METHOD OF BONDING ELECTRODE TO CATION EXCHANGE MEMBRANE

METHODE DE LIAISONNEMENT D'UNE ELECTRODE A UNE MEMBRANE ECHANGEUSE DE CATIONS

English Abstract

ABSTRACT OF THE DISCLOSURE
A cation exchange membrane made of a fluorinated
polymer is used in a form of ion exchange groups having the
formula <IMG>, wherein X represents an alkali metal atom,
an alkaline earth metal atom or -NRR' and R and R' respectively
represent hydrogen atom or a lower alkyl group; and m is a
valence for the group X. The membrane in the form of ion :
exchange groups having the formula -COOL, wherein L represents
hydrogen atom or a C1-C20 alkyl group, is melt-bonded to said
electrode and then, converting the ion exchange groups in the
form of -COOL into the ion exchange groups in the form of
<IMG>.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a method of bonding an electrode having a porosity
of 30 to 99% to a cation exchange membrane made of a fluorinated
polymer which is in a form having ion exchange groups having the
formula <IMG> wherein X represents an alkali metal atom, an
alkaline earth metal atom or NRR' and R and R' respectively re-
present hydrogen atom or a lower alkyl group, the ion exchange
capacity of carboxylic acid groups of said cation exchange membrane
being in a range of 0.5 to 2.5 meq/g. dry polymer; and m is a
valence for the group X, the improvement in which said membrane in
the form having ion exchange groups having the formula -COOL,
wherein L represents hydrogen atom of a C1-C20 alkyl group, is
melt-bonded to said electrode and then, the ion exchange groups
in the form of -COOL are converted into the ion exchange groups in
the form of <IMG>.
2. The method according to claim 1, wherein said elec-
trode is porous having a gas and liquid permeability, an average
pore diameter of from 0.01 to 100µ, and a thickness of 0.1 to 100µ.
3. The method according to claim 2, wherein said elec-
trode is a porous anode obtained by binding a powder of a platinum
group metal, or an electrically conductive oxide thereof or a
heat stabilized reduced oxide with a binder.
4. The method according to claim 2, wherein said elec-
trode is a porous cathode obtained by bonding a powder of a plati-
num group metal, an electrically conductive oxide thereof, an iron
group metal or Raney nickel with a binder.
5. The method according to claim 3 or 4, wherein said
binder is a fluorinated polymer.
18

6. The method according to claim 1, wherein said
cation exchange membrane is made of a fluorinated polymer
having the units
<IMG>
<IMG>
wherein X represents fluorine, chlorine or hydrogen atom or
-CF3; X' represents X or CF3(CF2)m; m represents an integer of
1 to 5; Y represents the following unit; <IMG> , <IMG> ,
<IMG> , <IMG> , <IMG>
and <IMG>
x, y and z respectively represent an integer of 1 to 10; Z and
Rf represent -F or C1-C10 perfluoroalkyl group; and A repre-
sents a functional group which is convertible into the group
having the formula <IMG> in the electrolysis.
7. The method according to claim 1 or 6, wherein
said cation exchange membrane is made of a perfluoropolymer.
8. The method according to claim 1, wherein said
cation exchange membrane is melt-bonded to said electrode with
the surface layer having ion exchange groups in the form of
-COOL in a thickness of at most 50µ.
9. The method according to claim 1, wherein the
bonding part of said cation exchange membrane bonded to said
electrode is melted at a melt-viscosity of from 102 to 109
poise.
10. The method according to claim 1, 8 or 9, wherein
the bonding part of said cation exchange membrane bonded to
said electrode is heated at 100 to 330°C and is bonded under
a pressure of 0.01 to 1000 kg/cm2.
19

11. The method according to claim 1, 8 or 9,
wherein said bonding is carried out by a heating means of a
press-heating device, an ultrasonic heating device, an impulse
heating device, a friction heating device or a high frequency
heating device.
12. The method according to claim 1, 2 or 3, in
which the molecular weight of the fluorinated polymer is in
the range of from 1 x 105 to 2 x 106.
13. The method according to claim 1, 2 or 3, in
which the molecular weight of the fluorinated polymer is in
the range of from 1.5 x 105 to 1 x 106.
14. The method according to claim 1, wherein said
electrode is formed with an electric conductive powder and
a binder and said hinder is bonded to said cation exchange
membrane in the form of ion exchange groups having the formula
-COOL.
15. The method according to claim 14, wherein said
binder is a fluorinated polymer.

