JP2010225535A - Composite sheet for direct methanol type fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a composite sheet for a direct methanol type fuel cell which is superior on methanol diffusion and can supply methanol to an anode at a large area with a diffusion and penetration effect even though a methanol solution feeding section from a fuel cartridge has a comparatively small area. <P>SOLUTION: The composite sheet for the direct methanol type fuel cell has a polyolefin resin layer, and a cellulose fiber layer continuously formed on at least one principal plane of the polyolefin resin layer. The content of a polyolefin resin is 10-35 wt.%, and the whole thickness of the polyolefin resin is ≤0.2 mm. <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 if 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. In addition, as in Patent Document 2, when polyurethane is used as the fuel introduction body, there is a problem that the deterioration due to methanol occurs and the diffusion performance is not stable.

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 has a polyolefin resin layer and a cellulose fiber layer continuously formed on at least one main surface of the polyolefin resin layer, and the content of the polyolefin resin is 10 to 35% by weight, And it is the composite sheet for direct methanol fuel cells whose total thickness is 0.2 mm or less.
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 includes a polyolefin resin layer and a cellulose fiber layer continuously formed on at least one main surface of the polyolefin resin layer. Furthermore, by defining the content and total thickness of the polyolefin resin, it becomes a composite sheet with extremely high methanol diffusivity while preventing deterioration and deformation due to methanol. The present inventors have found that a direct methanol fuel cell capable of realizing the above power generation characteristics can be obtained and completed the present invention.

The composite sheet for a direct methanol fuel cell of the present invention has a polyolefin resin layer and a cellulose fiber 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 11 weight%, and a preferable upper limit is 33 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 cellulose fibers include natural cellulose fibers such as cotton, hemp, wood (hardwood, conifer) pulp, non-wood pulp (bagasse pulp, straw pulp), and regenerated cellulose fibers such as rayon, polynosic, cupra, tencel, and lyocell. Examples include waste paper pulp.

The cellulose fiber includes semi-synthetic cellulose obtained by modifying pure cellulose, such as cellulose acetate. Pure cellulose fibers have high water retention but low strength. Therefore, by controlling the degree of acetylation of the cellulose acetate, the water retention, strength, etc. can be changed to obtain optimum cellulose fibers. Further, pure cellulose fibers and cellulose acetate fibers may be appropriately mixed and used.

The form of the cellulose fiber may be a short fiber or a long fiber, but is preferably a long fiber that hardly causes the fibers to fall off in the system. The cross-sectional shape may be circular or irregular, but a flat cross section is preferred.
In general, the fiber diameter is preferably 0.5 to 100 μm, and more preferably 2 to 70 μm.
In addition, the said fiber diameter is taken as the long diameter of a cross section in the case of an irregular cross section.

The upper limit of the total thickness of the composite sheet for a direct methanol fuel cell of the present invention is 0.2 mm. When the total thickness exceeds 0.2 mm, the methanol diffusibility decreases. A preferred lower limit is 0.05 mm, a preferred upper limit is 0.15 mm, a more preferred lower limit is 0.07 mm, and a more preferred upper limit is 0.13 mm.

As a specific configuration of the composite sheet for a direct methanol fuel cell of the present invention, the polyolefin resin layer (A) and the cellulose fiber layer (B) are (A) / (B) or (B) / (A). It may be a two-layer structure laminated as described above, or may be a three-layer structure laminated as (A) / (B) / (A) or (B) / (A) / (B). It may be a four-layer structure of (A) / (B) / (A) / (B). Especially, it is preferable to make the surface by the side of a fuel supply into a cellulose fiber 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 cellulose fibers 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 cellulose fiber layer and the polyolefin resin layer are integrated at the joint, and as a result, the methanol diffusion performance can be greatly improved. it can. In particular, it is preferable that the laminated interface has a structure in which a polyolefin resin having a porous shape is impregnated between cellulose fibers.

No particular limitation is imposed on the basis weight of the sheet made of the cellulose fibers, the preferred lower limit is 10 g / m ^2, the upper limit is preferably 30 g / m ^2. If the basis weight of the cellulose fiber sheet is less than 10 g / m ² , unevenness may occur when methanol is supplied, and if it exceeds 30 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 cellulose fiber, A preferable minimum is 0.04 mm and a preferable upper limit is 0.13 mm. If the thickness of the cellulose fiber sheet is less than 0.04 mm or exceeds 0.13 mm, a sufficient methanol diffusion effect may not be obtained.

