U.S. patent application number 15/695698 was filed with the patent office on 2018-09-20 for electrochemical reaction device and method of manufacturing anode for electrochemical reaction device.
This patent application is currently assigned to KABUSHIKI KAISHA TOSHIBA. The applicant listed for this patent is KABUSHIKI KAISHA TOSHIBA. Invention is credited to Ryota Kitagawa, Yuki Kudo, Satoshi Mikoshiba, Asahi MOTOSHIGE, Akihiko Ono, Yoshitsune Sugano, Jun Tamura, Takayuki Tsukagoshi, Eishi Tsutsumi, Masakazu Yamagiwa.
Application Number | 20180265995 15/695698 |
Document ID | / |
Family ID | 59791002 |
Filed Date | 2018-09-20 |
United States Patent
Application |
20180265995 |
Kind Code |
A1 |
MOTOSHIGE; Asahi ; et
al. |
September 20, 2018 |
ELECTROCHEMICAL REACTION DEVICE AND METHOD OF MANUFACTURING ANODE
FOR ELECTROCHEMICAL REACTION DEVICE
Abstract
An anode of an electrochemical reaction device includes: a stack
having a conductive substrate and an oxide layer on the conductive
substrate, the conductive substrate containing nickel or iron, and
the oxide layer containing a nickel oxide or an iron oxide; and an
oxidation catalyst layer disposed on the stack and containing an
oxidation catalyst to oxidize water. A Raman spectrum of the oxide
layer measured by a Raman spectroscopic analysis has a peak at a
Raman shift of 500 cm.sup.-1 or more and 600 cm.sup.-1 or less or
at a Raman shift of 1270 cm.sup.-1 or more and 1370 cm.sup.-1 or
less.
Inventors: |
MOTOSHIGE; Asahi; (Ota,
JP) ; Kitagawa; Ryota; (Setagaya, JP) ;
Sugano; Yoshitsune; (Kawasaki, JP) ; Ono;
Akihiko; (Kita, JP) ; Mikoshiba; Satoshi;
(Yamato, JP) ; Kudo; Yuki; (Yokohama, JP) ;
Tamura; Jun; (Chuo, JP) ; Yamagiwa; Masakazu;
(Yokohama, JP) ; Tsutsumi; Eishi; (Kawasaki,
JP) ; Tsukagoshi; Takayuki; (Kawasaki, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KABUSHIKI KAISHA TOSHIBA |
Minato-ku |
|
JP |
|
|
Assignee: |
KABUSHIKI KAISHA TOSHIBA
Minato-ku
JP
|
Family ID: |
59791002 |
Appl. No.: |
15/695698 |
Filed: |
September 5, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C25B 1/00 20130101; C25B
1/10 20130101; C25B 11/0405 20130101; C25B 1/04 20130101; C25B 9/08
20130101; Y02E 60/366 20130101; Y02E 60/36 20130101; C25B 3/04
20130101; C25B 11/0478 20130101; C25B 11/0415 20130101; C25B
11/0426 20130101 |
International
Class: |
C25B 11/04 20060101
C25B011/04; C25B 1/10 20060101 C25B001/10; C25B 9/08 20060101
C25B009/08 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 17, 2017 |
JP |
2017-053301 |
Claims
1. An electrochemical reaction device, comprising: an electrolytic
solution tank including a first room to store a first electrolytic
solution containing carbon dioxide and a second room to store a
second electrolytic solution containing water; a cathode disposed
inside the first room and configured to produce a carbon compound
by a reduction reaction of the carbon dioxide; an anode disposed
inside the second room and configured to produce oxygen by an
oxidation reaction of the water; and a power supply connected to
the cathode and the anode, wherein the anode includes: a stack
selected from the group consisting of a first stack and a second
stack, the first stack having a first conductive substrate and a
first oxide layer on the first conductive substrate, the first
conductive substrate containing nickel, the first oxide layer
containing a nickel oxide, the second stack having a second
conductive substrate and a second oxide layer on the second
conductive substrate, the second conductive substrate containing
iron, and the second oxide layer containing an iron oxide; and an
oxidation catalyst layer disposed on the stack and containing an
oxidation catalyst to oxidize the water, a Raman spectrum of the
first oxide layer measured by a Raman spectroscopic analysis has a
first peak at a Raman shift of 500 cm.sup.-1 or more and 600
cm.sup.-1 or less, or a Raman spectrum of the second oxide layer
measured by the Raman spectroscopic analysis has a second peak at a
Raman shift of 1270 cm.sup.-1 or more and 1370 cm.sup.-1 or
less.
