JPH1116589A - Phoshoric acid type fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively recover and recycle a phosphoric acid splashed by power generation in a cell, and allow stable operation for a long time without replenishing a phosphoric acid. SOLUTION: This cell is constituted by layering successively via a separator 6 a cell formed by arranging a porous carbon plate 4A provided with an anode 2 and a flowing groove for fuel gas on one main surface of a matrix 1 holding a phosphoric acid and a porous carbon plate 4B provided with a cathode 3 and a flowing groove for air on the other main surface. In this case, grooves extending to flowing directions of gases are provided in smooth faces opposite to electrodes of the porous carbon plates 4A, 4B, and a porous filler having smaller pores than that of the porous carbon plates 4A, 4B is filled into the grooves.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phosphoric acid fuel cell using phosphoric acid as an electrolyte and supplying fuel and an oxidizing agent to obtain electric energy by an electrochemical reaction. Related to the structure.

[0002]

2. Description of the Related Art FIG. 4 is an exploded perspective view showing the basic structure of a conventional phosphoric acid type fuel cell.
Generally, a phosphoric acid as an electrolyte is added to a flat matrix 1
And the anode 2
(Fuel electrode) and cathode 3 (oxidant electrode)
Further, on both outer surfaces thereof, a joined body of the porous carbon plate 4 facing the electrode portion and the porous carbon plate 5 facing the seal portion is arranged to form a cell, and the cells are sequentially laminated via the separator 6. It is customary. In this configuration, the fuel gas is supplied to the gas flow grooves provided on the porous carbon plate 4 facing the anode 2, and the oxidant gas ( By supplying (air), an electrochemical reaction is caused by a catalytic action on the electrode to take out electricity to the outside. The porous carbon plate 4 is not only provided with a gas flow groove for supplying gas, but also provided with a phosphate reservoir function of storing supplementary phosphoric acid in its pores. General.

[0003] Phosphoric acid used as an electrolyte has a very low vapor pressure, and there is no danger that phosphoric acid retained in the cell will be depleted in a short time.
A service life of up to 60,000 hours is required, and in such a long operation, the disappearance of phosphoric acid in the cell becomes a serious problem. That is, if the amount of phosphoric acid in the matrix 1 is insufficient, the fuel gas and the oxidizing gas supplied to the anode 2 and the cathode 3 are mixed with each other through the matrix 1, so that the output of the fuel cell becomes extremely high. Risk of explosion in some cases.

For this reason, various methods have been adopted in a phosphoric acid type fuel cell so that phosphoric acid does not run short. The simplest method is to replenish phosphoric acid from the outside. A typical example is to stop the operation of the fuel cell by taking advantage of a periodic inspection work performed about once a year, It is a method of replenishing phosphoric acid. Also, as another method, Ear
l H. BROWN and Carlton D. WHITT; INDUSTRIAL AN
D ENGINEERING CHEMISTRY, Vol.44, No.3, P.615 (195
As described in 2), utilizing the fact that the vapor pressure of phosphoric acid is temperature-dependent and the vapor pressure increases exponentially as the temperature rises, the outlet of the fuel gas or oxidant gas is cooled. There is a method of condensing the phosphoric acid contained in the gas and collecting it in the cell by lowering the temperature of the gas.

[0005]

Since the output voltage of a single unit cell of a phosphoric acid fuel cell is at most about 0.7 V, about 100 to 200 cells are usually stacked for practical use. It is configured to be electrically connected in series to output a voltage of a practical scale. In addition, because it generates heat energy equivalent to electric energy with power generation,
In order to secure a stable output, it is necessary to cool the stacked battery to keep the temperature constant. For this reason, the heat generated by inserting a cooling plate every few cells, for example, every 5 to 10 cells is taken out and used as a heat source for hot water supply and cooling / heating.

