Membrane electrode structure for fuel cells and method for manufacturing a membrane electrode structure for fuel cells

Abstract

This membrane electrode structure comprises: a membrane electrode assembly that is configured by joining an electrolyte membrane, a first gas diffusion electrode layer, and a second gas diffusion electrode layer in a first direction; a frame member that extends in a second direction that is orthogonal to the first direction and has an inner edge portion that forms an opening in which the membrane electrode assembly is disposed; a first sealing portion that is constituted by an adhesive and is provided so as to form a seal between a first surface, which is a surface on one side in the first direction of the inner edge portion of the frame member, and a first side end surface, which is an end surface in the second direction of a first gas diffusion layer that is included in the first gas diffusion electrode layer; and a second sealing portion that is constituted by an adhesive and is provided so as to form a seal between a second surface, which is a surface on the other side in the first direction of the inner edge portion of the frame member, and a second side end surface, which is an end surface in a second direction of a second gas diffusion layer that is included in the second gas diffusion electrode layer.

Description

Technical Field

[0001] The present invention relates to a membrane electrode assembly for a fuel cell and a method for manufacturing the membrane electrode assembly for a fuel cell.

Background Art

[0002] In recent years, in order to enable more people to access affordable, reliable, sustainable, and advanced energy, technological development related to fuel cells that contribute to energy efficiency has been carried out. As a technology related to a membrane electrode assembly used in this type of fuel cell, a membrane electrode assembly is known in which a pair of frames are laminated on both sides of an electrolyte membrane, and a pair of gas diffusion layers are further laminated on the outside thereof, and an adhesive is filled between the electrolyte membrane and the pair of frames (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the configuration described in Patent Document 1 above, since the adhesive is filled inside the frame and the gas diffusion layer, it is difficult to confirm the quality of the adhesiveness from the outside.

Means for Solving the Problems

[0005] One aspect of the present invention provides a membrane electrode structure for a fuel cell, comprising: an electrolyte membrane; a membrane electrode assembly formed by stacking an electrolyte membrane; a first gas diffusion electrode layer disposed along one surface of the electrolyte membrane; and a second gas diffusion electrode layer disposed along the other surface of the electrolyte membrane in a first direction; and a frame member having an inner edge that extends in a second direction perpendicular to the first direction and forms an opening in which the membrane electrode assembly is disposed, wherein the first gas diffusion electrode layer comprises a first gas diffusion layer to which a first reaction gas is supplied and a first electrode catalyst layer disposed between the electrolyte membrane and the first gas diffusion layer; and the second gas diffusion electrode layer comprises a second gas diffusion layer to which a second reaction gas is supplied and a second electrode catalyst layer disposed between the electrolyte membrane and the second gas diffusion layer. The membrane electrode structure for a fuel cell further comprises: a first sealing portion made of adhesive, provided to seal the space between a first surface, which is the surface on one side in a first direction of the inner edge of the frame member, and a first side end face, which is the end face in a second direction of the first gas diffusion layer; and a second sealing portion made of adhesive, provided to seal the space between a second surface, which is the surface on the other side in a first direction of the inner edge of the frame member, and a second side end face, which is the end face in a second direction of the second gas diffusion layer. The first sealing portion is provided from the first surface to the first side end face, in a range that does not exceed the outer edge on one side in a first direction of the first side end face; and the second sealing portion is provided from the second surface to the second side end face, in a range that does not exceed the outer edge on the other side in a first direction of the second side end face.

[0006] Another aspect of the present invention relates to a method for manufacturing a membrane electrode structure for a fuel cell, comprising: an electrolyte membrane; a membrane electrode assembly formed by stacking an electrolyte membrane; a first gas diffusion electrode layer disposed along one surface of the electrolyte membrane; and a second gas diffusion electrode layer disposed along the other surface of the electrolyte membrane in a first direction; and a frame member extending in a second direction perpendicular to the first direction and having an inner edge portion that forms an opening in which the membrane electrode assembly is disposed, wherein the inner edge portion of the frame member on one side in the first direction is contained in the first gas diffusion electrode layer A lamination step is performed in which the second gas diffusion layer, the second electrode catalyst layer, the electrolyte membrane, the inner edge of the frame member, the first electrode catalyst layer, and the first gas diffusion layer are sequentially laminated so that the first electrode catalyst layer and the second gas diffusion layer included in the electrolyte membrane and the second gas diffusion electrode layer are arranged on the other side of the inner edge of the frame member in the first direction, and an adhesive is applied to seal the space between the first surface, which is the surface on one side of the inner edge of the frame member in the first direction, and the first side end face, which is the end face of the first gas diffusion layer in the second direction. The method also includes a coating step of applying an adhesive to seal the space between a second surface, which is the other surface in the first direction of the inner edge of the frame member, and a second side end face, which is the end face in the second direction of the second gas diffusion layer, and a curing step of curing the adhesive applied in the coating step. Application The process includes applying adhesive from the first surface to the first side end face, within the limits not exceeding the outer edge of one side of the first side end face in the first direction, and applying adhesive from the second surface to the second side end face, within the limits not exceeding the outer edge of the other side of the second side end face in the first direction. [Effects of the Invention]

[0007] According to the present invention, it is possible to easily check the quality of adhesion from the outside while preventing substances that cause deterioration of the electrolyte membrane from penetrating into the interior. [Brief explanation of the drawing]

[0008] [Figure 1] A schematic perspective view showing the overall configuration of a fuel cell stack including a membrane electrode structure for a fuel cell according to an embodiment of the present invention. [Figure 2]A cross-sectional view along line II-II in Figure 1. [Figure 3] Figure 1 is a front view showing a schematic configuration of the membrane electrode structure for a fuel cell included in the fuel cell stack. [Figure 4] A cross-sectional view along line IV-IV in Figure 3. [Figure 5A] A diagram illustrating the lamination process included in the manufacturing method of a membrane electrode structure for a fuel cell according to an embodiment of the present invention. [Figure 5B] A diagram illustrating a coating step included in the manufacturing method of a membrane electrode structure for a fuel cell according to an embodiment of the present invention. [Figure 5C] A diagram illustrating a curing step included in the manufacturing method of a membrane electrode structure for a fuel cell according to an embodiment of the present invention. [Figure 6] A diagram showing the relationship between the cumulative amount of light irradiated onto a UV-curing adhesive and the temperature of the frame. [Modes for carrying out the invention]

[0009] Embodiments of the present invention will be described below with reference to Figures 1 to 6. The membrane electrode structure for fuel cells according to the embodiment of the present invention constitutes a power generation cell included in the fuel cell stack, which is the main body of the fuel cell. The fuel cell is mounted on a vehicle, for example, and generates electricity for driving the vehicle. First, the overall configuration of the fuel cell stack will be described in general terms. The fuel cell stack is sometimes simply called a fuel cell.