2. The device according to claim 1, wherein the second electrolytic
solution further contains at least one selected from the group
consisting of carbon dioxide, hydrogen carbonate ions, and
carbonate ions.
3. The device according to claim 1, wherein a thickness of the
first oxide layer or the second oxide layer is 2 .mu.m or less.
4. The device according to claim 1, wherein the oxidation catalyst
contains a metal containing at least one element selected from the
group consisting of Co, Fe, Ni, Mn, Ru, and Ir, a metal oxide, a
metal hydroxide, or a metal nitride.
5. The device according to claim 1, wherein the first oxide layer
is a thermal oxidization film of the first conductive substrate,
and the second oxide layer is a thermal oxidization film of the
second conductive substrate.
6. A method of manufacturing an anode for an electrochemical
reaction device, comprising: heating a first conductive substrate
containing nickle under an atmosphere containing oxygen to form a
first oxide layer containing a nickel oxide on the first conductive
substrate, or heating a second conductive substrate containing iron
under an atmosphere containing oxygen to form a second oxide layer
containing an iron oxide on the second conductive substrate; and
forming an oxidation catalyst layer on the first oxide layer or the
second oxide layer, the oxidation catalyst layer containing an
oxidation catalyst to oxidize water.
7. A method of manufacturing an anode for an electrochemical
reaction device, comprising: depositing a precursor of a nickel
oxide on a first conductive substrate containing nickel, or
depositing a precursor of an iron oxide on a second conductive
substrate containing iron; heating the precursor of the nickel
oxide under an atmosphere containing oxygen to form a first oxide
layer containing the nickel oxide, or heating the precursor of the
iron oxide under an atmosphere containing oxygen to form a second
oxide layer containing the iron oxide; and forming an oxidation
catalyst layer on the first or second oxide layer, the oxidation
catalyst layer containing an oxidation catalyst to oxidize water.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is based upon and claims the benefit of
priority from Japanese Patent Application No. 2017-053301, filed on
Mar. 17, 2017; the entire contents of which are incorporated herein
by reference.
FIELD
[0002] Embodiments described herein generally relate to an
electrochemical reaction device and a method of manufacturing an
anode for an electrochemical reaction device.
BACKGROUND
[0003] From the viewpoints of energy problems and environmental
problems, an artificial photosynthesis technology effectively
reducing CO.sub.2 by light energy such as photosynthesis of plants
has been required. The plants use a system that is excited by the
light energy called a Z scheme in two stages. That is, the plants
obtain electrons from water (H.sub.2O) by the light energy, and
synthesize cellulose and saccharides by reducing carbon dioxide
(CO.sub.2) by using these electrons. As a device performing
artificial photosynthesis, development of an electrochemical
reaction device reducing (decomposing) CO.sub.2 by the light energy
has been in progress.
[0004] The electrochemical reaction device includes a cathode and
an anode. The cathode and the anode are immersed in an electrolytic
solution containing water, carbon dioxide, and so on, for example.
The electrochemical reaction device produces oxygen by an oxidation
reaction of water caused by the anode, and produces a carbon
compound, hydrogen, and the like by a reduction reaction of carbon
dioxide caused by the cathode. In this manner, it is possible to
produce desired chemical substances by the reduction reaction and
the oxidation reaction in the electrochemical reaction device. In
order to increase the efficiency of the above-described reduction
reaction and oxidation reaction, it is preferred to use a catalyst
material having high catalytic activity. Further, a substrate
intended for supporting the catalyst material preferably has a high
durability against the electrolytic solution.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 is a schematic view illustrating a structure example
of an electrochemical reaction device.
[0006] FIG. 2 is a view showing an example of a SEM observation
image of an anode.
[0007] FIG. 3 is a view illustrating one example of a Raman
spectrum of an oxide layer.
[0008] FIG. 4 is a view illustrating one example of the Raman
spectrum of the oxide layer.
[0009] FIG. 5 is a view illustrating the relationship between time
and a current density resulting from measurement of a constant
potential of the anode.