Examples of the form of the sheet made of the cellulose fiber include a wet papermaking sheet, a wet-spun nonwoven fabric sheet, and a spunbond nonwoven fabric sheet.

The basis weight of the sheet made of the polyolefin-based resin is not particularly limited, but a preferable lower limit is 5 g / m ² and a preferable upper limit is 25 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 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 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 sheet made of the polyolefin-based resin include a spunbond nonwoven fabric sheet, a wet papermaking nonwoven fabric sheet, a wet-spun nonwoven fabric sheet, a melt blown nonwoven fabric sheet and other nonwoven fabric sheets, a porous sheet by film stretching, and a foamed porous sheet. .

In addition, by laminating the sheet made of cellulose fiber and the sheet made of polyolefin resin integrally by heat fusion, holes in the joint portion between the sheet made of polyolefin resin and the sheet made of cellulose fiber are formed. It can be easily fused and fixed with high adhesion without blocking.
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 direct methanol fuel cell composite sheet of the present invention is not particularly limited. For example, as described above, a sheet made of cellulose fiber and a sheet made of polyolefin resin are integrated by heat fusion. The method of laminating is mentioned.
Specifically, for example, a sheet in which a cellulose fiber sheet and a polyolefin resin sheet are stacked is passed through a pair of heated rollers, and the sheet is passed at a predetermined speed while applying nipping pressure. Methods 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.

2 is an enlarged photograph of the surface of a nonwoven fabric sheet made of polypropylene used in Example 1. FIG. 2 is an enlarged photograph of the surface of a wet papermaking sheet made of cellulose fibers used in Example 1. FIG. In Example 1, it is the enlarged photograph which image | photographed the surface by the side of the polypropylene layer after heat sealing | fusion. In Example 1, it is the enlarged photograph which image | photographed the surface by the side of the cellulose fiber after heat sealing | fusion. In Example 1, it is the enlarged photograph which image | photographed the cross section of the composite sheet after heat sealing | fusion. In Example 4, it is the enlarged photograph which image | photographed the cross section of the composite sheet after heat sealing | fusion.

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
Nonwoven sheet made of homopolypropylene on the main surface opposite to the methanol supply surface of a wet papermaking sheet (flat fiber cross-sectional shape, fiber diameter 5 to 55 μm, basis weight 20 g / m ² , thickness 0.07 mm) made of cellulose fiber (Melting point 164 ° C., circular fiber cross section, fiber diameter 0.8 to 8 μm, basis weight 10 g / m ² , thickness 0.10 mm) and by heating at 150 ° C. for 3 seconds using a hot press machine, Heat-sealing was performed to obtain a composite sheet (two layers) having a total thickness of 0.07 mm and a polypropylene content of 33% by weight. 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 the SEM photograph, and the minimum value to the maximum value 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.

(Confirmation of surface and cross-sectional state before and after thermal fusion)
Fig. 1 shows an enlarged photograph of the surface of the nonwoven fabric sheet made of polypropylene used in Example 1, Fig. 2 shows an enlarged photograph of the surface of the wet papermaking sheet made of cellulose fiber, and the surface on the polypropylene layer side after heat-sealing. Fig. 3 shows an enlarged photograph taken of Fig. 3, Fig. 4 shows an enlarged photograph taken of the surface on the cellulose fiber side after heat fusion, and Fig. 5 shows an enlarged photograph taken of a cross section of the composite sheet after heat fusion.
As shown in FIG. 3, the polypropylene layer is a porous body having innumerable pores, and a part of the polypropylene is impregnated into the cellulose fiber layer and integrated as shown in FIG.

(Example 2)
Wet paper making sheets of cellulose fibers (fiber cross-sectional shape flat, fiber diameter 5～55Myuemu, basis weight 20 g / ^{m 2,} thickness 0.07 mm) to the main surface of the methanol feed surface of the nonwoven fabric sheet (melting point 164 consisting of homopolypropylene ℃, fiber cross-section circle, fiber diameter 0.8-8μm, basis weight 10g / m ² , thickness 0.10mm), and heat fusion by heating at 150 ° C for 3 seconds using a hot press machine A composite sheet (two layers) having a total thickness of 0.07 mm and a polypropylene content of 33% by weight was obtained.

