U.S. patent application number 15/103924 was filed with the patent office on 2016-10-27 for alkaline water electrolysis diaphragm, method of manufacturing same, and alkaline water electrolyzer.
This patent application is currently assigned to KAWASAKI JUKOGYO KABUSHIKI KAISHA. The applicant listed for this patent is DE NORA PERMELEC LTD, KAWASAKI JUKOGYO KABUSHIKI KAISHA, THYSSENKRUPP UHDE CHLORINE ENGINEERS (JAPAN) LTD.. Invention is credited to Terumi HASHIMOTO, Takafumi ITO, Yuji KAMEI, Akihiro KATO, Jun KAWAGUCHI, Akiyoshi MANABE, Ikuo SHIMOMURA, Koki TAGUCHI, Tomonori TAKASE.
Application Number | 20160312371 15/103924 |
Document ID | / |
Family ID | 53402415 |
Filed Date | 2016-10-27 |
United States Patent
Application |
20160312371 |
Kind Code |
A1 |
KAMEI; Yuji ; et
al. |
October 27, 2016 |
ALKALINE WATER ELECTROLYSIS DIAPHRAGM, METHOD OF MANUFACTURING
SAME, AND ALKALINE WATER ELECTROLYZER
Abstract
An alkaline water electrolysis diaphragm includes: a polymer
porous layer containing at least one polymer compound selected from
polyether sulfone having a contact angle of 20 to 90.degree. and
polysulfone having the contact angle of 20 to 90.degree.; and an
organic fiber fabric layer coupled to the polymer porous layer. The
polyether sulfone having the contact angle of 20 to 90.degree. is
at least one polymer compound selected from the group made of
polyether sulfone, hydrophilic polyether sulfone, cationic
polyether sulfone, and cationic hydrophilic polyether sulfone. The
polysulfone having the contact angle of 20 to 90.degree. is at
least one polymer compound selected from the group made of
polysulfone, hydrophilic polysulfone, cationic polysulfone, and
cationic hydrophilic polysulfone.
Inventors: |
KAMEI; Yuji; (Himeji-shi,
JP) ; TAGUCHI; Koki; (Kobe-shi, JP) ;
SHIMOMURA; Ikuo; (Kakogawa-shi, JP) ; ITO;
Takafumi; (Kakogawa-shi, JP) ; KAWAGUCHI; Jun;
(Kyoto-shi, JP) ; TAKASE; Tomonori; (Kakogawa-shi,
JP) ; KATO; Akihiro; (Fujisawa-shi, JP) ;
MANABE; Akiyoshi; (Yokohama-shi, JP) ; HASHIMOTO;
Terumi; (Kurashiki-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KAWASAKI JUKOGYO KABUSHIKI KAISHA
DE NORA PERMELEC LTD
THYSSENKRUPP UHDE CHLORINE ENGINEERS (JAPAN) LTD. |
Kobe-shi, Hyogo
Fujisawa-city, Kanagawa
Chuo-ku, Tokyo |
|
JP
JP
JP |
|
|
Assignee: |
KAWASAKI JUKOGYO KABUSHIKI
KAISHA
Kobe-shi, Hyogo
JP
DE NORA PERMELEC LTD
Fujisawa-city, Kanagawa
JP
thyssenkrupp UHDE CHLORINE ENGINEERS (JAPAN) LTD.
Tokyo
JP
|
Family ID: |
53402415 |
Appl. No.: |
15/103924 |
Filed: |
December 16, 2014 |
PCT Filed: |
December 16, 2014 |
PCT NO: |
PCT/JP2014/006278 |
371 Date: |
June 13, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C25B 1/10 20130101; Y02E
60/36 20130101; Y02E 60/366 20130101; C25B 13/08 20130101; C25B
9/08 20130101 |
International
Class: |
C25B 13/08 20060101
C25B013/08; C25B 1/10 20060101 C25B001/10; C25B 9/08 20060101
C25B009/08 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 18, 2013 |
JP |
2013-261099 |
Claims
1. A alkaline water electrolysis diaphragm comprising: a polymer
porous layer containing at least one polymer compound selected from
polyether sulfone having a contact angle of 20 to 90.degree. and
polysulfone having the contact angle of 20 to 90.degree.; and an
organic fiber fabric layer coupled to the polymer porous layer.
2. The alkaline water electrolysis diaphragm according to claim 1,
wherein the polyether sulfone having the contact angle of 20 to
90.degree. is at least one polymer compound selected from the group
consisting of polyether sulfone, hydrophilic polyether sulfone,
cationic polyether sulfone, and cationic hydrophilic polyether
sulfone.
3. The alkaline water electrolysis diaphragm according to claim 1,
wherein the polysulfone having the contact angle of 20 to
90.degree. is at least one polymer compound selected from the group
consisting of polysulfone, hydrophilic polysulfone, cationic
polysulfone, and cationic hydrophilic polysulfone.
4. The alkaline water electrolysis diaphragm according to claim 1,
wherein each of the polyether sulfone having the contact angle of
20 to 90.degree. and the polysulfone having the contact angle of 20
to 90.degree. has a hydrophilic functional group or a hydrophilic
graft chain at a rate of 1 to 100% per polymer repeating unit.
5. The alkaline water electrolysis diaphragm according to claim 1,
wherein each of the polyether sulfone having the contact angle of
20 to 90.degree. and the polysulfone having the contact angle of 20
to 90.degree. has a cationic functional group at a rate of 1 to
100% per polymer repeating unit.
6. The alkaline water electrolysis diaphragm according to claim 1,
wherein the organic fiber fabric layer is made of organic fiber
non-woven fabric having a density of 0.1 to 0.7 g/cm.sup.3.
7. An alkaline water electrolyzer comprising: an electrolysis tank
including an anode chamber and a cathode chamber that are defined
by the alkaline water electrolysis diaphragm according to claim 1:
an anode provided in the anode chamber; a cathode provided in the
cathode chamber; and an elastic body having an electrical
conductivity and configured to press the cathode toward the
alkaline water electrolysis diaphragm such that the anode, the
alkaline water electrolysis diaphragm, and the cathode tightly
contact one another.
8. A method of manufacturing an alkaline water electrolysis
diaphragm, the method comprising: adding at least one polymer
compound selected from polyether sulfone having a contact angle of
20 to 90.degree. and polysulfone having the contact angle of 20 to
90.degree. to an organic solvent at a concentration of 12.5 to 30
wt. % to obtain a membrane forming solution; applying the membrane
forming solution to organic fiber fabric; and performing phase
separation of the membrane forming solution.
9. The method according to claim 8, wherein the polyether sulfone
having the contact angle of 20 to 90.degree. is at least one
polymer compound selected from the group consisting of polyether
sulfone, hydrophilic polyether sulfone, cationic polyether sulfone,
and cationic hydrophilic polyether sulfone.
10. The method according to claim 8, wherein the polysulfone having
the contact angle of 20 to 90.degree. is at least one polymer
compound selected from the group consisting of polysulfone,
hydrophilic polysulfone, cationic polysulfone, and cationic
hydrophilic polysulfone.
11. The method according to claim 8, wherein each of the polyether
sulfone having the contact angle of 20 to 90.degree. and the
polysulfone having the contact angle of 20 to 90.degree. has a
hydrophilic functional group or a hydrophilic graft chain at a rate
of 1 to 100% per polymer repeating unit.
