JPH08162134A - Phosphoric acid type fuel cell - Google Patents

Abstract

PURPOSE: To provide a long-lived and highly reliable phosphoric acid type fuel cell in which phosphoric acid in the cell can be immediately moved from the vicinity of a gas outlet port to the vicinity of a gas inlet port within a unit cell plane by changing at least either one of gas passages for fuel and oxidant. CONSTITUTION: In this phosphoric acid type fuel cell, a matrix layer for holding a phosphoric acid which is an electrolyte is interposed between gas diffusion electrodes, and a plurality of unit cells constituted so as to pass a fuel and an oxidant are laminated on the gas diffusion electrodes. A cooling plate is inserted and set every several cells, and gas manifolds 4 for supplying and discharging the fuel and the oxidant to and from the gas diffusion electrodes, respectively, are arranged on the side surfaces of the battery body. The space between the gas manifold 4 and the battery body is sealed. The following means are further added to this constitution: at least one of gas passages for fuel and oxidant gas is set so as to return and carry it from the center part of each unit cell to both the end part.

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 having a long life and high reliability.

[0002]

2. Description of the Related Art As is well known, there is a fuel cell as a device for directly obtaining electric energy from hydrogen and oxygen in fuels such as coal, oil and natural gas. In this fuel cell, a pair of porous electrodes are arranged with a matrix holding an electrolyte sandwiched between them, a fuel gas is circulated and brought into contact with the back surface of one electrode, and an oxidizer such as air is attached to the back surface of the other electrode. Gas is circulated and brought into contact with each other, and electric energy is taken out from between the electrodes by utilizing an electrochemical reaction occurring at this time. Examples of the electrolyte include molten carbonate, alkaline solution, acidic solution, solid polymer, and solid oxide.
Phosphoric acid fuel cells using phosphoric acid have been particularly developed for practical use.

FIG. 8 is a partial sectional view showing an example of the structure of a conventional phosphoric acid fuel cell body. In the figure, reference numeral 1 denotes a laminated cell, which is formed by laminating a plurality of unit cells each having a matrix holding a pair of gas diffusion electrodes having an air passage and a hydrogen passage. In the unit cell, the air flow passage and the hydrogen flow passage are orthogonal to each other. Moreover, since it is necessary to heat to the operating temperature at the time of start-up and to remove and cool the excess heat at the time of operation to maintain a constant temperature near 200 ° C., the cooling plate 7 as a temperature control body is inserted and installed every few cells. Has become. The laminated cell 1 is sandwiched between the upper and lower sides of a current collector plate 2, and the upper and lower sides of the current collector plate 2 are further sandwiched by a tightening plate 3, and the laminated cell 1 is clamped with a constant load to reduce contact resistance between laminated members. In addition, it has a gas sealability. Electric energy is taken out from the current collector plate 2.

Further, in order to supply and exhaust the oxidant and hydrogen to and from the battery body, a gas manifold 4 and a fluororubber molding packing 5 are arranged on the side surface of the battery body, and a space between the battery body and the molding packing 5 is provided. The sealant 6 made of fluororesin is fixed to the unit cell and is fixed to each unit cell so that the oxidant and the fuel are supplied and exhausted collectively. Phosphoric acid, which is the electrolyte, contains a matrix, an electrode substrate,
It is retained in the electrolyte storage layer or the cell periphery and edges. Therefore, phosphoric acid also has a function as a wet seal.

In the phosphoric acid fuel cell as described above, in each unit cell, the hydrogen supplied to the fuel electrode undergoes a reaction of H ₂ → 2H ⁺ + 2e ⁻ due to the catalytic action of the electrode.
This hydrogen ion H ⁺ moves in the phosphoric acid of the matrix and reaches the air electrode. Further, the electron e ⁻ flows from the fuel electrode through the external circuit, works through the electric power load, and reaches the air electrode. Oxygen O ₂ flowing in the air electrode due to the catalytic action of the air electrode
And the hydrogen ion H ⁺ and the electron e ⁻ are 4H ⁺ + O ₂ +4
Water is produced by the reaction e ⁻ → 2H ₂ O. This reaction gives electric energy to an external electric load, but if fuel and an oxidant are supplied, ideally, it is possible to permanently generate electric power.

[0006]

However, the phosphoric acid fuel cell as described above has the following problems to be solved. That is, phosphoric acid in the unit cell gradually scatters as the reaction gas is discharged during operation. As a result, when the phosphoric acid in the unit cell is reduced to an amount that cannot maintain the sealing function, the reaction gas cross-leaks, the battery performance deteriorates, and the operation becomes impossible.
Therefore, the stable usage period of the battery takes into consideration the scattering amount of phosphoric acid in the unit cell. The storage amount of phosphoric acid in the unit cell is determined by using the amount of scattered phosphoric acid as an excess amount.

