JP2008059908A - Polymer electrolyte fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell capable of stably operating without generating drop in cell characteristics caused by the expansion and contraction of a solid polymer electrolyte membrane even if starting and stop are repeated. <P>SOLUTION: The polymer electrolyte fuel cell is composed of cells in which a catalyst layer 2 is arranged on both sides of a flat plate-like solid polymer electrolyte membrane 1, a diffusion layer 5 is arranged on both outer surfaces of the catalyst layer 2, the catalyst layer 2 larger than the solid polymer electrolyte membrane 1 is joined to the central part on the solid polymer electrolyte membrane 1, a frame-shaped protection film 3 surrounds the outer periphery of the catalyst layer 2 and is joined to the outer peripheral part of the solid polymer electrolyte membrane 1, and at least one slit 8 extending in the direction surrounding the catalyst layer 2 is formed in the protection film 3. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a solid polymer electrolyte fuel cell that uses a solid polymer electrolyte membrane as an electrolyte to obtain electric energy through an electrochemical reaction, and more particularly, to a solid polymer electrolyte cell in which a cell is formed using a membrane-electrode assembly. The present invention relates to a molecular electrolyte fuel cell.

A polymer electrolyte fuel cell (PEFC) is a fuel cell using a solid polymer electrolyte membrane as an electrolyte, and has features such as high output density and long battery life.
FIG. 3 is a cross-sectional view showing an example of a basic structure of a cell of a conventional solid polymer electrolyte fuel cell. As shown in the figure, a catalyst layer 32 serving as an electrode is formed on both surfaces of a flat solid polymer electrolyte membrane 31 disposed in the center, and a frame-shaped protective film 33 is formed around each catalyst layer 32. To form a membrane-electrode assembly (MEA) 34 (see Patent Document 1 or Patent Document 2). Furthermore, a unit cell is formed by joining a diffusion layer 35 that performs a current collecting function and a gas diffusing function to the outer surfaces of the catalyst layer 32 and the protective film 33 and sandwiching them with a separator 36 having a gas flow groove 36a. Is configured. In general, a fuel cell is constituted by a fuel cell stack formed by stacking a plurality of unit cells having the above-described configuration.

  When manufacturing a fuel cell unit cell or fuel cell stack as described above, there may be a part where the gas supply to the electrode is obstructed or a part where the gas seal is insufficient and the part leaks to the outside. In order to avoid this, the positions of the catalyst layer 32 (electrode), the diffusion layer 35, the gas flow groove 36a, and the like must be accurately combined. Accordingly, the MEA 34 in which the catalyst layer 32 is bonded to both surfaces of the solid polymer electrolyte membrane 31 is previously bonded and integrated with the diffusion layer 35 to prevent positional deviation during assembly. As a method of integrating the MEA 34 and the diffusion layer 35, as shown in FIG. 4, the diffusion layer 35 is disposed on both sides of the MEA 34, and is sandwiched between a pair of press plates 38A and 38B and heated. The method of joining by crimping is generally used. The solid polymer electrolyte polymer such as perfluorosulfonic acid polymer mixed in the catalyst layer 32 is softened by being heated to the glass transition point or higher, and becomes a binder for joining the catalyst layer 32 and the diffusion layer 35. It is thought that both are joined.

  The material of the solid polymer electrolyte membrane 31 may be a solid polymer having a proton exchange group in the molecule and functioning as a proton conductive electrolyte, and a conventionally known ion exchange membrane or the like can be used. Specifically, polystyrene-based cation exchange membranes having sulfonic acid groups can be used as cationic conductive membranes, mixed membranes of fluorocarbon sulfonic acid and polyvinylidene fluoride, perfluorosulfonic acid polymers, etc. However, perfluorosulfonic acid polymers are preferred. As the perfluorosulfonic acid polymer, for example, Nafion (registered trademark; manufactured by DuPont) and the like are preferably used.

  For the catalyst layer 32, carbon powder carrying a metal catalyst such as a platinum group can be used. The catalyst layer can be formed by mixing the catalyst with, for example, a solution in which perfluorosulfonic acid polymer is dissolved, and applying the catalyst onto the solid polymer electrolyte membrane 31. Further, after mixing with a polymer to form a sheet in advance, it may be integrated with the solid polymer electrolyte membrane 31 by hot pressing or the like.