12. The method according to claim 8, wherein each of the polyether
sulfone having the contact angle of 20 to 90.degree. and the
polysulfone having the contact angle of 20 to 90.degree. has a
cationic functional group at a rate of 1 to 100% per polymer
repeating unit.
13. The method according to claim 8, wherein the organic fiber
fabric is organic fiber non-woven fabric having a density of 0.1 to
0.7 g/cm.sup.3.
14. The method according to claim 8, wherein the organic solvent is
selected from the group consisting of dimethyl sulfoxide (DMSO),
N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF),
dimethylacetamide (DMAc), and a mixture of these.
Description
TECHNICAL FIELD
[0001] The present invention relates to an alkaline water
electrolyzer, an alkaline water electrolysis diaphragm, and a
method of manufacturing the alkaline water electrolysis
diaphragm.
BACKGROUND ART
[0002] An alkaline water electrolyzer configured to generate oxygen
and hydrogen from water has been known. Typically, the alkaline
water electrolyzer includes one or more electrolysis units. For
example, the electrolysis unit of the alkaline water electrolyzer
described in PTL 1 includes: an electrolysis tank; an alkali
aqueous solution, such as a potassium hydroxide (KOH) aqueous
solution, stored in the electrolysis tank; two mesh-like electrodes
immersed in the alkali aqueous solution; a diaphragm held so as to
be sandwiched between the two electrodes and having ion
permeability; two power supply electrodes configured to supply
electric power to the respective electrodes; and plate
spring-shaped electrically-conductive members through which the
power supply electrodes are electrically connected to the
electrodes. In the alkaline water electrolyzer, when a voltage is
applied between the electrodes by supplying the electric power from
the power supply electrodes through the electrically-conductive
members to the electrodes, hydrogen is generated at a cathode side
of the electrolysis tank, and oxygen is generated at an anode side
of the electrolysis tank.
[0003] Examples of a conventionally-proposed electrolysis diaphragm
include: asbestos; non-woven fabric; an ion-exchange membrane; a
polymer porous membrane; and a composite membrane containing
inorganic substance and organic polymer. For example, PTL 1
describes an ion-permeable diaphragm formed by containing organic
fiber fabric in a mixture of: a hydrophilic inorganic material that
is a calcium phosphate compound or calcium fluoride; and an organic
binding material selected from polysulfone, polypropylene, and
polyvinylidene fluoride. Further, for example, PTL 2 describes an
ion-permeable diaphragm formed by containing extended organic fiber
fabric in a membrane forming mixture of: a particulate inorganic
hydrophilic material selected from antimony, zirconium oxide, and
zirconium hydroxide; and an organic binding agent selected from
fluorocarbon polymer, polysulfone, polypropylene, polyvinyl
chloride, and polyvinylbutyral.
CITATION LIST
Patent Literature
[0004] PTL 1: Japanese Laid-Open Patent Application Publication No.
2008-144262
[0005] PTL 2: Japanese Laid-Open Patent Application Publication No.
62-196390
SUMMARY OF INVENTION
Technical Problem
[0006] The present invention was made in light of the above prior
arts, and an object of the present invention is to provide a
diaphragm having a gas barrier property, low electrical resistance,
chemical strength, physical strength, and manufacturability for the
purpose of further increasing performance of an alkaline water
electrolyzer and reducing a cost of the alkaline water
electrolyzer.
Solution to Problem
[0007] The diaphragm of the alkaline water electrolyzer is required
to have (1) the gas barrier property, (2) electrolysis efficiency,
(3) the chemical strength, (4) the physical strength, and (5) the
manufacturability. Regarding item (1), the gas barrier property
denotes that only ions pass through the diaphragm, and generated
gas does not pass or dissipate. This is important for the purpose
of collecting high-purity hydrogen and oxygen. The gas barrier
property is affected by hydrophilicity of the surface of the
diaphragm. Regarding item (2), the electrolysis efficiency denotes
electrolysis efficiency of the alkaline water electrolyzer to which
the diaphragm is applied. The electrolysis efficiency is affected
by the hydrophilicity of the surface of the diaphragm and the
electrical resistance of the diaphragm. The hydrophilic prevents
the electrolysis efficiency from decreasing by bubbles adhering to
the surface of the diaphragm. The low electrical resistance (i.e.,
high ion conductivity) of the diaphragm is important for the
purpose of improving the electrolysis efficiency of the alkaline
water electrolyzer and increasing the productivity of hydrogen and
oxygen. Regarding item (3), heat resistance and alkali resistance
are required as the chemical strength. The required heat resistance
is set to such a level that the diaphragm can endure a temperature
(about 80.degree. C.) of the alkali aqueous solution. The required
alkali resistance is set to such a level that the diaphragm can
endure high-concentration alkali (for example, KOH of 25 wt. %) of
the alkali aqueous solution. Regarding item (4), abrasion
resistance with respect to friction between the diaphragm and the
electrode is required as the physical strength. As in the
electrolysis unit of PTL 1, when the electrode and the diaphragm
are in contact with each other, the electrode vibrates by the
generation of the bubbles from the surface of the electrode, and
this causes the friction between the electrode and the diaphragm.
If the diaphragm is worn away, the frequency of replacement of the
diaphragm increases, and this is not economical. In addition, a
problem is that the productivity of hydrogen and oxygen
deteriorates. Further, regarding item (5), manufacturability of
being able to industrially manufacture a large-scale diaphragm of
about 2,000 mm square is required. The alkaline water electrolyzer
can be configured as not only a small-scale alkaline water
electrolyzer but also a large-scale alkaline water electrolyzer,
such as a hydrogen manufacturing plant. Such a large-scale alkaline
water electrolyzer requires a diaphragm having a relatively large
area.
[0008] The present inventors have studied various diaphragm
materials and found that a polymer compound selected from the group
consisting of polyether sulfone and polysulfone is preferable since
such a polymer compound adequately has the chemical strength (the
heat resistance and the alkali resistance) required in the
diaphragm of the alkaline water electrolyzer. Further, to satisfy
the requirements of the gas barrier property and the electrolysis
efficiency in addition to the chemical strength, polyether sulfone
whose contact angle falls within a predetermined contact angle
range and/or polysulfone whose contact angle falls within the
predetermined contact angle range are used as a major component of
the diaphragm.
[0009] Furthermore, to satisfy the requirements of the physical
strength and the manufacturability, organic fiber non-woven fabric
having excellent tensile strength and rigidity or organic fiber
woven fabric having excellent tensile strength and rigidity is used
as a reinforcing layer of the diaphragm. This compensates the
physical strength and the manufacturability, which cannot be
adequately obtained only by the polymer porous membrane. Thus, the
diaphragm obtains the required properties. It should be noted that
the polymer porous membrane containing polyether sulfone or
polysulfone as the major component has a certain degree of physical
strength but does not satisfy the physical strength or
manufacturability required in the diaphragm of the alkaline water
electrolyzer.
[0010] An alkaline water electrolysis diaphragm according to the
present invention includes: a polymer porous layer containing at
least one polymer compound selected from polyether sulfone having a
contact angle of 20 to 90.degree. and polysulfone having the
contact angle of 20 to 90.degree.; and an organic fiber fabric
layer coupled to the polymer porous layer.