[0010] Figure 1 is a schematic perspective view showing the overall configuration of a fuel cell stack 100 according to an embodiment of the present invention. For convenience, the three mutually orthogonal axial directions shown in the figure will be defined as the longitudinal direction, the left-right direction, and the vertical direction, and the configuration of each part will be described according to this definition. These directions are not necessarily the same as the longitudinal, left-right, and vertical directions of a vehicle. For example, the longitudinal direction in Figure 1 may be the longitudinal direction of a vehicle, the left-right direction, or the vertical direction.

[0011] As shown in Figure 1, the fuel cell stack 100 has a cell stack 101 formed by stacking multiple power generation cells 1 in the front-to-back direction, and end units 102 positioned at both the front and rear ends of the cell stack 101, and the whole has a substantially rectangular parallelepiped shape. The length of the cell stack 101 in the left-to-right direction is longer than its length in the up-to-down direction. For convenience, Figure 1 shows a single power generation cell 1. The power generation cell 1 has an integrated electrode assembly (UEA) 2 having a membrane electrode assembly including an electrolyte membrane and an electrode, and a pair of front and rear separators 3, 3 positioned on both the front and rear sides of the integrated electrode assembly 2 and sandwiching the integrated electrode assembly 2. The integrated electrode assembly 2 and the separators 3 are arranged alternately in the front-to-back direction. Although not shown in the figure, a substantially box-shaped case with open front and rear sides is arranged around the cell stack 101. The front end face of the case and the front end unit 102, and the rear end face of the case and the rear end unit 102 are fastened together via bolts.

[0012] Figure 2 is a cross-sectional view of a portion of the cell laminate 101 (a cross-sectional view along the line II-II in Figure 1). As shown in Figure 2, the separator 3 has a front plate 31 and a rear plate 32, which are a pair of thin metal plates with a corrugated cross-section. The outer edges of the front plate 31 and the rear plate 32 are joined together by welding or the like, thereby forming the separator 3. The separator 3 is made of a conductive material with excellent corrosion resistance, such as stainless steel, titanium, or titanium alloy.

[0013] A cooling channel PAw is formed inside the separator 3, which is enclosed by the front plate 31 and the rear plate 32, through which a cooling medium flows. The flow of the cooling medium cools the power generation surface of the power generation cell 1. For example, water can be used as the cooling medium. The surfaces (front and rear) of the separator 3 facing the integrated electrode assembly 2 are formed to be uneven by press molding or the like so as to form a gas flow path between them and the integrated electrode assembly 2. More specifically, the front plate 31 and the rear plate 32 each have rib portions 301 that protrude toward the front and rear integrated electrode assembly 2, and recesses 302 that are formed in a concave shape connected to the rib portions 301.

[0014] The rear rib portion 301 abuts on the front surface 2a of the integrated electrode assembly 2, and the front rib portion 301 abuts on the rear surface 2b of the integrated electrode assembly 2. When the fuel cell stack 100 is assembled, a compressive load F is applied in the front-rear direction to the cell laminate 101, and in this state, the case and the front and rear end units 102 are fastened. After the assembly of the fuel cell stack 100 is completed, this compressive load F is maintained. Therefore, a predetermined surface pressure due to the compressive load F acts on the integrated electrode assembly 2 in the front-rear direction via the rib portion 301.

[0015] Between the front surface 2a of the integrated electrode assembly 2 and the rear plate 32 of the separator 3 facing the front surface 2a, a concave portion 302 forms an anode flow path PAa through which fuel gas flows. Between the rear surface 2b of the integrated electrode assembly 2 and the front plate 31 of the separator 3 facing the rear surface 2b, a concave portion 302 forms a cathode flow path PAc through which oxidant gas flows. As the fuel gas, for example, hydrogen gas containing hydrogen can be used, and as the oxidant gas, for example, air containing oxygen can be used.

[0016] FIG. 3 is a front view showing a schematic configuration of the integrated electrode assembly 2 as a membrane electrode structure. As shown in FIG. 3, the integrated electrode assembly 2 has a substantially rectangular membrane electrode assembly (MEA; Membrane Electrode Assembly) 20 and a frame frame 21 that supports the membrane electrode assembly 20. As shown in the detailed view of part A in FIG. 2, the membrane electrode assembly 20 has an electrolyte membrane 23, an anode electrode 24 provided on the front surface 231 of the electrolyte membrane 23, and a cathode electrode 25 provided on the rear surface 232 of the electrolyte membrane 23.

[0017] The electrolyte membrane 23 is, for example, a solid polymer electrolyte membrane, and a thin film of a perfluorosulfonic acid polymer containing moisture can be used. Not limited to fluorine-based electrolyte membranes, hydrocarbon-based electrolyte membranes can also be used.

[0018] The anode electrode 24 is formed on the front surface 231 of the electrolyte membrane 23, and includes an electrode catalyst layer 241 that serves as a reaction field for the electrode reaction, and a gas diffusion layer 242 that is provided on the front surface of the electrode catalyst layer 241 and diffuses and supplies the fuel gas. An intermediate layer (underlayer) can also be provided between the electrode catalyst layer 241 and the gas diffusion layer 242. The cathode electrode 25 is formed on the rear surface 232 of the electrolyte membrane 23, and includes an electrode catalyst layer 251 that serves as a reaction field for the electrode reaction, and a gas diffusion layer 252 that is provided on the rear surface of the electrode catalyst layer 251 and diffuses and supplies the oxidant gas. An intermediate layer (underlayer) can also be provided between the electrode catalyst layer 251 and the gas diffusion layer 252.

