Polymer electrolyte fuel cell and a polymer electrolyte fuel cell system which supply anode-side channels with a gas-liquid mixture

A polymer electrolyte fuel cell system with a polymer electrolyte fuel cell is made up of a cell main body, a mixture generator for generating a gas-liquid mixture by mixing fuel gas which has been supplied from a fuel gas supply with water, and a means for supplying the gas-liquid mixture to the anode-side channels. The gas-liquid mixture allows the solid-polymer film to be moistened without humidifying fuel gas and oxidant gas with a humidifier, and the cell main body to be cooled down without providing a cooling channel therein.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention is related to a polymer electrolyte fuel cell and a 
polymer electrolyte fuel cell system. 
2. Description of the Related Art 
A polymer electrolyte fuel cell is made up of a unit cell composed of an 
anode layer, a cathode layer, a solid-polymer film disposed therebetween, 
a member having channels facing the anode layer, and a member which has 
channels facing the cathode layer. 
The polymer electrolyte fuel cell is supplied with fuel gas, for example 
hydrogen-rich fuel gas, through the anode-side channels, and with oxidizer 
gas, such as air, through the cathode-side channels, thereby generating 
electricity through an electro-chemical reaction. 
Most polymer electrolyte fuel cells in current use are composed of a 
plurality of separators and a plurality of unit cells that are stacked 
alternately in order to obtain a higher voltage. Here, each of the 
separators has fuel gas channels and oxidizer gas channels. 
A problem faced by such polymer electrolyte fuel cells is that the heat 
generated during operation must be partially removed. Since heat radiation 
is not enough to maintain a predetermined temperature between about 
50.degree. C. and 100.degree. C., most polymer electrolyte fuel cells have 
to be provided with cooling channels for each group of several unit cells. 
As another problem, while a polymer electrolyte fuel cell is in operation, 
its solid-polymer film must be kept moist to maintain its ion 
conductivity. The water to be generated from the reaction between the fuel 
gas and the oxidizer gas contributes to the moistening of the 
solid-polymer film to some extent. However, since it is not sufficient, 
additional water must be supplied from outside the cell main body. 
In view of these problems, most polymer electrolyte fuel cells are provided 
with a humidifier outside the cell main body to humidify the fuel gas and 
the oxidant gas, and further provided with cooling channels within the 
cell main body. 
In contrast, Japanese Patent Publication No. 1-140562 (U.S. Ser. No. 
076,970) discloses a polymer electrolyte fuel cell which moistens the 
solid-polymer film by supplying the fuel gas with water spray using an 
aspirator, and cools the cell main body by having the supplied water 
evaporate from the cathode layers. 
However, the cooling performance of the water evaporation from the cathode 
layers is not sufficient for polymer electrolyte fuel cells that are 
large-sized or have a high output density. 
SUMMARY OF THE INVENTION 
In view of these problems, the object of the present invention is to 
provide a polymer electrolyte fuel cell and a polymer electrolyte fuel 
cell system that moisten the solid-polymer film without providing a 
humidifier which humidifies the fuel gas or the oxidizer gas, and that 
cool down the cell main body without providing cooling channels. 
The object of the present invention is achieved by a polymer electrolyte 
fuel cell which comprises the following components: 
a cell main body including a unit cell composed of an anode layer, a 
cathode layer, and a solid-polymer film disposed between the anode layer 
and the cathode layer, and a member provided with a plurality of channels 
facing the anode layer; 
a mixture supply unit that supplies the plurality of channels with a 
gas-liquid mixture which essentially consists of fuel gas and water; and 
an oxidant gas supply unit that supplies the cathode layer with oxidant 
gas. 
The object of the present invention is also achieved by a polymer 
electrolyte fuel cell system which comprises the following units: 
a cell main body including a unit cell composed of an anode layer, a 
cathode layer, and a solid-polymer film disposed between the anode layer 
and the cathode layer, and a member provided with a plurality of channels 
facing the anode layer; 
a mixture generator that generates a gas-liquid mixture by mixing water 
with fuel gas supplied from a fuel gas supply source; 
a mixture supply unit that supplies the plurality of channels with the 
gas-liquid mixture which has been generated by the mixture generator; and 
an oxidant gas supply unit that supplies the cathode layer with oxidant 
gas. 