  For the protective film 33, a conventionally known sheet-like plastic, rubber, elastomer or the like can be used. Specifically, fluorine-based materials such as polychlorotrifluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropene copolymer, tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer, polytetrafluoroethylene, etc. Examples thereof include polymers, polyethylene terephthalate, polyphenylene sulfide, and polyethylene naphthalate. In particular, when the solid polymer electrolyte membrane 31 is a perfluorosulfonic acid polymer, it is desirable to use the above-mentioned fluorine-based polymer having a melting point close to that. If it chooses in this way, the protective film 33 and the solid polymer electrolyte membrane 31 can be joined by heat sealing | fusion. Patent Document 3 discloses a method of bonding a protective film with an adhesive layer.

For the diffusion layer 35, a sheet-like carbon paper or carbon cloth formed from carbon fibers (carbon fibers) can be used. Further, the size of the diffusion layer 35 is preferably larger than the outer periphery of the catalyst layer 32 and smaller than the outer periphery of the protective film 33, and preferably has a size covering at least the catalyst layer 32 and the diffusion layer 35. The diffusion layer 35 is superposed on the adhesive layer on the MEA 34, sandwiched between a pair of press plates 38A and 38B, and bonded by heating and pressure bonding.
Japanese Patent No. 3052536 JP 2002-231274 A JP 2004-319153 A

  In the conventional solid polymer electrolyte fuel cell, as described above, an MEA is formed by providing a frame-shaped protective film on the outer periphery of the catalyst layer disposed on both sides of the solid polymer electrolyte membrane, and this MEA, diffusion layer, Since the cell is formed by laminating and thermocompression bonding, there is no fear that the solid polymer electrolyte membrane is damaged during the pressure bonding of the diffusion layer. However, this type of solid polymer electrolyte fuel cell is operated by supplying a humidified reaction gas to obtain good power generation characteristics and keeping the solid polymer electrolyte membrane moist. Is activated, the solid polymer electrolyte membrane becomes wet. When the operation is stopped, the solid polymer electrolyte membrane is dried. Therefore, when the start and stop of the fuel cell are repeated, the solid polymer electrolyte membrane repeatedly experiences a wet state and a dry state. On the other hand, since the solid polymer electrolyte membrane expands with an increase in the amount of water, it repeatedly expands and contracts when the wet state and the dry state are repeated. If the amount of expansion / contraction of the solid polymer electrolyte membrane is larger than the amount of expansion / contraction of the protective film surrounding it, the solid polymer electrolyte membrane may be wrinkled or broken due to repeated expansion / contraction. These phenomena are particularly likely to occur at the electrode ends having different elongation rates. When the electrolyte membrane is damaged at the electrode ends as described above, the battery characteristics deteriorate. Therefore, starting and stopping are repeated, and damage to the solid polymer electrolyte membrane proceeds, so that battery characteristics are deteriorated.

  The present invention has been made in consideration of the problems of the prior art as described above, and the object of the present invention is to improve the battery characteristics due to the expansion and contraction of the solid polymer electrolyte membrane even if the start and stop are repeated. An object of the present invention is to provide a solid polymer electrolyte fuel cell that can be stably operated without causing a decrease.

In order to achieve the above object, in the present invention,
(1) A flat solid polymer electrolyte membrane, a flat catalyst layer bonded to both surfaces of the solid polymer electrolyte membrane, and a flat diffusion layer bonded to both outer surfaces of the catalyst layer The catalyst layer having a size smaller than that of the solid polymer electrolyte membrane is bonded to the center of the solid polymer electrolyte membrane, and a frame-shaped protective film surrounds the outer periphery of the catalyst layer. In a solid polymer electrolyte fuel cell composed of cells formed by being joined to the outer edge of a solid polymer electrolyte membrane, the protective film includes at least one slit extending in a direction surrounding the catalyst layer. And

(2) Further, in the solid polymer electrolyte fuel cell of (1), the width of the slit provided in the protective film is 0.5 mm or less.
(3) Further, in the solid polymer electrolyte fuel cell according to (1) or (2), the shape of the slit provided in the protective film is such that the outer periphery of the corner portion of the catalyst layer is enclosed in an L shape. .

  (4) Further, in the solid polymer electrolyte fuel cell according to any one of (1) to (3), the protective film and the solid polymer electrolyte membrane are joined by thermocompression bonding.