[0019] The electrode catalyst layers 241 and 251 contain a catalyst metal that promotes the electrochemical reaction between hydrogen contained in the fuel gas and oxygen contained in the oxidant gas, an electrolyte (such as an ionomer) having proton conductivity, and carbon particles having electron conductivity. The gas diffusion layers 242 and 252 are composed of a conductive member having gas permeability, such as a carbon porous body. Since the gas diffusion layers 242 and 252 are mainly composed of carbon and fluorine, they have a water repellent function.

[0020] In the anode electrode 24, the fuel gas (hydrogen) supplied through the anode flow path PAa is ionized by the action of the catalyst, passes through the electrolyte membrane 23, and moves to the cathode electrode side. The electrons generated at this time pass through the external circuit and are taken out as electrical energy. In the cathode electrode 25, the oxidant gas (oxygen) supplied through the cathode flow path PAc reacts with the hydrogen ions guided from the anode electrode 24 and the electrons moved from the anode electrode 24, and water is generated. The generated water gives appropriate humidity to the electrolyte membrane 23, and the excess water is discharged to the outside of the integrated electrode assembly 2 along the gas flow.

[0021] The frame 21 in Figure 3 is a thin plate with a thickness of approximately 0.05 to 0.1 mm and is roughly rectangular in shape. It can be made of an insulating resin or rubber. For example, PEN (polyethylene naphthalate) or PPS (polyphenylene sulfide) can be used as constituent materials. In particular, in this embodiment, PPS is used as the constituent material of the frame 21. When PEN is used while immersed in water, hydrolysis occurs and its strength decreases over time. In contrast, PPS has high hydrolysis resistance and hardly decreases in strength over time.

[0022] A roughly rectangular opening 210 is provided in the center of the frame 21, and a membrane electrode assembly 20 is provided so as to cover the entire opening 210. The frame 21 has a roughly rectangular outer edge 221 and a roughly rectangular inner edge 222 inside the outer edge 221. The outer edge 221 refers to the outer edge of the frame 21 and its surrounding area, and the inner edge 222 refers to the inner edge of the frame 21 (the edge of the opening 210) and its surrounding area. An adhesive portion 40 is provided around the opening 210 in a frame shape by applying adhesive.

[0023] Point P in Figure 3 is the center point passing through the midpoint of the opening 210 in both the vertical and horizontal directions. On the left side of the opening 210 in the frame 21, three through holes 201 to 203 are opened vertically, penetrating the frame 21 in the front-to-back direction, and on the right side of the opening 210, three through holes 204 to 206 are opened vertically, penetrating the frame 21 in the front-to-back direction.

[0024] As shown in Figure 1, through holes 311 to 316 are opened in the front and rear separators 3 of the integrated electrode assembly 2 at positions corresponding to the through holes 201 to 206 of the frame 21, respectively, and the through holes 311 to 316 penetrate the separators 3 in the front-to-back direction. The through holes 311 to 316 communicate with the through holes 201 to 206 of the frame 21, respectively. The collection of these interconnected through holes 201 to 206 and 311 to 316 forms flow channels PA1 to PA6 (indicated by arrows for convenience) that penetrate the cell stack 101 and extend in the front-to-back direction. Flow channels PA1 to PA6 are sometimes called manifolds. Flow channels PA1 to PA6 are connected to a manifold outside the fuel cell stack 100.

[0025] The flow path PA1 (solid arrow) extending forward through through holes 201 and 311 is a fuel gas supply flow path. The flow path PA6 (solid arrow) extending backward through through holes 206 and 316 is a fuel gas discharge flow path. The fuel gas supply flow path PA1 and the fuel gas discharge flow path PA6 communicate with the anode flow path PAa (Figure 2), which is located opposite the front surface of the membrane electrode assembly 20. As shown by the solid arrow, fuel gas flows to the right through the anode flow path PAa via the fuel gas supply flow path PA1 and the fuel gas discharge flow path PA6. Communication between the anode flow path PAa and the other flow paths PA2 to PA5 is blocked via a seal (not shown).

[0026] The flow path PA4 (dotted arrow) extending forward through through holes 204 and 314 is an oxidant gas supply flow path. The flow path PA3 (dotted arrow) extending backward through through holes 203 and 313 is an oxidant gas discharge flow path. The oxidant gas supply flow path PA4 and the oxidant gas discharge flow path PA3 communicate with the cathode flow path PAc (Figure 2), which is provided opposite the rear surface of the film electrode assembly 20. As shown by the dotted arrow, the oxidant gas flows to the left through the cathode flow path PAc via the oxidant gas supply flow path PA4 and the oxidant gas discharge flow path PA3. Communication between the cathode flow path PAc and the other flow paths PA1, PA2, PA5, and PA6 is blocked via a seal portion (not shown).

[0027] The flow path PA5 (dotted arrow) extending forward through through holes 205 and 315 is a cooling medium supply flow path. The flow path PA2 (dotted arrow) extending backward through through holes 202 and 312 is a cooling medium discharge flow path. The cooling medium supply flow path PA5 and the cooling medium discharge flow path PA2 communicate with a cooling flow path PAw (Figure 2) provided inside the separator 3, and the cooling medium flows through the cooling flow path PAw via the cooling medium supply flow path PA5 and the cooling medium discharge flow path PA2. Communication between the cooling flow path PAw and the other flow paths PA1, PA3, PA4, and PA6 is blocked via a seal portion (not shown).