Description

1 171~26
The present invention relates to a method of bonding
an electrode to a cation exchange membrane. More particularly,
the present invention relates to a method of bonding a porous,
gas permeable, catalytic electrode to a cation exchange membrane
made of a fluorinated polymer having carboxylic acid groups as
cation exchange groups which is used in an electrolytic cell in
the production of an alkali metal hydroxide by electrolysis
of an aqueous solution of an alkali metal chloride at low
voltage and high current efficiency.
For the production of an alkali metal hydroxide by the
electrolysis of an aqueous solution of an alkali metal chloride,
the diaphragm method has been mainly employed instead of the
mercury method to avoid pollution of public facili-ties.
It has been proposed to use an ion exchange membrane in place of
asbestos as the diaphragm to produce the alkali metàl hydroxide
by electrolyzingan aqueous sol-ution of an alkali metal chloride so
as to obtain an alkali metal hydxoxide having high purity and
high concentration. It is of course always desirable to conserve
energy and thus it is desirable to minimize the cell voltage in
~such technology. Varlous methods have been proposed to decrease
the cell voltage. It has been proposed to improve materials,
components, shapes, and configurations of an anode and~a cathode
or to select a formulation and a type of ion exchange membrane.
These improvements have had a certain success. Most of them,
however, have disadvantages that the maximum concentration of an
alkali metal hydroxide obtained is not high and a substantial
increase in cell voltage or decrease in current efficiency occurs
in the case of an excess of concentration of the alkali metal
hydroxide over the maximum range and the durability of a low
cell voltage are not satisfactory. Thus, they have not been
always satisfactory for an industrial process.
It has heen also proposed to effect the electrolysis

0 2 ~
using a cation exchange membrane made o~ a fluorinated polymer
bonded to gas-liquid permeable catalytic anode on one surface
and a gas~liquid permeable catalytic cathode on the other
surface of the membrane (British Patent ~,009,795). This method
is very advantageous for the electrolysis a-t a lower cell
voltage because the electrical resistance caused by the electro-
lyte and the electric resistance caused b~ bubbles of hydrogen
gas and chlorine gas generated in the electrolysis, can be
substantially decreased which it has been considered to be
difficult to reduce in the electrolysis.
When a cation exchange membrane made of a fluorinated
polymer having carboxylic acid groups or sulfonic acid groups,
especially carboxylic acid groups, is used for said electrolysis
as an ion exchange membrane, an alkali metal hydroxide having.
a high concentration can be produced at a low cell voltage and
a high current efficiency. One of the important factors for
such an advantageous effect is to uniformly and firmly bond the
catalytic electrodes to the cation exchange membrane made of
a fluorinated polymer having carboxylic acid groups. When they
are not satisfactorily bonded or the bonding strength is low,
the cell voltage is increased or the electrodes arepeeled off
frorn the membrane by a gas generation at the interface of elec
trode and membrane. ~n adhesive is considered for bonding them.
~ost adhesives are poorly conductive and increase the elec-trically
resistance. No adhesive effective for bonding an electrode
to the cation exchange membrane made of a fluorinated polymer
has been suggested. The me~.t-bonding method has been considered
in which the surface of the membrane is partially melted to
bond to the electrode.
When a cation exchange membrane made of a fluorinated
polymer having carboxylic ac.id groups is used, it has been found
that the electrode is not satisfactorily bonded to the membrane