Example 3
Wet surface composed of two cellulose fibers on both main surfaces of a nonwoven fabric sheet composed 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) A paper sheet (flat fiber cross-sectional shape, fiber diameter of 5 to 55 μm, basis weight of 10 g / m ² , thickness of 0.04 mm) is placed and heated at 150 ° C. for 3 seconds using a hot press machine. A composite sheet (three layers) having a total thickness of 0.07 mm and a polypropylene content of 20% by weight was obtained.

Example 4
Wet surface composed of two cellulose fibers on both main surfaces of a nonwoven fabric sheet composed 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) A paper sheet (flat fiber cross-sectional shape, fiber diameter of 5 to 55 μm, basis weight of 20 g / m ² , thickness of 0.07 mm) is placed and heated at 150 ° C. for 3 seconds using a hot press machine. Thus, a composite sheet (three layers) having a total thickness of 0.13 mm and a polypropylene content of 11% by weight was obtained.

(Confirmation of cross-sectional state after heat fusion)
The enlarged photograph which image | photographed the cross section of the composite sheet after heat sealing | fusion in Example 4 is shown in FIG.

(Example 5)
Wet surface composed of two cellulose fibers on both main surfaces of a nonwoven fabric sheet composed of homopolypropylene (melting point 164 ° C., circular fiber cross section, fiber diameter 0.8-8 μm, basis weight 20 g / m ² , thickness 0.19 mm) A paper sheet (flat fiber cross-sectional shape, fiber diameter of 5 to 55 μm, basis weight of 30 g / m ² , thickness of 0.13 mm) is placed and heated at 150 ° C. for 3 seconds using a hot press machine for heat fusion. Thus, a composite sheet (three layers) having a total thickness of 0.2 mm and a polypropylene content of 25% by weight was obtained.

(Example 6)
It consists of two cellulose fibers on both main surfaces of a non-woven 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). A wet papermaking sheet (fiber cross-sectional shape flat, fiber diameter 5 to 55 μm, basis weight 20 g / m ² , thickness 0.07 mm) is placed and heated at 135 ° C. for 3 seconds using a hot press machine. A composite sheet (three layers) having a total thickness of 0.13 mm and a polyethylene content of 20% by weight was obtained.

(Comparative Example 1)
Nonwoven sheet made of homopolypropylene on the main surface opposite to the methanol supply surface of a wet papermaking sheet made of cellulose fibers (flat fiber cross-sectional shape, fiber diameter 5 to 55 μm, basis weight 30 g / m ² , thickness 0.13 mm) (Melting point 164 ° C., fiber cross-section circle, fiber diameter 0.8-8 μm, basis weight 20 g / m ² , thickness 0.19 mm) is placed and heated at 150 ° C. for 3 seconds using a hot press machine, Heat-sealing was performed to obtain a composite sheet (two layers) having a total thickness of 0.13 mm and a polypropylene content of 40% by weight.

(Comparative Example 2)
Wet surface composed of two cellulose fibers on both main surfaces of a nonwoven fabric sheet composed 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) A paper sheet (flat fiber cross-sectional shape, fiber diameter 5 to 55 μm, basis weight 27 g / m ² , thickness 0.12 mm) is placed and heated at 150 ° C. for 3 seconds using a hot press machine for heat fusion. Thus, a composite sheet (three layers) having a total thickness of 0.22 mm and a polypropylene content of 8% by weight was obtained.

(Comparative Example 3)
Wet surface composed of two cellulose fibers on both main surfaces of a nonwoven fabric sheet composed 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) A paper sheet (flat fiber cross-sectional shape, fiber diameter of 5 to 55 μm, basis weight of 37 g / m ² , thickness of 0.14 mm) is placed and heated at 150 ° C. for 3 seconds using a hot press machine for heat fusion. Thus, a composite sheet (three layers) having a total thickness of 0.23 mm and a polypropylene content of 12% by weight was obtained.

