JPH11185776A - Phosphoric acid fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stable characteristic of power generation, by preventing corrosion caused by phosphoric acid of separators. SOLUTION: Ribbed substrates 5 made of porous carbon material provided with gas circulating grooves 6 are set on both main surfaces of an electric cell 1 formed by sandwiching a matrix 2 by a fuel electrode 3 and an air electrode 4, then they are plurally piled through separators 7 to constitute the fuel battery. The ribbed substrates 5 are integrally formed with the separators 7 through sheets made of fluoroplastic, or surfaces facing to the separators 7 of the ribbed substrates 5 are applied with water-repellent treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a cell stack of a phosphoric acid type fuel cell in which electric energy is obtained by an electrochemical reaction using phosphoric acid as an electrolyte.

[0002]

2. Description of the Related Art FIG. 6 is an exploded sectional view schematically showing the basic structure of a conventional phosphoric acid fuel cell. As shown in the figure, a fuel cell 3 and an air electrode 4 are arranged on both main surfaces of a flat matrix 2 holding phosphoric acid as an electrolyte to constitute a unit cell 1, and a plurality of cells are provided on both outer surfaces thereof. The ribbed base material 5 made of porous carbon having the gas flow grooves 6 is disposed, and a large number of the constituent units are stacked via a separator 7 to form a battery stack. A manifold for supplying and discharging a reaction gas is installed on each side of the stacked battery stack, and fuel gas or air is supplied to the gas flow groove 6 of the base member 5 with ribs, whereby the cell 1
Then, an electrochemical reaction occurs, and a DC voltage as a series connection of unit cells is obtained at both ends of the battery stack. In FIG. 6, for easy understanding, the gas flow grooves 6 of the ribbed base material 5 are shown as grooves extending in a direction perpendicular to the paper of the drawing on both pole sides, but in an actual device. Generally, the gas supplied to both electrodes is arranged so as to flow in directions orthogonal to each other.

[0003] Since the battery stack is stacked as a series connection of single cells, one surface of the separator 7 disposed between the single cells is attached to the ribbed base material 5 on the fuel electrode side through which hydrogen gas flows. The other surface is in contact with the ribbed substrate 5 on the air electrode side where oxygen gas flows. Therefore, the separator 7 must have a sufficient gas barrier property so that these gases are not mixed to cause a reaction. Further, each cell is electrically connected via a separator 7. If the resistance of the separator 7 is large, the internal loss of the fuel cell will increase. Therefore, the separator 7 has excellent electric conductivity. There must be. Therefore, in a conventional phosphoric acid fuel cell, a gas-impermeable carbon material having a low porosity, for example, about several percent and a high bulk density is used as a material for a separator satisfying these conditions. ing.

[0004]

By the way, in the phosphoric acid type fuel cell, the phosphoric acid held in the matrix 2 gradually evaporates with the operation, and becomes a reaction gas, particularly a reaction air having a large flow rate. Since it is scattered and released to the outside, phosphoric acid for replenishment is stored in the pores of the ribbed base material 5 made of a porous carbon material, and this is used as a reservoir of phosphoric acid. A method of supplementing acid has been adopted.

For this reason, the ribbed substrate 5 of the separator 7
Is in contact with the phosphoric acid stored in the base material 5 with ribs. If the operation is continued for a long time, the surface of the separator 7 is corroded by the phosphoric acid, and stable power generation characteristics cannot be obtained. There is a point. SUMMARY OF THE INVENTION An object of the present invention is to provide a phosphoric acid type fuel cell which has a separator excellent in the reaction gas blocking performance and electric conductivity and is not likely to be corroded by phosphoric acid, and can be operated stably for a long period of time.

[0006]

In order to achieve the above-mentioned object, the present invention provides a unit cell comprising a flat matrix holding phosphoric acid sandwiched between a fuel electrode and an air electrode. After arranging a porous carbon base material having a gas flow groove in the phosphoric acid fuel cell configured by laminating a plurality of layers with a separator made of a gas impermeable carbon material interposed therebetween, (1) The porous carbon substrate and the separator, which are disposed in contact with each other, are integrally formed via a sheet made of a fluororesin. For example, PTFE (polytetrafluoroethylene), PFA (tetrafluoroethylene) Through a sheet made of ethylene / perfluoroalkyl vinyl ether copolymer) or FEP (tetrafluoroethylene / hexafluoropropylene copolymer). By pressure molding at a temperature equal to or higher than the melting temperature, they are integrally molded.

