U.S. patent application number 14/367309 was filed with the patent office on 2015-03-19 for high-load durable anode for oxygen generation and manufacturing method for the same.
The applicant listed for this patent is INDUSTRIE DE NORA S.P.A.. Invention is credited to Yi Cao, Takashi Furusawa, Kazuhiro Hitao, Akihiro Kato.
Application Number | 20150075978 14/367309 |
Document ID | / |
Family ID | 47559625 |
Filed Date | 2015-03-19 |
United States Patent
Application |
20150075978 |
Kind Code |
A1 |
Cao; Yi ; et al. |
March 19, 2015 |
HIGH-LOAD DURABLE ANODE FOR OXYGEN GENERATION AND MANUFACTURING
METHOD FOR THE SAME
Abstract
The present invention aims to provide a high-load durable anode
for oxygen generation and a manufacturing method for the same used
for industrial electrolyses including manufacturing of electrolytic
metal foils such as electrolytic copper foil, aluminum liquid
contact and continuously electrogalvanized steel plate, and metal
extraction, having superior durability under high-load electrolysis
conditions. The present invention features an anode for oxygen
generation and a manufacturing method for the same comprising a
conductive metal substrate and a catalyst layer containing iridium
oxide formed on the conductive metal substrate wherein the amount
of coating of iridium per time for the catalyst layer is 2
g/m.sup.2 or more, the coating is baked in a relatively high
temperature region of 430 degrees Celsius-480 degrees Celsius to
form the catalyst layer containing amorphous iridium oxide and the
catalyst layer containing the amorphous iridium oxide is post-baked
in a further high temperature region of 520 degrees Celsius-600
degrees Celsius to crystallize almost all amount of iridium oxide
in the catalyst layer.
Inventors: |
Cao; Yi; (Kanagawa, JP)
; Kato; Akihiro; (Kanagawa, JP) ; Hitao;
Kazuhiro; (Kanagawa, JP) ; Furusawa; Takashi;
(Kanagawa, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
INDUSTRIE DE NORA S.P.A. |
Milano |
|
IT |
|
|
Family ID: |
47559625 |
Appl. No.: |
14/367309 |
Filed: |
December 14, 2012 |
PCT Filed: |
December 14, 2012 |
PCT NO: |
PCT/JP2012/083168 |
371 Date: |
June 20, 2014 |
Current U.S.
Class: |
204/290.12 ;
204/192.38; 204/290.14; 427/126.5 |
Current CPC
Class: |
Y02E 60/36 20130101;
C25B 11/0405 20130101; C25B 1/04 20130101; Y02E 60/366 20130101;
C25B 11/0478 20130101; C25B 11/0484 20130101; C25B 1/02 20130101;
C25B 11/0473 20130101 |
Class at
Publication: |
204/290.12 ;
204/290.14; 427/126.5; 204/192.38 |
International
Class: |
C25B 11/04 20060101
C25B011/04; C25B 1/02 20060101 C25B001/02 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 26, 2011 |
JP |
2011-283846 |
Claims
1. An anode for oxygen generation comprising a conductive metal
substrate and a catalyst layer containing iridium oxide formed on
the conductive metal substrate, wherein the amount of coating of
iridium per time for the catalyst layer is 2 g/m.sup.2 or more, the
coating is baked in a high temperature region of 430 degrees
Celsius-480 degrees Celsius to form the catalyst layer containing
amorphous iridium oxide and the catalyst layer containing the
amorphous iridium oxide is post-baked in a high temperature region
of 520 degrees Celsius-600 degrees Celsius to crystallize almost
all amount of iridium oxide in the catalyst layer.
2. The anode for oxygen generation as in claim 1, comprising the
conductive metal substrate and the catalyst layer containing
iridium oxide formed on the conductive metal substrate, wherein the
amount of coating of iridium per time for the catalyst layer is 2
g/m.sup.2 or more and the degree of crystallinity of iridium oxide
in the catalyst layer after the post-bake is made to be 80% or
more.
3. The anode for oxygen generation, as in claim 1, comprising the
conductive metal substrate and the catalyst layer containing
iridium oxide formed on the conductive metal substrate, wherein the
amount of coating of iridium per time for the catalyst layer is 2
g/m.sup.2 or more and the crystallite diameter of iridium oxide in
the catalyst layer is made to be 9.0 nm or less.
4. The anode for oxygen generation, as in claim 1, comprising the
conductive metal substrate and the catalyst layer containing
iridium oxide formed on the conductive metal substrate, wherein an
arc ion plating base layer containing tantalum and titanium
ingredients is formed by the arc ion plating process on the
conductive metal substrate before the formation of the catalyst
layer.
5. A manufacturing method for an anode for oxygen generation
comprising a conductive metal substrate and a catalyst layer
containing iridium oxide, comprising: forming a catalyst layer
containing amorphous iridium oxide on the conductive metal
substrate by baking in a high temperature region of 430 degrees
Celsius-480 degrees Celsius; and post-baking the catalyst layer
containing amorphous iridium oxide in a high temperature region of
520 degrees Celsius-600 degrees Celsius to crystallize almost all
amount of iridium oxide in the catalyst layer, wherein the amount
of coating of iridium per time for the catalyst layer is 2
g/m.sup.2 or more.
6. The manufacturing method for the anode for oxygen generation, as
in claim 5, wherein the amount of coating of iridium per time for
the catalyst layer is 2 g/m.sup.2 or more and the catalyst layer
containing amorphous iridium oxide is formed on the surface of the
conductive metal substrate by baking in a high temperature region
of 430 degrees Celsius-480 degrees Celsius and the catalyst layer
containing amorphous iridium oxide is post-baked in a high
temperature region of 520 degrees Celsius-600 degrees Celsius to
make the degree of crystallinity of iridium oxide in the catalyst
layer to be 80% or more.
