Membrane electrode assembly for fuel cells and manufacturing method thereof

Abstract

A membrane electrode assembly includes: an electrolyte membrane; a cathode and an anode, each being stacked on the electrolyte membrane; and subgaskets bonded to a peripheral region of the electrolyte membrane, which is outside an active area, in which each of the cathode and the anode are stacked on the electrolyte membrane. The electrolyte membrane is disposed in at least a portion of the peripheral region of the electrolyte membrane, which is outside the active area, with a water discharge blocking region for preventing water in the electrolyte membrane from diffusing and being discharged to outside.

Claims

1. A membrane electrode assembly for fuel cells comprising: an electrolyte membrane; a cathode and an anode, each being stacked on the electrolyte membrane; and subgaskets bonded to a peripheral region of the electrolyte membrane, which is outside an active area, in which each of the cathode and the anode are stacked on the electrolyte membrane, wherein the peripheral region of the electrolyte membrane is outside the active area and includes a first peripheral region and a second peripheral region, the second peripheral region being outside the first peripheral region and including a water discharge blocking region for preventing water in the electrolyte membrane from diffusing and being discharged to outside, and wherein the water discharge blocking region is formed by metal cation substitution.

2. The membrane electrode assembly of claim 1, wherein the water discharge blocking region is formed in a portion of the peripheral region of the electrolyte membrane that is spaced apart from the active area.

3. The membrane electrode assembly of claim 1, wherein the water discharge blocking region extends along sides of the electrolyte membrane at the peripheral region of the electrolyte membrane to have a predetermined width.

4. The membrane electrode assembly of claim 1, wherein the subgaskets are stacked on the entire peripheral region of the electrolyte membrane excluding the active area, in which each of the cathode and the anode are stacked on the electrolyte membrane.

5. The membrane electrode assembly of claim 1, wherein the water discharge blocking region is formed in the peripheral region of the electrolyte membrane along four sides of the electrolyte membrane.

6. The membrane electrode assembly of claim 1, wherein the water discharge blocking region is formed in the peripheral region of the electrolyte membrane along two opposite sides of the electrolyte membrane, among four sides of the electrolyte membrane.

7. The membrane electrode assembly of claim 1, wherein the water discharge blocking region is formed in a portion of the peripheral region of the electrolyte membrane, which is spaced apart from the active area along sides of the electrolyte membrane, and has a predetermined width, and wherein a width of the water discharge blocking region is 0.5 times or less a total width of the peripheral region of the electrolyte membrane.

8. The membrane electrode assembly of claim 1, wherein the water discharge blocking region is formed as a result of protons coupled in a sulfonic acid group (SO.sub.3.sup.H.sup.+) of the electrolyte membrane being substituted by metal cations.

9. The membrane electrode assembly of claim 8, wherein the metal cations are selected from the group consisting of Na, Li, K, Ca, Mg, Cu, Zn, Ni, Fe, Cr, and Ai.

10. The membrane electrode assembly of claim 8, wherein the metal cations are bivalent or trivalent metal cations.

11. The membrane electrode assembly of claim 1, wherein the water discharge blocking region is disposed on the peripheral region of the electrolyte membrane in a lateral direction perpendicular to a stacking direction of the anode and the cathode on the electrolyte membrane.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above and other features of the present disclosure will now be described in detail with reference to certain exemplary embodiments thereof illustrated in the accompanying drawings which are given hereinbelow by way of illustration only, and thus are not limitative of the present disclosure, and wherein:

(2) FIG. 1 shows a membrane electrode assembly according to an embodiment of the present disclosure;

(3) FIG. 2 shows a membrane electrode assembly according to another embodiment of the present disclosure; and

(4) FIG. 3 shows a membrane electrode assembly according to a further embodiment of the present disclosure.

(5) It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various features illustrative of the basic principles of the disclosure. The specific design features of the present disclosure as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes, will be determined in part by the particular intended application and use environment.