(2) Alternatively, a sheet made of a fluororesin and a porous carbon sheet may be integrally formed and formed, for example, PTFE, PFA or FE.
The sheet made of P and the porous carbon sheet are molded under pressure at a temperature higher than the melting temperature, and the resulting composite sheet is molded integrally by pressure molding at a temperature higher than the melting temperature. It shall be constituted.

(3) Alternatively, the surface of the porous carbon substrate facing the separator or the surface of the separator is subjected to a water repellent treatment, for example, the surface of the porous carbon substrate facing the separator. Alternatively, after spraying or applying a fluororesin powder such as PTFE, PFA or FEP or a fluororesin dispersion on the surface of the separator, heat treatment is performed at a temperature equal to or higher than the melting point of the fluororesin.

If the porous carbon substrate and the separator are integrally formed as described in (1) above, the fluorocarbon resin, for example, PFA or FEP is melted, and particularly, the fluorine resin is contained in the porous carbon substrate. A resin permeable layer is formed and molded integrally. Therefore, the gas impermeable, separator made of a carbon material of good conductivity, there is no risk of direct contact with the phosphoric acid held in the porous carbon substrate, corrosion of the separator by phosphoric acid is avoided, It can be used stably for a long time.

According to the above (2), the porous carbon substrate and the separator are integrally formed via the porous carbon sheet into which the fluororesin, for example, PFA or FEP is melted and permeated. Therefore, similarly to the above (1), there is no possibility that the separator comes into direct contact with phosphoric acid, corrosion of the separator by phosphoric acid is avoided, and the separator can be used stably for a long period of time.

Further, according to the above (3), a fluororesin layer such as PTFE, PFA or FEP is formed on the surface of the porous carbon substrate facing the separator or on the separator surface, and the separator is made of phosphoric acid. This eliminates the possibility of direct contact with the separator, avoids corrosion of the separator by phosphoric acid, and enables stable use for a long period of time.

[0012]

<First Embodiment> FIG. 1 is an exploded sectional view schematically showing a basic structure of a first embodiment of a phosphoric acid fuel cell according to the present invention. The difference between the configuration of the present embodiment and the conventional example is that the ribbed substrate 5 made of a porous carbon material is formed integrally with the adjacent separator 7 by a sheet made of PFA made of a fluororesin.

FIG. 2 is a flow chart showing a process of integrally molding the ribbed base material 5 and the separator 7. As shown in the figure, a carbon plate for a gas-impermeable separator having a bulk density of 1.7 [g / cc] and a porosity of 7% and a thickness of 0.05 [m
m] PFA sheet, and a bulk density of 0.9 g
/ cc], a base material with ribs made of a porous carbon material having a porosity of 60% is laminated, and heated to 360 ° C. which exceeds the melting point of PFA (300 to 310 ° C.), and a pressure of 10 kg / cm ² is applied. In addition, a joined body of the separator and the base material is formed.

If the ribbed base material 5 and the separator 7 are integrally formed by such a process, the fluororesin PFA melts and penetrates into the porous ribbed base material 5,
As schematically shown in FIG. 1, the fluororesin permeable layer 8 is formed on the side of the separator 7 of the ribbed base material 5. Therefore, in this configuration, since the separator 7 is separated from the phosphoric acid held on the ribbed base material 5 by the fluororesin permeable layer 8, corrosion of the separator 7 by the phosphoric acid is avoided.

<Embodiment 2> FIG. 3 is an exploded sectional view schematically showing a basic structure of a second embodiment of the phosphoric acid type fuel cell according to the present invention. The feature of this embodiment is that the ribbed base material 5 made of a porous carbon material is formed integrally with the adjacent separator 7 by a fluorocarbon resin PFA sheet and a carbon sheet 9.

FIG. 4 is a flow chart showing a process of integrally molding the ribbed base material 5 and the separator 7 of this configuration example. As shown in the figure, a carbon plate for a gas impermeable separator having a bulk density of 1.7 [g / cc] and a porosity of 7% and a PFA sheet having a thickness of 0.05 [mm] were laminated, and then a bulk density of 0.4 [mm] was obtained. [G / cc], a porosity of 78%, a carbon sheet with a thickness of 0.12 [mm] are laminated, and a bulk density of 0.9 [g / c]
c], a ribbed base material made of a porous carbon material having a porosity of 60% is laminated, and heated to 360 ° C. as in Example 1,
By applying a pressure of 10 [kg / cm ² ], a joined body of the separator and the base material is formed.

