JP2006294603A - Direct type fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a direct type fuel cell having excellent power generation characteristics by securing an amount of fuel supplied to a catalyst layer and surely discharging a generated carbon dioxide gas. <P>SOLUTION: At least a part of an anode side passage is divided into a first partial passage located on the membrane electrode assembly side and a second partial passage located on the bottom side of the anode side passage by a film having water repellency and gas permeability in the depth direction of the anode side passage. Fuel is mainly passed through the first partial passage, and carbon dioxide is mainly passed through the second partial passage. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a solid polymer electrolyte fuel cell, and more particularly to a separator flow path of a direct fuel cell.

  With the increase in functionality of portable small electronic devices such as mobile phones, personal digital assistants (PDAs), notebook PCs, and video cameras, it is necessary to increase power consumption and continuous use time. Therefore, there is a strong demand for higher energy density of the on-board battery. Currently, lithium secondary batteries are mainly used as the above-mentioned on-board batteries, but it is predicted that the energy density will reach a limit at around 600 Wh / L around 2006. As an alternative power source, a polymer electrolyte type is used. Early commercialization of fuel cells (PEFC) is expected.

  In particular, a direct methanol fuel cell (DMFC, hereinafter simply referred to as “direct fuel cell”) that generates electricity by directly oxidizing the methanol or aqueous methanol solution, which is the fuel, into the cell without being reformed into hydrogen, and performing electrode oxidation. Is also attracting attention and is actively researched and developed. The reason is that the organic fuel has a high theoretical energy density and is easy to store, and further, the direct fuel cell system is easy to simplify.

  The cell structure of the direct fuel cell is obtained by joining an anode (fuel electrode) having a catalyst layer and a diffusion layer and a cathode (air electrode) having a catalyst layer and a diffusion layer on both sides of the polymer electrolyte membrane. A membrane electrode assembly (MEA) and a pair of separators sandwiching both sides of the membrane electrode assembly are provided. Electric power can be generated by supplying methanol or an aqueous methanol solution as fuel to the anode side and supplying air to the cathode side.

The electrode reaction of the direct fuel cell is as follows.
Anode: CH ₃ OH + H ₂ O → CO ₂ + 6H ⁺ + 6e ⁻ (1)
Cathode: (3/2) O ₂ + 6H ⁺ + 6e ⁻ → 3H ₂ O (2)
From equations (1) and (2), methanol and water react at the anode to produce carbon dioxide, protons and electrons, and the protons reach the cathode through the polymer electrolyte membrane, and oxygen at the cathode. It can be seen that protons and electrons via an external circuit are combined to produce water.

  However, there are some problems in putting this direct fuel cell into practical use. One of them relates to the discharge of carbon dioxide gas which is a reaction product. The carbon dioxide generated on the anode side passes through the diffusion layer on the anode side, then reaches the separator flow path, and is discharged outside through the flow path. A part of the carbon dioxide generated at this time stays in the diffusion layer and inhibits the diffusion of fuel to the catalyst layer, and gradually gathers into large bubbles. Then, the fuel is pushed out from the pores of the diffusion layer by the bubbles, the supply of the fuel to the catalyst layer is insufficient, and a part of the fuel is discharged unused. As a result, the power generation characteristics on the high current density side may be significantly degraded.

  As a method of improving such a problem, the anode separator is provided with a liquid fuel flow path and an exhaust flow path that are independent from each other (that is, completely separated), and has a liquid permeability and a liquid facing the liquid fuel flow path. It has been proposed to provide a diffusion layer having poor gas permeability and to provide a diffusion layer having gas permeability so as to face the exhaust passage (for example, JP-A-2002-175817).

However, the conventional techniques as described above still have room for improvement from the viewpoint of providing a direct fuel cell having sufficiently excellent power generation characteristics without reducing the fuel utilization efficiency.
According to the above technique, the problem relating to the discharge of carbon dioxide gas may be solved. However, since the completely separated liquid fuel flow path and exhaust flow path are provided in the separator on the anode side, when the fuel permeability of the diffusion layer is low, the surface of the catalyst layer in the region facing the exhaust flow path The amount of fuel supplied to the engine is insufficient, resulting in a decrease in output.