7. The manufacturing method for the anode for oxygen generation, as
in claim 5, wherein the amount of coating of iridium per time for
the catalyst layer is 2 g/m.sup.2 or more and the catalyst layer
containing amorphous iridium oxide is formed on the surface of the
conductive metal substrate by baking in a high temperature region
of 430 degrees Celsius-480 degrees Celsius and the catalyst layer
containing amorphous iridium oxide is post-baked in a high
temperature region of 520 degrees Celsius-600 degrees Celsius to
make crystallite diameter of iridium oxide in the catalyst layer to
be 9.0 nm or less.
8. The manufacturing method for the anode for oxygen generation, as
in claim 5, comprising the conductive metal substrate and the
catalyst layer containing iridium oxide formed on the conductive
metal substrate, wherein the arc ion plating base layer containing
tantalum and titanium ingredients is formed by the arc ion plating
process on the conductive metal substrate before the formation of
the catalyst layer.
Description
TECHNICAL FIELD
[0001] The present invention relates to an anode for oxygen
generation used for various industrial electrolyses and a
manufacturing method for the same; more in detail, it relates to a
high-load durable anode for oxygen generation and a manufacturing
method for the same used for industrial electrolyses including
manufacturing of electrolytic metal foils such as electrolytic
copper foil, aluminum liquid contact, and continuously
electrogalvanized steel plate, and metal extraction, having
superior durability under high-load electrolysis conditions.
BACKGROUND ART
[0002] In industrial electrolyses including manufacturing of
electrolytic copper foil, aluminum liquid contact, continuously
electrogalvanized steel plate and metal extraction, oxygen
generation is involved at the anode. For this reason, the anode
which is coated chiefly with iridium oxide having durability to
oxygen generation, as electrode catalyst, on the titanium metal
substrate has been widely applied. Generally speaking, in this type
of industrial electrolysis involving oxygen generation at the
anode, electrolysis is usually performed at a constant electric
current in view of production efficiency, energy saving, etc.
Current density has been in a range from several A/dm.sup.2 mainly
applied in the industrial fields including metal extraction to 100
A/dm.sup.2 at maximum for manufacturing electrolytic copper
foil.
[0003] However, nowadays, it is often seen that electrolysis is
performed at a current density of 300 A/dm.sup.2-700 A/dm.sup.2 or
more for higher product quality or for providing special
performance characteristics. Such high electric current is not
supplied to all the anodes installed to the industrial electrolysis
system, but rather, it is considered that an anode is installed as
an auxiliary one at a specific point where high-load electrolysis
condition is applied to provide special performance characteristics
to the product obtained from the electrolysis.
[0004] Under the electrolysis at such a high current density, the
electrode catalyst layer is highly loaded and electric current
tends to be concentrated there, causing rapid consumption of the
electrode catalyst layer. Moreover, organic substances or impurity
elements added for stabilizing products cause various
electrochemical and chemical reactions, the concentration of
hydrogen ion increases resulting from the oxygen generation
reaction, lowering the pH value, and consumption of electrode
catalyst is expedited.
[0005] One solution to solve these problems may be to increase the
surface area of the electrode catalyst layer so as to decrease the
actual electric current load. For instance, one solution is to
apply a substrate of mesh or punched metal, instead of conventional
plate substrates, to increase the surface area physically. Use of
these substrates, however, involves undesirable extra processing
costs. Furthermore, actual current density decreased by physically
increased surface area of the substrate does not improve the
electric current concentration at the electrode catalyst layer,
resulting in little suppression effect on catalyst consumption.
[0006] In the thermolysis formation method of the electrode
catalyst layer by repeating coating and baking, if the amount of
coating iridium per time is increased, it is simply considered that
the formed catalyst layer is soft and fluffy; but by this method
only, increase in the effective surface area of the catalyst layer
of the electrode is limited and improvements in consumption of the
catalyst layer under high-load conditions and in durability could
not be observed clearly.
[0007] As an electrode for this kind of electrolysis, electrode
with a low oxygen generation potential and a long service life is
required. Conventionally, as electrode of this type, an insoluble
electrode comprising a conductive metal substrate, such as
titanium, covered with a catalyst layer containing precious metal
or precious metal oxide has been applied. For example, PTL 1
discloses an insoluble electrode prepared in such a manner that a
catalyst layer containing iridium oxide and valve metal oxide is
coated on a substrate of conductive metals, such as titanium,
heated in oxidizing atmosphere and baked at a temperature of 650
degrees Celsius-850 degrees Celsius, to crystallize valve metal
oxide partially. This electrode, however, has the following
drawbacks. Since the electrode is baked at a temperature of 650
degrees Celsius or more, the metal substrate, such as of titanium
causes interfacial corrosion, and becomes poor conductor, causing
oxygen overvoltage to increase to an unserviceable degree as
electrode. Moreover, the crystallite diameter of iridium oxide in
the catalyst layer enlarges, resulting in decreased effective
surface area of the catalyst layer, leading to a poor catalytic
activity.
[0008] PTL 2 discloses use of an anode for copper plating and
copper foil manufacturing prepared in such a manner that a catalyst
layer comprising amorphous iridium oxide and amorphous tantalum
oxide in a mixed state is provided on a substrate of conductive
metal, such as titanium. This electrode, however, features
amorphous iridium oxide, and is insufficient in electrode
durability. The reason why durability decreases when amorphous
iridium oxide is applied is that amorphous iridium oxide shows
unstable bonding between iridium and oxygen, compared with
crystalline iridium oxide.
[0009] PTL 3 discloses an electrode coated with a catalyst layer
comprising a double layer structure by a lower layer of crystalline
iridium oxide and an upper layer of amorphous iridium oxide, in
order to suppress consumption of the catalyst layer and to enhance
durability of the electrode. The electrode disclosed by PTL 3 is
insufficient in electrode durability because the upper layer of the
catalyst layer is amorphous iridium oxide. Moreover, crystalline
iridium oxide exists only in the lower layer, not uniformly
distributed over the entire catalyst layer, resulting in
insufficient electrode durability.