(6) In the figures, reference numbers refer to the same or equivalent parts of the present disclosure throughout the several figures of the drawing.

DETAILED DESCRIPTION

(7) Hereinafter, the exemplary embodiment of the present disclosure will be described in detail with reference to the accompanying drawings to allow those skilled in the art to easily practice the present disclosure.

(8) Advantages and features of the present disclosure and methods for achieving the same will be clearly understood with reference to the following detailed description of embodiments in conjunction with the accompanying drawings.

(9) However, the present disclosure is not limited to the embodiments disclosed herein, but may be implemented in various different forms. The embodiments are merely given to make the disclosure of the present disclosure perfect and to perfectly instruct the scope of the disclosure to those skilled in the art, and the present disclosure should be defined by the scope of claims.

(10) In addition, in the description of the present disclosure, a detailed description of related known technologies and the like will be omitted when it makes the subject of the present disclosure unclear.

(11) The terms comprises and comprising described herein should be interpreted not to exclude other elements but to further include such other elements unless mentioned otherwise.

(12) The present disclosure provides a membrane electrode assembly for fuel cells configured such that it is possible to prevent water in an electrolyte membrane of the membrane electrode assembly from diffusing to a peripheral region of the electrolyte membrane, which is outside an active area of a fuel cell without reduction of fuel cell operation performance and damage to airtightness, thereby preventing the loss of the water used for fuel cell reaction in the electrolyte membrane, to improve efficiency in handling of water in the fuel cell, and to improve corrosion resistance of a stack and a manufacturing method thereof.

(13) FIG. 1 is a plan view and sectional views showing a membrane electrode assembly according to an embodiment of the present disclosure.

(14) As shown in FIG. 1, a membrane electrode assembly (MEA) 10 according to the present disclosure, which is used in a polymer electrolyte membrane fuel cell (PEMFC), includes a polymer electrolyte membrane 11 capable of moving protons, an anode 13 and a cathode 12 attached to opposite surfaces of the polymer electrolyte membrane 11, a catalyst for inducing a reaction between hydrogen, which is fuel gas, and air (or oxygen), which is oxidizing gas, being applied to the anode 13 and the cathode 12, and subgaskets 14 bonded to opposite surfaces of a peripheral region of the polymer electrolyte membrane 11.

(15) The membrane electrode assembly 10 has an area in which the anode 13 and the cathode 12 are bonded to the polymer electrolyte membrane 11, which is an area in which an electrochemical reaction occurs, i.e. an active area, to which the fuel gas and the oxidizing gas are supplied such that a reaction occurs in a fuel cell.

(16) That is, the cathode 12 and the anode 13 are attached to opposite surfaces of the membrane electrode assembly 10, and the area in which the cathode 12 and the anode 13 are bonded to the polymer electrolyte membrane 11 is an active area, in which reaction occurs in the fuel cell.

(17) In addition, the subgaskets 14 are bonded to the peripheral region of the polymer electrolyte membrane 11 excluding the active area, in which the cathode 12 and the anode 13 are bonded to the polymer electrolyte membrane 11. The subgaskets 14 may be bonded to the entire peripheral region of the polymer electrolyte membrane 11 excluding the active area.

(18) FIG. 1 is a plan view of the membrane electrode assembly. In addition, FIG. 1 is a sectional view taken along line X-X of the plan view and a sectional view taken along line Y-Y of the plan view. Here, line X-X may be a line extending in a longitudinal direction of the membrane electrode assembly 10 while passing through the active area, and line Y-Y may a line extending in the lateral direction of the membrane electrode assembly 10 while passing through the active area.

(19) Referring to FIG. 1, the active area of the membrane electrode assembly 10, in which the cathode 12 and the anode 13 are bonded to the polymer electrolyte membrane 11, is located in the middle of the membrane electrode assembly in a rectangular shape.

