U.S. patent application number 15/246652 was filed with the patent office on 2018-02-22 for reinforced composite membrane for water electrolysis and membrane electrode assembly having the same.
The applicant listed for this patent is Elchemtech Co., Ltd.. Invention is credited to Yun Ki CHOI, Hye Young JUNG, Chang Hwan MOON, Sang Bong MOON, Dae Jin YOON.
Application Number | 20180051380 15/246652 |
Document ID | / |
Family ID | 59354423 |
Filed Date | 2018-02-22 |
United States Patent
Application |
20180051380 |
Kind Code |
A1 |
YOON; Dae Jin ; et
al. |
February 22, 2018 |
REINFORCED COMPOSITE MEMBRANE FOR WATER ELECTROLYSIS AND MEMBRANE
ELECTRODE ASSEMBLY HAVING THE SAME
Abstract
Disclosed is a reinforced composite membrane for water
electrolysis, and a membrane electrode assembly having the same.
More particularly, the present invention relates to a reinforced
composite membrane for water electrolysis, and a membrane electrode
assembly (MEA), wherein a two-dimensionally woven fabric base,
layer that, minimizes swelling of the membrane in the X-axis and
Y-axis directions is covered on a hydrogen electrode to which high
pressure is applied or on hydrogen and oxygen electrodes by
three-dimensionally electrospun reinforcing fiber layers, the
reinforcing fiber layers minimizing swelling of the membrane in the
Z-axis direction, thereby reducing permeation of oxygen (O.sub.2)
via the hydrogen electrode and enabling operation under high
pressure due to high dimensional stability.
Inventors: |
YOON; Dae Jin; (Gyeonggi-do,
KR) ; MOON; Sang Bong; (Seoul, KR) ; JUNG; Hye
Young; (Seoul, KR) ; MOON; Chang Hwan; (Seoul,
KR) ; CHOI; Yun Ki; (Seoul, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Elchemtech Co., Ltd. |
Seoul |
|
KR |
|
|
Family ID: |
59354423 |
Appl. No.: |
15/246652 |
Filed: |
August 25, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
Y02E 60/366 20130101;
C25B 1/10 20130101; C25B 13/08 20130101; Y02E 60/36 20130101 |
International
Class: |
C25B 13/08 20060101
C25B013/08; C25B 1/10 20060101 C25B001/10 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 18, 2016 |
KR |
10-2016-0104921 |
Claims
1. A reinforced composite membrane for water electrolysis, the
reinforced composite membrane being manufactured by:
electrospinning fibers from a polyelectrolyte solution to opposite
surfaces of a polymer-woven fabric base layer, thus forming an
electrospun reinforcing fiber layer; and impregnating the
electrospun fiber reinforced layer with a polyelectrolyte
solution.
2. The reinforced composite membrane for electrolysis of claim 1,
wherein the polymer-woven fabric base layer is made of one or a
mixture of two or more selected from the group of
polyetheretherketone, polytetrafluoroethylene, polyimide,
polybenzimidazole, and polystyrene.
3. The reinforced composite membrane for water electrolysis of
claim 1, wherein the polyelectrolyte solution that forms the
electrospun reinforcing fiber layer or impregnates the electrospun
reinforcing fiber layer includes a fluorinated ionomer.
4. The reinforced composite membrane for water electrolysis of
claim 3, wherein the polyelectrolyte solution forming the
electrospun reinforcing fiber layer is a mixed electrolyte solution
that further includes a copolymer.
5. The reinforced composite membrane for water electrolysis of
claim 4, wherein, in the mixed electrolyte solution forming the
electrospun reinforcing fiber layer, the polyelectrolyte solution,
and the copolymer are mixed at a ratio of 4:1 to 1:1.
6. The reinforced composite membrane for water electrolysis of
claim 1, where in the polymer-woven fabric base layer is made by
weaving or laminating polymer fibers.
7. A membrane electrode assembly formed by bonding electrodes and a
polymer electrolyte membrane into a single body, wherein the
polymer electrolyte membrane is the reinforced composite membrane
for water electrolysis of claim 1.
