JPH0696777A - Solid polymer electrolytic fuel cell - Google Patents

Abstract

PURPOSE:To eliminate gas block by water and improve characteristic by satisfying a determined relational expression between the water holding force head of a gas passing groove provided on a separator and a head loss at passing a reaction gas in the gas passing groove. CONSTITUTION:A solid polymer electrolytic fuel cell is provided with a solid polymer electrolytic film, electrodes and a separator. In the solid polymer electrolytic film, the electrodes are closely adhered to and arranged on its two main surfaces, the separator supports the solid polymer electrolytic film having the electrodes arranged thereon, and the solid polymer electrolytic film contains water so that protons are diffused in the film. The separator has a gas passing groove for supplying a reaction gas of fuel gas or oxidizing agent gas to the electrodes, and when the water holding force head of the gas passing groove is S, and the head loss at passing the reaction gas in the gas passing groove is L, the relational expression of L>S is satisfied. When the passing groove has a depth 0.8mm and a width of 2.0mm, for example, and the relational expression of L>S is satisfied, a stable operating state can be provided, and water can be satisfactorily drained. Thus, gas block by water is eliminated, and characteristic can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid polymer electrolyte fuel cell separator, and more particularly to a gas flow channel of the separator.

[0002]

2. Description of the Related Art FIG. 3 is an exploded side view showing a conventional solid polymer electrolyte fuel cell unit cell. The anode 2 and the cathode 3 of the unit cell 6 are laminated in close contact with each other on the two main surfaces of the solid polymer electrolyte membrane 1, and on both outer sides thereof, a reaction gas is supplied from the outside into the electrode and an excess gas is supplied. A gas impermeable separator 5 provided with a gas flow groove 4 for discharging to the outside is laminated. The unit cell is usually 10 mm or less in thickness, and the larger the area, the lower the cost. Therefore, the unit cell is made as large as possible (about 1 m ² ).

The solid polymer electrolyte membrane 1 uses a polystyrene cation exchange membrane having a sulfonic acid group as a cation conductive membrane, or a perfluorocarbon sulfonic acid membrane (trade name, manufactured by DuPont, USA). Nafion membrane)
Are known. The solid polymer electrolyte membrane has a proton (hydrogen ion) exchange group in the molecule. When this membrane is saturated with water, it exhibits a specific resistance of 20 Ω · cm or less at room temperature and functions as a proton conductive electrolyte. The saturated water content of the membrane changes reversibly with temperature.

Each of the anode 2 and the cathode 3 is composed of a catalyst layer containing a catalyst active material, and an electrode base material which supports the catalyst layer and supplies a reaction gas and further has a function as a current collector. When the catalyst layer is brought into close contact with the solid polymer electrolyte membrane, and hydrogen, which is a fuel, is supplied to the anode side and oxygen or air is supplied to the cathode side as an oxidant, at the interface between the catalyst layer of each electrode and the solid polymer electrolyte membrane. The following electrochemical reactions occur.

Anode H ₂ → 2H ⁺ ＋ 2e ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ (1) Cathode 1/2 O ₂ ＋ 2H ⁺ ＋ 2e → H ₂ O ・ ・ ・ ・ ・ ・ ・ ・ ・ ・(2) That is, hydrogen and oxygen react with each other to produce water. The catalyst layer is generally formed of a platinum catalyst in the form of fine particles and a fluororesin having water repellency to water.

The separator prevents the permeation of gas and supplies the reaction gas evenly in the plane of the unit cell through the groove to collect the generated current to the outside. Since the voltage generated by the unit cell is 1 V or less, in practice, in order to increase the voltage, a large number of the unit cells are stacked in series and used as a stack. The operating temperature of the solid polymer electrolyte fuel cell is usually about 50 to 100 ° C. in order to reduce the specific resistance of the membrane and maintain high power generation efficiency.

[0007] In a fuel cell, a heat quantity generally equivalent to the generated power is generated as heat, and this heat causes a temperature distribution in the stack in which a large number of unit cells are stacked. Therefore, in the stack, a cooling plate is incorporated so that the temperature of the stack becomes uniform in the plane direction of the unit cells and the stacking direction of the stack. Here, water, air or the like is generally used as the cooling medium.