! ~ 71026
or the required satisfactory electrolytic characteris-tlcs are
not attained even though the membranes can be bonded, if the
form of carboxyllc aci.d yroups of the membrane is not appropxiate.
Such disadvantage has been found in the case that the membrane
having carboxylic acid groups having the formula ~~~C~ m X
is melt-bonded to the electrode wherein X represents an alkali
metal or alkaline earth metal atom or -NRR'; R and R' respectively
represent hydrogen atom or a lower alkyl group; and m is a valence
for X.
The present invention provides a method of bonding
an electrode to a cation exchange membrane without substantially
reducing the electrolytic characteristics and uniformly and
firmly contacting them without increasing the electric resistance.
According to the present invention there is provided ~n
a method of bonding an electrode to a cation exchange membrane
made of a fluorinated polymer whlch is used in a form of ion
exchange groups having the formula ( COO ~ X, wherein X
represents an alkali metal atom, an alkaline earth metal atom or
-NRR' and~R and R' respectively represent hydrogen atom or a
lower alkyl group; and m i5 a ~alence for the group X,
improvement in which said memhrane in the form of ion exchange
groups having the formula COOL, wherein L represents hydrogen
atom or a Cl-C20 alkyl group, is melt-bonded to said electrode
and then, the ion exchange groups in the form of -COOL are
converted into the ion exchange groups in the form of~ COO ~ X.
Thus, in accordance wi.th the present invention the
cation exchange membrane having the ion exchange groups in a
form of -COOL.wherein L represents hydrogen atom or a Cl - C
alkyl group .is bonded to the electrode.
The cation exchange membrane made of a fluorinated
polymer having carboxylic acid groups as ion exchange groups
bonded to the porous gas-liquid permeable electrode has the ion

2 6
exchange groups havin~ the ~ormula ( COO ~ X, where.in m and X
are defined above, for.use ~n the electrolysis of an aqueous
solution of an alkali metal chloriae. In the electrolysis, X
is preferably the same alkali metal atom as that of the alkali
metal chloride forming the electrolyte, The ion exchange capacity
of carboxylic acid groups is important since it relates to the
characteristics of the membrane in the electrolysis, and depends
upon the types of the fluorinated polymer forming the membrane,
and is preferably in a range of 0.5 to 2.5 meq/g. dry polymer
especially 1.0 to 2.0 meq/g. dry polymer in view of electrochemical
characteristics and mechanical characteristics. The cation
exchange membrane is preferably made of a fluorinated polymer
having the following units:
~- CF2-CXX '
CF2- 1 X
wherein X represents fluorine, chlorine or hydrogen atom or
-CF3; X' represents X or CF3(CF2 )m ; m represents an integer
of 1 to 5.
Typical examples of Y have the structures bonding A to
a fluorocarbon group such as
CF2 ~ A, -O-~-CF2 ~ A, --t--O--CF2-1F ~ A,
-CF----~O-CF2-CF ~ A, ~--O-CF2-ICF -tx--~O-CF2-ICF--ty--Aand
Z Z Rf
-O-CF2~ IF-o-cF2~cF2~ CF2-0-CF~A
x, y and z respectively represent an integer of 1 to 10; Z and
Rf represent -F or a Cl - C10 perfluoroalkyl group; and A
represents a functional group which is convertible to--~COO ~ X
during the electrolysis.
The N mole % of the units of- ( CF2 - CX~- is preferably