  Accordingly, an object of the present invention is to secure the amount of fuel supplied to the catalyst layer in order to solve the conventional problems as described above, and to more reliably discharge the generated carbon dioxide gas, which has excellent power generation characteristics. It is an object of the present invention to provide a direct fuel cell having

In order to solve the above problems, the direct fuel cell of the present invention is
A polymer electrolyte membrane; an anode joined to the first surface of the polymer electrolyte membrane; and a cathode joined to a second surface opposite to the first surface of the polymer electrolyte membrane. A membrane electrode assembly, an anode separator disposed on a first surface of the membrane electrode assembly, and a cathode disposed on a second surface opposite to the first surface of the membrane electrode assembly A direct fuel cell comprising a side separator,
The anode side separator has an anode side channel on the anode side, and the cathode side separator has a cathode side channel on the cathode side,
At least a part of the anode-side channel is a first partial flow located on the membrane electrode assembly side by a membrane having poor liquid permeability and gas permeability in the depth direction of the anode-side channel. Divided into a channel and a second partial channel located on the bottom side of the anode-side channel,
A fuel mainly flows through the first partial flow path, and carbon dioxide mainly flows through the second partial flow path.

  With such a configuration, it is possible to prevent carbon dioxide gas generated by power generation from staying in the anode-side flow path and the anode-side diffusion layer, and in particular, to prevent the fuel supply from being hindered to the anode-side catalyst layer. Become. In addition, the anode-side flow path is divided with respect to the depth direction of the anode-side flow path, and the fuel flows mainly to the portion in contact with the membrane electrode assembly. The fuel can be supplied from the entire portion to the anode side diffusion layer, and the fuel can be supplied uniformly to the entire surface of the anode side catalyst layer.

The film is at least one material selected from the group consisting of carbon, ceramic, glass and resin from the viewpoint of more reliably suppressing deterioration of battery characteristics due to corrosion by fuel and reaction with the catalyst layer. It is preferable that it is comprised with the porous body comprised by these. Therefore, the film may be composed of a composite material containing two or more materials.
The surface of the membrane on the membrane electrode assembly side is preferably subjected to water repellent treatment, and the surface of the membrane on the membrane electrode assembly side is preferably uneven.

Here, the porous body constituting the membrane is a gas-permeable member including micropores. This porous body may be, for example, a film, a sheet, or a net. In particular, the surface of the porous body is subjected to a water repellent treatment to form a water repellent layer, and the water repellent layer is controlled by controlling the thickness of the water repellent layer and the surface shape (unevenness) of the water repellent layer. It is possible to control the ability and the liquid repellency. As a result, it is possible to permeate the gas while blocking the liquid fuel, and to control the ratio of the liquid fuel permeation rate and the gas permeation rate.
That is, it is preferable that the film having poor liquid permeability and gas permeability is composed of a water repellent layer and a gas permeable layer. In this case, the water-repellent layer has poor liquid permeability, and the gas-permeable layer is composed of a porous body and has gas permeability.

Further, the second partial flow path through which carbon dioxide mainly flows is configured such that the area of a cross section substantially perpendicular to the length direction of the second partial flow path increases from upstream to downstream. Preferably it is.
Carbon dioxide generated at the anode (particularly the anode-side catalyst layer) passes through the anode-side diffusion layer and reaches the anode-side flow path of the anode-side separator. Since carbon dioxide is discharged to the outside through the anode-side flow path, the carbon dioxide gas occupancy is higher in the anode-side flow path on the downstream side than on the upstream side in the fuel flow direction. Therefore, if the second partial flow path through which carbon dioxide mainly flows is configured such that the area of the cross section substantially perpendicular to the length direction of the second partial flow path increases from upstream to downstream, Carbon dioxide can be discharged more smoothly.

In addition, the first partial flow path through which fuel mainly flows is configured such that the area of a cross section substantially perpendicular to the length direction of the first partial flow path decreases from upstream to downstream. It is preferable.
Since the amount of fuel decreases as the fuel is used for power generation, the area of the cross section substantially perpendicular to the length direction of the first partial flow path is upstream of the first partial flow path through which the fuel mainly flows. It is possible to configure so as to decrease toward the downstream side, and according to this configuration, the space can be used effectively.

  In the fuel cell described above, the membrane having poor liquid permeability and gas permeability needs to be fixed to any one of the wall surfaces constituting the anode flow path by adhesion, welding, pressure bonding, or the like. In this structure, the volume of the flow path through which the carbon dioxide gas flows and the volume of the flow path through which the fuel flow are determined by the liquid hardly permeable and gas permeable membrane. The volume ratio of these flow paths is an important factor that determines carbon dioxide emission and fuel supply. Therefore, it is necessary to fix the membrane that selectively permeates carbon dioxide gas to one of the wall surfaces constituting the anode flow channel so that the flow channel volume ratio does not change.