[0011] A method of manufacturing an alkaline water electrolysis
diaphragm according to the present invention includes: adding at
least one polymer compound selected from polyether sulfone having a
contact angle of 20 to 90.degree. and polysulfone having the
contact angle of 20 to 90.degree. to an organic solvent at a
concentration of 12.5 to 30 wt. % to obtain a membrane forming
solution; applying the membrane forming solution to organic fiber
fabric; and performing phase separation of the membrane forming
solution.
[0012] The polyether sulfone having the contact angle of 20 to
90.degree. may be at least one polymer compound selected from the
group consisting of polyether sulfone, hydrophilic polyether
sulfone, cationic polyether sulfone, and cationic hydrophilic
polyether sulfone. The polysulfone having the contact angle of 20
to 90.degree. may be at least one polymer compound selected from
the group consisting of polysulfone, hydrophilic polysulfone,
cationic polysulfone, and cationic hydrophilic polysulfone. The
hydrophilic polyether sulfone obtains the hydrophilicity by
introducing a hydrophilic functional group or a hydrophilic graft
chain into polyether sulfone. The hydrophilic polysulfone obtains
the hydrophilicity by introducing a hydrophilic functional group or
a hydrophilic graft chain into polysulfone. The cationic polyether
sulfone is obtained by introducing a cationic functional group to
polyether sulfone. The cationic polysulfone is obtained by
introducing a cationic functional group to polysulfone. When the
polymer compound as the diaphragm material is the hydrophilic
polyether sulfone and/or the hydrophilic polysulfone, the polymer
compound whose contact angle falls within a predetermined contact
angle range is stably supplied, and the hydrophilicity of the
diaphragm can be controlled. When the polymer compound as the
diaphragm material is the cationic polyether sulfone and/or the
cationic polysulfone, the ion permeability of the diaphragm can be
controlled. When the polymer compound of the diaphragm material is
the cationic hydrophilic polyether sulfone and/or the cationic
hydrophilic polysulfone, both the hydrophilicity and cationicity
can be given to the diaphragm, so that the diaphragm can obtain the
excellent ion permeability.
[0013] In the alkaline water electrolysis diaphragm and the method
of manufacturing alkaline water electrolysis diaphragm, each of the
polyether sulfone having the contact angle of 20 to 90.degree. and
the polysulfone having the contact angle of 20 to 90.degree. may
have a hydrophilic functional group or a hydrophilic graft chain at
a rate of 1 to 100% per polymer repeating unit. Further, in the
alkaline water electrolysis diaphragm and the method of
manufacturing alkaline water electrolysis diaphragm, each of the
polyether sulfone having the contact angle of 20 to 90.degree. and
the polysulfone having the contact angle of 20 to 90.degree. may
have a cationic functional group at a rate of 1 to 100% per polymer
repeating unit.
[0014] In the alkaline water electrolysis diaphragm, the organic
fiber fabric layer may be made of organic fiber non-woven fabric
having a density of 0.1 to 0.7 g/cm.sup.3. Similarly, in the method
of manufacturing the alkaline water electrolysis diaphragm, the
organic fiber fabric may be organic fiber non-woven fabric having a
density of 0.1 to 0.7 g/cm.sup.3.
[0015] In the method of manufacturing the alkaline water
electrolysis diaphragm, the organic solvent may be selected from
the group consisting of dimethyl sulfoxide (DMSO),
N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF),
dimethylacetamide (DMAc), and a mixture of these.
[0016] The alkaline water electrolyzer according to the present
invention includes: an electrolysis tank including an anode chamber
and cathode chamber that are defined by the alkaline water
electrolysis diaphragm according to any one of claims 1 to 6; an
anode provided in the anode chamber; a cathode provided in the
cathode chamber; and an elastic body having an electrical
conductivity and configured to press the cathode toward the
alkaline water electrolysis diaphragm such that the anode, the
alkaline water electrolysis diaphragm, and the cathode tightly
contact one another.
Advantageous Effects of Invention
[0017] The alkaline water electrolysis diaphragm of the present
invention includes the polymer porous layer and the organic fiber
fabric layer. The polymer porous layer maintains various chemical
properties of polyether sulfone and polysulfone, and the
hydrophilicity and chargeability of the polymer porous layer are
adjusted. The alkaline water electrolysis diaphragm excels in
chemical strength, and in addition, has the hydrophilicity and/or
the ion permeability which prevent the gas barrier property and the
electrolysis efficiency from deteriorating. Further, the alkaline
water electrolysis diaphragm of the present invention includes the
organic fiber fabric layer. With this, the physical strength of the
polymer porous layer is compensated, so that the manufacturability
is improved.
BRIEF DESCRIPTION OF DRAWINGS
[0018] FIG. 1A is a schematic cross-sectional view showing a
diaphragm according to one aspect of the present invention, the
diaphragm being configured such that a polymer porous layer is
formed on one surface of an organic fiber fabric layer.
[0019] FIG. 1B is a schematic cross-sectional view showing a
diaphragm according to another aspect of the present invention, the
diaphragm being configured such that polymer porous layers are
formed on both surfaces of an organic fiber fabric layer.
[0020] FIG. 2 is a diagram showing a schematic configuration of a
membrane forming apparatus for the alkaline water electrolysis
diaphragm according to one embodiment of the present invention.
[0021] FIG. 3 is a cross-sectional view showing a schematic
configuration of an electrolysis cell included in the alkaline
water electrolyzer.
[0022] FIG. 4 is a diagram showing a schematic configuration of a
testing apparatus.
[0023] FIG. 5 is a graph showing test results of the diaphragm
according to Example 1.
[0024] FIG. 6 is a graph showing test results obtained when a
polymer porous membrane according to Reference Example 1 is used as
the diaphragm.
[0025] FIG. 7 is a graph showing test results obtained when a
polymer porous membrane according to Reference Example 2 is used as
the diaphragm.
DESCRIPTION OF EMBODIMENTS
[0026] An embodiment of the present invention will be explained in
reference to the drawings. FIG. 1A is a schematic cross-sectional
view showing a diaphragm according to one aspect of the present
invention, the diaphragm being configured such that a polymer
porous layer is formed on one surface of an organic fiber fabric
layer. FIG. 1B is a schematic cross-sectional view showing a
diaphragm according to another aspect of the present invention, the
diaphragm being configured such that polymer porous layers are
formed on both surfaces of an organic fiber fabric layer. As shown
in FIGS. 1A and 1B, an alkaline water electrolysis diaphragm
(hereinafter may be simply referred to as a "diaphragm") 90
according to each of one aspect of the present invention and
another aspect of the present invention is constituted by a polymer
porous layer (hereinafter may be simply referred to as a "porous
layer") 91 and an organic fiber fabric layer (hereinafter may be
simply referred to as a "fabric layer") 92 and has ion
permeability, liquid petmeability, and gas impermeability. As shown
in FIG. 1A, the porous layer 91 may be formed on one surface of the
fabric layer 92. As shown in FIG. 1B, the porous layers 91 may be
formed on both surfaces of the fabric layer 92. An interface
between the porous layer 91 and the fabric layer 92 constitutes a
mixed layer 93 in which a polymer compound gets into fabric tissues
or structural gaps. The porous layer 91 and the fabric layer 92 are
coupled to each other by the mixed layer 93.