(Comparative Example 4)
Nonwoven sheet made of homopolypropylene on the main surface opposite to the methanol supply surface of wet papermaking sheet made of cellulose fiber (flat fiber cross-sectional shape, fiber diameter 5 to 55 μm, basis weight 9 g / m ² , thickness 0.04 mm) (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 by heating at 150 ° C. for 3 seconds using a hot press machine, Heat-sealing was performed to obtain a composite sheet (two layers) having a total thickness of 0.04 mm and a polypropylene content of 36% by weight.

(Comparative Example 5)
Wet surface composed of two cellulose fibers on both main surfaces of a nonwoven fabric sheet composed of homopolypropylene (melting point 164 ° C., circular fiber cross section, fiber diameter 0.8-8 μm, basis weight 30 g / m ² , thickness 0.30 mm) A paper sheet (flat fiber cross-sectional shape, fiber diameter of 5 to 55 μm, basis weight of 30 g / m ² , thickness of 0.13 mm) is placed and heated at 150 ° C. for 3 seconds using a hot press machine for heat fusion. Thus, a composite sheet (three layers) having a total thickness of 0.22 mm and a polypropylene content of 33% by weight was obtained.

(Comparative Example 6)
Nonwoven sheet made of 6 nylon on the main surface opposite to the methanol supply surface of wet papermaking sheet made of cellulose fibers (fiber flat cross section, fiber diameter 5 to 55 μm, basis weight 20 g / m ² , thickness 0.07 mm) (Melting point: 222 ° C., fiber cross-section circle, fiber diameter: 0.8-8 μm, basis weight: 10 g / m ² , thickness: 0.10 mm) and heating at 210 ° C. for 3 seconds using a hot press machine, Heat-sealing was performed to obtain a composite sheet (two layers) having a total thickness of 0.09 mm and a nylon content of 33% by weight.

(Comparative Example 7)
6 Nylon nonwoven fabric sheet (melting point 222 ° C., fiber cross-section circle, fiber diameter 0.8-8 μm, basis weight 20 g / m ² , thickness 0.19 mm) A paper sheet (flat fiber cross-sectional shape, fiber diameter of 5 to 55 μm, basis weight of 20 g / m ² , thickness of 0.07 mm) is placed and heated at 210 ° C. for 3 seconds using a hot press machine. Thus, a composite sheet (three layers) having a total thickness of 0.18 mm and a nylon content of 33% by weight was obtained.

(Comparative Example 8)
A wet papermaking sheet made of cellulose fibers (flat fiber cross-sectional shape, fiber diameter 5 to 55 μm, basis weight 20 g / m ² , thickness 0.07 mm, one layer) was used.

(Comparative Example 9)
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, one layer) 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 a micropipette is taken from 5 mm above the 1st layer (methanol IN side) surface. 10 μL of a special grade methanol reagent colored with a small amount of blue ink was dropped. 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 blue part shape of the dripping surface (front) and the opposite surface (back) is oval or circular, and the blue part areas of the front and back are equal
×: When there is no blue part on the back
Unevenness: When the blue part shape on the front and back is mosaic, and the blue part area on the back is small
In addition, regarding Comparative Examples 6, 7, and 8, deformation of the film was observed by dropping 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 (5)

Having a polyolefin resin layer and a cellulose fiber layer continuously formed on at least one main surface of the polyolefin resin layer;
The content of the polyolefin resin is 10 to 35% by weight, and
A composite sheet for a direct methanol fuel cell, wherein the total thickness is 0.2 mm or less. 2. The direct methanol fuel cell composite sheet according to claim 1, wherein a sheet made of cellulose fiber and a sheet made of polyolefin resin are integrally laminated by heat fusion. 3. The direct methanol fuel cell composite sheet according to claim 1, wherein the sheet made of cellulose fibers has a basis weight of 10 to 30 g / m ² and a thickness of 0.04 to 0.13 mm. The composite sheet for a direct methanol fuel cell according to claim 1, 2 or 3, wherein the sheet made of polyolefin resin has a basis weight of 5 to 20 g / m ² and a thickness of 0.05 to 0.25 mm. 5. The direct methanol fuel cell composite sheet according to claim 1, wherein the polyolefin-based resin is polypropylene.