The polymer electrolyte fuel cell and the polymer electrolyte fuel cell 
system of the above-explained construction have no need of providing a 
humidifier and internal cooling channels. This is because the channels are 
supplied with the gas-liquid mixture, so that the dispersion performance 
of the fuel gas onto the anode layers can be improved, and the water can 
function to cool down the cell main body. 
By dispersing the fuel gas in the gas-liquid mixture into the water, the 
dispersion performance of the fuel gas onto the anode layers can be 
further improved, and the water can function to cool down the cell main 
body efficiently. 
By forming the cell main body into the alternate stack of the plurality of 
unit cells and the plurality of plates, the cell main body can be cooled 
down without a cooling plate. 
By bubbling the fuel gas into the water that has been supplied to a 
manifold, the gas-liquid mixture can be generated within the manifold, and 
since the gas-liquid mixture is directly distributed among the channels, 
each channel can be supplied with a well-balanced gas-liquid mixture. 
By recovering a gas-liquid mixture which has been used in the cell main 
body for reproduction, the utilization of fuel gas can be improved because 
the fuel gas supplier has only to supply the exact amount of gas consumed 
by the cell reaction. 
By separating a recovered gas-liquid mixture into fuel gas and water, the 
water can be used to generate a new gas-liquid mixture. 
By using hydrogen as the fuel gas, the system can perform a stable 
operation for a long time period because the composition of the fuel gas 
never changes. 
By recycling water which has been obtained in the gas-liquid separator, 
only the exact amount of water lost mainly in evaporation through the 
solid-polymer film need be supplied. 
By generating a gas-liquid mixture by bubbling fuel gas into water reserved 
in a water tank, the dispersion performance of the fuel gas and the 
cooling effects can be both improved because the gas-liquid mixture 
includes fuel gas which is finely dispersed into the water. 
By positioning the exit of each channel as high as or higher than the 
entrance opening, and by providing the water tank lower than the entrance 
opening of each channel, the gas-liquid mixture which has been generated 
by the mixture generator can be supplied to each channel due to the 
pressure and buoyancy of the gas phase. Consequently, there is no need to 
provide a pump which supplies the gas-liquid mixture. In addition, by 
recovering the gas-liquid mixture from the exit of each channel and 
separating it into fuel gas and water, the fuel gas can be re-used. 
Consequently, the fuel gas which has been used in the cell main body is 
circulated to generate electricity, so that the utilization of fuel gas 
can be improved because the fuel gas supplier has only to supply the exact 
amount of gas which has been consumed. 
By connecting the gas-liquid separation tank and the water tank, water can 
be circulated for recycle.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Embodiment 1 
(The entire construction of the polymer electrolyte fuel cell system 1 of 
the present embodiment) 
FIG. 1 is a perspective view of the entire construction of the polymer 
electrolyte fuel cell system 1 of the present embodiment, and FIG. 2 is a 
schematic diagram thereof. 
As shown in these drawings, the polymer electrolyte fuel cell system 1 is 
composed of a cell main body 2 that generates electricity with air and a 
gas-liquid mixture, a fuel gas tank 3 as a fuel gas supplier, a gas-liquid 
mixture unit 4 attached to the cell main body 2 to generate a gas-liquid 
mixture from fuel gas and water, a gas-liquid separator 5 that recovers 
the gas-liquid mixture from the cell main body 2 and separates it into a 
fuel gas layer and a water layer, a fuel gas pump 6 that supplies the 
gas-liquid mixture unit 4 with fuel gas, a circulating water pump 7 that 
circulates water within the system 1, a heat exchanger 8 that cools down 
the circulating water, a water supply tank 9 to supply water, and an air 
supply fan 10 that supplies the cell main body 2 with air. 
In the present embodiment, a hydrogen cylinder is used as the fuel gas tank 
3. 
FIG. 3 is an exploded perspective view of the construction of the cell main 
body 2 and the gas-liquid mixture unit 4. 
The cell main body 2 is composed of a plurality of unit cells 20 and a 
plurality of separators 30 stacked alternately, and a pair of end boards 
40 and 41 shown in FIG. 4, which sandwich the alternately stacked unit 
cells 20 and the separators 30 therebetween. In the present embodiment, 
there are six unit cells 20 and seven separators 30. 
Each of the unit cells 20 includes an anode layer 22 shown in FIG. 2, a 
cathode layer 23, and a solid polymer film 21 disposed therebetween. 