  According to the present invention as described above, in particular, the amount of fuel supplied to the anode side catalyst layer can be secured, and the generated carbon dioxide gas can be discharged more reliably, and the direct type having excellent power generation characteristics A fuel cell can be realized.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected to the same or an equivalent part, and the overlapping description may be abbreviate | omitted.
FIG. 1 is a schematic cross-sectional view showing a preferred embodiment of a direct fuel cell 1 (single cell) according to the present invention. Although the direct fuel cell 1 in FIG. 1 includes one single cell, the direct fuel cell 1 of the present invention can also be used as a stack configured by stacking a plurality of single cells.

The direct fuel cell 1 includes a membrane electrode assembly 2 and an anode side separator 3a and a cathode side separator 3c that sandwich the membrane electrode assembly 2.
The membrane electrode assembly 2 includes a polymer electrolyte membrane 4 having hydrogen ion (cation) conductivity, and an anode 7 a and a cathode 7 c sandwiching the polymer electrolyte membrane 4. The anode 7a includes an anode side diffusion layer 6a and an anode side catalyst layer 5a, and is joined to the first surface of the polymer electrolyte membrane 4. On the other hand, the cathode 7c includes a cathode-side diffusion layer 6c and a cathode-side catalyst layer 5c, and is joined to a second surface facing the first surface of the polymer electrolyte membrane 4.

As shown in FIG. 1, the single cell 1 is mainly composed of a membrane electrode assembly 2 described later, a gasket 11, and a pair of separators 3a and 3c. The gasket 11 is used to prevent the leakage of fuel supplied to the membrane electrode assembly 2 to the outside, to prevent leakage of air to the outside, and to prevent mixing of the fuel and air. In a sandwiched state, they are arranged around the anode 7a and the cathode 7c.
First, each component of the direct fuel cell 1 of the present invention will be described.

As the polymer electrolyte membrane 4, various materials can be used as long as they are excellent in hydrogen ion conductivity, heat resistance and chemical stability, and are not particularly limited.
The anode side catalyst layer 5a and the cathode side catalyst layer 5c are in the form of a thin film. For example, the anode-side catalyst layer 5a and the cathode-side catalyst layer 5c are mainly catalyst particles obtained by supporting a metal catalyst on conductive particles (for example, conductive carbon particles), or metal catalyst particles and cations (hydrogen And an ion conductive polymer electrolyte.
For example, platinum (Pt) -ruthenium (Ru) alloy fine particles are suitably used as the metal catalyst of the anode side catalyst layer 5a, and Pt fine particles are suitably used as the metal of the cathode side catalyst layer 5c.

The anode-side diffusion layer 6a is made of a conductive porous material having both diffusibility of fuel, discharge of carbon dioxide generated by power generation, and electronic conductivity. Examples of the conductive porous material include carbon paper and carbon cloth.
The cathode-side diffusion layer 6c is made of a conductive porous material having both air diffusibility, discharge of water generated by power generation, and electronic conductivity. Examples of the conductive porous material include carbon paper and carbon cloth.

Next, the plate-like anode side separator 3a and cathode side separator 3c that are disposed outside the membrane electrode assembly 2 and mechanically fix the membrane electrode assembly 2 will be described.
An anode-side flow path for supplying fuel to the anode 7a and discharging electrode reaction products and unreacted reactants from the direct fuel cell 1 to a portion of the anode-side separator 3a that contacts the membrane electrode assembly 2 12a is formed. On the other hand, the cathode side separator 3c is in contact with the membrane electrode assembly 2 by supplying air to the cathode 7c and discharging the electrode reaction products and unreacted reactants from the direct type fuel cell 1. A flow path 12c is formed.

The material of the anode side separator 3a and the cathode side separator 3c is not particularly limited as long as it has airtightness, electronic conductivity, and electrochemical stability. For example, metal, carbon, a mixed material of graphite and resin, and the like can be given.
The structure of the cathode side flow path 12c of the cathode side separator 3c is not particularly limited, and various structures conventionally used can be adopted. The cathode side flow path 12c in FIG. And is composed of linear grooves (plural) extending in a direction perpendicular to the paper surface.

On the other hand, the direct fuel cell 1 of the present invention is characterized by the structure of the anode-side flow path 12a of the anode-side separator 3a.
The anode-side channel 12a is formed of linear grooves (not shown) that are separated by ribs and extend in a direction parallel to the paper surface, as with the cathode-side channel 12c. In addition to this, as shown in FIG. 1, the anode-side channel 12a in the present embodiment has a low liquid permeability in the depth direction of the anode-side channel 12a (the direction of the arrow X in FIG. 1). Divided into a first partial flow path 18 located on the membrane electrode assembly 2 side and a second partial flow path 19 located on the bottom side of the anode side flow path 12a by the gas permeable membrane 16 Has been. In the first partial flow path 18, fuel mainly flows in the direction of arrow Q, and in the second partial flow path 19, carbon dioxide mainly flows in the direction of arrow R.

