JPH081802B2 - Composite electrode substrate having different rib heights and method for manufacturing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite electrode substrate for phosphoric acid fuel cells and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, a fuel cell as a generator for generating clean energy, or as an openable / closable generator that can contribute to resource saving by leveling operation of thermal power or hydroelectric power generation or improving energy efficiency, etc. There is a high demand for the development and use of the peripheral system.

As a conventional fuel cell, there has been known a bipolar separator type fuel cell in which a bipolar separator obtained by rib-processing an impermeable graphite thin plate and a porous carbon material flat plate are used in combination. A monopolar fuel cell has been developed which is constructed by laminating a porous electrode substrate having a flat structure on one surface and a flat structure on the other surface, a catalyst layer, a matrix impregnated with an electrolyte and a separator sheet. . In this monopolar fuel cell, a reaction gas (oxygen or hydrogen) diffuses from a reaction gas passage formed by a rib provided on an electrode substrate to a flat electrode surface.

In such a fuel cell, two types of reaction gas passages are formed on both sides of the separator,
That is, the reaction gas passages on the fuel electrode side and the reaction gas passages on the air electrode side are usually formed to have the same cross-sectional area.

The electrode reaction of a phosphoric acid fuel cell is H ₂ + 1/2
Since O ₂ → H ₂ O, the ideal stoichiometric ratio between fuel (hydrogen) and oxygen is 2: 1. If both gases are used at the same pressure to obtain the same gas diffusion, In a fuel cell in which the cross-sectional areas of both gas passages are the same, it is theoretically possible to use 50% pure oxygen gas with respect to pure hydrogen gas.

However, in the actual operation of a fuel cell, oxygen is supplied by air,
Supply of hydrogen H ₂ in that LNG, LPG, etc. pretreated
Considering that the gas content is about 65-80%, and further considering the utilization ratio of fuel and air, the cross-sectional area of the fuel electrode side reaction gas hole and the air electrode side reaction gas hole is the same as above. In some fuel cells, the cross sectional area of the reaction gas passages on the fuel electrode side was excessive.

The excessive size of the reaction gas passages on the fuel electrode side is
Although it can be compensated by increasing the air flow rate commensurate with that, it is clear that it is preferable to use both gases at the same pressure in consideration of the movement of the gas with respect to the opposite electrode as described above.

Another problem with such a fuel cell is that the joining between the members has conventionally been performed using carbon cement, which is easily oxidized by phosphoric acid. There is a possibility that reaction gas may leak through the parts, and because the electrode substrate is manufactured in the shape of a thin plate, there was a problem in mechanical strength that it cracked during handling, especially when the substrate area was large. There are such things.

[0009]

DISCLOSURE OF THE INVENTION The present invention comprises a separator, a porous carbonaceous electrode part and an end seal part, and is a reaction gas on the fuel electrode side and the air electrode side which is suitable for the conditions of the fuel actually used. An object of the present invention is to provide a composite electrode substrate for a fuel cell, which has a cross-sectional area ratio of the channel.

Further, according to the present invention, the end portion of the porous carbonaceous electrode portion is sealed with the tetrafluoroethylene resin layer, and it is not necessary to perform a peripheral sealing treatment for preventing the reaction gas from leaking to the side surface of the battery. An object is to provide a composite electrode substrate for a fuel cell.

Still another object of the present invention is to provide a composite electrode substrate for a phosphoric acid fuel cell, which is excellent in phosphoric acid resistance.

Further objects and advantages of the present invention will be apparent to those skilled in the art from the following description.

The stoichiometric ratio of fuel (hydrogen) to oxygen in the phosphoric acid fuel cell is 2: 1. Since oxygen is supplied by air in the actual operation of the fuel cell, the oxygen content in the supply gas is It is about 20%. Further, the hydrogen supply gas is LNG, LPG or the like which has been reformed as described above and contains CO ₂ , steam and the like, and the hydrogen content is about 65 to 80%.

On the other hand, with respect to the reaction gas utilization rate expressed by the ratio of the reaction gas supply rate to the reaction gas supply rate, when the utilization rate exceeds a certain value, the battery terminal voltage starts to decrease, so that the utilization rate is limited. Actually, the hydrogen utilization rate must be 75% or less and the oxygen utilization rate must be 50% or less, which causes a problem in the conditions of the supply gas in the conventional electrode substrate.

