U.S. patent application number 16/462367 was filed with the patent office on 2019-11-07 for electrode for electrolysis.
This patent application is currently assigned to ASAHI KASEI KABUSHIKI KAISHA. The applicant listed for this patent is ASAHI KASEI KABUSHIKI KAISHA. Invention is credited to Yoshifumi KADO, Toyomitsu MIYASAKA, Makoto NISHIZAWA.
Application Number | 20190338429 16/462367 |
Document ID | / |
Family ID | 62195992 |
Filed Date | 2019-11-07 |
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United States Patent
Application |
20190338429 |
Kind Code |
A1 |
MIYASAKA; Toyomitsu ; et
al. |
November 7, 2019 |
ELECTRODE FOR ELECTROLYSIS
Abstract
An electrode for electrolysis according to the present invention
is an electrode for electrolysis including a conductive substrate;
and a catalyst layer formed on a surface of the conductive
substrate, wherein the catalyst layer comprises ruthenium element,
iridium element, titanium element, and at least one first
transition metal element selected from the group consisting of Sc,
V, Cr, Fe, Co, Ni, Cu, and Zn, a content ratio of the first
transition metal element contained in the catalyst layer based on 1
mol of the titanium element is 0.25 mol % or more and less than 3.4
mol %, and a D value being an indicator of an electric double layer
capacitance of the electrode for electrolysis is 120 C/m.sup.2 or
more and 420 C/m.sup.2 or less.
Inventors: |
MIYASAKA; Toyomitsu; (Tokyo,
JP) ; NISHIZAWA; Makoto; (Tokyo, JP) ; KADO;
Yoshifumi; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ASAHI KASEI KABUSHIKI KAISHA |
Tokyo |
|
JP |
|
|
Assignee: |
ASAHI KASEI KABUSHIKI
KAISHA
Tokyo
JP
|
Family ID: |
62195992 |
Appl. No.: |
16/462367 |
Filed: |
November 17, 2017 |
PCT Filed: |
November 17, 2017 |
PCT NO: |
PCT/JP2017/041559 |
371 Date: |
May 20, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C25B 9/00 20130101; C25B
11/0415 20130101; C25B 11/0494 20130101; C25B 1/46 20130101; C25B
9/10 20130101; C25B 11/0484 20130101 |
International
Class: |
C25B 11/04 20060101
C25B011/04; C25B 9/10 20060101 C25B009/10 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 22, 2016 |
JP |
2016-227066 |
Claims
1. An electrode for electrolysis comprising: a conductive
substrate; and a catalyst layer formed on a surface of the
conductive substrate, wherein the catalyst layer comprises
ruthenium element, iridium element, titanium element, and at least
one first transition metal element selected from the group
consisting of Sc, V, Cr, Fe, Co, Ni, Cu, and Zn, a content ratio of
the first transition metal element contained in the catalyst layer
based on 1 mol of the titanium element is 0.25 mol % or more and
less than 3.4 mol %, and a D value being an indicator of an
electric double layer capacitance of the electrode for electrolysis
is 120 C/m.sup.2 or more and 420 C/m.sup.2 or less.
2. The electrode for electrolysis according to claim 1, wherein the
first transition metal element forms a solid solution with a solid
solution of a ruthenium oxide, an iridium oxide, and a titanium
oxide.
3. The electrode for electrolysis according to claim 1, wherein the
first transition metal element comprises at least one metal element
selected from the group consisting of vanadium, cobalt, copper, and
zinc.
4. The electrode for electrolysis according to claim 1, wherein the
first transition metal element comprises vanadium element.
5. The electrode for electrolysis according to claim 1, wherein a
content ratio of the first transition metal element based on all
metal elements contained in the catalyst layer is 10 mol % or more
and 30 mol % or less.
6. The electrode for electrolysis according to claim 1, wherein a
content ratio of the first transition metal element contained in
the catalyst layer based on 1 mol of the ruthenium element is 0.3
mol or more and less than 2 mol.
7. The electrode for electrolysis according to claim 1, wherein the
D value is 120 C/m.sup.2 or more and 380 C/m.sup.2 or less.
8. A method for producing the electrode for electrolysis according
to claim 1, comprising: preparing a coating liquid comprising a
ruthenium compound, an iridium compound, a titanium compound and a
compound comprising the first transition metal element; coating at
least one surface of the conductive substrate with the coating
liquid to form a coating film; and calcining the coating film under
an oxygen-containing atmosphere to form the catalyst layer.
9. An electrolyzer comprising the electrode for electrolysis
according to claim 1.
Description
TECHNICAL FIELD
[0001] The present invention relates to an electrode for
electrolysis and a method for producing the same, and an
electrolyzer comprising the electrode for electrolysis.
BACKGROUND ART
[0002] Sodium chloride electrolysis by ion exchange membrane
process is a method for electrolyzing brine using electrode for
electrolysis to thereby produce caustic soda, chlorine, and
hydrogen. For the process of sodium chloride electrolysis by ion
exchange membrane process, a technique that can maintain low
electrolysis voltage over a long period of time is required for
power consumption reduction.
[0003] When the breakdown of electrolysis voltage is analyzed in
detail, it becomes clear that in addition to theoretically
necessary electrolysis voltage, voltage resulting from the
resistance of the ion exchange membrane and the structural
resistance of the electrolyzer, the overvoltage of the anode and
the cathode, which are electrodes for electrolysis, voltage
resulting from the distance between the anode and the cathode, and
the like are included. In addition, when electrolysis is continued
over a long period of time, voltage increase and the like induced
by various causes such as impurities in brine may occur.
[0004] Among the various electrolysis voltages described above,
studies have been conducted for the purpose of reducing the
overvoltage of the chlorine generating anode. For example, Patent
Literature 1 discloses the technique of an insoluble anode obtained
by coating a titanium substrate with an oxide of a platinum group
metal such as ruthenium. This anode is referred to as DSA
(registered trademark, Dimension Stable Anode). In addition, Non
Patent Literature 1 describes the historical developments in soda
electrolysis techniques using DSA.
[0005] Regarding the above-described DSA, also until now, various
improvements have been made and studies for performance improvement
have been conducted.
[0006] For example, Patent Literature 2 reports a chlorine
generating electrode obtained by alloying platinum and palladium,
paying attention to the low chlorine overvoltage and high oxygen
overvoltage of palladium in the platinum group. Patent Literature 3
and Patent Literature 4 propose an electrode obtained by subjecting
the surface of a platinum-palladium alloy to oxidation treatment to
form palladium oxide on the surface. In addition, Patent Literature
5 proposes an electrode coated with an external catalyst layer
containing an tin oxide as the main component and containing oxides
of ruthenium, iridium, palladium, and niobium. With this electrode,
an attempt is made to suppress an oxygen generation reaction in the
anode occurring simultaneously with chlorine generation, in order
to obtain high purity chlorine having a low oxygen
concentration.
CITATION LIST
Patent Literature
[0007] Patent Literature 1: Japanese Patent Publication No.
46-021884 [0008] Patent Literature 2: Japanese Patent Publication
No. 45-11014 [0009] Patent Literature 3: Japanese Patent
Publication No. 45-11015 [0010] Patent Literature 4: Japanese
Patent Publication No. 48-3954 [0011] Patent Literature 5: National
Publication of International Patent Application No. 2012-508326
Non Patent Literature
[0011] [0012] Non Patent Literature 1: Hiroaki Aikawa, "National
Museum of Nature and Science, Survey Reports on the Systemization
of Technologies No. 8", published by Independent Administrative
Institution National Museum of Nature and Science, Mar. 30, 2007, p
32
SUMMARY OF INVENTION
Technical Problem
[0013] However, a problem of the conventional anodes such as DSA
described in Patent Literature 1 is that the overvoltage
immediately after the start of electrolysis becomes high, and a
certain period is required before stabilization at low overvoltage
due to the activation of the catalyst, and therefore power
consumption loss occurs during electrolysis.
[0014] In addition, the chlorine generating electrodes described in
Patent Literatures 2 to 4 may have high overvoltage and low
durability. Further, in the production of the electrodes described
in Patent Literatures 3 and 4, it is necessary to use an alloy for
the substrate itself, and in addition, a complicated step is
required, such as forming an oxide on the substrate by thermal
decomposition followed by alloying by reduction and further the
formation of palladium oxide by electrolytic oxidation; great
improvement is thus needed both practically and in terms of the
production method.
[0015] The electrode described in Patent Literature 5 has a certain
effect on improvement in the electrolysis duration (electrode life)
of palladium (Note: palladium is considered to be poor in chemical
resistance), but cannot be said to sufficiently lower the chlorine
generating overvoltage.
[0016] As described above, the techniques described in Patent
Literatures 1 to 5 and Non Patent Literature 1 cannot provide an
electrode for electrolysis that has sufficiently low overvoltage at
the initial stage of electrolysis and allows electrolysis to be
carried out at low voltage and low power consumption over a long
period of time.