2 is a schematic perspective view of the anode-side separator 3a in FIG. 1 on the anode-side channel 12a side (a state where the membrane 16 is removed from the anode-side channel 12a). The anode-side flow path 12a in the present embodiment is composed of linear grooves (plural) extending in the direction of the arrow Y shown in FIG.
Further, slopes 15 extending in the direction of the arrow Y are provided at both ends of the groove in the direction of the arrow Z in FIG. When the membrane 16 is fixed to the slope 15, the anode-side channel 12a is divided into two in the direction of the arrow X, and the first partial channel 18 and the second partial channel as shown in FIG. 19 is formed.

The film 16 includes a water repellent layer 16A and a gas permeable layer 16B made of a porous material. The water repellent layer 16 </ b> A exhibits poor liquid permeability, and the gas permeable layer 16 </ b> B exhibits gas permeability.
Examples of the porous body constituting the gas permeable layer 16B include carbon paper, porous silica glass obtained by subjecting sodium borosilicate glass to heat treatment to cause phase separation and then acid treatment, zeolite, and polytetrafluoroethylene (PTFE). ) A water-repellent resin porous body such as a resin can be used.

  The water-repellent layer 16B is mainly composed of a water-repellent resin. For example, the water-repellent layer such as polytetrafluoroethylene (PTFE) resin fine particles or polytetrafluoroethylene-polyhexafluoropropylene copolymer (FEP) resin fine particles. It can be formed using a paste-like water-repellent ink mainly composed of water-based resin fine particles and a water-repellent binder such as a fluororesin or a silicone resin. For example, a spray coating method can be suitably used.

The surface of the water repellent layer 16A has an uneven shape. The uneven shape can be adjusted by appropriately controlling the composition such as the solid content concentration of the water-repellent ink and the coating conditions such as the drying temperature and the drying time.
Here, FIG. 3 is a partial cross-sectional view of the direct fuel cell 1 shown in FIG. 1 taken along the line P-P when the direct fuel cell 1 of the present embodiment is operating. As shown in FIG. 3, the anode side channel 12a has a membrane 16 having poor liquid permeability and gas permeability, the water repellent layer 16A is located on the membrane electrode assembly 2 side, and the anode side channel The gas permeable layer 16B is located on the bottom side of 12a.
As described above, the water repellent layer 16A is positioned on the membrane electrode assembly 2 side, and the gas permeable layer 16B is positioned on the bottom side of the anode-side channel 12a, so that the fuel mainly flows through the first partial channel 18. Carbon dioxide mainly flows through the second partial flow path 19.

As described above, the representative embodiments of the present invention have been described. However, the direct fuel cell of the present invention can be variously modified without departing from the effects of the present invention.
For example, in the above-described embodiment, the first partial flow path and the second partial flow are all made up of the plurality of grooves constituting the anode-side flow paths extending in parallel by the membrane having poor liquid permeability and gas permeability. Although the case where it divides | segments into 2 to a path | route was demonstrated, you may divide | segment into 1 to several out of the several groove | channel which comprises an anode side flow path.
Moreover, in the said embodiment, although the aspect which divides one groove | channel from one edge part (start end) to the other edge part (terminal) was demonstrated, in the range with which the effect of this invention is acquired. At least a part of one groove may be divided into two.

In addition, in order to supply fuel and air to the anode side channel 12a and the cathode side channel 12c, it is necessary to use a manifold that is a pipe for supplying fuel and air. As this manifold, either a conventionally known internal manifold or external manifold can be adopted.
EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated in more detail, this invention is not limited to these Examples at all.

Example 1
In this example, a direct fuel cell 1 of the present invention having the structure shown in FIG. 1 was produced.
30% by weight of Pt and Ru having an average particle size of 30 mm are supported on Ketjen Black EC (manufactured by AKZO Chemie), which is conductive carbon particles having an average primary particle size of 30 nm, respectively, and anode side catalyst particles (Pt: 30 wt. %, Ru: 30% by weight). Further, 50% by weight of Pt having an average particle size of 30 mm was supported on Ketjen Black EC to obtain cathode side catalyst particles (Pt: 50% by weight).