(20) In addition, the subgaskets 14 are bonded to the peripheral region of the polymer electrolyte membrane 11 excluding the middle active area, in which the cathode 12 and the anode 13 are bonded to the polymer electrolyte membrane 11. Each subgasket 14 has a rectangular opening formed in the middle thereof such that the middle active area is exposed through the opening, i.e. such that the cathode 12 and the anode 13 are exposed, through the opening.

(21) More specifically, each subgasket 14 is formed in a rectangular frame shape such that each subgasket 14 is located at the rectangular edge of the membrane electrode assembly 10. At this time, the subgaskets 14 may be stacked and bonded to the opposite surfaces of the polymer electrolyte membrane 11 at the peripheral region of the polymer electrolyte membrane 11, which is outside the cathode 12 and the anode 13 (i.e. the active area) such that the subgaskets 14 do not overlap the cathode 12 or the anode 13.

(22) Meanwhile, the membrane electrode assembly 10 according to the present disclosure further includes a water discharge blocking region 11a formed in at least a portion of the peripheral region of the polymer electrolyte membrane 11, to which the subgaskets 14 are bonded.

(23) The water discharge blocking region 11a is configured to prevent water in the polymer electrolyte membrane 11 from moving to the peripheral region of the polymer electrolyte membrane 11, which is outside the active area, due to diffusion thereof. That is, the water discharge blocking region 11a prevents water used for reaction in the fuel cell from diffusing to the peripheral region of the polymer electrolyte membrane 11 and being discharged out of the fuel cell, thereby preventing the water from being lost.

(24) By the provision of the water discharge blocking region 11a, it is possible to prevent the movement and diffusion of water to the peripheral region of the polymer electrolyte membrane 11 and the discharge of the water to the outside, thereby preventing loss of the water. Consequently, it is possible to prevent a stack from being corroded by water discharged from each cell, thereby improving the corrosion resistance of the stack. In addition, it is possible to improve efficiency in handling of water in the fuel cell.

(25) According to the present disclosure, the water discharge blocking region 11a is formed in the peripheral region of the polymer electrolyte membrane 11, to which the subgaskets 14 are bonded, by additional processing. After the processing, the peripheral region of the polymer electrolyte membrane 11 may perform a water discharge blocking function.

(26) In addition, the water discharge blocking region 11a may extend along sides of the polymer electrolyte membrane 11 at the peripheral region of the polymer electrolyte membrane 11 so as to have a predetermined width. As illustrated in FIG. 1, the water discharge blocking region 11a may extend along the entire peripheral region of the polymer electrolyte membrane 11 so as to have a rectangular frame shape.

(27) That is, as shown in FIG. 1, on the assumption that the peripheral region of the polymer electrolyte membrane 11, to which the subgaskets 14 are bonded, is formed in a rectangular frame shape, the water discharge blocking region 11a is formed in a portion of the peripheral region of the polymer electrolyte membrane 11 that is spaced apart from the active area by a predetermined distance so as to have a predetermined width.

(28) Since the water discharge blocking region 11a is formed in the peripheral region of the polymer electrolyte membrane 11, to which the subgaskets 14 are bonded, the subgaskets 14 are stacked and bonded to the water discharge blocking region 11a of the polymer electrolyte membrane 11.

(29) As shown in FIG. 1, the water discharge blocking region 11a is formed in the polymer electrolyte membrane 11 along four sides of the membrane electrode assembly 10, i.e. two long sides and two short sides thereof, so as to have a predetermined width at each side. The water discharge blocking region 11a is formed in a rectangular frame shape.

(30) The width of the water discharge blocking region 11a of the polymer electrolyte membrane 11 may be 0.5 times or less the total width of the peripheral region of the polymer electrolyte membrane 11.

(31) In short, the water discharge blocking region 11a of the polymer electrolyte membrane 11 is formed in a portion of the peripheral region of the polymer electrolyte membrane 11 excluding the active area (i.e. the electrochemical reaction area), in which the cathode 12 and the anode 13 are bonded to the polymer electrolyte membrane 11, i.e. the region in which the subgaskets are bonded to the polymer electrolyte membrane 11, spaced apart from the active area by a predetermined distance set at each side. At this time, the width of the water discharge blocking region 11a at an arbitrary position of each side may be 0.5 times or less the total width of the region in which the subgaskets are bonded to the polymer electrolyte membrane 11 at the same position.