[0028] The end units 102, located on both the front and rear sides of the cell stack 101, each have a terminal plate 4, an insulating plate 5, and an end plate 6. The rear end unit 102 has multiple through holes 102a to 102f that penetrate the end unit 102 in the front-rear direction. Through hole 102a opens on the extension of the fuel gas supply channel PA1 and communicates with the fuel gas supply channel PA1. Through hole 102b opens on the extension of the cooling medium discharge channel PA2 and communicates with the cooling medium discharge channel PA2. Through hole 102c opens on the extension of the oxidizer gas discharge channel PA3 and communicates with the oxidizer gas discharge channel PA3. Through hole 102d opens on the extension of the oxidizer gas supply channel PA4 and communicates with the oxidizer gas supply channel PA4. Through hole 102e opens on the extension of the cooling medium supply channel PA5 and communicates with the cooling medium supply channel PA5. The through-hole 102f opens on the extension of the fuel gas exhaust passage PA6 and communicates with the fuel gas exhaust passage PA6.

[0029] More specifically, a fuel gas tank containing high-pressure fuel gas is connected to the through-hole 102a via an ejector, injector, etc., and fuel gas is supplied to the fuel cell stack 100 through the through-hole 102a. Fuel gas is discharged from the through-hole 102f. A compressor for supplying oxidizer gas is connected to the through-hole 102d, and compressed oxidizer gas is supplied to the fuel cell stack 100 through the through-hole 102d. Oxidizer gas is discharged from the through-hole 102c. A pump for supplying cooling medium is connected to the through-hole 102e, and cooling medium is supplied to the fuel cell stack 100 through the through-hole 102e. Cooling medium is discharged from the through-hole 102b. The discharged cooling medium is cooled by heat exchange in a radiator and supplied back to the fuel cell stack 100 through the through-hole 102e.

[0030] The above is a general overview of the fuel cell stack 100. Next, the characteristic configuration of the integrated electrode assembly 2 as a membrane electrode structure for a fuel cell according to this embodiment will be described. The integrated electrode assembly 2 according to this embodiment is characterized by the configuration of the peripheral part of the opening 210 of the frame 21.

[0031] Figure 4 is a cross-sectional view along the line IV-IV in Figure 3, showing the configuration around the left inner edge 222 of the frame 21. The configuration around the inner edge 222 is the same along the entire circumference of the inner edge 222 along the opening 210. Hereafter, the direction to the right in Figure 4, that is, the direction toward the center point P in Figure 3 (towards the center), will be referred to as the inward direction or inner side, and the right side of Figure 4 will be referred to as the inside. Also, the direction to the left in Figure 4, that is, the direction toward the outer edge 221 in Figure 3, will be referred to as the outward direction or outer side, and the left side of Figure 4 will be referred to as the outside.

[0032] As shown in Figure 4, the electrode catalyst layer 251 and gas diffusion layer 252 constituting the cathode electrode 25, and the electrolyte membrane 23 are configured to be flat in the left-right direction from their left end faces 251a, 252a, and 23a (outer end faces). The left end face 251a of the electrode catalyst layer 251, the left end face 252a of the gas diffusion layer 252, and the left end face 23a of the electrolyte membrane 23 are located at the same position in the left-right direction. The rear end face 252b of the gas diffusion layer 252 corresponds to the rear end face of the integrated electrode assembly 2. The corner where the left end face 252a and the rear end face 252b of the gas diffusion layer 252 intersect is the trailing edge point P3.

[0033] The electrode catalyst layer 241 and the gas diffusion layer 242 constituting the anode electrode 24 are bent forward near their left end faces 241a and 242a (outer end faces) by the thickness of the frame 21 provided on the front surface of the electrolyte membrane 23. As a result, the anode-side electrode catalyst layer 241 is separated from the front surface 231 of the electrolyte membrane 23 near its left end face 241a. The rear surface 232 of the electrolyte membrane 23 remains bonded to the cathode-side electrode catalyst layer 251 throughout its entire length in the left-right direction. The left end face 241a of the electrode catalyst layer 241 and the left end face 242a of the gas diffusion layer 242 are located at the same position in the left-right direction. The front end face 242b of the gas diffusion layer 242 corresponds to the front end face of the integrated electrode assembly 2. The corner where the left end face 242a and the front end face 242b of the gas diffusion layer 242 intersect is the leading edge point P2.

[0034] The frame 21 is a frame-shaped member made of PPS, and is constructed to be flat in the left-right direction towards the opening 210 at its right end. The frame 21 has a front surface 211 and a rear surface 212. An adhesive layer 213 is provided on the rear surface 212 of the frame 21, with adhesive applied towards the opening 210. The rear surface 212 of the inner edge 222 of the frame 21 and the electrolyte membrane 23 are joined via the adhesive layer 213. The electrode catalyst layer 241 of the anode electrode 24 is laminated on the front surface 211 of the inner edge 222 of the frame 21.

[0035] At the intersection of the front surface 211 of the frame 21 and the left end surface 242a of the gas diffusion layer 242 of the anode electrode 24, an adhesive portion 40 (front adhesive portion 41) made of adhesive is provided, extending from the front surface 211 to the left end surface 242a. On the left end surface 242a of the gas diffusion layer 242, the front end of the front adhesive portion 41 is located in front of the left end surface 241a of the electrode catalyst layer 241, and within a range that does not exceed the leading edge point P2 of the gas diffusion layer 242. Therefore, in Figure 4, the front end of the front adhesive portion 41 coincides with the leading edge point P2, but the front end of the front adhesive portion 41 may be located behind the leading edge point P2.

[0036] At the intersection of the rear surface 212 of the frame 21 and the left end surface 252a of the gas diffusion layer 252 of the cathode electrode 25, an adhesive portion 40 (post-adhesion portion 42) made of adhesive is provided, extending from the rear surface 212 to the left end surface 252a. On the left end surface 252a of the gas diffusion layer 252, the rear end of the post-adhesion portion 42 is located behind the left end surface 251a of the electrode catalyst layer 251 and within a range that does not exceed the trailing edge point P3 of the gas diffusion layer 252. Therefore, in Figure 4, the rear end of the post-adhesion portion 42 coincides with the trailing edge point P3, but the rear end of the post-adhesion portion 42 may be located in front of the trailing edge point P3.