If a cooling plate is inserted every several cells as described above, the laminated battery is maintained at a predetermined temperature and a stable output can be obtained. , And the temperature of the cell close to the cooling plate is lower than the temperature of the cell located in the central portion between the cooling plates. On the other hand, as described above, the vapor pressure of phosphoric acid increases exponentially with the rise in temperature. Becomes

When externally supplying lost phosphoric acid, it is necessary to accurately determine the amount of lost phosphoric acid.
As described above, in the stacked battery, the temperature of the cell differs depending on the position where the cells are stacked, and the amount of phosphoric acid disappears accordingly. Therefore, it is difficult to accurately grasp the amount of phosphoric acid.
In particular, in order to achieve a life of 40,000 to 60,000 hours, phosphoric acid needs to be replenished several times, and it is practically impossible to know the required replenishing amount when the replenishment is performed several times. . For this reason, in the method of replenishing phosphoric acid from the outside, the replenishment amount of phosphoric acid is insufficient, the retention amount is insufficient, and the output of the fuel cell is extremely reduced. Becomes excessive, and the supply of the fuel gas or the oxidizing gas to the reaction portion is hindered, and a situation occurs in which the battery performance is significantly reduced.

Therefore, as a method of avoiding this disadvantage,
Recently, a method of recovering and recycling phosphoric acid in a cell has been attempted. As a general method of recovering phosphoric acid in the cell, the temperature near the outlet of the fuel gas or oxidizing gas is cooled to lower the temperature, and the phosphoric acid taken out of the battery together with these gases is condensed in the cell. There is a method of collecting. That is, in a stacked battery having a large number of cells stacked as shown in FIG. 4, the fuel gas flows through one of the gas flow grooves provided in the porous carbon plate 4 facing the anode of each cell. The oxidant gas flows from one side surface to the opposite side surface, and the oxidizing gas flows through the gas flow groove provided in the porous carbon plate 4 facing the cathode from one side surface to the opposite side surface. Flow perpendicular to
In this configuration, when the vicinity of the outlet of the fuel gas or the oxidizing gas is cooled, the phosphoric acid which evaporates due to the electrochemical reaction and stays in the gas reaches the dew point and is condensed. And returned to the matrix 1 for reuse.

However, in the method of cooling the vicinity of the gas outlet to condense and reuse the phosphoric acid,
The condensed phosphoric acid originally evaporates and scatters on the upstream side.To eliminate the shortage of phosphoric acid on the upstream side, which has been reduced due to evaporation and scatter, phosphoric acid taken in near the outlet of the porous carbon plate It is necessary to move the acid upstream. Since the porous carbon plate has a contact angle with phosphoric acid of 90 degrees or more, the phosphoric acid is buried in the porous carbon plate sequentially from a portion having a small pore diameter. In a porous carbon plate with a uniform pore size distribution, the maximum diameter of pores buried with phosphoric acid is smaller on the upstream side where phosphoric acid is scattered than on the downstream side where phosphoric acid is condensed. It is considered that the difference between the maximum diameters of the pores buried with the phosphoric acid becomes the driving force, and the phosphoric acid gradually moves from the downstream side to the upstream side.

As described above, a method of condensing and recycling the evaporated and scattered phosphoric acid by cooling the vicinity of the outlet of the gas has been attempted, but the condensed phosphoric acid on the downstream side in the porous carbon plate has been tried. Since the speed of movement to the more upstream side is not always sufficient, the amount of phosphoric acid retained on the upstream side becomes insufficient due to the insufficient amount of movement, and further, the amount of phosphoric acid in the condensing part on the downstream side becomes excessive, There is a disadvantage that the battery characteristics are significantly reduced.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art, and to effectively recover and reuse phosphoric acid which evaporates and scatters during power generation, and replenishes phosphoric acid from the outside. It is an object of the present invention to provide a phosphoric acid fuel cell which can operate stably for a long period of time.

[0012]

In order to achieve the above object, according to the present invention, an anode and a fuel gas are supplied to one main surface of a flat matrix holding phosphoric acid as an electrolyte. And a porous carbon plate having a gas flow groove for supplying an oxidant gas to the cathode on the other main surface. In a phosphoric acid type fuel cell configured by stacking a plurality of fuel cell single cells formed by arranging via a separator, at least one of an anode side porous carbon plate and a cathode side porous carbon plate. On the opposite surface of the portion of one of the porous carbon plates facing the electrode, a groove provided substantially in parallel with the gas flow direction of the gas flow groove provided on the porous carbon plate, and This Inside the groove, a porous filler having pores smaller in diameter than the pores facing the electrode of the porous carbon plate, for example, a mixture of carbon black and polytetrafluoroethylene, or silicon carbide. A porous filler composed of a mixture with polytetrafluoroethylene is to be filled.