If the ribbed substrate 5 and the separator 7 are integrally formed by such a process, the PFA is melted and permeates into the porous carbon sheet 9 and further into the ribbed substrate 5. Then, as shown by hatching in FIG. 3, the fluororesin permeable layer 8A is formed. Therefore, in the present configuration, the separator 7 is separated from the phosphoric acid held on the ribbed base material 5 by the fluororesin permeable layer 8A, so that the corrosion of the separator 7 due to the phosphoric acid is avoided. Further, in the present configuration, since the portion of the fluororesin permeable layer 8A of the ribbed base material 5 is suppressed to be smaller than that of the first embodiment, a decrease in the phosphoric acid holding capacity of the ribbed base material 5 is suppressed. There is an advantage that can be.

In the process of this embodiment shown in FIG.
After sequentially laminating the carbon plate for separator, PFA sheet, carbon sheet, and base material with ribs, they are heated and pressurized and joined, but the PFA sheet and the carbon sheet are preheated and pressurized. The separator may be laminated with a carbon plate for a separator and a substrate with ribs, and may be joined by heating and pressing.

In each of the above two embodiments, a PFA sheet is used as a sheet made of a fluororesin. However, the present invention is not limited to the application of a PFA sheet. The same effect can be obtained by using a sheet such as PTFE or PTFE and performing the pressure treatment at a temperature higher than the melting point to join the sheets.

<Embodiment 3> FIG. 5 is an exploded sectional view schematically showing the basic structure of a third embodiment of the phosphoric acid fuel cell according to the present invention. The feature of the configuration of the present embodiment is that a water repellent treatment is performed by spraying or applying a fluororesin powder or a fluororesin liquid on the surface of the ribbed base material 5 made of a porous carbon material on the separator 7 side. It is in.

In the water repellent treatment using the fluororesin powder, the surface of the ribbed substrate 5 made of a porous carbon material having an average pore diameter of 10 to 30 μm on the separator 7 side is coated with PTF.
After spraying E (polytetrafluoroethylene) powder by spraying, 350
The fluororesin layer 10 is formed on the surface of the ribbed base material 5 by performing a heat treatment at a temperature of ℃.

Since the ribbed substrate 5 has a function of storing phosphoric acid and collecting scattered phosphoric acid, the fluororesin layer 10 penetrates into the ribbed substrate 5 so as not to impair the function. It is preferable to form them on the surface as much as possible without forming them. Therefore, it is desirable to select an average particle diameter of the fluororesin powder to be used which is substantially the same as the average pore diameter of the ribbed base material 5.

Next, when the surface of the ribbed substrate 5 on the separator 7 side is subjected to water repellency treatment using a fluororesin liquid, a ribbed substrate made of a porous carbon material having an average pore diameter of 10 to 30 μm is used. 5 is coated with a fluororesin dispersion having a concentration of 20 to 60% by weight in which PTFE powder is dispersed in a surfactant or isopropyl alcohol, and then is coated with an electric furnace or a hot press.
The fluororesin layer 10 is formed on the surface of the ribbed base material 5 by performing a heat treatment at a temperature of ℃.

In this method, the base material 5 with ribs is also used.
It is desirable to adjust the particle size of the fluororesin powder and the concentration of the fluororesin dispersion so that the fluororesin dispersion does not excessively penetrate into the inside of the ribbed base material 5 in accordance with the average pore diameter of. Further, in this embodiment, the fluororesin layer 1
0 is formed of PTFE, but is not limited thereto, and PFA powder or FEP powder or the like may be used instead of the above-mentioned PTFE powder.

Further, in this embodiment, the surface of the ribbed base material 5 on the side of the separator 7 is subjected to the water repellent treatment with the fluororesin powder or the fluororesin liquid. The same effect can be obtained by subjecting the surface facing the substrate 5 to the water repellency treatment by the above-described method.

[0026]

As described above, according to the present invention, a unit cell in which a flat matrix holding phosphoric acid is sandwiched between a fuel electrode and an air electrode is provided with gas flow grooves on both main surfaces thereof. After arranging the porous carbon substrate, a separator made of a gas-impermeable carbon material is interposed, and in the phosphoric acid type fuel cell configured by The porous carbon substrate and the separator are integrally formed by (1) a sheet made of a fluororesin, for example, pressurized through a sheet made of PFA or FEP at a temperature higher than the melting temperature thereof. By molding, it was decided to be integrally molded, so that it was equipped with a separator that was excellent in reaction gas blocking performance and electrical conductivity, and that was not susceptible to corrosion by phosphoric acid. Thus, a phosphoric acid fuel cell that can be operated stably over a long period of time has been obtained.

