Abstract:
This solid polymer fuel cell has a plurality of stacked single battery modules having an electrolyte membrane, electrode layers disposed on both surfaces of the electrolyte membrane, and a pair of separators provided with a gas flow paths disposed on the inside surfaces so as to sandwich the electrode layers. The electrolyte membrane is provided with electrolyte material and a nonwoven fabric which is embedded in the electrolyte material. The nonwoven fabric is provided with a plurality of fused parts that are provided in a linear shape or spotted shape on a part of the nonwoven fabric that is a part corresponding to of the solid polymer fuel cell, wherein two or more nonwoven fibers are fused to each other and the thickness thereof is thinner than the membrane thickness of the unwoven fabric.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an electrolyte membrane for a polymer electrolyte fuel cell reinforced by a nonwoven fabric, a manufacturing method thereof, and a polymer electrolyte fuel cell. 
       BACKGROUND ART 
       [0002]    A fuel cell is composed of modules stacked as many as necessary. Each of the modules is composed by joining an electrolyte membrane causing power generating reaction with catalyst layers, and providing separators interposing the joined material in between. In order to seal a fuel gas, the electrolyte membrane is fixed to a frame that is usually made of resin, by injection molding of a fixing seal referred to as a gasket preventing the fuel gas from leaking. The electrolyte membrane fixed to the frame is provided between the separators, and the assembly is referred to as a module. 
         [0003]    In recent years, a proton conductive ion-exchange membrane has been used as the electrolyte membrane for a polymer electrolyte fuel cell. In particular, perfluorocarbon polymer (hereafter referred to as sulfonic perfluorocarbon polymer) is widely considered as its superior basic characteristics. One of the requirements for an actual electrolyte membrane used for a fuel cell is a low ohmic loss of the membrane. The ohmic loss of the membrane depends on the conductivity of an electrolyte polymer used for the membrane. 
         [0004]    Methods for reducing the electric resistance of a positive ion exchange film include increasing the concentration of sulfonate acid group and reducing the thickness of the membrane. However, a significant increase in the concentration of sulfonic acid group reduces a mechanical strength of the membrane and results in a creep in the membrane when operating the fuel cell for a long time, causing a problem of reduced durability of the fuel cell, for example. 
         [0005]    In addition, an electrolyte membrane having high concentration of sulfonic acid group significantly swells when absorbing moisture, and it tends to cause various disadvantages. For example, the dimensions of the membrane are likely to increase due to moisture generated at the time of power generation reaction, water vapor supplied with the fuel gas, and others. The increase in the dimension of the membrane contributes to forming “crinkles” in the membrane, and the “crinkles” fill grooves in separators, inhibiting flow of gas. Furthermore, by repeatedly stopping operation, the membrane swells and shrinks repeatedly. With this, the membrane or the electrodes fused to the membrane cracks, reducing the characteristics of the cell. 
         [0006]    Providing a reinforcement layer in an electrolyte membrane has been proposed as a technique for solving the problem described above (see PTL 1 to 7). 
         [0000]    As illustrated in  FIG. 12 , PTL 1 discloses a membrane-electrode assembly having solid-polymer electrolyte membrane  111  and porous sheet  113  provided as a reinforcement layer in electrolyte membrane  111 . According to the configuration of membrane electrode assembly in PTL 1, porous sheet  113  is present at a center part in the thickness direction of electrolyte membrane  111 , and reduces the change in dimension in the in-plane direction. 
       CITATION LIST 
     Patent Literature 
       [0000]    
       
         PTL 1 
         Japanese Patent Application Laid-Open No. 2006-100267 
         PTL 2 
         Japanese Patent Application Laid-Open No. 2009-230986 
         PTL 3 
         Japanese Patent Application Laid-Open No. 2003-317748 
         PTL 4 
         Japanese Patent Application Laid-Open No. 2008-47453 
         PTL 5 
         United Stated Patent Application Publication No. 2009/0239123 
         PTL 6 
         United Stated Patent Application Publication No. 2009/0258274 
         PTL 7 
         United Stated Patent Application Publication No. 2008/0138697 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0021]    However, in the configuration according to PTL 1, a region only with the electrolyte material (resin layer  125 ) is present on both surfaces of porous sheet  113 . Accordingly, resin layer  125  is not restricted by porous sheet  113  in the thickness direction, and swells due to water generated when a fuel cell generates power or moisture used for humidifying the fuel gas. When electrolyte membrane  111  swells, electrode layers  127  and  128  are expanded outward, pressing gas diffusion layers  133  and  134  against separators  141  and  142 . 
         [0022]    Gas diffusion layers  133  and  134  pressed against separators  141  and  142  respectively enter grooves  145  and  146  formed in separators  141  and  142 . By gas diffusion layers  133  and  134  entering grooves  145  and  146 , the spaces of grooves  145  and  146  are reduced, interrupting flow of fuel gas. As a result, there is a problem that the pressure of fuel gas is lost, reducing the electrical generating property of the fuel cell. 
         [0023]      FIG. 13  is a cross-sectional view illustrating an assembled cell module including a nonwoven fabric as a reinforcement layer in an electrolyte membrane. As illustrated in  FIG. 13 , when the nonwoven fabric is used as reinforcement layer  412 , the nonwoven fabric having a three-dimensional structure can be included in the full thickness direction of electrolyte membrane  431 . 
         [0024]      FIG. 14  is a schematic view illustrating electrolyte membrane  431  swelling due to moisture. Electrolyte membrane  431  has nonwoven fabric as a reinforcement layer in a solid polymer electrolyte. As illustrated in  FIG. 14 , since nonwoven fabric  521  has a structure in which nonwoven fibers are piled in layers, no force for controlling electrolyte membrane  431  is exerted in the thickness direction. When electrolyte membrane  431  absorbs moisture, the thickness between layers of nonwoven fabric  521  increases and swelling of the entire membrane in the thickness direction cannot be prevented as a result. When the electrolyte membrane  431  is swollen, electrode layers  127  and  128  are expanded outward, pressing gas diffusion layers  133  and  134  against separators  141  and  142 . 
