JP2011103180A - Composite sheet for direct methanol fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a composite sheet for a direct methanol fuel cell which is superior in methanol diffusivity and can supply methanol to an anode at a large area by the diffusion and penetration effect, even if an area of a methanol solution feeding section from a fuel cartridge is comparatively small. <P>SOLUTION: The composite sheet for the direct methanol fuel cell includes a polyolefin-based resin layer, and an electrospun cellulose fiber layer formed continuously on at least one principal surface of the polyolefin-based resin layer. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a composite sheet for a direct methanol fuel cell, which has excellent methanol diffusibility and can supply methanol to an anode in a large area by a diffusion permeation effect even when a methanol aqueous solution delivery part from a fuel cartridge has a relatively small area. .

Power consumption and continuous use time are increasing as portable small electronic devices such as mobile phones, personal digital assistants (PDAs), notebook PCs, video cameras, etc. have become multifunctional, and they are installed in portable small electronic devices. There is a strong demand for higher energy density of batteries.

Currently, lithium secondary batteries are mainly used as power sources for portable small electronic devices, but lithium secondary batteries are expected to reach a limit at an energy density of about 600 Wh / L. An early practical application of a fuel cell using a solid polymer electrolyte membrane is expected as a power source to replace the secondary battery.

Among fuel cells, the direct methanol fuel cell (DMFC) can generate electricity by supplying methanol as a fuel or methanol aqueous solution directly into the cell without reforming it into hydrogen. Development is underway. In addition, direct methanol fuel cells are attracting more attention from the viewpoints of high theoretical energy density of methanol, simplification of the system, ease of fuel storage, and the like.

In a direct methanol fuel cell, a method of supplying a methanol aqueous solution using a diffusion auxiliary device such as a pump or a fan is generally used. However, if diffusion auxiliary devices such as a pump and a fan are used, the overall system is hindered from being miniaturized. Therefore, there is a demand for a fuel supply system that is simplified and miniaturized without using them.

As such a fuel supply system, a method of supplying a methanol aqueous solution with high efficiency by utilizing natural diffusion such as capillary phenomenon has been studied. For example, Patent Document 1 discloses a fuel permeation made of a porous material. A method of introducing methanol to the anode by utilizing a capillary phenomenon by disposing a plate is disclosed. Patent Document 2 discloses a fuel introduction body made of a foam, a fiber bundle, a non-woven fiber or the like, and a foam such as a polyurethane foam is used. However, in these methods, since the diffusibility of methanol is insufficient, it is necessary to enlarge the contact surface between the liquid flow path from the fuel cartridge and the permeation plate, and there is a problem that it is difficult to reduce the size.

JP 2001-93540 A JP 2003-368866 A

In view of the above situation, the present invention is excellent in methanol diffusibility, and even if the methanol aqueous solution delivery part from the fuel cartridge has a relatively small area, methanol can be supplied to the anode in a large area by the diffusion permeation effect. An object is to provide a composite sheet for a direct methanol fuel cell.

The present invention is a composite sheet for a direct methanol fuel cell having a polyolefin resin layer and an electrospun nonwoven fabric layer continuously formed on at least one main surface of the polyolefin resin layer. The present invention is described in detail below.

As a result of intensive studies, the present inventors have determined that a sheet used for a direct methanol fuel cell is a polyolefin resin layer, and an electrospun nonwoven fabric layer continuously formed on at least one main surface of the polyolefin resin layer. With this configuration, since the composite sheet has extremely high methanol diffusibility while preventing deterioration and deformation due to methanol, a direct methanol fuel cell capable of realizing power generation characteristics at a higher current density can be obtained. As a result, the present invention has been completed.

The composite sheet for a direct methanol fuel cell of the present invention has a polyolefin resin layer and an electrospun nonwoven fabric layer continuously formed on at least one main surface of the polyolefin resin layer.

Since the polyolefin-based resin has hydrophobicity, it contributes to the diffusion performance of methanol, and the obtained sheet has high strength. Examples of the polyolefin resin include an α-olefin homopolymer and a copolymer with a different monomer mainly composed of an α-olefin. Specifically, for example, polyethylene, polypropylene, ethylene and 1 -Copolymers with α-olefins having 4 to 10 carbon atoms such as butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-decene, ethylene-vinyl acetate copolymer Examples thereof include a copolymer, an ethylene-acrylic acid copolymer, an ethylene-acrylic acid ester copolymer, an ethylene-methacrylic acid ester copolymer, an ethylene-vinyl acetate-methacrylic acid ester copolymer, and an ionomer resin. Of these, polypropylene is preferred.