Description
BACKGROUND OF THE INVENTION
Field of the Invention
[0001] The present invention relates generally to a reinforced
composite membrane for water electrolysis, and a membrane electrode
assembly having the same. More particularly, the present invention
relates to a reinforced composite membrane for water electrolysis,
and a membrane electrode assembly (MEA), wherein a
two-dimensionally woven fabric base layer that minimizes swelling
of the membrane, in the X-axis and Y-axis directions is covered on
a hydrogen electrode to which high pressure is applied or on
hydrogen and oxygen electrodes by three-dimensionally electrospun
reinforcing fiber layers, the reinforcing fiber layers minimizing
swelling of the membrane in the Z-axis direction, thereby reducing
permeation of oxygen (O.sub.2) via the hydrogen electrode and
enabling operation under high pressure due to high dimensional
stability.
DESCRIPTION OF THE RELATED ART
[0002] Generally, in a water electrolysis system, due to
characteristics of a polytetrafluoroethylene-based polymer known by
the name of Nafion (a trade name, E. I. DuPont de Nemours and Co.,
Inc.), which is mainly used as an electrolyte membrane, an oxygen
electrode (anode) electrode is continuously in contact with water,
and thus the membrane is operated in a wet state.
[0003] Here, the electrolyte membrane allows the transport of the
protons from the oxygen electrode to a hydrogen electrode through a
conductive path having irregularly formed porous networks, wherein
pore size is typically about 5-20 .ANG..
[0004] The membrane swelling due to solutions becomes severe when
the membrane is continuously in contact with water or alcohol. For
example, the swelling rate of a conventional Nafion membrane having
a thickness of 180 .mu.m is greater than or equal to 10% in the x
and y directions. As the membrane swells, spaces between the
clusters expand, and thus oxygen that should not be allowed to
permeate to the oxygen electrode permeates through porous path.
Therefore, hydrogen purity and dimensional stability decrease.
[0005] Under high pressure operation, as pressure of the hydrogen
electrode increases, permeation of oxygen generated in the oxygen
electrode is decreased. However, since pressure of the hydrogen
electrode is high, which causes swelling and contraction of the
membrane in one direction, pore space expands.
[0006] In addition, cracks are formed in the catalyst layer due to
swelling and contraction of the membrane in one direction, and thus
the catalyst layer is separated from the membrane. Consequently,
durability of the membrane is decreased.
[0007] Generally, in the case of diffusion layers composed of mesh
or sintered powder of titanium, fibers arid uneven elements having
a size at a micrometer scale cause cracks and pinholes in the
membrane. Such cracks and pinholes cause malfunction in the
electrolyte membrane cell stack and degradation of system
stability. In order to solve these problems and secure water
electrolyte stability, technology development for dimensionally
stable membrane is required.
[0008] As a document of related art, Korean Patent No.
10-2014-0000700 discloses a method of forming electrodes of
electrochemical device, the method including a process of pressing
a mat of electrospun nanofibers having three-dimensional structure
onto an electrolyte membrane. In this method, electrospun fibers
containing PAA, etc., Platinum catalyst particles, and ionomers are
discharged together to form a catalyst layer, which is applied to
PEMFC (polymer electrolyte membrane fuel cell). However, since the
electrospun fibers having a thickness from nm scale to .mu.m scale
are a polymer, a Nafion ionomer having low mechanical strength is
used as a main material.
[0009] Therefore, while having weakness against dimensional
stability and swelling, the method may increase the performance by
organic connection of three-dimensional networks of ionomers for
conducting hydrogen and uniformly distributed catalyst. However, in
water electrolysis of PBM (polymer electrolyte membrane), water
feed to the anode side is needed. Thus, the electrolyte membrane
having high dimensional stability and low swelling rate is
required.
[0010] Further, in the a hydrogen fuel cell system, it is required
to secure dimensional stability and swelling resistance of the
electrolyte membrane capable of being operated under pressure of
350 bar or 700 bar, at a temperature of 80.quadrature., otherwise
hydrogen crossover may occur, and thus potential risks and
performance degradation, for example, reduction in hydrogen purity
and the amount of generated hydrogen. Therefore, it is required to
develop a reinforced electrolyte membrane having three-dimensional
networks structure of the membrane and the catalyst layer so as to
secure dimensional stability thereof.