[0027] A major component of the porous layer 91 is at least one
polymer compound selected from polyether sulfone and polysulfone
each of which has a contact angle of 20 to 90.degree. at normal
temperature. The contact angle indicates wettability. The polyether
sulfone is at least one polymer compound selected from the group
consisting of polyether sulfone (polyether sulfone not having an
aryl group or polyether sulfone not having a below-described
hydrophilic group or cationic group at its terminal), hydrophilic
polyether sulfone, cationic polyether sulfone, and cationic
hydrophilic polyether sulfone. Further, the polysulfone is at least
one polymer compound selected from the group consisting of
polysulfone (polysulfone not having an aryl group or polysulfone
not having a below-described hydrophilic group or cationic group at
its terminal), hydrophilic polysulfone, cationic polysulfone, and
cationic hydrophilic polysulfone.
[0028] According to the diaphragm whose major component is the
polymer compound having the contact angle of less than 20.degree.,
wetting of the surface of the diaphragm by an electrolytic solution
increases, and this decreases the chemical strength of the
diaphragm. Further, the diaphragm whose major component is the
polymer compound having the contact angle of more than 90.degree.
is low in the gas barrier property and the electrolysis efficiency,
and therefore, is not suitable for use. The contact angle is
measured in such a manner that: a waterdrop is dropped onto a sheet
of the polymer compound to be measured; and an angle formed by the
waterdrop and the sheet of the polymer compound is measured at
normal temperature. In the present specification, the "normal
temperature" denotes a temperature of a solution which is not
particularly heated or cooled. Specifically, the normal temperature
is 0 to 40.degree. C. and is typically a temperature around 15 to
25.degree. C. determined by The Japanese Pharmacopoeia.
[0029] Chemical Formula 1 below shows a chemical structure of
polyether sulfone (PES). The hydrophilic polyether sulfone has the
aryl group of the polyether sulfone shown in Chemical Formula 1 or
has a hydrophilic functional group (hereinafter may be simply
referred to as a "hydrophilic group") or hydrophilic graft chain at
its terminal (its head and/or tail). The hydrophilic group is a
functional group selected from the group consisting of a hydroxyl
group, a carboxyl group, a sulfonate group, and the like. The
hydrophilic graft chain is hydrophilic polymer selected from the
group consisting of polyacrylamide, polyacrylic acid,
poly(2-hydroxyethyl methacrylate), and the like. The hydrophilic
group may be cationic. The polyether sulfone having the cationic
hydrophilic group, that is, the cationic hydrophilic polyether
sulfone is a polymer compound having both hydrophilicity and
cationicity. The cationic polyether sulfone has the aryl group of
the polyether sulfone shown in Chemical Formula 1 or has a cationic
functional group (hereinafter may be simply referred to as a
"cationic group") at its terminal (its head and/or tail). The
cationic group is, for example, a cationic amino group, such as an
aminomethyl group or an aminoethyl group.
##STR00001##
[0030] A rate of the hydrophilic group or hydrophilic graft chain
in the hydrophilic polyether sulfone is preferably 1 to 100% per
polymer repeating unit and more preferably 1 to 50% per polymer
repeating unit. The polyether sulfone in which the rate of the
hydrophilic group or hydrophilic graft chain is less than 1% per
polymer repeating unit becomes low in hydrophilicity. Further, the
polyether sulfone in which the rate of the hydrophilic group or
hydrophilic graft chain is more than 100% per polymer repeating
unit is poor in chemical stability.
[0031] A molecular weight of the hydrophilic polyether sulfone is
preferably in a range of 10,000 to 500,000 and more preferably in a
range of 40,000 to 300,000. If the molecular weight is less than
10,000, the porous layer significantly lacks the physical strength,
so that the formation of the porous layer becomes difficult.
Further, it is practically difficult to obtain the hydrophilic
polyether sulfone having the molecular weight of more than
500,000.
[0032] A rate of the cationic group in the cationic polyether
sulfone is preferably 1 to 100% per polymer repeating unit and more
preferably 1 to 50% per polymer repeating unit. The polyether
sulfone in which the rate of the cationic group is less than 1% per
polymer repeating unit is low in chargeability. Further, the
polyether sulfone in which the rate of the cationic group is more
than 100% per polymer repeating unit is poor in solubility to an
organic solvent.
[0033] A molecular weight of the cationic polyether sulfone is
preferably in a range of 10,000 to 1,000,000 and more preferably in
a range of 40,000 to 800,000. If the molecular weight is less than
10,000, the porous layer significantly lacks the physical strength,
so that the formation of the porous layer becomes difficult.
Further, it is practically difficult to obtain the cationic
polyether sulfone having the molecular weight of more than
1,000,000.
[0034] The contact angle of the polyether sulfone is 85 to
90.degree. at normal temperature. However, the hydrophilic
polyether sulfone may become a polymer compound that stably has a
desired contact angle by the hydrophilic group. By using this
hydrophilic polyether sulfone as the major component of the porous
layer, the hydrophilicity of the diaphragm can be adjusted.
Further, by using the cationic polyether sulfone as the major
component of the porous layer, the ion permeability of the
diaphragm can be adjusted. Furthermore, by using the cationic
hydrophilic polyether sulfone as the major component of the porous
layer, both the hydrophilicity and the cationicity can be given to
the diaphragm, so that the excellent ion permeability can be given
to the diaphragm.
[0035] Chemical Formula 2 below shows a chemical structure of
polysulfone (PSF). The hydrophilic polysulfone has the aryl group
of the polysulfone shown by Chemical Formula 2 or the hydrophilic
group or hydrophilic graft chain at its terminal (its head and/or
tail). The hydrophilic group is a functional group selected from
the group consisting of a hydroxyl group, a carboxyl group, a
sulfonate group, and the like. The hydrophilic group may be a
cationic hydrophilic group. The polysulfone having the cationic
hydrophilic group, that is, the cationic hydrophilic polysulfone is
a polymer compound having both the hydrophilicity and the
cationicity. Further, the cationic polysulfone has the aryl group
of the polysulfone shown in Chemical Formula 2 or has the cationic
group at its terminal (its head and/or tail). The cationic group
is, for example, a cationic amino group, such as an aminomethyl
group or an aminoethyl group.
##STR00002##
[0036] A rate of the hydrophilic group or hydrophilic graft chain
in the hydrophilic polysulfone is preferably 1 to 100% per polymer
repeating unit and more preferably 1 to 40% per polymer repeating
unit. The polysulfone in which the rate of the hydrophilic group or
hydrophilic graft chain is less than 1% per polymer repeating unit
becomes low in hydrophilicity. Further, the polysulfone in which
the rate of the hydrophilic group or hydrophilic graft chain is
more than 100% per polymer repeating unit is, poor in chemical
stability.
[0037] A molecular weight of the hydrophilic polysulfone is
preferably in a range of 10,000 to 500,000 and more preferably in a
range of 40,000 to 300,000. If the molecular weight is less than
10,000, the porous layer significantly lacks the physical strength,
so that the formation of the porous layer becomes difficult.
Further, it is practically difficult to obtain the hydrophilic
polysulfone having the molecular weight of more than 500,000.
[0038] A rate of the cationic group in the cationic polysulfone is
preferably 1 to 100% per polymer repeating unit and more preferably
1 to 50% per polymer repeating unit. The polysulfone in which the
rate of the cationic group is smaller than 1% per polymer repeating
unit is low in chargeability. Further, the polysulfone in which the
rate of the cationic group is more than 100% per polymer repeating
unit is poor in solubility to an organic solvent.