As described above, since the contact angle of the porous carbon plate with phosphoric acid is 90 degrees or more, the phosphoric acid cooled and condensed and taken in by the porous carbon plate has pores in the porous carbon plate. Are gradually filled in from the smaller diameter part.
Therefore, as described above, a groove is arranged substantially in parallel with the gas flow direction of the gas flow groove provided in the porous carbon plate, and a portion of the groove facing the electrode of the porous carbon plate is provided inside the groove. If a porous filler having pores smaller in diameter than the pores is filled, the phosphoric acid cooled and recovered near the gas outlet will be thinner than the porous filler in the groove having the pores. Since it easily moves to the upstream side through the hole, the shortage of phosphoric acid on the upstream side is avoided.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION

<Embodiment 1> FIG. 1 is an exploded perspective view showing a basic structure of a cell of an embodiment of a phosphoric acid fuel cell according to the present invention. In the figure, components having the same functions as the components of the conventional configuration example shown in FIG. 4 are denoted by the same reference numerals, and redundant description will be omitted. The configuration of this embodiment is different from the conventional example in the porous carbon plate 4A arranged opposite to the anode 2 and the porous carbon plate 4B arranged opposite to the cathode 3, which is used in the conventional example. The porous carbon plate 4 used in this embodiment is different from the porous carbon plate 4A and 4B used in this embodiment, whereas the porous carbon plate 4 is made of a porous carbon material having a uniform pore diameter distribution. A groove parallel to the gas flow direction is provided on the smooth surface opposite to the surface of FIG.
It is formed by filling a porous filler 7 having pores of 7 μm. Therefore, in the cell of this configuration, the phosphoric acid in the gas is condensed by cooling the vicinity of the gas outlet, and the collected phosphoric acid passes through the small pores of the porous filler at the gas inlet side. , It can be operated stably without shortage of phosphoric acid.

The above-mentioned porous filler is made of carbon black (trade name Vulcan XC-72 manufactured by Cabot Corporation).
To 100 g, 50 g of polytetrafluoroethylene (trade name: Teflon 30J manufactured by Du Pont-Mitsui Fluorochemicals Co., Ltd.) was added, and after mixing well, an aggregating agent was added to cause aggregation, and the obtained aggregate was separated by filtration. The obtained cake-like material is kneaded, formed into a shape conforming to the groove size, and fired at 280 ° C. Also, a porous filler having the same effect can be obtained by using the same silicon carbide as that used for the matrix instead of the carbon black.

Embodiment 2 FIG. 3 is an exploded perspective view showing a basic structure of a cell of another embodiment of the phosphoric acid fuel cell of the present invention. The feature of this configuration is that the porous carbon plate 4C arranged opposite to the anode 2 and the porous carbon plate 4D arranged opposite to the cathode 3 go from the inlet side of the flowing gas to the outlet side. It is characterized by being formed from a porous carbon material whose average pore diameter increases in accordance with the following. That is, in FIG. 2, the porous carbon plate 4A to which the fuel gas is supplied from the front left to the rear right is a porous carbon plate whose average pore diameter increases from the front left to the rear right in parallel with the flow direction of the fuel gas. The porous carbon plate 4B made of carbon material and supplied with air as an oxidant gas from the right front to the left rear has an average fineness from the right front to the left rear in parallel with the flow of air. It is formed from a porous carbon material having an increased pore size.

FIG. 3 shows A of the porous carbon plate 4D of FIG.
2 is a characteristic diagram showing the distribution of the average pore diameter on the A-plane in comparison with the conventional example. The gas inlet shown on the horizontal axis is at the right front end of the porous carbon plate 4D in FIG. It corresponds to the left rear end of 4D. The characteristics shown in the figure show the distribution of the average pore diameter of the conventional example, and the characteristics show the distribution of the average pore diameter of the porous carbon plate 4D of the present embodiment. The configuration is such that the average pore diameter increases from the inlet side to the outlet side of the supplied air, and the phosphoric acid condensed and recovered by cooling the outlet side of the air has the average pore diameter. It will easily move to a smaller entrance side.