         [0025]    Gas diffusion layers  133  and  134  pressed against separators  141  and  142  respectively enter grooves  145  and  146  formed in separators  141  and  142 . Since gas diffusion layers  133  and  134  enter grooves  145  and  146 , the spaces in grooves  145  and  146  become narrower. Since the flow of fuel gas is interrupted, the pressure of the fuel gas is lost, resulting in reduced electrical generating property of the fuel cell. 
         [0026]    PTL 2 and 5 disclose an electrolyte membrane for a polymer electrolyte fuel cell produced by hot roll pressing, having an ion-exchange resin as a main component reinforced by a nonwoven fabric made of fluorine resin with at least part of cross-points of its fibers fixed. PTL 3 discloses a solid electrolyte membrane formed by attaching glass electrolyte to a woven or nonwoven fabric having cross-points in its fibers fixed in a grid pattern, and stacking a fluorine-containing polymer films having a functional group on a front surface and a back surface of the woven or nonwoven fabric. PTL 6 and 7 suggest that a part of cross-points of fibers of an electrolyte membrane is fixed. While the stability in the dimensions of the electrolyte membrane would be achieved according to PTL 2, 3, and 5, none of PTL discloses a specific position of cross-points between fibers. Therefore, it is difficult to improve the accuracy in dimension of the electrolyte membrane especially when used for a fuel cell. 
         [0027]    PTL 4 discloses a method for manufacturing a fuel cell including the following steps: (i) impregnating a strip-shaped base with an insulating material by a printing method so as to form island-shaped electrolyte regions equally-spaced in the longitudinal direction, surrounded by a layer impregnated with the insulating material at the outer circumference; (ii) forming electrolyte membranes by impregnating the electrolyte region with an electrolyte; and (iii) forming a conductor penetrating part in the insulating material impregnated layer between the electrolyte membranes. However, this method involves complicated steps, and it was difficult to improve the dimensional accuracy due to problems such as accuracy in printing. 
         [0028]    The present invention has been conceived in order to solve the problems, and it is an object of the present invention to provide an electrolyte membrane for a polymer electrolyte fuel cell capable of reducing swelling not only in the in-plane direction but also in the thickness direction of the electrolyte membrane and maintaining the electrical generating property of the fuel cell, a manufacturing method thereof, and a polymer electrolyte fuel cell. 
         [0029]    Another object of the present invention is to provide an electrolyte membrane for polymer electrolyte fuel cell capable of suppressing the swelling in the thickness direction of the electrolyte membrane when containing moisture, and preventing a gas diffusion layer base for a fuel cell (hereafter also referred to as “GDL”) from entering a fuel gas flow path in a separator due to the swelling in the thickness direction, without reducing the proton conductivity. 
       Solution to Problem 
       [0030]    According to a first aspect of the present invention, a polymer electrolyte fuel cell includes: a plurality of cell modules that are stacked, in which: each of the cell modules includes: an electrolyte membrane; a plurality of electrode layers provided on an upper surface and a lower surface of the electrolyte membrane; and a pair of separators interposing the electrode layers, each of the separators having an inner surface with a gas flow path, the electrolyte membrane includes an electrolyte material and a nonwoven fabric included in the electrolyte material, and wherein the nonwoven fabric includes a plurality of fused parts provided in straight lines or dots in a power generating region of the polymer electrolyte fuel cell, the fused parts each being formed of two or more strands of nonwoven fiber fused to each other and the fused parts having a thickness smaller than a thickness of the nonwoven fabric. 
         [0031]    According to a second aspect of the present invention, an electrolyte membrane for a polymer electrolyte fuel cell, includes: an electrolyte membrane made of an electrolyte material; and a nonwoven fabric included in the electrolyte membrane, in which the nonwoven fabric includes a plurality of fused parts in which two or more strands of nonwoven fiber are fused to each other in straight lines or dots, the fused parts having a thickness smaller than a thickness of the nonwoven fabric. 
         [0032]    According to a third aspect of the present invention, a method for manufacturing an electrolyte membrane for a polymer electrolyte fuel cell, includes: providing a nonwoven fabric; forming a plurality of fused parts having a thickness smaller than a thickness of the nonwoven fabric by fusing two or more strands of nonwoven fiber in straight lines or dots; and forming an electrolyte membrane by impregnating the nonwoven fabric having the fused part formed with an electrolyte material. 
       Advantageous Effects of Invention 
       [0033]    According to the present invention, an electrolyte membrane for a polymer electrolyte fuel cell capable of reducing swelling not only in the in-plane direction but also in the thickness direction of the electrolyte membrane and maintaining the electrical generating property of the fuel cell, a manufacturing method thereof, and a polymer electrolyte fuel cell are provided. According to the present invention, since fibers in a part of the nonwoven fabric are fused, the electrolyte membrane is reinforced in the thickness direction, suppressing the swelling in the electrolyte membrane when the fuel cell is in operation, which secures high durability. 
         [0034]    In addition, according to the electrolyte membrane for polymer electrolyte fuel cell according to the present invention, it is possible to prevent the swelling in the thickness direction when the electrolyte membrane contains moisture, without reducing the proton conductivity. In addition, it is possible to prevent GDL from entering the fuel gas flow path in the separators, caused by the swelling in the thickness direction. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0035]      FIG. 1  is a cross-sectional view schematically illustrating an assembled cell module composing a polymer electrolyte fuel cell according to Embodiment 1; 
           [0036]      FIG. 2  is a partial cutaway top view of the cell module composing a polymer electrolyte fuel cell according to Embodiment 1; 
           [0037]      FIGS. 3A to 3C  are schematic views illustrating a method for creating fused parts of a nonwoven fabric by thermal compression fusing according to Embodiment 1; 
           [0038]      FIGS. 4A to 4C  are schematic views of a process for applying an electrolyte material for an electrolyte membrane according to Embodiment 1; 
           [0039]      FIGS. 5A to 5C  are other schematic views of a process for applying an electrolyte material for an electrolyte membrane according to Embodiment 1; 
           [0040]      FIGS. 6A to 6D  are other schematic views of a process for applying an electrolyte material for an electrolyte membrane according to Embodiment 1; 
           [0041]      FIG. 7  is a schematic view of a method for creating a fused part of a nonwoven fabric by a laser beam; 
           [0042]      FIG. 8  is a schematic view of a method for creating a fused part of a nonwoven fabric by an organic solvent; 
           [0043]      FIG. 9  is a partial cutaway top view of the cell module having fused parts in a grid pattern, composing a polymer electrolyte fuel cell according to Embodiment 2; 
           [0044]      FIG. 10  is a partial cutaway top view of the cell module having dotted fused parts, composing a polymer electrolyte fuel cell according to Embodiment 3; 
           [0045]      FIG. 11  is a partial cutaway top view of the cell module having a fused part along a flow path, composing a polymer electrolyte fuel cell according to Embodiment 4; 
           [0046]      FIG. 12  is a cross-sectional schematic view of a membrane electrode assembly disclosed in PTL 1; 
           [0047]      FIG. 13  is a cross-sectional view illustrating a conventional assembled cell module including a nonwoven fabric as a reinforcement layer in an electrolyte membrane; and 
           [0048]      FIG. 14  is a cross-sectional view illustrating a cell module including a nonwoven fabric as a reinforcement layer in an electrolyte membrane in a swollen state. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0049]    The following describes the present invention with reference to Embodiments. However, the present invention is not limited to the following embodiments. Same or similar reference numerals may be assigned to the components having the same or similar functions in the diagrams, and description for these components is omitted. Note that the drawings are schematic. Accordingly, specific dimension and others are determined based on the following description. Needless to say, relationships between dimensions and ratios may be different among drawings. 