DETAILED DESCRIPTION
[0010] An electrochemical reaction device according to an
embodiment comprises: an electrolytic solution tank including a
first room to store a first electrolytic solution containing carbon
dioxide and a second room to store a second electrolytic solution
containing water; a cathode disposed inside the first room and
configured to produce a carbon compound by a reduction reaction of
the carbon dioxide; an anode disposed inside the second room and
configured to produce oxygen by an oxidation reaction of the water;
and a power supply connected to the cathode and the anode. The
anode includes: a stack selected from the group consisting a first
stack and a second stack, the first stack having a first conductive
substrate and a first oxide layer on the first conductive
substrate, the first conductive substrate containing nickel, the
first oxide layer containing a nickel oxide, the second stack
having a second conductive substrate and a second oxide layer on
the second conductive substrate, the second conductive substrate
containing iron, and the second oxide layer containing an iron
oxide; and an oxidation catalyst layer disposed on the stack and
containing an oxidation catalyst to oxidize the water. A Raman
spectrum of the first oxide layer measured by a Raman spectroscopic
analysis has a first peak at a Raman shift of 500 cm.sup.-1 or more
and 600 cm.sup.-1 or less, or a Raman spectrum of the second oxide
layer measured by the Raman spectroscopic analysis has a second
peak at a Raman shift of 1270 cm.sup.-1 or more and 1370 cm.sup.-1
or less.
[0011] Hereinafter, there will be explained an embodiment with
reference to the drawings. The drawings are schematic and, for
example, dimensions such as thickness and width of components may
differ from actual dimensions of the components. Besides, in the
embodiment, substantially the same components are denoted by the
same reference signs and the description thereof will be omitted in
some cases. A term of "connect" in the specification is not limited
to a case of connecting directly but may include a meaning of
connecting indirectly.
[0012] FIG. 1 is a schematic view illustrating a composition
example of an electrochemical reaction device. The electrochemical
reaction device illustrated in FIG. 1 includes an electrolytic
solution tank 10, a cathode 31, an anode 32, a power supply 33, and
an ion exchanger 4.
[0013] The electrolytic solution tank 10 includes a room 111 and a
room 112. The shape of the electrolytic solution tank 10 is not
particularly limited as long as it is a solid shape having cavities
being the rooms. The electrolytic solution tank 10 contains quartz
white plate glass, polystyrol, methacrylate, and the like, for
example. A material transmitting light therethrough may be used for
a part of the electrolytic solution tank 10, and a resin material
may be used for its rest. Examples of the resin material include a
polyetheretherketone (PEEK) resin, a polyamide (PA) resin, a
polyvinylidene fluoride (PVDF) resin, a polyacetal (POM) resin
(copolymer), a polyphenyleneether (PPE) resin, an
acrylonitrile-butadiene-styrene copolymer (ABS), a polypropylene
(PP) resin, a polyethylene (PE) resin, and so on.
[0014] The room 111 stores an electrolytic solution 21. The
electrolytic solution 21 contains substances to be reduced such as
carbon dioxide, for example. Further, the electrolytic solution 21
may contain hydrogen ions. Changing the amount of water and
electrolytic solution components contained in the electrolytic
solution 21 can change the reactivity and thereby change the
selectivity of a substance to be reduced and the ratio of a
chemical substance to be produced. The room 111 partially has a
space portion having gases to be contained in reactants and
products. Further, a flow path to be connected to the room 111, and
the like may be provided. The flow path may be used as an
electrolytic solution flow path and a product flow path.
[0015] The room 112 stores an electrolytic solution 22. The
electrolytic solution 22 contains substances to be oxidized such
as, for example, water, or an organic matter such as alcohol or
amine, and an inorganic oxide such as iron oxide. The electrolytic
solutions 21, 22 may contain redox couples as necessary. As the
redox couple, for example, Fe.sup.3+/Fe.sup.2+ and
IO.sup.3-/I.sup.- can be cited. The electrolytic solution tank 10
may include a stirrer that stirs the electrolytic solutions 21,
22.
[0016] The electrolytic solution 22 may contain the same substance
as that in the electrolytic solution 21. In this case, the
electrolytic solution 21 and the electrolytic solution 22 may be
recognized as one electrolytic solution. The room 112 partially has
a space portion having gases to be contained in reactants and
products. Further, a flow path to be connected to the room 112, and
the like may be provided.
[0017] The pH of the electrolytic solution 22 is preferred to be
higher than the pH of the electrolytic solution 21. This
facilitates migration of hydrogen ions, hydroxide ions, and the
like. A liquid junction potential due to the different in pH allows
oxidation-reduction reaction to effectively proceed.
[0018] Examples of the electrolytic solution containing carbon
dioxide applicable to the electrolytic solution 21 include aqueous
solutions containing LiHCO.sub.3, NaHCO.sub.3, KHCO.sub.3,
CsHCO.sub.3, phosphoric acid, boric acid, and so on. The
electrolytic solution containing carbon dioxide may contain
alcohols such as methanol, ethanol, and acetone. The electrolytic
solution containing water may be the same as the electrolytic
solution containing carbon dioxide. However, the absorption amount
of carbon dioxide in the electrolytic solution containing carbon
dioxide is preferred to be high. Accordingly, as the electrolytic
solution containing carbon dioxide, a solution different from the
electrolytic solution containing water may be used. The
electrolytic solution containing carbon dioxide is preferred to be
an electrolytic solution that decreases the reduction potential of
carbon dioxide, has high ion conductivity, and contains a carbon
dioxide absorbent that absorbs carbon dioxide.