[0010] PTL 4 discloses an anode for zinc electrowinning in which a
catalyst layer containing amorphous iridium oxide as a prerequisite
and crystalline iridium oxide, as a mixed state is provided on a
substrate of conductive metal like titanium. PTL 5 discloses an
anode for cobalt electrowinning in which a catalyst layer
containing amorphous iridium oxide as a prerequisite and
crystalline iridium oxide, as a mixed state is provided on a
substrate of conductive metal like titanium. However, it is thought
that electrode durability of these two electrodes is not enough
because they contain a large amount of amorphous iridium oxide, as
prerequisite.
[0011] To solve these problems, the inventors of the present
invention have developed, aiming chiefly at decreasing oxygen
generation overvoltage for the case that the amount of coating of
iridium per time is 2 g/m.sup.2 or less, (1) the baking method to
form a catalyst layer in which crystalline iridium oxide and
amorphous iridium oxide coexist by low temperature baking (370
degrees Celsius-400 degrees Celsius) plus high temperature
post-bake (520 degrees Celsius-600 degrees Celsius); and (2) the
baking method to form a catalyst layer in which almost complete
crystalline iridium oxide only is contained by high temperature
baking (410 degrees Celsius-450 degrees Celsius) plus high
temperature post-bake (520 degrees Celsius-560 degrees Celsius);
and patent applications have been made for these two methods as of
the same date with the present application.
[0012] According to these two inventions, lead adhesion resistivity
can be achieved when the amount of iridium coating per time is 2
g/m.sup.2 or less, in the electrolysis condition of current density
not more than 100 A/dm.sup.2, and at the same time, improvement of
durability from increase of the effective area of catalyst layer
and reduction of oxygen generation overvoltage can be achieved.
[0013] Recently, however, in order to enhance the quality of
products or to provide special performance characteristics to
products, electrolysis at a current density of 300 A/dm.sup.2-700
A/dm.sup.2 or more has been frequently conducted. Recent trend is
that such high electric current is not supplied to all the anodes
installed to the industrial electrolysis system, but rather, an
auxiliary anode is installed at a specific point where high-load
electrolysis condition is applied to provide special performance
characteristics to products obtained from the electrolysis.
[0014] Under the electrolysis at such a high current density, the
electrode catalyst layer is highly loaded and electric current
tends to be concentrated there, causing rapid consumption of the
electrode catalyst layer. Moreover, organic substance or impurity
elements added for stabilizing product quality cause various
electrochemical and chemical reactions, the concentration of
hydrogen ion increases in concomitant with the oxygen generation
reaction, lowering the pH value, and consumption of electrode
catalyst is further expedited. From these phenomena, it became
clear that the enhancement of durability by the increase of the
effective area of catalyst layer and the reduction of oxygen
generation overvoltage may not always be achieved by the inventions
relating to the above-mentioned two patent applications by the
inventors of the present invention.
CITATION LIST
Patent Literature
[0015] PTL 1: JP2002-275697A (JP3654204B)
[0016] PTL 2: JP2004-238697A (JP3914162B)
[0017] PTL 3: JP2007-146215A
[0018] PTL 4: JP2009-293117A (JP4516617B)
[0019] PTL 5: JP2010-001556A (JP4516618B)
SUMMARY OF INVENTION
Technical Problem
[0020] In order to solve the above-mentioned problems, the present
invention aims to provide a high-load durable anode for oxygen
generation and a manufacturing method for the same, having a
superior durability under the conditions of high-load, which can
improve current distribution to the electrode catalyst layer,
suppress consumption of the electrode catalyst and improve
durability of the electrode catalyst by enlarging effective surface
area of the electrode catalyst layer under the conditions of
high-load.
Solution to Problem
[0021] As the first solution to achieve the above-mentioned
purposes, the present invention provides an anode for oxygen
generation comprising a conductive metal substrate and a catalyst
layer containing iridium oxide formed on the conductive metal
substrate, wherein the amount of coating of iridium per time for
the catalyst layer is 2 g/m.sup.2 or more, the coating is baked in
a relatively high temperature region of 430 degrees Celsius-480
degrees Celsius to form the catalyst layer containing amorphous
iridium oxide and the catalyst layer containing the amorphous
iridium oxide is post-baked in a further high temperature region of
520 degrees Celsius-600 degrees Celsius to crystallize almost all
amount of iridium oxide in the catalyst layer.
[0022] As the second solution to achieve the above-mentioned
purposes, the present invention provides an anode for oxygen
generation comprising a conductive metal substrate and a catalyst
layer containing iridium oxide formed on the conductive metal
substrate, wherein the amount of coating of iridium per time for
the catalyst layer is 2 g/m.sup.2 or more and the degree of
crystallinity of iridium oxide in the catalyst layer after the
post-baking is made to be 80% or more.
[0023] As the third solution to achieve the above-mentioned
purposes, the present invention provides an anode for oxygen
generation comprising a conductive metal substrate and a catalyst
layer containing iridium oxide formed on the conductive metal
substrate wherein the amount of coating of iridium per time for the
catalyst layer is 2 g/m.sup.2 or more and the crystallite diameter
of iridium oxide in the catalyst layer is 9.0 nm or less.
[0024] As the fourth solution to achieve the above-mentioned
purposes, the present invention provides an anode for oxygen
generation comprising a conductive metal substrate and a catalyst
layer containing iridium oxide formed on the conductive metal
substrate, wherein a base layer containing tantalum and titanium
ingredients is formed by the arc ion plating (hereafter called AIP)
process on the conductive metal substrate before the formation of
the catalyst layer.
[0025] As the fifth solution to achieve the above-mentioned
purposes, the present invention provides a manufacturing method for
an anode for oxygen generation, wherein the amount of coating of
iridium per time for a catalyst layer is 2 g/m.sup.2 or more and
the catalyst layer containing amorphous iridium oxide is formed by
baking in a relatively high temperature region of 430 degrees
Celsius-480 degrees Celsius and the catalyst layer containing
amorphous iridium oxide is post-baked in a further high temperature
region of 520 degrees Celsius-600 degrees Celsius to crystallize
almost all amount of iridium oxide in the catalyst layer.