The minimum with preferable melting | fusing point (it depends on the endothermic peak temperature of DSC) of the said polyolefin resin is 98 degreeC, and a preferable upper limit is 200 degreeC. If the melting point of the polyolefin resin is lower than 98 ° C., the heat generation of the fuel cell unit itself may cause structural destruction or functional deterioration due to deformation or melting. When the melting point of the polyolefin-based resin exceeds 200 ° C., the processing temperature of the composite sheet becomes high, so that composite processing at a high temperature is required, and the manufacturing apparatus and manufacturing cost may be increased.

The minimum with a preferable number average molecular weight of the said polyolefin resin is 3000, and a preferable upper limit is 60000. By setting the number average molecular weight within the above range, a direct methanol fuel cell composite sheet having excellent methanol diffusion performance can be obtained. In this specification, the number average molecular weight refers to that measured by gel permeation chromatography (GPC).

As the polyolefin resin used in the polyolefin resin layer, a polyolefin resin having the above-described composition may be used alone, or two or more polyolefin resins having the above-described composition may be used in combination. Moreover, when the said polyolefin resin layer is two or more layers, although the said polyolefin resin is good also as a thing of a different composition, in order to suppress the trouble by a deformation | transformation etc., it is preferable to set it as the same composition.

The lower limit of the content of the polyolefin resin in the composite sheet for a direct methanol fuel cell of the present invention is 10% by weight, and the upper limit is 35% by weight. When the content of the polyolefin-based resin is less than 10% by weight, the methanol diffusing performance decreases, and when it exceeds 35% by weight, the methanol permeability decreases. The minimum with preferable content of the said polyolefin resin is 20 weight%, and a preferable upper limit is 30 weight%. In addition, content of the said polyolefin resin represents content per unit area.

You may add well-known additives, such as antioxidant and a heat stabilizer, to the said polyolefin resin layer in the range which does not impair the essence of this invention.

Examples of the material used for the electrospun nonwoven fabric layer include elastomeric polymers (for example, thermoplastic elastomers such as urethane elastomers, polyester elastomers, and polyamide elastomers).

The electrospun nonwoven fabric layer used in the present invention is formed by an electrospinning deposition (ESD) method using a solution in which a material constituting the nonwoven fabric is dissolved in a solvent.

The lower limit of the average fiber diameter of the fibers constituting the nonwoven fabric layer is 0.3 μm, and the upper limit is 1.5 μm. When the average fiber diameter is less than 0.3 μm, it becomes difficult to spin the fiber, and when it exceeds 1.5 μm, the methanol diffusibility decreases. When the fiber has an irregular cross section, the major axis of the cross section is the fiber diameter. The average fiber diameter of the fiber is 30 on the SEM photograph of the electrospun nonwoven fabric layer (when the maximum fiber diameter is less than 5 μm, the magnification is 10,000 times, and when the minimum fiber diameter is 5 μm or more, the magnification is 300 times). It is defined by the average value when a point is marked.

The preferable lower limit of the standard deviation of the fiber diameter is 0.1 μm, and the preferable upper limit is 1 μm. By reducing the standard deviation as described above, the variation in fiber diameter becomes extremely small. As a result, the size of the gaps formed between the fibers is also less varied, so not only uneven impregnation is not likely to occur when the polyolefin resin is melted and impregnated, but also the depth in the thickness direction to be impregnated. And the unevenness at the interface of the polyolefin resin layer is reduced. As a result, the methanol diffusibility of the obtained direct methanol fuel cell composite sheet is greatly improved.

The cross-sectional shape of the fiber may be flat or irregular, but is preferably circular. By making the cross-sectional shape circular, methanol diffusibility is improved. Further, the form of the fiber may be a short fiber or a long fiber, but a long fiber that is less likely to cause the fibers to fall off in the system is preferable.

The upper limit of the total thickness of the composite sheet for a direct methanol fuel cell of the present invention is preferably 0.2 mm. When the total thickness exceeds 0.2 mm, the methanol diffusibility decreases. A preferred lower limit is 0.01 mm. If the total thickness is less than 0.01 mm, unevenness in methanol diffusion tends to occur. A more preferable lower limit is 0.05 mm, and a more preferable upper limit is 0.1 mm.