  A flat solid polymer electrolyte membrane, a flat catalyst layer bonded to both surfaces thereof, and a flat diffusion layer bonded to both outer surfaces of the catalyst layer, and the catalyst layer is a solid polymer A solid polymer electrolyte fuel cell composed of a cell formed by joining a central protective layer on an electrolyte membrane and a frame-shaped protective film surrounding the outer periphery of the catalyst layer and joined to the outer edge of the solid polymer electrolyte membrane If the protective film is provided with at least one slit extending in the direction surrounding the catalyst layer as in (1) above, the protective film is formed from the central portion of the solid polymer electrolyte membrane to the outer edge portion. It will be divided and touched. Therefore, the amount of expansion and contraction of the protective film caused by wetting and drying caused by starting and stopping of the fuel cell is alleviated, so that film breakage is prevented more than wrinkles at the electrode end, and deterioration of battery characteristics is suppressed. Is done.

  Moreover, if the width | variety of the slit with which a protective film is provided is 0.5 mm or less as said (2), as described in the below-mentioned Example, the fall of a battery characteristic will be suppressed reliably. Further, as described in (3) above, if the slit is shaped so as to surround the outer periphery of the corner portion of the catalyst layer in an L shape, the corner portion with the longest distance from the center portion to the outer edge portion is protected. Since the film is divided and comes into contact with the solid polymer electrolyte membrane, the expansion and contraction amount can be effectively relaxed without impairing the function as the protective film, and therefore, it is particularly suitable as a slit shape. In addition, as described in (4) above, the effect of providing the protective film with a slit as described above is particularly advantageous in a solid polymer electrolyte fuel cell in which a cell is formed by joining the protective film and the solid polymer electrolyte membrane by thermocompression bonding. It is valid.

  The best mode of the solid polymer electrolyte fuel cell of the present invention includes a flat solid polymer electrolyte membrane, a flat catalyst layer bonded to both surfaces of the solid polymer electrolyte membrane, A flat diffusion layer bonded to both outer surfaces, and the catalyst layer having a size smaller than that of the solid polymer electrolyte membrane is bonded to a central portion on the solid polymer electrolyte membrane, In a solid polymer electrolyte fuel cell comprising a cell formed by bonding a protective film to the solid polymer electrolyte membrane disposed around the outer periphery of the catalyst layer, the catalyst is formed on the protective film. A slit extending in a direction surrounding the layer, for example, a slit having a shape surrounding the outer periphery of the catalyst layer in an L shape, for example, at least one slit having a width of 5 mm or less is formed.

  FIG. 1 is a diagram of a cell showing an embodiment of a solid polymer electrolyte fuel cell of the present invention, wherein (a) is a plan view of an MEA constituting the cell, and (b) is a cross-sectional view of the cell. As shown in the figure, a catalyst layer 2 having a size smaller than that of the solid polymer electrolyte membrane 1 and a frame-like protective film 3 surrounding the outer periphery of the catalyst layer 2 are formed on both sides of the flat solid polymer electrolyte membrane 1. MEA 4 is formed, and diffusion layers 5 are further arranged on both outer surfaces to form an MEA-diffusion layer assembly. The feature of the cell of this example is that the protective film 3 is provided with a slit 8 extending in a direction surrounding the catalyst layer 2 as seen in FIG.

  The manufacturing method of the cell of this example is as follows. A perfluorosulfonic acid polymer (manufactured by DuPont: trade name Nafion 117, thickness 183 μm) of 160 mm × 160 mm is used as the solid polymer electrolyte membrane 1, and the inner periphery is 100 mm as a frame-shaped protective film 3 on both sides. A tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA) film having a size of 100 mm, a width of 30 mm, and a thickness of 50 μm was stacked. As shown in FIG. 1A, three slits 8 having a width of 0.5 mm were formed in the frame-shaped protective film 3 in advance. The slits 8 are formed so as to extend in a direction surrounding the space in which the catalyst layer 2 is installed, and three slits 8 are arranged every 5 mm, leaving 20 mm regions on each side of the frame. Next, a catalyst layer 2 is formed by thermocompression bonding a paste obtained by mixing platinum-supporting carbon and a perfluorosulfonic acid polymer solution (Nafion solution) into the frame of the protective film 3 on the solid polymer electrolyte membrane 1. did. The MEA thus formed and the diffusion layer 5 were integrated to obtain an MEA-diffusion layer assembly.