[0026] As the sixth solution to achieve the above-mentioned
purposes, the present invention provides a manufacturing method for
an anode for oxygen generation, wherein the amount of coating of
iridium per time for a catalyst layer is 2 g/m.sup.2 or more and
the catalyst layer containing amorphous iridium oxide is formed by
baking in a relatively high temperature region of 430 degrees
Celsius-480 degrees Celsius and the catalyst layer containing
amorphous iridium oxide is post-baked in a further high temperature
region of 520 degrees Celsius-600 degrees Celsius to make the
degree of crystallinity of iridium oxide in the catalyst layer to
be 80% or more.
[0027] As the seventh solution to achieve the above-mentioned
purposes, the present invention provides a manufacturing method for
an anode for oxygen generation, wherein the amount of coating of
iridium per time for a catalyst layer is 2 g/m.sup.2 or more and
the catalyst layer containing amorphous iridium oxide is formed by
baking in a relatively high temperature region of 430 degrees
Celsius-480 degrees Celsius and the catalyst layer containing
amorphous iridium oxide is post-baked in a further high temperature
region of 520 degrees Celsius-600 degrees Celsius to make the
crystallite diameter of iridium oxide in the catalyst layer to be
9.0 nm or less.
[0028] As the eighth solution to achieve the above-mentioned
purposes, the present invention provides a manufacturing method for
an anode for oxygen generation comprising a conductive metal
substrate and a catalyst layer containing iridium oxide formed on
the conductive metal substrate, wherein an AIP base layer
containing tantalum and titanium ingredients is formed by the AIP
process on the conductive metal substrate before the formation of
the catalyst layer.
Advantageous Effects of Invention
[0029] In the formation for the electrode catalyst layer containing
iridium oxide by the present invention, the amount of coating of
iridium per time of the catalyst layer is 2 g/m.sup.2 or more,
baking is conducted, instead of the conventional repeated baking
operations at 500 degrees Celsius or more, which are the perfect
crystal deposition temperature, by two steps: baking in a
relatively high temperature region of 430 degrees Celsius-480
degrees Celsius to form a catalyst layer containing amorphous
iridium oxide and post-baking in a further high temperature region
of 520 degrees Celsius-600 degrees Celsius to suppress the
crystallite diameter of iridium oxide in the electrode catalyst
layer preferably to 9.0 nm or less and to crystallize most of the
iridium oxide preferably to 80% or more in crystallinity. Thus, the
growth of crystallite diameter of iridium oxide was able to be
suppressed and the effective surface area of the catalyst layer was
able to be increased. Thus, according to the present invention, the
growth of crystallite diameter of iridium oxide can be suppressed.
As the reasons, the following are considered. The baking is
conducted by two stages: first, coating and baking is repeated in a
relatively high temperature region of 430 degrees Celsius-480
degrees Celsius and then post-baking in a further high temperature
of 520 degrees Celsius-600 degrees. Celsius. Compared with the
baking at a high temperature from the beginning by the conventional
method, crystallite diameter under the present invention will not
enlarge beyond a certain degree. If the growth of crystallite
diameter of iridium oxide is suppressed, the smaller the
crystallite diameter is, the larger the effective surface area of
the catalyst layer will be. Then, the oxygen generation overvoltage
of the electrode can be decreased, oxygen generation is promoted,
and the reaction to form PbO.sub.2 from lead ion can be suppressed.
In this way, PbO.sub.2 attachment and covering on the electrode
were suppressed.
[0030] Further, according to the present invention, simultaneously
with increase in the effective surface area of catalyst layer,
electric current is evenly distributed, that is, the concentration
of electric current is suppressed, and consumption of the catalyst
layer by electrolysis is reduced, which leads to improvement of
electrode durability.
[0031] Furthermore, according to the present invention, improved
quality of products and provision of special performance
characteristics to products are achieved by controlling the amount
of coating of iridium to 2 g/m.sup.2 or more per time. When
electrolysis is performed at a current density of 300
A/dm.sup.2-700 A/dm.sup.2 or more, or also an auxiliary anode is
provided at a specified spot under a high load electrolysis
conditions to give special performance characteristics to products
obtained from electrolysis, load to the electrode catalyst layer
can be lessened, electric current concentration can be prevented
and consumption of electrode catalyst layer can be suppressed.
BRIEF DESCRIPTION OF DRAWINGS
[0032] FIG. 1 is a graph indicating the change of degree of
crystallinity of iridium oxide (IrO.sub.2) of the catalyst layer by
baking temperature and post-bake temperature.
[0033] FIG. 2 is a graph indicating the change of crystallite
diameter of iridium oxide (IrO.sub.2) of the catalyst layer by
baking temperature and post-bake temperature.
[0034] FIG. 3 is a graph indicating the change of the electrostatic
capacity of the electrode by baking temperature and post-bake
temperature.
[0035] FIG. 4 is a graph indicating the dependence of oxygen
overvoltage on baking conditions.
DESCRIPTION OF EMBODIMENTS
[0036] The following explains embodiments of the present invention,
in detail, in reference to the figures. In the present invention,
it is found that if the effective surface area of the electrode
catalyst layer is increased to suppress adhesive reaction of lead
oxide to the electrode surface, oxygen generation overvoltage can
be reduced and then, oxygen generation is promoted and at the same
time the adhesive reaction of lead oxide can be suppressed. In
addition, the present invention has been completed from the idea
that it is necessary that iridium oxide of the catalyst layer is
mainly crystalline in order to improve the electrode durability at
the same time, and experiments were repeated.
[0037] In the present invention, a two-step baking is performed,
first, in a relatively high temperature region of 430 degrees
Celsius-480 degrees Celsius to form a catalyst layer containing
amorphous IrO.sub.2 in the baking, then, in a further high
temperature region of 520 degrees Celsius-600 degrees Celsius to
post-bake, through which the iridium oxide of the catalyst layer is
almost completely crystallized.