[0015]

The inventors of the present invention have calculated the cross-sectional areas of the reaction gas passages on the fuel electrode side and the reaction gas passages on the air electrode side calculated from the above numerical values assuming that two reaction gases are used at the same pressure. Based on the theoretical ratio of about 0.325: 1 to 0.410: 1, further considering that the hydrogen content may be slightly lower depending on the processing conditions of the hydrogen supply gas, the ratio may be about 1: 3 to.
It has been found that 2: 3 can meet the conditions of the actual feed gas.

Further, the inventors of the present invention obtained sufficient electrical characteristics (conductivity) and phosphoric acid resistance by joining the electrode member and the separator material by joining them with a tetrafluoroethylene resin dispersion, and thus, they are dense. The present invention has been completed by finding that sufficient endurance resistance to gas leakage, resistance to phosphoric acid and overall strength can be obtained by joining an end seal member of a carbon material to a separator material with a tetrafluoroethylene resin sheet.

That is, according to the present invention, a separator made of a dense carbon material and two porous carbonaceous electrodes each having a plurality of grooves joined to the separator to form a reaction gas passage and having the other surface of a flat plate shape. And an end seal part made of a dense carbon material, the electrode parts are joined by tetrafluoroethylene resin dispersion on both surfaces of the separator so that the reaction gas passages face each other at right angles, and the end part The seal portion is bonded to the extended portion of the separator, which is adjacent to the electrode peripheral edge portion parallel to the groove of the electrode portion and extends outward from the electrode peripheral edge, through the tetrafluoroethylene resin layer. A fuel cell electrode substrate having a structure, in which a cross-sectional area of a fuel gas side reaction gas passage and an air electrode side reaction gas of a reaction gas passage formed by the groove of the separator and the porous carbonaceous electrode portion are formed. The ratio of the hole tract area is 1: 3 to 2: 3
Is a composite electrode substrate for a fuel cell.

In the present invention, a tetrafluoroethylene resin dispersion is applied to both surfaces of a separator material made of a dense carbon material, and a plurality of grooves forming reaction gas passages are provided on one surface, and the other surface is flat. Of the two porous carbonaceous electrode members in which the size of the groove is such that the ratio of the cross-sectional area of the reaction gas passages on the fuel electrode side to the reaction gas passage on the air electrode side is 1: 3 to 2: 3. A separator material having a groove side aligned at a predetermined position of the separator material and fusion-bonded to each other, and adjacent to the peripheral edge portion of the electrode member parallel to the reaction gas passage and extending outward from the peripheral edge of the electrode portion. There is provided a method for producing the composite electrode substrate for a fuel cell, which comprises joining an end seal member made of a dense carbon material which is gas impermeable to the extended portion of the sheet via a fluororesin sheet.

Hereinafter, the electrode substrate of the present invention will be described in more detail with reference to the accompanying drawings. It should be noted that the drawings are exaggerated and do not represent the actual size. Those of ordinary skill in the art will appreciate the size of each member, and particularly the appropriate size with respect to thickness.

FIG. 1 is a perspective view of a composite electrode substrate of the present invention, in which a porous carbonaceous substrate and a separator are joined by a tetrafluoroethylene resin dispersion.

The composite electrode substrate of the present invention comprises a separator 1
And two electrode portions located on both sides of the separator having grooves that form reaction gas passages 5 and 6 together with the separator.
2 and an end seal portion 3 that seals the end portions of the electrode portion in the direction parallel to the reaction gas passages 5 and 6.

The separator 1 is larger than the electrode portion 2 and extends outwardly from the periphery of the electrode portion along the edge portion parallel to the reaction gas passages 5 and 6 of the electrode portion as shown in the figure. The end seal portion 3 is joined to the portion (the outer end of the extension portion of the separator coincides with the outer end of the end seal portion after the end seal portion is joined). The extended portion of the separator extending outward and the end seal portion 3 are joined together via a tetrafluoroethylene resin layer 4. The separator 1 and the protrusion forming the groove of the electrode part 2 are joined by a tetrafluoroethylene resin dispersion, and the reaction gas passages 5 and 6 are defined by the groove of the electrode part and the separator.

