Electrolyte membrane for solid polymer fuel cell, method for manufacturing same, and solid polymer fuel cell

A 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 surface so as to sandwich the electrode layer. 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 on a part of the nonwoven fabric that is a part corresponding to of the solid polymer fuel cell. Two or more nonwoven fibers are fused to each other, and the thickness thereof is thinner than the membrane thickness of the unwoven fabric.

TECHNICAL FIELD

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

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.

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.

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.

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.

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).

As illustrated inFIG. 12, PTL 1 discloses a membrane-electrode assembly having solid-polymer electrolyte membrane111and porous sheet113provided as a reinforcement layer in electrolyte membrane111. According to the configuration of membrane electrode assembly in PTL 1, porous sheet113is present at a center part in the thickness direction of electrolyte membrane111, and reduces the change in dimension in the in-plane direction.

CITATION LIST

Patent Literature

However, in the configuration according to PTL 1, a region only with the electrolyte material (resin layer125) is present on both surfaces of porous sheet113. Accordingly, resin layer125is not restricted by porous sheet113in 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 membrane111swells, electrode layers127and128are expanded outward, pressing gas diffusion layers133and134against separators141and142.

Gas diffusion layers133and134pressed against separators141and142respectively enter grooves145and146formed in separators141and142. By gas diffusion layers133and134entering grooves145and146, the spaces of grooves145and146are 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.

FIG. 13is a cross-sectional view illustrating an assembled cell module including a nonwoven fabric as a reinforcement layer in an electrolyte membrane. As illustrated inFIG. 13, when the nonwoven fabric is used as reinforcement layer412, the nonwoven fabric having a three-dimensional structure can be included in the full thickness direction of electrolyte membrane431.

FIG. 14is a schematic view illustrating electrolyte membrane431swelling due to moisture. Electrolyte membrane431has nonwoven fabric as a reinforcement layer in a solid polymer electrolyte. As illustrated inFIG. 14, since nonwoven fabric521has a structure in which nonwoven fibers are piled in layers, no force for controlling electrolyte membrane431is exerted in the thickness direction. When electrolyte membrane431absorbs moisture, the thickness between layers of nonwoven fabric521increases and swelling of the entire membrane in the thickness direction cannot be prevented as a result. When the electrolyte membrane431is swollen, electrode layers127and128are expanded outward, pressing gas diffusion layers133and134against separators141and142.

SUMMARY OF THE INVENTION

Gas diffusion layers133and134pressed against separators141and142respectively enter grooves145and146formed in separators141and142. Since gas diffusion layers133and134enter grooves145and146, the spaces in grooves145and146become 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.

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.

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.

The present invention has been conceived in order to solve the above problems. 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.

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

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.

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.

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

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.

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.

DETAILED DESCRIPTION OF THE INVENTION

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.

FIG. 1is a cross-sectional view schematically illustrating an assembled cell module composing a polymer electrolyte fuel cell according to Embodiment 1.

As illustrated inFIG. 1, cell module (cell)170composing a polymer electrolyte fuel cell according to Embodiment 1 includes electrolyte membrane410, electrode layers127and128provided in power generating regions422on an upper surface and a lower surface of electrolyte membrane410respectively, and a pair of separators141and142provided so as to interpose electrode layers127and128. Electrolyte membrane410includes an electrolyte material and nonwoven fabric516included 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. Separators141and142may include grooves145and146in parts corresponding to power generating region422inside in separators141and142, and gas flow paths147and148in a space defined by the bottom surfaces and the side surfaces of grooves145and146.

Cell module170further includes gas diffusion layer133between electrode layer127and separator141, and gas diffusion layer134between electrode layer128and separator142. Gaskets153and154are provided in membrane fixing part423at the ends of electrolyte membrane410.

FIG. 2is a partial cutaway top view of cell module170composing the polymer electrolyte fuel cell according to Embodiment 1. As illustrated inFIG. 2, cell module170includes substantially square-shaped frame160. Fuel gas inlet161is provided at the upper end of frame160, and fuel gas outlet162is provided at the lower end of frame160. Electrolyte membrane410is provided at a part of frame160, corresponding to power generating region422.

