Separator for solid polymer electrolyte fuel cell and...

Details Separator for solid polymer electrolyte fuel cell and... Separator for solid polymer electrolyte fuel cell and...

2002-03-26

2004-10-19

Weiner, Laura (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

With pressure equalizing means for liquid immersion operation

C429S006000, C429S247000, C427S122000

Reexamination Certificate

active

06805989

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a separator for a solid polymer electrolyte fuel cell using a solid polyelectrolyte and a process for producing the same. This type of separator is sometimes called a “bipolar plate” in the art. For convenience, the term “separator” will be used throughout the entire specification.
2. Prior Art
Conventional fuel cells using a solid polyelectrolyte have a construction, for example, as shown in
FIG. 1A
, i.e., a construction comprising; a solid polyelectrolyte film
50
; and two electrode films (an anode-side electrode film
51
and a cathode-side electrode film
52
) sandwiching the solid polyelectrolyte film
50
therebetween. In each of the electrode films, a catalyst layer, such as a platinum layer, is provided on and integrally with the solid polyelectrolyte film
50
side. Numeral
57
designates a sealing material for sealing the solid polyelectrolyte film
50
and the periphery of each of the anode-side electrode film
51
and the cathode-side electrode film
52
disposed respectively on both sides of the solid polyelectrolyte film
50
. Numeral
54
designates an anode-side separator which is abutted against the anode-side electrode film
51
. Grooves
53
for anode gas, such as hydrogen gas, are provided between the anode-side separator
54
and the anode-side electrode film
51
. Numeral
56
designates a cathode-side separator which is abutted against the cathode-side electrode film
52
. Grooves
55
for cathode gas, such as oxygen gas, are provided between the cathode-side separator
56
and the cathode-side electrode film
52
. Both the separators
54
,
56
should be formed of a material which is impermeable to gas and is electrically conductive. In general, the separators are fabricated of a carbon plate.
The mechanism of a reaction in the above fuel battery cell
58
will be explained. In the anode-side electrode film
51
, hydrogen gas, which has been externally supplied through the grooves
53
for anode gas, is passed through a gas diffusion layer within the electrode film
51
, reaches near a reaction zone, and is absorbed into the catalyst to form active hydrogen atoms. As shown in the following formula, the hydrogen atoms are reacted with hydroxyl ions in the electrolyte to give water. In this case, two electrons are passed through the electrode film
51
and are transmitted to the other electrode side through an external circuit.
H
2+
2OH
−
→2H
2
O+2e
−
On the other hand, in the presence of the catalyst, the cathode-side electrode film
52
receives two electrons from the electrode film
51
side, and oxygen molecules, which have been externally supplied through the grooves
55
for cathode gas, are reacted with water from the electrolyte to produce hydroxyl ions.
½O
2
+H
2
O→2OH
−
The hydroxyl ions produced in the cathode-side electrode film
52
move through the electrolyte and reach the anode-side electrode film
51
, and an electrical circuit is formed as a whole.
Therefore, the reaction in the whole fuel cell is as follows.
H
2
+½O
2
→2H
2
O
That is, in the reaction, hydrogen in the fuel gas is reacted with oxygen in the air to produce water.
In actual fuel cells, a fuel cell stack
60
having a laminate structure as shown in
FIG. 2
is adopted. The fuel cell stack
60
has a structure comprising: a laminate of a large number of fuel battery cells in a plate form as shown in
FIG. 1A
; and pipings for supplying fuel gas (hydrogen gas and oxygen gas) to the laminate. Regarding the pipings, in
FIG. 2
, numeral
61
designates an anode gas introduction pipe, numeral
62
an anode gas discharge pipe, numeral
63
a cathode gas introduction pipe, and numeral
64
a cathode gas discharge pipe.
In the fuel cell stack
60
, the separators used generally have a structure suitable for lamination, as shown in
FIG. 1
, wherein an anode-side separator
54
and a cathode-side separator
56
have been integrally provided respectively on the front and back sides. A specific structure thereof is as shown in
FIGS. 3 and 4
.
FIG. 4
is a cross-sectional view taken on line A—A of
FIG. 3
,
FIG. 3A
a left side view of
FIG. 4
, and
FIG. 3B
a right side view of FIG.
4
.
Regarding this separator, in
FIG. 1
, the grooves
53
for anode gas in the anode-side separator
54
and the grooves
55
for cathode gas in the cathode-side separator
56
are grooves which each extend in a direction perpendicular to the paper surface and are parallel to one another. In
FIGS. 3 and 4
, the grooves
53
for anode gas are grooves extending in the vertical direction of the paper surface of
FIG. 3A
, while the grooves
55
for cathode gas are grooves extending in the left and right direction of the paper surface of FIG.
3
B. The grooves
53
for anode gas cross the grooves
55
for cathode gas in the front-and-back-side relationship.
Regarding this separator, as shown in
FIGS. 3 and 4
, in the anode-side separator
54
, both ends of the grooves
53
for anode gas are respectively in communication with an introduction passage hole
65
connected to the anode gas introduction pipe
61
and a discharge passage hole
66
connected to the anode gas discharge pipe
62
. On the other hand, in the cathode-side separator
56
, both ends of the grooves
55
for cathode gas are respectively in communication with an introduction passage hole
67
connected to the cathode gas introduction pipe
63
and a discharge passage hole
68
connected to the cathode discharge pipe
64
.
The separators
54
,
56
having the above structure are generally prepared by forming grooves in a carbon plate. Therefore, for strength reasons, there is a restriction on an increase in opening area of the grooves
53
for anode gas and the grooves
55
for cathode gas. This poses a problem that the pressure loss is large in each gas passage and the supply efficiency of the fuel gas is lowered by a level corresponding to the pressure loss.
Further, in general, the carbon plate has excellent electrical conductivity and contact resistance. The carbon plate, however, is mechanically brittle. This poses a problem that, in forming the grooves, the width of peaks provided between grooves should be made wide to some extent for avoiding a lack of mechanical strength.
Further, since the peak portions are used in the state of being strongly pushed against the electrode films, in this pushed portion, the fuel gas (hydrogen gas) cannot be supplied to the electrode film side. This lowers the supply efficiency of the fuel gas and thus disadvantageously deteriorates power generation efficiency by a level corresponding to the supply efficiency lowering level.
Furthermore, in this type of fuel cell, the use of pure oxygen as an oxidizing agent is not cost effective, and there is a demand for the use of air per se. Since, however, the concentration of oxygen in the air is as low as about 20%, when the discharge of the air is not successfully carried out, the oxygen concentration on the cathode-side electrode film
52
side is relatively lowered in relationship with the fuel gas (hydrogen gas), disadvantageously leading to deteriorated power generation efficiency.
Further, on the cathode-side electrode film
52
side, protons are reacted with oxygen to give water, and, consequently, there is a fear of this water clogging the gas passage.
When all the above facts are taken into consideration, the fuel battery cell should inevitably has a very complicate structure.
On the other hand, a proposal has been made on a technique wherein a material is used which has been produced by providing a metal, which can realize complicate working with high accuracy, as the material for the separator and covering the surface of the metal with a metal nitride as a protective layer (Japanese Patent Laid-Open No. 353531/2000 entitled “SEPARATOR FOR SOLID POLYMER ELECTROLYTE FUEL CELL AND PROCESS FOR PRODUCING THE SAME”).
This technique is advantageous in that, when the metal is used as a separator, a thin sep

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