       Polymer Electrolyte Fuel Cell 
     Embodiment 1 
       [0050]      FIG. 1  is a cross-sectional view schematically illustrating an assembled cell module composing a polymer electrolyte fuel cell according to Embodiment 1. 
         [0051]    As illustrated in  FIG. 1 , cell module (cell)  170  composing a polymer electrolyte fuel cell according to Embodiment 1 includes electrolyte membrane  410 , electrode layers  127  and  128  provided in power generating regions  422  on an upper surface and a lower surface of electrolyte membrane  410  respectively, and a pair of separators  141  and  142  provided so as to interpose electrode layers  127  and  128 . Electrolyte membrane  410  includes an electrolyte material and nonwoven fabric  516  included in the electrolyte material as the reinforcement layer. Note that, as the electrolyte material, an ion-exchange resin that can fill interstices in a nonwoven fabric may be used. Separators  141  and  142  may include grooves  145  and  146  in parts corresponding to power generating region  422  inside in separators  141  and  142 , and gas flow paths  147  and  148  in a space defined by the bottom surfaces and the side surfaces of grooves  145  and  146 . 
         [0052]    Cell module  170  further includes gas diffusion layer  133  between electrode layer  127  and separator  141 , and gas diffusion layer  134  between electrode layer  128  and separator  142 . Gaskets  153  and  154  are provided in membrane fixing part  423  at the ends of electrolyte membrane  410 . 
         [0053]      FIG. 2  is a partial cutaway top view of cell module  170  composing the polymer electrolyte fuel cell according to Embodiment 1. As illustrated in  FIG. 2 , cell module  170  includes substantially square-shaped frame  160 . Fuel gas inlet  161  is provided at the upper end of frame  160 , and fuel gas outlet  162  is provided at the lower end of frame  160 . Electrolyte membrane  410  is provided at a part of frame  160 , corresponding to power generating region  422 . 
         [0054]    As illustrated in  FIG. 2 , nonwoven fabric  516  includes a plurality of fused parts  510 . Each of fused parts  510  is provided in a straight line in power generating region  422  in cell module  170 , includes two or more strands of nonwoven fiber fused, and has a thickness smaller than the thickness of nonwoven fabric  516 . Fused part  510  is preferably provided at a part corresponding to power generating region  422  in cell module  170 , particularly at a part corresponding to gas flow paths  147  and  148  in the separator, as illustrated in  FIG. 1 . This is because the electrical generating property of fuel cell may be maintained by reducing swelling not only in the in-plane direction, but also in the thickness direction of electrolyte membrane  410 . 
         [0055]    In Embodiment 1, straight fused parts  510  are provided parallel to sides of frame  160  in which fuel gas inlet  161  and fuel gas outlet  162  are not provided, that is, right end (left end). However, straight fused part  510  may be provided vertical to sides on which fuel gas inlet  161  and fuel gas outlet  162  of frame  160  are not provided, and may be provided diagonal to a side of frame  160 . 
         [0056]    Since it is necessary to bond two or more adjacent strands of fiber, fused part  510  is preferably wider than or equal to the width of adjacent fibers. Since nonwoven fabric  516  has a distribution of fibers of approximately 0.1 μm to 100 μm, it is preferable that the width of fused part  510  is 0.1 mm or more for fusing adjacent fibers. Note that, in Embodiment 1, the width of straight fused part  510  is approximately 1 mm. 
         [0057]    At fused part  510  in nonwoven fabric  516 , the interstices between strands of nonwoven fiber  516  are narrow or not present, which inhibits delivery of protons. If the distance between fused parts  510  is too small, the delivery of proton is inhibited, reducing the electrical generating property of the fuel cell. In contrast, if the distance between fused parts  510  is too large, the electrolyte material swells between fused parts  510 , changing the thickness of the membrane. Accordingly, in terms of the electrical generating property and prevention of the swelling in the thickness direction, it is preferable to set the distance W 1  between fused parts  510  in a range from 10 mm to 20 mm Note that, in Embodiment 1, the width of straight fused parts  510  W 1  is 20 mm. 
         [0058]    It is preferable to set the thickness of electrolyte membrane  410  in a range from 20 μm to 30 μm, and distance E 1  at fused part  510  as 20 mm. However, when the thickness of electrolyte membrane  410  is smaller than the range described above, the change in dimension with respect to thickness direction is small. Accordingly, the distance W 1  between straight fused parts  510  may be increased. Since the total area of fused part with respect to a power generating area is reduced, conduction of protons is improved. As a result, power generating efficiency of a fuel cell improves. 
         [0059]    The fused region of nonwoven fabric  516  is preferably at least 0.5% and at most 10% of a total area corresponding to power generating region  422  in nonwoven fabric  516 . If the area of the fused region is smaller than the lower limit value, it is difficult to maintain stability in the dimensions of the electrolyte membrane, and power generation efficiency is reduced if the area exceeds the upper limit value. 