[0037] A UV-curing adhesive that hardens when exposed to ultraviolet light is used for the front and rear bonding sections 40. For example, a UV-curing adhesive made of olefin resin can be used. Examples of such UV-curing adhesives include "UV-curable olefin resin TB3175, TB3178" manufactured by ThreeBond Corporation and "Aronics UVX-6654" manufactured by Toagosei Co., Ltd. Using these adhesives increases the curing speed and reduces the time required to manufacture the integrated electrode assembly 2.

[0038] Furthermore, the rapid temperature rise of the frame 21 during UV irradiation can be suppressed, and deformation such as warping and undulation of the frame 21 can be suppressed. In other words, in this embodiment, the frame 21 is constructed using PPS as the constituent material, but while PPS has high hydrolysis resistance, it has a higher thermal shrinkage rate than PEN. Therefore, if the amount of heat input during adhesive curing is large, the frame may deform due to thermal stress, and it may not be possible to achieve sufficient sealing performance between the frame and the separators 3 (Figure 1) in front of and behind it. For example, if a thermosetting adhesive is used, deformation of the frame 21 becomes a problem. In contrast, since UV-curing adhesives require less heat input than thermosetting adhesives, deformation of the frame 21 due to thermal stress is suppressed, and sufficient sealing performance can be ensured.

[0039] Separators 3 are positioned on both the front and rear sides of the frame 21. An anode channel PAa is formed between the front surface 211 of the frame 21 and the rear plate 32 (Figure 2) of the separator 3. A cathode channel PAc is formed between the rear surface 212 of the frame 21 and the front plate 31 (Figure 2) of the separator 3. Because the separator 3 contains iron as a component, the generated water and condensed water produced by the electrochemical reaction between the fuel gas and the oxidizer gas accumulate in the anode channel PAa and cathode channel PAc, and iron ions may dissolve into this stagnant water.

[0040] Since eluted iron ions can degrade the electrolyte membrane 23, it is necessary to configure the system to prevent water containing iron ions from penetrating the electrolyte membrane 23. Therefore, it is preferable to keep the electrolyte membrane 23 from being exposed to the channels PAa and PAc. Furthermore, the electrode catalyst layers 241 and 251 contain electrolytes such as ionomers, and electrolytes serve as pathways for water to penetrate. Therefore, it is preferable to keep the electrode catalyst layers 241 and 251 from being exposed to the channels PAa and PAc.

[0041] In this embodiment, a front adhesive portion 41 is provided from the front surface 211 of the frame 21 to the left end surface 242a of the gas diffusion layer 242 of the anode electrode 24, and a rear adhesive portion 42 is provided from the rear surface 212 of the frame 21 to the left end surface 252a of the gas diffusion layer 252 of the cathode electrode 25. As a result, the electrolyte membrane 23 and the electrode catalyst layers 241 and 251 are not exposed to the front and rear flow channels PAa and PAc of the frame 21. This blocks the entry path of moisture to the electrolyte membrane 23, preventing moisture containing iron ions from entering the electrolyte membrane 23. As a result, deterioration of the electrolyte membrane 23 can be suppressed, and the durability of the integrated electrode assembly 2 is improved.

[0042] A method for manufacturing a membrane electrode structure for a fuel cell according to an embodiment of the present invention will be described with reference to Figures 5A to 5C. In Figures 5A to 5C, the thickness of each part is highlighted. When manufacturing the integrated electrode assembly 2 as a membrane electrode structure for a fuel cell, first, as shown in Figure 5A, the cathode electrode 25, electrolyte membrane 23, frame 21, and anode electrode 24 are stacked in this order (stacking process).

[0043] More specifically, an anode electrode 24 is formed by first coating a gas diffusion layer 242 with an electrode catalyst layer 241, and a cathode electrode 25 is formed by coating a gas diffusion layer 252 with an electrode catalyst layer 251. Next, an electrolyte membrane 23 is bonded to the upper surface of the electrode catalyst layer 251 of the cathode electrode 25. Then, a frame 21 is bonded to the upper surface of the electrolyte membrane 23 via an adhesive layer 213. Next, the electrode catalyst layer 241 of the anode electrode 24 is bonded to the upper surface of the electrolyte membrane 23 via an opening 210 of the frame 21, and the outer end of the electrode catalyst layer 241 is laminated to the upper surface of the inner edge 222 of the frame 21. This forms a laminate 2A before the adhesive is applied. The frame 21 is made of PPS (polyphenylene sulfide).

[0044] Next, adhesive is applied to seal the space between the inner edge 222 of the frame 21, the electrolyte membrane 23, and the cathode electrode 25, and between the inner edge 222 of the frame 21 and the anode electrode 24 (application step). More specifically, as shown in Figure 5B, the laminate 2A obtained by the lamination step is placed on the stage 400. Then, UV-curing adhesive is applied around the entire circumference of the inner edge 222 using a dispenser 401 at the intersection of one side surface of the inner edge 222 of the frame 21 (front surface 211 in Figure 4) and the outer end surface of the anode electrode 24 (left end surface 241a, 242a in Figure 4) (adhesive section 40). That is, as shown in Figure 3, the adhesive is applied in a roughly rectangular shape along the opening 210 of the frame 21.

[0045] In this case, the adhesive is applied so as to cover at least the entire outer end surface of the electrode catalyst layer 241. In other words, the adhesive is applied so as to extend beyond the outer end surface of the electrode catalyst layer 241 (left end surface 241a in Figure 4) to the outer end surface of the gas diffusion layer 242 (left end surface 242a in Figure 4). However, the amount of adhesive applied is adjusted so that, when the adhesive hardens, the bonded portion 40 does not extend beyond the leading edge point P2 in Figure 4 to the front end surface 242b of the gas diffusion layer 242.

[0046] Similarly, UV-curing adhesive is applied using a dispenser 401 to the entire circumference of the inner edge 222 at the intersection of the other surface of the inner edge 222 of the frame 21 (rear surface 212 in Figure 4) and the outer end surfaces of the electrolyte membrane 23 and cathode electrode 25 (left end surfaces 23a, 251a, 252a in Figure 4). In this case, the adhesive is applied so as to cover at least the entire outer end surfaces of the electrolyte membrane 23 and electrode catalyst layer 251. In other words, the adhesive is applied so as to extend beyond the outer end surface of the electrode catalyst layer 251 (left end surface 251a in Figure 4) to the outer end surface of the gas diffusion layer 252 (left end surface 252a in Figure 4). However, the amount of adhesive applied is adjusted so that, during curing, the adhesive portion 40 does not extend beyond the trailing edge point P3 in Figure 4 to the trailing end surface 252b of the gas diffusion layer 252.