As illustrated inFIG. 2, nonwoven fabric516includes a plurality of fused parts510. Each of fused parts510is provided in a straight line in power generating region422in cell module170, includes two or more strands of nonwoven fiber fused, and has a thickness smaller than the thickness of nonwoven fabric516. Fused part510is preferably provided at a part corresponding to power generating region422in cell module170, particularly at a part corresponding to gas flow paths147and148in the separator, as illustrated inFIG. 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 membrane410.

In Embodiment 1, straight fused parts510are provided parallel to sides of frame160in which fuel gas inlet161and fuel gas outlet162are not provided, that is, right end (left end). However, straight fused part510may be provided vertical to sides on which fuel gas inlet161and fuel gas outlet162of frame160are not provided, and may be provided diagonal to a side of frame160.

Since it is necessary to bond two or more adjacent strands of fiber, fused part510is preferably wider than or equal to the width of adjacent fibers. Since nonwoven fabric516has a distribution of fibers of approximately 0.1 μm to 100 μm, it is preferable that the width of fused part510is 0.1 mm or more for fusing adjacent fibers. Note that, in Embodiment 1, the width of straight fused part510is approximately 1 mm.

At fused part510in nonwoven fabric516, the interstices between strands of nonwoven fiber516are narrow or not present, which inhibits delivery of protons. If the distance between fused parts510is too small, the delivery of proton is inhibited, reducing the electrical generating property of the fuel cell. In contrast, if the distance between fused parts510is too large, the electrolyte material swells between fused parts510, 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 W1between fused parts510in a range from 10 mm to 20 mm Note that, in Embodiment 1, the width of straight fused parts510W1is 20 mm.

It is preferable to set the thickness or electrolyte membrane410in a range from 20 μm to 30 μm, and distance WI at fused part510as 20 mm. However, when the thickness of electrolyte membrane410is smaller than the range described above, the change in dimension with respect to thickness direction is small. Accordingly, the distance WI between straight fused parts510may be increased. Since the total area of fused part with respect to a power generating area is reduced, conduction or protons is improved. As a result, power generating efficiency of a fuel cell improves.

The fused region of nonwoven fabric516is preferably at least 0.5% and at most 10% of a total area corresponding to power generating region422in nonwoven fabric516. 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 parts510are equally spaced, and it is more preferable that the distance between fused parts510is 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 membrane410, and power generation efficiency is reduced if the distance exceeds the upper limit value.

It is preferable that fused parts510are formed in a grid pattern. When used as a fuel cell, the grid pattern stabilizes the dimension of electrolyte membrane410and is more likely to reduce stress exerted from outside.

When a nonwoven fabric made of nonwoven fiber having large tension strength is used, distance W1between straight fused parts510may be increased. When distance W1between straight fused parts510is large, the total area of the fused part with respect to the total area of the part corresponding to power generating region422becomes small. Accordingly, the influence on the proton conduction also becomes small, which is advantageous. The ratio of fused part510to the total area of the part corresponding to power generating region422is preferably 0.5 to 10%, based on the line width and distance W1of the fused parts described above. Note that, the ratio of the part corresponding to power generating region422to the total area of fused parts510in embodiment 1 is approximately 5%.

The hardness of electrolyte membrane410at fused part510is different from a part that is not fused. Variation in hardness of electrolyte membrane410at membrane fixing part423causes variation in strength of fixing frame160and electrolyte membrane410. Accordingly, in order to stabilize the strength of fixing frame160and electrolyte membrane410, it is preferable that fused part510is only provided in power generating region422, not in membrane fixing part423.

As illustrated inFIG. 1, fused part510is formed at a part of nonwoven fabric516, which is formed by stacking nonwoven fibers in layers. In this case, it is preferable to set the thickness of fused part510as thin as possible while maintaining thickness412of nonwoven fabric516indicated by arrow412at a predetermined thickness. In the cross section in the thickness direction of nonwoven fabric516, it is preferable that nonwoven fabric516is in a shape connecting one main surface of the nonwoven fabric and the other main surface of the nonwoven fabric through fused part510as if the figures of number “8” are horizontally placed. This shape is for reducing the change in the dimension of electrolyte membrane410in the thickness direction. In addition, a propagation path for protons can be secured.