Next, an anode-side catalyst layer paste is prepared by mixing the anode-side catalyst particle isopropanol dispersion and the polymer electrolyte ethanol dispersion, and then highly dispersing the resulting mixture with a bead mill. The cathode-side catalyst layer paste was prepared by mixing the cathode-side catalyst particle isopropanol dispersion and the polymer electrolyte ethanol dispersion, and then highly dispersing the resulting mixture with a bead mill.
In the anode side catalyst layer paste and the cathode side catalyst layer paste, the weight ratio of the conductive carbon particles to the polymer electrolyte was 2: 1. As the polymer electrolyte, perfluorocarbon sulfonic acid ionomer (Flemion manufactured by Asahi Glass Co., Ltd.) was used.

  The anode-side catalyst layer paste and the cathode-side catalyst layer paste prepared as described above were each applied onto a resin sheet using a doctor blade, and then dried at room temperature in the atmosphere for 6 hours. Thereafter, the resin sheet after coating was cut into a size of 6 cm × 6 cm to obtain a sheet with an anode side catalyst layer (anode side catalyst sheet) and a sheet with a cathode side catalyst layer (cathode side catalyst sheet).

  With the obtained anode side catalyst sheet and cathode side catalyst sheet, the polymer electrolyte membrane 4 is sandwiched so that the catalyst layer faces the polymer electrolyte membrane 4, and hot pressing (135 ° C., 3 MPa, 15 minutes) is performed. The anode side catalyst layer and the cathode side catalyst layer were thermally transferred (bonded) to the polymer electrolyte membrane 4. As the polymer electrolyte membrane 4, a perfluoroalkylsulfonic acid ion exchange membrane (Nafion 117 manufactured by Du Pont) was used.

Next, the joined body of the anode side catalyst layer 5a, the polymer electrolyte membrane 4, and the cathode side catalyst layer 5b was obtained by peeling off the resin sheet. The amount of platinum (Pt) catalyst in the anode side catalyst layer 5a and the cathode side catalyst layer 5b was 2.0 mg / cm ² .
Thereafter, the anode-side diffusion layer 6a and the cathode-side diffusion layer 6c are laminated on the outer surfaces of the anode-side catalyst layer 5a and the cathode-side catalyst layer 5b, respectively, and bonded by hot pressing (135 ° C., 3 MPa, 15 minutes). did. For the anode side diffusion layer 6a and the cathode side diffusion layer 6c, carbon paper (TGP-H120 manufactured by Toray Industries, Inc.) was cut into a size of 6 cm × 6 cm.
Further, a gas seal material 11 was joined around the anode 7a and the cathode 7c by thermal welding (135 ° C., 4 MPa, 30 minutes) with the polymer electrolyte membrane 4 interposed therebetween, and a membrane electrode assembly (MEA) 2 was produced. .

An anode separator 3a having the structure shown in FIG. 2 (outer dimensions: 10 cm × 10 cm, thickness: 4 mm) was produced by cutting a resin-impregnated graphite material.
Specifically, a groove having dimensions of width (2 × t ₁ + t ₄ ) 4 mm, start end depth (t ₂ ) 1 mm, and end depth (t ₆ ) 0.6 mm was formed. Further, on both sides in the groove, a width (t ₁ ) of 1 mm (ie, t ₄ = 2 mm), a start end depth (t ₂ ) of 1 mm (ie, a start end height t ₅ = 0 mm of the slope 15), and a terminal end Two slopes 15 having a height (t ₃ ) of 0.3 mm were provided.

Next, a film 16 having water repellency and gas permeability was prepared for installation on the slope 15 in the anode-side channel 12a.
The membrane 16 is made of polytetrafluoroethylene (PTFE) resin fine particles and silicone resin on the surface of a gas permeable layer 16B obtained by cutting carbon paper (TGP-H120 manufactured by Toray Industries, Inc.) into a width of 2 mm. A water-repellent layer 16A (thickness of about 40 μm) is formed by spray coating with a super water-repellent agent (HIREC 1450 manufactured by NTT Advanced Technology Co., Ltd.) as the main component and then drying at 70 ° C. for 20 minutes. Obtained.

  A carbon adhesive (ST-201 manufactured by Nisshinbo Co., Ltd.) is applied to the surface of the slope 15, and the membrane 16 produced as described above is positioned so that the gas permeable layer 16B is positioned on the bottom side of the anode-side channel 12a. And it installed on the said slope 15 and adhered so that the water-repellent layer 16A might be located in the membrane electrode assembly 2 side.