As a specific structure of the composite sheet for a direct methanol fuel cell of the present invention, the polyolefin resin layer (A) and the electrospun nonwoven fabric layer (B) are (A) / (B) or (B) / (A). It may be a two-layer structure laminated as shown in FIG. 5 or a three-layer structure laminated like (A) / (B) / (A) or (B) / (A) / (B). It may be a four-layer structure of (A) / (B) / (A) / (B). Of these, the surface on the fuel supply side is preferably an electrospun nonwoven fabric layer (B).

The composite sheet for a direct methanol fuel cell of the present invention is preferably formed by integrally laminating a sheet made of an electrospun nonwoven fabric and a sheet made of a polyolefin resin by heat fusion. The direct methanol fuel cell composite sheet obtained by such a method has a structure in which the electrospun nonwoven fabric layer and the polyolefin resin layer are integrated at the joint, and as a result, the methanol diffusion performance is greatly improved. Can do. In particular, the laminated interface is preferably a structure in which a polyolefin resin having a porous shape is impregnated between fibers constituting the electrospun nonwoven fabric.

The basis weight of the sheet made of the electrospun nonwoven fabric is not particularly limited, but a preferable lower limit is 10 g / m ² and a preferable upper limit is 25 g / m ² . If the basis weight of the electrospun nonwoven fabric sheet is less than 10 g / m ² , unevenness may occur during methanol supply, and if it exceeds 25 g / m ² , a sufficient methanol diffusion effect may not be obtained. .

Although it does not specifically limit as thickness of the sheet | seat which consists of the said electrospun nonwoven fabric, A preferable minimum is 0.01 mm and a preferable upper limit is 0.10 mm. The thickness of the sheet made of the electrospun nonwoven fabric is 0.0.
If it is less than 1 mm or exceeds 0.10 mm, a sufficient methanol diffusion effect may not be obtained.

The sheet made of the electrospun nonwoven fabric is manufactured by an electrospinning process separately from the sheet made of the polyolefin resin to be laminated, but the sheet made of the polyolefin resin is previously placed on the collecting plate of the electrospinning apparatus. It can also be produced by arranging and directly laminating on the sheet.

The sheet made of the electrospun nonwoven fabric is obtained by a method of manufacturing a nonwoven fabric of fine fibers on a substrate by discharging a resin solution or a hot melt resin from a nozzle with a fine pore diameter under a condition where a high voltage electric field is applied. By manufacturing by this method, it is possible to obtain a sheet made of fibers with extremely small variations in fiber diameter.

No particular limitation is imposed on the basis weight of the sheet made of the polyolefin resin, preferable lower limit is 5 g / m ^2, the upper limit is preferably 14 g / m ^2. If the basis weight of the polyolefin resin sheet is less than 5 g / m ² , unevenness may occur during methanol supply, and if it exceeds 14 g / m ² , methanol permeation may be inhibited.

Although it does not specifically limit as thickness of the sheet | seat consisting of the said polyolefin resin, A preferable minimum is 0.05 mm and a preferable upper limit is 0.25 mm. If the thickness of the polyolefin resin sheet is less than 0.05 mm or exceeds 0.25 mm, a sufficient methanol diffusion effect may not be obtained.

Examples of the form of the polyolefin resin sheet include spunbond nonwoven fabric sheets, wet papermaking nonwoven fabric sheets, wet-spun nonwoven fabric sheets, nonwoven fabric sheets such as melt blown nonwoven fabric sheets, porous sheets obtained by film stretching, and foamed porous sheets. .

In addition, by integrally combining the sheet made of the electrospun nonwoven fabric and the sheet made of polyolefin resin by heat fusion, the sheet made of polyolefin resin is joined to the sheet made of electrospun nonwoven fabric, It can be easily fused and fixed with high adhesion without blocking the holes. The temperature at the time of heat-sealing is performed at a temperature higher than the melting point of the polyolefin-based resin, but it can also be fused at a temperature lower than the melting point of the polyolefin-based resin.

The method for producing the composite sheet for a direct methanol fuel cell of the present invention is not particularly limited. For example, as described above, a sheet made of an electrospun nonwoven fabric and a sheet made of a polyolefin resin are integrated by heat fusion. The method of laminating is mentioned. Specifically, for example, a sheet of an electrospun nonwoven fabric and a sheet of polyolefin resin are passed through a pair of heated rollers, and the sheet passes at a predetermined speed while applying nipping pressure. And the like.