[0039] A molecular weight of the cationic polysulfone is preferably
in a range of 10,000 to 500,000 and more preferably in a range of
40,000 to 300,000. If the molecular weight is less than 10,000, the
porous layer significantly lacks the physical strength, so that the
formation of the porous layer becomes difficult. Further, it is
practically difficult to obtain the cationic polysulfone having the
molecular weight of more than 500,000.
[0040] The contact angle of the polysulfone is 85 to 90.degree. at
normal temperature. However, the hydrophilic polysulfone may become
a polymer compound that stably has a desired contact angle by the
hydrophilic group. By using this hydrophilic polysulfone as the
major component of the porous layer, the hydrophilicity of the
diaphragm can be adjusted. Further, by using the cationic
polysulfone as the major component of the porous layer, the ion
permeability of the diaphragm can be adjusted. Furthermore, by
using the cationic hydrophilic polysulfone as the major component
of the porous layer, both the hydrophilicity and the cationicity
can be given to the diaphragm, so that the excellent ion
permeability can be given to the diaphragm.
[0041] The porous layer may further contain a hydrophilic inorganic
material selected from titanium oxide (TiO.sub.2), zirconium oxide
(ZrO.sub.2), and a mixture of titanium oxide (TiO.sub.2) and
zirconium oxide (ZrO.sub.2). When the porous layer contains the
hydrophilic inorganic material, further improvement of the ion
conductivity of the diaphragm is expected.
[0042] The fabric layer is formed by organic fiber non-woven fabric
or organic fiber woven fabric selected from polypropylene (PP) and
polyphenylene sulfide (PPS). The polypropylene is high in physical
strength and has an insulation property, heat resistance, and
alkali resistance. The polyphenylene sulfide is high in physical
strength and has heat resistance and alkali resistance. Each of the
polypropylene non-woven fabric, the polypropylene woven fabric, the
polyphenylene sulfide non-woven fabric, and the polyphenylene
sulfide woven fabric having the above properties adequately has the
physical strength and chemical strength required in the diaphragm
of the alkaline water electrolyzer, so that these are preferable as
the diaphragm material. Further, by using such organic fiber
non-woven fabric or such organic fiber woven fabric, the
manufacturability can be given to the diaphragm as described
below.
[0043] Table 1 below shows: properties (materials and densities) of
the organic fiber non-woven fabric of samples S1 to S6; and
evaluation results of the samples as the diaphragm material. A
polymer porous membrane layer made of the hydrophilic polyether
sulfone is formed on the organic fiber non-woven fabric of each of
the samples S1 to S6, and the non-woven fabric of each of the
samples S1 to S6 is evaluated based on the electrolysis efficiency
and a membrane formation state.
TABLE-US-00001 TABLE 1 Non-woven fabric Density Evaluation Samples
material (g/cm.sup.3) (Good or No good) S1 PPS 0.48-0.55 Good S2
PPS 0.68-0.94 No good S3 PP 0.38 Good S4 PP 0.43 Good S5 PP
0.16-0.34 Good S6 PP 0.36-0.45 Good
[0044] According to the sample S2, the electrolysis efficiency is
extremely low, and the polymer porous membrane layer separates from
the organic fiber non-woven fabric. According to the evaluation
results, the density of the organic fiber non-woven fabric forming
the fabric layer of the diaphragm is preferably 0.1 to 0.7
g/cm.sup.3 and especially desirably 0.3 to 0.6 g/cm.sup.3. The
diaphragm using the organic fiber non-woven fabric having the
density of less than 0.1 g/cm.sup.3 cannot sufficiently obtain the
gas barrier property. The diaphragm using the organic fiber
non-woven fabric having the density of more than 0.7 g/cm.sup.3 may
lack the electrolysis efficiency or cause a membrane formation
failure.
[0045] Method of Manufacturing Alkaline Water Electrolysis
Diaphragm
[0046] The diaphragm according to the present embodiment is
manufactured by a phase separation method using the polymer
compound and the organic fiber fabric. FIG. 2 is a diagram showing
a schematic configuration of a membrane forming apparatus 1 for the
alkaline water electrolysis diaphragm according to one embodiment
of the present invention. The membrane forming apparatus 1 can
continuously manufacture the diaphragms.
[0047] As shown in FIG. 2, the membrane forming apparatus 1
includes: a coating unit 5; a chemical liquid tank 6; an unwinding
drum 2 that is a web roll of fabric 21; a winding drum 12
configured to wind a product (diaphragm); and a water tank 13 in
which the winding drum 12 is immersed in water. The membrane
forming apparatus 1 further includes: a plurality of guide rollers
3, 4, 7, and 11 that form a transfer pathway for the fabric 21 and
the product, the transfer pathway extending from the unwinding drum
2 through the coating unit 5 and the chemical liquid tank 6 to the
winding drum 12; a driving roller 8 and nip roller 9 configured to
transfer the fabric 21 (product) along the transfer pathway; and a
slitter 10 configured to cut the transferred product into a desired
size.
[0048] The coating unit 5 includes a slit through which a membrane
forming solution 22 flows out. The coating unit 5 applies the
membrane forming solution 22 to the surface of the moving fabric 21
at a predetermined thickness. The coating unit 5 can apply the
membrane forming solution 22 to one selected surface of the fabric
21 or both surfaces of the fabric 21. The membrane forming solution
22 is supplied to the coating unit 5 from a solution supply device
(not shown). The membrane forming solution 22 is prepared in the
solution supply device in such a manner that the polymer compound
in powder form and an additive that acts on a structure (pore
diameter, pore distribution, etc.) of the porous layer are
dissolved in an organic solvent.
[0049] When the weight of the membrane forming solution is regarded
as 100% as a reference, the concentration of the polymer compound
in the membrane forming solution 22 is 12.5 to 30 wt. % and
preferably 15 to 25 wt. %. When the concentration of the polymer
compound in the membrane forming solution 22 is less than 12.5 wt.
%, a membrane (porous layer) having an adequate strength cannot be
obtained. Further, when the concentration of the polymer compound
in the membrane forming solution 22 exceeds 30 wt. %, the diameter
of the pore formed becomes extremely small, and this deteriorates
the electrolysis efficiency of the electrolysis apparatus to which
the diaphragm is applied.
[0050] The organic solvent of the membrane forming solution needs
to be an organic solvent in which polyether sulfone, polysulfone,
hydrophilic polyether sulfone, hydrophilic polysulfone, cationic
polyether sulfone, and cationic polysulfone can be dissolved and
which has miscibility with water. For example, such organic solvent
can be selected from the group consisting of dimethyl sulfoxide
(DMSO), N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF),
dimethylacetamide (DMAc), and a mixture of these.
[0051] In the membrane forming apparatus 1, the fabric 21 is
unwound from the unwinding drum 2 to move along the transfer
pathway to the coating unit 5. While the fabric 21 passes through
the coating unit 5, the membrane forming solution 22 is applied to
both surfaces of the fabric 21 or one surface of the fabric 21. A
part of the membrane forming solution 22 applied is impregnated in
the fabric 21. The fabric 21 to which the membrane forming solution
22 is applied is then immersed in a chemical liquid (nonsolvent) 23
in the chemical liquid tank 6. Herein, the fabric 21 to which the
membrane forming solution 22 is applied is entirely immersed in the
chemical liquid 23. However, the fabric 21 to which the membrane
forming solution 22 is applied may be immersed in the chemical
liquid 23 such that at least the membrane forming solution 22
contacts the chemical liquid 23. In the chemical liquid tank 6,
phase separation of the membrane forming solution 22 applied to the
fabric 21 occurs, so that a porous structure of the polymer
compound is formed. Thus, the polymer compound in the membrane
forming solution 22 solidifies, and as a result, the porous layer
is formed on the fabric 21. It should be noted that the chemical
liquid (nonsolvent) is preferably water in light of cost and the
like.