Here, as shown in FIG. 4, the anode side flow path 12a of the anode side separator 3a was formed. FIG. 4 is a front view of the anode separator 3a according to the present embodiment as viewed from the anode flow path 12a side.
As shown in FIG. 4, the anode-side separator 3a in the present embodiment is substantially rectangular, and the anode-side flow path 12a has seven linear grooves 12a _{1 that} connect the supply port 3a ₁ and the discharge port 3a _2. It consists of In the present embodiment, the film 16 is installed in all seven linear grooves 12a ₁ . In addition, the part shown with a broken line in FIG. 4 is a part (electrode part) corresponding to the anode 7a (refer FIG. 1).

As the cathode-side separator 3c, one having the same structure as that shown in FIG. 4 is used except that the slope 15 and the film 16 are not provided and the depth and width of the grooves constituting the flow path are constant. It was.
However, when assembling the direct type fuel cell 1, the seven linear grooves 12a1 of the anode-side channel 12a and the linear grooves (not shown) of the cathode-side channel 12c are orthogonal to each other. The anode side separator 3a and the cathode side separator 3c were arranged.

Finally, the membrane / electrode assembly 2 obtained as described above is sandwiched between the anode-side separator 3a and the cathode-side separator 3b to obtain a laminate, and a current collector plate, a heater, An insulating plate and an end plate were arranged, and the whole was fixed with a fastening rod (not shown). The fastening pressure at this time was 20 kgf / cm ² per area of the anode side separator 3a and the cathode side separator 3b.
The direct fuel cell (cell 1) of the present invention was produced by the method as described above.

<< Comparative Example 1 >>
A fuel cell (battery 2) was produced in the same manner as in Example 1 except that the membrane 16 was not provided in the anode-side flow path 12a of the anode-side separator 3a.

<< Comparative Example 2 >>
Carbon paper (TGP-H120 manufactured by Toray Industries, Inc.) is cut into a size of 6 cm × 6 cm as the anode side diffusion layer 6a, and 10% by weight of polytetrafluoroethylene-polyhexafluoropropylene copolymer serving as a thermosetting resin The coalescence (FEP) was impregnated. Next, a water-absorbing polymer gel having fuel permeability (Junron PW-150 manufactured by Nippon Pure Chemical Industries, Ltd.), an aqueous dispersion of Nafion (manufactured by Du Pont), polyethylene oxide as a binder, Were mixed to prepare a slurry mixture.

  Next, carbon paper impregnated with FEP is prepared, and on one side of the carbon paper, a portion facing the anode-side flow path 12a when the carbon paper is incorporated in the direct fuel cell 1 as the anode-side diffusion layer 6a. A mask was placed in the area other than. The slurry-like mixture was applied and imprinted on both sides of the carbon paper on which the mask was placed, and then the mask was removed. In this way, an anode side diffusion layer 6a in which a fuel permeation layer was formed in a region where the fuel permeable material was applied was obtained.

In this comparative example, an anode side separator 33a having the structure shown in FIG. 5 was used. FIG. 5 is a front view of the anode side separator 33a used in this comparative example as seen from the anode side flow path side.
In this anode side separator 33a, a fuel supply passage 38 for supplying fuel gas to the anode 7a and a gas exhaust passage 39 for discharging carbon dioxide and the like are alternately provided in parallel. .

  The opening area of the fuel supply flow path 38 was set to be the same as the opening area of the anode-side flow path 12a used in Example 1. Further, a gas exhaust passage 39 is provided between the fuel supply passages 38, and the terminal portion 38A of the fuel supply passage 38 and the start portion 39A of the gas exhaust passage 39 are anodes indicated by broken lines. It closed in the part (electrode part) corresponding to 7a.

  A fuel cell (cell 3) was produced in the same manner as in Example 1 except that the anode-side diffusion layer 6a and anode-side separator 33a produced as described above were used and the membrane 16 was not used.

<< Comparative Example 3 >>
A fuel cell (cell 4) was produced in the same manner as in Example 1 except that the water repellent layer 16A was not provided on the membrane 16.

Example 2
The anode side separator 3a anode side flow path 12a provided in the, except that setting the starting end height t ₅ of the slope 15 to 0.3 mm, to prepare a fuel cell in the same manner as in Example 1 (Battery 5) .

Example 3
In the anode-side flow path 12a provided in the anode-side separator 3a, a groove portion having a start end depth (t ₂ ) of 0.6 mm and a end depth (t ₆ ) of 1 mm is formed, and the start end height of the slope 15 is formed. the t ₅ and 0.3 mm, except that the termination height (t ₃₎ was set to 0.7mm were fabricated fuel cell in the same manner as in example 1 (cell 6).