[0038] Through the experiments conducted by inventors of the
present invention, it has been proved that the catalyst layer
containing amorphous iridium oxide, which can greatly increase the
effective surface area, consumes amorphous iridium oxide quite
rapidly by electrolysis and durability is reduced relatively. In
other words, it is considered that the electrode durability cannot
be improved unless iridium oxide of the catalyst layer is
crystallized. Therefore, in order to achieve the purpose of the
present invention that the effective surface area of the electrode
catalyst layer is increased and the overvoltage of the electrode is
reduced, the present invention applies two-step baking: high
temperature baking plus high temperature post-baking in order to
control the crystallite diameter of iridium oxide of the catalyst
layer, through which iridium oxide crystal, smaller in size than
the conventional product precipitates, resulting in increased
effective surface area of the electrode catalyst layer and reduced
overvoltage.
[0039] In the present invention, a catalyst layer containing
amorphous iridium oxide is formed on the surface of the conductive
metal substrate by baking in a relatively high temperature region
of 430 degrees Celsius-480 degrees Celsius; thereafter, the
catalyst layer of amorphous iridium oxide is post-baked in a
further high temperature region of 520 degrees Celsius-600 degrees
Celsius to crystallize the iridium oxide in the catalyst layer
almost completely.
[0040] According to the present invention, improved quality of
products and provision of special performance characteristics to
products are achieved by controlling the amount of coating of
iridium to 2 g/m.sup.2 or more per time. When electrolysis is
performed at a current density of 300 A/dm.sup.2-700 A/dm.sup.2 or
more, or also an auxiliary anode is provided at a specified spot
under a high load electrolysis conditions to give special
performance characteristics to products obtained from electrolysis,
load to the electrode catalyst layer can be lessened, electric
current concentration can be prevented and consumption of electrode
catalyst layer can be suppressed.
[0041] The baking temperature in a relatively high temperature
region of 430 degrees Celsius-480 degrees Celsius and the
post-baking temperature in a further high temperature region of 520
degrees Celsius-600 degrees Celsius are determined by the crystal
particle size and the degree of crystallinity of iridium oxide to
be formed in the catalyst layer, and the catalyst layer with a low
oxygen overvoltage and a high corrosion resistance is formed in the
above-mentioned temperature region.
[0042] In the present invention, the growth of the crystallite
diameter of iridium oxide was able to be suppressed and the
effective surface area of the catalyst layer was able to be
increased by controlling the crystallite diameter of the iridium
oxide in the electrode catalyst layer to a small number, preferably
equal to or less than 9.0 nm and most of the iridium oxide was
crystallized, preferably, to the degree of crystallinity equal to
or more than 80%.
[0043] Prior to forming the catalyst layer, if the AIP base layer
containing tantalum and titanium components is provided on the
conductive metal substrate, it is possible to prevent further
interfacial corrosion of the metal substrate.
[0044] The base layer consisting of TiTaO.sub.x oxide layer may be
applied instead of the AIP base layer.
[0045] The catalyst layer was formed in such a manner that
hydrochloric acid aqueous solution of IrCl.sub.3/Ta.sub.2Cl.sub.5
as a coating liquid was coated on the AIP coated titanium substrate
at 3 g-Ir/m.sup.2 per time and baked at a temperature by which part
of IrO.sub.2 crystallizes (430-480 degrees Celsius). After
repeating the coating and baking process until the necessary
support amount of the catalyst was obtained, one hour post-bake was
conducted at a further high temperature (520 degrees Celsius-600
degrees Celsius). In this way, the electrode sample was prepared.
The prepared sample was measured for IrO.sub.2 crystalline of the
catalyst layer by X-ray diffraction, oxygen generation overvoltage,
electrostatic capacity of electrode, etc. and evaluated for
sulfuric acid electrolysis and gelatin-added sulfuric acid
electrolysis and lead adherence test.
[0046] As a result, it has been found that most of the IrO.sub.2 of
the formed catalyst layer was crystalline, the crystallite diameter
became smaller, and the electrode effective surface area increased.
Accelerated life evaluation was carried out and found that, as to
be described later, sulfuric acid electrolysis life was about 1.4
times that of the conventional product, and gelatin-added sulfuric
acid electrolysis life was about 1.5 times that of the conventional
product, proving improvement in durability.
[0047] The experimental conditions and methods by the present
invention are as follows.
[0048] In order to investigate formation temperature of amorphous
iridium oxide and the range of post-bake temperature for successive
crystallization, a sample shown in Table 1 was manufactured and
subjected to measurements of X-ray diffraction, cyclic voltammetry,
oxygen overvoltage, etc.
[0049] The surface of titanium plate (JIS-I) was subjected to the
dry blast with iron grit (G120 size), followed by pickling in an
aqueous solution of concentrated hydrochloric acid for 10 minutes
at the boiling point for cleaning treatment of the metal substrate
of the electrode. The cleaned metal substrate of the electrode was
set to the AIP unit applying Ti--Ta alloy target as a vapor source
and a coating of tantalum and titanium alloy was applied as the
base layer on the surface of the metal substrate of the electrode.
Coating condition is shown in Table 1.
TABLE-US-00001 TABLE 1 Target(vapor source) Alloy disk comprising
Ta:Ti = 60 wt %:40 wt % (back surface cooling) Vacuum pressure 1.5
.times. 10.sup.-2 Pa or less Metal substrate temperature 500
degrees Celsius or less Coating pressure 3.0 .times. 10.sup.-1~4.0
.times. 10.sup.-1 Pa Vapor source charge power 20~30 V, 140~160 A
Coating time 15~20 minutes Coating thickness 2 micuron (weight
increase conversion)
[0050] The coated metal substrate was heat-treated at 530 degrees
Celsius in an electric furnace of air circulation type for 180
minutes.
