JPS6322025B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in air-cooled fuel cells.

Matrix fuel cells that use acidic electrolytes operate at high temperatures of around 170 to 180 degrees, so they require cooling. Generally, a method is used in which air is used as a cooling medium and the air as a reaction gas supplied to the anode is also used as a cooling gas, but with this method, as the battery stack becomes larger, the flow rate of air supplied to the anode becomes excessive. This has the disadvantage that the electrolyte in the matrix evaporates, impairing battery performance. Therefore, a method has also been proposed in which a dedicated cooling path is formed that is isolated from the electrodes. This is to form an air passage at the joint surface of the two-part carbon gas separation plate, and gas mixing occurs through this joint surface, particularly the joint surface of the portion facing the fuel gas supply manifold. Conventionally, conductive rubber packing and adhesives have been used to prevent this, but they deteriorate due to long-term operation of batteries at high temperatures, impairing airtightness, and their low resistance causes voltage drops. There were some shortcomings.

The present invention is characterized in that an expanded graphite layer is used as a packing material on the joining surface of two plates having recesses that constitute cooling passages during joining. This is to prevent mixing between the two and to reduce internal resistance.

The expanded graphite referred to here is obtained by expanding the interlayers of graphite crystal structure, and an example of its preparation is shown below. That is, graphite is a hexagonal hexagonal plate-like flat crystal, as shown in FIG. 1, and has a layered structure formed by a series of six carbon rings. This graphite is wet-oxidized using a mixed acid of concentrated sulfuric acid and concentrated nitric acid, and a strong oxidizing agent such as potassium chlorate or potassium dichromate, and then rapidly heated at a high temperature of 900°C or more. The space between the layers expands 50 to 1000 times in the C-axis direction.

The expanded graphite obtained in this way constitutes porous particles that are thermochemically stable, highly conductive, and highly lubricating, and has extremely good moldability and can be processed without the need for any binders. The conductivity after pressure molding shows a value close to the value inherent to graphite.

Embodiments of the present invention will be described below with reference to the drawings. In a fuel cell, unit cells each consisting of negative and positive gas electrodes 1 and 2 and an electrolyte matrix 3 are stacked with a carbon gas separation plate 4 interposed therebetween. Each gas separation plate 4 has fuel gas supply grooves 5 such as hydrogen gas and air supply grooves 6 arranged in intersecting directions on its upper and lower surfaces, respectively, and on the back surfaces of the negative and positive electrodes 1 and 2, respectively. Hydrogen gas and air are supplied.

In such a battery stack, a cooling plate 7 is provided in place of the separation plate 4 every few cells. This cooling plate has two plates 8, 8 joined together to form a cooling passage 9 on the joint surface, but the upper and lower surfaces of the cooling plate contain hydrogen gas and air as in the case of the gas separation plate. Each supply groove 5', 6' is arranged and also functions as a gas separation plate. On the joint surface of the two plates 8, 8,
As shown in FIGS. 3 and 4, the expanded graphite is inserted in the form of a sheet, and the expanded graphite layer 10 is compressed by the tightening force of the battery stack to maintain airtightness and conductivity between the joint surfaces. .

The layer 10 may be sandwiched over the entire joint surface as shown in FIG. 3, but it may also be inserted only in the joint portion corresponding to the hydrogen gas supply surface of the battery stack, as shown in FIG.

Hydrogen gas is sent to the back of the cathode from an introduction manifold (not shown) through the supply grooves 5 and 5' of each separation plate 4 and cooling plate 7, and the reacted gas is discharged from an output manifold (not shown). . On the other hand, the air is separated from the introduction manifold (not shown) into a reaction gas flowing to the back side of the anode through each supply groove 6 and a cooling gas flowing into the cooling passage 9 of the cooling plate 7, and passes through the battery stack.
These reaction gas and cooling gas (temperature increased to approximately 180° C.) are discharged together through a discharge manifold (not shown).

When both gases are supplied in this manner, hydrogen gas may enter the air passage 9 from the joint portion of the cooling plate 7 on both sides of the battery stack in the hydrogen gas flow direction, or
Due to the opposite case, there will be no mixing of both gases.

As described above, the present invention uses an expanded graphite layer as a packing material for the joint surface when two cooling plates that also serve as gas separation plates are joined to form a cooling passage on the joint surface. The layer is an extremely good packing material due to the conductivity, high airtightness, and elasticity of expanded graphite, which prevents mixing of both gases and reduces contact resistance, demonstrating excellent characteristics as an air-cooled fuel cell.

[Brief explanation of the drawing]

Fig. 1 is a graphite crystal structure diagram for explaining the expanded graphite referred to in the present invention, Fig. 2 is a partially cutaway perspective view of a battery stack showing the inside, and Figs. 3 and 4 are both from this book. FIG. 5 is a perspective view of a cooling plate according to the invention, and FIG. 5 is a perspective view of a battery stack according to the invention. 1... Cathode, 2... Anode, 3... Electrolyte matrix, 4... Gas separation plate, 5, 5'... Fuel gas supply groove, 6, 6'... Air supply groove, 7... Cooling plate ( two plates), 9...cooling passage, 10...expanded graphite layer.

Claims (1)

[Claims] 1. A cooling plate for a fuel cell, characterized in that expanded graphite is used as a packing material on the joint surface of two plates each having a recess that forms a cooling air passage when joined.