[0019] As the electrolytic solution containing water applicable to
the electrolytic solution 22, for example, an aqueous solution
containing an arbitrary electrolyte can be used. This solution is
preferred to be an aqueous solution accelerating an oxidation
reaction of water. Examples of the aqueous solution containing an
electrolyte include aqueous solutions containing phosphoric acid
ions (PO.sub.4.sup.2-), boric acid ions (BO.sub.3.sup.3-), sodium
ions (Na.sup.+), potassium ions (K.sup.+), calcium ions
(Ca.sup.2+), lithium ions (Li.sup.+), cesium ions (CO+), magnesium
ions (Mg.sup.2+), chloride ions (Cl.sup.+), hydrogen carbonate ions
(HCO.sub.3.sup.+), carbonate ions (CO.sub.3.sup.-), and so on.
[0020] As the above-described electrolytic solution, for example,
an ionic liquid that is made of a salt of cations such as
imidazolium ions or pyridinium ions and anions such as
BF.sub.4.sup.- or PF.sub.6.sup.- and that is in a liquid state in a
wide temperature range, or its aqueous solution can be used. Other
examples of the electrolytic solution include amine solutions of
ethanolamine, imidazole, and pyridine, or aqueous solutions
thereof. Examples of amine include primary amine, secondary amine,
and tertiary amine. These electrolytic solutions may have high ion
conductivity, have a property of absorbing carbon dioxide, and have
characteristics of decreasing the reduction energy.
[0021] Examples of the primary amine include methylamine,
ethylamine, propylamine, butylamine, pentylamine, hexylamine, and
so on. Hydrocarbons of the amine may be substituted by alcohol,
halogen, or the like. Examples of the amine whose hydrocarbons are
substituted include methanolamine, ethanolamine, chloromethyl
amine, and so on. Further, an unsaturated bond may exist. These
hydrocarbons are the same in the secondary amine and the tertiary
amine.
[0022] Examples of the secondary amine include dimethylamine,
diethylamine, dipropylamine, dibutylamine, dipentylamine,
dihexylamine, dimethanolamine, diethanolamine, dipropanolamine, and
so on. The substituted hydrocarbons may be different. This also
applies to the tertiary amine. Examples in which the hydrocarbons
are different include methylethylamine, methylpropylamine, and so
on.
[0023] Examples of the tertiary amine include trimethylamine,
triethylamine, tripropylamine, tributylamine, trihexylamine,
trimethanolamine, triethanolamine, tripropanolamine,
tributanolamine, triexanolamine, methyl diethylamine,
methyldipropylamine, and so on.
[0024] Examples of the cation of the ionic liquid include
1-ethyl-3-methylimidazolium ions, 1-methyl-3-propylimidazolium
ions, 1-butyl-3-methylimidazole ions, 1-methyl-3-pentylimidazolium
ions, 1-hexyl-3-methylimidazolium ions, and so on.
[0025] A second place of the imidazolium ion may be substituted.
Examples of the cation having the imidazolium ion in which the
second place is substituted include 1-ethyl-2,3-dimethylimidazolium
ions, 1-2-dimethyl-3-propylimidazolium ions,
1-butyl-2,3-dimethylimidazolium ions,
1,2-dimethyl-3-pentylimidazolium ions,
1-hexyl-2,3-dimethylimidazolium ions, and so on.
[0026] Examples of the pyridinium ion include methylpyridinium,
ethylpyridinium, propylpyridinium, butylpyridinium,
pentylpyridinium, hexylpyridinium, and so on. In both of the
imidazolium ion and the pyridinium ion, an alkyl group may be
substituted, or an unsaturated bond may exist.
[0027] Examples of the anion include fluoride ions, chloride ions,
bromide ions, iodide ions, BF.sub.4.sup.-, PF.sub.6.sup.-,
CF.sub.3COO.sup.-, CF.sub.3SO.sub.3.sup.31 , NO.sub.3.sup.31 ,
SCN.sup.-, (CF.sub.3SO.sub.2).sub.3C.sup.31,
bis(trifluoromethoxysulfonyl)imide,
bis(trifluoromethoxysulfonyl)imide,
bis(perfluoroethylsulfonyl)imide, and so on. A dipolar ion in which
the cation and the anion of the ionic liquid are coupled by
hydrocarbons may be used. A buffer solution such as a potassium
phosphate solution may be supplied to the rooms 111, 112.