(32) If the width of the water discharge blocking region 11a is greater than 0.5 times the total width of the region in which the subgaskets are bonded to the polymer electrolyte membrane 11, the water discharge blocking region 11a, which is formed by metal cation substitution, as will be described below, is too close to the active area (i.e. the electrochemical reaction area), with the result that electrochemical reaction (i.e. fuel cell reaction) may be affected.

(33) Unlike the embodiment of FIG. 1, the water discharge blocking region 11a may be formed in a portion of the peripheral region of the polymer electrolyte membrane 11, more specifically, only two opposite sides of the polymer electrolyte membrane 11, among the four sides of the polymer electrolyte membrane 11.

(34) FIGS. 2 and 3 show embodiments in which the water discharge blocking region 11a is formed in only two opposing sides of the polymer electrolyte membrane 11. FIG. 2 shows an embodiment in which the water discharge blocking region 11a is formed in only two opposing long sides of the polymer electrolyte membrane 11, among the four sides of the polymer electrolyte membrane 11. FIG. 3 shows an embodiment in which the water discharge blocking region 11a is formed in only two opposing short sides of the polymer electrolyte membrane 11, among the four sides of the polymer electrolyte membrane 11.

(35) In each embodiment, the water discharge blocking region 11a may be spaced apart from the active area by a predetermined distance at each side, as described above. Even in the embodiments of FIGS. 2 and 3, the width of the water discharge blocking region 11a at an arbitrary position of each side may be 0.5 times or less the total width of the region in which the subgaskets are bonded to the polymer electrolyte membrane 11 at the same position.

(36) That is, in embodiments of FIGS. 1 to 3, the width of the water discharge blocking region 11a at an arbitrary position of each side may be less than the distance from the active area.

(37) The reasons for this are that the water discharge blocking region 11a is spaced apart from the active area, in which the cathode 12 and the anode 13 are bonded to the polymer electrolyte membrane 11 and that the peripheral region of the polymer electrolyte membrane 11 (i.e. the region in which the subgaskets 14 are bonded to the polymer electrolyte membrane 11) outside the active area of the polymer electrolyte membrane 11 is divided into a portion forming the water discharge blocking region 11a and a portion forming only the polymer electrolyte membrane 11.

(38) According to an embodiment of the present disclosure, the water discharge blocking region 11a may be formed by applying a solution containing metal cations to the polymer electrolyte membrane 11 such that protons coupled in a sulfonic acid group (SO.sub.3.sup.H.sup.+) of the polymer electrolyte membrane 11 are substituted by the metal cations.

(39) That is, in the present disclosure, the water discharge blocking region 11a for blocking the movement of water may be formed in the polymer electrolyte membrane 11. The property of a portion of the peripheral region of the polymer electrolyte membrane 11 corresponding to the water discharge blocking region 11a is changed by selective cation substitution such that a specific region in the polymer electrolyte membrane 11 forms the water discharge blocking region 11a.

(40) The water discharge blocking region 11a is realized by changing the property of a portion of the region in which the subgaskets 14 are bonded to the polymer electrolyte membrane 11 by cation substitution. Consequently, the water discharge blocking region 11a blocks the movement of water in the polymer electrolyte membrane 11 to the outside, whereby it is possible to prevent the water from being discharged to the outside.