[0047] Next, as shown in Figure 5C, ultraviolet light is irradiated from the ultraviolet irradiation unit 402 onto the adhesive portion 40 of the laminate 2A to which the adhesive has been applied in the coating step, thereby curing the adhesive portion 40 (curing step). The hatched area AR10 in Figure 5C is the irradiation range of the ultraviolet light emitted from the ultraviolet irradiation unit 402, and the entire adhesive portion 40 is included in the irradiation range. This allows the entire adhesive portion 40 to be cured at once, resulting in high work efficiency.

[0048] Since the frame 21 is made of PPS, which has a relatively high thermal shrinkage rate, the ultraviolet irradiance and integrated light quantity are set during the curing process to prevent deformation such as warping or undulation of the frame 21 due to thermal shrinkage. Figure 6 shows the relationship between the integrated ultraviolet light quantity J and the temperature (frame temperature) T of the frame 21. Characteristic f1 (solid line) is the characteristic obtained under a first irradiance W1 (e.g., 230 mW / cm2), and characteristic f2 (dotted line) is the characteristic obtained under a second irradiance W2 (e.g., 450 mW / cm2), which is higher than the first irradiance W1.

[0049] As is clear from characteristics f1 and f2, the lower the illuminance and the smaller the integrated light quantity J, which is the sum of illuminance and time, the lower the temperature T of the frame 21. If the predetermined temperature Ta is the temperature at which the frame 21 begins to soften (softening temperature) or the softening temperature with a predetermined margin added, then in this embodiment, the illuminance W and integrated light quantity J are set so that the temperature of the frame 21 in the curing process is below the predetermined temperature Ta. This makes it possible to suppress deformation of the frame 21. The predetermined temperature Ta is, for example, 60°C. If the temperature of the adhesive is low, it takes a long time for the adhesive to harden. Therefore, considering work efficiency, it is preferable that the temperature of the frame 21 is above the predetermined temperature (for example, 40°C) and below the predetermined temperature Ta.

[0050] The ultraviolet irradiation unit 402 is integrated with the conveyor 403. In the curing process, as shown in Figure 5C, a nitrogen atmosphere space SP10 filled with nitrogen (inert gas) is formed above the conveyor 403. The stage 400 is then moved into this space SP10, and the adhesive is cured by irradiating it with ultraviolet light in the nitrogen atmosphere. In other words, the ultraviolet-curable adhesive is cured under nitrogen purging. This reduces the oxygen concentration in space SP10, making it easy to reduce the cumulative light intensity J. As a result, the temperature of the frame 21 during the curing process can be limited to a predetermined temperature Ta or below while suppressing the decrease in ultraviolet irradiance. Therefore, the adhesive can be cured in a short time while suppressing deformation of the frame 21, thereby improving work efficiency.

[0051] Furthermore, irradiating the adhesive portion 40 with ultraviolet light under nitrogen purging reduces the energy required for substances to adhere to the surface of the adhesive portion 40 (surface adhesion energy) compared to irradiating with ultraviolet light under conditions other than nitrogen purging. Surface adhesion energy corresponds to viscosity, and if the surface adhesion energy of the adhesive portion 40 is high, water is more likely to remain on the surface of the adhesive portion 40, which may impair power generation stability. In contrast, by reducing the surface adhesion energy of the adhesive portion 40 by irradiating it with ultraviolet light under nitrogen purging, water does not accumulate on the surface of the adhesive portion 40, and power generation stability can be ensured.

[0052] This embodiment can provide the following effects and advantages. (1) The integrated electrode assembly 2 as a membrane electrode structure for a fuel cell comprises a membrane electrode assembly 20 formed by stacking an electrolyte membrane 23, an anode electrode 24 arranged along the front surface 231 of the electrolyte membrane 23, and a cathode electrode 25 arranged along the rear surface 232 of the electrolyte membrane 23 in the front-rear direction, and a frame 21 having an inner edge portion 222 that extends in the vertical and horizontal directions and forms an opening 210 in which the membrane electrode assembly 20 is placed (Figures 2 and 3). The anode electrode 24 has a gas diffusion layer 242 to which fuel gas is supplied and an electrode catalyst layer 241 disposed between the electrolyte membrane 23 and the gas diffusion layer 242, and the cathode electrode 25 has a gas diffusion layer 252 to which oxidant gas is supplied and an electrode catalyst layer 251 disposed between the electrolyte membrane 23 and the gas diffusion layer 252 (Figure 2). The integrated electrode assembly 2 further comprises a pre-adhesive portion 41 made of adhesive, which is provided to seal the space between the front surface 211 of the inner edge 222 of the frame 21 and the outer end surface (left end surface 242a) of the gas diffusion layer 242, and a post-adhesive portion 42 made of adhesive, which is provided to seal the space between the rear surface 212 of the inner edge 222 of the frame 21 and the outer end surface (left end surface 252a) of the gas diffusion layer 252 (Figure 4).

[0053] With this configuration, the outer end faces of the electrolyte membrane 23 and the electrode catalyst layers 241 and 251 are covered by the pre-adhesion portion 41 and the post-adhesion portion 42 without being exposed to the channels PAa and PAc. As a result, not only the electrolyte membrane 23 but also the electrode catalyst layers 241 and 251, which could serve as pathways for moisture, are blocked from the channels PAa and PAc, thus preventing moisture containing iron ions eluted from the separator 3 from reaching the electrolyte membrane 23 via the electrode catalyst layers 241 and 251. Consequently, degradation of the electrolyte membrane 23 is suppressed, and its lifespan is extended. Furthermore, since the adhesive portion 40 is exposed to the channels PAa and PAc, the quality of adhesion at the adhesive portion 40 can be easily checked from the outside.