Example 4
In the anode-side flow path 12a provided in the anode-side separator 3a, a groove portion having dimensions of a start end depth (t ₂ ) of 0.6 mm and an end depth (t ₆ ) of 0.6 mm is formed, and the start end of the slope 15 is formed. the height t ₅ and 0.3mm, except that the termination height (t ₃₎ was set to 0.3mm were fabricated fuel cells in the same manner as in example 1 (cell 7).

Example 5
In the anode-side flow path 12a provided in the anode-side separator 3a, a groove having a termination depth (t ₆ ) of 1 mm is formed, the start end height t ₅ of the slope 15 is set to 0 mm, and the termination height (t ₃ ) Was set to 0.7 mm, and a fuel cell (cell 8) was produced in the same manner as in Example 1.

[Evaluation test]
A 4M methanol aqueous solution is supplied at a flow rate of 0.5 cc / min to the anode side flow passage 12a of the batteries 1 to 8, and air is supplied to the cathode side flow passage 12C at a flow rate of 0.5 L / min. Electric power was generated for 10 minutes under the condition of a current density of 150 mA / cm ² .
The voltage after power generation for 10 minutes was measured, and the amount of methanol discharged from the anode 7a side was measured.

  However, the voltage of the battery 2 was set to 100, and the voltages of the batteries 1 and 3 to 6 were expressed as indices with respect to the voltage of the battery 2. In addition, the methanol discharge amount of the battery 2 was 100, and the methanol discharge amounts of the batteries 1 and 3 to 6 were expressed as an index with respect to the methanol discharge amount of the battery 2. The units were aligned.

In Table 1, the change from the upstream to the downstream of the cross-sectional area of the second partial flow path (carbon dioxide (CO ₂ ) discharge flow path) 19 is described. The change from the upstream to the downstream of the cross-sectional area of the first partial flow path (fuel supply flow path) 18 is also described.
In addition, a change from the upstream side to the downstream side of the cross-sectional area of the anode-side channel 12a (the linear groove 12a ₁ in FIG. 4) including the first partial channel 18 and the second partial channel 19 is also described. .
Further, Table 2 shows the depth (start end and end) of the groove part constituting the anode side flow path, and the height (start end and end point) of the slope provided in the groove part.

  As shown in Table 1, in Example 1, the discharge amount of methanol from the anode side is reduced to about ３ compared to Comparative Example 1 (when no membrane is used). This is because carbon dioxide gas generated by power generation passes through the membrane, suppressing the carbon dioxide gas from staying in the anode-side flow path and the anode-side diffusion layer, making it difficult for the fuel and carbon dioxide gas to coexist. It is presumed that.

In Example 1, the voltage is divided into Comparative Example 2 (that is, the anode side channel for carbon dioxide emission is divided into a first partial channel for fuel supply and a second partial channel for exhaust gas). ) About 23%.
In Comparative Example 2, as shown in FIG. 6, since the gas exhaust passage 39 is separately provided in the anode side separator 33a, the fuel supply amount is increased on the surface of the anode side catalyst layer 6a in the region facing the gas exhaust passage 39. It is thought that the shortage resulted in a voltage drop. FIG. 6 is a schematic partial cross-sectional view obtained by cutting the fuel cell of Comparative Example 2 at a portion corresponding to the line SS in FIG.

On the other hand, in the case of Example 1, as shown in FIG. 3, the first partial flow located on the membrane electrode assembly 2 side in the depth direction of the anode side flow channel 12a is arranged on the anode side flow channel 12a. The channel 18 and the second partial channel 19 located on the bottom side of the anode side channel 12a were divided into two. Therefore, it is considered that the fuel can be supplied to the anode side diffusion layer 6a from the entire opening of the first partial flow path 18, and the fuel can be supplied uniformly to the entire surface of the anode side catalyst layer 5a. It is done.
As in Comparative Example 2, the ratio of the opening area between the fuel supply flow path 38 and the gas exhaust flow path 39 is changed to increase the opening area occupancy of the fuel supply flow path 38. It is possible to reduce the fuel supply shortage to the region facing the flow path 39 to some extent. However, as long as the gas exhaust passage 39 is provided separately, the same fuel supply state as in the first embodiment cannot be formed.

  In Comparative Example 3, only the gas permeable layer 16B of Example 1 was used and the water-repellent layer 16A was not provided, but the methanol discharge amount of Comparative Example 3 was not significantly different from that of Comparative Example 1. This is considered to be because the gas permeable layer 16B allows not only the carbon dioxide gas but also the fuel to pass therethrough because there is no water repellent layer 16A.