[0017] The present invention has been made in order to solve the
above-described problems. Therefore, an object of the present
invention is to provide an electrode for electrolysis that can
reduce overvoltage at the initial stage of electrolysis and allows
electrolysis to be carried out at low voltage and low power
consumption over a long period of time, and a method for producing
the same, and an electrolyzer comprising the electrode for
electrolysis.
Solution to Problem
[0018] The present inventors have studied diligently in order to
solve the above problems. As a result, the present inventors have
found that by adjusting, in a particular range, a numerical value
that is an indicator of the electric double layer capacitance of an
electrode for electrolysis having a catalyst layer containing
predetermined metal elements at a predetermined ratio, the
overvoltage at the initial stage of electrolysis can be reduced,
and electrolysis can be carried out at low voltage and low power
consumption over a long period of time, thereby completing the
present invention.
[0019] Specifically, the present invention is as follows.
[1]
[0020] An electrode for electrolysis comprising:
[0021] a conductive substrate; and
[0022] a catalyst layer formed on a surface of the conductive
substrate, wherein
[0023] the catalyst layer comprises ruthenium element, iridium
element, titanium element, and at least one first transition metal
element selected from the group consisting of Sc, V, Cr, Fe, Co,
Ni, Cu, and Zn,
[0024] a content ratio of the first transition metal element
contained in the catalyst layer based on 1 mol of the titanium
element is 0.25 mol % or more and less than 3.4 mol %, and
[0025] a D value being an indicator of an electric double layer
capacitance of the electrode for electrolysis is 120 C/m.sup.2 or
more and 420 C/m.sup.2 or less.
[2]
[0026] The electrode for electrolysis according to [1], wherein the
first transition metal element forms a solid solution with a solid
solution of a ruthenium oxide, an iridium oxide, and a titanium
oxide.
[3]
[0027] The electrode for electrolysis according to [1] or [2],
wherein the first transition metal element comprises at least one
metal element selected from the group consisting of vanadium,
cobalt, copper, and zinc.
[4]
[0028] The electrode for electrolysis according to any of [1] to
[3], wherein the first transition metal element comprises vanadium
element.
[5]
[0029] The electrode for electrolysis according to any of [1] to
[4], wherein a content ratio of the first transition metal element
based on all metal elements contained in the catalyst layer is 10
mol % or more and 30 mol % or less.
[6]
[0030] The electrode for electrolysis according to any of [1] to
[5], wherein a content ratio of the first transition metal element
contained in the catalyst layer based on 1 mol of the ruthenium
element is 0.3 mol or more and less than 2 mol.
[7]
[0031] The electrode for electrolysis according to any of [1] to
[6], wherein the D value is 120 C/m.sup.2 or more and 380 C/m.sup.2
or less.
[8]
[0032] A method for producing the electrode for electrolysis
according to any of [1] to [7], comprising the steps of:
[0033] preparing a coating liquid comprising a ruthenium compound,
an iridium compound, a titanium compound and a compound comprising
the first transition metal element;
[0034] coating at least one surface of the conductive substrate
with the coating liquid to form a coating film; and
[0035] calcining the coating film under an oxygen-containing
atmosphere to form the catalyst layer.
[9]
[0036] An electrolyzer comprising the electrode for electrolysis
according to any of [1] to [7].
Advantageous Effects of Invention
[0037] The present invention provides an electrode for electrolysis
that can reduce overvoltage at the initial stage of electrolysis
and allows electrolysis to be carried out at low voltage and low
power consumption over a long period of time.
BRIEF DESCRIPTION OF DRAWINGS
[0038] FIG. 1 illustrates a cross-sectional schematic view
according to one example of an electrolyzer of the present
embodiment.
[0039] FIG. 2 illustrates a graph showing the results of plotting
and linearly approximating the measured values of V/Ti obtained by
XPS depth profile analysis and actual values of V/Ti added in
coating liquids, for four samples having different element ratios
(molar ratios) between V and Ti.
DESCRIPTION OF EMBODIMENTS
[0040] An embodiment for carrying out the present invention
(hereinafter simply referred to as "present embodiment") will be
described in detail below. The present embodiment below is an
illustration for describing the present invention and is not
intended to limit the present invention to the following contents.
Appropriate modifications can be made to the present invention
without departing from the spirit thereof.
[0041] An electrode for electrolysis of the present embodiment is
an electrode for electrolysis comprising a conductive substrate;
and a catalyst layer formed on a surface of the conductive
substrate, wherein the catalyst layer comprises ruthenium element,
iridium element, titanium element, and at least one first
transition metal element selected from the group consisting of
scandium, vanadium, chromium, iron, cobalt, nickel, copper, and
zinc (these transition metal elements are hereinafter also
collectively referred to as "first transition metal elements").
Further, the electrode for electrolysis of the present embodiment
is configured such that the content ratio of the first transition
metal element contained in the catalyst layer based on 1 mol of the
titanium element is 0.25 mol % or more and less than 3.4 mol %, and
the D value being an indicator of the electric double layer
capacitance of the electrode for electrolysis is 120 C/m.sup.2 or
more and 420 C/m.sup.2 or less.
[0042] In the present embodiment, using the first transition metal
element in addition to the ruthenium element, the iridium element,
and the titanium element in the catalyst layer provides an
electrode for electrolysis in which the peak position of the peak
attributed to Ru 3d5/2 derived from RuO.sub.2, measured by X-ray
photoelectron spectroscopy (XPS), shifts from 280.5 eV for
RuO.sub.2 to the high binding energy side. For charging correction
in XPS, correction is performed so that the binding energy of Ti
2p3/2 is 458.4 eV. The shift of the peak position of Ru 3d5/2 to
the high binding energy side indicates a state in which Ru is more
oxidized in terms of the charge, and this is considered to be due
to the addition of the first transition metal element. For example,
when vanadium is added as the first transition metal element, the
following polarization occurs.
RuO.sub.2+VO.sub.2->RuO.sub.2.sup..delta.++VO.sub.2.sup..delta.-
[0043] RuO.sub.2.sup..delta.+ is an active adsorption site for
adsorbing chlorine and promotes chlorine adsorption, and thus
chlorine generating overvoltage can be reduced.
[0044] Although limitation to the above-described mechanism of
action is not intended, the electrode for electrolysis of the
present embodiment has the above-described configuration, and
therefore when electrolysis is performed using the electrode for
electrolysis, the overvoltage at the initial stage of the
electrolysis can be reduced and the electrolysis can be performed
at low voltage and low power consumption over a long period of
time. The electrode for electrolysis of the present embodiment can
be preferably used as a chlorine generating electrode particularly
for sodium chloride electrolysis by ion exchange membrane
process.
(Conductive Substrate)
[0045] The electrode for electrolysis of the present embodiment may
be used in brine of a high concentration close to saturation in a
chlorine gas generating atmosphere. Therefore, as the material of
the conductive substrate in the present embodiment,
corrosion-resistant valve metals are preferred. Examples of the
valve metals include, but are not limited to, titanium, tantalum,
niobium, and zirconium. From the viewpoint of economy and affinity
for the catalyst layer, titanium is preferred.
[0046] The shape of the conductive substrate is not particularly
limited, and a suitable shape can be selected according to the
purpose. For example, shapes such as an expanded shape, a porous
plate shape, and a wire mesh shape are preferably used. The
thickness of the conductive substrate is preferably 0.1 to 2
mm.
[0047] The surface of the conductive substrate to be in contact
with the catalyst layer is preferably subjected to surface area
increasing treatment in order to improve adhesiveness to the
catalyst layer. Examples of the method of surface area increasing
treatment include, but are not limited to, blasting treatment using
cut wires, a steel grid, an alumina grid, or the like; and acid
treatment using sulfuric acid or hydrochloric acid. Of these
treatments, a method of forming irregularities on the surface of
the conductive substrate by blasting treatment and then further
performing acid treatment is preferred.
(Catalyst Layer)
[0048] The catalyst layer to be formed on the surface of the
conductive substrate subjected to the above-described treatment
comprises ruthenium element, iridium element, titanium element, and
a first transition metal element.
[0049] The ruthenium element, the iridium element, and the titanium
element are each preferably in the form of an oxide.
[0050] Examples of the ruthenium oxide include, but are not limited
to, RuO.sub.2.
[0051] Examples of the iridium oxide include, but are not limited
to, IrO.sub.2.
[0052] Examples of the titanium oxide include, but are not limited
to, TiO.sub.2.
[0053] In the catalyst layer in the present embodiment, the
ruthenium oxide, the iridium oxide, and the titanium oxide
preferably form a solid solution. When the ruthenium oxide, the
iridium oxide, and the titanium oxide form a solid solution, the
durability of the ruthenium oxide improves further.
[0054] A solid solution generally refers to a material in which two
or more types of substances dissolve in each other, and the whole
is a uniform solid phase. Examples of the substances forming the
solid solution include metal simple substances and metal oxides.