However, when the battery that had been operated for a long time was disassembled and the distribution of phosphoric acid in the cell plane was measured,
The distribution of phosphoric acid amount in the unit cell plane as shown in (3) was obtained. That is, the distribution of phosphoric acid in the cell was smallest on the gas inlet side and large on the gas outlet side. By the way, the following movements of phosphoric acid are expected in the cell plane. That is, in the portion where the phosphoric acid is reduced, the phosphoric acid moves from the surroundings due to the capillary force of the porous body that constitutes the electrode plate, and finally becomes evenly distributed in the cell plane.

However, the fact that phosphoric acid is non-uniform in the cell plane is due to the following phenomenon. That is, the rate of phosphoric acid was extremely high in the vicinity of the gas inlet, and the supply rate of phosphoric acid to the portion where the phosphoric acid decreased was not in time for the disappearance rate of phosphoric acid, resulting in an uneven distribution. Here, the greater the amount of phosphoric acid disappears near the gas inlet, the more phosphoric acid becomes vapor at the gas inlet where the phosphoric acid vapor pressure in the gas is the lowest. As the concentration of P increases, the evaporation amount of phosphoric acid in that portion decreases. Therefore, the partial pressure of phosphoric acid vapor in the gas flowing through the gas flow path gradually approaches saturation as the flow distance increases. This is shown in FIG.

Therefore, even if the amount of phosphoric acid in the unit cell is such that the sealing function can still be maintained as a whole, the amount of phosphoric acid locally decreases near the gas inlet in the plane of the cell. . Therefore, a local gas leak occurred and the battery life became shorter than expected.

The present invention has been made to solve the above problems, and a first object thereof is to allow phosphoric acid in a cell to flow from the vicinity of the gas outlet to the vicinity of the gas inlet in the unit cell plane.
It is to provide a phosphoric acid fuel cell that is immediately moved.

A second object is to provide a phosphoric acid fuel cell which can return and distribute the reaction gas in the cell. A third object is to provide a phosphoric acid fuel cell in which the distribution of phosphoric acid in the plane of the unit cell is reduced near the gas inlet and the distribution is uniform again. The fourth purpose is
An object of the present invention is to provide a phosphoric acid fuel cell capable of detecting that the amount of phosphoric acid at the gas inlet in the plane of the unit cell has decreased below the stable use limit.

[0012]

In order to achieve the above-mentioned object, the first aspect of the present invention is that a matrix layer holding phosphoric acid as an electrolyte is interposed between gas diffusion electrodes, and the gas diffusion electrodes are provided in the gas diffusion electrodes. A plurality of unit cells configured to flow fuel and oxidizer are stacked, and a cooling plate is inserted every few cells.
A phosphoric acid-type fuel that is installed and has a gas manifold that supplies and discharges fuel and an oxidant to and from the gas diffusion electrode on the side surface of the cell body, and that seals between the gas manifold and the cell body. In the battery, at least one gas of the fuel and the oxidant is configured so that a flow path of the gas returns from the central portion of each unit cell to both end portions and flows.

[0013]

According to claim 1 of the present invention, phosphoric acid disappears in the vicinity of the gas inlet in the plane of the unit cell, but the gas is generated by the capillary force of the porous body forming the electrode plate from the phosphoric acid storage portion near the gas outlet. Since it is immediately moved and supplied to the vicinity of the inlet, it is possible to provide a phosphoric acid fuel cell having a long life and high reliability.

[0014]

EXAMPLES Examples of the phosphoric acid fuel cell of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic view of an example of this embodiment. As shown in the figure, the reaction gas enters from the gas supply port of the gas manifold 4, is supplied to the central portion of the cell, is guided to one gas manifold 4 provided on the opposite side, and is further returned to both ends of the cell. Is discharged.
The other manifold 4 is provided with a partition plate 8 for separating the supply gas and the exhaust gas. Here, the partition plate 8 is provided with a phosphoric acid resistant and heat resistant coating 9. The partition plate 8 may be installed by welding and fixing to the inner wall surface of the gas manifold, or may be fixed by a phosphoric acid-resistant and heat-resistant sealing material 10 and an adhesive 11. Further, the cell laminated surface is brought into contact with and sealed by the fluororubber packing 5 and the fluororesin seal 6 in the same manner as that provided around the gas manifold.

With this structure, phosphoric acid disappears first near the gas inlet in the cell plane, but since the vicinity of the gas outlet where much phosphoric acid remains is near the phosphoric acid disappearing portion, the electrode plate Due to the capillary force of the porous body constituting the, the phosphoric acid is easily moved from the vicinity of the gas outlet to the vicinity of the gas inlet. Therefore, local depletion of phosphoric acid in the vicinity of the gas inlet in the cell plane can be prevented, so that a highly reliable fuel cell can be provided.

FIG. 2 is a diagram showing the operation modes of the phosphoric acid fuel cell of this embodiment. In this example, the phosphoric acid at the gas inlet portion first disappears, but before the phosphoric acid disappears and cross leak occurs and battery operation becomes impossible, the battery is temporarily stopped and kept at, for example, 50 ° C. for a certain period of time. store. The timing to stop is predicted empirically or experimentally and is predetermined. During storage, phosphoric acid gradually moves from the periphery in the cell plane to the portion where phosphoric acid is reduced by capillary force. Since the temperature is low during storage, evaporation of phosphoric acid hardly occurs. Therefore, by storing the phosphoric acid for a certain period of time, the phosphoric acid in the cell plane becomes evenly distributed.

