Solid oxide electrolyte fuel cell

Details Solid oxide electrolyte fuel cell Solid oxide electrolyte fuel cell

1994-07-11

2001-11-13

Chaney, Carol (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

With pressure equalizing means for liquid immersion operation

C429S006000, C429S006000, C429S006000

Reexamination Certificate

active

06316138

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a solid oxide electrolyte fuel cell (SOFC), and more particularly to an SOFC available, besides for power generating purpose, as an electrolyte cell of hydro-electrolysis, CO-electrolysis or the like.
2. Description of the Prior Art
As an SOFC in the prior art, a construction proposed by the applicant of this application and disclosed in Laid-Open Japanese Utility Model Specification No. 4-8259 (1992), has been known.
FIG. 3
in the accompanying drawings of the present application is equivalent to
FIG. 1
in this laid-open U.M. specification, which shows an outline of the proposed construction.
In
FIG. 3
, reference numeral
1
designates a generating layer composed of a solid oxide layer
2
and a fuel electrode
3
and an oxygen electrode
4
respectively disposed on the opposite sides of the solid oxide layer
2
. Above and under the generating layer
1
are disposed laminated layers
8
a
and
8
b
each consisting of an interconnector layer
5
and an oxygen electrode
6
and a fuel electrode
7
respectively laminated on the opposite sides of the interconnector layer
5
. An outside crest portion
9
of the fuel electrode
3
on the upper side of the generating layer
1
is bonded with the fuel electrode
7
of the upper laminated layer
8
a, and a fuel passage
10
is formed of a space reserved therebetween. On the other hand, an outside crest portion
11
of the oxygen electrode
4
on the under side of the generating layer
1
is bonded with the oxygen electrode
6
of the lower laminated layer
8
b
, and an oxidizer passage
12
is formed of a space reserved therebetween.
As explained in the above-referred laid-open Japanese U.M. specification, in contrast to the structure so far considered a main current, the above-described structure is a really important proposal in this technical field in that members not directly concerned in power generation such as support members interposed between the generating layer
1
and the laminated layers
8
a
and
8
b
are made unnecessary.
It is to be noted that while an SOFC has a power generation efficiency exceeding 60% and is ranked at an important level in view of measures for energy control, a countermeasure such as reduction of a manufacturing cost is necessitated. Although the SOFC structure in the prior art shown in
FIG. 3
achieved an important improvement in this respect, it still involved a problem that the oxygen electrodes
6
and the fuel electrodes
7
forming the laminated layers
8
a
and
8
b
, which are not directly concerned in power generation per se, were necessary.
In the above-described construction, since the generating layer
1
employed a dimpled structure, electrons produced in the generating layer
1
would concentrate to a dimpled portion (recessed portion), and hence, if the dimpled portion is in itself directly bonded with the interconnector layer, an electric resistance becomes large. The reason for the necessity of the oxygen electrodes
6
and the fuel electrodes
7
forming the laminated layers
8
a
and
8
b
is because it was intended to bring the dimpled portions into contact with the corresponding electrode
6
or
7
so that the produced electrons can diffuse and a lateral flow of electrons can be generated.
SUMMARY OF THE INVENTION
It is therefore one object of the present invention to provide an improved solid oxide fuel cell (SOFC) which preserves the merit of the above-described SOFC in the prior art and yet has its electric resistance minimized, and also whose manufacturing cost is reduced by decreasing component members.
According to a principal feature of the present invention, in order to achieve the above-mentioned object in a solid oxide fuel cell comprising a generating layer formed by disposing a fuel electrode and an oxygen electrode on the opposite sides of a solid oxide layer shaped in a dimpled structure, the following construction is employed for the above-mentioned generating layer.
A generating layer consisting of three layers of a fuel electrode, a solid oxide layer and an oxygen electrode is shaped in a dimpled structure having recessed portions formed on its respective surfaces, protruded portions on the side of the fuel electrode outside of the above-mentioned recessed portions are electrically bonded with an interconnector layer via a first conductive adhesive, and protruded portions on the side of the oxygen electrode outside of recessed portions of another generating layer are electrically bonded with the same interconnector layer via a second conductive adhesive as opposed to the first-mentioned protruded portions.
Generally, in an SOFC, since yttria-stabilized-zirconia (hereinafter abbreviated as YSZ) formed as ceramics is employed for the solid oxide layer, contrivance is made so as to prevent cracking of the solid oxide layer caused by thermal deformation of the generating layer composed of cell component members having different coefficients of thermal expansion and constrained by one another by equalizing the coefficients of thermal expansion of the respective cell component members.
Therefore, in the SOFC according to the present invention also, it is required to use fuel electrode material, oxygen electrode material and interconnector material having coefficients of thermal expansion matched to that of the solid oxide layer, and materials having negligibly small specific electric resistances are employed. As representative examples of the materials, the following materials are available on the basis of results of experiments conducted by the inventors of the present invention:
interconnector material: LaSrCrO
3
(1 mm in thickness)
fuel passage side:
conductivity 1 S/cm, resistance 0.1 &OHgr;·cm
2
oxidizer passage side:
conductivity 30 S/cm, resistance 0.003 &OHgr;·cm
2
average:
conductivity 10 S/cm, resistance 0.01 &OHgr;·cm
2
oxygen electrode material: LaSrMnO
3
(50 &mgr;m in thickness)
conductivity 20 S/cm, resistance 2.5×10
−4
&OHgr;·cm
2
fuel electrode material:
Ni/YSZ (60:40) (50 &mgr;m in thickness)
conductivity 500-1000 S/cm,
resistance 1−0.5×10
−5
&OHgr;·cm
2
The numerals of resistance above all indicate resistance values per unit area as measured in the thicknesswise direction. As will be apparent from the above data, partly from the reason that the interconnector layer is necessitated to have a thickness enough for in itself reserving a mechanical strength as a structural member, the interconnector layer has a predominantly high electric resistance, and so, it is necessary to minimize the length of this electric flow passage. Furthermore, if the above-described data are applied to an electric flow passage schematically shown in
FIG. 4
, when a pitch of dimples is chosen to be 3 mm, that is, a lateral path length of electrons is 1.5 mm, a thickness of an interconnector layer
5
made of LaSrCrO
3
is 2 mm and thicknesses of a fuel electrode made of Ni/YSZ and an oxygen electrode made of LaSrCrO
3
are varied, an overall resistance of the three-layer structure would change as indicated in the following Table-1:
TABLE-1
Thickness of Oxygen Electrode
50 &mgr;m
100 &mgr;m
150 &mgr;m
200 &mgr;m
Thickness
 50 &mgr;m
0.25
0.14
0.10
0.085
of Fuel
100 &mgr;m
0.25
0.14
0.10
0.081
Electrode
150 &mgr;m
0.25
0.14
0.10
0.080
200 &mgr;m
0.25
0.13
0.10
0.079
Unit: &OHgr; · cm
2
As will be obvious from Table-1 above, while the thickness on the fuel electrode side could be chosen to be 50 &mgr;m at maximum, on the oxygen electrode side an electric resistance largely depends upon the thickness, and so, in order to reduce an electric resistance the thickness must be chosen thick.
Whereas, according to the present invention, since a resistance caused by lateral flows of electrons in an electrode is not present, upon connecting an oxygen electrode of a generating layer with an interconnector layer, it is only necessitated to apply a relatively thin adhesive (normally the same material as the oxygen electrode is used) to such extent tha

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