Particularly in the case of a solid solution of metal oxides
preferred for the present embodiment, two or more types of metal
atoms are irregularly arranged on equivalent lattice points in a
unit lattice in the oxide crystal structure. Specifically, a
substitutional solid solution is preferred in which a ruthenium
oxide, an iridium oxide, and a titanium oxide mix with each other,
and in terms of the ruthenium oxide, ruthenium atoms are replaced
by iridium atoms or titanium atoms or both of these. The dissolved
state is not particularly limited, and a partially dissolved region
may be present.
[0055] The size of the unit lattice in the crystal structure
changes slightly due to dissolution. The degree of this change can
be confirmed, for example, from the fact that in the measurement of
powder X-ray diffraction, the diffraction pattern due to the
crystal structure does not change, and the peak position due to the
size of the unit lattice changes.
[0056] In the catalyst layer in the present embodiment, for the
content ratio of the ruthenium element, the iridium element, and
the titanium element, it is preferred that the content ratio of the
iridium element is 0.06 to 3 mol and the content ratio of the
titanium element is 0.2 to 8 mol, based on 1 mol of the ruthenium
element; it is more preferred that the content ratio of the iridium
element is 0.2 to 3 mol and the content ratio of the titanium
element is 0.2 to 8 mol, based on 1 mol of the ruthenium element;
it is further preferred that the content ratio of the iridium
element is 0.3 to 2 mol and the content ratio of the titanium
element is 0.2 to 6 mol, based on 1 mol of the ruthenium element;
and it is particularly preferred that the content ratio of the
iridium element is 0.5 to 1.5 mol and the content ratio of the
titanium element is 0.2 to 3 mol, based on 1 mol of the ruthenium
element. By setting the content ratio of the three types of
elements in the above-described ranges, the long-term durability of
the electrode for electrolysis tends to improve more. Iridium,
ruthenium, and titanium may each be contained in the catalyst layer
in the form of a material other than an oxide, for example, as a
metal simple substance.
[0057] The catalyst layer in the present embodiment comprises the
first transition metal element together with the above-described
ruthenium element, iridium element, and titanium element. The
existence form of the first transition metal element is not
particularly limited, and the first transition metal element should
be contained in the catalyst layer whether, for example, it is in
the form of an oxide or is a metal simple substance or an alloy. In
the present embodiment, from the viewpoint of the durability of the
catalyst layer, the first transition metal element preferably forms
a solid solution with the solid solution of the ruthenium oxide,
the iridium oxide, and the titanium oxide. The formation of such a
solid solution can be confirmed, for example, by XRD. The above
solid solution can be formed by adjusting calcination temperature
in forming the catalyst layer, the amount of the first transition
metal element added, and the like in suitable ranges.
[0058] In the present embodiment, from the viewpoint of achieving
both the voltage and durability of the catalyst layer, the first
transition metal element preferably comprises a metal element
selected from the group consisting of vanadium, cobalt, copper, and
zinc, and the first transition metal element more preferably
comprises vanadium element.
[0059] The content ratio of the first transition metal element
based on all metal elements contained in the catalyst layer in the
present embodiment is preferably 10 mol % or more and 30 mol % or
less, more preferably more than 10 mol % and 22.5 mol % or less,
and further preferably 12 mol % or more and 20 mol % or less. When
the first transition metal element comprises vanadium, the content
ratio of vanadium based on all metal elements contained in the
catalyst layer especially preferably satisfies the above range.
[0060] The above content ratio is mainly derived from the actual
ratio of elements added in a coating liquid prepared in a preferred
method for producing an electrode for electrolysis described later,
and can be confirmed by depth profile analysis by cross-sectional
STEM-EDX or X-ray photoelectron spectroscopy (XPS) described
later.
[0061] When the content ratio of the first transition metal element
is 10 mol % or more, chlorine generating overvoltage or
electrolysis voltage tends to be able to be reduced from the
initial stage of electrolysis. When the content ratio of the first
transition metal element is 30 mol % or less, the durability of the
ruthenium oxide tends to be sufficiently ensured.
[0062] The content ratio of the first transition metal element
contained in the catalyst layer in the present embodiment based on
1 mol of the ruthenium element is preferably 0.3 mol or more and
less than 2 mol, more preferably 0.5 mol or more and less than 2
mol, and further preferably 0.5 mol or more and less than 1.8 mol.
When the first transition metal element comprises vanadium, the
content ratio of vanadium based on 1 mol of the ruthenium element
contained in the catalyst layer especially preferably satisfies the
above range.
[0063] The above content ratio is mainly derived from the actual
ratio of the elements added in the coating liquid prepared in the
preferred method for producing an electrode for electrolysis
described later, and can be confirmed by the depth profile analysis
by cross-sectional STEM-EDX or X-ray photoelectron spectroscopy
(XPS) described later.
[0064] When the content ratio of the first transition metal element
is 0.3 mol or more as the number of moles based on 1 mol of the
ruthenium element, chlorine generating overvoltage or electrolysis
voltage tends to be able to be reduced from the initial stage of
electrolysis, and the D value being an indicator of electric double
layer capacitance described later tends to be able to be
sufficiently increased. When the content ratio of the first
transition metal element is less than 2 mol, the durability of the
ruthenium oxide tends to be sufficiently ensured.
[0065] The content ratio of the first transition metal element
contained in the catalyst layer in the present embodiment based on
1 mol of the titanium element, is 0.25 mol or more and less than
3.4 mol, preferably 0.25 mol or more and less than 2.6 mol. When
the first transition metal element comprises vanadium, the content
ratio of vanadium based on 1 mol of the titanium element contained
in the catalyst layer especially preferably satisfies the above
range.
[0066] The above content ratio is mainly derived from the actual
ratio of the elements added in the coating liquid prepared in the
preferred method for producing an electrode for electrolysis
described later, and can be confirmed by the depth profile analysis
by cross-sectional STEM-EDX or X-ray photoelectron spectroscopy
(XPS) described later.
[0067] When the content ratio of the first transition metal element
is 0.25 mol or more as the number of moles based on 1 mol of the
titanium element, chlorine generating overvoltage or electrolysis
voltage tends to be able to be reduced from the initial stage of
electrolysis, and the D value being an indicator of electric double
layer capacitance described later tends to be able to be
sufficiently increased. When the content ratio of the first
transition metal element is less than 3.4 mol, the durability of
the ruthenium oxide tends to be sufficiently ensured.
[0068] The element ratio (molar ratio) between V and Ti in the
catalyst layer in the electrode for electrolysis can be confirmed,
for example, by depth profile analysis by cross-sectional STEM-EDX
or X-ray photoelectron spectroscopy (XPS). For example, a method
for obtaining the element ratio (molar ratio) between V and Ti in a
catalyst layer comprising ruthenium element, iridium element,
titanium element, and vanadium element as the first transition
metal element by XPS depth profile quantitative analysis will be
shown below. Here, a Ti substrate is used as a conductive
substrate.
[0069] The XPS measurement conditions can be as follows.
[0070] apparatus: PHI 5000 VersaProbe II manufactured by ULVAC-PHI,
INC.,
[0071] excitation source: monochromatic AlK.alpha. (15 kV.times.0.3
mA),
[0072] analysis size: about 200 .mu.m .PHI.,
[0073] photoelectron take-off angle: 45.degree.,
[0074] Pass Energy: 46.95 eV (Narrow scan)
[0075] The Ar.sup.+ sputtering conditions can be as follows.
[0076] acceleration voltage: 2 kV,
[0077] raster range: 2 mm square,
[0078] with Zalar rotation.
[0079] For the method of calculation of concentration, the
spectroscopic levels of photoelectron peaks used for the
quantification of Ru, Ir, Ti, and V are Ru 3d, Ir 4f, Ti 2p, and V
2p3/2. Ru 3p3/2 and Ti 3s overlap Ti 2p and Ir 4f respectively, and
therefore quantification can be performed by the following
procedure.
(1) The area intensities of the peaks (hereinafter peak area
intensities) of Ru 3d, Ir 4f (including Ti 3s), Ti 2p (including Ru
3p3/2), and V 2p3/2 at each sputtering time (each depth) are
obtained using analysis software "MaltiPak" associated with the
apparatus. (2) The peak area intensity of Ru 3p3/2 is calculated
based on the peak area intensity of Ru 3d. The calculation is
performed using the ratio of Corrected RSF (relative sensitivity
factor corrected by the value of pass energy) in MaltiPak. This is
subtracted from the peak area intensity of Ti 2p including Ru 3p3/2
to calculate the peak area intensity of only Ti 2p. (3) The peak
area intensity of Ti 3s is calculated based on the corrected peak
area intensity of Ti 2p using the ratio of Corrected RSF. This is
subtracted from the peak area intensity of Ir 4f including Ti 3s to
calculate the peak area intensity of only Ir 4f.