[0052] The fabric 21 on which the porous layer is formed as above
is then sandwiched between the driving roller 8 and the nip roller
9. Thus, the thickness of the fabric 21 is uniformized, and excess
water is removed from the fabric 21. Then, the fabric 21 is cut by
the slitter 10 into an appropriate size and wound by the winding
drum 12. The winding drum 12 is immersed in water in the water tank
13. The product (alkaline water electrolysis diaphragm) wound by
the winding drum 12 is held in a wet state.
[0053] Since the diaphragm manufactured as above includes the
fabric 21 as a base, the porous layer does not break or extend
during manufacturing. Therefore, severe adjustment of a transfer
speed of the fabric 21 in the membrane forming apparatus 1 is not
required, and a manufacturing speed can be made higher than a
conventional manufacturing speed. Further, by using a web roll of
wide fabric 21, a diaphragm (a square shape having 2,000 mm on each
side) larger than a conventionally used diaphragm can be
manufactured. As above, the manufacturability is improved by
including the fabric layer in the diaphragm.
[0054] The thickness of the diaphragm manufactured as above is
adjusted by the thickness of the membrane forming solution applied
to the fabric 21. The thickness of the diaphragm is preferably 100
to 700 .mu.m although it depends on the thickness of the fabric
layer. If the thickness of the diaphragm is less than 100 .mu.m,
the physical strength required in the diaphragm for the alkaline
water electrolysis may be inadequate. If the thickness of the
diaphragm exceeds 700 .mu.m, the electrical resistance of the
diaphragm easily increases, and the electrolysis efficiency
decreases.
[0055] In the above embodiment, the diaphragms are continuously
manufactured using the membrane forming apparatus 1 shown in FIG.
2. However, the method of manufacturing the diaphragm is not
limited to this. For example, the diaphragm may be manufactured in
such a manner that: fabric is spread on a smooth surface, such as a
glass plate, made of an inert material; a membrane forming solution
is uniformly applied to the fabric at a predetermined thickness;
the phase separation of the membrane forming solution is performed;
and the fabric is removed from the smooth surface.
[0056] Further, in the above embodiment, to form the porous layer,
the fabric 21 to which the membrane forming solution 22 is applied
is immersed in the chemical liquid 23. Instead of this, the
membrane forming solution 22 applied to the fabric 21 may be
brought into contact with humidified air.
[0057] The diaphragm manufactured as above is used in, for example,
the alkaline water electrolyzer explained below. FIG. 3 is a
cross-sectional view showing an outline of an electrolysis cell 30
included in the alkaline water electrolyzer.
[0058] As shown in FIG. 3, the electrolysis cell 30 includes an
electrolysis tank 29 in which an anode chamber 48 and a cathode
chamber 49 are provided so as to sandwich a diaphragm 33. Each of
the anode chamber 48 and the cathode chamber 49 includes: a supply
port for the electrolytic solution; and a discharge port for the
electrolytic solution after the electrolysis and the gas (hydrogen
or oxygen). An anode assembly 31 is provided at the anode chamber
48 side with respect to the diaphragm 33 in the electrolysis tank
29. The anode assembly 31 includes: a mesh-like anode 31a; an anode
frame 31b provided around the anode 31a; and a connecting terminal
31c provided at the anode frame 31b. A cathode assembly 32 is
provided at the cathode chamber 49 side with respect to the
diaphragm 33 in the electrolysis tank 29. The cathode assembly 32
includes: a mesh-like cathode 32a; a cathode frame 32b provided at
the cathode 32a so as to be located at an opposite side of the
diaphragm 33; a connecting terminal 32c provided at the cathode
frame 32b; and an elastic body 32d provided between the cathode 32a
and the cathode frame 32b and having electrical conductivity. The
cathode 32a is pressed against the diaphragm 33 by the elastic body
32d. Thus, the anode 31a and the diaphragm 33 tightly contact each
other, and the diaphragm 33 and the cathode 32a tightly contact
each other. As above, the electrolysis cell 30 has a zero-gap
structure that is low in solution resistance. The elastic body 32d
according to the present embodiment is a plate spring, but the
elastic body 32d is not limited to the plate spring.
[0059] In the electrolysis cell 30 configured as above, the
diaphragm 33 is provided such that: the porous layer faces the
anode 31a; and the fabric layer faces the cathode 32a. If the
diaphragm 33 is provided such that the fabric layer faces the anode
31a, oxygen generated at the anode 31a adheres to the fabric layer
of the diaphragm 33, and this increases the electrical resistance
of the diaphragm 33 and therefore decreases the electrolysis
efficiency. Thus, it is not preferable to provide the diaphragm 33
such that the fabric layer faces the anode 31a.
EXAMPLES
Example 1
[0060] A diaphragm according to Example 1 was obtained by a
nonsolvent induction phase separation method using, as the
hydrophilic polyether sulfone, polyether sulfone (Sumikaexcel
(trademark) 5003PS produced by Sumitomo Chemical Company, contact
angle of 65 to 74.degree., rate of hydroxyl group per polymer
repeating unit of 89%) having a hydroxyl group at its terminal and
also using, as the fabric, PPS non-woven fabric (Torcon paper
(trademark) PS0100 produced by Toray Industries, Inc., thickness of
0.21 mm, density of 0.48 to 0.55 g/cm.sup.3). Specifically, first,
the hydrophilic polyether sulfone was added to
N-methyl-2-pyrrolidone (produced by Daishin Chemical Co., Ltd.) at
a concentration of 15 wt. % and stirred for 24 hours to obtain an
adequately uniform solution. The solution was left at rest for 24
hours to adequately remove bubbles from the solution. Thus, the
membrane forming solution was prepared. Next, fabric was spread on
a glass plate, and the membrane forming solution was applied to the
fabric at a uniform thickness. The glass plate to which the
membrane forming solution was applied was then immersed in the
chemical liquid (water) to remove the organic solvent. The fabric
was then removed from the glass plate. Thus, the diaphragm was
obtained. The thickness of the diaphragm according to Example 1 was
500 to 700 .mu.m.
Example 2
[0061] A diaphragm according to Example 2 was obtained by a
nonsolvent induction phase separation method using polysulfone
(Ultrason (trademark) S6010 produced by BASF Japan Ltd., molecular
weight of 50,000, contact angle of 85 to 90.degree., rate of
hydroxyl group per polymer repeating unit of 0) and PPS non-woven
fabric (Torcon paper (trademark) PS0100 produced by Toray
Industries, Inc.). Specifically, the polyether sulfone was added to
N-methyl-2-pyrrolidone (produced by Daishin Chemical Co., Ltd.) at
a concentration of 15 wt. %, and the membrane forming solution was
prepared in the same manner as in Example 1. By using this membrane
forming solution, the diaphragm was obtained in the same manner as
in Example 1. The thickness of the diaphragm according to Example 2
was 500 to 700 .mu.m.
REFERENCE EXAMPLES
[0062] In Reference Examples, polymer porous membranes simulating
the porous layer constituting the diaphragm for the alkaline water
electrolyzer were produced.
