting
forth the broad scope of the invention are approximations, the
numerical values set forth in the specific examples are reported as
precisely as possible. Any numerical value, however, inherently
contains certain errors necessarily resulting from the standard
deviation found in their respective testing measurements. Moreover,
all ranges disclosed herein are to be understood to encompass any
and all subranges (including all fractional and whole values)
subsumed therein.
[0063] The invention encompasses any and all possible combinations
of some or all of the various embodiments described herein. It
should also be understood that various changes and modifications to
the presently preferred embodiments described herein will be
apparent to those skilled in the art. Such changes and
modifications can be made without departing from the spirit and
scope of the invention and without diminishing its intended
advantages. It is therefore intended that such changes and
modifications be covered by the appended claims.
[0064] Furthermore, the advantages described above are not
necessarily the only advantages of the invention, and it is not
necessarily expected that all of the described advantages will be
achieved with every embodiment of the invention.
* * * * *