[0080] The measured value of the element ratio (molar ratio)
between V and Ti in the catalyst layer obtained by XPS depth
profile quantitative analysis is the ratio of the value obtained by
summing the peak area intensities of V 2p3/2 at depths in the depth
range of the catalyst layer in which V is detected and dividing the
sum by the Corrected RSF of V 2p3/2 to the value obtained by
summing the peak area intensities of Ti 2p at depths and dividing
the sum by the Corrected RSF of Ti 2p, based on the following
calculation formula. The depth range of the catalyst layer in which
the peak area intensities of the elements are summed is, for
example, the depth range from the outermost surface until the
signal of Ti derived from the Ti substrate begins to be detected,
when the catalyst layer is a single layer. Here, when the catalyst
layer is a multilayer, the depth range is the depth range of each
catalyst layer for the layers other than the catalyst layer formed
directly on the Ti substrate surface, and the depth range until the
signal of Ti derived from the Ti substrate begins to be detected,
for the catalyst layer formed directly on the Ti substrate
surface.
V / Ti .ident. the value obtained by summing the peak area
intensities of V 2 p 3 / 2 at depths and dividing the sum by the
Corrected RSF of V 2 p 3 / 2 the value obtained by summing the peak
area intensities of Ti 2 p after correction at depths and dividing
the sum by the Corrected RSF of Ti 2 p ##EQU00001##
[0081] FIG. 2 shows the results of the following four samples a to
d having different element ratios (molar ratios) between V and Ti,
in which the measured values of V/Ti obtained by XPS depth profile
analysis by the above-described measurement method and actual
values of V/Ti for the amounts of V and Ti added in coating liquids
are plotted.
(Sample a) an Electrode for Electrolysis Having an Actual V/Ti
Ratio Added of 0.11
[0082] An electrode for electrolysis obtained by the same method as
in Example 1 described later except that a conductive substrate is
coated using a coating liquid a formulated so that the element
ratio (molar ratio) of ruthenium, iridium, titanium, and vanadium
is 23.75:23.75:47.5:5.
(Sample b) an Electrode for Electrolysis Having an Actual V/Ti
Ratio Added of 0.22
[0083] An electrode for electrolysis obtained by the same method as
in Example 1 except that a conductive substrate is coated using a
coating liquid b formulated so that the element ratio (molar ratio)
of ruthenium, iridium, titanium, and vanadium is
22.5:22.5:45:10.
(Sample c) an Electrode for Electrolysis Having an Actual V/Ti
Ratio Added of 0.35
[0084] An electrode for electrolysis obtained by the same method as
in Example 1 described later. (Sample d) an electrode for
electrolysis having an actual V/Ti ratio added of 1.13
[0085] An electrode for electrolysis obtained by the same method as
in Example 3 described later.
[0086] As FIG. 2 showed a positive correlation between the measured
and actual V/Ti values, and the element ratio (molar ratio) between
V and Ti in a catalyst layer comprising ruthenium element, iridium
element, titanium element and vanadium element can be obtained by
referring to a calibration curve. When the components contained in
the catalyst layer are changed, the element ratio (molar ratio)
between V and Ti in the catalyst layer can be obtained by referring
to a calibration curve of measured and actual V/Ti values by the
same method.
[0087] In the electrode for electrolysis of the present embodiment,
the catalyst layer may be composed of only one layer or may be a
multilayer structure of two or more layers. When the catalyst layer
is a multilayer structure, the content ratio of the first
transition metal element contained in at least one layer therein
based on 1 mol of the titanium element should be 0.25 mol or more
and less than 3.4 mol, and other layers need not satisfy the
content ratio.
[0088] The electrode for electrolysis of the present embodiment is
characterized in that the D value being an indicator of electric
double layer capacitance is 120 C/m.sup.2 or more and 420 C/m.sup.2
or less. The D value is more preferably 120 C/m.sup.2 or more and
380 C/m.sup.2 or less, further preferably 150 C/m.sup.2 or more and
360 C/m.sup.2 or less. When the D value is 120 C/m.sup.2 or more,
chlorine generating overvoltage can be suppressed, and electrolysis
voltage can be decreased. When the D value is 420 C/m.sup.2 or
less, the durability of the ruthenium oxide can be maintained.
[0089] The D value being an indicator of electric double layer
capacitance here is a value calculated using the concept of
electric double layer capacitance, and it is considered that the
larger the surface area of the electrode (that is, the specific
surface area of the catalyst layer on the electrode) is, the larger
the value is. For example, by adjusting the content of the first
transition metal element in the above-described preferred range,
the D value can be in the above-described range. Particularly, by
increasing the content of the first transition metal element, the D
value also tends to increase. By increasing calcination temperature
in forming the catalyst layer (post-baking temperature), the D
value tends to decrease. Specifically, the D value can be
calculated using the values of electrolysis current density
(A/m.sup.2) measured with respect to certain sweep rates (V/s) by a
method described in Examples described later, that is, cyclic
voltammetry. In more detail, an inherent current density difference
(difference between current density during forward sweep and
current density during backward sweep) is obtained for each sweep
rate, and data are plotted with the vertical axis being the product
of the current density difference and 0.3 V, the sweep range, and
the horizontal axis being the sweep rate, and the slope when the
plots are linearly approximated is the D value. Here, the product
of the current density difference and 0.3 V, the sweep range, is
well proportional to the sweep rate, and therefore the D value can
be expressed by the following formula (a). By setting the D value
being an indicator of electric double layer capacitance in the
above-described range, overvoltage at the initial stage of
electrolysis can be reduced without impairing the durability of the
obtained electrode for electrolysis.
D(C/m.sup.2)=[difference in electrolysis current
density(A/m.sup.2).times.0.3(V)]/[sweep rate(V/s)] (a)
[0090] When the catalyst layer in the present embodiment contains
ruthenium element, iridium element, titanium element, and a first
transition metal element, and further the content ratio of the
first transition metal element and the titanium element is in a
particular range, the function as an catalyst for electrolysis
associated with an increase in the D value being an indicator of
electric double layer capacitance improves, and overvoltage at the
initial stage of electrolysis can be reduced.
[0091] The catalyst layer in the present embodiment may contain
only the ruthenium element, the iridium element, the titanium
element, and the first transition metal element described above, as
constituent elements, or may comprise another metal element in
addition to these. Specific examples of another metal element
include, but are not limited to, elements selected from tantalum,
niobium, tin, platinum, and the like. Examples of the existence
form of these other metal elements include being present as metal
elements contained in oxides.
[0092] When the catalyst layer in the present embodiment comprises
another metal element, its content ratio is preferably 20 mol % or
less, more preferably 10 mol % or less, as the molar ratio of
another metal element to all metal elements contained in the
catalyst layer.
[0093] The thickness of the catalyst layer in the present
embodiment is preferably 0.1 to 5 .mu.m, more preferably 0.5 to 3
.mu.m. By setting the thickness of the catalyst layer at the
above-described lower limit value or more, initial electrolysis
performance tends to be able to be sufficiently maintained. By
setting the thickness of the catalyst layer at the above-described
upper limit value or less, an electrode for electrolysis excellent
in economy tends to be obtained.
[0094] The catalyst layer may comprise only one layer, or the
number of catalyst layers may be two or more.
[0095] When the number of catalyst layers is two or more, at least
one of them should be the catalyst layer in the present embodiment.
When the number of catalyst layers is two or more, at least the
outermost layer is preferably the catalyst layer in the present
embodiment. A mode of having two or more catalyst layers in the
present embodiment with the same composition or different
compositions is also preferred.
[0096] Even when the number of catalyst layers is two or more, the
thickness of the catalyst layer in the present embodiment is
preferably 0.1 to 5 .mu.m, more preferably 0.5 to 3 .mu.m, as
described above.
(Method for Producing Electrode for Electrolysis)
[0097] Next, one example of a method for producing an electrode for
electrolysis of the present embodiment will be described in
detail.
[0098] The electrode for electrolysis of the present embodiment can
be produced, for example, by forming a catalyst layer comprising
ruthenium element, iridium element, titanium element, and a first
transition metal element on a conductive substrate subjected to the
above-described surface area increasing treatment. The formation of
the catalyst layer is preferably performed by a thermal
decomposition method.
[0099] In the production method according to the thermal
decomposition method, the catalyst layer can be formed by coating a
conductive substrate with a coating liquid comprising a mixture of
compounds (precursors) containing the above elements followed by
calcination under an oxygen-containing atmosphere for the thermal
decomposition of the components in the coating liquid. According to
this method, the electrode for electrolysis can be produced with
high productivity in a smaller number of steps than in conventional
production methods.
[0100] The thermal decomposition here means calcining metal salts
or the like being precursors under an oxygen-containing atmosphere
to decompose them into metal oxides or metals and gaseous
substances. The obtained decomposition products can be controlled
by the metal species contained in the precursors blended into the
coating liquid as starting materials, the types of metal salts, the
atmosphere in which thermal decomposition is performed, and the
like. Usually, under an oxidizing atmosphere, many metals tend to
easily form oxides. In an industrial production process of an
electrode for electrolysis, thermal decomposition is usually
performed in air. Also in the present embodiment, the range of
oxygen concentration in calcination is not particularly limited,
and performing calcination in air is sufficient. However, air may
be flowed into a calcining furnace, or oxygen may be supplied, as
needed.