According to the present invention, a direct methanol type that is excellent in methanol diffusibility and can supply methanol in a large area to the anode by the diffusion permeation effect even if the methanol aqueous solution delivery part from the fuel cartridge has a relatively small area. A composite sheet for a fuel cell can be provided. In addition to efficient diffusion supply of high-concentration methanol aqueous solution, it can be made thin, and by using natural diffusion using fibers, diffusion auxiliary equipment such as pumps and fans can be used. Therefore, it can be suitably used for a small direct methanol fuel cell.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

(Example 1) A thermoplastic polyurethane resin (urethane elastomer, trade name: Pandex 1185, manufactured by DIC Bayer Polymer Co., Ltd.) was dissolved in DMF to obtain a 23 wt% DMF solution. This was filled in a solution filling portion of an electrospinning apparatus (ES-2300 (device name), manufactured by Huence Co., Ltd.) and subjected to electrospinning by applying a voltage of 55 kV to produce an electrospun nonwoven fabric. The diameter of the metal nozzle used at this time was 26 G (inner diameter: 0.23 mm), and the distance to the collector was 15 cm. The obtained electrospun nonwoven fabric had a thickness of 0.05 mm, a basis weight of 14 g / m ² , and an average fiber diameter of 1.1 μm. The obtained nonwoven fabric is hereinafter referred to as an electrospun nonwoven fabric 1. On the main surface opposite to the methanol supply surface of the electrospun nonwoven fabric 1, a nonwoven fabric sheet made of homopolypropylene (melting point 164 ° C., circular fiber cross section, fiber diameter 0.8-8 μm, basis weight 5 g / m ² , thickness 0. 07 mm), and heat-sealed by heating at 150 ° C. for 3 seconds using a hot press machine. At this time, in order to control the thickness of the composite sheet, a brass spacer having a thickness of 0.08 mm was juxtaposed between the hot press hot plates. A composite sheet having a total thickness of 0.08 mm and a polypropylene content of 26% by weight was obtained. Here, each sheet thickness was measured using a digital thickness gauge (manufactured by Mitutoyo Corporation, measuring part φ20 mm). As for the fiber diameter, 30 points were marked on a SEM photograph at a magnification of 10,000 times, and the minimum value to the maximum value, the average value (average fiber diameter), and the standard deviation were recorded. Each sheet basis weight, was converted to the weight measured by weight per 1 m ² of the test piece of 25 mm × 200 mm.

(Example 2) A nonwoven sheet made of homopolypropylene (melting point: 164 ° C, circular fiber cross section, fiber diameter: 0.8 to 8 µm) on the main surface serving as the methanol supply surface of the same electrospun nonwoven fabric 1 as used in Example 1. And a basis weight of 5 g / m ² , a thickness of 0.07 mm), and heat-sealed by heating at 150 ° C. for 3 seconds using a hot press machine. At this time, in order to control the thickness of the composite sheet, a brass spacer having a thickness of 0.08 mm was juxtaposed between the hot press hot plates. A composite sheet having a total thickness of 0.08 mm and a polypropylene content of 26% by weight was obtained.

(Example 3) A thermoplastic polyurethane resin (urethane elastomer, trade name: Pandex 1185, manufactured by DIC Bayer Polymer Co., Ltd.) was dissolved in DMF to obtain a 23 wt% DMF solution. This was filled in a solution filling portion of the same electrospinning apparatus as described above, and electrospun was performed by applying a voltage of 55 kV to produce an electrospun nonwoven fabric. The diameter of the metal nozzle used at this time was 26 G (inner diameter: 0.23 mm), and the distance to the collector was 15 cm. The obtained electrospun nonwoven fabric had a thickness of 0.07 mm, a basis weight of 24 g / m ² , and an average fiber diameter of 1.1 μm. The obtained nonwoven fabric is hereinafter referred to as an electrospun nonwoven fabric 2. On the main surface of the electrospun nonwoven fabric 2 opposite to the methanol supply surface, a nonwoven fabric sheet made of homopolypropylene (melting point 164 ° C., circular fiber cross section, fiber diameter 0.8-8 μm, basis weight 10 g / m ² , thickness 0. 10 mm), and heat-sealed by heating at 150 ° C. for 3 seconds using a hot press machine. At this time, in order to control the thickness of the composite sheet, a brass spacer having a thickness of 0.05 mm was juxtaposed between the hot plates of the hot press. A composite sheet having a total thickness of 0.05 mm and a polypropylene content of 29% by weight was obtained.