         [0060]    It is preferable that fused parts  510  are equally spaced, and it is more preferable that the distance between fused parts  510  is at least 10 mm and at most 20 mm. If the distance is smaller than the lower limit value, it is difficult to maintain stability in dimension of electrolyte membrane  410 , and power generation efficiency is reduced if the distance exceeds the upper limit value. 
         [0061]    It is preferable that fused parts  510  are formed in a grid pattern. When used as a fuel cell, the grid pattern stabilizes the dimension of electrolyte membrane  410  and is more likely to reduce stress exerted from outside. 
         [0062]    When a nonwoven fabric made of nonwoven fiber having large tension strength is used, distance W 1  between straight fused parts  510  may be increased. When distance W 1  between straight fused parts  510  is large, the total area of the fused part with respect to the total area of the part corresponding to power generating region  422  becomes small. Accordingly, the influence on the proton conduction also becomes small, which is advantageous. The ratio of fused part  510  to the total area of the part corresponding to power generating region  422  is preferably 0.5 to 10%, based on the line width and distance W 1  of the fused parts described above. Note that, the ratio of the part corresponding to power generating region  422  to the total area of fused parts  510  in embodiment 1 is approximately 5%. 
         [0063]    The hardness of electrolyte membrane  410  at fused part  510  is different from a part that is not fused. Variation in hardness of electrolyte membrane  410  at membrane fixing part  423  causes variation in strength of fixing frame  160  and electrolyte membrane  410 . Accordingly, in order to stabilize the strength of fixing frame  160  and electrolyte membrane  410 , it is preferable that fused part  510  is only provided in power generating region  422 , not in membrane fixing part  423 . 
         [0064]    As illustrated in  FIG. 1 , fused part  510  is formed at a part of nonwoven fabric  516 , which is formed by stacking nonwoven fibers in layers. In this case, it is preferable to set the thickness of fused part  510  as thin as possible while maintaining thickness  412  of nonwoven fabric  516  indicated by arrow  412  at a predetermined thickness. In the cross section in the thickness direction of nonwoven fabric  516 , it is preferable that nonwoven fabric  516  is in a shape connecting one main surface of the nonwoven fabric and the other main surface of the nonwoven fabric through fused part  510  as if the figures of number “8” are horizontally placed. This shape is for reducing the change in the dimension of electrolyte membrane  410  in the thickness direction. In addition, a propagation path for protons can be secured. 
         [0065]    Furthermore, the thickness of the fused part  510  is not particularly limited as long as the change in the dimension of electrolyte membrane  410  is reduced and the propagation path for the protons is secured. More specifically, the thickness of nonwoven fabric  516  is preferably 5 to 65% of the thickness of the electrolyte membrane, and the thickness of fused part  510  is preferably 5 to 50% of the thickness of nonwoven fabric  516 . 
         [0066]    The fuel cell uses power generating reaction by propagation of protons. Accordingly, the higher a ratio of interstices of nonwoven fibers is, the higher the electrical generating property achieved becomes. Nonwoven fabric  516  manufactured by electrospinning has fiber having a small diameter, and thus the ratio of interstices per unit area of nonwoven fabric  516  can be increased. Accordingly, it is preferable to use nonwoven fabric  516  manufactured by electrospinning. 
         [0067]    The temperature of electrolyte membrane  410  reaches approximately 80° C. when the fuel cell is in operation. Therefore, as a material for the nonwoven fabric  516 , a material having sufficient heat-resistance and chemical stability in the temperature range is preferably used. As a specific material for nonwoven fabric  516 , polyvinylidene difluoride (hereafter referred to as “PVDF”) is preferably used considering its heat resistance and chemical stability, and that a nonwoven fiber can be formed by electrospinning. Instead of PVDF, polyvinylfluoride (hereafter referred to as “PVF”) may be used. Alternatively, a copolymer consisting of PVDF and PVF as monomer units may be used. Alternatively, a mixture of PVDF and PVF may also be used. A hydrophobic material is preferable as a material for nonwoven fabric  516 . By providing nonwoven fabric  516  made of a hydrophobic material inside electrolyte membrane  410 , unnecessary moisture produced in electrolyte membrane  410  by power-generating reaction is drained, making it possible to reduce unnecessary swelling caused by the moisture. 
         [0068]    In order to reduce the change in the dimension of electrolyte membrane  410  due to swelling and shrinking, electrolyte membrane  410  preferably has sufficient mechanical property, such as tension strength and an elongation. When the molecular weight is too low, a mechanical strength is reduced, and when the molecular weight is too high, solubility is reduced, making it difficult to form a solution. It is preferable that the molecular weight of PVDF is 150,000 to 550,000. 
         [0069]    In order to form a nonwoven fiber of PVDF by the electrospinning, a solution obtained by dissolving PVDF in dimethylacetamide (hereafter referred to as DMAC) as a solvent is preferably used. Other solvents such as dimethyl sulfoxide, dimethyl formamide, and acetone may be used. Note that, when a polar solvent is used, PVDF is more likely to be melt. 
         [0070]    A preferable concentration of solution is from 10% to 25%. The preferable concentration of the solution is defined as described above because when the concentration is lower than the lower limit, it is difficult achieve a sufficient diameter of fiber, making it difficult to prevent the change in the dimensions of electrolyte membrane  410  due to swelling and shrinking. Furthermore, if the concentration of the solution is higher than the upper limit, sufficient electrostatic burst cannot be obtained when forming nonwoven fibers by the electrospinning. As a result, the distance between the fibers is reduced, inhibiting proton propagation that is one of the functions of electrolyte membrane  410 . 
         [0071]    &lt;Method for Manufacturing Polymer Electrolyte Fuel Cell&gt; 
         [0072]    A method for manufacturing an electrolyte membrane for a polymer electrolyte fuel cell will be described. 
         [0073]    The method for manufacturing electrolyte membrane for an polymer electrolyte fuel cell includes: providing a nonwoven fabric; forming a plurality of fused parts having a thickness smaller than a thickness of the nonwoven fabric by fusing two or more strands of nonwoven fiber in straight lines or dots; and forming an electrolyte membrane by impregnating the nonwoven fabric having the fused part formed with an electrolyte material. In Embodiment 1, a method in which nonwoven fabric  516  manufactured by the electrospinning is fused by thermal compression fusing will be described step by step. 