FIG. 4 is a side view showing a stack of a conventional solid polymer electrolyte fuel cell. Cooling plates 7 are alternately stacked for each plurality of unit cells 6, and a current collector plate 8, an insulating plate 9 and a tightening plate 10 are stacked on both ends of the cooling plates 7, and tightened with tightening bolts 11 to form a stack 12. . Power is supplied to the stack from the outside by supplying fuel and an oxidant to the unit cell, and a cooling medium is supplied to the cooling plate to remove excess heat for cooling. The flow direction of the gas inside the unit cell in the stack thus stacked is such that the supply side is on the upper side and the discharge side is on the lower side with respect to the gravity direction.

As described above, in the solid polymer electrolyte fuel cell, when the solid polymer electrolyte membrane as the electrolyte holding layer is saturated with water, the specific resistance of the membrane becomes small and the membrane functions as a proton conductive electrolyte. Therefore, in order to keep the power generation efficiency of the solid polymer electrolyte fuel cell high, it is necessary to keep the water content of the membrane saturated. For this reason, conventionally, in order to prevent the membrane from drying and maintain power generation efficiency, the reaction gas is supplied with water to increase the humidity of the reaction gas and then supplied to the fuel cell. Methods have been implemented to reduce water evaporation and prevent the membrane from drying out.

As described above, water is generated as a reaction product in the power generation of the fuel cell, and the generated water is discharged out of the fuel cell together with the surplus reaction gas. Therefore, the amount of water contained in the gas can be distributed in the flow direction of the reaction gas in the unit cell. That is, the reaction gas contains a large amount of water in an amount corresponding to the reaction product water on the downstream side (outlet side) of the gas flow with respect to the upstream side (supply side) of the gas flow in the unit cell. Therefore, when the supplied gas is humidified to a saturated state and supplied to the solid polymer electrolyte fuel cell, the gas on the outlet side contains supersaturated water vapor. As a result, water corresponding to supersaturation on the gas outlet side becomes liquid water.
The liquid water closes the gas flow channel and hinders the gas flow. If the gas flow is obstructed, the gas supply to the electrode becomes insufficient and the reaction efficiency decreases. Therefore, it is extremely important in operation that the excess liquid water is promptly discharged to the outside.

[0011]

However, in the conventional gas flow channel, water is condensed due to the reaction product water containing supersaturated water vapor in the reaction gas at the downstream portion of the gas flow. Therefore, there is a problem that liquid water stays in the gas flow groove to block the gas flow groove, and as a result, the free movement of the reaction gas is hindered and the output of the battery becomes unstable.

If the amount of water in the supply gas is reduced in order to prevent the output from becoming unstable, the film will dry and the internal resistance of the battery will increase, leading to a decrease in output. It is also possible to increase the groove width and groove depth so that the water in the gas flow groove will flow down naturally, but if the groove width is increased, the electrical contact between the separator and the electrode deteriorates, and the current flow efficiency increases. There is a problem that it becomes difficult to collect current and remove heat generated in the electrodes, and increasing the groove depth increases the thickness of the separator.

The present invention has been made in view of the above points, and an object thereof is to provide a solid polymer electrolyte fuel cell having excellent characteristics without gas blockage due to water by optimizing the gas passage groove of the separator. Especially.

[0014]

According to the present invention, the above-mentioned object has a solid polymer electrolyte membrane, an electrode, and a separator, and the solid polymer electrolyte membrane has electrodes adhered to its two main surfaces. And the separator sandwiches the solid polymer electrolyte membrane on which the electrode is arranged, the solid polymer electrolyte membrane contains water and protons diffuse in the membrane, and the separator is a fuel gas or an oxidant gas on the electrode. S has a gas flow groove for supplying the reaction gas of S, and S is the holding power of water in the gas flow groove, and L is the head loss when the reaction gas flows through the gas flow groove. This is achieved by satisfying the relational expression (I).

[0015]

## EQU00002 ## Head loss L> water holding power head S ... (I)

[0016]

When the relational expression (I) is satisfied, water does not accumulate in the gas flow groove. In relational expression (I), the water retention head S determines the size and material of the gas flow groove. Head loss L
Determines the gas flow groove size, gas flow velocity, and gas properties.