[0011] Korean patent No. 10-1285709 discloses a method of
manufacturing the reinforced electrolyte membrane as a multi-layer
having more than three layers. However, the method uses the
multi-layer having more than three layers such that additional
processes may be included. In addition, as the reinforced
electrolyte membrane has many layers, contact, interface may act as
a large resistance. Consequently, hydrogen ion resistance and mass
transfer resistance, etc. increase.
[0012] In order to resolve such two technical problems, in Korean
patent No. 10-0897104, dimensional stability and swelling degree
can be controlled by using sheets having various patterns and
utilizing various materials as the support, wherein the sheet may
be ePTFE (expanded PTFE, expanded polytetrafluoroethylene), etc.
However, in this case, the controlling of the dimensional stability
and swelling degree is typically possible in the x and y
directions. In addition, after slightly applying a Nafion ionomer
an the sheet or immersing the sheet in a Nafion ionomer solution,
the Nafion electrolyte membrane is pressed. Therefore, there are
still problems with, interface resistance and dimensional stability
in the z direction (in the thickness direction).
DOCUMENTS OF RELATED ART
[0013] (Patent document 1) Korean Patent Application Publication
No. 10-2014-0000700 (2014 Jan. 3);
[0014] (Patent document 2) Korean Patent No. 10-1285703 (2013 Jul.
8);
[0015] (Patent document 3) Korean Patent No. 10-0897104 (2009 May
4).
SUMMARY OF THE INVENTION
[0016] Accordingly, the present invention has been made keeping in
mind the above problems occurring in the related art, and the
present invention is intended to propose a reinforced composite
membrane for water electrolysis, the reinforced composite membrane
being configured to maintain an ion-exchange property via a polymer
electrolyte matrix, contain a woven base layer therein that
prevents the membrane from swelling two-dimensionally in the X-axis
and Y-axis directions, and include electrospun fibers that prevent
the membrane from swelling three-dimensionally in the Z-axis
direction, thus improving the purity of hydrogen (H.sub.2) by
minimizing swelling of the membrane and permeation of water and
oxygen (O.sub.2) thereto due to such swelling.
[0017] Further, another object of the present invention is to
propose a reinforced composite membrane for water electrolysis, the
reinforced composite membrane having high dimensional stability of
an oxygen electrode and a hydrogen electrode under high-pressure
operating conditions, thereby having improved thermal, mechanical,
and chemical durability.
[0018] Moreover, a further object of the present invention is to
propose a reinforced composite membrane for water electrolysis, the
reinforced composite membrane capable of reducing manufacturing
costs by using substrates that are less expensive than a
conventional Nation membrane, and being mass-produced by selecting
raw materials suitable for easy application to a mass-production
process.
[0019] Furthermore, a still further object of the present invention
is to propose a reinforced composite membrane having a low
coefficient of swelling and low hydrogen crossover, and a membrane
electrode assembly (MEA) having the reinforced composite membrane,
the membrane electrode assembly being applied to a PEM fuel cell
stack. The membrane electrode assembly (MEA) is produced using the
reinforced composite membrane of the present invention as a polymer
electrolyte membrane (PEM) , wherein the membrane electrode
assembly is produced through a process of blending catalytic
particles, and electrospinning the blended compound, or through an
additional process of forming a catalyst layer.
[0020] The foregoing is intended merely to aid in the understanding
of the background of the present invention, and is not intended to
mean that the present invention falls within the purview of the
related art that is already known to those skilled in the art.
[0021] The reinforced composite membrane for water electrolysis
according to the present invention is manufactured by the following
method: electrospinning fibers from a polyelectrolyte solution to
opposite surfaces of a polymer-woven fabric base layer, thus
forming an electrospun reinforcing fiber layer; and integrating the
electrospun fiber reinforced layer with a polyelectrolyte
solution.
[0022] Further, in the reinforced composite membrane for water
electrolysis according to the present invention, the polymer-woven
fabric base layer may be made of one or a mixture of two or more
selected from the group of polyetheretherketone,
polytetrafluoroethylene, polyimide, polybenzimidazole, and
polystyrene.
[0023] Further, in the reinforced composite membrane for water
electrolysis according to the present invention, the
polyelectrolyte solution that forms the electrospun reinforcing
fiber layer or with which the electrospun reinforcing fiber layer
is impregnated may include a fluorinated ionomer.