[0028] The cathode 31 is a cathode for the electrochemical reaction
device. The cathode 31 is disposed in the room 111 to be immersed
in the electrolytic solution 21. The cathode 31 contains a
reduction catalyst intended for producing a carbon compound and
hydrogen by the reduction reaction of carbon dioxide, for example.
Examples of the reduction catalyst include materials decreasing
activation energy for reducing the carbon dioxide. In other words,
the examples include materials that lower an overvoltage when
carbon compounds are produced by the reduction reaction of carbon
dioxide. For example, a metal material or a carbon material can be
used. As the metal material, for example, a metal such as gold,
aluminum, copper, silver, platinum, palladium, or nickel, or an
alloy containing the metal can be used. As the carbon material, for
example, graphene, carbon nanotube (CNT), fullerene, ketjen black,
or the like can be used. The reduction catalyst is not limited to
these, and, for example, a metal complex such as a Ru complex or a
Re complex, or an organic molecule having an imidazole skeleton or
a pyridine skeleton may be used as the reduction catalyst. Besides,
a plurality of materials may be mixed.
[0029] The carbon compound to be produced by the reduction reaction
differs depending on the kind of the reduction catalyst or the
like, and examples thereof include carbon monoxide (CO), formic
acid (HCOOH), methane (CH.sub.4), methanol (CH.sub.3OH), ethane
(C.sub.2H.sub.6), ethylene (C.sub.2H.sub.4), ethanol
(C.sub.2H.sub.5OH), formaldehyde (HCHO), ethylene glycol, and so
on.
[0030] The reduction catalyst can be regenerated from a
deterioration state by cleaning by means of electrical
oxidation-reduction such as Cyclic Voltammetry (CV), adding a
compound having a cleaning function, or a cleaning effect by means
of heat, light, or the like. The cathode 31 is preferred to be one
that can be used for or endure such a regeneration of the reduction
catalyst. Further, the electrochemical reaction device preferably
has such a regenerative function of the reduction catalysts.
[0031] The cathode 31 may have a structure of, for example, a
thin-film shape, a lattice shape, a granular shape, or a wire
shape. The cathode 31 does not necessarily have to be provided with
the reduction catalyst. A reduction catalyst provided separately
from the cathode 31 may be electrically connected to the cathode
31.
[0032] The anode 32 is an anode for the electrochemical reaction
device. The anode 32 is disposed in the room 112 to be immersed in
the electrolytic solution 22. The anode 32 includes a conductive
substrate 321, an oxide layer 322, and an oxidation catalyst layer
323.
[0033] The conductive substrate 321 contains nickel or iron, for
example. The conductive substrate 321 is not limited to having a
plate shape, and may have a porous shape, a thin-film shape, a
lattice shape, a granular shape, or a wire shape.
[0034] The oxide layer 322 is provided in contact with the
conductive substrate 321. The oxide layer 322 may cover the entire
surface of the conductive substrate 321. In the case of using the
conductive substrate 321 containing nickel, the oxide layer 322
contains a nickel oxide. In the case of using the conductive
substrate 321 containing iron, the oxide layer 322 contains an iron
oxide.
[0035] The oxide layer 322 may be formed by performing a heat
treatment at 300.degree. C. or more on the conductive substrate 321
in the presence of oxygen, for example. That is, the oxide layer
322 may have a thermal oxidization film of the conductive substrate
321, for example. Further, the oxide layer 322 may be formed in a
manner that by using a electrodeposition method, or the like, a
precursor of the nickel oxide is deposited on the conductive
substrate 321 containing nickel or a precursor of the iron oxide is
deposited on the conductive substrate 321 containing iron, to then
be heat treated in the presence of oxygen. A metal oxide precursor
may be formed by a vacuum deposition method, a sputtering method,
or the like, for example.
[0036] Physical properties of the oxide layer 322 can be analyzed
by a Raman spectroscopic analysis and a Scanning Electron
Microscope (SEM) observation, for example.
[0037] FIG. 2 is a SEM observation image showing a structure
example of a nickel oxide layer formed by heat treating a nickel
substrate at 900.degree. C. or more for one hour. The oxide layer
322 preferably has a thickness thicker than that of a natural oxide
film. When the oxide layer 322 has a thickness equal to or less
than that of the natural oxide film, an effect by the oxide layer
322 cannot be obtained sufficiently in some cases. Further, a sheet
resistance of the oxide layer 322 is preferred to be 1 .OMEGA./ or
less. Therefore, the oxide layer 322 preferably has a thickness
whose sheet resistance does not exceed 1 .OMEGA./. For example, the
thickness of the oxide layer 322 is preferred to be 2 .mu.m or
less. This makes it possible to suppress generation of resistance
when voltage is applied. When the oxide layer 322 having a
thickness greater than 2.mu.m is formed, the sheet resistance
increases, so that the effect of the oxide layer 322 cannot be
obtained sufficiently in some cases.