[0101] As a preferred mode of the method for producing an electrode
for electrolysis of the present embodiment, the method preferably
comprises the steps of preparing a coating liquid containing a
ruthenium compound, an iridium compound, a titanium compound, and a
compound comprising a first transition metal element; coating at
least one surface of a conductive substrate with the coating liquid
to form a coating film; and calcining the coating film under an
oxygen-containing atmosphere to form a catalyst layer. The
ruthenium compound, the iridium compound, the titanium compound,
and the compound comprising the first transition metal element
correspond to precursors containing the metal elements contained in
the catalyst layer in the present embodiment. An electrode for
electrolysis having a uniform catalyst layer can be produced by the
above-described method.
[0102] For the compounds contained in the coating liquid, the
ruthenium compound, the iridium compound, and the titanium compound
may be oxides but need not necessarily be oxides. For example, they
may be metal salts or the like. Examples of these metal salts
include, but are not limited to, any one selected from the group
consisting of chloride salts, nitrates, dinitrodiammine complexes,
nitrosyl nitrates, sulfates, acetates, and metal alkoxides.
[0103] Examples of the metal salt of the ruthenium compound
include, but are not limited to, ruthenium chloride and ruthenium
nitrate.
[0104] Examples of the metal salt of the iridium compound include,
but are not limited to, iridium chloride and iridium nitrate.
[0105] Examples of the metal salt of the titanium compound include,
but are not limited to, titanium tetrachloride.
[0106] For the compounds contained in the coating liquid, the
compound containing the first transition metal element may be an
oxide but need not necessarily be an oxide. For example, the
compound is preferably one or more selected from the group
consisting of an oxoacid of vanadium and a salt thereof; a chloride
of vanadium; and a nitrate of vanadium.
[0107] Examples of the countercation in the above oxoacid salt can
include, but are not limited to, Na.sup.+, K.sup.+, and
Ca.sup.2+.
[0108] As specific examples of such compounds, specific examples of
the oxoacid or the salt thereof can include sodium metavanadate,
sodium orthovanadate, and potassium orthovanadate; specific
examples of the chloride can include vanadium chloride; and
specific examples of the nitrate can include vanadium nitrate.
[0109] The above compounds are appropriately selected and used
according to the desired metal element ratio in the catalyst
layer.
[0110] The coating liquid may further comprise another compound
other than compounds included in the above-described compounds.
Examples of another compound include, but are not limited to, metal
compounds containing metal elements such as tantalum, niobium, tin,
platinum, and rhodium; and organic compounds containing metal
elements such as tantalum, niobium, tin, platinum, and rhodium.
[0111] The coating liquid is preferably a liquid composition
obtained by dissolving or dispersing the above compound group in an
appropriate solvent. The solvent of the coating liquid used here
can be selected according to the types of the above compounds. For
example, water; and alcohols such as butanol can be used. The total
compound concentration in the coating liquid is not particularly
limited but is preferably 10 to 150 g/L from the viewpoint of
properly controlling the thickness of the catalyst layer.
[0112] The method for coating a surface on a conductive substrate
with the coating liquid is not limited to the following, and, for
example, a dipping method in which a conductive substrate is
immersed in the coating liquid, a method in which the coating
liquid is applied to a surface of a conductive substrate with a
brush, a roll method in which a conductive substrate is passed over
a sponge-like roll impregnated with the coating liquid, and an
electrostatic coating method in which spray atomization is
performed with a conductive substrate and the coating liquid
charged with opposite charges can be used. Among these coating
methods, the roll method and the electrostatic coating method are
preferred from the viewpoint of being excellent in industrial
productivity. A coating film of the coating liquid can be formed on
at least one surface of a conductive substrate by these coating
methods.
[0113] After the conductive substrate is coated with the coating
liquid, the step of drying the coating film is preferably performed
as needed. The coating film can be more firmly formed on the
surface of the conductive substrate by this drying step. The drying
conditions can be appropriately selected according to the
composition and solvent species of the coating liquid, and the
like. The drying step is preferably performed at a temperature of
10 to 90.degree. C. for 1 to 20 minutes.
[0114] After the coating film of the coating liquid is formed on
the surface of the conductive substrate, the coating is calcined
under an oxygen-containing atmosphere. The calcination temperature
can be appropriately selected according to the composition and
solvent species of the coating liquid. The calcination temperature
is preferably 300 to 650.degree. C. When the calcination
temperature is less than 300.degree. C., the decomposition of the
precursors such as the ruthenium compound is insufficient, and a
catalyst layer comprising ruthenium oxide and the like may not be
obtained. When the calcination temperature is more than 650.degree.
C., the conductive substrate may undergo oxidation, and therefore
the adhesiveness of the interface between the catalyst layer and
the substrate may decrease. This tendency should be regarded as
important particularly when a substrate made of titanium is used as
the conductive substrate.
[0115] The calcination time is preferably long. On the other hand,
from the viewpoint of the productivity of the electrode, adjustment
is preferably performed so that the calcination time is not
excessively long. Considering these, one calcination time is
preferably 5 to 60 minutes.
[0116] It is possible to repeat the steps of the coating, drying,
and calcination of the catalyst layer described above a plurality
of times as needed, to form the catalyst layer to the desired
thickness. It is also possible to form the catalyst layer, and then
further perform long time calcination as needed, to further improve
the stability of the chemically, physically, and thermally
extremely stable catalyst layer. As the conditions of the long time
calcination, 400 to 650.degree. C. for about 30 minutes to 4 hours
is preferred.
[0117] The electrode for electrolysis of the present embodiment has
low overvoltage even at the initial stage of electrolysis and
allows electrolysis at low voltage and low power consumption over a
long period of time. Therefore, the electrode for electrolysis of
the present embodiment can be used for various types of
electrolysis. Particularly, the electrode for electrolysis of the
present embodiment is preferably used as a chlorine generating
anode and more preferably used as an anode for sodium chloride
electrolysis by ion exchange membrane process.
(Electrolyzer)
[0118] An electrolyzer of the present embodiment comprises the
electrode for electrolysis of the present embodiment. In this
electrolyzer, initial voltage in electrolysis is reduced. FIG. 1
shows a cross-sectional schematic view according to one example of
the electrolyzer of the present embodiment.
[0119] An electrolyzer 200 comprises electrolyte solutions 210, a
container 220 for containing the electrolyte solutions 210, an
anode 230 and a cathode 240 immersed in the electrolyte solutions
210, an ion exchange membrane 250, and wiring 260 for connecting
the anode 230 and the cathode 240 to a power supply. In the
electrolyzer 200, the space on the anode side divided by the ion
exchange membrane 250 is referred to as an anode chamber, and the
space on the cathode side is referred to as a cathode chamber. The
electrolyzer of the present embodiment can be used for various
types of electrolysis. As a typical example thereof, a case where
the electrolyzer of the present embodiment is used for the
electrolysis of an alkali chloride aqueous solution will be
described below.
[0120] As the electrolyte solutions 210 supplied to the
electrolyzer of the present embodiment, for example, an alkali
chloride aqueous solution such as a 2.5 to 5.5 normal (N) sodium
chloride aqueous solution (brine) or potassium chloride aqueous
solution can be used in the anode chamber, and a dilute alkali
hydroxide aqueous solution (for example, sodium hydroxide aqueous
solution or potassium hydroxide aqueous solution) or water can be
used in the cathode chamber.
[0121] As the anode 230, the electrode for electrolysis of the
present embodiment is used.
[0122] As the ion exchange membrane 250, for example, a fluororesin
film having an ion exchange group can be used. Specific examples
thereof can include "Aciplex" (R) F6801 (manufactured by Asahi
Kasei Corporation). As the cathode 240, a hydrogen generating
cathode being an electrode obtained by coating a conductive
substrate with a catalyst, or the like is used. As this cathode, a
known one can be adopted. Specific examples include a cathode
obtained by coating a nickel substrate with nickel, nickel oxide,
an alloy of nickel and tin, a combination of activated carbon and
an oxide, ruthenium oxide, platinum, or the like; and a cathode
obtained by forming a coating of ruthenium oxide on a wire mesh
substrate made of nickel.
[0123] The configuration of the electrolyzer of the present
embodiment is not particularly limited and may be unipolar or
bipolar. The materials constituting the electrolyzer are not
particularly limited, but, for example, as the material of the
anode chamber, titanium and the like resistant to alkali chlorides
and chlorine are preferred; and as the material of the cathode
chamber, nickel and the like resistant to alkali hydroxides and
hydrogen are preferred.
[0124] The electrode for electrolysis of the present embodiment
(the anode 230) may be disposed at an appropriate interval from the
ion exchange membrane 250, and can be used without any problem even
if disposed in contact with the ion exchange membrane 250. The
cathode 240 may be disposed at an appropriate interval from the ion
exchange membrane 250, and even a contact type electrolyzer without
an interval from the ion exchange membrane 250 (zero-gap base
electrolyzer) can be used without any problem.