         [0074]    (i) Step for Providing Nonwoven Fabric 
         [0075]    First, nonwoven fabric  516  is manufactured by the electrospinning. Here, the electrospinning refers to a method for manufacturing microfiber, and includes applying a high voltage between a polymer solution in a syringe and a collector electrode and pressing the solution out of the syringe, such that the solution that is pressed out of the syringe is charged, fine fibers are produced from the charged solution, and the fine fibers are adhered to the collector. 
         [0076]    More specifically, an electrospinning apparatus is provided. A nonwoven fabric is manufactured by filling a syringe with PVDF solution containing PVDF dissolved in DMAC, and subsequently applying a voltage between the syringe and the collector electrode at approximately 20 kV and a pressure for injection at approximately 30 kPa. 
         [0077]    (ii) Step for Forming Fused Part 
         [0078]      FIGS. 3A to 3C  are schematic diagrams illustrating a method for creating a fused part of nonwoven fabric by the thermal compression fusing according to Embodiment 1. First, compression jigs  611  and  612  having projections  613  are provided. Jigs  611  and  612  provided preferably include projections  613  at parts corresponding to gas flow paths  147  and  148  of separators. Subsequently, compression jigs  611  and  612  are provided above and below nonwoven fabric  516 , such that nonwoven fabric  516  is interposed between compression jigs  611  and  612 . Subsequently, heat is transferred to nonwoven fabric  516  substantially at the same time as a pressure is applied such that projections  613  contact nonwoven fabric  516 . By the thermal compression fusing on a part of nonwoven fabric  516 , nonwoven fabric  516  having fused part  510  is formed. Since nonwoven fabric  516  includes layers of nonwoven fiber stacked, by fusing nonwoven fabric  516  using the thermal compression fusing, nonwoven fibers contact each other in the thickness direction of electrolyte membrane  410 , allowing secure fusing. 
         [0079]    As compression jigs  611  and  612 , aluminum jigs are preferably used. This is because aluminum does not contribute much to the degradation of the electrolyte membrane, even when aluminum is present in the electrolyte membrane. If a compression jig made of iron, copper, chromium or others is used, when a foreign metal material such as iron, copper, or chromium enters the electrolyte membrane, iron ion, copper ion, and others may cause a chemical reaction such as substitution of a functional group in the electrolyte membrane material. Accordingly, in order to prevent reduction in the electrical generating property due to degradation in electrolyte membrane  410 , it is preferable not to use iron, copper, and chromium as a material for compression jigs  611  and  612 . 
         [0080]    As compression jigs  611  and  612 , a resin such as polytetrafluoroethylene (PTFE) or glass may be used for reducing the possibility of contamination, although the heat transfer property will be reduced. 
         [0081]    When performing thermal compression fusing nonwoven fabric  516 , the temperature of compression jigs  611  and  612  is preferably set in a range from 120° C. to 170° C. When the set temperature is too high, nonwoven fabric  516  is depolymerized due to thermal degradation and has decreased tension strength, losing its function as a reinforcement layer in electrolyte membrane  410 . 
         [0082]    When performing thermal compression, a pressure applied to nonwoven fabric  516  and time for applying the pressure may be determined to be the most suitable pressure and time depending on the temperature for compression jigs  611  and  612 , such that the resin material for nonwoven fabric  516  is melt by the heat and neighboring fibers may be fused. 
         [0083]    In addition to the thermal fusing, the fusing may be performed by irradiating nonwoven fabric with a laser beam. Alternatively, the fusing may be performed by fusing nonwoven fabric using an organic solvent, or supplying a solution containing a material for the nonwoven fabric dissolved to the part to be fused. A large-scale apparatus such as a roller press is required for thermal compression. However, the methods using irradiation of a laser beam and an organic solvent do not require such a large-scale apparatus. 
         [0084]    The fused region of nonwoven fabric  516  is preferably in a range from at least 0.5% to at most 10% of a total area corresponding to power generating region  422  in nonwoven fabric  516 . If the area of the fused region is smaller than the lower limit value, it is difficult to maintain stability in the dimensions of the electrolyte membrane, and power generation efficiency is reduced if the area exceeds the upper limit value. It is preferable that fused parts are equally spaced, and it is more preferable that the distance between the fused parts is at least 10 mm and at most 20 mm If the area of the fused region is smaller than the lower limit value, it is difficult to maintain stability in dimension of the electrolyte membrane, and power generation efficiency is reduced if the area exceeds the upper limit value. It is preferable that fused parts are formed in a grid pattern. When used as a fuel cell, the grid pattern stabilizes the dimension of the electrolyte membrane and is more likely to reduce stress exerted from outside. 
         [0085]    (iii) Step for Forming Electrolyte Membrane 
         [0086]      FIGS. 4A to 4C  are schematic diagrams illustrating a method for manufacturing electrolyte membrane  410  according to Embodiment 1. First, as illustrated in  FIG. 4A , polyethylene terephthalate sheet (PET base)  711  is prepared as a base. Nonwoven fabric  516  having fused part  510  is placed on PET base  711 . Subsequently, nonwoven fabric  516  is impregnated with electrolyte solution  712 , as illustrated in  FIG. 4B . With the process described above, electrolyte membrane  410  as illustrated in  FIG. 4C  is manufactured. 
         [0087]    As electrolyte solution  712 , a mixed solvent of water and ethanol is preferable. In order to impregnate nonwoven fabric  516  made of PVDF having fused part  510  with electrolyte solution  712 , it is preferable that the ratio of water in the solvent is lower than or equal to half. When the ratio of water in the solvent is greater than or equal to 50%, electrolyte solution  712  does not seep through due to hydrophobic property of PVDF, preventing proper application. 
         [0088]    Alternatively, electrolyte solution  712  may be applied on nonwoven fabric  516  having fused part  510 , using a bar coater (not illustrated). Alternatively, electrolyte solution  712  may be applied using a slit die, or by printing or spraying. It is preferable that a nonwoven fabric having a high rate of interstices per unit area is fully impregnated with the electrolyte solution. 
         [0089]    After electrolyte solution  712  is applied, the solvent is vaporized so as to dry the solution. Note that, it is preferable that an electrolyte solution having the density adjusted is applied to form an electrolyte membrane having a predetermined thickness after drying. 