[0038] FIG. 3 is a view illustrating a Raman spectrum of an oxide
layer formed by heat treating a nickel substrate for one hour. FIG.
3 reveals that the Raman spectrum of the oxide layer formed by heat
treating the nickel substrate at 300.degree. C. or more has a peak
at a Raman shift of 500 cm.sup.-1 to 600 cm.sup.-1. A natural oxide
film of the nickle substrate does not have the above-described peak
similarly to the case of no heat treatment, so that the Raman
spectroscopic analysis makes it possible to determine whether or
not the oxide layer 322 is the natural oxide film.
[0039] FIG. 4 is a view illustrating a Raman spectrum of an oxide
layer formed by heat treating an iron substrate for one hour. FIG.
4 reveals that the Raman spectrum of the oxide layer formed by heat
treating the iron substrate at 300.degree. C. or more has a peak at
a Raman shift of 1270 cm.sup.-1 to 1370 cm.sup.-1. A natural oxide
film of the iron substrate does not have the above-described peak
similarly to the case of no heat treatment, so that the Raman
spectroscopic analysis makes it possible to determine whether or
not the oxide layer 322 is the natural oxide film.
[0040] The oxidation catalyst layer 323 is provided in contact with
the surface of the oxide layer 322. The oxidation catalyst layer
contains an oxidation catalyst intended for oxidizing water to
produce oxygen and the like. As the oxidation catalyst, a material
that lowers activation energy for oxidizing the water can be cited.
In other words, a material that lowers an overvoltage when oxygen
and hydrogen ions are produced by an oxidation reaction of the
water can be cited. At least one of constituent elements of the
oxidation catalyst of water formed on the metal oxide may be the
same as the constituent element of the metal substrate, and
examples of the constituent element includes a metal, an oxide of
metal, a hydroxide of metal, a nitride of metal, and so on. As a
metallic element, for example, Co, Fe, Ni, Mn, Ru, Ir, and so on
can be cited. The oxidation catalyst may contain two or more
elements. For example, a metal and a metal oxide may be combined. A
metal oxide and a metal hydroxide may be combined. One of the
metals and another of them may be combined.
[0041] Examples of the oxidation catalyst include a binary metal
oxide, a ternary metal oxide, a quaternary metal oxide, and so on.
Examples of the binary metal oxide include manganese oxide (Mn--O),
iridium oxide (Ir--O), nickel oxide (Ni--O), cobalt oxide (Co--O),
iron oxide (Fe--O), tin oxide (Sn--O), indium oxide (In--O),
ruthenium oxide (Ru--O), and so on. Examples of the ternary metal
oxide include Ni--Co--O, La--Co--O, Ni--La--O, Sr--Fe--O, and so
on. Examples of the quaternary metal oxide include Pb--Ru--Ir--O,
La--Sr--Co--O, and so on. The oxidation catalyst is not limited to
the above, and a metal complex such as a Ru complex or a Fe complex
can also be used.
[0042] The oxidation catalyst layer 323 is formed by, for example,
a sputtering method, a vapor deposition method, an already known
vacuum film forming method such as an Atomic Layer Deposition (ALD)
method, an electrodeposition method, an already known wet film
forming method such as electroless plating, or the like.
[0043] The power supply 33 is electrically connected to the cathode
31 and the anode 32. With use of electric energy supplied from the
power supply 33, the reduction reaction by the cathode 31 and the
oxidation reaction by the anode 32 are performed. For example, a
wire may connect the power supply 33 and the cathode 31 and connect
the power supply 33 and the anode 32. The case of connecting the
power supply 33 and the cathode 31 or the anode 32 by a wire or the
like is advantageous as a system because the constituent elements
are separated by function.
[0044] The power supply 33 converts renewable energy into electric
energy. Examples of the power supply 33 includes: a system power
supply; a power supply that converts kinetic energy such as wind
power, water power, geothermal power, or tidal power, or potential
energy into electric energy; a photoelectric conversion element
that converts light energy into electric energy; power supplies
such as a fuel cell and a storage battery that convert chemical
energy into electric energy; a device that converts vibrational
energy such as sound into electric energy; and so on. The
photoelectric conversion element has a function of separating
charges using energy of irradiating light such as sunlight.