~ :~ 7~026
in a range of 1 to 40 mole % especially 3 to 25 mole % in view
of the above-mentioned ion exchange capacity of -the membrane.
The molecular welght of the fluorinated polymer for
the cation exchange membrane used in the present invention is
important since it relates to the electrochemical characteristics
of the resulting rnembrane. The molecular weight of the fluorin-
ated polymer is preferably in the range of 1 x 105 to 2 x 106,
especially 1.5 x 105 to 1 x 106.
In the production of the perfluoro polyer, various
processes can be employed.
In the preparation of such perfluoro polymer, one or
more monomers for forming -the-units (~) and (N) can be used, if
necessary, with a third monomer so as to improve the
characteristics of the membrane. For example, the flexibility
of the membrane can be improved by incorporating CF2 = CFORf (Rf
is a Cl - C10 perfluoroalkyl group), or the mechanical strength
of the membrane can be improved by crosslinking the copolymer
with a divinyl monomex such as CF2=CF-CF=CF2 or CF2=CFO(CF2)1 3
CF=CF2.
The copolymerization of the ~luorinated olefin monomer
and a monomer having carboxylic acid group or a functional group
which is convertible into carboxylic acid group and, if necessary,
,.~i; '~f~ d fS~ er~ c~ f~e.
.~ the ~ r monomer/can be carried out by a conventional process.
The polymerization can be carried out if necessary, using a
solvent such as halohydrocarbons by catalytic polymerization,
thermal polymerization or radiation-induced polymerization.
The particular me-thod of fabrication of the ion exchange
membrane from the resulting copolymer is not critical, for
example it can be a conventional method such as the press-moulding
3U method, the roll-molding method, the extrusiQn-moulding method,
the solution spreading method, the dispersion molding method or
the powder moldiny method. The thickness of the membrane is

2 6
preferably 20 to 600 microns especially 50 to 400 microns. The
cation exchange membrane used in the present invention can be
fabricated by blending a polyolefin such as polyethylene, poly-
propylene, preferably a fluorinated polymer such as polytetra-
fluoroethylene and a copolymer of ethylene and tetrafluoroe-thylene.
The ~embrane can be reinforced by supporting said
copolymer on a fabric, such as a woven fabric or a net, a non-
woven fabric or a porous film made of said polymer to be blended.
The weight of the polymers for the blend or the suppoxt is not
considered in the measurement of the ion exchange capacity.
When the functional groups of the ca-tion exchange
membrane for bonding to the electrode are in the form of -COOL
(L is defined above), the-membrane can be bonded to the electrode
without any modification. When the functional groups of the
membrane are in the form of ( COO ~ X, (X and m are defined
above), the groups are converted into the groups in the form of
-COOL (L is defined above).
The conversion of the ion exchange groups into the
form of -COOL need not be effected in the whole of the membrane
and only t~le surface layer bonding to the electrode need to be
converted, preferably in a thickness oE less than 30~ , especially
less than 50~. The method of conversion of the ion exchange
~'C'LIpS~
groups may be selected depending upon the type of the ~u~ X
and L. For example, ln order to convert the ion exchange groups
into -COO~I groups, the membrane is brought into contact with an
aqueous solution of an inorganic acid or an organic acid,
preferably in the presence of a polar organic compound. The
inorganic acid may be hydrochloric acid, sulfonic acid, nitric
acid and phosphoric acid. The organic acid may be acetic
acid, propionic acid, perfluoroacetic acid, and p-toluenesulEonic
acid. The acid is usually used as an aqueous solution having a
concentration of 0.5 to 90 wt.%.
--6~

2 6
The polar organic compound which is ~t-i-eé~ added,
may be methanol, ethanol, propanol, ethyleneglyco], dimethyl-
sulfo~ide, acetic acid and phenol. The polar organic acid is
preferably added to the aqueous solution of the acid at a
concentra~ion of 5 to 90 wt.%. The contacting trea-tment of the
membrane with the aqueous solu-tion of the acid is preferably
carried out at 10 to 120~C for 30 minutes to 20 hours.
When the ion exchange groups are converted into -COOL
groups wherein L is a Cl - C20 alkyl group, the groups are
converted into the acid form and then, further converted into
khe ester form by reaction with the corresponding alcohol. The
acid form can be also converted into the acid halide form by
~ l osf~J~o r .~5
reaction with ~s~h3r~s trichloride or phosphorus oxychloride,
and then converted into the ester form by reaction with an
alcohol. The groups in the acid form can be also converted into
the aeid anhydride form by reaction with acetic anhydride or
perfluoroacetic anhydride and then converted into the groups in
the ester form by reaction with an alcohol. If necessary, the
mem~rane (-~-COO ~ ~ type ) is treated with a chloride, sueh as
~0 thionyl chloride, phosphorus trichloride, phosphorus oxychloride,
at 0 to 120C for 1 to 25 hours so as to convert the groups
--~ COO ~ X into the groups in the form of acid anhydride and
then, is treated with an alcohol to convert the groups in the
ester form. The membrane (-~-COO ~ X type ) can be treated
in:an alcohol in the presence of the organic acid or -the inorganie
acid to convert the groups of -~COO ~ X into the groups of
-COOL. The aleohol used for the esterifieation of the acid, the
acid halide or the acid anhydride is preferably a Cl - C20
aleohol, sueh as methanol, ethanol, propanol, butanol, dodeeyl
alcohol and sebaeyl aleohol. In the esterification, the membrane
can be dippea into an aqueous solution of an inorganic acid or
organie acid which is the sarne or different from the acid used for