Each separator 30 has an anode-side channel set 31 on the side facing the 
anode layer 22, and a cathode-side channel set 32 on the other side facing 
the cathode layer 23 shown in FIG. 2. 
In FIG. 3, the anode layers 22 and the cathode-side channel sets 32 are not 
shown because they are behind the cathode layers 23 and the anode-side 
channel set 31, respectively. 
An unillustrated water repellant current collector is provided between each 
anode layer 22 and each anode-side channel set 31, and also between each 
cathode layer 23 and each cathode-side channel set 32. 
The solid-polymer films 21 are 0.13 mm thick rectangular films made from 
Nafion 115 (Du Pont, U.S.A.), and each solid-polymer film 21 has four 
holes 24-27 at the corners to form internal manifolds. 
The anode layers 22 and the cathode layers 23, both of which are made from 
carbon-supported platinum and have a predetermined thickness, are pressed 
onto the center of the solid-polymer films 21 with a hot press. The amount 
of platinum is regulated to be 0.7 mg/cm.sup.2. 
Each of the separators 30, which are approximately the same size as the 
solid polymer films 21, has four holes 34-37 at the corners to form the 
internal manifolds in the same manner as the solid polymer films 21. 
The anode-side channel sets 31 are formed in a vertical direction, whereas 
the cathode-side channel sets 32 are formed in a horizontal direction. 
The holes 34 and the holes 35 are diagonally opposite to each other on the 
separators 30. To connect each hole 34, each hole 35, and each anode-side 
channel set 31, a manifold groove 38 and a manifold groove 39 are 
respectively provided above and below the anode-side channel set 31, which 
runs in the vertical direction. 
In the same manner, the holes 36 and the holes 37 are diagonally opposite 
to each other on the separators 30. To connect each hole 36, each hole 37, 
and each cathode-side channel set 32, a manifold groove and a manifold 
groove are provided along either side of the cathode-side channel set 32, 
which runs in the horizontal direction. 
The end board 40 also has four holes 44-47 shown in FIG. 1 so that four 
cylindrical manifolds 14-17 whose openings are on the end board 40 side 
are formed in the direction in which the unit cells 20 and the separators 
30 are stacked. The upper manifolds 14 and 16 includes the holes 24, 34, 
and 44, and the holes 26, 36, and 46, respectively. The lower manifolds 15 
and 17 have the holes 35 and 45, and the holes 27, 37, and 47, 
respectively. 
In the present embodiment, these manifolds 14, 15, 16, and 17 are used to 
supply a gas-liquid mixture, to expel the gas-liquid mixture, to supply 
air, and to expel the air, respectively. 
The gas-liquid mixture unit 4, which is positioned inside the upper 
manifold 14, is composed of a cylindrical bubbler 51 which bubbles fuel 
gas into water in the upper manifold 14, a cylindrical holder 52 which 
holds the bubbler 51 inside the upper manifold 14, and a cylindrical 
stopper 53 to seal the opening of the upper manifold 14. 
FIG. 4 is a sectional view of the upper manifold 14 and the gas-liquid 
mixture unit 4. As shown in FIGS. 3 and 4, the bubbler 51 has 
approximately the same length as the upper manifold 14 and is made from a 
sintered metal with a 5 .mu.m mesh diameter. The fuel gas enters the 
gas-liquid mixture unit 4 via its gas opening 54, which pierces the 
cylindrical stopper 53, and is evenly dispersed into the water in the 
cylindrical holder 52. 
The cylindrical holder 52, which fits into the upper manifold 14, has a 
slit 52a along the side which faces the manifold groove 38. 
The cylindrical stopper 53 is provided with a water opening 55 through 
which water enters the cylindrical holder 52. The cylindrical stopper 53 
seals the opening of the upper manifold 14 when it is fitted into the hole 
44 of the end board 40. 
The following will be explained with reference to FIGS. 1 and 2 again. 
The gas-liquid separator 5 is composed of a sealed container 60, a 
recovered gas-liquid mixture opening 61 on the side, a fuel gas opening 63 
and a fuel gas exit 64 on the top, and a water opening 62 and a water exit 
65 at the bottom. 