  In order to investigate the effect of the protective film 3 provided with the slits 8 as in the above examples, the start / stop test was performed on the manufactured MEA-diffusion layer assembly to examine the change in the cell voltage. In this start / stop test, one cycle was 3 hours, the current density was operated in the range of 00.3 A / cm2, the cell temperature was changed to 25-80 ° C, and the humidity was changed in the range of 25100%. FIG. 2 is a characteristic diagram showing a change in cell voltage after repeated start / stop in comparison with a conventional example. In the figure, the vertical axis shows the measured voltage value normalized by the initial voltage as an average value of five cells. The characteristic A shown by the solid line is the characteristic of the cell of the example, and the characteristic B shown by the dotted line. These are the characteristics of the cell by the conventional manufacturing method. As can be seen in the figure, the cell with the manufacturing method in the above example was started up while the cell voltage dropped to 55% of the original voltage after 100 times of starting / stopping. / 95% of the initial voltage is maintained even after repeating 100 times, and by providing a slit in the protective sheet as in the example, concentration of film breakage and wrinkles on the electrode edge is avoided, and the battery It can be seen that the characteristics are maintained.

  In this embodiment, the width of the slit provided in the protective sheet is selected to be 0.5 mm, and three slits are arranged at intervals of 5 mm. However, the wider the slit width, the greater the mechanical strength of the protective sheet. However, the narrower the slit, the better. The width should not exceed 0.5 mm selected in this embodiment. In addition, if the number of slits is increased, the amount of expansion and contraction of the protective sheet is reduced, which is more effective in preventing wrinkles at the end of the electrode and preventing film breakage. However, if the number of slits is increased excessively, Since mechanical strength becomes weak, it is necessary to consider this mechanical strength. As in this embodiment, if the slits having a width of 0.5 mm or less are arranged with an interval of 5 mm or more, stable power generation operation can be performed without causing mechanical damage.

  As described above, in the present invention, as described in claim 1, the protective film constituting the cells of the solid polymer electrolyte fuel cell is provided with at least one slit extending in the direction surrounding the catalyst layer. Therefore, the amount of expansion and contraction of the protective film caused by wetting and drying caused by the start / stop of the fuel cell is alleviated, and wrinkles at the end of the electrode are prevented and film breakage is prevented. A fuel cell with little deterioration in battery characteristics even after repeated stops was obtained. Therefore, the present invention can be effectively applied to various solid polymer electrolyte fuel cells.

  Moreover, since the slit with which the protective film was equipped will function more effectively if it is as described in Claim 2, 3, or 4, it is a solid with little deterioration of a battery characteristic even if it starts / stops repeatedly. It is suitable as a polymer electrolyte fuel cell.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure of the cell which shows the Example of the solid polymer electrolyte fuel cell of this invention, (a) is a top view of MEA (membrane-electrode assembly) which comprises a cell, (b) is sectional drawing of a cell The characteristic view which showed the change of the cell voltage after repeating starting / stopping of the cell of an Example compared with the prior art example Sectional drawing which shows an example of the basic structure of the cell of the conventional solid polymer electrolyte fuel cell Explanatory drawing of integration method of MEA and diffusion layer by hot press

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Solid polymer electrolyte membrane 2 Catalyst layer 3 Protective film 4 MEA (membrane-electrode assembly)
5 Diffusion layer 8 Slit

Claims (4)

A flat solid polymer electrolyte membrane, a flat catalyst layer bonded to both surfaces of the solid polymer electrolyte membrane, and a flat diffusion layer bonded to both outer surfaces of the catalyst layer, and The catalyst layer having a size smaller than that of the solid polymer electrolyte membrane is bonded to the center of the solid polymer electrolyte membrane, and a frame-shaped protective film surrounds the outer periphery of the catalyst layer. In the solid polymer electrolyte fuel cell constituted by cells formed by being joined to an outer edge portion, the protective film includes at least one slit extending in a direction surrounding the catalyst layer. Solid polymer electrolyte fuel cell. The solid polymer electrolyte fuel cell according to claim 1, wherein the slit provided in the protective film has a width of 0.5 mm or less. 3. The solid polymer electrolyte fuel cell according to claim 1, wherein the slit provided in the protective film is provided in a shape surrounding an outer periphery of a corner portion of the catalyst layer in an L shape. The solid polymer electrolyte fuel cell according to any one of claims 1 to 3, wherein the protective film and the solid polymer electrolyte membrane are joined by thermocompression bonding.

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