the conversion of the groups of ~ COO -~m--X. The di.pping
treatment is preferably carried out at 30 to 120C for 30 minutes
to 40 hours.
When the cation exchanye membrane made of a fluorinated
polymer havi.ng the groups of -COOL is bonded to th~ electrode,
it is pre*erable to have a desired melt-viscosity in the molten
state. It has been found that the desired melt-viscostiy is usu-
ally in a range of 102 to 101 poise, preferably 103 to 109 poise.
The membrane is melted under the appxopriate conditions of a
temperature and a pressure so as to give the desired melt-viscosity.
When the pressure is high, the temperature can be lower. How-
ever, ~hen the pressure is low, the temperature should be high.
. When the ion exchange groups of the membrane are in the
form of -COOL, the decomposition temperature of the fluorinated
polymer (the temperature at which 5~ of a weight loss of the poly-
mer occurs in raising the temperature at a rate of 10C/min. in an
N2 atmosphere) is in a range of 350 to 370C. Therefore, the de-
composition of the fluorinated polymer of the membrane is not
caused by bonding the pOI OUS electrode to the membrane. Although
parts of the membrane intrude into the pores on the surface o~ the
electrode in the bonding, the porous electrode is not damaged and
maintains the stable bonding for a long time, and maintains the
low cell voltage stable for a long time.
In bonding the electrode to the surface of the cation
exchange membrane made of a fluorinated polymer the surface of
the membrane is heated to about lO0 to 330C preferahly about 120
to 300C. It is sufficient to apply a pressure of from 0.01 to
1000 kg/cm2, preferably l to 300 kg/cm2 to the bonding area. The
means for heating in the bonding step may be a press-heating device,
an ultrasonic wave heating device, an impulse heating device and a

~ ~71~26
~riction heating device. When the membrane is in the form of
-COOH, it is possible to use a high frequency heating device.
In order to improve the bonding strength, it is
possihle to pretreat the surface of the membrane, for example b~
a sand-blast treatment of the bonding surface or applying a coating
of a swelling agen-t or a solvent for the fluorinated polymer
(-COOL type) on the bonding surface. The bonding conditions
depends upon the bonding method, the type of the fluorinated
polymer forming the membrane and the thickness of the membrane.
For example/ with the impulse heating device, the bonding
operation is carried out at a temperature from 130 to 350C under
a pressure of 0.1 to 300 kg/cm2 for 30 seconds to 1 hour.
In the present invention, at least one of the anode
and the cathode is bonded to the cation exchange membrane. It
is sufficient to convert the groups on the bonding surface into
the groups in the form of -COOL in the case of bonding the
electrode on only one surface of the membrane. The electrode
bonded to the membrane should have a permeability for the gas
generated by the electrolysis and the electrolyte. In order to
have such a property, the electrode should be a porous substrate,
preferably a layer having a thickness of 0.1 to 100~, especially
1 to 50 ~. In such a porous electrode, the pore diametèr, the
porosity and the air permeability should be in the desired
ranges. The electrodes used as the anode and the cathode
preferably have an average porosity of 0.01 to 100~ and a porosity
o~ 30 to 99%. When the average pore diameter and the porosity
are less than said ranges, the gas, such as hydrogen and
chlorine, generated by the electrolysis are not easily removed
from the electrode causing high electric resistance~ When they
are above said ranges, the electric resistance is disadvantageously
large. When the average pore diameter is in the range of 0.1 to
501J, and the porosity is in the range o 35 to 95 %, the gas