[0024] Further, in the reinforced Composite membrane for water
electrolysis according to the present invention, the
polyelectrolyte solution forming the electrospun reinforcing fiber
layer is a mixed electrolyte solution that may further include a
copolymer.
[0025] Further, in the reinforced composite membrane for water
electrolysis according to the present invention, the
mixed-electrolyte solution forming the electrospun reinforcing
fiber layer, the polyelectrolyte solution, and the copolymer may be
mixed at a ratio of 4:1 to 1:1.
[0026] Further, in the reinforced composite membrane for water
electrolysis according to the present invention, the polymer-woven
fabric base layer may be made by weaving or laminating polymer
fibers.
[0027] Meanwhile, a membrane electrode assembly according to the
present invention is characterized in that, in the membrane
electrode assembly formed by bonding electrodes and a polymer
electrolyte membrane into a single body, the polymer electrolyte
membrane is a reinforced composite membrane for water electrolysis
of the present invention.
[0028] The above-described reinforced composite membrane according
to the present invention has advantages of maintaining an
ion-exchange property (ion conductivity) due to the woven fabric
base layer that prevents the membrane from swelling
two-dimensionally in the X-axis and Y-axis directions, and the
electrospun fibers that prevent the membrane from swelling
three-dimensionally in the Z-axis direction, thus improving the
purity of hydrogen (H.sub.2) by minimizing the swelling of the
membrane and the permeation of water and oxygen (O.sub.2)
therethrough due to swelling.
[0029] Further, the reinforced composite membrane according to the
present invention has an advantage of securing high dimensional
stability of an oxygen electrode and a hydrogen electrode under
high-pressure operating conditions, thereby having improved
thermal, mechanical, and chemical durability.
[0030] Further, the reinforced composite membrane according to the
present invention has an advantage of reducing manufacturing costs
by using substrates that are less expensive than a conventional
Nafion membrane, and being mass-produced by selecting raw materials
suitable for easy application to a mass-production process.
[0031] Meanwhile, the present invention provide a membrane
electrode assembly (MEA) produced through a process of blending
catalytic particles, and electrospinning the blended compound, or
through an additional process of forming a catalyst layer using the
reinforced composite membrane of the present invention as a polymer
electrolyte membrane (PEM), whereby the present invention further
provides a PEM fuel cell stack having the membrane electrode
assembly (MEA).
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] The above and other objects, features and other advantages
of the present invention will be more clearly understood from the
following detailed description when taken in conjunction with the
accompanying drawings, in which:
[0033] FIG. 1 is a schematic view showing a reinforced composite
membrane of the present invention;
[0034] FIG. 2 is a schematic view showing the rate of swelling of a
reinforced composite membrane of the present invention in the X, Y,
and Z directions;
[0035] FIG. 3 is a SEM image showing a reinforced composite
membrane of the present invention;
[0036] FIG. 4 is a graph showing the diameter of electrospun fibers
depending on a mix ratio of a Nafion ionomer to a copolymer;
[0037] FIG. 5 is a photo showing an actual image of a reinforced
composite membrane according to the present invention;
[0038] FIG. 6 is a cross-sectional SEM image showing a membrane
electrode assembly (MEA) that is manufactured using a reinforced
composite membrane according to the present invention; and
[0039] FIG. 7 is a graph showing the water electrolysis performance
of a membrane electrode assembly (MEA) that is manufactured using a
reinforced composite membrane according to the present invention,
the graph showing cell voltage depending on applied current
density.
DETAILED DESCRIPTION OF THE INVENTION
[0040] Example embodiments of the present invention are disclosed
herein. However, specific structural and functional details
disclosed herein are merely representative for purposes of
describing example embodiments of the present invention; however,
example embodiments of the present invention may be embodied in
many alternate forms and should not be construed as limited to
example embodiments of the present invention set forth herein.