[0051] Then, the coating solution prepared by dissolving iridium
tetrachloride and tantalum pentachloride in concentrated
hydrochloric acid was applied on the coated metal substrate. After
drying, the thermal decomposition coating was conducted for 15
minutes in the electric furnace of air circulation type at a
temperature shown in Table 2 to form an electrode catalyst layer
comprising mixture oxides of iridium oxide and tantalum oxide. The
amount of coating solution was determined so that the thickness of
coating per time of the coating solution corresponds to approx. 3.0
g/m.sup.2, as iridium metal. This coating-baking operation was
repeated nine times to obtain the electrode catalyst layer of
approx. 27.0 g/m.sup.2, as converted for metal iridium.
[0052] Then, the coated sample with catalyst layer was subjected to
the post bake in the electric furnace of air circulation type for
one hour at a temperature shown in Table 2 to manufacture an
electrode for electrolysis. In addition, a sample not subjected to
post-bake was manufactured for comparison purpose.
[0053] Baking temperature and post-bake temperature of each sample
are shown in Table 2.
Experimental Items for Evaluation
[0054] (1) Degree of crystallinity and measurement of crystallite
diameter
[0055] IrO.sub.2 crystallinity and crystallite diameter of the
catalyst layer were measured by X-rays diffractometry.
[0056] The degree of crystallinity was estimated from the
diffraction peak intensity.
(2) Electrostatic capacity of electrode
[0057] Method: cyclic voltammetry
[0058] Electrolyte: 150 g/L H.sub.2SO.sub.4 aq.
[0059] Electrolysis temperature: 60 degrees Celsius
[0060] Electrolysis area: 10.times.10 mm.sup.2
[0061] Counter electrode: Zr plate (20 mm.times.70 mm)
[0062] Reference electrode: Mercurous sulphate electrode (SSE)
(3) Measurement of oxygen overvoltage
[0063] Method: current interrupt method
[0064] Electrolyte: 150 g/L H.sub.2SO.sub.4 aq.
[0065] Electrolysis temperature: 60 degrees Celsius
[0066] Electrolysis area: 10.times.10 mm.sup.2
[0067] Counter electrode: Zr plate (20 mm.times.70 mm)
[0068] Reference electrode: Mercurous sulphate electrode (SSE)
TABLE-US-00002 TABLE 2 Oxygen generation Baking Post-bake Degree of
Crystallite Electrostatic overvoltage temperature temperature
crystallinity diameter capacity (V vs. SSE Sample No. (.degree. C.)
(.degree. C.) (%) (nm) (C/m.sup.2) @100 A/dm.sup.2) 1 430 none 0 0
88.8 0.851 2 520 100 7.7 21.6 0.963 3 560 100 7.8 15.4 0.987 4 600
100 7.7 11.6 1.021 5 480 none 72 9.3 13.7 0.983 6 520 85 8.5 18.1
1.011 7 560 82 8.5 14.4 1.031 8 600 98 8.7 14.5 1.035 9 500-520
none 100 9.1 7.6 1.051 (Conventional product)
[0069] The changes of IrO.sub.2 crystal characteristics by the
baking temperature and the post-bake temperature were as
follows.
[0070] As for the estimation of degree of crystallinity, the
intensity of the crystal diffraction peak (.theta.=28 degrees) of
each sample is expressed as a ratio when compared with the
intensity of the crystal diffraction peak (.theta.=28 degrees) of
the conventional product which is assumed as 100. The results are
given in Table 2. In addition, FIG. 1 is a graph showing the degree
of crystallinity based on the data in Table 2.
[0071] As is clear from Table 2 and FIG. 1, the degree of
crystallinity of iridium oxide after post-bake of Samples 2-4 and
Samples 6-8 of the example by the present invention, which had been
subjected to baking in a relatively high temperature region of 430
degrees Celsius-480 degrees Celsius plus post-bake in a further
high temperature region of 520 degrees Celsius-600 degrees Celsius
was 80% or more. On the other hand, iridium oxide attributable to
the electrode catalyst layer treated by the baking at 430 degrees
Celsius without post-bake (Sample 1) did not show a clear peak,
proving that the catalyst layer of this sample comprises amorphous
iridium oxide. The degree of crystallinity of the electrode
catalyst layer baked at 480 degrees Celsius without post-bake
(Sample 5) was 72% with a lot of remaining amorphous iridium oxide.
In addition, Sample 9, which is a conventional product was fully
crystallized, showing the degree of crystallinity being 100%, but
the crystallite diameter increases to 9.1 nm, resulting in a low
value of the electrostatic capacity of electrode at 7.6 with small
effective surface area.
[0072] In other words, as the change of the degree of crystallinity
by a high temperature post-bake, clear peak of IrO.sub.2
attributable to the electrode catalyst layer was observed after
baking at 430 degrees Celsius and post-bake in a further high
temperature, showing that amorphous IrO.sub.2 of the catalyst layer
had changed to crystalline by a high temperature post-bake. In
addition, it was found that the peak intensity was similar to that
of the conventional product at any post-bake temperatures, showing
that amorphous IrO.sub.2 did not remain. On the other hand, the
products treated by the baking at 480 degrees Celsius showed a
further high degree of crystallinity by a high temperature
post-bake. However, it was found that a small amount of amorphous
IrO.sub.2 still existed after post-bake at 520 degrees Celsius and
560 degrees Celsius. By contrast, the degree of crystallinity of
IrO.sub.2 after the post-bake at 600 degrees Celsius was almost
equivalent to the conventional product, showing full
crystallization.
[0073] Then, the crystallite diameter was calculated from X-ray
diffraction. The results are shown in Table 2. FIG. 2 was prepared
based on the data in Table 2 relating to the crystallite
diameter.