The recovered gas-liquid mixture opening 61 is connected with the lower 
manifold 15 via a pipe 71. The fuel gas exit 64 is connected with the gas 
opening 54 of the gas-liquid mixture unit 4 via a pipe 72, which runs 
through the fuel gas pump 6. The water opening 65 is connected with the 
water opening 55 of the cylindrical stopper 53 via a pipe 73, which runs 
through the circulating water pump 7 and the heat exchanger 8. 
The fuel gas opening 63 is connected with the fuel gas tank 3 via a pipe 74 
with a pressure regulating valve 3a, which regulates the supply of fuel 
gas to the sealed container 60 under a predetermined pressure. 
(The operation of the polymer electrolyte fuel cell system 1) 
In the gas-liquid mixture unit 4, the fuel gas supplied through the gas 
opening 54 is dispersed into the water supplied through the water opening 
55 into the cylindrical holder 52, and as a result, a gas-liquid mixture 
is generated. 
The generated gas-liquid mixture goes through each manifold groove 38, is 
distributed among the channels of each anode-side channel set 31 while 
generating electricity, united at each manifold groove 39, and expelled 
from the lower manifold 15. 
While the gas-liquid mixture goes through the anode-side channel sets 31, 
it moistens the solid polymer films 21, and at the same time cools down 
the cell main body 2, thus functioning as cooling water. 
Since the generated gas-liquid mixture is directly distributed among the 
channels of each anode-side channel set 31 without going through a pipe, 
each anode-side channel set 31 is supplied with a well-balanced gas-liquid 
mixture. The amount of the gas-liquid mixture to be supplied to each 
anode-side channel set 31, and the ratio between water and fuel gas in the 
gas-liquid mixture is regulated by changing the amount of water to be 
supplied with the circulating water pump 7 and the amount of gas to be 
supplied with the fuel gas pump 6. This regulation enables the function of 
the gas-liquid mixture as a cooling medium and the security of sufficient 
fuel gas to the anode layers 22. 
As mentioned before, the water repellant current collector provided between 
each anode layer 22 and each anode-side channel set 31 prevents each anode 
layer 22 from sinking into the gas-liquid mixture during a long operation. 
As a result, fuel gas is successfully supplied to the reaction site of 
each anode layer 22. 
The gas-liquid mixture expelled from the lower manifold 15 travels through 
the pipe 71 to the gas-liquid separator 5 via the recovered mixture 
opening 61. In the gas-liquid separator 5, the gas-liquid mixture is 
separated into a fuel gas layer (top layer) and a water layer (bottom 
layer). The fuel gas supplied from the fuel gas tank 3 is mixed with the 
fuel gas which has entered the gas-liquid separator 5 through the fuel gas 
opening 63, recovered as a fuel gas layer, and expelled from the fuel gas 
exit 64. The fuel gas thus expelled is sent to the gas-liquid mixture unit 
4 through the gas opening 54 with the fuel gas pump 6. 
On the other hand, the water separated from the fuel gas by the gas-liquid 
separator 5 is cooled down to a predetermined temperature while it travels 
through the heat exchanger 8, and enters the gas-liquid mixture unit 4 
through the water opening 55 with the circulating water pump 7. 
In the gas-liquid mixture unit 4, the fuel gas sent with the fuel gas pump 
6 is bubbled into the water sent with the circulating water pump 7, and as 
a result, a new gas-liquid mixture is generated. 
As explained hereinbefore, in the system 1, a new gas-liquid mixture is 
generated from the gas-liquid mixture recovered from the cell main body 2 
and the fuel gas sent from the fuel gas tank 3, and supplied to the cell 
main body 2. 
When the water level in the gas-liquid separator 5 is lowered, water is 
supplied from the water supply tank 9 through the water supply opening 62, 
so that the amount of the circulating water is maintained at a certain 
level even if some water is lost in evaporation while it travels through 
the unit cells 20 to the cathode-side channel sets 32. 
The air supplied by the air supply fan 10 to the upper manifold 16 travels 
through a manifold groove, is distributed among the channels of each 
cathode-side channel set 32, united at the manifold groove, and expelled 
from the lower manifold 17 outside the cell main body 2. 
(The effects of the polymer electrolyte fuel cell system 1) 
In the system 1, the solid-polymer films 21 are moistened while the 
gas-liquid mixture travels through the anode-side channel sets 31. 
Consequently, there is no need for providing a humidifier which humidifies 
the fuel gas or oxidant gas. 