[0041] FIG. 1 is a schematic view showing a reinforced composite
membrane of the present invention, FIG. 2 is a schematic view
showing the rate of swelling of a reinforced composite membrane of
the present invention in the X, Y, and Z directions, FIG. 3 is a
SEM image showing a reinforced composite membrane of the present
invention, and FIG. 4 is a graph showing the diameter of
electrospun fibers depending on a mix ratio of a Nafion ionomer to
a copolymer. Further, FIG. 5 is a photo showing an actual image of
a reinforced composite membrane according to the present invention,
FIG. 6 is a cross-sectional SEM image showing a membrane electrode
assembly (MEA) manufactured using a reinforced composite membrane
according to the present invention, and FIG. 7 is a graph showing
the water electrolysis performance of a membrane electrode assembly
(MEA) manufactured using a reinforced composite membrane according
to the present invention, the graph showing cell voltage depending
on applied current density.
[0042] The reinforced composite membrane according to the present
invention is configured by forming an electrospun reinforcing fiber
layer 102 by electrospinning fibers from a polyelectrolyte solution
on opposite surfaces of a polymer-woven fabric base layer 101 and
impregnating the electrospun reinforcing fiber layer 102 with the
polyelectrolyte solution.
[0043] FIG. 1 is a cross-sectional schematic view showing the
reinforced composite membrane according to the present invention.
As shown in FIG. 1, the reinforced composite polymer electrolyte
membrane for water electrolysis is prepared by electrospinning
polymer fibers on the polymer-woven fabric base layer 101, such as
a PTFE (Polytetrafluoroethylene) sheet, so as to form the
electrospun reinforcing fiber layer 102, and impregnating the
electrospun reinforcing fiber layer 102 with a polyelectrolyte
solution, such as a PFSA-based polymer matrix, so as to form a
polyelectrolyte impregnation layer 103.
[0044] Here, the polymer-woven fabric base layer 101 such as PTFE,
plays the role of reducing a phenomenon of swelling of the polymer
electrolyte membrane in the X and Y directions. Whereas, the
electrospun reinforcing fiber layer 102 plays the role of reducing
the phenomenon of swelling of the polymer electrolyte membrane in
the Z direction. The electrospun reinforcing fiber layer 102 is
prepared by electrospinning a fiber from a mixed electrolyte
solution composed of the polyelectrolyte solution of a
perfluorinated compound or a hydrocarbon compound, and a copolymer
on the polymer-woven fabric base layer 101.
[0045] FIG. 2 is a schematic view showing the rate of swelling of
the reinforced composite membrane of the present invention in the
X, Y, and Z directions. Referring to FIG. 3, how the polymer-woven
fabric base layer 101 of FIG. 1 and the reinforced, composite
membrane are together able to prevent the swelling phenomenon in
three dimensions will be understood.
[0046] The polymer-woven fabric base layer 101 is made of one or a
mixture of two or more selected from the group of
polyetheretherketone, polytetrafluoroethylene, polyimide,
polybenzimidazole, and polystyrene. Further, the polyelectrolyte
solution for forming the electrospun reinforcing fiber layer 102 or
impregnating the electrospun reinforcing fiber layer 102 may
include a fluorinated ionomer.
[0047] Further, in the mixed electrolyte solution forming the
electrospun reinforcing fiber layer 102, the polyelectrolyte
solution, and the copolymer are mixed at a ratio of 4:1 to 1:1.
[0048] Meanwhile, a membrane electrode assembly is formed by
bonding electrodes and a polymer electrolyte membrane into a single
body, wherein the reinforced composite membrane for water
electrolysis is adapted for the membrane electrode assembly
according to the present invention.
[0049] Hereinafter, the reinforced composite membrane for water
electrolysis according to the present invention is described in
more detail through examples, but the examples described below are
merely used to illustrate the present invention, and the scope of
the present invention is not limited thereby.
EXAMPLE 1
[0050] 1. Preparation of an electrospun reinforcing fiber layer
[0051] The electrospun reinforcing fiber layer 102 is formed on an
ePTFE (expanded PTPE) film, having a thickness of 20 .mu.m and
serving as the polymer-woven fabric base layer 101, through an
electrospinning method. Here, conditions suitable for
electrospinning fibers from the polyelectrolyte solution and the
copolymer are given in the following Table 1.