[0125] The electrolysis conditions of the electrolyzer of the
present embodiment are not particularly limited, and the
electrolyzer of the present embodiment can be operated under known
conditions. For example, electrolysis is preferably carried out
with the electrolysis temperature adjusted at 50 to 120.degree. C.
and the current density adjusted at 0.5 to 10 kA/m.sup.2.
[0126] The electrode for electrolysis of the present embodiment can
decrease electrolysis voltage in sodium chloride electrolysis
compared to conventional techniques. Therefore, according to the
electrolyzer of the present embodiment comprising the electrode for
electrolysis, power consumption required for sodium chloride
electrolysis can be decreased.
[0127] Further, the electrode for electrolysis of the present
embodiment has a chemically, physically, and thermally extremely
stable catalyst layer and therefore is excellent in long-term
durability. Thus, according to the electrolyzer of the present
embodiment comprising the electrode for electrolysis, the catalytic
activity of the electrode is maintained high over a long time, and
high purity chlorine can be stably produced.
EXAMPLES
[0128] The present embodiment will be described in more detail
below based on Examples. The present embodiment is not limited only
to these Examples.
[0129] First, the evaluation methods in the Examples and
Comparative Examples will be shown below.
(Sodium Chloride Electrolysis by Ion Exchange Membrane Process
Test)
[0130] As an electrolytic cell, an electrolytic cell including an
anode cell having an anode chamber, and a cathode cell having a
cathode chamber was provided.
[0131] Each of the electrodes for electrolysis prepared in the
Examples and the Comparative Examples was cut to a predetermined
size (95.times.110 mm=0.01045 m.sup.2) to provide a test electrode,
and the test electrode was mounted on the rib in the anode chamber
of the anode cell by welding and used as an anode.
[0132] As the cathode, one obtained by coating a wire mesh
substrate made of nickel with a catalyst of ruthenium oxide was
used. First, an expanded substrate made of metal nickel, as a
current collector, was cut to the same size as the anode and welded
on the rib in the cathode chamber of the cathode cell, then a
cushion mat obtained by knitting wires made of nickel was placed,
and the cathode was disposed thereon.
[0133] As the gasket, a rubber gasket made of EPDM (ethylene
propylene diene) was used, and an ion exchange membrane was
sandwiched between the anode cell and the cathode cell. As this ion
exchange membrane, a sodium chloride electrolysis cation exchange
membrane "Aciplex" (R) F6801 (manufactured by Asahi Kasei
Corporation) was used.
[0134] In order to measure chlorine overvoltage, a platinum wire
coated with PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether
copolymer) in which the coating of a portion of about 1 mm at a tip
was removed to expose platinum was fixed to the surface of the
anode opposite to the ion exchange membrane by tying with a string
made of polytetrafluoroethylene, and used as a reference electrode.
During the electrolysis test, the reference electrode was supposed
to give chlorine generating potential due to an atmosphere
saturated with generated chlorine gas. Therefore, the result
obtained by subtracting the potential of the reference electrode
from the potential of the anode was evaluated as the chlorine
overvoltage of the anode.
[0135] On the other hand, as electrolysis voltage, the potential
difference between the cathode and the anode was measured.
[0136] In order to measure the initial electrolysis performance of
the anode, for the overvoltage and the electrolysis voltage, values
7 days after the start of electrolysis were respectively measured.
For the electrolysis conditions, electrolysis was performed at a
current density of 6 kA/m.sup.2, a brine concentration of 205 g/L
in the anode cell, a NaOH concentration of 32 wt % in the cathode
cell, and a temperature of 90.degree. C. As the electrolytic
rectifier, "PAD36-100LA" (manufactured by KIKUSUI ELECTRONICS
CORPORATION) was used.
(Acceleration Test)
[0137] The same electrolytic cell as the above-described sodium
chloride electrolysis by ion exchange membrane process test was
used except that as the test electrode mounted in the anode cell,
one cut to a size of 58.times.48 mm=0.002748 m.sup.2 was used.
[0138] For the electrolysis conditions, electrolysis was performed
at a current density of 6 kA/m.sup.2, a brine concentration of 205
g/L in the anode cell, a NaOH concentration of 32 wt % in the
cathode cell, and a temperature of 90.degree. C. In order to
confirm the durability of the test electrode, a series of
operations, the stop of electrolysis, water washing in the
electrolytic cell (10 minutes), and the start of electrolysis, was
performed at a frequency of once every 7 days, and chlorine
overvoltage (anode overvoltage) was measured every 7 days after the
start of electrolysis. Further, the residual ratios of Ru and Ir in
the catalyst layer in the test electrode after electrolysis
(100.times.content before electrolysis/content after electrolysis;
%) were calculated using numerical values obtained by the X-ray
fluorescence measurement (XRF) of the metal components before and
after electrolysis. As the XRF measurement apparatus, Niton
XL3t-800 or XL3t-800s (trade name, manufactured by Thermo
Scientific) was used.
(D Value being Indicator of Electric Double Layer Capacitance)
[0139] A test electrode was cut to a size of 30.times.30 mm=0.0009
m.sup.2 and fixed to an electrolytic cell by a screw made of
titanium. A platinum mesh was used for the counter electrode, and
electrolysis was performed in a NaCl aqueous solution at 85 to
90.degree. C. and a brine concentration of 205 g/L at electrolysis
current densities of 1 kA/m.sup.2, 2 kA/m.sup.2, and 3 kA/m.sup.2
for 5 minutes each and at 4 kA/m.sup.2 for 30 minutes so that the
test anode evolved chlorine.
[0140] After the above-described electrolysis, using Ag/AgCl for a
reference electrode, in the applied potential range of 0 V to 0.3
V, at sweep rates of 10 mV/s, 30 mV/s, 50 mV/s, 80 mV/s, 100 mV/s,
and 150 mV/s, a cyclic voltammogram was measured, and electrolysis
current density at 0.15 V that was the center of the applied
potential range during forward sweep from 0 V to 0.3 V, and
electrolysis current density at 0.15 V that was the center of the
applied potential range during backward sweep from 0.3 V to 0 V
were measured, and the difference between the two electrolysis
current densities was obtained at each sweep rate described above.
The product of the difference in electrolysis current density
obtained at each sweep rate and 0.3 V, the sweep range, was
generally directly proportional to the sweep rate, and the slope
was calculated as the D value (C/m.sup.2) being an indicator of
electric double layer capacitance.
Example 1
[0141] As a conductive substrate, an expanded substrate made of
titanium in which the larger dimension (LW) of the opening was 6
mm, the smaller dimension (SW) of the opening was 3 mm, and the
plate thickness was 1.0 mm was used. This expanded substrate was
calcined in the air at 540.degree. C. for 4 hours to form an oxide
film on the surface, and then subjected to acid treatment in 25 wt
% sulfuric acid at 85.degree. C. for 4 hours for pretreatment for
providing fine irregularities on the surface of the conductive
substrate.
[0142] Next, while a ruthenium nitrate aqueous solution
(manufactured by Furuya Metal Co., Ltd., ruthenium concentration
100 g/L) was cooled to 5.degree. C. or less with dry ice and
stirred, titanium tetrachloride (manufactured by Wako Pure Chemical
Industries, Ltd.) was added in small amounts, and then an iridium
chloride aqueous solution (manufactured by TANAKA KIKINZOKU KOGYO
K.K., iridium concentration 100 g/L) and vanadium(III) chloride
(manufactured by KISHIDA CHEMICAL Co., Ltd.) were further added in
small amounts, so that the element ratio (molar ratio) of
ruthenium, iridium, titanium, and vanadium was 21.25:21.25:42.5:15.
Thus, a coating liquid A1 being an aqueous solution having a total
metal concentration of 100 g/L was obtained.
[0143] This coating liquid A1 was injected into the
liquid-receiving vat of a coating machine, a sponge roll made of
EPDM was rotated to suck up the coating liquid A1 for impregnation,
and a roll made of PVC was disposed so as to be in contact with the
upper portion of the sponge roll. Then, the conductive substrate
subjected to the pretreatment was passed between the sponge roll
made of EPDM and the roll made of PVC for coating. Immediately
after the coating, the conductive substrate after the above coating
was passed between two sponge rolls made of EPDM wrapped with
cloths to wipe off the excess coating liquid. Then, drying was
performed at 50.degree. C. for 10 minutes, and then calcination was
performed in the air at 400.degree. C. for 10 minutes.
[0144] The cycle comprising the above roll coating, drying, and
calcination was further repeated three times with the increased
calcination temperature of 450.degree. C., and finally calcination
at 520.degree. C. for 1 hour was further performed to form a
blackish brown catalyst layer on the conductive substrate to make
an electrode for electrolysis.