In addition, the gas-liquid mixture which travels through the anode-side 
channel sets 31 cools down the cell main body 2 by functioning as cooling 
water. This cooling effect is greater than that is obtained from the 
evaporation of water from the cathode layers 23. 
Furthermore, the gas-liquid mixture to be generated by the gas-liquid 
mixture unit 4 includes water and fuel gas finely dispersed into the 
water. Consequently, the water cools the cell main body 2 as efficiently 
as ordinary cooling water, while the fuel gas is efficiently supplied to 
the anode layers 22. 
EMBODIMENT 2 
(The entire construction of the polymer electrolyte fuel cell system 101 of 
the present embodiment) 
FIG. 5 is a perspective view of the entire construction of the polymer 
electrolyte fuel cell system 101 of the present embodiment, and FIG. 6 is 
a schematic diagram thereof. In the present embodiment, the like 
components are labeled with like reference numerals with respect to the 
first embodiment, and the description of these components is not repeated. 
In common with the system 1 of the first embodiment, the polymer 
electrolyte fuel cell system 101 includes the cell main body 2, the fuel 
gas tank 3, the gas-liquid mixture unit 4, the fuel gas pump 6, the water 
supply tank 9, and the air supply fan 10. The system 101 further includes 
a separation tank 102 which recovers a gas-liquid mixture from the cell 
main body 2 and separates it into a fuel gas layer and a water layer, a 
buffer tank 103 which mixes the fuel gas obtained in the separation tank 
102 with the fuel gas from the fuel gas tank 3, and a cooling fan 104 
which cools down the water layer of the separation tank 102. 
In the system 101, the gas-liquid mixture unit 4 is positioned inside the 
lower manifold 15 of the cell main body 2, and a gas-liquid mixture is 
expelled from the upper manifold 14, whereas in the system 1 of the first 
embodiment, the gas-liquid mixture unit 4 is positioned inside the upper 
manifold 14, and a gas-liquid mixture is expelled from the lower manifold 
15. 
The separation tank 102 is disposed beside the end board 40, approximately 
as high as the cell main body 2. The separation tank 102 is composed of a 
sealed container 110 with a recovered mixture opening 111 on a side 
surface, a fuel gas exit 113 on a top surface, a supply water opening 112 
and a water exit 114 on other side surfaces. 
The cooling fan 104 sends air to the bottom of the separation tank 102, 
thereby cooling the water layer in the separation tank 102 down to a 
predetermined temperature. 
The recovered mixture opening 111 is connected with the upper manifold 14 
via a pipe 121. The fuel gas exit 113 is connected with the buffer tank 
103 via a pipe 122. The gas opening 54 of the gas-liquid mixture unit 4 is 
connected with the buffer tank 103 via a pipe 123, which goes through the 
fuel gas pump 6. 
The separation tank 102 and the lower manifold 15 are connected with each 
other as a result of the water exit 114 and the water opening 55 of the 
gas-liquid mixture unit 4 being connected with each other via a pipe 124. 
The fuel gas tank 3 and the buffer tank 103 are connected with each other 
via a pipe 125 with the pressure regulating valve 3a. The pressure 
regulating valve 3a regulates the amount of fuel gas to be supplied into 
the buffer tank 103 under a fixed pressure. 
When the water level of the separator tank 102 is lowered, water is 
supplied from the water supply tank 9 with a water supply pump 9a, so that 
the amount of circulating water is maintained at a certain level. 
(The operation of the polymer electrolyte fuel cell system 101) 
Since the water contained in the separation tank 102 is maintained at a 
certain level, there is always some water at the bottom of the separation 
tank 102. Also, the lower manifold 15, which is connected with the 
separation tank 102, is automatically supplied with water. 
In the gas-liquid mixture unit 4, the fuel gas to be supplied through the 
gas opening 54 is dispersed into the water in the lower manifold 15, and 
as a result, a gas-liquid mixture is generated. 
The gas-liquid mixture thus generated travels upward due to the pressure 
and buoyancy of the gas phase. To be more specific, the gas-liquid mixture 
travels through each manifold groove 39, is distributed among the channels 
of each anode-side channel set 31, goes up along the channels, is united 
at each manifold groove 38, and is expelled from the upper manifold 14. 