         [0090]    After electrolyte solution  712  applied is dry, annealing is performed so as to crystallize the electrolyte. Crystallizing the electrolyte improves its durability. In this case, it is preferable that annealing is performed in an air atmosphere under the atmospheric pressure. It is even more preferable that the annealing is performed under a nitrogen atmosphere which is a gas inert to the electrolyte. Annealing in a reduced pressure state prevents bubbles and pin holes from appearing in electrolyte solution  712  applied. 
         [0091]    It is preferable that the temperature for annealing is higher by 10° C. or more than the glass-liquid transition temperature of the electrolyte material. If the annealing temperature is too low, sufficient crystallization does not occur, making it unable to secure durability of electrolyte membrane  410 . It is preferable that the annealing time is at least 30 minutes and at most 2 hours. If the annealing time is too short, sufficient crystallization does not occur. If the annealing time is too long, excessive crystallization occurs, reducing proton conductivity. 
         [0092]    (Variation 1 of Manufacturing Method) 
         [0093]      FIGS. 5A to 5C  are schematic diagrams for applying an electrolyte material in an electrolyte membrane according to Variation of Embodiment 1. In Embodiment 1, electrolyte membrane  410  is obtained by applying electrolyte solution  712  to nonwoven fabric  516  on PET base  711  and drying electrolyte solution  712 , as illustrated in  FIGS. 4A to 4C . However, as illustrated in  FIG. 5A , electrolyte solution  712  is applied on PET base  711  beforehand, and nonwoven fabric  516  having fused part  510  is provided before the solvent in electrolyte solution  712  dries, as illustrated in  FIG. 5B , such that nonwoven fabric  516  sinks in electrolyte solution  712 . When electrolyte membrane  410  is formed by sinking nonwoven fabric  516  having fused part  510  in the electrolyte solution applied, nonwoven fabric  516  having fused parts  510  is preferably fully soaked in electrolyte solution  712 . With the process described above, electrolyte membrane  410  as illustrated in  FIG. 5C  is manufactured. 
         [0094]    When nonwoven fabric  516  having fused parts  510  is exposed from electrolyte solution  712 , irregularity is formed on the surface of electrolyte membrane  410  by nonwoven fabric  516  exposed from electrolyte membrane  410 . If water generated when the fuel cell generates power accumulates in the irregularity, the water inhibits movement of electrons and gas, and there is a possibility that the electrical generating property is reduced. Accordingly, it is preferable that nonwoven fabric  516  is not exposed to electrolyte membrane  410 . 
         [0095]    (Variation 2 of Manufacturing Method) 
         [0096]      FIGS. 6A to 6D  are schematic diagrams illustrating processes for applying an electrolyte material, in an electrolyte membrane according to Variation of Embodiment 1. First, electrolyte solution  712  is applied on PET base  711  in advance, as illustrated in  FIG. 6A . Subsequently, after applied electrolyte solution  712  is dry as illustrated in  FIG. 6B , nonwoven fabric  516  having fused parts  510  is placed on the electrolyte material ( 712 ). Subsequently, electrolyte solution  712  is applied on nonwoven fabric  516 , forming electrolyte membrane  410 , as illustrated in  FIG. 6C . With this, as illustrated in  FIG. 6D , layer  713  only composed of the electrolyte may be formed above and below nonwoven fabric  516 . As a result, protons are likely to be transported from catalyst layers  127  and  128  formed above and below electrolyte membrane  410 , improving electrical generating property. 
         [0097]      FIG. 7  is a schematic diagram illustrating a method for fusing nonwoven fabric  516  using laser beam  621 . A predetermined pattern of fused part  510  can be formed by collecting laser beam  621  oscillated by laser oscillator  622  on nonwoven fabric  516  using concentrating optics  623 , and scanning nonwoven fabric  516  with laser beam  621  using driving scanning system (not illustrated). In  FIG. 7 , the pattern of fused part  510  is formed by scanning nonwoven fabric  516  with laser beam  621 . However, the work (nonwoven fabric  516 ) may be moved, while laser beam  621  can be fixed. Accordingly, it is possible to maintain a positional accuracy of an optical device adjusted at high accuracy for a long time. 
         [0098]    Alternatively, an optical system including a combination of mirror galvanometer (not illustrated) and fθ lens (not illustrated) may be used. With this configuration, it is possible to reduce the size of mechanism since it is not necessary to use a driving scanning system. Furthermore, productivity for forming fused part  510  can be improved. In addition, by splitting the laser beam through a diffraction grating (not illustrated) such as DOE and nonwoven fabric  516  is irradiated with split laser beams at the same time, the pattern on fused part  510  is collectively formed, improving the productivity in forming fused part  510 . 
         [0099]    Laser beam  621  may be continuous wave laser beam  621  or pulsed wave laser beam  621 . When patterning fused part  510  by sweeping laser beam  621  or moving the work (nonwoven fabric  516 ), continuous wave laser beam  621  is preferably used. When pulsed laser beam  621  is used, laser beam  621  is intermittently oscillated. Accordingly, when the scanning speed of laser beam  621  or moving speed of the work (nonwoven fabric  615 ) is sufficiently high, the fused part is formed discontinuously by pulsed laser beam  621  fusing only a region irradiated with pulsed laser beam  621 . 
         [0100]    Since nonwoven fabric  516  is fused by absorbing laser beam  621  for heating, laser beam  621  having a wavelength in an infrared range is preferable, and laser beam  621  having a wavelength in the near infrared range such as a semiconductor laser and a carbon dioxide laser is even more preferable. 
         [0101]      FIG. 8  is a schematic diagram illustrating a method for fusing nonwoven fabric  516  using organic solvent  633 . Fused part  511  is formed by supplying organic solvent  633  to fused part  511  and melting nonwoven fabric  516  in a solvent. When supplying organic solvent  633  to fused part  511 , a small amount of organic solvent  633  may be supplied by filling syringe  631  with organic solvent  633  and extruding organic solvent  633  from nozzle  632  attached to an end. 
         [0102]    In Embodiment 1, an air-pulse dispenser (not illustrated) may be used for extruding organic solvent  633 . For patterning fused part  510 , the syringe or the nozzle may be moved, or the work (nonwoven fabric) may be moved. 