Reference Example 1
[0063] A polymer porous membrane according to Reference Example 1
was obtained by a nonsolvent induction phase separation method
using polyether sulfone (Sumikaexcel (trademark) 5003PS produced by
Sumitomo Chemical Company) having a hydroxyl group at its terminal.
Specifically, first, the hydrophilic polyether sulfone was added to
N-methyl-2-pyrrolidone (produced by Daishin Chemical Co., Ltd.) at
a concentration of 15 wt. % and stirred for 24 hours to obtain an
adequately uniform solution. The solution was left at rest for 24
hours to adequately remove bubbles from the solution. Thus, the
membrane forming solution was prepared. Next, the membrane forming
solution was uniformly applied to a smooth glass plate at a
predetermined thickness. The glass plate to which the membrane
forming solution was applied was then immersed in a chemical liquid
(water) to remove the organic solvent. The formed membrane was
removed from the glass plate. Thus, the polymer porous membrane was
obtained. The thickness of the polymer porous membrane according to
Reference Example 1 was 150 to 250 .mu.m.
Reference Example 2
[0064] A polymer porous membrane according to Reference Example 2
was obtained by a nonsolvent induction phase separation method
using polysulfone having a sulfonate group. Specifically, the
hydrophilic polysulfone was added to N-methyl-2-pyrrolidone
(produced by Daishin Chemical Co., Ltd.) at a concentration of 15
wt. %, and the membrane forming solution was prepared in the same
manner as in Reference Example 1. By using this membrane forming
solution, the polymer porous membrane was obtained in the same
manner as in Reference Example 1. The thickness of the polymer
porous membrane according to Reference Example 2 was 150 to 250
.mu.m.
Reference Example 3
[0065] A polymer porous membrane according to Reference Example 3
was obtained by a nonsolvent induction phase separation method
using polysulfone (Ultrason (trademark) S6010 produced by BASF
Japan Ltd.). Specifically, the polyether sulfone was added to
N-methyl-2-pyrrolidone (produced by Daishin Chemical Co., Ltd.) at
a concentration of 15 wt. %, and the membrane forming solution was
prepared in the same manner as in Reference Example 1. By using
this membrane forming solution, the polymer porous membrane was
obtained in the same manner as in Reference Example 1.
Comparative Example
[0066] As Comparative Example 1 for comparison with Examples and
Reference Examples, a commercially available fluorine-based
ion-exchange membrane (Flemion (trademark) F8020SP produced by
Asahi Glass Co., Ltd.) mostly used in chlor-alkali process to
manufacture chlorine caustic soda was used.
[0067] Performance Test of Diaphragm
[0068] Performances of the diaphragms according to Examples 1 and 2
and performances of the polymer porous membranes according to
Reference Examples 1, 2, and 3 were measured by a testing apparatus
50 schematically shown in FIG. 4. The testing apparatus 50 includes
the electrolysis cell 30, an electrolytic solution storage tank 51,
a DC power supply device 65, a computer 66, and the like. A KOH
aqueous solution that is the electrolytic solution is generated and
stored in the electrolytic solution storage tank 51. The
electrolytic solution is supplied from the electrolytic solution
storage tank 51 through a pipe 55 to the anode chamber 48 of the
electrolysis cell 30. Further, the electrolytic solution is
supplied from the electrolytic solution storage tank 51 through a
pipe 58 to the cathode chamber 49 of the electrolysis cell 30. By
control of the computer 66, a predetermined DC current flows from
the DC power supply device 65 to the electrodes of the electrolysis
cell 30. Although not shown, the testing apparatus 50 includes: a
voltmeter configured to measure a voltage between the anode 31a and
cathode 32a of the electrolysis cell 30; and an overvoltage
measuring device configured to measure oxygen overvoltage and
hydrogen overvoltage. Measurement results of the voltmeter and the
overvoltage measuring device are analyzed by the computer 66.
Oxygen is generated by water electrolysis in the anode chamber 48
of the electrolysis cell 30, and the KOH aqueous solution and the
oxygen are discharged from the anode chamber 48 through a pipe 61.
Hydrogen is generated by water electrolysis in the cathode chamber
49 of the electrolysis cell 30, and the KOH aqueous solution and
the hydrogen are discharged from the cathode chamber 49 through a
pipe 62. The oxygen concentration of the discharged hydrogen and
the hydrogen concentration of the discharged oxygen are measured by
a concentration measuring device (not shown).
[0069] The electrolytic solution (KOH aqueous solution) supplied
from the electrolytic solution storage tank 51 to the electrolysis
cell 30 had a concentration of 25 wt. % and a temperature of
80.degree. C. Regarding the electrodes of the testing apparatus, a
pure nickel mesh was used as the anode, and an active cathode for
hydrogen generation was used as the cathode. The density of the
current supplied from the power supply device 65 to the
electrolysis cell 30 was 40 A/dm.sup.2. A cell voltage, the
hydrogen concentration of the generated oxygen, the oxygen
concentration of the generated hydrogen, the oxygen overvoltage,
and the hydrogen overvoltage were measured in the testing apparatus
50 configured as above. The cell voltage was measured by a cell
voltage measuring device. In the performance tests of the
diaphragms according to Examples 1 and 2, the electrolysis cell 30
in which an electrolysis area of the electrolysis tank was 1
dm.sup.2 was used. In the performance tests of the diaphragms
according to Reference Example 1, 2, and 3, the electrolysis cell
30 in which the electrolysis area of the electrolysis tank was 0.2
dm.sup.2 was used.
[0070] Table 2 shows measurement results regarding an average cell
voltage, the hydrogen concentration of the generated oxygen, the
oxygen concentration of the generated hydrogen, and water
permeability (permeated water flow rate) when each of the
diaphragms according to Examples 1 and 2 and the ion-exchange
membranes according to Comparative Example 1 was applied to the
testing apparatus 50, and the alkaline water electrolysis was
performed for 2,000 hours. The average cell voltage shown in Table
2 was obtained in such a manner that: each measured value was
corrected as a voltage value at 80.degree. C.; and a difference
between each corrected value and a corrected value of Comparative
Example 1 was calculated. The water permeability of each of the
alkaline water electrolysis diaphragms according to Examples, the
ion-exchange membrane according to Comparative Example, and the
polymer porous membranes according to Reference Examples is
represented by the permeated water flow rate measured using a
filtration device (stirring type ultra holder UHP-43K produced by
ADVANTEC). The filtration device is configured such that permeated
water is obtained by applying predetermined water pressure to the
membrane using a gas bomb. The membrane (the alkaline water
electrolysis diaphragm, the ion-exchange membrane, or the polymer
porous membrane) was placed at a predetermined position of the
filtration device, and water pressure of 0.2 MPa was applied to the
membrane using inert (nitrogen) gas for 10 to 20 seconds, and as a
result, the permeated water was generated. During this operation,
the flow rate of the permeated water was measured three times using
an electronic balance, and an average value of the measured flow
rates of the permeated water was regarded as the permeated water
flow rate. The water permeability of the membrane was evaluated
based on this permeated water flow rate. Therefore, the water
permeability was a value calculated using the gas pressure, the
area of the membrane, the measurement time, and the permeated water
flow rate.