In the composite electrode substrate of the present invention, the ratio of the cross-sectional area of the fuel electrode side reaction gas passage 5 to the air electrode side reaction gas passage 6 is 1: 3 to 2: 3. Although the cross-sectional shape of the reaction gas passage satisfying the above-mentioned cross-sectional area ratio can be arbitrary, from the viewpoint of the effect that the thickness of the composite electrode substrate itself can be made thin, the performance and mechanical strength of the battery itself, and the like, In the case of a reaction gas passage that is normally formed in a rectangular shape, the width is the same on the fuel electrode side and the air electrode side, and the cross-sectional area is different due to different heights (differences in the groove of the electrode part). Preferably.

Regarding the reaction gas passages, the one shown in the drawing has a rectangular cross-sectional shape and extends linearly in parallel with the sealed end from the opened one end to the other end. Any shape may be used as long as it can sufficiently supply the reaction gas that diffuses into the part. For example, if the rib portion forming the groove of the electrode portion has a trapezoidal cross section or the groove is non-linear, it is possible to disperse the stress received by the composite electrode substrate. Etc. are advantageous.

In the composite electrode substrate of the present invention, the electrode part is made of porous carbonaceous material and has an average bulk density of 0.3 to 0.9 g / cc.
It is preferable that the gas permeability is 200 ml / cm ² · hr · mmAq or more and the electric resistance is 200 mΩ · cm or less.

The separator has an average bulk density of 1.4 g / cc or more,
Gas permeability 10 ^-6 ml / cm ² · hr · mmAq or less, electrical resistance 10
A dense carbon material with a thickness of 2 mm or less at mΩ · cm or less is preferable,
The thing baked at 2000 degreeC or more is more preferable.

The end seal portion is preferably a dense carbon material having an average bulk density of 1.4 g / cc or more and a gas permeability of 10 ⁻⁴ ml / cm ² · hr · mmAq or less.

As described above, in the composite electrode substrate for a fuel cell of the present invention, the end portion parallel to the reaction gas passage of the electrode portion is
It is sealed by joining the end seal part of the dense carbon material to the separator via the tetrafluoroethylene resin layer, but the leak amount leaking to the outside through the end seal part including the joint part is not diffused. Although it is dominant and is not so much affected by pressure, in the present invention, the amount of leak gas per unit peripheral length per unit length under a differential pressure of 500 mmAq is expressed as [leak gas amount / (side length). (Differential pressure)]. Then, 10 ⁻² ml / cm · hr · mmAq or less is preferable.

In the composite electrode substrate of the present invention, the end seal portion is joined to the extended portion of the separator through a tetrafluoroethylene resin (abbreviated as PTFE, melting point 327 ° C., heat distortion temperature 121 ° C.) layer. The thickness of the tetrafluoroethylene resin layer is about 50 μm.

Materials and manufacturing methods used for manufacturing the composite electrode substrate of the present invention are described below, but the present invention is not limited to this range.

As the electrode member, a mixture of short carbon fibers, a binder, and an organic particulate substance is heat-pressed and molded (see, for example, JP-A-59-68170). 20-60% by weight of short carbon fibers with a length of 2 mm or less, phenol resin
A mixture of 20 to 50% by weight and 20 to 50% by weight of organic particulate matter (pore control material) is used at a molding temperature of 100 to 180 ° C and a molding pressure.
297-9901 kPa (2-100 kgf / cm ² G), pressure holding time 1-6
A porous carbonaceous material obtained by firing a product molded under the condition of 0 minutes at 800 ° C. or higher is preferable.

As the separator material, a dense carbon plate having a firing shrinkage of 0.2% or less when fired at 2000 ° C. is preferable.

The composite electrode substrate of the present invention is manufactured as follows.