[0074] The crystal diameter of the amorphous IrO.sub.2 formed by
the baking at 430 degrees Celsius without post-bake is indicated as
"0". It was found that if post-bake is applied, amorphous IrO.sub.2
was crystallized, but the crystallite diameter of the formed
crystal became smaller than that of the conventional product. In
addition, there is little mutual dependence observed between the
post-bake temperature and the crystallite diameter of
IrO.sub.2.
[0075] On the other hand, the crystallite diameter of the baked
product in 480 degrees Celsius followed by post-bake gave a smaller
one than the conventional product, regardless of the post-bake
temperature. In other words, crystallinity of IrO.sub.2 of the
catalyst layer formed in a low temperature baking increased by
post-bake, but the increasing of IrO.sub.2 crystallite diameter was
able to be suppressed.
[0076] As is evident from the data on the crystallite diameter in
Table 2 and FIG. 2, the crystallite diameter of iridium oxide after
post-bake of Samples 2-4 and Samples 6-8 of the examples by the
present invention, which was subjected to baking in a relatively
high temperature region of 430 degrees Celsius-480 degrees Celsius
plus post-bake in a further high temperature region of 520 degrees
Celsius-600 degrees Celsius was 9.0 nm or less. On the other hand,
iridium oxide attributable to the electrode catalyst layer treated
by the baking at 430 degrees Celsius without post-bake (Sample 1)
did not show a clear peak, proving that the catalyst layer of this
sample comprises amorphous iridium oxide. The crystallite diameter
of the electrode catalyst layer baked at 480 degrees Celsius
without post-bake (Sample 5) was large to 9.3 nm. The crystallite
diameter of iridium oxide of Sample 9, which is the conventional
product, was as large as 9.1 nm.
[0077] Then, measurements were made about the change of effective
surface area of the electrode catalyst layer prepared by high
temperature baking in a relatively high temperature region of 430
degrees Celsius-480 degrees Celsius plus post-bake in a further
high temperature region of 520 degrees Celsius-600 degrees
Celsius.
[0078] Electrostatic capacity of the electrode calculated by the
cyclic voltammetry method is shown in Table 2. Electrostatic
capacity of the electrode is proportional to the effective surface
area of electrode, and it may be right to say that the higher the
capacity, the higher the effective surface area also is. FIG. 3
shows the relationship between the electrostatic capacity and the
baking conditions of the catalyst layer, based on the data in Table
2.
[0079] As is clear from Table 2 and FIG. 3, the electrostatic
capacity of the electrode of Samples 2-4 and Samples 6-8 of the
example by the present invention, which were subjected to baking in
a relatively high temperature region of 430 degrees Celsius-480
degrees Celsius plus post-bake in a further high temperature region
of 520 degrees Celsius-600 degrees Celsius increased to a high
point of 11.6 or more. On the other hand, IrO.sub.2 of the catalyst
layer formed by baking at 430 degrees Celsius without post-bake
(Sample 1) showed the largest effective surface area (the
electrolytic capacity of the electrode), since it is amorphous.
After conducting post-bake, the effective surface area (the
electrolytic capacity of the electrode) decreased since IrO.sub.2
was crystallized, but it was still higher compared with the
conventional product. This may be because the formed crystallite
diameter was smaller than the conventional product. In addition, it
was observed that the electrode effective surface area (the
electrolytic capacity of the electrode) tended to decrease with the
increasing of post-bake temperature.
[0080] Also, it has been found that if post-bake is conducted after
the baking at 480 degrees Celsius (Samples 5-8), the effective
surface areas (the electrolytic capacity of the electrode) are
almost the same regardless of the post-bake temperature, meanwhile
they doubled compared with the conventional product. This is
probably due to a smaller IrO.sub.2 crystallite diameter compared
with the conventional product and also a small amount of amorphous
IrO.sub.2 remaining. Moreover, even if the post-bake temperature is
increased, there was no change in the electrode effective surface
area (the electrolytic capacity of the electrode).
[0081] The oxygen generation overvoltage (V vs. SSE @ 100
A/dm.sup.2) of each sample was measured. The results are shown in
Table 2. In addition, the dependence of the oxygen generation
overvoltage on baking conditions is shown in FIG. 4. The trend of
changing in the graph of FIG. 4 was reverse to that of FIG. 3. With
increase of the electrode effective surface area, the oxygen
generation overvoltage of the samples tended to decrease. As the
reason, it is considered that increased electrode effective surface
area contributed to dispersion of electric current distribution,
lowering the actual electric current.
[0082] The product with the largest effective surface area baked at
430 degrees Celsius without post-bake showed the lowest oxygen
overvoltage, but oxygen overvoltage increased as a result of
decreased effective surface area by post-bake. Similar trend was
observed with the product baked at 480 degrees Celsius in
dependence of oxygen overvoltage on the post-bake temperature. In
addition, the oxygen overvoltage of these samples was found to be
higher than that of the conventional product. This seems to be
because the surface area increased compared with the conventional
product.
[0083] In Table 2 and FIG. 4, it is indicated oxygen overvoltage of
Samples 2-4 and Samples 6-8 of the examples by the present
invention, which were subjected to baking in a relatively high
temperature region of 430 degrees Celsius-480 degrees Celsius plus
post-bake in a further high temperature region of 520 degrees
Celsius-600 degrees Celsius decreased.
[0084] As mentioned above, the electrode manufactured by the baking
means of baking in a relatively high temperature region of 430
degrees Celsius-480 degrees Celsius plus post-bake in a further
high temperature region of 520 degrees Celsius-600 degrees Celsius,
features to have a smaller IrO.sub.2 crystal of the catalyst layer
compared with the conventional product and an increased electrode
surface area. In these samples, electric current distribution can
be dispersed under a high-load condition and actual electric
current load was decreased, from which such effects as suppression
of catalyst consumption and improvement in durability can be
expected.
EXAMPLES
[0085] The following describes examples by the present invention;
provided, however, the present invention is not limited to these
examples.