2¢
is easily removed ~rom the electrode and the electric resistance
may be small. Stable operation can be continued for a long time.
The substances for forming the porous electrodes may
be as follows:-
The substances suitable for the anode include platinumgroup metals such as Pt, Ir, Pd and Ru, alloys thereof and oxides
of the platinum group metal or alloy, a heat-stabilized reducible
oxide of the platinum group metal or alloy and graphite. When
the platinum group metal, the alloy or the oxide of the metal or
alloy is used for the anode, the cell ~oltage may be advantageously
decreased in the electrolysis of the alkali metal chloride.
The substances suitable for the cathode include platinum
group metals, alloys thereof, graphite, nickel, Raney nickel,
developed Raney nickel and stainless steel and iron group metals.
When the platinum group metal or the alloy or the Raney
nickel is used for the cathode, the overvoltage for forming hydro-
gen may be advantageously decreased in the electrolysis of water
or an aqueous solution of the alkali metal chloride.
The porous electrodes can be prepared from the above sub-
stances for the anode and cathode by the following processes.
The powdery substances having an average particle dia-
me~er of from 0.01 to lOOy, preferably 0.1 to 50~, is bound, if
necessary with a suitable binder. The binder is preferably a
fluorinated polymer especially polytetrafluoroethylene. An
aqueous dispersion of polytetrafluoroethylene having an average
diameter of less than 1~ is preferably used. The wei~ht ra~io of
the binder to the powdery substrate for the electrode is prefer-
ably in a range~of 0.05 to 5 wt. parts, especially 0.1 to 3 wt.
parts per 10 wt. parts of the powdery substance for the electrode.
When the weight ratio of binder is too high, the potential of the
electrode is disadvantageously high whereas when
-- 10 --

~ 3 71 0~
it is too low, the powdery substance of the electrode is dis-
advantageously separated~ In the preparation of the electrodes,
it is possible to incorporate a desired solvent or surfactant
so as to uniformly blend the powdery substance for the electrode
and the binder. It is also possible to incorporate an electri.c
conductive filler, such as graphite, or a water soluble additive,
such as carboxymethyl cellulose and polyvinyl alcohol. The
components are thoroughly mixed and deposited as a cake on a
filter by a filtering method. The cake is contacted with the
cation exchange membrane under pressure~ The mixture of the
components for the electrode can be prepared in a form of a paste
and the paste is coated on the cation exchange membrane. The
paste can be also coated on an aluminum foil and the paste layer
is contacted with the cation exchange membrane to form the
electrode layer on the membrane. The method of forming the elec-
.
trode layer on the cation exchange membrane disclosed in U.S.Patent 3,134,~97 can be employed.
The porous electrode layer on the cation exchange
membrane can be bonded on the membrane by the press-bonding
machine and the like according to this invention. A part of the
porou~ electrode layer is preferably embedded into the surface
layer of the membrane. The cation exchange membrane bonded to the
electrode is in the form of -COOL. The ion exchange groups in
the form of -COOL are converted into the groups in the form of
---t COO ~ X by suitable treatment such as a hydrolysis or a
neutralization.
The electrolytic cell having the electrode layers and
the cation exchange membrane may be a unipolar or bipolar type
electrolytic cell. As material for the electrolytic cell, a
material which is resistant to the aqueous solution of alkali
metal chloride and chlorine, such as titanium, is used for the
anode compartment and a material which is resistant to the alkali