Examples of the photoelectric conversion element include a pin
junction solar cell, a pn-junction solar cell, an amorphous silicon
solar cell, a multijunction solar cell, a single crystal silicon
solar cell, a polycrystalline silicon solar cell, a dye-sensitized
solar cell, an organic thin-film solar cell, and so on. Further,
the photoelectric conversion element may form a stack with the
cathode 31 and the anode 32 inside the electrolytic solution tank
10.
[0045] The ion exchanger 4 can selectively make anions or cations
flow. This makes it possible to change the electrolytic solutions
that are in contact with the cathode 31 and the anode 32
respectively into electrolytic solutions containing substances
different from each other, and the difference in ionic strength,
the difference in pH, or the like makes it possible to accelerate
the reduction reaction. Further, using the ion exchanger 4 makes it
possible to separate the electrolytic solution 21 and the
electrolytic solution 22. The ion exchanger 4 has a function of
making some ions contained in an electrolytic solution in which
both electrodes are immersed transmit therethrough, namely has a
function of blocking one kind or more of ions contained in the
electrolytic solution. Thereby, it is possible to make the pH
differ between the two electrolytic solutions, for example.
[0046] As the ion exchanger 4, for example, cation-exchange
membranes such as Nafion (registered trademark) and Flemion
(registered trademark), and anion-exchange membranes such as
NEOSEPTA (registered trademark) and SELEMION (registered trademark)
can be cited. Further, when it is not necessary to control ion
migration between the two electrolytic solutions, the ion exchanger
4 is not necessarily provided.
[0047] The electrochemical reaction device may include a stirrer in
order to accelerate supply of ions or a substance to the surface of
the electrode. The electrochemical reaction device may include
measurement devices such as a thermometer, a pH sensor, a
conductivity measuring device, an electrolytic solution analyzer,
and a gas analyzer, and by including these measurement devices,
parameters in the electrochemical reaction device are preferably
controlled.
[0048] The electrochemical reaction device may be a batch-type
reaction device, or may also be a flow-type reaction device. In the
case of the flow-type reaction device, a supply flow path and a
discharge flow path of an electrolytic solution are desirably
secured. As for the cathode 31 and the anode 32 included in the
electrochemical reaction device, a part of the cathode 31 only
needs to be in contact with the electrolytic solution 21, and a
part of the anode 32 only needs to be in contact with the
electrolytic solution 22.
[0049] Next, there will be explained an operation example of the
electrochemical reaction device. Here, the case of producing carbon
monoxide is explained as one example.
[0050] The case where as the electrolytic solutions 21, 22, an
electrolytic solution containing water and carbon dioxide is used
to produce carbon monoxide is explained.
[0051] Around the anode 32, as expressed by the following formula
(1), the water undergoes an oxidation reaction and loses electrons,
and oxygen and hydrogen ions are produced. At least one of the
produced hydrogen ions migrates to the room through the ion
exchanger 4.
2H.sub.2O.fwdarw.4H.sup.++O.sub.2+4e.sup.- (1)
[0052] Around the cathode 31, as expressed by the following formula
(2), the carbon dioxide undergoes a reduction reaction, and the
hydrogen ions react with the carbon dioxide while receiving the
electrons, and carbon monoxide is produced. Further, in addition to
the carbon monoxide, hydrogen may be produced by the hydrogen ions
receiving the electrons. At this time, the hydrogen may be produced
simultaneously with the carbon monoxide.
2CO.sub.2+4H++4e .sup.-.fwdarw.2CO+H.sub.2O (2)
[0053] The power supply 33 needs to have an open-circuit voltage
equal to or more than a potential difference between a standard
oxidation-reduction potential of the oxidation reaction and a
standard oxidation-reduction potential of the reduction reaction.
For example, the standard oxidation-reduction potential of the
oxidation reaction in the formula (1) is 1.23 [V/vs. NHE]. The
standard oxidation-reduction potential of the reduction reaction in
the formula (2) is -0.1 [V/vs. NHE]. In this case, the open-circuit
voltage needs to be 1.33 [V] or more in the reactions of the
formula (1) and the formula (2).
[0054] The open-circuit voltage of the power supply 33 is preferred
to be higher than the potential difference between the standard
oxidation-reduction potential of the oxidation reaction and the
standard oxidation-reduction potential of the reduction reaction by
a value of overvoltages or more. For example, each overvoltage of
the oxidation reaction in the formula (1) and the reduction
reaction in the formula (2) is 0.2 [V]. The open-circuit voltage is
preferred to be 1.73 [V] or more in the reactions of the formula
(1) and the formula (2).
