Polymer electrolyte fuel cell device

Details Polymer electrolyte fuel cell device Polymer electrolyte fuel cell device

2000-02-25

2002-05-07

Kalafut, Stephen (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

With pressure equalizing means for liquid immersion operation

C429S010000

Reexamination Certificate

active

06383676

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to polymer electrolyte fuel cells which comprise an anode, a cathode and a polymer electrolyte membrane provided between the anode and cathode and which is adapted to generate electric power by supplying a fuel gas containing hydrogen to the anode and an oxidizer gas to the cathode.
BACKGROUND OF THE INVENTION
Attention has been directed in recent years to fuel cells having a high energy conversion efficiency and producing no harmful substance by an electricity generating reaction. Polymer electrolyte fuel cells which operate at a low temperature of not higher than 100° C. are known as such fuel cells.
FIG. 4
shows the electricity generating principle of polymer electrolyte fuel cells. A fuel cell
50
is fabricated by arranging an anode
55
and a cathode
56
at opposite sides of a polymer electrolyte membrane
54
of ionically conductive solid high polymer, and further arranging a fuel chamber
57
and an oxidizer chamber
58
at opposite sides of the arrangement. The anode
55
and the cathode
56
are interconnected by an external circuit
59
.
The hydrogen H
2
contained in the fuel gas supplied to the fuel chamber
57
is separated into hydrogen ions H
+
and electrons e
−
at the anode
55
. The hydrogen ions H
+
migrate through the polymer electrolyte membrane
54
toward the cathode
56
, while the electrons e
−
flow through the external circuit
59
toward the cathode
56
.
At the cathode
56
, the oxygen O
2
contained in the oxidizer gas supplied to the oxidizer chamber
58
reacts with the hydrogen ions H
+
and the electrons e
−
, producing water H
2
O.
In this way, the cell in its entirety produces water from hydrogen and oxygen and generates an electromotive force.
Since the single fuel cell
50
is small in electromotive force, a plurality of fuel cells
50
are usually connected to one another in series to provide a polymer electrolyte fuel cell device.
For example,
FIG. 3
shows a fuel cell device
5
of the polymer electrolyte type which comprises a plurality of fuel cells
50
each in the form of a flat plate and connected in series as fitted to one another into an assembly. The fuel cells
50
connected in series are supplied with hydrogen gas or like fuel gas and air or like oxidizer gas for the fuel cells
50
to generate electric power and deliver the power to the outside.
Each fuel cell
50
of the device
5
is formed with a plurality of fuel gas channels (not shown) extending vertically and a plurality of oxidizer gas channels
53
extending horizontally.
The fuel cell
50
disposed at one end of the device has a fuel gas inlet
51
a
, while the fuel cell
50
disposed at the other end thereof has a fuel gas outlet
52
a
. The fuel cells
50
other than these end cells
50
are each formed with a fuel gas supply through bore
51
and a fuel gas discharge through bore
52
.
By fitting the fuel cells
50
to one another, the fuel gas inlet
51
a
and the fuel gas supply through bores
51
are held in communication with one another to form a fuel gas supply passageway, and the fuel gas discharge through bores
52
and the fuel gas outlet
52
a
are held in communication with one another to form a fuel gas discharge passageway.
The fuel cell device
5
of the polymer electrolyte type is further provided with an oxidizer gas supply manifold
6
on the side thereof where the oxidizer gas channels
53
are exposed for supplying the oxidizer gas to the channels
53
.
The manifold
6
has, for example, an opening facing downward and also an opening facing this side, such that the oxidizer gas taken in through the downward opening is sent into the oxidizer gas channels
53
.
With the fuel cell device
5
described, the fuel gas is fed to the fuel gas inlet
51
a
as indicated by a solid-line arrow in the drawing, distributed to the fuel gas channels formed in each fuel cell
50
via the fuel gas supply passageway and subjected to an electricity generating reaction while flowing down these channels. The portion of the fuel gas remaining unreacted and reaching the fuel gas discharge through bores
52
after flowing through the fuel gas channels flows through the fuel gas discharge passageway provided by the bores
52
and is discharged to the outside from the fuel gas outlet
52
a
as indicated in a solid-line arrow in the drawing.
On the other hand, the oxidizing gas is taken in from the downward opening of the manifold
6
as indicated by broken-line arrows in the drawing, sent into the oxidizer gas channels
53
through the side opening and subjected to the electricity generating reaction while flowing through the channels
53
. The portion of the oxidizing gas remaining unreacted and reaching the outlets of the channels
53
after flowing through the channels
53
is discharged to the outside from the outlets as indicated by broken-line arrows.
However, the fuel cell device
5
has the problem that during the generating operation, the water content of the polymer electrolyte membranes
54
decreases to result in reduced ionic conductivity, rendering the cells no longer serviceable as such.
Accordingly we have filed a patent application on a polymer electrolyte fuel cell wherein unreacted fuel gas and unreacted oxidizer gas are subjected to a combustion reaction, and the resulting water is supplied to a polymer electrolyte membrane to wet the membrane (JP-A No. 40179/1999).
This fuel cell nevertheless has the problem that the oxidizer gas supplied to the oxidizer chamber contains organic impurities such as kerosene and methanol, permitting the impurities to reach the surface of the cathode and inhibit the electrode catalytic reaction, lowering the cell voltage.
Accordingly, a fuel cell is proposed which has an air electrode to be supplied with clean air obtained by burning air by a combustion catalytic device for removing impurities from the air (JP-A No. 94200/1995).
However, the proposed fuel cell has the problem of being low in overall efficiency since the fuel gas remaining unreacted for power generation is discarded to the outside without being reused.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a polymer electrolyte fuel cell device which comprises a polymer electrolyte membrane prevented from drying and which affords a high cell voltage without impairment and achieves a higher overall efficiency than in the prior art.
The present invention provides a polymer electrolyte fuel cell device which comprises at least one fuel cell
10
having an anode
15
, a cathode
16
and a polymer electrolyte membrane
14
provided between the anode and the cathode for causing the fuel cell
10
to generate electric power by supplying a fuel gas containing hydrogen to the anode
15
and supplying an oxidizer gas to the cathode
16
. The fuel cell device is characterized by introducing, into a combustion unit
3
, the unreacted portion of the fuel gas discharged from the fuel cell
10
and the whole amount of the oxidizer gas to be fed to the cathode
16
to burn the unreacted fuel gas and burn the impurities contained in the oxidizer gas by partly consuming the oxygen contained in the oxidizer gas, and supplying the oxidizer gas discharged from the combustion unit
3
to the cathode
16
.
With the fuel cell device of the invention, the unreacted portion of a fuel gas discharged from the fuel cell
10
is supplied to the combustion unit
3
, and an oxidizer gas is supplied from outside to the unit
3
.
In the combustion unit
3
, the hydrogen contained in the unreacted fuel gas and the oxygen contained in the oxidizer gas undergo a combustion reaction to produce water. The impurities contained in the oxidizer gas also undergo a combustion reaction, whereby the impurities are decomposed into water and carbon dioxide. The oxidizer gas to be supplied to the combustion unit
3
contains oxygen in an amount required for the combustion reactions and an electricity generating reaction.
Accordingly, the combustion unit
3
discharges an oxidizer gas which co

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