A tetrafluoroethylene resin dispersion is formed on both surfaces of a separator material made of a dense carbon plate to a thickness of 0.01 to
After coating with 0.5 mm, the grooves for forming the reaction gas passages were previously formed so that the ratio of the reaction electrode passage cross-sectional area of the fuel electrode side to the reaction gas passage cross-sectional area of the air electrode side was 1: 3 to 2: 3. 2
Set the two electrode members so that the sides with grooves on both sides of the separator material are the joint surfaces, and 199 kPa (1 kgf / cm ² G)
Fusion bonding is performed at the above pressure and at a temperature of approximately 270 ° C or higher.

The tetrafluoroethylene resin dispersion is used as a dispersion in 10 to 70% by weight of the tetrafluoroethylene resin, for example about 60% by weight, for example in water.

Incidentally, the tetrafluoroethylene resin is a non-conductive substance, but the conductivity between the porous carbonaceous electrode member and the separator is sufficiently secured. This is because both members are joined in such a manner that the porous carbonaceous electrode member is impregnated with the tetrafluoroethylene resin applied to the separator material at the time of pressure bonding in the above joining, so that both members have sufficient strength. It is considered that the two members can be sufficiently contacted at the same time when they are joined.

After the electrode member and the separator member are joined, gas is impermeable to the extended portion of the separator material which is adjacent to the peripheral edge portion of the electrode member parallel to the reaction gas passage and extends outward from the peripheral edge of the electrode member. End seal member made of a dense carbonaceous material, through a tetrafluoroethylene resin sheet,
Fusion bonding is performed in the same manner as described above.

Appropriate conditions for joining the porous carbonaceous electrode member and the separator material by the above-mentioned tetrafluoroethylene resin dispersion, and the joining of the separator material and the end seal member through the above-mentioned tetrafluoroethylene resin sheet are used. It is particularly advantageous because it can be performed simultaneously if selected and the number of steps can be reduced.

The porous carbonaceous electrode member having a groove forming a gas passage can be molded by filling a raw material mixture into a mold having a predetermined shape and press-molding it, or once molding it into a flat plate shape (further firing. Although it can be formed by any method such as cutting grooves afterwards, it is preferable to extrude the raw material mixture after kneading and press-form by roll or stamping from the viewpoint of productivity and uniformity of the product.

[0040]

Since the composite electrode substrate for a fuel cell of the present invention obtained as described above has a reaction gas passage cross-sectional area that matches the conditions of the reaction gas actually supplied,
Compared to an electrode substrate that has the same reaction gas passage cross-sectional area on the fuel electrode side and the air electrode side, the reaction gas passage cross-sectional area on the fuel electrode side is maintained while maintaining the same performance when operating as a fuel cell. Since it can be made small, that is, the height of the reaction gas passage can be made low, the thickness of the composite electrode substrate itself can be made thin.

For example, in a normal composite electrode substrate having a thickness of 3.8 to 4.0 mm, since the reaction gas passages are formed at a height of 1.0 to 1.4 mm, the maximum thickness can be reduced to about 0.6 to 0.9 mm. The total thickness of the composite electrode substrate can be reduced by about 15 to 24%. This not only contributes to downsizing of the fuel cell, but also can reduce electric thickness and thermal resistance by about 15 to 24% due to the reduction in thickness, and thus higher fuel efficiency can be expected.

The composite electrode substrate for a fuel cell of the present invention is
Since the end seal part is integrally joined to the separator at the end of the electrode part through the tetrafluoroethylene resin layer, the gas seal is excellent in resistance to gas leakage, and the reaction gas required for a normal fuel cell It is not necessary to perform a peripheral sealing process to prevent leakage to the side of the battery.

Further, the electrode portion and the separator are joined by a tetrafluoroethylene resin dispersion,
Further, since the end seal portion and the separator are joined and integrated via the tetrafluoroethylene resin layer, the phosphoric acid resistance is excellent, and it is particularly useful as a phosphoric acid fuel cell electrode substrate.

Further, since the end seal portions are arranged and joined evenly across the both sides of the thin plate-like electrode portion with the separator sandwiched therebetween, they have a reinforcing effect, and as a result, when manufacturing a fuel cell, etc. Excellent handling.

[Brief description of drawings]

FIG. 1 is a perspective view of a composite electrode substrate of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Separator, 2 ... Porous carbonaceous electrode part, 3 ... End seal part, 4 ... Tetrafluoroethylene resin layer, 5 ... Fuel electrode side reaction gas passageway, 6. ..Reaction gas passages on the air electrode side.