Comparative Example 1
[0145] While a ruthenium chloride aqueous solution (manufactured by
TANAKA KIKINZOKU KOGYO K.K., ruthenium concentration 100 g/L) was
cooled to 5.degree. C. or less with dry ice and stirred, titanium
tetrachloride (manufactured by Wako Pure Chemical Industries, Ltd.)
was added in small amounts, and then an iridium chloride aqueous
solution (manufactured by TANAKA KIKINZOKU KOGYO K.K., iridium
concentration 100 g/L) was further added in small amounts, so that
the element ratio (molar ratio) of ruthenium, iridium, and titanium
was 25:25:50. Thus, a coating liquid B1 being an aqueous solution
having a total metal concentration of 100 g/L was obtained. An
electrode for electrolysis was made by the same method as in
Example 1 except that this coating liquid B1 was used, and the
cycle comprising roll coating, drying, and calcination was
performed with the first calcination temperature set at 440.degree.
C. and then repeated three times with the increased calcination
temperature of 475.degree. C., and finally calcination at
520.degree. C. for 1 hour was further performed.
Example 2
[0146] An electrode for electrolysis was made by the same method as
in Example 1 except that the conductive substrate was coated using
a coating liquid A2 formulated so that the element ratio (molar
ratio) of ruthenium, iridium, titanium, and vanadium was
25.45:25.45:30:19.1.
Example 3
[0147] An electrode for electrolysis was made by the same method as
in Example 1 except that the conductive substrate was coated using
a coating liquid A3 formulated so that the element ratio (molar
ratio) of ruthenium, iridium, titanium, and vanadium was
28.75:28.75:20:22.5.
Example 4
[0148] An electrode for electrolysis was made by the same method as
in Example 1 except that the conductive substrate was coated using
a coating liquid A4 formulated so that the element ratio (molar
ratio) of ruthenium, iridium, titanium, and vanadium was
32.05:32.05:10:25.9.
Example 5
[0149] An electrode for electrolysis was made by the same method as
in Example 1 except that the conductive substrate was coated using
a coating liquid A5 formulated so that the element ratio (molar
ratio) of ruthenium, iridium, titanium, and vanadium was
17.5:17.5:35:30.
[0150] Table 1 shows the configuration (the metal composition of
the coating liquid used for the formation of the catalyst layer) of
each of the electrodes for electrolysis made in Examples 1 to 5 and
Comparative Example 1 respectively, together with the measured D
value being an indicator of electric double layer capacitance. The
unit "mol %" in the table means molar percentage (actual value of
ratio of the elements added) based on all metal elements contained
in the formed catalyst layer. A value of first transition metal
element/Ru and a value of first transition metal element/Ti were
values calculated from the actual value of ratio of the elements
added.
TABLE-US-00001 TABLE 1 Metal elements [mol %] First transition
First transition First transition metal metal D value Ru Ir Ti
metal element element/Ru element/Ti [C/m.sup.2] Example 1 21.25
21.25 42.5 15 0.71 0.35 296 Comparative 25 25 50 0 0 0 48 Example 1
Example 2 25.45 25.45 30 19.1 0.75 0.64 161 Example 3 28.75 28.75
20 22.5 0.78 1.13 222 Example 4 32.05 32.05 10 25.9 0.81 2.59 251
Example 5 17.5 17.5 35 30 1.71 0.86 353
[Sodium Chloride Electrolysis by Ion Exchange Membrane Process
Test]
[0151] The sodium chloride electrolysis by ion exchange membrane
process test was carried out using the electrodes for electrolysis
made in Examples 1 to 5 and Comparative Example 1 respectively. The
results are shown in Table 2.
TABLE-US-00002 TABLE 2 Electrolysis Anode voltage [V] overvoltage
[V] 6 kA/m.sup.2 6 kA/m.sup.2 Example 1 2.94 0.032 Comparative 2.99
0.057 Example 1 Example 2 2.94 0.034 Example 3 2.92 0.032 Example 4
2.92 0.032 Example 5 2.91 0.031
[0152] The electrolysis voltage at a current density of 6
kA/m.sup.2 was 2.94 V for Example 1 and 2, 2.92 V for Example 3 and
4, and 2.91 V for Example 5. All were extremely low values compared
with 2.99 V for Comparative Example 1.
[0153] The anode overvoltage was 0.032 V for Example 1, 0.034 V for
Example 2, 0.032 V for Example 3 and Example 4, and 0.031 V for
Example 5. All were low values compared with 0.057 V for
Comparative Example 1.
Example 6
[0154] An electrode for electrolysis was made by the same method as
in Example 1 except that the conductive substrate was coated using
a coating liquid A6 formulated so that the element ratio (molar
ratio) of ruthenium, iridium, titanium, and vanadium was
37:33.35:11.15:18.5, and the cycle comprising roll coating, drying,
and calcination was performed with the first calcination
temperature set at 310.degree. C. and then repeated three times
with the increased calcination temperature of 520.degree. C., and
further, calcination at 520.degree. C. for 1 hour was
performed.
Example 7
[0155] An electrode for electrolysis was made by the same method as
in Example 1 except that the conductive substrate was coated using
a coating liquid A7 formulated so that the element ratio (molar
ratio) of ruthenium, iridium, titanium, and vanadium was
31.25:28.1:9.4:31.25, and the cycle comprising roll coating,
drying, and calcination was performed with the first calcination
temperature set at 380.degree. C. and then repeated three times
with the increased calcination temperature of 450.degree. C., and
further, calcination at 450.degree. C. for 1 hour was
performed.
Example 8
[0156] An electrode for electrolysis was made by the same method as
in Example 1 except that a ruthenium chloride aqueous solution
(manufactured by TANAKA KIKINZOKU KOGYO K.K., ruthenium
concentration 100 g/L) rather than the ruthenium nitrate aqueous
solution was used, the conductive substrate was coated using a
coating liquid A8 formulated so that the element ratio (molar
ratio) of ruthenium, iridium, titanium, and vanadium was
19.6:20.2:47.09:13.11, and the cycle comprising roll coating,
drying, and calcination was repeated eight times with the
calcination temperatures set at 393.degree. C., and then
calcination at 485.degree. C. for 1 hour was further performed.
Example 9
[0157] An electrode for electrolysis was made by the same method as
in Example 1 except that a ruthenium chloride aqueous solution
(manufactured by TANAKA KIKINZOKU KOGYO K.K., ruthenium
concentration 100 g/L) rather than the ruthenium nitrate aqueous
solution was used, cobalt(II) chloride hexahydrate (manufactured by
Wako Pure Chemical Industries, Ltd.) rather than vanadium(III)
chloride was used, the conductive substrate was coated using a
coating liquid A9 formulated so that the element ratio (molar
ratio) of ruthenium, iridium, titanium, and cobalt was 50:3:30:17,
and the cycle comprising roll coating, drying, and calcination was
performed with the first calcination temperature set at 440.degree.
C. and then repeated three times with the increased calcination
temperature of 475.degree. C., and finally calcination at
520.degree. C. for 1 hour was further performed.
Example 10
[0158] An electrode for electrolysis was made by the same method as
in Example 1 except that copper(II) nitrate trihydrate
(manufactured by Wako Pure Chemical Industries, Ltd.) rather than
vanadium(III) chloride was used, and the conductive substrate was
coated using a coating liquid A10 formulated so that the element
ratio (molar ratio) of ruthenium, iridium, titanium, and copper was
32.05:32.05:10:25.9.
Example 11
[0159] An electrode for electrolysis was made by the same method as
in Example 1 except that zinc(II) nitrate hexahydrate (manufactured
by Wako Pure Chemical Industries, Ltd.) rather than vanadium(III)
chloride was used, and the conductive substrate was coated using a
coating liquid A11 formulated so that the element ratio (molar
ratio) of ruthenium, iridium, titanium, and zinc was
32.05:32.05:10:25.9.
Comparative Example 2
[0160] An electrode for electrolysis was made by the same method as
in Example 1 except that the conductive substrate was coated using
a coating liquid B2 formulated so that the element ratio (molar
ratio) of ruthenium, iridium, titanium, and vanadium was
20:18:60:2, a ruthenium chloride aqueous solution (manufactured by
TANAKA KIKINZOKU KOGYO K.K., ruthenium concentration 100 g/L) was
used for the formulation of the coating liquid, and the cycle
comprising roll coating, drying, and calcination was performed with
the first calcination temperature set at 450.degree. C., and then
repeated three times with the same calcination temperatures, and
further, calcination at 450.degree. C. for 1 hour was
performed.
Comparative Example 3
[0161] An electrode for electrolysis was made by the same method as
in Example 1 except that the conductive substrate was coated using
a coating liquid B3 formulated so that the element ratio (molar
ratio) of ruthenium, iridium, titanium, and vanadium was
22.7:20.5:34.1:22.7, and the cycle comprising roll coating, drying,
and calcination was performed with the first calcination
temperature set at 380.degree. C., and then repeated three times
with the same calcination temperatures, and finally calcination at
590.degree. C. for 1 hour was further performed.