[0054] (2) The adhesives constituting the pre-bonding portion 41 and the post-bonding portion 42 are each ultraviolet-curing adhesives. The frame 21 is constructed using polyphenylene sulfide (PPS) as its constituent material. By using PPS, which has high hydrolysis resistance, the lifespan of the frame 21 can be extended. Furthermore, by using an ultraviolet-curing adhesive, the temperature of the frame 21 during adhesive curing can be easily kept below a predetermined temperature Ta. As a result, deformation of the PPS, which has a high thermal shrinkage rate, can be suppressed, and sufficient sealing performance can be ensured at the connection between the frame 21 and the separator 3.

[0055] (3) The front adhesive portion 41 is provided from the front surface 211 to the left end surface 242a of the frame 21, within a range that does not exceed the leading edge point P2 of the outer end surface (left end surface 242a) of the gas diffusion layer 242, and the rear adhesive portion 42 is provided from the rear surface 212 to the left end surface 252a of the frame 21, within a range that does not exceed the trailing edge point P3 of the outer end surface (left end surface 252a) of the gas diffusion layer 252 (Figure 4). If the adhesive portion 40 exceeds the leading edge point P2 of the gas diffusion layer 242 or the trailing edge point P3 of the gas diffusion layer 252, the end surface of the separator 3 and the end surfaces 242b, 252b of the gas diffusion layers 242, 252 will not be in uniform contact, which may cause variations in the stacking state of the cell laminate 101. In contrast, by limiting the thickness of the adhesive portion 40 in the front-to-back direction so as not to exceed the leading edge point P2 or the trailing edge point P3, variations in the stacking state of the cell laminate 101 can be suppressed.

[0056] (4) The manufacturing method for the membrane electrode structure for fuel cells as a manufacturing method for the integrated electrode assembly 2 described above is such that the electrode catalyst layer 241 and gas diffusion layer 242 included in the anode electrode 24 are arranged on the front surface 211 side of the inner edge 222 of the frame 21, and the electrolyte membrane 23 and the electrode catalyst layer 251 and gas diffusion layer 252 included in the cathode electrode 25 are arranged on the rear surface 212 side of the inner edge 222 of the frame 21, such that the gas diffusion layer 252, electrode catalyst layer 251, electrolyte membrane 23, and inner edge 222 of the frame 21 are arranged. The process includes a lamination step of sequentially laminating the electrode catalyst layer 241 and the gas diffusion layer 242; a coating step of applying adhesive to seal the space between the front surface 211 of the inner edge 222 of the frame 21 and the outer end surface (left end surface 242a) of the gas diffusion layer 242, and also applying adhesive to seal the space between the rear surface 212 of the inner edge 222 of the frame 21 and the outer end surface (left end surface 252a) of the gas diffusion layer 252; and a curing step of curing the adhesive applied to the adhesive portion 40 in the coating step (Figures 5A to 5C). This prevents moisture containing iron ions, which are a factor in the deterioration of the electrolyte membrane 23, from reaching the electrolyte membrane 23. In addition, the quality of the adhesion of the adhesive portion 40 can be easily checked from the outside.

[0057] (5) The frame 21 is constructed using polyphenylene sulfide as a constituent material. The curing process includes curing the adhesive at a predetermined temperature Ta or below that which corresponds to the softening temperature of the frame 21 (Figure 6). This makes it possible to extend the lifespan of the frame 21 while suppressing deformation of the frame 21.

[0058] (6) The adhesive applied in the coating step is an ultraviolet-curing adhesive. The curing step includes irradiating the adhesive portion 40 with ultraviolet light so that the temperature of the frame 21 is below a predetermined temperature Ta (Figure 5C). This makes it easy to suppress deformation of the frame 21 when the adhesive is curing.

[0059] (7) The curing process includes curing the adhesive of the bonded portion 40 under a nitrogen atmosphere (Figure 5C). This reduces the time required for the adhesive to cure, thereby improving work efficiency when manufacturing the integrated electrode assembly 2. In addition, the surface adhesion energy of the bonded portion 40 is reduced, ensuring power generation stability.

[0060] The above embodiment can be modified into various forms. Several modifications are described below. In the above embodiment, an anode electrode 24 is arranged as a first gas diffusion electrode layer along the front surface 231 (one side) of the electrolyte membrane 23, and a cathode electrode 25 is arranged as a second gas diffusion electrode layer along the rear surface 232 (the other side). More specifically, an anode electrode 24 having a gas diffusion layer 242 (first gas diffusion layer) to which fuel gas (first reaction gas) is supplied and an electrode catalyst layer 241 (first electrode catalyst layer), and a cathode electrode 25 having a gas diffusion layer 252 (second gas diffusion layer) to which oxidant gas (second reaction gas) is supplied and an electrode catalyst layer 251 (second electrode catalyst layer), are arranged on both sides of the electrolyte membrane 23, but the configuration of the membrane electrode assembly 20 is not limited to this.

[0061] In the above embodiment, the frame 21 extends in a left-right direction (second direction) perpendicular to the front-to-back direction (first direction), which is the stacking direction of the film electrode assembly 20. However, the direction in which the frame member extends is not limited to that described above. In the above embodiment, a front adhesive portion 41 (first sealing portion) is provided to seal the space between the front surface 211 (first surface) of the inner edge portion 222 of the frame 21 and the left end surface 242a (first side end surface) of the gas diffusion layer 242. A rear adhesive portion 42 (second sealing portion) is provided to seal the space between the rear surface 212 (second surface) of the inner edge portion 222 of the frame 21 and the left end surface 252a (second side end surface) of the gas diffusion layer 252. More specifically, a front adhesive portion 41 was provided within the range not exceeding the front edge point P2 (outer edge), which is the corner on the front side (one side in the first direction) of the left end face 242a, and a rear adhesive portion 42 was provided within the range not exceeding the rear edge point P3 (outer edge), which is the corner on the rear side (the other side in the first direction) of the left end face 252a. In this case, an ultraviolet-curing adhesive such as an olefin resin was used, but other ultraviolet-curing adhesives can also be used.