Claims (6)

[Claims] 1. A separator made of a dense carbon material, two porous carbonaceous electrode portions having a plurality of grooves bonded to the separator to form a reaction gas passageway on one surface, and a flat surface on the other surface, and dense carbon. It is composed of an end seal part made of a material, and the electrode parts are joined to both surfaces of the separator by tetrafluoroethylene resin dispersion so that the reaction gas passages face each other at right angles, and the end seal part is the above. A fuel having a structure in which it is joined to an extended portion of the separator which is adjacent to the peripheral edge of the electrode portion parallel to the groove of the electrode portion and extends outward from the peripheral edge of the electrode portion through a tetrafluoroethylene resin layer. The electrode substrate for a battery, wherein the ratio of the cross-sectional area of the fuel electrode side reaction gas passage to the air electrode side reaction gas passage cross-sectional area of the reaction gas passage formed by the groove of the separator and the porous carbonaceous electrode portion. Is 1: 3 to 2: 3, the composite electrode substrate for a fuel cell. 2. The porous carbonaceous electrode portion is 0.3 to 0.9.
Bulk density of g / cc, 200 ml / cm ² · hr · mmA
The composite electrode substrate for a fuel cell according to claim 1, which has a gas permeability of q or more and an electric resistance of 200 mΩ · cm or less. 3. The separator has a bulk density of 1.4 g / cc or more, a gas permeability of 10 ⁻⁶ ml / cm ² · hr · mmAq or less, an electric resistance of 10 mΩ · cm or less, and 2 mm.
The composite electrode substrate for a fuel cell according to claim 1 or 2, which is a dense carbon material having the following thickness. 4. A patent characterized in that the end seal portion is a dense carbon material having a bulk density of 1.4 g / cc or more and a gas permeability of 10 ⁻⁴ ml / cm ² · hr · mmAq or less. The composite electrode substrate for a fuel cell according to any one of claims 1 to 3. 5. A tetrafluoroethylene resin dispersion having a resin content of 10 to 70% by weight is applied to both sides of a separator material made of a dense carbon material in a thickness of 0.01 to 0.5 mm to form a reaction gas hole. The plurality of grooves are provided on one side and the other side is flat, and the size of the grooves is such that the ratio of the cross sectional area of the reaction gas passages on the fuel electrode side to the reaction gas passage on the air electrode side is 1: 3 to 2: The two porous carbonaceous electrode members that are to be No. 3 are aligned with the grooved side at a predetermined position of the separator material, a pressure of 199 kPa or more, a temperature of 270 ° C. or more, and a pressing time of 1 to 60 minutes. Gas impermeable through the tetrafluoroethylene resin sheet to the extended portion of the separator material that is fusion-bonded and is adjacent to the peripheral edge portion of the electrode member parallel to the groove and extends outward from the peripheral edge of the electrode portion. End seal made of dense carbon material A separator made of a dense carbon material, and two porous carbonaceous electrode parts each having a plurality of grooves bonded to the separator to form a reaction gas passageway on one surface and the other surface being a flat plate; It is composed of an end seal part made of a dense carbon material, and the electrode parts are joined by a tetrafluoroethylene resin dispersion on both surfaces of the separator so that the reaction gas passages face each other at right angles, and the end seal part is Of a structure in which an extended portion of the separator, which is adjacent to the peripheral edge portion of the electrode portion parallel to the groove of the electrode portion and extends outward from the peripheral edge portion of the electrode portion, is joined via a tetrafluoroethylene resin layer A fuel cell electrode substrate, which is a ratio of a reaction electrode side reaction gas passage cross-sectional area and an air electrode side reaction gas passage cross-sectional area of a reaction gas passage formed by a separator and a groove of a porous carbonaceous electrode portion. Is from 1: 3
A method for producing a composite electrode substrate for a fuel cell, which is 2: 3. 6. A porous carbonaceous electrode member comprising short carbon fibers,
The manufacturing method according to claim 5, characterized in that the molded member obtained by integrally heat-press molding a mixture of the binder and the organic particulate matter is fired to be manufactured.