The gas-liquid mixture expelled from the upper manifold 14 enters the 
separation tank 102 via the pipe 121, and is separated into a fuel gas 
layer (top layer) and a water layer (bottom layer). The fuel gas layer 
enters the buffer tank 103 via the pipe 122. 
In the buffer tank 103, the fuel gas from the fuel gas tank 3 and the fuel 
gas from the pipe 122 are mixed. The mixed fuel gas is supplied to the 
gas-liquid mixture unit 4 via the gas opening 54 with the fuel gas pump 6. 
On the other hand, the water layer separated from the fuel gas layer in the 
separation tank 102 is cooled down to a predetermined temperature with the 
cooling fan 104, and automatically sent to the lower manifold 15 via the 
water opening 55 through the pipe 124. 
In the gas-liquid mixture unit 4, the fuel gas from the buffer tank 103 is 
dispersed into the water from the separation tank 102, and as a result, a 
new gas-liquid mixture is generated. 
As explained hereinbefore, in the system 101, a new gas-liquid mixture is 
generated from the gas-liquid mixture recovered from the cell main body 2 
and the fuel gas to be supplied from the fuel gas tank 3, and supplied to 
the cell main body 2. 
In the present embodiment, the anode-side channel sets 31 are disposed in 
the vertical direction; however, the exits may be disposed as high as or 
higher than the entrance openings because the gas-liquid mixture proceeds 
by the pressure and buoyancy of the gas phase. 
(The effects of the polymer electrolyte fuel cell system 101) 
In common with the system 1 of the first embodiment, the solid-polymer 
films 21 in the system 101 are moistened while the gas-liquid mixture 
travels through the anode-side channel sets 31, so that there is no need 
for providing a humidifier which humidifies fuel gas or oxidizer gas. 
In addition, the gas-liquid mixture which travels through the anode-side 
channel sets 31 cools down the cell main body 2 by functioning as cooling 
water. 
In the system 101, the gas-liquid mixture automatically travels through the 
anode-side channel sets 31 due to the pressure of the fuel gas to be 
supplied to the gas-liquid mixture unit 4 and the buoyancy of the 
gas-liquid mixture, so that the circulating water pump 7 of the first 
embodiment is dispensable. 
(Others) 
In the present invention, a gas-liquid mixture travels through the channels 
facing the anode layers 22, and the fuel gas contained in the gas-liquid 
mixture is supplied to the anode layers 22. The reason of water being 
supplied in the form of a mixture with fuel gas is that hydrogen as an 
active principle of the fuel gas has an excellent dispersion performance 
to allow water be supplied onto the anode layers 22, so that there is no 
harm on the cell performance. 
In contrast, the oxidant gas to be supplied onto the cathode layers 23 has 
poor dispersion performance, so that supplying it in the form of a mixture 
with water would decrease the cell performance. 
In the above embodiments, hydrogen is used as fuel gas, so that the 
composition of the fuel gas circulating within the system never changes 
during a long time operation, which leads to the achievement of a stable 
cell. 
In contrast, when a hydrogen-rich reformed gas is used as fuel gas, the 
components other than hydrogen are believed to accumulate in the 
circulating fuel gas during a long time operation. To avoid the 
accumulation, the circulating fuel gas should preferably be replaced by 
fresh gas from the fuel gas tank 3 in the case of a long period of 
operation. 
If hydrogen is used as the fuel gas, the system 1 or 101 can perform a 
stable operation for a long time period because the composition of the 
fuel gas never changes. 
Furthermore, in the cell main body 2 of the above embodiments, the 
gas-liquid mixture unit 4 is positioned in an internal manifold; however, 
it may be positioned in an external manifold. 
In the above embodiments, a gas-liquid mixture is generated by bubbling 
fuel gas into water which travels through a manifold with the bubbler 51 
made from a sintered metal. However, a spray nozzle or an aspirator may be 
used instead of the bubbler 51. Furthermore, a gas-liquid mixture 
generator composed of a water tank and a bubbler may be provided 
separately from the cell main body 2. 
The cell main body 2 of the above embodiments is composed of six unit cells 
and seven separators stacked alternately; however, the cell main body 2 
may be composed of a single unit cell. 
Although the present invention has been fully described by way of examples 
with reference to the accompanying drawings, it is to be noted that 
various changes and modifications will be apparent to those skilled in the 
art. Therefore, unless such changes and modifications depart from the 
scope of the present invention, they should be construed as being included 
therein.