Polymer electrolyte fuel cell

Details Polymer electrolyte fuel cell Polymer electrolyte fuel cell

2002-09-11

2004-08-03

Alejandro, Raymond (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

With pressure equalizing means for liquid immersion operation

C429S006000, C429S006000, C429S006000

Reexamination Certificate

active

06770396

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a polymer electrolyte fuel cell to be used for a portable power source, an electric vehicle, a cogeneration system, and so on.
It is a fundamental principle, on which a polymer electrolyte fuel cell is based, that a fuel gas supplied to the anode side of an electrolyte membrane-electrode assembly (MEA hereafter) electrochemically reacts with an oxidant gas supplied to the cathode side of the MEA through the electrolyte membrane so as to produce water, whereby an electric energy and a thermal energy are simultaneously generated, the electric energy being used depending on uses and needs.
A representative structure of such fuel cell is shown in
FIG. 1
, wherein a lower half thereof is a front view and an upper half is mainly a cross-sectional view.
Referring to
FIG. 1
, MEA
10
comprises a polymer electrolyte membrane
11
and two electrodes, i.e. cathode
12
and anode
13
, sandwiching the membrane
11
. At outer peripheries of the cathode and the anode, gaskets
14
and
15
are respectively arranged so as to prevent the supplied fuel gas and oxidant gas from leaking to outside and from mixing with each other.
A basic unit of a fuel cell, namely unit cell, is such a structure that an MEA is sandwiched by an anode side separator plate having a gas flow channel to supply and exhaust the fuel gas to and from the anode, and by a cathode side separator plate having a gas flow channel to supply and exhaust the oxidant gas to and from the cathode.
A stacked fuel cell is one made by stacking several tens to several hundreds of such unit cells provided with a cooling unit for every 2 to 3 unit cells, which is called cell stack. In
FIG. 1
, four kinds of separator plates are used, and only four unit cells are schematically shown for simplifying the drawing. A cathode side separator plate
22
placed at the leftmost end of the cell stack
16
has an oxidant gas flow channel
32
, while an anode side separator plate
21
placed at the rightmost end of the cell stack
16
has a fuel gas flow channel
31
. Each of separator plates
20
placed among MEAs has an oxidant gas flow channel
34
on a surface thereof facing the cathode, and also has a fuel gas flow channel
33
on a surface thereof facing the anode, so that each separator plate
20
functions both as a cathode side separator plate and an anode side separator plate. A cooling unit comprises a composite separator plate made by combining an anode side separator plate
23
and a cathode side separator plate
24
. The cathode side separator plate
24
has an oxidant gas flow channel
36
on a surface thereof facing the cathode, and also has a cooling water flow channel
38
on an opposite surface thereof. The anode side separator plate
23
has a fuel gas flow channel
35
on a surface thereof facing the anode, and also has a cooling water flow channel
37
on an opposite surface thereof. By joining the separator plates
23
and
24
in a manner that the cooling water flow channels thereof face each other, one composite cooling water flow channel is formed by the flow channels
37
and
38
.
On each of the both ends of the cell stack
16
, a current collecting plate
6
, an insulating plate and an end plate are stacked in this order. They are tightened by bolts
70
penetrating therethrough and nuts
71
, and are supplied with a tightening pressure by use of washers
73
.
In this stacked fuel cell, the end plates, the insulating plates, the current collecting plates and the MEAs have common inlet side manifold holes and common outlet side manifold holes. The reactive gases and the cooling water are supplied to the respective separator plates through the inlet side manifold holes, and are exhausted through the outlet side manifold holes. With reference to
FIG. 1
, an inlet side manifold hole
18
a
for oxidant gas in the cell stack
16
is shown.
FIG. 1
also shows a manifold hole
1
a
provided at one end plate
4
, and an inlet pipe
2
a
having an end thereof welded to an edge of the manifold hole
1
a
. The oxidant gas introduced from the pipe
2
a
flows through the manifold holes provided at the insulating plate, the current collecting plate and the inlet side manifold hole
18
a
of the cell stack
16
, and flows into the oxidant gas flow channels of the respective cathode side separator plates for reaction, wherein an excessive oxidant gas and products produced by the reaction are exhausted out of an oxidant gas outlet pipe
2
b
provided at the other end plate through outlet side manifold holes. Similarly, the fuel gas is introduced into an introduction pipe
3
a
welded to one end plate
4
, and flows through fuel gas inlet side manifold holes, fuel gas flow channels of the separators and outlet side manifold holes, and is then exhausted out of a fuel gas outlet pipe
3
b.
Each current collecting plate
6
is a metal plate for collecting the electric power from the serially stacked cell stack and for connecting the same to the outside. Usually, the current collecting plate is made of stainless steel, cupper, brass or the like, and is often provided with a coating such as plated gold for the purpose of decreasing the contact resistance and increasing the corrosion resistance. Each insulating plate
5
is a resin plate for electrically insulating the end plate
4
and the current collecting plate
6
. Each of the end plates
4
is a tightening plate for evenly applying a tightening pressure to the cell stack, and is usually made of a machined stainless steel, wherein pipes for introducing and exhausting the reactive gases and the cooling water are welded to the end plates. Further, for securing sealing among above described elements, they usually have grooves for receiving O-rings at peripheral portions around the manifold holes, whereby the O-rings placed in the grooves function the sealing. In
FIG. 1
, O-rings
8
a
,
8
b
and
28
and those without reference numerals are shown.
According to conventional fuel cells, usually a tightening pressure of about 10.0 to 20.0 kgf/cm
2
is used for tightening the cell stack in order to decrease the contact resistance among the electrolyte membranes, electrodes and separators and to secure the gas sealing properties of the gaskets. Therefore, the end plates are generally made of metal materials having high mechanical strengths, wherein the cell stack is tightened by applying a tightening pressure to the end plates at both ends thereof, using a combination of tightening bolts and springs or washers. Further, since the supplied humidified gases and the cooling water touch portions of the end plates, usually stainless steel materials, which have high corrosion resistances, are selected from among metal materials and used for the end plates in order to avoid corrosions by such gases and water. The current collecting plates are usually made of metal materials having higher electric conductivities than those of carbon materials, and are in some cases subjected to surface treatment for lowering contact resistances. Furthermore, the end plates at the both ends of the cell stack are electrically connected to each other by the tightening bolts, the insulating plates having electrically insulating properties are each inserted between the current collecting plate and the end plate for securing insulation between them.
The separator plates to be used for such polymer electrolyte fuel cell need to have high electric conductivity, high gas tightness to the reactive gases, and high corrosion resistance to the reaction during oxidization and reduction of hydrogen and oxygen, namely high acid resistance. For these reasons, conventional separator plates in some cases are made of carbon plates having high gas-impermeabilities, with gas flow channels being made by cutting the surfaces of the carbon plates, or in other cases are each made by pressing a mixture of a graphite powder and a binder with a pressing mold having a configuration for forming gas flow channels, and by firing the same.
Recently, metal plates such as stainless steel ar

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