[0017]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a dimensional diagram showing a separator of a solid polymer electrolyte fuel cell according to an embodiment of the present invention. The present separator can be easily manufactured by filling a pressing die with a mixed powder of graphite carbon particle powder and phenol resin powder and heating and pressing at 180 ° C. for 5 minutes. In this embodiment, the groove depth is 0.8 mm and the separator thickness is 1.
The groove width is 8 mm, the width is 2.0 mm, and the length is 100 mm. The thickness of the separator can be made thinner than before.

The water retention head generated in the gas flow groove is about 15 mm in water column. When air is flown through the gas flow groove at a flow rate of 0.5 m / s, a head loss of about 20 mm is generated in the water column. FIG. 2 is a diagram showing the characteristics of the solid polymer electrolyte fuel cell according to the embodiment of the present invention. It can be seen that a stable operation state is obtained and water is discharged well.

Specific examples of the gas flow grooves and the gas properties are shown in Table 1.

[0020]

[Table 1] As shown in Table 1, when the relational expression (I) is satisfied, no water is retained and good results are obtained.

[0021]

According to the present invention, a solid polymer electrolyte membrane, an electrode, and a separator are provided, and the solid polymer electrolyte membrane has two main surfaces on which electrodes are closely attached, and the separator is the electrode. Sandwiching the solid polymer electrolyte membrane in which the solid polymer electrolyte membrane is placed, the solid polymer electrolyte membrane contains water and protons diffuse in the membrane, and the separator is a gas passage that supplies a reaction gas of fuel gas or oxidant gas to the electrode. S and L satisfy the relational expression (I), where S is the water retention head of the gas flow groove and S is the head loss when the reaction gas flows through the gas flow groove. Therefore, it is possible to obtain a solid polymer electrolyte fuel cell having excellent stability without water remaining in the gas flow channels.

[0022]

## EQU00003 ## Head loss L> water retention head S ... (I)

[Brief description of drawings]

FIG. 1 is a dimensional diagram showing a separator of a solid polymer electrolyte fuel cell according to an embodiment of the present invention.

FIG. 2 is a diagram showing characteristics of a solid polymer electrolyte fuel cell according to an embodiment of the present invention.

FIG. 3 is an exploded side view showing a unit cell of a conventional solid polymer electrolyte fuel cell.

FIG. 4 is a side view showing a stack of a conventional solid polymer electrolyte fuel cell.

[Explanation of symbols]

 1 Solid Polymer Electrolyte Membrane 2 Anode 3 Cathode 4 Gas Flow Groove 5 Separator 6 Single Cell 7 Cooling Plate 8 Current Collector 9 Insulating Plate 10 Tightening Plate 11 Tightening Bolt 12 Stack

Claims (4)

[Claims] 1. A solid polymer electrolyte membrane, an electrode, and a separator, wherein the solid polymer electrolyte membrane has two major surfaces on which the electrodes are in close contact, and the separator is a solid on which the electrodes are arranged. The polymer electrolyte membrane is sandwiched, the solid polymer electrolyte membrane contains water and the protons diffuse in the membrane, and the separator has a gas flow groove for supplying the reaction gas of fuel gas or oxidant gas to the electrode. , S is the water retention head of the gas flow groove, and L is the head loss when the reaction gas flows through the gas flow groove, and S and L satisfy the relational expression (I). Solid polymer electrolyte fuel cell. ## EQU00001 ## Head loss L> water holding power head S ... (I) 2. The solid polymer electrolyte fuel cell according to claim 1, wherein the electrode comprises an electrode base material and an electrode catalyst layer laminated on the electrode base material. 3. The solid polyelectrolyte fuel cell according to claim 1, wherein the separator is formed by mixing graphite carbon powder and phenol resin powder and hot pressing them. 4. The fuel cell according to claim 1, wherein when the relational expression (I) is satisfied, the gas flow groove has a groove width of 2.0.
mm, the groove depth is 0.8 mm, the groove length is 100 mm, and the gas flow rate is 0.5 m / s. A solid polymer electrolyte fuel cell.