~ 171~2~
metal hydroxide of high concentration and hydrogen, such as iron,
stainless steel or nickel, is used for the cathode compartment
in the electrolysis of an alkali metal chloride.
When the porous electrodes are used in the present
invention, each current collector for feeding the current i5
placed outside each electrode. The current collectors usually
have the same or higher overvoltage for chlorine or hydrogen
compared ~ith that of the electrodes. For example, the current
collector at the anode side is made of a precious metai or a
valve metal coated with a precious metal or oxide thereof and
-the current collector at the cathode side is made of nickel,
stainless steel or expanded metal in a form of a mesh or a net.
The current collectors are contacted with the porous electrodes
under a pressure.
In the present invention, the process condition for the
electrolysis of an aqueous solution of an alkali metal chloride
may be those conditions disclosed in the prior art, such as in
Brltish Patent 1,009,795.
~ For example, an aqueous solution of an alkali metal
chloride (2.5 to S.O Normal~ is fed into the anode compartment
and water or a dilute solution of an alkali metal hydroxide is
fed into the cathode compartment and the electrolysis is
preferably carried;out at ~0 to 120C and a current density of
10 to 100 A/dm .
In the electrolysis, calcium ions or magnesium ions or
the other heavy metal ions in the aqueous solu-tion of the alkali
metal chloride cause the deterioration of the cation exchange
membrane and accordingly, they should be reduced as far as
possible. In order to prevent the generation of oxygen in the
anode compartment, it is advantageous to incorporate an acid,
such as hydrochloric acid, in the aqueous solution of the alkali
metal chloride.
-12-
~. .

2 ~
The process for producing the alkali metal hydroxide
and chlorine by the electrolysis of the aqueous solution of the
alkali metal chloride has been illustrated. The present invention
is not limited to the embodiment and can be also applied for the
preparation of the cells for an electrolysis of water, an elec-
trolysis of a desired alkali metal salt, such as sodium sulfate
and a fuel cell.
The present invention will be further illustrated by
the following Examples and References.
EXAMPLE 1:
Platinum black powder was suspended in water and a
dispersion of polytetra1uoroèthylene (Teflon 30 J a trademark
of the ~u Pont Company) was~added at a weight ratio of poly-
tetrafluoroethylene to platïnum black of 1/10. A non-ionic
surfactant (Triton X-100 a~trademark of Rohm & E~aas Co.) was
added dropwise and the mixture was blended with an ultrasonifi-
cation whilst cooling with ice. The mixture was sucked on a
porous polytetrafluroèthylene membrane to provide a thin layer
made of platinum black (5 mg/cm2) for the anode. A thin layer
made of a stabilized Raney nickel (7 mg/cm2) for a cathode was
obtained by the same ~rocess.
A cation exchange membrane made of a copolymer of
2 2 CF2 CFO(CF2)3COOCH3 having an ion exchange
capacity of 1.45 meg/g. polymer and a thickness of 250~ was used.
Both the electrode layers were contacted with each of the surfaces
of the cation exchange membrane so as to each have a porous
polytetrafluoroethylene membrane on the outer surface. They
were heated and pressed at 150C under a pressure of 25 kg/cm2
to bond the electrode layers to the cation exchange membrane
and then,-the porous polytetrafluoroethylene membranes were
peeled off to obtain the cation exchange membrane bonding the
electrodes.

.. o ~ ~
The cation exchange memhrane bonding the electrodes was
dipped in 2S wt.~ of an aqueous solution of sodium hydroxide at
90C for 16 hours to hydrolyze the cation exchange membrane. A
nickel mesh (40 mesh) and a platinum mesh (40 mesh) as the current
collectors were respectively contacted with the anode and the
cathode under pressure.
The electrolysis was carried out whilst maintaining a
4 Normal concentration of sodium chloride in the anode compart-
ment and maintaining a 35 wt.% concentration of sodium hydroxide
as the catholyte by feeding water into the cathode compartment~
The results are as follows.
Current density Cell voltage (V)
(A/dm )
2.7~
2.84
3O06
3.27
The current efficiency for producing sodium hydroxide
at a current density of 20 A/dm was 94%. When the electrolysis
at 20 A/dm2 was continued for 100 days, the cell voltage remained
at the initial 2.85 V.
REFERENCE 1:
Thin layers as the cathode and the anode were prepared by
the process of Example 1. A cation exchange membrane made of a
copolymer of CF2 = CF2 and CF2 ~ CFO(CF2)3COOH3 having an ion
exchange capacity of 1.45 meq/g. polymer and a thickness of 250~
was used. Both of the electrode layers were heat-bonded on each
of the surfaces of the cation exchange membrane at 200C under a
pressure of 100 kg/cm to obtain the cation exchange membrane
having the electrodes on both surfaces.
In accordance with the process of Example 1, the electroly-
sis was carried
- 14 -