[0062] In the above embodiment, as part of the curing process, a space SP10 with a nitrogen atmosphere is formed below the ultraviolet irradiation section 402, and ultraviolet light is irradiated over the entire adhesive section 40 in the nitrogen atmosphere. However, the configuration of the apparatus for performing the curing process is not limited to this.

[0063] In the above embodiment, an example of applying the fuel cell stack 100 to a vehicle was described, but the fuel cell stack having the fuel cell membrane electrode structure of the present invention can also be applied to mobile bodies other than vehicles such as aircraft and ships, robots, and various industrial machines.

[0064] The above description is merely an example, and the present invention is not limited by the embodiments and modifications described above, as long as the features of the present invention are not impaired. It is also possible to arbitrarily combine one or more of the above embodiments and modifications, and to combine modifications with each other.

[0065] 1 Power generation cell, 2 Integrated electrode assembly, 21 Frame, 23 Electrolyte membrane, 23a Left end face, 24 Anode electrode, 25 Cathode electrode, 40 Adhesive section, 41 Front adhesive section, 42 Rear adhesive section, 100 Fuel cell stack, 210 Opening, 211 Front face, 212 Rear face, 222 Inner edge, 241, 251 Electrode catalyst layer, 241a, 251a Left end face, 242, 252 Gas diffusion layer, 252a Left end face, P2 Front edge point, P3 Rear edge point, PAa Anode channel, PAc Cathode channel

Claims

1. A membrane electrode assembly is formed by stacking an electrolyte membrane, a first gas diffusion electrode layer arranged along one surface of the electrolyte membrane, and a second gas diffusion electrode layer arranged along the other surface of the electrolyte membrane in a first direction. A membrane electrode structure for a fuel cell comprising: a frame member having an inner edge portion that extends in a second direction perpendicular to the first direction and forms an opening in which the membrane electrode assembly is arranged, The first gas diffusion electrode layer comprises a first gas diffusion layer to which a first reaction gas is supplied, and a first electrode catalyst layer disposed between the electrolyte membrane and the first gas diffusion layer. The second gas diffusion electrode layer comprises a second gas diffusion layer to which a second reaction gas is supplied, and a second electrode catalyst layer disposed between the electrolyte membrane and the second gas diffusion layer. The aforementioned membrane electrode structure for fuel cell is A first sealing portion, made of adhesive, is provided to seal the space between the first surface, which is one side surface of the inner edge of the frame member in the first direction, and the first side end face, which is the end face of the first gas diffusion layer in the second direction. The frame member further comprises a second sealing portion made of adhesive, which is provided to seal the space between the second surface, which is the other surface of the inner edge of the frame member in the first direction, and the second side end face, which is the end face of the second gas diffusion layer in the second direction. The first sealing portion is provided from the first surface to the first side end face, in a range that does not exceed the outer edge of one side of the first side end face in the first direction, The membrane electrode structure for a fuel cell is characterized in that the second sealing portion is provided from the second surface to the second end face, in a range that does not exceed the outer edge on the other side of the second end face in the first direction.

2. In the membrane electrode structure for a fuel cell according to claim 1, The adhesive of the first sealing portion and the adhesive of the second sealing portion are each ultraviolet-curing adhesives. The aforementioned frame member is characterized by being constructed of polyphenylene sulfide as a constituent material, and is a membrane electrode structure for a fuel cell.

3. A method for manufacturing a membrane electrode structure for a fuel cell, comprising: an electrolyte membrane; a membrane electrode assembly formed by stacking an electrolyte membrane; a first gas diffusion electrode layer disposed along one surface of the electrolyte membrane; and a second gas diffusion electrode layer disposed along the other surface of the electrolyte membrane in a first direction; and a frame member extending in a second direction perpendicular to the first direction and having an inner edge portion that forms an opening in which the membrane electrode assembly is disposed. A lamination step is performed to sequentially laminate the second gas diffusion layer, the second electrode catalyst layer, the electrolyte membrane, the inner edge of the frame member, the first electrode catalyst layer, and the first gas diffusion layer, such that the first electrode catalyst layer and the first gas diffusion layer included in the first gas diffusion electrode layer are arranged on one side of the inner edge of the frame member in the first direction, and the electrolyte membrane and the second electrode catalyst layer and the second gas diffusion layer included in the second gas diffusion electrode layer are arranged on the other side of the inner edge of the frame member in the first direction, The application step includes applying adhesive to seal the space between the first surface, which is one side surface of the inner edge of the frame member in the first direction, and the first side end face, which is the end face of the first gas diffusion layer in the second direction, and applying adhesive to seal the space between the second surface, which is the other side surface of the inner edge of the frame member in the first direction, and the second side end face, which is the end face of the second gas diffusion layer in the second direction, The process includes a curing step for curing the adhesive applied in the above coating step, The method for manufacturing a membrane electrode structure for a fuel cell is characterized in that the coating step includes applying an adhesive from the first surface to the first side end face, within a range that does not exceed the outer edge of one side of the first side end face in the first direction, and applying an adhesive from the second surface to the second side end face, within a range that does not exceed the outer edge of the other side of the second side end face in the first direction.

4. In the method for manufacturing a membrane electrode structure for a fuel cell according to claim 3, The frame member is constructed using polyphenylene sulfide as its constituent material. A method for manufacturing a membrane electrode structure for a fuel cell, characterized in that the curing step includes curing the adhesive at a predetermined temperature or lower corresponding to the softening temperature of the frame member.

5. In the method for manufacturing a membrane electrode structure for a fuel cell according to claim 4, The adhesive applied in the aforementioned coating step is an ultraviolet-curing adhesive. A method for manufacturing a membrane electrode structure for a fuel cell, characterized in that the curing step includes irradiating the adhesive with ultraviolet light so that the temperature of the frame member becomes below the predetermined temperature.

6. In a method for manufacturing a membrane electrode structure for a fuel cell according to any one of claims 3 to 5, A method for manufacturing a membrane electrode structure for a fuel cell, characterized in that the curing step includes curing the adhesive under a nitrogen atmosphere.

Images