Solid electrolyte fuel cell having anode comprising metal...

Details Solid electrolyte fuel cell having anode comprising metal... Solid electrolyte fuel cell having anode comprising metal...

2000-06-02

2002-04-30

Brouillette, Gabrielle (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

With pressure equalizing means for liquid immersion operation

C429S047000, C429S047000, C429S010000

Reexamination Certificate

active

06379830

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a solid electrolyte fuel cell. More particularly, the present invention relates to a solid electrolyte fuel cell equipped with a solid electrolyte device which has electrodes formed on both surfaces of an oxygen ion-conductive solid electrolyte substrate and in which an oxygen-containing gas is supplied to the electrode on the cathode side of the solid electrolyte device while methane gas, as fuel, is supplied to the electrode on the anode side.
2. Description of the Related Art
Solid electrolyte fuel cells are expected to provide a higher power generation efficiency than the power generation efficiency of thermal power generation or the like. Therefore, numerous studies regarding fuel cells have been done. As shown in
FIG. 10
, a solid electrolyte fuel cell uses a burned body of stabilized zirconia containing yttria (Y
2
O
3
)(hereinafter called merely the “YSZ burned body”) as an oxygen ion-conductive solid electrolyte substrate
100
. (This stabilized zirconia will be hereinafter called “YSZ” in some cases.) The solid electrolyte fuel cell further includes a solid electrolyte device
106
having electrodes
102
and
104
a
formed on both surfaces of the solid electrolyte substrate
100
.
Of the electrodes
102
and
104
a
of this solid electrolyte device
106
, the electrode
102
is made of lanthanum strontium manganese oxide [ (La
0.85
Sr
0.15
)
0.90
MnO
3
], and is used as the cathode. Oxygen or an oxygen-containing gas is supplied to this electrode
102
. The other electrode
104
a
comprises a porous platinum layer, and is used as the anode. Methane gas, as fuel, is supplied to this electrode
104
a.
Oxygen (O
2
) supplied to the electrode
102
of the solid electrolyte device
106
shown in
FIG. 10
is ionized to oxygen ions (O
2−
) at the boundary between the electrode
102
and the solid electrolyte substrate
100
. The oxygen ions (O
2−
) are transferred by the solid electrolyte substrate
100
to the electrode
104
a
. The oxygen ions (O
2−
) so transferred to the electrode
104
a
react with methane (CH
4
) gas supplied to the electrode
104
a
, forming water (H
2
O), carbon dioxide (CO
2
), hydrogen (H
2
) and carbon monoxide (CO). Since the oxygen ions emit electrons during this reaction, a potential difference develops between the electrode
102
and the electrode
104
a
. When the electrodes
102
and
104
a
are electrically connected to an external circuit
108
, the electrons of the electrode
104
a
flow through the external circuit
108
to the electrode
102
(indicated by an arrow). Electric power can thus be obtained from the solid electrolyte fuel cell.
Incidentally, the operating temperature of the solid electrolyte fuel cell shown in
FIG. 10
is approximately 1,000° C.
The solid electrolyte device
106
shown in
FIG. 10
has durability against the high operating temperature, but has low power generation performance such as terminal current density and discharge current density. Therefore, further improvements of the cell performance are required.
A solid electrolyte device
110
shown in
FIG. 11
has been used. The solid electrolyte device
110
substantially comprises a solid electrolyte substrate
112
made of YSZ, and the electrode
104
b
as the anode is formed at one of the ends of this solid electrolyte substrate
112
. The electrode
104
b
is made of the mixture of YSZ, that forms the solid electrolyte substrate
112
, and cermet particles
114
,
144
comprising of nickel (Ni) and nickel oxide (NiO).
Incidentally, the electrode
102
as the cathode, that is formed at the other end of the solid electrolyte substrate
112
, is made of lanthanum strontium manganese oxide in the same way as the electrode
102
of the solid electrolyte device
106
shown in FIG.
10
.
The solid electrolyte fuel cell using the solid electrolyte device
110
(hereinafter called the “Ni-YSZ cermet solid electrode device
110
” in some cases) shown in
FIG. 11
has an improved power generation performance, such as discharge current density and terminal current density, in comparison with the solid electrolyte fuel cell using the solid electrolyte device
106
shown in FIG.
10
.
However, the operating temperature of the solid electrolyte fuel cell using the solid electrolyte device
110
shown in
FIG. 11
, at which power can be obtained in a stable way, is at least about 920° C. Power cannot be obtained stably at a temperature lower than 920° C. The phenomenon of a gradual drop of activity of the solid electrolyte substrate
110
occurs at an operating temperature higher than 920° C. Therefore, an improvement in the heat-resistant property of the solid electrolyte substrate
110
is required.
When a dry methane gas, after the removal of moisture, is supplied as fuel to the electrode
104
b
as the anode, the reactivity between the methane gas and the oxygen ions drops with the result that the solid electrolyte fuel cell fails to exhibit its full performance. For this reason, moisture-containing wet methane gas is supplied to the electrode
104
b
at present so as to secure reactivity between the methane gas and the oxygen ions.
The reaction between the methane gas and the high-temperature vapor is the endothermic reaction. Therefore, the temperature on the side of the electrode
140
b
drops, and carbon that is formed with the drop of the reaction temperature adheres to the electrode
104
b
and promotes a drop in activity of the solid electrolyte device
110
. In other words, stable power generation is difficult.
It is therefore an object of the present invention to provide a solid electrolyte fuel cell that has an improved power generation performance, such as discharge current density and terminal current density, and has the maximum heat-resistance of the solid electrolyte device.
SUMMARY OF THE INVENTION
As a result of studies to solve the problem described above, the inventors of this invention have found that a solid electrolyte fuel cell using the solid electrolyte device
200
shown in
FIG. 12
has an improved power generation performance, such as discharge current density and terminal current density, in comparison with the solid electrolyte fuel cell shown in
FIG. 10
, and can stably generate power even at an operating temperature of less than 920° C. Some of the present inventors proposed a solid electrolyte fuel cell using the solid electrolyte device
200
shown in
FIG. 12
in “Progress in Battery & Battery Materials”, Vol. 17, April (1998), p. 137-143.
In the solid electrolyte device
200
shown in
FIG. 12
, electrodes
102
and
104
c
are formed on both surfaces of a solid electrolyte substrate
100
comprising a YSZ burned body. The electrode
102
used as the cathode is formed of lanthanum strontium manganese oxide [(La
0.85
Sr
0.15
)
0.90
MnO
3
]. Metal oxide particles
202
,
202
made of PdCoO
2
are blended in a porous platinum layer that forms the electrode
104
c
used as the anode.
However, power generation performance, such as discharge current density and terminal current density, of the solid electrolyte device
200
shown in
FIG. 12
, is not yet sufficient.
Therefore, the inventors of the present invention have further studied solid electrolyte fuel cells to improve the power generation performance, such as discharge current density and terminal current density, and the thermal and chemical stability of the solid electrolyte device. As a result, the present inventors have found that the power generation performance of the electrolyte fuel cell, such as discharge current density and terminal current density, and the heat-resistant property of the solid electrolyte device, can be improved remarkably when the solid electrolyte fuel cell has the solid electrolyte fuel device formed by blending metal particles of CoNiO
2
in the porous platinum layer forming the electrode on the anode side, or the solid electrolyte fuel device has an oxide layer, in which metal oxide particles of PdCoO
2
are sintered, on the

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