Example 1
[0086] The surface of titanium plate (JIS-I) was subjected to the
dry blast with iron grit (G120 size), followed by pickling in an
aqueous solution of concentrated hydrochloric acid for 10 minutes
at the boiling point for cleaning treatment of the metal substrate
of the electrode. The cleaned metal substrate of the electrode is
set to the AIP unit applying Ti--Ta alloy target as a vapor source
and a coating of tantalum and titanium alloy was applied as the AIP
base layer on the surface of the metal substrate of the electrode.
Coating condition is shown in Table 1.
[0087] The coated metal substrate was treated at 530 degrees
Celsius in an electric furnace of air circulation type for 180
minutes.
[0088] Then, the coating solution prepared by dissolving iridium
tetrachloride and tantalum pentachloride in concentrated
hydrochloric acid is applied on the coated metal substrate. After
drying, the thermolysis coating was conducted for 15 minutes in the
electric furnace of air circulation type at 480 degrees Celsius to
form an electrode catalyst layer comprising mixture oxides of
iridium oxide and tantalum oxide. The amount of coating solution
was determined so that the thickness of coating per time of the
coating solution corresponds to approx. 3.0 g/m.sup.2, as iridium
metal. This coating-baking operation was repeated nine times to
obtain the electrode catalyst layer of approx. 27.0 g/m.sup.2,
converted for metal iridium.
[0089] The X-ray diffraction was carried out for this sample. A
clear peak of iridium oxide attributable to the electrode catalyst
layer was observed, but the intensity of the peak was lower than
that of Comparative Example 1, indicating that crystalline
IrO.sub.2 had been partially precipitated.
[0090] Next, an electrode for electrolysis was manufactured in such
a manner that the sample coated with the catalyst layer is
post-baked in an electric furnace of air circulation type at 520
degrees Celsius for one hour.
[0091] The X-ray diffraction was carried out for the sample with
post-baking. A clear peak of iridium oxide attributable to the
electrode catalyst layer was observed, but the intensity of the
peak was still lower than that of Comparative Example 1, though was
higher than before the post-bake. From this, it has been known that
the degree of crystallinity of the catalyst layer formed by the low
temperature baking, before the post-bake, has increased, but
amorphous IrO.sub.2 still remains partially.
[0092] About the electrode for electrolysis prepared in the
above-mentioned manner, two types of life evaluation test were
conducted for: Pure sulfuric acid solution and sulfuric acid
solution with gelatin. Results are shown in Table 4. When compared
with Comparative Example 1 (Conventional Product) in Table 4, the
life for sulfuric acid electrolysis was 1.7 times and the life of
gelatin-added sulfuric acid electrolysis was 1.1 times, identifying
that durability to both sulfuric acid and organic additive has
improved.
TABLE-US-00003 TABLE 3 Sulfuric acid Gelatin-added electrolysis
sulfuric acid electrolysis Current density 500 A/dm.sup.2 300
A/dm.sup.2 Electrolyte 150 g/L 150 g/L of H.sub.2SO.sub.4 aq. + 50
ppm of H.sub.2SO.sub.4 aq. gelatin Electrolysis 60.degree. C.
temperature Counter electrode Zr plate Criterion of At the time
when a cell voltage increased electrolysis life 1.0 V than an
initial cell voltage.
Example 2
[0093] The electrode for evaluation was manufactured in the same
manner as with Example 1 except that post-bake was conducted in an
electric furnace of air circulation type for one hour at 560
degrees Celsius and the same electrolysis evaluation was
performed.
[0094] The X-ray diffraction performed after post-bake showed the
degree of IrO.sub.2 crystallinity and crystallite diameter of the
catalyst layer equivalent to Example 1.
[0095] As shown in Table 4, when compared with Comparative Example
1 (Conventional Product) in Table 4, the life of sulfuric acid
electrolysis was 1.5 times and the life of gelatin-added sulfuric
acid electrolysis was 1.3 times, identifying that durability to
both sulfuric acid and organic additive has improved.
Comparative Example 1
[0096] The electrode catalyst layer comprising the mixture oxide of
iridium oxide and tantalum oxide was formed as with Example 1, but
changing the baking temperature in the electric furnace of
circulation air type to 520 degrees Celsius and the baking time to
fifteen minutes. The electrode thus manufactured without post-bake
was evaluated for electrolysis by the X-ray diffraction as with
Example 1.
[0097] The X-ray diffraction was performed on this sample, from
which a clear peak of iridium oxide attributable to the electrode
catalyst layer was observed, verifying that IrO.sub.2 in the
catalyst layer is crystalline.
[0098] Life evaluation was made as with Example 1. From the results
shown in Table 4, it has been made clear that the method of the low
temperature baking plus high temperature post-bake, as suggested in
the present invention, improves durability in electrolysis under
high-load conditions.
Comparative Example 2
[0099] In the same manner as with Example 1 except that post-bake
was carried out, the electrode for evaluation was manufactured and
electrolysis evaluation was carried out in the same manner with
Example 1.
[0100] As shown in Table 4, lives of the electrode baked at 480
degrees Celsius without post-bake for sulfuric acid electrolysis
and gelatin-added sulfuric acid electrolysis were equivalent to
that of the conventional product, proving no improvement in
durability.
TABLE-US-00004 TABLE 4 Baking Post-bake Life of sulfuric Life of
gelatin-added temperature temperature acid electrolysis sulfuric
acid electrolysis (.degree. C.) (.degree. C.) (hr) (hr) Example 1
480 520 4182 1084 2 480 560 3665 1304 Comparative 1 520 -- 2508 978
Example 2 480 -- 2604 1073
INDUSTRIAL APPLICABILITY
[0101] The present invention relates to an anode for oxygen
generation used for various industrial electrolyses and a
manufacturing method for the same; more in detail, it is applicable
to a high-load durable anode for oxygen generation used for
industrial electrolyses including manufacturing of electrolytic
metal foils such as electrolytic copper foil, aluminum liquid
contact, continuously electrogalvanized steel plate and metal
extraction, having superior durability under high-load electrolysis
conditions.
* * * * *