(Example 4) One-component polyether-based polyurethane resin solution (moisture permeable polyurethane, trade name: Heimlen Y-210B, nonvolatile content 30%, manufactured by Dainichi Seika Kogyo Co., Ltd.) was mixed with DMF and MEK mixed solvent (1: 1 ( Using a volume ratio)), the solution was diluted so that the non-volatile content was 23% by weight, filled in a solution filling portion of the same electrospinning apparatus as described above, and electrospun by applying a voltage of 55 kV. The diameter of the metal nozzle used at this time was 21 G (inner diameter: 0.51 mm), and the distance to the collector was 15 cm. The obtained electrospun nonwoven fabric had a thickness of 0.07 mm, a basis weight of 24 g / m ² , and an average fiber diameter of 1.4 μm. The obtained nonwoven fabric is hereinafter referred to as an electrospun nonwoven fabric 3. On the main surface of the electrospun nonwoven fabric 3 opposite to the methanol supply surface, a nonwoven fabric sheet made of high-density polyethylene (melting point: 129 ° C., circular fiber cross section, fiber diameter: 0.8-8 μm, basis weight: 10 g / m ² , thickness: 0 .10 mm) was placed and heated at 135 ° C. for 3 seconds using a hot press machine, and heat-sealed. At this time, in order to control the thickness of the composite sheet, a brass spacer having a thickness of 0.1 mm was juxtaposed between the hot plates of the hot press. A composite sheet having a total thickness of 0.1 mm and a polyethylene content of 29% by weight was obtained.

Comparative Example 1 A composite sheet having a total thickness of 0.03 mm and a polypropylene content of 26% by weight was obtained in the same manner as in Example 1 except that the thickness of the brass spacer was 0.03 mm.

Comparative Example 2 A composite sheet having a total thickness of 0.11 mm and a polypropylene content of 29% by weight was obtained in the same manner as in Example 3 except that the thickness of the brass spacer was 0.11 mm.

(Comparative Example 3) in place of the nonwoven fabric sheet made of homopolypropylene having a basis weight of 10 g / ^{m 2,} the nonwoven fabric sheet (melting point 164 ° C. consisting homopropylene, fiber a circular cross section, the fiber diameter 0.8～8Myuemu, basis weight 15 g / m ² and a thickness of 0.14 mm) was used in the same manner as in Example 3 to obtain a composite sheet having a total thickness of 0.05 mm and a polypropylene content of 38% by weight.

Comparative Example 4 The electrospun nonwoven fabric 2 used in Example 3 was used.

(Comparative example 5) The nonwoven fabric sheet (melting | fusing point 164 degreeC, fiber cross-section circle, fiber diameter 0.8-8micrometer, basic weight 10g / m < ² >, thickness 0.10mm, 1 layer) which consists of homopolypropylene was used.

(Evaluation) (Methanol permeation diffusivity test) About the sheet | seat obtained by the Example and the comparative example, a sheet | seat is mounted in the circular frame shape of inner diameter 76mm, outer diameter 86mm, and height 20mm, and the 1st layer (methanol IN side) 10 μL of a special grade methanol reagent colored with a small amount of blue ink using a micropipette was dropped from 5 mm above the surface. After the dropping, the sheet was visually observed, and the blue portion was judged to be due to methanol penetration and evaluated according to the following criteria.

(Methanol permeability) ○: When the shape of the blue part on the opposite side (back) and the opposite side (back) is oval or circular and the area of the blue part on the front and back is equal ×: When there is no blue part on the back Unevenness: When the front and back blue part shapes are mosaic, and the back blue part area is small In addition, as for Comparative Example 4, deformation of the film was observed due to the dropwise addition of methanol, and it was determined that the dimensions were unstable and the function was not stable.

According to the present invention, a direct methanol type that is excellent in methanol diffusibility and can supply methanol in a large area to the anode by the diffusion permeation effect even if the methanol aqueous solution delivery part from the fuel cartridge has a relatively small area. A composite sheet for a fuel cell can be provided. In addition to efficient diffusion supply of high-concentration methanol aqueous solution, it can be made thin, and by using natural diffusion using fibers, diffusion auxiliary equipment such as pumps and fans can be used. Therefore, it can be suitably used for a small direct methanol fuel cell.

Claims (4)

A composite sheet for a direct methanol fuel cell, comprising a polyolefin resin layer and an electrospun nonwoven fabric layer continuously formed on at least one main surface of the polyolefin resin layer. 2. The direct methanol fuel cell composite sheet according to claim 1, wherein a sheet made of an electrospun nonwoven fabric and a sheet made of a polyolefin resin are integrally laminated by heat fusion. The composite sheet for a direct methanol fuel cell according to claim 1 or 2, wherein the content of the polyolefin resin is 10 to 35% by weight. 4. The direct methanol fuel cell composite sheet according to claim 1, wherein the polyolefin resin is polypropylene.