Comparative Example 4
[0162] An electrode for electrolysis was made by the same method as
in Example 1 except that the conductive substrate was coated using
a coating liquid B4 formulated so that the element ratio (molar
ratio) of ruthenium, iridium, titanium, and vanadium was
28.6:25.7:42.8:2.9, and the cycle comprising roll coating, drying,
and calcination was performed with the first calcination
temperature set at 450.degree. C. and then repeated three times
with the increased calcination temperature of 520.degree. C., and
further, calcination at 520.degree. C. for 1 hour was
performed.
Comparative Example 5
[0163] An electrode for electrolysis was made by the same method as
in Example 1 except that the conductive substrate was coated using
a coating liquid B5 formulated so that the element ratio (molar
ratio) of ruthenium, iridium, titanium, and vanadium was
18.5:16.7:55.55:9.25, a ruthenium chloride aqueous solution
(manufactured by TANAKA KIKINZOKU KOGYO K.K., ruthenium
concentration 100 g/L) was used for the formulation of the coating
liquid, and the cycle comprising roll coating, drying, and
calcination was performed with the first calcination temperature
set at 310.degree. C. and then repeated three times with the
increased calcination temperature of 380.degree. C., and finally
calcination at 590.degree. C. for 1 hour was further performed.
Comparative Example 6
[0164] An electrode for electrolysis was made by the same method as
in Example 1 except that manganese nitrate (manufactured by Wako
Pure Chemical Industries, Ltd.) was used instead of the
vanadium(III) chloride in Example 1, and the conductive substrate
was coated using a coating liquid B6 formulated so that the element
ratio (molar ratio) of ruthenium, iridium, titanium, and manganese
was 21.25:21.25:42.5:15.
Comparative Example 7
[0165] An electrode for electrolysis was made by the same method as
in Example 1 except that zinc nitrate (manufactured by Wako Pure
Chemical Industries, Ltd.) was used instead of the vanadium(III)
chloride in Example 1, and the conductive substrate was coated
using a coating liquid B7 formulated so that the element ratio
(molar ratio) of ruthenium, iridium, titanium, and zinc was
21.25:21.25:42.5:15.
Comparative Example 8
[0166] An electrode for electrolysis was made by the same method as
in Example 1 except that palladium nitrate (manufactured by Wako
Pure Chemical Industries, Ltd.) was used instead of the
vanadium(III) chloride in Example 1, the conductive substrate was
coated using a coating liquid B8 formulated so that the element
ratio (molar ratio) of ruthenium, iridium, titanium, and palladium
was 16.9:15.4:50.8:16.9, and the cycle comprising roll coating,
drying, and calcination was performed with the first calcination
temperature set at 450.degree. C. and then repeated three times
with the increased calcination temperature of 520.degree. C., and
finally calcination at 590.degree. C. for 1 hour was further
performed.
Comparative Example 9
[0167] An electrode for electrolysis was made by the same method as
in Example 1 except that the conductive substrate was coated using
a coating liquid B9 formulated so that the element ratio (molar
ratio) of ruthenium, titanium, and vanadium was 40:40:20, a
ruthenium chloride aqueous solution (manufactured by TANAKA
KIKINZOKU KOGYO K.K., ruthenium concentration 100 g/L) was used for
the formulation of the coating liquid, and the cycle comprising
roll coating, drying, and calcination was performed with the first
calcination temperature set at 440.degree. C. and then repeated
three times with the increased calcination temperature of
475.degree. C., and finally calcination at 520.degree. C. for 1
hour was further performed.
[0168] Table 3 shows the configuration (the metal composition of
the coating liquid used for the formation of the catalyst layer) of
each of the electrodes for electrolysis made in Examples 6 to 11
and Comparative Examples 2 to 9 respectively, together with the
measured D value being an indicator of electric double layer
capacitance. The unit "mol %" in the table means molar percentage
(feed ratio) based on all metal elements contained in the formed
catalyst layer. A value of first transition metal element/Ru and a
value of first transition metal element/Ti were values calculated
from the feed ratio.
TABLE-US-00003 TABLE 3 Metal elements [mol %] First First First
transition transition transition metal element metal metal Another
element/ element/ D value Ru Ir Ti V element .sup.(*.sup.) Ru Ti
[C/m.sup.2] Example 6 37 33.35 11.15 18.5 -- 0.50 1.66 139 Example
7 31.25 28.1 9.4 31.25 -- 1.00 3.32 309 Example 8 19.6 20.2 47.09
13.11 -- 0.67 0.28 304 Example 9 50 3 30 -- 17 0.34 0.57 173
Example 10 32.05 32.05 10 -- 25.9 0.81 2.59 260 Example 11 32.05
32.05 10 -- 25.9 0.81 2.59 326 Comparative Example 2 20 18 60 2 --
0.10 0.03 48 Comparative Example 3 22.7 20.5 34.1 22.7 -- 1.00 0.67
103 Comparative Example 4 28.6 25.7 42.8 2.9 -- 0.10 0.07 33
Comparative Example 5 18.5 16.7 55.55 9.25 -- 0.50 0.17 54
Comparative Example 6 21.25 21.25 42.5 -- -- -- -- 197 Comparative
Example 7 21.25 21.25 42.5 -- 15 0.71 0.35 119 Comparative Example
8 16.9 15.4 50.8 -- 16.9 1.00 0.33 35 Comparative Example 9 40 --
40 20 -- 0.50 0.50 161 Co for Example 9, Cu for Example 10, Zn for
Example 11, Zn for Comparative Example 7, Pd for Comparative
Example 8
[Acceleration Test]
[0169] The acceleration test was carried out using the electrodes
for electrolysis made in Examples 1 to 11 and Comparative Examples
1 to 9 respectively. The results are shown in Table 4. For
Comparative Example 9, the durability of ruthenium was low, and
therefore the evaluation results at the point in time when the test
was stopped after 14 days are shown.
TABLE-US-00004 TABLE 4 Anode overvoltage [V] Ru residual Ir
residual 6 kA/m.sup.2 ratio [%] ratio [%] After 1 day After 21 days
After 21 days After 21 days Example 1 0.031 0.032 97 98 Example 2
0.034 0.036 91 93 Example 3 0.030 0.033 88 90 Example 4 0.031 0.032
83 84 Example 5 0.030 0.031 76 78 Example 6 0.035 0.034 86 90
Example 7 0.032 0.034 52 46 Example 8 0.031 0.039 96 95 Example 9
0.044 0.030 71 80 Example 10 0.045 0.036 90 95 Example 11 0.036
0.034 89 88 Comparative 0.071 0.055 95 96 Example 1 Comparative
0.070 0.064 95 98 Example 2 Comparative 0.042 0.044 84 87 Example 3
Comparative 0.110 0.093 95 96 Example 4 Comparative 0.050 0.060 91
94 Example 5 Comparative 0.072 0.048 93 96 Example 6 Comparative
0.063 0.043 99 100 Example 7 Comparative 0.045 0.076 92 94 Example
8 Comparative 0.030 0.038 .sup.(.asterisk-pseud.) 23
.sup.(.asterisk-pseud.) -- Example 9 Comparative Example 9: a value
at the point in time when the test was stopped after 14 days in the
test
[0170] When the acceleration test for 21 days was carried out, the
followings were found.
[0171] For the electrodes for electrolysis of Examples 1 to 11, the
anode overvoltage 1 day after the start of the test was 0.030 to
0.045 V, and the anode overvoltage after 21 days was 0.030 to 0.039
V. In contrast to these, for the electrodes for electrolysis of
Comparative Examples 1 to 8, the anode overvoltage 1 day after the
start of the test was 0.042 to 0.110 V, and the anode overvoltage
after 21 days was 0.043 to 0.093 V. In this manner, it was verified
that the Examples allowed electrolysis at low voltage and low power
consumption at the initial stage of the electrolysis and over a
long period of time, compared with the Comparative Examples.
[0172] In addition, for Examples 1 to 11, the Ru and Ir residual
ratios were both high even 21 days after the start of the test,
compared with Comparative Example 9 for which the anode overvoltage
was at the same level, and it was verified that while the anode
overvoltage was maintained low, the durability in long-term
electrolysis was also sufficient.
[0173] This application claims the priority based on Japanese
Patent Application No. 2016-227066 filed on Nov. 22, 2016, the
contents of which are incorporated herein by reference.
INDUSTRIAL APPLICABILITY
[0174] The electrode for electrolysis of the present invention
provides low chlorine generating overvoltage and allows
electrolysis at low voltage and low power consumption and therefore
can be preferably used in the field of sodium chloride
electrolysis. Particularly, the electrode for electrolysis of the
present invention is useful as an anode for sodium chloride
electrolysis by ion exchange membrane process, and can produce high
purity chlorine gas having low oxygen gas concentration at low
voltage and low power consumption over a long period of time.
REFERENCE SIGNS LIST
[0175] 200 electrolyzer for electrolysis [0176] 210 electrolyte
solution [0177] 220 container [0178] 230 anode (electrode for
electrolysis) [0179] 240 cathode [0180] 250 ion exchange membrane
[0181] 260 wiring
* * * * *