` ~ ~7~02~
out. The results are as follows.
Current density Cell voltage (V)
(A/dm2 )
2.85
3'05
3.31
3.60
The current ef~iciency for producing sodium hydroxide
at a current density of 20 A/dm2 was 91%. ~7hen the electrolysis
at 20 A/dm2 was continued for 10 days, the electrodes were
partially peeled off from the cation exchange membrane ~eeeby
being impossible to continue the electrolysis.
EXAMPLE 2:
A cation exchange membrane made of a copolymer of
CF2 = CF2 and CF2 = CFO(CF2)3COOCH3 having an ion exchange
capacity of 1.43 meg/g. polymer and a thickness of Z40~ ~Jas
dipped into a 25 wt.% aqueous solution of sodium hydroxide at
90C for 16 hours and then, it was aipped into lN-HCl. at the
ambient temperature for 24 hours and dried in air.
A paste A was prepared by blending 5 wt. parts of
platinum black powder having a particle diameter of less than
44~, 0.8 wt. part of 60 wt. % of aqueous dispersion of poly- ~-
tetrafluoroethylene (PTFE) having a particle diameter of less
than 1~ and 10 wt. parts of 1.5 wt.~ of aqueous solution of
carboxymethyl cellulose. The paste A was screen-printed on one
surface of the treated cation exchange membrane and the printed ~-
layer was dried in air to solifify the paste thereby forming an
anode layer containing platinum black in an amount of 2 mg/cm2.
A paste B was prepared by blending 5 wt. parts of
stabilized Raney nickel obtained by dissolving aluminum component
from Raney nickel alloy with a base and partially oxidizing it,
10 wt. parts of an aqueous solution of 1.5 wt.~ carboxymethyl
-15-

~ ~ 7:l~2~
cellulose and 0.8 wto parts of a 60 wt.% aqueous dispersion of
polytetrafluoroethylene. The paste B was screen-prin-ted on the
other surface of the treated cation exchange membrane thereby
forming a cathode layer containing stabilized Raney nickel in an
amount of 5 mg/cm2. The printed layers were bonded to the cation
exchange membrane at 165C under a pressure of 60 kg/cm and then,
dipped into a 25 wt.% aqueous solution of sodium hydroxide at
90C for 16 hours.
A platinum gauze (40 mesh) was contacted with the
platinum black layer and a nickel gauze (20 mesh) was contacted
with the stabilized Raney nickel layer under pressure.
The electrolysis was carried out whilst maintaining
a 4 Normal concentration of sodium chloride in the anode compart-
ment and maintaining a 35 wt.% concentration of sodium hydroxide
as the catholyte by feeding water into the cathode compartment.
The result 5 are as follows.
Current density Cell voltage (V)
tA/dm2 )
2.65
20 20 2.87
3.05
3.20
The current efficiency for producing sodium hydroxide
at a current density of 20 A/dm2 was 93%.
EXAMPLE 3:
Tlle cathode and anode thin layers were prepared by the
same process as in Example 1 except that polytetrafluoroethylene
was not added :in the electrode layer. Both of the electrode
layers which do not contain polytetrafluoroethylene as a binder
were heat-bonded on each surface of the cation exchange membrane
at 160~C under a pressure of 60 kg/cm . The cation exchange
membrane with electrode layers on both surface was obtained. In
-16~

~ :~ 7 10~,
accordance with the process and condition of Example 1, the
electrolysis was carried out. The results are as follows.
Current density (A/dm ) Cell voltage (V)
2.82
3.23
The current efficiency for producing sodium hydroxide
at a current density of 20 A/cm was 92%.
';
~17-