         [0103]    For melting nonwoven fabric  516 , organic solvent  633  used for producing a solution used for electrospinning may be used. Alternatively, another solvent capable of melting nonwoven fabric  516  may be used. 
         [0104]    The present invention is not limited to Embodiment 1 described above, and other embodiments which are variations of Embodiment 1 may be possible. Embodiments 2 to 4 will be described as follows as variations of Embodiment 1, focusing on the differences from Embodiment 1. 
       Embodiment 2 
       [0105]      FIG. 9  is a partial cutaway top view of cell module  170 A having fused parts in a grid pattern, composing a polymer electrolyte fuel cell according to Embodiment 2. As illustrated in  FIG. 9 , fused part  513  of nonwoven fabric included in electrolyte membrane  410 A is arranged in a grid pattern in a region corresponding to power generating region  422  in Embodiment 2. 
         [0106]    It is preferable that a line width of fused part  513  in a grid pattern is approximately 0.1 mm or wider for fusing adjacent fibers. Note that in Embodiment 2, the line width of fused part  513  is set as 1 mm. 
         [0107]    It is preferable that distance W 2  between grid-shaped fused parts  513  is in a range from 10 mm to 20 mm in consideration of the electrical generating property and preventing swelling in the thickness direction. More specifically, when the distance between fused parts  513  in a grid pattern is too large, the electrolyte material swells between the grid-shaped fused parts  513 , changing the thickness. 
         [0108]    In Embodiment 2, it is preferable that the thickness of electrolyte membrane  410 A is set to be in a range from 20 to 30 μm, and that the distance between the grid-shaped fused parts  513  is set to be 20 mm. However, when electrolyte membrane  410 A is thin, the change in the dimensions in the in-plane direction is smaller than the change in the dimensions in the thickness direction. Accordingly, the distance between fused parts  513  may be increased. A reduction in a total area of fused parts  513  with respect to a total area of the part corresponding to power generating region  422  allows better conduction of protons, which improves power generating efficiency of a fuel cell. 
         [0109]    Alternatively, when a nonwoven fabric made of a nonwoven fiber having large tension strength is used, the distance between fused parts  513  may be increased. When the distance between fused parts  513  is large, the ratio of the total area of the fused parts  513  to the total area of the part corresponding to power generating region  422  becomes small. Accordingly, this is preferable since the influence on proton conduction is reduced. 
         [0000]    The ratio of fused parts  513  to the total area of the part corresponding to power generating region  422  is preferably 0.5 to 10%, based on the line width and distance of fused parts  513  described above. Note that, the ratio of the part corresponding to power generating region  422  to the total area of fused parts  513  is approximately 5% in Embodiment 2. 
       Embodiment 3 
       [0110]      FIG. 10  is a partial cutaway top view of cell module  170 B having dotted fused parts, composing a polymer electrolyte fuel cell according to Embodiment 3. As illustrated in  FIG. 10 , fused parts  514  of the nonwoven fabric included in electrolyte membrane  410 B are arranged in dots within a region corresponding to power generating region  422 . 
         [0111]    It is preferable that the diameter of dotted fused parts  514  is approximately 0.1 mm or larger so as to fuse adjacent fibers. Note that in embodiment 3, the diameter of fused part  514  is set as 1 mm. 
         [0112]    Distance W 2  between dotted fused parts  514  is preferably in a range from 10 mm to 20 mm. The distance between dotted fused parts  514  here is set as 20 mm. When the distance between dotted fused parts  514  is too large, the electrolyte material swells between dotted fused parts  514 , resulting in a change in the thickness. 
         [0113]    In Embodiment 3, the thickness of electrolyte membrane  410 B is preferably set as 20 to 30 nm, and the distance between dotted fused parts  514  is preferably set as 20 mm. However, when electrolyte membrane  410 B is thin, the change in the dimension in the thickness direction is small. Accordingly, the distance between fused parts  514  may be increased. When the distance between fused parts  514  is large, the ratio of the total area of the fused parts  514  to the total area of the part corresponding to power generating region  422  becomes small. Accordingly, this is preferable since the influence on proton conduction is reduced. 
       Embodiment 4 
       [0114]      FIG. 11  is a partial cutaway top view of cell module  170 C having fused parts along flow paths composing a polymer electrolyte fuel cell according to Embodiment 4. As illustrated in  FIG. 11 , fused part  410 C of nonwoven fabric included in Embodiment 4 is arranged along fuel gas flow paths  147  and  148  provided on separators  141  and  142  in  FIG. 1 , in a region corresponding to power generation region  422 . 
         [0115]    In Embodiment 4, fused parts  515  may be line-shaped or dotted as long as fused parts  515  are arranged along fuel gas flow paths  147  and  148 . Here, the line width or the diameter of a dot of fused part  515  is set as approximately 1 mm. In Embodiment 4, since the widths of the fibers have a distribution ranging from approximately 0.1 to 100 μm, the line width or the diameter of the dot of fused part  515  along the flow path is preferably 0.1 mm or greater for fusing two or more adjacent fibers. 
       EXAMPLES 
     Example 1 
     Production of Nonwoven Fabric (Nonwoven Fiber) Material 
       [0116]    PVDF was dissolved into DMAc by mixing 80 g of DMAc with 20 g of PVDF in pellets (manufactured by Arkema, molecular weight 275,000) and stirring the mixture by a rotation revolution mixer. 
         [0117]    [Forming Nonwoven Fabric] 
         [0118]    A nonwoven fiber manufacturing apparatus (manufactured by Panasonic Factory Solutions) to be used for electrospinning was provided. A 24G (inner diameter 0.31 mm, outer diameter 0.57 mm, and needle length 15 mm) nozzle made of stainless steel was attached to the end of a disposable syringe having a capacity of 10 mL. 
         [0119]    A nonwoven fabric was manufactured under the following conditions: distance from a collector to the nozzle was set as 120 mm; the voltage applied between the collector and the nozzle was set as 20 kV; and the pressure for injecting the solution was set as 30 kPa. The diameters of fibers in the nonwoven fabric formed on the collector had a distribution from 400 nm to 1100 nm, and the average diameter was 700 nm. The ratio of interstices per unit area of the nonwoven fabric was approximately 90%. 