(2) Further, a sheet made of a fluororesin and a porous carbon sheet are integrally formed and molded, and for example, a sheet made of PFA or FEP and a porous carbon sheet are melted at a melting temperature. Pressure molding at the above temperature, through the obtained composite sheet,
Even if it is formed integrally by pressure molding at a temperature equal to or higher than the melting temperature, a separator having excellent reaction gas blocking performance and electric conductivity and no corrosion by phosphoric acid is provided. Therefore, it is suitable as a phosphoric acid type fuel cell which can be stably operated for a long time.

(3) Alternatively, the surface of the porous carbon substrate facing the separator or the surface of the separator may be subjected to water repellency treatment, for example, the surface of the porous carbon substrate facing the separator. Alternatively, after spraying or applying a fluororesin powder such as PTFE, PFA or FEP or a fluororesin dispersion on the surface of the separator, and heat-treating at a temperature equal to or higher than the melting point of the fluororesin, the reaction gas blocking performance and the electrical conductivity Therefore, a phosphoric acid fuel cell which can be operated stably for a long period of time can be obtained.

[Brief description of the drawings]

FIG. 1 is an exploded sectional view schematically showing a basic configuration of a first embodiment of a phosphoric acid fuel cell according to the present invention.

FIG. 2 is a flowchart showing an integrated molding step of a ribbed base material and a separator according to the first embodiment.

FIG. 3 is an exploded sectional view schematically showing a basic configuration of a second embodiment of the phosphoric acid fuel cell of the present invention.

FIG. 4 is a flowchart showing an integrated molding process of a ribbed base material and a separator according to a second embodiment.

FIG. 5 is an exploded sectional view schematically showing a basic configuration of a third embodiment of the phosphoric acid fuel cell of the present invention.

FIG. 6 is an exploded sectional view schematically showing a basic configuration of a conventional phosphoric acid fuel cell.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Single cell 2 Matrix 3 Fuel electrode 4 Air electrode 5 Base with ribs 6 Gas flow groove 7 Separator 8, 8A Fluororesin permeable layer 9 Carbon sheet 10 Fluororesin layer

Claims (7)

[Claims] 1. A unit cell comprising a flat matrix holding phosphoric acid sandwiched between a fuel electrode and an air electrode, and a porous carbon substrate provided with gas flow grooves on both main surfaces thereof. In a phosphoric acid fuel cell including a plurality of gas-impermeable carbon material-separated separators interposed therebetween, the porous carbon substrate and the separator are interposed via a sheet made of a fluororesin. A phosphoric acid fuel cell, which is integrally formed. 2. A unit cell in which a flat matrix holding phosphoric acid is sandwiched between a fuel electrode and an air electrode, and a porous carbon base material provided with gas flow grooves on both main surfaces thereof is provided. In a phosphoric acid fuel cell configured by laminating a plurality of separators made of a gas-impermeable carbon material, the porous carbon substrate and the separator are made of a sheet made of a fluororesin and a porous material. A phosphoric acid type fuel cell formed integrally with the carbon sheet through the carbon sheet. 3. The phosphoric acid fuel cell according to claim 2, wherein the sheet made of the fluororesin and the porous carbon sheet are pressure-formed at a temperature equal to or higher than the melting temperature of the fluororesin. A phosphoric acid type fuel cell. 4. The phosphoric acid fuel cell according to claim 1, wherein the porous carbon substrate and the separator are pressure-formed at a temperature equal to or higher than a melting temperature of the fluororesin. A phosphoric acid type fuel cell characterized by the above-mentioned. 5. A unit cell in which a flat matrix holding phosphoric acid is sandwiched between a fuel electrode and an air electrode, and a porous carbon substrate having gas flow grooves on both main surfaces thereof is disposed. In a phosphoric acid fuel cell configured by stacking a plurality of layers by interposing a separator made of a gas impermeable carbon material, a surface of the porous carbon substrate facing the separator or a surface of the separator A phosphoric acid type fuel cell which has been subjected to water repellency treatment. 6. The phosphoric acid fuel cell according to claim 5, wherein the water repellency treatment is performed by spraying or applying a fluororesin powder or a fluororesin dispersion, and then performing a heat treatment at a temperature equal to or higher than the melting point of the fluororesin. A phosphoric acid type fuel cell having a step of performing. 7. The phosphoric acid fuel cell according to claim 1, wherein the fluororesin is PTF.
E (polytetrafluoroethylene), PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer), or FEP (tetrafluoroethylene /
(Hexafluoropropylene copolymer).