Furthermore, the thickness of the fused part510is not particularly limited as long as the change in the dimension of electrolyte membrane410is reduced and the propagation path for the protons is secured. More specifically, the thickness of nonwoven fabric516is preferably 5 to 65% of the thickness of the electrolyte membrane, and the thickness of fused part510is preferably 5 to 50% of the thickness of nonwoven fabric516.

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 fabric516manufactured by electrospinning has fiber having a small diameter, and thus the ratio of interstices per unit area of nonwoven fabric516can be increased. Accordingly, it is preferable to use nonwoven fabric516manufactured by electrospinning.

The temperature of electrolyte membrane410reaches approximately 80° C. when the fuel cell is in operation. Therefore, as a material for the nonwoven fabric516, a material having sufficient heat-resistance and chemical stability in the temperature range is preferably used. As a specific material for nonwoven fabric516, 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 fabric516. By providing nonwoven fabric516made of a hydrophobic material inside electrolyte membrane410, unnecessary moisture produced in electrolyte membrane410by power-generating reaction is drained, making it possible to reduce unnecessary swelling caused by the moisture.

In order to reduce the change in the dimension of electrolyte membrane410due to swelling and shrinking, electrolyte membrane410preferably 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.

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.

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 membrane410due 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 membrane410.

<Method for Manufacturing Polymer Electrolyte Fuel Cell>

A method for manufacturing an electrolyte membrane for a polymer electrolyte fuel cell will be described.

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 fabric516manufactured by the electrospinning is fused by thermal compression fusing will be described step by step.

(i) Step for Providing Nonwoven Fabric

First, nonwoven fabric516is 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.

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.

(ii) Step for Forming Fused Part

FIGS. 3A to 3Care schematic diagrams illustrating a method for creating a fused part of nonwoven fabric by the thermal compression fusing according to Embodiment 1. First, compression jigs611and612having projections613are provided. Jigs611and612provided preferably include projections613at parts corresponding to gas flow paths147and148of separators. Subsequently, compression jigs611and612are provided above and below nonwoven fabric516, such that nonwoven fabric516is interposed between compression jigs611and612. Subsequently, heat is transferred to nonwoven fabric516substantially at the same time as a pressure is applied such that projections613contact nonwoven fabric516. By the thermal compression fusing on a part of nonwoven fabric516, nonwoven fabric516having fused part510is formed. Since nonwoven fabric516includes layers of nonwoven fiber stacked, by fusing nonwoven fabric516using the thermal compression fusing, nonwoven fibers contact each other in the thickness direction of electrolyte membrane410, allowing secure fusing.

As compression jigs611and612, 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 membrane410, it is preferable not to use iron, copper, and chromium as a material for compression jigs611and612.

As compression jigs611and612, 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.

When performing thermal compression fusing nonwoven fabric516, the temperature of compression jigs611and612is preferably set in a range from 120° C. to 170° C. When the set temperature is too high, nonwoven fabric516is depolymerized due to thermal degradation and has decreased tension strength, losing its function as a reinforcement layer in electrolyte membrane410.

When performing thermal compression, a pressure applied to nonwoven fabric516and time for applying the pressure may be determined to be the most suitable pressure and time depending on the temperature for compression jigs611and612, such that the resin material for nonwoven fabric516is melt by the heat and neighboring fibers may be fused.

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.

The fused region of nonwoven fabric516is preferably in a range from at least 0.5% to at most 10% of a total area corresponding to power generating region422in nonwoven fabric516. 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.

(iii) Step for Forming Electrolyte Membrane

As electrolyte solution712, a mixed solvent of water and ethanol is preferable. In order to impregnate nonwoven fabric516made of PVDF having fused part510with electrolyte solution712, 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 solution712does not seep through due to hydrophobic property of PVDF, preventing proper application.

Alternatively, electrolyte solution712may be applied on nonwoven fabric516having fused part510, using a bar coater (not illustrated). Alternatively, electrolyte solution712may 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.

After electrolyte solution712is 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.