(41) Prior research on the polymer electrolyte membrane shows that when metal cations, such as Na.sup.+, Ca.sup.2+, and Fe.sup.3+, are exposed to the membrane, ion conductivity is reduced and membrane dehydration occurs (Kitiya Hongsirikam et al., J. Power Sources, 195, 7213-7220 (2010); Michael J. Kelly et al., J. Power Sources, 145, 249-252 (2005); D. A. Shores and G. A. Deluga, Basic materials corrosion issues, Ch. 23 in Handbook of Fuel CellsFundamentals, Technology and Applications, Edited by Wolf Vielstich, Hubert A. Gasteiger, Arnold Lamm., Volume 3, John Wiley & Sons, Ltd. (2003)).

(42) The reason for this is that protons coupled in a sulfonic acid group (SO.sub.3.sup.H.sup.+) of the membrane are substituted by cations, which exhibit higher affinity for a sulfonic group (SO.sub.3.sup.) of the membrane than the protons, to disturb coupling between the protons and water molecules.

(43) In particular, multivalent cations, rather than monovalent cations, are strongly affected.

(44) If the above phenomenon occurs in the active area of the membrane electrode assembly, ion conductivity is reduced, whereby the performance of the fuel cell is greatly lowered.

(45) However, in the case in which cation substitution is performed in the peripheral region of the polymer electrolyte membrane 11 outside the active area, i.e. the region in which the subgaskets 14 are bonded to the polymer electrolyte membrane 11, the water content of the membrane may be reduced without affecting the fuel cell reaction, thereby greatly reducing the amount of water discharged out of the membrane electrode assembly.

(46) In the present disclosure, therefore, the polymer electrolyte membrane 11 includes a water discharge blocking region 11a formed in the peripheral region of the polymer electrolyte membrane 11 outside the active area by selective cation substitution.

(47) The water discharge blocking region 11a in the polymer electrolyte membrane 11 is formed in at least a portion of the outer part of the region in which the subgaskets 14 are bonded to the polymer electrolyte membrane 11, excluding the active area, which is an electrochemical reaction part.

(48) Hereinafter, a process of forming the water discharge blocking region in the polymer electrolyte membrane will be described.

(49) First, as a method of forming the water discharge blocking region 11a in a selected region of the polymer electrolyte membrane 11, opposite surfaces of the polymer electrolyte membrane 11, excluding the water discharge blocking region 11a, are covered with a masking member (not shown), and a metal cation solution having a metal cation precursor dissolved in a solvent is applied to the exposed region of the polymer electrolyte membrane 11, which is not covered by the masking member, through a wet process, such as spraying, brushing, or rolling.

(50) Alternatively, the water discharge blocking region may be simultaneously formed in the peripheral region of the polymer electrolyte membrane outside the active area of the cell by spraying a metal cation solution to the side surfaces of a fuel cell stack after assembling the fuel cell stack. However, the present disclosure is not limited thereto.

(51) In the present disclosure, the metal (M) cation solution may include a metal cation precursor represented by [Chemical Formula 1] below and a solvent.
M(X)n[Chemical Formula 1]

(52) Where M may be selected from a group consisting of Na, Li, K, Ca, Mg, Cu, Zn, Ni, Fe, Cr, and Al, and X may be selected from a group consisting of chloride, sulfate, acetate, nitrate, hydroxide, and a combination thereof.

(53) In addition, n is set based on the valence of M.

(54) In the present disclosure, the metal cation solution may include one or more metal cation precursors. The metal cations, generated from the metal (M), may be bivalent metal cations. More specifically, the metal cations may be bivalent or trivalent metal cations.

(55) In addition, the concentration of the metal cations in the solution may be at least 1 mol %. If the concentration of the metal cations is less than 1 mol %, cation substitution is not sufficiently performed, with the result that water discharge blocking efficiency may be reduced.

(56) The solvent is used to dissolve the metal cation precursor. One or a mixture of two or more selected from a group consisting of de-ionized water, methanol, ethanol, iso-propyl alcohol, 1-propanol, and 2-methoxyethanol may be used as the solvent. De-ionized water may be used.

(57) After the metal cation solution is applied to a selected region of the polymer electrolyte membrane 11 to form the water discharge blocking region 11a, as described above, the polymer electrolyte membrane 11 is dried and the masking member is removed for a time sufficient to perform cation substitution.