         [0120]    In order to improve productivity, 5 disposable syringes each having a capacity of 10 mL were provided. 5 nozzles were arranged in a straight line having intervals of 15 mm in between. The nozzles are scanned at a speed of 5 mm/s, and a nonwoven fabric having a uniform thickness was formed by scanning a plurality of times in a predetermined activation. A nonwoven fabric of 300 mm was manufactured. Mass per unit area was set as 1.28 mg/cm 2 , and the thickness of the nonwoven fabric was set as 25 nm. 
         [0121]    [Production of Fused Part] 
         [0122]    Fusing jigs made of aluminum were used. One set of fusing jigs were provided for the upper surface and the lower surface. Each of the fusing jigs had a straight-line projection. The fusing jig was approximately 300 mm. A nonwoven fabric was clamped between the jigs for the upper surface and the lower surface, and heat and pressure were applied to the nonwoven fabric by using a heat press machine. A straight-line fused part was created in the nonwoven fabric by applying a pressure of approximately 1 MPa at 130° C. for 2 minutes. 
         [0123]    [Method for Forming Electrolyte Membrane] 
         [0124]    As an electrolyte solution, a perfluorocarbon sulfonic acid solution (Nafion®, manufactured by Du Pont, SE-20092) was used. The nonwoven fabric having fused parts are impregnated with the electrolyte solution, using a bar coater. The nonwoven fabric was impregnated with the electrolyte solution such that the thickness of the nonwoven fabric after drying and baking the impregnated nonwoven fabric would be 30 μm. Drying/baking was performed at 120° C. for one hour. PET base was removed after drying and baking so as to obtain an electrolyte membrane having a nonwoven fabric with fused parts as a reinforcement layer. 
         [0125]    [Measurement of Dry/Wet Dimensional Change Rate] 
         [0126]    An initial dimension of the electrolyte membrane was determined as follows: first, the electrolyte membrane was cut in a square having 30 mm on each side to create a sample; and the vertical length and the horizontal length of the sample were measured after leaving the sample in an atmosphere of temperature 25° C. and humidity 50% for 16 hours. Subsequently, the vertical length and the horizontal length of the sample were measured after the sample was soaked in deionized water at 80° C. The value was divided by the initial dimension, and the result was determined as the dry/wet dimensional change rate. Table 1 shows the results. 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                 Comparative 
                 Comparative 
               
               
                   
                 Example 1 
                 Example 1 
                 Example 2 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 In-plane direction 
                 102.14% 
                 118.30% 
                 102.57% 
               
               
                 dimensional change rate 
               
               
                 Thickness direction 
                 122.21% 
                 141.80% 
                 167.76% 
               
               
                 dimensional change rate 
               
               
                   
               
             
          
         
       
     
       Comparative Example 1 
       [0127]    A nonwoven fabric as a reinforcement layer was not used, and a perfluorocarbon sulfonic acid solution (Nafion® manufactured by Du Pont, SE-20092) was used as an electrolyte solution. An appropriate amount of the electrolyte solution was applied on a PET base, using a bar coater such that the thickness of an electrolyte membrane obtained after drying and baking would be 30 μm. Drying/baking was performed at 120° C. for one hour. The PET base is removed after the drying and baking, forming an electrolyte membrane. Dry/wet dimensional change rate was measured in the same manner as Example 1. Table 1 shows the results. 
       Comparative Example 2 
       [0128]    As an electrolyte solution, a perfluorocarbon sulfonic acid solution (Nafion®, manufactured by Du Pont SE-20092) was used. The nonwoven fabric was impregnated with the electrolyte solution using a bar coater. The nonwoven fabric was impregnated such that the thickness of the nonwoven fabric after drying and baking the impregnated nonwoven fabric would be 30 μm. Drying/baking was performed at 120° C. for one hour. A PET base was removed after the drying and baking, and the electrolyte membrane having a nonwoven fabric with fused parts as a reinforcement layer was obtained. A dry/wet dimensional change rate was measured in the same manner as Example 1. Table 1 shows the results. 
         [0129]    The dimensional change rate in the planar direction in Comparative Example 2 was 102.57%, compared to 118.30% in Comparative Example 1. It is assumed that the nonwoven fabric provided on the entire surface as the reinforcement layer reduces the amount of dimensional change in the planar direction. In contrast, the dimensional change rate in the thickness direction was 167.76%, compared to 141.80%. Since the nonwoven fabric is piled in layers and provided in the electrolyte membrane in the thickness direction, it is assumed that the dimension in the thickness direction increased by swelling due to the electrolyte containing moisture. 
         [0130]    The dimensional change rate in the planar direction in Example 1 is 102.14%, which is substantially same as 102.57% in Comparative Example 2. It is assumed that the dimensional change is substantially the same since the nonwoven fabric has the fused part provided on the entire surface. In contrast, the dimensional change rate in the thickness direction is 122.21% in Example 1, compared to 167.76% in Comparative Example 2. It is assumed that the dimension in the thickness direction is reduced by preventing expansion between the layers due to swelling of the electrolyte caused by moisture, using fused part provided on the nonwoven fabric layered. 
         [0131]    The present application claims the priority of an earlier Japanese patent application filed by the same applicant, that is, Japanese Patent Application No. 2011-173510 filed on Aug. 9, 2011, the entire content of which is incorporated by reference herein. 
       INDUSTRIAL APPLICABILITY 
       [0132]    According to the present invention, a nonwoven fabric used for reinforcing an electrolyte membrane can be effectively manufactured. Therefore, an electrolyte membrane which is thin has a high mechanical strength, high dimensional stability when containing moisture and low resistance can be manufactured. A membrane-electrode assembly obtained by using the electrolyte membrane produces a polymer electrolyte fuel cell having high electric characteristics and high durability, and is applicable to a household cogeneration system, an in-car fuel cell system, a power source for a base station used for mobile communication, and others. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           127 ,  128  Electrode layer 
           133 ,  134  Gas diffusion layer 
           141 ,  142  Separator 
           145 ,  146  Groove 
           147 ,  148  Gas flow path 
           153 ,  154  Gasket 
           160  Frame 
           161  Fuel gas inlet 
           162  Fuel gas outlet 
           170  Cell module (cell) 
           410  Electrolyte membrane 
           422  Power generating region 
           423  Membrane fixing part 
           510  Fused part 
           516  Nonwoven fabric