[0055] The electrochemical reaction device in the embodiment
includes the oxide layer on the surface of the conductive substrate
of the anode, and the oxidation catalyst layer on the surface of
the oxide layer. When as the first electrolytic solution and the
second electrolytic solution, an electrolytic solution containing
at least one of carbon dioxide, hydrogen carbonate ions, and
carbonate ions, for example, is used without the oxide layer being
provided, the conductive substrate is easily dissolved in the
above-described electrolytic solution. Therefore, the conductive
substrate being dissolved facilitates peeling of the oxidation
catalyst layer. This causes a decrease in durability of the anode.
In contrast to this, providing the oxide layer on the surface of
the conductive substrate makes it possible to suppress dissolution
of the conductive substrate in the above-described electrolytic
solution, so that it is possible to suppress peeling of the
oxidation catalyst layer and improve the durability of the
anode.
[0056] The above-described anode is not limited to an anode for the
above-described electrochemical reaction device, and can be used as
an electrode for an electrochemical reaction device such as an
existing battery or electrolysis cell. As the electrolysis cell,
for example, a photoelectrochemical reaction cell, a water
electrolysis cell, and so on can be cited. Similarly to an alkaline
water electrolysis cell, the electrolysis cell may have an anode
and a cathode, and include a structure in which the anode and the
cathode are immersed in an electrolytic tank and are separated by a
diaphragm. Similarly to a solid polymer electrolyte cell, the
electrolysis cell may have a membrane electrode assembly (MEA)
structure that is a stack of an anode, a solid polymer membrane,
and a cathode. These cells are driven by a system power source, or
by an external power source of renewable energy such as sunlight,
wind power, or geothermal power, for example.
EXAMPLE
[0057] In this example, a comparison was made between a sample of
an anode fabricated by performing a heat treatment before forming
an oxidation catalyst layer (Example 1) and a sample of an anode
fabricated without performing the above-described heat treatment
(Comparative example 1) in terms of durability.
[0058] There will be explained a method of manufacturing the sample
of the anode in Example 1. A 1 cm.sup.2 nickel porous body
substrate was introduced into a firing furnace to be burned at
400.degree. for one hour, to then form a nickel oxide layer. A
Raman spectrum of the oxide layer measured by a Raman spectroscopic
analysis had a peak at a Raman shift of 500 to 600 cm.sup.-1.
[0059] A 2 mm upper portion of a nickel plate having a 2 mm width
and a 7 cm length was bonded to a lower portion of the sample of
the above-described porous body substrate by a metal pressing
machine and a Kapton tape was applied to a portion of the nickel
plate, which was not bonded to the sample, and thereby only the
sample portion was exposed.
[0060] The above-described sample was immersed in an aqueous
solution containing nickel nitrate hexahydrate
(Ni(NO.sub.3).sub.2.6H.sub.2O) (0.1M), and as a counter electrode,
a Pt mesh electrode was used, and -0.75 V was applied to an Ag/AgCl
(saturated KCl) reference electrode for 30 minuted, to thereby
electrodeposit nickel hydroxide on the above-described sample. By
the above-described steps, the sample of the anode in Example 1 was
fabricated.
[0061] Further, of an H-type cell, the above-described sample was
installed in a first room and in a second room, a Pt mesh counter
electrode was installed. A glass filter was installed between the
first and second rooms, and for an electrolytic solution, an
aqueous solution in which potassium hydrogen carbonate (KHCO.sub.3)
was dissolved (1M) was used. To an Ag/AgCl (saturated KCl)
reference electrode, -0.9 V was applied to measure a constant
potential.
Comparative Example 1
[0062] A sample of an anode in Comparative example 1 was fabricated
by steps similar to those in Example 1 except that the
above-described heat treatment was omitted, and similarly to
Example 1, its constant potential was measured.
[0063] FIG. 5 is a view illustrating the relationship between time
and a current density resulting from measurement of the current
density of the samples of the anodes in Example 1 and Comparative
example 1. The solid line indicates Example 1 and the dotted line
indicates Comparative example 1. The current density measurement
result using the anode in Example 1 revels that Example 1 is
excellent in durability because a current value higher than that of
the current density measurement result using the anode in
Comparative example 1 is maintained.
[0064] While certain embodiments have been described, these
embodiments have been presented by way of example only, and are not
intended to limit the scope of the inventions. Indeed, the novel
embodiments described herein may be embodied in a variety of other
forms; furthermore, various omissions, substitutions and changes in
the form of the embodiments described herein may be made without
departing from the spirit of the inventions. The accompanying
claims and their equivalents are intended to cover such forms or
modifications as would fall within the scope and spirit of the
inventions.
* * * * *