The porous carbon plate 4D having the average pore diameter distribution as described above can be prepared, for example, by preparing several types of pore-forming agents having different particle diameters when producing the porous carbon plate, By arranging the particles gradually smaller in particle diameter toward the gas outlet side, it is possible to obtain a porous carbon plate having a substantially desired average pore diameter distribution.

Further, in the present embodiment, both the porous carbon plate 4A disposed opposite to the anode 2 and the porous carbon plate 4B disposed opposite to the cathode 3 are connected to the inlet of the gas flowing therethrough. From the side to the exit side, the average pore diameter is to be formed from a porous carbon material that increases, but even if only one of them is formed from the porous carbon material as described above, Needless to say, by cooling the outlet side, the phosphoric acid scattered in the gas is condensed and collected, easily moved to the inlet side having a small average pore diameter, and reused.

[0020]

As described above, according to the present invention, an anode and a gas flow groove for supplying a fuel gas to the anode are provided on one main surface of the flat matrix holding phosphoric acid as an electrolyte. And a porous carbon plate having
On the other main surface, a plurality of fuel cell single cells formed by arranging a cathode and a porous carbon plate having a gas flow groove for supplying an oxidizing gas to the cathode are provided via a separator. In the phosphoric acid fuel cell configured by lamination, at least one of the porous carbon plate on the anode side and the porous carbon plate on the cathode side, opposite to the portion facing the electrode of the porous carbon plate, The porous carbon plate has a gas flow groove provided in the gas flow groove substantially parallel to the gas flow direction, and the inside of the groove has a narrow portion facing the electrode of the porous carbon plate. A porous filler having pores smaller than the pores, for example, a mixture of carbon black and polytetrafluoroethylene, or a mixture of silicon carbide and polytetrafluoroethylene Even when the porous filler is filled, similarly, phosphoric acid is effectively recovered and reused, so that a phosphate-type fuel cell that can be operated stably for a long time without externally supplying phosphoric acid It is suitable as.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view showing a basic configuration of a cell of an embodiment of a phosphoric acid fuel cell of the present invention.

FIG. 2 is an exploded perspective view showing a basic configuration of a cell of another embodiment of the phosphoric acid fuel cell of the present invention.

FIG. 3 is a characteristic diagram showing the distribution of the average pore diameter on the AA plane of the porous carbon plate of the cell of the embodiment shown in FIG. 2 in comparison with the conventional example.

FIG. 4 is an exploded perspective view showing a basic configuration of a cell of a conventional phosphoric acid fuel cell.

[Explanation of symbols]

 Reference Signs List 1 matrix 2 anode 3 cathode 4A porous carbon plate (anode facing portion) 4B porous carbon plate (cathode facing portion) 4C porous carbon plate (anode facing portion) 4D porous carbon plate (cathode facing portion) 5 porous carbon Plate (seal part) 6 Separator 7 Porous filler

Claims (3)

[Claims] An anode and a porous carbon plate having a gas flow groove for supplying a fuel gas to the anode are provided on one main surface of a flat matrix holding phosphoric acid as an electrolyte, On the other main surface, a plurality of fuel cell single cells formed by arranging a cathode and a porous carbon plate having a gas flow groove for supplying an oxidizing gas to the cathode are provided via a separator. In the phosphoric acid type fuel cell configured by stacking, at least one of the porous carbon plate on the anode side and the porous carbon plate on the cathode side is opposed to a portion opposed to an electrode of the porous carbon plate. The surface is provided with a groove arranged substantially in parallel with the gas flow direction of the gas flow groove provided in the porous carbon plate, and inside the groove, facing the electrode of the porous carbon plate. Part of A phosphoric acid fuel cell characterized by being filled with a porous filler having pores smaller in diameter than the pores. 2. The phosphoric acid type according to claim 1, wherein the porous filler comprises a mixture of carbon black and polytetrafluoroethylene, or a mixture of silicon carbide and polytetrafluoroethylene. Fuel cell. 3. At least one of the porous carbon plate on the anode side and the porous carbon plate on the cathode side has an electrolyte reservoir function of preliminarily storing an electrolyte held in a matrix. The phosphoric acid fuel cell according to claim 1, wherein the phosphoric acid fuel cell is configured.