(58) The polymer electrolyte membrane 11 may be dried using a natural drying method. Alternatively, a hot air drying method or a vacuum drying method may be used in order to reduce drying time.

(59) After the masking member is removed to obtain the polymer electrolyte membrane 11, the cathode 12 and the anode 13 are stacked on the polymer electrolyte membrane 11, and the subgaskets 14 are stacked and bonded to the polymer electrolyte membrane 11 using an ordinary process.

(60) After the cathode 12 and the anode 13 are formed, the water discharge blocking region 11a may be formed.

(61) As a result, the water discharge blocking region, which is formed by metal cation substitution, is formed in the peripheral region of the polymer electrolyte membrane, which is outside the active area of the membrane electrode assembly, whereby it is possible to achieve an excellent handling property owing to the subgaskets, which is required of the membrane electrode assembly, to maintain the airtightness of the fuel cell, and to prevent the diffusion of water to the peripheral region of the fuel cell through the use of the water discharge blocking region.

(62) Consequently, it is possible to improve efficiency in handling of water in the fuel cell, to improve corrosion resistance of the stack, and to improve safety in travel of a vehicle.

(63) In FIGS. 1 to 3, A and A indicate the electrochemical reaction part, i.e. the active area of the membrane electrode assembly, in which the cathode 12 and the anode 13 are bonded to the polymer electrolyte membrane 11, and B and B indicate the region in which the subgaskets 14 are bonded to the polymer electrolyte membrane 11, i.e. the peripheral region of the polymer electrolyte membrane 11, which is outside the active area.

(64) More specifically, A indicates the length of the active area, and A indicates the width of the active area.

(65) In addition, B indicates the width of the peripheral region at each short side, and B indicates the width of the peripheral region at each long side.

(66) In addition, B1 and B1 indicate a portion of the peripheral region of the polymer electrolyte membrane 11 in which cation substitution has not been performed, i.e. a cation un-substitution region, which is provided to separate the active area of the polymer electrolyte membrane 11 and the water discharge blocking region 11a from each other.

(67) B1 indicates the width of the cation un-substitution region at each short side (i.e. the distance between the active area the water discharge blocking region), and B1 indicates the width of the cation un-substitution region at each long side (i.e. the distance between the active area the water discharge blocking region).

(68) In addition, B2 and B2 indicate the water discharge blocking region 11a of the polymer electrolyte membrane 11, which is formed by selective cation substitution. In the embodiment of FIG. 1, the water discharge blocking region 11a is formed at four sides of the polymer electrolyte membrane 11. In the embodiment of FIG. 2, the water discharge blocking region 11a is formed at two opposing long sides of the polymer electrolyte membrane 11. In the embodiment of FIG. 3, the water discharge blocking region 11a is formed at two opposing short sides of the polymer electrolyte membrane 11.

(69) As described above, B20.5B and B20.5B are shown in the embodiment of FIG. 1, and B20.5B is shown in the embodiment of FIG. 2.

(70) In addition, B20.5B is described in the embodiment of FIG. 3.

(71) As is apparent from the above description, in the membrane electrode assembly for fuel cells according to the present disclosure and the manufacturing method thereof, the water discharge blocking region, which is formed by metal cation substitution, is formed in the peripheral region of the polymer electrolyte membrane, which is outside the active area of the membrane electrode assembly, whereby it is possible to achieve an excellent handling property due to the subgaskets, which is required of the membrane electrode assembly, to maintain the airtightness of the fuel cell, and to prevent the diffusion of water to the peripheral region of the fuel cell through the use of the water discharge blocking region.

(72) Consequently, it is possible to improve efficiency in handling of water in the fuel cell, to improve the corrosion resistance of the stack, and to improve safety in travel of a vehicle.

(73) The disclosure has been described in detail with reference to embodiments thereof. However, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the disclosure, the scope of which is defined in the appended claims and their equivalents.