After electrolyte solution712applied 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 solution712applied.

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 membrane410. 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.

FIGS. 5A to 5Care schematic diagrams for applying an electrolyte material in an electrolyte membrane according to Variation of Embodiment 1. In Embodiment 1, electrolyte membrane410is obtained by applying electrolyte solution712to nonwoven fabric516on PET base711and drying electrolyte solution712, as illustrated inFIGS. 4A to 4C. However, as illustrated inFIG. 5A, electrolyte solution712is applied on PET base711beforehand, and nonwoven fabric516having fused part510is provided before the solvent in electrolyte solution712dries, as illustrated inFIG. 5B, such that nonwoven fabric516sinks in electrolyte solution712. When electrolyte membrane410is formed by sinking nonwoven fabric516having fused part510in the electrolyte solution applied, nonwoven fabric516having fused parts510is preferably fully soaked in electrolyte solution712. With the process described above, electrolyte membrane410as illustrated inFIG. 5Cis manufactured.

When nonwoven fabric516having fused parts510is exposed from electrolyte solution712, irregularity is formed on the surface of electrolyte membrane410by nonwoven fabric516exposed from electrolyte membrane410. 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 fabric516is not exposed to electrolyte membrane410.

FIGS. 6A to 6Dare schematic diagrams illustrating processes for applying an electrolyte material, in an electrolyte membrane according to Variation of Embodiment 1. First, electrolyte solution712is applied on PET base711in advance, as illustrated inFIG. 6A. Subsequently, after applied electrolyte solution712is dry as illustrated inFIG. 6B, nonwoven fabric516having fused parts510is placed on the electrolyte material (712). Subsequently, electrolyte solution712is applied on nonwoven fabric516, forming electrolyte membrane410, as illustrated inFIG. 6C. With this, as illustrated inFIG. 6D, layer713only composed of the electrolyte may be formed above and below nonwoven fabric516. As a result, protons are likely to be transported from catalyst layers127and128formed above and below electrolyte membrane410, improving electrical generating property.

FIG. 7is a schematic diagram illustrating a method for fusing nonwoven fabric516using laser beam621. A predetermined pattern of fused part510can be formed by collecting laser beam621oscillated by laser oscillator622on nonwoven fabric516using concentrating optics623, and scanning nonwoven fabric516with laser beam621using driving scanning system (not illustrated). InFIG. 7, the pattern of fused part510is formed by scanning nonwoven fabric516with laser beam621. However, the work (nonwoven fabric516) may be moved, while laser beam621can be fixed. Accordingly, it is possible to maintain a positional accuracy of an optical device adjusted at high accuracy for a long time.

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 part510can be improved. In addition, by splitting the laser beam through a diffraction grating (not illustrated) such as DOE and nonwoven fabric516is irradiated with split laser beams at the same time, the pattern on fused part510is collectively formed, improving the productivity in forming fused part510.

Laser beam621may be continuous wave laser beam621or pulsed wave laser beam621. When patterning fused part510by sweeping laser beam621or moving the work (nonwoven fabric516), continuous wave laser beam621is preferably used. When pulsed laser beam621is used, laser beam621is intermittently oscillated. Accordingly, when the scanning speed of laser beam621or moving speed of the work (nonwoven fabric615) is sufficiently high, the fused part is formed discontinuously by pulsed laser beam621fusing only a region irradiated with pulsed laser beam621.

Since nonwoven fabric516is fused by absorbing laser beam621for heating, laser beam621having a wavelength in an infrared range is preferable, and laser beam621having a wavelength in the near infrared range such as a semiconductor laser and a carbon dioxide laser is even more preferable.

FIG. 8is a schematic diagram illustrating a method for fusing nonwoven fabric516using organic solvent633. Fused part510is formed by supplying organic solvent633to fused part510and melting nonwoven fabric516in a solvent. When supplying organic solvent633to fused part510, a small amount of organic solvent633may be supplied by filling syringe631with organic solvent633and extruding organic solvent633from nozzle632attached to an end.

In Embodiment 1, an air-pulse dispenser (not illustrated) may be used for extruding organic solvent633. For patterning fused part510, the syringe or the nozzle may be moved, or the work (nonwoven fabric) may be moved.