FIG. 3 shows immediately before the stop of the phosphoric acid fuel cell,
The change of the phosphoric acid amount distribution after storage is shown. After storage, the distribution of phosphoric acid returns to its original value, and the system is restarted. The battery life can be further extended by repeating such an operation method.

Further, as shown in FIG. 5, a sensor 13 for detecting the electric potential is provided near the gas inlet in the cell plane. 6A and 6B are diagrams for explaining in detail the installation portion of the sensor. FIG. 6A is a side view and FIG. 6B is a sectional view.

According to FIG. 6, a platinum fine wire 14 is selected for the potential detecting sensor 13, two platinum wires 14 are made parallel to each other, and each platinum wire 14 is made of a phosphoric acid resistant and heat resistant insulator such as polytetrafluoroethylene. Insert it into the tube 15. Although the tip portion of the tube 15 is closed, the side surface of the tube, which is several mm from the tip, is partially cut within a range of several mm so that the platinum wire is exposed.

The sensor 13 thus obtained is inserted from the gas groove of the fuel electrode on the side surface of the cell stack. The exposed portion of the platinum wire at the tip of the sensor is filled with the matrix material 16 impregnated with phosphoric acid, and is electrically connected to phosphoric acid in the anode electrode substrate. The matrix material (SiC + H ₃ PO ₄ ) 16 has an average particle size of 1 to 5 μm.
m SiC is selected and contains phosphoric acid. Although the battery potential can be measured by this sensor 13, when the phosphoric acid in the matrix is locally depleted at the portion where the sensor 13 is embedded, the measured potential changes abruptly. The timing to stop is detected. As described above, according to this embodiment, it is possible to prevent local depletion of phosphoric acid in the vicinity of the gas inlet in the cell plane, so that a highly reliable fuel cell can be provided.

FIG. 7 is a schematic view of another embodiment of the present invention. The gas partition plate 8 of the present embodiment is provided in a larger number as compared with the embodiment of FIG. 1, and the distance at which the gas flow is reversed is narrower. That is, by providing a plurality of partition plates 8, the disappearing portion of phosphoric acid in the vicinity of the gas inlet becomes narrower, so that the movement / supply of phosphoric acid from the surroundings by capillary force is easier than in the embodiment of FIG. Will be done.

[0022]

As described above, according to the present invention,
Even if phosphoric acid disappears at the gas inlet in the plane of the cell, it is immediately moved and supplied from the surroundings, so it is possible to prevent early deterioration of cell performance due to the occurrence of local cross leaks, and highly reliable phosphoric acid fuel. A battery can be provided. Also, by regularly stopping, storing, and starting, the distribution of phosphoric acid reduced on the gas inlet side during storage can be made uniform, so that the battery life can be extended and highly reliable phosphorous can be obtained. An acid fuel cell can be provided.

[Brief description of drawings]

FIG. 1 is a plan view of an embodiment of the present invention.

FIG. 2 is a diagram showing an operation mode of the phosphoric acid fuel cell of FIG.

FIG. 3 is a diagram showing changes in the phosphoric acid amount distribution before and after the phosphoric acid fuel cell of FIG. 1 is stopped.

FIG. 4 is a diagram showing a relationship between a gas flow distance of a phosphoric acid fuel cell and phosphoric acid vapor pressure.

FIG. 5 is a plan view of a phosphoric acid fuel cell showing an installation portion of a sensor of the present invention.

6A and 6B are detailed views of a portion where a sensor is installed, in which FIG. 6A is a side view and FIG. 6B is a sectional view.

FIG. 7 is a plan view of another embodiment of the present invention.

FIG. 8 is a partial cross-sectional view of a conventional phosphoric acid fuel cell.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Laminated cell, 2 ... Current collecting plate, 3 ... Tightening plate, 4 ... Gas manifold, 5 ... Fluorine rubber type packing, 6 ... Fluorine resin type seal, 7 ... Cooling plate, 8 ... Partition plate, 9 ... Phosphorus acid resistance , Heat resistant coating, 10 ... sealing material, 11 ... adhesive, 13 ... potential detection sensor, 14 ... platinum wire, 15 ...
Tube, 16 ... Matrix material

Claims (1)

[Claims] 1. A plurality of unit cells each having a structure in which a matrix layer holding phosphoric acid as an electrolyte is interposed between gas diffusion electrodes, and a fuel and an oxidant are circulated in the gas diffusion electrodes. A cooling plate is inserted and installed for each battery, a gas manifold for supplying and discharging fuel and oxidant to and from the gas diffusion electrode is arranged on the side surface of the battery body, and a seal is provided between the gas manifold and the battery body. In the phosphoric acid fuel cell, the flow path of the gas of at least one of the fuel and the oxidant is configured so as to flow from the central portion of each unit cell to both ends thereof to flow. Type fuel cell.