TABLE-US-00001 TABLE 1 Applied Spray Spray Voltage Nozzle #
Distance X-Y jog Speed Condition 8 kV #27 140 mm 47 mm 200
.mu.l/min
[0052] Specifically, the polymer electrolyte membrane having the
PTFE wen fabric base layer 101 of a thickness of 20 .mu.m is placed
on a conductive metal plate at a temperature of 90.quadrature., and
a Nafion solution is loaded into an electrospinning syringe while
the spray distance between a nozzle and the plate is maintained at
140 mm. Further, an x-y jog is set to 47 mm, and the Nafion
solution is sprayed at a speed of 20 .mu.l/min.
[0053] Here, the diameter of the electrospun fibers in the
electrospun reinforcing fiber layer 102 according to the present
invention is observed under the following conditions. In order to
prepare the electrospinning solution, the Nafion ionomer, which is
the main ingredient, and a copolymer, such as (poly acetic acid) or
PEO (polyethylene oxide), is mixed at a mix ratio of 4:1 to 1:1.
When the mix ratio is adjusted from 4:1 to 1:1, the diameter of an
electrospun fiber of the electrospun reinforcing fiber layer 102 is
variable. In Example 1, in order to obtain the electrospun fiber
having a diameter of 0.8 .mu.m as shown in Table 2 and FIG. 4,
showing the diameter of an electrospun fiber depending on the mix
ratio of the Nafion ionomer to a copolymer, the electrospinning
solution is prepared by adjusting a mix ratio to 2:1, and the total
solid content of the composition is adjusted to 1.875 wt % using an
IPA solvent.
[0054] Table 2 and FIG. 4 show the diameter of an electrospun.
fiber depending on a mix ratio of the Nafion ionomer as the
polyelectrolyte solution, to PEO (polyethylene oxide), as the
copolymer. As the content of PEO is increased, the diameter of the
electrospun fiber was increased to micrometer scale. On the other
hand, as the content of the Nafion ionomer is increased, the
diameter of the electrospun fiber is decreased. If the diameter of
the electrospun fiber is too great, the ion conductivity of the
reinforced composite membrane may be affected. On the other hand,
if the diameter of the electrospun fiber is too small, the
mechanical strength of the electrospun fiber is reduced. Thus, it
is preferred that the electrospun reinforcing fiber layer 102 may
be formed by using an electrospun fiber having a diameter of about
1 .mu.m.
[0055] The thickness and the image of the electrospun reinforcing
fiber layer 102 prepared through the above-described method are
observed through SEM (scanning electron microscope) . As shown in
FIG. 3, the polymer electrolyte membrane having a relatively
uniform thickness on the micrometer scale is prepared using the
electrospun fibers forming three-dimensional networks.
TABLE-US-00002 TABLE 2 Diameter of Fiber 0.4 .mu.m 0.8 .mu.m 5
.mu.m Nafion/PEO ratio 4:1 2:1 1:1 Total Weight % 1.2 wt % 1.875 wt
% 1.75 wt %
[0056] 2. Impregnation with the polymer electrolyte solution
[0057] A PTFE woven fabric base layer 101 having a thickness of 10
to 200 .mu.m and the electrospun reinforcing fiber layer 102
thereon is impregnated with the Nafion solution in an amount
sufficient to immerse all layers (1.2 times of pore surface area)
on a flat glass sheet that is maintained level. After that,
distilled water and the IPA solvent are completely dried in a
vacuum drying machine at a temperature of about 80-90.degree. C.
for at least 24 hours. Thus, the reinforced composite membrane for
water electrolysis is produced.
EXAMPLE 2
[0058] A reinforced composite membrane for water electrolysis
according to the present invention is prepared by the same process
of Example 1 except that a PFTE woven fabric having a thickness of
4,000 .mu.m is used as a polymer-woven fabric base layer 101.
[0059] As could be confirmed in the photo showing an actual
reinforced composite membrane for water electrolysis in FIG. 5, the
reinforced composite membrane for water electrolysis produced under
the above-mentioned conditions is a polymer electrolyte membrane in
which the PTFE woven fabric base layer 101 shows little
opacity.
[0060] In the case of a polymer electrolyte ionomer used in the
present invention, the polymer electrolyte ionomer is a transparent
polymer material. The impregnated and dried membrane has a
polymer-woven fabric base layer 101 that appears transparent when
observed with the naked eye. Particularly, in Example 1, an actual
e-PTFE film is a translucent white film. As the Nafion ionomer is
impregnated into the membrane, the pores in the opaque parts of the
layers are filled therewith.