TABLE-US-00002 TABLE 2 Comparative Example 1 Example 1 Hydrophilic
Example 2 Ion-exchange polyether sulfone + Polysulfone + PPS
membrane for brine PPS nonwoven fabric nonwoven fabric electrolysis
Average cell voltage [V] -0.38 -0.35 0 (difference from Comparative
Example 1) Average hydrogen 0.03 0.06 0.14 concentration of
generated oxygen [%] Average oxygen 0.06 0.08 0.05 concentration of
generated hydrogen [%] Water permeability 5,400 2,900 0
[l/m.sup.2/h/atm]
[0071] As is clear from Table 2, the cell voltage in each of
Examples 1 and 2 is lower than that in Comparative Example 1. To be
specific, the electrolysis efficiency when the diaphragm of Example
1 or 2 is used as the diaphragm of the alkaline water electrolyzer
is higher than that when the ion-exchange membrane of Comparative
Example 1 is used. Further, in Examples 1 and 2, both the average
oxygen concentration of the generated hydrogen and the average
hydrogen concentration of the generated oxygen are not more than
0.1%, that is, low values. To be specific, the diaphragm according
to each of Examples 1 and 2 has an adequately high gas barrier
property as with the ion-exchange membrane according to Comparative
Example 1. Especially, the gas barrier property of the diaphragm
according to Example 1 is more excellent than that of the diaphragm
according to Example 2. Although the water permeability in
Comparative Example 1 is zero, each of Examples 1 and 2 has the
water permeability. As above, since the diaphragm according to each
of Examples 1 and 2 has the high gas barrier property and the water
permeability, it is preferable as the diaphragm of the alkaline
water electrolyzer.
[0072] FIG. 5 shows measurement results regarding the cell voltage,
the oxygen overvoltage, and the hydrogen overvoltage when the
diaphragm according to Example 1 was applied to the testing
apparatus 50, and the water electrolysis was performed for 2,000
hours. In FIG. 5, a vertical axis shows the cell voltage (V) and
the overvoltage (mV), and a horizontal axis shows an electrolysis
time (h). After 60 to 84 hours from the start of the test, the
average cell voltage shown in FIG. 5 is -0.34 V with respect to
Comparative Example 1. After 2,089 to 2,113 hours from the start of
the test, the average cell voltage shown in FIG. 5 is -0.38 V with
respect to Comparative Example 1. As above, the cell voltage is
maintained at a relatively low value in a long-time operation
(2,000 hours or more). Further, the oxygen overvoltage and the
hydrogen overvoltage are also maintained at relatively low values
in a long-time operation (2,000 hours or more). An electrolysis
voltage is represented by a sum of a theoretical electrolysis
voltage, an overvoltage, and solution resistance. This shows that
since the low solution resistance of the diaphragm according to
Example 1 is maintained, the relatively low cell voltage (i.e.,
high electrolysis efficiency) is maintained.
[0073] Table 3 shows measurement results regarding the average cell
voltage, the average hydrogen concentration of the generated
oxygen, and the water permeability (permeated water flow rate) when
each of the polymer porous membranes according to Reference
Examples 1, 2, and 3 and the ion-exchange membrane according to
Comparative Example 1 was applied as the diaphragm to the testing
apparatus 50, and the water electrolysis was performed for 72
hours. The average cell voltage shown in Table 3 was obtained in
such a manner that: each measured value was corrected as a voltage
value at 80.degree. C.; and a difference between each corrected
value and a corrected value of Comparative Example 1 was
calculated.
TABLE-US-00003 TABLE 3 Reference Comparative Example 1 Reference
Example 1 Hydrophilic Example 2 Reference Ion-exchange polyether
Hydrophilic Example 3 membrane for brine sulfone polysulfone
Polysulfone electrolysis Average cell voltage [V] -0.38 -0.33 -0.26
0 (difference from Comparative Example 1) Average oxygen 0.10 0.17
0.08 0.15 concentration of generated hydrogen [%] Water
permeability 2,900 4,200 3,100 0 [l/m.sup.2/h/atm]
[0074] As is clear from Table 3, the cell voltage of each of
Reference Examples 1, 2, and 3 is lower than that in Comparative
Example 1. To be specific, the electrolysis efficiency when the
polymer porous membrane of each of Reference Examples 1, 2, and 3
is used as the diaphragm of the alkaline water electrolyzer is
higher than that when the ion-exchange membrane according to
Comparative Example 1 is used. Therefore, the electrolysis
efficiency when the diaphragm including the porous layer having the
same components as the polymer porous membrane of any of Reference
Examples 1, 2, and 3 is used in the alkaline water electrolyzer can
be expected to be higher than that when the ion-exchange membrane
according to Comparative Example 1 is used as the diaphragm.
[0075] The average oxygen concentration of the generated hydrogen
in each of Reference Examples 1 and 3 is lower than that in
Comparative Example 1. The average oxygen concentration of the
generated hydrogen in Reference Example 2 is slightly higher than
that in Comparative Example 1. However, the average oxygen
concentration of the generated hydrogen in Reference Example 2 is a
preferable value for the diaphragm of the alkaline water
electrolyzer. To be specific, the polymer porous membrane according
to each of Reference Examples 1, 2, and 3 has the gas barrier
property that is adequately high for the diaphragm of the alkaline
water electrolyzer. Although the water permeability in Comparative
Example 1 is zero, each of Reference Examples 1, 2, and 3 has the
water permeability. Therefore, the diaphragm including the porous
layer having the same components as the polymer porous membrane of
any of Reference Examples 1, 2, and 3 can be expected to have both
the preferable gas barrier property and water permeability for the
diaphragm of the alkaline water electrolyzer.
[0076] FIG. 6 shows measurement results regarding the cell voltage
when the polymer porous membrane according to Reference Example 1
was applied as the diaphragm to the testing apparatus 50, and the
water electrolysis was performed for 72 hours. FIG. 7 shows
measurement results regarding the cell voltage when the polymer
porous membrane according to Reference Example 2 was applied as the
diaphragm to the testing apparatus 50, and the water electrolysis
was performed for 72 hours. In the graphs of FIGS. 6 and 7, a
vertical axis shows the cell voltage (V), and a horizontal axis
shows the electrolysis time (h). It is clear from FIGS. 6 and 7
that when the polymer porous membrane according to each of
Reference Examples 1 and 2 is used as the diaphragm, and the
alkaline water electrolysis is performed, a relatively low cell
voltage, that is, high electrolysis efficiency is maintained for 72
hours.
REFERENCE SIGNS LIST
[0077] 1 membrane forming apparatus [0078] 2 unwinding drum [0079]
3, 4, 7, 11 guide roller [0080] 5 coating unit [0081] 6 chemical
liquid tank [0082] 8 driving roller [0083] 9 nip roller [0084] 10
slitter [0085] 12 winding drum [0086] 13 water tank [0087] 30
electrolysis cell [0088] 31 anode assembly [0089] 31a anode [0090]
31b anode frame [0091] 31c connecting terminal [0092] 32 cathode
assembly [0093] 32a cathode [0094] 32b cathode frame [0095] 32c
connecting terminal [0096] 32d elastic body [0097] 33 diaphragm
[0098] 35 electrolysis tank [0099] 48 anode chamber [0100] 49
cathode chamber [0101] 50 testing apparatus [0102] 51 electrolytic
solution storage tank [0103] 90 alkaline water electrolysis
diaphragm [0104] 91 polymer porous layer [0105] 92 organic fiber
fabric layer [0106] 93 mixed layer
* * * * *