For melting nonwoven fabric516, organic solvent633used for producing a solution used for electrospinning may be used. Alternatively, another solvent capable of melting nonwoven fabric516may be used.

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.

FIG. 9is a partial cutaway top view of cell module170A having fused parts in a grid pattern, composing a polymer electrolyte fuel cell according to Embodiment 2. As illustrated inFIG. 9, fused part513of nonwoven fabric included in electrolyte membrane410A is arranged in a grid pattern in a region corresponding to power generating region422in Embodiment 2.

It is preferable that a line width of fused part513in a grid pattern is approximately 0.1 mm or wider for fusing adjacent fibers. Note that in Embodiment 2, the line width of fused part513is set as 1 mm.

It is preferable that distance W2between grid-shaped fused parts513is 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 parts513in a grid pattern is too large, the electrolyte material swells between the grid-shaped fused parts513, changing the thickness.

In Embodiment 2, it is preferable that the thickness of electrolyte membrane410A is set to be in a range from 20 to 30 μm, and that the distance between the grid-shaped fused parts513is set to be 20 mm. However, when electrolyte membrane410A 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 parts513may be increased. A reduction in a total area of fused parts513with respect to a total area of the part corresponding to power generating region422allows better conduction of protons, which improves power generating efficiency of a fuel cell.

Alternatively, when a nonwoven fabric made of a nonwoven fiber having large tension strength is used, the distance between fused parts513may be increased. When the distance between fused parts513is large, the ratio of the total area of the fused parts513to the total area of the part corresponding to power generating region422becomes small. Accordingly, this is preferable since the influence on proton conduction is reduced.

The ratio of fused parts513to the total area of the part corresponding to power generating region422is preferably 0.5 to 10%, based on the line width and distance of fused parts513described above. Note that, the ratio of the part corresponding to power generating region422to the total area of fused parts513is approximately 5% in Embodiment 2.

FIG. 10is a partial cutaway top view of cell module170B having dotted fused parts, composing a polymer electrolyte fuel cell according to Embodiment 3. As illustrated inFIG. 10, fused parts514of the nonwoven fabric included in electrolyte membrane410B are arranged in dots within a region corresponding to power generating region422.

It is preferable that the diameter of dotted fused parts514is approximately 0.1 mm or larger so as to fuse adjacent fibers. Note that in embodiment 3, the diameter of fused part514is set as 1 mm.

Distance W2between dotted fused parts514is preferably in a range from 10 mm to 20 mm. The distance between dotted fused parts514here is set as 20 mm. When the distance between dotted fused parts514is too large, the electrolyte material swells between dotted fused parts514, resulting in a change in the thickness.

In Embodiment 3, the thickness of electrolyte membrane410B is preferably set as 20 to 30 nm, and the distance between dotted fused parts514is preferably set as 20 mm. However, when electrolyte membrane410B is thin, the change in the dimension in the thickness direction is small. Accordingly, the distance between fused parts514may be increased. When the distance between fused parts514is large, the ratio of the total area of the fused parts514to the total area of the part corresponding to power generating region422becomes small. Accordingly, this is preferable since the influence on proton conduction is reduced.

FIG. 11is a partial cutaway top view of cell module170C having fused parts along flow paths composing a polymer electrolyte fuel cell according to Embodiment 4. As illustrated inFIG. 11, fused part515of nonwoven fabric included in Embodiment 4 is arranged along fuel gas flow paths147and148provided on separators141and142inFIG. 1, in a region corresponding to power generation region422.

In Embodiment 4, fused parts515may be line-shaped or dotted as long as fused parts515are arranged along fuel gas flow paths147and148. Here, the line width or the diameter of a dot of fused part515is 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 part515along the flow path is preferably 0.1 mm or greater for fusing two or more adjacent fibers.

EXAMPLES

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.

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.

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 (i.e., the diameter of each fiber is in a range of 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%.

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/cm2, and the thickness of the nonwoven fabric was set as 25 μm.

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.

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.

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.

Comparative Example 1

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

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.

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.

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.

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

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