Test Example
[0061] 1. Evaluation of Properties of Polymer Electrolyte
Membrane
[0062] Table 3 shows properties of Nafion 117 by comparing
Comparative Example 1 and Examples 1 and 2.
TABLE-US-00003 TAELE 3 Proton Swelling Thickness Conductivity
Tensile Tensile rate (.mu.m) (S/cm) Strength elongation (%)
Comparative 180 0.09 330 250 14 Example 1 (Nafion 117) Example 1 50
0.10 460 121 <5 Example 2 430 0.05 840 2 <5
(1) Proton Conductivity
[0063] The proton conductivity depending on the temperature of the
polymer electrolyte membrane according to Examples 1 and 2 and
Comparative Example 1 was measured using a Solarton 1260
impedance/gain phase analyzer. Here, proton conductivity (S/cm) is
given by measuring a resistance value (.OMEGA.), then multiplying
the surface area by the result obtained by dividing the thickness
of the polymer electrolyte membrane by the resistance value.
(2) Evaluation of Mechanical Property
[0064] The tensile strength and tensile elongation of the polymer
electrolyte membrane according to Examples 1 to 2 and Comparative
Example 1 were measured in accordance with ASTM D882 using a
universal testing machine (UTM). The measurement speed was 50
mm/min. A 200N load cell was used, and the span (gauge length) was
set to be 100 mm under standard temperature and humidity conditions
((25.+-.2).degree. C., (45.+-.5)% R.H.).
[0065] Examples 1 and 2 show that the polymer electrolyte membrane
has much higher tensile strength than the conventional Nafion 117
membrane, which is a very encouraging result for the polymer
electrolyte membrane having a small thickness in accordance with
Example 1. Due to the relatively small thickness, the membrane of
the present invention exhibits excellent water electrolysis
performance and high tensile strength, thereby suggesting that the
membrane of the present invention is highly applicable as a polymer
electrolyte membrane that is able to bear high pressure.
(3) Evaluation of Swelling Rate
[0066] The swelling rate of the polymer electrolyte membrane
prepared in accordance with Examples 1 and 2 and Comparative
Example 1 was measured. For evaluation, after the prepared membrane
was soaked in distilled water for a day, the swelling rate was
calculated using the following equation.
Swelling rate (%)=[(x or y length of membrane after swelling, x or
y length of membrane before swelling)/x or y length of membrane
before swelling].times.100 Equation 1
[0067] (4) Results
[0068] As shown in Table 3, Example 1 provides a membrane having
proton conductivity that is higher than the proton conductivity of
the conventional Nafion 117 membrane, a thickness of 50 .mu.m,
which is significantly less than the thickness of a conventional
Nafion 117 membrane, high tensile strength, and a swelling rate
less than or equal to 5%.
[0069] Examples 1 and 2 show polymer electrolyte membranes having
much higher tensile strength than the conventional Nafion 117
membrane, which is a very encouraging result for the polymer
electrolyte membrane, which has a small thickness in accordance
with Example 1. Due to the relatively small thickness, the membrane
of the present invention exhibits excellent water electrolysis
performance and high tensile strength, thereby enabling the
membrane of the present invention to be highly applicable as a
polymer electrolyte membrane that is able to bear high
pressure.
[0070] In other words, while a conventional Nafion 212 membrane
having a thickness of 50 .mu.m which is significantly less than the
conventional Nafion 117 membrane of Example 1, has tensile strength
of less than 330 bar, Example 1 according to the present invention
exhibits higher tensile strength of 460 bar, thereby enabling
operation under high pressure.
[0071] As a result, Examples 1 and 2 exhibit the swelling rate of
less than 5%, which is a very low value compared with the
conventional Nafion 117 membrane of Comparative Example 1. The PTFE
woven fabric base layer 101 and the electrospun reinforcing fiber
layer 102 have dimensional stability in water by supporting the
Nafion polymer matrix in the x, y, and z directions.