In the second embodiment, the size of the second partial flow path 19 in which the carbon dioxide gas flows in the first embodiment is constant from the upstream to the downstream of the fuel flow, and the methanol discharge amount is larger than that in the first embodiment. It has become. This is presumably because part of the liquid fuel was vaporized due to the large volume of the gas layer upstream of the fuel flow, permeated through the gas permeable layer, and was discharged unused.
In the fifth embodiment, the anode-side flow path of the first embodiment is made constant from the upstream to the downstream of the fuel flow, and the methanol discharge amount is slightly larger than that of the first embodiment. This is presumed to be because part of the liquid fuel vaporized, passed through the gas permeable layer, and was discharged unused because the volume of the gas layer on the downstream side of the fuel flow was large. The

  The polymer electrolyte fuel cell of the present invention, which is used directly without reforming methanol or aqueous methanol as a fuel into hydrogen, is a portable compact such as a mobile phone, a personal digital assistant (PDA), a notebook PC and a video camera. It is useful as a power source for electronic equipment. It can also be applied to power sources for electric scooters.

It is a schematic sectional drawing which shows the structure of the direct type fuel cell 1 (single cell) in embodiment and Example of this invention. FIG. 2 is a schematic perspective view of the anode-side separator 3a in FIG. 1 on the anode-side channel 12a side (a state where the membrane 16 is removed from the anode-side channel 12a). 1 is a partial cross-sectional view of the direct fuel cell 1 shown in FIG. 1 taken along the line P-P (a cross-sectional view of the membrane electrode assembly 2 and the anode separator 3a portion) when the direct fuel cell 1 of the present embodiment is in operation. ). FIG. 3 is a front view of the anode separator 3a used in Example 1 as viewed from the anode flow path side. It is the front view seen from the anode side channel side of anode side separator 33a used for comparative example 2. FIG. 6 is a schematic partial cross-sectional view (a cross-sectional view of the membrane electrode assembly 2 and anode-side separator 33a portion) obtained by cutting the fuel cell of Comparative Example 2 at a portion corresponding to the SS line in FIG. 5.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Single cell, 2 ... Membrane electrode assembly, 3a ... Anode side separator, 3c ... Cathode side separator, 4 ... Polymer electrolyte membrane, 5a ... Anode side catalyst layer, 5c ... Cathode side catalyst layer, 6a ... Anode side gas diffusion layer, 6c ... Cathode side gas diffusion layer, 7a ... Anode, 7c ... Cathode, 11 ... Gasket, 12a ...・ Anode-side channel, 13... Rib, 16... Liquid poorly permeable and gas permeable membrane, 16A... Water repellent layer, 16B. , A second partial flow path

Claims (7)

A polymer electrolyte membrane; an anode joined to the first surface of the polymer electrolyte membrane; and a cathode joined to a second surface opposite to the first surface of the polymer electrolyte membrane. A membrane electrode assembly, an anode separator disposed on a first surface of the membrane electrode assembly, and a cathode disposed on a second surface opposite to the first surface of the membrane electrode assembly A direct fuel cell comprising a side separator,
The anode-side separator has an anode-side channel on the anode-side surface, and the cathode-side separator has a cathode-side channel on the cathode-side surface,
At least a part of the anode-side channel is a first partial flow located on the membrane electrode assembly side by a membrane having poor liquid permeability and gas permeability in the depth direction of the anode-side channel. Divided into a channel and a second partial channel located on the bottom side of the anode-side channel,
A direct fuel cell characterized in that fuel mainly flows through the first partial flow path and carbon dioxide flows mainly through the second partial flow path.   The direct fuel cell according to claim 1, wherein the membrane includes a porous body.   3. The direct fuel cell according to claim 2, wherein the porous body is composed of at least one selected from the group consisting of carbon, ceramic, glass and resin.   The direct fuel cell according to claim 1, wherein a water repellent treatment is performed on the membrane electrode assembly side of the membrane.   The direct fuel cell according to claim 1, wherein a surface of the membrane on the membrane electrode assembly side has irregularities.   The said 2nd partial flow path is comprised so that the area of the cross section substantially perpendicular | vertical to the length direction of the said 2nd partial flow path may increase toward upstream from downstream. Direct fuel cell.   The said 1st partial flow path is comprised so that the area of the cross section substantially perpendicular | vertical to the length direction of the said 1st partial flow path may decrease toward upstream from downstream. Direct fuel cell.

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