[0072] 2. Fabrication of Membrane Electrode Assembly and Evaluation
of Performance of Water Electrolysis Cell
[0073] The membrane electrode assembly (MEA) is prepared through
the decal transfer method, which is considered a representative
method for preparing an MEA. Here, Pt/C (30 wt % on Vulcan XC-72)
and IrRuO2 nanoparticles (homemade) are respectively used as an
oxygen electrode catalyst and a hydrogen electrode catalyst. The
catalyst loading rates are respectively set to 2 mg/cm.sup.2 and 4
mg/cm.sup.2.
[0074] The membrane, from which impurities have been removed
through a pretreatment process, is dried. Thereafter, a thermal
compression is carried out on catalyst layers that are formed on
the PTFE sheet through electro-spraying or doctor blading, at 5 MPa
pressure and a temperature of 120-130.degree. C. for 2 minutes in
the directions of zero, 120, and 240 degrees. Thereafter, the PTFE
sheet is removed from surfaces of the membrane, and carbon paper
and Ti fiber electrodes are prepared for the hydrogen electrode and
the oxygen electrode by cutting them, and the carbon paper and Ti
fiber electrodes are processed through thermal compression at
120.degree. C., under 5 Mpa, and for 2 minutes, thereby forming a
membrane electrode assembly (MEA).
[0075] FIG. 6 is a cross-sectional SEM image showing a membrane
electrode assembly (MEA) that is manufactured using a reinforced
composite membrane according to the present invention. To prepare
the membrane electrode assembly (MEA), the ePTFE film is used as
the polymer-woven fabric base layer 101, the electrospun
reinforcing fiber layer 102 is formed on opposite surfaces of the
polymer-woven fabric base layer 101 through electrospinning, and
thus the polymer electrolyte impregnated layer 103 is formed on
both sides of electrodes by impregnation with the Nafion ionomer,
which is one of the perfluorinated polymer electrolyte materials.
Thereafter, the oxygen electrode layer 104 and the hydrogen
electrode layer 105 are bonded through thermocompression bonding,
whereby the membrane electrode assembly (MEA) is prepared.
[0076] FIG. 7 is a graph measuring a voltage value as a function of
applied current density, and shows the results of evaluation of
water electrolysis performance of the membrane electrode assembly
(MEA) prepared in accordance with the above-described method of the
present invention. The water electrolysis of the membrane electrode
assembly (MEA) according to the present invention was evaluated by
comparing a conventional Nafion 212 membrane having a thickness of
50 .mu.m with a conventional Nafion membrane 115 (N115) membrane
having a thickness of 125 .mu.m. Here, the performance difference
was confirmed by comparing the membranes only under the same
catalyst layer preparation conditions.
[0077] The performance of reinforced electrode membrane according
to the present invention can be seen in FIG. 7, Example 1 (sample
#1 in FIG. 5), in which an ePTFE film having a thickness of 50
.mu.m was used as the polymer-woven fabric base layer 101, exhibits
cell voltage of 1 mA/cm.sup.2 and voltage of 95%, compared with the
conventional Nafion 212 (N212) membrane having the same thickness
of 50 .mu.m. Also, Example 2 (sample #2 in FIG. 5), using an ePTFE
film having a thickness of 4,000 .mu.m as the polymer-woven fabric
base layer 101, exhibits performance similar to N115 and N212 under
low-current density conditions. However, as current density
increases, Example 2 (sample #2 in FIG. 5) exhibits better
performance than N212. In particular, Example 1 (sample #1 in FIG.
5), using the membrane having the same thickness as that of N212,
exhibits better performance than N115, having a thickness of 125
.mu.m, as well as N212.
[0078] When considering the results pertaining to the tensile
strength of the membrane electrode assembly (MEA), shown in Table
3, and the water electrolysis performance thereof, shown in FIG. 7,
the tensile strength of N212 is lower than N117, which has a
thickness of 180 .mu.m. Based on the conventional Nafion membranes,
which show a great difference in tensile strength depending on the
thicknesses of the membranes, the superiority of the present
invention is thus clearly exhibited.
[0079] Although a preferred embodiment of the present invention has
been described for illustrative purposes, those skilled in the art
will appreciate that various modifications, additions and
substitutions are possible, without departing from the scope and
spirit of the invention as disclosed in the accompanying
claims.
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